Skeletal muscle, despite being endowed with progenitor cells capable of repairing damaged tissue, often undergoes the formation of scar tissue following an injury, which hinders proper anatomical and functional restoration. Photobiomodulation (PBM) represents an innovative and promising therapy for the treatment of tissue injuries, involving the application of light with wavelengths ranging from 400 to 1100 nm, using laser or LED devices. It is hypothesized that PBM may have a strong influence on the regulation of the secretory activity of mesenchymal stromal cells (MSCs) located in various tissues of adult individuals. MSCs are a subset of cells involved in tissue homeostasis and regeneration. These cells are localized in specific areas called "niches" and, although generally in a state of relative quiescence, are activated by specific stimuli that trigger their proliferative and regenerative potential. While the mechanism of action of MSCs in tissue regeneration is not yet fully understood, the benefits seem to mainly depend on paracrine mechanisms, involving the release of bioactive molecules, such as immunomodulatory and anti-inflammatory factors, predominantly contained in extracellular vesicles (EVs). EVs are classified into exosomes, microvesicles (MVs), and apoptotic bodies, and can be distinguished by their size and cellular origin. Exosomes, in particular, contain various molecules, including proteins, lipids, mRNA, miRNA, mitochondrial DNA, and other non-coding RNAs. To date, there are very few studies on the effect of PBM in modulating the secretory activity of MSCs, especially regarding the repair of muscle and tendons following injuries. Therefore, the goal of this research is to evaluate the secretory activity of MSCs after PBM treatment, analyzing the content of the different subpopulations of secretory vesicles and investigating the differences in the presence of anti-inflammatory and pro-regenerative factors, with particular attention to the repair of muscle and tendons.
