C-Jun NH2 terminal kinase (JNK) is an essential mediator of Toll-like receptor 2-induced corneal inflammation

TLRs play an important role in the host inflammatory response to bacteria and bacterial products by activating a cascade of intracellular events leading to production of proinflammatory and chemotactic cytokines. To determine the role of MAPKs in TLR-induced corneal inflammation, we stimulated human corneal epithelial (HCE) cells with TLR2 ligands, tripalmitoyl-S-glycero-Cys(Lys) 4 (Pam3Cys) or inactivated Staphylococcus aureus, and examined the time course of expression of MAPKs and the effect of MAPK inhibition on IkB alpha degradation and CXC chemokine production. We found that S. aureus and Pam3Cys stimulate phosphorylation of JNK, p38 MAPK, and ERK within 4 h and that blockade of JNK, but not p38 or ERK phosphorylation, had an inhibitory effect on IkB alpha degradation and CXC chemokine production. To determine if JNK is also important in TLR2- induced corneal inflammation in vivo, we examined JNK1(-/-) mice and pharmacological inhibitors in a murine model of TLR2-induced corneal inflammation which is characterized by neutrophil recruitment to the corneal stroma and development of corneal haze. We found that corneal inflammation was significantly impaired in JNK1(-/-) mice compared with control mice, and in mice treated with the JNK inhibitor compared with vehicle control. Taken together with results from HCE cells, these findings demonstrate that JNK has an essential role in TLR2-induced corneal inflammation.