Galectin-1 is a novel factor that regulates myotube growth in regenerating skeletal muscles

Adult skeletal muscles have a vigorous regenerative capacity in response to chemical, mechanical or physical injuries. Muscle satellite cells play a critical role in skeletal muscle regeneration. Activated satellite cells (myoblasts) proliferate and then differentiate. Differentiated myoblasts fuse with each other to form multinucleated myotubes, and the growth of myotubes is induced by both fusion with additional myoblasts and reinnervation of motor neurons. Cellular and molecular events underlying the regenerative processes are regulated by critical factors, which are produced by satellite cells, myoblasts, myotubes, extracellular matrix and inflammatory cells. Galectin-1 is abundantly synthesized in adult skeletal muscles, but its roles in muscle regeneration have not been fully elucidated. We reviewed previous studies on the function of galectin-1 regarding myogenesis in vivo and in vitro, and discussed the roles of this lectin in regenerating skeletal muscles based on our observations. In intact adult muscles, galectin-1 was associated with basement membranes of myofibers. After muscle injury, galectin-1 immunoreactivity was increased within the cytoplasm of activated satellite cells. Thereafter, differentiated myoblasts lost galectin-1 immunoreactivity, but galectin-1 expression associated with basement membranes was detected in myotubes. Administration of anti-galectin-1 antibody, which perturbs the function of galectin-1, decreased the size of myotubes. Furthermore, muscle injury induced abundant expression of galectin-1 in damaged intramuscular nerve axons. We conclude that galectin-1 is a novel factor that promotes both myoblast fusion and axonal growth following muscle injury, and consequently, regulates myotube growth in regenerating skeletal muscles.