Overexpression of NOX2 Exacerbates AngII-Mediated Cardiac Dysfunction and Metabolic Remodelling

Abstract

The present study aimed to examine the effects of low doses of angiotensin II (AngII) on cardiac function, myocardial substrate utilization, energetics, and mitochondrial function in C57Bl/6J mice and in a transgenic mouse model with cardiomyocyte specific upregulation of NOX2 (csNOX2 TG). Mice were treated with saline (sham), 50 or 400 ng/kg/min of AngII (AngII₅₀ and AngII₄₀₀) for two weeks. In vivo blood pressure and cardiac function were measured using plethysmography and echocardiography, respectively. Ex vivo cardiac function, mechanical efficiency, and myocardial substrate utilization were assessed in isolated perfused working hearts, and mitochondrial function was measured in left ventricular homogenates. AngII₅₀ caused reduced mechanical efficiency despite having no effect on cardiac hypertrophy, function, or substrate utilization. AngII₄₀₀ slightly increased systemic blood pressure and induced cardiac hypertrophy with no effect on cardiac function, efficiency, or substrate utilization. In csNOX2 TG mice, AngII₄₀₀ induced cardiac hypertrophy and in vivo cardiac dysfunction. This was associated with a switch towards increased myocardial glucose oxidation and impaired mitochondrial oxygen consumption rates. Low doses of AngII may transiently impair cardiac efficiency, preceding the development of hypertrophy induced at higher doses. NOX2 overexpression exacerbates the AngII -induced pathology, with cardiac dysfunction and myocardial metabolic remodelling.

Keywords: NOX2; angiotensin II; cardiac disease; cardiac efficiency; cardiac hypertrophy; hypertension.

Figure 1

Mechanical efficiency (A–C), myocardial oxygen consumption in mechanically unloaded hearts (MVO_2unloaded, D–F) and MVO₂ for processes associated with excitation-contraction coupling (MVO_2ECC, G–I), measured in isolated perfused hearts from C57BL/6J, wild-type (WT), and csNOX2 transgenic (TG) mice treated for two weeks with micro-osmotic pumps containing either saline (sham), 50 or 400 ng/kg/min angiotensin II (AngII₅₀ and AngII₄₀₀). The data are presented as mean ± SEM. * p < 0.05 vs. sham.

Figure 2

Palmitate (A–C) and glucose (D–F) oxidation rates assessed in isolated working hearts from C57BL/6J, wild-type (WT), and csNOX2 transgenic (TG) mice treated for two weeks with micro-osmotic pumps containing either saline (sham), 50 or 400 ng/kg/min angiotensin II (AngII₅₀ and AngII₄₀₀). The data are presented as mean ± SEM. * p < 0.05 vs. WT.

Figure 3

Oxygen consumption rate measured in homogenate from frozen left ventricular heart tissue from C57BL/6J, wild-type (WT), and cardiomyocyte specific NOX2 transgenic (TG) mice treated for two weeks with micro-osmotic pumps containing either saline (sham), 50 or 400 ng/kg/min angiotensin II (AngII₅₀ and AngII₄₀₀). (A) Sham and AngII₅₀. (B) Sham and AngII₄₀₀. (C) WT AngII₄₀₀ and TG AngII₄₀₀. Basal, homogenate with cytochrome C; Complex I (CI), homogenate and NADH; Complex II (CII) is homogenate with rotenone (CI-blocker) and succinate; Residual Oxygen consumption (ROX), homogenate with malonate (CII-blocker) and antimycin A (CIII-blocker). Data are means ± SEM. * p < 0.05 vs. WT.