Abstract 112: Cardiac-specific Constitutive Activation of Nrf2 Induces Reductive Stress and Pathological Cardiac Remodeling

Abstract

Background: Heart failure is a growing cause of human morbidity and mortality. Supplementations of free radical scavenging antioxidants have largely failed to protect the myocardium from oxidative stress diseases. While endogenous transcriptional activation of antioxidants appears to be promising, their chronic effects are unknown. Here, we tested a hypothesis that chronic activation of antioxidant system will result in reductive stress (RS) and lead to pathological cardiac hypertrophy. Methods: Novel transgenic (TG) mice expressing constitutively active Nrf2 in the heart (α-MHC-caNrf2-TG) and their littermates were used to study the effects on structure and function of the myocardium. Myocardial glutathione redox state (GSH/GSSG), transcript levels (qPCR), and protein (immunoblotting) for Nrf2-related antioxidants and structure and function analysis (echocardiography - Vevo2100 Imager) in Non-transgenic (NTg), TG-low and TG-high mice (n=6-12/gp.) were performed at 6-8 months of age. Further, changes in cardiomyocytes and rate of survival in TG mice were analyzed. Results: Kaplan-Meier survival plots demonstrated 10 and 40% mortality in TG-low and TG-high, respectively, compared to NTG by 60 weeks of age. The myocardial glutathione and its redox ratio (GSH/GSSG) were significantly increased (p<0.05) in the TG-low and TG-high compared with NTg mice indicates development of RS. A significant increase in Nrf2-ARE (promoter) binding with increased expression of antioxidant genes and proteins (p<0.05) were noted in TG vs. NTg mice. Increased heart-to-body weight and heart weight to tibia length ratios were prominent in TG-high relative to NTg or TG-low mice. Histological analyses (WGA, H&E staining) showed increased cardiomyocyte size, ventricular wall thickening and decreased chamber volume in TG mice. Echocardiography analyses revealed significant hypertrophic cardiomyopathy with abnormally increased ejection fraction (HCM i EF) due to chronic reductive stress. Conclusion: Thus, basal attenuation of the obligatory oxidative signaling with chronic activation of Nrf2-antioxidants could shift the redox equilibrium to “reductive” side and thereby causing pathological cardiac remodeling.