Role of SNRK in cardiac metabolism and development of heart failure

Heart failure (HF) is a major cause of morbidity and mortality in the developed world, but the molecular mechanisms that lead to the development of HF are not totally understood. Mammalian Snf1-related kinase (SNRK) is a serine/threonine kinase with sequence similarity to AMP-activated kinases (AMPK); however, its primary function is unknown. To better define the function of SNRK in cardiac metabolism, we have generated a transgenic (TG) mouse that overexpresses SNRK in the heart. SNRK TG mice display 30-50% less glucose and fatty acid (FA) oxidation and have reduced oxygen consumption despite maintaining normal cardiac function, suggesting that they are more efficient in substrate utilization. The mechanism for metabolic efficiency appears to be through improved mitochondrial coupling, as the levels of uncoupling protein (UCP) 3 are reduced in SNRK TG mice, and state 3/state 4 respiration is increased. To determine the mechanism by which SNRK regulates mitochondrial coupling, we performed a yeast two hybrid screen to identify novel binding partners of SNRK. Tribbles homolog 3 (Trib3), a negative regulator of Akt activation and glucose metabolism, was found to bind to and be upregulated by SNRK. We also showed that SNRK regulates UCP3 and mitochondrial coupling through a pathway that involves Trib3 and PPARα. The central hypothesis of this proposal is that SNRK affects cardiac metabolism by reducing substrate utilization and increasing mitochondrial coupling, and that SNRK overexpression protects against the development of HF through its effects on cardiac metabolism. In Aim 1, we will assess whether SNRK knockout (KO) mice (which we have generated in our lab) will have the opposite phenotype of the TG mice, i.e., increased glucose and FA metabolism with similar cardiac force. We will also assess the role of Trib3, UCP3 and PPARα in this process. In Aim 2, we will test whether the reduced glucose and FA metabolism that occurs in the hearts of SNRK TG mice is mediated through Trib3. We will cross SNRK TG mice with Trib3 KO mice, followed by measurement of glucose and FA metabolism. We will also investigate the mechanism of post-translational regulation of Trib3 by SNRK. Finally, in Aim 3, we hypothesize that SNRK is protective against the development of HF and ischemic damage, and will determine the mechanism for this protective effects. We will subject SNRK TG mice to ischemia-reperfusion and pressure overload, followed by the measurement of cardiac function and reactive oxygen species (ROS) production. To determine the mechanism, we will assess the role of Trib3/PPAR/UCP3 pathway in this process both in vitro and in vivo. Our studies showing that SNRK reduces FA and glucose metabolism and improves mitochondrial coupling promise to advance our knowledge of the role of cardiac metabolism in HF, and may lead to the development of novel therapies for this disorder.