Abstract 4339547: Nicotinamide Nucleoside Transhydrogenase (NNT) loss-of-function attenuates oxidative stress-associated myocardial fibrosis and diastolic dysfunction in cardiometabolic HFpEF

Background: The absence of effective, disease-modifying therapies continues to limit clinical management of cardiometabolic heart failure with preserved ejection fraction (cHFpEF). Although the “two-hit” murine model of high-fat diet and 0.5% N(ω)-nitro-L-arginine methyl ester (HFD+L-NAME) has been heralded as a reproducible model of cHFpEF, we previously discovered that C57BL/6J mice are resistant to developing diastolic dysfunction under this regimen. Both the mechanistic basis of - and therapeutic opportunities underlying - this cardioprotection remained undefined. Methods: Genetic strain-specific single-nucleus transcriptomic analysis identified disease-relevant gene programs via human GWAS trait mapping to enrich cardiomyocyte mitochondrial redox homeostasis and oxidative metabolic gene expression. Because C57BL/6J mice are known to harbor a loss-of-function mutation affecting the inner mitochondrial membrane Nnt , we developed 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 C57BL/6N mice with wild-type ( Nnt +/+ ) or loss-of-function ( Nnt -/- ) Nnt were challenged to HFD+L-NAME or control diets for 9 weeks (n = 10). Tissue was analyzed via histologic analysis and HPLC-MS for molecular and functional analysis. Results: Only C57BL/6N Nnt +/+ - and not 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 EDPVR (0.09 vs 0.04 mmHg/μL, P = 5.1e -3 ), and myocardial fibrosis ( P = 2.3e -2 ). Tandem LC/MS exposed a functional reversal of Nnt dynamics, showing a 40.0% reduction in NAD + ( P = 8.4e -3 ) and a 38.8% reduction in GSH:GSSG ( P = 2.6e -2 ) only in Nnt +/+ mice. Using single-nucleus ligand-receptor analysis and human GWAS trait mapping, we found fibroblast growth factor 1 (Fgf1) as an NNT-dependent paracellular signal that promotes myocardial fibrosis in HFpEF mice. Conclusions: These data establish a mechanistic link between mitochondrial redox regulation and HFpEF pathogenesis, whereby functional Nnt promotes diastolic dysfunction in the HFD+L-NAME model. Furthermore, Fgf1 represents an Nnt -responsive paracellular signaling axis that promotes myocardial fibrosis, highlighting both as novel targets for therapeutic intervention.