NOX4-driven mitochondrial oxidative stress in aging promotes myocardial remodeling and increases susceptibility to...

Aging-associated mitochondrial oxidative stress has been implicated in ventricular tachyarrhythmias (VT), but the specific proarrhythmic mechanisms of mitochondrial pro-oxidative systems remain unclear. NADPH oxidase 4 (NOX4) expression in the heart increases with age, leading to mitochondrial oxidative stress, dysfunction, and adverse myocardial remodeling. This study investigated the susceptibility to aging-associated ventricular arrhythmia and the associated triggers and substrates using transgenic mice with mitochondria-targeted Nox4 overexpression (Nox4TG mice). Nox4TG mice showed a significantly higher incidence of pacing-induced VT, associated with shorter action potential duration (APD) due to increased transient outward potassium currents. Fractional sarcoplasmic reticulum (SR) Ca²⁺ release and Ca²⁺ leak remained intact despite these changes. However, the frequency of Ca²⁺ sparks was reduced, and ryanodine receptor 2 (RyR2) oxidation was observed. Compensatory upregulation of SERCA expression in response to RyR2 inhibition accelerated SR Ca²⁺ reuptake and improved cardiomyocyte mechanical relaxation. Nox4TG mice exhibited extensive ventricular fibrosis and marked pro-inflammatory macrophage infiltration, with elevated TNF, TGF-β, and MKI67 expression. Treatment with Setanaxib, a NOX1/NOX4 inhibitor, or co-expression of mitochondrial catalase in Nox4TG (Nox4TG + mCAT) mice, mitigated fibrosis, reduced inflammation, and protected against VT. These findings suggest that mitochondrial NOX4 overexpression promotes VT through electrical remodeling and pro-arrhythmogenic structural changes despite RyR2 oxidation and dysfunction. In conclusion, aging-related NOX4-driven mitochondrial oxidative stress increases the risk of VT by promoting changes in the electrical and structural properties of the myocardium, highlighting potential therapeutic strategies that target NOX4 in cardiac pathologies associated with aging.