Pathophysiological role of NAMPT in endothelial function
Authors: Ramirez Francisco , Cabrera Jody , Gao Lei , Razan Md , Yuan Jason , Makino Ayako 
Published: May 2023

Introduction: Nicotinamide phosphoribosyltransferase (NAMPT) is a multitask peptide with two major functions based on its locations; intracellular and extracellular (iNAMPT and eNAMPT, respectively). iNAMPT is the rate-limiting enzyme of NAD+ synthesis via the salvage pathway. eNAMPT acts as a cytokine. During aging, NAD+ level is reduced, resulting in metabolic disorder. However, recent evidence shows that increased NAMPT level is implicated in many cardiovascular diseases. In this study, we investigate whether and how NAMPT contributes to coronary endothelial function. Materials and Methods: Inducible type 2 diabetic (T2D) mice were generated by administering a single injection of STZ (75 mg/kg, i.p.) and feeding a high-fat diet. TALLYHO (TH), a polygenic T2D model purchased from Jackson Laboratory. Mouse cardiac endothelial cells (CECs) were isolated for molecular biological experiments. Isometric tension was conducted in third-order coronary arteries (CAs). Mitochondrial ROS concentration and gap junction activity were assessed in human CEC. Results: T2D mice exhibited elevated levels of NAMPT in the serum compared to the controls. In addition, T2D and TH mice showed increased NAMPT in mouse CECs compared to their controls. Endothelium-dependent relaxation (EDR), assessed by ACh administration, was significantly attenuated in CAs from T2D mice compared to the controls, while there was no difference in EC-independent relaxation between two groups, assessed by sodium nitroprusside (SNP) application. To identify whether increased NAMPT levels lead to endothelial dysfunction, we applied NAMPT or NAD+ to control CAs or CECs and examined endothelial function. Treatment with NAMPT or NAD+ in CAs inhibited EDR without affecting EC-independent relaxation. ACh induces EDR via the production of NO and PGI2, and by inducing endothelial hyperpolarization. Therefore, we examined the effect of NAMPT and NAD+ on the production of mitochondrial ROS (a modifier of NO bioavailability) and the activity of gap junction (a path of electrical propagation). Mitochondrial ROS concentration was significantly elevated in NAMPT- and NAD+-treated CECs compared to vehicle-treated cells. Treatment with NAMPT and NAD+ also reduced gap junction activity in CECs. High-glucose (25mM) treatment attenuated gap junction activity, and FK866 (an iNAMPT inhibitor) significantly improved it toward the level in cells with normal glucose media (5 mM). Conclusion: Diabetic mice show elevated NAMPT levels in the serum and CECs, and NAMPT- and NAD+-administration attenuate EDR via increasing mitochondrial ROS production and/or decreasing gap junction activity. These data imply that attenuated EDR in diabetic mice might be due to increased eNAMPT in the blood and iNAMPT in CECs. Therefore, inhibition of NAMPT could be a new therapeutic strategy for endothelial dysfunction in diabetes. Supported by NIH R01HL142214 and DOD W81XWH2110472. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.