Hepatocyte Growth Factor from Mechanically Stretched Skeletal Muscle Satellite Cells and the Role of pH and Nitric Oxide

Application of mechanical stretch to cultured adult rat muscle satellite cells results in release of hepatocyte growth factor (HGF) and accelerated entry into the cell cycle. Stretch-activation of cultured rat muscle satellite cells was observed only when medium pH was between 7.1 and 7.5, even though activation of satellite cells was accelerated by exogenous HGF over a pH range from 6.9 to 7.8. Furthermore, HGF was only released in stretched cultures when the pH of the medium was between 7.1 and 7.4. Conditioned medium (CM) from stretched satellite cell cultures stimulated activation of un-stretched satellite cells, and the addition of anti-HGF neutralizing antibodies to stretch-conditioned medium inhibited the stretch-activation response. Conditioned medium from satellite cells that were stretched in the presence of nitric oxide synthase (NOS) inhibitor, N G-nitro-L-arginine methyl ester hydrochloride (L-NAME), did not accelerate activation of un-stretched control satellite cells, and HGF was not released into the medium. Conditioned medium from un-stretched cells that were treated with a NO donor, sodium nitroprusside dihydrate (SNP), was able to accelerate the activation of satellite cells in vitro, and HGF was found in the conditioned medium. Immunoblot analysis indicated that both neuronal and endothelial NOS isoforms were present in satellite cell cultures. Furthermore, assays of NOS activity in stretched satellite cell cultures demonstrated that NOS is stimulated when satellite cells are stretched in vitro. These experiments indicate that stretch triggers an intracellular cascade of events including NO synthesis, that results in HGF release and satellite cell activation.