Exosomes Derived from Bone Mesenchymal Stem Cells with the Stimulation of Fe(3)O(4) Nanoparticles and Static Magnetic Field Enhance Wound Healing Through Upregulated miR-21-5p

BACKGROUND: Both magnetic nanoparticles (MNPs) and exosomes derived from bone mesenchymal stem cells (BMSC-Exos) have been reported to improve wound healing. In this study, novel exosomes (mag-BMSC-Exos) would be fabricated from BMSCs with the stimulation of MNPs and a static magnetic field (SMF) to further enhance wound repair. METHODS: Mag-BMSC-Exos, namely, exosomes derived from BMSCs preconditioned with Fe(3)O(4) nanoparticles and a SMF, together with BMSC-Exos were both first isolated by ultracentrifugation, respectively. Afterwards, we conducted in vitro experiments, including scratch wound assays, transwell assays, and tube formation assays, and established an in vivo wound healing model. The miRNA expression profiles were compared between BMSC-Exos and mag-BMSC-Exos to detect the potential mechanism of improving wound healing. At last, the function of exosomal miR-21-5p during wound healing was confirmed by utilizing a series of gain- and loss-of-function experiments in vitro. RESULTS: The optimal working magnetic condition was 50 µg/mL Fe(3)O(4) nanoparticles combined with 100 mT SMF. In vitro, mag-BMSC-Exo administration promoted proliferation, migration and angiogenesis to a greater extent than BMSC-Exo administration. Local transplantation of mag-BMSC-Exos into rat skin wounds resulted in accelerated wound closure, narrower scar widths and enhanced angiogenesis compared with BMSC-Exo transplantation. Notably, miR-21-5p was found to be highly enriched in mag-BMSC-Exos and served as a critical mediator in mag-BMSC-Exo-induced regulatory effects through inhibition of SPRY2 and activation of the PI3K/AKT and ERK1/2 signaling pathways. CONCLUSION: Mag-BMSC-Exos can further enhance wound healing than BMSC-Exos by improving angiogenesis and fibroblast function, and miR-21-5p upregulation in mag-BMSC-Exos might be the potential mechanism. This work offers an effective and promising protocol to improve wound healing in clinic.