Intracellular signal pathway and ischemic tolerance of the liver in the presence of molecular - Toward the next generation of liver preconditioning

为阐明热休克预适应抑制肝脏缺血再灌注损伤的作用机制，本实验研究了热休克预适应对肝脏缺血再灌注时激活的转录因子及转录因子激活的信号通路的影响。此外，还检测了受上述转录基因调控的基因的表达。热休克预适应组大鼠缺血再灌流后核因子-kB明显激活，而热休克预适应组则明显抑制核因子-kB的激活。结果表明，热休克预适应对核因子-kB活性的抑制与再灌注期依赖IKK的I-kB降解减少有关。此外，有人认为分子伴侣HSP72参与了这种减少I-kB降解的过程。结果表明，热休克预适应抑制了NF-kB的活化，降低了促炎症介质iNOS、TNF-α和MIP-2mRNA的表达，降低了血清和肝组织中肿瘤坏死因子-α的水平，降低了血清和肝组织中CINC的水平，减少了中性粒细胞的浸润。另一方面，热休克预适应组肝脏缺血再灌流后，另一转录因子AP-1迅速激活。伴随着这种激活，血红素加氧酶-1被表达。尽管AP-1的激活被认为在体外可以诱导肝细胞的凋亡，但AP-1的激活在体外对肝细胞的凋亡有很好的抑制作用。热休克预适应有效地改变了肝脏缺血再灌注过程中的信号转导通路，是提高肝脏缺血耐受性的重要机制。

In order to elucidate the mechanism in the suppression of ischemia reperfusion injury by heat shock preconditioning, effect of heat shock preconditioning on the transcription factors which are activated upon ischemia-reperfusion of the liver and on the signal pathways along which transcriptional factors are activated was investigated. In addition, expressions of the genes that are regulated by these transcriptional genes above were also examined. Activation of NF-kB was significantly suppressed in the group of heat shock preconditioning although NF-kB was markedly activated after ischemia and reperfusion in the control group. It was revealed that this suppression of NF-kB activation by heat shock preconditioning was connected with the reduction of IKK-mdependent I-kB degradation during reperfusion period. Furthermore, it was suggested that molecular chaperone, HSP72, participated in this reduction of I-kB degradation. As the result that NF-kB activation was suppressed, expression of mRNA for proinflammatory mediators like iNOS, TNF-a and MIP-2 ; serum TNF-a level ; CINC level in the serum as well as liver tissue ; and neutrophil infiltration were significantly decreased in the group of heat shock preconditioning. On the other hand, another transcription factor, AP- 1, was activated rapidly after ischemia-reperfusion of the liver in the heat shock preconditioning group. Concomitantly with this activation, hemeoxygenase-1 was expressed. Interestigly, apoptosis of the hepatocytes was well suppressed although AP-1 activation is considered to induce apoptosis in vitro. This result of suppressed apoptosis in this vivo model seems to be the consequence of maintained hepatic microcirculation due to reduced inflanimatory reactions during early reperfusion period.Heat shock preconditioning effectively modified the signal transduction pathways during ischemia-reperfusion of the liver and seemed to be an important mechanism to confer an ischemic tolerance.