Activation of skeletal muscle Nrf2 protects the heart against ischemia-reperfusion injury in male mice

Introduction Physical activity is associated with protection against myocardial ischemia-reperfusion (I/R) injury, and activation of nuclear factor erythroid 2-related factor 2 (Nrf2) is one exercise-responsive pathway in skeletal muscle (SkM). The present study specifically tested the hypothesis that selective genetic activation of SkM Nrf2 improves acute myocardial tolerance to I/R. Methods Experiments were carried out using iMS- Keap1 f l o x / f l o x mice, a transgenic animal where the Nrf2-antioxidant system is selectively activated/enhanced in SkM by knockout (KO) Keap1. Under isoflurane anesthesia, a Millar pressure transducer was advanced into the left ventricular (LV) cavity to continuously record hemodynamics throughout 60 min of ischemia and 60 min of reperfusion; cardiac contractility index (CCI) and Tau were used to assess systolic and diastolic function. Myocardial infarction was quantified by TTC staining. In a separate cohort not subjected to I/R, NQO1, SOD2, and Nrf2 protein abundance was assessed by Western blot in soleus muscle, LV myocardium, and ultracentrifugation-derived plasma particle fractions, and myocardial proteomics was performed. Results Our results show that SkM-specific Keap1 deletion increased Nrf2 protein in SkM but not in myocardium. Ischemia impaired LV function in both WT and KO mice, whereas reperfusion produced further deterioration in WT but partial recovery of systolic and diastolic function in KO mice. Infarct size was also smaller in KO mice as compared with the WT control. NQO1 and SOD2 abundance was increased in SkM, plasma particle fractions, and myocardium of KO mice. Exploratory myocardial proteomics identified basal genotype-associated differences involving oxidative stress, energy metabolism, and cell-adhesion/cytoskeletal pathways. Discussion SkM-specific Nrf2 activation is therefore associated with improved acute myocardial tolerance to I/R and with increased antioxidant protein abundance in SkM, plasma particle fractions, and myocardium. Circulating extracellular particles are possible mediators of this association, but their tissue of origin, cargo localization, myocardial uptake, and functional contribution remain unproven. New & noteworthy Selective genetic activation of skeletal muscle Nrf2 was associated with smaller myocardial infarcts and improved LV systolic and diastolic function during acute I/R in male mice. In a separate non-I/R cohort, NQO1 and SOD2 abundance was increased in skeletal muscle, ultracentrifugation-derived plasma particle fractions, and myocardium. These findings identify a basal systemic phenotype associated with skeletal muscle Nrf2 activation; circulating extracellular particles remain possible, but unproven, mediators.