Knockdown of ANGPTL2 promotes cardiac left ventricular dysfunction in mice via up‐regulation of NOX4

Introduction Angiopoietin‐like 2 (ANGPTL2) is a pro‐inflammatory and pro‐oxidative glycoprotein that induces vascular endothelial dysfunction in mice and promotes atherosclerosis. Higher circulating levels of ANGPTL2 have been reported in patients with heart failure, but the potentially deleterious effect of ANGPTL2 on cardiac function is ill defined. Our aim was to investigate the cardiac function of adult mice knockdown for angptl2 (KD mice). Hypothesis Based on the available data in the literature, we hypothesized that KD for angptl2 would be cardioprotective. Methods Cardiac function was measured by high frequency echocardiography in adult 7‐month old KD and wild‐type (WT) littermates. Gene expression was measured by quantitative RT‐PCR. Results In contrast to our hypothesis, when compared to WT mice (n=32), KD mice (n=31) exhibited a left ventricular (LV) systolic dysfunction, characterized by a reduced fractional shortening (35.8±1.0 vs 32.2±1.2%, p<0.05), a reduced ejection fraction (71.6±1.3 vs 66.4±1.8%, p<0.05), a lower lateral (2.3±0.1 vs 2.1±0.1 cm/s, p<0.05) and septal (2.5±0.1 vs 2.2±0.1 cm/s, p<0.05) contractility. This LV systolic dysfunction observed in KD mice was reproduced in WT mice exposed to a cardiac pressure overload generated by transverse aortic constriction (TAC); in KD mice, TAC did not further alter cardiac function. Interestingly, we observed that cardiac NADPH oxidase Nox4 mRNA expression tended to be higher in KD mice (+13%, p>0.05). NOX4 is known to produce H 2 O 2 , a deleterious hypertrophic stimulus in cardiomyocytes. Cardiac Nox4 was strongly and negatively correlated with fractional shortening (r=−0.836, p<0.001) and ejection fraction (r=−0.839, p<0.001) in KD mice only (sham and TAC mice, n=15), i.e. the higher Nox4 , the worse LV dysfunction. In contrast, Nox4 expression was not correlated with markers of LV dysfunction in WT mice (sham and TAC, n=12; p>0.05). We then tested the effects of repressing, or not, cardiac expression of Nox4 by a single injection of cardiac specific associated adenovirus AAV9 delivering a NOX4 targeted shRNA (shNOX4) or a scramble shRNA (SCR), in both WT and KD mice. The shNOX4, which significantly reduced cardiac Nox4 mRNA expression (‐34%, p<0.05), fully reversed LV systolic dysfunction in KD mice (Table ). In contrast, in WT mice AAV9‐shNOX4 had no effect (Table ). Conclusion Knockdown of ANGPTL2 promotes LV systolic dysfunction that can be reversed by the decrease of NOX4 expression in the heart of KD mice. Support or Funding Information This work was funded by grants from the Canadian Institutes of Health Research (PJT‐162446) and by the Foundation of the Montreal Heart Institute. WT‐SCR (n=5) KD‐SCR (n=7) WT‐shNOX4 (n=8) KD‐shNOX4 (n=5) Fractional shortening (%) 38.6±2.8 27.7±1.7 35.3±1.8 37.4±2.4 Ejection fraction (%) 74.9±3.5 60.1±2.7 71.1±2.2 73.7±3.0 Lateral contractility (cm/s) 2.5±0.1 1.7±0.1 2.4±0.1 2.3±0.1 Septal contractility (cm/s) 2.7±0.1 2.0±0.1 2.6±0.1 2.7±0.1

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