Growth factor and cytokine interactions in myogenesis Part I The effect of TNF-alpha and IFN gamma on IGF-I-dependent differentiation in mouse C2C12 myogenic cells

The aim of this study was to examine the potential interactions of IGF-I with TNF-α and IFN-γ with regard to regulation of the myogenesis and proliferative potential of mouse C2C12 myoblasts. The stimulation of myogenesis by IGF-I (30 nmol/l) was manifested by an enhanced myoblast fusion and expression of myosin heavy chain (MHC) during the first 3 days of differentiation. IGF-I-dependent fusion and MHC expression was reduced by TNF-α and IFN-γ. Both cytokines prevented the stimulatory effect of IGF-I on MyoD expression with minor modification of the myogenin level. Both TNF-α and IFN-γ activated the expression of cyclin A in myoblasts restimulated to proliferation; however, when used in combination with IGF-I these cytokines prevented the rise in cyclin A induced by growth factor. In conclusion: i) TNF-α and IFN-γ reduce IGF-I-dependent myogenesis which was manifested by the reduction of myoblast fusion and MHC cellular levels, ii) Molecular mechanisms of inhibitory action of TNF-α and IFN-γ on IGF-I-mediated differentiation involve a decrease in MyoD whereas myogenin level plays a minor role, iii) TNF-α and IFN-γ increase the proliferative potential of myoblasts; however, they reduced the mitogenic effect of IGF-I, manifested by a decrease of IGF-I-stimulated cyclin A expression in myoblasts reinduced to proliferation. Interactions among IGF-I and proinflammatory cytokines are therefore important to establish a number of myoblasts and the onset of myogenesis during muscle regeneration.