Energy-ubiquitin-dependent muscle proteolysis during sepsis in rats is regulated by glucocorticoids

Recent studies suggest that sepsis-induced increase in muscle proteolysis mainly reflects energy-ubiquitin-dependent protein breakdown. We tested the hypothesis that glucocorticoids activate the energy-ubiquitin-dependent proteolytic pathway in skeletal muscle during sepsis. Rats underwent induction of sepsis by cecal ligation and puncture or were sham-operated and muscle protein breakdown rates were measured 16 h later. The glucocorticoid receptor antagonist RU 38486 or vehicle was administered to groups of septic and sham-operated rats. In other experiments, dexamethasone (2.5 or 10 mg/kg) was injected subcutaneously in normal rats. Total and myofibrillar proteolysis was determined in incubated extensor digitorum longus muscles as release of tyrosine and 3-methylhistidine, respectively. Energy-dependent proteolysis was determined in incubated muscles depleted of energy with 2-deoxyglucose and 2,4-dinitrophenol. Levels of muscle ubiquitin mRNA and free and conjugated ubiquitin were determined by Northern and Western blot, respectively. RU 38486 inhibited the sepsis-induced increase in total and myofibrillar energy-dependent protein breakdown rates and blunted the increase in ubiquitin mRNA levels and free ubiquitin. Some, but not all, sepsis-induced changes in ubiquitin protein conjugates were inhibited by RU 38486. Injection of dexamethasone in normal rats increased energy-dependent proteolysis and ubiquitin mRNA levels. The results suggest that glucocorticoids regulate the energy-ubiquitin-dependent proteolytic pathway in skeletal muscle during sepsis.