MiR-877, an exosomal miRNA from mechanical stretch induced adipose derived stromal cells, enhances fracture healing in nonunion rats with type 2 diabetes mellitus.

BACKGROUND

Bone nonunion or delayed union is a serious complication in diabetic patients with fractures, urgently requiring novel therapeutic strategies. Exosomes derived from stromal cells are naturally occurring nanoparticles carrying bioactive molecules that mediate intercellular communication and play crucial roles in diabetic fracture repair. Importantly, mechanical stimuli can modulate the cargo composition of exosomes, influencing bone healing outcomes. Here, we investigate for the first time whether exosomes derived from mechanically stretched adipose-derived stromal cells (MS-ADSC-Exos) enhance fracture healing in a type 2 diabetes mellitus (T2DM) nonunion model, and elucidate their underlying mechanisms.

METHODS

Exosomes secreted by ADSCs subjected to different magnitudes of cyclic mechanical stretch (0%, 6%, 18%; designated NMS, LMS, and HMS-ADSC-Exos) were applied to rat bone marrow mesenchymal stromal cells (BMSCs) and human umbilical vein endothelial cells (HUVECs) in vitro. Osteogenic differentiation, proliferation, migration, and angiogenesis were evaluated by Alizarin Red S and ALP staining, tube formation, scratch, and migration assays, respectively. Western blotting and immunofluorescence assessed osteogenic marker expression. In vivo, MS-ADSC-Exos or PBS were locally injected into the fracture sites of diabetic rat femoral nonunion models for 3 consecutive days post-operation. Bone regeneration was evaluated by micro-CT and histological analyses at 4 weeks. miRNA profiles of MS-ADSC-Exos were characterized by RNA sequencing, bioinformatics, and qRT-PCR. Functional roles of miR-877 were further validated via mimic and inhibitor transfection assays.

RESULTS

In this study, it is shown that exosomes secreted from ADSCs induced via lower mechanical stretch can enhance fracture healing through the promotion of osteogenesis and angiogenesis in a rat model of nonunion with T2DM. Our results suggested miR-877 was significantly upregulated in LMS-ADSC-Exos, and can be transferred into BMSCs and HUVECs, which promotes osteogenesis and angiogenesis in diabetic conditions.

CONCLUSIONS

This study reveals a novel mechanobiological mechanism whereby mechanical stretch modulates exosomal miRNA content to potentiate fracture repair. Transplantation of LMS-ADSC-Exos accelerates bone regeneration via miR-877-mediated osteogenic and angiogenic pathways. These findings highlight the therapeutic potential of mechanically stimulated ADSC-derived exosomes as natural bioactive nanotherapeutics for diabetic fracture nonunion.