Phospholipase Cε links G protein-coupled receptor activation to inflammatory astrocytic responses

Neuroinflammation plays a major role in the pathophysiology of diseases of the central nervous system, and the role of astroglial cells in this process is increasingly recognized. Thrombin and the lysophospholipids lysophosphatidic acid and sphingosine 1-phos-phate (S1P) are generated during injury and can activate G protein-coupled receptors (GPCRs) on astrocytes. We postulated that GPCRs that couple to Ras homolog gene family, member A (RhoA) induce inflammatory gene expression in astrocytes through the small GTPase responsive phospholipase epsilon (PLC epsilon). Using primary astrocytes from wild-type and PLC epsilon knockout mice, we demonstrate that 1-h treatment with thrombin or SIP increases cyclooxygenase 2 (COX-2) mRNA levels similar to 10-fold and that this requires PLC epsilon. Interleukin-6 and interleukin-1 beta mRNA levels are also increased in a PLC epsilon-dependent manner. Thrombin, lysophosphatidic acid, and S1P increase COX-2 protein expression through a mechanism involving RhoA, catalytically active PLC epsilon, sustained activation of protein kinase D (PKD), and nuclear translocation of NF-kappa B. Endogenous ligands that are released from astrocytes in an in vitro wounding assay also induce COX-2 expression through a PLC epsilon- and NF-kappa B-dependent pathway. Additionally, in vivo stab wound injury activates PKD and induces COX-2 and other inflammatory genes in WT but not in PLC epsilon knockout mouse brain. Thus, PLC epsilon links GPCRs to sustained PKD activation, providing a means for GPCR ligands that couple to RhoA to induce NF-kappa B signaling and promote neuroinflammation.