Abstract
Lysosomes are organelles that play a crucial role in the degradation of endocytosed molecules, phagocytosed macromolecules and autophagic substrates. The membrane of lysosomes contains several highly glycosylated membrane proteins, and lysosome-associated membrane protein (LAMP)-1 and LAMP-2 account for a major portion of the lysosomal membrane glycoproteins. Although it is well known that LAMP-2 deficiency causes Danon disease, which is characterized by cardiomyopathy, myopathy and mental retardation, the roles of lysosomal membrane proteins including LAMP-1 and LAMP-2 in myogenesis are not fully understood. In this study, to understand the role of LAMP proteins in the course of differentiation of myoblasts into myotubes, we used C2C12 myoblasts and found that the protein and mRNA levels of LAMP-1 and LAMP-2 were increased in the course of differentiation of C2C12 myoblasts into myotubes. Then, we investigated the effects of LAMP-1 or LAMP-2 knockdown on C2C12 myotube formation, and found that LAMP-1 or LAMP-2 depletion impaired the differentiation of C2C12 myoblasts and reduced the diameter of C2C12 myotubes. LAMP-2 knockdown more severely impaired C2C12 myotube formation compared with LAMP-1 knockdown, and knockdown of LAMP-1 did not exacerbate the suppressive effects of LAMP-2 knockdown on C2C12 myotube formation. In addition, knockdown of LAMP-1 or LAMP-2 decreased the expression levels of myogenic regulatory factors, MyoD and myogenin. These results demonstrate that both LAMP-1 and LAMP-2 are involved in C2C12 myotube formation and LAMP-2 may contribute dominantly to it.