Sirtuins-Mediated System-Level Regulation of Mammalian Tissues at the Interface between Metabolism and Cell Cycle: A Systematic Review

Mitochondrial Adaptation in Skeletal Muscle: Impact of Obesity, Caloric Restriction, and Dietary Compounds

PURPOSE OF REVIEW: The global obesity epidemic has become a major public health concern, necessitating comprehensive research into its adverse effects on various tissues within the human body. Among these tissues, skeletal muscle has gained attention due to its susceptibility to obesity-related alterations. Mitochondria are primary source of energy production in the skeletal muscle. Healthy skeletal muscle maintains constant mitochondrial content through continuous cycle of synthesis and degradation. However, obesity has been shown to disrupt this intricate balance. This review summarizes recent findings on the impact of obesity on skeletal muscle mitochondria structure and function. In addition, we summarize the molecular mechanism of mitochondrial quality control systems and how obesity impacts these systems. RECENT FINDINGS: Recent findings show various interventions aimed at mitigating mitochondrial dysfunction in obese model, encompassing strategies including caloric restriction and various dietary compounds. Obesity has deleterious effect on skeletal muscle mitochondria by disrupting mitochondrial biogenesis and dynamics. Caloric restriction, omega-3 fatty acids, resveratrol, and other dietary compounds enhance mitochondrial function and present promising therapeutic opportunities.

Sodium-glucose cotransporter-2 inhibitors protect tissues via cellular and mitochondrial pathways: Experimental and clinical evidence

Mitochondrial dysfunction is a key driver of cardiovascular disease (CVD) in metabolic syndrome and diabetes. This dysfunction promotes the production of reactive oxygen species (ROS), which cause oxidative stress and inflammation. Angiotensin II, the main mediator of the renin-angiotensin-aldosterone system, also contributes to CVD by promoting ROS production. Reduced activity of sirtuins (SIRTs), a family of proteins that regulate cellular metabolism, also worsens oxidative stress. Reduction of energy production by mitochondria is a common feature of all metabolic disorders. High SIRT levels and 5' adenosine monophosphate-activated protein kinase signaling stimulate hypoxia-inducible factor 1 beta, which promotes ketosis. Ketosis, in turn, increases autophagy and mitophagy, processes that clear cells of debris and protect against damage. Sodium-glucose cotransporter-2 inhibitors (SGLT2i), a class of drugs used to treat type 2 diabetes, have a beneficial effect on these mechanisms. Randomized clinical trials have shown that SGLT2i improves cardiac function and reduces the rate of cardiovascular and renal events. SGLT2i also increase mitochondrial efficiency, reduce oxidative stress and inflammation, and strengthen tissues. These findings suggest that SGLT2i hold great potential for the treatment of CVD. Furthermore, they are proposed as anti-aging drugs; however, rigorous research is needed to validate these preliminary findings.

Decreasing Intracellular Entropy by Increasing Mitochondrial Efficiency and Reducing ROS Formation-The Effect on the Ageing Process and Age-Related Damage

A hypothesis is presented to explain how the ageing process might be influenced by optimizing mitochondrial efficiency to reduce intracellular entropy. Research-based quantifications of entropy are scarce. Non-equilibrium metabolic reactions and compartmentalization were found to contribute most to lowering entropy in the cells. Like the cells, mitochondria are thermodynamically open systems exchanging matter and energy with their surroundings-the rest of the cell. Based on the calculations from cancer cells, glycolysis was reported to produce less entropy than mitochondrial oxidative phosphorylation. However, these estimations depended on the CO2 concentration so that at slightly increased CO2, it was oxidative phosphorylation that produced less entropy. Also, the thermodynamic efficiency of mitochondrial respiratory complexes varies depending on the respiratory state and oxidant/antioxidant balance. Therefore, in spite of long-standing theoretical and practical efforts, more measurements, also in isolated mitochondria, with intact and suboptimal respiration, are needed to resolve the issue. Entropy increases in ageing while mitochondrial efficiency of energy conversion, quality control, and turnover mechanisms deteriorate. Optimally functioning mitochondria are necessary to meet energy demands for cellular defence and repair processes to attenuate ageing. The intuitive approach of simply supplying more metabolic fuels (more nutrients) often has the opposite effect, namely a decrease in energy production in the case of nutrient overload. Excessive nutrient intake and obesity accelerate ageing, while calorie restriction without malnutrition can prolong life. Balanced nutrient intake adapted to needs/activity-based high ATP requirement increases mitochondrial respiratory efficiency and leads to multiple alterations in gene expression and metabolic adaptations. Therefore, rather than overfeeding, it is necessary to fine-tune energy production by optimizing mitochondrial function and reducing oxidative stress; the evidence is discussed in this paper.

The Expansion of Sirtuin Gene Family in Gilthead Sea Bream (Sparus aurata)-Phylogenetic, Syntenic, and Functional Insights across the Vertebrate/Fish Lineage

The Sirtuin (SIRT1-7) family comprises seven evolutionary-conserved enzymes that couple cellular NAD availability with health, nutrition and welfare status in vertebrates. This study re-annotated the sirt3/5 branch in the gilthead sea bream, revealing three paralogues of sirt3 (sirt3.1a/sirt3.1b/sirt3.2) and two of sirt5 (sirt5a/sirt5b) in this Perciform fish. The phylogeny and synteny analyses unveiled that the Sirt3.1/Sirt3.2 dichotomy was retained in teleosts and aquatic-living Sarcopterygian after early vertebrate 2R whole genome duplication (WGD). Additionally, only certain percomorphaceae and gilthead sea bream showed a conserved tandem-duplicated synteny block involving the mammalian-clustered sirt3.1 gene (psmd13-sirt3.1a/b-drd4-cdhr5-ctsd). Conversely, the expansion of the Sirt5 branch was shaped by the teleost-specific 3R WGD. As extensively reviewed in the literature, human-orthologues (sirt3.1/sirt5a) showed a high, conserved expression in skeletal muscle that increased as development advanced. However, recent sirt3.2 and sirt5b suffered an overall muscle transcriptional silencing across life, as well as an enhanced expression on immune-relevant tissues and gills. These findings fill gaps in the ontogeny and differentiation of Sirt genes in the environmentally adaptable gilthead sea bream, becoming a good starting point to advance towards a full understanding of its neo-functionalization. The mechanisms originating from these new paralogs also open new perspectives in the study of cellular energy sensing processes in vertebrates.

Metabolic imbalance driving immune cell phenotype switching in autoimmune disorders: Tipping the balance of T- and B-cell interactions

The interplay between the immune system and the metabolic state of a cell is intricate. In all phases of an immune response, the corresponding metabolic changes shall occur to support its modulation, in addition to the signalling through the cytokine environment and immune receptor stimulation. While autoimmune disorders may develop because of a metabolic imbalance that modulates switching between T-cell phenotypes, the effects that the interaction between T and B cells have on one another's cellular metabolism are yet to be understood in disease context. Here, we propose a perspective which highlights the potential of targeting metabolism to modulate T- and B-cell subtypes populations as well as T-B and B-T cell interactions to successfully treat autoimmune disorders. Specifically, we envision how metabolic changes can tip the balance of immune cells interactions, through definite mechanisms in both health and disease, to explain phenotype switches of B and T cells. Within this scenario, we highlight targeting metabolism that link inflammation, immunometabolism, epigenetics and ageing, is critical to understand inflammatory disorders. The combination of treatments targeting immune cells that cause (T/B) cell phenotype imbalances, and the metabolic pathways involved, may increase the effectiveness of treatment of autoimmune disorders, and/or ameliorate their symptoms to improve patients' quality of life.

Cellular and Mitochondrial Pathways Contribute to SGLT2 Inhibitors-mediated Tissue Protection: Experimental and Clinical Data

In metabolic syndrome and diabetes, compromised mitochondrial function emerges as a critical driver of cardiovascular disease, fueling its development and persistence, culminating in cardiac remodeling and adverse events. In this context, angiotensin II - the main interlocutor of the renin-angiotensin-aldosterone system - promotes local and systemic oxidative inflammatory processes. To highlight, the low activity/expression of proteins called sirtuins negatively participates in these processes, allowing more significant oxidative imbalance, which impacts cellular and tissue responses, causing tissue damage, inflammation, and cardiac and vascular remodeling. The reduction in energy production of mitochondria has been widely described as a significant element in all types of metabolic disorders. Additionally, high sirtuin levels and AMPK signaling stimulate hypoxia- inducible factor 1 beta and promote ketonemia. Consequently, enhanced autophagy and mitophagy advance through cardiac cells, sweeping away debris and silencing the orchestra of oxidative stress and inflammation, ultimately protecting vulnerable tissue from damage. To highlight and of particular interest, SGLT2 inhibitors (SGLT2i) profoundly influence all these mechanisms. Randomized clinical trials have evidenced a compelling picture of SGLT2i emerging as game-changers, wielding their power to demonstrably improve cardiac function and slash the rates of cardiovascular and renal events. Furthermore, driven by recent evidence, SGLT2i emerge as cellular supermolecules, exerting their beneficial actions to increase mitochondrial efficiency, alleviate oxidative stress, and curb severe inflammation. Its actions strengthen tissues and create a resilient defense against disease. In conclusion, like a treasure chest brimming with untold riches, the influence of SGLT2i on mitochondrial function holds untold potential for cardiovascular health. Unlocking these secrets, like a map guiding adventurers to hidden riches, promises to pave the way for even more potent therapeutic strategies.

Cytoplasmic SIRT1 promotes paclitaxel resistance in ovarian carcinoma through increased formation and survival of polyploid giant cancer cells

Therapeutic resistance is a notable cause of death in patients with ovarian carcinoma. Polyploid giant cancer cells (PGCCs), commonly arising in tumor tissues following chemotherapy, have recently been considered to contribute to drug resistance. As a type III deacetylase, Sirtuin1 (SIRT1) plays essential roles in the cell cycle, cellular senescence, and drug resistance. Accumulating evidence has suggested that alteration in its subcellular localization via nucleocytoplasmic shuttling is a critical process influencing the functions of SIRT1. However, the roles of SIRT1 subcellular localization in PGCC formation and subsequent senescence escape remain unclear. In this study, we compared the differences in the polyploid cell population and senescence state of PGCCs following paclitaxel treatment between tumor cells overexpressing wild-type SIRT1 (WT SIRT1) and those expressing nuclear localization sequence (NLS)-mutated SIRT1 (SIRT1NLSmt ). We investigated the involvement of cytoplasmic SIRT1 in biological processes and signaling pathways, including the cell cycle and cellular senescence, in ovarian carcinoma cells' response to paclitaxel treatment. We found that the SIRT1NLSmt tumor cell population contained more polyploid cells and fewer senescent PGCCs than the SIRT1-overexpressing tumor cell population. Comparative proteomic analyses using co-immunoprecipitation (Co-IP) combined with liquid chromatography-mass spectrometry (LC-MS)/MS showed the differences in the differentially expressed proteins related to PGCC formation, cell growth, and death, including CDK1 and CDK2, between SIRT1NLSmt and SIRT1 cells or PGCCs. Our results suggested that ovarian carcinoma cells utilize polyploidy formation as a survival mechanism during exposure to paclitaxel-based treatment via the effect of cytoplasmic SIRT1 on PGCC formation and survival, thereby boosting paclitaxel resistance. © 2023 The Pathological Society of Great Britain and Ireland.

Interplay between Systemic Glycemia and Neuroprotective Activity of Resveratrol in Modulating Astrocyte SIRT1 Response to Neuroinflammation

The flow of substances between the blood and the central nervous system is precisely regulated by the blood-brain barrier (BBB). Its disruption due to unbalanced blood glucose levels (hyper- and hypoglycemia) occurring in metabolic disorders, such as type 2 diabetes, can lead to neuroinflammation, and increase the risk of developing neurodegenerative diseases. One of the most studied natural anti-diabetic, anti-inflammatory, and neuroprotective compounds is resveratrol (RSV). It activates sirtuin 1 (SIRT1), a key metabolism regulator dependent on cell energy status. The aim of this study was to assess the astrocyte SIRT1 response to neuroinflammation and subsequent RSV treatment, depending on systemic glycemia. For this purpose, we used an optimized in vitro model of the BBB consisting of endothelial cells and astrocytes, representing microvascular and brain compartments (MC and BC), in different glycemic backgrounds. Astrocyte-secreted SIRT1 reached the highest concentration in hypo-, the lowest in normo-, and the lowest in hyperglycemic backgrounds. Lipopolysaccharide (LPS)-induced neuroinflammation caused a substantial decrease in SIRT1 in all glycemic backgrounds, as observed earliest in hyperglycemia. RSV partially counterbalanced the effect of LPS on SIRT1 secretion, most remarkably in normoglycemia. Our results suggest that abnormal glycemic states have a worse prognosis for RSV-therapy effectiveness compared to normoglycemia.

Physiological Approaches Targeting Cellular and Mitochondrial Pathways Underlying Adipose Organ Senescence

The adipose organ is involved in many metabolic functions, ranging from the production of endocrine factors to the regulation of thermogenic processes. Aging is a natural process that affects the physiology of the adipose organ, leading to metabolic disorders, thus strongly impacting healthy aging. Cellular senescence modifies many functional aspects of adipose tissue, leading to metabolic alterations through defective adipogenesis, inflammation, and aberrant adipocytokine production, and in turn, it triggers systemic inflammation and senescence, as well as insulin resistance in metabolically active tissues, leading to premature declined physiological features. In the various aging fat depots, senescence involves a multiplicity of cell types, including mature adipocytes and immune, endothelial, and progenitor cells that are aging, highlighting their involvement in the loss of metabolic flexibility, one of the common features of aging-related metabolic disorders. Since mitochondrial stress represents a key trigger of cellular senescence, and senescence leads to the accumulation of abnormal mitochondria with impaired dynamics and hindered homeostasis, this review focuses on the beneficial potential of targeting mitochondria, so that strategies can be developed to manage adipose tissue senescence for the treatment of age-related metabolic disorders.

PGC-1α Is a Master Regulator of Mitochondrial Lifecycle and ROS Stress Response

Mitochondria play a major role in ROS production and defense during their life cycle. The transcriptional activator PGC-1α is a key player in the homeostasis of energy metabolism and is therefore closely linked to mitochondrial function. PGC-1α responds to environmental and intracellular conditions and is regulated by SIRT1/3, TFAM, and AMPK, which are also important regulators of mitochondrial biogenesis and function. In this review, we highlight the functions and regulatory mechanisms of PGC-1α within this framework, with a focus on its involvement in the mitochondrial lifecycle and ROS metabolism. As an example, we show the role of PGC-1α in ROS scavenging under inflammatory conditions. Interestingly, PGC-1α and the stress response factor NF-κB, which regulates the immune response, are reciprocally regulated. During inflammation, NF-κB reduces PGC-1α expression and activity. Low PGC-1α activity leads to the downregulation of antioxidant target genes resulting in oxidative stress. Additionally, low PGC-1α levels and concomitant oxidative stress promote NF-κB activity, which exacerbates the inflammatory response.

Multifunctional activity-based chemical probes for sirtuins

The sirtuin family of NAD⁺-dependent protein deacylases has gained significant attention during the last two decades, owing to their unique enzymatic activities as well as their critical roles in a broad array of cellular events. Innovative chemical probes are heavily pursued for the functional annotation and pharmacological perturbation of this group of "eraser" enzymes. We have developed several series of activity-based chemical probes (ABPs) to interrogate the functional state of active sirtuins in complex biological samples. They feature a simple Ala-Ala-Lys tripeptide backbone with a thioacyl "warhead", a photoaffinity group (benzophenone or diazirine), and a bioorthogonal group (terminal alkyne or azido) for conjugation to reporters. When applied in a comparative fashion, these probes reveal the changes of active sirtuin contents under different physiological conditions. Additionally, they can also be utilized in a competitive manner for inhibitor discovery. The Nobel-winning "click" conjugation to a fluorophore allows the visualization of the active enzymes, while the covalent adduct to a biotin leads to the affinity capture of the protein of interest. Furthermore, the "clickable" tag enables the easy access to proteolysis targeting chimeras (PROTACs) that effectively degrade human SIRT2 in HEK293 cells, albeit at micromolar concentrations. These small molecule probes offer unprecedented opportunities to investigate the biological functions and physiological relevance of the sirtuin family.

Sirtuins and redox signaling interplay in neurogenesis, neurodegenerative diseases, and neural cell reprogramming

Since the discovery of Neural Stem Cells (NSCs) there are still mechanism to be clarified, such as the role of mitochondrial metabolism in the regulation of endogenous adult neurogenesis and its implication in neurodegeneration. Although stem cells require glycolysis to maintain their stemness, they can perform oxidative phosphorylation and it is becoming more and more evident that mitochondria are central players, not only for ATP production but also for neuronal differentiation's steps regulation, through their ability to handle cellular redox state, intracellular signaling, epigenetic state of the cell, as well as the gut microbiota-brain axis, upon dietary influences. In this scenario, the 8-oxoguanine DNA glycosylase (OGG1) repair system would link mitochondrial DNA integrity to the modulation of neural differentiation. On the other side, there is an increasing interest in NSCs generation, from induced pluripotent stem cells, as a clinical model for neurodegenerative diseases (NDs), although this methodology still presents several drawbacks, mainly related to the reprogramming process. Indeed, high levels of reactive oxygen species (ROS), associated with telomere shortening, genomic instability, and defective mitochondrial dynamics, lead to pluripotency limitation and reprogramming efficiency's reduction. Moreover, while a physiological or moderate ROS increase serves as a signaling mechanism, to activate differentiation and suppress self-renewal, excessive oxidative stress is a common feature of NDs and aging. This ROS-dependent regulatory effect might be modulated by newly identified ROS suppressors, including the NAD⁺-dependent deacetylase enzymes family called Sirtuins (SIRTs). Recently, the importance of subcellular localization of NAD synthesis has been coupled to different roles for NAD in chromatin stability, DNA repair, circadian rhythms, and longevity. SIRTs have been described as involved in the control of both telomere's chromatin state and expression of nuclear gene involved in the regulation of mitochondrial gene expression, as well as in several NDs and aging. SIRTs are ubiquitously expressed in the mammalian brain, where they play important roles. In this review we summarize the current knowledge on how SIRTs-dependent modulation of mitochondrial metabolism could impact on neurogenesis and neurodegeneration, focusing mainly on ROS function and their role in SIRTs-mediated cell reprogramming and telomere protection.

The Mechanistic Roles of Sirtuins in Breast and Prostate Cancer

Simple Summary

There are diverse reports of the dual role of sirtuin genes and proteins in breast and prostate cancers. This review discusses the current information on the tumor promotion or suppression roles of SIRT1–7 in breast and prostate cancers. Precisely, we highlight that sirtuins regulate various proteins implicated in proliferation, apoptosis, autophagy, chemoresistance, invasion, migration, and metastasis of both breast and prostate cancer. We also provide evidence of the direct regulation of sirtuins by miRNAs, highlighting the consequences of this regulation in breast and prostate cancer. Overall, this review reveals the potential value of sirtuins as biomarkers and/or targets for improved treatment of breast and prostate cancers.

Abstract

Mammalian sirtuins (SIRT1–7) are involved in a myriad of cellular processes, including apoptosis, proliferation, differentiation, epithelial-mesenchymal transition, aging, DNA repair, senescence, viability, survival, and stress response. In this review, we discuss the current information on the mechanistic roles of SIRT1–7 and their downstream effects (tumor promotion or suppression) in cancers of the breast and prostate. Specifically, we highlight the involvement of sirtuins in the regulation of various proteins implicated in proliferation, apoptosis, autophagy, chemoresistance, invasion, migration, and metastasis of breast and prostate cancer. Additionally, we highlight the available information regarding SIRT1–7 regulation by miRNAs, laying much emphasis on the consequences in the progression of breast and prostate cancer.

Estrogen signaling as a bridge between the nucleus and mitochondria in cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide. Epidemiological studies indicate that pre-menopausal women are more protected against the development of CVDs compared to men of the same age. This effect is attributed to the action/effects of sex steroid hormones on the cardiovascular system. In this context, estrogen modulates cardiovascular function in physiological and pathological conditions, being one of the main physiological cardioprotective agents. Here we describe the common pathways and mechanisms by which estrogens modulate the retrograde and anterograde communication between the nucleus and mitochondria, highlighting the role of genomic and non-genomic pathways mediated by estrogen receptors. Additionally, we discuss the presumable role of bromodomain-containing protein 4 (BRD4) in enhancing mitochondrial biogenesis and function in different CVD models and how this protein could act as a master regulator of estrogen protective activity. Altogether, this review focuses on estrogenic control in gene expression and molecular pathways, how this activity governs nucleus-mitochondria communication, and its projection for a future generation of strategies in CVDs treatment.

Possible role of SIRT1 and SIRT3 in post-translational modifications in human breast milk during the neonatal period

We measured free and proteinic concentrations of native and modified amino acids from post-translational modifications (PTMs) and correlated them with the activity of SIRT1 and SIRT3 in the pellet and aqueous phases of human breast milk samples of ten lactating women during the neonatal period. SIRT1 and SIRT3 correlated directly with citrullination, asymmetric dimethylation and glycation of L-arginine, hydroxylation and glycation of L-lysine. SIRT1 and SIRT3 correlated inversely with the hydroxylation of L-proline. SIRT1 and SITR3 tended to correlate inversely with oxidative stress measured as malondialdehyde. Our study suggests that SIRT1 and SIRT3 may modulate PTMs in human breast milk cells.

Cardiac Acetylation in Metabolic Diseases

Lysine acetylation is a highly conserved mechanism that affects several biological processes such as cell growth, metabolism, enzymatic activity, subcellular localization of proteins, gene transcription or chromatin structure. This post-translational modification, mainly regulated by lysine acetyltransferase (KAT) and lysine deacetylase (KDAC) enzymes, can occur on histone or non-histone proteins. Several studies have demonstrated that dysregulated acetylation is involved in cardiac dysfunction, associated with metabolic disorder or heart failure. Since the prevalence of obesity, type 2 diabetes or heart failure rises and represents a major cause of cardiovascular morbidity and mortality worldwide, cardiac acetylation may constitute a crucial pathway that could contribute to disease development. In this review, we summarize the mechanisms involved in the regulation of cardiac acetylation and its roles in physiological conditions. In addition, we highlight the effects of cardiac acetylation in physiopathology, with a focus on obesity, type 2 diabetes and heart failure. This review sheds light on the major role of acetylation in cardiovascular diseases and emphasizes KATs and KDACs as potential therapeutic targets for heart failure.

Possible role of transcription factors (BSX, NKX2.1, IRX3 and SIRT1) in the regulation of appetite in goldfish (Carassius auratus)

The homeobox genes play important roles in the embryonic development of animals. Recent evidence suggests they might also regulate feeding and act as transcription factors of appetite regulators. Examples of these genes are a brain-specific homeobox transcription factor (BSX), NK2 homeobox 1 (NKX2.1) and the Iroquois homeobox 3 (IRX3). Sirtuin1 (SIRT1) acts as a transcription factor for nutrient (e.g. lipid, glucose) homeostasis and responds to stress and nutrient availability, and has been shown to interact with appetite regulators. Very little is known about the role of these genes in the regulation of feeding and nutrient homeostasis in fish. In this study, we assessed the roles of BSX, NKX2.1, IRX3 and SIRT1 in the central regulation of feeding in goldfish by examining their mRNA brain distribution, assessing the effects of fasting on their brain expression and assessing the effects of peripheral injections of cholecystokinin (CCK, a brain-gut peptide), on their brain expression. All genes showed a widespread distribution in the brain, with high levels in the hypothalamus. In both hypothalamus and telencephalon, fasting induced increases in BSX, IRX3 and NKX2.1 expressions but had no effect on SIRT1 expression levels. CCK injections increased hypothalamic expression levels of IRX3 and SIRT1, and telencephalic expression levels of NKX2.1 and SIRT1, with no effect on either hypothalamic BSX or NKX2.1 expression levels or telencephalon BSX or IRX3 expression levels. Our results suggest that, in goldfish as in mammals, central BSX, NKX2.1, IRX3 and SIRT1 are present in regions of the brain regulating feeding, are sensitive to nutrient status and interact with appetite-regulating peptides.

Nuclear Sirtuins and the Aging of the Immune System

The immune system undergoes major changes with age that result in altered immune populations, persistent inflammation, and a reduced ability to mount effective immune responses against pathogens and cancer cells. Aging-associated changes in the immune system are connected to other age-related diseases, suggesting that immune system rejuvenation may provide a feasible route to improving overall health in the elderly. The Sir2 family of proteins, also called sirtuins, have been broadly implicated in genome homeostasis, cellular metabolism, and aging. Sirtuins are key responders to cellular and environmental stress and, in the case of the nuclear sirtuins, they do so by directing responses to chromatin that include gene expression regulation, retrotransposon repression, enhanced DNA damage repair, and faithful chromosome segregation. In the immune system, sirtuins instruct cellular differentiation from hematopoietic precursors and promote leukocyte polarization and activation. In hematopoietic stem cells, sirtuins safeguard quiescence and stemness to prevent cellular exhaustion. Regulation of cytokine production, which, in many cases, requires NF-κB regulation, is the best-characterized mechanism by which sirtuins control innate immune reactivity. In adaptive immunity, sirtuins promote T cell subset differentiation by controlling master regulators, thereby ensuring an optimal balance of helper (Th) T cell-dependent responses. Sirtuins are very important for immune regulation, but the means by which they regulate immunosenescence are not well understood. This review provides an integrative overview of the changes associated with immune system aging and its potential relationship with the roles of nuclear sirtuins in immune cells and overall organismal aging. Given the anti-aging properties of sirtuins, understanding how they contribute to immune responses is of vital importance and may help us develop novel strategies to improve immune performance in the aging organism.

Mechanisms of Hydroxyurea-Induced Cellular Senescence: An Oxidative Stress Connection?

Hydroxyurea (HU) is a water-soluble antiproliferative agent used for decades in neoplastic and nonneoplastic conditions. HU is considered an essential medicine because of its cytoreduction functions. HU is an antimetabolite that inhibits ribonucleotide reductase, which causes a depletion of the deoxyribonucleotide pool and dramatically reduces cell proliferation. The proliferation arrest, depending on drug concentration and exposure, may promote a cellular senescence phenotype associated with cancer cell therapy resistance and inflammation, influencing neighboring cell functions, immunosuppression, and potential cancer relapse. HU can induce cellular senescence in both healthy and transformed cells in vitro, in part, because of increased reactive oxygen species (ROS). Here, we analyze the main molecular mechanisms involved in cytotoxic/genotoxic HU function, the potential to increase intracellular ROS levels, and the principal features of cellular senescence induction. Understanding the mechanisms involved in HU's ability to induce cellular senescence may help to improve current chemotherapy strategies and control undesirable treatment effects in cancer patients and other diseases.

Adaptation-Driven Evolution of Sirtuin 1 (SIRT1), a Key Regulator of Metabolism and Aging, in Marmot Species

The sirtuin protein family plays a role in the lifespan of various species and is involved in numerous key metabolic processes. To understand the evolutionary role of sirtuins in marmots, a long-living rodent species group with remarkable metabolic shutdown during hibernation, we conducted a phylogeny-based substitution rate analysis of coding genes based on genetic information of seven marmot species. We show that sirtuin 1 (SIRT1) has evolved under positive selection in the marmot lineage. We pinpoint three amino acid changes in four different marmot species that underlie the signal of positive selection and that may favor increased longevity in marmots. Based on a computational structural analysis we can show that all three substitutions affect the secondary structure of the same region in human SIRT1. We propose that the identified region is close to the catalytic domain and that the potential structural changes may impact the catalytic activity of the enzyme and therefore might be playing a functional role in marmot's extended lifespan and metabolic shutdown.

Analysis of Sirtuin 1 and Sirtuin 3 at Enzyme and Protein Levels in Human Breast Milk during the Neonatal Period

Breast feeding is regarded as the preferred nutrition modality for children during the first few months of life. It not only furthers growth and development but also is supposed to impact later life. The first 1000 days are regarded as a critical window for development, even beyond infancy. The physiological basis underlying this beneficial effect is not clear. Sirtuins are important regulatory proteins of metabolism and are supposed to play a critical role in ageing and longevity as well as in diseases. In the present study, we developed novel methods to assay sirtuin 1 and sirtuin 3 at enzyme activity (via fluorometry) and protein levels (by Western blot) in the aqueous phase and in the cell pellet of human breast milk and assessed the impact of ongoing lactation during the neonatal period. Sirtuin activities in the aqueous phase were negatively correlated with the duration of lactation in the neonatal period. There was no correlation of sirtuin activities in the cell pellet with the duration of lactation. The amounts of sirtuin 1 and sirtuin 3 measured by Western blot were negatively correlated with the lactation period.