Involvement of the GLUT 3 transporter in myogenic regulation

We have recently demonstrated a close relationship between the GLUT 3 transporter and the myogenic ability of rat skeletal L6 myoblasts [1]. This investigation examined the effects of over- and under-expression of the GLUT 3 transporter on both biochemical and morphological differentiation. L6 transfectants expressing two to five times the normal L6 GLUT 3 transcript level were impaired in the expression of myogenesis-associated genes, such as myogenin, MLC, MHC and TnT, and in myotube formation. Similar defects were also observed in myoblast mutants expressing less than 20% of the normal GLUT 3 level. Forced expression of an exogenous GLUT 3 cDNA could partially rescue the myogenic defect of these GLUT 3 mutants. However, such myogenic defects were not observed in L6 GLUT 3 antisense transfectants expressing 39% of the normal L6 GLUT 3 level. These data suggest that myogenic differentiation will proceed only within a critical level of the GLUT 3 transporter. The optimal GLUT 3 content for myogenesis ranges from around 2 x 10(5) to 5 x 10(5) molecules per cell in day 2 cultures; GLUT 3 levels outside this range have a negative effect on myogenesis. Our data suggest that GLUT 3 may regulate myogenesis by modulating the levels of signal transducers required for expression of myogenin and muscle-specific contractile protein genes.