ApoE lipidation state directs immunometabolic reprogramming of human microglia.

INTRODUCTION

ApoE ε4 is the strongest genetic risk factor for Alzheimer's disease (AD). Emerging evidence suggests that ApoE4 increases AD risk by disrupting microglial metabolism and function. However, whether ApoE lipidation state contributes to microglial dysfunction remains poorly understood.

METHODS

Human microglia were treated with lipid-free (LF) or lipid-bound ApoE3 or ApoE4. Label-free, live-cell holotomography and global proteomics were used to assess isoform- and lipidation-specific effects on lipid droplet (LD) dynamics, mitochondrial morphology, and microglial phenotype.

RESULTS

ApoE4 treatment resulted in fewer but enlarged LDs and increased mitochondrial fragmentation compared to ApoE3, effects that were enhanced by lipid-bound ApoE4. Proteomic analyses revealed a strong type I interferon response in cells exposed to LF-ApoE, which was exacerbated by LF-ApoE4.

DISCUSSION: These findings indicate that lipid-bound ApoE4 drives metabolic reprogramming, whereas LF-ApoE4 promotes inflammatory signaling, identifying ApoE lipidation as a critical modifier of ApoE4-associated AD risk.