Molecular mechanism for Alzheimer’s disease: searching for the possible therapeutic targets

Sungkwon Chung Dept. of PhysiologySungkyunkwan Univ. School of Medicine

Facts on Alzheimer’s disease (AD) It attacks and slowly steals the minds of its victims. Symptoms of the disease include:

memory loss confusionimpaired judgment personality changesdisorientation loss of language skills.

Always fatal, Alzheimer's disease is the most common form of irreversible dementia.

65-74 years : 10%, 75-84: 20%, 85 and older: 50% It is estimated that by 2020, 30 million people will be affected

by this devastating disorder worldwide and by 2050, the number could increase to 45 million.

Facts on Alzheimer’s disease (AD)

The average cost for nursing home care is $42,000 per year, and the average lifetime cost of care for an individual with Alzheimer’s is $174,000. Medicare costs for beneficiaries with Alzheimer’s are over $100 billion.

Alzheimer's disease is a progressive, irreversible brain disorder with no known cause or cure.National Institute on AgingAlzheimer's Disease, Causes and Risk Factors “Scientists do not yet fully understand what causes Alzheimer's disease. There probably is not one single cause,

but several factors that affect each person differently.”

Alzheimer’s disease sporadic (late on-set): > 95% of patients - Epidemiological Factors

HypercholesterolaemiaHypertensionHyperrhomocysteinaemiaDiabete mellitusMetabolic syndromeSmokingSystemic inflammationIncreased fat intake and obesity

genetic (early on-set): < 5% of patients (FAD)- ApoE ε4 polymorphism - mutations in APP- mutations in presenilin 1, 2 (PS1, PS2)

Amyloid plaques and Neurofibrillary tangles

Amyloid cascade hypothesis

Amyloid Precursor Protein (APP) and its metabolites Citron, Nature Rev. Neurosci., 2004

APP → AβNotch1 → NICDp75NTR → p75-ICD

Roberson & Nucke, Science, 2006

Q1:

Even though potent inhibitors for γ-secretase had been developed, it could not be used for the patients. Why?

I. Functional role of presenilinin Ca2+ regulation

The core of the -secretase complex

Yoo et al., 2000

Presenilin as negative regulatorof capacitative Ca2+ entry (CCE)

Effect of a CCE inhibitor, SKF, on A42 generation

Presenilin as part of -secretase

Presenilin as negative regulator of CCE

Leissring et al., J.C.B., 2000

Yoo et al., Neuron, 2000

CCE pathway may serve as a putative therapeutic target for Alzheimer’s disease.

II. Finding molecular identity of CCE

Down-regulation of IMIC in FAD PS mutantsA B

C D

0 150 300 450-120

-90

-60

-30

0

wt PS M146L L286V ∆E9

I MIC

(pA

/pF)

Time (s)

-40

-60

-80

-100

-120

*

∆E9

*

L286Vwt PS

I MIC (p

A/p

F)I C

RA

C(p

A/p

F)

0

-1

-2

-3

-4

∆E9wt PS L286V

0 150 300 450

-0.9

-0.6

-0.3

0.0

wt PS M146L L286V ∆E9

Time (s)

I /I

o

f IM

AX

MIC

Recovery of IMIC from PS mutant cells by PIP2

PP

P

PI(4,5)P2 PI(4)PPI(3,4,5)P3

PP P

IP3 + DAG PI(4,5)P2PLC

Down-regulation of PIP2 in PS mutant cells

Correlation of the level of PIP2 and Aβ42 generation

TRPM7-like MIC currents underlie the mechanism for PS-mediated modulation of Ca2+ influx.

The down-regulation of PIP2 levels and the generation of Aβ42 were correlated.

Up-regulation of PIP2 levels will be a possible therapeutic target Alzheimer’s disease.

III. Ginsenoside: Modulator for -secretase via PIP2

Structure & function of gisenosides

A42-lowering effect of Rg3

A42-lowering effect of ginsenosides

A42-lowering effect of Rg3, Rk1

A42-lowering effect of Rg3 is specific for APP

Increase of PI(4)P by Rg3

Increase of PI(4)P by Rg3 via activation of PI4KII

PI4KII decreases production of A42

A42-lowering effect of Rg3 in vivo

← PI4KII↑← Rg3

IV. Activator for -secretase?

42, sAPP ELISA assay

0

20

40

60

80

100

120

5g/ml25g/mlconcentration

A42

(% o

f con

trol)

CTL 100g/ml

MeOH extract (CN1-M)

BuOH (B)EtOAc (E)Hexane (H)Dichloromethane (M)

0

20

40

60

80

100

120

A42

(% o

f con

trol)

CTL B E H M

0

20

40

60

80

100

120

A42

(% o

f con

trol)

CTL E1 E2 E3 E4

HPCL Fractions (E1, E2, E3, E4)

0

20

40

60

80

100

120

A42

(% o

f con

trol)

CTL 1 2 3 4 5 6

E1 HPCL Fractions (1,2,3,4,5,6)

0

20

40

60

80

100

50M10M 25M concentration

A40

(% o

f con

trol)

CTL 5M0

20

40

60

80

100

50M10M 25M concentration

A42

(% o

f con

trol)

CTL 5M

Dose dependent effect of E1-4-4 on A42 and A40 secretion

0

20

40

60

80

100

50M25M10M

concentration

sAPP

(%

of c

ontro

l)

CTL 5M

CN1-M-E1-4-4 increases sAPP, and decreases sAPP

-secretase or-secretase

monoclonalantibody

Cell-free

CN1-M-E1-4-4 may directly activates -secretase

Q2:

Amyloidogenic Aβ42 is produced by the activity of γ-secretase. However, activators for -secretase is considered as good therapeutic drug. Why?