Involvement of reactive oxygen species-mediated NF-κB activation in TNF-α-induced cardiomyocyte hypertrophy

We examined the intracellular signaling mechanism for tumor necrosis factor-alpha (TNF-alpha)-induced cardiac hypertrophy in isolated rat neonatal cardiomyocytes, TNF-alpha enhanced the expression of a kappaB-dependent reporter gene construct in a dose-dependent manner, which was transiently transfected in cardiomyocytes. Electrophoretic mobility shift assay demonstrated that TNF-alpha induced nuclear factor-kappaB (NF-kappaB)-specific DNA binding. Cultured cardiomyocytes were infected with a recombinant adenoviral vector expressing a degradation-resistant mutant of IkappaBalpha (AdIkappaBalpha32/36A). The IkappaBalpha mutant suppressed NF-kappaB activation induced by TNF-alpha. In cardiomyocytes infected with AdIkappaBalpha32/36A, TNF-alpha-induced hypertrophic responses, including increases in cell size, protein synthesis and atrial natriuretic factor production and enhancement of sarcomeric organization, were remarkably attenuated compared to the cells infected with an adenovirus expressing bacterial beta-galactosidase. Using a reactive oxygen species (ROS)-sensitive fluorescent dye, 2', 7'-dichlorofluorescin, we observed an increase in fluorescent signal in cardiomyocytes over time, upon addition of TNF-alpha Preincubation of n-acetyl cysteine (NAC), an antioxidant, prior to TNF-alpha treatment, abolished TNF-alpha -induced ROS generation. NAC abolished TNF-alpha-induced NF-kappaB activation and hypertrophic responses. These findings indicated that TNF-alpha-induced cardiomyocyte hypertrophy is mediated through NF-kappaB activation via the generation of ROS. (C) 2002 Elsevier Science Ltd.