PKC-dependent Activation Of P44/42MAPKs In Signal Transduction Pathways During Hepatocyte Ischemic Preconditioning

Background After one or several times of short-time ischemic reperfusion,tissues or organs can survive successive prolonged ischemia and reperfusion,a phenomenon so called ischemic preconditioning,IP. Since the introduction of IP concept by Mr. Murry in 1986,researchers have developed different protocols for various tissues and organs of different kinds of animals,leading to the conclusion that IP is a universal preservation method. Thus far,evidences concerning the IP mechanism in organ preservation are mostly from studies on myocardium. It is considered that the effect of IP are the results of diversified elements working in concerto,among which the activation of signaling cascade of protein kinase C (PKC) and mitogen-activated protein kinases(MAPKs) plays an important role.It is postulated that IP induces the release of endogenous protective molecules that interact with cognate receptors to activate PLC through mediation of the chincough virus sensitive proteins. PLC hydrolyzes membrane phospholipid and produces diacylglyccerol (DAG),that,by working together with calcium hydronium,translocates PKC from cytoplasm to cell membrane and activates PKC. PKC phosphorylated membranous substrates and initiate a series signal transduction to regulate protective gene expression and enhance cellular resistance to ischemia and reperfusion.Although there have been reports that IP conveys protective signals to hepatocytes,few studies have been published on intracellular protective mechanism. It remains to be elucidated whether PKC dependent P44/42 MAPKs pathways are involved in the regulation of protective protein,such as heat shock protein,HSP.Objective By establishing an in vitro IP model for hepatocytes and an in vivo model for rat liver,to investigate the significance of PKC and P44/42 MAPKs signal transduction in IP.Methods Through a normal liver cell IP model,PKC inhibitor,activator and MEK inhibitor were utilized to analyze the phosphorylation of PKC and P44/42 MAPKs. The cellular ultrastructure,HSP expression and viability were also observed. Through an in vivo rat liver IP model that was treated with various drugs,we further analyzed in vivo phosphorylation of PKC and P44/42 MAPKs,HSP expression and AST/ALT concentration. And,cellular structure and ultrastructure were also observed. All the data were statistically analyzed.Results Similar results were obtained both in vivo and in vitro IP models. Compared with the control without IP,the phosphorylation of PKC and P44/42 MAPKs and the expression of HSP were obviously increased in IP treated models. Similar phosphorylation of P44/42 MAPKs,expression of HSP and cellular changes were also found in PKC activated group. In contrast,opposite changes were found in PKC or MEK inhibited groups. Conclusion Both in vitro and in vivo IP models have shown that PKC activation plays a pivotal role in the activation of P44/42 MAPKs pathway that participates in the preservation of liver cells. At the same time,HSP expression is regulated by signals in P44/42 MAPKs pathway.