Kanichai Manoj, Ferguson Damien, Prendergast Patrick J, Campbell Veronica A
Department of Physiology, Trinity College Institute of Neuroscience, Trinity College, Dublin, Ireland.
J Cell Physiol. 2008 Sep;216(3):708-15. doi: 10.1002/jcp.21446.
Mesenchymal stem cells (MSCs) are multipotent cells capable of developing along the chondrogenic, osteogenic and adipogenic lineages. As such, they have received interest as a potential cell source for tissue engineering strategies. Cartilage is an avascular tissue and thus resides in a microenvironment with reduced oxygen tension. The aim of this study was to examine the effect of a low oxygen environment on MSC differentiation along the chondrogenic route. In MSCs exposed to chondrogenic growth factors, transforming growth factor-beta and dexamethasone, in a hypoxic environment (2% oxygen), the induction of collagen II expression and proteoglygan deposition was significantly greater than that observed when cells were exposed to the chondrogenic growth factors under normoxic (20% oxygen) conditions. The transcription factor, hypoxia-inducible factor-1alpha (HIF-1alpha), is a crucial mediator of the cellular response to hypoxia. Following exposure of MSCs to hypoxia (2% oxygen), HIF-1alpha translocated from the cytosol to the nucleus and bound to its target DNA consensus sequence. Similarly, hypoxia evoked an increase in phosphorylation of both AKT and p38 mitogen activated protein kinase, upstream of HIF-1alpha activation. Furthermore, the PI3 kinase/AKT inhibitor, LY294002, and p38 inhibitor, SB 203580, prevented the hypoxia-mediated stabilisation of HIF-1alpha. To assess the role of HIF-1alpha in the hypoxia-induced increase in chondrogenesis, we employed an siRNA knockdown approach. In cells exposed to HIF-1alpha siRNA, the hypoxia-induced enhancement of chondrogenesis, as evidenced by upregulation of collagen II, sox-9 and proteoglycan deposition, was absent. This provides evidence for HIF-1alpha being a key mediator of the beneficial effect of a low oxygen environment on chondrogenesis.
间充质干细胞（MSCs）是多能细胞，能够沿着软骨生成、骨生成和脂肪生成谱系分化。因此，它们作为组织工程策略的潜在细胞来源受到了关注。软骨是一种无血管组织，因此处于氧张力降低的微环境中。本研究的目的是研究低氧环境对MSCs沿软骨生成途径分化的影响。在低氧环境（2%氧气）中，将MSCs暴露于软骨生成生长因子、转化生长因子-β和地塞米松时，与在常氧（20%氧气）条件下将细胞暴露于软骨生成生长因子相比，胶原蛋白II表达的诱导和蛋白聚糖沉积显著增加。转录因子缺氧诱导因子-1α（HIF-1α）是细胞对缺氧反应的关键介质。将MSCs暴露于缺氧（2%氧气）后，HIF-1α从细胞质转移到细胞核并与其靶DNA共有序列结合。同样，缺氧引起HIF-1α激活上游的AKT和p38丝裂原活化蛋白激酶磷酸化增加。此外，PI3激酶/AKT抑制剂LY294002和p38抑制剂SB 203580可阻止缺氧介导的HIF-1α稳定。为了评估HIF-1α在缺氧诱导的软骨生成增加中的作用，我们采用了siRNA敲低方法。在暴露于HIF-1α siRNA的细胞中，缺氧诱导的软骨生成增强（如胶原蛋白II、sox-9上调和蛋白聚糖沉积所证明）不存在。这为HIF-1α是低氧环境对软骨生成有益作用的关键介质提供了证据。
