Isolation of FAP Cells from Mouse Dystrophic Skeletal Muscle Using Fluorescence Activated Cell Sorting

A population of muscle resident CD45-, CD31- cells expressing the mesenchymal PDGF receptor alpha (PDGFRα) as well as Sca-1 was first isolated in healthy mouse muscles in Uezumi et al. (2010). In the same year, Joe et al. (2010) identified and purified fibro-adipogenic precursors (FAPs), cells located into the interstitial space between myofibers close to vessels, negative for CD45, CD31,α7-Integrin, but expressing CD34, Sca-1. Both groups demonstrated that these cells are not myogenic in vitro or in vivo, but they are capable of differentiating in vitro towards both fibrogenic and adipogenic lineage (Uezumi et al., 2011). Further marker analysis indicates that the two groups identified independently the same cell population (Natarajan et al., 2010). FAPs are an important source of fibrosis and adipogenesis in dystrophic skeletal muscle (Natarajan et al., 2010; Cordani et al., 2014). We have recently demonstrated that Nitric Oxide regulates FAP fate inhibiting in vitro their differentiation into adipocytes. In mdx mice, an animal model of DMD, fed with a diet containing the nitric oxide donating drug, Molsidomine, the number of PDGFRα+ cells was reduced as well as the deposition of both skeletal muscle fat and connective tissues (Cordani et al., 2014). Here we described a method to isolate in both wild type and in mdx dystrophic muscle pure population of FAPs by double selection for SCA-1 and PDGFRα positivity in absence of the satellite cell markers SM/C2.6 and α7integrin as well of the pan-lymphocytes marker CD45 or endothelial marker CD31