Mitochondrial NNT promotes diastolic dysfunction in cardiometabolic Heart Failure with Reduced Ejection Fraction (HFpEF)

Clinical management of heart failure with preserved ejection fraction (HFpEF) is hindered by a lack of disease-modifying therapies capable of altering its distinct pathophysiology. Despite the widespread implementation of a “two-hit” model of cardiometabolic HFpEF to inform precision therapy, which utilizes ad libitum high-fat and 0.5% N(ω)-nitro-L-arginine methyl ester (HFD+L-NAME) diet, we observe that C57BL6/J mice exhibit less cardiac diastolic dysfunction in response to HFD+L-NAME. Genetic strain-specific single-nucleus transcriptomic analysis identified disease-relevant genes that enrich oxidative metabolic pathways within cardiomyocytes. Because C57BL/6J mice are known to harbor a loss-of-function mutation affecting the inner mitochondrial membrane protein nicotinamide nucleotide transhydrogenase (Nnt), we used an isogenic model of Nnt loss-of-function to determine whether intact NNT is necessary for the pathological cardiac manifestations of HFD+L-NAME. Twelve-week-old mice cross-bred to isolate wild-type (Nnt+/+) or loss-of-function (Nnt-/-) Nnt in the C57BL/6N background, were challenged with HFD+L-NAME for 9 weeks (n = 6-10). Nnt+/+ mice exhibited impaired ventricular diastolic relaxation and pathological remodeling, as assessed via E/e’ (42.8 vs. 21.5, P = 1.2e-10), E/A (2.3 vs 1.4, P = 4.1e-2), diastolic stiffness (0.09 vs 0.04 mmHg/μL, P = 5.1e-3), and myocardial fibrosis (P = 2.3e-2). Liquid chromatography and mass spectroscopy exposed a 40.0% reduction in NAD+ (P = 8.4e-3) and a 38.8% reduction in GSH:GSSG (P = 2.6e-2) among Nnt+/+ mice after HFD+L-NAME feeding. Using single-nucleus ligand-receptor analysis, we implicate fibroblast growth factor 1 (Fgf1) as a putative NNT-dependent mediator of cardiomyocyte-to-fibroblast signaling of myocardial fibrosis. Together, these findings underscore the pivotal role of mitochondrial dysfunction in HFpEF pathogenesis and position both NNT and Fgf1 as novel therapeutic targets.