Mature adipocytes inhibit differentiation of myogenic cells but stimulate proliferation of fibro-adipogenic precursors derived from trout muscle in vitro.

Abstract Interactions between tissues and cell types, mediated by cytokines or direct cell-cell exchanges, regulate growth. To determine whether mature adipocytes influence the in vitro development of trout mononucleated muscle cells, we developed an indirect coculture system, and showed that adipocytes (5×10 6 cells/well) derived from perivisceral adipose tissue increased the proliferation (BrdU + ) of the mononucleated muscle cells (26% versus 39%; P<0.001) while inhibiting myogenic differentiation (myosin + ) (25% versus 15%; P<0.001). Similar effects were obtained with subcutaneous adipose tissue-derived adipocytes, although requiring more adipocytes (3×10 7 cells/well versus 5×10 6 cells/well). Conditioned media recapitulated these effects, stimulating proliferation (31% versus 39%; p<0.001) and inhibiting myogenic differentiation (32% versus 23%; p<0.001). Adipocytes began to reduce differentiation after 24 hours, whereas proliferation stimulation was observed after 48 hours. While adipocytes did not change pax7 + and myoD1/2 + percentages, they reduced myogenin + cells showing inhibition from early differentiation stage. Finally, adipocytes increased BrdU + cells in the Pdgfrα + population but not in the myoD + one. Collectively, our results demonstrate that trout adipocytes promote fibro-adipocyte precursor proliferation while inhibiting myogenic cells differentiation in vitro , suggesting the key role of adipose tissue in regulating fish muscle growth.