Molecular mechanisms in angiogenic reconstruction of sinusoidal endothelium in regenerating and developing liver

最近，一些实验研究表明，肝窦内皮细胞的增殖对于肝主要组织丢失后的肝再生是必不可少的。在肝再生过程中，增殖的肝细胞表达多种血管生成生长因子，包括血管内皮生长因子及其受体，以诱导血管生成。已经证实，缺氧诱导因子-1α(HIF-1α)转录包括血管内皮生长因子在内的多种血管生成生长因子来感知缺氧。然而，HIF-1α在肝再生过程中的表达谱尚不清楚。本研究对大鼠肝切除70%后再生肝组织中缺氧诱导因子-1α的表达进行了研究。免疫印迹法检测肝组织中HIF1、α、FMS样酪氨酸激酶-1(Flt-1)的表达，激光多普勒检测肝血流量，免疫组织化学法检测肝窦内皮细胞面积和HIF-1a的定位。肝血流于术后24小时达高峰(P=0.002)，36小时最低(P=0.006)。肝切除后72小时内皮细胞面积最小(P&lt；0.001)。肝切除后2 4h和120h分别检测到胞核HIF1α和VEGF峰。而Flt-1水平在肝切除后持续升高。HIF-1α在肝切除后24小时、36小时和72小时明显升高(P&lt；0.05)。综上所述，在再生大鼠肝脏中，核HIF-1α的表达高峰出现在表达之前。HIF-1α水平升高可能是肝切除后肝细胞指数性生长所致的一过性低氧所致。

Recently, several reports have experimentally shown that sinusoidal endothelial cell proliferation is essential for liver regeneration after major hepatic tissue loss. Several angiogenic growth factors including vascular endothelial growth factor (VEGF) and its receptors are expressed by the proliferating hepatocytes to induce angiogenesis during liver regeneration. It has been well established that hypoxia inducible factor-1α (HIF-1α) transcribes several angiogenic growth factors including VEGF for sensing hypoxia. However, the expression profile of HIF-1α during liver regeneration is not known. In the present study, expression of HIF-1α was evaluated in the regenerating liver following 70% partial hepatectomy in rats. Expressions of nuclear HIF-1α VEGF and fms-like tyrosine kinase-1 (flt-1) were measured by Western blot, liver blood flow by using a laser Doppler and sinusoidal endothelial cell area and HIF-1a localization were studied by immunohistochemistry. Liver blood flow peaked at 24h (P=0.002 compared with control) and was lowest at 36h after hepatectomy (P=0.006). Endothelial cell area was lowest at 72h after hepatectomy (P<0.001). Nuclear HIF-1α and VEGF peaks were recognized at 24h and 120h after hepatectomy, respectively. However, flt-1 level was continuously elevated after hepatectomy. HIF-1α mRNA increased at 24h, 36h and 72h after hepatectomy (P<0.05). In conclusions, the peak expression of nuclear HIF-1α was observed before VEGF expression in the regenerating rat liver. The elevated level of HIF-1α might be the result of transient hypoxia induced by exponential growth of hepatocytes following hepatectomy.