Regulation of muscle cell proliferation by extracts from crushed muscle

Cell culture studies were conducted to determine whether myotrophic factors were released from mature murine or bovine muscle following a crush injury. Murine crushed muscle extract (mCME) was added to C2 muscle (satellite) cell cultures at concentrations of 0, 50, 100, 200, and 400 micrograms of total protein/mL. Bovine crushed muscle extract (bCME) was added at concentrations of 0, 100, 200, 400, and 500 micrograms/mL. Murine CME and bCME at each concentration caused an increase (P < .01) in [3H]TdR incorporation into muscle cells compared to control cultures. The saturating concentrations (P < .01) of CME in the presence of 2% FBS were approximately 200 and 400 micrograms/mL for murine and bovine extracts, respectively. Murine CME or bCME acted in an additive fashion with independent, saturating concentrations of the insulin-like growth factors (IGF-I and IGF-II), basic fibroblast growth factor (bFGF), and transforming growth factor-beta (TGF-beta) to increase (P < .01) C2 muscle cell proliferation. Subsequently, in separate experiments, mCME or bCME acted additively with a combination of all growth factors to increase (P < .01) cell proliferation. Combining mCME and bCME at saturating levels in one treatment was not (P > .05) additive to that elicited by either CME alone. These results suggest that myotrophic factors are released following injury in mature skeletal muscle, and they are not species-specific.