Synovial Stem Cell Biology

关节软骨没有表现出内源性修复，部分原因是组织中缺乏干/祖细胞，而邻近的滑膜中有大量的间充质干细胞(MSCs)，在体外和体内都能分化为软骨。我们已经证明关节内的MSCs对微环境的变化非常敏感，滑液的变化可以调节细胞的软骨形成潜力。此外，我们还发现损伤/关节炎/炎症关节的MSCs在特定的培养条件下不能完全分化为软骨细胞，而来自正常关节的MSCs具有完全的功能。我们对这种效应进行了深入的研究，发现有证据表明CCL2/MCP-1是从滑膜巨噬细胞分泌出来的，现在有初步证据表明，这些巨噬细胞可能作为滑膜干细胞的巢。干细胞的生态位被假设为提供了一个能够指导干细胞活动的微环境。在干细胞活性随年龄增长而下降的情况下，这一利基被认为特别重要，在这种情况下，随着常驻干细胞群体证明在维护和修复方面越来越不足，组织动态平衡的丧失会加剧。然而，体外证据表明，这些干细胞从壁龛分离后仍然具有功能，这强烈表明干细胞壁龛可能在衰老和疾病过程中失效。*我的计划的目标是阐明人和小鼠膝关节滑膜内巨噬细胞和滑膜间充质干细胞之间存在的调节反馈机制，并了解这些途径如何在体外、体外和体内调节干细胞的命运。这将通过以下目标来实现：*目标1(体外)：确定由巨噬细胞产生的哪些信号分子调节滑膜间充质干细胞，并分析这种能力是否通过改变巨噬细胞的激活状态而增强。*目标2(体外)：使用基于脂质体的定向方法将巨噬细胞从滑膜中移除时，测定滑膜间充质干细胞功能的变化。*目标3(体内)：量化当在滑膜干细胞内改变巨噬细胞数量或激活状态时，滑膜间充质干细胞介导的组织修复的变化。**这项研究计划将在细胞生物学和生物工程领域取得重大进展，这将有助于i)了解巨噬细胞在滑膜干细胞生态位中的作用，包括这些细胞如何调节干细胞潜力；以及ii)潜在开发新的和改进的组织工程/再生医学方法的框架，以恢复和/或维持衰老或损伤后的正常关节功能。

Articular cartilage does not exhibit endogenous repair, in part because of a lack of stem/progenitor cells in the tissue, whereas the adjacent synovial membrane is abundant with mesenchymal stem cells (MSCs) capable of differentiating into cartilage both in vitro and in vivo. We have demonstrated that the MSCs within the joint are very sensitive to changes in the micro-environment and that changes in the synovial fluid can regulate the chondrogenic potential of the cells. In addition, we have also found that MSCs from injured/arthritic/inflamed joints are incapable of fully differentiating into chondrocytes under specific culturing conditions whereas MSCs from normal joints are fully functional. We have explored this effect in great depth and found evidence that suggests CCL2/MCP-1 is being secreted from synovial macrophages and now have preliminary evidence that these macrophage cells may be acting as a synovial stem cell niche. The stem cell niche is hypothesized to provide a micro-environment that is capable of directing stem cell activity. The niche is thought to be particularly important in regards to the decline of stem cell activity with aging, in which a loss of tissue homeostasis progresses as the resident stem cell populations prove to be increasingly inadequate in terms of maintenance and repair. However, in vitro evidence demonstrates that these stem cells when separated from the niche are still functional, strongly suggesting that the stem cell niche maybe failing during aging and disease processes.*The objective of my program is to elucidate the regulatory feedback mechanisms that exist between macrophages and synovial MSCs within human and mouse knee joint synovium and understand how these pathways regulate stem cell fate in vitro, ex vivo and in vivo. This will be achieved by undertaking the following aims:*Aim 1 (In vitro): Determine which signaling molecules produced by macrophages regulate synovial MSCs, and assay if this ability is augmented through modification of the macrophage activation state. *Aim 2 (Ex vivo): Assay for changes in synovial MSC function when macrophages are removed from the synovium using a targeted liposomal based approach.*Aim 3 (In vivo): Quantify changes in synovial MSC mediated tissue repair when macrophage number or activation state is experimentally modified within the synovial stem cell niche. **This program of research will result in significant advances in the field of cell biology and bioengineering by contributing to i) the understanding of the role of macrophages in the synovial stem cell niche including how these cell regulate stem cell potential; and ii) a framework for the potential development of new and improved tissue engineering / regenerative medicine approaches to restoring and/or maintaining normal joint function with aging or after injury.