Objective:To investigate the effect of transforming growth factor (TGF- β) signal in muscle fiber itself during inflammation/immunity response on intramuscular inflammation. Methods:Sixteen wild C57BL/6 mice (wild group) and sixteen mice with skeletal muscle-specific deficiency of T βRⅡ (knock-out group) between 4-8 weeks of age were selected for this study. Acute muscle injury in mice was induced by injection of myotoxin cardiotoxin (CTX) into gastrocnemius. The differences in intramuscular inflammation were compared between the wild and knock-out groups on 0, 4, 7 and 10 d after CTX injection by observing exudation of mononuclear phagocytes, macrophages, M1 type macrophages, CD4 +T cells and helpers T cells (Th1, 2&17). Two newborn C57BL/6 wild mice and 2 SM TGF- βr2-/- knock-out mice were selected to culture primary myoblasts in vitro which were divided into 2 groups: an interferon group subjected to interferon simulation and a control group subjected to addition of an equal amount of solvent. The differences in expression of IL-6, IL-10, MCP-1, MIP-1α, H-2K b, H2-Ea, Toll-like receptor (TLR)3 and TLR7 were compared between the interferon and control groups, as well as between the wild and knock-out groups. Results:On 4&7 d after CTX injection, the ratios of mononuclear/macrophage (75.73%±3.62%, 45.27%± 2.32%), macrophages (38.67%±2.76%, 24.87%±2.19%), M1 macrophages (43.21%±0.11%, 30.43%±2.19%), CD4 +T cells (20.13%±1.62%, 5.67%±0.32%) in the muscle tissue from the knock-out mice were significantly higher than those from the wild mice (58.52%±2.43%, 29.21%±2.45%; 20.63%±2.32%, 16.23%±1.25%; 24.98%±0.35%, 14.23%±1.69%; 10.70%±0.43%, 2.50%±0.45%), with a majority of Th1&Th17 ( P<0.05). In vitro results showed that the levels of IL-6, MCP-1, MIP-1α, H-2K b, H2-Ea and TLR3 were significantly upregulated in the interferon group compared with the control group and that such upregulation in the nock-out mice was more significant than in the wild mice ( P<0.05). Conclusions:Endogenous TGF- β signal activation plays a role in the functional recovery after muscle trauma, because it is involved in the regulation of immune behavior of muscle fibers, thus affecting intramuscular inflammation and muscle regeneration.

Objective To investigate the effect of E2 signaling in myofibers on muscular macrophage efferocytosis in mice with cardiotoxin-induced acute skeletal muscle injury.Methods Female wild-type C57BL/6 mice with and without ovariectomy and male C57BL/6 mice were given a CTX injection into the anterior tibial muscle to induce acute muscle injury,followed by intramuscular injection of β-estradiol(E2)or 4-hydroxytamoxifen(4-OHT).The changes in serum E2 of the mice were detected using ELISA,and the number,phenotypes,and efferocytosis of the macrophages in the inflammatory exudates and myofiber regeneration and repair were evaluated using immunofluorescence staining and flow cytometry.C2C12 cells were induced to differentiate into mature myotubes,which were treated with IFN-γ for 24 before treatment with β-Estradiol or 4-OHT.The treated myotubes were co-cultured with mouse peritoneal macrophages in a 1:2 ratio,followed by addition of PKH67-labeled apoptotic mouse mononuclear spleen cells induced by UV irradiation,and macrophage efferocytosis was observed using immunofluorescence staining and flow cytometry.Results Compared with the control mice,the female mice with ovariectomy showed significantly increased mononuclear macrophages in the inflammatory exudates,with increased M1 cell percentage,reduced M2 cell percentage and macrophage efferocytosis in the injured muscle,and obviously delayed myofiber regeneration and repair.In the cell co-culture systems,treatment of the myotubes with β-estradiol significantly increased the number and proportion of M2 macrophages and macrophage efferocytosis,while 4-OHT treatment resulted in the opposite changes.Conclusion In injured mouse skeletal muscles,myofiber E2 signaling promotes M1 to M2 transition to increase macrophage efferocytosis,thereby relieving inflammation and promoting muscle regeneration and repair.

Objective To investigate the effect of E2 signaling in myofibers on muscular macrophage efferocytosis in mice with cardiotoxin-induced acute skeletal muscle injury.Methods Female wild-type C57BL/6 mice with and without ovariectomy and male C57BL/6 mice were given a CTX injection into the anterior tibial muscle to induce acute muscle injury,followed by intramuscular injection of β-estradiol(E2)or 4-hydroxytamoxifen(4-OHT).The changes in serum E2 of the mice were detected using ELISA,and the number,phenotypes,and efferocytosis of the macrophages in the inflammatory exudates and myofiber regeneration and repair were evaluated using immunofluorescence staining and flow cytometry.C2C12 cells were induced to differentiate into mature myotubes,which were treated with IFN-γ for 24 before treatment with β-Estradiol or 4-OHT.The treated myotubes were co-cultured with mouse peritoneal macrophages in a 1:2 ratio,followed by addition of PKH67-labeled apoptotic mouse mononuclear spleen cells induced by UV irradiation,and macrophage efferocytosis was observed using immunofluorescence staining and flow cytometry.Results Compared with the control mice,the female mice with ovariectomy showed significantly increased mononuclear macrophages in the inflammatory exudates,with increased M1 cell percentage,reduced M2 cell percentage and macrophage efferocytosis in the injured muscle,and obviously delayed myofiber regeneration and repair.In the cell co-culture systems,treatment of the myotubes with β-estradiol significantly increased the number and proportion of M2 macrophages and macrophage efferocytosis,while 4-OHT treatment resulted in the opposite changes.Conclusion In injured mouse skeletal muscles,myofiber E2 signaling promotes M1 to M2 transition to increase macrophage efferocytosis,thereby relieving inflammation and promoting muscle regeneration and repair.