Red photobiomodulation promotes skeletal myoblast differentiation and counteracts TGF-β1’ anti-myogenic effects in vitro: evidence from morpho-functional analyses

Adult skeletal muscle regenerates lost damaged tissue mainly thanks to the activity of a population of resident stem cells namely satellite cells (SCs). In the case of chronic or severe damage, SCs’ functionality may be compromised by the occurrence of an aberrant fibrotic reparative response1. Strategies aimed to improve the muscle intrinsic regenerative capacity while limiting the excessive deposition of fibrotic tissue may be promising. In this perspective, photobiomodulation (PBM) (i.e. application of light with 400-1100 nm wavelength using different laser or LED devices, power density less than 100 mW/cm2 and energy density less than 10 J/cm2 at target) may represent a valid option based on its well-known pro-regenerative effects and increasing evidence of its antifibrotic potential. However, PBM's effects on skeletal muscle are controversial and there are no univocal guidelines for its use2,3. To this aim we evaluated the effects of different treatments of red PBM (laser diode 635±5 nm, energy density: 0.4, 4 and 8 J/cm2, single exposure) on murine C2C12 myoblasts undergoing differentiation in the presence or absence of TGF-β1 (2ng/ml) for 24, 48 and 72h and on differentiated myotubes (72h). Morphological analyses revealed that red PBM with 4 J/cm2 energy density improved myoblast differentiation and did not affect viability and features of differentiated myotube. Red PBM with 4 J/cm2 energy density was able to counteract the anti-myogenic action of transforming growth factor (TGF)-β1. These results were corroborated by electrophysiological recordings of membrane passive properties and ion currents. This study provides experimental evidence for the pro-myogenic effects of red PBM and the essential groundwork for further investigation.