ABSTRACT: IFNg is an essential and pleiotropic activator of monocytes, but little is known about the changes in cellular metabolism required for IFNg-induced activation. We sought to characterize and elucidate the mechanisms by which IFNg reprograms monocyte metabolism to support its immunologic activities. Monocytes from healthy controls and patients with gain-of-function mutations in STAT1 (STAT1 GOF), or loss-of-function mutations in mitochondrial complex I (Leigh syndrome) and NADPH oxidase (chronic granulomatous disease, CGD) were metabolically phenotyped. We found that IFNg increased oxygen consumption rates (OCR), indicative of reactive oxygen species generation by both mitochondria and NADPH oxidase. Transcriptional profiling of human monocyte derived macrophages revealed that this oxidative phenotype was driven by an IFNg-induced reprogramming of NAD+ metabolism, which is dependent on nicotinamide phosphoribosyltransferase (NAMPT)-mediated NAD+ salvage to generate NADH and NADPH for oxidation by mitochondrial complex I and NADPH oxidase, respectively. Monocytes from patients with STAT1 GOF demonstrated higher than normal OCR, while monocytes from Leigh syndrome and CGD patients demonstrated reduced OCR. Chemical inhibition of NAMPT completely abrogated the IFNg-induced oxygen consumption, comparable to levels observed in CGD patients. These data identify an IFNg-induced, NAMPT-dependent, NAD+ salvage pathway that is critical for IFNg activation of human monocytes.
Project description:Loss of NADPH oxidase activity in phagocytes leads to altered cellular responses and exaggerated inflammation in Chronic Granulomatous Disease (CGD). We sought to assess the effects of Nox2 absence on monocyte-derived macrophages (MoMacs) in gp91phox-/y mice during zymosan-induced peritonitis. MoMacs from CGD and wild type (WT) peritonea were lavaged and characterized over time. Though the numbers harvested from both genotypes were virtually identical, there were marked differences in maturation: newly recruited WT MoMacs rapidly enlarged and matured with loss of Ly6C and gain of MHCII, CD206 and CD36, while MoMacs in CGD remained small and were mostly Ly6C+MHCII-. RNAseq analyses showed few intrinsic differences between genotypes in newly recruited MoMacs, but significant differences over time. WT MoMacs demonstrated changes in metabolism, adhesion and reparative functions, while CGD MoMacs remained inflammatory. Labeling with PKH dye demonstrated that while WT MoMacs were mostly recruited within the first 24 hours and remained in the peritoneum while maturing and enlarging, CGD monocytes continued to stream into the peritoneum for days with many migrating to the diaphragm where they were found in fibrin(ogen) clots surrounding clusters of neutrophils in what appeared to be nascent granulomata. Importantly, these observations appeared to be entirely driven by the milieu: adoptive transfer of CGD MoMacs into inflamed peritonea of WT mice resulted in immunophenotypic maturation and behavior, and conversely, altered maturation/behavior of WT MoMacs was seen after adoptive transfer into inflamed peritonea of CGD mice. These data demonstrate heightened recruitment and fundamental failure of MoMac maturation in CGD.
Project description:Neural stem/progenitor cell (NSPC) proliferation and self-renewal, as well as insult-induced differentiation, decrease markedly with age, but 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 for 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 injury. These phenotypes recapitulate defects in NSPCs during aging, implicating Nampt-mediated NAD+ biosynthesis as a mediator of these age-associated functional declines. Total RNA obtained from neurospheres derived from postnatal hippocampi subjected to 48 hours in vitro of incubation with Nampt-specific inhibitor FK866 (10 nM, 4 samples) or vehicle (DMSO, 1:1000, 4 samples).
Project description:NAD is an obligate co-factor for the catabolism of metabolic fuels in all cell types. However, the availability of NAD in several tissues can become limited during genotoxic stress and the course of natural aging. The point at which NAD restriction imposes functional limitations on tissue physiology remains unknown. We examined this question in murine skeletal muscle by specifically depleting Nampt, an essential enzyme in the NAD salvage pathway. Knockout mice exhibited a dramatic 85% decline in intramuscular NAD content, accompanied by fiber degeneration and progressive loss of both muscle strength and treadmill endurance. Administration of the NAD precursor nicotinamide riboside rapidly ameliorated functional deficits and restored muscle mass, despite having only a modest effect on the intramuscular NAD pool. Additionally, lifelong overexpression of Nampt preserved muscle NAD levels and exercise capacity in aged mice, supporting a critical role for tissue-autonomous NAD homeostasis in maintaining muscle mass and function. Messenger RNA was isolated from quadriceps muscle of mice from three different age groups and three different genotypes. Wildtype mice were aged 4, 7, and 24 months. Mice deficient for Nampt in skeletal muscle (mNKO) were aged 7 months. Mice overexpressing Nampt in skeletal muscle were aged 4 and 24 months.
Project description:Type 2 diabetes (T2D) has become an epidemic in our modern lifestyle, likely due to calorie-rich diets overwhelming our adaptive metabolic pathways. One such pathway is mediated by nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in mammalian NAD+ biosynthesis, and the NAD+-dependent protein deacetylase SIRT1. Here we show that NAMPT-mediated NAD+ biosynthesis is severely compromised in metabolic organs by high-fat diet (HFD). Strikingly, nicotinamide mononucleotide (NMN), a product of the NAMPT reaction and a key NAD+ intermediate, ameliorates glucose intolerance by restoring NAD+ levels in HFD-induced T2D mice. NMN also enhances hepatic insulin sensitivity and restores gene expression related to oxidative stress, inflammatory response, and circadian rhythm, partly through SIRT1 activation. Furthermore, NAD+ and NAMPT levels show significant decreases in multiple organs during aging, and NMN improves glucose intolerance and lipid profiles in age-induced T2D mice. These findings provide critical insights into a novel intervention against diet- and age-induced T2D. 4 regular chow fed mice (RC1-4) vs 4 high-fat diet fed (HFD) (HFD1a-4a) mice were analyzed on one chip (Chip-A). 4 HFD mice (HFD1b-4b) vs 4 HFD-NMN treated mice (NMN1-4) were examined on the other chip (Chip-B).
Project description:Ovarian cancer follows a characteristic progression pattern, forming multiple tumor masses enriched with cancer stem cells (CSCs) within the abdomen. Most patients become resistant to standard platinum-based drugs, necessitating a change in treatment approach. To target CSCs, inhibiting NAMPT, which is the rate-limiting enzyme in the salvage pathway for NAD+ synthesis, has been explored. KPT-9274 is an innovative drug targeting both NAMPT and PAK4. However, its effectiveness against ovarian cancer had not been validated. Here, we show the efficacy and mechanisms of KPT-9274 in treating 3D-cultured spheroids that are resistant to platinum-based drugs. In these spheroids, KPT-9274 not only inhibited NAD+ production in NAMPT-dependent cell lines, but also suppressed NADPH and ATP production, indicating reduced mitochondrial function. It also downregulated expression of inflammation and gene repair-related genes. Moreover, by altering PAK4's mostly cytoplasmic localization, the compound hindered kinase activity, leading to decreased phosphorylation of S6 Ribosomal protein, AKT, and β-Catenin in the cytoplasm and its suppression was NAD+- dependent. These findings suggest that KPT-9274 could be a promising treatment for ovarian cancer patients resistant to platinum drugs, emphasizing the need for precision medicine to identify the specific NAD+-producing pathway a tumor relies on before treatment.
Project description:Cellular senescence is a stable cell growth arrest that is implicated in tissue aging and cancer. Senescent cells are characterized by an upregulation of proinflammatory and immunosuppressive cytokines and chemokines, which is termed as senescence-associated secretory phenotype (SASP). NAD+ metabolism plays a critical role in both tissue aging and cancer. However, the role of NAD+ metabolism in regulating the SASP is not well understood. Here we show that nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of the NAD+ salvage pathway, governs the strengths of proinflammatory SASP during senescence. In contrast to downregulation of NAMPT during replicative senescence, NAMPT is upregulated during oncogene-induced senescence. NAMPT selectively regulates proinflammatory, but not immunosuppressive, SASP. NAMPT is regulated by HMGA1 through a distal enhancer element during senescence. HMGA1/NAMPT/NAD+ signaling axis promotes proinflammatory SASP through enhancing glycolysis and mitochondria respiration. Mechanistically, HMGA1/NAMPT promotes proinflammatory SASP through NAD+-mediated suppression of AMPK kinase, which suppresses p53-mediated inhibition of p38MAPK to enhance NFb activity. SASP regulation by NAD+ metabolism is independent of senescence-associated cell growth arrest. An increase in NAD+ levels is sufficient to convert SASP from low to high levels during replicative senescence. Together, we conclude that NAD+ metabolism governs the strengths of proinflammatory SASP. Given the tumor promoting effects of proinflammatory SASP, our results suggest that anti-ageing dietary NAD+ augmentation should be administered with precision.
Project description:NAMPT is expressed in all cells during normal cell homeostasis. However, melanoma cells have a higher energetic demand and increase NAMPT expression. Our data show that IFNg signaling upregulates NAMPT in both human and mouse melanoma cells leading to increased cell growth and expression kinetics. The purpose of this experiment was to identify how IFNg inducible Nampt alters cell kinetics and we did this by treating melanoma cells with the combination of IFNg and FK866.
Project description:Neural stem/progenitor cell (NSPC) proliferation and self-renewal, as well as insult-induced differentiation, decrease markedly with age, but 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 for 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 injury. These phenotypes recapitulate defects in NSPCs during aging, implicating Nampt-mediated NAD+ biosynthesis as a mediator of these age-associated functional declines.
Project description:Reactive oxygen species (ROS) production is a conserved immune response, primarily mediated in Arabidopsis by the respiratory burst oxidase homolog D (RBOHD), a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase associated with the plasma membrane. A rapid increase in NADPH is necessary to fuel RBOHD proteins and hence maintain ROS production. However, the molecular mechanism underlying the NADPH generation for fueling RBOHD remains unclear. In this study, we isolated a new mutant allele of flagellin-insensitive 4 (FIN4), encoding the first enzyme in de novo NAD biosynthesis. fin4 mutants show reduced NADPH levels and impaired ROS production. However, FIN4 and other genes involved in the NAD- and NADPH-generating pathways are not highly upregulated upon elicitor treatment. Therefore, we hypothesized that a cytosolic NADP-linked dehydrogenase might be post-transcriptionally activated to keep the NADPH supply close to RBOHD. RPM1-INDUCED PROTEIN KINASE (RIPK), a receptor-like cytoplasmic kinase, regulates broad-spectrum ROS signaling in plant immunity. We then isolated the proteins associated with RIPK and identified NADP-malic enzyme 2 (NADP-ME2), an NADPH-generating enzyme. Compared with wild-type plants, nadp-me2 mutants display decreased NADP-ME activity, lower NADPH levels, as well as reduced ROS production in response to immune elicitors. Furthermore, we found that RIPK can directly phosphorylate NADP-ME2 and enhance its activity in vitro. The phosphorylation of NADP-ME2 S371 residue contributes to ROS production upon immune elicitor treatment and the susceptibility to the necrotrophic bacterium, Pectobacterium carotovorum. Overall, our study suggests that RIPK activates NADP-ME2 to rapidly increase cytosolic NADPH, hence fueling RBOHD to sustain ROS production in plant immunity.