The role of sirtuins in cellular homeostasis

Overview of the mammalian ADP-ribosyl-transferases clostridia toxin-like (ARTCs) family

Mono-ADP-ribosylation is a reversible post-translational protein modification that modulates the function of proteins involved in different cellular processes, including signal transduction, protein transport, transcription, cell cycle regulation, DNA repair and apoptosis. In mammals, mono-ADP-ribosylation is mainly catalyzed by members of two different classes of enzymes: ARTCs and ARTDs. The human ARTC family is composed of four structurally related ecto-mono-ARTs, expressed at the cell surface or secreted into the extracellular compartment that are either active mono-ARTs (hARTC1, hARTC5) or inactive proteins (hARTC3, hARTC4). The human ARTD enzyme family consists of 17 multidomain proteins that can be divided on the basis of their catalytic activity into polymerases (ARTD1-6), mono-ART (ARTD7-17), and the inactive ARTD13. In recent years, ADP-ribosylation was intensively studied, and research was dominated by studies focusing on the role of this modification and its implication on various cellular processes. The aim of this review is to provide a general overview of the ARTC enzymes. In the following sections, we will report the mono-ADP-ribosylation reactions that are catalysed by the active ARTC enzymes, with a particular focus on hARTC1 that recently has been intensively studied with the discovery of new targets and functions.

Resveratrol up-regulates ATP2A3 gene expression in breast cancer cell lines through epigenetic mechanisms

Resveratrol (RSV) is a phytoestrogen which has been related to chemoprevention of several types of cancer. In this work, we show up to a 6-fold increased expression of ATP2A3 gene induced by RSV that triggers apoptosis and changes of intracellular Ca²⁺ management in MCF-7 and MDA-MB-231 breast cancer cell lines. We explored epigenetic mechanisms for that RSV-induced ATP2A3 up-regulation. The results indicate that RSV-induced ATP2A3 up-regulation correlates with about 50% of reduced HDAC activity and reduced nuclear HDAC2 expression and occupancy on ATP2A3 promoter, increasing the global acetylation of histone H3 and the enrichment of histone mark H3K27Ac on the proximal promoter of the ATP2A3 gene in MDA-MB-231 cells. We also quantified HAT activity, finding that it can be boosted with RSV treatment; however, pharmacological inhibition of p300, one of the main HATs, did not have significant effects in RSV-mediated ATP2A3 gene expression. Additionally, DNMT activity was also reduced in cells treated with RSV, as well as the expression of Methyl-DNA binding proteins MeCP2 and MBD2. However, analysis of the methylation pattern of ATP2A3 gene promoter showed un-methylated promoter in both cell lines. Taken together, the results of this work help to explain, at the molecular level, how ATP2A3 gene is regulated in breast cancer cells, and the benefits of RSV intake observed in epidemiological data, studies with animals, and in vitro models.

Detection of InDel variations within seven candidate genes and their associations with phenotypic traits in three cattle breeds

The Xinjiang brown cattle, Red steppe cattle, and Yunling cattle are indigenous cultivated cattle breeds in Chinese frontier provinces, and they produce high-grade beef and milk products, however, their genetic diversity in many important genes related to excellent meat and milk production is still unknown. Our previous studies have found that several candidate genes (e.g., SREBP1c and PAX7) were associated with bovine economically important phenotypic traits, but none has been reported in the above-mentioned three cattle breeds. Since the InDel (insertion/deletion) marker becomes a useful tool applied in the animal molecular breeding, herein, we firstly found that the InDel variations of seven candidate genes in these cattle. Results showed that the genotypic and allelic distributions of these seven genes were remarkably different among these three cattle (p < 0.05 or p < 0.01). Furthermore, the InDel variations of SREBP1c and PAX7 genes were significantly associated with eight phenotypic traits in Xinjiang brown cattle (p < 0.05 or p < 0.01), respectively, suggesting that they can become the useful DNA markers.

Role of N-terminus in function and dynamics of sirtuin 7: an in silico study

The sirtuin family comprises seven NAD⁺-dependent histone deacetylases named SIRT1 to SIRT7. The least investigated SIRT7 is currently considered as a promising therapeutic target for cardiovascular diseases, diabetes and different types of cancer. So far, its structure was not experimentally resolved, except of a fragment of its N-terminus. The aim of this study was to create in silico model of SIRT7 containing its core together with N-terminus, which is known to affect the enzyme's catalytic activity and to find pockets that could be targeted by structure-based virtual screening. Homology model of SIRT7 was prepared using X-ray structures of other sirtuins and a resolved fragment of the N-terminus of SIRT7 as templates. All atom-unbiased molecular dynamics simulations were performed. It was found that N-terminus of SIRT7 remains in spatial proximity of the catalytic core for considerable fraction of time, and therefore, it may affect its catalytic activity by helping the enzyme to hold the substrate peptide. It may also participate in holding and release of the cofactor. Preferred orientations of NAD⁺ and acetyl-lysine inside SIRT7 were found, with all components forming a stable complex. Molecular dynamics provided an ensemble of conformations that will be targeted with virtual screening. Reliable in silico structure of SIRT7 will be a useful tool in searching for its inhibitors, which can be potential drugs in cancer treatment.Communicated by Ramaswamy H. Sarma.

Sirtuin 2 enhances allergic asthmatic inflammation

Allergic eosinophilic asthma is a chronic condition causing airway remodeling resulting in lung dysfunction. We observed that expression of sirtuin 2 (Sirt2), a histone deacetylase, regulates the recruitment of eosinophils after sensitization and challenge with a triple antigen: dust mite, ragweed, and Aspergillus fumigatus (DRA). Our data demonstrate that IL-4 regulates the expression of Sirt2 isoform 3/5. Pharmacological inhibition of Sirt2 by AGK2 resulted in diminished cellular recruitment, decreased CCL17/TARC, and reduced goblet cell hyperplasia. YM1 and Fizz1 expression was reduced in AGK2-treated, IL-4-stimulated lung macrophages in vitro as well as in lung macrophages from AGK2-DRA-challenged mice. Conversely, overexpression of Sirt2 resulted in increased cellular recruitment, CCL17 production, and goblet cell hyperplasia following DRA challenge. Sirt2 isoform 3/5 was upregulated in primary human alveolar macrophages following IL-4 and AGK2 treatment, which resulted in reduced CCL17 and markers of alternative activation. These gain-of-function and loss-of-function studies indicate that Sirt2 could be developed as a treatment for eosinophilic asthma.

SIRT1 Deacetylates SC35 and Suppresses Its Function in Tau Exon 10 Inclusion

Approximately equal amounts of 3R-tau and 4R-tau resulting from alternative splicing of tau exon 10 is necessary to maintain normal brain function. Dysregulation of alternative splicing of tau exon 10 and the imbalance of 3R-tau/4R-tau have been seen in inherited and sporadic tauopathies. Splicing factor SC35 (also name as SRSF2) plays an important role in promoting tau exon 10 inclusion. SC35 is post-translationally modified by phosphorylation and acetylation, but the role of acetylation in SC35-medicated tau exon 10 inclusion is unknown. Sirtuin type 1 (SIRT1) is an enzyme that deacetylates proteins and associates with age-related disease such as Alzheimer's disease. In the present study, we determined the role of SIRT1 in SC35 acetylation and in the alternative splicing of tau exon 10. We found that SIRT1 interacts with and deacetylates SC35, and inhibits SC35-promoted tau exon 10 inclusion. Substituting K52 residue of SC35 by arginine impairs the role of SC35 in tau exon 10 inclusion. These results suggest that SIRT1 may serve as a therapeutic target for tauopathy by regulating SC35-mediated tau exon 10 splicing.

Molecular mechanisms of neuroprotective effect of adjuvant therapy with phenytoin in pentylenetetrazole-induced seizures: Impact on Sirt1/NRF2 signaling pathways

Current anticonvulsant therapies are principally aimed at suppressing neuronal hyperexcitability to prevent or control the incidence of seizures. However, the role of oxidative stress processes in seizures led to the proposition that antioxidant compounds may be considered as promising candidates for limiting the progression of epilepsy. Accordingly, the aim of this study is to determine if coenzyme Q10 (CoQ10) and alpha-tocopherol (α-Toc) have a neuroprotective effect in rats against the observed oxidative stress and inflammation during seizures induced by pentylenetetrazole (PTZ) in rats, and to study their interactions with the conventional antiseizure drug phenytoin (PHT), either alone or in combination. Overall, the data revealed that α-Toc and CoQ10 supplementation can ameliorate PTZ-induced seizures and recommended that nuclear factor erythroid 2-related factor 2 (NRF2) and silencing information regulator 1 (Sirt1) signaling pathways may exemplify strategic molecular targets for seizure therapies. The results of the present study provide novel mechanistic insights regarding the protective effects of antioxidants and suggest an efficient therapeutic strategy to attenuate seizures. Additionally, concurrent supplementation of CoQ10 and α-Toc may be more effective than either antioxidant alone in decreasing inflammation and oxidative stress in both cortical and hippocampal tissues. Also, CoQ10 and α-Toc effectively reverse the PHT-mediated alterations in the brain antioxidant status when compared to PHT only.

The Role of SIRT3 in the Brain Under Physiological and Pathological Conditions

Sirtuin enzymes are a family of highly seven conserved protein deacetylases, namely SIRT1 through SIRT7, whose enzymatic activities require the cofactor nicotinamide adenine dinucleotide (NAD⁺). Sirtuins reside in different compartments within cells, and their activities have been shown to regulate a number of cellular pathways involved in but not limited to stress management, apoptosis and inflammatory responses. Given the importance of mitochondrial functional state in neurodegenerative conditions, the mitochondrial SIRT3 sirtuin, which is the primary deacetylase within mitochondria, has garnered considerable recent attention. It is now clear that SIRT3 plays a major role in regulating a host of mitochondrial molecular cascades that can contribute to both normal and pathophysiological processes. However, most of the currently available knowledge on SIRT3 stems from studies in non-neuronal cells, and the consequences of the interactions between SIRT3 and its targets in the CNS are only beginning to be elucidated. In this review, we will summarize current advances relating to SIRT3, and explore how its known functions could influence brain physiology.

More to NAD+ than meets the eye: A regulator of metabolic pools and gene expression in Arabidopsis

Since its discovery more than a century ago, nicotinamide adenine dinucleotide (NAD⁺) is recognised as a fascinating cornerstone of cellular metabolism. This ubiquitous energy cofactor plays vital roles in metabolic pathways and regulatory processes, a fact emphasised by the essentiality of a balanced NAD⁺ metabolism for normal plant growth and development. Research on the role of NAD in plants has been predominantly carried out in the model plant Arabidopsis thaliana (Arabidopsis) with emphasis on the redox properties and cellular signalling functions of the metabolite. This review examines the current state of knowledge concerning how NAD can regulate both metabolic pools and gene expression in Arabidopsis. Particular focus is placed on recent studies highlighting the complexity of metabolic regulations involving NAD, more particularly in the mitochondrial compartment, and of signalling roles with respect to interactions with environmental fluctuations most specifically those involving plant immunity.

Aberrant Caspase Activation in Laminin-α2-Deficient Human Myogenic Cells is Mediated by p53 and Sirtuin Activity

Background:

Mutations in the LAMA2 gene encoding laminin-α2 cause congenital muscular dystrophy Type 1A (MDC1A), a severe recessive disease with no effective treatment. Previous studies have shown that aberrant activation of caspases and cell death through a pathway regulated by BAX and KU70 is a significant contributor to pathogenesis in laminin-α2-deficiency.

Objectives:

To identify mechanisms of pathogenesis in MDC1A.

Methods:

We used immunocytochemical and molecular studies of human myogenic cells and mouse muscles—comparing laminin-α2-deficient vs. healthy controls—to identify mechanisms that regulate pathological activation of caspase in laminin-α2-deficiency.

Results:

In cultures of myogenic cells from MDC1A donors, p53 accumulated in a subset of nuclei and aberrant caspase activation was inhibited by the p53 inhibitor pifithrin-alpha. Also, the p53 target BBC3 (PUMA) was upregulated in both MDC1A myogenic cells and Lama2–/– mouse muscles. In addition, studies with sirtuin inhibitors and SIRT1 overexpression showed that caspase activation in MDC1A myotubes was inversely related to sirtuin deacetylase activity. Caspase activation in laminin-α2-deficiency was, however, not associated with increased phosphorylation of p38 MAPK.

Conclusions:

Aberrant caspase activation in MDC1A cells was mediated both by sirtuin deacetylase activity and by p53. Interventions that inhibit aberrant caspase activation by targeting sirtuin or p53 function could potentially be useful in ameliorating MDC1A.

Detection of Insertions/Deletions Within SIRT1, SIRT2 and SIRT3 Genes and Their Associations with Body Measurement Traits in Cattle

Growth traits are complex quantitative traits controlled by numerous candidate genes, and they can be well-evaluated using body measurement traits. As the members of the nicotinamide adenine dinucleotide-dependent family of histone deacetylases, class I sirtuin genes (including SIRT1, SIRT2 and SIRT3) play crucial roles in regulating lipid metabolism, cellular growth and metabolism, suggesting that they are potential candidate genes affecting body measurement traits in animals. Hence, the objective of this work aimed to detect novel insertions/deletions (indels) of SIRT1, SIRT2 and SIRT3 genes in 955 cattle belonging to five breeds, as well as to evaluate their effects on body measurement traits. Herein, the novel 12-bp indel of SIRT1 gene, the 7-bp indel of SIRT2 gene and the 26-bp indel of SIRT3 gene were firstly reported, respectively. The association analysis indicated that the indels within SIRT1 and SIRT2 genes were significantly associated with body measurement traits such as body weight, chest circumference, height at hip cross, hip width, body height, etc. (P < 0.05 or P < 0.01). Therefore, based on these findings, the two novel indel variants within bovine SIRT1 and SIRT2 genes could be considered as potential molecular markers for growth traits in cattle selection practices and breeding.

SIRT1 activation with neuroheal is neuroprotective but SIRT2 inhibition with AK7 is detrimental for disconnected motoneurons

Sirtuin 1 (SIRT1) activity is neuroprotective, and we have recently demonstrated its role in the retrograde degenerative process in motoneurons (MNs) in the spinal cord of rats after peripheral nerve root avulsion (RA) injury. SIRT2 has been suggested to exert effects opposite those of SIRT1; however, its roles in neurodegeneration and neuron response after nerve injury remain unclear. Here we compared the neuroprotective potentials of SIRT1 activation and SIRT2 inhibition in a mouse model of hypoglossal nerve axotomy. This injury induced a reduction of around half MN population within the hypoglossal nucleus by a non-apoptotic neurodegenerative process triggered by endoplasmic reticulum (ER) stress that resulted in activation of the unfolded protein response mediated by IRE1α and XBP1 by 21 days post injury. Both SIRT1 activation with NeuroHeal and SIRT2 inhibition with AK7 protected NSC-34 motor neuron-like cells against ER stress in vitro. In agreement with the in vitro results, NeuroHeal treatment or SIRT1 overexpression was neuroprotective of axotomized hypoglossal MNs in a transgenic mouse model. In contrast, AK7 treatment or SIRT2 genetic depletion in mice inhibited damaged MN survival. To resolve the in vitro/in vivo discrepancies, we used an organotypic spinal cord culture system that preserves glial cells. In this system, AK7 treatment of ER-stressed organotypic cultures was detrimental for MNs and increased microglial nuclear factor-κB and the consequent transcription of cytotoxic pro-inflammatory factors similarly. The results highlight the importance of glial cells in determining the neuroprotective impact of any treatment.

The NAD+-Dependent Family of Sirtuins in Cerebral Ischemia and Preconditioning

SIGNIFICANCE

Sirtuins are an evolutionarily conserved family of NAD+-dependent lysine deacylases and ADP ribosylases. Their requirement for NAD+ as a cosubstrate allows them to act as metabolic sensors that couple changes in the energy status of the cell to changes in cellular physiological processes. NAD+ levels are affected by several NAD+-producing and NAD+-consuming pathways as well as by cellular respiration. Thus their intracellular levels are highly dynamic and are misregulated in a spectrum of metabolic disorders including cerebral ischemia. This, in turn, compromises several NAD+-dependent processes that may ultimately lead to cell death. Recent Advances: A number of efforts have been made to replenish NAD+ in cerebral ischemic injuries as well as to understand the functions of one its important mediators, the sirtuin family of proteins through the use of pharmacological modulators or genetic manipulation approaches either before or after the insult. Critical Issues and Future Directions: The results of these studies have regarded the sirtuins as promising therapeutic targets for cerebral ischemia. Yet, additional efforts are needed to understand the role of some of the less characterized members and to address the sex-specific effects observed with some members. Sirtuins also exhibit cell-type-specific expression in the brain as well as distinct subcellular and regional localizations. As such, they are involved in diverse and sometimes opposing cellular processes that can either promote neuroprotection or further contribute to the injury; which also stresses the need for the development and use of sirtuin-specific pharmacological modulators. Antioxid. Redox Signal. 28, 691-710.

The role of ion disequilibrium in induction of root cell death and autophagy by environmental stresses

Environmental stresses such as salinity, drought, oxidants, heavy metals, hypoxia, extreme temperatures and others can induce autophagy and necrosis-type programmed cell death (PCD) in plant roots. These reactions are accompanied by the generation of reactive oxygen species (ROS) and ion disequilibrium, which is induced by electrolyte/K+ leakage through ROS-activated ion channels, such as the outwardly-rectifying K+ channel GORK and non-selective cation channels. Here, we discuss mechanisms of the stress-induced ion disequilibrium and relate it with ROS generation and onset of morphological, biochemical and genetic symptoms of autophagy and PCD in roots. Based on our own data and that in the literature, we propose a hypothesis on the induction of autophagy and PCD in roots by loss of cytosolic K+. To support this, we present data showing that in conditions of salt stress-induced autophagy, gork1-1 plants lacking root K+ efflux channel have fewer autophagosomes compared with the wild type. Overall, literature analyses and presented data strongly suggest that stress-induced root autophagy and PCD are controlled by the level of cytosolic potassium and ROS.

Melatonin and Vitamin D Orchestrate Adipose Derived Stem Cell Fate by Modulating Epigenetic Regulatory Genes

Melatonin, that regulates many physiological processes including circadian rhythms, is a molecule able to promote osteoblasts maturation in vitro and to prevent bone loss in vivo, while regulating also adipocytes metabolism. In this regard, we have previously shown that melatonin in combination with vitamin D, is able to counteract the appearance of an adipogenic phenotype in adipose derived stem cells (ADSCs), cultured in an adipogenic favoring condition. In the present study, we aimed at evaluating the specific phenotype elicited by melatonin and vitamin D based medium, considering also the involvement of epigenetic regulating genes. ADSCs were cultured in a specific adipogenic conditioned media, in the presence of melatonin alone or with vitamin D. The expression of specific osteogenic related genes was evaluated at different time points, together with the histone deacetylases epigenetic regulators, HDAC1 and Sirtuins (SIRT) 1 and 2. Our results show that melatonin and vitamin D are able to modulate ADSCs commitment towards osteogenic phenotype through the upregulation of HDAC1, SIRT 1 and 2, unfolding an epigenetic regulation in stem cell differentiation and opening novel strategies for future therapeutic balancing of stem cell fate toward adipogenic or osteogenic phenotype.

ADP-Ribosylation, a Multifaceted Posttranslational Modification Involved in the Control of Cell Physiology in Health and Disease

Posttranslational modifications (PTMs) regulate protein functions and interactions. ADP-ribosylation is a PTM, in which ADP-ribosyltransferases use nicotinamide adenine dinucleotide (NAD⁺) to modify target proteins with ADP-ribose. This modification can occur as mono- or poly-ADP-ribosylation. The latter involves the synthesis of long ADP-ribose chains that have specific properties due to the nature of the polymer. ADP-Ribosylation is reversed by hydrolases that cleave the glycosidic bonds either between ADP-ribose units or between the protein proximal ADP-ribose and a given amino acid side chain. Here we discuss the properties of the different enzymes associated with ADP-ribosylation and the consequences of this PTM on substrates. Furthermore, the different domains that interpret either mono- or poly-ADP-ribosylation and the implications for cellular processes are described.

NAD+ : A key metabolic regulator with great therapeutic potential

Nicotinamide adenine dinucleotide (NAD⁺ ) is a ubiquitous metabolite that serves an essential role in the catabolism of nutrients. Recently, there has been a surge of interest in NAD⁺ biology, with the recognition that NAD⁺ influences many biological processes beyond metabolism, including transcription, signalling and cell survival. There are a multitude of pathways involved in the synthesis and breakdown of NAD⁺ , and alterations in NAD⁺ homeostasis have emerged as a common feature of a range of disease states. Here, we provide an overview of NAD⁺ metabolism and summarise progress on the development of NAD⁺ -related therapeutics.

Cardioprotective Effects of SIRT6 in a Mouse Model of Transverse Aortic Constriction-Induced Heart Failure

SIRT6, a member of the NAD (+)-dependent class III deacetylase sirtuin family, plays important roles in the maintenance of cardiovascular homeostasis. Telomere shortening is a risk factor for age-associated diseases, including heart disease. In the present study, we investigated the role of SIRT6 and telomerase in a mouse model of transverse aortic constriction (TAC)-induced heart failure. SIRT6, telomerase reverse transcriptase (TERT), and telomere repeat binding factor (TRF)-1 were significantly downregulated in TAC mice compared with their expression in sham-operated mice. Lentiviral vector-mediated overexpression of SIRT6 upregulated TERT and TRF1 and increased the survival of mice after TAC. Echocardiography and hemodynamic measurements as well as histological analyses indicated that SIRT6 overexpression attenuated TAC-induced heart dysfunction and decreased TAC-induced cardiac inflammatory responses, reducing cardiac fibrosis and decreasing infarct size. Taken together, our findings indicate that SIRT6 protects the myocardium against damage and this effect may be mediated by the modulation of telomeres. Our findings linking SIRT6 and telomere integrity in the heart warrant further investigation into the underlying mechanisms and support SIRT6 as a promising therapeutic target for the treatment of cardiovascular diseases.

NAD+ dependent deacetylase Sirtuin 5 rescues the innate inflammatory response of endotoxin tolerant macrophages by promoting acetylation of p65

The induction and persistence of a hypo-inflammatory and immunosuppressive state in severe sepsis is commonly associated with increased risks of secondary infections and mortality. Toll-like receptor (TLR)-triggered inflammatory response of macrophages/monocytes plays an important role in determining the outcome of hyper-inflammation during the acute phase and the hypo-inflammation during immunosuppressive phase of sepsis. However, the mechanisms for controlling hypo-inflammatory response in endotoxin tolerant macrophages remain to be fully understood. Considering that metabolic control of inflammation is an emerging field and the balance between AMP/ATP and oxidized NAD⁺/reduced NADH is associated with inflammation and metabolism, we analyzed the level of NAD⁺ in TLR-triggered innate inflammatory response, and found that the decreased level of NAD⁺ was significantly related to the increased inflammatory cytokine production both in vivo and in vitro. By screening the expression and function of NAD⁺ dependent type III deacetylase Sirtuin family members, we found that SIRT5 and SIRT1/2 had opposite expression patterns and functions in macrophages. SIRT5 deficiency decreased TLR-triggered inflammation in both acute and immunosuppressive phases of sepsis. Interestingly, cytoplasmic SIRT5 counteracted the inhibitory effects of SIRT2 and enhanced the innate inflammatory responses in macrophages and even in endotoxin-tolerant macrophages by promoting acetylation of p65 and activation of NF-κB pathway. Mechanistically, SIRT5 competed with SIRT2 to interact with NF-κB p65, in a deacetylase activity-independent way, to block the deacetylation of p65 by SIRT2, which consequently led to increased acetylation of p65 and the activation of NF-κB pathway and its downstream cytokines. Our study discovered the new functions of different Sirtuin members in sepsis, indicating that targeting of Sirtuin family members at different sepsis phases can be helpful to precisely control the progression of sepsis.

Characterization and mutational analysis of a nicotinamide mononucleotide deamidase from Agrobacterium tumefaciens showing high thermal stability and catalytic efficiency

NAD⁺ has emerged as a crucial element in both bioenergetic and signaling pathways since it acts as a key regulator of cellular and organismal homeostasis. Among the enzymes involved in its recycling, nicotinamide mononucleotide (NMN) deamidase is one of the key players in the bacterial pyridine nucleotide cycle, where it catalyzes the conversion of NMN into nicotinic acid mononucleotide (NaMN), which is later converted to NAD⁺ in the Preiss-Handler pathway. The biochemical characteristics of bacterial NMN deamidases have been poorly studied, although they have been investigated in some firmicutes, gamma-proteobacteria and actinobacteria. In this study, we present the first characterization of an NMN deamidase from an alphaproteobacterium, Agrobacterium tumefaciens (AtCinA). The enzyme was active over a broad pH range, with an optimum at pH 7.5. Moreover, the enzyme was quite stable at neutral pH, maintaining 55% of its activity after 14 days. Surprisingly, AtCinA showed the highest optimal (80°C) and melting (85°C) temperatures described for an NMN deamidase. The above described characteristics, together with its high catalytic efficiency, make AtCinA a promising biocatalyst for the production of pure NaMN. In addition, six mutants (C32A, S48A, Y58F, Y58A, T105A and R145A) were designed to study their involvement in substrate binding, and two (S31A and K63A) to determine their contribution to the catalysis. However, only four mutants (C32A, S48A Y58F and T105A) showed activity, although with reduced catalytic efficiency. These results, combined with a thermal and structural analysis, reinforce the Ser/Lys catalytic dyad mechanism as the most plausible among those proposed.

Comments on the history of medical-biological studies of aging, the birth of scientific gerontology

Recent books (Immunity. How Elie Metchnikoff changed the course of modern medicine and Expectations of Life) reviewed the important contribution of Metchnikoff to the emergence of gerontology as a new branch of biomedical sciences. Here, we insist on Metchnikoff's contribution and pivotal role in the emergence of nutrition as a science and its importance for health and longevity. The discovery of phagocytosis by Metchnikoff and of its evolutionary ancestry are at the origin of the emergence of cellular immunity as an independent science besides humoral immunity. The longevity of Metchnikoff (71years) at a time when average life expectancy of men did hardly pass 50years certainly contributed to the acceptance of his teachings. The recent increase of the senior population in most advanced countries is a good opportunity to review the contributions of nutrition to longevity.

The NAD+ precursor nicotinic acid improves genomic integrity in human peripheral blood mononuclear cells after X-irradiation

NAD⁺ is an essential cofactor for enzymes catalyzing redox-reactions as well as an electron carrier in energy metabolism. Aside from this, NAD⁺ consuming enzymes like poly(ADP-ribose) polymerases and sirtuins are important regulators involved in chromatin-restructuring processes during repair and epigenetics/transcriptional adaption. In order to replenish cellular NAD⁺ levels after cleavage, synthesis starts from precursors such as nicotinamide, nicotinamide riboside or nicotinic acid to match the need for this essential molecule. In the present study, we investigated the impact of supplementation with nicotinic acid on resting and proliferating human mononuclear blood cells with a focus on DNA damage and repair processes. We observed that nicotinic acid supplementation increased NAD⁺ levels as well as DNA repair efficiency and enhanced genomic stability evaluated by micronucleus test after x-ray treatment. Interestingly, resting cells displayed lower basal levels of DNA breaks compared to proliferating cells, but break-induction rates were identical. Despite similar levels of p53 protein upregulation after irradiation, higher NAD⁺ concentrations led to reduced acetylation of this protein, suggesting enhanced SIRT1 activity. Our data reveal that even in normal primary human cells cellular NAD⁺ levels may be limiting under conditions of genotoxic stress and that boosting the NAD⁺ system with nicotinic acid can improve genomic stability.

Lysine Acetylation and Deacetylation in Brain Development and Neuropathies

Embryonic development is critical for the final functionality and maintenance of the adult brain. Brain development is tightly regulated by intracellular and extracellular signaling. Lysine acetylation and deacetylation are posttranslational modifications that are able to link extracellular signals to intracellular responses. A wealth of evidence indicates that lysine acetylation and deacetylation are critical for brain development and functionality. Indeed, mutations of the enzymes and cofactors responsible for these processes are often associated with neurodevelopmental and psychiatric disorders. Lysine acetylation and deacetylation are involved in all levels of brain development, starting from neuroprogenitor survival and proliferation, cell fate decisions, neuronal maturation, migration, and synaptogenesis, as well as differentiation and maturation of astrocytes and oligodendrocytes, to the establishment of neuronal circuits. Hence, fluctuations in the balance between lysine acetylation and deacetylation contribute to the final shape and performance of the brain. In this review, we summarize the current basic knowledge on the specific roles of lysine acetyltransferase (KAT) and lysine deacetylase (KDAC) complexes in brain development and the different neurodevelopmental disorders that are associated with dysfunctional lysine (de)acetylation machineries.

Therapeutic role of sirtuins in neurodegenerative disease and their modulation by polyphenols

Searching for effective therapeutic agents‏‎ to ‎‏prevent‏ ‏neurodegeneration ‎is a challenging task due ‎to ‎the growing list of neurodegenerative disorders associated with a multitude of inter-related pathways.‎ The induction and inhibition of several different signaling pathways has been shown to slow down and/or attenuate ‎neurodegeneration and decline in cognition and locomotor function. Among these signaling pathways, a new class of enzymes known as sirtuins or silent information regulators of gene transcription has been shown to play important regulatory roles in the ageing process. SIRT1, a nuclear sirtuin, has received ‎particular interest due to its role as a deacetylase for several metabolic and signaling proteins involved in stress response, apoptosis, mitochondrial function, self-renewal, and ‎neuroprotection. ‎A new strategy to treat ‎neurodegenerative diseases is targeted therapy. In ‎this ‎paper, we‎ ‎ reviewed up-to-date findings regarding the targeting of ‎SIRT1 by polyphenolic ‎compounds,‎ ‎as a ‎new ‎‏approach in the search for novel, safe and effective treatments for ‎ ‎neurodegenerative ‎diseases. ‎.

Sirtuins and Their Roles in Brain Aging and Neurodegenerative Disorders

Sirtuins (SIRT1-SIRT7) are unique histone deacetylases (HDACs) whose activity depends on NAD⁺ levels and thus on the cellular metabolic status. SIRTs regulate energy metabolism and mitochondrial function. They orchestrate the stress response and damage repair. Through these functions sirtuins modulate the course of aging and affect neurodegenerative diseases. SIRTSs interact with multiple signaling proteins, transcription factors (TFs) and poly(ADP-ribose) polymerases (PARPs) another class of NAD⁺-dependent post-translational protein modifiers. The cross-talk between SIRTs TFs and PARPs is a highly promising research target in a number of brain pathologies. This review describes updated results on sirtuins in brain aging/neurodegeneration. It focuses on SIRT1 but also on the roles of mitochondrial SIRTs (SIRT3, 4, 5) and on SIRT6 and SIRT2 localized in the nucleus and in cytosol, respectively. The involvement of SIRTs in regulation of insulin-like growth factor signaling in the brain during aging and in Alzheimer's disease was also focused. Moreover, we analyze the mechanism(s) and potential significance of interactions between SIRTs and several TFs in the regulation of cell survival and death. A critical view is given on the application of SIRT activators/modulators in therapy of neurodegenerative diseases.