Nasrallah Rabab, Knezevic Kathy, Thai Thuan, Thomas Shane R, Göttgens Berthold, Lacaud Georges, Kouskoff Valerie, Pimanda John E
Lowy Cancer Research Centre and the Prince of Wales Clinical School, UNSW Australia, Sydney, NSW 2052, Australia Cancer Research UK Manchester Institute, The University of Manchester, Manchester, M20 4BX, UK.
Lowy Cancer Research Centre and the Prince of Wales Clinical School, UNSW Australia, Sydney, NSW 2052, Australia.
Biol Open. 2015 May 15;4(7):819-29. doi: 10.1242/bio.011494.
During embryonic development, hematopoietic cells develop by a process of endothelial-to hematopoietic transition of a specialized population of endothelial cells. These hemogenic endothelium (HE) cells in turn develop from a primitive population of FLK1(+) mesodermal cells. Endoglin (ENG) is an accessory TGF-β receptor that is enriched on the surface of endothelial and hematopoietic stem cells and is also required for the normal development of hemogenic precursors. However, the functional role of ENG during the transition of FLK1(+) mesoderm to hematopoietic cells is ill defined. To address this we used a murine embryonic stem cell model that has been shown to mirror the temporal emergence of these cells in the embryo. We noted that FLK1(+) mesodermal cells expressing ENG generated fewer blast colony-forming cells but had increased hemogenic potential when compared with ENG non-expressing cells. TIE2(+)/CD117(+) HE cells expressing ENG also showed increased hemogenic potential compared with non-expressing cells. To evaluate whether high ENG expression accelerates hematopoiesis, we generated an inducible ENG expressing ES cell line and forced expression in FLK1(+) mesodermal or TIE2(+)/CD117(+) HE cells. High ENG expression at both stages accelerated the emergence of CD45(+) definitive hematopoietic cells. High ENG expression was associated with increased pSMAD2/eNOS expression and NO synthesis in hemogenic precursors. Inhibition of eNOS blunted the ENG induced increase in definitive hematopoiesis. Taken together, these data show that ENG potentiates the emergence of definitive hematopoietic cells by modulating TGF-β/pSMAD2 signalling and increasing eNOS/NO synthesis.
在胚胎发育过程中，造血细胞通过特定内皮细胞群向内皮-造血转变的过程发育而来。这些造血内皮（HE）细胞又由原始的FLK1(+)中胚层细胞群体发育而来。内皮糖蛋白（ENG）是一种辅助性转化生长因子-β（TGF-β）受体，在内皮细胞和造血干细胞表面富集，也是造血前体细胞正常发育所必需的。然而，ENG在FLK1(+)中胚层向造血细胞转变过程中的功能作用尚不清楚。为了解决这个问题，我们使用了一种小鼠胚胎干细胞模型，该模型已被证明能够反映这些细胞在胚胎中的时间出现情况。我们注意到，与不表达ENG的细胞相比，表达ENG的FLK1(+)中胚层细胞产生的原始集落形成细胞较少，但造血潜能增加。与不表达ENG的细胞相比，表达ENG的TIE2(+)/CD117(+) HE细胞也显示出造血潜能增加。为了评估高ENG表达是否能加速造血，我们构建了一种可诱导表达ENG的胚胎干细胞系，并在FLK1(+)中胚层细胞或TIE2(+)/CD117(+) HE细胞中强制表达。两个阶段的高ENG表达均加速了CD45(+)定型造血细胞的出现。高ENG表达与造血前体细胞中磷酸化SMAD2（pSMAD2）/内皮型一氧化氮合酶（eNOS）表达增加和一氧化氮（NO）合成增加有关。抑制eNOS可减弱ENG诱导的定型造血增加。综上所述，这些数据表明，ENG通过调节TGF-β/pSMAD2信号通路和增加eNOS/NO合成来增强定型造血细胞的出现。
