APOE genotypes and oxidized lipids in Alzheimer’s Disease

Abstract Background The APOE4 allele is a strong risk factor for late‐onset and early‐onset forms but APOE4 is neither a prerequisite for, nor sufficient to cause, AD. Despite decades of research, the exact mechanisms underlying how ApoE4 contributes to AD pathogenesis remain incompletely defined. Astrocytes are homeostatic cells of the central nervous system and play a pivotal role in maintaining neuronal health and survival. Brain metabolic enzyme activity is altered in ApoE4 carriers where mitochondrial oxidative phosphorylation is disrupted and is accompanied by increased oxidative stress. In this study, we aim to investigate the hypothesis that the astrocytic oxidised phospholipids and oxysterol profile is affected by ApoE genotype influencing mitochondrial bioenergetics and altering redox state. Method Human iPSC lines for APOE3/3, APOE 4/4 and APOE knockout were maintained in mTeSRTM1 culture medium and transformed to neural precursor cells. Neural precursor cells were then transformed to pure astrocyte cultures using published protocols. Cells were collected and lipids were extracted using methyl‐tert‐butyl ether (MTBE). Oxidised phosphatidylcholines and oxysterols were measured using liquid chromatography mass spectrometry (ABSciex 5500). Mitochondrial bioenergetics were measured by Seahorse technology. Result Compared to APOE3/3 astrocytes, a slower growth rate was observed for APOE4/4 cells. APOE4/4 cells showed increased levels of oxysterols (24‐hydroxycholesterol (24‐OHC), 27‐hydroxycholesterol (27‐OHC), 7β‐hydroxycholesterol (7β‐OHC) and 7‐ketocholesterol (7KC) and increased levels of short‐chain, oxidised phosphatidylcholines (POVPC; 1‐palmitoyl‐2‐(5‐oxovaleroyl)‐sn‐glycero‐3‐phosphorylcholine, PONPC; 1‐palmitoyl‐2‐(9‐oxo‐nonanoyl)‐sn‐glycero‐3‐phosphocholine and PGPC; 1‐palmitoyl‐2‐glutaryl‐sn‐glycero‐3‐phosphocholine). Conclusion This study shows that the potential to investigate discrete oxidised lipids in APOE genotypes. By studying the profile of oxylipids and mitochondrial bioenergetics, this work will inform future studies into mitochondrial metabolism and targeting oxylipids in mitochondria to improve brain cell health and in AD.