Sericin Scaffolds Carrying MiR29-EVs-treated Primary Myoblasts For Skeletal Muscle Injury Repair

Objective: To evaluate the repair effect of sericin scaffolds carrying mi R29-EVstreated primary myoblasts in the treatment of severe skeletal muscle injury.Methods: We extracted and identified primary myoblasts.Sericin scaffolds were prepared and their effects on myoblasts and fibroblasts were studied.Mi R29-EVs were extracted and identified,and the effect of mi R29-EVs on primary myoblasts was verified.CTX injection resulted in severe tibial anterior muscle injury in C57/BL6 mice,and the effect of sericin scaffolds carrying mi R29-EVs-treated primary myoblasts in the treatment of severe skeletal muscle injury model in the early stage of injury(2 weeks and 4 weeks)was evaluated histologically and functionally.Results: The purity of the extracted primary myoblasts is 85%.Primary myoblasts can fuse with each other to form myotubes in vitro,meeting the needs of muscle repair.The porosity and average pore size of sericin scaffolds is 93% and 173?m,respectively.Sericin scaffolds can support the adhesion and growth of primary myoblasts.Sericin scaffolds were basically degraded in vivo after 6 weeks,and the degradation solution downregulated the levels of fibrosis-related proteins Col1a1 and Vimentin in vitro.As nucleic acid carrier,EVs have excellent biocompatibility,high delivery efficiency and protect mi R29 from degradation.Mi R29-EVs promote myoblasts differentiation into myotubes with or without TGF-?1 stimulation.Mi R29-EVs can upregulate the m RNA levels of Myo D1,My HC,Myogenin,?-actin,Troponin,which are related to the differentiation of myoblasts,and downregulate the m RNA levels of their fibrosisrelated genes Col1A1,Col1A2,Col3A1,?-SMA,Vimentin and target genes Yy1 and Lims1,thereby promoting myoblasts differentiation into myotubes and inhibiting myofibroblast transformation.After severe skeletal muscle injury,sericin scaffolds carrying mi R29-EVs-treated primary myoblasts can effectively restore the normal structure of muscle fibers,reduce fibrosis after skeletal muscle injury and enhance the muscle contraction function in a short period of time.Conclusion: The in vivo application of sericin scaffolds carrying mi R29-EVs-treated primary myoblasts is an effective treatment for severe skeletal muscle injury.