Distraction osteogenesis (DO) is a clinically effective procedure to regenerate large bone defects. However, the treatment duration is undesirably lengthy, especially in elderly patients. Exosomes derived from mesenchymal stem cells (MSC-Exos) could exert the beneficial effects while avoiding the possible complications of stem cell transplantation. This study aimed to evaluate the effects of MSC-Exos on bone regeneration during DO in older rats. Exosomes were isolated from the supernatants of young bone marrow mesenchymal stem cells (BMSCs) through ultra-centrifugation, and characterized using transmission electron microscopy, western blot, and tunable resistive pulse sensing analysis. The effects of MSC-Exos on the proliferation and differentiation of older BMSCs were evaluated using CCK-8 assay, ALP and ARS staining, and qRT-PCR. Unilateral tibial DO model was established on older Sprague-Dawley rats and MSC-Exos or phosphate buffer saline was locally injected into the distraction gaps after distraction weekly. Bone regeneration were evaluated using X-ray, Micro-CT, mechanical test, and histological staining. The MSC-Exos were round or cup-shaped vesicles ranging from 60 to 130 nm in diameter and expressed markers including CD9, CD63, and TSG101. The in vitro results indicated that MSC-Exos could enhance the proliferation and osteogenic differentiation of older BMSCs. Bone regeneration was markedly accelerated in rats treated with MSC-Exos according to the results of X-ray, micro-CT, and histological analysis. The distracted tibias from the MSC-Exos group also demonstrated better mechanical properties. These results suggest that MSC-Exos promote DO-mediated bone regeneration in older rats through enhancing the proliferation and osteogenic capacity of BMSCs.

中文翻译：

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年轻的间充质干细胞分泌的外来体在老年大鼠的牵张成骨过程中促进新骨形成。

牵引成骨术（DO）是一种临床有效的程序，可以再生大的骨缺损。然而，治疗持续时间不希望地长，特别是在老年患者中。间充质干细胞（MSC-Exos）衍生的外泌体可以发挥有益的作用，同时避免了干细胞移植的可能并发症。这项研究旨在评估MSC-Exos对老年大鼠DO期间骨再生的影响。通过超速离心从年轻的骨髓间充质干细胞（BMSCs）的上清液中分离外泌体，并使用透射电子显微镜，蛋白质印迹和可调电阻脉冲传感分析进行表征。使用CCK-8分析，ALP和ARS染色以及qRT-PCR评估了MSC-Exos对较老BMSCs增殖和分化的影响。在较老的Sprague-Dawley大鼠上建立单侧胫骨DO模型，每周分心后将MSC-Exos或磷酸盐缓冲盐水局部注入分心间隙。使用X射线，Micro-CT，机械测试和组织学染色评估骨再生。MSC-Exos是直径在60到130 nm之间的圆形或杯状囊泡，表达的标记包括CD9，CD63和TSG101。体外实验结果表明，MSC-Exos可以增强老年BMSCs的增殖和成骨分化。根据X射线，显微CT和组织学分析的结果，用MSC-Exos处理的大鼠的骨再生明显加快。MSC-Exos组分散的胫骨也表现出更好的机械性能。