Role of tristetraprolin in cardiac fatty acid metabolism and development of heart failure

Heart failure (HF) is a major cause of morbidity and mortality in the developed world, and despite recent advances, its prevalence continues to grow. Thus, it is crucial to devise new and effective therapies for this disorder. HF is associated with perturbations in cardiomyocyte energy metabolism, including defects in fatty acid (FA) metabolism. Tristetraprolin (TTP) is a tandem zinc finger protein that binds to AU-rich elements (ARE) in the 3’-untranslated region (UTR) of target mRNA molecules, resulting in their degradation. It was originally discovered in 1990 as a protein induced by insulin, however, global TTP knockout (KO) mice displayed systemic inflammatory disease (due to TTP regulation of TNFα mRNA). Thus, very few studies have focused on the role of TTP in metabolism, despite genetic studies linking TTP to metabolic syndrome in humans. Our recent results suggest that TTP levels are increased in HF, and that it regulates FA oxidation in cardiomyocytes. Our mechanistic studies suggest that TTP-mediated regulation of FA metabolism may be through TTP binding and degradation of peroxisome proliferator-activated receptors (PPAR)-α mRNA. The objective of this proposal is to elucidate the role of TTP in the regulation of FA metabolismin the heart, and its role in the development of HF through its regulation of cardiac FA metabolism. Our central hypothesis is that TTP regulates cardiac FA metabolism through downregulation of PPARα, and that it exacerbates the development of HF by downregulating FA metabolism. We propose two aims to explore our hypothesis (Fig): Specific Aim 1: To determine whether TTP regulates cardiac lipid metabolism through its regulation of PPARα. Our results show that TTP deletion in cardiomyocytes results in an increase in PPARα and FA uptake and metabolism. In this Aim, we hypothesize that TTP directly alters cardiac FA homeostasis through a PPARα–dependent pathway. To test this hypothesis, we will first determine whether TTP directly interacts with PPARα by performing deletion studies of the 3’-UTR AREs within PPARα, and RNA co-immunoprecipitation (co-IP) of TTP with PPARα. We will also study the effects of TTP deletion on cardiac FA metabolism in isolated hearts from cardiac specific TTP KO (csTTP-KO) mice by performing metabolic studies in an ex vivo heart perfusion setup. To determine whether changes in lipid homeostasis are mediated through PPARα, we will simultaneously knockdown (KD) PPARα and TTP, followed by measurement of changes in FA metabolism. Specific Aim 2: To determine whether TTP plays a role in the development of HF and whether this is dependent on its effects on FA metabolism. Our preliminary data indicate that global TTP KO mice have improved cardiac function after TAC. We hypothesize that TTP deletion protects against the development of HF through its regulation of FA metabolism. To test this hypothesis, we will subject csTTP-KO mice to pressure overload and coronary ligation, and will assess cardiac function. To determine the role of PPARα, we will cross TTP-KO mice with PPARα KO mice (which we have available in our lab), and will assess cardiac response to pressure overload or ischemia. Similar mechanistic studies will be done in isolated cardiomyocytes, and cell death and reactive oxygen species production will be measured. The major goal of this proposal is to elucidate the role of TTP in FA metabolism and to characterize the mechanism for these regulations. The proposed experiments are a logical and compelling sequence of experiments designed to follow up on our key observati