Myofiber directs macrophages IL-10-Vav1-Rac1 efferocytosis pathway in inflamed muscle following CTX myoinjury by activating the intrinsic TGF-β signaling

Background To explore the role of skeletal muscle specific TGF-beta signaling on macrophages efferocytosis in inflamed muscle caused by Cardiotoxin (CTX) injection. Methods CTX myoinjury was manipulated in TGF-beta r2(flox/flox) (control) mice or transgenic mice with TGF-beta receptor 2 ( TGF-beta r2) being specifically deleted in skeletal muscle (SM TGF-beta r2(-/-)). Gene levels of TGF-beta signal molecules, special inflammatory mediators in damaged muscle or in cultured and differentiated myogenic precursor cells (MPC-myotubes) were monitored by transcriptome microarray or qRT-PCR. TGF-beta pathway molecules, myokines and embryonic myosin heavy chain in regenerating myofibers, the phenotype and efferocytosis of macrophages were evaluated by immunofluorescence, immunoblotting, Luminex, or FACS analysis. In vitro apoptotic cells were prepared by UV-irradiation. Results In control mice, TGF-beta-Smad2/3 signaling were significantly up-regulated in regenerating centronuclear myofibers after CTX-myoinjury. More severe muscle inflammation was caused by the deficiency of muscle TGF-beta signaling, with the increased number of M1, but the decreased number of M2 macrophages. Notably, the deficiency of TGF-beta signaling in myofibers dramatically affected on the ability of macrophages to conduct efferocytosis, marked by the decreased number of Annexin-V(-)F4/80(+)Tunel(+) macrophages in inflamed muscle, and the impaired uptake of macrophages to -PKH67(+) apoptotic cells transferred into damaged muscle. Further, our study suggested that, the intrinsic TGF-beta signaling directed IL-10-Vav1-Rac1 efferocytosis signaling in muscle macrophages. Conclusions Our data demonstrate that muscle inflammation can be suppressed potentially by activating the intrinsic TGF-beta signaling in myofibers to promote IL-10 dependent-macrophages efferocytosis.

Automated summary

This study investigated the role of skeletal muscle specific TGF-beta signaling in macrophages efferocytosis in inflamed muscle caused by Cardiotoxin (CTX) injection. The results showed that deficiency of muscle TGF-beta signaling led to more severe muscle inflammation and altered macrophage populations. Furthermore, the lack of TGF-beta signaling in myofibers significantly impaired the ability of macrophages to phagocytose apoptotic cells.