Exosomal transfer of bone marrow mesenchymal stem cell-derived miR-340 attenuates endometrial fibrosis

Bone marrow mesenchymal stem cells (BMSCs) have potential therapeutic benefits for the treatment of endometrial diseases and injury. BMSCs interact with uterus parenchymal cells by direct contact or indirect secretion of growth factors to promote functional recovery. In this study, we found that BMSC treatment in rats subjected to mechanical damage (MD) significantly increased microRNA-340 (miR-340) levels in the regenerated endometrium. Then we employed knockin and knockdown technologies to upregulate or downregulate the miR-340 level in BMSCs (miR-340⁺ BMSCs or miR-340^- BMSCs) and their corresponding exosomes, respectively, to test whether exosomes from BMSCs mediate miR-340 transfer. We found that the exosomes released from the primitive BMSCs or miR-340⁺ BMSCs but not miR-340^- BMSCs increased the miR-340 levels in primary cultured endometrial stromal cells (ESCs) compared with control. Further verification of this exosome-mediated intercellular communication was performed using exosomal inhibitor GW4869. Tagging exosomes with red fluorescent protein demonstrated that exosomes were released from BMSCs and transferred to adjacent ESCs. Compared with controls, rats receiving primitive BMSC treatment significantly improved functional recovery and downregulated collagen 1α1, α-SMA and transforming growth factor (TGF)-β1 at day 14 after MD. The outcomes were significantly enhanced by miR-340⁺ BMSC treatment, and were significantly weakened by miR-340^- BMSC treatment, compared with primitive BMSC treatment. In vitro studies reveal that miR-340 transferred from BMSCs suppresses the upregulated expression of fibrotic genes in ESCs induced by TGF-β1. These data suggest that the effective antifibrotic function of BMSCs is able to transfer miR-340 to ESCs by exosomes, and that enhancing the transfer of BMSC-derived miR-340 is an alternative modality in preventing intrauterine adhesion.