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

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.