Cholesterol, APOE, and ACholesterol, APOE, and Aßßin cell and animal modelsin cell and animal models

of Alzheimerof Alzheimer’’s diseases disease

G. William RebeckG. William Rebeck

Georgetown UniversityGeorgetown University

Connections between cholesterol and Alzheimer’s disease

• APOE

• Epidemiology– Increased risk of AD associated with high cholesterol in

mid-life

– Decreased risk of AD associated with use of statins

• Cell culture– High cholesterol - more Aß

– Low cholesterol - less Aß

Connections between cholesterol and Alzheimer’s disease:

animal models

• Niemann-Pick type C disease– Intracellular cholesterol transport

• Statin treatment of TgAPP mice– Cholesterol lowering drugs

• High cholesterol diets for TgAPP mice

Niemann Pick type C disease

Burns et al, J Neurosci (2003) 23:5645

Atorvastatin (Lipitor) reduces brain Aß in PS-APP mice

Aß40 Aß421000

500

pmol

/g 600300

200100

control control statinstatin controlcontrol statinstatinn=6 n=10

p<0.005n=6 n=10

p<0.00005

Petanceska, 2003

High cholesterol diet increases brain Aß in PS-APP mice

Aß detection by IP/mass spectroscopy

0.0

0.10.20.30.4

1-42 1-40 1-38 1-34Aß Peptide

Rel

ativ

e Pe

ak In

tens

ity basal diet high cholesterol*

**

****

Refolo, 2000

Brain Aß levels are modulated by hypercholesterolemia and a cholesterol-lowering drug

0

200

400

600

800

basal diethigh cholesterol dietbasal +vehiclebasal diet + BM15.766

Total Aß(pmol/g)

Aß ELISA

Refolo, 2001

Oversimplified cholesterol hypothesis

APOE

High brain cholesterol

levels

increasedbrain Aß

diet AD

statins

Georgetown University

Hyang-Sook HoeMark BurnsGeetanjali ChakrabortyChris HarrisCasandra Cartagena

Yasuji Matsuoka

Paul Aisen

NKI

Suzana PetanceskaKaren Duff

MGH

Brad HymanMike IrizarryAmy Deng

Oversimplified cholesterol hypothesis

APOE

High brain cholesterol

levels

increasedbrain Aß

diet AD

statins

How to detect effects on brain cholesterol

• Most brain cholesterol is in myelin– Measure non-myelin lipids

• Alterations in brain cholesterol affect cholesterol homeostasis genes– Cleavage of SREBP to regulate gene

transcription

– Generation of oxysterols to regulate gene transcription

Proteolysis of SREBP by low cholesterol levels

LDL receptorHMG CoAreductase

(reminiscent of APP proteolysis)

Induction of LXR by high cholesterol levels

Induction of genes in neuroblastoma cells by LXR activation:

gene chip analysis of mRNA

fold change

• ABC-G1 4.2

• ABC-A1 2.6

• SREBP-1 2.3

• Fatty acid CoA ligase 1.7

• Stearoyl CoA desaturase 1.7

ApoE levels are altered by LXR agonists and cholesterol

TO TO/RA control RA

BV-2cells

apoE

control cholesterol lovastatin primaryglialcultures

apoE

Activation of LXR induces cholesterol efflux to apoE

0.00

2.00

4.00

6.00

8.00

10.00

12.00

control TO apoE apoE + TO apoAi apoAI + TO

% E

fflux

**

*

APOE genotype alters levels of SREBP cleaved fragment

SREBP-1 ELISA

wt E3 E475

100

125

*

% wt

control

GFAP-APOE mice (APOE replacement mice)

Diet and a cholesterol-lowering drug affect brain APOE mRNA

Treatment Plasma Cholesterol (mg/dl)

High cholesterol 200

Vehicle 75

BM 15.766 28

Petanceska, 2004

Brain-permeable statins affect brain cholesterol

Vehicle Zocor Mevacor Lipitor50

70

90

110

*

SynaptosomalPlasmaMembraneCholesterol(% control)

Lipophilicity: ++ ++ --

Oversimplified cholesterol hypothesis

APOE

High brain cholesterol

levels

increasedbrain Aß

diet AD

statins

APOE-ε4 increases brain Aß levels

Aβ 42

wt E3 E40.0

2.5

5.0

7.5

10.0*

GFAP-APOE mice(APOE replacement mice)

Statins decrease brain Aß

Vehicle MevacorZocor Lipitor

0

5

10

15

***

*

*****

0

2

4

6

* * *

Aß40fmol/g

Aß42fmol/g

Vehicle MevacorZocor Lipitor

How could effects on brain cholesterol alter Aß levels?

• Effects on membrane (like SREBP)– APP is transmembrane

α-, ß-, γ-secretases are transmembrane proteins

• Effects on gene expression (downstream)– Cholesterol equilibrium mechanisms

APOE affects γ-secretase activity in lipid rafts

wt E3 E40

100

200

300

*

Arb

itrar

yun

its

Cholesterol could affect Aßlevels through induction of LXR system

Activation of LXR increases secreted Aß42 levels

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

control TO -901317 control TO -901317

**

Aß42levels

24 hours 48 hours

••Therapeutic potential for statin treatment?Therapeutic potential for statin treatment?

importance of blood brain barrier?importance of blood brain barrier?

••Testing of other cholesterolTesting of other cholesterol--altering drugs?altering drugs?

••Potential for dietary reduction in cholesterol?Potential for dietary reduction in cholesterol?

••APOE genotypeAPOE genotype--statin interactions?statin interactions?

24-Hydroxycholesterol induces ABCA1 expression in Neuro2A cells

con 22OH 24OH 24OH

RA RA

ABC-A1

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Burns et al, J Neurosci (2003) 23:5645

APOE genotype alters cholesterol hydroxylation

wt ko E2 E3 E40.0

0.1

0.2

nm/m

g

Ben Wolozin

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Tontonoz and Mangelsdorf, 2003

Niemann Pick type C

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Burns et al, J Neurosci (2003) 23:5645

3 Hydroxy-3-methylglutaryl-CoA

Statins

Cholesterolsynthesis

Mevalonate

Farnesyl pyrophosphate

Squalene

Desmosterol

BM15.766

Cholesterol