The role of phospholipase c‐epsilon in COX‐2 expression and inflammation

Abstract

Brain injury triggers a response characterized by astrocyte proliferation, inflammatory gene expression, and migration. During injury thrombin is generated and can activate the G‐protein coupled protease‐activated receptor 1 (PAR1). Using primary mouse astrocytes, we demonstrated that PAR1 activation triggers phosphoinositide hydrolysis through the novel phospholipase C epsilon (PLCε). Here we asked whether PLCε signaling mediates inflammatory gene expression in astrocytes in response to PAR1 activation. Thrombin stimulation induces 8 and 2.5‐fold increases in COX‐2 mRNA and protein expression, respectively, and these are significantly inhibited in PLCε KO astrocytes. Protein kinase D (PKD) is also activated in response to thrombin and lost in PLCε KO astrocytes, and studies using siRNA or inhibitors show PKD activation is important for COX‐2 expression. Furthermore, we found that thrombin induces NFκB translocation, which in turn regulates COX‐2 expression and that this is dependent on PLCε and PKD. Finally, using scratch assays and a stab wound model to mimic astrogliosis in vitro and in vivo, respectively, we demonstrate PLCε dependent COX‐2 expression. Our studies show that PLCε is the link between activation of PAR1 and COX‐2 expression and this is mediated through PKD and NFκB activation. In vitro and in vivo data indicate that this pathway has important implications in astrogliosis.