FIGURE 7.

Summary of the fusion and nonfusion roles of satellite cells. This schematic (constructed with BioRender.com, with permission) provides a general overview of how satellite cells can respond to mechanical overload. The fusion role has been well defined, and this involves satellite cell proliferation (acute response) followed by the fusion of a subpopulation of satellite cells to increase myonuclear number. The nonfusion role involves satellite cells secreting exosomes containing microRNA (and presumably other cargo). Exosomes can transport this cargo to myofiber and nonmyofiber cell types in the interstitial space to regulate gene expression. In the example pictured, satellite cells are regulating gene expression in myofibers and fibrogenic cells, and this may affect extracellular matrix remodeling during myofiber hypertrophy (as discussed in main text). Satellite cells are likely to communicate with other cell types, and this is also illustrated via cell-cell communication with vascular endothelial cells. ECM, extracellular matrix.