Matthews Brya G, Grcevic Danka, Wang Liping, Hagiwara Yusuke, Roguljic Hrvoje, Joshi Pujan, Shin Dong-Guk, Adams Douglas J, Kalajzic Ivo
Department of Reconstructive Sciences, University of Connecticut Health Center, Farmington, CT, USA.
J Bone Miner Res. 2014;29(5):1283-94. doi: 10.1002/jbmr.2140.
Fracture healing is a regenerative process that involves coordinated responses of many cell types, but characterization of the roles of specific cell populations in this process has been limited. We have identified alpha smooth muscle actin (αSMA) as a marker of a population of mesenchymal progenitor cells in the periosteum that contributes to osteochondral elements during fracture healing. Using a lineage tracing approach, we labeled αSMA-expressing cells, and characterized changes in the periosteal population during the early stages of fracture healing by histology, flow cytometry, and gene expression profiling. In response to fracture, the αSMA-labeled population expanded and began to differentiate toward the osteogenic and chondrogenic lineages. The frequency of mesenchymal progenitor cell markers such as Sca1 and PDGFRα increased after fracture. By 6 days after fracture, genes involved in matrix production and remodeling were elevated. In contrast, genes associated with muscle contraction and Notch signaling were downregulated after fracture. We confirmed that activating Notch signaling in αSMA-labeled cells inhibited differentiation into osteogenic and adipogenic lineages in vitro and ectopic bone formation in vivo. By characterizing changes in a selected αSMA-labeled progenitor cell population during fracture callus formation, we have shown that modulation of Notch signaling may determine osteogenic potential of αSMA-expressing progenitor cells during bone healing.
骨折愈合是一个涉及多种细胞类型协调反应的再生过程，但特定细胞群在此过程中的作用表征一直有限。我们已将α平滑肌肌动蛋白（αSMA）鉴定为骨膜中间充质祖细胞群的标志物，该细胞群在骨折愈合过程中对骨软骨成分有贡献。使用谱系追踪方法，我们标记了表达αSMA的细胞，并通过组织学、流式细胞术和基因表达谱分析来表征骨折愈合早期骨膜细胞群的变化。对骨折的反应是，αSMA标记的细胞群扩大并开始向成骨和成软骨谱系分化。骨折后，间充质祖细胞标志物如Sca1和PDGFRα的频率增加。骨折后6天，参与基质产生和重塑的基因表达上调。相反，与肌肉收缩和Notch信号传导相关的基因在骨折后下调。我们证实，激活αSMA标记细胞中的Notch信号传导可在体外抑制其向成骨和成脂谱系的分化，并在体内抑制异位骨形成。通过表征骨折痂形成过程中选定的αSMA标记祖细胞群的变化，我们表明Notch信号传导的调节可能决定骨愈合过程中表达αSMA的祖细胞的成骨潜力。
