Background: Heart failure with preserved ejection fraction (HFpEF) represents a common clinical endpoint of structural and metabolic diseases which impair myocardial diastolic relaxation and increase myocardial stiffness. The disease mechanisms are poorly understood and the therapeutic options for HFpEF are currently limited. Although myocardial REDOX perturbations are known to accompany HFpEF, the role of mitochondrial oxidative stress in the pathophysiology of diastolic dysfunction requires further investigation. While in healthy hearts nicotinamide nucleotide transhydrogenase (NNT) serves as an antioxidant by regenerating NADPH from NADH, NNT switches to a pro-oxidative manner thus becoming a critical source for ROS in situations of increased metabolic demand. These observations implicate that NNT might also contribute to the redox perturbations in HFpEF and thus could become a potential novel therapeutic target. 

AIM: Determining the role of NNT in the development of HFpEF in vivo

Methods and Results: BL/6J NNT -/- were crossed to BL/6N NNT +/+ mice and the offspring was separated in NNT -/-  and NNT +/+ mice.   12-week-old NNT -/- and NNT +/+ mice were subjected to a combination of high-fat diet and 0.5% N(ω)-nitro-L-arginine methyl ester treatment (HFD+L-NAME) for 9 weeks (n=6-10). Strikingly, only NNT +/+ mice manifested systemic features of cardiometabolic syndrome following 9 weeks HFD-L-NAME, characterized by obesity (body weight increase by 23.2% vs 3% in NNT -/-, p=0.003), glucose intolerance (48668 vs. 29810 AUC in GTT NNT -/-, p=0.006), and reduced treadmill running (exercise capacity 273.9m vs. 492.1m in NNT -/-).  Echocardiographic analysis revealed severe diastolic dysfunction in the NNT +/+ mice compared to NNT -/-  mice (E/e’44.48 vs 30.88 (p < 0.001) and E/A 2.29 vs 1.81 (p= 0.007) ratios). Severe diastolic dysfunction was confirmed by left ventricular pressure-volume loop (PV loop) analysis (99.69 vs. 79.47 mmHg/µl ). Thus, only the NNT +/+ mice developed cardiac manifestations of HFpEF upon HFD+L-NAME treatment.

Cardiac transcriptome analysis exhibited an upregulation of genes involved in oxidative stress pathways e.g., Nos1, Slc11A1 (p=0.004), in HFD+L-NAME fed NNT +/+ mice. Via Western blot analysis we found a marked upregulation of iNOS following HFD+L-NAME administration only in NNT +/+ mice, indicating nitrosative stress-induced cardiometabolic manifestations of HFpEF upon HFD-L-NAME.

Conclusion: Our observations demonstrate that the loss of NNT protects against detrimental HFD+L-NAME-induced cardiac and systemic alterations in mice. We therefore present a previously unknown adaptive role of NNT and thereby potentially mitochondrial ROS production in the HFpEF syndrome. Thus, targeting mitochondrial ROS production in HFpEF patients might become a new potential therapeutic approach.