Apoptosis in the skeletal muscle of rats with heart failure is associated with increased serum levels of TNF-alpha and sphingosine

Skeletal muscle in congestive heart failure (CHF) is responsible for increa sed fatigability, decreased endurance and exercise capacity. A specific myo pathy 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-alpha) has been described. Howeve r, a direct effect of TNF-alpha on skeletal muscle has not been described y et. In this paper we put forward the hypothesis that TNF-alpha plays an ind irect effect on skeletal myocytes. In an animal model of CHE the monocrotal ine-treated rat, we have observed a significant (P<0.001) increase of circu lating TNF-<alpha> that is paralleled by increased serum levels of the endo genous 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 m arked increase of myocyte apoptosis (from 1.4 +/- 2.4 to 40.1 +/- 39.5 nucl ei/mm(3), P<0.04). We correlated plasma levels of TNF-alpha with those of S PH and in turn with the magnitude of apoptosis. Linear regression showed a significant correlation between TNF-alpha SPH. and apoptosis (r(2) = 0.74. P = 0.004 and r(2) = 0.87, P = 0.001 respectively). Analysis of covariance showed that TNF-alpha and SPH were independently correlated with the number of apoptotic nuclei (P=0.0001). In parallel in vitro experiments, where in creasing concentrations of SPH were applied to skeletal muscle cells in cul ture, we observed a dose-dependent increase in apoptosis. These results sug gest that TNF-alpha -induced SPH production may be responsible for skeletal muscle apoptosis. The link between TNF-alpha and skeletal muscle apoptosis could be represented by the second messenger SPH which can directly induce apoptosis in these cells. (C) 2001 Academic Press.