Research Services, Ralph H. Johnson Department of Veterans Affairs Medical Center, Charleston, SC, USA; Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, SC, USA.
Department of Orthopedics, Medical University of South Carolina, Charleston, SC, USA.
Cytotherapy. 2018 Nov;20(11):1371-1380. doi: 10.1016/j.jcyt.2018.07.004. Epub 2018 Oct 16.
Previous studies identified a circulating human osteoblastic population that expressed osteocalcin (OCN), increased following fracture and pubertal growth, and formed mineralized colonies in vitro and bone in vivo. A subpopulation expressed CD34, a hematopoietic/endothelial marker. These findings led to our hypothesis that hematopoietic-derived CD34OCN cells exist in the circulation of mice and are modulated after fracture.
Flow cytometry was used to identify CD34OCN cells in male B6.SJL-PtprcPepc/BoyJ and Vav-Cre/mTmG (VavR) mice. Non-stabilized tibial fractures were created by three-point bend. Fractures were longitudinally imaged by micro-computed tomography, and immunofluorescent staining was used to evaluate CD34OCN cells within fracture callus. AMD3100 (10 mg/kg) was injected subcutaneously for 3 days and the CD34OCN population was evaluated by flow cytometry.
Circulating CD34OCN cells were identified in mice and confirmed to be of hematopoietic origin (CD45; Vav1) using two mouse models. Both circulating and bone marrow-derived CD34OCN cells peaked three weeks post-non-stabilized tibial fracture, suggesting association with cartilage callus transition to bone and early mineralization. Co-expression of CD34 and OCN in the fracture callus at two weeks post-fracture was observed. By three weeks, there was 2.1-fold increase in number of CD34OCN cells, and these were observed throughout the fracture callus. AMD3100 altered CD34OCN cell levels in peripheral blood and bone marrow.
Together, these data demonstrate a murine CD34OCN circulating population that may be directly involved in fracture repair. Future studies will molecularly characterize CD34OCN cells, determine mechanisms regulating their contribution, and examine if their number correlates with improved fracture healing outcomes.
先前的研究鉴定出一种循环的人类成骨细胞群体，该群体表达骨钙素（OCN），在骨折和青春期生长后增加，并在体外形成矿化集落和体内骨。亚群表达 CD34，一种造血/内皮标志物。这些发现导致我们假设存在于雄性 B6.SJL-PtprcPepc/BoyJ 和 Vav-Cre/mTmG（VavR）小鼠循环中的造血衍生的 CD34OCN 细胞，并在骨折后受到调节。
使用流式细胞术鉴定 B6.SJL-PtprcPepc/BoyJ 和 Vav-Cre/mTmG（VavR）雄性小鼠中的 CD34OCN 细胞。通过三点弯曲法创建非稳定胫骨骨折。通过微计算机断层扫描对骨折进行纵向成像，并使用免疫荧光染色评估骨折痂中的 CD34OCN 细胞。皮下注射 AMD3100（10mg/kg）3 天，并通过流式细胞术评估 CD34OCN 群体。
在两种小鼠模型中，鉴定出小鼠循环中的 CD34OCN 细胞，并证实其为造血起源（CD45；Vav1）。未稳定胫骨骨折后 3 周，循环和骨髓来源的 CD34OCN 细胞均达到峰值，提示与软骨痂向骨的过渡和早期矿化有关。在骨折后 2 周的骨折痂中观察到 CD34 和 OCN 的共表达。3 周时，CD34OCN 细胞数量增加了 2.1 倍，并且这些细胞在整个骨折痂中均有观察到。AMD3100 改变了外周血和骨髓中 CD34OCN 细胞的水平。
总之，这些数据表明存在一种可能直接参与骨折修复的鼠 CD34OCN 循环群体。未来的研究将对 CD34OCN 细胞进行分子表征，确定调节其贡献的机制，并检查其数量是否与改善骨折愈合结果相关。
