Abstract 12526: Snf1-related Kinase Improves Cardiac Mitochondrial Efficiency by Decreasing Mitochondrial Uncoupling

Abstract

Introduction: Ischemic heart disease limits oxygen and metabolic substrate availability to the heart, resulting in cardiac tissue death. Snf1-related Kinase (SNRK) is a serine/threonine kinase with sequence similarity to AMP-activated protein kinase, but its function is unknown. We found that SNRK is increased in hearts from patients with ischemic cardiomyopathy, and our gene array data suggested that SNRK alters metabolic genes. Here, we assessed the hypothesis that SNRK improves cardiac metabolic efficiency and mitochondrial uncoupling, and protects against ischemia/reperfusion (I/R) injury. Results: Cardiac-specific SNRK transgenic (TG) mice displayed decreased glycolysis, glucose oxidation, and palmitate oxidation compared to wild type littermate controls in perfused working hearts. However, cardiac power, contractility, ATP, and triglyceride and glycogen stores were maintained, while oxygen consumption was reduced, demonstrating that SNRK TG mice have increased cardiac metabolic efficiency. Consistent with improved cardiac metabolic efficiency, SNRK TG mice exhibited decreased infarct size after I/R. Mitochondria from SNRK TG mice also had reduced respiration, and increased respiratory control ratio and mitochondrial membrane potential, indicating reduced mitochondrial uncoupling. Uncoupling protein 3 (UCP3) levels were also decreased. Conversely, hearts from heterozygous SNRK knockout mice had increased glucose and palmitate oxidation and UCP3. SNRK knockdown in cardiac cells decreased mitochondrial efficiency, which was abolished with UCP3 knockdown. To determine the mechanism for the regulation of UCP3 by SNRK, we performed yeast two-hybrid assay, and identified tribbles homolog 3 (Trib3) to bind to SNRK. Furthermore, Trib3 enabled downregulation of UCP3 by downregulating the expression of PPARα. Conclusions: Our results demonstrate that overexpression of SNRK decreases cardiac metabolic substrate usage and oxygen consumption but maintains cardiac function and enhanced mitochondrial coupling. We also identify a binding partner of SNRK, Trib3, which is upregulated by SNRK in mice and mediates the regulation of PPARα and UCP3 by SNRK.