Hepatic regeneration and extracellular matrix

3年来的研究成果之一是发现70%肝部分切除后3、7、4天的III型和IV型前胶原基因的表达在前2周较其他天数增加2~3倍。BrdU染色检测肝部分切除后肝细胞DNA合成的时间进程表明，肝再生始于门静脉，向中央静脉进行性再生。这一结果表明，肝再生不是一下子发生的，而是像波浪一样逐渐扩大。此外，用抑制胶原合成的Proly 4-羟基酶抑制剂预处理，显著抑制肝脏DNA合成。因此，肝部分切除后的肝再生需要细胞外基质，例如胶原蛋白。另一方面，大鼠注射猪血清可通过激活转化生长因子-β而诱导肝纤维化，而不引起肝细胞死亡。在该模型中，与未处理的大鼠相比，用猪血清处理的大鼠肝部分切除后24小时DNA合成减少了约50%。猪血清治疗可显著增加肝组织中转化生长因子-β蛋白浓度和III型胶原基因的表达。因此，这一结果表明细胞外基质的过度产生阻碍了肝脏的再生。在未来，我们计划研究添加4-羟基脯氨酸酶抑制剂是否通过抑制细胞外基质的过度产生来加速肝再生。

One of the achievements during these 3 years is the finding that the expression of types III,and IV procollagen mRNA increased 2-3 fold at days of 3,7,4 compared with other days during the first 2 weeks after 70% partial hepatectomy. The time course of DNA synthesis in hepatocytes after partial hepatectomy detected by BrdU staining indicated that hepatic regeneration starts from the portal tract and progresses to the central vein. This result suggests that hepatic regeneration occurs not all at once but expands gradually like a wave. Also, pretreatment with proly 4-hydroxylase inhibitor, an agent inhibiting collagen synthesis, significantly suppressed hepatic DNA synthesis. Thus, extracellular matrix, e.g., collagens, is required for hepatic regeneration after partial hepatectomy. On the other hand, the injection of pig serum into rats can induce liver fibrosis by the activation of TGF-beta without hepatocytes cell death. In this model, treatment with pig serum reduced DNA synthesis about by 50% 24 h after partial hepatectomy compared with that untreated rats. Treatment with pig serum significantly increased the concentration of TGF-beta protein and the expression of type III pocollagen mRNA in the liver. Therefore, this result indicates that excessive production of extracellular matrix prevents hepatic regeneration. In the future, we plan to investigate whether addition of prolyl 4-hydroxylase inhibitor accelerates hepatic regeneration by inhibiting the excessive production of extracellular matrix.