The Effect of ApoE Genotype, Plasmalogen Biosynthesis, and Reverse Cholesterol Transport Biomarkers on Cognition and Odds of Alzheimer’s Disease in Elderly Persons

Dayan Goodenowe1, Tara Smith1, Vijitha Senanayake1, Bassirou Chitou1, Asuka Mochizuki1, Sue E. Leurgans2, David A. Bennett2

1Phenomenome Discoveries Inc., Saskatoon, Saskatchewan, Canada. 2Rush Alzheimer’s Disease Center, Rush University Medical Center, Chicago, IL, USA

Reduced cholesterol transport, Apolipoprotein E (ApoE) ε4 and depleted plasmalogens (PlsEtn) are hypothesized to be mechanistically involved in the etiology of dementia and AD pathology. Serum biomarkers of PlsEtn biosynthesis were measured in 862 elderly subjects and the relationships between cholesterol transport biomarkers, ApoE allele status, cognition and incident AD was determined.

Plasmalogens and Cognition – Mechanism and Post-Mortem Studies

Plasmalogens and AD Pathology – Mechanism and Post-Mortem Studies

Plasmalogens and Cholesterol Regulation

Plasmalogen Biosynthesis – Associations with Age and Cognition

Plasmalogens and Cognition – Serum Studies

• Higher age and ApoE ε4 genotype were associated with lower cognition and higher odds of AD

• ApoE ε2 genotype, higher PBV, and a higher HDL-C/TC ratio were associated with higher cognition

• ApoE ε2 genotype and higher PBV were associated with lower odds of AD

• The PBV association with cognition was 2.5-times larger than the ApoE association with cognition

PlsEtn-20:4

Seru

m P

lsEt

n Le

vel

CN Low Mod Severe

-DHA-PlsEtnCognitive Impairment

Amyloid plaques are formed when APP is metabolized by β-

secretase. β-secretase is located in the cholesterol-rich

lipid raft region of the membrane

Normal/healthy APP metabolism occurs via α-

secretase. α-secretase is located in the phospholipid rich region

of the membrane

When membranes are enriched with DHA-plasmalogens, in vitro, α-secretase levels are increased and the formation

of pathological amyloid (Aβ1-42) peptides is reduced

Post-mortem human brain analyses reveal that persons with high levels of DHA-plasmalogens have

low levels of Alzheimer’s pathology(Rush University, n=100, corrected for age, education, and gender)

The fusion and release of neurotransmitters from

presynaptic vesicles is critical for normal neuron function

PlsEtn-18:1

PtdEtn-20:4PtdEtn-18:1

In vitro studies have shown that adequate membrane levels of

polyunsaturated fatty acid (PUFA) containing plasmalogens (PlsEtn) are needed for membrane fusion

Post-mortem human brain analyses reveal that persons with high levels of DHA-plasmalogens have

higher cognition(Rush University, n=100, corrected for age, education, and gender)

Background and Introduction

Serum levels of DHA-PlsEtn are decreased in cognitively impaired subjects. Subjects with

severe cognitive impairment have lower levels than subjects with mild cognitive impairment (Goodenowe et al., 2007)

ApoE is the predominant cholesterol transport protein in the brain. The different ApoE isoforms

have significantly different cholesterol efflux activity (ε2> ε 3> ε4 , Michikawa, 2000)

When membranes are enriched with DHA-plasmalogens, sterol-O-acetyltransferase (SOAT)

levels are increased, resulting in increased cholesterol esterification and increased

cholesterol efflux, which results in decreased cellular cholesterol levels (Mankidy et al., 2011)

-ε2-ε3-ε4

40-49 50-59 60-69 70-79 80+ Total NCI MCI AD Total146 166 104 92 93 601 156 208 208 572

Age Distribution Population Controls Alzheimer Disease + Controls

• Overall plasmalogen biosynthesis is stable from age 40-79 and then decreases;

• Plasmalogen Biosynthesis is decreased in subjects with cognitive impairment;

• Subjects with severe cognitive impairment have lower PBV than subjects with mild cognitive impairment (Goodenowe et al, 2015)

Seru

m P

BV

An overall Plasmalogen Biosynthesis Value (PBV) can be generated by determining the ratio of key plasmalogen

precursors and products (Goodenowe et al., 2015)

Plasmalogens are synthetized in

peroxisomes by specialized enzymes

Average age: 71+/-9

Clinical Variables Outcome Analysis:Cognition and AD

Outcome Analysis:Contribution of Variables

Results – ApoE, RCT, PBV, and AD

ApoE - PBV Interaction Analyses

Conclusions•Low PBV is the largest contributor (other than age) to reduced cognition in the elderly with an overall effect size 2.5-times larger than ApoE genotype;•High PBV or ApoE ε2 genotype is associated with increased RCT (HDL-C/TC ratio);•High PBV neutralizes the increased probability of AD associated with the ApoE ε4 genotype independent of its effect on RCT.

ε4

ε3

ε2ε4

ε3

ε2

e2 e3 e4PBV (Mean -1SD) 0.104 -0.129 -0.362PBV (Mean) 0.165 0.006 -0.235PBV (Mean +1SD) 0.226 0.141 -0.109

e2 e3 e4PBV (Mean -1SD) 0.022 0.122 0.229PBV (Mean) 0.016 0.071 0.151PBV (Mean +1SD) 0.012 0.040 0.096

Probability of AD Global Cognition

HDL-C / Total Cholesterol HDL-C / Total Cholesterol

• PBV significantly affected the probability of AD in ApoE e3 and e4 carriers;

• PBV significantly affected the cognition level in ApoE e2, e3 and e4 carriers;

• Both ApoE and PBV were associated with HDL-C/TC ratio;

• PBV affected the HDL-C/TC ratio in e2 and e3 carriers but not e4 carriers;

• The PBV effect on HDL-C/TC is not a viable mechanism to explain the PBV effect on e4 carriers.

ApoE and Cholesterol Regulation