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Proteolysis‐targeting chimeras (PROTACs) have emerged as a promising strategy for targeted protein degradation and drug discovery. To overcome the inherent limitations of conventional PROTACs, an innovative drugtamer‐PROTAC conjugation approach is developed to enhance tumor targeting and antitumor potency. Specifically, a smart prodrug is designed by conjugating "drugtamer" to a nicotinamide phosphoribosyltransferase (NAMPT) PROTAC using a tumor microenvironment responsible linker. The "drugtamer" consists of fluorouridine nucleotide and DNA‐like oligomer. Compared to NAMPT PROTAC and the combination of PROTAC + fluorouracil, the designed prodrug AS‐2F‐NP demonstrates superior tumor targeting, efficient cellular uptake, improved in vivo potency and reduced side effects. This study provides a promising strategy for the precise delivery of PROTAC and synergistic antitumor agents. [ABSTRACT FROM AUTHOR]

Nicotinamide phosphoribosyltransferase (NAMPT) is a metabolic enzyme with key roles in inflammation. Previous studies have examined the consequences of its upregulated expression in cancer cells themselves, but studies are limited with respect to its role in the other cells within the tumor microenvironment (TME) during colorectal cancer (CRC) progression. Using single‐cell RNA sequencing (scRNA‐seq) data, it is founded that NAMPT is highly expressed in SPP1+ tumor‐associated macrophages (TAMs), a unique subset of TAMs associated with immunosuppressive activity. A NAMPThigh gene signature in SPP1+ TAMs correlated with worse prognostic outcomes in CRC patients. The effect of Nampt deletion in the myeloid compartment of mice during CRC development is explored. NAMPT deficiency in macrophages resulted in HIF‐1α destabilization, leading to reduction in M2‐like TAM polarization. NAMPT deficiency caused significant decreases in the efferocytosis activity of macrophages, which enhanced STING signaling and the induction of type I IFN‐response genes. Expression of these genes contributed to anti‐tumoral immunity via potentiation of cytotoxic T cell activity in the TME. Overall, these findings suggest that NAMPT‐initiated TAM‐specific genes can be useful in predicting poor CRC patient outcomes; strategies aimed at targeting NAMPT may provide a promising therapeutic approach for building an immunostimulatory TME in CRC progression. [ABSTRACT FROM AUTHOR]

Nicotinamide adenine dinucleotide (NAD+) is an essential coenzyme with diverse biological functions in DNA synthesis. Nicotinamide phosphoribosyltransferase (NAMPT) is a key rate‐limiting enzyme involved in NAD+ biosynthesis in mammals. We developed the first chemical tool for optical control of NAMPT and NAD+ in biological systems using photoswitchable proteolysis‐targeting chimeras (PS‐PROTACs). An NAMPT activator and dimethylpyrazolazobenzene photoswitch were used to design highly efficient PS‐PROTACs, enabling up‐ and down‐reversible regulation of NAMPT and NAD+ in a light‐dependent manner and reducing the toxicity associated with inhibitor‐based PS‐PROTACs. PS‐PROTAC was activated under 620 nm irradiation, realizing in vivo optical manipulation of antitumor activity, NAMPT, and NAD+. [ABSTRACT FROM AUTHOR]

Nicotinamide adenine dinucleotide (NAD+) is an essential coenzyme with diverse biological functions in DNA synthesis. Nicotinamide phosphoribosyltransferase (NAMPT) is a key rate‐limiting enzyme involved in NAD+ biosynthesis in mammals. We developed the first chemical tool for optical control of NAMPT and NAD+ in biological systems using photoswitchable proteolysis‐targeting chimeras (PS‐PROTACs). An NAMPT activator and dimethylpyrazolazobenzene photoswitch were used to design highly efficient PS‐PROTACs, enabling up‐ and down‐reversible regulation of NAMPT and NAD+ in a light‐dependent manner and reducing the toxicity associated with inhibitor‐based PS‐PROTACs. PS‐PROTAC was activated under 620 nm irradiation, realizing in vivo optical manipulation of antitumor activity, NAMPT, and NAD+. [ABSTRACT FROM AUTHOR]

Nicotinamide adenine dinucleotide (NAD+) is an essential coenzyme with diverse biological functions in DNA synthesis. Nicotinamide phosphoribosyltransferase (NAMPT) is a key rate‐limiting enzyme involved in NAD+ biosynthesis in mammals. We developed the first chemical tool for optical control of NAMPT and NAD+ in biological systems using photoswitchable proteolysis‐targeting chimeras (PS‐PROTACs). An NAMPT activator and dimethylpyrazolazobenzene photoswitch were used to design highly efficient PS‐PROTACs, enabling up‐ and down‐reversible regulation of NAMPT and NAD+ in a light‐dependent manner and reducing the toxicity associated with inhibitor‐based PS‐PROTACs. PS‐PROTAC was activated under 620 nm irradiation, realizing in vivo optical manipulation of antitumor activity, NAMPT, and NAD+. [ABSTRACT FROM AUTHOR]

Nicotinamide adenine dinucleotide (NAD+) is an essential coenzyme with diverse biological functions in DNA synthesis. Nicotinamide phosphoribosyltransferase (NAMPT) is a key rate‐limiting enzyme involved in NAD+ biosynthesis in mammals. We developed the first chemical tool for optical control of NAMPT and NAD+ in biological systems using photoswitchable proteolysis‐targeting chimeras (PS‐PROTACs). An NAMPT activator and dimethylpyrazolazobenzene photoswitch were used to design highly efficient PS‐PROTACs, enabling up‐ and down‐reversible regulation of NAMPT and NAD+ in a light‐dependent manner and reducing the toxicity associated with inhibitor‐based PS‐PROTACs. PS‐PROTAC was activated under 620 nm irradiation, realizing in vivo optical manipulation of antitumor activity, NAMPT, and NAD+. [ABSTRACT FROM AUTHOR]

Metabolic reprogramming is a hallmark of cancer. The nicotinamide phosphoribosyltransferase (NAMPT)‐mediated salvage pathway maintains sufficient cellular NAD levels and is required for tumorigenesis and development. However, the molecular mechanism by which NAMPT contributes to HBV‐associated hepatocellular carcinoma (HCC) remains not fully understood. In the present study, our results showed that NAMPT protein was obviously upregulated in HBV‐positive HCC tissues compared with HBV‐negative HCC tissues. NAMPT was positively associated with aggressive HCC phenotypes and poor prognosis in HBV‐positive HCC patients. NAMPT overexpression strengthened the proliferative, migratory, and invasive capacities of HBV‐associated HCC cells, while NAMPT‐insufficient HCC cells exhibited decreased growth and mobility. Mechanistically, we demonstrated that NAMPT activated SREBP1 (sterol regulatory element‐binding protein 1) by increasing the expression and nuclear translocation of SREBP1, leading to the transcription of SREBP1 downstream lipogenesis‐related genes and the production of intracellular lipids and cholesterol. Altogether, our data uncovered an important molecular mechanism by which NAMPT promoted HBV‐induced HCC progression through the activation of SREBP1‐triggered lipid metabolism reprogramming and suggested NAMPT as a promising prognostic biomarker and therapeutic target for HBV‐associated HCC patients. [ABSTRACT FROM AUTHOR]

Oocyte maturation defect can lead to maternal reproduction disorder. NAMPT is a rate‐limiting enzyme in mammalian NAD+ biosynthesis pathway, which can regulate a variety of cellular metabolic processes including glucose metabolism and DNA damage repair. However, the function of NAMPT in porcine oocytes remains unknown. In this study, we showed that NAMPT involved into multiple cellular events during oocyte maturation. NAMPT expressed during all stages of porcine oocyte meiosis, and inhibition of NAMPT activity caused the cumulus expansion and polar body extrusion defects. Mitochondrial dysfunction was observed in NAMPT‐deficient porcine oocytes, which showed decreased membrane potential, ATP and mitochondrial DNA content, increased oxidative stress level and apoptosis. We also found that NAMPT was essential for spindle organization and chromosome arrangement based on Ac‐tubulin. Moreover, lack of NAMPT activity caused the increase of lipid droplet and affected the imbalance of lipogenesis and lipolysis. In conclusion, our study indicated that lack of NAMPT activity affected porcine oocyte maturation through its effects on mitochondria function, spindle assembly and lipid metabolism. [ABSTRACT FROM AUTHOR]

Osteoarthritis (OA) is a degenerative disease that occurs mostly in the elderly, and its specific pathogenesis is still unknown, but recent studies have found that circular RNA generally display aberrant expression in OA. Our study explored the expression characteristics and mechanism of action of circ‐NT5C2 in OA. Circ‐NT5C2, microRNA‐142‐5p (miR‐142‐5p), and nicotinamide phosphoribosyltransferase (NAMPT) mRNA levels were measured using RT‐qPCR. Western blot was employed to assess the protein level of NAMPT and extracellular matrix (ECM) production‐related markers. The viability, proliferation, apoptosis and inflammation were examined using 3‐(4, 5‐dimethylthiazol‐2‐yl)‐2, 5‐diphenyltetrazolium bromide (MTT) assay, 5‐ethynyl‐2′‐deoxyuridine (EdU) assay, flow cytometry, and enzyme‐linked immunosorbent assay, respectively. Relationship between miR‐142‐5p and circ‐NT5C2 or NAMPT was demonstrated by dual‐luciferase reporter system and RNA immunoprecipitation assay. We reported that circ‐NT5C2 and NAMPT were greatly upregulated, and miR‐142‐5p level was constrained in OA tissues and in a cell model. Circ‐NT5C2 silencing alleviated IL‐1β‐induced inhibitory effects on chondrocyte proliferation and ECM generation, meanwhile the promotional role of IL‐1β on chondrocyte apoptosis and inflammation was also weakened. The targeting relationship of miR‐142‐5p with either circ‐NT5C2 or NAMPT was confirmed. Knockdown of miR‐142‐5p reversed the suppressive effects of circ‐NT5C2 silencing on the OA progression in vitro, and NAMPT overexpression also attenuated the effects of miR‐142‐5p upregulation in an OA cell model. Collectively, circ‐NT5C2 accelerated the OA process by targeting the miR‐142‐5p/NAMPT axis. This study provides valuable information to find a better treatment for OA. [ABSTRACT FROM AUTHOR]

Endoplasmic reticulum (ER) stress has been reported to be transmitted from tumor cells to immune cells via exosome and implicated in immune escape. However, the influence of ER stress on monocytes in chronic lymphocytic leukemia (CLL) cells is largely unknown. Here, we observed the expression of ER stress markers (GRP78, ATF6, PERK, IRE1a, and XBP1s) in CLL cells. The increasing mRNA expression of these ER stress response components was positively correlated with more aggressive disease. Exosome from ER stress inducer tunicamycin (TM)‐primed CLL cells (ERS‐exo) up‐regulated the expression of ER stress marker on monocytes, indicating ER stress is transmissible in vitro via exosome. Treatment with ERS‐exo promoted the survival of monocytes and induced phenotypic changes with a significantly larger percentage of CD14+CD16+monocytes. Finally, we identified exosome‐mediated transfer of extracellular nicotinamide phosphoribosyltransferase (eNAMPT) from ER stressed CLL cells into monocytes as a novel mechanism through which ERS‐exo regulated monocytes. Exosomal eNAMPT up‐regulated nicotinamide adenine dinucleotide (NAD+) production which subsequently activated SIRT1‐C/EBPβ signaling pathway in monocytes. Our results suggest the role of ER stress in mediating immunological dysfunction in CLL. [ABSTRACT FROM AUTHOR]

Aging is associated with a loss of metabolic homeostasis, with cofactors such as nicotinamide adenine dinucleotide (NAD+) declining over time. The decrease in NAD+ production has been linked to the age‐related loss of circulating extracellular nicotinamide phosphoribosyltransferase (eNAMPT), the rate‐limiting enzyme in the NAD+ biosynthetic pathway. eNAMPT is found almost exclusively in extracellular vesicles (EVs), providing a mechanism for the distribution of the enzyme in different tissues. Currently, the physiological cause for the release of eNAMPT is unknown, and how it may be affected by age and physical exercise. Here, we show that release of small EVs into the bloodstream is stimulated following moderate intensity exercise in humans. Exercise also increased the eNAMPT content in EVs, most prominently in young individuals with higher aerobic fitness. Both mature fit and young unfit individuals exhibited a limited increase in EV‐eNAMPT release following exercise, indicating that this mechanism is related to both the age and physical fitness of a person. Notably, unfit mature individuals were unable to increase the release of eNAMPT in EVs after exercise, suggesting that lower fitness levels and aging attenuate this important signalling mechanism in the body. EVs isolated from exercising humans containing eNAMPT were able to alter the abundance of NAD+ and SIRT1 activity in recipient cells compared to pre‐exercise EVs, indicating a pathway for inter‐tissue signalling promoted through exercise. Our results suggest a mechanism to limit age‐related NAD+ decline, through the systemic delivery of eNAMPT via EVs released during exercise. [ABSTRACT FROM AUTHOR]

The prevalence of non‐alcoholic fatty liver disease (NAFLD) is increasing worldwide, and new treatments are sorely needed. Nicotinamide adenine dinucleotide (NAD+) has been proposed as a potential target to prevent and reverse NAFLD. NAD+ is an important redox factor for energy metabolism and is used as a substrate by a range of enzymes, including sirtuins (SIRT), which regulates histone acetylation, transcription factor activity and mitochondrial function. NAD+ is also a precursor for reduced nicotinamide adenine dinucleotide phosphate (NADPH), which is an important component of the antioxidant defense system. NAD+ precursors such as nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) are available as over‐the‐counter dietary supplements, and oral supplementation with these precursors increases hepatic NAD+ levels and prevents hepatic lipid accumulation in pre‐clinical models of NAFLD. NAD+ precursors have also been found to improve hepatic mitochondrial function and decrease oxidative stress in pre‐clinical NAFLD models. NAD+ repletion also prevents NAFLD progression to non‐alcoholic steatohepatitis (NASH), as NAD+ precursor supplementation is associated with decreased hepatic stellate cell activation, and decreased fibrosis. However, initial clinical trials have only shown modest effects when NAD+ precursors were administrated to people with obesity. We review the available pre‐clinical investigations of NAD+ supplementation for targeting NAFLD, and discuss how data from the first clinical trials can be reconciled with observations from preclinical research. [ABSTRACT FROM AUTHOR]

Maternal aging can impair the quality and decrease the developmental competence of ovulated oocytes. In this study, compromised germinal vesicle breakdown (GVBD) was found in aged mice oocytes. Furthermore, we observed increased reactive oxygen species (ROS) and mitochondrial Ca2+ levels, along with reduced mitochondrial temperature in aged oocytes. Maternal aging also changed the crotonylation level in oocytes. Forkhead box O3 (FoxO3a), a member of the forkhead protein family involved in the regulation of cell survival and life span reached a peak level in the metaphase II stage. Compared with a younger group, FoxO3a expression increased in aged oocytes. Intracellular localization of FoxO3a changed from the cytoplasm to chromatin in response to aging. The expression of the upstream regulator nicotinamide‐phosphoribosyltransferase (Nampt) peaked in the GVBD stage. Moreover, Nampt expression was increased in aged oocytes, and more intense staining of Nampt was found in aged mice ovary. To further study the role of Nampt in mitochondrial function, specific agonist P7C3 and inhibitor FK866 were applied to aged oocytes, and FK866 significantly decreased adenosine triphosphate and mitochondrial membrane potential. In conclusion, mitochondrial dysfunction in aged oocytes was associated with elevated FoxO3a, and suppression of Nampt could further impair mitochondrial function. [ABSTRACT FROM AUTHOR]

Most physiological processes in mammals are subjected to daily oscillations that are governed by a circadian system. The circadian rhythm orchestrates metabolic pathways in a time‐dependent manner and loss of circadian timekeeping has been associated with cellular and system‐wide alterations in metabolism, redox homeostasis, and inflammation. Here, we investigated the expression of clock and clock‐controlled genes in multiple tissues (suprachiasmatic nucleus, spinal cord, gastrocnemius muscle, and liver) from mutant hSOD1‐linked amyotrophic lateral sclerosis (ALS) mouse models. We identified tissue‐specific changes in the relative expression, as well as altered daily expression patterns, of clock genes, sirtuins (Sirt1, Sirt3, and Sirt6), metabolic enzymes (Pfkfb3, Cpt1, and Nampt), and redox regulators (Nrf2, G6pd, and Pgd). In addition, astrocytes transdifferentiated from induced pluripotent stem cells from SOD1‐linked and FUS RNA binding protein‐linked ALS patients also displayed altered expression of clock genes. Overall, our results raise the possibility of disrupted cross‐talk between the suprachiasmatic nucleus and peripheral tissues in hSOD1G93A mice, preventing proper peripheral clock regulation and synchronization. Since these changes were observed in symptomatic mice, it remains unclear whether this dysregulation directly drives or it is a consequence of the degenerative process. However, because metabolism and redox homeostasis are intimately entangled with circadian rhythms, our data suggest that altered expression of clock genes may contribute to metabolic and redox impairment in ALS. Since circadian dyssynchrony can be rescued, these results provide the groundwork for potential disease‐modifying interventions. [ABSTRACT FROM AUTHOR]

A main feature of aged organisms is the accumulation of senescent cells. Accumulated senescent cells, especially stress‐induced premature senescent cells, in aged organisms lead to the decline of the regenerative potential and function of tissues. We recently reported that the over‐expression of NAMPT, which is the rate‐limiting enzyme in mammalian NAD+ salvage pathway, delays replicative senescence in vitro. However, whether Nampt‐overexpressing cells are tolerant of stress‐induced premature senescence remains unknown. Here, we show that primary mouse embryonic fibroblasts derived from Nampt‐overexpressing transgenic mice (Nampt Tg‐MEF cells) possess resistance against stress‐induced premature senescence in vitro. We found that higher oxidative or endoplasmic reticulum (ER) stress is required to induce premature senescence in Nampt Tg‐MEF cells compared to wild‐type cells. Moreover, we found that Nampt Tg‐MEF cells show acute expression of unfolded protein response (UPR)‐related genes, which in turn would have helped to restore proteostasis and avoid cellular senescence. Our results demonstrate that NAMPT/NAD+ axis functions to protect cells not only from replicative senescence, but also from stress‐induced premature senescence in vitro. We anticipate that in vivo activation of NAMPT activity or increment of NAD+ would protect tissues from the accumulation of premature senescent cells, thereby maintaining healthy aging. [ABSTRACT FROM AUTHOR]

Background: Among the different types of cancer, pancreatic cancer, particularly pancreatic ductal adenocarcinoma (PDAC), is the most lethal malignancy, with poor early detection rates and prognosis. The aim of the present study was to investigate the potential genetic effects of the single‐nucleotide polymorphisms (SNPs) in ABCB1 (rs1045642, rs3789243, rs4148737), APOB (rs693, rs1042031), CAV1 (rs12672038, rs1997623, rs3807987, rs7804372), and NAMPT (rs9034, rs2505568, rs61330082) on PDAC. Methods: A total of 273 patients with PDAC and 263 healthy controls were genotyped using PCR and direct Sanger sequencing. Unconditional logistic regression models were used to evaluate the potential effects of the genotypes, alleles, and haplotypes on the risk of developing PDAC. Results: Patients with PDAC possessed a considerably lower frequency of genotypes AG, GG, and allele G at ABCB1 rs4148737 compared with controls. Based on age, sex, smoking status, drinking status, diabetes, and family history of cancer, stratified analyses showed a significant correlation between SNPs at rs4148737 and PDAC. According to specific SNPs, eight haplotypes were constructed along with ABCB1 rs4148737, rs1045642, and rs3789243. Carriers with haplotypes ACC and ATC were more susceptible to developing PDAC, whereas haplotypes GCC and GTC were associated with a reduced likelihood of developing PDAC. The distributions of the other SNPs in each group were not significantly associated with PDAC risk. Conclusions: These results suggested that genetic polymorphisms of ABCB1 rs4148737 may influence an individual's risk of developing PDAC. [ABSTRACT FROM AUTHOR]

It is of current interest to target cancer metabolism as treatment for many malignancies, including ovarian cancer (OVC), in which few druggable driver mutations have been identified. Nicotinamide phosphoribosyltransferase (NAMPT), a rate‐limiting enzyme in the NAD salvage pathway, is a potential therapeutic target in OVC. However, factors that determine responsiveness to NAMPT inhibition are not fully understood. Here, we report that OVC cell lines can be divided into subgroups exhibiting NAMPT‐dependent or NAMPT‐independent glycolysis, and these metabolic differences correlate with vulnerability to NAMPT inhibition. Interestingly, cells showing NAMPT‐dependent glycolysis were enriched in a group of cells lacking BRCA1/2 gene mutations. Our findings suggest the importance of selecting appropriate patients for NAMPT‐targeting therapy in OVC. [ABSTRACT FROM AUTHOR]

Aim: Neurons in the arcuate nucleus of the hypothalamus are involved in regulation of food intake and energy expenditure, and dysregulation of signalling in these neurons promotes development of obesity. The role of the rate‐limiting enzyme in the NAD+ salvage pathway, nicotinamide phosphoribosyltransferase (NAMPT), for regulation energy homeostasis by the hypothalamus has not been extensively studied. Methods: We determined whether Nampt mRNA or protein levels in the hypothalamus of mice were affected by diet‐induced obesity, by fasting and re‐feeding, and by leptin and ghrelin treatment. Primary hypothalamic neurons were treated with FK866, a selective inhibitor of NAMPT, or rAAV carrying shRNA directed against Nampt, and levels of reactive oxygen species (ROS) and mitochondrial respiration were assessed. Fasting and ghrelin‐induced food intake was measured in mice in metabolic cages after intracerebroventricular (ICV)‐mediated FK866 administration. Results: NAMPT levels in the hypothalamus were elevated by administration of ghrelin and leptin. In diet‐induced obese mice, both protein and mRNA levels of NAMPT decreased in the hypothalamus. NAMPT inhibition in primary hypothalamic neurons significantly reduced levels of NAD+, increased levels of ROS, and affected the expression of Agrp, Pomc and genes related to mitochondrial function. Finally, ICV‐induced NAMPT inhibition by FK866 did not cause malaise or anhedonia, but completely ablated fasting‐ and ghrelin‐induced increases in food intake. Conclusion: Our findings indicate that regulation of NAMPT levels in hypothalamic neurons is important for the control of fasting‐ and ghrelin‐induced food intake. [ABSTRACT FROM AUTHOR]

Key points: This is the first long‐term human clinical trial to report on effects of nicotinamide riboside (NR) on skeletal muscle mitochondrial function, content and morphology.NR supplementation decreases nicotinamide phosphoribosyltransferase (NAMPT) protein abundance in skeletal muscle.NR supplementation does not affect NAD metabolite concentrations in skeletal muscle.Respiration, distribution and quantity of muscle mitochondria are unaffected by NR.NAMPT in skeletal muscle correlates positively with oxidative phosphorylation Complex I, sirtuin 3 and succinate dehydrogenase. Preclinical evidence suggests that the nicotinamide adenine dinucleotide (NAD+) precursor nicotinamide riboside (NR) boosts NAD+ levels and improves diseases associated with mitochondrial dysfunction. We aimed to determine if dietary NR supplementation in middle‐aged, obese, insulin‐resistant men affects mitochondrial respiration, content and morphology in skeletal muscle. In a randomized, placebo‐controlled clinical trial, 40 participants received 1000 mg NR or placebo twice daily for 12 weeks. Skeletal muscle biopsies were collected before and after the intervention. Mitochondrial respiratory capacity was determined by high‐resolution respirometry on single muscle fibres. Protein abundance and mRNA expression were measured by Western blot and quantitative PCR analyses, respectively, and in a subset of the participants (placebo n = 8; NR n = 8) we quantified mitochondrial fractional area and mitochondrial morphology by laser scanning confocal microscopy. Protein levels of nicotinamide phosphoribosyltransferase (NAMPT), an essential NAD+ biosynthetic enzyme in skeletal muscle, decreased by 14% with NR. However, steady‐state NAD+ levels as well as gene expression and protein abundance of other NAD+ biosynthetic enzymes remained unchanged. Neither respiratory capacity of skeletal muscle mitochondria nor abundance of mitochondrial associated proteins were affected by NR. Moreover, no changes in mitochondrial fractional area or network morphology were observed. Our data do not support the hypothesis that dietary NR supplementation has significant impact on skeletal muscle mitochondria in obese and insulin‐resistant men. Future studies on the effects of NR on human skeletal muscle may include both sexes and potentially provide comparisons between young and older people. Key points: This is the first long‐term human clinical trial to report on effects of nicotinamide riboside (NR) on skeletal muscle mitochondrial function, content and morphology.NR supplementation decreases nicotinamide phosphoribosyltransferase (NAMPT) protein abundance in skeletal muscle.NR supplementation does not affect NAD metabolite concentrations in skeletal muscle.Respiration, distribution and quantity of muscle mitochondria are unaffected by NR.NAMPT in skeletal muscle correlates positively with oxidative phosphorylation Complex I, sirtuin 3 and succinate dehydrogenase. [ABSTRACT FROM AUTHOR]

NAD+ is a cofactor required for glycolysis, tricarboxylic acid cycle, and complex I enzymatic reaction. In mammalian cells, NAD+ is predominantly synthesized through the salvage pathway, where nicotinamide phosphoribosyltransferase (NAMPT) is the rate‐limiting enzyme. Previously, we demonstrated that NAMPT exerts a neuroprotective effect in ischemia through the suppression of mitochondrial dysfunction. Mammalian cells maintain distinct NAD+ pools in the cytosol, mitochondria, and nuclei. However, it is unknown whether mitochondria have an intact machinery for NAD+ salvage, and if so, whether it plays a dominant role in bioenergetics, mitochondrial function, and neuronal protection after ischemia. Here, using mouse primary cortical neuron and cortical tissue preparations, and multiple technologies including cytosolic and mitochondrial subfractionation, viral over‐expression of transgenes, molecular biology, and confocal microscopy, we provided compelling evidence that neuronal mitochondria possess an intact machinery of NAMPT‐mediated NAD+ salvage pathway, and that NAMPT and nicotinamide mononucleotide adenylyltransferase 3 (NMNAT3) are localized in the mitochondrial matrix. By knocking down NMNAT1‐3 and NAMPT with siRNA, we found that NMNAT3 has a larger effect on basal and ATP production‐related mitochondrial respiration than NMNAT1‐2 in primary cultured neurons, while NMNAT1‐2 have a larger effect on glycolytic flux than NMNAT3. Using an oxygen glucose deprivation model, we found that mitochondrial, cytoplasmic, and non‐subcellular compartmental over‐expressions of NAMPT have a comparable effect on neuronal protection and suppression of apoptosis‐inducing factor translocation. The current study provides novel insights into the roles of subcellular compartmental NAD+ salvage pathways in NAD+ homeostasis, bioenergetics, and neuronal protection in ischemic conditions. [ABSTRACT FROM AUTHOR]

Tumor‐associated neutrophils (TANs) regulate many processes associated with tumor progression, and depending on the microenvironment, they can exhibit pro‐ or antitumor functions. However, the molecular mechanisms regulating their tumorigenicity are not clear. Using transplantable tumor models, we showed here that nicotinamide phosphoribosyltransferase (NAMPT), a molecule involved in CSF3R downstream signaling, is essential for tumorigenic conversion of TANs and their pro‐angiogenic switch. As a result tumor vascularization and growth are strongly supported by these cells. Inhibition of NAMPT in TANs leads to their antitumor conversion. Adoptive transfer of such TANs into B16F10‐tumor bearing mice attenuates tumor angiogenesis and growth. Of note, we observe that the regulation of NAMPT signaling in TANs, and its effect on the neutrophil tumorigenicity, are analogous in mice and human. NAMPT is up‐regulated in TANs from melanoma and head‐and‐neck tumor patients, and its expression positively correlates with tumor stage. Mechanistically, we found that targeting of NAMPT suppresses neutrophil tumorigenicity by inhibiting SIRT1 signaling, thereby blocking transcription of pro‐angiogenic genes. Based on these results, we propose that NAMPT regulatory axis is important for neutrophils to activate angiogenic switch during early stages of tumorigenesis. Thus, identification of NAMPT as the critical molecule priming protumor functions of neutrophils provides not only mechanistic insight into the regulation of neutrophil tumorigenicity, but also identifies a potential pathway that may be targeted therapeutically in neutrophils. This, in turn, may be utilized as a novel mode of cancer immunotherapy. What's new? Depending on the microenvironment, tumor‐associated neutrophils (TANs) can exhibit pro‐ or antitumor functions. The molecular mechanisms regulating such polarization remain unclear, however. Here, the authors demonstrate the contribution of NAMPT, a molecule involved in CSF3R downstream signaling, to the tumorigenic conversion of TANs. They found that pro‐tumor TANs are characterized with high NAMPT expression, and that targeting of NAMPT suppresses neutrophil tumorigenicity by inhibiting SIRT1 signaling, thereby blocking transcription of pro‐angiogenic genes. Identification of NAMPT as a critical molecule priming pro‐tumor functions not only provides mechanistic insight into the regulation of neutrophil tumorigenicity but also represents a promising immunotherapy approach. [ABSTRACT FROM AUTHOR]

In bone remodeling, osteoclasts are recruited via increased production of RANKL (receptor activator of nuclear factor‐κB ligand) and migrate to the bone surface, aided by matrix metalloproteinases (MMPs). NAMPT (nicotinamide phosphoribosyl transferase), which catalyzes the rate‐limiting step in the NAD+ salvage pathway, increases during in vitro osteogenic differentiation and inhibits RANKL‐induced osteoclast differentiation. Alveolar bone loss, due to disturbance of the remodeling process, is a major feature of periodontitis. Thus, we investigated the role of NAMPT in a synchronized alveolar bone remodeling rat model. NAMPT expression increased in osteogenic cells during the remodeling activation phase, in parallel with RANKL and MMP‐2 expression. Inhibition of NAMPT activity, by systemic delivery of its selective inhibitor FK866, decreased the recruitment of osteoclasts, but not their activity. In vitro, NAMPT mRNA, and protein expression also increased during osteoblast differentiation in primary calvarial osteoblast cultures. Recombinant NAMPT and NMN, its direct metabolite, dose‐dependently increased bone marker expression, including that of sialoprotein (BSP) and osteocalcin (OC), whereas their expression was inhibited by FK866 treatment. Recombinant NAMPT did not regulate MMP‐2, −9, MMP‐13, or RANKL/OPG mRNA expression in osteoblasts. Our data suggest that de novo NAMPT synthesis in osteoblasts controls cell differentiation through osteoclast recruitment during the activation of bone remodeling. [ABSTRACT FROM AUTHOR]

Abstract: Aim: Glucagon‐like peptide‐1 is an incretin hormone secreted by the intestinal L‐cell with a circadian rhythm that parallels expression of the core clock gene, Bmal1. Although feeding rats a high‐fat/high‐sucrose Western diet impairs rhythmic glucagon‐like peptide‐1 release, the mechanisms underlying this effect remain unclear. Therefore, the aim of this study was to determine the pathway(s) by which the saturated fat, palmitate, a major component of the Western diet, impairs circadian glucagon‐like peptide‐1 secretion. Methods: Murine mGLUTag L‐cells were synchronized, and the effects of palmitate pre‐treatment on gene expression and glucagon‐like peptide‐1 secretion were determined, in addition to metabolite quantification, mitochondrial function analysis and enzyme inhibition and activation assays. Glucagon‐like peptide‐1 secretion was also analysed in ileal crypt cultures from control and Bmal1 knockout mice. Results: Pre‐treatment with palmitate dampened Bmal1 mRNA and protein expression and glucagon‐like peptide‐1 secretion at 8 but not 20 hours after cell synchronization (P < .05‐.001). Glucagon‐like peptide‐1 release was also impaired in Bmal1 knockout cultures as compared to wild‐type controls (P < .001). Palmitate pre‐treatment reduced expression of the Bmal1 downstream target, nicotinamide phosphoribosyltransferase, the rate‐limiting enzyme in the synthesis of NAD+. This was paralleled by dampening of total NAD+ levels, as well as impaired mitochondrial function and ATP production (P < .05‐.001). Whereas direct inhibition of nicotinamide phosphoribosyltransferase also decreased glucagon‐like peptide‐1 release, activation of this enzyme restored glucagon‐like peptide‐1 secretion in the presence of palmitate. Conclusion: Palmitate impairs L‐cell clock function at the peak of Bmal1 gene expression, thereby impairing mitochondrial function and ultimately rhythmic glucagon‐like peptide‐1 secretion. [ABSTRACT FROM AUTHOR]

Senescent cells accumulate in tissues of aged animals and deteriorate tissue functions. The elimination of senescent cells from aged mice not only attenuates progression of already established age-related disorders, but also extends median lifespan. Nicotinamide phosphoribosyltransferase ( NAMPT), the rate-limiting enzyme in mammalian NAD+ salvage pathway, has shown a protective effect on cellular senescence of human primary cells. However, it still remains unclear how NAMPT has a protective impact on aging in vitro and in vivo. In this study, we found that primary mouse embryonic fibroblast ( MEF) cells undergo progressive decline of NAMPT and NAD+ contents during serial passaging before becoming senescent. Furthermore, we showed that constitutive Nampt over-expression increases cellular NAD+ content and delays cellular senescence of MEF cells in vitro. We further found that constitutive Nampt over-expression increases SIRT1 activity, increases the expression of antioxidant genes, superoxide dismutase 2 and catalase and promotes resistance against oxidative stress. These findings suggest that Nampt over-expression in MEF cells delays cellular senescence by the mitigation of oxidative stress via the upregulation of superoxide dismutase 2 and catalase gene expressions by SIRT1 activation. [ABSTRACT FROM AUTHOR]

Osteoarthritis (OA) is a chronic disease pathologically characterized by articular cartilage degeneration and damage. Currently, studies have found that circular RNA (circRNA) is involved in intracellular RNA regulating network and is closely related to the occurrence and development of diseases, therefore it may become a new biological marker and therapeutic target. After stimulating chondrocytes with interleukin-1 beta (IL-1β), hsa_circ_0005105 expression was significantly upregulated, while miR-26a expression was significantly inhibited. Hsa_circ_0005105 did not influence miR-26a expression but inhibited its transcriptional activity so as to upregulate the expression of its target NAMPT. Studies further indicated that hsa_circ_0005105 can inhibit the expression of type II collagen and aggrecan, promote the expression of MMP-13 and ADAMTS-4, and the generation of PGE2, IL-6, and IL-8, but the linear sequence of hsa_circ_0005105 cannot. MiR-26a has the opposite effect, and hsa_circ_0005105 can antagonize the function of miR-26a. When NAMPT expression was downregulated, the above function of hsa_circ_0005105 was significantly weakened. Therefore, hsa_circ_0005105 can promote extracellular matrix (ECM) degradation by regulating the expression of miR-26a target NAMPT. These findings will provide new targets for treatment and prevention of OA and other orthopedic diseases. [ABSTRACT FROM AUTHOR]

Nicotinamide adenine dinucleotide (NAD+) biosynthetic pathway, mediated by nicotinamide phosphoribosyltransferase (NAMPT), a key NAD+ biosynthetic enzyme, plays a pivotal role in controlling many biological processes, such as metabolism, circadian rhythm, inflammation, and aging. Over the past decade, NAMPT-mediated NAD+ biosynthesis, together with its key downstream mediator, namely the NAD+-dependent protein deacetylase SIRT1, has been demonstrated to regulate glucose and lipid metabolism in a tissue-dependent manner. These discoveries have provided novel mechanistic and therapeutic insights into obesity and its metabolic complications, such as insulin resistance, an important risk factor for developing type 2 diabetes and cardiovascular disease. This review will focus on the importance of adipose tissue NAMPT-mediated NAD+ biosynthesis and SIRT1 in the pathophysiology of obesity and insulin resistance. We will also critically explore translational and clinical aspects of adipose tissue NAD+ biology. [ABSTRACT FROM AUTHOR]

One of the most important events in vertebrate evolutionary history is the water-to-land transition, during which some morphological and physiological changes occurred in concert with the loss of specific genes in tetrapods. However, the molecular mechanisms underlying this transition have not been well explored. To explore vertebrate adaptation to different oxygen levels during the water-to-land transition, we performed comprehensive bioinformatics and experimental analysis aiming to investigate the NAMPT family in vertebrates. NAMPT, a rate-limiting enzyme in the salvage pathway of NAD+ biosynthesis, is critical for cell survival in a hypoxic environment, and a high level of NAMPT significantly augments oxidative stress in normoxic environments. Phylogenetic analysis showed that NAMPT duplicates arose from a second round whole-genome duplication event. NAMPTA existed in all classes of vertebrates, whereas NAMPTB was only found in fishes and not tetrapods. Asymmetric evolutionary rates and purifying selection were the main evolutionary forces involved. Although functional analysis identified several functionally divergent sites during NAMPT family evolution, in vitro experimental data demonstrated that NAMPTA and NAMPTB were functionally conserved for NAMPT enzymatic function in the NAD+ salvage pathway. In situ hybridization revealed broad NAMPTA and NAMPTB expression patterns, implying regulatory functions over a wide range of developmental processes. The morpholino-mediated knockdown data demonstrated that NAMPTA was more essential than NAMPTB for vertebrate embryo development. We propose that the retention of NAMPTB in water-breathing fishes and its loss in air-breathing tetrapods resulted from vertebrate adaptation to different oxygen levels during the water-to-land transition. [ABSTRACT FROM AUTHOR]

Hepatic circadian transcription, considered to be driven by the liver clock, is largely influenced by food even uncoupling it from the suprachiasmatic nucleus (SCN). In SCN lesioned rats (SCNx) we determined the influence of a physiological feeding schedule on the entrainment of clock and clock‐controlled (CCG) genes in the liver. We show that clock genes and the CCG Rev‐erbα and peroxisome proliferator‐activated receptor alpha (PPARα) in food‐scheduled intact and SCNx have a robust diurnal differential expression persisting after a 24 h fast. However, hepatic nicotinamide phosphoribosyl transferase (Nampt) shows time dependent changes that are lost in intact animals under fasting; moreover, it is unresponsive to the nutrient status in SCNx, indicating a poor reliance on liver clock genes and highlighting the relevance of SCN‐derived signals for its metabolic status‐related expression.Physiological feeding cycles entrain the liver clock of SCNx rats, and persist under fasting. Similar as the liver clock, Rev‐erbα and PPARα can be entrained by feeding cycles. Transcription of Nampt in the liver of SCNx rats does not reflect the rhythm of the clock genes. Hepatic expression of Nampt and Sirt1 requires the SCN to reflect the metabolic status. The SCN is essential for the robust time‐dependent differential expression of Id2 in liver. [ABSTRACT FROM AUTHOR]

Background: Disruption of cellular metabolite levels can adversely impact development. Specifically, loss-of-function of the C. elegans NAD+ salvage biosynthesis gene PNC-1 results in an array of developmental phenotypes. Intriguingly, PNC-1 and its functional equivalent in vertebrates are secreted, but the contributions of the extracellular enzymes are poorly understood. We sought to study the tissue-specific requirements for PNC-1 expression and to examine the role of the secreted isoform. Results: A thorough analysis of PNC-1 expression did not detect expression in tissues that require PNC-1 function. Limited expression of both the secreted and intracellular PNC-1 isoforms provided function at a distance from the tissues with phenotypes. We also find that the secreted isoform contributes to in vivo PNC-1 activity. Furthermore, uv1 cell survival has the most stringent requirements in terms of PNC-1 expression pattern or level. Conclusions: Using careful promoter analysis and a restricted expression approach, we have shown that both the secreted and the intracellular PNC-1 isoforms function cell non-autonomously, and that the PNC-1a isoform is functionally relevant in vivo. Our work suggests a model where PNC-1 function is provided cell non-autonomously by a mix of intra and extracellular activity, most likely requiring NAD+ salvage metabolite transport between tissues. Developmental Dynamics 243:965-976, 2014. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Neural stem/progenitor cell ( NSPC) proliferation and self-renewal, as well as insult-induced differentiation, decrease markedly with age. The molecular mechanisms responsible for these declines remain unclear. Here, we show that levels of NAD+ and nicotinamide phosphoribosyltransferase ( Nampt), the rate-limiting enzyme in mammalian NAD+ biosynthesis, decrease with age in the hippocampus. Ablation of Nampt in adult NSPCs reduced their pool and proliferation in vivo. The decrease in the NSPC pool during aging can be rescued by enhancing hippocampal NAD+ levels. Nampt is the main source of NSPC NAD+ levels and required for G1/ S progression of the NSPC cell cycle. Nampt is also critical in oligodendrocytic lineage fate decisions through a mechanism mediated redundantly by Sirt1 and Sirt2. Ablation of Nampt in the adult NSPCs in vivo reduced NSPC-mediated oligodendrogenesis upon insult. These phenotypes recapitulate defects in NSPCs during aging, giving rise to the possibility that Nampt-mediated NAD+ biosynthesis is a mediator of age-associated functional declines in NSPCs. [ABSTRACT FROM AUTHOR]

NAD biosynthesis is emerging as a key regulator of immune cell functions. Accordingly, inhibitors of the NAD-synthesizing enzyme nicotinamide phosphoribosyltransferase (NAMPT) have anti-inflammatory effects, counteract hematological malignancies and are being tested in clinical trials. Still, their effect on different cell types still waits to be fully investigated. Here we show that the NAMPT inhibitor FK866 induces NAD depletion in various mouse organs but selectively causes dramatic atrophy of the spleen red pulp. Accordingly, in cultured mouse lymphocytes exposed to FK866, NAD contents drop to 50% of basal values within 2 days, a condition sufficient to prompt complete cell death. Cultures of human lymphocytes are more resistant to FK866 and sustain a 50% NAD reduction for 5 days before dying. Death of both cell types can be prevented by different NAD precursors, indicating critical NAD homeostasis in lymphocytes. Indeed, inhibition of the NAD-consuming enzyme poly(ADP-ribose) polimerase-1 suffices to prevent FK866-induced NAD depletion and death of both lymphocyte types. Poly(ADP-ribose) polymerase-1-null lymphocytes also undergo lower NAD depletion and reduced cell death when exposed to the drug. At variance with other cell types, neither apoptosis nor autophagy are exclusively responsible for lymphocyte death by FK866, consistent with a general impairment of lymphocyte homeostasis following NAD depletion. Data demonstrate a unique sensitivity of resting lymphocytes to NAD-depleting agents, providing new hints of relevance to lymphocyte biology and therapeutic interventions with NAMPT inhibitors. [ABSTRACT FROM AUTHOR]

Over 100 years after its first discovery, several new aspects of the biology of the redox co-factor NAD are rapidly emerging. NAD, as well as its precursors, its derivatives, and its metabolic enzymes, have been recently shown to play a determinant role in a variety of biological functions, from the classical role in oxidative phosphorylation and redox reactions to a role in regulation of gene transcription, lifespan and cell death, from a role in neurotransmission to a role in axon degeneration, and from a function in regulation of glucose homeostasis to that of control of circadian rhythm. It is also becoming clear that this variety of specialized functions is regulated by the fine subcellular localization of NAD, its related nucleotides and its metabolic enzymatic machinery. Here we describe the known NAD biosynthetic and catabolic pathways, and review evidence supporting a specialized role for NAD metabolism in a subcellular compartment-dependent manner. [ABSTRACT FROM AUTHOR]

Aging is associated with a loss of metabolic homeostasis, with cofactors such as nicotinamide adenine dinucleotide (NAD + ) declining over time. The decrease in NAD + production has been linked to the age-related loss of circulating extracellular nicotinamide phosphoribosyltransferase (eNAMPT), the rate-limiting enzyme in the NAD + biosynthetic pathway. eNAMPT is found almost exclusively in extracellular vesicles (EVs), providing a mechanism for the distribution of the enzyme in different tissues. Currently, the physiological cause for the release of eNAMPT is unknown, and how it may be affected by age and physical exercise. Here, we show that release of small EVs into the bloodstream is stimulated following moderate intensity exercise in humans. Exercise also increased the eNAMPT content in EVs, most prominently in young individuals with higher aerobic fitness. Both mature fit and young unfit individuals exhibited a limited increase in EV-eNAMPT release following exercise, indicating that this mechanism is related to both the age and physical fitness of a person. Notably, unfit mature individuals were unable to increase the release of eNAMPT in EVs after exercise, suggesting that lower fitness levels and aging attenuate this important signalling mechanism in the body. EVs isolated from exercising humans containing eNAMPT were able to alter the abundance of NAD + and SIRT1 activity in recipient cells compared to pre-exercise EVs, indicating a pathway for inter-tissue signalling promoted through exercise. Our results suggest a mechanism to limit age-related NAD + decline, through the systemic delivery of eNAMPT via EVs released during exercise., (© 2022 The Authors. Aging Cell published by Anatomical Society and John Wiley & Sons Ltd.)

Ageing is associated with a variety of pathophysiological changes, including development of insulin resistance, progressive decline in β-cell function and chronic inflammation, all of which affect metabolic homeostasis in response to nutritional and environmental stimuli. SIRT1, the mammalian nicotinamide adenine dinucleotide ( NAD)-dependent protein deacetylase, and nicotinamide phosphoribosyltransferase ( NAMPT), the rate-limiting NAD biosynthetic enzyme, together comprise a novel systemic regulatory network, named the ' NAD World', that orchestrates physiological responses to internal and external perturbations and maintains the robustness of the physiological system in mammals. In the past decade, an accumulating body of evidence has demonstrated that SIRT1 and NAMPT, two essential components in the NAD World, play a critical role in regulating insulin sensitivity and insulin secretion throughout the body. In this article, we will summarize the physiological significance of SIRT1 and NAMPT-mediated NAD biosynthesis in metabolic regulation and discuss the ideas of functional hierarchy and frailty in determining the robustness of the system. We will also discuss the potential of key NAD intermediates as effective nutriceuticals for the prevention and the treatment of age-associated metabolic complications, such as type 2 diabetes. [ABSTRACT FROM AUTHOR]

Oncogenic rearrangements of the TFE3 transcription factor gene are found in two distinct human cancers. These include ASPSCR1-TFE3 in all cases of alveolar soft part sarcoma ( ASPS) and ASPSCR1-TFE3, PRCC-TFE3, SFPQ-TFE3 and others in a subset of paediatric and adult RCCs. Here we examined the functional properties of the ASPSCR1-TFE3 fusion oncoprotein, defined its target promoters on a genome-wide basis and performed a high-throughput RNA interference screen to identify which of its transcriptional targets contribute to cancer cell proliferation. We first confirmed that ASPSCR1-TFE3 has a predominantly nuclear localization and functions as a stronger transactivator than native TFE3. Genome-wide location analysis performed on the FU-UR-1 cell line, which expresses endogenous ASPSCR1-TFE3, identified 2193 genes bound by ASPSCR1-TFE3. Integration of these data with expression profiles of ASPS tumour samples and inducible cell lines expressing ASPSCR1-TFE3 defined a subset of 332 genes as putative up-regulated direct targets of ASPSCR1-TFE3, including MET (a previously known target gene) and 64 genes as down-regulated targets of ASPSCR1-TFE3. As validation of this approach to identify genuine ASPSCR1-TFE3 target genes, two up-regulated genes bound by ASPSCR1-TFE3, CYP17A1 and UPP1, were shown by multiple lines of evidence to be direct, endogenous targets of transactivation by ASPSCR1-TFE3. As the results indicated that ASPSCR1-TFE3 functions predominantly as a strong transcriptional activator, we hypothesized that a subset of its up-regulated direct targets mediate its oncogenic properties. We therefore chose 130 of these up-regulated direct target genes to study in high-throughput RNAi screens, using FU-UR-1 cells. In addition to MET, we provide evidence that 11 other ASPSCR1-TFE3 target genes contribute to the growth of ASPSCR1-TFE3-positive cells. Our data suggest new therapeutic possibilities for cancers driven by TFE3 fusions. More generally, this work establishes a combined integrated genomics/functional genomics strategy to dissect the biology of oncogenic, chimeric transcription factors. Copyright © 2013 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

FK866 is a specific inhibitor of NAMPT and induces apoptosis of leukemic cells by depletion of intracellular NAD+. Since up-regulation of NAMPT is associated with several cases of cancers, including leukemias, we asked whether in leukemic cells inhibition of NAMPT involves p53 pathway. We observed that FK866 induced apoptosis and reduced cell proliferation in NB-4, OCI-AML3 and MOLM-13 cell lines. In contrast, the leukemia cell lines, K-562 and Kasumi, containing nonfunctional p53 were relatively unaffected by FK866 treatment. Importantly, direct inhibition of sirtuins significantly reduced the viability of NB-4, OCI-AML3 and MOLM-13 cell lines. Activation of p53 by FK866 involved increased acetylation of p53 at lysine 382 with subsequent increase in the expression of p21 and BAX. Further, knockdown of p53 attenuated the effects of FK866 on apoptosis and cell cycle arrest, which was partly associated with decreased expression of p21 and BAX. Our results suggest the role of p53 acetylation pathway in the anti-leukemic effect of FK866. [ABSTRACT FROM AUTHOR]

PARP inhibitors have been proposed as a potential targeted therapy for patients with triple-negative (ER-, PR-, HER2-negative) breast cancers. However, it is as yet unclear as to whether single agent or combination therapy using PARP inhibitors would be most beneficial. To better understand the mechanisms that determine the response to PARP inhibitors, we investigated whether enzymes involved in metabolism of the PARP substrate, β-NAD+, might alter the response to a clinical PARP inhibitor. Using an olaparib sensitization screen in a triple-negative (TN) breast cancer model, we identified nicotinamide phosphoribosyltransferase (NAMPT) as a non-redundant modifier of olaparib response. NAMPT is a rate-limiting enzyme involved in the generation of the PARP substrate β-NAD+ and the suppression of β-NAD+ levels by NAMPT inhibition most likely explains these observations. Importantly, the combination of a NAMPT small molecule inhibitor, FK866, with olaparib inhibited TN breast tumour growth in vivo to a greater extent than either single agent alone suggesting that assessing NAMPT/PARP inhibitor combinations for the treatment of TN breast cancer may be warranted. [ABSTRACT FROM AUTHOR]

Abstract: Many countries are facing social and economic problems due to increased elderly demographics. With these demands, it is now critical to understand the fundamental regulatory mechanism for aging and longevity in mammals. Our studies on the mammalian NAD-dependent deacetylase SIRT1 and nicotinamide phosphoribosyltransferase (NAMPT)-mediated systemic NAD biosynthesis led us to propose a comprehensive model for the systemic regulatory network connecting metabolism and aging, termed the “NAD World”. In this article, I will discuss the importance of SIRT1 and NAMPT-mediated NAD biosynthesis in the NAD World and the system dynamics of this hierarchical network for the connection between metabolism and aging. [Copyright &y& Elsevier]

NAMPT encodes an enzyme catalysing the rate-limiting step in NAD biosynthesis. The extracellular form of the enzyme is known as adipokine visfatin. We detected SNP AM999341:g.669T>C (referred to as 669T>C) in intron 9 and SNP FN392209:g.358A>G (referred to as 358A>G) in the promoter of the gene. RH mapping linked the gene to microsatellite SW944. Linkage analysis placed the gene on the current USDA - USMARC linkage map at position 92 cM on SSC9. Association analyses were performed in a wild boar × Meishan F family (W × M), with 45 traits recorded (growth and fattening, fat deposition, muscling, meat quality, stress resistance and other traits), and in a commercial Landrace × Chinese-European (LCE) synthetic population with records for 15 traits (growth, fat deposition, muscling, intramuscular fat, meat colour and backfat fatty acid content). In the W × M, SNP 669T>C was associated with muscling, fat deposition, growth and fattening, meat quality and other traits and in the LCE with muscling, meat quality and backfat fatty acid composition. In the W × M, SNP 358A>G was associated with muscling, fat deposition, growth and other traits. After correction for multiple testing, the NAMPT haplotypes were associated in the W × M with, in descending order, muscling ( q = 0.0056), growth ( q = 0.0056), fat deposition ( q = 0.0109), fat-to-meat ratio ( q = 0.0135), cooling losses ( q = 0.0568) and longissimus pH ( q = 0.0695). The SNPs are hypothesized to be in linkage disequilibrium with a causative mutation affecting energy metabolism as a whole rather than fat metabolism alone. [ABSTRACT FROM AUTHOR]

Abstract: Sir2 mediates lifespan extension in lower eukaryotes but whether its mammalian homolog, sirtuin 1, silent mating type information regulation 2 homolog (SIRT1), is a longevity protein is controversial. We stably introduced the SIRT1 gene into human vascular smooth muscle cells (SMCs) and observed minimal extension of replicative lifespan. However, SIRT1 activity was found to be exquisitely dependent on nicotinamide phosphoribosyltransferase (Nampt) activity. Moreover, overexpression of Nampt converted SIRT1-overexpressing SMCs to senescence-resistant cells together with heightened SIRT1 activity, suppressed p21, and strikingly lengthened replicative lifespan. Thus, SIRT1 can markedly postpone SMC senescence, but this requires overcoming an otherwise vulnerable nicotinamide adenine dinucleotide salvage reaction in aging SMCs. [Copyright &y& Elsevier]

Agouti-related protein (AgRP) neurons in the arcuate nucleus of the hypothalamus regulates food intake and whole-body metabolism. NAD+ regulates multiple cellular processes controlling energy metabolism. Yet, its role in hypothalamic AgRP neurons to control food intake is poorly understood. Here, we aimed to assess whether genetic deletion of nicotinamide phosphoribosyltransferase (Nampt), a rate-limiting enzyme in NAD+ production, affects AgRP neuronal function to impact whole-body metabolism and food intake. Metabolic parameters during fed and fasted states, and upon systemic ghrelin and leptin administration were studied in AgRP-specific Nampt knockout (ARNKO) mice. We monitored neuropeptide expression levels and density of AgRP neurons in ARNKO mice from embryonic to adult age. NPY cells were used to determine effects of NAMPT inhibition on neuronal viability, energy status, and oxidative stress in vitro. In these cells, NAD+ depletion reduced ATP levels, increased oxidative stress, and promoted cell death. Agrp expression in the hypothalamus of ARNKO mice gradually decreased after weaning due to progressive AgRP neuron degeneration. Adult ARNKO mice had normal glucose and insulin tolerance, but exhibited an elevated respiratory exchange ratio (RER) when fasted. Remarkably, fasting-induced food intake was unaffected in ARNKO mice when evaluated in metabolic cages, but fasting- and ghrelin-induced feeding and body weight gain decreased in ARNKO mice when evaluated outside metabolic cages. Collectively, deletion of Nampt in AgRP neurons causes progressive neurodegeneration and impairs fasting and ghrelin responses in a context-dependent manner. Our data highlight an essential role of Nampt in AgRP neuron function and viability. [ABSTRACT FROM AUTHOR]

Aim: Neurons in the arcuate nucleus of the hypothalamus are involved in regulation of food intake and energy expenditure, and dysregulation of signalling in these neurons promotes development of obesity. The role of the rate-limiting enzyme in the NAD + salvage pathway, nicotinamide phosphoribosyltransferase (NAMPT), for regulation energy homeostasis by the hypothalamus has not been extensively studied., Methods: We determined whether Nampt mRNA or protein levels in the hypothalamus of mice were affected by diet-induced obesity, by fasting and re-feeding, and by leptin and ghrelin treatment. Primary hypothalamic neurons were treated with FK866, a selective inhibitor of NAMPT, or rAAV carrying shRNA directed against Nampt, and levels of reactive oxygen species (ROS) and mitochondrial respiration were assessed. Fasting and ghrelin-induced food intake was measured in mice in metabolic cages after intracerebroventricular (ICV)-mediated FK866 administration., Results: NAMPT levels in the hypothalamus were elevated by administration of ghrelin and leptin. In diet-induced obese mice, both protein and mRNA levels of NAMPT decreased in the hypothalamus. NAMPT inhibition in primary hypothalamic neurons significantly reduced levels of NAD + , increased levels of ROS, and affected the expression of Agrp, Pomc and genes related to mitochondrial function. Finally, ICV-induced NAMPT inhibition by FK866 did not cause malaise or anhedonia, but completely ablated fasting- and ghrelin-induced increases in food intake., Conclusion: Our findings indicate that regulation of NAMPT levels in hypothalamic neurons is important for the control of fasting- and ghrelin-induced food intake., (© 2020 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.)

Aging decreases skeletal muscle mass and strength, but aerobic and resistance exercise training maintains skeletal muscle function. NAD+ is a coenzyme for ATP production and a required substrate for enzymes regulating cellular homeostasis. In skeletal muscle, NAD+ is mainly generated by the NAD+ salvage pathway in which nicotinamide phosphoribosyltransferase (NAMPT) is rate‐limiting. NAMPT decreases with age in human skeletal muscle, and aerobic exercise training increases NAMPT levels in young men. However, whether distinct modes of exercise training increase NAMPT levels in both young and old people is unknown. We assessed the effects of 12 weeks of aerobic and resistance exercise training on skeletal muscle abundance of NAMPT, nicotinamide riboside kinase 2 (NRK2), and nicotinamide mononucleotide adenylyltransferase (NMNAT) 1 and 3 in young (≤35 years) and older (≥55 years) individuals. NAMPT in skeletal muscle correlated negatively with age (r2 = 0.297, P < 0.001, n = 57), and VO2peak was the best predictor of NAMPT levels. Moreover, aerobic exercise training increased NAMPT abundance 12% and 28% in young and older individuals, respectively, whereas resistance exercise training increased NAMPT abundance 25% and 30% in young and in older individuals, respectively. None of the other proteins changed with exercise training. In a separate cohort of young and old people, levels of NAMPT, NRK1, and NMNAT1/2 in abdominal subcutaneous adipose tissue were not affected by either age or 6 weeks of high‐intensity interval training. Collectively, exercise training reverses the age‐dependent decline in skeletal muscle NAMPT abundance, and our findings highlight the value of exercise training in ameliorating age‐associated deterioration of skeletal muscle function. [ABSTRACT FROM AUTHOR]