Metabolic and molecular insights into an essential role of nicotinamide phosphoribosyltransferase

Cryptic phosphoribosylase activity of NAMPT restricts the virion incorporation of viral proteins

As obligate intracellular pathogens, viruses activate host metabolic enzymes to supply intermediates that support progeny production. Nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of salvage nicotinamide adenine dinucleotide (NAD+) synthesis, is an interferon-inducible protein that inhibits the replication of several RNA and DNA viruses through unknown mechanisms. Here, we show that NAMPT restricts herpes simplex virus type 1 (HSV-1) replication by impeding the virion incorporation of viral proteins owing to its phosphoribosyl-hydrolase (phosphoribosylase) activity, which is independent of the role of NAMPT in NAD+ synthesis. Proteomics analysis of HSV-1-infected cells identifies phosphoribosylated viral structural proteins, particularly glycoproteins and tegument proteins, which are de-phosphoribosylated by NAMPT in vitro and in cells. Chimeric and recombinant HSV-1 carrying phosphoribosylation-resistant mutations show that phosphoribosylation promotes the incorporation of structural proteins into HSV-1 virions and subsequent virus entry. Loss of NAMPT renders mice highly susceptible to HSV-1 infection. Our work describes an additional enzymatic activity of a metabolic enzyme in viral infection and host defence, offering a system to interrogate the roles of protein phosphoribosylation in metazoans.

Function of NAD metabolism in white adipose tissue: lessons from mouse models

Nicotinamide Adenine Dinucleotide (NAD) is an endogenous substance in redox reactions and regulates various functions in metabolism. NAD and its precursors are known for their anti-ageing and anti-obesity properties and are mainly active in the liver and muscle. Boosting NAD+ through supplementation with the precursors, such as nicotinamide mononucleotide (NMN) or nicotinamide riboside (NR), enhances insulin sensitivity and circadian rhythm in the liver, and improves mitochondrial function in the muscle. Recent evidence has revealed that the adipose tissue could be another direct target of NAD supplementation by attenuating inflammation and fat accumulation. Moreover, murine studies with genetically modified models demonstrated that nicotinamide phosphoribosyltransferase (NAMPT), a NAD regulatory enzyme that synthesizes NMN, played a critical role in lipogenesis and lipolysis in an adipocyte-specific manner. The tissue-specific effects of NAD+ metabolic pathways indicate a potential of the NAD precursors to control metabolic stress particularly via focusing on adipose tissue. Therefore, this narrative review raises an importance of NAD metabolism in white adipose tissue (WAT) through a variety of studies using different mouse models.

eNAMPT is a novel therapeutic target for mitigation of coronary microvascular disease in type 2 diabetes

AIMS/HYPOTHESIS

Individuals with diabetes are at high risk of cardiovascular complications, which significantly increase morbidity/mortality. Coronary microvascular disease (CMD) is recognised as a critical contributor to the increased cardiac mortality observed in people with diabetes. Therefore, there is an urgent need for treatments that are specific to CMD. eNAMPT (extracellular nicotinamide phosphoribosyltransferase) is a damage-associated molecular pattern and TLR4 ligand, whose plasma levels are elevated in people with diabetes. This study was thus designed to investigate the pathogenic role of intracellular nicotinamide phosphoribosyltransferase (iNAMPT) and eNAMPT in promoting the development of CMD in a preclinical murine model of type 2 diabetes.

METHODS

An inducible type 2 diabetic mouse model was generated by a single injection of low-dose streptozocin (75 mg/kg, i.p.) combined with a high-fat diet for 16 weeks. The in vivo effects of i/eNAMPT inhibition on cardiac endothelial cell (CEC) function were evaluated by using Nampt+/- heterozygous mice, chronic administration of eNAMPT-neutralising monoclonal antibody (mAb) or use of an NAMPT enzymatic inhibitor (FK866).

RESULTS

As expected, diabetic wild-type mice exhibited significantly lower coronary flow velocity reserve (CFVR), a determinant of coronary microvascular function, compared with control wild-type mice. eNAMPT plasma levels or expression in CECs were significantly greater in diabetic mice than in control mice. Furthermore, in comparison with diabetic wild-type mice, diabetic Nampt+/- heterozygous mice showed markedly improved CFVR, accompanied by increased left ventricular capillary density and augmented endothelium-dependent relaxation (EDR) in the coronary artery. NAMPT inhibition by FK866 or an eNAMPT-neutralising mAb significantly increased CFVR in diabetic mice. Furthermore, administration of the eNAMPT mAb upregulated expression of angiogenesis- and EDR-related genes in CECs from diabetic mice. Treatment with either eNAMPT or NAD+ significantly decreased CEC migration and reduced EDR in coronary arteries, partly linked to increased production of mitochondrial reactive oxygen species.

CONCLUSIONS/INTERPRETATION

These data indicate that increased i/eNAMPT expression contributes to the development of diabetic coronary microvascular dysfunction, and provide compelling support for eNAMPT inhibition as a novel and effective therapeutic strategy for CMD in diabetes.

Enhancement of PPARα-Inhibited Leucine Metabolism-Stimulated β-Casein Synthesis and Fatty Acid Synthesis in Primary Bovine Mammary Epithelial Cells

Leucine, a kind of branched-chain amino acid, plays a regulatory role in the milk production of mammalian mammary glands, but its regulatory functions and underlying molecular mechanisms remain unknown. This work showed that a leucine-enriched mixture (LEUem) supplementation increased the levels of milk protein and milk fat synthesis in primary bovine mammary epithelial cells (BMECs). RNA-seq of leucine-treated BMECs indicated alterations in lipid metabolism, translation, ribosomal structure and biogenesis, and inflammatory response signaling pathways. Meanwhile, the supplementation of leucine resulted in mTOR activation and increased the expression of BCKDHA, FASN, ACC, and SCD1. Interestingly, the expression of PPARα was independently correlated with the leucine-supplemented dose. PPARα activated by WY-14643 caused significant suppression of lipogenic genes expression. Furthermore, WY-14643 attenuated leucine-induced β-casein synthesis and enhanced the level of BCKDHA expression. Moreover, promoter analysis revealed a peroxisome-proliferator-response element (PPRE) site in the bovine BCKDHA promoter, and WY-14643 promoted the recruitment of PPARα onto the BCKDHA promoter. Together, the present data indicate that leucine promotes the synthesis of β-casein and fatty acid and that PPARα-involved leucine catabolism is the key target.

The Interferon-inducible NAMPT acts as a protein phosphoribosylase to restrict viral infection

As obligate intracellular pathogens, viruses often activate host metabolic enzymes to supply intermediates that support progeny production. Nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of the salvage NAD+ synthesis, is an interferon-inducible protein that inhibits the replication of several RNA and DNA viruses with unknown mechanism. Here we report that NAMPT restricts herpes simplex virus 1 (HSV-1) replication via phosphoribosyl-hydrolase activity toward key viral structural proteins, independent of NAD+ synthesis. Deep mining of enriched phosphopeptides of HSV-1-infected cells identified phosphoribosylated viral structural proteins, particularly glycoproteins and tegument proteins. Indeed, NAMPT de-phosphoribosylates viral proteins in vitro and in cells. Chimeric and recombinant HSV-1 carrying phosphoribosylation-resistant mutations show that phosphoribosylation promotes the incorporation of structural proteins into HSV-1 virions and subsequent virus entry. Moreover, loss of NAMPT renders mice highly susceptible to HSV-1 infection. The work describes a hidden enzyme activity of a metabolic enzyme in viral infection and host defense, offering a system to interrogate roles of phosphoribosylation in metazoans.

NAD+ salvage governs the immunosuppressive capacity of mesenchymal stem cells

Mesenchymal stem/stromal cells (MSCs) possess robust immunoregulatory functions and are promising therapeutics for inflammatory disorders. This capacity is not innate but is activated or 'licensed' by inflammatory cytokines. The licensing mechanism remains unclear. Here, we examined whether inflammatory cytokines metabolically reprogrammed MSCs to confer this immunoregulatory capacity. In response to stimulation by inflammatory cytokines, MSCs exhibited a dramatic increase in the consumption of glucose, which was accompanied by an enhanced use of nicotinamide adenine dinucleotide (NAD+) and increased expression of nicotinamide phosphoribosyltransferase (NAMPT), a central enzyme in the salvage pathway for NAD+ production. When NAD+ synthesis was blocked by inhibiting or depleting NAMPT, the immunosuppressive function of MSCs induced by inflammatory cytokines was greatly attenuated. Consequently, when NAD+ metabolism in MSCs was perturbed, their therapeutic benefit was decreased in mice suffering from inflammatory bowel disease and acute liver injury. Further analysis revealed that NAMPT-driven production of NAD+ was critical for the inflammatory cytokine-induced increase in glycolysis in MSCs. Furthermore, the increase in glycolysis led to succinate accumulation in the tricarboxylic acid cycle, which led to hypoxia-inducible factor 1α (HIF-1α) stabilization and subsequently increased the transcription of key glycolytic genes, thereby persistently maintaining glycolytic flux. This study demonstrated that unlike its proinflammatory role in immune cells, NAD+ metabolism governs the anti-inflammatory function of MSCs during inflammation.

The NAD salvage pathway in mesenchymal cells is indispensable for skeletal development in mice

NAD is an essential co-factor for cellular energy metabolism and multiple other processes. Systemic NAD+ deficiency has been implicated in skeletal deformities during development in both humans and mice. NAD levels are maintained by multiple synthetic pathways but which ones are important in bone forming cells is unknown. Here, we generate mice with deletion of Nicotinamide Phosphoribosyltransferase (Nampt), a critical enzyme in the NAD salvage pathway, in all mesenchymal lineage cells of the limbs. At birth, NamptΔPrx1 exhibit dramatic limb shortening due to death of growth plate chondrocytes. Administration of the NAD precursor nicotinamide riboside during pregnancy prevents the majority of in utero defects. Depletion of NAD post-birth also promotes chondrocyte death, preventing further endochondral ossification and joint development. In contrast, osteoblast formation still occurs in knockout mice, in line with distinctly different microenvironments and reliance on redox reactions between chondrocytes and osteoblasts. These findings define a critical role for cell-autonomous NAD homeostasis during endochondral bone formation.

Interactions between Intestinal Homeostasis and NAD+ Biology in Regulating Incretin Production and Postprandial Glucose Metabolism

The intestine has garnered attention as a target organ for developing new therapies for impaired glucose tolerance. The intestine, which produces incretin hormones, is the central regulator of glucose metabolism. Glucagon-like peptide-1 (GLP-1) production, which determines postprandial glucose levels, is regulated by intestinal homeostasis. Nicotinamide phosphoribosyltransferase (NAMPT)-mediated nicotinamide adenine dinucleotide (NAD⁺) biosynthesis in major metabolic organs such as the liver, adipose tissue, and skeletal muscle plays a crucial role in obesity- and aging-associated organ derangements. Furthermore, NAMPT-mediated NAD⁺ biosynthesis in the intestines and its upstream and downstream mediators, adenosine monophosphate-activated protein kinase (AMPK) and NAD⁺-dependent deacetylase sirtuins (SIRTs), respectively, are critical for intestinal homeostasis, including gut microbiota composition and bile acid metabolism, and GLP-1 production. Thus, boosting the intestinal AMPK-NAMPT-NAD⁺-SIRT pathway to improve intestinal homeostasis, GLP-1 production, and postprandial glucose metabolism has gained significant attention as a novel strategy to improve impaired glucose tolerance. Herein, we aimed to review in detail the regulatory mechanisms and importance of intestinal NAMPT-mediated NAD⁺ biosynthesis in regulating intestinal homeostasis and GLP-1 secretion in obesity and aging. Furthermore, dietary and molecular factors regulating intestinal NAMPT-mediated NAD⁺ biosynthesis were critically explored to facilitate the development of new therapeutic strategies for postprandial glucose dysregulation.

Kynurenine pathway metabolites modulated the comorbidity of IBD and depressive symptoms through the immune response

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is defined as chronic inflammation in the gastrointestinal tract. Notably, more than 20% of people with IBD experience depressive symptoms. Understanding the immunological mechanism of chronic intestinal inflammation on cognitive behavior has become a key research focus. Previous studies have shown that a dysregulated immune response contributes to chronic inflammation and depressive symptoms. The tolerant phenotype exhibited by immune cells regulates the course of chronic inflammation in distinct ways. In addition, neuroglia, such as microglia and astrocytes specific to the brain, are also influenced by deregulated inflammation to mediate the development of depressive symptoms. The kynurenine pathway (KP), a significant tryptophan metabolic pathway, transforms tryptophan into a series of KP metabolites that modulate chronic inflammation and depressive symptoms. In particular, indoleamine 2,3-dioxygenase 1 (IDO1), a rate-limiting enzyme in the KP, is activated by chronic inflammation and leads to the production of kynurenine. In addition, disruption of the brain-gut axis induced by IBD allows kynurenine to cross the blood-brain barrier (BBB) and form a series of neuroactive kynurenine metabolites in glial cells. Among them, quinolinic acid continuously accumulates in the brain, indicating depression. Thus, KP metabolites are critical for driving the comorbidity of IBD and depressive symptoms. In this review, the pathological mechanism of KP metabolite-mediated chronic intestinal inflammation and depressive symptoms by regulating the immune response is summarized according to the latest reports.

Beyond Pellagra-Research Models and Strategies Addressing the Enduring Clinical Relevance of NAD Deficiency in Aging and Disease

Research into the functions of nicotinamide adenine dinucleotide (NAD) has intensified in recent years due to the insight that abnormally low levels of NAD are involved in many human pathologies including metabolic disorders, neurodegeneration, reproductive dysfunction, cancer, and aging. Consequently, the development and validation of novel NAD-boosting strategies has been of central interest, along with the development of models that accurately represent the complexity of human NAD dynamics and deficiency levels. In this review, we discuss pioneering research and show how modern researchers have long since moved past believing that pellagra is the overt and most dramatic clinical presentation of NAD deficiency. The current research is centered on common human health conditions associated with moderate, but clinically relevant, NAD deficiency. In vitro and in vivo research models that have been developed specifically to study NAD deficiency are reviewed here, along with emerging strategies to increase the intracellular NAD concentrations.

Regulation of differentiation and generation of osteoclasts in rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA), which affects nearly 1% of the world's population, is a debilitating autoimmune disease. Bone erosion caused by periarticular osteopenia and synovial pannus formation is the most destructive pathological changes of RA, also leads to joint deformity and loss of function,and ultimately affects the quality of life of patients. Osteoclasts (OCs) are the only known bone resorption cells and their abnormal differentiation and production play an important role in the occurrence and development of RA bone destruction; this remains the main culprit behind RA.

METHOD

Based on the latest published literature and research progress at home and abroad, this paper reviews the abnormal regulation mechanism of OC generation and differentiation in RA and the possible targeted therapy.

RESULT

OC-mediated bone destruction is achieved through the regulation of a variety of cytokines and cell-to-cell interactions, including gene transcription, epigenetics and environmental factors. At present, most methods for the treatment of RA are based on the regulation of inflammation, the inhibition of bone injury and joint deformities remains unexplored.

DISCUSSION

This article will review the mechanism of abnormal differentiation of OC in RA, and summarise the current treatment oftargeting cytokines in the process of OC generation and differentiation to reduce bone destruction in patients with RA, which isexpected to become a valuable treatment choice to inhibit bone destruction in RA.

Metabolic control of histone acetylation for precise and timely regulation of minor ZGA in early mammalian embryos

Metabolism feeds into the regulation of epigenetics via metabolic enzymes and metabolites. However, metabolic features, and their impact on epigenetic remodeling during mammalian pre-implantation development, remain poorly understood. In this study, we established the metabolic landscape of mouse pre-implantation embryos from zygote to blastocyst, and quantified some absolute carbohydrate metabolites. We integrated these data with transcriptomic and proteomic data, and discovered the metabolic characteristics of the development process, including the activation of methionine cycle from 8-cell embryo to blastocyst, high glutaminolysis metabolism at blastocyst stage, enhanced TCA cycle activity from the 8-cell embryo stage, and active glycolysis in the blastocyst. We further demonstrated that oxidized nicotinamide adenine dinucleotide (NAD⁺) synthesis is indispensable for mouse pre-implantation development. Mechanistically, in part, NAD⁺ is required for the exit of minor zygotic gene activation (ZGA) by cooperating with SIRT1 to remove zygotic H3K27ac. In human, NAD⁺ supplement can promote the removal of zygotic H3K27ac and benefit pre-implantation development. Our findings demonstrate that precise and timely regulation of minor ZGA is controlled by metabolic dynamics, and enhance our understanding of the metabolism of mammalian early embryos.

Redox regulation of the immune response

The immune-inflammatory response is associated with increased nitro-oxidative stress. The aim of this mechanistic review is to examine: (a) the role of redox-sensitive transcription factors and enzymes, ROS/RNS production, and the activity of cellular antioxidants in the activation and performance of macrophages, dendritic cells, neutrophils, T-cells, B-cells, and natural killer cells; (b) the involvement of high-density lipoprotein (HDL), apolipoprotein A1 (ApoA1), paraoxonase-1 (PON1), and oxidized phospholipids in regulating the immune response; and (c) the detrimental effects of hypernitrosylation and chronic nitro-oxidative stress on the immune response. The redox changes during immune-inflammatory responses are orchestrated by the actions of nuclear factor-κB, HIF1α, the mechanistic target of rapamycin, the phosphatidylinositol 3-kinase/protein kinase B signaling pathway, mitogen-activated protein kinases, 5' AMP-activated protein kinase, and peroxisome proliferator-activated receptor. The performance and survival of individual immune cells is under redox control and depends on intracellular and extracellular levels of ROS/RNS. They are heavily influenced by cellular antioxidants including the glutathione and thioredoxin systems, nuclear factor erythroid 2-related factor 2, and the HDL/ApoA1/PON1 complex. Chronic nitro-oxidative stress and hypernitrosylation inhibit the activity of those antioxidant systems, the tricarboxylic acid cycle, mitochondrial functions, and the metabolism of immune cells. In conclusion, redox-associated mechanisms modulate metabolic reprogramming of immune cells, macrophage and T helper cell polarization, phagocytosis, production of pro- versus anti-inflammatory cytokines, immune training and tolerance, chemotaxis, pathogen sensing, antiviral and antibacterial effects, Toll-like receptor activity, and endotoxin tolerance.

Nicotinamide riboside relieves the severity of experimental necrotizing enterocolitis by regulating endothelial function via eNOS deacetylation

BACKGROUND

Nicotinamide adenine dinucleotide (NAD+) is involved in regulating oxidative stress. Although NAD+ is associated with various health issues, its role in the intestinal microcirculation in necrotizing enterocolitis (NEC) remains to be confirmed. In the current study, we explored whether nicotinamide riboside (NR), a natural NAD + precursor, ameliorates the severity of NEC through endothelial nitric oxide synthase(eNOS) signaling.

METHODS

A mouse experimental NEC model was induced by formula gavage and hypoxia in full-term mouse pups. Intestinal endothelial cells (MIMECs) were isolated and subjected to stress using tumor necrosis factor (TNF)-α. NR was administered to assess the intestinal microcirculation and lipid peroxidation levels and to explore the involved signaling pathways.

RESULTS

NAD + levels were reduced after induction of NEC stress, which was associated with intestinal injury. NR administration promoted NAD + levels, attenuated oxidative stress and relieved the symptoms of experimental NEC, which were relevant to increased intestinal microcirculatory perfusion through the sirtuin (SIRT) 1 pathway in experimental NEC mice. However, this improvement was not found in eNOS-knockout mice. Consistently, MIMECs exposed to TNFα showed decreased SIRT1 activity associated with increased eNOS acetylation, which could bring about endothelial dysfunction due to limited nitric oxide production. NR administration increased the NAD + content and repressed the production of reactive oxygen species (ROS) in MIMECs under TNFα stress. NR also promoted SIRT1 activity and accordingly suppressed the eNOS acetylation levels under TNFα stress.

CONCLUSION

The current data indicate that NR administration improves the survival of experimental NEC mice via SIRT1-associated eNOS acetylation/deacetylation modulation, which is implicated in endothelial dysfunction. Although NR is commonly found in the human diet, it may also be a promising strategy for NEC treatment because of its pathogenic association with NEC.

Targeting NAD+: is it a common strategy to delay heart aging?

Heart aging is the main susceptible factor to coronary heart disease and significantly increases the risk of heart failure, especially when the aging heart is suffering from ischemia-reperfusion injury. Numerous studies with NAD+ supplementations have suggested its use in anti-aging treatment. However, systematic reviews regarding the overall role of NAD+ in cardiac aging are scarce. The relationship between NAD+ signaling and heart aging has yet to be clarified. This review comprehensively summarizes the current studies on the role of NAD+ signaling in delaying heart aging from the following aspects: the influence of NAD+ supplementations on the aging heart; the relationship and cross-talks between NAD+ signaling and other cardiac aging-related signaling pathways; Importantly, the therapeutic potential of targeting NAD+ in delaying heart aging will be discussed. In brief, NAD+ plays a vital role in delaying heart aging. However, the abnormalities such as altered glucose and lipid metabolism, oxidative stress, and calcium overload could also interfere with NAD+ function in the heart. Therefore, the specific physiopathology of the aging heart should be considered before applying NAD+ supplementations. We believe that this article will help augment our understanding of heart aging mechanisms. In the meantime, it provides invaluable insights into possible therapeutic strategies for preventing age-related heart diseases in clinical settings.

Intestinal Epithelial NAD+ Biosynthesis Regulates GLP-1 Production and Postprandial Glucose Metabolism in Mice

Obesity is associated with perturbations in incretin production and whole-body glucose metabolism, but the precise underlying mechanism remains unclear. Here, we tested the hypothesis that nicotinamide phosphoribosyltransferase (NAMPT), which mediates the biosynthesis of nicotinamide adenine dinucleotide (NAD+), a key regulator of cellular energy metabolism, plays a critical role in obesity-associated intestinal pathophysiology and systemic metabolic complications. To this end, we generated a novel mouse model, namely intestinal epithelial cell-specific Nampt knockout (INKO) mice. INKO mice displayed diminished glucagon-like peptide-1 (GLP-1) production, at least partly contributing to reduced early-phase insulin secretion and postprandial hyperglycemia. Mechanistically, loss of NAMPT attenuated the Wnt signaling pathway, resulting in insufficient GLP-1 production. We also found that diet-induced obese mice had compromised intestinal NAMPT-mediated NAD+ biosynthesis and Wnt signaling pathway, associated with impaired GLP-1 production and whole-body glucose metabolism, resembling the INKO mice. Finally, administration of a key NAD+ intermediate, nicotinamide mononucleotide (NMN), restored intestinal NAD+ levels and obesity-associated metabolic derangements, manifested by a decrease in ileal Proglucagon expression and GLP-1 production as well as postprandial hyperglycemia in INKO and diet-induced obese mice. Collectively, our study provides mechanistic and therapeutic insights into intestinal NAD+ biology related to obesity-associated dysregulation of GLP-1 production and postprandial hyperglycemia.

Maintenance of NAD+ Homeostasis in Skeletal Muscle during Aging and Exercise

Nicotinamide adenine dinucleotide (NAD) is a versatile chemical compound serving as a coenzyme in metabolic pathways and as a substrate to support the enzymatic functions of sirtuins (SIRTs), poly (ADP-ribose) polymerase-1 (PARP-1), and cyclic ADP ribose hydrolase (CD38). Under normal physiological conditions, NAD+ consumption is matched by its synthesis primarily via the salvage pathway catalyzed by nicotinamide phosphoribosyltransferase (NAMPT). However, aging and muscular contraction enhance NAD+ utilization, whereas NAD+ replenishment is limited by cellular sources of NAD+ precursors and/or enzyme expression. This paper will briefly review NAD+ metabolic functions, its roles in regulating cell signaling, mechanisms of its degradation and biosynthesis, and major challenges to maintaining its cellular level in skeletal muscle. The effects of aging, physical exercise, and dietary supplementation on NAD+ homeostasis will be highlighted based on recent literature.

Metabolic Enzyme Triosephosphate Isomerase 1 and Nicotinamide Phosphoribosyltransferase, Two Independent Inflammatory Indicators in Rheumatoid Arthritis: Evidences From Collagen-Induced Arthritis and Clinical Samples

Metabolic intervention is a novel anti-rheumatic approach. The glycolytic regulator NAMPT has been identified as a therapeutic target of rheumatoid arthritis (RA), while other metabolic regulators coordinating NAMPT to perpetuate inflammation are yet to be investigated. We continuously monitored and validated expression changes of Nampt and inflammatory indicators in peripheral while blood cells from rats with collagen-induced arthritis (CIA). Gene transcriptional profiles of Nampt+ and Nampt++ samples from identical CIA rats were compared by RNA-sequencing. Observed gene expression changes were validated in another batch of CIA rats, and typical metabolic regulators with persistent changes during inflammatory courses were further investigated in human subjects. According to expression differences of identified genes, RA patients were assigned into different subsets. Clinical manifestation and cytokine profiles among them were compared afterwards. Nampt overexpression typically occurred in CIA rats during early stages, when iNos and Il-1β started to be up-regulated. Among differentially expressed genes between Nampt+ and Nampt++ CIA rat samples, changes of Tpi1, the only glycolytic enzyme identified were sustained in the aftermath of acute inflammation. Similar to NAMPT, TPI1 expression in RA patients was higher than general population, which was synchronized with increase in RFn as well as inflammatory monocytes-related cytokines like Eotaxin. Meanwhile, RANTES levels were relatively low when NAMPT and TPI1 were overexpressed. Reciprocal interactions between TPI1 and HIF-1α were observed. HIF-1α promoted TPI1 expression, while TPI1 co-localized with HIF-1α in nucleus of inflammatory monocytes. In short, although NAMPT and TPI1 dominate different stages of CIA, they similarly provoke monocyte-mediated inflammation.

A Humanized Monoclonal Antibody Targeting Extracellular Nicotinamide Phosphoribosyltransferase Prevents Aggressive Prostate Cancer Progression

Prostate cancer (PCa) is the major cause of cancer-related death in males; however, effective treatments to prevent aggressive progression remain an unmet need. We have previously demonstrated that secreted extracellular nicotinamide phosphoribosyltransferase (eNAMPT) is a multifunctional innate immunity regulator that promotes PCa invasion. In the current study, we further investigate the therapeutic effects of an eNAMPT-neutralizing humanized monoclonal antibody (ALT-100 mAb) in preclinical PCa orthotopic xenograft models. We utilized human aggressive PCa cells (DU145 or PC3) for prostate implantation in SCID mice receiving weekly intraperitoneal injections of either ALT-100 mAb or IgG/PBS (control) for 12 weeks. Prostatic tumors and solid organs were examined for tumor growth, invasion, and metastasis and for biochemical and immunohistochemistry evidence of NFκB activation. ALT-100 mAb treatment significantly improved overall survival of SCID mice implanted with human PCa orthotopic prostate xenografts while inducing tumor necrosis, decreasing PCa proliferation and reducing local invasion and distal metastases. The ALT-100 mAb inhibits NFκB phosphorylation and signaling in PCa cells both in vitro and in vivo. This study demonstrates that eNAMPT neutralization effectively prevents human PCa aggressive progression in preclinical models, indicating its high potential to directly address the unmet need for an effective targeted therapy for patients with aggressive PCa.

NAMPT-derived NAD+ fuels PARP1 to promote skin inflammation through parthanatos cell death

Several studies have revealed a correlation between chronic inflammation and nicotinamide adenine dinucleotide (NAD+) metabolism, but the precise mechanism involved is unknown. Here, we report that the genetic and pharmacological inhibition of nicotinamide phosphoribosyltransferase (Nampt), the rate-limiting enzyme in the salvage pathway of NAD+ biosynthesis, reduced oxidative stress, inflammation, and keratinocyte DNA damage, hyperproliferation, and cell death in zebrafish models of chronic skin inflammation, while all these effects were reversed by NAD+ supplementation. Similarly, genetic and pharmacological inhibition of poly(ADP-ribose) (PAR) polymerase 1 (Parp1), overexpression of PAR glycohydrolase, inhibition of apoptosis-inducing factor 1, inhibition of NADPH oxidases, and reactive oxygen species (ROS) scavenging all phenocopied the effects of Nampt inhibition. Pharmacological inhibition of NADPH oxidases/NAMPT/PARP/AIFM1 axis decreased the expression of pathology-associated genes in human organotypic 3D skin models of psoriasis. Consistently, an aberrant induction of NAMPT and PARP activity, together with AIFM1 nuclear translocation, was observed in lesional skin from psoriasis patients. In conclusion, hyperactivation of PARP1 in response to ROS-induced DNA damage, fueled by NAMPT-derived NAD+, mediates skin inflammation through parthanatos cell death.

NAD+ Metabolism and Diseases with Motor Dysfunction

Neurodegenerative diseases result in the progressive deterioration of the nervous system, with motor and cognitive impairments being the two most observable problems. Motor dysfunction could be caused by motor neuron diseases (MNDs) characterized by the loss of motor neurons, such as amyotrophic lateral sclerosis and Charcot-Marie-Tooth disease, or other neurodegenerative diseases with the destruction of brain areas that affect movement, such as Parkinson's disease and Huntington's disease. Nicotinamide adenine dinucleotide (NAD+) is one of the most abundant metabolites in the human body and is involved with numerous cellular processes, including energy metabolism, circadian clock, and DNA repair. NAD+ can be reversibly oxidized-reduced or directly consumed by NAD+-dependent proteins. NAD+ is synthesized in cells via three different paths: the de novo, Preiss-Handler, or NAD+ salvage pathways, with the salvage pathway being the primary producer of NAD+ in mammalian cells. NAD+ metabolism is being investigated for a role in the development of neurodegenerative diseases. In this review, we discuss cellular NAD+ homeostasis, looking at NAD+ biosynthesis and consumption, with a focus on the NAD+ salvage pathway. Then, we examine the research, including human clinical trials, focused on the involvement of NAD+ in MNDs and other neurodegenerative diseases with motor dysfunction.

Expression and localization of apelin and its receptor in the testes of diabetic mice and its possible role in steroidogenesis

Type 1 diabetes mellitus (T1DM) is a metabolic disorder with severe hyperglycemia, one of the complications of which is testicular dysfunctions, androgen deficiency and decreased male fertility. In the diabetic testes, the expression and signaling pathways of leptin and a number of other adipokines are significantly changed. However, there is no information on the localization and expression of adipokine, apelin and its receptor (APJ) in the diabetic testes, although there is information on the involvement of apelin in the regulation of reproductive functions. The aim of this study was to investigate the expression and localization of apelin and APJ in the testes of mice with streptozotocin-induced T1DM and to estimate the effects of agonist (apelin-13) and antagonist (ML221) of APJ on the testosterone production by diabetic testis explants in the in vitro conditions. We first detected the expression of apelin and its receptor in the mouse testes, and showed an increased intratesticular expression of apelin and APJ along with the reduced testosterone secretion in T1DM. Using imunohistochemical approach, we showed that apelin and APJ are localized in the Leydig and germ cells, and in diabetes, the amount of these proteins was significantly higher than in the control mice. The diabetic testes had a decrease in germ cell proliferation (the reduced PCNA and GCNA levels) and an increase in apoptosis (the increased active caspase-3 and decreased BCL2 levels). These results suggest an involvement of apelin and APJ in T1DM-induced testicular pathogenesis. Treatment of the cultured testis explants with ML221 significantly increased the testosterone secretion, whereas apelin-13 was ineffective. Thus, hyperapelinemia in the testes can significantly contribute to testicular pathogenesis in T1DM, and pharmacological inhibition of apelin receptors can improve testicular steroidogenesis.

Association of serum vaspin, apelin, and visfatin levels and stroke risk in a Chinese case-control study

Adipose tissue acts as an active endocrine organ secreting a number of adipokines and may be involved in biological mechanism of stroke. Vaspin, apelin, and visfatin play important roles in the regulation of vascular disorders.Our aim was to evaluate whether the concentrations of vaspin, apelin, and visfatin were associated with stroke risk.A total of 235 patients with stroke (156 patients with ischemic stroke and 79 patients with hemorrhagic stroke) and 235 age- and gender-matched healthy controls were included in this study. A sandwich ELISA was developed to measure the serum vaspin, apelin, and visfatin levels.There was a statistically significant difference in the median levels of serum vaspin, apelin, and visfatin levels between stroke cases and controls (vaspin: 1.50 vs 1.07 ng/ml; apelin: 1.56 vs 1.32 pg/ml; visfatin: 23.40 vs 19.65 ng/ml; all P values <.001). Multiple logistic regression analysis showed that, serum vaspin and visfatin levels were significantly inversely associated with increased risk of stroke, and the odds ratios (ORs) in the highest tertile were 2.25 [95% confidence interval (CI) 1.38-3.67; P for trend <.001] for vaspin and 2.56 (95% CI 1.46-4.47; P for trend <.001) for visfatin, respectively, compared with the lowest tertile. Higher apelin levels were marginally associated with lower stroke risk (P for trend =.060).Our study indicated that higher vaspin, apelin, and visfatin levels might be associated with increased stroke risk. Necessary prospective cohort studies should be conducted to confirm this association in the future.

Macrophages provide a transient muscle stem cell niche via NAMPT secretion

Skeletal muscle regenerates through the activation of resident stem cells. Termed satellite cells, these normally quiescent cells are induced to proliferate by wound-derived signals¹. Identifying the source and nature of these cues has been hampered by an inability to visualize the complex cell interactions that occur within the wound. Here we use muscle injury models in zebrafish to systematically capture the interactions between satellite cells and the innate immune system after injury, in real time, throughout the repair process. This analysis revealed that a specific subset of macrophages 'dwell' within the injury, establishing a transient but obligate niche for stem cell proliferation. Single-cell profiling identified proliferative signals that are secreted by dwelling macrophages, which include the cytokine nicotinamide phosphoribosyltransferase (Nampt, which is also known as visfatin or PBEF in humans). Nampt secretion from the macrophage niche is required for muscle regeneration, acting through the C-C motif chemokine receptor type 5 (Ccr5), which is expressed on muscle stem cells. This analysis shows that in addition to their ability to modulate the immune response, specific macrophage populations also provide a transient stem-cell-activating niche, directly supplying proliferation-inducing cues that govern the repair process that is mediated by muscle stem cells. This study demonstrates that macrophage-derived niche signals for muscle stem cells, such as NAMPT, can be applied as new therapeutic modalities for skeletal muscle injury and disease.

Nicotinamide adenine dinucleotide (NAD+): essential redox metabolite, co-substrate and an anti-cancer and anti-ageing therapeutic target

Nicotinamide adenine dinucleotide (NAD+) and its reduced form NADH are essential coupled redox metabolites that primarily promote cellular oxidative (catabolic) metabolic reactions. This enables energy generation through glycolysis and mitochondrial respiration to support cell growth and survival. In addition, many key enzymes that regulate diverse cell functions ranging from gene expression to proteostasis require NAD+ as a co-substrate for their catalytic activity. This includes the NAD+-dependent sirtuin family of protein deacetylases and the PARP family of DNA repair enzymes. Whilst their vital activity consumes NAD+ which is cleaved to nicotinamide, several pathways exist for re-generating NAD+ and sustaining NAD+ homeostasis. However, there is growing evidence of perturbed NAD+ homeostasis and NAD+-regulated processes contributing to multiple disease states. NAD+ levels decline in the human brain and other organs with age and this is associated with neurodegeneration and other age-related diseases. Dietary supplementation with NAD+ precursors is being investigated to counteract this. Paradoxically, many cancers have increased dependency on NAD+. Clinical efforts to exploit this have so far shown limited success. Emerging new opportunities to exploit dysregulation of NAD+ metabolism in cancers are critically discussed. An update is also provided on other key NAD+ research including perturbation of the NAD+ salvage enzyme NAMPT in the context of the tumour microenvironment (TME), methodology to study subcellular NAD+ dynamics in real-time and the regulation of differentiation by competing NAD+ pools.

NAD+ metabolism, stemness, the immune response, and cancer

NAD⁺ was discovered during yeast fermentation, and since its discovery, its important roles in redox metabolism, aging, and longevity, the immune system and DNA repair have been highlighted. A deregulation of the NAD⁺ levels has been associated with metabolic diseases and aging-related diseases, including neurodegeneration, defective immune responses, and cancer. NAD⁺ acts as a cofactor through its interplay with NADH, playing an essential role in many enzymatic reactions of energy metabolism, such as glycolysis, oxidative phosphorylation, fatty acid oxidation, and the TCA cycle. NAD⁺ also plays a role in deacetylation by sirtuins and ADP ribosylation during DNA damage/repair by PARP proteins. Finally, different NAD hydrolase proteins also consume NAD⁺ while converting it into ADP-ribose or its cyclic counterpart. Some of these proteins, such as CD38, seem to be extensively involved in the immune response. Since NAD cannot be taken directly from food, NAD metabolism is essential, and NAMPT is the key enzyme recovering NAD from nicotinamide and generating most of the NAD cellular pools. Because of the complex network of pathways in which NAD⁺ is essential, the important role of NAD⁺ and its key generating enzyme, NAMPT, in cancer is understandable. In the present work, we review the role of NAD⁺ and NAMPT in the ways that they may influence cancer metabolism, the immune system, stemness, aging, and cancer. Finally, we review some ongoing research on therapeutic approaches.

FOSL1 is a novel mediator of endotoxin/lipopolysaccharide-induced pulmonary angiogenic signaling

Systemic sepsis is a known risk factor for bronchopulmonary dysplasia (BPD) in premature infants, a disease characterized by dysregulated angiogenesis and impaired vascular and alveolar development. We have previoulsy reported that systemic endotoxin dysregulates pulmonary angiogenesis resulting in alveolar simplification mimicking BPD in neonatal mice, but the underlying mechanisms remain unclear. We undertook an unbiased discovery approach to identify novel signaling pathways programming sepsis-induced deviant lung angiogenesis. Pulmonary endothelial cells (EC) were isolated for RNA-Seq from newborn C57BL/6 mice treated with intraperitoneal lipopolysaccharide (LPS) to mimic systemic sepsis. LPS significantly differentially-regulated 269 genes after 6 h, and 1,934 genes after 24 h. Using bioinformatics, we linked 6 h genes previously unknown to be modulated by LPS to 24 h genes known to regulate angiogenesis/vasculogenesis to identify pathways programming deviant angiogenesis. An immortalized primary human lung EC (HPMEC-im) line was generated by SV40 transduction to facilitate mechanistic studies. RT-PCR and transcription factor binding analysis identified FOSL1 (FOS like 1) as a transcriptional regulator of LPS-induced downstream angiogenic or vasculogenic genes. Over-expression and silencing studies of FOSL1 in immortalized and primary HPMEC demonstrated that baseline and LPS-induced expression of ADAM8, CXCR2, HPX, LRG1, PROK2, and RNF213 was regulated by FOSL1. FOSL1 silencing impaired LPS-induced in vitro HPMEC angiogenesis. In conclusion, we identified FOSL1 as a novel regulator of sepsis-induced deviant angiogenic signaling in mouse lung EC and human fetal HPMEC.

Nicotinamide phosphoribosyltransferase postpones rat bone marrow mesenchymal stem cell senescence by mediating NAD+-Sirt1 signaling

In vitro replicative senescence affects MSC characteristics and functionality, thus severely restricting their application in regenerative medicine and MSC-based therapies. Previously, we found that MSC natural senescence is accompanied by altered intracellular nicotinamide adenine dinucleotide (NAD⁺) metabolism, in which Nampt plays a key role. However, whether Nampt influences MSC replicative senescence is still unclear. Our study showed that Nampt expression is down-regulated during MSC replicative senescence. Nampt depletion via a specific Nampt inhibitor FK866 or Nampt knockdown in early passage MSCs led to enhanced senescence as indicated by senescence-like morphology, reduced proliferation, and adipogenic and osteogenic differentiation, and increased senescence-associated-β-galactosidase activity and the expression of the senescence-associated factor p16^INK4a. Conversely, Nampt overexpression ameliorated senescence-associated phenotypic features in late passage MSCs. Further, Nampt inhibition resulted in reduced intracellular NAD⁺ content, NAD⁺/NADH ratio, and Sirt1 activity, whereas overexpression had the opposite effects. Exogenous intermediates involved in NAD⁺ biosynthesis not only rescued replicative senescent MSCs but also alleviated FK866-induced MSC senescence. Thus, Nampt suppresses MSC senescence via mediating NAD⁺-Sirt1 signaling. This study provides novel mechanistic insights into MSC replicative senescence and a promising strategy for the severe shortage of cells for MSC-based therapies.

Time-Restricted Eating: Benefits, Mechanisms, and Challenges in Translation

Eating out of phase with daily circadian rhythms induces metabolic desynchrony in peripheral metabolic organs and may increase chronic disease risk. Time-restricted eating (TRE) is a dietary approach that consolidates all calorie intake to 6- to 10-h periods during the active phase of the day, without necessarily altering diet quality and quantity. TRE reduces body weight, improves glucose tolerance, protects from hepatosteatosis, increases metabolic flexibility, reduces atherogenic lipids and blood pressure, and improves gut function and cardiometabolic health in preclinical studies. This review discusses the importance of meal timing on the circadian system, the metabolic health benefits of TRE in preclinical models and humans, the possible mechanisms of action, the challenges we face in implementing TRE in humans, and the possible consequences of delaying initiation of TRE.

The interplay between oxidative stress and bioenergetic failure in neuropsychiatric illnesses: can we explain it and can we treat it?

Nitro-oxidative stress and lowered antioxidant defences play a key role in neuropsychiatric disorders such as major depression, bipolar disorder and schizophrenia. The first part of this paper details mitochondrial antioxidant mechanisms and their importance in reactive oxygen species (ROS) detoxification, including details of NO networks, the roles of H₂O₂ and the thioredoxin/peroxiredoxin system, and the relationship between mitochondrial respiration and NADPH production. The second part highlights and identifies the causes of the multiple pathological sequelae arising from self-amplifying increases in mitochondrial ROS production and bioenergetic failure. Particular attention is paid to NAD⁺ depletion as a core cause of pathology; detrimental effects of raised ROS and reactive nitrogen species on ATP and NADPH generation; detrimental effects of oxidative and nitrosative stress on the glutathione and thioredoxin systems; and the NAD⁺-induced signalling cascade, including the roles of SIRT1, SIRT3, PGC-1α, the FOXO family of transcription factors, Nrf1 and Nrf2. The third part discusses proposed therapeutic interventions aimed at mitigating such pathology, including the use of the NAD⁺ precursors nicotinamide mononucleotide and nicotinamide riboside, both of which rapidly elevate levels of NAD⁺ in the brain and periphery following oral administration; coenzyme Q₁₀ which, when given with the aim of improving mitochondrial function and reducing nitro-oxidative stress in the brain, may be administered via the use of mitoquinone, which is in essence ubiquinone with an attached triphenylphosphonium cation; and N-acetylcysteine, which is associated with improved mitochondrial function in the brain and produces significant decreases in oxidative and nitrosative stress in a dose-dependent manner.

Aerobic and resistance exercise training reverses age-dependent decline in NAD+ salvage capacity in human skeletal muscle

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.

Fasting- and ghrelin-induced food intake is regulated by NAMPT in the hypothalamus

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.

Age-related NAD+ decline

Nicotinamide adenine dinucleotide (NAD+) is an essential metabolite that is reported to decline in concentration in tissues of aged animals. Strategies to increase NAD+ availability have shown promise in treating many conditions in rodents, including age-related degeneration, which has in turn driven intense interest in the effects of supplements on human health. However, many aspects of NAD+ metabolism remain poorly understood, and human data are limited. Here, we discuss the state of the evidence for an age-related decline in NAD+, along with potential mechanistic explanations, including increased consumption or decreased synthesis of NAD+ and changes in the composition of cells or tissues with age. Key challenges for the field involve the development of better tools to resolve information on the NAD+ content of specific cells and subcellular compartments as well as determining the threshold levels at which NAD+ depletion triggers physiological consequences in different tissues. Understanding how NAD+ metabolism changes with age in humans may ultimately allow the design of more targeted strategies to maintain its availability, such as inhibition of key consumers in specific tissues or direct delivery of precursors to sites of deficiency. In the meantime, human clinical trials with oral supplements are poised to provide some of the first direct evidence as to whether increasing NAD+ availability can impact human physiology. Thus, it is an exciting time for NAD+ research, with much remaining to be learned in terms of both basic biology and potential therapeutic applications.

Silencing of NAMPT leads to up-regulation of insulin receptor substrate 1 gene expression in U87 glioma cells

Objective. The aim of the present study was to investigate the effect of adipokine NAMPT (nicotinamide phosphoribosyltransferase) silencing on the expression of genes encoding IRS1 (insulin receptor substrate 1) and some other proliferation related proteins in U87 glioma cells for evaluation of the possible significance of this adipokine in intergenic interactions.

Methods. The silencing of NAMPT mRNA was introduced by NAMPT specific siRNA. The expression level of NAMPT, IGFBP3, IRS1, HK2, PER2, CLU, BNIP3, TPD52, GADD45A, and MKI67 genes was studied in U87 glioma cells by quantitative polymerase chain reaction. Anti-visfatin antibody was used for detection of NAMPT protein by Western-blot analysis.

Results. It was shown that the silencing of NAMPT mRNA led to a strong down-regulation of NAMPT protein and significant modification of the expression of IRS1, IGFBP3, CLU, HK2, BNIP3, and MKI67 genes in glioma cells and a strong up-regulation of IGFBP3 and IRS1 and down-regulation of CLU, BNIP3, HK2, and MKI67 gene expressions. At the same time, no significant changes were detected in the expression of GADD45A, PER2, and TPD52 genes in glioma cells treated by siRNA specific to NAMPT. Furthermore, the silencing of NAMPT mRNA suppressed the glioma cell proliferation.

Conclusions. Results of this investigation demonstrated that silencing of NAMPT mRNA with corresponding down-regulation of NAMPT protein and suppression of the glioma cell proliferation affected the expression of IRS1 gene as well as many other genes encoding the proliferation related proteins. It is possible that dysregulation of most of the studied genes in glioma cells after silencing of NAMPT is reflected by a complex of intergenic interactions and that NAMPT is an important factor for genome stability and regulatory mechanisms contributing to the control of glioma cell metabolism and proliferation.

Involvement of Novel Adipokines, Chemerin, Visfatin, Resistin and Apelin in Reproductive Functions in Normal and Pathological Conditions in Humans and Animal Models

It is well known that adipokines are endocrine factors that are mainly secreted by white adipose tissue. Their central role in energy metabolism is currently accepted. More recently, their involvement in fertility regulation and the development of some reproductive disorders has been suggested. Data concerning the role of leptin and adiponectin, the two most studied adipokines, in the control of the reproductive axis are consistent. In recent years, interest has grown about some novel adipokines, chemerin, visfatin, resistin and apelin, which have been found to be strongly associated with obesity and insulin-resistance. Here, we will review their expression and role in male and female reproduction in humans and animal models. According to accumulating evidence, they could regulate the secretion of GnRH (Gonadotropin-Releasing Hormone), gonadotropins and steroids. Furthermore, their expression and that of their receptors (if known), has been demonstrated in the human and animal hypothalamo-pituitary-gonadal axis. Like leptin and adiponectin, these novel adipokines could thus represent metabolic sensors that are able to regulate reproductive functions according to energy balance changes. Therefore, after investigating their role in normal fertility, we will also discuss their possible involvement in some reproductive troubles known to be associated with features of metabolic syndrome, such as polycystic ovary syndrome, gestational diabetes mellitus, preeclampsia and intra-uterine growth retardation in women, and sperm abnormalities and testicular pathologies in men.

NAMPT overexpression alleviates alcohol-induced hepatic steatosis in mice

Nicotinamide phosphoribosyltransferase (NAMPT) is a rate-limiting enzyme in mammalian nicotinamide adenine dinucleotide (NAD)⁺ biosynthesis. Through its NAD⁺-biosynthetic activity, NAMPT influences the activity of NAD⁺-dependent enzymes, such as sirtuins. NAMPT is able to modulate processes involved in the pathogenesis of non-alcohol induced fatty liver disease (NAFLD), but the roles NAMPT plays in development of alcoholic liver disease (ALD) still remain unknown. Here, we show that ethanol treatment suppresses the expression of Nampt in hepatocytes. Consistently, chronic ethanol administration also reduces Nampt expression in the mouse liver. We next demonstrate that hepatocytes infected with Ad-NAMPT adenovirus exhibit significantly elevated intracellular NAD⁺ levels and decreased ethanol-induced triglyceride (TG) accumulation. Similarly, adenovirus-mediated overexpression of NAMPT in mice ameliorates ethanol induced hepatic steatosis. Moreover, we demonstrate that SIRT1 is required to mediate the effects of NAMPT on reduction of hepatic TG accumulation and serum ALT, AST levels in ethanol-fed mice. Our results provide important insights in targeting NAMPT for treating alcoholic fatty liver disease.

Intestinal phosphate absorption: The paracellular pathway predominates?

IMPACT STATEMENT

This review summarizes the work on transcellular intestinal phosphate absorption, arguing why this pathway is not the predominant pathway in humans consuming a "Western" diet. We then highlight the recent evidence which is strongly consistent with paracellular intestinal phosphate absorption mediating the bulk of intestinal phosphate absorption in humans.

Epigenetic regulation of NfatC1 transcription and osteoclastogenesis by nicotinamide phosphoribosyl transferase in the pathogenesis of arthritis

Nicotinamide phosphoribosyltransferase (NAMPT) functions in NAD synthesis, apoptosis, and inflammation. Dysregulation of NAMPT has been associated with several inflammatory diseases, including rheumatoid arthritis (RA). The purpose of this study was to investigate NAMPT’s role in arthritis using mouse and cellular models. Collagen-induced arthritis (CIA) in DBA/1J Nampt^+/− mice was evaluated by ELISA, micro-CT, and RNA-sequencing (RNA-seq). In vitro Nampt loss-of-function and gain-of-function studies on osteoclastogenesis were examined by TRAP staining, nascent RNA capture, luciferase reporter assays, and ChIP-PCR. Nampt-deficient mice presented with suppressed inflammatory bone destruction and disease progression in a CIA mouse model. Nampt expression was required for the epigenetic regulation of the Nfatc1 promoter and osteoclastogenesis. Finally, RNA-seq identified 690 differentially expressed genes in whole ankle joints which associated (P < 0.05) with Nampt expression and CIA. Selected target was validated by RT-PCR or functional characterization. We have provided evidence that NAMPT functions as a genetic risk factor and a potential therapeutic target to RA.

From the Cover: Inhibitors of Nicotinamide Phosphoribosyltransferase Cause Retinal Damage in Larval Zebrafish

Nicotinamide phosphoribosyltransferase (NAMPT) has been investigated as a target for oncology because it catalyzes a rate-limiting step in cellular energy metabolism to produce nicotinamide adenine dinucleotide. Small molecule inhibitors of NAMPT have been promising drug candidates but preclinical development has been hindered due to associated retinal toxicity. Here we demonstrate that larval zebrafish can predict retinal toxicity associated with this mechanism revealing an attractive alternative method for identifying such toxicities. Zebrafish permit higher throughput testing while using far lower quantities of test article compared with mammalian systems. NAMPT inhibitor-associated toxicity manifested in zebrafish as a loss of response to visual cues compared with auditory cues. Zebrafish retinal damage associated with NAMPT inhibitor treatment was confirmed through histopathology. Ranking 6 NAMPT inhibitors according to their impact on zebrafish vision revealed a positive correlation with their in vitro potencies on human tumor cells. This correlation indicates translatable pharmacodynamics between zebrafish and human NAMPT and is consistent with on-target activity as the cause of retinal toxicity associated with NAMPT inhibition. Together, these data illustrate the utility of zebrafish for identifying compounds that may cause ocular toxicity in mammals, and, likewise, for accelerating development of compounds with improved safety margins.

The chemistry of the vitamin B3 metabolome

The functional cofactors derived from vitamin B3 are nicotinamide adenine dinucleotide (NAD⁺), its phosphorylated form, nicotinamide adenine dinucleotide phosphate (NADP⁺) and their reduced forms (NAD(P)H). These cofactors, together referred as the NAD(P)(H) pool, are intimately implicated in all essential bioenergetics, anabolic and catabolic pathways in all forms of life. This pool also contributes to post-translational protein modifications and second messenger generation. Since NAD⁺ seats at the cross-road between cell metabolism and cell signaling, manipulation of NAD⁺ bioavailability through vitamin B3 supplementation has become a valuable nutritional and therapeutic avenue. Yet, much remains unexplored regarding vitamin B3 metabolism. The present review highlights the chemical diversity of the vitamin B3-derived anabolites and catabolites of NAD⁺ and offers a chemical perspective on the approaches adopted to identify, modulate and measure the contribution of various precursors to the NAD(P)(H) pool.

The c-MYC/NAMPT/SIRT1 feedback loop is activated in early classical and serrated route colorectal cancer and represents a therapeutic target

We have recently identified a positive feedback loop in which c-MYC increases silent information regulator 1 (SIRT1) protein level and activity through transcriptional activation of nicotinamide phosphoribosyltransferase (NAMPT) and NAD⁺ increase. Here, we determined the relevance of the c-MYC-NAMPT-SIRT1 feedback loop, including the SIRT1 inhibitor deleted in breast cancer 1 (DBC1), for the development of conventional and serrated colorectal adenomas. Immunohistochemical analyses of 104 conventional adenomas with low- and high-grade dysplasia and of 157 serrated lesions revealed that elevated expression of c-MYC, NAMPT, and SIRT1 characterized all conventional and serrated adenomas, whereas DBC1 was not differentially regulated. Analyzing publicly available pharmacogenomic databases from 43 colorectal cancer cell lines demonstrated that responsiveness towards a NAMPT inhibitor was significantly associated with alterations in PTEN and TGFBR2, while features such as BRAF or RNF43 alterations, or microsatellite instability typical for serrated route colorectal cancer, showed increased sensitivities for inhibition of NAMPT and SIRT1. Our findings suggest an activation of the c-MYC-NAMPT-SIRT1 feedback loop that may crucially contribute to initiation and development of both routes to colorectal cancer. Targeting of NAMPT or SIRT1 may represent novel therapeutic strategies with putative higher sensitivity of the serrated route colorectal cancer subtype.

Diet-dependent gene expression highlights the importance of Cytochrome P450 in detoxification of algal secondary metabolites in a marine isopod

Isopods of the genus Idotea have an unusual ability to feed on algae containing high amounts of chemical defense molecules, such as species of the genera Fucus and Ulva. In this study, we compared gene expression patterns of Idotea balthica individuals fed with Fucus vesiculosus to individuals fed with Ulva lactuca. We generated the first-ever transcriptome assembly for this species, and found 3,233 differentially expressed genes across feeding regimes. However, only a handful of biological functions were enriched with regard to differentially expressed genes, the most notable being "alkaloid metabolic process". Within this category, we found eight differentially expressed cytochrome P450 (CYP) unigenes, all of which had a higher expression in the U. lactuca diet treatment. A phylogenetic analysis showed that the differentially expressed CYP genes are closely related to a CYP gene described from the hepatopancreas of the spiny lobster Panulirus argus, and we hypothesize that these transcripts are involved in metabolite detoxification. This is a first step in the understanding of this algae-grazer interaction, and will form a basis for future work to characterize cytochrome P450 functioning in marine crustaceans.

NAD metabolism: Implications in aging and longevity

Nicotinamide adenine dinucleotide (NAD) is an important co-factor involved in numerous physiological processes, including metabolism, post-translational protein modification, and DNA repair. In living organisms, a careful balance between NAD production and degradation serves to regulate NAD levels. Recently, a number of studies have demonstrated that NAD levels decrease with age, and the deterioration of NAD metabolism promotes several aging-associated diseases, including metabolic and neurodegenerative diseases and various cancers. Conversely, the upregulation of NAD metabolism, including dietary supplementation with NAD precursors, has been shown to prevent the decline of NAD and exhibits beneficial effects against aging and aging-associated diseases. In addition, many studies have demonstrated that genetic and/or nutritional activation of NAD metabolism can extend the lifespan of diverse organisms. Collectively, it is clear that NAD metabolism plays important roles in aging and longevity. In this review, we summarize the basic functions of the enzymes involved in NAD synthesis and degradation, as well as the outcomes of their dysregulation in various aging processes. In addition, a particular focus is given on the role of NAD metabolism in the longevity of various organisms, with a discussion of the remaining obstacles in this research field.

The emergence of the nicotinamide riboside kinases in the regulation of NAD+ metabolism

The concept of replenishing or elevating NAD+ availability to combat metabolic disease and ageing is an area of intense research. This has led to a need to define the endogenous regulatory pathways and mechanisms cells and tissues utilise to maximise NAD+ availability such that strategies to intervene in the clinical setting are able to be fully realised. This review discusses the importance of different salvage pathways involved in metabolising the vitamin B3 class of NAD+ precursor molecules, with a particular focus on the recently identified nicotinamide riboside kinase pathway at both a tissue-specific and systemic level.

Dysregulation of NAD+ Metabolism Induces a Schwann Cell Dedifferentiation Program

The Schwann cell (SC) is the major component of the peripheral nervous system (PNS) that provides metabolic and functional support for peripheral axons. The emerging roles of SC mitochondrial function for PNS development and axonal stability indicate the importance of SC metabolism in nerve function and in peripheral neuropathies associated with metabolic disorders. Nicotinamide adenine dinucleotide (NAD+) is a crucial molecule in the regulation of cellular metabolism and redox homeostasis. Here, we investigated the roles of NAD+ metabolism in SC functions in vivo by mutating NAMPT, the rate-limiting enzyme of NAD+ biosynthesis, specifically in SCs. NAMPT SC knock-out male and female mice (NAMPT SCKO mice) had delayed SC maturation in development and developed hypomyelinating peripheral neuropathy without axon degeneration or decreased SC survival. JUN, a master regulator of SC dedifferentiation, is elevated in NAMPT SCKO SCs, suggesting that decreased NAD+ levels cause them to arrest at an immature stage. Nicotinic acid administration rescues the NAD+ decline and reverses the SC maturation defect and the development of peripheral neuropathy, indicating the central role of NAD+ in PNS development. Upon nicotinic acid withdrawal in adulthood, NAMPT SCKO mice showed rapid and severe peripheral neuropathy and activation of ERK/MEK/JUN signaling, which in turn promotes SC dedifferentiation. These data demonstrate the importance of NAD+ metabolism in SC maturation and nerve development and maintenance and suggest that altered SC NAD+ metabolism could underlie neuropathies associated with diabetes and aging.SIGNIFICANCE STATEMENT In this study, we showed that Schwann cell differentiation status is critically dependent on NAD+ homeostasis. Aberrant regulation of NAD+ biosynthesis via NAMPT deletion results in a blockade of Schwann cell maturation during development and severe peripheral neuropathy without significant axon loss. The phenotype can be rescued by supplementation with nicotinic acid; however, withdrawal of nicotinic acid leads to Schwann cell dedifferentiation, myelination defects, and death. These results provide new therapeutic possibilities for peripheral neuropathies associated with NAD+ decline during aging or diabetes.

Up-regulation of SFTPB expression and attenuation of acute lung injury by pulmonary epithelial cell-specific NAMPT knockdown

Although a deficiency of surfactant protein B (SFTPB) has been associated with lung injury, SFTPB expression has not yet been linked with nicotinamide phosphoribosyltransferase (NAMPT), a potential biomarker of acute lung injury (ALI). The effects of Nampt in the pulmonary epithelial cell on both SFTPB expression and lung inflammation were investigated in a LPS-induced ALI mouse model. Pulmonary epithelial cell-specific knockdown of Nampt gene expression, achieved by the crossing of Nampt gene exon 2 floxed mice with mice expressing epithelial-specific transgene Cre or by the use of epithelial-specific expression of anti-Nampt antibody cDNA, significantly attenuated LPS-induced ALI. Knockdown of Nampt expression was accompanied by lower levels of bronchoalveolar lavage (BAL) neutrophil infiltrates, total protein and TNF-α levels, as well as lower lung injury scores. Notably, Nampt knockdown was also associated with significantly increased BAL SFTPB levels relative to the wild-type control mice. Down-regulation of NAMPT increased the expression of SFTPB and rescued TNF-α-induced inhibition of SFTPB, whereas overexpression of NAMPT inhibited SFTPB expression in both H441 and A549 cells. Inhibition of NAMPT up-regulated SFTPB expression by enhancing histone acetylation to increase its transcription. Additional data indicated that these effects were mainly mediated by NAMPT nonenzymatic function via the JNK pathway. This study shows that pulmonary epithelial cell-specific knockdown of NAMPT expression attenuated ALI, in part, via up-regulation of SFTPB expression. Thus, epithelial cell-specific knockdown of Nampt may be a potential new and viable therapeutic modality to ALI.-Bi, G., Wu, L., Huang, P., Islam, S., Heruth, D. P., Zhang, L. Q., Li, D.-Y., Sampath, V., Huang, W., Simon, B. A., Easley, R. B., Ye, S. Q. Up-regulation of SFTPB expression and attenuation of acute lung injury by pulmonary epithelial cell-specific NAMPT knockdown.

Adipokines in neurovascular diseases

Adipose tissue is now described as an endocrine organ secreting a number of adipokines contributing to the development of inflammation and metabolic imbalance, but also endothelial dysfunction, vascular remodeling, atherosclerosis, and ischemic stroke. Leptin, adiponectin, and resistin are the most studied adipokines which play important roles in the regulation of cardiovascular homeostasis. Leptin and adiponectin mediate both proatherogenic and antiatherogenic responses. Leptin and adiponectin have been linked to the development of coronary heart disease and may be involved in the underlying biological mechanism of ischemic stroke. Resistin, a pro-inflammatory cytokine, is predictive of atherosclerosis and poor clinical outcomes in patients with coronary artery disease and ischemic stroke. The changes in serum levels of novel adipokines apelin, visfatin are also associated with acute ischemic stroke. These adipokines have been proposed as potential prognostic biomarkers of cardiovascular mortality/morbidity and therapeutic targets in patients with cardiometabolic diseases. In this article, we summarize the biologic role of the adipokines and discuss the link between dysfunctional adipose tissue and metabolic/inflammation imbalance, consequently endothelial damage, progression of atherosclerotic disease, and the occurrence of ischemic stroke.