Modulation of the microenvironment by growth factors regulates the in vivo growth of skeletal myoblasts.

OBJECTIVE: To investigate the optimal microenvironment for efficient myoblast transplantation in vivo.
MATERIALS AND METHODS: The effects of co-culture with growth factors, including basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF), insulin-like growth factor-I) and platelet-derived growth factor (PDGF), on in vitro growth, migration and proteolytic activity of mouse skeletal myoblasts were investigated. Myoblasts were co-injected with growth factors into the subcutis and bladder wall of nude mice, and its impact on the growth patterns of myoblasts in vivo assessed.
RESULTS: There was dose-dependent stimulation of in vitro myoblast growth after treatment with each of the four growth factors, but bFGF induced the most marked increase in the growth of myoblasts. Treatment of myoblasts with all types of growth factors also resulted in a dose-dependent increase in the in vitro migration of myoblasts, and PDGF had the most prominent effect on myoblast migration. Increased secretion of matrix metalloproteinase-9 (MMP-9) in myoblasts induced by growth factors was proportional to their increased migration capacity, which was partly inhibited by SB-3CT, an inhibitor of MMP-9. The in vivo growth of myoblasts was significantly enhanced by co-injection with all types of growth factor into both the subcutis and bladder wall, but this effect was most marked 1 and 2 weeks after co-injection with bFGF and PDGF, respectively. Furthermore, there was synergistic in vivo growth of myoblasts by co-injection of both bFGF and PDGF compared with that achieved with either agent alone.
CONCLUSIONS: These findings suggest that modulation of the microenvironment using growth factors, particularly bFGF and PDGF, could provide the optimum condition for effective myoblast transplantation in vivo.