Molecular mechanism for Alzheimer’s disease : searching for the possible therapeutic targets Sungkwon Chung Dept. of Physiology Sungkyunkwan 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 lossconfusion impaired judgment personality changes disorientationloss of language skills.  Always fatal, Alzheimer's disease is the most common form of irreversible dementia.  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 Aging Alzheimer'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 Hypercholesterolaemia Hypertension Hyperrhomocysteinaemia Diabete mellitus Metabolic syndrome Smoking Systemic inflammation Increased 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 → Aβ Notch1 → NICD p75 NTR → 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 presenilin in Ca 2+ regulation

The core of the  -secretase complex

Yoo et al., 2000 Presenilin as negative regulator of capacitative Ca 2+ entry (CCE)

Effect of a CCE inhibitor, SKF, on A  42 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 I MIC in FAD PS mutants AB CD wt PS M146L L286V ∆E9 I MIC (pA/pF) Time (s) * ∆E9 * L286V wt PS I MIC (pA/pF) I CRAC (pA/pF) ∆ E9 wt PS L286V wt PS M146L L286V ∆E9 Time (s) I /I of I MAX MIC

Recovery of I MIC from PS mutant cells by PIP 2

P P P PI(4,5)P2PI(4)PPI(3,4,5)P3 P P P IP 3 + DAG PI(4,5)P2 PLC

Down-regulation of PIP 2 in PS mutant cells

Correlation of the level of PIP 2 and Aβ42 generation

 TRPM7-like MIC currents underlie the mechanism for PS-mediated modulation of Ca 2+ influx.  The down-regulation of PIP 2 levels and the generation of Aβ42 were correlated.  Up-regulation of PIP 2 levels will be a possible therapeutic target Alzheimer’s disease.

III. Ginsenoside: Modulator for  -secretase via PIP 2

Structure & function of gisenosides

A  42-lowering effect of Rg3

A  42-lowering effect of ginsenosides

A  42-lowering effect of Rg3, Rk1

A  42-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 A  42

A  42-lowering effect of Rg3 in vivo

← PI4KII  ↑← Rg3

IV. Activator for  -secretase?  42, sAPP  ELISA assay

MeOH extract (CN1-M) BuOH (B) EtOAc (E) Hexane (H) Dichloromethane (M) HPCL Fractions (E1, E2, E3, E4) E1 HPCL Fractions (1,2,3,4,5,6)

Dose dependent effect of E1-4-4 on A  42 and A  40 secretion

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

 -secretase or  -secretase monoclonal antibody 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?