The effect of endotoxin on skeletal muscle protein gene expression in the rat.

Sepsis is associated with net breakdown of skeletal muscle protein, mediated partly by reduced rates of muscle protein synthesis. This study investigated the role of altered gene expression for specific muscle proteins in mediating reduced protein synthesis in a rat model of acute severe sepsis. Adult rats were given a single sublethal intraperitoneal dose of endotoxin (bacterial lipopolysaccharide). Protein, RNA and DNA contents of muscle were measured and changes in expression of mRNA in tibialis anterior and extensor digitorum longus muscles were detected by quantification of Northern blots at 6, 24, 48 and 72 hr after endotoxin and in animals starved for 24 hr. Results showed that at 24 hr after endotoxin there was a loss of about 14% of muscle protein content. No reduction in mRNA was found at any time point for beta-myosin heavy chain (MHC), fast-MHC, alpha-actin, skeletal muscle troponin or carbonic anhydrase III (CA III); rather, at 48 hr there was increased expression of beta-MHC (224 +/- 123% control) and CA III (202 +/- 56%). Blocking TNF-alpha by pre-treatment with a monoclonal antibody did not appear to influence this. Total RNA content of muscle was reduced to 67% of the control values 24 hr after LPS, although this was no different to pair-fed animals starved for 24 hr. It is concluded that reduced protein synthesis in skeletal muscle in early acute sepsis is not primarily associated with reduced muscle protein gene expression.