Chemotaxis of skeletal muscle satellite cells

Migration of myogenic cells occurs extensively during both embryogenesis and regeneration of skeletal muscle and is important in myoblast gene therapy, but little is known about factors that promote chemotaxis of these cells. We have used satellite cells from adult rats purified by Percoll density gradient centrifugation to test growth factors and wound fluids for chemotactic activity in blind-well Boyden chambers. Of a variety of growth factors tested only hepatocyte growth factor (HGF) and transforming growth factor-beta (TGF-beta) exhibited significant chemotactic activity. The dose-response curves for both of these factors was bell-shaped with maximum activity in the 1-10 ng/ml range. Checkerboard analysis of TGF-beta showed that chemotaxis occurred only in response to a positive concentration gradient. An extract of rat platelets also exhibited chemotactic activity for satellite cells. Half-maximal activity of this material was about 3 micrograms/ml, and there was no evidence of inhibition of migration at high concentrations. Checkerboard analysis of platelet extract exhibited evidence of both chemotaxis and chemokinesis, or increase in random motility of cells. Inhibition experiments showed that most, but not all, of the chemotactic activity in platelet extract could be blocked with a neutralizing antibody to TGF-beta. A saline extract of crushed muscle was found to contain both mitogenic and motogenic factors for satellite cells. The two activities were present in different fractions after heparin affinity chromatography. We propose that the proliferation and migration of satellite cells during regeneration is regulated by overlapping gradients of several effector molecules released at the site of muscle injury. These molecules may also be useful for enhancing the dispersion of injected myoblasts during gene therapy.