Cardiac-specific overexpression of tumor necrosis factor-alpha causes oxidative stress and contractile dysfunction in mouse diaphragm

Background-We have developed a transgenic mouse with cardiac-restricted ove rexpression of tumor necrosis factor-alpha (TNF-alpha). These mice develop a heart failure phenotype characterized by left ventricular dysfunction and remodeling, pulmonary edema, and elevated levels of TNF-alpha in the perip heral circulation from cardiac spillover. Given that TNF-alpha causes atrop hy and loss of function in respiratory muscle, we asked whether transgenic mice developed diaphragm dysfunction and whether contractile losses were ca used by oxidative stress or tissue remodeling. Methods and Results-Muscles excised from transgenic mice and littermate con trols were studied in vitro with direct electrical stimulation. Cytosolic o xidant levels were measured with 2',7'-dichlorofluorescin diacetate; emissi ons of the oxidized product were detected by fluorescence microscopy. Force generation by the diaphragm of transgenic animals was 47% less than contro l (13.2+/-0.8 [+/-SEM] versus 25.1+/-0.6 N/cm(2); P<0.001); this weakness w as associated with greater intracellular oxidant levels (P<0.025) and was p artially reversed by 30-minute incubation with the antioxidant N-acetylcyst eine 10 mmol/L (P<0.01). Exogenous TNF-alpha 500 mu mol/L increased oxidant production in diaphragm of wild-type mice and caused weakness that was inh ibited by N-acetylcysteine, suggesting that changes observed in the diaphra gm of transgenic animals were mediated by TNF-alpha. There were no differen ces in body or diaphragm weights between transgenic and control animals, no r was there evidence of muscle injury or apoptosis. Conclusions-Elevated circulating levels of TNF-alpha provoke contractile dy sfunction in the diaphragm through an endocrine mechanism thought to be med iated by oxidative stress.