Temporal expression of growth factor genes of primary porcine satellite cells during myogenesis

The present experiment was undertaken to study the transcription of members of the insulin-like growth factor (IGF) system and myostatin in porcine satellite cells through myogenesis and to study the effects of 1 mu mol/L insulin on stimulating fusion. Cultured cells were harvested at 50 and 80% confluence and at days 1, 2, 3 and 4 following induction of fusion and differentiation. Increased levels of myogenin transcription and creatine kinase from 50% confluence until day 2 indicated that fusion and differentiation were induced. The mRNA abundance of IGF-I (P < 0.001), IGF-II (P < 0.001), IGF binding protein (BP) 5 (P < 0.01), type I IGF receptor (P < 0.001) and myostatin (P < 0.01) increased from proliferation to differentiation. Insulin stimulated differentiation as indicated by elevated creatine kinase activity (P < 0.001) but did not affect myogenin mRNA abundance (P= 0.98). Insulin downregulated transcription of IGF-I (P < 0.01) and during the first 2 days after switching to differentiation medium insulin downregulated IGF receptor transcription (P < 0.001), whereas insulin did not affect transcription of IGF-II (P= 0.06), IGFBP5 (P= 0.76) or myostatin (P= 0.50). In conclusion, transcriptions of IGF-I, IGF-II, type I IGF receptor, IGFBP5 and myostatin were changed during myogenesis, suggesting autocrine/ paracrine roles in regulating the transition from proliferation to differentiation of porcine satellite cells.