Alterations in Skeletal Muscle Gene Expression in the Rat with Chronic Congestive Heart Failure

Abstract

Congestive heart failure is often associated with skeletal muscle abnormalities that contribute to early fatigue and acidosis. Up to the present time, however, the mechanisms responsible for these changes are unclear. Myocardial infarctions were produced by coronary ligation in adult Sprague–Dawley rats. At 20 weeks, 10 control rats, and 15 animals with heart failure [defined by elevated LVEDP (26.1±3.1 v2.5±0.5 mmHg) and RV hypertrophy (300±21 g v158±9 mg) ] underwent in vivomeasurements of total body, and soleus total protein and myosin heavy chain (MHC) synthesis by [ 3H]leucine constant infusion. Soleus muscle was also analysed for protein content, and MHC isoenzyme content by SDS-PAGE. Northern blotting also was used to determine levels of the mRNA's encoding type I, IIa, IIb, and IIx MHC, α-skeletal actin, COX III, SDH and GAPDH. Soleus muscles in heart failure rats were smaller than controls (112±6 v126±5 mg) and the degree of atrophy was significant when corrected for body mass (0.38±0.02 v0.46±0.02 mg/g, P=0.007). Although there was no significant difference in plasma leucine flux (an index of whole-body protein synthesis), soleus muscle total and MHC synthesis was reduced in heart failure animals. Whereas the Type I MHC isoenzyme ( βMHC) was the only MHC detected in the soleus of control animals, type II MHC isoenzyme comprised 11.8±3.1% of the MHC in the heart failure group. Furthermore, steady-state mRNA levels encoding βMHC were significantly depressed in the heart failure rats, where those encoding Types IIb and IIx MHC were increased. Steady-state mRNA levels of α-skeletal actin, cytochrome C oxidase (COX III) and succinate dehydrogenase (SDH) were also significantly depressed. This animal model of chronic heart failure is associated with quantitative and qualitative alterations in skeletal muscle gene expression that are similar to those reported in skeletal muscle of patients with chronic heart failure. The altered phenotype and impaired metabolic capacity may contribute to exercise intolerance in CHF.