Abstract 323: Overexpression of Coupling Factor 6 Causes Salt-Induced Congestive Heart Failure by Tissue Acidosis-Mediated Reactive Oxygen Species

Reactive oxygen species (ROS) is associated with the development of congestive heart failure (CHF) in animals and humans. We have showed that coupling factor (CF6), a component of ATP synthase, suppresses prostacyclin and nitric oxide generation by intracellular acidosis, which is closely related to the generation of ROS and CHF. On the other hand, high salt intake, one of the most important factors to initiate and exacerbate CHF, increases ROS generation. We thus investigated the role of CF6 in the genesis of CHF by using transgenic mice (TG) overexpressing CF6 and exposing them to high-salt diet. In TG, the introduced gene of human CF6 was expressed in overall tissues including the heart, and upregulated by 2 fold. Baseline echocardiographic data, ROS generation, protein expression of sarcoplasmic/endoplasmic reticulum of Ca 2+ -ATPase (SERCA)-2, associated with cardiac muscle relaxation, and phospholamban, and the gene expression related to ATP synthesis and glycolysis, and the genes α- and β-MHC in the heart were similar between 7-week-old TG and wild type mice (WT). When the mice were fed with high-salt diet (8% salt) for 20–24 weeks, fractional shortening of the left ventricle was decreased in TG compared to WT (29±3% vs 39±2%, p< 0.05). The protein expression of SERCA-2 was decreased by 90±29% in TG compared with WT, whereas that of phospholamban, an inhibitor of SERCA-2, was increased by 141±31% in TG (both p< 0.05). In cDNA microarray analysis of the heart, the genes related to ATP synthesis, such as ATP synthase (0.29±0.10 fold) and cytochrome C (0.30±0.04), and those related to glycolysis were decreased in TG mice (all p< 0.05). The gene expression of β-MHC as the fetal isoform of MHC was increased in TG heart, whereas that of α-MHC as the adult isoform was unchanged. The myocardial level of 8-iso-prostaglandin F 2α , a marker of ROS generation, was increased by 83±31% in TG compared with WT (p< 0.05). The mortality rate at the period of 35 weeks was greater in TG (7/14 (50%)) than in WT (1/13 (8%)) (p< 0.05 by log rank test), although neither TG nor WT were dead under normal salt diet. These suggest that CF6 induces the development of mitochondrial dysfunction and systolic and diastolic dysfunction, and eventually causes CHF by enhancing of ROS generation.