Hepatic regeneration and extracellular matrix

3年来的主要研究成果之一是发现70%肝部分切除术后第3、7、4天肝组织中Ⅲ、Ⅳ型前胶原mRNA的表达较其他时间增加2-3倍。BrdU染色检测肝部分切除后肝细胞DNA合成的时间过程表明，肝再生从门脉开始，并进展到中央静脉。这一结果表明，肝再生不是突然发生的，而是像波浪一样逐渐扩展。此外，用脯氨酸4-羟化酶抑制剂（一种抑制胶原合成的药物）预处理可显著抑制肝DNA合成。因此，细胞外基质，例如，胶原是部分肝切除后肝再生所必需的。另一方面，将猪血清注射到大鼠中可以通过激活TGF-β诱导肝纤维化，而没有肝细胞死亡。在此模型中，与未处理的大鼠相比，部分肝切除术后24 h，用猪血清处理使DNA合成减少约50%。用猪血清处理显著增加了肝脏中TGF-β蛋白的浓度和III型前胶原mRNA的表达。因此，该结果表明，细胞外基质的过度产生阻止了肝再生。在未来，我们计划研究是否加入脯氨酰4-羟化酶抑制剂通过抑制细胞外基质的过度产生加速肝再生。

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.