Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
Stem Cells. 2013 Jan;31(1):104-16. doi: 10.1002/stem.1215.
Multipotential stromal cells or mesenchymal stem cells (MSCs) have been proposed as aids in regenerating bone and adipose tissues, as these cells form osteoblasts and adipocytes. A major obstacle to this use of MSC is the initial loss of cells postimplantation. This cell death in part is due to ubiquitous nonspecific inflammatory cytokines such as FasL generated in the implant site. Our group previously found that soluble epidermal growth factor (sEGF) promotes MSC expansion. Furthermore, tethering EGF (tEGF) onto a two-dimensional surface altered MSC responses, by restricting epidermal growth factor receptor (EGFR) to the cell surface, causing sustained activation of EGFR, and promoting survival from FasL-induced death. sEGF by causing internalization of EGFR does not support MSC survival. However, for tEGF to be useful in bone regeneration, it needs to allow for MSC differentiation into osteoblasts while also protecting emerging osteoblasts from apoptosis. tEGF did not block induced differentiation of MSCs into osteoblasts, or adipocytes, a common default MSC-differentiation pathway. MSC-derived preosteoblasts showed increased Fas levels and became more susceptible to FasL-induced death, which tEGF prevented. Differentiating adipocytes underwent a reduction in Fas expression and became resistant to FasL-induced death, with tEGF having no further survival effect. tEGF protected undifferentiated MSC from combined insults of FasL, serum deprivation, and physiologic hypoxia. Additionally, tEGF was dominant in the face of sEGF to protect MSC from FasL-induced death. Our results suggest that MSCs and differentiating osteoblasts need protective signals to survive in the inflammatory wound milieu and that tEGF can serve this function.
多能基质细胞或间充质干细胞 (MSCs) 已被提议作为帮助再生骨和脂肪组织的辅助手段，因为这些细胞可以形成成骨细胞和脂肪细胞。这种 MSC 应用的一个主要障碍是植入后细胞的初始丢失。这种细胞死亡部分是由于植入部位产生的普遍存在的非特异性炎症细胞因子，如 FasL。我们的小组之前发现，可溶性表皮生长因子 (sEGF) 可促进 MSC 扩增。此外，EGF（tEGF）与二维表面结合改变了 MSC 的反应，通过将表皮生长因子受体 (EGFR) 限制在细胞表面，导致 EGFR 的持续激活，并促进 FasL 诱导的死亡的存活。sEGF 通过引起 EGFR 的内化，不支持 MSC 的存活。然而，为了使 tEGF 在骨再生中有用，它需要允许 MSC 分化为成骨细胞，同时保护新出现的成骨细胞免受细胞凋亡的影响。tEGF 并没有阻止 MSC 分化为成骨细胞或脂肪细胞，这是 MSC 分化的常见默认途径。MSC 来源的前成骨细胞显示 Fas 水平增加，并对 FasL 诱导的死亡变得更加敏感，而 tEGF 则可以预防这种死亡。分化的脂肪细胞 Fas 表达减少，并对 FasL 诱导的死亡产生抗性，而 tEGF 则没有进一步的生存作用。tEGF 可保护未分化的 MSC 免受 FasL、血清剥夺和生理性缺氧的联合损伤。此外，tEGF 在面对 sEGF 时具有优势，可以保护 MSC 免受 FasL 诱导的死亡。我们的结果表明，MSC 和分化的成骨细胞需要保护信号才能在炎症性创伤环境中存活，而 tEGF 可以发挥这种作用。
