Targeting the microglial phosphatidylethanolamine synthesis pathway promotes GABARAP-associated phagocytosis and Aβ clearance in Alzheimer’s disease

Abstract

Alzheimer’s disease (AD) is a major cause of dementia and a prevalent age-related neurodegenerative disorder characterized by progressive cognitive impairment and memory loss. Although metabolic activation or dysfunction of microglia is implicated in AD pathogenesis, the phospholipid metabolism–associated signaling mechanisms within microglia remain poorly defined. In this study, we demonstrate that quinolinic acid (QA), a byproduct of tryptophan catabolism via the kynurenine pathway, activates the microglial Kennedy pathway—responsible for de novo phosphatidylethanolamine (PE) biosynthesis—by upregulating the enzymes EPT1 and ETNK1. This activation markedly enhances the synthesis of PE species enriched in polyunsaturated fatty acids. Concurrently, QA significantly increases the expression of gamma-aminobutyric acid receptor–associated protein (GABARAP), promotes its lipidation, and facilitates the GABARAP-associated phagocytosis (GAP) of Aβ oligomers by microglia. Knockdown of EPT1 and ETNK1 attenuated QA-induced PE synthesis and impaired the GAP of Aβ oligomers, whereas inhibition of GABARAP lipidation via STBD1 deconjugase substantially reduced QA-mediated GAP. QA administration upregulated microglial Gabarap expression and decreased the Aβ plaque burden in the hippocampus of AD (5xFAD) mice, whereas Gabarap knockdown abrogated QA-induced microglial clearance of Aβ. Collectively, these findings reveal a paradoxically beneficial role of QA in activating a microglia-specific signaling cascade that promotes PE biosynthesis and GAP, thereby enhancing Aβ clearance and mitigating AD pathology. Targeting the microglial PE synthesis pathway and GAP may represent a promising therapeutic strategy to ameliorate Aβ accumulation and slow AD progression.