Metabolic pathways in cardiac physiology and heart failure

PROJECT SUMMARY - ABSTRACT Central to the development of HF are derangements in cardiac metabolism and a shift in fuel utilization. A recent clinical report of arterial/coronary sinus metabolomics identified glutamine as the most abundant metabolite released from the failing heart (i.e., production of glutamine rather than catabolism). Glutamine metabolism is directly linked to bioenergetics, mitochondrial function, redox state, nitrogen balance, and the biosynthesis of nucleic acids and proteins. Furthermore, we’ve recently shown that glutaminolysis is necessary for myofibroblast differentiation and persistence, that underlies cardiac fibrosis. Coupled together, these findings directed us to investigate if cardiomyocyte (CM) glutamine production plays a pivotal role in fibroblast activation and cardiac fibrosis. In preliminary data generated for the current proposal, we found an appreciable level of CM glutamine production during stress. Further, we discovered a significant increase in the expression of glutamine synthetase (GS; glutamate➞glutamine; GLUL gene) and numerous glutamine transporters in models of HF and in HF patients. These findings support the concept of enhanced CM glutamine production, and excretion in the stressed heart. To test the role of GS in cardiac pathophysiology, we generated a CM- specific, tamoxifen-inducible knockout model (GSfl/fl x αMHC-iCre; GS-cKO) and subjected mice to pressure- overload-induced HF (TAC). Loss of CM glutamine synthesis preserved LV structure and function and strikingly decreased fibrotic remodeling. In summation, our results suggest paracrine metabolite signaling from CMs may be a primary mechanism for fibroblast activation in the diseased heart. In addition to changes in fibroblast activation and ECM deposition, we also noted changes in CM metabolism, including increased mitochondrial respiratory capacity. In this project we will test the central hypothesis that targeting cardiomyocyte glutamine synthesis is a multipronged therapeutic strategy to increase bioenergetics, restore redox balance, and reduce fibroblast activation and fibrosis in HF. 1) We will examine if targeting CM glutamine synthesis reduces HF development, HFrEF and HFpEF models. 2) Determine if CM-derived glutamine is a signal/fuel for fibroblast activation, proliferation and myofibroblast differentiation/identity in the stressed heart. 3) Define the impact of targeting glutamine synthetase on cardiomyocyte metabolism, energetics, redox, and nitrogen balance. All models and methodologies for the proposal have been generated and validated. The proposed studies will allow for the first-time a causal examination of glutamine synthesis in cardiac physiology and disease.