Involvement of Reactive Oxygen Species-mediated NF- κ B Activation in TNF- α -induced Cardiomyocyte Hypertrophy

We examined the intracellular signaling mechanism for tumor necrosis factor- α (TNF-α )-induced cardiac hypertrophy in isolated rat neonatal cardiomyocytes. TNF- α enhanced the expression of a κ B-dependent reporter gene construct in a dose-dependent manner, which was transiently transfected in cardiomyocytes. Electrophoretic mobility shift assay demonstrated that TNF- α induced nuclear factor- κ B (NF- κ B)-specific DNA binding. Cultured cardiomyocytes were infected with a recombinant adenoviral vector expressing a degradation-resistant mutant of I κ B α (AdI κ B α 32/36A). The Iκ B α mutant suppressed NF- κ B activation induced by TNF- α. In cardiomyocytes infected with AdI κ B α 32/36A, TNF- α -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 β -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- α. Preincubation of n-acetyl cysteine (NAC), an antioxidant, prior to TNF- α treatment, abolished TNF- α -induced ROS generation. NAC abolished TNF-α -induced NF- κ B activation and hypertrophic responses. These findings indicated that TNF-α -induced cardiomyocyte hypertrophy is mediated through NF- κ B activation via the generation of ROS.