Gene Expression of Muscle-Specific Ubiquitin Ligase, Atrogin-1/MAFbx, Positively Correlates with Skeletal Muscle Proteolysis in Food-Deprived Broiler Chickens

Abstract

A relationship between skeletal muscle proteolysis and mRNA expression of atrogin-1/MAFbx, a muscle-specific ubiquitin ligase, was examined in food-deprived broiler chickens. In response to food deprivation for 24 and 48h, body and muscle weights decreased in a time-dependent manner. Muscle free Nτ-methylhistidine content, an index of myofibrillar proteolysis, was 1.8-fold and 2.5-fold greater than that of fed controls following 24 and 48h of food deprivation, respectively. Gene expression of atrogin-1/MAFbx drastically increased in response to food deprivation in a time-dependent manner. At 48h of food deprivation, the induction of atrogin-1/MAFbx mRNA expression level elevated up to 20-fold greater than that of fed controls. By contrast, mRNA expression levels of 20S proteasome C1 and C2 subunits tended to decrease with time. No significant difference was seen in the change of ubiquitin mRNA expression. A highly significant linear negative relationship (r2=0.754, P<0.001) was found between atrogin-1/MAFbx expression and muscle mass, while a highly significant linear positive relationship (r2=0.784, P<0.001) was found between atrogin-1/MAFbx expression and muscle free Nτ-methylhistidine content. These results indicate that atrogin-1/MAFbx plays a critical role in the development of muscle proteolysis and its gene expression is a reliable index of muscle proteolysis in broiler chickens.