VEGF和Angiopoietin家族在早期人胚肝发育过程中的作用

Roles of vascular endothelial growth factor and Angiopoietin family in early stage of human liver development

目的:观察血管内皮细胞生长因子A(VEGFA)、血管内皮细胞生长因子C(VEGFC)、Angiopo- ietin-1(Ang-1)、Angiopoietin-2(Ang-2)及其受体在发育第3-5 wk人胚胎肝的表达,以了解早期人胚发育过程中血管内皮细胞、造血干细胞与肝干细胞之间的相互关系．方法:实验用发育3,4,5 wk人胚胎标本各8例(共24例),石蜡切片,连续切片,进行 CD34、VEGFA、VEGFC、fms样酪氨酸激酶-1(FLT-1)、胚胎肝激酶1(Flk-1)、FLT-4、 Ang-1、Ang-2、Tie-2免疫组化染色,光镜下观察．结果:3 wk时靠近肝芽的间充质中的血管内皮细胞多,而肝芽内未见血管内皮细胞及造血细胞;4 wk时,肝索形成处可见较多正在形成的新生血管增多,肝索间开始出现少量的造血细胞;5 wk时肝索间出现原始的肝血窦结构,血窦内造血细胞的数量较4 wk明显增多. 发育的3-5 wk,部分肝干细胞及血细胞中出现 VEGFA阳性反应,多数肝细胞及内皮细胞中均有VEGFC免疫反应,而造血细胞中无．多数肝干细胞和少数血管内皮细胞呈flt-1和flk-1 阳性,造血细胞呈flt-1、flk-1免疫反应阴性, 而呈flt-4阳性．肝干细胞强表达Ang-2,而造血细胞表达其受体Tie-2,与此同时,内皮细胞表达Ang-1和Ang-2,而不表达其受体Tie-2．结论:来自肝干细胞的VEGFA信号可使内皮细胞分化、增殖并形成血管;来自内皮细胞的VEGFC、Angiopoietin信号对肝干细胞的生长和分化起作用;造血细胞分泌的VEGFA 可以通过旁分泌途径调节肝干细胞的发育;造血细胞的发育依赖于肝干细胞产生的 VEGFC和Ang-2．

AIM： To explore the association among hepatic stem cells, endothelial cells, and hematopoietic stem cells during liver development by observing the expression of vascular endothelial growth factor A （VEGFA）, VEGFC, Angiopoietin （Ang）-1, Ang-2 and their receptors in the human embryonic liver of 3-5 wk. METHODS： Paraffin sections were prepared from 24 embryos of 3, 4, and 5 wk. Immunohistochemistry staining was performed to observe the development of hepatic stem cells, endothelial cells and hematopoietic stem cell as well as the expression of CD34, VEGFA, VEGFC, Ang-1, Ang-2, and their receptors, and fit-1, ilk-1, fit-4, and Tie-2 under light microscope. RESULTS： Endothelial cells predominated in mesenchyme adjacent to the liver bud at 3 wk, but not in the bud. At 4 wk, the cells in the liver bud migrated into the domain of transversum mesenchyme, where endothelial cells began to form vascular structures, and branched to form a number of hepatic cords. A few hematopoietic cells were seen scattered between the liver cords at 5 wk, and primitive sinusoids, which came from vitelline veins, appeared between the hepatic cords. The numbers of hematopoetic cells were increased in comparison with those at 4 wk. VEGFA was expressed by some hepatic stem cells and hematopoetic cells during 3-5 wk. At the same time, most of hepatic stem cells and endothelial cells were positive for VEGFC, while hematopoetic cells were VEGFC-negative. flt-1 and flk-1 positive reaction was found in most of hepatic stem cells and a few endothelial cells. The hematopoetic cells were negative for fit-1 and flk-1, but positive for flt-4. Hepatic stem cells expressed Ang-2, while hematopoetic cells expressed its receptor Tie-2. Meanwhile, endothelial cells expressed Ang-1 and Ang-2, but didn＇t express Tie-2. CONCLUSION： Hepatic stem cells may induce the growth and differentiation of vascular endothelial cells through VEGFA signals. The development of hepatic stem cells is affected by VEGFC, angiopoietin secreted by endothelial cells and VEGFA produced by hematopoetic cells. Meanwhile, the development of hematopoietic cells depended on the VEGFC and Ang-2 produced by hepatic stem cells.