The TRPV1-PKM2-SREBP1 axis maintains microglial lipid homeostasis in Alzheimer's disease.

Microglia are progressively activated by inflammation and exhibit phagocytic dysfunction in the pathogenesis of neurodegenerative diseases. Lipid-droplet-accumulating microglia were identified in the aging mouse and human brain; however, little is known about the formation and role of lipid droplets in microglial neuroinflammation of Alzheimer's disease (AD). Here, we report a striking buildup of lipid droplets accumulation in microglia in the 3xTg mouse brain. Moreover, we observed significant upregulation of PKM2 and sterol regulatory element binding protein 1 (SREBP1) levels, which were predominantly localized in microglia of 3xTg mice. PKM2 dimerization was necessary for SREBP1 activation and lipogenesis of lipid droplet-accumulating microglia. RNA sequencing analysis of microglia isolated from 3xTg mice exhibited transcriptomic changes in lipid metabolism, innate inflammation, and phagocytosis dysfunction; these changes were improved with capsaicin-mediated pharmacological activation of TRPV1 via inhibition of PKM2 dimerization and reduction of SREBP1 activation. Lipid droplet-accumulating microglia exhibited increased mitochondrial injury accompanied by impaired mitophagy, which was abrogated upon of TRPV1 activation. Capsaicin also rescued neuronal loss, tau pathology, and memory impairment in 3xTg mice. Our study suggests that TRPV1-PKM2-SREBP1 axis regulation of microglia lipid metabolism could be a therapeutic approach to alleviate the consequences of AD.