Transient exposure of human myoblasts to tumor necrosis factor-α inhibits serum and insulin-like growth factor-I stimulated protein synthesis

Tumor necrosis factor-α (TNF-α) induces cachexia and is postulated to be responsible for muscle wasting in several pathophysiological conditions. The purpose of the present study was to investigate whether exposure of human myoblasts to TNF-α could directly inhibit the ability of serum or insulin- like growth factor I (IGF-I) to stimulate protein synthesis as assessed by the incorporation of [³H]phenylalanine into protein. Serum and IGF-I stimulated protein synthesis dose dependently. Half-maximal stimulation of protein synthesis occurred at 05% serum and 8 ng/ml of IGF-I, respectively. TNF-α inhibited IGF-I-stimulated protein synthesis in a dose-dependent manner. Additionally, as little as 2 ng/ml of TNF-α impaired the ability of IGF-I to stimulate protein synthesis by 33% and, at a dose of 100 ng/ml, TNF- α completely prevented the increase in protein synthesis induced by either serum or a maximally stimulating dose of IGF-I. Inhibition of protein synthesis was independent of whether TNF-α and growth factors were added to cells simultaneously or if the cells were pretreated with growth factors. Exposure of myoblasts to TNF-α for 10 min completely inhibited serum- induced stimulation of protein synthesis. TNF-α, inhibited protein synthesis up to 48 h after addition of the cytokine. TNFα also inhibited serum- stimulated protein synthesis in human myoblasts that were differentiated into myotubes. In contrast, exposure of myoblasts to TNF-α had no effect on IGF- 1 binding and failed to alter the ability of either IGF-1 or serum to stimulate [³H]thymidine uptake. These data indicate that transient exposure of myoblasts or myotubes to TNF-α inhibits protein synthesis. Thus, the anabolic actions of IGF-1 on muscle protein synthesis may be impaired during catabolic conditions in which TNF-α is over expressed.