How proinflammatory cytokines may impair growth and cause muscle wasting

Thissen, Jean-Paul [UCL]

Background: Cytokines, such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-1 beta and IL-6, that are released in response to injury are thought to inhibit growth and cause muscle wasting, at least in part by inhibiting anabolic hormones such as insulin-like growth factor I (IGF-I). Because critical illness in humans is accompanied by high circulating concentrations of growth hormone (GH), which is the main stimulus for IGF-I production by the liver, resistance to GH is thought to contribute to the IGF-I decline observed in catabolic diseases. While TNF-alpha seems to cause GH resistance mainly through downregulation of liver GH receptor expression, IL6 may inhibit the GH-stimulated Janus kinase and signal transducer and activator of transcription pathways by induction of suppressors of cytokine signaling proteins. Elevations in circulating IGF binding protein-1 levels, as observed in many catabolic situations, may play a role in the decline in muscle mass by decreasing the rate of protein synthesis in skeletal muscle. Furthermore, the increase in local muscle cytokines produced during inflammation makes the muscle GH-resistant and reduces its own IGF-I production. Finally, not only decreased IGF-I production by muscle, but also decreased muscle sensitivity to the anabolic effects of IGF-I, may contribute to muscle wasting observed in response to severe stress. Conclusions: Taken together, proinflammatory cytokines may contribute to the growth retardation and muscle wasting that occur after injury by impairing the GH/IGF-I axis at several levels. Copyright (c) 2007 S. Karger AG, Basel.