Exosomal miR-9-5p secreted by bone marrow-derived mesenchymal stem cells alleviates osteoarthritis by inhibiting syndecan-1

Mesenchymal stem cells (MSCs) have been demonstrated to serve as targets for the treatment of osteoarthritis (OA) and exosomes derived from MSCs also display chondroprotective effects. This study aims to investigate the regulatory role of exosomal microRNA-9-5p (miR-9-5p) secreted by bone marrow-derived MSCs (BM-MSCs) on OA in a rat model induced by anterior cruciate ligament/medial collateral ligament transection. Luciferase reporter assay was conducted to verify the putative miR-9-5p binding sites to 3 ' UTR of syndecan-1 (SDC1). Additionally, an intra-articular injection of miR-9-5p carried by BM-MSC-derived exosomes or liposomes into rats with OA-like damage was performed to ascertain the role of exosomal miR-9-5p and a gain-of-function study of SDC1 was carried out to explore the potential mechanism in relation to SDC1. Subsequently, the expression of SDC1 was determined and the levels of inflammatory factors (IL-1, IL-6, TNF-alpha and CRP) and oxidative stress injury indicators (NO, MDA, iNOS, COX2 and SOD), the contents of AKP as well as the levels of OA-related factors (MMP-13, COMP and OCN) were measured. Injection of miR-9-5p-contained exosomes resulted in an alleviation of inflammation and OA-like damage, which was evidenced by downregulated levels of inflammatory factors, reduced oxidative stress injury and decreased OCN, MMP-13, COMP and AKP levels. As a target gene of miR-9-5p, the upregulation of SDC1 led to aggravation of inflammation and OA-like damage, which is opposite to exosomal miR-9-5p. To conclude, these findings suggest the anti-inflammatory and chondroprotective effects of BM-MSC-derived exosomal miR-9-5p on OA via regulation of SDC1.