Metabolism and Circadian Rhythms—Implicationsfor Obesity
Oren Froy
Institute of Biochemistry, Food Science, and Nutrition, Robert H. Smith Faculty of Agriculture, Food and Environment,The Hebrew University of Jerusalem, Rehovot 76100, Israel
Obesity has become a serious public health problem and a major risk factor for the development of illnesses,such as insulin resistance and hypertension. Human homeostatic systems have adapted to daily changes inlight and dark in a way that the body anticipates the sleep and activity periods. Mammals have developedan endogenous circadian clock located in the suprachiasmatic nuclei of the anterior hypothalamus thatresponds to the environmental light-dark cycle. Similar clocks have been found in peripheral tissues, suchas the liver, intestine, and adipose tissue, regulating cellular and physiological functions. The circadian clockhas been reported to regulate metabolism and energy homeostasis in the liver and other peripheral tissues.This is achieved by mediating the expression and/or activity of certain metabolic enzymes and transportsystems. In return, key metabolic enzymes and transcription activators interact with and affect the core clockmechanism. In addition, the core clock mechanism has been shown to be linked with lipogenic and adi-pogenic pathways. Animals with mutations in clock genes that disrupt cellular rhythmicity have providedevidence for the relationship between the circadian clock and metabolic homeostasis. In addition, clinicalstudies in shift workers and obese patients accentuate the link between the circadian clock and metabolism.This review will focus on the interconnection between the circadian clock and metabolism, with implicationsfor obesity and how the circadian clock is influenced by hormones, nutrients, and timed meals. (EndocrineReviews 31: 1–24, 2010)
I. Introduction
II. Circadian RhythmsA. Circadian rhythms in mammalsB. Circadian rhythms, well-being, and life span
III. The Biological ClockA. The location of the mammalian biological clockB. The biological clock at the molecular levelC. Circadian rhythms in peripheral clocks
IV. The Biological Clock and Energy HomeostasisA. SCN efferentsB. SCN afferentsC. Effect of neuropeptides and hormones on SCND. Circadian rhythms and metabolismE. Effect of metabolism on circadian rhythmsF. Effect of feeding regimens on circadian rhythms
V. The Biological Clock and ObesityA. SCN connection to adipose tissueB. Effect of circadian rhythms on lipid metabolismC. Effect of high-fat diet on circadian rhythmsD. Circadian rhythms and body weightE. Clock mutations and metabolic disordersF. Sleep, shift work, and obesity
VI. Summary and Conclusions
I. Introduction
Obesity has become a serious and growing publichealth problem (1). Previous ways to combat obe-
sity have failed, and new approaches need to be taken. Thebiological clock regulates the expression and/or activity ofenzymes and hormones involved in metabolism. How-ever, recently, there is a growing body of evidence thatmetabolism, food consumption, timed meals, and somenutrients feed back to entrain circadian clocks. Moreover,disruption of circadian rhythms leads to metabolic disor-ders. This review will summarize recent findings concern-
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ing the relationship between metabolism and circadianrhythms with implications for obesity.
II. Circadian Rhythms
A. Circadian rhythms in mammalsThe rotation of earth around its axis imparts light and
dark cycles of 24 h. Organisms on earth developed theability to predict these cycles and evolved to restrict theiractivity to the night or day, being nocturnal or diurnal,respectively. By developing an endogenous circadian�circa (about) and dies (day)� clock that is entrained toexternal stimuli, animals and plants ensure that physio-logical processes are performed at the appropriate, opti-mal time of day or night (2). In mammals, the circadianclock influences nearly all aspects of physiology and be-havior, including sleep-wake cycles, cardiovascular activ-ity, endocrine system, body temperature, renal activity,physiology of the gastrointestinal tract, and hepatic me-tabolism (2, 3).
B. Circadian rhythms, well-being, and life spanThe control of the circadian clock over human patho-
physiology is demonstrated in epidemiological studies.Clinical epidemiology in humans indicates that myocar-dial infarction, pulmonary edema, hypertensive crises,and asthma and allergic rhinitis attacks all peak at certaintimes during the day (4–6). A number of other disorders,e.g., psychological and sleep disorders, are associated withirregular or pathological functioning of the central bio-logical clock (3). In this day and age, there is a need toextend wakefulness or repeatedly invert the normal sleep-wake cycle. As a result, travelers experience the conditionknown as jet lag, with its associated symptoms of fatigue,disorientation, and insomnia. Similarly, shift workers ex-hibit altered nighttime melatonin levels and reproductivehormone profiles that could increase the risk of hormone-related diseases (7). These findings reveal the negative ef-fect of disruption of circadian rhythms on physiology. Dis-ruption of circadian coordination has also been found toaccelerate cancer proneness and malignant growth, sug-gesting that the circadian clock controls tumor progres-sion (7–9). Also, chronic reversal of the external light-darkcycle at weekly intervals resulted in a significant decreasein the survival time of cardiomyopathic hamsters (10).Circadian rhythms change with normal aging, including ashift in the phase and decrease in amplitude (11–13). In-deed, longevity in hamsters is decreased with a disruptionof rhythmicity and is increased in older animals given fetalsuprachiasmatic implants that restore higher amplituderhythms (14). Thus, disruption of circadian coordinationmay be manifested by hormone imbalance, psychological
and sleep disorders, cancer proneness, and reduced lifespan (3, 7–10, 15). In contrast, resetting of circadianrhythms has led to well-being and increased longevity (14,16). These findings reveal the prominent influence of thecircadian clock on human physiology and pathophysiology.
III. The Biological Clock
A. The location of the mammalian biological clockIn mammals, the central circadian clock is located in the
suprachiasmatic nuclei (SCN) of the anterior hypothala-mus in the brain. The SCN clock is composed of multiple,single-cell circadian oscillators, which, when synchro-nized, generate coordinated circadian outputs that regu-late overt rhythms (17–20). Similar clock oscillators havebeen found in peripheral tissues, such as the liver, intes-tine, heart, and retina (3, 21–23) (Fig. 1). SCN oscillationis not exactly 24 h; therefore, it is necessary to entrain thecircadian pacemaker each day to the external light-darkcycle to prevent drifting (or free-running) out of phase.Light is the most potent synchronizer for the SCN (24).Light is perceived by the retina, and the signal is transmit-ted via the retinohypothalamic tract (RHT) to the SCN (3,25, 26). As a result, vasoactive intestinal polypeptide, anintrinsic SCN factor, acutely activates and synchronizesSCN neurons and coordinates behavioral rhythms (27,28). The SCN sends signals to peripheral oscillators toprevent the dampening of circadian rhythms in these tis-sues. The SCN accomplishes this task via neuronal con-nections or circulating humoral factors (29) (Fig. 1), al-though the mechanisms are not fully understood. Severalhumoral factors expressed cyclically by the SCN, such asTGF� (30), prokineticin 2 (31), and cardiotrophin-like
SCN
Adipose tissue Liver Muscle
Hormones, Metabolic pathways
Autonomic innervation, Humoral factors
Food, Feeding regimens
Light
Locomotor activity, Sleep-wake cycle,
Blood pressure
Fig. 1. Resetting signals of the central and peripheral clocks. Light isabsorbed through the retina and is transmitted to the SCN via the RHT.The SCN then dictates the entrainment of peripheral oscillators viahumoral factors or autonomic innervation. As a result, tissue-specifichormone expression and secretion and metabolic pathways exhibitcircadian oscillation. In addition, the SCN dictates rhythms oflocomotor activity, sleep-wake cycle, blood pressure, and bodytemperature. Food and feeding regimens affect either peripheral clocksor the central clock in the SCN.
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cytokine (32), have been shown to affect peripheral clocksbecause their intracerebroventricular injection inhibitednocturnal locomotor activity. In turn, SCN rhythms canbe altered by neuronal and endocrine inputs (33) (see Sec-tion IV.B). Complete destruction of SCN neurons abol-ishes overall circadian rhythmicity in the periphery, be-cause of loss of synchrony among individual cells anddamping of the rhythm at the population level. However,at the cellular level each cell oscillates, but with a differentphase (34, 35). Thus, the central circadian clock (oftentermed the “master” clock) is located within the SCN (36,37), whereas peripheral clocks (often termed “slave”clocks) are found within non-SCN cells of the organism,including other regions of the central nervous system (3,21–23, 38).
B. The biological clock at the molecular levelIn mammals, the clock is an intracellular mechanism
sharing the same molecular components in SCN neu-rons and peripheral cells (39). Generation of circadianrhythms is dependent on the concerted coexpression ofspecific clock genes. Transcriptional-translational feed-back loops lie at the very heart of the core clock mecha-nism. Many clock gene products function as transcriptionfactors that possess PAS (PER, ARNT, SIM) and basichelix-loop-helix domains involved in protein-protein andprotein-DNA interactions, respectively. These factors ul-timately activate or repress their own expression and,thus, constitute a self-sustained transcriptional feedbackloop. Changes in concentration, subcellular localization,posttranslational modifications (phosphorylation, acety-lation, deacetylation, SUMOylation), and delays betweentranscription and translation lead to the approximately24-h cycle (2, 3, 40, 41).
The genes encoding the core clock mechanisms includecircadian locomotor output cycles kaput (Clock), brainand muscle-Arnt-like 1 (Bmal1), Period1 (Per1), Period2(Per2), Period3 (Per3), Cryptochrome1 (Cry1), and Cryp-tochrome2 (Cry2). In the mouse, the first clock gene iden-tified encodes the transcription factorCLOCK(42),whichdimerizes with BMAL1 to activate transcription (Fig. 2).CLOCK and BMAL1, two basic helix-loop-helix-PAStranscription factors, are capable of activating transcrip-tion upon binding to E-box (5�- CACGTG-3�) and E-box-like promoter sequences (3). BMAL1 can also dimerizewith other CLOCK homologs, such as neuronal PAS do-main protein 2 (NPAS2), to activate transcription and sus-tain rhythmicity (43, 44). PERIOD (PER1, PER2, andPER3) and two CRYPTOCHROME (CRY1 and CRY2)proteins operate as negative regulators (20, 45, 46) (Fig.2). Thus, CLOCK:BMAL1 heterodimers bind to E-boxsequences and mediate transcription of a large number ofgenes, including those of the negative feedback loop Pers
and Crys. When PERs and CRYs are produced in the cy-toplasm, they oligomerize and translocate to the nucleusto inhibit CLOCK:BMAL1-mediated transcription (Fig.2). Pers and Bmal1 have robust oscillation in oppositephases correlating with their opposing functions (38). Allthe aforementioned clock genes exhibit a 24-h rhythm inSCN cells and peripheral tissues, except for Clock, whichhas been shown not to oscillate in the SCN (40). Recentstudies have demonstrated that CLOCK has intrinsic hi-stone acetyltransferase activity, suggesting that rhythmicactivation of chromatin remodeling may underlie theclock transcriptional network (47, 48). Indeed, cyclic hi-stone acetylation and methylation have been observed onthe promoters of several clock genes (48–53).
Several other players appear to be important to sustainclock function. Casein kinase I epsilon (CKI�) is thoughtto phosphorylate the PER proteins and, thereby, enhancetheir instability and degradation (40, 54–56). CKI� alsophosphorylates and partially activates the transcriptionfactor BMAL1 (57). Bmal1 expression is negatively reg-ulated by the transcription factor reverse erythroblastosisvirus � (REV-ERB�) (58), which recruits histone deacety-lase complexes (59). Bmal1 expression is positively regu-lated by retinoic acid receptor-related orphan receptor �
(ROR�) and ROR� (60) via the ROR response element(RORE) (61). Thus, Bmal1 oscillation is driven by a rhyth-mic change in RORE occupancy by RORs and REV-ERB�.This alternating promoter occupancy occurs becauseREV-ERB� levels are robustly rhythmic, a result of directtranscriptional activation of the Rev-erb� gene by the het-erodimer CLOCK:BMAL1 (58) (Fig. 2).
C. Circadian rhythms in peripheral clocksThe fraction of cyclically expressed transcripts in each
peripheral tissue ranges between 5 and 20% of the totalpopulation, and the vast majority of these genes are tissue-specific (2, 23, 62–69). These findings emphasize the cir-cadian control over a large portion of the transcriptomesin peripheral tissues. Considering the circadian gene ex-pression in peripheral tissues, it is difficult to determinewhether the SCN clock drives these rhythmic patterns di-rectly or indirectly by driving rhythmic feeding, activity,and/or body temperature, which, in turn, contribute todriving rhythms in gene expression in the periphery. In anelegant study, it was shown that tetracycline-responsive,hepatocyte-specific overexpression of REV-ERB�, whichcaused constitutive repression of Bmal1 transcription (seeSection III.B) when the tetracycline analog doxycyclinewas absent, resulted in the loss of clock function. Microar-ray analysis of livers after removal of doxycycline from thefood revealed that the great majority of the 351 rhythmicgenes was abolished, indicating that these genes are nor-mally driven by the local liver clock and not by rhythmic
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systemic signals. Interestingly, 31 genes, among which wasthe core clock gene mPer2, still exhibited robust circadianpatterns of expression, suggesting that this small subset ofrhythmic liver genes is driven by systemic signal indepen-dent of the liver clock (70). Thus, for a peripheral tissue,such as the liver, signals from the central SCN clock or thelocal endogenous clock may control rhythmic gene ex-pression (70, 71). Indeed, as mentioned in Section III.A,peripheral rhythms persist in the periphery at the cellularlevel even without SCN control (34, 35).
IV. The Biological Clock andEnergy Homeostasis
A. SCN efferentsThe SCN provides its most intense output to the sub-
paraventricular zone (SPZ) and dorsomedial hypothala-mus (DMH) (72, 73). SCN fibers have also been shown toterminate in and around the arcuate nucleus (ARC) in the
ventromedial hypothalamus (VMH) and in the ventralpart of the lateral hypothalamus, suggesting an interactionwith areas involved in food intake and organization ofactivity (74) (Fig. 3). The SPZ and DMH, which are in-nervated by the SCN, have many outputs to other regionsin the brain, including the paraventricular nucleus (PVN),the lateral hypothalamus, ventrolateral preoptic nucleus,and medial preoptic area (MPOA), that regulate cortico-steroid release, wakefulness/feeding, sleep, and thermo-regulation, respectively (Fig. 3). The role of the SPZ andDMH in regulating circadian rhythms was determined us-ing lesion studies (75, 76). Destruction of the ventral SPZreduced circadian rhythms of sleep-wakefulness and lo-comotor activity but had little effect on circadian regula-tion of body temperature (76). Conversely, degenerationof the dorsal SPZ disrupted circadian regulation of bodytemperature with minimal effect on sleep-wakefulness andlocomotor activity (76). Thus, ventral SPZ regulates sleep-wakefulness, whereas dorsal SPZ regulates body temper-
E-boxCLOCK BMAL1
Rorα ~
E-box Per1-3CLOCK BMAL1
E-box Cry1-2CLOCK BMAL1
~~
CLOCK BMAL1
RORsREV-ERBs
Clock ~Bmal1PPRE RORE ~
NucleusCytoplasm
PERsCRYs
E-boxCLOCK BMAL1
~Rev-erbαPPRE
PPARα
E-boxCLOCK BMAL1
Pparα ~
PERsCRYs
PERsCRYs
Fig. 2. The core mechanism of the mammalian circadian clock and its link to energy metabolism. The cellular oscillator is composed of a positivelimb (CLOCK and BMAL1) and a negative limb (CRYs and PERs). CLOCK and BMAL1 dimerize in the cytoplasm and translocate to the nucleus. TheCLOCK:BMAL1 heterodimer then binds to enhancer E-box sequences located in the promoter region of Per and Cry genes to activate theirtranscription. After translation, PERs and CRYs undergo nuclear translocation and inhibit CLOCK:BMAL1, resulting in decreased transcription oftheir own genes. The autoregulatory transcription–translation loop comprising CLOCK:BMAL1 and PER–CRY constitutes the core clock andgenerates 24-h rhythms of gene expression. CLOCK:BMAL1 heterodimer also induces the transcription of Rev-erb� and Ror�. ROR� and REV-ERB�regulate lipid metabolism and adipogenesis, and also participate in the regulation of Bmal1 expression. ROR� stimulates and REV-ERB� inhibitsBmal1 transcription, acting through ROR elements (RORE). CLOCK:BMAL1 heterodimer also mediates the transcription of Ppar�, a nuclearreceptor involved in glucose and lipid metabolism. PPAR� activates transcription of Rev-erb� by binding to a PPRE. PPAR� also induces Bmal1expression, acting through PPRE located in its promoter.
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ature (72). Ablation of DMH cell bodies, which receiveinputs from both the SCN and the SPZ, resulted in severeimpairment of circadian-regulated sleep-wakefulness,locomotor activity, corticosteroid secretion, and feed-ing (75). Thus, DMH and VMH constitute a gatewaybetween the master pacemaker neurons of the SCN andcell bodies located within brain centers in the hypothal-amus (77) (Fig. 3).
The ventral and dorsal borders of the PVN, the locationof preautonomic nervous system neurons, are selectivelyinnervated by fibers of the SCN (78). The SCN can controlenergy homeostasis by providing its output to preauto-nomic neurons in the hypothalamus that are connected tothe parasympathetic and sympathetic systems (79). Stud-ies have shown that many interneurons, which projectfrom the SCN to the PVN, contain �-aminobutyric acid asneurotransmitter and inhibit the PVN (80, 81). Thus, itseems that the SCN is capable of controlling peripheraltissues not only by the secretion of humoral signals butalso by affecting the two branches of the autonomic ner-vous system, i.e., the sympathetic and parasympatheticsystems (Fig. 3).
B. SCN afferentsThere are two major ways by which metabolic infor-
mation may reach the SCN: 1) the sympathetic and para-sympathetic branches of the autonomic nervous system;
and 2) hormones or nutrients, such as glucose,that cross the blood-brain barrier. From thesites where visceral sympathetic informationenters the brain (the dorsal horn) and visceralparasympathetic information enters the brain(the nucleus of the tractus solitarius), no pro-jections are known to the SCN. Thus, it ispossible that autonomic information is trans-mitted first to the PVN and then to the SCN(Fig. 3). This seems to be different for infor-mation circulating in the bloodstream. Areasfree of the blood-brain barrier, where metab-olites and hormones in the bloodstream candirectly reach receptors on neurons, are cir-cumventricular organs. Injection of the neu-ronal tracer cholera toxin B into the ventro-medial ARC (vmARC) resulted in thevisualization of an elaborate network of pro-jections to many targets within and outsidethe hypothalamus (74). The vmARC is con-sidered the site where information from thecirculation can reach the hypothalamus, ei-ther via its connection with the circumven-tricular median eminence or through hor-mones that cross the blood-brain barrier andbind to its membrane-bound receptors. The
dense reciprocal interaction between the vmARC and theSCN provides the anatomical basis for the link betweencirculating metabolic information and the SCN (74). Thisanatomical connection between vmARC and SCN mayform the basis upon which the SCN is informed aboutcirculating hormones and the vmARC about the time ofthe day (Fig. 3). Gut-derived polypeptides have beenshown to affect circadian rhythms. For example, gastrin-releasing peptide, a mediator of both feeding and loco-motor activity, mediates light-like resetting of the SCN(82); peptide tyrosine-tyrosine has also been shown tocorrelate with alterations to wakefulness and sleep ar-chitecture (83). However, the effect of peptide tyrosine-tyrosine and gastrin-releasing peptide is presumablymediated via vagal afferents that travel through the au-tonomic nervous system to the SCN rather than directlyfrom the vmARC.
C. Effect of neuropeptides and hormones on SCNSeveral brain regions have been associated with energy
homeostasis. These regions are the VMH, PVN, DMH,and ARC located at the mediobasal hypothalamus. De-struction of VMH, PVN, and DMH results in obesity,whereas ablation of the lateral hypothalamus results inanorexia (84). At the molecular level, the melanocortinsystem plays a major role in the neural control of energyhomeostasis (85, 86). Leptin, a satiety signal, stimulates
Fig. 3. SCN afferents and efferents. The SCN can be entrained by light, hormonesand nutrients, and neuronal connections (green arrows). The SCN sends neuronalconnections to the ARC, MPOA, PVN, and SPZ (blue arrows). Hormones and nutrientsmay affect the ARC directly. The ARC controls expression of orexins and MCH in LH.The SPZ innervates the DMH, which, in turn, innervates PVN, VLPO, and LH,regulating corticosteroid production, sleep, and feeding, respectively. MPOA, PVN,and DMH through the autonomic nervous system regulate adipose tissue, liver, andother peripheral tissues (red arrows). In turn, gut-derived hormones, nutrients, andabdominal distension signal to the brain through the autonomic nervous system. LH,Lateral hypothalamus; ORX, orexins; Raphe, brainstem raphe nuclei; VLPO,ventrolateralpreoptic area.
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proopiomelanocortin (POMC)-andcocaine- andamphet-amine-regulated transcript-expressing neurons within theARC to produce �-melanocyte-stimulating hormone (�-MSH), which subsequently activates the melanocortin 4receptor (MC4R) and results in decreased food intake andincreased energy expenditure (87, 88). In humans, muta-tions in the POMC and MC4R genes are associated withmorbid obesity (89–94). In parallel, leptin suppresses adistinct set of neuropeptide Y (NPY)- and agouti-relatedprotein (AgRP)-expressing neurons within the ARC. In theabsence of leptin, such as during fasted state, NPY/AgRP-expressing neurons release AgRP, an antagonist of theMC4R (95–97) causing decreased energy expenditure andincreased appetite (98–102). Thus, agonists (�-melano-cyte-stimulating hormone) and antagonists (AgRP) of theMC4R determine the weight-regulating effects of leptin inthe central nervous system. Leptin can be the bridge be-tween energy homeostasis and circadian control, due to itscircadian oscillation (see Section IV.D) and expression ofits receptor in several hypothalamic regions. Receptors forleptin and ghrelin are present on SCN cells (74, 103, 104),so it is possible that these hormones bind directly to SCNneurons, similarly to their effect on NPY/AgRP-neurons.Activation of vmARC neurons by systemic administrationof the ghrelin mimetic GH-releasing peptide-6 combinedwith SCN tracing showed that vmARC neurons transmitfeeding-related signals to the SCN (74). This injection in-duced Fos in the vmARC and resulted in attenuation oflight-induced phase delay in mice and light-induced Fosexpression in the SCN in rats (105). Administration ofghrelin to SCN slices or SCN explants in vitro causedphase shifts in Per2::luc reporter gene expression. How-ever, administration of ghrelin to wild-type mice onlycaused phase shifts after 30 h of food deprivation, whereasip injection of ghrelin did not cause phase shifts in wild-type mice fed ad libitum (106). Thus, it seems that ghrelinand leptin may affect the SCN directly or through their effecton the ARC, which is then relayed to the SCN (Fig. 3).
Hypothalamic neuropeptides, such as NPY, AgRP, andPOMC, are also expressed according to a pronounceddiurnal rhythm, although the extent to which these oscil-lations are entrained by feeding, light, or nutrient signalingremains uncertain (107). In addition to its being a clock-controlled output gene, NPY is involved in communicat-ing nonphotic signals to the SCN via the intergeniculateleaflet (108) (Fig. 3). In addition, serotonergic signalingpathways from the raphe nuclei that influence feeding andenergy metabolism in the hypothalamus have been shownto modulate both SCN oscillations and sleep (109) (Fig. 3).Therefore, these signaling systems appear to be involved ina feedback loop that links feeding and metabolic state tothe SCN. Recently, the NPY/AgRP system has been shown
to be further connected to the SCN clock. Disruption ofthe brain-specific homeobox factor Bsx, encoding a keyregulator of hypothalamic NPY/AgRP neuron develop-ment (110), yielded mice that were resistant to obesitywhen crossed with leptin-deficient obese (ob) mice anddisplayed attenuated onset and dampened amplitude ofnocturnal locomotor activity. Further analysis of thesemutant mice may shed light on the linkage between theSCN and NPY/AgRP neurons.
ARC neurons project to multiple nuclei involved infeeding behavior (99, 111–113), such as the lateral hypo-thalamus,whichproduces thehunger-stimulatingneuropep-tidesmelanin-concentratinghormone(MCH),orexinA,andorexin B (114–116) (Fig. 3). Targeted deletion studies ofMCH resulted in hypophagic lean mice with a high met-abolic rate and demonstrated that MCH acts downstreamof leptin and the melanocortin system (117). Orexins Aand B are two neuropeptides generated from a single tran-script that display a circadian rhythm of expression andare strongly induced by fasting (118, 119). Indeed, mutantmice, in which Clock function is impaired, exhibit signif-icantly higher energy intake and almost complete ablationof rhythmic expression in Cart and Orexin (120). Intra-cerebroventricular injection of orexin A stimulates foodintake acutely in rats, in part through excitation of NPY inthe ARC (118, 121). Orexins also play a role in the reg-ulation of sleep-wake rhythms because mutations in theorexin B receptor (119, 122) and deletion of the orexingene (123) caused narcolepsy and obesity (124, 125). Allthese findings demonstrate the intricate relationships be-tween circadian rhythms and energy homeostasis.
D. Circadian rhythms and metabolismMany hormones involved in metabolism, such as insu-
lin (126), glucagon (127), adiponectin (128), corticoste-rone (129), leptin, and ghrelin (130, 131), have beenshown to exhibit circadian oscillation. Leptin, an adipo-cyte-derived circulating hormone that acts at specific re-ceptors in the hypothalamus to suppress appetite and in-crease metabolism, is extremely important in obesity.Leptin exhibits striking circadian patterns in both geneexpression and protein secretion, with peaks during thesleep phase in humans (132). Neither feeding time noradrenalectomy affected the rhythmicity of leptin release.However, ablation of the SCN has been shown to elimi-nate leptin circadian rhythmicity in rodents, suggestingthat the central circadian clock regulates leptin expression(133). In addition, SCN-lesioned rats, as opposed to intactanimals, showed no elevation in plasma free fatty acids(FFAs) after ip administration of leptin, suggesting a rolefor SCN in leptin function (134).
In addition to the endocrine control, the circadian clockhas been reported to regulate metabolism and energy ho-
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meostasis in peripheral tissues (135, 136). This is achievedby mediating the expression and/or activity of certain met-abolic enzymes and transport systems (137, 138) involvedin cholesterol metabolism, amino acid regulation, drugand toxin metabolism, the citric acid cycle, and glycogenand glucose metabolism (77, 126, 139–141). Some exam-ples are glycogen phosphorylase (142), cytochrome oxi-dase (143), lactate dehydrogenase (144), acetyl-CoA car-boxylase (145, 146), malic enzyme, fatty acid synthase,glucose-6-phosphate dehydrogenase (145), and manymore. Moreover, lesion of rat SCN abolishes diurnal vari-ations in whole body glucose homeostasis (147), alteringnot only rhythms in glucose utilization rates but also en-dogenous hepatic glucose production. Indeed, the SCNprojects to the preautonomic PVN neurons to control he-patic glucose production (148). Similarly, glucose uptakeand the concentration of the primary cellular metaboliccurrency ATP in the brain and peripheral tissues have beenfound to fluctuate around the circadian cycle (139, 148,149). In addition, a large number of nuclear receptorsinvolved in lipid and glucose metabolism has been foundto exhibit circadian expression (150).
E. Effect of metabolism on circadian rhythmsThe effect of metabolism on the master or peripheral
clocks could arise from feeding, food metabolites, or hor-
mones whose secretion is controlled by food or its absence.Several studies have identified single nutrients capable ofresetting or phase-shifting circadian rhythms, such as glu-cose (151–154), amino acids (154), sodium (155, 156),ethanol (157, 158), caffeine (159), thiamine (160, 161),and retinoic acid (162, 163). In addition to nutrients, hor-mones that regulate metabolism can also induce or resetcircadian rhythms through regulation of clock gene ex-pression. For example, in Rat-1 fibroblast cultures, insulincauses an acute induction of Per1 mRNA production(164). Glucocorticoids were shown to induce circadiangene expression in cultured rat-1 fibroblasts and tran-siently change the phase of circadian gene expression inliver, kidney, and heart (165, 166). Interestingly, it wasrecently reported that leptin causes up-regulation of Per2and Clock gene expression in mouse osteoblasts that ex-hibit endogenous circadian rhythms (167).
Recent experiments have suggested that cellular energylevels are capable of influencing rhythms (168). CLOCKand its homolog NPAS2 can bind efficiently to BMAL1and consequently to E-box sequences in the presence ofreduced nicotinamide adenine dinucleotides (NADH andNADPH) (Fig. 4A). On the other hand, the oxidized formsof the nicotinamide adenine dinucleotides (NAD� andNADP�) inhibit DNA binding of CLOCK:BMAL1 or
NAD+ NAMNAD(P)H
E-boxCLOCK BMAL1
E-boxCLOCK BMAL1
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xAc
Ac
REV-ERBs
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PGC-1α
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Ac
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PPRE RORE
PGC-1αPPARα
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CRYs
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AMPK AMP
PP
AMPK AMP
ADPATP
A
B
SIRT1
SIRT1
Ac ADP-r
Ac ADP-r
Ac
x
REV-ERBs
x
Fig. 4. The role of NAD�/NAD(P)H levels in the core clock mechanism. A, High NAD(P)H levels promote CLOCK:BMAL1 binding to E-boxsequences leading to the acetylation of BMAL1 and expression of Pers, Crys, and other clock-controlled genes. The negative feedback loop, PERs:CRYs binds to CLOCK:BMAL1, and consequently PERs are acetylated. When NAD� levels rise as a result of AMPK activation by high AMP levels,SIRT1 deacetylates PERs and BMAL1, relieving PERs:CRYs repression and another cycle begins. B, Expression of Bmal1 and Rev-erb� genes arecontrolled by PPAR� and binding of RORs to RORE sequences. RORs need a coactivator, PGC-1�, which is phosphorylated by AMPK. In parallel,AMPK activation leads to an increase in NAD� levels, which, in turn activate SIRT1. SIRT1 activation leads to PGC-1� deacetylation and activation.Ac-ADP-r, Acetyl adenosine diphosphate ribose; NAM, nicotinamide.
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NPAS2:BMAL1 (168, 169). Because the NAD(P)�/NAD(P)H redox equilibrium depends on the metabolicstate of the cell, this ratio could dictate the binding ofCLOCK/NPAS2:BMAL1 to E-boxes and result in phase-shifting of cyclic gene expression (137, 168, 169). How-ever, the role of redox on circadian rhythms needs to beinvestigated in vivo.
In addition to NAD�, AMP is another cellular indicatorof low energy. Interestingly, AMP-activated protein ki-nase (AMPK), an important nutrient sensor, has beenfound to phosphorylate Ser-389 of CKI�, resulting in in-creased CKI� activity and degradation of mPER2. mPER2degradation leads to a phase advance in the circadian ex-pression pattern of clock genes in wild-type mice (170). Inaddition, the expression profile of clock-related genes,such as Per1 and Cry2, in skeletal muscle in response to5-amino-4-imidazole-carboxamide riboside, an AMPKactivator, as well as the diurnal shift in energy utilization,is impaired in AMPK�3 subunit knockout mice (171).Because AMPK has been implicated in feeding regula-tion (172) and it serves as an energy sensor, it could beone of the links to integrate the circadian clock withmetabolism (Fig. 4).
Another protein, recently found to link metabolismwith the circadian clock, is SIRT1. SIRT1 is the mamma-lian homolog of yeast Sir2, an NAD�-dependent histonedeacetylase involved in transcriptional silencing and ge-nome stability and a key factor in the longevity responseto caloric restriction (173, 174). Recent studies show thatSIRT1 interacts directly with CLOCK and deacetylatesBMAL1 and PER2 (175, 176) (Fig. 4A). It seems that afterbinding to E-box, CLOCK and CBP/p300 acetylate his-tones H3 and H4 (47) and BMAL1 (177). BMAL1 acet-ylation potentiates its binding by the repressive PER/CRYcomplex (177), and, as a result, PER2 is acetylated (175).When acetylated, PER2 (175) and possibly BMAL1 (176)are more stable (Fig. 4A). SIRT1 then becomes activatedand starts deacetylating BMAL1, PER2, and histones(178). Deacetylated PER2 is further phosphorylated anddegraded, and a new cycle begins. It has also been shownthat CLOCK:BMAL1 heterodimer regulates the circadianexpression of nicotinamide phosphoribosyltransferase, arate-limiting enzyme in the NAD� salvage pathway.SIRT1 is recruited to the Nampt promoter and contributesto the circadian synthesis of its own coenzyme (179). Mostrecently, it has been shown that AMPK enhances SIRT1activity by increasing cellular NAD� levels, resulting in thedeacetylation and modulation of the activity of down-stream SIRT1 targets (180) (Fig. 4A). The levels of NAD�
together with the cycling of SIRT1 determine the activityand robustness of transcription.
F. Effect of feeding regimens on circadian rhythmsSimilarly to the control of the circadian clock on me-
tabolism, feeding is a very potent synchronizer (zeitgeber)for peripheral clocks (Fig. 1). Limiting the time and du-ration of food availability with no calorie reduction istermed restricted feeding (RF) (39, 137, 181, 182). Ani-mals that receive food ad libitum everyday at the same timefor only a few hours adjust to the feeding period within afew days and consume their daily food intake during thatlimited time (38, 183, 184). Restricting food to a partic-ular time of day has profound effects on the behavior andphysiology of animals. Two to 4 h before the meal, theanimals display food anticipatory behavior, which is dem-onstrated by an increase in locomotor activity, body tem-perature, corticosterone secretion, gastrointestinal motil-ity, and activity of digestive enzymes (181, 183, 185, 186),all of which are known output systems of the biologicalclock. RF is dominant over the SCN and drives rhythms inarrhythmic and clock mutant mice and animals with le-sioned SCN, regardless of the lighting conditions (181,187–191). In most incidents, RF affects circadian oscilla-tors in peripheral tissues, such as liver, kidney, heart, andpancreas, with no effect on the central pacemaker in theSCN (39, 137, 182, 189, 190, 192, 193). Thus, RF un-couples the SCN from the periphery, suggesting that nu-tritional regulation of clock oscillators in peripheral tis-sues may play a direct role in coordinating metabolicoscillations (194). Many physiological activities that arenormally dictated by the SCN master clock, such as he-patic P450 activity, body temperature, locomotor activity,and heart rate, are phase-shifted by RF to the time of foodavailability (141, 188, 189, 195, 196). As soon as foodavailability returns to normal, the SCN clock, whosephase remains unaffected, resets the peripheral oscillators(192). The location of this food-entrainable oscillator hasbeen elusive. Lesions in the dorsomedial hypothalamic nu-cleus (DMH) (197–200), the brainstem parabrachial nu-clei (198, 201), and the core and shell regions of nucleusaccumbens (202, 203) revealed that these brain regionsmay be involved in food-entrainable oscillator output, butthey cannot fully account for the oscillation (204). Neithervagal signals nor leptin are critical for the entrainment(205, 206). CLOCK (207) or BMAL1 (208) and otherclock genes (209) have been shown not to be necessary forfood anticipatory activity. However, it has recently beendemonstrated that mPer2 mutant mice did not exhibitwheel-running food anticipation (210, 211). Thus, the ef-fect of RF on circadian rhythms warrants further study.
Calorie restriction (CR) refers to a dietary regimen lowin calories without malnutrition. CR restricts the amountof calories derived from carbohydrates, fats, or proteins to60–75% of ad libitum-fed animals (212). It has been doc-
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umented that calorie restriction significantly extends thelife span of rodents by up to 50% (213, 214). In additionto the increase in life span, CR also delays the occurrenceof age-associated pathophysiological changes, such ascancer, diabetes, kidney disease, and cataracts (214–217).Theories on how CR modulates aging and longevityabound, but the exact mechanism is still unknown (214).As opposed to RF, CR entrains the clock in the SCN (218–221), indicating that calorie reduction could affect thecentral oscillator. CR during the daytime affects the tem-poral organization of the SCN clockwork and circadianoutputs in mice under light-dark cycle. In addition, CRaffects photic responses of the circadian system, indicatingthat energy metabolism modulates gating of photic inputsin mammals (220). These findings suggest that synchro-nization of peripheral oscillators during CR could beachieved directly due to the temporal eating, as has beenreported for RF (189, 192, 193), or by synchronizing theSCN (218–220), which in turn sends humoral or neuronalsignals to entrain the peripheral tissues (38, 222).
During intermittent fasting (IF), food is available adlibitum every other day. IF-treated mice eat on the daysthey have access to food approximately twice as much asthose having continuous access to food (223, 224). Simi-larly to calorically restricted animals (214), IF-fed animalsexhibit increased life span incomparisonwith thead libitum-fed control (225) as well as improved glucose metabolism,cardio-protection, neuro-protection (223, 226 –230), andincreased resistance to cancer (224). The IF-induced ben-eficial effects are thought to occur independently of theoverall caloric intake, but the underlying mechanisms arestill unknown. One suggested mechanism is stimulation ofcellular stress pathways induced by the IF regimen (223,231, 232). Recently, it has been shown that when food wasintroduced during the light period, mice exhibited almostarrhythmicity in clock gene expression in the liver. Unlikedaytime feeding, nighttime feeding yielded rhythms sim-ilar to those generated during ad libitum feeding (233).The fact that IF can affect circadian rhythms differentlydepending on the timing of food availability suggests thatthis regimen affects the SCN clock, similarly to CR. SCNresetting by IF and CR could be involved in the healthbenefits conferred by these regimens (222).
V. The Biological Clock and Obesity
A. SCN connection to adipose tissueThe daily rhythm in adipose leptin production strongly
suggests a direct control of adipose tissue activity by thebiological clock (133). Indeed, injection of the pseudora-bies virus into white adipose tissue (WAT) led to labelingin SCN neurons (234, 235). WAT is innervated by the
sympathetic nervous system leading to the mobilization oflipid stores (236, 237) and by the parasympathetic ner-vous system resulting in anabolism (238). To test whetherthe SCN uses its projections to preautonomic PVN neu-rons to control the mobilization of lipid stores, similarly toits control over hepatic glucose production (see SectionIV.A), the �-aminobutyric acid-antagonist bicucilline wasinfused into the PVN, and plasma glucose, leptin, and FFAlevels were measured (148). Contrary to plasma glucoseconcentrations, plasma FFA and plasma leptin concentra-tions were not affected by bicucilline treatment in thePVN. Also, PVN lesions did not attenuate fasting-inducedlipid mobilization (148). Viral tracing from WAT, besidesthe PVN, was found especially in the MPOA, an area im-plicated in lipidmetabolism, theDMH,and theARC(234,235). Thus, it seems that the SCN uses different outputs tocontrol glucose (via the PVN) and lipid (via the MPOA)metabolism (148).
B. Effect of circadian rhythms on lipid metabolismCircadian clocks have been shown to be present in in-
guinal WAT, epididymal WAT, and brown adipose tissue(67, 239, 240). Diurnal variations in the sensitivity of ad-ipose tissue to adrenaline-induced lipolysis persist ex vivo,suggesting that the intrinsic nature of the adipocyte ex-hibits a diurnal variation (241). Recent transcriptomestudies revealed rhythmic expression of clock and adipo-kine genes, such as resistin, adiponectin, and visfatin, invisceral fat tissue (128). The expression of these mediatorsis blunted in obese patients (133, 242, 243). Fatty acidtransport protein 1 (Fatp1), fatty acyl-CoA synthetase 1(Acs1), and adipocyte differentiation-related protein (Adrp)exhibit diurnal variations in expression, suggesting thatnocturnal expression of FATP1, ACS1, and ADRP willpromote higher rates of fatty acid uptake and storage oftriglyceride in rodents (244).
Recent molecular studies established the involvementof BMAL1 activity in the control of adipogenesis and lipidmetabolism in mature adipocytes. Embryonic fibroblastsfrom Bmal1�/� knockout mice failed to differentiate intoadipocytes. Loss of BMAL1 expression led to a significantdecrease in adipogenesis and gene expression of severalkey adipogenic/lipogenic factors �peroxisome prolifera-tor-activated receptor (PPAR) �2, adipocyte fatty acid-bindingprotein2 (aP2),CCAATenhancerbindingprotein� (C/EBP�), C/EBP�, sterol regulatory element-bindingprotein 1a (SREBP-1a), phosphoenolpyruvate carboxyki-nase, fatty acid synthase�. Furthermore, overexpression ofBMAL1 in adipocytes increased lipid synthesis activity.These results indicate that BMAL1, a master regulator ofcircadian rhythm, also plays important roles in the regu-lation of adipose differentiation and lipogenesis in matureadipocytes (245).
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Recently, a comprehensive survey of nuclear receptormRNA profiles in white and brown adipose tissue, liver,and skeletal muscle in mice revealed that approximately50% of the known nuclear receptors exhibit rhythmic ex-pression (150). Because these receptors sense various lip-ids, vitamins, and fat-soluble hormones, they serve as di-rect links between nutrient-sensing pathways and thecircadian control of gene expression. The circadian rhyth-micity of a nuclear receptor family member, PPAR�, pro-vides an example of a reciprocal link between circadianand lipid metabolic processes. The CLOCK:BMAL het-erodimer mediates transcription of PPAR�, which subse-quently binds to the peroxisome-proliferator responseelement (PPRE) and activates transcription of Bmal1(246–248) (Figs. 1 and 4B). Bmal1 has also been shown tobe regulated by PPAR� in cells of the aorta (249). PPAR�
regulates the transcription of genes involved in lipid andglucose metabolism upon binding of endogenous FFAs.Thus, PPAR� may play a unique role at the intersection ofcircadian and lipid metabolic pathways.
Another example for the relationship between nuclearreceptors and the biological clock is seen with retinoicacid. Retinoic acid has been shown to up-regulate Per1and Per2 expression in an E-box-dependent manner inmouse fibroblast NIH3T3 cells (163). Similarly, retinoicacid can phase-shift Per2 expression in vivo and in serum-induced smooth muscle cells in vitro (162). However,when retinoic acid is administered to cells expressing theretinoic acid receptors RAR� or RXR�, the ligand-recep-tor complex competes with BMAL1 for binding toCLOCK or NPAS2 in vascular cells. These interactions neg-atively regulate CLOCK/NPAS2:BMAL1-mediated tran-scriptional activation of clock gene expression (162, 163).
An important candidate to link between the circadianclock and lipid metabolism is REV-ERB�. This proadipo-genic transcription factor, whose levels increase dramat-ically during adipocyte differentiation (250), exhibitsstriking diurnal variations in expression in murine adiposetissue (244) and rat liver (251). During adipocyte differ-entiation, REV-ERB� has been shown to act downstreamof the differentiation factor PPAR� by facilitating geneexpression of PPAR target genes, including Ap2 andC/ebp�, but it has no effect on C/ebp� or SREBP-1 geneexpression (252, 253). Ectopic REV-ERB� expression in3T3L1 preadipocytes promotes their differentiation intomature adipocytes (252). In addition to its role in lipidmetabolism and adipocyte differentiation, REV-ERB� is anegative regulator of Bmal1 expression (58), as mentionedabove (Figs. 1 and 4B). In contrast, ROR�, which regu-lates lipogenesis and lipid storage in skeletal muscle, is apositive regulator of Bmal1 expression (60, 254, 255)(Figs. 1 and 4B). Interestingly, CLOCK:BMAL1 het-
erodimer regulates the expression of both Rev-erb� andRor� (58, 60, 256) (Figs. 1 and 4B). Mice deficient inROR� or REV-ERB� have impaired circadian rhythmsof locomotor activity and clock gene expression (58,60). The PPAR� coactivator, PGC-1� (peroxisome pro-liferator-activated receptor-coactivator 1a), a transcrip-tional coactivator that regulates energy metabolism, isrhythmically expressed in the liver and skeletal muscle ofmice. PGC-1� stimulates the expression of Bmal1 andRev-erb� through coactivation of the ROR family of or-phan nuclear receptors (257, 258) (Fig. 4B). Mice lackingPGC-1� show abnormal diurnal rhythms of activity, bodytemperature, and metabolic rate due to aberrant expres-sion of clock genes and those involved in energy metabo-lism. Analyses of PGC-1�-deficient fibroblasts and micewith liver-specific knockdown of PGC-1� indicate that it isrequired for cell-autonomous clock function (257). Acety-lated PGC-1� is also a substrate for SIRT1 (see Section IV.E)(180) (Fig. 4B). Thus, PPAR�, PPAR�, REV-ERB�, ROR�,and PGC-1� are key components of the circadian oscillatorthat integrate the mammalian clock and lipid metabolism.The interconnection between the clock core mechanism andlipogenic and adipogenic pathways emphasizes why clockdisruption leads to metabolic disorders (see Section V.E).
C. Effect of high-fat diet on circadian rhythmsFew studies show that a high-fat diet leads to minimal
effects on the rhythmic expression of clock genes in vis-ceral adipose tissue and liver (259, 260). However, recentstudies have shown that introduction of a high-fat diet toanimals leads to rapid changes in both the period of lo-comotor activity in constant darkness and to increasedfood intake during the normal rest period under light-darkconditions (261). These changes in behavioral rhythmicitycorrelated with disrupted clock gene expression withinhypothalamus, liver, and adipose tissue, as well as withaltered cycling of hormones and nuclear hormone recep-tors involved in fuel utilization, such as leptin, TSH, andtestosterone in mice, rats, and humans (261–266). Fur-thermore, a high-fat diet modulates carbohydrate metab-olism by amplifying circadian variation in glucose toler-ance and insulin sensitivity (267).
In addition to the disruption of clock gene expression,high-fat diet induced a phase delay in clock and clock-controlled genes (265). Recently, AMPK has been foundto phosphorylate Ser-389 of CKI�, resulting in increasedCKI� activity and degradation of mPER2. mPER2 degra-dation leads to a phase advance in the circadian expressionpattern of clock genes in wild-type mice (170) (see SectionIV.E). As the levels of mAMPK decline under a high-fatdiet (265), it is plausible that the changes seen in the ex-pression phase of genes under a high-fat diet are mediatedby changes in AMPK levels. In addition to its effect on gene
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expression, high-fat feeding led to impaired adjustment tolocal time by photic resetting, including slower rate ofreentrainment of behavioral and body temperaturerhythms after “jet-lag” tests (6-h advanced light-dark cy-cle) and reduced phase-advance responses to light. Theseresults correlated with reduction in c-FOS and P-ERK ex-pression in the SCN in response to light-induced phaseshifts (268).
D. Circadian rhythms and body weightFluctuations in body weight have been associated with
changes in day length in various species, suggesting a cen-tral role for the circadian clock in regulating body weight.For example, in Siberian hamsters, modulation of bodyweight depends on photoperiod acting via the temporalpattern of melatonin secretion from the pineal gland (269,270). In studies performed on sheep, adipose tissue leptinlevels were modulated by day length independently offood intake, body fatness, and gonadal activity. In addi-tion, increasing the length of the photoperiod resulted inincreased activity of the lipogenesis-promoting proteinslipoprotein lipase and malic enzyme, independent of thenutritional status (271, 272). In humans, studies havedemonstrated an increased incidence of obesity amongshift workers (273–275) (see Section V.F).
In obese subjects, leptin retains diurnal variation in re-lease, but with lower amplitude (276). Leptin 24-h levelswere lower in obese compared with nonobese adolescentgirls, suggesting that blunted circadian variation may playa role in leptin resistance and obesity (277). Circadianpatterns of leptin concentration were distinctly differentbetween adult women with upper-body or lower-bodyobesity, with a delay in peak values of leptin of approxi-mately 3 h in women with upper-body obesity (278). In-deed, leptin and the leptin receptor knockouts in animalsor mutations in humans have been demonstrated to pro-duce morbid, early onset obesity, hypoleptinemia, hy-perphagia, hyperinsulinemia, and hyperglycemia (279–282). Similarly to leptin, the rhythmic expression ofresistin and adiponectin was greatly blunted in obese (KK)and obese, diabetic (KK-Ay) mice (128). In humans, cir-culating adiponectin levels exhibit both ultradian pulsa-tility and a diurnal variation. In the latter case, the patternof adiponectin release is out of phase with leptin with asignificant decline at night, reaching a nadir in the earlymorning (243). In obese subjects, adiponectin levels weresignificantly lower than lean controls, although the obesegroup had significantly higher average pulse height andvalley concentrations (283). In rats, melatonin, a synchro-nizer of the SCN clock, decreased weight gain in responseto high-fat diet and decreased plasma leptin levels within3 wk. These effects were independent of total food con-sumption (284). Thus, it seems that the circadian clock
plays a major role in determining body weight probably byinfluencing the expression and secretion of hormones (seeSection V.E).
E. Clock mutations and metabolic disordersRecent studies have suggested that disruption of circa-
dian rhythms in the SCN and peripheral tissues may leadto manifestations of the metabolic syndrome (5, 285,286). Circadian control of glucose metabolism is impli-cated by the variation in glucose tolerance and insulinaction across the day (287, 288). Evidence suggests thatloss of circadian rhythmicity of glucose metabolism maycontribute to the development of metabolic disorders,such as type 2 diabetes, in both rodents (289–291) andhumans (288, 292). For example, daily cycles of insulinsecretion and glucose tolerance are lost in patients withtype 2 diabetes (288, 293), as are daily variations inplasma corticosterone levels and locomotor activity instreptozotocin-induced diabetic rats (289, 290). In addi-tion, some clock genes exhibited altered expression in theliver, heart, and kidney in diabetic animals (23, 294, 295).These findings indicate that a critical relationship existsbetween endogenous circadian rhythms and diabetes. Thefindings also suggest that the time of day may be an im-portant consideration for the diagnosis and treatment ofmetabolic disorders, such as type 2 diabetes (296, 297).Interestingly, the oscillations of clock (Bmal1, Per1, Per2,Cry1, Cry2, and Dbp) and adipokine genes were mildlysuppressed in the adipose tissue of obese KK mice andgreatly suppressed in the adipose of obese, diabetic (KK-Ay)mice compared with wild-type mice (128). Similarly,obese diabetic mice exhibited circadian oscillation of mostgenes in the liver, but some genes had attenuated, but stillrhythmic, expression (298). In addition, in type 1 diabetespatients, lipolysis increased earlier in the evening than inhealthy controls and remained elevated throughout thenight, indicating that lipolysis shows a distinct circadianrhythm that is altered in type 1 diabetes patients (299).These findings point to the tight relationship between dis-ruption of circadian rhythms and metabolic disorders.
The most compelling linkage between metabolic disor-ders and the circadian clock is demonstrated by the phe-notypes of clock gene mutants and knockouts. Severalstrains with varying effects on metabolism have thus farbeen examined. Homozygous C57BL/6J Clock�19 mice,with a truncated exon 18 and deleted exon 19 of the Clockgene, have a greatly attenuated diurnal feeding rhythm,are hyperphagic and obese, and develop a metabolic syn-drome of hyperleptinemia, hyperlipidemia, hepatic steato-sis, and hyperglycemia (120). Loss of circadian rhythms inClock�19 mutant mice was accompanied by attenuatedexpression of hypothalamic peptides associated with en-ergy balance, such as ghrelin and orexin (120). In addition,
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Clock�19 mice (C57BL/6J) had impaired conversion ofpyruvate to glucose, together with alterations in liverphosphoenolpyruvate carboxykinase enzyme activity,which is indicative of altered gluconeogenesis. Insulin ad-ministration caused significantly greater hypoglycemia inClock�19 mutant mice than in wild-type mice (267). In-creased insulin sensitivity was also seen in Clock�19 mu-tant, melatonin-producing mice of the BALB/c/CBA back-ground together with fasting hypoglycemia in young adultmales, fasting hyperglycemia in older females, and sub-stantially impaired glucose tolerance overall (300). InClock�19 on a Jcl:ICR background, serum levels of tri-glyceride and FFA were significantly lower than in wild-type control mice, whereas total cholesterol and glucose,insulin, and leptin levels did not differ (301). Similarly,unlike C57BL/6J Clock�19 mutant mice (120), neithermale nor female Jcl:ICR Clock�19 mutant mice wereobese, and they mostly had low or normal fasting plasmaglucose rather thanhyperglycemia, lowplasmaFFAratherthan hyperlipidemia, and normal plasma leptin ratherthan hyperleptinemia. Combination of the Clock�19 mu-tation (Jcl:ICR) with the leptin knockout (ob/ob) resultedin significantly heavier mice than the ob/ob phenotype(302). However, in Jcl:ICR Clock�19 mutant mice, high-fat diet amplified the diurnal variation in glucose toleranceand insulin sensitivity, and obesity was attenuatedthrough impaired dietary fat absorption (301). Triglycer-ide content in the liver was significantly less increased inJcl:ICR Clock�19 mutant mice fed a high-fat diet com-pared with wild-type mice. Jcl:ICR Clock�19 mutant micehad attenuated daily rhythms of Acsl4 (acyl-coenzyme Asynthetase long-chain 4) and Fabp1 (fatty acid bindingprotein 1) gene expression in the liver under both normaland high-fat diet conditions compared with wild-typemice, which could have led to the attenuated accumulationof triglycerides in the liver under a high-fat diet (303). InClock�19 mutant, melatonin-producing mice of the BALB/c/CBA background, relative weight of epigonadal fat com-pared with body weight was not significantly differentbetween male wild-type and mutant mice fed a high-fatdiet (300). Although the effects on metabolism were vari-able, due to strain differences, the overall picture is thatdisruption of the clock gene leads to disruption of meta-bolic pathways.
Bmal1�/� knockout mice, similarly to C57BL/6JClock�19 mutant mice, exhibited suppressed diurnal vari-ations in glucose and triglycerides as well as abolishedgluconeogenesis. Liver-specific deletion of Bmal1 showeda direct effect of the liver clock on glucose metabolism, asexhibited by hypoglycemia during fasting, exaggeratedglucose clearance, and loss of rhythmic expression of he-patic glucose regulatory genes (304). Although recovery
from insulin-induced hypoglycemia was impaired inC57BL/6J Clock�19 mutant and Bmal1�/� knockout mice,the counter-regulatory response of corticosterone and glu-cagon was retained (267). Thus, it seems that CLOCK andBMAL1 regulate the recovery from insulin-induced hypo-glycemia, glucose tolerance, insulin sensitivity, and fat ab-sorption. However, the impaired recovery from insulin-in-duced hypoglycemia in C57BL/6J Clock�19 mutant andBmal1�/� knockout mice, in contrast with the increased in-sulin sensitivity in BALB/c/CBA Clock�19 mutant, melato-nin-producing mice, further emphasizes the role of the ge-netic background in metabolic responses.
Mutation in another central clock gene, Per2 (mPer2�/�
mice), exhibits no glucocorticoid rhythm although the cor-ticosterone response to hypoglycemia is intact. In addition,the diurnal feeding rhythm is absent in mPer2�/� mice. Al-thoughfoodconsumption is similarduring the lightanddarkperiods on high-fat diet, mPer2�/� mice develop significantobesity (305). The Per2 gene has also been implicated in cellcycle regulation and was suggested to function as a tumorsuppressor in thymocytes (8). In addition, mPer2�/� miceexhibit increased bone density in mice (167). Because boneand adipose tissue share a common ontogeny, it is possiblethat these findings may also have implications for adipogen-esis (306).
Alterations in lipid and glucose homeostasis also occurwith mutations in clock-related genes, such as the Noc-turnin, a deadenylase involved in posttranscriptional reg-ulation of rhythmic gene expression (307, 308). Noctur-nin�/� mice have normal feeding behavior as well asnormal food intake and activity levels, but they are resis-tant to diet-induced obesity. The Nocturnin�/� mice alsohave changes in glucose tolerance and improved whole-body insulin sensitivity. This phenotype is probably due tolack of rhythmicity in genes important for lipid uptake ormetabolism because these mice exhibit loss of these lipidpathways (309). Disruption in rhythms of digestionand/or absorption of fat could explain the high-fat-resis-tant phenotype of both Nocturnin�/� and Jcl:ICRClock�19 mutant mice.
F. Sleep, shift work, and obesitySleep is one of the clock-controlled output systems. A
large body of evidence accumulated thus far suggests thatshort sleep duration is associated with increased bodymass index (BMI; weight in kilograms divided by thesquare of height in meters) and elevated incidence of type2 diabetes (310–314). Clinical studies have also identifiedchanges in many aspects of energy metabolism after just afew days of partial sleep restriction. Furthermore, shortsleepers have significantly reduced circulating levels of theanorectic hormone leptin, increased levels of the orexi-genic hormone ghrelin, and increased hunger and appetite
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(313, 315). These neuroendocrine changes could explain,in part, reports of increased appetite after sleep loss (316).The relationship between BMI and reported total sleeptime per 24 h showed that overweight (BMI � 25–29.9kg/m2) and obese (BMI � 30–39.9 kg/m2) patients sleptless than patients with normal BMI. Interestingly, ex-tremely obese subjects (BMI � 40 kg/m2) averaged greatertotal sleep time than the obese subjects (317). Indeed, pre-vious studies have reported that obese patients were sleep-ier during the day and more likely to experience disturbedsleep at night compared with normal-weight controls(318). Daytime sleepiness could not wholly be explainedby disturbed nighttime sleep, suggesting that a circadianabnormality likely underlies the daytime sleepiness ob-served in the obese patients (318). Morning levels of cy-tokines associated with obesity, e.g., TNF-� and IL-6,were significantly elevated in patients with sleep apneacompared with controls and also significantly correlatedwith excessive daytime sleepiness (319). In addition, sleepdeprivation leads to obesity (320) and affects plasma lep-tin levels (321). The diurnal amplitude of leptin was re-duced during 88 h of sleep deprivation and returned to-ward normal during the period of recovery sleep (321).
Shift work is another example in which the normalsynchrony between the light-dark cycle, sleeping, and eat-ing is disturbed. Shift work has been associated with car-diovascular disease, obesity, diabetes, and other metabolicdisturbances (274, 322). Night-shift workers, whose ac-tivity period is reversed in relation to the day/night cycle,are much more likely to develop the metabolic syndrome(323). Even when a group of students were switched fromdaytime activity with the last meal between 1900 and2000 h to nighttime activity with the last meal at 2300 to2400 h, after 3 wk they exhibited much higher insulin andglucose levels throughout the 24 h than the daytime stu-dents (324). Among obese adults with type 2 diabetes,night-eating disorder was reported more frequently (325).People who habitually sleep less than 6 h or more than 9 hper night have increased risk of developing type 2 diabetesand impaired glucose tolerance (314). It has been reportedthat obesity, high triglycerides, and low concentrations ofhigh-density lipoprotein cholesterol seem to cluster to-gether more often in shift workers than in day workers(274, 275). Similarly, duration of shift work was directlyrelated to BMI and waist to hip ratio independent of age,sex, smoking status, physical activity, and educationallevel (273, 326, 327). Recently, it has been reported thatsubjects who experienced 38 h of continued wakefulnessstill exhibit significant endogenous circadian rhythms inleptin, glucose, and insulin with peaks around the usualtime of waking (328). Feeding during the period of wake-fulness was associated with systematic increases in leptin
levels, whereas fasting during recovery sleep was associ-ated with systematic decreases in leptin levels, glucose, andinsulin (328). Shea et al. (328) suggested that alterations inthe sleep/wake schedule would lead to an increased dailyrange in circulating leptin, with lowest leptin upon awak-ening, which, by influencing food intake and energy bal-ance, could be implicated in the increased prevalence ofobesity in the shift-work population. These findings pointto the adipocyte as an important factor in the developmentof obesity associated with shift work. Thus, shift work andsleep deprivation are associated with increased adiposity,findings that have been linked to the sleep-associated peakin leptin secretion.
High-fat diet and obesity also affect sleep itself. Micefed a high-fat diet have increased sleep time, particularlyin the non-rapid eye movement (NREM) stage, but de-creasedsleepconsolidation(329).Similarly, theobese leptin-deficient ob/ob mice and rats harboring mutations in theleptin receptor exhibit increased NREM sleep time, de-creased sleep consolidation, decreased locomotor activity,and a smaller compensatory rebound response to acutesleep deprivation (311, 330, 331). On the other hand,acute administration of leptin decreases rapid eye move-ment sleep and increases NREM sleep time in rats (332).It is beyond the scope of this review to explore the inter-connection between metabolism and sleep. However, be-cause many of the primary neuropeptides and neurotrans-mitters involved in the regulation of energy homeostasisalso mediate sleep-wake states, these findings provide ev-idence that sleep loss and obesity are “interacting epidem-ics” (reviewed in Ref. 333).
VI. Summary and Conclusions
The prominent influence of the circadian clock on humanphysiology is demonstrated by the temporal and pro-nounced activity of a plethora of systems, such as sleep-wake cycles, feeding behavior, metabolism, and physio-logical and endocrine activity. Western lifestyle leads tohigh food consumption, inactivity during the active pe-riod, enhanced activity in the rest period, and shortenedsleep period. This lifestyle may cause high parasympa-thetic output to the viscera leading to obesity, hyperinsu-linemia, and hyperlipidemia, or high sympathetic outputto the muscle and heart leading to vasoconstriction andhypertension. Indeed, disrupted biological rhythms mightlead to attenuated circadian feeding rhythms, disruptedmetabolism, cancer proneness, and reduced life expect-ancy. Disruptions of rhythms together with genetic back-ground increase the risk to develop these health compli-cations. Findings in murine models show the strong linkbetween genetic background and circadian rhythm dis-
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ruption in determining the severity of metabolic disorders.Unfortunately, circadian rhythms in metabolism are oftenoverlooked in both treatments and design of clinical andanimal studies. Because food components and feedingtime have the ability to reset bodily rhythms, it is of ex-treme importance to further investigate the relationshipbetween food, feeding, and the biological clock at the mo-lecular level.Resetting thebiological clockby foodor feed-ing time may lead to better functionality of physiologicalsystems, preventing metabolic disorders, promoting well-being, and extending life span.
Acknowledgments
Address all correspondence and requests for reprints to: Oren Froy, In-stitute of Biochemistry, Food Science, and Nutrition, Robert H. SmithFaculty of Agriculture, Food and Environment, The Hebrew Universityof Jerusalem, Rehovot 76100, Israel. E-mail: [email protected].
This work was supported by Nutricia Research Foundation Grant2008-16, 2009-E3 and Binational USA–Israel Science Foundation (BSF)Grant 2007101.
Disclosure Summary: The author has nothing to disclose.
References
1. Wyatt SB, Winters KP, Dubbert PM 2006 Overweight andobesity: prevalence, consequences, and causes of a growingpublic health problem. Am J Med Sci 331:166–174
2. Panda S, Hogenesch JB, Kay SA 2002 Circadian rhythmsfrom flies to human. Nature 417:329–335
3. Reppert SM, Weaver DR 2002 Coordination of circadiantiming in mammals. Nature 418:935–941
4. Maron BJ, Kogan J, Proschan MA, Hecht GM, RobertsWC 1994 Circadian variability in the occurrence of suddencardiac death in patients with hypertrophic cardiomyopa-thy. J Am Coll Cardiol 23:1405–1409
5. Staels B 2006 When the Clock stops ticking, metabolicsyndrome explodes. Nat Med 12:54–55
6. Burioka N, Fukuoka Y, Takata M, Endo M, Miyata M,Chikumi H, Tomita K, Kodani M, Touge H, Takeda K,Sumikawa T, Yamaguchi K, Ueda Y, Nakazaki H, SuyamaH, Yamasaki A, Sano H, Igishi T, Shimizu E 2007 Circa-dian rhythms in the CNS and peripheral clock disorders:function of clock genes: influence of medication for bron-chial asthma on circadian gene. J Pharmacol Sci 103:144–149
7. Davis S, Mirick DK 2006 Circadian disruption, shift workand the risk of cancer: a summary of the evidence and stud-ies in Seattle. Cancer Causes Control 17:539–545
8. Fu L, Pelicano H, Liu J, Huang P, Lee C 2002 The circadiangene Period2 plays an important role in tumor suppressionand DNA damage response in vivo. Cell 111:41–50
9. Filipski E, King VM, Li X, Granda TG, Mormont MC,Claustrat B, Hastings MH, Levi F 2003 Disruption of cir-cadian coordination accelerates malignant growth in mice.Pathol Biol 51:216–219
circadian desynchronization decreases the survival of an-imals with cardiomyopathic heart disease. Am J Physiol275:H2334–H2337
11. Scarbrough K, Losee-Olson S, Wallen EP, Turek FW 1997Aging and photoperiod affect entrainment and quantita-tive aspects of locomotor behavior in Syrian hamsters.Am J Physiol 272:R1219–R1225
12. Yamazaki S, Straume M, Tei H, Sakaki Y, Menaker M,Block GD 2002 Effects of aging on central and peripheralmammalian clocks. Proc Natl Acad Sci USA 99:10801–10806
13. Hofman MA, Swaab DF 2006 Living by the clock: thecircadian pacemaker in older people. Ageing Res Rev5:33–51
14. Hurd MW, Ralph MR 1998 The significance of circadianorganization for longevity in the golden hamster. J BiolRhythms 13:430–436
15. Kondratov RV, Kondratova AA, Gorbacheva VY,Vykhovanets OV, Antoch MP 2006 Early aging and age-related pathologies in mice deficient in BMAL1, the corecomponent of the circadian clock. Genes Dev 20:1868–1873
16. Karasek M 2004 Melatonin, human aging, and age-relateddiseases. Exp Gerontol 39:1723–1729
17. Welsh DK, Logothetis DE, Meister M, Reppert SM 1995Individual neurons dissociated from rat suprachiasmaticnucleus express independently phased circadian firingrhythms. Neuron 14:697–706
18. Liu C, Weaver DR, Strogatz SH, Reppert SM 1997 Cellularconstruction of a circadian clock: period determination inthe suprachiasmatic nuclei. Cell 91:855–860
19. Herzog ED, Takahashi JS, Block GD 1998 Clock controlscircadian period in isolated suprachiasmatic nucleus neu-rons. Nat Neurosci 1:708–713
20. Reppert SM, Weaver DR 2001 Molecular analysis of mam-malian circadian rhythms. Annu Rev Physiol 63:647–676
21. Lee C, Etchegaray JP, Cagampang FR, Loudon AS,Reppert SM 2001 Posttranslational mechanisms regulatethe mammalian circadian clock. Cell 107:855–867
22. Froy O, Chapnik N 2007 Circadian oscillation of innateimmunity components in mouse small intestine. Mol Im-munol 44:1964–1970
23. Young ME 2006 The circadian clock within the heart: po-tential influence on myocardial gene expression, metabo-lism, and function. Am J Physiol Heart Circ Physiol 290:H1–H16
24. Quintero JE, Kuhlman SJ, McMahon DG 2003 The bio-logical clock nucleus: a multiphasic oscillator network reg-ulated by light. J Neurosci 23:8070–8076
25. Gooley JJ, Lu J, Chou TC, Scammell TE, Saper CB 2001Melanopsin in cells of origin of the retinohypothalamictract. Nat Neurosci 4:1165
26. Lucas RJ, Freedman MS, Lupi D, Munoz M, David-GrayZK, Foster RG 2001 Identifying the photoreceptive inputsto the mammalian circadian system using transgenic andretinally degenerate mice. Behav Brain Res 125:97–102
27. Harmar AJ, Marston HM, Shen S, Spratt C, West KM,Sheward WJ, Morrison CF, Dorin JR, Piggins HD, ReubiJC, Kelly JS, Maywood ES, Hastings MH 2002 TheVPAC(2) receptor is essential for circadian function in themouse suprachiasmatic nuclei. Cell 109:497–508
28. Maywood ES, Reddy AB, Wong GK, O’Neill JS, O’Brien
14 Froy Circadian Rhythms, Metabolism, and Obesity Endocrine Reviews, February 2010, 31(1):1–24
JA, McMahon DG, Harmar AJ, Okamura H, HastingsMH 2006 Synchronization and maintenance of timekeep-ing in suprachiasmatic circadian clock cells by neuropep-tidergic signaling. Curr Biol 16:599–605
29. Le Minh N, Damiola F, Tronche F, Schutz G, Schibler U2001 Glucocorticoid hormones inhibit food-inducedphase-shifting of peripheral circadian oscillators. EMBO J20:7128–7136
30. Kramer A, Yang FC, Snodgrass P, Li X, Scammell TE,Davis FC, Weitz CJ 2001 Regulation of daily locomotoractivity and sleep by hypothalamic EGF receptor signaling.Science 294:2511–2515
31. Cheng MY, Bullock CM, Li C, Lee AG, Bermak JC,Belluzzi J, Weaver DR, Leslie FM, Zhou QY 2002 Proki-neticin 2 transmits the behavioural circadian rhythm of thesuprachiasmatic nucleus. Nature 417:405–410
32. Kraves S, Weitz CJ 2006 A role for cardiotrophin-like cy-tokine in the circadian control of mammalian locomotoractivity. Nat Neurosci 9:212–219
33. Saeb-Parsy K, Lombardelli S, Khan FZ, McDowall K,Au-Yong IT, Dyball RE 2000 Neural connections of hy-pothalamic neuroendocrine nuclei in the rat. J Neuroen-docrinol 12:635–648
34. Yoo SH, Yamazaki S, Lowrey PL, Shimomura K, Ko CH,Buhr ED, Siepka SM, Hong HK, Oh WJ, Yoo OJ, MenakerM, Takahashi JS 2004 PERIOD2::LUCIFERASE real-timereporting of circadian dynamics reveals persistent circa-dian oscillations in mouse peripheral tissues. Proc NatlAcad Sci USA 101:5339–5346
35. Welsh DK, Yoo SH, Liu AC, Takahashi JS, Kay SA 2004Bioluminescence imaging of individual fibroblasts revealspersistent, independently phased circadian rhythms ofclock gene expression. Curr Biol 14:2289–2295
36. Matsumoto S, Basil J, Jetton AE, Lehman MN, Bittman EL1996 Regulation of the phase and period of circadianrhythms restored by suprachiasmatic transplants. J BiolRhythms 11:145–162
37. LeSauter J, Lehman MN, Silver R 1996 Restoration ofcircadian rhythmicity by transplants of SCN “micropunches.”J Biol Rhythms 11:163–171
38. Froy O, Chapnik N, Miskin R 2006 Long-lived �MUPAtransgenic mice exhibit pronounced circadian rhythms.Am J Physiol Endocrinol Metab 291:E1017–E1024
39. Schibler U, Ripperger J, Brown SA 2003 Peripheral circa-dian oscillators in mammals: time and food. J Biol Rhythms18:250–260
40. Dunlap JC 1999 Molecular bases for circadian clocks. Cell96:271–290
41. Cardone L, Hirayama J, Giordano F, Tamaru T, PalvimoJJ, Sassone-Corsi P 2005 Circadian clock control bySUMOylation of BMAL1. Science 309:1390–1394
42. Vitaterna MH, King DP, Chang AM, Kornhauser JM,Lowrey PL, McDonald JD, Dove WF, Pinto LH, TurekFW, Takahashi JS 1994 Mutagenesis and mapping of amouse gene, Clock, essential for circadian behavior. Sci-ence 264:719–725
43. Asher G, Schibler U 2006 A CLOCK-less clock. TrendsCell Biol 16:547–549
44. Debruyne JP, Noton E, Lambert CM, Maywood ES,Weaver DR, Reppert SM 2006 A clock shock: mouseCLOCK is not required for circadian oscillator function.Neuron 50:465–477
45. Zylka MJ, Shearman LP, Weaver DR, Reppert SM 1998Three Period homologs in mammals: differential light re-sponses in the suprachiasmatic circadian clock and oscil-lating transcripts outside of brain. Neuron 20:1103–1110
46. Froy O, Chang DC, Reppert SM 2002 Redox potential:differential roles in dCRY and mCRY1 functions. CurrBiol 12:147–152
47. Doi M, Hirayama J, Sassone-Corsi P 2006 Circadian reg-ulator CLOCK is a histone acetyltransferase. Cell 125:497–508
48. Nakahata Y, Grimaldi B, Sahar S, Hirayama J, Sassone-Corsi P 2007 Signaling to the circadian clock: plasticity bychromatin remodeling. Curr Opin Cell Biol 19:230–237
49. Etchegaray JP, Lee C, Wade PA, Reppert SM 2003 Rhyth-mic histone acetylation underlies transcription in the mam-malian circadian clock. Nature 421:177–182
50. Curtis AM, Seo SB, Westgate EJ, Rudic RD, Smyth EM,Chakravarti D, FitzGerald GA, McNamara P 2004 His-tone acetyltransferase-dependent chromatin remodelingand the vascular clock. J Biol Chem 279:7091–7097
51. Naruse Y, Oh-hashi K, Iijima N, Naruse M, Yoshioka H,Tanaka M 2004 Circadian and light-induced transcriptionof clock gene Per1 depends on histone acetylation anddeacetylation. Mol Cell Biol 24:6278–6287
52. Ripperger JA, Schibler U 2006 Rhythmic CLOCK-BMAL1binding to multiple E-box motifs drives circadian Dbptranscription and chromatin transitions. Nat Genet 38:369–374
53. Etchegaray JP, Yang X, DeBruyne JP, Peters AH, WeaverDR, Jenuwein T, Reppert SM 2006 The polycomb groupprotein EZH2 is required for mammalian circadian clockfunction. J Biol Chem 281:21209–21215
54. Whitmore D, Cermakian N, Crosio C, Foulkes NS, PandoMP, Travnickova Z, Sassone-Corsi P 2000 A clockworkorgan. Biol Chem 381:793–800
55. Eide EJ, Virshup DM 2001 Casein kinase I: another cog inthe circadian clockworks. Chronobiol Int 18:389–398
56. Eide EJ, Woolf MF, Kang H, Woolf P, Hurst W, CamachoF, Vielhaber EL, Giovanni A, Virshup DM 2005 Control ofmammalian circadian rhythm by CKI�-regulated protea-some-mediated PER2 degradation. Mol Cell Biol 25:2795–2807
57. Eide EJ, Kang H, Crapo S, Gallego M, Virshup DM 2005Casein kinase I in the mammalian circadian clock. Meth-ods Enzymol 393:408–418
58. Preitner N, Damiola F, Lopez-Molina L, Zakany J,Duboule D, Albrecht U, Schibler U 2002 The orphan nu-clear receptor REV-ERB� controls circadian transcriptionwithin the positive limb of the mammalian circadian os-cillator. Cell 110:251–260
59. Yin L, Lazar MA 2005 The orphan nuclear receptor Rev-erb � recruits the N-CoR/histone deacetylase 3 corepressorto regulate the circadian Bmal1 gene. Mol Endocrinol 19:1452–1459
60. Sato TK, Panda S, Miraglia LJ, Reyes TM, Rudic RD,McNamaraP,NaikKA,FitzGeraldGA,KaySA,HogeneschJB2004 A functional genomics strategy reveals Rora as acomponent of the mammalian circadian clock. Neuron 43:527–537
61. Ueda HR, Hayashi S, Chen W, Sano M, Machida M,Shigeyoshi Y, Iino M, Hashimoto S 2005 System-level
Endocrine Reviews, February 2010, 31(1):1–24 edrv.endojournals.org 15
62. Kornmann B, Preitner N, Rifat D, Fleury-Olela F, SchiblerU 2001 Analysis of circadian liver gene expression byADDER, a highly sensitive method for the display of dif-ferentially expressed mRNAs. Nucleic Acids Res 29:E51–1
63. Akhtar RA, Reddy AB, Maywood ES, Clayton JD, KingVM, Smith AG, Gant TW, Hastings MH, Kyriacou CP2002 Circadian cycling of the mouse liver transcriptome, asrevealed by cDNA microarray, is driven by the suprachi-asmatic nucleus. Curr Biol 12:540–550
64. Duffield GE, Best JD, Meurers BH, Bittner A, Loros JJ,Dunlap JC 2002 Circadian programs of transcriptionalactivation, signaling, and protein turnover revealed by mi-croarray analysis of mammalian cells. Curr Biol 12:551–557
65. Storch KF, Lipan O, Leykin I, Viswanathan N, Davis FC,Wong WH, Weitz CJ 2002 Extensive and divergent circa-dian gene expression in liver and heart. Nature 417:78–83
66. Kita Y, Shiozawa M, Jin W, Majewski RR, Besharse JC,Greene AS, Jacob HJ 2002 Implications of circadian geneexpression in kidney, liver and the effects of fasting onpharmacogenomic studies. Pharmacogenetics 12:55–65
67. Zvonic S, Ptitsyn AA, Conrad SA, Scott LK, Floyd ZE,Kilroy G, Wu X, Goh BC, Mynatt RL, Gimble JM 2006Characterization of peripheral circadian clocks in adiposetissues. Diabetes 55:962–970
69. McCarthy JJ, Andrews JL, McDearmon EL, Campbell KS,Barber BK, Miller BH, Walker JR, Hogenesch JB,Takahashi JS, Esser KA 2007 Identification of the circa-dian transcriptome in adult mouse skeletal muscle. PhysiolGenomics 31:86–95
70. Kornmann B, Schaad O, Bujard H, Takahashi JS, SchiblerU 2007 System-driven and oscillator-dependent circadiantranscription in mice with a conditionally active liver clock.PLoS Biol 5:e34
71. Froy O, Chapnik N, Miskin R 2008 The suprachiasmaticnuclei are involved in determining circadian rhythms dur-ing restricted feeding. Neuroscience 155:1152–1159
72. Saper CB, Lu J, Chou TC, Gooley J 2005 The hypotha-lamic integrator for circadian rhythms. Trends Neurosci28:152–157
73. Saper CB, Scammell TE, Lu J 2005 Hypothalamic regula-tion of sleep and circadian rhythms. Nature 437:1257–1263
74. Yi CX, van der Vliet J, Dai J, Yin G, Ru L, Buijs RM 2006Ventromedial arcuate nucleus communicates peripheralmetabolic information to the suprachiasmatic nucleus. En-docrinology 147:283–294
75. Chou TC, Scammell TE, Gooley JJ, Gaus SE, Saper CB, LuJ 2003 Critical role of dorsomedial hypothalamic nucleusin a wide range of behavioral circadian rhythms. J Neurosci23:10691–10702
76. Lu J, Zhang YH, Chou TC, Gaus SE, Elmquist JK,Shiromani P, Saper CB 2001 Contrasting effects of ibote-nate lesions of the paraventricular nucleus and subpara-ventricular zone on sleep-wake cycle and temperature reg-ulation. J Neurosci 21:4864–4874
77. Ramsey KM, Marcheva B, Kohsaka A, Bass J 2007 Theclockwork of metabolism. Annu Rev Nutr 27:219–240
78. Buijs RM, Wortel J, Van Heerikhuize JJ, Feenstra MG, TerHorst GJ, Romijn HJ, Kalsbeek A 1999 Anatomical andfunctional demonstration of a multisynaptic suprachias-matic nucleus adrenal (cortex) pathway. Eur J Neurosci11:1535–1544
79. Buijs RM, Scheer FA, Kreier F, Yi C, Bos N, GoncharukVD, Kalsbeek A 2006 Organization of circadian functions:interaction with the body. Prog Brain Res 153:341–360
80. Roland BL, Sawchenko PE 1993 Local origins of someGABAergic projections to the paraventricular and su-praoptic nuclei of the hypothalamus in the rat. J CompNeurol 332:123–143
81. Shekhar A, Katner JS 1995 Dorsomedial hypothalamicGABA regulates anxiety in the social interaction test. Phar-macol Biochem Behav 50:253–258
82. Gamble KL, Allen GC, Zhou T, McMahon DG 2007 Gastrin-releasing peptide mediates light-like resetting of the supra-chiasmatic nucleus circadian pacemaker through cAMPresponse element-binding protein and Per1 activation.J Neurosci 27:12078–12087
83. Akanmu MA, Ukponmwan OE, Katayama Y, Honda K2006 Neuropeptide-Y Y2-receptor agonist, PYY3–36 pro-motes non-rapid eye movement sleep in rat. Neurosci Res54:165–170
84. Anand BK, Brobeck JR 1951 Localization of a “feedingcenter” in the hypothalamus of the rat. Proc Soc Exp BiolMed 77:323–324
85. Fan W, Boston BA, Kesterson RA, Hruby VJ, Cone RD1997 Role of melanocortinergic neurons in feeding and theagouti obesity syndrome. Nature 385:165–168
86. Huszar D, Lynch CA, Fairchild-Huntress V, Dunmore JH,Fang Q, Berkemeier LR, Gu W, Kesterson RA, Boston BA,Cone RD, Smith FJ, Campfield LA, Burn P, Lee F 1997Targeted disruption of the melanocortin-4 receptor resultsin obesity in mice. Cell 88:131–141
88. Cone RD 2005 Anatomy and regulation of the centralmelanocortin system. Nat Neurosci 8:571–578
89. Krude H, Biebermann H, Luck W, Horn R, Brabant G,Gruters A 1998 Severe early-onset obesity, adrenal insuf-ficiency and red hair pigmentation caused by POMC mu-tations in humans. Nat Genet 19:155–157
90. Yeo GS, Farooqi IS, Aminian S, Halsall DJ, Stanhope RG,O’Rahilly S 1998 A frameshift mutation in MC4R associ-ated with dominantly inherited human obesity. Nat Genet20:111–112
91. Vaisse C, Clement K, Guy-Grand B, Froguel P 1998 Aframeshift mutation in human MC4R is associated with adominant form of obesity. Nat Genet 20:113–114
92. Hinney A, Schmidt A, Nottebom K, Heibult O, Becker I,Ziegler A, Gerber G, Sina M, Gorg T, Mayer H, SiegfriedW, Fichter M, Remschmidt H, Hebebrand J 1999 Severalmutations in the melanocortin-4 receptor gene including anonsense and a frameshift mutation associated with dom-inantly inherited obesity in humans. J Clin EndocrinolMetab 84:1483–1486
93. Farooqi IS, Yeo GS, Keogh JM, Aminian S, Jebb SA, ButlerG, Cheetham T, O’Rahilly S 2000 Dominant and recessive
16 Froy Circadian Rhythms, Metabolism, and Obesity Endocrine Reviews, February 2010, 31(1):1–24
inheritance of morbid obesity associated with melanocor-tin 4 receptor deficiency. J Clin Invest 106:271–279
94. Vaisse C, Clement K, Durand E, Hercberg S, Guy-Grand B,Froguel P 2000 Melanocortin-4 receptor mutations are afrequent and heterogeneous cause of morbid obesity. J ClinInvest 106:253–262
95. Ollmann MM, Wilson BD, Yang YK, Kerns JA, Chen Y,Gantz I, Barsh GS 1997 Antagonism of central melano-cortin receptors in vitro and in vivo by agouti-related pro-tein. Science 278:135–138
96. Quillan JM, Sadee W, Wei ET, Jimenez C, Ji L, Chang JK1998 A synthetic human Agouti-related protein-(83–132)-NH2 fragment is a potent inhibitor of melanocortin recep-tor function. FEBS Lett 428:59–62
97. Rossi M, Kim MS, Morgan DG, Small CJ, Edwards CM,Sunter D, Abusnana S, Goldstone AP, Russell SH, StanleySA, Smith DM, Yagaloff K, Ghatei MA, Bloom SR 1998 AC-terminal fragment of Agouti-related protein increasesfeeding and antagonizes the effect of �-melanocyte stimu-lating hormone in vivo. Endocrinology 139:4428–4431
98. Baskin DG, Breininger JF, Schwartz MW 1999 Leptin re-ceptor mRNA identifies a subpopulation of neuropeptideY neurons activated by fasting in rat hypothalamus. Dia-betes 48:828–833
99. Elias CF, Aschkenasi C, Lee C, Kelly J, Ahima RS, BjorbaekC, Flier JS, Saper CB, Elmquist JK 1999 Leptin differen-tially regulates NPY and POMC neurons projecting to thelateral hypothalamic area. Neuron 23:775–786
100. Elias CF, Kelly JF, Lee CE, Ahima RS, Drucker DJ, SaperCB, Elmquist JK 2000 Chemical characterization of leptin-activated neurons in the rat brain. J Comp Neurol 423:261–281
101. Marsh DJ, Miura GI, Yagaloff KA, Schwartz MW, BarshGS, Palmiter RD 1999 Effects of neuropeptide Y deficiencyon hypothalamic agouti-related protein expression and re-sponsiveness to melanocortin analogues. Brain Res 848:66–77
102. Stephens TW, Basinski M, Bristow PK, Bue-Valleskey JM,Burgett SG, Craft L, Hale J, Hoffmann J, Hsiung HM,Kriauciunas A, MacKellar W, Rosteck Jr PR, Schoner B,Smith D, Tinsley FC, Zhang XY, Heiman M 1995 The roleof neuropeptide Y in the antiobesity action of the obesegene product. Nature 377:530–532
103. Guan XM, Hess JF, Yu H, Hey PJ, van der Ploeg LH 1997Differential expression of mRNA for leptin receptor iso-forms in the rat brain. Mol Cell Endocrinol 133:1–7
104. Zigman JM, Jones JE, Lee CE, Saper CB, Elmquist JK 2006Expression of ghrelin receptor mRNA in the rat and themouse brain. J Comp Neurol 494:528–548
105. Yi CX, Challet E, Pevet P, Kalsbeek A, Escobar C, BuijsRM 2008 A circulating ghrelin mimetic attenuates light-induced phase delay of mice and light-induced Fos expres-sion in the suprachiasmatic nucleus of rats. Eur J Neurosci27:1965–1972
106. Yannielli PC, Molyneux PC, Harrington ME, GolombekDA 2007 Ghrelin effects on the circadian system of mice.J Neurosci 27:2890–2895
107. Kalra SP, Dube MG, Pu S, Xu B, Horvath TL, Kalra PS1999 Interacting appetite-regulating pathways in the hy-pothalamic regulation of body weight. Endocr Rev 20:68–100
108. Yannielli P, Harrington ME 2004 Let there be “more”
light: enhancement of light actions on the circadian systemthrough non-photic pathways. Prog Neurobiol 74:59–76
109. Challet E 2007 Minireview: entrainment of the suprachi-asmatic clockwork in diurnal and nocturnal mammals. En-docrinology 148:5648–5655
110. Sakkou M, Wiedmer P, Anlag K, Hamm A, Seuntjens E,Ettwiller L, Tschop MH, Treier M 2007 A role for brain-specific homeobox factor Bsx in the control of hyperphagiaand locomotory behavior. Cell Metab 5:450–463
111. Cowley MA, Smart JL, Rubinstein M, Cerdan MG, DianoS, Horvath TL, Cone RD, Low MJ 2001 Leptin activatesanorexigenic POMC neurons through a neural network inthe arcuate nucleus. Nature 411:480–484
112. Elmquist JK, Ahima RS, Elias CF, Flier JS, Saper CB 1998Leptin activates distinct projections from the dorsomedialand ventromedial hypothalamic nuclei. Proc Natl Acad SciUSA 95:741–746
113. Elmquist JK, Elias CF, Saper CB 1999 From lesions toleptin: hypothalamic control of food intake and bodyweight. Neuron 22:221–232
114. Flier JS, Maratos-Flier E 1998 Obesity and the hypothal-amus: novel peptides for new pathways. Cell 92:437–440
115. Friedman JM, Halaas JL 1998 Leptin and the regulation ofbody weight in mammals. Nature 395:763–770
116. Schwartz MW, Woods SC, Porte Jr D, Seeley RJ, BaskinDG 2000 Central nervous system control of food intake.Nature 404:661–671
117. Shimada M, Tritos NA, Lowell BB, Flier JS, Maratos-FlierE 1998 Mice lacking melanin-concentrating hormone arehypophagic and lean. Nature 396:670–674
118. Sutcliffe JG, de Lecea L 2000 The hypocretins: excitatoryneuromodulatory peptides for multiple homeostatic sys-tems, including sleep and feeding. J Neurosci Res 62:161–168
119. Willie JT, Chemelli RM, Sinton CM, Yanagisawa M 2001To eat or to sleep? Orexin in the regulation of feeding andwakefulness. Annu Rev Neurosci 24:429–458
120. Turek FW, Joshu C, Kohsaka A, Lin E, Ivanova G, Mc-Dearmon E, Laposky A, Losee-Olson S, Easton A, JensenDR, Eckel RH, Takahashi JS, Bass J 2005 Obesity andmetabolic syndrome in circadian Clock mutant mice. Sci-ence 308:1043–1045
122. Lin L, Faraco J, Li R, Kadotani H, Rogers W, Lin X, QiuX, de Jong PJ, Nishino S, Mignot E 1999 The sleep disordercanine narcolepsy is caused by a mutation in the hypocretin(orexin) receptor 2 gene. Cell 98:365–376
123. Hara J, Beuckmann CT, Nambu T, Willie JT, ChemelliRM, Sinton CM, Sugiyama F, Yagami K, Goto K, YanagisawaM, Sakurai T 2001 Genetic ablation of orexin neurons inmice results in narcolepsy, hypophagia, and obesity. Neu-ron 30:345–354
124. Nishino S, Mignot E 2002 Article reviewed: Plasmaorexin-A is lower in patients with narcolepsy. Sleep Med3:377–378
125. Fujiki N, Yoshida Y, Zhang S, Sakurai T, Yanagisawa M,Nishino S 2006 Sex difference in body weight gain andleptin signaling in hypocretin/orexin deficient mouse mod-els. Peptides 27:2326–2331
126. La Fleur SE, Kalsbeek A, Wortel J, Buijs RM 1999 A su-
Endocrine Reviews, February 2010, 31(1):1–24 edrv.endojournals.org 17
prachiasmatic nucleus generated rhythm in basal glucoseconcentrations. J Neuroendocrinol 11:643–652
127. Ruiter M, La Fleur SE, van Heijningen C, van der Vliet J,Kalsbeek A, Buijs RM 2003 The daily rhythm in plasmaglucagon concentrations in the rat is modulated by thebiological clock and by feeding behavior. Diabetes 52:1709–1715
128. Ando H, Yanagihara H, Hayashi Y, Obi Y, Tsuruoka S,Takamura T, Kaneko S, Fujimura A 2005 Rhythmic mes-senger ribonucleic acid expression of clock genes and adi-pocytokines in mouse visceral adipose tissue. Endocrinol-ogy 146:5631–5636
129. De Boer SF, Van der Gugten J 1987 Daily variations inplasma noradrenaline, adrenaline and corticosterone con-centrations in rats. Physiol Behav 40:323–328
130. Ahima RS, Prabakaran D, Flier JS 1998 Postnatal leptinsurge and regulation of circadian rhythm of leptin by feed-ing. Implications for energy homeostasis and neuroendo-crine function. J Clin Invest 101:1020–1027
131. Bodosi B, Gardi J, Hajdu I, Szentirmai E, Obal Jr F,Krueger JM 2004 Rhythms of ghrelin, leptin, and sleep inrats: effects of the normal diurnal cycle, restricted feeding,and sleep deprivation. Am J Physiol Regul Integr CompPhysiol 287:R1071–R1079
132. Kalra SP, Bagnasco M, Otukonyong EE, Dube MG, KalraPS 2003 Rhythmic, reciprocal ghrelin and leptin signaling:new insight in the development of obesity. Regul Pept 111:1–11
133. Kalsbeek A, Fliers E, Romijn JA, La Fleur SE, Wortel J,Bakker O, Endert E, Buijs RM 2001 The suprachiasmaticnucleus generates the diurnal changes in plasma leptin lev-els. Endocrinology 142:2677–2685
134. Shen J, Tanida M, Niijima A, Nagai K 2007 In vivo effectsof leptin on autonomic nerve activity and lipolysis in rats.Neurosci Lett 416:193–197
135. Froy O 2007 The relationship between nutrition and cir-cadian rhythms in mammals. Front Neuroendocrinol 28:61–71
136. Green CB, Takahashi JS, Bass J 2008 The meter of me-tabolism. Cell 134:728–742
137. Hirota T, Fukada Y 2004 Resetting mechanism of centraland peripheral circadian clocks in mammals. Zoolog Sci21:359–368
138. Kohsaka A, Bass J 2007 A sense of time: how molecularclocks organize metabolism. Trends Endocrinol Metab 18:4–11
139. La Fleur SE 2003 Daily rhythms in glucose metabolism:suprachiasmatic nucleus output to peripheral tissue. J Neu-roendocrinol 15:315–322
140. Davidson AJ, Castanon-Cervantes O, Stephan FK 2004Daily oscillations in liver function: diurnal vs circadianrhythmicity. Liver Int 24:179–186
141. Froy O 2009 Cytochrome p450 and the biological clock inmammals. Curr Drug Metab 10:104–115
142. Frederiks WM, Marx F, Bosch KS 1987 Diurnal variationin glycogen phosphorylase activity in rat liver. A quanti-tative histochemical study. Eur J Cell Biol 43:339–341
143. XimenesdaSilvaA,GendrotG,Serviere J,LavialleM2000Daily changes of cytochrome oxidase activity within thesuprachiasmatic nucleus of the Syrian hamster. NeurosciLett 286:139–143
144. Rivera-Coll A, Fuentes-Arderiu X, Díez-Noguera A 1993
Circadian rhythms of serum concentrations of 12 enzymesof clinical interest. Chronobiol Int 10:190–200
145. Fukuda H, Iritani N 1991 Diurnal variations of lipogenicenzyme mRNA quantities in rat liver. Biochim BiophysActa 1086:261–264
146. Davies SP, Carling D, Munday MR, Hardie DG 1992 Di-urnal rhythm of phosphorylation of rat liver acetyl-CoAcarboxylase by the AMP-activated protein kinase, demon-strated using freeze-clamping. Effects of high-fat diets. EurJ Biochem 203:615–623
147. Cailotto C, La Fleur SE, Van Heijningen C, Wortel J,Kalsbeek A, Feenstra M, Pevet P, Buijs RM 2005 The su-prachiasmatic nucleus controls the daily variation ofplasma glucose via the autonomic output to the liver: arethe clock genes involved? Eur J Neurosci 22:2531–2540
148. Kalsbeek A, Ruiter M, La Fleur SE, Cailotto C, Kreier F,Buijs RM 2006 The hypothalamic clock and its control ofglucose homeostasis. Prog Brain Res 153:283–307
149. Yamazaki S, Ishida Y, Inouye S 1994 Circadian rhythms ofadenosine triphosphate contents in the suprachiasmaticnucleus, anterior hypothalamic area and caudate putamenof the rat—negative correlation with electrical activity.Brain Res 664:237–240
150. Yang X, Downes M, Yu RT, Bookout AL, He W, StraumeM, Mangelsdorf DJ, Evans RM 2006 Nuclear receptorexpression links the circadian clock to metabolism. Cell126:801–810
151. Stephan FK, Davidson AJ 1998 Glucose, but not fat, phaseshifts the feeding-entrained circadian clock. Physiol Behav65:277–288
152. Young ME, Wilson CR, Razeghi P, Guthrie PH, TaegtmeyerH 2002 Alterations of the circadian clock in the heart bystreptozotocin-induced diabetes. J Mol Cell Cardiol 34:223–231
154. IwanagaH,YanoM,MikiH,OkadaK,AzamaT,TakiguchiS, Fujiwara Y, Yasuda T, Nakayama M, Kobayashi M,Oishi K, Ishida N, Nagai K, Monden M 2005 Per2 geneexpressions in the suprachiasmatic nucleus and liver dif-ferentially respond to nutrition factors in rats. JPEN J Par-enter Enteral Nutr 29:157–161
155. Mohri T, Emoto N, Nonaka H, Fukuya H, Yagita K,Okamura H, Yokoyama M 2003 Alterations of circadianexpressions of clock genes in Dahl salt-sensitive rats fed ahigh-salt diet. Hypertension 42:189–194
156. WaddingtonLamontE,HarbourVL,Barry-ShawJ,RenteriaDiaz L, Robinson B, Stewart J, Amir S 2007 Restrictedaccess to food, but not sucrose, saccharine, or salt, syn-chronizes the expression of Period2 protein in the limbicforebrain. Neuroscience 144:402–411
157. Chen CP, Kuhn P, Advis JP, Sarkar DK 2004 Chronic eth-anol consumption impairs the circadian rhythm of pro-opiomelanocortin and period genes mRNA expression inthe hypothalamus of the male rat. J Neurochem 88:1547–1554
158. Spanagel R, Rosenwasser AM, Schumann G, Sarkar DK2005 Alcohol consumption and the body’s biologicalclock. Alcohol Clin Exp Res 29:1550–1557
18 Froy Circadian Rhythms, Metabolism, and Obesity Endocrine Reviews, February 2010, 31(1):1–24
159. Antle MC, Steen NM, Mistlberger RE 2001 Adenosine andcaffeine modulate circadian rhythms in the Syrian hamster.Neuroreport 12:2901–2905
160. Langlais PJ, Hall T 1998 Thiamine deficiency-induced dis-ruptions in the diurnal rhythm and regulation of body tem-perature in the rat. Metab Brain Dis 13:225–239
161. Bennett MR, Schwartz WJ 1999 Altered circadian rhyth-micity is an early sign of murine dietary thiamine defi-ciency. J Neurol Sci 163:6–10
162. McNamara P, Seo SB, Rudic RD, Sehgal A, Chakravarti D,FitzGerald GA 2001 Regulation of CLOCK and MOP4 bynuclear hormone receptors in the vasculature: a humoralmechanism to reset a peripheral clock. Cell 105:877–889
163. Shirai H, Oishi K, Ishida N 2006 Bidirectional CLOCK/BMAL1-dependent circadian gene regulation by retinoicacid in vitro. Biochem Biophys Res Commun 351:387–391
164. Balsalobre A, Marcacci L, Schibler U 2000 Multiple sig-naling pathways elicit circadian gene expression in cul-tured Rat-1 fibroblasts. Curr Biol 10:1291–1294
165. BalsalobreA,BrownSA,MarcacciL,TroncheF,KellendonkC, Reichardt HM, Schutz G, Schibler U 2000 Resetting ofcircadian time in peripheral tissues by glucocorticoid sig-naling. Science 289:2344–2347
167. Fu L, Patel MS, Bradley A, Wagner EF, Karsenty G 2005The molecular clock mediates leptin-regulated bone for-mation. Cell 122:803–815
168. Rutter J, Reick M, Wu LC, McKnight SL 2001 Regulationof clock and NPAS2 DNA binding by the redox state ofNAD cofactors. Science 293:510–514
169. Rutter J, Reick M, McKnight SL 2002 Metabolism and thecontrol of circadian rhythms. Annu Rev Biochem 71:307–331
170. Um JH, Yang S, Yamazaki S, Kang H, Viollet B, Foretz M,Chung JH 2007 Activation of 5�-AMP-activated kinasewith diabetes drug metformin induces casein kinase I�(CKI�)-dependent degradation of clock protein mPER2.J Biol Chem 282:20794–20798
171. Vieira E, Nilsson EC, Nerstedt A, Ormestad M, Long YC,Garcia-Roves PM, Zierath JR, Mahlapuu M 2008 Rela-tionship between AMPK and the transcriptional balance ofclock-related genes in skeletal muscle. Am J Physiol Endo-crinol Metab 295:E1032–E1037
172. Martin TL, Alquier T, Asakura K, Furukawa N, PreitnerF, Kahn BB 2006 Diet-induced obesity alters AMP kinaseactivity in hypothalamus and skeletal muscle. J Biol Chem281:18933–18941
173. Blander G, Guarente L 2004 The Sir2 family of proteindeacetylases. Annu Rev Biochem 73:417–435
174. Dali-Youcef N, Lagouge M, Froelich S, Koehl C,Schoonjans K, Auwerx J 2007 Sirtuins: the ‘magnificentseven,’ function, metabolism and longevity. Ann Med 39:335–345
175. Asher G, Gatfield D, Stratmann M, Reinke H, Dibner C,Kreppel F, Mostoslavsky R, Alt FW, Schibler U 2008SIRT1 regulates circadian clock gene expression throughPER2 deacetylation. Cell 134:317–328
176. Nakahata Y, Kaluzova M, Grimaldi B, Sahar S, HirayamaJ, Chen D, Guarente LP, Sassone-Corsi P 2008 The NAD�-
177. Hirayama J, Sahar S, Grimaldi B, Tamaru T, TakamatsuK, Nakahata Y, Sassone-Corsi P 2007 CLOCK-mediatedacetylation of BMAL1 controls circadian function. Nature450:1086–1090
178. Belden WJ, Dunlap JC 2008 SIRT1 is a circadian deacety-lase for core clock components. Cell 134:212–214
179. Nakahata Y, Sahar S, Astarita G, Kaluzova M, Sassone-Corsi P 2009 Circadian control of the NAD� salvage path-way by CLOCK-SIRT1. Science 324:654–657
180. Canto C, Gerhart-Hines Z, Feige JN, Lagouge M, NoriegaL, Milne JC, Elliott PJ, Puigserver P, Auwerx J 2009 AMPKregulates energy expenditure by modulating NAD� me-tabolism and SIRT1 activity. Nature 458:1056–1060
181. Stephan FK 2002 The “other” circadian system: food as aZeitgeber. J Biol Rhythms 17:284–292
182. Cassone VM, Stephan FK 2002 Central and peripheralregulation of feeding and nutrition by the mammalian cir-cadian clock: implications for nutrition during mannedspace flight. Nutrition 18:814–819
183. Honma KI, Honma S, Hiroshige T 1983 Critical role offood amount for prefeeding corticosterone peak in rats.Am J Physiol 245:R339–R344
184. Grasl-Kraupp B, Bursch W, Ruttkay-Nedecky B, WagnerA, Lauer B, Schulte-Hermann R 1994 Food restrictioneliminates preneoplastic cells through apoptosis and an-tagonizes carcinogenesis in rat liver. Proc Natl Acad SciUSA 91:9995–9999
185. Saito M, Murakami E, Suda M 1976 Circadian rhythms indisaccharidases of rat small intestine and its relation tofood intake. Biochim Biophys Acta 421:177–179
186. Comperatore CA, Stephan FK 1987 Entrainment of duo-denal activity to periodic feeding. J Biol Rhythms 2:227–242
187. Stephan FK, Swann JM, Sisk CL 1979 Anticipation of24-hr feeding schedules in rats with lesions of the supra-chiasmatic nucleus. Behav Neural Biol 25:346–363
188. Mistlberger RE 1994 Circadian food-anticipatory activity:formal models and physiological mechanisms. NeurosciBiobehav Rev 18:171–195
189. Hara R, Wan K, Wakamatsu H, Aida R, Moriya T,Akiyama M, Shibata S 2001 Restricted feeding entrainsliver clock without participation of the suprachiasmaticnucleus. Genes Cells 6:269–278
190. Oishi K, Miyazaki K, Ishida N 2002 Functional CLOCK isnot involved in the entrainment of peripheral clocks to therestricted feeding: entrainable expression of mPer2 andBmal1 mRNAs in the heart of Clock mutant mice on Jcl:ICR background. Biochem Biophys Res Commun 298:198–202
191. Horikawa K, Minami Y, Iijima M, Akiyama M, Shibata S2005 Rapid damping of food-entrained circadian rhythmof clock gene expression in clock-defective peripheral tis-sues under fasting conditions. Neuroscience 134:335–343
192. Damiola F, Le Minh N, Preitner N, Kornmann B, Fleury-Olela F, Schibler U 2000 Restricted feeding uncouples cir-cadian oscillators in peripheral tissues from the centralpacemaker in the suprachiasmatic nucleus. Genes Dev 14:2950–2961
193. Stokkan KA, Yamazaki S, Tei H, Sakaki Y, Menaker M
Endocrine Reviews, February 2010, 31(1):1–24 edrv.endojournals.org 19
2001 Entrainment of the circadian clock in the liver byfeeding. Science 291:490–493
194. Lin JD, Liu C, Li S 2008 Integration of energy metabolismand the mammalian clock. Cell Cycle 7:453–457
195. Boulamery-Velly A, Simon N, Vidal J, Mouchet J,Bruguerolle B 2005 Effects of three-hour restricted foodaccess during the light period on circadian rhythms of tem-perature, locomotor activity, and heart rate in rats. Chro-nobiol Int 22:489–498
196. Hirao J, Arakawa S, Watanabe K, Ito K, Furukawa T 2006Effects of restricted feeding on daily fluctuations of hepaticfunctions including p450 monooxygenase activities in rats.J Biol Chem 281:3165–3171
197. MiedaM,WilliamsSC,RichardsonJA,TanakaK,YanagisawaM 2006 The dorsomedial hypothalamic nucleus as a pu-tative food-entrainable circadian pacemaker. Proc NatlAcad Sci USA 103:12150–12155
198. Gooley JJ, Schomer A, Saper CB 2006 The dorsomedialhypothalamic nucleus is critical for the expression of food-entrainable circadian rhythms. Nat Neurosci 9:398–407
199. Landry GJ, Simon MM, Webb IC, Mistlberger RE 2006Persistence of a behavioral food-anticipatory circadianrhythm following dorsomedial hypothalamic ablation inrats. Am J Physiol Regul Integr Comp Physiol 290:R1527–R1534
200. Landry GJ, Yamakawa GR, Webb IC, Mear RJ,Mistlberger RE 2007 The dorsomedial hypothalamic nu-cleus is not necessary for the expression of circadian food-anticipatory activity in rats. J Biol Rhythms 22:467–478
201. Davidson AJ, Cappendijk SL, Stephan FK 2000 Feeding-entrained circadian rhythms are attenuated by lesions ofthe parabrachial region in rats. Am J Physiol Regul IntegrComp Physiol 278:R1296–R1304
202. Mistlberger RE, Mumby DG 1992 The limbic system andfood-anticipatory circadian rhythms in the rat: ablationand dopamine blocking studies. Behav Brain Res 47:159–168
203. Mendoza J, Angeles-Castellanos M, Escobar C 2005 Dif-ferential role of the accumbens Shell and Core subterrito-ries in food-entrained rhythms of rats. Behav Brain Res158:133–142
204. Davidson AJ 2006 Search for the feeding-entrainable cir-cadian oscillator: a complex proposition. Am J PhysiolRegul Integr Comp Physiol 290:R1524–R1526
205. Comperatore CA, Stephan FK 1990 Effects of vagotomyon entrainment of activity rhythms to food access. PhysiolBehav 47:671–678
206. Mistlberger RE, Marchant EG 1999 Enhanced food-an-ticipatory circadian rhythms in the genetically obeseZucker rat. Physiol Behav 66:329–335
207. Pitts S, Perone E, Silver R 2003 Food-entrained circadianrhythms are sustained in arrhythmic Clk/Clk mutant mice.Am J Physiol Regul Integr Comp Physiol 285:R57–R67
208. Pendergast JS, Nakamura W, Friday RC, Hatanaka F,Takumi T, Yamazaki S 2009 Robust food anticipatoryactivity in BMAL1-deficient mice. PLoS ONE 4:e4860
209. Storch KF, Weitz CJ 2009 Daily rhythms of food-antici-patory behavioral activity do not require the known cir-cadian clock. Proc Natl Acad Sci USA 106:6808–6813
210. Feillet CA, Ripperger JA, Magnone MC, Dulloo A,Albrecht U, Challet E 2006 Lack of food anticipation inPer2 mutant mice. Curr Biol 16:2016–2022
212. Masoro EJ, Shimokawa I, Higami Y, McMahan CA, YuBP 1995 Temporal pattern food intake not a factor in theretardation of aging processes by dietary restriction. J Ger-ontol A Biol Sci Med Sci 50A:B48–B53
213. Koubova J, Guarente L 2003 How does calorie restrictionwork? Genes Dev 17:313–321
214. Masoro EJ 2005 Overview of caloric restriction and age-ing. Mech Ageing Dev 126:913–922
215. Weindruch R, Sohal RS 1997 Seminars in medicine of theBeth Israel Deaconess Medical Center. Caloric intake andaging. N Engl J Med 337:986–994
216. Roth GS, Lane MA, Ingram DK, Mattison JA, Elahi D,Tobin JD, Muller D, Metter EJ 2002 Biomarkers of caloricrestriction may predict longevity in humans. Science 297:811
217. Roth GS, Mattison JA, Ottinger MA, Chachich ME, LaneMA, Ingram DK 2004 Aging in rhesus monkeys: relevanceto human health interventions. Science 305:1423–1426
218. Challet E, Solberg LC, Turek FW 1998 Entrainment incalorie-restricted mice: conflicting zeitgebers and free-run-ning conditions. Am J Physiol 274:R1751–R1761
219. Challet E, Caldelas I, Graff C, Pevet P 2003 Synchroniza-tion of the molecular clockwork by light- and food-relatedcues in mammals. Biol Chem 384:711–719
220. Mendoza J, Graff C, Dardente H, Pevet P, Challet E 2005Feeding cues alter clock gene oscillations and photic re-sponses in the suprachiasmatic nuclei of mice exposed to alight/dark cycle. J Neurosci 25:1514–1522
221. Resuehr D, Olcese J 2005 Caloric restriction and melato-nin substitution: effects on murine circadian parameters.Brain Res 1048:146–152
222. Froy O, Miskin R 2007 The interrelations among feeding,circadian rhythms and ageing. Prog Neurobiol 82:142–150
223. Anson RM, Guo Z, de Cabo R, Iyun T, Rios M, HagepanosA, Ingram DK, Lane MA, Mattson MP 2003 Intermittentfasting dissociates beneficial effects of dietary restrictionon glucose metabolism and neuronal resistance to injuryfrom calorie intake. Proc Natl Acad Sci USA 100:6216–6220
224. Descamps O, Riondel J, Ducros V, Roussel AM 2005 Mi-tochondrial production of reactive oxygen species and in-cidence of age-associated lymphoma in OF1 mice: effect ofalternate-day fasting. Mech Ageing Dev 126:1185–1191
225. Goodrick CL, Ingram DK, Reynolds MA, Freeman JR,Cider N 1990 Effects of intermittent feeding upon bodyweight and lifespan in inbred mice: interaction of genotypeand age. Mech Ageing Dev 55:69–87
226. Contestabile A, Ciani E, Contestabile A 2004 Dietary re-striction differentially protects from neurodegeneration inanimal models of excitotoxicity. Brain Res 1002:162–166
227. Mattson MP 2005 Energy intake, meal frequency, andhealth: a neurobiological perspective. Annu Rev Nutr 25:237–260
228. Sharma S, Kaur G 2005 Neuroprotective potential of di-etary restriction against kainate-induced excitotoxicity inadult male Wistar rats. Brain Res Bull 67:482–491
229. Ahmet I, Wan R, Mattson MP, Lakatta EG, Talan M 2005Cardioprotection by intermittent fasting in rats. Circulation112:3115–3121
20 Froy Circadian Rhythms, Metabolism, and Obesity Endocrine Reviews, February 2010, 31(1):1–24
230. Mager DE, Wan R, Brown M, Cheng A, Wareski P,Abernethy DR, Mattson MP 2006 Caloric restriction andintermittent fasting alter spectral measures of heart rateand blood pressure variability in rats. FASEB J 20:631–637
231. Mattson MP, Duan W, Wan R, Guo Z 2004 Prophylacticactivation of neuroprotective stress response pathways bydietary and behavioral manipulations. NeuroRx 1:111–116
232. Mattson MP 2008 Dietary factors, hormesis and health.Ageing Res Rev 7:43–48
233. Froy O, Chapnik N, Miskin R 2009 Effect of intermittentfasting on circadian rhythms in mice depends on feedingtime. Mech Ageing Dev 130:154–160
234. Bamshad M, Aoki VT, Adkison MG, Warren WS, BartnessTJ 1998 Central nervous system origins of the sympatheticnervous system outflow to white adipose tissue. Am JPhysiol 275:R291–R299
235. Bartness TJ, Bamshad M 1998 Innervation of mammalianwhite adipose tissue: implications for the regulation of to-tal body fat. Am J Physiol 275:R1399–R1411
236. Cantu RC, Goodman HM 1967 Effects of denervation andfasting on white adipose tissue. Am J Physiol 212:207–212
237. Youngstrom TG, Bartness TJ 1998 White adipose tissuesympathetic nervous system denervation increases fat padmass and fat cell number. Am J Physiol 275:R1488–R1493
238. Kreier F, Fliers E, Voshol PJ, Van Eden CG, Havekes LM,Kalsbeek A, Van Heijningen CL, Sluiter AA, MettenleiterTC, Romijn JA, Sauerwein HP, Buijs RM 2002 Selectiveparasympathetic innervation of subcutaneous and intra-abdominal fat—functional implications. J Clin Invest 110:1243–1250
239. Zvonic S, Floyd ZE, Mynatt RL, Gimble JM 2007 Circa-dian rhythms and the regulation of metabolic tissue func-tion and energy homeostasis. Obesity (Silver Spring) 15:539–543
240. Loboda A, Kraft WK, Fine B, Joseph J, Nebozhyn M,Zhang C, He Y, Yang X, Wright C, Morris M, ChalikondaI, Ferguson M, Emilsson V, Leonardson A, Lamb J, Dai H,Schadt E, Greenberg HE, Lum PY 2009 Diurnal variationof the human adipose transcriptome and the link to met-abolic disease. BMC Med Genomics 2:7
241. Suzuki M, Shimomura Y, Satoh Y 1983 Diurnal changes inlipolytic activity of isolated fat cells and their increasedresponsiveness to epinephrine and theophylline with mealfeeding in rats. J Nutr Sci Vitaminol (Tokyo) 29:399–411
242. Saad MF, Riad-Gabriel MG, Khan A, Sharma A, MichaelR, Jinagouda SD, Boyadjian R, Steil GM 1998 Diurnal andultradian rhythmicity of plasma leptin: effects of genderand adiposity. J Clin Endocrinol Metab 83:453–459
243. Gavrila A, Peng CK, Chan JL, Mietus JE, Goldberger AL,Mantzoros CS 2003 Diurnal and ultradian dynamics ofserum adiponectin in healthy men: comparison with leptin,circulating soluble leptin receptor, and cortisol patterns.J Clin Endocrinol Metab 88:2838–2843
244. Bray MS, Young ME 2007 Circadian rhythms in the de-velopment of obesity: potential role for the circadian clockwithin the adipocyte. Obes Rev 8:169–181
245. Shimba S, Ishii N, Ohta Y, Ohno T, Watabe Y, Hayashi M,Wada T, Aoyagi T, Tezuka M 2005 Brain and muscleArnt-like protein-1 (BMAL1), a component of the molec-
ular clock, regulates adipogenesis. Proc Natl Acad Sci USA102:12071–12076
246. Oishi K, Shirai H, Ishida N 2005 CLOCK is involved in thecircadian transactivation of peroxisome-proliferator-acti-vated receptor � (PPAR�) in mice. Biochem J 386:575–581
247. Inoue I, Shinoda Y, Ikeda M, Hayashi K, Kanazawa K,Nomura M, Matsunaga T, Xu H, Kawai S, Awata T,Komoda T, Katayama S 2005 CLOCK/BMAL1 is involvedin lipid metabolism via transactivation of the peroxisomeproliferator-activated receptor (PPAR) response element.J Atheroscler Thromb 12:169–174
248. CanapleL,RambaudJ,Dkhissi-BenyahyaO,RayetB,TanNS, Michalik L, Delaunay F, Wahli W, Laudet V 2006Reciprocal regulation of brain and muscle Arnt-like pro-tein 1 and peroxisome proliferator-activated receptor �defines a novel positive feedback loop in the rodent livercircadian clock. Mol Endocrinol 20:1715–1727
249. Wang N, Yang G, Jia Z, Zhang H, Aoyagi T, Soodvilai S,Symons JD, Schnermann JB, Gonzalez FJ, Litwin SE, YangT 2008 Vascular PPAR� controls circadian variation inblood pressure and heart rate through Bmal1. Cell Metab8:482–491
250. Chawla A, Lazar MA 1993 Induction of Rev-ErbA �, anorphan receptor encoded on the opposite strand of the�-thyroid hormone receptor gene, during adipocyte differ-entiation. J Biol Chem 268:16265–16269
251. Torra IP, Tsibulsky V, Delaunay F, Saladin R, Laudet V,Fruchart JC, Kosykh V, Staels B 2000 Circadian and glu-cocorticoid regulation of Rev-erb � expression in liver.Endocrinology 141:3799–3806
252. Fontaine C, Dubois G, Duguay Y, Helledie T, Vu-Dac N,Gervois P, Soncin F, Mandrup S, Fruchart JC, Fruchart-Najib J, Staels B 2003 The orphan nuclear receptor Rev-Erb� is a peroxisome proliferator-activated receptor(PPAR) � target gene and promotes PPAR�-induced adi-pocyte differentiation. J Biol Chem 278:37672–37680
253. Duez H, Staels B 2008 Rev-erb � gives a time cue to me-tabolism. FEBS Lett 582:19–25
254. Lau P, Nixon SJ, Parton RG, Muscat GE 2004 ROR�regulates the expression of genes involved in lipid ho-meostasis in skeletal muscle cells: caveolin-3 and CPT-1 aredirect targets of ROR. J Biol Chem 279:36828–36840
255. Akashi M, Takumi T 2005 The orphan nuclear receptorROR� regulates circadian transcription of the mammaliancore-clock Bmal1. Nat Struct Mol Biol 12:441–448
256. Ueda HR, Chen W, Adachi A, Wakamatsu H, Hayashi S,Takasugi T, Nagano M, Nakahama K, Suzuki Y, SuganoS, Iino M, Shigeyoshi Y, Hashimoto S 2002 A transcriptionfactor response element for gene expression during circa-dian night. Nature 418:534–539
257. Liu C, Li S, Liu T, Borjigin J, Lin JD 2007 Transcriptionalcoactivator PGC-1� integrates the mammalian clock andenergy metabolism. Nature 447:477–481
259. Yanagihara H, Ando H, Hayashi Y, Obi Y, Fujimura A2006 High-fat feeding exerts minimal effects on rhythmicmRNA expression of clock genes in mouse peripheral tis-sues. Chronobiol Int 23:905–914
260. Satoh Y, Kawai H, Kudo N, Kawashima Y, Mitsumoto A2006 Time-restricted feeding entrains daily rhythms of en-
Endocrine Reviews, February 2010, 31(1):1–24 edrv.endojournals.org 21
ergy metabolism in mice. Am J Physiol Regul Integr CompPhysiol 290:R1276–R1283
261. Kohsaka A, Laposky AD, Ramsey KM, Estrada C, JoshuC, Kobayashi Y, Turek FW, Bass J 2007 High-fat dietdisrupts behavioral and molecular circadian rhythms inmice. Cell Metab 6:414–421
263. Cha MC, Chou CJ, Boozer CN 2000 High-fat diet feedingreduces the diurnal variation of plasma leptin concentra-tion in rats. Metabolism 49:503–507
264. Cano P, Jimenez-Ortega V, Larrad A, Reyes Toso CF,Cardinali DP, Esquifino AI 2008 Effect of a high-fat diet on24-h pattern of circulating levels of prolactin, luteinizinghormone, testosterone, corticosterone, thyroid-stimulat-ing hormone and glucose, and pineal melatonin content, inrats. Endocrine 33:118–125
265. Barnea M, Madar Z, Froy O 2009 High-fat diet delays andfasting advances the circadian expression of adiponectinsignaling components in mouse liver. Endocrinology 150:161–168
266. Kaneko K, Yamada T, Tsukita S, Takahashi K, Ishigaki Y,Oka Y, Katagiri H 2009 Obesity alters circadian expres-sions of molecular clock genes in the brainstem. Brain Res1263:58–68
267. Rudic RD, McNamara P, Curtis AM, Boston RC, Panda S,Hogenesch JB, Fitzgerald GA 2004 BMAL1 and CLOCK,two essential components of the circadian clock, are in-volved in glucose homeostasis. PLoS Biol 2:e377
268. Mendoza J, Pevet P, Challet E 2008 High-fat feeding altersthe clock synchronization to light. J Physiol 586:5901–5910
269. Gorman MR 2003 Differential effects of multiple short daylengths on body weights of gonadectomized Siberian ham-sters. Physiol Biochem Zool 76:398–405
270. Morgan PJ, Ross AW, Mercer JG, Barrett P 2003 Photo-periodic programming of body weight through the neu-roendocrine hypothalamus. J Endocrinol 177:27–34
271. Bocquier F, Bonnet M, Faulconnier Y, Guerre-Millo M,Martin P, Chilliard Y 1998 Effects of photoperiod andfeeding level on perirenal adipose tissue metabolic activityand leptin synthesis in the ovariectomized ewe. ReprodNutr Dev 38:489–498
272. Faulconnier Y, Bonnet M, Bocquier F, Leroux C, ChilliardY 2001 Effects of photoperiod and feeding level on adiposetissue and muscle lipoprotein lipase activity and mRNAlevel in dry non-pregnant sheep. Br J Nutr 85:299–306
273. Di Lorenzo L, De Pergola G, Zocchetti C, L’Abbate N,Basso A, Pannacciulli N, Cignarelli M, Giorgino R, SoleoL 2003 Effect of shift work on body mass index: results ofa study performed in 319 glucose-tolerant men working ina Southern Italian industry. Int J Obes Relat Metab Disord27:1353–1358
274. Karlsson B, Knutsson A, Lindahl B 2001 Is there an asso-ciation between shift work and having a metabolic syn-drome? Results from a population based study of 27,485people. Occup Environ Med 58:747–752
275. Karlsson BH, Knutsson AK, Lindahl BO, Alfredsson LS2003 Metabolic disturbances in male workers with rotat-ing three-shift work. Results of the WOLF study. Int ArchOccup Environ Health 76:424–430
276. Licinio J 1998 Longitudinally sampled human plasma lep-tin and cortisol concentrations are inversely correlated.J Clin Endocrinol Metab 83:1042
277. Heptulla R, Smitten A, Teague B, Tamborlane WV, MaYZ, Caprio S 2001 Temporal patterns of circulating leptinlevels in lean and obese adolescents: relationships to insu-lin, growth hormone, and free fatty acids rhythmicity.J Clin Endocrinol Metab 86:90–96
278. Perfetto F, Tarquini R, Cornelissen G, Mello G, TempestiniA, Gaudiano P, Mancuso F, Halberg F 2004 Circadianphase difference of leptin in android versus gynoid obesity.Peptides 25:1297–1306
279. Zhang Y, Proenca R, Maffei M, Barone M, Leopold L,Friedman JM 1994 Positional cloning of the mouse obesegene and its human homologue. Nature 372:425–432
280. Montague CT, Farooqi IS, Whitehead JP, Soos MA, RauH, Wareham NJ, Sewter CP, Digby JE, Mohammed SN,Hurst JA, Cheetham CH, Earley AR, Barnett AH, Prins JB,O’Rahilly S 1997 Congenital leptin deficiency is associatedwith severe early-onset obesity in humans. Nature 387:903–908
281. Strobel A, Issad T, Camoin L, Ozata M, Strosberg AD1998 A leptin missense mutation associated with hypogo-nadism and morbid obesity. Nat Genet 18:213–215
282. ClementK,VaisseC,LahlouN,Cabrol S,PellouxV,CassutoD, Gourmelen M, Dina C, Chambaz J, Lacorte JM,Basdevant A, Bougneres P, Lebouc Y, Froguel P,Guy-Grand B 1998 A mutation in the human leptin recep-tor gene causes obesity and pituitary dysfunction. Nature392:398–401
283. Yildiz BO, Suchard MA, Wong ML, McCann SM, LicinioJ 2004 Alterations in the dynamics of circulating ghrelin,adiponectin, and leptin in human obesity. Proc Natl AcadSci USA 101:10434–10439
284. Puchalski SS, Green JN, Rasmussen DD 2003 Melatonineffect on rat body weight regulation in response to high-fatdiet at middle age. Endocrine 21:163–167
285. Broberger C 2005 Brain regulation of food intake and ap-petite: molecules and networks. J Intern Med 258:301–327
286. Buijs RM, Kreier F 2006 The metabolic syndrome: a braindisease? J Neuroendocrinol 18:715–716
287. Gagliardino JJ, Hernandez RE, Rebolledo OR 1984 Chro-nobiological aspects of blood glucose regulation: a newscope for the study of diabetes mellitus. Chronobiologia11:357–379
288. Van Cauter E, Polonsky KS, Scheen AJ 1997 Roles of cir-cadian rhythmicity and sleep in human glucose regulation.Endocr Rev 18:716–738
289. Velasco A, Huerta I, Marin B 1988 Plasma corticosterone,motor activity and metabolic circadian patterns in strep-tozotocin-induced diabetic rats. Chronobiol Int 5:127–135
290. Oster MH, Castonguay TW, Keen CL, Stern JS 1988 Cir-cadian rhythm of corticosterone in diabetic rats. Life Sci43:1643–1645
291. Shimomura Y, Takahashi M, Shimizu H, Sato N, UeharaY, Negishi M, Inukai T, Kobayashi I, Kobayashi S 1990Abnormal feeding behavior and insulin replacement inSTZ-induced diabetic rats. Physiol Behav 47:731–734
292. Spallone V, Bernardi L, Ricordi L, Solda P, Maiello MR,Calciati A, Gambardella S, Fratino P, Menzinger G 1993Relationship between the circadian rhythms of blood pres-
22 Froy Circadian Rhythms, Metabolism, and Obesity Endocrine Reviews, February 2010, 31(1):1–24
sure and sympathovagal balance in diabetic autonomicneuropathy. Diabetes 42:1745–1752
293. Boden G, Chen X, Polansky M 1999 Disruption of circa-dian insulin secretion is associated with reduced glucoseuptake in first-degree relatives of patients with type 2 di-abetes. Diabetes 48:2182–2188
294. Oishi K, Kasamatsu M, Ishida N 2004 Gene- and tissue-specific alterations of circadian clock gene expression instreptozotocin-induced diabetic mice under restrictedfeeding. Biochem Biophys Res Commun 317:330–334
295. Herichova I, Zeman M, Stebelova K, Ravingerova T 2005Effect of streptozotocin-induced diabetes on daily expres-sion of per2 and dbp in the heart and liver and melatoninrhythm in the pineal gland of Wistar rat. Mol Cell Biochem270:223–229
296. Schmidt MI, Hadji-Georgopoulos A, Rendell M, MargolisS, Kowarski A 1981 The dawn phenomenon, an earlymorning glucose rise: implications for diabetic intradayblood glucose variation. Diabetes Care 4:579–585
297. Troisi RJ, Cowie CC, Harris MI 2000 Diurnal variation infasting plasma glucose: implications for diagnosis of dia-betes in patients examined in the afternoon. JAMA 284:3157–3159
298. Ando H, Oshima Y, Yanagihara H, Hayashi Y, TakamuraT, Kaneko S, Fujimura A 2006 Profile of rhythmic geneexpression in the livers of obese diabetic KK-A(y) mice.Biochem Biophys Res Commun 346:1297–1302
299. Hagstrom-Toft E, Bolinder J, Ungerstedt U, Arner P 1997A circadian rhythm in lipid mobilization which is altered inIDDM. Diabetologia 40:1070–1078
300. Kennaway DJ, Owens JA, Voultsios A, Boden MJ, VarcoeTJ 2007 Metabolic homeostasis in mice with disruptedClock gene expression in peripheral tissues. Am J PhysiolRegul Integr Comp Physiol 293:R1528–R1537
301. Oishi K, Atsumi G, Sugiyama S, Kodomari I, KasamatsuM, Machida K, Ishida N 2006 Disrupted fat absorptionattenuates obesity induced by a high-fat diet in Clock mu-tant mice. FEBS Lett 580:127–130
302. Oishi K, Ohkura N, Wakabayashi M, Shirai H, Sato K,Matsuda J, Atsumi G, Ishida N 2006 CLOCK is involvedin obesity-induced disordered fibrinolysis in ob/ob mice byregulating PAI-1 gene expression. J Thromb Haemost4:1774–1780
303. Kudo T, Tamagawa T, Kawashima M, Mito N, Shibata S2007 Attenuating effect of clock mutation on triglyceridecontents in the ICR mouse liver under a high-fat diet. J BiolRhythms 22:312–323
304. Lamia KA, Storch KF, Weitz CJ 2008 Physiological sig-nificance of a peripheral tissue circadian clock. Proc NatlAcad Sci USA 105:15172–15177
305. Yang S, Liu A, Weidenhammer A, Cooksey RC, McClainD, Kim MK, Aguilera G, Abel ED, Chung JH 2009 The roleof mPer2 clock gene in glucocorticoid and feedingrhythms. Endocrinology 150:2153–2160
306. Gimble JM, Zvonic S, Floyd ZE, Kassem M, Nuttall ME2006 Playing with bone and fat. J Cell Biochem 98:251–266
307. Baggs JE, Green CB 2003 Nocturnin, a deadenylase inXenopus laevis retina: a mechanism for posttranscrip-tional control of circadian-related mRNA. Curr Biol 13:189–198
JC, Green CB 2007 Immediate early response of the cir-cadian polyA ribonuclease nocturnin to two extracellularstimuli. RNA 13:745–755
309. Green CB, Douris N, Kojima S, Strayer CA, Fogerty J,Lourim D, Keller SR, Besharse JC 2007 Loss of Nocturnin,a circadian deadenylase, confers resistance to hepatic ste-atosis and diet-induced obesity. Proc Natl Acad Sci USA104:9888–9893
310. Hasler G, Buysse DJ, Klaghofer R, Gamma A, Ajdacic V,Eich D, Rossler W, Angst J 2004 The association betweenshort sleep duration and obesity in young adults: a 13-yearprospective study. Sleep 27:661–666
311. Megirian D, Dmochowski J, Farkas GA 1998 Mechanismcontrolling sleep organization of the obese Zucker rats.J Appl Physiol 84:253–256
312. Nilsson PM, Roost M, Engstrom G, Hedblad B, BerglundG 2004 Incidence of diabetes in middle-aged men is relatedto sleep disturbances. Diabetes Care 27:2464–2469
313. Taheri S, Lin L, Austin D, Young T, Mignot E 2004 Shortsleep duration is associated with reduced leptin, elevatedghrelin, and increased body mass index. PLoS Med 1:e62
314. Gottlieb DJ, Punjabi NM, Newman AB, Resnick HE,Redline S, Baldwin CM, Nieto FJ 2005 Association of sleeptime with diabetes mellitus and impaired glucose tolerance.Arch Intern Med 165:863–867
315. Spiegel K, Tasali E, Penev P, Van Cauter E 2004 Briefcommunication: sleep curtailment in healthy young men isassociated with decreased leptin levels, elevated ghrelinlevels, and increased hunger and appetite. Ann Intern Med141:846–850
316. Spiegel K, Leproult R, Van Cauter E 1999 Impact of sleepdebt on metabolic and endocrine function. Lancet 354:1435–1439
317. Vorona RD, Winn MP, Babineau TW, Eng BP, FeldmanHR, Ware JC 2005 Overweight and obese patients in aprimary care population report less sleep than patientswith a normal body mass index. Arch Intern Med 165:25–30
318. Vgontzas AN, Bixler EO, Tan TL, Kantner D, Martin LF,Kales A 1998 Obesity without sleep apnea is associatedwith daytime sleepiness. Arch Intern Med 158:1333–1337
319. Vgontzas AN, Papanicolaou DA, Bixler EO, Kales A,TysonK,ChrousosGP1997Elevationofplasmacytokinesin disorders of excessive daytime sleepiness: role of sleepdisturbance and obesity. J Clin Endocrinol Metab 82:1313–1316
320. Sekine M, Yamagami T, Handa K, Saito T, Nanri S,Kawaminami K, Tokui N, Yoshida K, Kagamimori S 2002A dose-response relationship between short sleeping hoursand childhood obesity: results of the Toyama Birth CohortStudy. Child Care Health Dev 28:163–170
324. Qin LQ, Li J, Wang Y, Wang J, Xu JY, Kaneko T 2003 Theeffects of nocturnal life on endocrine circadian patterns inhealthy adults. Life Sci 73:2467–2475
325. Allison KC, Crow SJ, Reeves RR, West DS, Foreyt JP,Dilillo VG, Wadden TA, Jeffery RW, Van Dorsten B,Stunkard AJ 2007 Binge eating disorder and night eatingsyndrome in adults with type 2 diabetes. Obesity (SilverSpring) 15:1287–1293
326. van Amelsvoort LG, Schouten EG, Kok FJ 1999 Durationof shiftwork related to body mass index and waist to hipratio. Int J Obes Relat Metab Disord 23:973–978
327. Parkes KR 2002 Shift work and age as interactive predic-tors of body mass index among offshore workers. Scand JWork Environ Health 28:64–71
328. Shea SA, Hilton MF, Orlova C, Ayers RT, Mantzoros CS2005 Independent circadian and sleep/wake regulation of
adipokines and glucose in humans. J Clin EndocrinolMetab 90:2537–2544
329. Jenkins JB, Omori T, Guan Z, Vgontzas AN, Bixler EO,Fang J 2006 Sleep is increased in mice with obesity inducedby high-fat food. Physiol Behav 87:255–262
330. Danguir J 1989 Sleep patterns in the genetically obeseZucker rat: effect of acarbose treatment. Am J Physiol 256:R281–R283
332. Sinton CM, Fitch TE, Gershenfeld HK 1999 The effects ofleptin on REM sleep and slow wave � in rats are reversedby food deprivation. J Sleep Res 8:197–203
333. Laposky AD, Bass J, Kohsaka A, Turek FW 2008 Sleep andcircadian rhythms: key components in the regulation ofenergy metabolism. FEBS Lett 582:142–151
24 Froy Circadian Rhythms, Metabolism, and Obesity Endocrine Reviews, February 2010, 31(1):1–24
