Exosomes derived from inflammatory myoblasts promote M1 polarization and break the balance of myoblast proliferation/differentiation

BACKGROUND Acute muscle injuries are one of the most common injuries in sports.Severely injured muscles are prone to re-injury due to fibrotic scar formation caused by prolonged inflammation.How to regulate inflammation and suppress fibrosis is the focus of promoting muscle healing.Recent studies have found that myoblasts and macrophages play important roles in the inflammatory phase following muscle injury;however,the crosstalk between these two types of cells in the inflammatory environment,particularly the exosome-related mechanisms,had not been well studied.AIM To evaluate the effects of exosomes from inflammatory C2C12 myoblasts(IFC2C12-Exos)on macrophage polarization and myoblast proliferation/differentiation.METHODS A model of inflammation was established in vitro by lipopolysaccharide stimulation of myoblasts.C2C12-Exos were isolated and purified from the supernatant of myoblasts by gradient centrifugation.Multiple methods were used to identify the exosomes.Gradient concentrations of IF-C2C12-Exos were added to normal macrophages and myoblasts.PKH67 fluorescence tracing was used to identify the interaction between exosomes and cells.Microscopic morphology,Giemsa stain,and immunofluorescence were carried out for histological analysis.Additionally,ELISA assays,flow cytometry,and western blot were conducted to analyze molecular changes.Moreover,myogenic proliferation was assessed by the BrdU test,scratch assay,and CCK-8 assay.RESULTS We found that the PKH-67-marked C2C12-Exos can be endocytosed by both macrophages and myoblasts.IF-C2C12-Exos induced M1 macrophage polarization and suppressed the M2 phenotype in vitro.In addition,these exosomes also stimulated the inflammatory reactions of macrophages.Further-more,we demonstrated that IF-C2C12-Exos disrupted the balance of myoblast proliferation/differentiation,leading to enhanced proliferation and suppressed fibrogenic/myogenic differentiation.CONCLUSION IF-C2C12-Exos can induce M1 polarization,resulting in a sustained and aggravated inflammatory environment that impairs myoblast differentiation,and leads to enhanced myogenic proliferation.These results demonstrate why prolonged inflammation occurs after acute muscle injury and provide a new target for the regulation of muscle regeneration.

Fungal pyrrolidine-containing metabolites inhibit alkaline phosphatase activity in bone morphogenetic protein-stimulated myoblastoma cells

Fibrodysplasia ossificans progressiva(FOP)is a rare autosomal dominant congenital disorder characterized by progressive heterotopic ossification in muscle tissues.A constitutively activated mutation of a bone morphogenetic protein(BMP)receptor,ALK2,has been identified in patients with FOP.We report here that four structurally related compounds,lucilactaene,hydroxylucilactaene,NG-391 and NG-393,produced by fungal strain Fusarium sp.B88,inhibit BMP signaling in vitro.Alkaline phosphatase activity,a marker enzyme of osteoblastic differentiation,was decreased in C2C12 myoblasts stably expressing mutant ALK2 by treatment with those compounds with IC_(50) values of 5.7,6.8,6.9 and 6.1 mM,respectively.Furthermore,NG-391 and NG-393 inhibited BMP-specific luciferase reporter activity,which is directly regulated by transcription factor Smads,with IC50 values of 1.4 and 2.1 mM,respectively.These findings suggest that these fungal metabolites may provide a new direction in the development of FOP therapeutics.