Identification of factors that promote satellite cell motility

Abstract

An important but poorly understood aspect of stem cell-mediated skeletal muscle regeneration is stem cell recruitment and motility within the damaged tissue; a failure to spread after therapeutic engraftment is also a key stumbling block in cell-based therapies for muscle disease. Acute muscle damage results in the local release of diffusible factors, many of which have potential to promote either chemokinesis or chemotaxis, but to date no comprehensive survey of damage-induced motogens has been published. We generated crushed muscle extract (CME) to obtain a physiologically-relevant sample of secreted factors from damaged muscle; we propose that components of CME will promote satellite cell motility within the injured tissue in a concentration-dependent manner. Using in vitro tests of motility and chemotaxis, we have shown that total CME as well as known components such as HGF and SDF-1 are both motogenic and chemotactic for primary mouse satellite cells. To identify other active components, we used size-exclusion and affinity chromatography to fractionate CME and test the fractions for motogenic potential. Utilizing this approach we have identified and validated a novel factor, Wnt5b, as a satellite cell motogen in vitro. Wnt-5b is both chemokinetic and chemotactic for primary mouse satellite cells and this motility is dose dependent. Additional fractionation of CME using heparin affinity chromatography has identified Annexin A2 and Galectin-1 as putative motogens present in high activity fractions of CME. Ongoing work is aimed at validating Annexin A2 and Galectin-1 as additional novel satellite cell motogens. Identification of these signals and an understanding of their activity individually and collectively will add significantly to our understanding of skeletal muscle regeneration.