Modulation of melanocortin signaling ameliorates uremic cachexia.

Insulin-like growth factor (IGF)-I increases muscle mass while myostatin inhibits its development. Muscle wasting is common in patients with uremic cachexia and may be due to imbalance of this regulation. We had proposed a central mechanism involving leptin and melanocortin signaling in the pathogenesis of uremic cachexia since agouti-related peptide (AgRP), a melanocortin-4 receptor antagonist, reduced uremic cachexia. Here we found that injection of AgRP into the cerebral ventricles resulted in a gain of body mass and improved metabolic rate regulation in a mouse model of uremic cachexia. These salutary effects occurred independent of increased protein and calorie intake. Myostatin mRNA and protein concentrations were increased while those of IGF-I were decreased in the skeletal muscle of uremic mice. AgRP treatment partially corrected these uremia-induced changes. Suppressor of cytokine signaling-2 gene expression (SOCS2) was significantly increased in uremic animals and AgRP reduced this expression. We suggest that AgRP improves uremic cachexia and muscle wasting by a peripheral mechanism involving the balance between myostatin and IGF-I.