Abstract 13114: P22 phox Protects the Heart Against Pressure Overload

Abstract

Introduction: p22 phox forms a complex with NADPH oxidases, major sources of O 2 - and H 2 O 2 . However, the role of p22 phox during stress remains to be elucidated. Purpose: To investigate the role of endogenous p22 phox during pressure overload (PO). Methods and Results: The level of p22 phox protein in isolated cardiomyocytes after 4 weeks of transverse aortic constriction (TAC) was significantly higher than after sham operation (1.7-fold, p<0.05). The cardiac phenotype of cardiac-specific p22 phox knockout ( p22 phox cKO) mice was normal at baseline. However, four weeks after TAC, p22 phox cKO mice exhibited a lower left ventricular ejection fraction (32.0±10.0 vs 53.2±8.4%, p<0.05), a higher lung weight to tibial length ratio (23.0±6.0 vs 13.1±6.6, p<0.05), and more interstitial fibrosis (6.1±1.0 vs 4.4±1.1%, p<0.05) than control mice, indicating that the loss of p22 phox exacerbates TAC-induced cardiac dysfunction. The level of oxidative stress in the heart, evaluated by dityrosine immunoblot, was significantly lower in p22 phox cKO mice than in control mice (0.71±0.04 vs 1.00±0.04, p<0.01). The peak Ca 2+ amplitude in isolated cardiomyocytes was lower in p22 phox cKO mice than in control mice at baseline (2.4±0.1 vs 3.0±0.2, p<0.01). Although mRNA expression of SERCA2a did not differ, there was significantly less SERCA2a protein in p22 phox cKO mice than in control mice (0.62±0.10 vs 1.00±0.23, p<0.01) at baseline. The amount of biotinylated iodoacetamide labeled SERCA2a was significantly smaller in p22 phox cKO hearts than in control mouse hearts (0.4-fold, p<0.01), indicating that cysteine residues in SERCA2a are oxidized to a greater extent in p22 phox cKO hearts than in control mouse hearts. Since cysteine oxidation decreases the stability of SERCA2a, our results suggest that p22 phox stabilizes SERCA2a by preventing cysteine oxidation. Conclusions: Endogenous p22 phox is protective against PO, possibly by maintaining SERCA2a stability.