REPERFUSION AFTER LIVER-TRANSPLANTATION IN RATS DIFFERENTIALLY ACTIVATES THE MITOGEN-ACTIVATED PROTEIN-KINASES

The injury resulting from cold ischemia and warm reperfusion during li ver transplantation is a major clinical problem that limits graft succ ess, Kupffer cell activation plays a pivotal role in reperfusion injur y, and Kupffer cell products, including free radicals and tumor necros is factor alpha (TNF-alpha), are implicated as damaging agents, Howeve r, the second messengers and signaling pathways that are activated by the stress of hepatic ischemia/reperfusion remain unknown. The purpose of this study is to assess the activation of the three known vertebra te mitogen activated protein kinase (MAPKs) and the activating protein 1 (AP-1) transcription factor in response to ischemia and reperfusion in the transplanted rat liver, There was a potent, sustained inductio n of c-jun N-terminal kinase (JNK), but not of the related MAPKs extra cellular signal-regulated kinases (ERK) or p38, upon reperfusion after transplantation. TNF-alpha messenger RNA (mRNA) levels and transcript ion factors AP-1 and nuclear factor-kappa B (NF-kappa B) were induced in the liver after 60 minutes of reperfusion, Finally, there was an el evation of ceramide, but not diacylglycerol or sphingosine, in the tra nsplanted liver, Ceramide is a second messenger generated by TNF-alpha treatment and is an activator of JNK. Because JNK activation preceded the elevations in ceramide and TNF-alpha mRNA, these results suggest that increased hepatic TNF-alpha and ceramide may perpetuate JNK induc tion, but that they are not the initiating signals of JNK activation d uring reperfusion injury in the transplanted liver.