Phosphatidylinositol 4-phosphate 5-kinase alpha contributes to Toll-like receptor 2-mediated immune responses in microglial cells stimulated with lipoteichoic acid

Abstract

Phosphatidylinositol 4,5-bisphosphate (PIP2) is an important lipid regulator of membrane signaling and remodeling processes. Accumulating evidence indicates a link between PIP2 metabolism and Toll-like receptor (TLR) signaling, a key transducer of immune responses such as inflammation, phagocytosis, and autophagy. Microglia are immune effector cells that serve as macrophages in the brain. Here, we examined the potential role of phosphatidylinositol 4-phosphate 5-kinase alpha (PIP5Kalpha), a PIP2-producing enzyme, in TLR2 signaling in microglial cells. Treatment of BV2 microglial cells with lipoteichoic acid (LTA), a TLR2 agonist, increased PIP5Kalpha expression in BV2 and primary microglial cells, but not in primary cultures from TLR2-deficient mice. PIP5Kalpha knockdown of BV2 cells with shRNA significantly suppressed LTA-induced activation of TLR2 downstream signaling, including the production of proinflammatory cytokines and phosphorylation of NF-kappaB, JNK, and p38 MAP kinase. Such suppression was reversed by complementation of PIP5Kalpha. PIP5Kalpha knockdown lowered PIP2 levels and impaired LTA-induced plasma membrane targeting of TIRAP, a PIP2-dependent adaptor required for TLR2 activation. Besides, PIP5Kalpha knockdown inhibited phagocytic uptake of E. coli particles and autophagy-related vesicle formation triggered by LTA. Taken together, these results support that PIP5Kalpha can positively mediate TLR2-associated immune responses through PIP2 production in microglial cells.