Role of Extracellular Long-Chain Acyl-carnitines in the Normal and Stressed Heart - PROJECT SUMMARY Heart failure (HF) is a significant cause of cardiovascular-related death in the United States, with its incidence increasing by over 40% when accompanied by obesity. The obese-HF phenotype is particularly common in HF with a preserved ejection fraction, a major unmet medical need. The adverse interaction between obesity and HF appears due, in part, to compromised myocardial metabolic fuel availability and flexibility. The heart's high energy demand relies on ATP, mostly derived from FFA oxidation in mitochondria. Long chain fatty acids (LCFA), which have over 12 carbons, are transported into mitochondria for beta oxidation through the acyl-carnitine cycle. Our recent study found marked reductions in myocardial medium and long chain acyl-carnitines in human HF as compared to controls, yet corresponding plasma levels were normal or elevated. This raises the question of whether extracellular acylcarnitines (ex-ACs) can be taken up from plasma by the heart to be used for fuel, and if in HF this process is diminished. In new preliminary data, I now show there is lower expression of the plasma membrane LCFA transporters (CD36, FATP3) and the protein needed to add carnitine to the FA (carnitine palmitoyltransferase 1b, CPT1b). Whether this plays a key role in impeding ex-AC uptake by the myocytes or the heart, and the fate of any ex-AC that is internalized is unknown. This project tests the hypothesis that ex-ACs are taken up and undergo beta- oxidation by myocytes in vitro to contribute to ATP synthesis, O2 consumption, and CO2 generation. The studies explore the fate of ex-ACs in cardiomyocytes and their utilization in both normal and stressed cells and hearts. In Aim 1, I test the hypothesis that ex-ACs are taken up by cardiomyocytes via the critical membrane transporter CD36, or if not, by another currently unknown transporter, and once taken up they undergo beta oxidation. These studies utilize radiolabeled (14C) and heavy labeled (13C) palmitoyl-carnitine and oleoyl-carnitine, each contrasted to their FFA form (palmitic acid and oleic acid) to determine cellular uptake and beta oxidation. The role of critical transporters, carnitine modulators/recyclers are tested using pharmacological or genetic based loss of function studies. In Aim 2, I explore the fate of ex-AC in vivo, comparing normal mice to those under acute and chronic pressure overload via transverse aortic constriction (TAC). I will further examine the addition of a metabolic stress induced by chronic high fat diet. To understand the uptake and processing in vivo, I will inject 13C labeled acyl-carnitines into the bloodstream and measure organ specific uptake and downstream catabolic incorporation of the labeled carbon (e.g into Krebs cycle intermediates). My goal is to understand the mechanisms and metabolic consequences of ex-AC pertinent to cardiomyocyte metabolism, with the ultimate hope of enhancing their use as fuel in heart failure. This research may provide insights to address the major unmet medical needs in HF, particularly in the context of obesity and HFpEF.
