EM.P.1.08 Low temperature-induced inhibition of myogenic differentiation is cancelled by IGF-I and vitamin C

To study the effect of low temperature on expressions of myogenic regulatory factors (MRFs) and myotube formation, we cultured the mouse myoblast cell line C2C12 at 30 °C, 35 °C and 38 °C. The myoblasts fused into multinucleated myotubes within 4 days after the induction of differentiation at 38 °C. Myotube formation was delayed but relatively normal at 35 °C, whereas it was blocked at 30 °C. Myoblasts cultured at 30 °C expressed MyoD, which is required for myogenic determination, but not myogenin, which mediates terminal differentiation. At 30 °C, Id3, which acts as a negative regulator of MRFs and decreases upon the initiation of differentiation at 38 °C, was continuously expressed and the expressions of the muscle-specific microRNAs were not upregulated. We also investigated the expressions of MyoD and myogenin during mouse satellite cell activation in single fiber culture as an in vivo model and found that the expression of myogenin, but not of MyoD, was inhibited at 30 °C. These low temperature-induced inhibitions of myogenic differentiation were cancelled by insulin-like growth factors (IGFs) and l-ascorbic acid phosphate, stabilized vitamin C (VC). C2C12 myoblast cells cultured in the medium containing IGF-I (or IGF-II) and VC at 30 °C expressed myogenin and then fused into multinucleated myotubes, while their Id3 expression decreased and the expressions of the muscle-specific microRNAs were upregulated. IGF-I and VC also increased endogenous IGF-II expression at 30 °C, suggesting that the IGF-II auto-regulation loop was upregulated. These results suggest that physical body temperature plays an important role in the regulation of myogenic differentiation, but it can be substituted for chemical factors. Level of IGF expression might be responsible for the thermal sensitivity of muscle cell differentiation in homothermal animals.