Alois Alzheimer(1864-1915)
Epidemiology 1-AD is the most common form of dementia, accounting for >60% of all the cases.
2-Most of the cases of AD ARE SPORADIC. The prevalence of inherited forms of AD is <0.1%.
3-Risk factors for sporadic AD:-aging-head injuries-hormonal changes-vascular diseases-inflammation-ApoE e4 allele polymorphism-exposure to metals, like Cu++ and Zn++
Alzheimer’s disease
http://scienceblogs.com/neurophilosophy/Alzheimer
A nissl stain tissue section (left) and a Bielkhowsky’s stain section from Augustine Deter’s brain (right)
First description of tangle and plaque pathology by Alois Alzheimer (1901)
Alzheimer’s disease
AD is a progressive neurodegenerative disorder affecting the elderly population. Once it starts, it progresses with aging.
It is characterized by the presence of lesions both at an extracellular level (the -amyloid plaques), and at an intracellular levels (the Neurofibrillary tangles, NFT).
The presence of the lesions correlates with both reduction in the volume of the brain (as a consequence of the neurodegenerative phenomena), and with cognitive decline associated to loss of memory.
AD is a form of Dementia.
The loss of intellectual functions (such as thinking, remembering, and
reasoning) of sufficient severity to interfere with a person’s daily
functioning.
Dementia is not a disease itself but rather a group of symptoms that may
accompany certain diseases or conditions. Symptoms may also include
changes in personality, mood, and behavior.
Dementia is irreversible when caused by disease or injury but may be
reversible when caused by drugs, alcohol, hormone or vitamin imbalances,
or depression.
Definition of Dementia
Increasing and persistent forgetfulness
Difficulty performing familiar tasks
Problems with finding the right words to express your thoughts
Disorientation with time and place
Poor or impaired judgment
Problems with abstract thinking
Putting everyday items in illogical places
Mood, behavior or personality changes.
Symptoms in AD
Someone withAlzheimer's diseasesymptoms
Someone with normalage-related memorychanges
Forgets entire experiences Forgets part of an experienceRarely remembers later Often remembers later
Is gradually unable to followwritten/spoken directions
Is usually able to followwritten/spoken directions
Is gradually unable to usenotes as reminders
Is usually able to use notes asreminders
Is gradually unable to carefor self
Is usually able to care for self
Comparison between AD signs and age-related memory changes
Normal
AD
MRI
www.elements4health.com
PET
Anatomy of the Alzheimer’s disease brain
Alzheimer’s disease: characterized by extracellular depositions, the -amyloid plaque, and intracellular depositions, the Neurofibrillary Tangles (NFT) comprised of Paired Helical Filaments (PHF), aggregates of hyperphosphorylated protein tau.
Deposition of fibrillar proteinacious material in Alzheimer’s disease
Origin of NFTs and the mechanism of tau pathology
1- Tau is a microtubule-associated protein that regulates cytoskeleton structure.
2- Tau is hyperphosphorylated in AD.
3- When highly phosphorylated, tau is sequestered into aggregates (PHF and NFT) and causes disruption of microtubules, that ultimately leads to cell death.
www.emdbiosciences.com
Origin of the -amyloid plaque
1-Amyloidogenic processing of the Amyloid Precursor Protein APP, and generation of the the -amyloid peptides (A37-43).
The -Amyloid Plaque
amyloidogenic processing pathway
A
APPTMD
NH2 COOH
1-secretase 2-secretase
Mechanisms of A pathology:
Plaque: unknownA: oligomers affect synaptic activity and neurotransmitter release
The -amyloid plaque
1- -amyloid is DIFFERENT from amyloid. -amyloid contains specifically the -amyloid peptide, an approximately 4kDa peptide (A40, A42) deriving from the amyloid precursor protein APP when it undergoes the so called amyloidogenic pathway. -amyloid plaque contains also ubiquitin and other proteins coming from degenerative neurons and glial cells.
2- The -amyloid peptide is insoluble in water. When released from the precursor protein it assumes a -sheet conformation that makes it hydrophobic.
3- -amyloid peptides forms oligomers that may affect neurotransmitter release and synaptic plasticity. Oligomers will further aggregates in larger structures called fibrils, that will form the core of the -amyloid plaque, depositing in the extracellular matrix.
4- The size of the plaque will increase following the progression of the disease. Scientific clear evidences are still missing in order to understand whether the plaque is a consequence or a cause of AD. Indeed, A andplaques formation are associated to neuronal death. Inherited forms of AD lead to substantial increase of Aproduction.
Where do -Amyloid peptides come from?
From the processing so called AMYLOIDOGENIC of the larger precursor APP (Amyloid Precursor Protein)
APP processing and formation of aggregates of beta-amyloid
sAPP
A
secretase
secretase
C99
TMDAPP
secretase secretase
Amyloidogenic processing of APP
NH2 COOH
COOHNH2
Structure of the -Amyloid peptide
25-35, the most critical region for the change of conformation from -sheet to -sheet
Genetic of AD
-Depending on the kind of mutation and on the gene that carries it, the onset of the disease is SIGNIFICANTLY EARLIER than in sporadic cases (<before 65 years of age).
All the mutations are autosomal dominant, and involve
*APP protein
*Members of the -secretase complex, like Presenilin 1 (PS1) and Presenilin 2 (PS2)
Mutations on APP
Chromosome 21. Relation to Down’s syndrome (Trisomy 21; excess of APP transcript induces plaque formation already at early age, and progresses with aging).
Swedish mutation: K670M/N671L, facilitates the amyloidogenic processing of APP by increasing the affinity for and the cleavage by -secretase of ~100 times.Dutch Mutation: E693Q, induces cerebral amyloidosis Arctic Mutation:E693G enhances -Amyloid protofibril formationLondon Mutation: V717I, Affects the cleavage of -secretase
K670M/N671L
Swedish MutationV717ILondon Mutation
E693GArctic Mutation
sAPP
A
secretase
secretase
C99
TMDAPP
secretase!!! secretase!!!
Amyloidogenic processing of APP
NH2 COOH
COOHNH2
K670M/N671L V717I
E693G
Mutations on Presenilins
PS1 (on chromosome 14) PS2 (on chromosome 1) are ~450 aa long aspartyl proteases comprised of 7- to 8- transmembrane spanning domains. They are the catalytic part of a tetrameric protein complex called -secretase, able to cleave APP at the end of the sequence for b-Amyloid peptides, generating -Amyloid species.
More than 70 mutations on PS1 gene account for inherited AD.
Two mutations on PS2 gene account for inherited AD.
Hardy and Selkoe, 2002
PS1 mutations and APP
sAPP
A
secretase
secretase/mutantPS1
C99
TMDAPP
secretase secretase
Amyloidogenic processing of APP
NH2 COOH
COOHNH2
The -Amyloid Plaque
Alois Alzheimer: “miliary bodies (the plaques) and dense bundles of fibrils (NFT)”
Characteristic of the -amyloid plaque
-is extracellular
-normally, it has a core composed of the -amyloid peptide
-it can be cored (with an intensely stained core with a weak periphery stain-halo) or diffused, which do not have a core and the immunoreactivity is uniform over the plaque.
-aggregation is massive in the center, and diffused at the sides (disaggregation hypothesis?)
-diameter ranges between 20m and 90m
-is composed of dystrophic neurites, -amyloid peptides (40/42/43), ubiquitin, tau protein and other proteins, some involved in the generation of -amyloid, like the secretases.
Amyloid: definition
Insoluble fibrous protein aggregations sharing specific structural traits:-Insolubility in water--sheet conformation-largest aggregates deposit extracellularly-positive to the staining with specific dyes, such as Congo Red -associated with tissue degeneration (cause or consequence?)
-Amyloid
Are formations of amyloid characterized by a core specifically formed by -amyloid peptides, a product of the so called amyloidgenic processing of a larger precursor, the protein APP (Amyloid Precursor Protein)
Congo red staining of amyloid plaques
Under polarized light Under unpolarized light
Prion’s disease
Unpolarized light Polarized light
AD
Congophylic plaques
How to specifically detect -Amyloid plaques?
Using antibodies that specifically recognize the different -Amyloid peptides, A 1-40, A 1-42, A 1-
43
-Amyloid peptides
40/42 43
-Amyloid plaques depositions follow the progression of AD
A40, A42 and A43 are part of the -amyloid plaque in AD
Levels of deposited A40, A42 and A43 follow the progression of the disease
Diagnosis of AD
At the moment, the exact diagnosis for AD can be performed only post-mortem by means of immunohistochemistry, verifying the presence of the -amyloid plaques in the patient’s brain section using specific anti -amyloid antibodies.
However, a clinical diagnosis for AD is based on
Neuropsycologic evaluation: behavioral and cognitive tests (MMSE, CDR). Diagnosis of a possible or probable AD (“Dementia of AD type”).
Imaging techniques:MRI to detect changes in the volume of the brainPET analysis to identify areas of the brain with reduced glucose utilization
Progress has been done in the direction of using dyes/compounds that specifically recognize the -amyloid structure in both MRI and PET analysis. This would improve the quality of the diagnosis, identifying the structures (-amyloid plaques) that are specific for AD.
Normal Alzheimer’s diseases
MRI
Computer graphic
MRI in Alzheimer’s disease (AD)
Study on age-related morphologic neuronal changes
Cortical thickness decreases with age
Number of cortical neurons does not decrease with age
Cerebral volume loss is associated with aging, but not necessarily with neuronal death and/or with AD.Need for diagnostic tools more specific than MRI.
Characteristics of a biomarker for diagnostic purposes
-It should be already changed in the initial steps of the disease: implications for an early diagnosis of the disease, with deep impact in the success of the treatment.
-The method to access the biomarker must not be invasive
-The molecule used as a biomarker must be specific for that disease, and not be involved in other diseases. The mechanisms behind the specific changes in the disease must be clear.
-The method of analysis must be reproducible :-) and must not be expensive
-Ideally, the levels of the biomarker, once identified, should follow the progression of the disease (linear progression).
Possible biomarkers in AD
-Levels of -amyloid peptides in the CSF of patients. Concerns regarding:
•The method used to take the sample of CSF (spinal injection, which is invasive).
•In the CSF of AD patients, the levels of the different species of -amyloid peptides, in particular the most aggressive A42, do not always follow the progression of the disease. In fact, levels of A42 raise in the early stages of the diseases, but drop in the late, advanced stages of the disease, maybe indicating increased deposition of secreted A42 into plaques in the brain.
•It is very difficult to correlate the amount of biomarker (in particular A42) to the amount of deposited plaques in the different stages of the disease.
•Cerebrospinal levels of hyperphoshorylated tau. However, since tau is involved also in other neurodegenerative phenomena called taupaties, it is questionable how it could be considered as a biomarker specific for AD.
Immune response
ApoptosisHematopoiesis
18 predictive AD-related plasma signaling molecules
Ray et al.,
Probable AD diagnosis via identification of changes in the 18 markers
The Pittsburgh Compound B PIB is specifically up-taken in AD brains
PIB is differentially retained in brain areas more susceptible to AD
Control
Control
AD
AD
Topography of PIB retention in AD brain
In AD brains, PIB uptake correlates with the progression of the disease
?Are plaques a CAUSE or a CONSEQUENCE of neurite dysfunction?
Appearance of a novel plaque is a fast process that takes 1 week
Meyer-Luehamnn et al., Nature, 2008, 451:720
Meyer-Luehamnn et al., Nature, 2008, 451:720
Formation of a plaque can occur within 24 hours
Meyer-Luehamnn et al., Nature, 2008, 451:720
Plaques recruit activated microglia: a possible role of microglia limiting the size of the plaque
Meyer-Luehamnn et al., Nature, 2008, 451:720
Plaque formation induces neurites curvature
Soluble beta-Amyloid critically contributes to the formation of the plaques
Soluble and insoluble beta-Amyloid and toxic functions
Beta-Amyloid peptides can be detected in the ISF
Amyloid plaques develop in J20APPTg mice without changes in the precursor APP
Levels of soluble ISF Abeta decrease with disease progressing…
…whereas levels of insoluble Abeta increase
Higher levels of exogenous, NOT newly synthesized Abeta are sequestered from the ISF in plaque-rich animals
Demonstration that the plaque attracts soluble Abeta
Explanation why levels of Abeta 42 in the CSF DO NOT follow the progression of the disease
The many ways the system tries to get rid of the Abeta peptides
Insulin Degrading Enzyme (IDE) is crucial for Abeta degradation
IDE levels are reduced in brain areas affected by AD
Decreased A plaque burden in animals overexpressing Insulin Degrading Enzyme (IDE) and Neprilysin
Leissring et al.,
Is there anything we can do to help the system get rid of the plaques?
Y E S ! H E A L T H Y L I F E S T Y L E !!
Abeta plaques are reduced in APPTg mice in enriched environment
Abeta plaques are reduced in APPTg mice in enriched environment
Environmental enrichment reduces the amyloid load
Both levels of soluble and insoluble Abeta decrease with environmental enrichment
Activity of IDE and neprilysin are increased with environmental enrichment:Abeta clearance is favored
Exercise reduces the levels of markers of AD in CFS:Reduced levels of Abeta42…
…and tau, phosphorylated tau
Decreased exercise associates with increased risk of AD
