Enhanced phosphatidylinositol 4-phosphate 5-kinase α expression and PI(4,5)P2 production in LPS-stimulated microglia

Microglia are the major glial cells responsible for immune responses against harmful substances in the central nervous system. Type I phosphatidylinositol 4-phosphate 5-kinase α (PIP5Kα) and its lipid product, phosphatidylinositol 4,5-bisphosphate (PI[4,5]P2), regulate important cell surface functions. Here, we report that lipopolysaccharide (LPS) significantly enhanced PIP5Kα mRNA and protein expression levels in a time- and concentration-dependent manner in microglia. Furthermore, LPS stimulation led to a robust increase in PI(4,5)P2 in the plasma membrane, demonstrated by PI(4,5)P2 immunostaining or PI(4,5)P2 imaging using a PI(4,5)P2-specific probe, tubby (R332H), fused to yellow fluorescent protein. Phosphatidylinositol 3-kinase, p38 mitogen-activated protein kinase (MAPK), p42/44 MAPK, and c-Jun N-terminal kinase signaling pathway inhibitors clearly reduced PIP5Kα expression, indicating that these pathways are necessary for LPS-induced PIP5Kα expression. In addition, inhibition of nuclear factor-κB and Sp1 transcription factors interfered with the LPS-induced upregulation of PIP5Kα. Delivery of PI(4,5)P2 into microglia increased the expression of interleukin-1β and tumor necrosis factor α. These findings indicate that PIP5Kα upregulation and the subsequent rise in PI(4,5)P2 in LPS-stimulated microglia may positively regulate microglial inflammatory responses.