Impaired cardiac BCAA catabolism associated with impaired myocardial efficiency during exercise in a porcine model with multiple risk factors

Abstract

Abstract Background Diabetes mellitus (DM), chronic kidney disease (CKD) and consumption of a high-fat diet (HFD), are well known risk factors for diastolic heart failure. We recently developed a multiple comorbidity swine model (MCS), with DM (streptozotocin), HFD and CKD (kidney embolization), and showed that 6 months of sustained hyperglycemia, hypercholesterolemia and kidney dysfunction resulted in inflammation and oxidative stress associated with coronary microvascular dysfunction and left ventricular diastolic dysfunction. Additionally, MCS animals showed impaired myocardial efficiency during exercise as demonstrated by increased myocardial oxygen consumption (Fig. A), suggesting an impairment in myocardial mitochondrial function. Purpose Here we used a combined omics (single nuclei RNA sequencing and proteomics) approach to study the molecular pathways involved in mitochondrial dysfunction. Methods 15 MCS and 10 healthy control female swine were included in the study. Proteome analysis and single nuclei RNA sequencing, was performed on frozen left ventricle myocardial samples. Results Proteome analysis of MCS hearts showed reduced expression of branched-chain amino acid (BCAA) catabolism proteins (Fig. B), most notably BCAT2, MCCC1 and MCCC2. Single nuclei RNA sequencing of a subgroup of the same animals demonstrated a downregulation of these genes specifically in cardiomyocyte subpopulations. Besides being a source of ATP, via oxidative phosphorylation in mitochondria, BCAAs, encompassing essential amino acids (leucine, valine and isoleucine), act as signaling molecules. Thus, increased BCAA levels reduce insulin sensitivity, modulate mitochondrial substrate utilization and impair mitochondrial function, resulting in increased mitochondrial production of reactive oxygen species (ROS). These findings are consistent with our data in the MCS swine indicating that impaired BCAA metabolism was found in the myocardium of animals with comorbidities and were associated with increased ROS levels (8-isoprostane 12.9±0.8 pg/mg protein in MCS vs 10.3±0.5 in healthy animals, P=0.02 by T-test) and impaired myocardial efficiency during exercise (Fig. A). Conclusion Taken together, these findings suggest an essential role of altered BCAA cardiomyocyte metabolism resulting in mitochondrial dysfunction, increased oxidative stress and subsequent alterations in the myocardial function.Fig.