Mechanism of sinusoidal endothelial cell proliferation and maturation during hepatic regeneration

目的：肝部分切除术后肝窦再生的调控机制尚不清楚。方法：研究大鼠肝切除70%后再生肝组织和离体肝细胞中血管生成素(Ang)-1、Ang- 2、Tie-2和血管内皮生长因子（VEGF）的表达。分别用增殖细胞核抗原（PCNA）和TUNEL染色评价窦状内皮细胞（SECs）的增殖和凋亡情况。结果：VEGF mRNA表达升高，在肝切除术后72 h达到峰值，随后呈下降趋势。肝切除前ang1 mRNA的表达水平可检测到，并在96 h时缓慢升高，达到峰值。而ang2 mRNA在肝切除前几乎未检测到，但在120 h和144 h时被显著诱导。在离体细胞中，VEGF mRNA主要在肝细胞部分表达。同时，Ang-1和Ang-2 mRNA在肝星状细胞（HSC）和SEC组中均有表达，但在后者中更为显著。SECs的PCNA标记指数缓慢升高，在72 h时达到峰值，而在120 ~ 144 h时出现凋亡的SECs。结论：肝细胞分泌VEGF可能在SEC增殖中起关键作用，其次是Ang-1升高，可能促进了窦状动脉成熟。因此，在缺乏VEGF的情况下，主要从hsc中释放的Ang-2可能会导致多余的SECs凋亡，从而停止再生过程。在肝切除术后肝窦再生过程中，Ang-Tie系统与VEGF在调节SEC增殖与凋亡之间的平衡中起关键作用。

AIMS : The regulatory mechanisms of sinusoidal regeneration after partial hepatectomy remain poorly understood.METHODS : We investigated the expression of angiopoietin (Ang)-1, Ang- 2, Tie-2, and vascular endothelial growth factor (VEGF) in both regenerating liver tissue and isolated liver cells after 70% hepatectomy in rats. Proliferation and apoptosis of sinusoidal endothelial cells (SECs) were also evaluated with proliferating cell nuclear antigen (PCNA) and TUNEL staining, respectively.Results : VEGF mRNA expression was increased with a peak at 72 h after hepatectomy, decreasing thereafter. The expression of Ang-1 mRNA was present at detectable levels before hepatectomy and was increased slowly with a peak at 96 h. Meanwhile, Ang-2 mRNA was hardly detected before hepatectomy, but was remarkably induced at 120 h and 144 h. In isolated cells, VEGF mRNA expression was found mainly in the hepatocyte fraction. Meanwhile, mRNA for Ang-1 and Ang-2 was found in the SEC and hepatic stellate cell (HSC) fractions, but was more prominent in the latter. The PCNA labeling index of SECs increased slowly, reaching a peak at 72 h, whereas apoptotic SECs were detected between 120 h and 144 h.Conclusions : VEGF secreted by hepatocytes may play a key role in SEC proliferation, followed by increased Ang-1, presumably promoting sinusoidal maturation. Thereafter, Ang-2 mainly released from HSCs in the absence of VEGF may contribute to apoptosis of superfluous SECs for cessation of the regenerative process. Ang-Tie system, together with VEGF, plays a critical role in regulating balance between SEC proliferation and apoptosis during sinusoidal regeneration after hepatectomy.