Apoptosis in the Skeletal Muscle of Rats with Heart Failure is Associated with Increased Serum Levels of TNF-α and Sphingosine

Skeletal muscle in congestive heart failure (CHF) is responsible for increased fatigability, decreased endurance and exercise capacity. A specific myopathy with increased expression of fast myosin heavy chains (MHCs), myocyte atrophy, secondary to myocyte apoptosis, that is triggered by high levels of circulating tumor necrosis factor (TNF- α) has been described. However, a direct effect of TNF- α on skeletal muscle has not been described yet. In this paper we put forward the hypothesis that TNF- α plays an indirect effect on skeletal myocytes. In an animal model of CHF, the monocrotaline-treated rat, we have observed a significant (P<0.001) increase of circulating TNF- α that is paralleled by increased serum levels of the endogenous second messenger, sphingosine (SPH), (from 0.71±0.15 to 1.32±0.39 nmoles/ml, P<0.01). In the tibialis anterior (TA) muscle we found a marked increase of myocyte apoptosis (from 1.4±2.4 to 40.1±39.5 nuclei/mm3, P<0.04). We correlated plasma levels of TNF- α with those of SPH and in turn with the magnitude of apoptosis. Linear regression showed a significant correlation between TNF- α, SPH, and apoptosis (r2=0.74, P=0.004 andr2 =0.87, P=0.001 respectively). Analysis of covariance showed that TNF- α and SPH were independently correlated with the number of apoptotic nuclei (P=0.0001). In parallel in vitro experiments, where increasing concentrations of SPH were applied to skeletal muscle cells in culture, we observed a dose-dependent increase in apoptosis. These results suggest that TNF- α -induced SPH production may be responsible for skeletal muscle apoptosis. The link between TNF- α and skeletal muscle apoptosis could be represented by the second messenger SPH, which can directly induce apoptosis in these cells.