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. Two cohorts of 12-week-old male and female mice possessing wild-type (NNT+/+) or deleted (NNT-/-) NNT were provided an ad libitum high-fat and 0.5% N(ω)-nitro-L-arginine methyl ester (HFD+LNAME) diet for 9 weeks (n = 6-10).