Characterization of myogenic factors derived from a stable macrophage cell line

The interplay between macrophages and muscle precursors, critical for myogenesis, is still poorly known. We have already reported that the murine macrophage cell line J774 can produce, in the absence of serum, a Macrophage-Conditioned Medium (MCM) that contains muscle specific growth factors. Here we show that MCM can strongly stimulate (up to 2 fold) the proliferation rate of primary rat myoblasts and pure rat satellite cells. Interestingly, in both cases cell division and cytoplasmic growth were partially uncoupled by MCM, with a loss of 30-35% of the mean cell mass respect to control. Primary rat myoblasts, fully inhibited to form myotubes when co-cultured with other cell types, could instead produce a very extensive network of contractile myotubes if exposed to MCM. Some of the in vitro properties of MCM were also compared to those of purified myogenic factors. The presence of known myogenic factors in active MCM preparations is also under investigation. The potential usefulness of MCM for expanding myoblast populations will be discussed.