Regenerating myofiber with activating of TGF-β signaling contributes to macrophage efferocytosis through enhancing Tregs response in inflamed muscle

BackgroundThis study aimed to investigate the role of myofiber-specific TGF-β signaling in the development of muscle inflammation by modulating Treg-cell-mediated macrophage efferocytosis.MethodsCTX-induced muscle injury was performed in the tibialis anterior (TA) of control (TGF-βr2flox/flox) and transgenic mice with skeletal muscle-specific deletion of TGF-β receptor 2 (SM TGF-βr2−/−). Gene levels of regulatory T cell (Treg) activation markers and inflammatory mediators produced by macrophages or Tregs were assessed using qRT-PCR.

Intramuscular infiltration of Tregs and macrophages, as well macrophage phenotypes, efferocytic function, and associated signaling molecules, were evaluated using hematoxylin and eosin (HE) staining, immunofluorescence, immunoblotting and FACS analysis. The correlation of myofibers with Tregs-mediated macrophage efferocytosis were addressed under an in vitro co-culture system, which including Tregs, macrophages, and the differentiated myogenic precursor cells (MPC-myotubes) isolated from control or SM TGF-βr2−/−mice.

Apoptotic cells were generated by UV irradiation prior to transfer into inflamed muscle.ResultsDeficiency in muscle TGF-β signaling resulted in more severe muscle inflammation, characterized by an increased number of M1 macrophages and a decreased number of M2 macrophages.