REGULATION OF PROLIFERATION AND DIFFERENTIATION OF MYOBLASTS DERIVED FROM ADULT-MOUSE SKELETAL-MUSCLE BY SPECIFIC ISOFORMS OF PDGF

The expression of receptors and the mitogenic response to PDGF by C2 myoblasts, derived from adult mouse skeletal muscle, was investigated. Employing 125I-PDGF binding assays, we showed that the cells exhibit high level binding of PDGF-BB (∼165 × 103 molecules/cell at saturation) and much lower binding of the PDGF-AA and PDGF-AB (6-12 × 103 molecules/cell at saturation). This indicates that the C2 myoblasts express high levels of PDGF receptor β-subunits and low levels of α-subunits. PDGF-BB enhances the proliferation of C2 cells maintained in 2% FCS by about fivefold. PDGF-AB had a moderate effect on cell proliferation (less than twofold) and PDGF-AA had no effect. Inverse effects of PDGF isoforms on the frequency of differentiated myoblasts were observed; the frequency of myosin-positive cells was reduced in the presence of PDGF-BB while PDGF-AA and PDGF-AB had no effect. PDGF may thus act to increase the number of myoblasts that participate in muscle regeneration following muscle trauma by stimulating the proliferation and by inhibiting the differentiation of myogenic cells.