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 alpha (PIP5K alpha) and its lipid product, phosphatidylinositol 4,5-bisphosphate (PI[4,5]P-2), regulate important cell surface functions. Here, we report that lipopolysaccharide (LPS) significantly enhanced PIP5K alpha 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)P-2 in the plasma membrane, demonstrated by PI(4,5)P-2 immunostaining or PI(4,5)P-2 imaging using a P(4,5)P-2-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 PIP5K alpha expression, indicating that these pathways are necessary for LPS-induced PIP5K alpha expression. In addition, inhibition of nuclear factor-kappa B and Sp1 transcription factors interfered with the LPS-induced upregulation of PIP5K alpha. Delivery of PI(4,5)P-2 into microglia increased the expression of interleukin-1 beta and tumor necrosis factor alpha. These findings indicate that PIP5K alpha upregulation and the subsequent rise in PI(4,5)P-2 in LPS-stimulated microglia may positively regulate microglial inflammatory responses. (C) 2010 Elsevier Ltd. All rights reserved.