Studies on apoptosis of hepatocyte and carcinogenesis in Fah.deficiency

遗传性酪氨酸血症1（HT1）是由于富马酰乙酰乙酸水解酶基因FAH（编码酪氨酸分解代谢途径中的最后一种酶）突变所致。HT1患者有严重的肝损害和肝细胞癌，因此必须为这些儿童进行肝移植。我们开发了双突变小鼠，其中主要纯合缺陷（FAH-/-）的表型完全被另一纯合突变等位基因（HPD-/-）掩盖。在该模型中，可以通过体内基因转移或通过代谢程序重建固有缺陷。这些方法促进了对肝细胞损伤的早期过程的研究，并且清楚地表明肝细胞死亡是由于细胞凋亡。尿黑酸（HGA）可诱导肝细胞凋亡，并发生急性肝功能衰竭，Fah ^<-/-> Hpd ^<-/->肝衰竭前细胞色素c从线粒体中释放，我们还发现半胱天冬酶抑制剂在预防HGA诱导的肝衰竭方面非常有效。双突变小鼠中的HGA。推测延胡索酰乙酰乙酸酯可能通过诱导细胞色素c的释放，进而激活1型遗传性酪氨酸血症患者肝细胞内的caspase级联反应，从而导致肝细胞损伤。

Hereditary tyrosinemia 1(HT1) is due to mutations in the fumarylacetoacetate hydrolase gene FAH, encoding the last enzyme in the tyrosine catabolic pathway. HT1 patients have severe liver damage and hepatocellular carcinomas, hence liver transplantation has to be done for such children. We developed double mutant mice in which the phenotype of the primary homozygous defect (FAH-/-) is completely concealed by another homozygous mutant allele (HPD-/-). In this model, the inherent defect can be reconstituted by in vivo gene transfer or by a metabolic procedure. These approaches facilitated investigations on the early process of hepatocyte injury, and it became clear that the hepatocyte death was due to apoptosis. Apoptosis of hepatocytes was induced and an acute onset of liver failure occurred following administration of homogentisic acid (HGA), the intermediate metabolite between HPD and FAH.Cytochrome c was released from mitochondria prior to liver failure in the Fah^<-/-> Hpd^<-/-> double mutant mice following the administration of HGA.We also found that caspase inhibitors were highly effective in preventing the liver failure induced by HGA in the double mutant mice. It is highly likely that fumarylacetoacetate apparently induces the release of cytochrome c which in turn triggers activation of the caspase cascade in hepatocytes of subjects with hereditary tyrosinemia type 1.These knowledge on the hepatic injury in HT1 will facilitate understanding of carcinogenesis in FAH deficiency.