Bone marrow mesenchymal stem cell (BMSC)-derived exosomes have been found to enhance fracture healing. In addition, microRNAs contributing to the healing of various bone fractures have attracted widespread attention in recent years, but knowledge of the mechanisms by which they act is still very limited. In this study, we clarified the function of altered microRNA-19b (miR-19b) expression in BMSCs in fracture healing. We modulated miR-19b expression via mimics/inhibitors in BMSCs and via agomirs in mice to explore the effects of these changes on osteogenic factors, bone cell mineralization and the healing status of modeled fractures. Through gain- and loss-of function assays, the binding affinity between miR-19b and WWP1/Smurf2 was identified and characterized to explain the underlying mechanism involving the KLF5/β-catenin signaling pathway. miR-19b promoted the differentiation of human BMSCs into osteoblasts by targeting WWP1 and Smurf2. Overexpression of WWP1 or Smurf2 degraded the target protein KLF5 in BMSCs through ubiquitination to inhibit fracture healing. KLF5 knockdown delayed fracture healing by modulating the Wnt/β-catenin signaling pathway. Furthermore, miR-19b enhanced fracture healing via the KLF5/β-catenin signaling pathway by targeting WWP1 or Smurf2. Moreover, miR-19b was found to be enriched in BMSC-derived exosomes, and treatment with exosomes promoted fracture healing in vivo. Collectively, these results indicate that mesenchymal stem cell-derived exosomal miR-19b represses the expression of WWP1 or Smurf2 and elevates KLF5 expression through the Wnt/β-catenin signaling pathway, thereby facilitating fracture healing.

已发现骨髓间充质干细胞 (BMSC) 衍生的外泌体可促进骨折愈合。此外，近年来，有助于各种骨折愈合的 microRNA 引起了广泛关注，但对其作用机制的了解仍然非常有限。在这项研究中，我们阐明了改变的 microRNA-19b (miR-19b) 在 BMSCs 中表达在骨折愈合中的作用。我们通过 BMSCs 中的模拟物/抑制剂和小鼠中的 agomirs 调节 miR-19b 表达，以探索这些变化对成骨因子、骨细胞矿化和模型骨折愈合状态的影响。通过功能增益和损失测定，鉴定并表征了 miR-19b 和 WWP1/Smurf2 之间的结合亲和力，以解释涉及 KLF5/β-连环蛋白信号通路的潜在机制。miR-19b 通过靶向 WWP1 和 Smurf2 促进人 BMSCs 向成骨细胞的分化。WWP1 或 Smurf2 的过表达通过泛素化降解 BMSCs 中的靶蛋白 KLF5 以抑制骨折愈合。KLF5 敲低通过调节 Wnt/β-catenin 信号通路延迟骨折愈合。此外，miR-19b 通过 KLF5/β-catenin 信号通路靶向 WWP1 或 Smurf2 促进骨折愈合。此外，发现 miR-19b 富含 BMSC 衍生的外泌体，外泌体治疗促进了体内骨折愈合。总之，这些结果表明间充质干细胞来源的外泌体 miR-19b 通过 Wnt/β-catenin 信号通路抑制 WWP1 或 Smurf2 的表达并提高 KLF5 的表达，从而促进骨折愈合。