Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Ontario, Canada.
Mol Cell Neurosci. 2011 Jun;47(2):145-53. doi: 10.1016/j.mcn.2011.03.010. Epub 2011 Apr 2.
Oxygen (O₂) tension has emerged as a major regulator of stem cell (SC) biology. Low O₂ concentrations that are toxic to mature cells can confer advantage to stem and early progenitors, while superoxide stress remains a constant threat in aerobic biology and may be partially avoided through sequestration of SCs in the relatively hypoxic stem or regenerative niche. Using primary retina-derived retinal progenitor cells (RPCs) and the R28 progenitor cell line in vitro, we show that RPCs are sensitive to hydrogen peroxide (H₂O₂) induced damage and resistant to moderate levels of low oxygen stress (1% O₂). Under hypoxic conditions, multipotent RPCs upregulate Epo receptors, and Epo, along with insulin, protects against both superoxide- and severe hypoxia- (0.25% O₂) induced apoptosis through activation of the canonical PI3K/Akt/mTOR pathway. This survival advantage is sensitive to inhibitors of PI3K and mTOR. We further demonstrate phosphorylation of the p70S6 ribosomal kinase, a downstream mediator of PI3K/Akt/mTOR and translational activator. Overall, these data confirm that RPCs are sensitive to superoxide stress and resistant to hypoxia and that this resistance is mediated in part by Epo. They further suggest that manipulation of RPCs ex vivo prior to ocular delivery, or the in vivo delivery of exogenous survival factors at the time of cell implantation, could enhance the success of regenerative therapies aimed to restore sight.
氧（O₂）张力已成为干细胞（SC）生物学的主要调节剂。对成熟细胞有毒的低氧浓度可以为干细胞和早期祖细胞带来优势，而超氧化物应激仍然是有氧生物学的一个持续威胁，并且可以通过将 SC 隔离在相对低氧的干细胞或再生龛位来部分避免。我们使用原代视网膜衍生的视网膜祖细胞（RPCs）和体外 R28 祖细胞系，表明 RPCs 对过氧化氢（H₂O₂）诱导的损伤敏感，对中度低氧应激（1%O₂）有抗性。在低氧条件下，多能性 RPC 上调 Epo 受体，Epo 与胰岛素一起通过激活经典的 PI3K/Akt/mTOR 通路，保护细胞免受超氧化物和严重低氧（0.25%O₂）诱导的细胞凋亡。这种生存优势对 PI3K 和 mTOR 的抑制剂敏感。我们进一步证明了 p70S6 核糖体激酶的磷酸化，PI3K/Akt/mTOR 的下游介质和翻译激活剂。总的来说，这些数据证实 RPCs 对超氧化物应激敏感，对低氧有抗性，这种抗性部分是由 Epo 介导的。它们进一步表明，在眼部给药前对 RPC 进行体外操作，或在细胞植入时体内给予外源性生存因子，可以提高旨在恢复视力的再生疗法的成功率。
