AHA Postdoc Sumeyye Yar:The role of an mRNA binding protein, tristetraprolin (TTP), in the regulation of cardiac branched-chain amino acid (BCAA) catabolism

Heart failure (HF) is a major health epidemic in developed countries, however, its underlying pathology is not well characterized. Tristetraprolin (TTP, originally discovered to be regulated by insulin) is a tandem zinc finger protein that binds to AU-rich elements (ARE) in the 3’-untranslated region (UTR) of target mRNA molecules, and induces their degradation. TTP knockout (KO) mice display systemic inflammation due to its role in the degradation of TNFα mRNA, thus very few studies have assessed the role of TTP in metabolism. We recently showed that TTP regulates cellular iron by conserving this metal for essential proteins. In addition, our recent studies suggest that TTP regulates branched-chain amino acid (BCAA) metabolism, and binds to and regulates the mRNA of a key enzyme in this process; branched-chain α–ketoacid acid dehydrogenase complex (BCKDC)-E2 subunit. Furthermore, we demonstrated that TTP regulates lipoic acid (LA) synthase (LIAS), the rate-limiting enzyme in LA synthesis, which is essential for BCKDC activity. The central hypothesis of this proposal is that TTP regulates cardiac BCAA metabolism through LA-dependent and –independent pathways, the latter mediated by its regulation of BCKDC. We also propose that deletion of cardiac TTP is protective against the development of HF due to its effects on BCAA metabolism. In Aim 1, we will determine whether TTP decreases BCAA catabolism through degradation of BCKDC-E2 mRNA and through decreasing its lipoylation. We will use cardiac cells with TTP KD and heart tissue from global and cardiac-specific (cs) TTP-KO mice, and will assess their cardiac and systemic BCAA levels. To demonstrate whether changes in BCAA with TTP KO are through LIAS and/or BCKDC-E2, we will perform similar studies with TTP KD and BCKDC-E2 or LIAS KD in vitro. We will also assess whether TTP directly binds to and regulates BCKDC-E2 and LIAS. In Aim 2, we will determine whether TTP plays a role in the development of HF and whether this is dependent on BCAA metabolism. We will subject global and csTTP-KO mice and their littermate controls to pressure overload and coronary ligation and will assess their cardiac function and metabolism. Furthermore, to determine the role of BCKDC in this process, we will cross csTTP-KO mice with protein phosphatase 2Cm KO mice (which have reduced BCKDC activity), and will assess cardiac response to pressure overload or ischemia.