Studies on apoptosis of hepatocyte and carcinogenesis in Fah.deficiency

遗传性酪氨酸血症1(HT1)是由富马酸乙酰乙酸酯水解酶基因FAH突变引起的，FAH编码酪氨酸分解代谢途径的最后一种酶。HT1患者有严重的肝脏损害和肝细胞癌，因此必须为这类儿童进行肝移植。我们开发了双突变小鼠，其中初级纯合缺陷(FAH-/-)的表型被另一个纯合子突变等位基因(HpD-/-)完全掩盖。在这个模型中，固有的缺陷可以通过体内基因转移或通过代谢过程来重建。这些方法有助于研究肝细胞损伤的早期过程，明确了肝细胞的死亡是由于细胞凋亡所致。在Fah^&lt；-/-&gt；-/-&gt；-/-&gt；双富马酸乙酰乙酸酯很可能明显地诱导细胞色素c的释放，进而触发遗传性酪氨酸血症1型患者肝细胞中caspase级联的激活。了解HT1的肝损伤将有助于理解FAH缺乏的致癌机制。

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.