Nicotinamide Phosphoribosyl Transferase/Pre-B Cell Colony-Enhancing Factor/Visfatin Is Required for Lymphocyte Development and Cellular Resistance to Genotoxic Stress

Abstract

*Nicotinamide phosphoribosyl transferase (Nampt)/pre-B cell colony-enhancing factor (PBEF)/visfatin is a protein displaying multiple functional properties. Originally described as a cytokine-like protein able to regulate B cell development, apoptosis, and glucose metabolism, this protein also plays an important role in NAD biosynthesis. To gain insight into its physiological role, we have generated a mouse strain expressing a conditional Nampt allele. Lack of Nampt expression strongly affects development of both T and B lymphocytes. Analysis of hemizygous cells and in vitro cell lines expressing distinct levels of Nampt illustrates the critical role of this protein in regulating intracellular NAD levels. Consequently, a clear relationship was found between intracellular Nampt levels and cell death in response to the genotoxic agent MNNG (N-methyl-N-nitro-N-nitrosoguanidine), confirming that this enzyme represents a key regulator of cell sensitivity to NAD-consuming stress secondary to poly(ADP-ribose) polymerases overactivation. By using mutant forms of this protein and a well-characterized pharmacological inhibitor (FK866), we unequivocally demonstrate that the ability of the Nampt to regulate cell viability during genotoxic stress requires its enzymatic activity. Collectively, these data demonstrate that Nampt participates in cellular resistance to genotoxic/oxidative stress, and it may confer to cells of the immune system the ability to survive during stressful situations such as inflammation.

Liver X Receptor (LXR) activation negatively regulates visfatin expression in macrophages

“…LXR activation reduced intracellular NAD+ concentration to a comparable extent as previously observed in NIH-3T3 murine fibroblasts transduced with visfatin specific shRNA, leading to 20-40% of NAD reduction, whereas cells over-expressing visfatin increased total intracellular NAD+ levels by 15-25% [17]. We suggest that the slightly decrease of intracellular NAD + concentration by LXR agonists is the consequence of visfatin mRNA reduction.…”

“…We suggest that the slightly decrease of intracellular NAD + concentration by LXR agonists is the consequence of visfatin mRNA reduction. Based on the large body of evidence suggesting a major role for NAD in controlling cell survival, altered NAD metabolism can directly affect macrophage lifespan [17]. NAD+ is a cofactor of many deacetylases of the Sirtuin family, especially SIRT1.…”

Intracellular nicotinamide adenine dinucleotide promotes TNF-induced necroptosis in a sirtuin-dependent manner

“…20 In keeping with the general role of NAD + as a survival factor in cells exposed to genotoxic stress, genetic ablation of Nampt and/or treatment with a specific NAMPT inhibitor (FK866) sensitized cells to the toxic effects of alkylating agents. 16,18 Similarly, overexpression of a catalytically active recombinant NAMPT protected the NIH-3T3 cell line from the toxicity of the same DNA alkylating agents, 18 further establishing a functional link between NAD + biosynthesis and sensitivity to stress-induced, PARP1-dependent cell death.…”

“…18 TNF is a pleiotropic cytokine regulating many cellular functions and known to induce several forms of cell death, including apoptosis and the recently uncovered regulated form of necrosis termed necroptosis. 21,22 In contrast to apoptosis, necroptosis is largely independent of the so-called executioner caspase (such as caspase-3, 6 and 7) activity and is initiated by the formation of a signaling complex comprising the receptorinteracting serine-threonine kinase 1 (RIPK1), RIPK3 and the recently identified mixed lineage kinase domain-like protein MLKL.…”

“…The protective role of NAD + in PARP1-dependent cell death has been indeed amply documented. [13][14][15][16][17][18] In mammals, nicotinamide (Nam) acts as the main precursor for NAD + biosynthesis and nicotinamide phosphoribosyl tranferase (NAMPT) is the rate-limiting enzyme for NAD + biosynthesis from Nam. 19 Nampt deficiency in mice leads to lethality and the heterozygous animals suffer from significant perturbations related to their NAD + metabolism.…”