Department of Internal Medicine, Innovative Research Institute for Cell Therapy, Seoul National University Hospital, Korea.
EMBO Mol Med. 2012 Sep;4(9):924-38. doi: 10.1002/emmm.201101107. Epub 2012 Jul 23.
Hypoxic microenvironment plays an important role in determining stem cell fates. However, it is controversial to which direction between self-renewal and differentiation the hypoxia drives the stem cells. Here, we investigated whether a short exposure to hypoxia (termed 'hypoxic-priming') efficiently directed and promoted mouse embryonic stem cells (mESCs) to differentiate into vascular-lineage. During spontaneous differentiation of embryoid bodies (EBs), hypoxic region was observed inside EB spheroids even under normoxic conditions. Indeed, hypoxia-primed EBs more efficiently differentiated into cells of vascular-lineage, than normoxic EBs did. We found that hypoxia suppressed Oct4 expression via direct binding of HIF-1 to reverse hypoxia-responsive elements (rHREs) in the Oct4 promoter. Furthermore, vascular endothelial growth factor (VEGF) was highly upregulated in hypoxia-primed EBs, which differentiated towards endothelial cells in the absence of exogenous VEGF. Interestingly, this differentiation was abolished by the HIF-1 or VEGF blocking. In vivo transplantation of hypoxia-primed EBs into mice ischemic limb elicited enhanced vessel differentiation. Collectively, our findings identify that hypoxia enhanced ESC differentiation by HIF-1-mediated inverse regulation of Oct4 and VEGF, which is a novel pathway to promote vascular-lineage differentiation.
低氧微环境在决定干细胞命运方面起着重要作用。然而，低氧将干细胞向自我更新还是分化方向驱动，这一问题仍存在争议。在这里，我们研究了短暂暴露于低氧（称为“低氧预适应”）是否能有效地将小鼠胚胎干细胞（mESCs）定向并促进其分化为血管谱系。在胚状体（EBs）的自发分化过程中，即使在常氧条件下，EB 球体内部也观察到低氧区域。事实上，与常氧 EBs 相比，低氧预适应的 EBs 更有效地分化为血管谱系细胞。我们发现，低氧通过 HIF-1 与 Oct4 启动子中的反向缺氧反应元件（rHRE）的直接结合来抑制 Oct4 表达。此外，低氧预适应的 EBs 中血管内皮生长因子（VEGF）高度上调，而在没有外源性 VEGF 的情况下，这些细胞分化为内皮细胞。有趣的是，这种分化被 HIF-1 或 VEGF 阻断所抑制。将低氧预适应的 EBs 体内移植到小鼠缺血肢体中，可诱发增强的血管分化。总之，我们的研究结果表明，低氧通过 HIF-1 介导的 Oct4 和 VEGF 的反向调节增强 ESC 分化，这是促进血管谱系分化的新途径。
