NSUN2-engineered human umbilical cord mesenchymal stem cell-derived exosomes ameliorate tendon injury by promoting DNM2 expression.

BACKGROUND: Tendon injuries are a common musculoskeletal problem, often leading to chronic pain and disability. Current treatment options, including surgical interventions and physical therapy, have limitations in terms of efficacy and potential complications. Human umbilical cord mesenchymal stem cells (HUCMSCs) are a promising source of mesenchymal stem cells (MSCs), and exosomes derived from HUCMSCs have been shown to mediate various biological processes. This study aims to investigate the role of HUCMSC-derived exosomes in tendon injuries and the underlying mechanism. METHODS: Exosomes were isolated from HUCMSCs using differential centrifugation. Cell viability was assessed using a cell counting kit-8 assay. Cell proliferation was measured by a 5-Ethynyl-2'-deoxyuridine assay. Transwell invasion assays were conducted to analyze cell invasion, and wound-healing assays were used to evaluate cell migration. Quantitative real-time PCR (qRT-PCR) was employed to analyze DNM2 mRNA expression. Western blotting was used to detect the protein expression of NOP2/Sun RNA methyltransferase 2 (NSUN2), C cluster of differentiation 63 (CD63), CD81, and dynamin 2 (DNM2). m5C methylated RNA immunoprecipitation and RNA immunoprecipitation (RIP) assays were performed to analyze the association of NSUN2 with DNM2. Additionally, an RIP assay was conducted to study the interaction among Y-box binding protein 1 (YBX1), NSUN2, and DNM2 in injured tenocytes. Rats were subjected to superficial tendon excision and partial transection of the deep Achilles tendon to induce tendon injury. Hematoxylin and eosin (HE) staining was used to analyze the pathological conditions of Achilles tendon tissues, and an immunohistochemistry (IHC) assay was performed to detect the positive expression rates of NSUN2 protein. RESULTS: HUCMSC-derived exosomes significantly promoted the proliferation, migration, and invasion of injured tenocytes. Overexpression of NSUN2 also enhanced the proliferative, migratory and invasive abilities of injured tenocytes. The exosomes derived from NSUN2-overexpressing HUCMSCs showed a more pronounced promoting effect on injured tenocyte proliferation, migration, and invasion compared to control exosomes. NSUN2 stabilized DNM2 mRNA expression through m5C methylation modification. YBX1 interacted with NSUN2 to stabilize DNM2 expression. In addition, knockdown of DNM2 attenuated the promoting effects of HUCMSC-derived exosomes with NSUN2 overexpression on the proliferation, migration, and invasion of injured tenocytes. Moreover, exosomes derived from NSUN2-overexpressing HUCMSCs improved tendon injury in a rat model, as indicated by enhanced pathological conditions within the tendon tissues. CONCLUSION: HUCMSC-derived exosomal NSUN2 played a crucial role in ameliorating tendon injury by promoting DNM2 expression. The findings suggest that exosomes from NSUN2-overexpressing HUCMSCs could serve as a novel therapeutic strategy for tendon repair and regeneration.