Previously, we showed that extracellular matrices (ECMs), produced ex vivo by various types of stromal cells, direct bone marrow mesenchymal stem cells (BM-MSCs) in a tissue-specific manner and recapitulate physiologic changes characteristic of the aging microenvironment. In particular, BM-MSCs obtained from elderly donors and cultured on ECM produced by young BM stromal cells showed improved quantity, quality and osteogenic differentiation. In the present study, we searched for matrix components that are required for a functional BM-MSC niche by comparing ECMs produced by BM stromal cells from “young” (≤25 y/o) versus “elderly” (≥60 y/o) donors. With increasing donor age, ECM fibrillar organization and mechanical integrity deteriorated, along with the ability to promote BM-MSC proliferation and responsiveness to growth factors. Proteomic analyses revealed that the matricellular protein, Cyr61/CCN1, was present in young, but undetectable in elderly, BM-ECM. To assess the role of Cyr61 in the BM-MSC niche, we used genetic methods to down-regulate the incorporation of Cyr61 during production of young ECM and up-regulate its incorporation in elderly ECM. The results showed that Cyr61-depleted young ECM lost the ability to promote BM-MSC proliferation and growth factor responsiveness. However, up-regulating the incorporation of Cyr61 during synthesis of elderly ECM restored its ability to support BM-MSC responsiveness to osteogenic factors such as BMP-2 and IGF-1. We next examined aging bone and compared bone mineral density and Cyr61 content of L4-L5 vertebral bodies in “young” (9–11 m/o) and “elderly” (21–33 m/o) mice. Our analyses showed that low bone mineral density was associated with decreased amounts of Cyr61 in osseous tissue of elderly versus young mice. Our results strongly demonstrate a novel role for ECM-bound Cyr61 in the BM-MSC niche, where it is responsible for retention of BM-MSC proliferation and growth factor responsiveness, while depletion of Cyr61 from the BM niche contributes to an aging-related dysregulation of BM-MSCs. Our results also suggest new potential therapeutic targets for treating age-related bone loss by restoring specific ECM components to the stem cell niche.

此前，我们表明，由各种类型的基质细胞离体产生的细胞外基质（ECM）以组织特异性方式引导骨髓间充质干细胞（BM-MSC），并重现衰老微环境的生理变化特征。特别是，从老年供体获得的 BM-MSCs 在年轻 BM 基质细胞产生的 ECM 上培养，显示出数量、质量和成骨分化的改善。在本研究中，我们通过比较“年轻”（≤25岁）与“老年”（≥60岁）的BM基质细胞产生的ECM，寻找功能性BM-MSC生态位所需的基质成分。捐助者。随着供体年龄的增加，ECM 纤维组织和机械完整性以及促进 BM-MSC 增殖的能力和对生长因子的反应性均恶化。蛋白质组学分析表明，基质细胞蛋白 Cyr61/CCN1 存在于年轻人中，但在老年人 BM-ECM 中检测不到。为了评估 Cyr61 在 BM-MSC 生态位中的作用，我们使用遗传方法下调年轻 ECM 产生过程中 Cyr61 的掺入，并上调其在老年 ECM 中的掺入。结果表明，Cyr61耗尽的年轻ECM失去了促进BM-MSC增殖和生长因子反应的能力。然而，在老年 ECM 合成过程中上调 Cyr61 的掺入恢复了其支持 BM-MSC 对成骨因子（如 BMP-2 和 IGF-1）反应的能力。接下来，我们检查了老化的骨骼，并比较了“年轻”（9-11 m/o）和“老年”（21-33 m/o）小鼠的骨矿物质密度和 L4-L5 椎体的 Cyr61 含量。 我们的分析表明，与年轻小鼠相比，低骨密度与老年小鼠骨组织中 Cyr61 含量的减少有关。我们的结果有力地证明了 ECM 结合的 Cyr61 在 BM-MSC 生态位中的新作用，它负责保留 BM-MSC 增殖和生长因子反应性，而 BM 生态位中 Cyr61 的耗尽会导致与衰老相关的失调BM-MSC。我们的研究结果还提出了通过将特定 ECM 成分恢复到干细胞生态位来治疗与年龄相关的骨质流失的新潜在治疗靶点。