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Fueling genome maintenance: On the versatile roles of NAD+ in preserving DNA integrity

2022; Elsevier BV; Volume: 298; Issue: 6 Linguagem: Inglês

10.1016/j.jbc.2022.102037

ISSN

1083-351X

Autores

Joanna A. Ruszkiewicz, Alexander Bürkle, Aswin Mangerich,

Tópico(s)

Biochemical and Molecular Research

Resumo

NAD+ is a versatile biomolecule acting as a master regulator and substrate in various cellular processes, including redox regulation, metabolism, and various signaling pathways. In this article, we concisely and critically review the role of NAD+ in mechanisms promoting genome maintenance. Numerous NAD+-dependent reactions are involved in the preservation of genome stability, the cellular DNA damage response, and other pathways regulating nucleic acid metabolism, such as gene expression and cell proliferation pathways. Of note, NAD+ serves as a substrate to ADP-ribosyltransferases, sirtuins, and potentially also eukaryotic DNA ligases, all of which regulate various aspects of DNA integrity, damage repair, and gene expression. Finally, we critically analyze recent developments in the field as well as discuss challenges associated with therapeutic actions intended to raise NAD+ levels. NAD+ is a versatile biomolecule acting as a master regulator and substrate in various cellular processes, including redox regulation, metabolism, and various signaling pathways. In this article, we concisely and critically review the role of NAD+ in mechanisms promoting genome maintenance. Numerous NAD+-dependent reactions are involved in the preservation of genome stability, the cellular DNA damage response, and other pathways regulating nucleic acid metabolism, such as gene expression and cell proliferation pathways. Of note, NAD+ serves as a substrate to ADP-ribosyltransferases, sirtuins, and potentially also eukaryotic DNA ligases, all of which regulate various aspects of DNA integrity, damage repair, and gene expression. Finally, we critically analyze recent developments in the field as well as discuss challenges associated with therapeutic actions intended to raise NAD+ levels. DNA is constantly exposed to a plethora of damaging factors of both exogenous and endogenous origin, such as replication stress, alkylating and oxidative molecules, or UV radiation. To protect DNA from lesions caused by such stressors and to ensure genomic stability, cells have developed several pathways that recognize and repair specific DNA lesions (Fig. 1). Thus, in particular, small lesions are subject to direct reversal mediated by single proteins, for example, O6-alkylguanine-DNA alkyltransferase repairs O-alkylated DNA damage, and the alkB homolog dioxygenases reverse N-alkylated base adducts (1Eker A.P. Quayle C. Chaves I. van der Horst G.T. DNA repair in mammalian cells: direct DNA damage reversal: elegant solutions for nasty problems.Cell Mol. Life Sci. 2009; 66: 968-980Crossref PubMed Scopus (43) Google Scholar). Yet, the majority of repair mechanisms involves multiple events mediated by different proteins and orchestrated in a complex network of DNA repair pathways: base excision repair (BER) targets small lesions like oxidized bases and apuric/apyrimidic sites, in a mechanism overlapping with single-strand break repair. Larger nucleotide adducts are removed by nucleotide excision repair, and mismatch repair targets errors produced during DNA replication and recombination. Double-strand breaks (DSBs) are repaired either through homologous recombination or nonhomologous end-joining (NHEJ) comprising a canonical pathway (C-NHEJ) or alternative end-joining (A-EJ). As a comprehensive review of DNA repair pathways falls outside the scope of this article, we refer the reader to other in-depth review articles on this topic (2Jackson S.P. Bartek J. The DNA-damage response in human biology and disease.Nature. 2009; 461: 1071-1078Crossref PubMed Scopus (3527) Google Scholar, 3Scully R. Panday A. 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Interestingly, numerous NAD+-dependent reactions are involved in the preservation of genomic stability, cellular response to DNA damage, and other pathways concerning nucleic acids, such as gene expression or cell proliferation. Thus, the cellular NAD+ status influences genomic stability and sensitivity to DNA-damaging agents (9Durkacz B.W. Omidiji O. Gray D.A. Shall S. ADP-ribose)n participates in DNA excision repair.Nature. 1980; 283: 593-596Crossref PubMed Google Scholar, 10Weidele K. Beneke S. Burkle A. The NAD(+) precursor nicotinic acid improves genomic integrity in human peripheral blood mononuclear cells after X-irradiation.DNA Repair (Amst). 2017; 52: 12-23Crossref PubMed Scopus (0) Google Scholar, 11Weitberg A.B. Effect of nicotinic acid supplementation in vivo on oxygen radical-induced genetic damage in human lymphocytes.Mutat. Res. 1989; 216: 197-201Crossref PubMed Scopus (0) Google Scholar, 12Spronck J.C. Kirkland J.B. Niacin deficiency increases spontaneous and etoposide-induced chromosomal instability in rat bone marrow cells in vivo.Mutat. Res. 2002; 508: 83-97Crossref PubMed Scopus (45) Google Scholar, 13Kostecki L.M. Thomas M. Linford G. Lizotte M. Toxopeus L. Bartleman A.P. et al.Niacin deficiency delays DNA excision repair and increases spontaneous and nitrosourea-induced chromosomal instability in rat bone marrow.Mutat. Res. 2007; 625: 50-61Crossref PubMed Scopus (0) Google Scholar). Of note, NAD+ depletion in aging and age-related diseases implies supplementation of NAD+ boosting molecules as a plausible strategy in addressing age-dependent DNA damage (7Katsyuba E. Romani M. Hofer D. Auwerx J. NAD(+) homeostasis in health and disease.Nat. Metab. 2020; 2: 9-31Crossref PubMed Scopus (130) Google Scholar, 14Sharif T. Martell E. Dai C. Ghassemi-Rad M.S. Kennedy B.E. Lee P.W.K. et al.Regulation of cancer and cancer-related genes via NAD.Antioxid. Redox Signal. 2019; 30: 906-923Crossref PubMed Scopus (0) Google Scholar, 15Covarrubias A.J. Perrone R. Grozio A. Verdin E. NAD(+) metabolism and its roles in cellular processes during ageing.Nat. Rev. Mol. Cel. Biol. 2021; 22: 119-141Crossref PubMed Scopus (0) Google Scholar). Here, we first introduce the reader to the NAD+ biosynthesis and major cellular roles of this ubiquitous and versatile molecule. Furthermore, we turn our focus on the NAD+-dependent molecular mechanisms involved in mammalian genome maintenance. We concisely review both well-established concepts as well as new findings in the field. Finally, we discuss current controversies around NAD+-dependent therapeutic approaches that target various pathophysiological conditions in the light of its role in genome maintenance processes. In mammals, NAD+ is synthesized from various precursors ingested through the diet, such as forms of vitamin B3: nicotinic acid (NA), nicotinamide (NAM), and nicotinamide riboside (NR); as well as the essential amino acid tryptophan (Trp), which is metabolized via three major pathways: (i) salvage pathway, (ii) de novo pathway, and (iii) Preiss–Handler pathway (Fig. 2). In addition, alternative precursors such as nicotinic acid riboside (NAR) (16Kulikova V. Shabalin K. Nerinovski K. Dolle C. Niere M. Yakimov A. et al.Generation, release, and uptake of the NAD precursor nicotinic acid riboside by human cells.J. Biol. Chem. 2015; 290: 27124-27137Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar), biosynthesis intermediates, such as nicotinamide mononucleotide (NMN) (17Ratajczak J. Joffraud M. Trammell S.A. Ras R. Canela N. Boutant M. et al.NRK1 controls nicotinamide mononucleotide and nicotinamide riboside metabolism in mammalian cells.Nat. Commun. 2016; 7: 13103Crossref PubMed Scopus (164) Google Scholar), or products of NAD+ consumption (NAM, NMN, and NR) are salvaged to replenish cellular NAD+ pools. In order to supply cells with "fresh" exogenous precursors, those can enter the cell during a passive process (e.g., NAM) or via membrane transporters—members of the solute carrier transporter family (for Trp and NA) or equilibrative nucleoside transporter (for NR and NAR). Furthermore, exogenous NMN can be taken up by cells, yet the cellular transport of this precursor molecule remains unclear (18Grozio A. Mills K.F. Yoshino J. Bruzzone S. Sociali G. Tokizane K. et al.Slc12a8 is a nicotinamide mononucleotide transporter.Nat. Metab. 2019; 1: 47-57Crossref PubMed Scopus (91) Google Scholar, 19Schmidt M.S. Brenner C. Absence of evidence that Slc12a8 encodes a nicotinamide mononucleotide transporter.Nat. Metab. 2019; 1: 660-661Crossref PubMed Scopus (17) Google Scholar), with some studies suggesting that NMN uptake requires the prior conversion to NR by glycohydrolase, cluster of differentiation 73 (CD73) (20Kulikova V. Shabalin K. Nerinovski K. Yakimov A. Svetlova M. Solovjeva L. et al.Degradation of extracellular NAD(+) intermediates in cultures of human HEK293 cells.Metabolites. 2019; 9: 293Crossref Scopus (0) Google Scholar, 21Wilk A. Hayat F. Cunningham R. Li J. Garavaglia S. Zamani L. et al.Extracellular NAD(+) enhances PARP-dependent DNA repair capacity independently of CD73 activity.Sci. Rep. 2020; 10: 651Crossref PubMed Scopus (25) Google Scholar). The salvage pathway is a primary source of NAD+ in mammals (22Magni G. Amici A. Emanuelli M. Raffaelli N. Ruggieri S. Enzymology of NAD+ synthesis.Adv. Enzymol. Relat. Areas Mol. Biol. 1999; 73: 135-182PubMed Google Scholar) (Fig. 2). The first and rate-limiting step in this pathway—conversion of NAM to NMN, catalyzed by nicotinamide phosphoribosyl transferase (NAMPT)—is crucial in cellular NAD+ synthesis because numerous NAD+-consuming reactions release NAM. The enzyme NAMPT is present both extracellularly (eNAMPT) and intracellularly (iNAMPT) in the cytoplasm and nucleus, whereas its mitochondrial presence is disputed (23Garten A. Schuster S. Penke M. Gorski T. de Giorgis T. Kiess W. Physiological and pathophysiological roles of NAMPT and NAD metabolism.Nat. Rev. Endocrinol. 2015; 11: 535-546Crossref PubMed Scopus (287) Google Scholar). Besides, NMN can be produced during ATP-dependent phosphorylation of NR by nicotinamide riboside kinase (17Ratajczak J. Joffraud M. Trammell S.A. Ras R. Canela N. Boutant M. et al.NRK1 controls nicotinamide mononucleotide and nicotinamide riboside metabolism in mammalian cells.Nat. Commun. 2016; 7: 13103Crossref PubMed Scopus (164) Google Scholar), and cleavage of the NR glycosidic bond by purine nucleoside phosphorylase produces NAM. Moreover, nicotinamide riboside kinase and purine nucleoside phosphorylase convert NAR to NAMN and NA, respectively, which feed the Preiss–Handler pathway (see later) (24Belenky P. Christensen K.C. Gazzaniga F. Pletnev A.A. Brenner C. Nicotinamide riboside and nicotinic acid riboside salvage in fungi and mammals. Quantitative basis for Urh1 and purine nucleoside phosphorylase function in NAD+ metabolism.J. Biol. Chem. 2009; 284: 158-164Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar). In the second (and final) step of the salvage pathway, NMN is converted to NAD+ by ATP-dependent nicotinamide mononucleotide adenylyl transferase (NMNAT). This enzyme in human tissues exists in three isoforms: the most ubiquitous nuclear NMNAT1, cytoplasmic NMNAT2 (25Hicks A.N. Lorenzetti D. Gilley J. Lu B. Andersson K.E. Miligan C. et al.Nicotinamide mononucleotide adenylyltransferase 2 (Nmnat2) regulates axon integrity in the mouse embryo.PLoS One. 2012; 7e47869Crossref Scopus (51) Google Scholar), and mitochondrial NMNAT3, whose function remains controversial (26Berger F. Lau C. Dahlmann M. Ziegler M. Subcellular compartmentation and differential catalytic properties of the three human nicotinamide mononucleotide adenylyltransferase isoforms.J. Biol. Chem. 2005; 280: 36334-36341Abstract Full Text Full Text PDF PubMed Scopus (359) Google Scholar, 27Yamamoto M. Hikosaka K. Mahmood A. Tobe K. Shojaku H. Inohara H. et al.Nmnat3 is dispensable in mitochondrial NAD level maintenance in vivo.PLoS One. 2016; 11e0147037Crossref Scopus (43) Google Scholar, 28Ziegler M. Monné M. Nikiforov A. Agrimi G. Heiland I. Palmieri F. Welcome to the family: identification of the NAD+ transporter of animal mitochondria as member of the solute carrier family SLC25.Biomolecules. 2021; 11: 880Crossref PubMed Scopus (2) Google Scholar). In addition, NMNAT catalyzes the formation of nicotinic acid adenine dinucleotide (NAAD) from NAMN, which comes from either Preiss–Handler or de novo pathways. In the Preiss–Handler pathway, NAMN is produced from NA by nicotinic acid phosphoribosyl transferase (29Piacente F. Caffa I. Ravera S. Sociali G. Passalacqua M. Vellone V.G. et al.Nicotinic acid phosphoribosyltransferase regulates cancer cell metabolism, susceptibility to NAMPT inhibitors, and DNA repair.Cancer Res. 2017; 77: 3857-3869Crossref PubMed Scopus (45) Google Scholar). In the de novo pathway, Trp is first transformed to quinolinic acid in the multistep process during the kynurenine pathway, and then quinolinic acid is converted to NAMN by quinolinic acid phosphoribosyl transferase. While originally thought to play a minor role in mammalian NAD+ synthesis, it has been recently suggested that the de novo pathway may play an important role in NAD+ homeostasis in humans (30Shi H. Enriquez A. Rapadas M. Martin E. Wang R. Moreau J. et al.NAD deficiency, congenital malformations, and niacin supplementation.New Engl. J. Med. 2017; 377: 544-552Crossref PubMed Scopus (0) Google Scholar, 31Poyan Mehr A. Tran M.T. Ralto K.M. Leaf D.E. Washco V. Messmer J. et al.De novo NAD(+) biosynthetic impairment in acute kidney injury in humans.Nat. Med. 2018; 24: 1351-1359Crossref PubMed Scopus (134) Google Scholar). In the final step of both Preiss–Handler or de novo pathways, NAAD is amidated to NAD+ by the cytosolic enzyme NAD+ synthase, which requires ATP, and ammonia or l-glutamine (32Hara N. Yamada K. Terashima M. Osago H. Shimoyama M. Tsuchiya M. Molecular identification of human glutamine- and ammonia-dependent NAD synthetases. Carbon-nitrogen hydrolase domain confers glutamine dependency.J. Biol. Chem. 2003; 278: 10914-10921Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar). Cellular NAD+ levels are maintained in the range of 100 μM in the cytoplasm and nucleus and 200 μM in mitochondria (8Kulkarni C.A. Brookes P.S. Cellular compartmentation and the redox/nonredox functions of NAD.Antioxid. Redox Signal. 2019; 31: 623-642Crossref PubMed Scopus (0) Google Scholar). Such differences in subcellular NAD+ pools reflect its biological functions (see later) and are variable in tissues with different metabolic roles. Similarities in nuclear and cytoplasmic levels are likely because of the passive diffusion of NAD+ and its precursors through nuclear pores (33Cambronne X.A. Stewart M.L. Kim D. Jones-Brunette A.M. Morgan R.K. Farrens D.L. et al.Biosensor reveals multiple sources for mitochondrial NAD(+).Science. 2016; 352: 1474-1477Crossref PubMed Scopus (209) Google Scholar), although the detailed relationships between nuclear and cytoplasmic pools appear to be complex, since depletion of NAD+ in one compartment cannot be fully compensated by the other pool (28Ziegler M. Monné M. Nikiforov A. Agrimi G. Heiland I. Palmieri F. Welcome to the family: identification of the NAD+ transporter of animal mitochondria as member of the solute carrier family SLC25.Biomolecules. 2021; 11: 880Crossref PubMed Scopus (2) Google Scholar). As NAD+ has an overall negative charge, it is unable to passively cross lipid bilayers in mitochondria and other cellular membranes. Therefore, for a long time, the cytoplasmic/nuclear NAD+ pool has been thought to be strictly separated from the mitochondrial one, and it remained rather obscure how mitochondria build up their significant intraorganelle NAD+ levels. However, recently, this issue had been at least partially resolved. Thus, in 2020, a series of studies demonstrated the existence of a mitochondrial NAD+ carrier, that is, solute carrier transporter family SLC25A51 (or MCART1), providing mechanistic insight how mitochondria are supplied with NAD+ (28Ziegler M. Monné M. Nikiforov A. Agrimi G. Heiland I. Palmieri F. Welcome to the family: identification of the NAD+ transporter of animal mitochondria as member of the solute carrier family SLC25.Biomolecules. 2021; 11: 880Crossref PubMed Scopus (2) Google Scholar, 34Girardi E. Agrimi G. Goldmann U. Fiume G. Lindinger S. Sedlyarov V. et al.Epistasis-driven identification of SLC25A51 as a regulator of human mitochondrial NAD import.Nat. Commun. 2020; 11: 6145Crossref PubMed Scopus (25) Google Scholar, 35Kory N. Uit de Bos J. van der Rijt S. Jankovic N. Güra M. Arp N. et al.MCART1/SLC25A51 is required for mitochondrial NAD transport.Sci. 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Scheuplein F. et al.Extracellular NAD and ATP: partners in immune cell modulation.Purinergic Signal. 2007; 3: 71-81Crossref PubMed Scopus (128) Google Scholar) or active transport, for example, via connexin hemichannels like connexin 43 (39Billington R.A. Travelli C. Ercolano E. Galli U. Roman C.B. Grolla A.A. et al.Characterization of NAD uptake in mammalian cells.J. Biol. Chem. 2008; 283: 6367-6374Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar, 40Pillai V.B. Sundaresan N.R. Kim G. Gupta M. Rajamohan S.B. Pillai J.B. et al.Exogenous NAD blocks cardiac hypertrophic response via activation of the SIRT3-LKB1-AMP-activated kinase pathway.J. Biol. Chem. 2010; 285: 3133-3144Abstract Full Text Full Text PDF PubMed Scopus (294) Google Scholar). In turn, extracellular NAD+ can be degraded to precursors that can be taken up into the cell (41Grozio A. Sociali G. Sturla L. Caffa I. Soncini D. Salis A. et al.CD73 protein as a source of extracellular precursors for sustained NAD+ biosynthesis in FK866-treated tumor cells.J. Biol. Chem. 2013; 288: 25938-25949Abstract Full Text Full Text PDF PubMed Scopus (95) Google Scholar). Depending on the individual tissue, NAD+ molecules have a quite variable half-life that varies from 15 min to 15 h (42Rechsteiner M. Hillyard D. Olivera B.M. Turnover at nicotinamide adenine dinucleotide in cultures of human cells.J. Cell. Physiol. 1976; 88: 207-217Crossref PubMed Scopus (39) Google Scholar, 43Chini C.C.S. Zeidler J.D. Kashyap S. Warner G. Chini E.N. Evolving concepts in NAD(+) metabolism.Cell Metab. 2021; 33: 1076-1087Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar, 44Liu L. Su X. Quinn W.J. Hui S. Krukenberg K. Frederick D.W. et al.Quantitative analysis of NAD synthesis-breakdown fluxes.Cell Metab. 2018; 27: 1067-1080.e1065Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar). Therefore, in tissues with high fluxes such as the small intestine and spleen, quick and efficient biosynthesis is necessary to compensate for a rapid cellular consumption via numerous NAD+-dependent reactions. Numerous biochemical reactions require NAD+ as a cosubstrate (Fig. 2). NAD+ and its reduced form (NADH) are critical regulators of cellular bioenergetics, serving as cofactors in reactions of glucose metabolism, fatty acid β-oxidation, or the tricarboxylic acid cycle. For example, NAD+ is reduced to NADH during glycolysis by GAPDH. In turn, NADH is oxidized by lactate dehydrogenase, when pyruvate is converted to lactate under anaerobic conditions. NADH is a cofactor for fatty acid desaturases, and NAD+ is essential for alcohol dehydrogenase. NAD+/NADH-dependent malate dehydrogenase (malate–aspartate shuttle) and glycerol-3-phosphate dehydrogenase (glycerol-3-phosphate shuttle) generate reducing equivalents transported across the membrane into the mitochondria. There, NAD+ is reduced by pyruvate dehydrogenase complex and the tricarboxylic acid cycle enzymes: malate dehydrogenase, α-ketoglutarate dehydrogenase, and isocitrate dehydrogenase. NAD+ is also reduced by hydroxyacyl-CoA dehydrogenase in β-oxidation during fatty acid metabolism. Subsequently generated NADH is the major reducing factor in complex I mitochondrial electron transport chain, for the transfer of electrons in oxidative phosphorylation that produces ATP. Thus, the NAD+/NADH abundance reflects the energy status of the cell (7Katsyuba E. Romani M. Hofer D. Auwerx J. NAD(+) homeostasis in health and disease.Nat. Metab. 2020; 2: 9-31Crossref PubMed Scopus (130) Google Scholar, 45Xiao W. Wang R.S. Handy D.E. Loscalzo J. NAD(H) and NADP(H) redox couples and cellular energy metabolism.Antioxid. Redox Signal. 2018; 28: 251-272Crossref PubMed Scopus (235) Google Scholar). ATP-dependent NAD+ kinases (NADKs) in the cytosol (cNADK) and mitochondria (mNADK) phosphorylate NAD+ to NADP+, which together with its reduced form NADPH, is critical for the maintenance of cellular redox homeostasis. It regenerates molecules responsible for xenobiotic detoxification, for example, cytochrome P450, and eradication of reactive oxygen species (ROS), such as GSH, thioredoxin, or peroxiredoxin (46Agledal L. Niere M. Ziegler M. The phosphate makes a difference: cellular functions of NADP.Redox Rep. 2010; 15: 2-10Crossref PubMed Scopus (113) Google Scholar). NADP+ is also a cosubstrate for glucose-6-phosphate dehydrogenase, a key enzyme in the pentose phosphate pathway, which produces precursors for the synthesis of nucleotides and aromatic amino acids. Moreover, it contributes to the synthesis of fatty acids and nicotinic acid adenine dinucleotide phosphate, which serves as a second messenger for intracellular calcium (Ca2+) signaling (46Agledal L. Niere M. Ziegler M. The phosphate makes a difference: cellular functions of NADP.Redox Rep. 2010; 15: 2-10Crossref PubMed Scopus (113) Google Scholar, 47Tedeschi P.M. Bansal N. Kerrigan J.E. Abali E.E. Scotto K.W. Bertino J.R. NAD+ kinase as a therapeutic target in cancer.Clin. Cancer Res. 2016; 22: 5189-5195Crossref PubMed Scopus (43) Google Scholar). Because of its reducing role, NADP+ is found predominantly in the reduced state, with NADP+/NADPH ratios 1:200, which contrasts the NAD+/NADH ratio of 1000:1 in the cytoplasm and of 10:1 in the mitochondria (48Veech R.L. Eggleston L.V. Krebs H.A. The redox state of free nicotinamide-adenine dinucleotide phosphate in the cytoplasm of rat liver.Biochem. J. 1969; 115: 609-619Crossref PubMed Google Scholar). In addition to the numerous reactions where NAD(P)+/NAD(P)H couples serve as an electron carrier, NAD+ can be also irreversibly consumed (Fig. 3). ADP-ribosyl transferases (ARTs) cleave the N-glycosidic bond, which releases NAM and ADP-ribose (ADPR) and further covalently attach the latter to the target molecule. Cholera toxin–like ADP-ribosyltransferases are localized often in the extracellular space and catalyze the addition of a single ADPR unit, called mono-ADP-ribosylation. Diphtheria toxin–like ADP-ribosyltransferases (ARTDs; also called poly-ADP-ribose polymerases [PARPs]) come in three flavors: (i) without any known enzymatic activity, (ii) as mono-ARTs catalyzing mono-ADP-ribosylation, or (iii) as poly-ARTs, catalyzing the attachment of numerous ADPR moieties, forming poly-ADP-ribose (PAR) chains in the process called poly(ADP-ribosyl)ation (PARylation). ADP-ribosylation is a post-translational modification that serves multiple cellular functions, such as signal transduction, energy metabolism, intracellular trafficking, or cell death (49Aredia F. Scovassi A.I. Poly(ADP-ribose): a signaling molecule in different paradigms of cell death.Biochem. Pharmacol. 2014; 92: 157-163Crossref PubMed Scopus (85) Google Scholar, 50Gupte R. Liu Z. Kraus W.L. PARPs and ADP-ribosylation: recent advances linking molecular functions to biological outcomes.Genes Dev. 2017; 31: 101-126Crossref PubMed Scopus (329) Google Scholar, 51Reber J.M. Mangerich A. Why structure and chain length matter: on the biological significance underlying the structural heterogeneity of poly(ADP-ribose).Nucl. Acids Res. 2021; 49: 8432-8448Crossref PubMed Scopus (0) Google Scholar). Yet, one of its major roles is the maintenance of nuclear homeostasis, regulation of DNA repair mechanism, chromatin remodeling, and transcription (52Azarm K. Smith S. Nuclear PARPs and genome integrity.Genes Dev. 2020; 34: 285-301Crossref PubMed Scopus (35) Google Scholar). NAD+ is also consumed by histone deacetylases known as sirtuins (SIRTs). They use NAD+ as an acceptor during the transfer of acetyl (Ac) and other groups from target protein, which is a common post-translational modification, implemented in numerous cellular pathways, including those involved in genomic maintenance (53Roos W.P. Krumm A. The multifaceted influence of histone deacetylases on DNA damage signalling and DNA repair.Nucl. Acids Res. 2016; 44: 10017-10030PubMed Google Scholar, 54Kosciuk T. Wang M. Hong J.Y. Lin H. Updates on the epigenetic roles of sirtuins.Curr. Opin. Chem. Biol. 2019; 51: 18-29Crossref PubMed Scopus (26) Google Scholar). Another family of NAD+ consuming enzymes are glycohydrolases (NADases), such as CD73, CD38, or sterile α and TIR motif–containing 1. Apart from generating ADPR, this enzyme exhibits ADP-ribosyl cyclase activity, which produces cyclic ADPR, a second messenger in Ca2+ signaling. For instance, CD38 is a major extracellular NAD+ consumer, and its activity has a wide range of implications in the context of infection, metabolic dysfunction, aging, or tumor biology (55Aksoy P. White T.A. Thompson M. Chini E.N. Regulation of intracellular levels of NAD: a novel role for CD38.Biochem. Biophys. Res. Commun. 2006; 345: 1386-1392Crossref PubMed Scopus (209) Google Scholar, 56Lee H.C. Zhao Y.J. Resolving the topological enigma in Ca(2+) signaling by cyclic ADP-ribose and NAADP.J. Biol. Chem. 2019; 294: 19831-19843Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar). For more information regarding NAD+ multiple cellular roles, we refer the reader to recent reviews (7Katsyuba E. Romani M. Hofer D. Auwerx J. NAD(+) homeostasis in health and disease.Nat. Metab. 2020; 2: 9-31Crossref PubMed Scopus (130) Google Scholar, 43Chini C.C.S. Zeidler J.D. Kashyap S. Warner G. Chini E.N. Evolving concepts in NAD(+) metabolism.Cell Metab. 2021; 33: 1076-1087Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar, 45Xiao W. Wang R.S. Handy D.E. Loscalzo J. NAD(H) and NADP(H) redox couples and cellular energy metabolism.Antioxid. Redox Signal. 2018; 28: 251-272Crossref PubMed Scopus (235) Google Scholar). In further parts of this review, we focus exclusively on NAD+-dependent pathways involved in the maintenance of genome integrity. There is now a growing body of evidence that NAD+-dependent processes are heavily involved in genome maintenance and DNA repair mechanisms (57Saville K.M. Clark J. Wilk A. Rogers G.D. Andrews J.F. Koczor C.A. et al.NAD(+)-mediated regulation of mammalian base excision repair.DNA Repair. 2020; 93: 102930Crossref PubMed Scopus (0) Google Scholar). This is exemplified in a study by Kiss et al. (58Kiss A. Ráduly A.P. Regdon Z. Polgár Z. Tarapcsák S. Sturniolo I. et al.Targeting nuclear NAD(+) synthesis inhibits DNA repair, impairs metabolic adaptation and increases chemosensitivity of U-2OS osteosarcoma cells.Cancers (Basel). 2020; 12: 1180Crossref Scopus (15) Google Scholar), demonstrating that CRISPR–Cas9-generated NMNAT1 U2OS knockout cells show reduced intracellular NAD+ levels, which was accompanied by hypersensitivity toward DNA-damaging cisplatin treatment. Furthermore, this study revealed that genetic inactivation of NMNAT1 completely blocked PARP1 activation in the nucleus, leading to increased γ-H2A.X DNA damage foci formation (58Kiss A. Ráduly A.P. Regdon Z. Polgár Z. Tarapcsák S. Sturniolo I. et al.Targeting nuclear NAD(+) synthesis inhibits DNA repair, impairs metabolic adaptation and increases chemosensitivity of U-2OS osteosarcoma cells.Ca

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