Abstract 24047: G Protein-coupled Receptor Kinase 2 Negatively Regulates Fatty Acid Utilization and Mitochondrial Bioenergetics

Abstract

During cardiac injury or stress, G protein-coupled receptor (GPCR) kinase 2 (GRK2) expression levels and activity are increased, leading to a desensitization of myocardial β-adrenergic receptors (βARs) and contributing to the loss of contractile reserve. Up-regulated GRK2 has been shown to be pathogenic in the post-injured heart and is involved in the promotion of heart failure (HF). There is evidence that GRK2 has other, non-GPCR dependent pathological functions within cardiomyocytes. For example, GRK2 localizes to the mitochondria following oxidative stress, where it acts as a pro-death kinase and decreases fatty acid utilization. As metabolic substrate utilization and bioenergetics are key parameters in the maintenance of cardiomyocyte contractility, our objective is to examine the role of GRK2 on metabolism and bioenergetics in the adult heart. We hypothesize that desensitization of βARs via an increase in GRK2 will result in decreased fatty acid-fueled respiration and will compromise cardiomyocyte function. Conversely, ablation of GRK2 will result in increased respiration and function, under these conditions. Our results show that basal respiration, maximal respiration, and reserve respiratory capacity (RRC) are highest in the presence of palmitate versus glucose (1.6, 3, and 7.2-fold, respectively), accompanied by increased (1.3-fold) ATP levels. Moreover, basal and maximal respiration was decreased (1.6 and 1.2-fold, respectively) cardiomyocytes isolated from cardiac-specific GRK2 transgenic mice. This correlates with a decrease in ATP levels and in vivo cardiac fatty acid uptake (1-fold and 1.6-fold, respectively). Conversely, cardiomyocytes isolated from βARKct, a peptide inhibitor of GRK2, transgenic mice or GRK2 knockout mice, show increased maximal respiration (1.5 and 1.4-fold, respectively) and RRC (2.7 and 2.2-fold, respectively) with fatty acids. This correlates with an increase in ATP levels (1.2-1.9-fold). Thus, we propose that increased GRK2, as seen during heart failure, compromises fatty acid-driven mitochondrial respiration, while GRK2 inhibition under these conditions enhances RRC, which is known to improve cellular survival during stress.