SIRT6 protects human endothelial cells from DNA damage, telomere dysfunction, and senescence

Sirtuin 6 attenuates angiotensin II-induced vascular adventitial aging in rat aortae by suppressing the NF-κB pathway

Adventitia-induced vascular remodeling plays an important role in vascular aging. However, the mechanism remains unclear. In this study, we found that sirtuin 6 (SIRT6) expression was downregulated in the aortae of aged rats compared with those of young rats. Adventitial fibroblasts (AFs) were isolated and cultured from rat aortae to clarify the relationship between SIRT6 expression and vascular aging. Lentivirus-mediated SIRT6 knockdown promoted the aging phenotype in AFs, affecting proliferation, collagen secretion, migration, and α-smooth muscle actin expression. Moreover, angiotensin II (Ang II) decreased SIRT6 expression, activated the NF-κB pathway, and led to vascular aging. The NF-κB pathway inhibitor BAY 11-7082 reduced Ang II-induced nuclear translocation of the NF-κB p65 subunit and other effects of Ang II, such as AF proliferation, collagen secretion, and migration. Mechanistically, SIRT6 suppression increased acetyl-NF-κB p65 (Lys310) expression and NF-κB transcriptional activity in SIRT6-knockdown AFs. SIRT6 could directly bind to the p65 subunit and attenuate Ang II-induced NF-κB activation and vascular aging. In summary, this study was the first to correlate SIRT6 expression and adventitia-induced vascular senescence. SIRT6 maybe a biomarker of vascular aging, and activating SIRT6 maybe a therapeutic strategy for delaying vascular aging.

Telomere damage promotes vascular smooth muscle cell senescence and immune cell recruitment after vessel injury

Accumulation of vascular smooth muscle cells (VSMCs) is a hallmark of multiple vascular pathologies, including following neointimal formation after injury and atherosclerosis. However, human VSMCs in advanced atherosclerotic lesions show reduced cell proliferation, extensive and persistent DNA damage, and features of premature cell senescence. Here, we report that stress-induced premature senescence (SIPS) and stable expression of a telomeric repeat-binding factor 2 protein mutant (TRF2^T188A) induce senescence of human VSMCs, associated with persistent telomeric DNA damage. VSMC senescence is associated with formation of micronuclei, activation of cGAS-STING cytoplasmic sensing, and induction of multiple pro-inflammatory cytokines. VSMC-specific TRF2^T188A expression in a multicolor clonal VSMC-tracking mouse model shows no change in VSMC clonal patches after injury, but an increase in neointima formation, outward remodeling, senescence and immune/inflammatory cell infiltration or retention. We suggest that persistent telomere damage in VSMCs inducing cell senescence has a major role in driving persistent inflammation in vascular disease.

Anna Uryga and Mandy Grootaert et al. combine cell culture and animal models to examine how senescence of human vascular smooth muscle cells (VSMCs) and persistent telomere damage drive inflammation. Their results suggest that telomere injury can be the primary cause of premature senescence in VSMCs, and that DNA damage can be a major cause of persistent inflammation in vascular disease.

SIRT6 in Senescence and Aging-Related Cardiovascular Diseases

SIRT6 belongs to the nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases and has established diverse roles in aging, metabolism and disease. Its function is similar to the Silent Information Regulator 2 (SIR2), which prolongs lifespan and regulates genomic stability, telomere integrity, transcription, and DNA repair. It has been demonstrated that increasing the sirtuin level through genetic manipulation extends the lifespan of yeast, nematodes and flies. Deficiency of SIRT6 induces chronic inflammation, autophagy disorder and telomere instability. Also, these cellular processes can lead to the occurrence and progression of cardiovascular diseases (CVDs), such as atherosclerosis, hypertrophic cardiomyopathy and heart failure. Herein, we discuss the implications of SIRT6 regulates multiple cellular processes in cell senescence and aging-related CVDs, and we summarize clinical application of SIRT6 agonists and possible therapeutic interventions in aging-related CVDs.

The Two-Faced Role of SIRT6 in Cancer

Simple Summary

Cancer therapy relies on the employment of different strategies aimed at inducing cancer cell death through different mechanisms, including DNA damage and apoptosis induction. One of the key regulators of these pathways is the epigenetic enzyme SIRT6, which has been shown to have a dichotomous function in cell fate determination and, consequently, cancer initiation and progression. In this review, we aim to summarize the current knowledge on the role of SIRT6 in cancer. We show that it can act as both tumor suppressor and promoter, even in the same cancer type, depending on the biological context. We then describe the most promising modulators of SIRT6 which, through enzyme activation or inhibition, may impair tumor growth. These molecules can also be used for the elucidation of SIRT6 function, thereby advancing the current knowledge on this crucial protein.

Abstract

Sirtuin 6 (SIRT6) is a NAD⁺-dependent nuclear deacylase and mono-ADP-ribosylase with a wide spectrum of substrates. Through its pleiotropic activities, SIRT6 modulates either directly or indirectly key processes linked to cell fate determination and oncogenesis such as DNA damage repair, metabolic homeostasis, and apoptosis. SIRT6 regulates the expression and activity of both pro-apoptotic (e.g., Bax) and anti-apoptotic factors (e.g., Bcl-2, survivin) in a context-depending manner. Mounting evidence points towards a double-faced involvement of SIRT6 in tumor onset and progression since the block or induction of apoptosis lead to opposite outcomes in cancer. Here, we discuss the features and roles of SIRT6 in the regulation of cell death and cancer, also focusing on recently discovered small molecule modulators that can be used as chemical probes to shed further light on SIRT6 cancer biology and proposed as potential new generation anticancer therapeutics.

SIRT6 enhances telomerase activity to protect against DNA damage and senescence in hypertrophic ligamentum flavum cells from lumbar spinal stenosis patients

Lumbar spinal stenosis (LSS) is a condition wherein patients exhibit age-related fibrosis, elastin-to-collagen ratio reductions, and ligamentum flavum hypertrophy. This study was designed to assess the relationship between SIRT6 and telomerase activity in hypertrophic ligamentum flavum (LFH) cells from LSS patients. We observed significant reductions in SIRT6, TPP1, and POT1 protein levels as well as increases in telomerase reverse transcriptase (TERT) levels and telomerase activity in LFH tissues relative to non- hypertrophic ligamentum flavum (LFN) tissues. When SIRT6 was overexpressed in these LFH cells, this was associated with significant increases in telomerase activity and a significant reduction in fibrosis-related protein expression. These effects were reversed, however, when telomerase activity was inactivated by hTERT knockdown in these same cells. SIRT6 overexpression was further found to reduce the frequency of senescence-associated β-galactosidase (SA-β-Gal)-positive LFH cells and to decrease p16, MMP3, and L1 mRNA levels and telomere dysfunction-induced foci (TIFs) in LFH cells. In contrast, hTERT knockdown-induced telomerase inactivation eliminated these SIRT6-dependent effects. Overall, our results indicate that SIRT6 functions as a key protective factor that prevents cellular senescence and telomere dysfunction in ligamentum flavum cells, with this effect being at least partially attributable to SIRT6-dependent telomerase activation.

SIRT6 promotes angiogenesis and hemorrhage of carotid plaque via regulating HIF-1α and reactive oxygen species

As a member of Sirtuins family, SIRT6 participates in the physiological and pathological progress of DNA repair, anti-aging, metabolism, and so on. Several studies have demonstrated that knockdown of SIRT6 inhibited the development of atherosclerosis (AS), indicated SIRT6 as a protective factor for AS. However, we confirmed SIRT6 was significantly overexpressed in human unstable carotid plaques compared with stable carotid plaques. This result indicated a more complex role of SIRT6 in AS. Furthermore, we constructed mice model with unstable carotid plaque and injected them with SIRT6 overexpressed adeno-associated virus (AAV-SIRT6). AAV-SIRT6 significantly promoted angiogenesis as well as hemorrhage in plaques. In vitro, we demonstrated overexpression of SIRT6 prevented HIF-1α from degradation by deubiquitination at K37 and K532 of HIF-1α, thus promoted the expression of HIF-1α under both normoxia and hypoxia in human umbilical vein endothelial cells (HUVECs). Through regulating HIF-1α, overexpression of SIRT6 promoted invasion, migration, proliferation, as well as tube formation ability of HUVECs. Interestingly, under different conditions, SIRT6 played different roles in the function of HUVECs. Under oxidative stress, another important pathological environment for AS, SIRT6 bound to the promoter of Catalase, a main reactive oxygen species scavenger, and depleted H3K56 acetylation, thus inhibited expression and activity of Catalase at the transcriptional level. Subsequently, inhibited Catalase promoted reactive oxygen species (ROS) under oxidative stress. Accumulated ROS further aggravated oxidative stress injury of HUVECs. On one hand, SIRT6 promoted angiogenesis in plaque via HIF-1α under hypoxia. On the other hand, SIRT6 promoted injury of neovascular via ROS under oxidative stress. It is this process of continuous growth and damage that leads to hemorrhage in carotid plaque. In conclusion, we innovatively confirmed SIRT6 promoted the angiogenesis and IPH via promoting HIF-1α and ROS in different environments, thus disclosed the unknowing danger of SIRT6.

SIRT6 Protects Smooth Muscle Cells From Senescence and Reduces Atherosclerosis

Supplemental Digital Content is available in the text.

Vascular smooth muscle cell (VSMC) senescence promotes atherosclerosis and features of plaque instability, in part, through lipid-mediated oxidative DNA damage and telomere dysfunction. SIRT6 (Sirtuin 6) is a nuclear deacetylase involved in DNA damage response signaling, inflammation, and metabolism; however, its role in regulating VSMC senescence and atherosclerosis is unclear.

Potential Anti-Aging Substances Derived from Seaweeds

Aging is a major risk factor for many chronic diseases, such as cancer, cardiovascular disease, and diabetes. The exact mechanisms underlying the aging process are not fully elucidated. However, a growing body of evidence suggests that several pathways, such as sirtuin, AMP-activated protein kinase, insulin-like growth factor, autophagy, and nuclear factor erythroid 2-related factor 2 play critical roles in regulating aging. Furthermore, genetic or dietary interventions of these pathways can extend lifespan by delaying the aging process. Seaweeds are a food source rich in many nutrients, including fibers, polyunsaturated fatty acids, vitamins, minerals, and other bioactive compounds. The health benefits of seaweeds include, but are not limited to, antioxidant, anti-inflammatory, and anti-obese activities. Interestingly, a body of studies shows that some seaweed-derived extracts or isolated compounds, can modulate these aging-regulating pathways or even extend lifespans of various animal models. However, few such studies have been conducted on higher animals or even humans. In this review, we focused on potential anti-aging bioactive substances in seaweeds that have been studied in cells and animals mainly based on their anti-aging cellular and molecular mechanisms.

Sirtuin 6: A potential therapeutic target for cardiovascular diseases

Cardiovascular diseases (CVDs) are serious diseases endangering human health due to high morbidity and mortality worldwide, and numerous signal molecules are involved in this pathological process. As a member of the Sirtuin family NAD ⁺-dependent deacetylases, indeed, Sirtuin 6 (SIRT6) plays an important role in regulating biological homeostasis, longevity, and various diseases. More importantly, SIRT6 performs as an indispensable role in glucose and lipid metabolism, inflammation and genomic stability for the occurrence and development of various CVDs. Recent advances: among sirtuins, SIRT6 was frequently unveiled thanks for its protective roles against heart failure, cardiovascular remodeling and atherosclerosis, and identified as an essential intervention target of CVDs, bringing SIRT6 into the focus of clinical interest. Herein, we provide an overview of the current molecular mechanism through which SIRT6 regulates CVDs, and we highlight a potential therapeutic target for CVDs.

Epigenetics and Vascular Senescence-Potential New Therapeutic Targets?

Epigenetics is defined as the heritable alterations of gene expression without changes to the coding sequence of DNA. These alterations are mediated by processes including DNA methylation, histone modifications, and non-coding RNAs mechanisms. Vascular aging consists of both structural and functional changes in the vasculature including pathological processes that drive progression such as vascular cell senescence, inflammation, oxidation stress, and calcification. As humans age, these pathological conditions gradually accumulate, driven by epigenetic alterations, and are linked to various aging-related diseases. The development of drugs targeting a spectrum of epigenetic processes therefore offers novel treatment strategies for the targeting of age-related diseases. In our previous studies, we identified HDAC4, JMJD3, Fra-1, and GATA4 as potential pharmacological targets for regulating vascular inflammation, injury, and senescence.

Age-related epigenetic drift deregulates SIRT6 expression and affects its downstream genes in human peripheral blood mononuclear cells

Sirtuin 6 (SIRT6) exerts a protective effect on health and extends the lives of model organisms. We, therefore, aimed to clarify whether age-related epigenetic drift is responsible for differences in SIRT6 expression in peripheral blood mononuclear cells (PBMCs) of healthy young (n = 55, mean age 27.5 ± 4.4 years), middle-aged (n = 51, 65.4 ± 3.3 years), and long-lived (n = 51, 93.9 ± 3.6 years) humans. In silico analysis was performed using the STRING network. No age-related differences were observed in the percentage of SIRT6 CpG island methylation. However, the age affected the expression of miR-34a-5p, miR-125a-5p, miR-186-5p, miR-342-5p and miR-766-3p (all p < 0.0001), miR-181-2-3p and Let-7c (both p = 0.0003), and miR-103a-3p (p = 0.0069). A negative association was observed between SIRT6 mRNA and miR-186-5p (r_s = -0.25, p = 0.026), and a positive association was observed with miR-34a-5p (r_s = 0.31, p = 0.0055) and miR-181a-2-3p (r_s = 0.39, p = 0.0002). SIRT6 mRNA also negatively correlated with the expression of TP53 (r_s = -0.41, p = 0.0126) and MYC (r_s = -0.35, p = 0.0448). Notably, the expression of several miRNAs and genes was similar in young and long-lived groups but different from the middle-aged group. We conclude that age-related epigenetic changes can affect the expression of SIRT6 in PBMCs and, in this way, possibly influence immunosenescence. Moreover, molecular events could differentiate 'normal' ageing from that of long-lived individuals.

Carotid Disease and Ageing: A Literature Review on the Pathogenesis of Vascular Senescence in Older Subjects

Aging is a natural process that affects all systems of the human organism, leading to its inability to adapt to environmental changes. Advancing age has been correlated with various pathological conditions, especially cardiovascular and cerebrovascular diseases. Carotid artery (CA) is mainly affected by age-induced functional and morphological alterations causing atheromatous disease. The evolvement of biomedical sciences has allowed the elucidation of many aspects of this condition. Symptomatic carotid disease (CD) derives from critical luminar stenosis or eruption of an atheromatous plaque due to structural modifications of the vessels, such as carotid intima-media thickening. At a histologic level, the aforementioned changes are mediated by elastin fragmentation, collagen deposition, immune cell infiltration, and accumulation of cytokines and vasoconstrictors. Underlying mechanisms include chronic inflammation and oxidative stress, dysregulation of cellular homeostatic systems, and senescence. Thus, there is an imbalance in components of the vessel wall, which fails to counteract exterior stress stimuli. Consequently, arterial relaxation is impaired and atherosclerotic lesions progress. This is a review of current evidence regarding the relationship of aging with vascular senescence and CD. A deeper understanding of these mechanisms can contribute to the production of efficient prevention methods and targeted therapeutic strategies.

The important role of histone deacetylases in modulating vascular physiology and arteriosclerosis

Cardiovascular diseases are the leading cause of deaths in the world. Endothelial dysfunction followed by inflammation of the vessel wall leads to atherosclerotic lesion formation that causes ischemic heart and myocardial hypertrophy, which ultimately progress into cardiac dysfunction and failure. Histone deacetylases (HDACs) have been recognized to play crucial roles in cardiovascular disease, particularly in the epigenetic regulation of gene transcription in response to a variety of stresses. The unique nature of HDAC regulation includes that HDACs form a complex co-regulatory network with other transcription factors, deacetylate histones and non-histone proteins to facilitate the regulatory mechanism of the vascular system. The selective HDAC inhibitors are considered as the most promising target in cardiovascular disease, especially for preventing cardiac hypertrophy. In this review, we discuss our present knowledge of the cellular and molecular basis of HDACs in mediating the biological function of vascular cells and related pharmacologic interventions in vascular disease.

Sirtuins family as a target in endothelial cell dysfunction: implications for vascular ageing

The vascular endothelium is a protective barrier between the bloodstream and the vasculature that may be disrupted by different factors such as the presence of diseased states. Diseases like diabetes and obesity pose a great risk toward endothelial cell inflammation and oxidative stress, leading to endothelial cell dysfunction and thereby cardiovascular complications such as atherosclerosis. Sirtuins are NAD⁺-dependent histone deacetylases that are implicated in the pathophysiology of cardiovascular diseases, and they have been identified to be important regulators of endothelial cell function. A handful of recent studies suggest that disbalance in the regulation of endothelial sirtuins, mainly sirtuin 1 (SIRT1), contributes to endothelial cell dysfunction. Herein, we summarize how SIRT1 and other sirtuins may contribute to endothelial cell function and how presence of diseased conditions may alter their expressions to cause endothelial dysfunction. Moreover, we discuss how the beneficial effects of exercise on the endothelium are dependent on SIRT1. These mainly include regulation of signaling pathways related to endothelial nitric oxide synthase phosphorylation and nitric oxide production, mitochondrial biogenesis and mitochondria-mediated apoptotic pathways, oxidative stress and inflammatory pathways. Sirtuins as modulators of the adverse conditions in the endothelium hold a promising therapeutic potential for health conditions related to endothelial dysfunction and vascular ageing.

Plasma exosomes in OSA patients promote endothelial senescence: effect of long-term adherent continuous positive airway pressure

Obstructive sleep apnea (OSA) is associated with increased risk for end-organ morbidities, which can collectively be viewed as accelerated aging. Vascular senescence is an important contributor to end-organ dysfunction. Exosomes are released ubiquitously into the circulation, and transfer their cargo to target cells facilitating physiological and pathological processes. Plasma exosomes from 15 patients with polysomnographically diagnosed OSA at baseline (OSA-T1) after 12 months of adherent continuous positive airway pressure (CPAP) treatment (OSA-T2), 13 untreated OSA patients at 12-month intervals (OSA-NT1, OSA-NT2), and 12 controls (CO1 and CO2) were applied on naïve human microvascular endothelialcells-dermal (HMVEC-d). Expression of several senescence gene markers including p16 (CDKN2A), SIRT1, and SIRT6 and immunostaining for β-galactosidase activity (x-gal) were performed. Endothelial cells were also exposed to intermittent hypoxia (IH) or normoxia (RA) or treated with hydrogen peroxide (H2O2), stained with x-gal and subjected to qRT-PCR. Exosomes from OSA-T1, OSA-NT1, and OSA-NT2 induced significant increases in x-gal staining compared to OSA-T2, CO1, and CO2 (p-value < 0.01). p16 expression was significantly increased (p < 0.01), while SIRT1 and SIRT6 expression levels were decreased (p < 0.02 and p < 0.009). Endothelial cells exposed to IH or to H2O2 showed significant increases in x-gal staining (p < 0.001) and in senescence gene expression. Circulating exosomes in untreated OSA induce marked and significant increases in senescence of naïve endothelial cells, which are only partially reversible upon long-term adherent CPAP treatment. Furthermore, endothelial cells exposed to IH or H2O2 also elicit similar responses. Thus, OSA either directly or indirectly via exosomes may initiate and exacerbate cellular aging, possibly via oxidative stress-related pathways.

Sirt6 deletion in bone marrow-derived cells increases atherosclerosis - Central role of macrophage scavenger receptor 1

AIMS

Sirtuin 6 (Sirt6) is a NAD⁺-dependent deacetylase that plays a key role in DNA repair, inflammation and lipid regulation. Sirt6-null mice show severe metabolic defects and accelerated aging. Macrophage-foam cell formation via scavenger receptors is a key step in atherogenesis. We determined the effects of bone marrow-restricted Sirt6 deletion on foam cell formation and atherogenesis using a mouse model.

METHODS AND RESULTS

Sirt6 deletion in bone marrow-derived cells increased aortic plaques, lipid content and macrophage numbers in recipient Apoe^-/- mice fed a high-cholesterol diet for 12 weeks (n = 12-14, p < .001). In RAW macrophages, Sirt6 overexpression reduced oxidized low-density lipoprotein (oxLDL) uptake, Sirt6 knockdown enhanced it and increased mRNA and protein levels of macrophage scavenger receptor 1 (Msr1), whereas levels of other oxLDL uptake and efflux transporters remained unchanged. Similarly, in human primary macrophages, Sirt6 knockdown increased MSR1 protein levels and oxLDL uptake. Double knockdown of Sirt6 and Msr1 abolished the increase in oxLDL uptake observed upon Sirt6 single knockdown. FACS analyses of macrophages from aortic plaques of Sirt6-deficient bone marrow-transplanted mice showed increased MSR1 protein expression. Double knockdown of Sirt6 and the transcription factor c-Myc in RAW cells abolished the increase in Msr1 mRNA and protein levels; c-Myc overexpression increased Msr1 mRNA and protein levels.

CONCLUSIONS

Loss of Sirt6 in bone marrow-derived cells is proatherogenic; hereby macrophages play an important role given a c-Myc-dependent increase in MSR1 protein expression and an enhanced oxLDL uptake in human and murine macrophages. These findings assign endogenous SIRT6 in macrophages an important atheroprotective role.

Role of Sirtuins in Tumor Angiogenesis

Generally, changes in the metabolic status of cells under conditions like hypoxia and accumulation of lactate can be sensed by various sensing mechanisms, leading to modulation of a number of signal transduction pathways and transcription factors. Several of the proangiogenic cytokines like VEGF, FGF, PDGF, TGF-β, Ang-2, ILs, etc. are secreted by cancer cells, under hypoxic microenvironment. These cytokines bind to their receptors on the endothelial cells and activates a number of signaling pathways including Akt/PIP3, Src, p38/MAPK, Smad2/3, etc., which ultimately results in the proliferation and migration of endothelial cells. Transcription factors that are activated in response to the metabolic status of tumors include HIFs, NF-κb, p53, El-2, and FOXO. Many of these transcription factors has been reported to be regulated by a class of histone deacetylase called sirtuins. Sirtuins are NAD+ dependent histone deacetylases that play pivotal role in the regulation of tumor cell metabolism, proliferation, migration and angiogenesis. The major function of sirtuins include, deacetylation of histones as well as some non-histone proteins like NF-κB, FOXOs, PPAR⋎, PGC1-α, enzymes like acetyl coenzymeA and structural proteins like α tubulin. In the cell, sirtuins are generally considered as the redox sensors and their activities are dependent on the metabolic status of the cell. Understanding the intricate regulatory mechanisms adopted by sirtuins, is crucial in devising effective therapeutic strategies against angiogenesis, metastasis and tumor progression. Keeping this in mind, the present review focuses on the role of sirtuins in the process of tumor angiogenesis and the regulatory mechanisms employed by them.

SIRT3 Regulation of Mitochondrial Quality Control in Neurodegenerative Diseases

Neurodegenerative diseases are disorders that are characterized by a progressive decline of motor and/or cognitive functions caused by the selective degeneration and loss of neurons within the central nervous system. The most common neurodegenerative diseases are Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). Neurons have high energy demands, and dysregulation of mitochondrial quality and function is an important cause of neuronal degeneration. Mitochondrial quality control plays an important role in maintaining mitochondrial integrity and ensuring normal mitochondrial function; thus, defects in mitochondrial quality control are also significant causes of neurodegenerative diseases. The mitochondrial deacetylase SIRT3 has been found to have a large effect on mitochondrial function. Recent studies have also shown that SIRT3 has a role in mitochondrial quality control, including in the refolding or degradation of misfolded/unfolded proteins, mitochondrial dynamics, mitophagy, and mitochondrial biogenesis, all of which are affected in neurodegenerative diseases.

Mechanisms of Vascular Aging

Aging of the vasculature plays a central role in morbidity and mortality of older people. To develop novel treatments for amelioration of unsuccessful vascular aging and prevention of age-related vascular pathologies, it is essential to understand the cellular and functional changes that occur in the vasculature during aging. In this review, the pathophysiological roles of fundamental cellular and molecular mechanisms of aging, including oxidative stress, mitochondrial dysfunction, impaired resistance to molecular stressors, chronic low-grade inflammation, genomic instability, cellular senescence, epigenetic alterations, loss of protein homeostasis, deregulated nutrient sensing, and stem cell dysfunction in the vascular system are considered in terms of their contribution to the pathogenesis of both microvascular and macrovascular diseases associated with old age. The importance of progeronic and antigeronic circulating factors in relation to development of vascular aging phenotypes are discussed. Finally, future directions and opportunities to develop novel interventions to prevent/delay age-related vascular pathologies by targeting fundamental cellular and molecular aging processes are presented.

Sirtuins and NAD+ in the Development and Treatment of Metabolic and Cardiovascular Diseases

The sirtuin family of nicotinamide adenine dinucleotide-dependent deacylases (SIRT1-7) are thought to be responsible, in large part, for the cardiometabolic benefits of lean diets and exercise and when upregulated can delay key aspects of aging. SIRT1, for example, protects against a decline in vascular endothelial function, metabolic syndrome, ischemia-reperfusion injury, obesity, and cardiomyopathy, and SIRT3 is protective against dyslipidemia and ischemia-reperfusion injury. With increasing age, however, nicotinamide adenine dinucleotide levels and sirtuin activity steadily decrease, and the decline is further exacerbated by obesity and sedentary lifestyles. Activation of sirtuins or nicotinamide adenine dinucleotide repletion induces angiogenesis, insulin sensitivity, and other health benefits in a wide range of age-related cardiovascular and metabolic disease models. Human clinical trials testing agents that activate SIRT1 or boost nicotinamide adenine dinucleotide levels are in progress and show promise in their ability to improve the health of cardiovascular and metabolic disease patients.

Exposure to jet lag aggravates depression-like behaviors and age-related phenotypes in rats subject to chronic corticosterone

Our previous finding demonstrated that chronic corticosterone (CORT) may be involved in mediating the pathophysiology of premature aging in rats. Frequent jet lag increases the risk for many diseases, including obesity and type 2 diabetes, and is associated with the aging processes. However, the effect of jet lag on CORT-induced depression and its association with aging phenotypes remain unclear. In this study, the rats were exposed to both CORT and jet lag treatment, and the differences were analyzed and compared to rats with single CORT treatment. Our results showed that jet lag treatment aggravated CORT-induced depression-like behavior evidenced by sucrose intake test, forced swimming test, and open field test. Additionally, this treatment aggravated the shortening of telomeres, which possibly resulted in decreased telomerase activity, and downregulated the expression of telomere-binding factor 2 (TRF2) and telomerase reverse transcriptase compared to that in CORT rats, as revealed by quantitative real-time-polymerase chain reaction and western blot analysis, respectively. The shortening of telomeres may have been caused by increased oxidative stress, which was associated with the inhibition of sirtuin 3. Exposure to jet lag also aggravated the degeneration of mitochondrial functions, as shown by the decreases in the mRNA expression of COX1, ND1, and Tfam. Our findings provide physiological evidence that jet lag exposure may worsen stress-induced depression and age-related abnormalities.

The angiotensin-(1-7)/Mas receptor axis protects from endothelial cell senescence via klotho and Nrf2 activation

Endothelial cell senescence is a hallmark of vascular aging that predisposes to vascular disease. We aimed to explore the capacity of the renin–angiotensin system (RAS) heptapeptide angiotensin (Ang)‐(1‐7) to counteract human endothelial cell senescence and to identify intracellular pathways mediating its potential protective action. In human umbilical vein endothelial cell (HUVEC) cultures, Ang II promoted cell senescence, as revealed by the enhancement in senescence‐associated galactosidase (SA‐β‐gal+) positive staining, total and telomeric DNA damage, adhesion molecule expression, and human mononuclear adhesion to HUVEC monolayers. By activating the G protein‐coupled receptor Mas, Ang‐(1‐7) inhibited the pro‐senescence action of Ang II, but also of a non‐RAS stressor such as the cytokine IL‐1β. Moreover, Ang‐(1‐7) enhanced endothelial klotho levels, while klotho silencing resulted in the loss of the anti‐senescence action of the heptapeptide. Indeed, both Ang‐(1‐7) and recombinant klotho activated the cytoprotective Nrf2/heme oxygenase‐1 (HO‐1) pathway. The HO‐1 inhibitor tin protoporphyrin IX prevented the anti‐senescence action evoked by Ang‐(1‐7) or recombinant klotho. Overall, the present study identifies Ang‐(1‐7) as an anti‐senescence peptide displaying its protective action beyond the RAS by consecutively activating klotho and Nrf2/HO‐1. Ang‐(1‐7) mimetic drugs may thus prove useful to prevent endothelial cell senescence and its related vascular complications.

Slowing Down Ageing: The Role of Nutrients and Microbiota in Modulation of the Epigenome

The human population is getting ageing. Both ageing and age-related diseases are correlated with an increased number of senescent cells in the organism. Senescent cells do not divide but are metabolically active and influence their environment by secreting many proteins due to a phenomenon known as senescence associated secretory phenotype (SASP). Senescent cells differ from young cells by several features. They possess more damaged DNA, more impaired mitochondria and an increased level of free radicals that cause the oxidation of macromolecules. However, not only biochemical and structural changes are related to senescence. Senescent cells have an altered chromatin structure, and in consequence, altered gene expression. With age, the level of heterochromatin decreases, and less condensed chromatin is more prone to DNA damage. On the one hand, some gene promoters are easily available for the transcriptional machinery; on the other hand, some genes are more protected (locally increased level of heterochromatin). The structure of chromatin is precisely regulated by the epigenetic modification of DNA and posttranslational modification of histones. The methylation of DNA inhibits transcription, histone methylation mostly leads to a more condensed chromatin structure (with some exceptions) and acetylation plays an opposing role. The modification of both DNA and histones is regulated by factors present in the diet. This means that compounds contained in daily food can alter gene expression and protect cells from senescence, and therefore protect the organism from ageing. An opinion prevailed for some time that compounds from the diet do not act through direct regulation of the processes in the organism but through modification of the physiology of the microbiome. In this review we try to explain the role of some food compounds, which by acting on the epigenetic level might protect the organism from age-related diseases and slow down ageing. We also try to shed some light on the role of microbiome in this process.

Hyperglycemia affects global 5-methylcytosine and 5-hydroxymethylcytosine in blood genomic DNA through upregulation of SIRT6 and TETs

Background

Accumulating evidence suggests that epigenetic changes play key roles in the pathogenesis of type 2 diabetes mellitus (T2DM). However, the dynamic regulation of 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) in diabetic peripheral blood DNA remains to be elucidated.

Results

We collected fasting blood samples (104 patients and 108 healthy controls) and glucose-stimulated blood samples at different time points (11 patients and 5 healthy controls underwent oral glucose tolerance test (OGTT)), as well as blood samples from six couples of diabetic and control rats. A HPLC-MS/MS system was used for quantifying global 5mC and 5hmC in genomic DNA from white blood cells (WBCs), and qPCR was performed for detecting mRNA expression of SIRT6 and TETs. We found that global 5mC decreased, while global 5hmC increased in both patients and diabetic rats, with lower 5mC being a risk factor of T2DM (OR = 0.524, 95%CI 0.402–0.683, p = 1.64 × 10⁻⁶). The OGTT data from patients showed that 5mC declined within 1 h and then returned to the fasting status at 2 h, while 5hmC rose from 0.5 h to 3 h with increasing glucose. However, the similar patterns were not found in the controls. The mRNA expression of TET2, TET3, and SIRT6 was upregulated in patients (p = 0.012, p = 0.026, and p = 0.035, respectively). The similar results were observed in diabetic OGTT and rats. Correlation analysis indicated that SIRT6 was positively correlated with TET2 in humans (r = 0.277, p < 0.001) and rats (r = 0.942, p < 0.001), in addition to a correlation between glucose and SIRT6 (r = 0.162, p = 0.045) and TET2 (r = 0.174, p = 0.036).

Conclusions

Hyperglycemia appeared to promote the mRNA expression of SIRT6 and TETs, which in turn might cause the dynamic changes of 5mC and 5hmC in WBCs from T2DM patients.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0660-y) contains supplementary material, which is available to authorized users.

Diabetes, Incretin Therapy and Thoracic Aortic Aneurysm - What Does the Evidence Show?

Epidemiological evidence supports a reduced prevalence of Thoracic Aortic Aneurysm (TAA) and Abdominal Aortic Aneurysm (AAA) in patients with Diabetes (DM). The mechanisms underlying this negative association are unknown. Some studies support that hyperglycemia has effects on the Extracellular Matrix (ECM), resulting in collagen cross-links and altered proteolytic activity, which ultimately counteracts aneurysm formation. However, recent experimental research indicates that incretin- based anti-diabetic therapy and Glucagon-Like Peptide-1 (GLP-1) may reduce the formation of TAA. GLP-1 is a peptide hormone, released from intestinal L-cells in response to hormonal, neural and nutrient stimuli. In addition to potentiation of meal-stimulated insulin secretion, GLP-1 signaling exerts numerous pleiotropic effects on various tissues, including protective effects on the myocardium and vascular endothelium. Recent studies also report protective effects of GLP-1 based therapy on the formation of aneurysms in animal models and direct effects of GLP-1 signaling on the molecular mechanisms suggested to influence TAA formation, including inflammation, proteolytic activity and collagen composition. In this narrative review, we present the available evidence for effects of GLP-1 on experimental aneurysm development and discuss the potential role of GLP-1 in aneurysm formation based on available data from pre-clinical and clinical studies.

Wnt9a Promotes Renal Fibrosis by Accelerating Cellular Senescence in Tubular Epithelial Cells

Cellular senescence is associated with renal disease progression, and accelerated tubular cell senescence promotes the pathogenesis of renal fibrosis. However, the underlying mechanism is unknown. We assessed the potential role of Wnt9a in tubular cell senescence and renal fibrosis. Compared with tubular cells of normal subjects, tubular cells of humans with a variety of nephropathies and those of several mouse models of CKD expressed high levels of Wnt9a that colocalized with the senescence-related protein p16INK4A Wnt9a expression level correlated with the extent of renal fibrosis, decline of eGFR, and expression of p16INK4A Furthermore, ectopic expression of Wnt9a after ischemia-reperfusion injury (IRI) induced activation of β-catenin and exacerbated renal fibrosis. Overexpression of Wnt9a exacerbated tubular senescence, evidenced by increased detection of p16INK4A expression and senescence-associated β-galactosidase activity. Conversely, shRNA-mediated knockdown of Wnt9a repressed IRI-induced renal fibrosis in vivo and impeded the growth of senescent tubular epithelial cells in culture. Notably, Wnt9a-induced renal fibrosis was inhibited by shRNA-mediated silencing of p16INK4A in the IRI mouse model. In a human proximal tubular epithelial cell line and primary renal tubular cells, Wnt9a remarkably upregulated levels of senescence-related p16INK4A, p19ARF, p53, and p21 and decreased the phosphorylation of retinoblastoma protein. Wnt9a also induced senescent tubular cells to produce TGF-β1, which promoted proliferation and activation in normal rat kidney fibroblasts. Thus, Wnt9a drives tubular senescence and fibroblast activation. Furthermore, the Wnt9a-TGF-β pathway appears to create a reciprocal activation loop between senescent tubular cells and activated fibroblasts that promotes and accelerates the pathogenesis of renal fibrosis.

SIRT6 facilitates directional telomere movement upon oxidative damage

Oxidative damage to telomeres leads to telomere attrition and genomic instability, resulting in poor cell viability. Telomere dynamics contribute to the maintenance of telomere integrity; however, whether oxidative damage induces telomere movement and how telomere mobility is regulated remain poorly understood. Here, we show that oxidative damage at telomeres triggers directional telomere movement. The presence of the human Sir2 homolog, Sirtuin 6 (SIRT6) is required for oxidative damage-induced telomeric movement. SIRT6 knock out (KO) cells show neither damage-induced telomere movement nor chromatin decondensation at damaged telomeres; both are observed in wild type (WT) cells. A deacetylation mutant of SIRT6 increases damage-induced telomeric movement in SIRT6 KO cells as well as WT SIRT6. SIRT6 recruits the chromatin-remodeling protein SNF2H to damaged telomeres, which appears to promote chromatin decondensation independent of its deacetylase activity. Together, our results suggest that SIRT6 plays a role in the regulation of telomere movement upon oxidative damage, shedding new light onto the function of SIRT6 in telomere maintenance.

Impairment of an Endothelial NAD+-H2S Signaling Network Is a Reversible Cause of Vascular Aging

A decline in capillary density and blood flow with age is a major cause of mortality and morbidity. Understanding why this occurs is key to future gains in human health. NAD precursors reverse aspects of aging, in part, by activating sirtuin deacylases (SIRT1-SIRT7) that mediate the benefits of exercise and dietary restriction (DR). We show that SIRT1 in endothelial cells is a key mediator of pro-angiogenic signals secreted from myocytes. Treatment of mice with the NAD+ booster nicotinamide mononucleotide (NMN) improves blood flow and increases endurance in elderly mice by promoting SIRT1-dependent increases in capillary density, an effect augmented by exercise or increasing the levels of hydrogen sulfide (H2S), a DR mimetic and regulator of endothelial NAD+ levels. These findings have implications for improving blood flow to organs and tissues, increasing human performance, and reestablishing a virtuous cycle of mobility in the elderly.

Effect of KNDC1 overexpression on the senescence of human umbilical vein endothelial cells

Kinase non-catalytic C-lobe domain containing 1 (KNDC1) exists in dendrites, guanine nucleotide exchange factor complexes and neuronal cell bodies as a putative protein-protein interaction module that regulates a number of signaling pathways. Previous studies have demonstrated that the knockdown of KNDC1 delays human umbilical vein endothelial cell (HUVEC) senescence. However, the effect of KNDC1 overexpression on HUVEC function remains unclear. In the present study, an adenovirus vector carrying KNDC1 was constructed and then transfected into endothelial cells to observe cell senescence. Furthermore, the effect of KNDC1 overexpression on HUVEC senescence was investigated in vitro and the underlying molecular mechanism was investigated. Senescence-associated β-galactosidase staining was used to determine cellular senescence and reactive oxygen species (ROS) were monitored to detect the level of cell oxidative stress. The mRNA transcription level and protein expression were analyzed by reverse transcription-quantitative polymerase chain reaction and western blot analysis, respectively. The results demonstrated that KNDC1 overexpression possibly inhibited HUVEC activity and function and promoted HUVEC senescence. Mechanistic studies demonstrated that KNDC1 triggered a p53-ROS positive feedback loop, which serves a crucial role in regulating senescence. In conclusion, to the best of the authors' knowledge, this is the first time that KNDC1-adenovirus vector inhibition of HUVEC proliferation by activating the p53 signaling pathway has been reported. Theoretically, the results of the present study also support KNDC1 as a therapeutic target for future anti-senescence.

Chronic corticosterone-induced depression mediates premature aging in rats

BACKGROUND

Stress hormones such as corticosterone (CORT) play an essential role in the development of depression. Chronic CORT administration has been shown to induce dysfunction in the hypothalamic-pituitary-adrenal axis leading to depression, which was in turn associated with accelerated aging. However, the effect of CORT administration on aging remains unclear.

METHODS

Rats were acclimatized for 1 week and then injected daily with CORT (40mg/kg) or vehicle (n = 10 each) for 21 consecutive days. Age-related indexes were then compared between CORT-treated rats and control rats.

RESULTS

CORT induced affective behaviors indicative of depressive-like symptoms in rats, including reduced sucrose preference and increased immobility time in the forced swimming test. CORT-treated rats exhibited telomere shortening, possibly contributing to decreased telomerase activity and down-regulated expression of telomere-binding factor 2, correlated with enhanced oxidative damage. This was associated with inhibition of sirtuin 3 leading to reduced activities of superoxide dismutase 2 and glutathione reductase. CORT-treated rats showed degenerated mitochondrial functions represented by decreased adenosine triphosphate production, decreased nicotinamide adenine dinucleotide⁺ content, and decreased activity of nicotinamide phosphoribosyltransferase.

LIMITATIONS

The group sample sizes were small, and only male rats and a single dose level of CORT were used.

CONCLUSION

These findings demonstrate that CORT-induced depression may be involved in mediating the pathophysiology of premature aging in rats.

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

SIGNIFICANCE

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

SIRT1 and SIRT6 Signaling Pathways in Cardiovascular Disease Protection

SIGNIFICANCE

Oxidative stress represents the common hallmark of pathological conditions associated with cardiovascular disease (CVD), including atherosclerosis, heart failure, hypertension, aging, diabetes, and other vascular system-related diseases. The sirtuin (SIRT) family, comprising seven proteins (SIRT1-SIRT7) sharing a highly conserved nicotinamide adenine dinucleotide (NAD+)-binding catalytic domain, attracted a great attention for the past few years as stress adaptor and epigenetic enzymes involved in the cellular events controlling aging-related disorder, cancer, and CVD. Recent Advances: Among sirtuins, SIRT1 and SIRT6 are the best characterized for their protective roles against inflammation, vascular aging, heart disease, and atherosclerotic plaque development. This latest role has been only recently unveiled for SIRT6. Of interest, in recent years, complex signaling networks controlled by SIRT1 and SIRT6 common to stress resistance, vascular aging, and CVD have emerged.

CRITICAL ISSUES

We provide a comprehensive overview of recent developments on the molecular signaling pathways controlled by SIRT1 and SIRT6, two post-translational modifiers proven to be valuable tools to dampen inflammation and oxidative stress at the cardiovascular level.

FUTURE DIRECTIONS

A deeper understanding of the epigenetic mechanisms through which SIRT1 and SIRT6 act in the signalings responsible for onset and development CVD is a prime scientific endeavor of the upcoming years. Multiple "omic" technologies will have widespread implications in understanding such mechanisms, speeding up the achievement of selective and efficient pharmacological modulation of sirtuins for future applications in the prevention and treatment of CVD. Antioxid. Redox Signal. 28, 711-732.

3' UTR lengthening as a novel mechanism in regulating cellular senescence

Cellular senescence has been viewed as a tumor suppression mechanism and also as a contributor to individual aging. Widespread shortening of 3' untranslated regions (3' UTRs) in messenger RNAs (mRNAs) by alternative polyadenylation (APA) has recently been discovered in cancer cells. However, the role of APA in the process of cellular senescence remains elusive. Here, we found that hundreds of genes in senescent cells tended to use distal poly(A) (pA) sites, leading to a global lengthening of 3' UTRs and reduced gene expression. Genes that harbor longer 3' UTRs in senescent cells were enriched in senescence-related pathways. Rras2, a member of the Ras superfamily that participates in multiple signal transduction pathways, preferred longer 3' UTR usage and exhibited decreased expression in senescent cells. Depletion of Rras2 promoted senescence, while rescue of Rras2 reversed senescence-associated phenotypes. Mechanistically, splicing factor TRA2B bound to a core "AGAA" motif located in the alternative 3' UTR of Rras2, thereby reducing the RRAS2 protein level and causing senescence. Both proximal and distal poly(A) signals showed strong sequence conservation, highlighting the vital role of APA regulation during evolution. Our results revealed APA as a novel mechanism in regulating cellular senescence.

Sirt6 overexpression suppresses senescence and apoptosis of nucleus pulposus cells by inducing autophagy in a model of intervertebral disc degeneration

Treatment of intervertebral disc degeneration (IDD) seeks to prevent senescence and death of nucleus pulposus (NP) cells. Previous studies have shown that sirt6 exerts potent anti-senescent and anti-apoptotic effects in models of age-related degenerative disease. However, it is not known whether sirt6 protects against IDD. Here, we explored whether sirt6 influenced IDD. The sirt6 level was reduced in senescent human NP cells. Sirt6 overexpression protected against apoptosis and both replicative and stress-induced premature senescence. Sirt6 also activated NP cell autophagy both in vivo and in vitro. 3-methyladenine (3-MA) and chloroquine (CQ)-mediated inhibition of autophagy partially reversed the anti-senescent and anti-apoptotic effects of sirt6, which regulated the expression of degeneration-associated proteins. In vivo, sirt6 overexpression attenuated IDD. Together, the data showed that sirt6 attenuated cell senescence, and reduced apoptosis, by triggering autophagy that ultimately ameliorated IDD. Thus, sirt6 may be a novel therapeutic target for IDD treatment.

SIRT6 protects against endothelial dysfunction and atherosclerosis in mice

SIRT6 is an important member of sirtuin family that represses inflammation, aging and DNA damage, three of which are causing factors for endothelial dysfunction. SIRT6 expression is decreased in atherosclerotic lesions from ApoE^−/− mice and human patients. However, the role of SIRT6 in regulating vascular endothelial function and atherosclerosis is not well understood. Here we show that SIRT6 protects against endothelial dysfunction and atherosclerosis. Global and endothelium-specific SIRT6 knockout mice exhibited impaired endothelium-dependent vasorelaxation. Moreover, SIRT6^+/− haploinsufficient mice fed a high-fat diet (HFD) also displayed impaired endothelium-dependent vasorelaxation. Importantly, SIRT6^+/−;ApoE^−/− mice after HFD feeding exhibited exacerbated atherosclerotic lesion development, concurrent with increased expression of the proinflammatory cytokine VCAM-1. Loss- and gain-of-SIRT6 function studies in cultured human endothelial cells (ECs) showed that SIRT6 attenuated monocyte adhesion to ECs. RNA-sequencing profiling revealed that SIRT6 overexpression decreased the expression of multiple atherosclerosis-related genes, including proatherogenic gene TNFSF4 (tumor necrosis factor superfamily member 4). Chromatin immunoprecipitation assays showed that SIRT6 decreased TNFSF4 gene expression by binding to and deacetylating H3K9 at TNFSF4 gene promoter. Collectively, these findings demonstrate that SIRT6 play a pivotal role in maintaining endothelial function and increased SIRT6 activity could be a new therapeutic strategy to combat atherosclerotic disease.

SIRT6 delays cellular senescence by promoting p27Kip1 ubiquitin-proteasome degradation

Sirtuin6(SIRT6) has been implicated as a key factor in aging and aging-related diseases. However, the role of SIRT6 in cellular senescence has not been fully understood. Here, we show that SIRT6 repressed the expression of p27^Kip1 (p27) in cellular senescence. The expression of SIRT6 was reduced during cellular senescence, whereas enforced SIRT6 expression promoted cell proliferation and antagonized cellular senescence. In addition, we demonstrated that SIRT6 promoted p27 degradation by proteasome and SIRT6 decreased the acetylation level and protein half-life of p27. p27 acetylation increased its protein stability. Furthermore, SIRT6 directly interacted with p27. Importantly, p27 was strongly acetylated and had a prolonged protein half-life with the reduction of SIRT6 when cells were senescent, compared with those young cells. Finally, SIRT6 markedly rescued senescence induced by p27. Our findings indicate that SIRT6 decreases p27 acetylation, leading to its degradation via ubiquitin-proteasome pathway and then delays cellular senescence.

NAMPT and NAMPT-controlled NAD Metabolism in Vascular Repair

Vascular repair plays important roles in postischemic remodeling and rehabilitation in cardiovascular and cerebrovascular disease, such as stroke and myocardial infarction. Nicotinamide adenine dinucleotide (NAD), a well-known coenzyme involved in electron transport chain for generation of adenosine triphosphate, has emerged as an important controller regulating various biological signaling pathways. Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme for NAD biosynthesis in mammals. NAMPT may also act in a nonenzymatic manner, presumably mediated by unknown receptor(s). Rapidly accumulating data in the past decade show that NAMPT and NAMPT-controlled NAD metabolism regulate fundamental biological functions in endothelial cells, vascular smooth muscle cells, and endothelial progenitor cells. The NAD-consuming proteins, including sirtuins, poly-ADP-ribose polymerases (PARPs), and CD38, may contribute to the regulatory effects of NAMPT-NAD axis in these cells and vascular repair. This review discusses the current data regarding NAMPT and NAMPT-controlled NAD metabolism in vascular repair and the clinical potential translational application of NAMPT-related products in treatment of cardiovascular and cerebrovascular disease.

The sirtuin 6 prevents angiotensin II-mediated myocardial fibrosis and injury by targeting AMPK-ACE2 signaling

Sirtuin 6 (SIRT6) is an important modulator of cardiovascular functions in health and diseases. However, the exact role of SIRT6 in heart disease is poorly defined. We hypothesized that SIRT6 is a negative regulator of angiotensin II (Ang II)-mediated myocardial remodeling, fibrosis and injury. The male Sprague-Dawley rats were randomized to Ang II (200 ng/kg/min) infusion with an osmotic minipump and pretreated with recombinant plasmids adeno-associated viral vector (AAV)-SIRT6 (pAAV-SIRT6) or pAAV-GFP for 4 weeks. Ang II triggered downregulated levels of SIRT6 and angiotensin-converting enzyme 2 (ACE2) and upregulated expression of connective tissue growth factor (CTGF) and proinflammatory chemokine fractalkine (FKN), contributing to enhanced cardiac fibrosis and ultrastructural injury. Reduced levels of phosphorylated pAMPK-α, increased myocardial hypertrophy and impaired heart dysfunction were observed in both Ang II-induced hypertensive rats and ACE2 knockout rats, characterized with increases in heart weight and left ventricular (LV) posterior wall thickness and decreases in LV ejection fraction and LV fractional shortening. More importantly, pAAV-SIRT6 treatment strikingly potentiated cardiac levels of pAMPKα and ACE2 as well as decreased levels of CTGF, FKN, TGFβ1, collagen I and collagen III, resulting in alleviation of Ang II-induced pathological hypertrophy, myocardial fibrosis, cardiac dysfunction and ultrastructural injury in hypertensive rats. In conclusion, our findings confirmed cardioprotective effects of SIRT6 on pathological remodeling, fibrosis and myocardial injury through activation of AMPK-ACE2 signaling and suppression of CTGF-FKN pathway, indicating that SIRT6 functions as a partial agonist of ACE2 and targeting SIRT6 has potential therapeutic importance for cardiac fibrosis and heart disease.

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

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

Multiple pathways of SIRT6 at the crossroads in the control of longevity, cancer, and cardiovascular diseases

Sirtuin 6 (SIRT6) is a member of the sirtuin family NAD⁺-dependent deacetylases with multiple roles in controlling organism homeostasis, lifespan, and diseases. Due to its complex and opposite functional roles, this sirtuin is considered a two-edged sword in health and disease. Indeed, SIRT6 improves longevity, similarly to the founding yeast member, silent information regulator-2 (Sir2), and modulates genome stability, telomere integrity, transcription, and DNA repair. Its deficiency is associated with chronic inflammation, diabetes, cardiac hypertrophy, obesity, liver dysfunction, muscle/adipocyte disorders, and cancer. Besides, pieces of evidence showed that SIRT6 is a promoter of specific oncogenic pathways, thus disclosing its dual role regarding cancer development. Collectively, these findings suggest that multiple mechanisms, to date not entirely known, underlie the intriguing roles of SIRT6. Here we provide an overview of the current molecular mechanisms through which SIRT6 controls cancer and heart diseases, and describe its recent implications in the atherosclerotic plaque development.

Sirtuins, a promising target in slowing down the ageing process

Ageing is a plastic process and can be successfully modulated by some biomedical approaches or pharmaceutics. In this manner it is possible to delay or even prevent some age-related pathologies. There are some defined interventions, which give promising results in animal models or even in human studies, resulting in lifespan elongation or healthspan improvement. One of the most promising targets for anti-ageing approaches are proteins belonging to the sirtuin family. Sirtuins were originally discovered as transcription repressors in yeast, however, nowadays they are known to occur in bacteria and eukaryotes (including mammals). In humans the family consists of seven members (SIRT1-7) that possess either mono-ADP ribosyltransferase or deacetylase activity. It is believed that sirtuins play key role during cell response to a variety of stresses, such as oxidative or genotoxic stress and are crucial for cell metabolism. Although some data put in question direct involvement of sirtuins in extending human lifespan, it was documented that proper lifestyle including physical activity and diet can influence healthspan via increasing the level of sirtuins. The search for an activator of sirtuins is one of the most extensive and robust topic of research. Some hopes are put on natural compounds, including curcumin. In this review we summarize the involvement and usefulness of sirtuins in anti-ageing interventions and discuss the potential role of curcumin in sirtuins regulation.

SIRT6 Depletion Suppresses Tumor Growth by Promoting Cellular Senescence Induced by DNA Damage in HCC

The role of Sirtuin 6 (SIRT6) as a tumor suppressor or oncogene in liver cancer remains controversial. Thus, we identified the specific role of SIRT6 in the progression of hepatocellular carcinoma (HCC). SIRT6 expression was significantly higher in HCC cell lines and HCC tissues from 138 patients than in an immortalized hepatocyte cell line, THLE-2 and non-tumor tissues, respectively. SIRT6 knockdown by shRNA suppressed the growth of HCC cells and inhibited HCC tumor growth in vivo. In addition, SIRT6 silencing significantly prevented the growth of HCC cell lines by inducing cellular senescence in the p16/Rb- and p53/p21-pathway independent manners. Microarray analysis revealed that the expression of genes involved in nucleosome assembly was apparently altered in SIRT6-depleted Hep3B cells. SIRT6 knockdown promoted G2/M phase arrest and downregulation of genes encoding histone variants associated with nucleosome assembly, which could be attributed to DNA damage. Taken together, our findings suggest that SIRT6 acts as a tumor promoter by preventing DNA damage and cellular senescence, indicating that SIRT6 represents a potential therapeutic target for the treatment of HCC.

Exercise during pregnancy decreases doxorubicin-induced cardiotoxic effects on neonatal hearts

Cancer treatment with Doxorubicin (DOX) is limited due its dose-dependent cardiotoxicity, mainly related to the oxidative stress production. In experimental models of DOX treatment exercise can be used as a beneficial adjuvant therapy. This work aimed to investigate the effects of exercise during pregnancy on DOX-induced cardiotoxicity in cardiomyocytes of progeny, examining the possible intergenerational cardioprotective effects of maternal exercise. For this purpose pregnant rats were divided in control and exercise groups and pre-treated during gestational days. Hearts of newborns were used to obtain a culture of cardiomyocytes to be treated with DOX for analyses of cell viability, apoptosis and necrosis; ROS production; DNA damage; SOD and CAT activities; and Sirt6 protein expression. The results showed that exercise during pregnancy induced an increase in the viability of neonatal cardiomyocytes and a decrease in DOX-induced apoptotic and necrotic death which were correlated to the decrease in ROS production and an increase in antioxidant defenses. Exercise also protected neonatal cardiomyocytes from DOX-induced DNA damage, demonstrating a reduction in the oxidative DNA breaks. Likewise, exercise induced an increase in expression of Sirt6 in neonatal cardiomyocytes. Therefore, these results demonstrate for the first time that exercise performed by mothers protects the neonatal heart against DOX-induced toxicity. Our data demonstrate the intergenerational effect of exercise in cardiomyocytes of progeny, where the modulation of oxidative stress through antioxidant enzymes, and DNA integrity via Sirt6, were induced due to exercise in mothers, increasing the resistance of the neonatal heart against DOX toxicity.