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

最近，一些报道实验表明，肝窦内皮细胞增殖是重要的肝组织损失后的肝再生。包括血管内皮生长因子（VEGF）及其受体在内的几种血管生成生长因子由增殖的肝细胞表达以在肝再生期间诱导血管生成。低氧诱导因子-1 α（hypoxia inducible factor-1α，HIF-1α）通过转录VEGF等多种血管生成因子来感受低氧。然而，HIF-1α在肝再生过程中的表达谱尚不清楚。在本研究中，HIF-1α在大鼠70%肝部分切除后再生肝中的表达进行了评估。Western blot检测细胞核HIF-1α、VEGF和fms样酪氨酸激酶-1（flt-1）的表达，激光多普勒检测肝血流量，免疫组化检测肝窦内皮细胞面积和HIF-1a定位。肝血流量在术后24 h达到峰值（与对照组相比P=0.002），术后36 h达到最低值（P=0.006）。内皮细胞面积在术后72 h最低（P<0.001）。HIF-1α和VEGF分别在术后24 h和120 h出现高峰。肝切除术后flt-1水平持续升高。HIF-1α mRNA在术后24、36、72 h均明显升高（P<0.05）。结论：在大鼠再生肝中，细胞核HIF-1α的表达高峰出现在VEGF表达之前。HIF-1α水平升高可能是肝切除后肝细胞指数生长引起短暂缺氧的结果。

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.