TREM2 promotes Aβ phagocytosis by upregulating C/EBPα-dependent CD36 expression in microglia.

TREM2 plays a critical role in the alleviation of Alzheimer's disease by promoting Aβ phagocytosis by microglia, but the detailed molecular mechanism underlying TREM2-induced direct phagocytic activity of Aβ remains to be revealed. We found that learning and memory functions were improved in aged TREM2 TG mice, with the opposite effects in KO mice. The amount of phagocytosed Aβ was significantly reduced in the primary microglia of KO mice. CD36 expression in primary microglia was greater in TG than in WT mice but was substantially decreased in KO mice. The expression of C/EBPα, an upstream transcriptional activator of CD36, was also elevated in primary microglia of TG mice but decreased in KO mice. The transcription of CD36 was markedly increased by TREM2 overexpression, and this effect was suppressed by a mutation of the C/EBPα binding site on the CD36 promoter. The TREM2-induced expression of CD36 and C/EBPα was inhibited by treatment with PI3K/AKT signaling blockers, and phosphorylation of AKT was elevated in TREM2-overexpressing BV2 cells. The present study provides evidence that TREM2 is required for preventing loss of memory and learning in Alzheimer's disease by regulating C/EBPα-dependent CD36 expression and the consequent Aβ phagocytosis.