Restoration of Mitochondrial NAD+ Levels Delays Stem Cell Senescence and Facilitates Reprogramming of Aged Somatic Cells

β-Nicotinamide mononucleotide supplementation prolongs the lifespan of prematurely aged mice and protects colon function in ageing mice

Ageing is defined as the degeneration of physiological functions in numerous tissues and organs of an organism, which occurs with age. As we age, the gut undergoes a series of changes and weaknesses that may contribute to overall ageing. Emerging evidence suggests that β-nicotinamide mononucleotide (NMN) plays a role in regulating intestinal function, but there is still a lack of literature on its role in maintaining the colon health of ageing mice. In our research, Zmpste24-/- mice proved that NMN prolonged their life span and delayed senescence. This study was designed to investigate the effects of long-term intervention on regulating colon function in ageing mice. Our results indicated that NMN improved the pathology of intestinal epithelial cells and intestinal permeability by upregulating the expression of intestinal tight junction proteins and the number of goblet cells, increasing the release of anti-inflammatory factors, and increasing beneficial intestinal bacteria. NMN increased the expression of the proteins SIRT1, NMNAT2, and NMNAT3 and decreased the expression of the protein P53. It also regulated the activity of ISCs by increasing Wnt/β-catenin and Lgr5. Our findings also revealed that NMN caused a significant increase in the relative abundance of Akkermansia muciniphila and Bifidobacterium pseudolongum and notable differences in metabolic pathways related to choline metabolism in cancer. In summary, NMN supplementation can delay frailty in old age, aid healthy ageing, and delay gut ageing.

Nystagmus in the B6(CG)Tyr(c-2J)/J Albino Mouse: A Functional and RNA-Seq Analysis

Purpose

Infantile nystagmus syndrome (INS) is a gaze-holding disorder characterized by conjugate, uncontrolled eye oscillations that can result in significant visual acuity loss. INS is often associated with albinism, but the mechanism is unclear. Albino mice have nystagmus; however, a pigmented mouse with a tyr mutation making it phenotypically albino, the B6(CG)-Tyr(c-2J)/J (B6 albino), had not been tested. We tested optokinetic response (OKR) in B6 albino and control mice. RNA-Seq was performed on extraocular muscles (EOM), tibialis anterior (TA) muscle, abducens (CN6), and oculomotor (CN3) neurons to uncover molecular differences that may contribute to nystagmus.

Methods

OKR was measured using an ISCAN system. RNA was isolated from four tissues to identify differentially expressed genes and validated with qPCR and immunohistochemistry. Ingenuity pathway analyses identified top biological pathways.

Results

All B6 albino mice tested had nystagmus. Differential RNA expression analysis showed 383 genes differentially expressed in EOM, 70 in CN3, 20 in CN6, and 639 in the TA. Two genes were differentially expressed in all four tissues: wdfy1 and nnt. Differences were validated by qPCR and immunostaining.

Conclusions

The tyr mutation in B6 albino mice, genotypically pigmented and phenotypically albino, is sufficient to result in spontaneous nystagmus. The two genes with decreased expression in the B6 albino tissues examined, wdfy1 and nnt, have been implicated in mitochondrial dysfunction and stem cell maintenance in other systems. Their function in extraocular muscle is unknown. These studies suggest that this mouse model of nystagmus may allow molecular identification of candidate nystagmus-related genes.

RNA-binding proteins in cellular senescence

Cellular senescence is a state of irreversible cell cycle arrest that is triggered and controlled by various external and/or internal factors. Among them, the regulation of senescence-associated genes is an important molecular event that plays a role in senescence. The regulation of gene expression can be achieved by various types of modulating mechanisms, and RNA-binding proteins (RBPs) are commonly known as critical regulators targeting a global range of transcripts. RBPs bind to RNA-binding motifs of the target transcripts and are involved in post-transcriptional processes such as RNA transport, stabilization, splicing, and decay. These RBPs may also play critical roles in cellular senescence by regulating the expression of senescence-associated genes. The biological functions of RBPs in controlling cellular senescence are being actively studied. Herein, we summarized the RBPs that influence cellular senescence, particularly by regulating processes such as the senescence-associated secretory phenotype, cell cycle, and mitochondrial function.

Cocoa Polyphenol Extract Inhibits Cellular Senescence via Modulation of SIRT1 and SIRT3 in Auditory Cells

Cocoa, rich in polyphenols, has been reported to provide many health benefits due to its antioxidant properties. In this study, we investigated the effect of Cocoa polyphenols extract (CPE) against oxidative stress-induced cellular senescence using a hydrogen peroxide (H2O2)-induced cellular senescence model in three auditory cells lines derived from the auditory organ of a transgenic mouse: House Ear Institute-Organ of Corti 1 (HEI-OC1), Organ of Corti-3 (OC-k3), and Stria Vascularis (SV-k1) cells. Our results showed that CPE attenuated senescent phenotypes, including senescence-associated β-galactosidase expression, cell proliferation, alterations of morphology, oxidative DNA damage, mitochondrial dysfunction by inhibiting mitochondrial reactive oxygen species (mtROS) generation, and related molecules expressions such as forkhead box O3 (FOXO3) and p53. In addition, we determined that CPE induces expression of sirtuin 1 (SIRT1) and sirtuin 3 (SIRT3), and it has a protective role against cellular senescence by upregulation of SIRT1 and SIRT3. These data indicate that CPE protects against senescence through SIRT1, SIRT3, FOXO3, and p53 in auditory cells. In conclusion, these results suggest that Cocoa has therapeutic potential against age-related hearing loss (ARHL).

Bone regeneration strategies based on organelle homeostasis of mesenchymal stem cells

The organelle modulation has emerged as a crucial contributor to the organismal homeostasis. The mesenchymal stem cells (MSCs), with their putative functions in maintaining the regeneration ability of adult tissues, have been identified as a major driver to underlie skeletal health. Bone is a structural and endocrine organ, in which the organelle regulation on mesenchymal stem cells (MSCs) function has most been discovered recently. Furthermore, potential treatments to control bone regeneration are developing using organelle-targeted techniques based on manipulating MSCs osteogenesis. In this review, we summarize the most current understanding of organelle regulation on MSCs in bone homeostasis, and to outline mechanistic insights as well as organelle-targeted approaches for accelerated bone regeneration.

Sirtuins and chemokines as markers of replicative and induced senescence of human endotheliocytes

Background. One of the factors of the pathogenesis of atherosclerosis and other cardiovascular diseases is induced endothelial senescence. In this regard, the urgent task of molecular biology and medicine is the search for molecules that affect the process of vascular endotheliocytes senescence.The aim. To assess the expression of Sirt-1,3,6 and chemokines IL-4, CXCL11 in the replicative and induced senescence of human endotheliocytes.Materials and methods. The study was conducted on the primary culture of isolated human umbilical vein endothelial cells (HUVECs). HUVECs were cultured under conditions of replicative (natural) and lipopolysaccharide induced senescence.Results. The synthesis of Sirt-1,3,6, IL-4 and CXCL11 was evaluated using western blot analysis. We revealed a decrease in Sirt-1,3,6 synthesis by 1.6–1.8 times (р < 0.05) in the conditions of HUVEC replicative senescence. Induced senescence of endotheliocytes is characterized by a more pronounced decrease (1.7–3.4 times; р < 0.05) in the Sirt-1,3,6 synthesis. CXCL11 synthesis increases by 1.4 times (р < 0.05) in replicative and by 3.4 times (р < 0.05) in induced HUVEC senescence. IL-4 synthesis increases by 4.7 times in conditions of induced HUVEC senescence and doesn’t have changes in replicative senescence of endotheliocytes.Conclusion. These data obtained indicate that sirtuins and chemokines play an important role in the development of endothelial dysfunction observed in natural and induced senescence.

Nicotinamide Mononucleotide Supplementation Improves Mitochondrial Dysfunction and Rescues Cellular Senescence by NAD+/Sirt3 Pathway in Mesenchymal Stem Cells

In vitro expansion-mediated replicative senescence has severely limited the clinical applications of mesenchymal stem cells (MSCs). Accumulating studies manifested that nicotinamide adenine dinucleotide (NAD⁺) depletion is closely related to stem cell senescence and mitochondrial metabolism disorder. Promoting NAD⁺ level is considered as an effective way to delay aging. Previously, we have confirmed that nicotinamide mononucleotide (NMN), a precursor of NAD⁺, can alleviate NAD⁺ deficiency-induced MSC senescence. However, whether NMN can attenuate MSC senescence and its underlying mechanisms are still incompletely clear. The present study herein showed that late passage (LP) MSCs displayed lower NAD⁺ content, reduced Sirt3 expression and mitochondrial dysfunction. NMN supplementation leads to significant increase in intracellular NAD⁺ level, NAD⁺/ NADH ratio, Sirt3 expression, as well as ameliorated mitochondrial function and rescued senescent MSCs. Additionally, Sirt3 over-expression relieved mitochondrial dysfunction, and retrieved senescence-associated phenotypic features in LP MSCs. Conversely, inhibition of Sirt3 activity via a selective Sirt3 inhibitor 3-TYP in early passage (EP) MSCs resulted in aggravated cellular senescence and abnormal mitochondrial function. Furthermore, NMN administration also improves 3-TYP-induced disordered mitochondrial function and cellular senescence in EP MSCs. Collectively, NMN replenishment alleviates mitochondrial dysfunction and rescues MSC senescence through mediating NAD⁺/Sirt3 pathway, possibly providing a novel mechanism for MSC senescence and a promising strategy for anti-aging pharmaceuticals.

Cellular senescence: the good, the bad and the unknown

Cellular senescence is a ubiquitous process with roles in tissue remodelling, including wound repair and embryogenesis. However, prolonged senescence can be maladaptive, leading to cancer development and age-related diseases. Cellular senescence involves cell-cycle arrest and the release of inflammatory cytokines with autocrine, paracrine and endocrine activities. Senescent cells also exhibit morphological alterations, including flattened cell bodies, vacuolization and granularity in the cytoplasm and abnormal organelles. Several biomarkers of cellular senescence have been identified, including SA-βgal, p16 and p21; however, few markers have high sensitivity and specificity. In addition to driving ageing, senescence of immune and parenchymal cells contributes to the development of a variety of diseases and metabolic disorders. In the kidney, senescence might have beneficial roles during development and recovery from injury, but can also contribute to the progression of acute kidney injury and chronic kidney disease. Therapies that target senescence, including senolytic and senomorphic drugs, stem cell therapies and other interventions, have been shown to extend lifespan and reduce tissue injury in various animal models. Early clinical trials confirm that senotherapeutic approaches could be beneficial in human disease. However, larger clinical trials are needed to translate these approaches to patient care.

Reduced nicotinamide adenine dinucleotide phosphate in redox balance and diseases: a friend or foe?

The nicotinamide adenine dinucleotide (NAD⁺/NADH) and nicotinamide adenine dinucleotide phosphate (NADP⁺/NADPH) redox couples function as cofactors or/and substrates for numerous enzymes to retain cellular redox balance and energy metabolism. Thus, maintaining cellular NADH and NADPH balance is critical for sustaining cellular homeostasis. The sources of NADPH generation might determine its biological effects. Newly-recognized biosynthetic enzymes and genetically encoded biosensors help us better understand how cells maintain biosynthesis and distribution of compartmentalized NAD(H) and NADP(H) pools. It is essential but challenging to distinguish how cells sustain redox couple pools to perform their integral functions and escape redox stress. However, it is still obscure whether NADPH is detrimental or beneficial as either deficiency or excess in cellular NADPH levels disturbs cellular redox state and metabolic homeostasis leading to redox stress, energy stress, and eventually, to the disease state. Additional study of the pathways and regulatory mechanisms of NADPH generation in different compartments, and the means by which NADPH plays a role in various diseases, will provide innovative insights into its roles in human health and may find a value of NADPH for the treatment of certain diseases including aging, Alzheimer's disease, Parkinson's disease, cardiovascular diseases, ischemic stroke, diabetes, obesity, cancer, etc.

Regulation of Gene Expression through Food—Curcumin as a Sirtuin Activity Modulator

The sirtuin family comprises NAD⁺-dependent protein lysine deacylases, mammalian sirtuins being either nuclear (SIRT1, SIRT2, SIRT6, and SIRT7), mitochondrial (SIRT3, SIRT4, and SIRT5) or cytosolic enzymes (SIRT2 and SIRT5). They are able to catalyze direct metabolic reactions, thus regulating several physiological functions, such as energy metabolism, stress response, inflammation, cell survival, DNA repair, tissue regeneration, neuronal signaling, and even circadian rhythms. Based on these data, recent research was focused on finding molecules that could regulate sirtuins’ expression and/or activity, natural compounds being among the most promising in the field. Curcumin (1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) can induce, through SIRT, modulation of cancer cell senescence, improve endothelial cells protection against atherosclerotic factors, enhance muscle regeneration in atrophy models, and act as a pro-longevity factor counteracting the neurotoxicity of amyloid-beta. Although a plethora of protective effects was reported (antioxidant, anti-inflammatory, anticancer, etc.), its therapeutical use is limited due to its bioavailability issues. However, all the reported effects may be explained via the bioactivation theory, which postulates that curcumin’s observed actions are modulated via its metabolites and/or degradation products. The present article is focused on bringing together the literature data correlating the ability of curcumin and its metabolites to modulate SIRT activity and its consequent beneficial effects.

Cell Senescence and Central Regulators of Immune Response

Pathways regulating cell senescence and cell cycle underlie many processes associated with ageing and age-related pathologies, and they also mediate cellular responses to exposure to stressors. Meanwhile, there are central mechanisms of the regulation of stress responses that induce/enhance or weaken the response of the whole organism, such as hormones of the hypothalamic-pituitary-adrenal (HPA) axis, sympathetic and parasympathetic systems, thymic hormones, and the pineal hormone melatonin. Although there are many analyses considering relationships between the HPA axis and organism ageing, we found no systematic analyses of relationships between the neuroendocrine regulators of stress and inflammation and intracellular mechanisms controlling cell cycle, senescence, and apoptosis. Here, we provide a review of the effects of neuroendocrine regulators on these mechanisms. Our analysis allowed us to postulate a multilevel system of central regulators involving neurotransmitters, glucocorticoids, melatonin, and the thymic hormones. This system finely regulates the cell cycle and metabolic/catabolic processes depending on the level of systemic stress, stage of stress response, and energy capabilities of the body, shifting the balance between cell cycle progression, cell cycle stopping, senescence, and apoptosis. These processes and levels of regulation should be considered when studying the mechanisms of ageing and the proliferation on the level of the whole organism.

Metabolic Remodeling Impacts the Epigenetic Landscape of Dental Mesenchymal Stem Cells

Epigenetic regulation can dynamically adjust the gene expression program of cell fate decision according to the cellular microenvironment. Emerging studies have shown that metabolic activities provide fundamental components for epigenetic modifications and these metabolic-sensitive epigenetic events dramatically impact the cellular function of stem cells. Dental mesenchymal stem cells are promising adult stem cell resource for in situ injury repair and tissue engineering. In this review, we discuss the impact of metabolic fluctuations on epigenetic modifications in the oral and maxillofacial regions. The principles of the metabolic link to epigenetic modifications and the interaction between metabolite substrates and canonical epigenetic events in dental mesenchymal stem cells are summarized. The coordination between metabolic pathways and epigenetic events plays an important role in cellular progresses including differentiation, inflammatory responses, and aging. The metabolic-epigenetic network is critical for expanding our current understanding of tissue homeostasis and cell fate decision and for guiding potential therapeutic approaches in dental regeneration and infectious diseases.

Metabolic Regulation: A Potential Strategy for Rescuing Stem Cell Senescence

Stem cell senescence and exhaustion are closely related to organ failure and individual aging, which not only induces age-related diseases, but also hinders stem cell applications in regenerative medicine. Thus, it's imminent to find effective ways to delay and retrieve stem cell senescence. Metabolic abnormalities are one of the main characteristics of age-associated declines in stem cell function. Understanding the underlying mechanisms may reveal potential strategies for ameliorating age-associated phenotypes and treating age-related diseases. This review focuses on recent advances in the association between metabolism including glucose, lipid, glutamine and NAD⁺ metabolism and stem cell senescence, as well as the other properties like proliferation and differentiation. Layers of studies are summarized to demonstrate how metabolism varies in senescent stem cells and how metabolic reprogramming regulates stem cell senescence. Additionally, we mentioned some recent progress in therapeutic strategies to rejuvenate dysfunctional aged stem cells. Finally, a brief conclusion about the prospect of metabolic regulation as a potential strategy for rescuing stem cell senescence is displayed. Stem cell senescence is induced by the metabolic reprogramming. The metabolic alterations of glucose, lipid, glutamine and NAD⁺ can conversely facilitate or inhibit stem cell senescence. Glycolysis, OXPHOS and PPP are all attenuated. But gluconeogenesis alterations still remain unclear. In lipid metabolisms, both FAO and DNL are suppressed. As for the glutamine metabolism, stem cells' dependence on glutamine is enhanced. Last, NAD⁺ metabolism undergoes a down-regulated synthesis and up-regulated consumption. All these alterations can be potential targets for reversing stem cell senescence.

Sirt1 protects subventricular zone derived neural stem cells from DNA double strand breaks and contributes to olfactory function maintenance in aging mice

DNA damage is assumed to accumulate in stem cells over time and their ability to withstand this damage and maintain tissue homeostasis is a key determinant of aging. Nonetheless, relatively few studies have investigated whether DNA damage does indeed accumulate in stem cells and whether this contributes to stem cell aging and functional decline. Here, we found that, compared with young mice, DNA double strand breaks (DSBs) are reduced in subventricular zone (SVZ)-derived neural stem cells (NSCs) of aged mice, which was achieved partly through the adaptive upregulation of Sirt1 expression and non-homologous end joining (NHEJ)-mediated DNA repair. Sirt1 deficiency abolished this effect, leading to stem cell exhaustion, olfactory memory decline, and accelerated aging. The reduced DSBs and the upregulation of Sirt1 expression in SVZ-derived NSCs with age may represent a compensatory mechanism that evolved to protect stem cells from excessive DNA damage, as well as mitigate memory loss and other stresses during aging.

Reproducibility of developmental neuroplasticity in in vitro brain tissue models

The current prevalence of neurodevelopmental, neurodegenerative diseases, stroke and brain injury stimulates studies aimed to identify new molecular targets, to select the drug candidates, to complete the whole set of preclinical and clinical trials, and to implement new drugs into routine neurological practice. Establishment of protocols based on microfluidics, blood-brain barrier- or neurovascular unit-on-chip, and microphysiological systems allowed improving the barrier characteristics and analyzing the regulation of local microcirculation, angiogenesis, and neurogenesis. Reconstruction of key mechanisms of brain development and even some aspects of experience-driven brain plasticity would be helpful in the establishment of brain in vitro models with the highest degree of reliability. Activity, metabolic status and expression pattern of cells within the models can be effectively assessed with the protocols of system biology, cell imaging, and functional cell analysis. The next generation of in vitro models should demonstrate high scalability, 3D or 4D complexity, possibility to be combined with other tissues or cell types within the microphysiological systems, compatibility with bio-inks or extracellular matrix-like materials, achievement of adequate vascularization, patient-specific characteristics, and opportunity to provide high-content screening. In this review, we will focus on currently available and prospective brain tissue in vitro models suitable for experimental and preclinical studies with the special focus on models enabling 4D reconstruction of brain tissue for the assessment of brain development, brain plasticity, and drug kinetics.

Overexpression of NMNAT3 improves mitochondrial function and enhances anti-oxidative stress of bone marrow mesenchymal stem cells via the NAD+-Sirt3 pathway

Oxidative stress damage is a common problem in bone marrow mesenchymal stem cell (BMSC) transplantation. Under stress conditions, the mitochondrial function of BMSCs is disrupted, which accelerates senescence and apoptosis of BMSCs, ultimately leading to poor efficacy. Therefore, improving mitochondrial function and enhancing the anti-oxidative stress capacity of BMSCs may be an effective way of improving the survival rate and curative effect of BMSCs. In this study, we have confirmed that overexpression of nicotinamide mononucleotide adenylyl transferase 3 (NMNAT3) improves mitochondrial function and resistance to stress-induced apoptosis in BMSCs. We further revealed the mechanism of NMNAT3-mediated resistance to stress-induced apoptosis in BMSCs. We increased the level of nicotinamide adenine dinucleotide (NAD+) by overexpressing NMNAT3 in BMSCs and found that it could significantly increase the activity of silent mating type information regulation 2 homolog 3 (Sirt3) and significantly decrease the acetylation levels of Sirt3-dependent deacetylation-related proteins isocitrate dehydrogenase 2 (Idh2) and Forkhead-box protein O3a (FOXO3a). These findings show that NMNAT3 may increase the activity of Sirt3 by increasing NAD+ levels. Our results confirm that the NMNAT3-NAD+-Sirt3 axis is a potential mechanism for improving mitochondrial function and enhancing anti-oxidative stress of BMSCs. In this study, we take advantage of the role of NMNAT3 in inhibiting stress-induced apoptosis of BMSCs and provide new methods and ideas for breaking through the bottleneck of transplantation efficacy of BMSCs in the clinic.

The Role of SIRT3 in the Osteoporosis

SIRT3 is an NAD⁺-dependent deacetylase in the mitochondria with an extensive ability to regulate mitochondrial morphology and function. It has been reported that SIRT3 participates in the occurrence and development of many aging-related diseases. Osteoporosis is a common aging-related disease characterized by decreased bone mass and fragility fractures, which has caused a huge burden on society. Current research shows that SIRT3 is involved in the physiological processes of senescence of bone marrow mesenchymal stem cells (BMSCs), differentiation of BMSCs and osteoclasts. However, the specific effects and mechanisms of SIRT3 in osteoporosis are not clear. In the current review, we elaborated on the physiological functions of SIRT3, the cell types involved in bone remodeling, and the role of SIRT3 in osteoporosis. Furthermore, it also provided a theoretical basis for SIRT3 as a therapeutic target for osteoporosis.

Age-Dependent Decline of NAD+-Universal Truth or Confounded Consensus?

Nicotinamide adenine dinucleotide (NAD⁺) is an essential molecule involved in various metabolic reactions, acting as an electron donor in the electron transport chain and as a co-factor for NAD⁺-dependent enzymes. In the early 2000s, reports that NAD⁺ declines with aging introduced the notion that NAD⁺ metabolism is globally and progressively impaired with age. Since then, NAD⁺ became an attractive target for potential pharmacological therapies aiming to increase NAD⁺ levels to promote vitality and protect against age-related diseases. This review summarizes and discusses a collection of studies that report the levels of NAD⁺ with aging in different species (i.e., yeast, C. elegans, rat, mouse, monkey, and human), to determine whether the notion that overall NAD⁺ levels decrease with aging stands true. We find that, despite systematic claims of overall changes in NAD⁺ levels with aging, the evidence to support such claims is very limited and often restricted to a single tissue or cell type. This is particularly true in humans, where the development of NAD⁺ levels during aging is still poorly characterized. There is a need for much larger, preferably longitudinal, studies to assess how NAD⁺ levels develop with aging in various tissues. This will strengthen our conclusions on NAD metabolism during aging and should provide a foundation for better pharmacological targeting of relevant tissues.

Inhibiting bridge integrator 2 phosphorylation leads to improved oocyte quality, ovarian health and fertility in aging and after chemotherapy in mice

Female ovaries degenerate about 20 years earlier than testes leading to reduced primordial follicle reserve and a reduction in oocyte quality. Here we found that bridge integrator 2 (BIN2) is enriched in mouse ovaries and oocytes and that global knockout of this protein improves both female fertility and oocyte quality. Quantitative ovarian proteomics and phosphoproteomics showed that Bin2 knockout led to a decrease in phosphorylated ribosomal protein S6 (p-RPS6), a component of the mammalian target of rapamycin pathway and greatly increased nicotinamide nucleotide transhydrogenase (NNT), the free-radical detoxifier. Mechanistically, we find that phosphorylation of BIN2 at Thr423 and Ser424 leads to its translocation from the membrane to the cytoplasm, subsequent phosphorylation of RPS6 and inhibition of Nnt translation. We synthesized a BIN2-penetrating peptide (BPP) designed to inhibit BIN2 phosphorylation and found that a 3-week BPP treatment improved primordial follicle reserve and oocyte quality in aging and after chemotherapy-induced premature ovarian failure without discernible side effects.

Epigenetic Clock and Circadian Rhythms in Stem Cell Aging and Rejuvenation

This review summarizes the current understanding of the interaction between circadian rhythms of gene expression and epigenetic clocks characterized by the specific profile of DNA methylation in CpG-islands which mirror the senescence of all somatic cells and stem cells in particular. Basic mechanisms of regulation for circadian genes CLOCK-BMAL1 as well as downstream clock-controlled genes (ССG) are also discussed here. It has been shown that circadian rhythms operate by the finely tuned regulation of transcription and rely on various epigenetic mechanisms including the activation of enhancers/suppressors, acetylation/deacetylation of histones and other proteins as well as DNA methylation. Overall, up to 20% of all genes expressed by the cell are subject to expression oscillations associated with circadian rhythms. Additionally included in the review is a brief list of genes involved in the regulation of circadian rhythms, along with genes important for cell aging, and oncogenesis. Eliminating some of them (for example, Sirt1) accelerates the aging process, while the overexpression of Sirt1, on the contrary, protects against age-related changes. Circadian regulators control a number of genes that activate the cell cycle (Wee1, c-Myc, p20, p21, and Cyclin D1) and regulate histone modification and DNA methylation. Approaches for determining the epigenetic age from methylation profiles across CpG islands in individual cells are described. DNA methylation, which characterizes the function of the epigenetic clock, appears to link together such key biological processes as regeneration and functioning of stem cells, aging and malignant transformation. Finally, the main features of adult stem cell aging in stem cell niches and current possibilities for modulating the epigenetic clock and stem cells rejuvenation as part of antiaging therapy are discussed.

The Effects of SRT1720 Treatment on Endothelial Cells Derived from the Lung and Bone Marrow of Young and Aged, Male and Female Mice

Angiogenesis is critical for successful fracture healing. Age-related alterations in endothelial cells (ECs) may cause impaired bone healing. Therefore, examining therapeutic treatments to improve angiogenesis in aging may enhance bone healing. Sirtuin 1 (SIRT1) is highly expressed in ECs and its activation is known to counteract aging. Here, we examined the effects of SRT1720 treatment (SIRT1 activator) on the growth and function of bone marrow and lung ECs (BMECs and LECs, respectively), derived from young (3-4 month) and old (20-24 month) mice. While aging did not alter EC proliferation, treatment with SRT1720 significantly increased proliferation of all LECs. However, SRT1720 only increased proliferation of old female BMECs. Vessel-like tube assays showed similar vessel-like structures between young and old LECs and BMECs from both male and female mice. SRT1720 significantly improved vessel-like structures in all LECs. No age, sex, or treatment differences were found in migration related parameters of LECs. In males, old BMECs had greater migration rates than young BMECs, whereas in females, old BMECs had lower migration rates than young BMECs. Collectively, our data suggest that treatment with SRT1720 appears to enhance the angiogenic potential of LECs irrespective of age or sex. However, its role in BMECs is sex- and age-dependent.

NAD+ homeostasis in human health and disease

Depletion of nicotinamide adenine dinucleotide (NAD+ ), a central redox cofactor and the substrate of key metabolic enzymes, is the causative factor of a number of inherited and acquired diseases in humans. Primary deficiencies of NAD+ homeostasis are the result of impaired biosynthesis, while secondary deficiencies can arise due to other factors affecting NAD+ homeostasis, such as increased NAD+ consumption or dietary deficiency of its vitamin B3 precursors. NAD+ depletion can manifest in a wide variety of pathological phenotypes, ranging from rare inherited defects, characterized by congenital malformations, retinal degeneration, and/or encephalopathy, to more common multifactorial, often age-related, diseases. Here, we discuss NAD+ biochemistry and metabolism and provide an overview of the etiology and pathological consequences of alterations of the NAD+ metabolism in humans. Finally, we discuss the state of the art of the potential therapeutic implications of NAD+ repletion for boosting health as well as treating rare and common diseases, and the possibilities to achieve this by means of the different NAD+ -enhancing agents.

Welcome to the Family: Identification of the NAD+ Transporter of Animal Mitochondria as Member of the Solute Carrier Family SLC25

Subcellular compartmentation is a fundamental property of eukaryotic cells. Communication and metabolic and regulatory interconnectivity between organelles require that solutes can be transported across their surrounding membranes. Indeed, in mammals, there are hundreds of genes encoding solute carriers (SLCs) which mediate the selective transport of molecules such as nucleotides, amino acids, and sugars across biological membranes. Research over many years has identified the localization and preferred substrates of a large variety of SLCs. Of particular interest has been the SLC25 family, which includes carriers embedded in the inner membrane of mitochondria to secure the supply of these organelles with major metabolic intermediates and coenzymes. The substrate specificity of many of these carriers has been established in the past. However, the route by which animal mitochondria are supplied with NAD⁺ had long remained obscure. Only just recently, the existence of a human mitochondrial NAD⁺ carrier was firmly established. With the realization that SLC25A51 (or MCART1) represents the major mitochondrial NAD⁺ carrier in mammals, a long-standing mystery in NAD⁺ biology has been resolved. Here, we summarize the functional importance and structural features of this carrier as well as the key observations leading to its discovery.

SIRT3 consolidates heterochromatin and counteracts senescence

Sirtuin 3 (SIRT3) is an NAD⁺-dependent deacetylase linked to a broad range of physiological and pathological processes, including aging and aging-related diseases. However, the role of SIRT3 in regulating human stem cell homeostasis remains unclear. Here we found that SIRT3 expression was downregulated in senescent human mesenchymal stem cells (hMSCs). CRISPR/Cas9-mediated depletion of SIRT3 led to compromised nuclear integrity, loss of heterochromatin and accelerated senescence in hMSCs. Further analysis indicated that SIRT3 interacted with nuclear envelope proteins and heterochromatin-associated proteins. SIRT3 deficiency resulted in the detachment of genomic lamina-associated domains (LADs) from the nuclear lamina, increased chromatin accessibility and aberrant repetitive sequence transcription. The re-introduction of SIRT3 rescued the disorganized heterochromatin and the senescence phenotypes. Taken together, our study reveals a novel role for SIRT3 in stabilizing heterochromatin and counteracting hMSC senescence, providing new potential therapeutic targets to ameliorate aging-related diseases.

Oxidative stress induces cell death partially by decreasing both mRNA and protein levels of nicotinamide phosphoribosyltransferase in differentiated PC12 cells

Background.

Multiple studies have indicated crucial roles of NAD⁺ deficiency in several neurological diseases and aging. It is critical to discover the mechanisms underlying the NAD⁺ deficiency. A decreased level of Nicotinamide phosphoribosyltransferase (Nampt)—an important enzyme in the salvage pathway of NAD⁺ synthesis—has been found under certain pathological conditions, while the mechanisms underlying the Nampt decrease are unclear. The purpose of this study is to test the hypothesis that oxidative stress can produce decreased Nampt, and to investigate the biological effects of Nampt on NAD⁺ synthesis and cell survival under both basal and oxidative stress conditions.

Methods.

We used differentiated PC12 cells as a cellular model to investigate the effects of oxidative stress on the levels of Nampt. Multiple assays, including flow cytometry-based cell death assays and NAD⁺ assays were conducted.

Results.

First, oxidative stress can decrease the levels of Nampt mRNA and Nampt protein; second, Nampt plays significant roles in NAD⁺ synthesis under both basal conditions and oxidative stress conditions; third, Nampt plays critical roles in cell survival under both basal conditions and oxidative stress conditions; and fourth, oxidative stress produced decreased NAD⁺ levels and cell survival partially by decreasing Nampt. Collectively, our study has indicated that oxidative stress is a pathological factor leading to decreased Nampt, which plays important roles in oxidative stress-produced decreases in NAD⁺ levels and cell survival. Our findings have indicated major roles of Nampt in maintaining NAD⁺ levels and cell survival under both basal and oxidative stress conditions.

Downregulation of DUOX1 function contributes to aging-related impairment of innate airway injury responses and accelerated senile emphysema

Aging is associated with a gradual loss of lung function due to increased cellular senescence, decreased regenerative capacity, and impaired innate host defense. One important aspect of innate airway epithelial host defense to nonmicrobial triggers is the secretion of alarmins such as IL-33 and activation of type 2 inflammation, which were previously found to depend on activation of the NADPH oxidase (NOX) homolog DUOX1, and redox-dependent signaling pathways that promote alarmin secretion. Here, we demonstrate that normal aging of C57BL/6J mice resulted in markedly decreased lung innate epithelial type 2 responses to exogenous triggers such as the airborne allergen Dermatophagoides pteronyssinus, which was associated with marked downregulation of DUOX1, as well as DUOX1-mediated redox-dependent signaling. DUOX1 deficiency was also found to accelerate age-related airspace enlargement and decline in lung function but did not consistently affect other features of lung aging such as senescence-associated inflammation. Intriguingly, observations of age-related DUOX1 downregulation and enhanced airspace enlargement due to DUOX1 deficiency in C57BL/6J mice, which lack a functional mitochondrial nicotinamide nucleotide transhydrogenase (NNT), were much less dramatic in C57BL/6NJ mice with normal NNT function, although the latter mice also displayed impaired innate epithelial injury responses with advancing age. Overall, our findings indicate a marked aging-dependent decline in (DUOX1-dependent) innate airway injury responses to external nonmicrobial triggers, but the impact of aging on DUOX1 downregulation and its significance for age-related senile emphysema development was variable between different C57BL6 substrains, possibly related to metabolic alterations due to differences in NNT function.

Molecular and functional characteristics of megakaryocytes and platelets in aging

PURPOSE OF REVIEW

Advances in medical care and preventive measures have contributed to increasing life expectancy. Therefore, it is critical to expand our understanding of the physiological and pathophysiological adaptations of the hematological system in aging. We highlight and review the findings from recent investigations aimed at understanding the effects of aging on megakaryocytes and platelets.

RECENT FINDINGS

Biochemical and transcriptomic studies of megakaryocytes and platelets from older humans and mice have advanced our understanding of the molecular and functional characteristics of megakaryocytes and platelets during aging. These studies have led to the identification of metabolic and inflammatory pathways associated with the generation of hyperreactive platelets that may significantly contribute to the high incidence of thrombosis in aging.

SUMMARY

By increasing our research efforts to understand and identify the characteristics of megakaryocytes and platelets in aging, we will increase our potential to develop novel therapies aimed at decreasing the incidence of aging-associated thrombosis. These efforts will also serve as a foundation to better understand the role of megakaryocytes and platelets in other age-related hematological conditions with high thrombotic risk such as clonal hematopoiesis of indeterminate potential and myeloproliferative neoplasms.

Identification of a Goat Intersexuality-Associated Novel Variant Through Genome-Wide Resequencing and Hi-C

Background: Polled intersex syndrome (PIS) leads to reproductive disorders in goats and exerts a heavy influence on goat breeding. Since 2001, the core variant of an 11.7 kb deletion at ~129 Mb on chromosome 1 (CHI1) has been widely used as a genetic diagnostic criterion. In 2020, a ~0.48 Mb insertion within the PIS deletion was identified by sequencing in XX intersex goats. However, the suitability of this variation for the diagnosis of intersex goats worldwide and its further molecular genetic mechanism need to be clarified.

Results: The whole-genome selective sweep of intersex goats from China was performed with whole-genome next-generation sequencing technology for large sample populations and a case–control study on interbreeds. A series of candidate genes related to the goat intersexuality phenotype were found. We further confirmed that a ~0.48 Mb duplicated fragment (including ERG and KCNJ15) downstream of the ~20 Mb PIS region was reversely inserted into the PIS locus in intersex Chinese goats and was consistent with that in European Saanen and Valais black-necked goats. High-throughput chromosome conformation capture (Hi-C) technology was then used to compare the 3D structures of the PIS variant neighborhood in CHI1 between intersex and non-intersex goats. A newly found structure was validated as an intrachromosomal rearrangement. This inserted duplication changed the original spatial structure of goat CHI1 and caused the appearance of several specific loop structures in the adjacent ~20 kb downstream region of FOXL2.

Conclusions: Results suggested that the novel complex PIS variant genome was sufficient as a broad-spectrum clinical diagnostic marker of XX intersexuality in goats from Europe and China. A series of private dense loop structures caused by segment insertion into the PIS deletion might affect the expression of FOXL2 or other neighboring novel candidate genes. However, these structures require further in-depth molecular biological experimental verification. In general, this study provided new insights for future research on the molecular genetic mechanism underlying female-to-male sex reversal in goats.

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.

Metabolic Dysregulation Contributes to the Progression of Alzheimer's Disease

Alzheimer's disease (AD) is an incurable neurodegenerative disease. Numerous studies have demonstrated a critical role for dysregulated glucose metabolism in its pathogenesis. In this review, we summarize metabolic alterations in aging brain and AD-related metabolic deficits associated with glucose metabolism dysregulation, glycolysis dysfunction, tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS) deficits, and pentose phosphate pathway impairment. Additionally, we discuss recent treatment strategies targeting metabolic defects in AD, including their limitations, in an effort to encourage the development of novel therapeutic strategies.

Mesenchymal Stem Cell Senescence and Rejuvenation: Current Status and Challenges

Over the past decades, mesenchymal stem cell (MSC)-based therapy has been intensively investigated and shown promising results in the treatment of various diseases due to their easy isolation, multiple lineage differentiation potential and immunomodulatory effects. To date, hundreds of phase I and II clinical trials using MSCs have been completed and many are ongoing. Accumulating evidence has shown that transplanted allogeneic MSCs lose their beneficial effects due to immunorejection. Nevertheless, the function of autologous MSCs is adversely affected by age, a process termed senescence, thus limiting their therapeutic potential. Despite great advances in knowledge, the potential mechanisms underlying MSC senescence are not entirely clear. Understanding the molecular mechanisms that contribute to MSC senescence is crucial when exploring novel strategies to rejuvenate senescent MSCs. In this review, we aim to provide an overview of the biological features of senescent MSCs and the recent progress made regarding the underlying mechanisms including epigenetic changes, autophagy, mitochondrial dysfunction and telomere shortening. We also summarize the current approaches to rejuvenate senescent MSCs including gene modification and pretreatment strategies. Collectively, rejuvenation of senescent MSCs is a promising strategy to enhance the efficacy of autologous MSC-based therapy, especially in elderly patients.

[Effects of nicotinamide mononucleotide adenylyl transferase 3 on mitochondrial function and anti-oxidative stress of rabbit bone marrow mesenchymal stem cells via regulating nicotinamide adenine dinucleotide levels]

OBJECTIVE

To investigate the effect of nicotinamide mononucleotide adenosyl transferase 3 (NMNAT3) on the mitochondrial function and anti-oxidative stress of rabbit bone marrow mesenchymal stem cells (BMSCs) under oxidative stress in vitro by regulating nicotinamide adenine dinucleotide (NAD +) levels.

METHODS

The bone marrow of femur and tibia of New Zealand white rabbits were extracted. BMSCs were isolated and cultured in vitro by density gradient centrifugation combined with adherent culture. The third generation cells were identified by flow cytometry and multi-directional induction. Overexpression of NMNAT3 gene was transfected into rabbit BMSCs by enhanced green fluorescent protein (EGFP) labeled lentivirus (BMSCs/Lv-NMNAT3-EGFP), and then the expression of NMNAT3 was detected by real-time fluorescence quantitative PCR (qRT-PCR) and Western blot and cell proliferation by cell counting kit 8 (CCK-8) method. BMSCs transfected with negative lentivirus (BMSCs/Lv-EGFP) and untransfected BMSCs were used as controls. The oxidative stress injury cell model was established by using H 2O 2 to treat rabbit BMSCs. According to the experimental treatment conditions, they were divided into 4 groups: Group A was normal BMSCs without H 2O 2 treatment; untransfected BMSCs, BMSCs/Lv-EGFP, and BMSCs/Lv-NMNAT3-EGFP in groups B, C, and D were treated with H 2O 2 simulated oxidative stress, respectively. The effects of NMNAT3 on the mitochondrial function of BMSCs under oxidative stress [changes of mitochondrial membrane potential, NAD + and adenosine triphosphate (ATP) levels], the changes of anti-oxidative stress ability of BMSCs [reactive oxygen species (ROS) and malondialdehyde (MDA) levels, manganese superoxide dismutase (Mn-SOD) and catalase (CAT) activities], and the effects of BMSCs on senescence and apoptosis [senescence associated-β-galactosidase (SA-β-gal) staining and TUNEL staining] were detected after 24 hours of treatment.

RESULTS

The rabbit BMSCs were successfully isolated and cultured in vitro. The stable strain of rabbit BMSCs with high expression of NMNAT3 gene was successfully obtained by lentiviral transfection, and the expressions of NMNAT3 gene and protein significantly increased ( P<0.05). There was no significant difference in the trend of cell proliferation compared with normal BMSCs. After treatment with H 2O 2, the function of mitochondria was damaged and apoptosis increased in all groups. However, compared with groups B and C, the group D showed that the mitochondrial function of BMSCs improved, the membrane potential increased, the level of NAD + and ATP synthesis of mitochondria increased; the anti-oxidative stress ability of BMSCs enhanced, the levels of ROS and MDA decreased, and the activities of antioxidant enzymes (Mn-SOD, CAT) increased; and the proportion of SA-β-gal positive cells and the rate of apoptosis decreased. The differences in all indicators between group D and groups B and C were significant ( P<0.05).

CONCLUSION

NMNAT3 can effectively improve the mitochondrial function of rabbit BMSCs via increasing the NAD + levels, and enhance its anti-oxidative stress and improve the survival of BMSCs under oxidative stress conditions.

Nicotinamide adenine dinucleotide induces a bivalent metabolism and maintains pluripotency in human embryonic stem cells

Nicotinamide adenine dinucleotide (NAD⁺ ) and its precursor metabolites are emerging as important regulators of both cell metabolism and cell state. Interestingly, the role of NAD⁺ in human embryonic stem cell (hESC) metabolism and the regulation of pluripotent cell state is unresolved. Here we show that NAD⁺ simultaneously increases hESC mitochondrial oxidative metabolism and partially suppresses glycolysis and stimulates amino acid turnover, doubling the consumption of glutamine. Concurrent with this metabolic remodeling, NAD⁺ increases hESC pluripotent marker expression and proliferation, inhibits BMP4-induced differentiation and reduces global histone 3 lysine 27 trimethylation, plausibly inducing an intermediate naïve-to-primed bivalent metabolism and pluripotent state. Furthermore, maintenance of NAD⁺ recycling via malate aspartate shuttle activity is identified as an absolute requirement for hESC self-renewal, responsible for 80% of the oxidative capacity of hESC mitochondria. Our findings implicate NAD⁺ in the regulation of cell state, suggesting that the hESC pluripotent state is dependent upon cellular NAD⁺ .

Nicotinamide Riboside Enhances Mitochondrial Proteostasis and Adult Neurogenesis through Activation of Mitochondrial Unfolded Protein Response Signaling in the Brain of ALS SOD1G93A Mice

Amyotrophic lateral sclerosis (ALS) is caused by the progressive degeneration of motor neurons in the spinal cord, the brain stem, and the motor cortex. So far, there is still a lack of effective drugs. Nicotinamide adenine dinucleotide (NAD+) takes part in redox reactions and the NAD-dependent signaling pathway. The NAD+ decline is related with many neurological diseases, leading to the accumulation of neurotoxic protein in the central nervous system. Moreover, the NAD+ supplementation is shown to promote neural stem cells/neuronal precursor cells (NSCs/NPCs) pool maintenance. Regulatory mechanisms and functions of NAD+ metabolism in ALS are still unknown. Thus, we hypothesized the aggregation of human SOD1 toxic protein and the fate of NSCs/NPCs in the ALS disease could be improved by the administration of nicotinamide riboside (NR), an NAD+ precursor. In this study, we treated SOD1G93A transgenic and wild-type mice by the oral administration of 20 mg/ml NR starting at 50 days of age. Effects of NR on the body weight, the motor function, the onset and the survival were assessed during the experiment. The expression of mutant hSOD1 protein, mitochondrial unfolded protein response (UPRmt) related protein, mitophagy markers and NAD+ metabolism related protein were detected by immunoblotting. Effects of NR on the NSCs/NPCs in neurogenic niches of brain were identified by the immunofluorescence staining. Our investigation elucidated that the NR treatment exhibited better hanging wire endurance but did not postpone the onset or extend the life span of SOD1G93A mice. Besides, we observed that the NR repletion promoted the clearance of mitochondrial hSOD1 neurotoxic protein. Meanwhile, the mitochondrial function pathway was disrupted in the brain of SOD1G93A mice. What's more, we demonstrated that the inadequate function of NAD+ salvage synthesis pathway was the primary explanation behind the decline of NAD+, and the NR treatment enhanced the proliferation and migration of NSCs/NPCs in the brain of SOD1G93A mice. At last, we found that levels of UPRmt related protein were significantly increased in the brain of SOD1G93A mice after the NR treatment. In summary, these findings reveal that the administration of NR activates UPRmt signaling, modulates mitochondrial proteostasis and improves the adult neurogenesis in the brain of SOD1G93A mice.

Where Metabolism Meets Senescence: Focus on Endothelial Cells

Despite the decline in their proliferative potential, senescent cells display a high metabolic activity. Senescent cells have been shown to acquire a more glycolytic state even in presence of high oxygen levels, in a way similar to cancer cells. The diversion of pyruvate, the final product of glycolysis, away from oxidative phosphorylation results in an altered bioenergetic state and may occur as a response to the enhanced oxidative stress caused by the accumulation of dysfunctional mitochondria. This metabolic shift leads to increased AMP/ATP and ADP/ATP ratios, to the subsequent AMPK activation, and ultimately to p53-mediated growth arrest. Mounting evidences suggest that metabolic reprogramming is critical to direct considerable amounts of energy toward specific activities related to the senescent state, including the senescence-associated secretory phenotype (SASP) and the modulation of immune responses within senescent cell tissue microenvironment. Interestingly, despite the relative abundance of oxygen in the vascular compartment, healthy endothelial cells (ECs) produce most of their ATP content from the anaerobic conversion of glucose to lactate. Their high glycolytic rate further increases during senescence. Alterations in EC metabolism have been identified in age-related diseases (ARDs) associated with a dysfunctional vasculature, including atherosclerosis, type 2 diabetes and cardiovascular diseases. In particular, higher production of reactive oxygen species deriving from a variety of enzymatic sources, including uncoupled endothelial nitric oxide synthase and the electron transport chain, causes DNA damage and activates the NAD+-consuming enzymes polyADP-ribose polymerase 1 (PARP1). These non-physiological mechanisms drive the impairment of the glycolytic flux and the diversion of glycolytic intermediates into many pathological pathways. Of note, accumulation of senescent ECs has been reported in the context of ARDs. Through their pro-oxidant, pro-inflammatory, vasoconstrictor, and prothrombotic activities, they negatively impact on vascular physiology, promoting both the onset and development of ARDs. Here, we review the current knowledge on the cellular senescence-related metabolic changes and their contribution to the mechanisms underlying the pathogenesis of ARDs, with a particular focus on ECs. Moreover, current and potential interventions aimed at modulating EC metabolism, in order to prevent or delay ARD onset, will be discussed.

Update on the role of Sirtuin 3 in cell differentiation: A major metabolic target that can be pharmacologically controlled

Cell differentiation is a fundamental biological event in which a precursor stem cell is turning into a specialized somatic cell. It is thus crucial for the development, tissue turnover and regeneration in mammals. Among the numerous changes taking place in a cell during a differentiation programme, the biology of mitochondria, the central organelle mainly responsible for energy homeostasis and stress adaptation, is deeply modified. These modifications are now well recognized as taking an active part to the completion of the differentiation programme. Indeed, mitochondrial biogenesis and metabolic shift are observed during cell differentiation, adapting many syntheses, calcium homeostasis, ATP and reactive oxygen species production, to the needs. These mitochondrial functions are substantially regulated by the post-translational modifications of the mitochondrial proteins among which lysine acetylation is essential. This mitoacetylome is then globally controlled by the balance between spontaneous/enzymatically-catalysed protein acetylation and the NAD⁺-dependent deacetylation mediated by Sirtuin 3. This enzyme is now considered as a major regulator of the function of the organelle. Regarding the requirement of these mitochondrial adaptations, the subsequent growing interest for this enzyme recently extended to the investigation of the mechanisms driving cell differentiation. This review summarizes the currently available information about the significance of SIRT3 in cell differentiation in physio-pathological contexts. We also suggest a control of the differentiation-activated autophagy by SIRT3, a hypothesis supported by recent findings establishing a causal link between SIRT3 and autophagy. Eventually, an update on the present pharmacological modulators of SIRT3 in a context of cell differentiation is discussed.

Regulation of Glucose Metabolism by NAD+ and ADP-Ribosylation

Cells constantly adapt their metabolic pathways to meet their energy needs and respond to nutrient availability. During the last two decades, it has become increasingly clear that NAD⁺, a coenzyme in redox reactions, also mediates several ubiquitous cell signaling processes. Protein ADP-ribosylation is a post-translational modification that uses NAD⁺ as a substrate and is best known as part of the genotoxic stress response. However, there is increasing evidence that NAD⁺-dependent ADP-ribosylation regulates other cellular processes, including metabolic pathways. In this review, we will describe the compartmentalized regulation of NAD⁺ biosynthesis, consumption, and regeneration with a particular focus on the role of ADP-ribosylation in the regulation of glucose metabolism in different cellular compartments.

Subcellular compartmentalization of NAD+ and its role in cancer: A sereNADe of metabolic melodies

Nicotinamide adenine dinucleotide (NAD+) is an essential biomolecule involved in many critical processes. Its role as both a driver of energy production and a signaling molecule underscores its importance in health and disease. NAD+ signaling impacts multiple processes that are dysregulated in cancer, including DNA repair, cell proliferation, differentiation, redox regulation, and oxidative stress. Distribution of NAD+ is highly compartmentalized, with each subcellular NAD+ pool differentially regulated and preferentially involved in distinct NAD+-dependent signaling or metabolic events. Emerging evidence suggests that targeting NAD+ metabolism is likely to repress many specific mechanisms underlying tumor development and progression, including proliferation, survival, metabolic adaptations, invasive capabilities, heterotypic interactions with the tumor microenvironment, and stress response including notably DNA maintenance and repair. Here we provide a comprehensive overview of how compartmentalized NAD+ metabolism in mitochondria, nucleus, cytosol, and extracellular space impacts cancer formation and progression, along with a discussion of the therapeutic potential of NAD+-targeting drugs in cancer.

Mitochondrial Regulation of Stem Cells in Bone Homeostasis

Mitochondria have emerged as key contributors to the organismal homeostasis, in which mitochondrial regulation of stem cells is becoming increasingly important. Originated from mesenchymal stem cell (MSC) and hematopoietic stem cell (HSC) lineage commitments and interactions, bone is a representative organ where the mitochondrial essentiality to stem cell function has most recently been discovered, underlying skeletal health, aging, and diseases. Furthermore, mitochondrial medications based on modulating stem cell specification are emerging to provide promising therapies to counteract bone aging and pathologies. Here we review the cutting-edge knowledge regarding mitochondrial regulation of stem cells in bone homeostasis, highlighting mechanistic insights as well as mitochondrial strategies for augmented bone healing and tissue regeneration.

Sirtuin signaling in cellular senescence and aging

Sirtuin is an essential factor that delays cellular senescence and extends the organismal lifespan through the regulation of diverse cellular processes. Suppression of cellular senescence by Sirtuin is mainly mediated through delaying the age-related telomere attrition, sustaining genome integrity and promotion of DNA damage repair. In addition, Sirtuin modulates the organismal lifespan by interacting with several lifespan regulating signaling pathways including insulin/IGF-1 signaling pathway, AMP-activated protein kinase, and forkhead box O. Although still controversial, it is suggested that the prolongevity effect of Sirtuin is dependent with the level of and with the tissue expression of Sirtuin. Since Sirtuin is also believed to mediate the prolongevity effect of calorie restriction, activators of Sirtuin have attracted the attention of researchers to develop therapeutics for age-related diseases. Resveratrol, a phytochemical rich in the skin of red grapes and wine, has been actively investigated to activate Sirtuin activity with consequent beneficial effects on aging. This article reviews the evidences and controversies regarding the roles of Sirtuin on cellular senescence and lifespan extension, and summarizes the activators of Sirtuin including Sirtuin-activating compounds and compounds that increase the cellular level of nicotinamide dinucleotide.

Effect of YAP on an Immortalized Periodontal Ligament Stem Cell Line

Objective

To establish an immortalized human periodontal ligament stem cell line (hPDLSC) and investigate whether and how YAP mediates the establishment of the stem cell line.

Methods

Primary hPDLSCs were cultured and transfected with lentivirus containing the telomerase reverse transcriptase (TERT) gene. The expression of TERT was detected via the polymerase chain reaction (PCR) and real-time quantitative PCR (RT-PCR). Flow cytometry was employed to detect surface markers of hPDLSCs and TERT-hPDLSCs. The cell counting kit-8 (CCK-8) and 5-ethynyl-2'-deoxyuridine (EdU) methods were used to examine the proliferation ability of the cells. Flow cytometry and TUNEL staining were employed to examine the cell apoptosis rate. The β-galactosidase staining assay was used to assess the rate of cell senescence. The osteogenic differentiation ability of the cells was detected via alkaline phosphatase (ALP) staining and Alizarin red staining assays. BALB/c mice were employed to determine the tumorigenicity of TERT-hPDLSCs. The expression levels of YAP and other proteins in the Hippo signaling pathway were detected by Western blotting. Verteporfin was used to inhibit the binding of YAP to the downstream target gene TEAD.

Results

TERT-hPDLSCs showed stable high expression of TERT, even at the thirtieth passage after transfection with lentivirus containing the TERT gene. Compared with primary hPDLSCs, TERT-hPDLSCs exhibited a stronger proliferation ability and lower cell apoptosis and senescence rates while maintaining the same osteogenetic differentiation ability as primary hPDLSCs. The transfection of hPDLSCs with lentivirus containing the TERT gene did not lead to tumorigenesis in nude mice. The Hippo signaling pathway was inactivated in TERT-hPDLSCs compared to hPDLSCs. When treated with verteporfin, the proliferation of TERT-hPDLSCs decreased, while the apoptosis and senescence rates of these cells increased. However, TERT-hPDLSCs still showed a stronger proliferation ability and lower cell apoptosis and senescence rates than hPDLSCs treated with verteporfin at the same concentration.

Conclusions

Overexpression of TERT in hPDLSCs resulted in the successful establishment of an immortalized periodontal ligament stem cell line. TERT may regulate the biological characteristics of hPDLSCs through the Hippo/YAP signaling pathway. hPDLSCs could be a feasible resource for stem cell research and a promising resource for stem cell therapy.

Cytoplasmic and Mitochondrial NADPH-Coupled Redox Systems in the Regulation of Aging

The reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) protects against redox stress by providing reducing equivalents to antioxidants such as glutathione and thioredoxin. NADPH levels decline with aging in several tissues, but whether this is a major driving force for the aging process has not been well established. Global or neural overexpression of several cytoplasmic enzymes that synthesize NADPH have been shown to extend lifespan in model organisms such as Drosophila suggesting a positive relationship between cytoplasmic NADPH levels and longevity. Mitochondrial NADPH plays an important role in the protection against redox stress and cell death and mitochondrial NADPH-utilizing thioredoxin reductase 2 levels correlate with species longevity in cells from rodents and primates. Mitochondrial NADPH shuttles allow for some NADPH flux between the cytoplasm and mitochondria. Since a decline of nicotinamide adenine dinucleotide (NAD⁺) is linked with aging and because NADP⁺ is exclusively synthesized from NAD⁺ by cytoplasmic and mitochondrial NAD⁺ kinases, a decline in the cytoplasmic or mitochondrial NADPH pool may also contribute to the aging process. Therefore pro-longevity therapies should aim to maintain the levels of both NAD⁺ and NADPH in aging tissues.

NAD+ Deficiency Is a Common Central Pathological Factor of a Number of Diseases and Aging: Mechanisms and Therapeutic Implications

Increasing evidence has indicated critical roles of nicotinamide adenine dinucleotide, oxidized form (NAD⁺) in various biological functions. NAD⁺ deficiency has been found in models of a number of diseases such as cerebral ischemia, myocardial ischemia, and diabetes, and in models of aging. Applications of NAD⁺ or other approaches that can restore NAD⁺ levels are highly protective in these models of diseases and aging. NAD⁺ produces its beneficial effects by targeting at multiple pathological pathways, including attenuating mitochondrial alterations, DNA damage, and oxidative stress, by modulating such enzymes as sirtuins, glyceraldehyde-3-phosphate dehydrogenase, and AP endonuclease. These findings have suggested great therapeutic and nutritional potential of NAD⁺ for diseases and senescence. Recent Advances: Approaches that can restore NAD⁺ levels are highly protective in the models of such diseases as glaucoma. The NAD⁺ deficiency in the diseases and aging results from not only poly(ADP-ribose) polymerase-1 (PARP-1) activation but also decreased nicotinamide phosphoribosyltransferase (Nampt) activity and increased CD38 activity. Significant biological effects of extracellular NAD⁺ have been found. Increasing evidence has suggested that NAD⁺ deficiency is a common central pathological factor in a number of diseases and aging. Critical Issues and Future Directions: Future studies are required for solidly establishing the concept that "NAD⁺ deficiency is a common central pathological factor in a number of disease and aging." It is also necessary to further investigate the mechanisms underlying the NAD⁺ deficiency in the diseases and aging. Preclinical and clinical studies should be conducted to determine the therapeutic potential of NAD⁺ for the diseases and aging.

Current understanding and future perspectives of the roles of sirtuins in the reprogramming and differentiation of pluripotent stem cells

In mammalian cells, there are seven members of the sirtuin protein family (SIRT1-7). SIRT1, SIRT6, and SIRT7 catalyze posttranslational modification of proteins in the nucleus, SIRT3, SIRT4, and SIRT5 are in the mitochondria and SIRT2 is in the cytosol. SIRT1 can deacetylate the transcription factor SOX2 and regulate induced pluripotent stem cells (iPSCs) reprogramming through the miR-34a-SIRT1-p53 axis. SIRT2 can regulate the function of pluripotent stem cells through GSK3β. SIRT3 can positively regulate PPAR gamma coactivator 1-alpha (PGC-1α) expression during the differentiation of stem cells. SIRT4 has no direct role in regulating reprogramming but may have the potential to prevent senescence of somatic cells and to facilitate the reprogramming of iPSCs. SIRT5 can deacetylate STAT3, which is an important transcription factor in regulating pluripotency and differentiation of stem cells. SIRT6 can enhance the reprogramming efficiency of iPSCs from aged skin fibroblasts through miR-766 and increase the expression levels of the reprogramming genes including Sox2, Oct4, and Nanog through acetylation of histone H3 lysine 56. SIRT7 plays a regulatory role in the process of mesenchymal-to-epithelial transition (MET), which has been suggested to be a crucial process in the generation of iPSCs from fibroblasts. In this review, we summarize recent findings of the roles of sirtuins in the metabolic reprogramming and differentiation of stem cells and discuss the bidirectional changes in the gene expression and activities of sirtuins in the commitment of differentiation of mesenchymal stem cells (MSCs) and reprogramming of somatic cells to iPSCs, respectively. Thus, understanding the molecular basis of the interplay between different sirtuins and mitochondrial function will provide new insights into the regulation of differentiation of stem cells and iPSCs formation, respectively, and may help design effective stem cell therapies for regenerative medicine. Impact statement This is an extensive review of the recent advances in our understanding of the roles of some members of the sirtuins family, such as SIRT1, SIRT2, SIRT3, and SIRT6, in the regulation of intermediary metabolism during stem cell differentiation and in the reprogramming of somatic cells to form induced pluripotent stem cells (iPSCs). This article provides an updated integrated view on the mechanisms by which sirtuins-mediated posttranslational protein modifications regulate mitochondrial biogenesis, bioenergetics, and antioxidant defense in the maintenance and differentiation of stem cells and in iPSCs formation, respectively.

Telomere and its role in the aging pathways: telomere shortening, cell senescence and mitochondria dysfunction

Aging is a biological process characterized by a progressive functional decline in tissues and organs, which eventually leads to mortality. Telomeres, the repetitive DNA repeat sequences at the end of linear eukaryotic chromosomes protecting chromosome ends from degradation and illegitimate recombination, play a crucial role in cell fate and aging. Due to the mechanism of replication, telomeres shorten as cells proliferate, which consequently contributes to cellular senescence and mitochondrial dysfunction. Cells are the basic unit of organismal structure and function, and mitochondria are the powerhouse and metabolic center of cells. Therefore, cellular senescence and mitochondrial dysfunction would result in tissue or organ degeneration and dysfunction followed by somatic aging through multiple pathways. In this review, we summarized the main mechanisms of cellular senescence, mitochondrial malfunction and aging triggered by telomere attrition. Understanding the molecular mechanisms involved in the aging process may elicit new strategies for improving health and extending lifespan.

Oxidative Stress in Stem Cell Aging

Stem cell aging is a process in which stem cells progressively lose their ability to self-renew or differentiate, succumb to senescence or apoptosis, and eventually become functionally depleted. Unresolved oxidative stress and concomitant oxidative damages of cellular macromolecules including nucleic acids, proteins, lipids, and carbohydrates have been recognized to contribute to stem cell aging. Excessive production of reactive oxygen species and insufficient cellular antioxidant reserves compromise cell repair and metabolic homeostasis, which serves as a mechanistic switch for a variety of aging-related pathways. Understanding the molecular trigger, regulation, and outcomes of those signaling networks is critical for developing novel therapies for aging-related diseases by targeting stem cell aging. Here we explore the key features of stem cell aging biology, with an emphasis on the roles of oxidative stress in the aging process at the molecular level. As a concept of cytoprotection of stem cells in transplantation, we also discuss how systematic enhancement of endogenous antioxidant capacity before or during graft into tissues can potentially raise the efficacy of clinical therapy. Finally, future directions for elucidating the control of oxidative stress and developing preventive/curative strategies against stem cell aging are discussed.

Mitochondrial Metabolism and Aging in Yeast

Mitochondrial functionality is one of the main factors involved in cell survival, and mitochondrial dysfunctions have been identified as an aging hallmark. In particular, the insurgence of mitochondrial dysfunctions is tightly connected to mitochondrial metabolism. During aging, both mitochondrial oxidative and biosynthetic metabolisms are progressively altered, with the development of malfunctions, in turn affecting mitochondrial functionality. In this context, the relation between mitochondrial pathways and aging is evolutionarily conserved from single-celled organisms, such as yeasts, to complex multicellular organisms, such as humans. Useful information has been provided by the yeast Saccharomyces cerevisiae, which is being increasingly acknowledged as a valuable model system to uncover mechanisms underlying cellular longevity in humans. On this basis, we review the impact of specific aspects of mitochondrial metabolism on aging supported by the contributions brought by numerous studies performed employing yeast. Initially, we will focus on the tricarboxylic acid cycle and oxidative phosphorylation, describing how their modulation has consequences on cellular longevity. Afterward, we will report information regarding the importance of nicotinamide adenine dinucleotide (NAD) metabolism during aging, highlighting its relation with mitochondrial functionality. The comprehension of these key points regarding mitochondrial metabolism and their physiological importance is an essential first step for the development of therapeutic interventions that point to increase life quality during aging, therefore promoting "healthy aging," as well as lifespan itself.

EphB2 signaling-mediated Sirt3 expression reduces MSC senescence by maintaining mitochondrial ROS homeostasis

Disruption of mitochondrial reactive oxygen species (mtROS) homeostasis is a key factor inducing UCB-MSC senescence. Accordingly, preventing mtROS accumulation will help in suppressing the UCB-MSC senescence. In this study, we observed that the expressions of EphrinB2 and EphB2 were inversely regulated by UCB-MSC passage-dependent manner. EphB2 signaling induced mitochondrial translocation of Sirt3. The knockdown of SIRT3 inhibited the effect of EphB2 signaling in UCB-MSCs. Subsequently, EphrinB2-Fc induced the nuclear translocation of Nrf-2 via c-Src phosphorylation dependent manner, and Sirt3 expression was regulated by Nrf-2. Among Sirt3 target genes, EphB2 signaling increased MnSOD and reduced the mtROS level in UCB-MSCs. Furthermore, the deacetylase effect of Sirt3 enhanced the MnSOD activity by deacetylation at the lysine 68 residue and therapeutic effect of UCB-MSCs on skin-wound healing was increased by EphB2 activation. In conclusion, the EphB2 can serve as a novel target for the optimizing the therapeutic use of UCB-MSCs in wound repair by MnSOD-mediated mtROS scavenging through EphB2/c-Src signaling pathway and Nrf-2-dependent Sirt3 expression.