SIRT1 but not its increased expression is essential for lifespan extension in caloric-restricted mice

Unlocking the potential of Mesenchymal stem cells in liver Fibrosis: Insights into the impact of autophagy and aging

Liver fibrosis is a chronic liver disease characterized by extracellular matrix protein accumulation, potentially leading to cirrhosis or hepatocellular carcinoma. Liver cell damage, inflammatory responses, and apoptosis due to various reasons induce liver fibrosis. Although several treatments, such as antiviral drugs and immunosuppressive therapies, are available for liver fibrosis, they only provide limited efficacy. Mesenchymal stem cells (MSCs) have become a promising therapeutic option for liver fibrosis, because they can modulate the immune response, promote liver regeneration, and inhibit the activation of hepatic stellate cells that contribute to disease development. Recent studies have suggested that the mechanisms through which MSCs gain their antifibrotic properties involve autophagy and senescence. Autophagy, a vital cellular self-degradation process, is critical for maintaining homeostasis and protecting against nutritional, metabolic, and infection-mediated stress. The therapeutic effects of MSCs depend on appropriate autophagy levels, which can improve the fibrotic process. Nonetheless, aging-related autophagic damage is associated with a decline in MSC number and function, which play a crucial role in liver fibrosis development. This review summarizes the recent advancements in the understanding of autophagy and senescence in MSC-based liver fibrosis treatment, presenting the key findings from relevant studies.

Relating aging and autophagy: a new perspective towards the welfare of human health

The most common factor that contributes to aging is the loss of proteostasis, resulting in an excess amount of non-functional/damaged proteins. These proteins lead to various age-associated phenotypes such as cellular senescence and dysfunction in the nutrient-sensing pathways. Despite the various factors that can contribute to aging, it is still a process that can be changed. According to recent advances in the field of biology, the ability to alter the pathways that are involved in aging can improve the lifespan of a person. Autophagy is a process that helps in preserving survival during stressful situations, such as starvation. It is a common component of various anti-aging interventions, including those that target the insulin/IGF-1 and rapamycin signaling pathways. It has been shown that altered autophagy is a common feature of old age and its impaired regulation could have significant effects on the aging process. This review aims to look into the role of autophagy in aging and how it can be used to improve one's health.

Investigating Physiopathological Roles for Sirtuins in a Mouse Model

Sirtuins are identified as NAD+-dependent class III histone deacetylases (HDAC) and are involved in a variety of cellular activities, including energy metabolism, DNA repair, epigenetics, gene expression, cell proliferation, differentiation, and survival. Using genetically modified model organisms, sirtuins are proved to be one of the most conserved aging-regulatory and longevity-promoting genes/pathways among species. Of the seven sirtuins, SIRT7 is the only sirtuin that localizes in the nucleolus. SIRT7 senses endogenous and environmental stress to maintain physiological homeostasis. Sirt7 deficient and transgenic mice provide a useful tool to understand the mechanisms of aging and related pathologies. In this chapter, we summarized the most widely applied methods to understand the physiopathological function of SIRT7 in mice.

Dietary restriction in senolysis and prevention and treatment of disease

Aging represents a key risk factor for a plethora of diseases. Targeting detrimental processes which occur during aging, especially before onset of age-related disease, could provide drastic improvements in healthspan. There is increasing evidence that dietary restriction (DR), including caloric restriction, fasting, or fasting-mimicking diets, extend both lifespan and healthspan. This has sparked interest in the use of dietary regimens as a non-pharmacological means to slow aging and prevent disease. Here, we review the current evidence on the molecular mechanisms underlying DR-induced health improvements, including removal of senescent cells, metabolic reprogramming, and epigenetic rejuvenation.

Cellular senescence in ischemia/reperfusion injury

Ischemia/reperfusion (IR) injury, a main reason of mortality and morbidity worldwide, occurs in many organs and tissues. As a result of IR injury, senescent cells can accumulate in multiple organs. Increasing evidence shows that cellular senescence is the underlying mechanism that transforms an acute organ injury into a chronic one. Several recent studies suggest senescent cells can be targeted for the prevention or elimination of acute and chronic organ injury induced by IR. In this review, we concisely introduce the underlying mechanism and the pivotal role of premature senescence in the transition from acute to chronic IR injuries. Special focus is laid on recent advances in the mechanisms as well as on the basic and clinical research, targeting cellular senescence in multi-organ IR injuries. Besides, the potential directions in this field are discussed in the end. Together, the recent advances reviewed here will act as a comprehensive overview of the roles of cellular senescence in IR injury, which could be of great significance for the design of related studies, or as a guide for potential therapeutic target.

Evaluating the beneficial effects of dietary restrictions: A framework for precision nutrigeroscience

Dietary restriction (DR) has long been viewed as the most robust nongenetic means to extend lifespan and healthspan. Many aging-associated mechanisms are nutrient responsive, but despite the ubiquitous functions of these pathways, the benefits of DR often vary among individuals and even among tissues within an individual, challenging the aging research field. Furthermore, it is often assumed that lifespan interventions like DR will also extend healthspan, which is thus often ignored in aging studies. In this review, we provide an overview of DR as an intervention and discuss the mechanisms by which it affects lifespan and various healthspan measures. We also review studies that demonstrate exceptions to the standing paradigm of DR being beneficial, thus raising new questions that future studies must address. We detail critical factors for the proposed field of precision nutrigeroscience, which would utilize individualized treatments and predict outcomes using biomarkers based on genotype, sex, tissue, and age.

Involvement of Autophagy in Ageing and Chronic Cholestatic Diseases

Autophagy is a “housekeeping” lysosomal degradation process involved in numerous physiological and pathological processes in all eukaryotic cells. The dysregulation of hepatic autophagy has been described in several conditions, from obesity to diabetes and cholestatic disease. We review the role of autophagy, focusing on age-related cholestatic diseases, and discuss its therapeutic potential and the molecular targets identified to date. The accumulation of toxic BAs is the main cause of cell damage in cholestasis patients. BAs and their receptor, FXR, have been implicated in the regulation of hepatic autophagy. The mechanisms by which cholestasis induces liver damage include mitochondrial dysfunction, oxidative stress and ER stress, which lead to cell death and ultimately to liver fibrosis as a compensatory mechanism to reduce the damage. The stimulation of autophagy seems to ameliorate the liver damage. Autophagic activity decreases with age in several species, whereas its basic extends lifespan in animals, suggesting that it is one of the convergent mechanisms of several longevity pathways. No strategies aimed at inducing autophagy have yet been tested in cholestasis patients. However, its stimulation can be viewed as a novel therapeutic strategy that may reduce ageing-dependent liver deterioration and also mitigate hepatic steatosis.

A comprehensive overview of the complex relationship between epigenetics, bioactive components, cancer, and aging

Among age-related diseases, the incidence of cancer increases significantly due to the overlap of some molecular pathways between cancer and aging. While the genetic influence on the human lifespan is estimated to be about 20-25%, epigenetic changes play an important role in modulating individual health status, aging. Aging and age-related conditions are processes that can be modified by both genetic, environmental factors, including dietary habits. Epigenetics is a new discipline has significant potential to be applied for the prevention, management of certain carcinomas and diseases. Epigenetic modifications may play an important role in disease occurrence and pathogenesis. Some nutritional components can be significantly effective in the prevention of breast, skin, esophagus, colorectal, prostate, pancreatic, lung cancers. It contains minerals, vitamins, and some bioactive components (curcumin, indole 3 carbinol, di-indolylmethane, sulforaphane, epigallocatechin-3-gallate, genistein, resveratrol, pterostilbene, apigenin, etc.) regulatory processes. However, compelling evidence suggests that dietary habits can manipulate the aging process and/or its consequences, have health benefits. Aging processes become complex when combined with the relational role of bioactive nutritional components on gene expression. In this review, the relationship between epigenetic processes caused by DNA methylylation, histone modification, non-coding m-RNA, and telomerase activity, the risk of aging and cancer is discussed.

Silent Information Regulator T1 in Aqueous Humor of Patients with Age-Related Macular Degeneration

Purpose:

The purpose of this study is to compare the aqueous humor level of Silent Information Regulator T1 (SIRT1) between patients with Age-related Macular Degeneration (AMD) and cataract patients.

Materials and Methods:

Aqueous humor level of SIRT1 was measured by enzyme-linked immunosorbent assay in 13 patients with wet-type AMD (n=13, AMD group) and 13 patients with cataracts (cataract group). In addition, the thickness of each retinal layer was determined by optical coherence tomography.

Results:

The aqueous humor level of SIRT1 was significantly lower in the AMD group than in the cataract group (p=0.007). In the AMD group, the SIRT1 level was positively correlated with the thickness of the retinal ganglion cell layer (r=0.31) and the inner nuclear layer (r=0.76).

Conclusion:

The aqueous level of SIRT1 decreased as the ganglion cell layer and inner nuclear layer became thinner, suggesting that reduction of SIRT1 activity might be involved in the pathogenesis of this disease.

Sirtuin1 in vascular endothelial function, an overview

Sirtuin1 is a nutrient-sensitive class III histone deacetylase which is a well-known regulator of organismal lifespan. It has been extensively studied for its role in metabolic regulation as well. Along with its involvement in ageing and metabolism, Sirtuin1 directly deacetylates many critical proteins controlling cardiovascular pathophysiology. Studies using conditional expression and deletion of Sirtuin1 have revealed that it functions in a highly tissue/organ-specific manner. In the vasculature, Sirtuin1 controls endothelial homoeostasis by governing the expression of inflammatory mediators, oxidants and essential transcription factors. Adding to this complexity, Sirtuin1 expression and/or function is also governed by some of these target proteins. Therefore, the importance of better understanding the organ and tissue specificity of Sirtuin1 is highly desirable. Considering the huge volume of research done in this field, this review focuses on Sirtuin1 targets regulating vascular endothelial function. Here, we summarize the discovery of Sirtuin1 as a transcription controller and the further identification of direct target proteins involved in the vascular physiology. Overall, this review presents a holistic picture of the complex cross-talk involved in the molecular regulation of vascular physiology by Sirtuin1.

Vascular Aging in Rodent Models: Contrasting Mechanisms Driving the Female and Male Vascular Senescence

Increasing scientific interest has been directed to sex as a biological and decisive factor on several diseases. Several different mechanisms orchestrate vascular function, as well as vascular dysfunction in cardiovascular and metabolic diseases in males and females. Certain vascular sex differences are present throughout life, while others are more evident before the menopause, suggesting two important and correlated drivers: genetic and hormonal factors. With the increasing life expectancy and aging population, studies on aging-related diseases and aging-related physiological changes have steeply grown and, with them, the use of aging animal models. Mouse and rat models of aging, the most studied laboratory animals in aging research, exhibit sex differences in many systems and physiological functions, as well as sex differences in the aging process and aging-associated cardiovascular changes. In the present review, we introduce the most common aging and senescence-accelerated animal models and emphasize that sex is a biological variable that should be considered in aging studies. Sex differences in the cardiovascular system, with a focus on sex differences in aging-associated vascular alterations (endothelial dysfunction, remodeling and oxidative and inflammatory processes) in these animal models are reviewed and discussed.

SGLT2 Inhibitors as Calorie Restriction Mimetics: Insights on Longevity Pathways and Age-Related Diseases

Sodium-glucose cotransporter-2 (SGLT2) inhibitors induce glycosuria, reduce insulin levels, and promote fatty acid oxidation and ketogenesis. By promoting a nutrient deprivation state, SGLT2 inhibitors upregulate the energy deprivation sensors AMPK and SIRT1, inhibit the nutrient sensors mTOR and insulin/IGF1, and modulate the closely linked hypoxia-inducible factor (HIF)-2α/HIF-1α pathways. Phosphorylation of AMPK and upregulation of adiponectin and PPAR-α favor a reversal of the metabolic syndrome which have been linked to suppression of chronic inflammation. Downregulation of insulin/IGF1 pathways and mTOR signaling from a reduction in glucose and circulating amino acids promote cellular repair mechanisms, including autophagy and proteostasis which confer cellular stress resistance and attenuate cellular senescence. SIRT1, another energy sensor activated by NAD+ in nutrient-deficient states, is reciprocally activated by AMPK, and can deacetylate and activate transcription factors, such as PCG-1α, mitochondrial transcription factor A (TFAM), and nuclear factor E2-related factor (NRF)-2, that regulate mitochondrial biogenesis. FOXO3 transcription factor which target genes in stress resistance, is also activated by AMPK and SIRT1. Modulation of these pathways by SGLT2 inhibitors have been shown to alleviate metabolic diseases, attenuate vascular inflammation and arterial stiffness, improve mitochondrial function and reduce oxidative stress-induced tissue damage. Compared with other calorie restriction mimetics such as metformin, rapamycin, resveratrol, and NAD+ precursors, SGLT2 inhibitors appear to be the most promising in the treatment of aging-related diseases, due to their regulation of multiple longevity pathways that closely resembles that achieved by calorie restriction and their established efficacy in reducing cardiovascular events and all-cause mortality. Evidence is compelling for the role of SGLT2 inhibitors as a calorie restriction mimetic in anti-aging therapeutics.

Calorie Restriction and SIRT1 Overexpression Induce Different Gene Expression Profiles in White Adipose Tissue in Association with Metabolic Improvement

INTRODUCTION

Calorie restriction (CR) exerts multiple effects on health, including the amelioration of systemic insulin resistance. Although the precise mechanisms by which CR improves glucose homeostasis remain poorly defined, SIRT1 has been suggested to act as a central mediator of the cellular responses to CR. Here, we aim at identifying the mechanisms by which CR and SIRT1 modulate white adipose tissue (WAT) function, a key tissue in the control of glucose homeostasis.

MATERIAL AND METHODS

A gene expression profiling study using DNA microarrays is conducted in WAT of control and SIRT1 transgenic mice fed ad libitum (AL) and mice subjected to 40% CR.

RESULTS

Gene expression profiling reveals a relatively low degree of overlap between the transcriptional programs regulated by SIRT1 and CR. Gene networks related to extracellular matrix appear commonly downregulated by SIRT1/CR, whereas mitochondrial biogenesis is enhanced exclusively by CR. Moreover, WAT inflammation is reduced by CR and SIRT1, although their anti-inflammatory effects appeared to be achieved by regulating different gene networks related to the immune system.

CONCLUDING REMARKS

In WAT, SIRT1 does not mediate most of the effects of CR on gene expression. Still, gene networks differentially regulated by SIRT1 and CR converge to reduce WAT inflammation.

Build-UPS and break-downs: metabolism impacts on proteostasis and aging

Perturbation of metabolism elicits cellular stress which profoundly modulates the cellular proteome and thus protein homeostasis (proteostasis). Consequently, changes in the cellular proteome due to metabolic shift require adaptive mechanisms by molecular protein quality control. The mechanisms vitally controlling proteostasis embrace the entire life cycle of a protein involving translational control at the ribosome, chaperone-assisted native folding, and subcellular sorting as well as proteolysis by the proteasome or autophagy. While metabolic imbalance and proteostasis decline have been recognized as hallmarks of aging and age-associated diseases, both processes are largely considered independently. Here, we delineate how proteome stability is governed by insulin/IGF1 signaling (IIS), mechanistic target of Rapamycin (TOR), 5′ adenosine monophosphate-activated protein kinase (AMPK), and NAD-dependent deacetylases (Sir2-like proteins known as sirtuins). This comprehensive overview is emphasizing the regulatory interconnection between central metabolic pathways and proteostasis, indicating the relevance of shared signaling nodes as targets for future therapeutic interventions.

Inhibition of Cdc42 activity extends lifespan and decreases circulating inflammatory cytokines in aged female C57BL/6 mice

Cdc42 is a small RhoGTPase regulating multiple functions in eukaryotic cells. The activity of Cdc42 is significantly elevated in several tissues of aged mice, while the Cdc42 gain‐of‐activity mouse model presents with a premature aging‐like phenotype and with decreased lifespan. These data suggest a causal connection between elevated activity of Cdc42, aging, and reduced lifespan. Here, we demonstrate that systemic treatment of aged (75‐week‐old) female C57BL/6 mice with a Cdc42 activity‐specific inhibitor (CASIN) for 4 consecutive days significantly extends average and maximum lifespan. Moreover, aged CASIN‐treated animals displayed a youthful level of the aging‐associated cytokines IL‐1β, IL‐1α, and INFγ in serum and a significantly younger epigenetic clock as based on DNA methylation levels in blood cells. Overall, our data show that systemic administration of CASIN to reduce Cdc42 activity in aged mice extends murine lifespan.

Brd2 haploinsufficiency extends lifespan and healthspan in C57B6/J mice

Aging in mammals is the gradual decline of an organism's physical, mental, and physiological capacity. Aging leads to increased risk for disease and eventually to death. Here, we show that Brd2 haploinsufficiency (Brd2+/-) extends lifespan and increases healthspan in C57B6/J mice. In Brd2+/- mice, longevity is increased by 23% (p<0.0001), and, relative to wildtype animals (Brd2+/+), cancer incidence is reduced by 43% (p<0.001). In addition, relative to age-matched wildtype mice, Brd2 heterozygotes show healthier aging including: improved grooming, extended period of fertility, and lack of age-related decline in kidney function and morphology. Our data support a role for haploinsufficiency of Brd2 in promoting healthy aging. We hypothesize that Brd2 affects aging by protecting against the accumulation of molecular and cellular damage. Given the recent advances in the development of BET inhibitors, our research provides impetus to test drugs that target BRD2 as a way to understand and treat/prevent age-related diseases.

Mechanisms of Lifespan Regulation by Calorie Restriction and Intermittent Fasting in Model Organisms

Genetic and pharmacological interventions have successfully extended healthspan and lifespan in animals, but their genetic interventions are not appropriate options for human applications and pharmacological intervention needs more solid clinical evidence. Consequently, dietary manipulations are the only practical and probable strategies to promote health and longevity in humans. Caloric restriction (CR), reduction of calorie intake to a level that does not compromise overall health, has been considered as being one of the most promising dietary interventions to extend lifespan in humans. Although it is straightforward, continuous reduction of calorie or food intake is not easy to practice in real lives of humans. Recently, fasting-related interventions such as intermittent fasting (IF) and time-restricted feeding (TRF) have emerged as alternatives of CR. Here, we review the history of CR and fasting-related strategies in animal models, discuss the molecular mechanisms underlying these interventions, and propose future directions that can fill the missing gaps in the current understanding of these dietary interventions. CR and fasting appear to extend lifespan by both partially overlapping common mechanisms such as the target of rapamycin (TOR) pathway and circadian clock, and distinct independent mechanisms that remain to be discovered. We propose that a systems approach combining global transcriptomic, metabolomic, and proteomic analyses followed by genetic perturbation studies targeting multiple candidate pathways will allow us to better understand how CR and fasting interact with each other to promote longevity.

Sirt1 during childhood is associated with microvascular function later in life

Microvascular dysfunction often precedes other age-related macrovascular conditions and predicts future cardiovascular risk. Sirtuin 1 (Sirt1) has recently emerged as a protein that protects the vasculature and reduces the risk of cardiovascular diseases. We tested the hypothesis that lower Sirt1 during childhood is associated with a reduced microvascular function during adulthood. Thirty-four adults (34 ± 3 yr) from the Augusta Heart Study returned to participate in the present clinical observational study. Sirt1 was assessed in samples collected during both adulthood and participants' childhood (16 ± 3 yr), and data were divided based on childhood Sirt1 concentrations: <3 ng/dL (LowCS; n = 16) and ≥3 ng/dL (HighCS; n = 18). MVF was evaluated in all of the adults using laser-Doppler flowmetry coupled with three vascular reactivity tests: 1) local thermal hyperemia (LTH), 2) post-occlusive reactive hyperemia (PORH), and 3) iontophoresis of acetylcholine (ACh). The hyperemic response to LTH was significantly (P ≤ 0.044) lower in the LowCS than in the HighCS group. Similarly, the LowCS also exhibited an ameliorated (P ≤ 0.045) response to the PORH test and lower (P ≤ 0.008) vasodilation in response to iontophoresis of ACh when compared with the HighCS. Positive relationships were identified between childhood Sirt1 and all MVF reactivity tests (r≥0.367, P ≤ 0.004). Novel observations suggest that lower Sirt1 during childhood is associated with premature microvascular dysfunction in adulthood. These findings provide evidence that Sirt1 may play a critical role in microvascular function and have therapeutic potential for the prevention of age-associated vascular dysfunction in humans.NEW & NOTEWORTHY With a longitudinal cohort, novel observations from the present study demonstrate that individuals who had lower Sirt1 early in life exhibit premature microvascular dysfunction during adulthood and may be at higher risk to develop CVD. These results provide experimental evidence that Sirt1 may play an important role in microvascular function with age and represent a potential therapeutic target to prevent premature vascular dysfunction.

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.

Effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on ageing: Molecular mechanisms

Human ageing is determined by degenerative alterations and processes with different manifestations such as gradual organ dysfunction, tissue function loss, increased population of aged (senescent) cells, incapability of maintaining homeostasis and reduced repair capacity, which collectively lead to an increased risk of diseases and death. The inhibitors of HMG-CoA reductase (statins) are the most widely used lipid-lowering agents, which can reduce cardiovascular morbidity and mortality. Accumulating evidence has documented several pleiotropic effects of statins in addition to their lipid-lowering properties. Recently, several studies have highlighted that statins may have the potential to delay the ageing process and inhibit the onset of senescence. In this review, we focused on the anti-ageing mechanisms of statin drugs and their effects on cardiovascular and non-cardiovascular diseases.

Methionine Restriction Extends Lifespan in Progeroid Mice and Alters Lipid and Bile Acid Metabolism

Dietary intervention constitutes a feasible approach for modulating metabolism and improving the health span and lifespan. Methionine restriction (MR) delays the appearance of age-related diseases and increases longevity in normal mice. However, the effect of MR on premature aging remains to be elucidated. Here, we describe that MR extends lifespan in two different mouse models of Hutchinson-Gilford progeria syndrome (HGPS) by reversing the transcriptome alterations in inflammation and DNA-damage response genes present in this condition. Further, MR improves the lipid profile and changes bile acid levels and conjugation, both in wild-type and in progeroid mice. Notably, treatment with cholic acid improves the health span and lifespan in vivo. These results suggest the existence of a metabolic pathway involved in the longevity extension achieved by MR and support the possibility of dietary interventions for treating progeria.

Mechanisms of Calorie Restriction: A Review of Genes Required for the Life-Extending and Tumor-Inhibiting Effects of Calorie Restriction

This review focuses on mechanisms of calorie restriction (CR), particularly the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis as an evolutionary conserved signal that regulates aging and lifespan, underlying the effects of CR in mammals. Topics include (1) the relation of the GH-IGF-1 signal with chronic low-level inflammation as one of the possible causative factors of aging, that is, inflammaging, (2) the isoform specificity of the forkhead box protein O (FoxO) transcription factors in CR-mediated regulation of cancer and lifespan, (3) the role for FoxO1 in the tumor-inhibiting effect of CR, (4) pleiotropic roles for FoxO1 in the regulation of disorders, and (5) sirtuin (Sirt) as a molecule upstream of FoxO. From the evolutionary view, the necessity of neuropeptide Y (Npy) for the effects of CR and the pleiotropic roles for Npy in life stages are also emphasized. Genes for mediating the effects of CR and regulating aging are context-dependent, particularly depending on nutritional states.

Extension of Cellular Lifespan by Methionine Restriction Involves Alterations in Central Carbon Metabolism and Is Mitophagy-Dependent

Methionine restriction (MR) is one of only a few dietary manipulations known to robustly extend healthspan in mammals. For example, rodents fed a methionine-restricted diet are up to 45% longer-lived than control-fed animals. Tantalizingly, ongoing studies suggest that humans could enjoy similar benefits from this intervention. While the benefits of MR are likely due, at least in part, to improved cellular stress tolerance, it remains to be determined exactly how MR extends organismal healthspan. In previous work, we made use of the yeast chronological lifespan (CLS) assay to model the extension of cellular lifespan conferred by MR and explore the genetic requirements for this extension. In these studies, we demonstrated that both dietary MR (D-MR) and genetic MR (G-MR) (i.e., impairment of the cell’s methionine biosynthetic machinery) significantly extend the CLS of yeast. This extension was found to require the mitochondria-to-nucleus retrograde (RTG) stress signaling pathway, and was associated with a multitude of gene expression changes, a significant proportion of which was also dependent on RTG signaling. Here, we show work aimed at understanding how a subset of the observed expression changes are causally related to MR-dependent CLS extension. Specifically, we find that multiple autophagy-related genes are upregulated by MR, likely resulting in an increased autophagic capacity. Consistent with activated autophagy being important for the benefits of MR, we also find that loss of any of several core autophagy factors abrogates the extended CLS observed for methionine-restricted cells. In addition, epistasis analyses provide further evidence that autophagy activation underlies the benefits of MR to yeast. Strikingly, of the many types of selective autophagy known, our data clearly demonstrate that MR-mediated CLS extension requires only the autophagic recycling of mitochondria (i.e., mitophagy). Indeed, we find that functional mitochondria are required for the full benefit of MR to CLS. Finally, we observe substantial alterations in carbon metabolism for cells undergoing MR, and provide evidence that such changes are directly responsible for the extended lifespan of methionine-restricted yeast. In total, our data indicate that MR produces changes in carbon metabolism that, together with the oxidative metabolism of mitochondria, result in extended cellular lifespan.

3,4-Dimethoxychalcone induces autophagy through activation of the transcription factors TFE3 and TFEB

Caloric restriction mimetics (CRMs) are natural or synthetic compounds that mimic the health-promoting and longevity-extending effects of caloric restriction. CRMs provoke the deacetylation of cellular proteins coupled to an increase in autophagic flux in the absence of toxicity. Here, we report the identification of a novel candidate CRM, namely 3,4-dimethoxychalcone (3,4-DC), among a library of polyphenols. When added to several different human cell lines, 3,4-DC induced the deacetylation of cytoplasmic proteins and stimulated autophagic flux. At difference with other well-characterized CRMs, 3,4-DC, however, required transcription factor EB (TFEB)- and E3 (TFE3)-dependent gene transcription and mRNA translation to trigger autophagy. 3,4-DC stimulated the translocation of TFEB and TFE3 into nuclei both in vitro and in vivo, in hepatocytes and cardiomyocytes. 3,4-DC induced autophagy in vitro and in mouse organs, mediated autophagy-dependent cardioprotective effects, and improved the efficacy of anticancer chemotherapy in vivo. Altogether, our results suggest that 3,4-DC is a novel CRM with a previously unrecognized mode of action.

Mitochondria, Telomeres and Telomerase Subunits

Mitochondrial functions and telomere functions have mostly been studied independently. In recent years, it, however, has become clear that there are intimate links between mitochondria, telomeres, and telomerase subunits. Mitochondrial dysfunctions cause telomere attrition, while telomere damage leads to reprogramming of mitochondrial biosynthesis and mitochondrial dysfunctions, which has important implications in aging and diseases. In addition, evidence has accumulated that telomere-independent functions of telomerase also exist and that the protein component of telomerase TERT shuttles between the nucleus and mitochondria under oxidative stress. Our previously published data show that the RNA component of telomerase TERC is also imported into mitochondria, processed, and exported back to the cytosol. These data show a complex regulation network where telomeres, nuclear genome, and mitochondria are co-regulated by multi-localization and multi-function proteins and RNAs. This review summarizes the connections between mitochondria and telomeres, the mitochondrion-related functions of telomerase subunits, and how they play a role in crosstalk between mitochondria and the nucleus.

Cachexia/Protein energy wasting syndrome in CKD: Causation and treatment

Cachexia is a multifactorial syndrome defined by significant body weight loss, fat and muscle mass reduction, and increased protein catabolism. Protein energy wasting (PEW) is characterized as a syndrome of adverse changes in nutrition and body composition being highly prevalent in patients with CKD, especially in those undergoing dialysis, and it is associated with high morbidity and mortality in this population. Multiple mechanisms are involved in the genesis of these adverse nutritional changes in CKD patients. There is no obvious distinction between PEW and cachexia from a pathophysiologic standpoint and should be considered as part of the spectrum of the same nutritional disorder in CKD with similar management approaches for prevention and treatment based on current understanding. A plethora of factors can affect the nutritional status of CKD patients requiring a combination of therapeutic approaches to prevent or reverse protein and energy depletion. At present, there is no effective pharmacologic intervention that prevents or attenuates muscle atrophy in catabolic conditions like CKD. Prevention and treatment of uremic muscle wasting involve optimal nutritional support, correction of acidosis, and physical exercise. There has been emerging consistent evidence that active treatment, perhaps by combining nutritional interventions and resistance exercise, may be able to improve but not totally reverse or prevent the supervening muscle wasting and weakness. Active research into more direct pharmacological treatment based on basic mechanistic research is much needed for this unmet medical need in patients with CKD.

Lifespan-increasing drug nordihydroguaiaretic acid inhibits p300 and activates autophagy

Aging is characterized by the progressive loss of physiological function in all organisms. Remarkably, the aging process can be modulated by environmental modifications, including diet and small molecules. The natural compound nordihydroguaiaretic acid (NDGA) robustly increases lifespan in flies and mice, but its mechanism of action remains unclear. Here, we report that NDGA is an inhibitor of the epigenetic regulator p300. We find that NDGA inhibits p300 acetyltransferase activity in vitro and suppresses acetylation of a key p300 target in histones (i.e., H3K27) in cells. We use the cellular thermal shift assay to uniquely demonstrate NDGA binding to p300 in cells. Finally, in agreement with recent findings indicating that p300 is a potent blocker of autophagy, we show that NDGA treatment induces autophagy. These findings identify p300 as a target of NDGA and provide mechanistic insight into its role in longevity.

Physical Exercise Improves Aging-Related Changes in Angiotensin, IGF-1, SIRT1, SIRT3, and VEGF in the Substantia Nigra

Dysregulation of tissue renin-angiotensin system (RAS) is involved in oxidative and inflammatory processes observed in major aging-related diseases, including neurodegenerative diseases such as Parkinson's disease (PD). Physical exercise has beneficial effects against aging-related changes, dopaminergic neuron vulnerability, and PD progression. The present study indicates that sedentary aged rats have an increase in activity of the nigral angiotensin (Ang) II/Ang type 1 receptor (AT1) axis (ie, the pro-oxidative pro-inflammatory arm), and a decrease in the activity of the RAS protective arm (ie, Ang II/AT2 and Ang 1-7/Mas receptor axis) in comparison with young rats. In addition, sedentary aged rats showed a decrease in levels of nigral IGF-1, SIRT1, SIRT3, and VEGF. Treadmill running induced a significant increase in levels of IGF-1, SIRT1, SIRT3, and VEGF, as well as an increase in expression of the protective Ang 1-7/Mas axis and inhibition of the Ang II/AT1 axis. The exercise-induced increase in IGF-1 and sirtuins may mediate the effects of exercise on the nigral RAS. However, exercise may induce the increase in VEGF and modulation of RAS activity by different pathways. Exercise, via RAS, contributes to inhibition of the pro-oxidative and proinflammatory state that increase dopaminergic neuron vulnerability and risk of PD with aging.

Identification and Application of Gene Expression Signatures Associated with Lifespan Extension

Several pharmacological, dietary, and genetic interventions that increase mammalian lifespan are known, but general principles of lifespan extension remain unclear. Here, we performed RNA sequencing (RNA-seq) analyses of mice subjected to 8 longevity interventions. We discovered a feminizing effect associated with growth hormone regulation and diminution of sex-related differences. Expanding this analysis to 17 interventions with public data, we observed that many interventions induced similar gene expression changes. We identified hepatic gene signatures associated with lifespan extension across interventions, including upregulation of oxidative phosphorylation and drug metabolism, and showed that perturbed pathways may be shared across tissues. We further applied the discovered longevity signatures to identify new lifespan-extending candidates, such as chronic hypoxia, KU-0063794, and ascorbyl-palmitate. Finally, we developed GENtervention, an app that visualizes associations between gene expression changes and longevity. Overall, this study describes general and specific transcriptomic programs of lifespan extension in mice and provides tools to discover new interventions.

Impaired SIRT1 activity leads to diminution in glomerular endowment without accelerating age-associated GFR decline

Glomerular filtration rate (GFR) declines with age such that the prevalence of chronic kidney disease is much higher in the elderly. SIRT1 is the leading member of the sirtuin family of NAD+ -dependent lysine deacetylases that mediate the health span extending properties of caloric restriction. Since reduction in energy intake has also been shown to decrease age-related kidney disease in rodents, we hypothesized that a diminution in SIRT1 activity would accelerate the GFR decline and structural injury with age. To test this hypothesis, we compared changes in the kidney structure and function in control mice and mice that carry a point mutation at a conserved histidine (H355Y) of SIRT1 that renders the enzyme catalytically inactive. Taking advantage of this mouse model along with the disector/fractionator technique for glomerular counting and direct measurements of GFR by inulin clearance, we assessed the impact of SIRT1 inactivity on kidney aging. At 14 months of age, SIRT1 catalytically inactive (Sirt1Y/Y ) mice had lower GFRs and fewer glomeruli than their wild-type (Sirt1+/+ ) counterparts. This was not, however, due to either accelerated GFR decline or increased glomerulosclerosis and loss, but rather to reduced glomerular endowment in Sirt1Y/Y mice. Moreover, the compensatory glomerular hypertrophy and elevated single nephron GFR that customarily accompany reduction in nephron number were absent in Sirt1Y/Y mice. These findings suggest a role for SIRT1 not only in determining nephron endowment but also in orchestrating the response to it.

Chemical Screening Approaches Enabling Drug Discovery of Autophagy Modulators for Biomedical Applications in Human Diseases

Autophagy is an intracellular degradation pathway for malfunctioning aggregation-prone proteins, damaged organelles, unwanted macromolecules and invading pathogens. This process is essential for maintaining cellular and tissue homeostasis that contribute to organismal survival. Autophagy dysfunction has been implicated in the pathogenesis of diverse human diseases, and therefore, therapeutic exploitation of autophagy is of potential biomedical relevance. A number of chemical screening approaches have been established for the drug discovery of autophagy modulators based on the perturbations of autophagy reporters or the clearance of autophagy substrates. These readouts can be detected by fluorescence and high-content microscopy, flow cytometry, microplate reader and immunoblotting, and the assays have evolved to enable high-throughput screening and measurement of autophagic flux. Several pharmacological modulators of autophagy have been identified that act either via the classical mechanistic target of rapamycin (mTOR) pathway or independently of mTOR. Many of these autophagy modulators have been demonstrated to exert beneficial effects in transgenic models of neurodegenerative disorders, cancer, infectious diseases, liver diseases, myopathies as well as in lifespan extension. This review describes the commonly used chemical screening approaches in mammalian cells and the key autophagy modulators identified through these methods, and highlights the therapeutic benefits of these compounds in specific disease contexts.

Drugs targeting SIRT1, a new generation of therapeutics for osteoporosis and other bone related disorders?

With an aging population and limited treatment options, osteoporosis currently represents a significant public health challenge. Recent animal studies indicate that longevity-associated SIRT1 may serve as an attractive pharmacological target for the treatment of osteoporosis and other bone related disorders. Pre-clinical studies demonstrate that mice treated with SIRT1 agonists show protection against age-related, post-menopausal, and disuse models of osteoporosis. Conversely, SIRT1 knockout models display low bone mass phenotypes associated with increased bone resorption and decreased bone formation. This review summarizes recent animal and human experimental data showing that pharmacological activation of SIRT1 may act in a manner that current treatments do not, namely by treating the imbalance in bone remodeling that is the root cause of osteoporosis and other bone disorders.

Dietary ursolic acid improves health span and life span in male Drosophila melanogaster

The health and life span of Drosophila melanogaster are partly determined by intestinal barrier integrity, metabolic rate as well as stress response and the expression of longevity-associated genes, depending on genetic and dietary factors. Ursolic acid (UA) is a naturally occurring triterpenoid exhibiting potential antimicrobial, anti-inflammatory, and antiobesity activity and counteracting age-related deficits in muscle strength. In this study, UA was dietarily administered to w1118 D. melanogaster which significantly elongated the health and life span of males. Spargel (srl) is the Drosophila orthologue of mammalian peroxisome proliferator-activated receptor-gamma coactivator 1 α(PGC1α), an important regulator of energy homeostasis and mitochondrial function. Our results indicate that the health-promoting effect of UA, demonstrated by a significant increase in climbing activity, occurs via an upregulation of srl expression leading to a metabolic shift in the fly without reducing fecundity or gut integrity. Moreover, UA affected the flies' microbiota in a manner that contributed to life span extension. Srl expression and microbiota both seem to be affected by UA, as we determined by using srl-mutant and axenic flies. © 2018 BioFactors, 45(2):169-186, 2019.

Modulating SIRT1 activity variously affects thymic lymphoma development in mice

SIRT1 is a protein deacetylase with a broad range of biological functions, many of which are known to be important in carcinogenesis, however much of the literature regarding the role of SIRT1 in cancer remains conflicting. In this study we assessed the effect of SIRT1 on the initiation and progression of thymic T cell lymphomas. We employed mouse strains in which SIRT1 activity was absent or could be reversibly modulated in conjunction with thymic lymphoma induction using either the N-nitroso-N-methylurea (NMU) carcinogenesis or the nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) transgene. Decreased SIRT1 activity reduced the development of thymic lymphomas in the NMU-treated mice but was permissive for the formation of lung adenomas. Conversely, in the NPM-ALK transgenic mice, decreased SIRT1 activity had a modest promoting effect in the development of thymic lymphomas. The results of the work presented here add to the growing body of evidence that sirt1 is neither an outright oncogene nor a tumor suppressor. These opposing results in two models of the same disease suggest that the influence of sirt1 on carcinogenesis may lie in a role in tumor surveillance.

NMJ maintenance and repair in aging

As the final output of the somatic nervous system, the neuromuscular junction (NMJ) is essential for all voluntary movements. The NMJ is also necessary for connected cells to function and survive. Because of this central role, much effort has been devoted to understanding the effects of aging, diseases, and injuries on the NMJ. These efforts have revealed a close relationship between aberrant changes at NMJs and its three cellular components - the presynaptic site on motor axons, the postsynaptic region on muscle fibers and perisynaptic Schwann cells. Here, we review the morphological and molecular changes associated with aging NMJs in rodents and humans. We also provide an overview of factors with potential roles in maintaining and repairing adult and aged NMJs.

Disruption of the beclin 1-BCL2 autophagy regulatory complex promotes longevity in mice

Autophagy increases the lifespan of model organisms; however, its role in promoting mammalian longevity is less well-established1,2. Here we report lifespan and healthspan extension in a mouse model with increased basal autophagy. To determine the effects of constitutively increased autophagy on mammalian health, we generated targeted mutant mice with a Phe121Ala mutation in beclin 1 (Becn1F121A/F121A) that decreases its interaction with the negative regulator BCL2. We demonstrate that the interaction between beclin 1 and BCL2 is disrupted in several tissues in Becn1 F121A/F121A knock-in mice in association with higher levels of basal autophagic flux. Compared to wild-type littermates, the lifespan of both male and female knock-in mice is significantly increased. The healthspan of the knock-in mice also improves, as phenotypes such as age-related renal and cardiac pathological changes and spontaneous tumorigenesis are diminished. Moreover, mice deficient in the anti-ageing protein klotho 3 have increased beclin 1 and BCL2 interaction and decreased autophagy. These phenotypes, along with premature lethality and infertility, are rescued by the beclin 1(F121A) mutation. Together, our data demonstrate that disruption of the beclin 1-BCL2 complex is an effective mechanism to increase autophagy, prevent premature ageing, improve healthspan and promote longevity in mammals.

The variable role of SIRT1 in the maintenance and differentiation of mesenchymal stem cells

SIRT1 is an NAD+-dependent deacetylase that acts as a nutrient sensitive regulator of longevity. SIRT1 also acts as a key regulator of mesenchymal stem cells (MSCs), adult stem cells that give rise to tissues such as bone, fat, muscle and cartilage. This review focuses on how SIRT1 regulates the self-renewal, multipotency and differentiation of MSCs. The variable role of SIRT1 in promoting the differentiation of MSCs towards certain lineages, while repressing others, will be examined within the broader context of aging, calorie restriction, and regenerative medicine. Finally, recent animal and human studies will be highlighted which paint an overall salutary role for SIRT1 in protecting MSCs (and resulting tissues) from age-related atrophy and dysfunction.

Dietary Restriction and Glycolytic Inhibition Reduce Proteotoxicity and Extend Lifespan via NHR-49

Mechanisms mediating protective effects of dietary restriction during aging are of great interest since activating such mechanisms protect against a wide range of age-related diseases. In mammals key metabolic responses to nutritional deprivation are mediated by the transcription factor PPAR-alpha, which is activated by free fatty acids and promotes lipid metabolism while inhibiting glucose metabolism. The C. elegans gene nhr-49 appears to function similarly in C. elegans. Here we report that protective effects of dietary restriction and inhibition of glucose metabolism to increase lifespan wild-type C. elegans and reduce toxicity in a polyQ model of Huntington's disease in C. elegans are dependent on NHR-49 and its co-activator CREB-Binding Protein (CBP). We have previously demonstrated that inhibition of cbp blocks protective effects of dietary restriction and blocks the molecular switch from glucose metabolism to alternative substrates. Conversely, increased glucose concentration and inhibition of cbp reduce lifespan and increase proteotoxicity. Lactate and inhibition of ETC complex II mimicked toxic effects of glucose on proteotoxicity whereas pyruvate and inhibition of ETC complex I protected against glucose-enhanced proteotoxicity. These results support that PPAR-alpha-like activity mediates protective effects of dietary restriction by reducing glucose metabolism via reducing production of NADH, and corroborate and extend recent studies demonstrating that PPPAR-alpha agonists increase lifespan in C. elegans dependent on NHR-49.

A ternary complex model of Sirtuin4-NAD+-Glutamate dehydrogenase

Sirtuin4 (Sirt4) is one of the mammalian homologues of Silent information regulator 2 (Sir2), which promotes the longevity of yeast, C. elegans, fruit flies and mice. Sirt4 is localized in the mitochondria, where it contributes to preventing the development of cancers and ischemic heart disease through regulating energy metabolism. The ADP-ribosylation of glutamate dehydrogenase (GDH), which is catalyzed by Sirt4, downregulates the TCA cycle. However, this reaction mechanism is obscure, because the structure of Sirt4 is unknown. We here constructed structural models of Sirt4 by homology modeling and threading, and docked nicotinamide adenine dinucleotide⁺ (NAD⁺) to Sirt4. In addition, a partial GDH structure was docked to the Sirt4-NAD⁺ complex model. In the ternary complex model of Sirt4-NAD⁺-GDH, the acetylated lysine 171 of GDH is located close to NAD⁺. This suggests a possible mechanism underlying the ADP-ribosylation at cysteine 172, which may occur through a transient intermediate with ADP-ribosylation at the acetylated lysine 171. These results may be useful in designing drugs for the treatment of cancers and ischemic heart disease.

Metabolic Aspects of Aging

Metabolic interventions involving undernutrition but not malnutrition (e.g., caloric restriction, CR) are effective strategies for improving both health and longevity in species ranging from lower organisms to nonhuman primates. Initial human trials to test the effects of sustained, reduced energy intake have yielded promising health benefits. Through intense research efforts in understanding the molecular mechanisms of CR, three cellular pathways have now been identified although the precise details remain unknown. More recently, circadian regulation has been recognized as a novel mediator for CR effects in mice. Harnessing the molecular insights into CR, novel nutritional interventions and pharmacological application of CR mimetics have been tested showing great promise in simultaneously improving metabolic function and providing overall health benefits. Additional research is needed to identify efficacious therapeutics that can be safely and practically translated to human studies in promoting healthspan.

High Levels of SIRT1 Expression as a Protective Mechanism Against Disease-Related Conditions

SIRT1 protein, a member of Silent Information Regulator 2 (Sir2) protein family, have gained considerable attention as epigenetic regulators for a great area in the human physiology. Changes in sirtuin expression are critical in several diseases, including metabolic syndrome, cardiovascular diseases, cancer and neurodegeneration. Here, we provide an overview of the association of the increasing level of SIRT1 protein for regulating some disease related conditions such as obesity, cardiovascular diseases and neurodegeneration. This review also provides a detailed molecular understanding of the interaction of the some basic molecules with increasing SIRT1 levels rather than reduction of the SIRT1 expression. In this context, the current approaches to enhancing the expression of SIRT1 points the importance of epigenetics in several age-related diseases to provide a healthy aging by developing novel therapies which can prevent or damp the progression of some diseases.

SIRT1 is a positive regulator of in vivo bone mass and a therapeutic target for osteoporosis

Overexpression or pharmacological activation of SIRT1 has been shown to extend the lifespan of mice and protect against aging-related diseases. Here we show that pharmacological activation of SIRT1 protects in two models of osteoporosis. Ovariectomized female mice and aged male mice, models for post-menopausal and aging-related osteoporosis, respectively, show significant improvements in bone mass upon treatment with SIRT1 agonist, SRT1720. Further, we find that calorie restriction (CR) results in a two-fold upregulation of sirt1 mRNA expression in bone tissue that is associated with increased bone mass in CR mice. Reciprocally, SIRT1 whole-body knockout (KO) mice, as well as osteoblast and osteoclast specific KOs, show a low bone mass phenotype; though double knockout mice (containing SIRT1 deleted in both osteoblasts and osteoclasts) do not show a more severe phenotype. Altogether, these findings provide strong evidence that SIRT1 is a positive regulator of bone mass and a promising target for the development of novel therapeutics for osteoporosis.

Identification of tissue-specific transcriptional markers of caloric restriction in the mouse and their use to evaluate caloric restriction mimetics

Caloric restriction (CR) without malnutrition has been shown to retard several aspects of the aging process and to extend lifespan in different species. There is strong interest in the identification of CR mimetics (CRMs), compounds that mimic the beneficial effects of CR on lifespan and healthspan without restriction of energy intake. Identification of CRMs in mammals is currently inefficient due to the lack of screening tools. We have performed whole‐genome transcriptional profiling of CR in seven mouse strains (C3H/HeJ, CBA/J, DBA/2J, B6C3F1/J, 129S1/SvImJ, C57BL/6J, and BALB/cJ) in white adipose tissue (WAT), gastrocnemius muscle, heart, and brain neocortex. This analysis has identified tissue‐specific panels of genes that change in expression in multiple mouse strains with CR. We validated a subset of genes with qPCR and used these to evaluate the potential CRMs bezafibrate, pioglitazone, metformin, resveratrol, quercetin, 2,4‐dinitrophenol, and L‐carnitine when fed to C57BL/6J 2‐month‐old mice for 3 months. Compounds were also evaluated for their ability to modulate previously characterized biomarkers of CR, including mitochondrial enzymes citrate synthase and SIRT3, plasma inflammatory cytokines TNF‐α and IFN‐γ, glycated hemoglobin (HbA1c) levels and adipocyte size. Pioglitazone, a PPAR‐γ agonist, and L‐carnitine, an amino acid involved in lipid metabolism, displayed the strongest effects on both the novel transcriptional markers of CR and the additional CR biomarkers tested. Our findings provide panels of tissue‐specific transcriptional markers of CR that can be used to identify novel CRMs, and also represent the first comparative molecular analysis of several potential CRMs in multiple tissues in mammals.

SIRT1 ameliorates oxidative stress induced neural cell death and is down-regulated in Parkinson's disease

Background

Sirtuins (SIRTs) are NAD⁺ dependent lysine deacetylases which are conserved from bacteria to humans and have been associated with longevity and lifespan extension. SIRT1, the best studied mammalian SIRT is involved in many physiological and pathological processes and changes in SIRT1 have been implicated in neurodegenerative disorders, with SIRT1 having a suggested protective role in Parkinson’s disease. In this study, we determined the effect of SIRT1 on cell survival and α-synuclein aggregate formation in SH-SY5Y cells following oxidative stress.

Results

Over-expression of SIRT1 protected SH-SY5Y cells from toxin induced cell death and the protection conferred by SIRT1 was partially independent of its deacetylase activity, which was associated with the repression of NF-кB and cPARP expression. SIRT1 reduced the formation of α-synuclein aggregates but showed minimal co-localisation with α-synuclein. In post-mortem brain tissue obtained from patients with Parkinson’s disease, Parkinson’s disease with dementia, dementia with Lewy bodies and Alzheimer’s disease, the activity of SIRT1 was observed to be down-regulated.

Conclusions

These findings suggests a negative effect of oxidative stress in neurodegenerative disorders and possibly explain the reduced activity of SIRT1 in neurodegenerative disorders. Our study shows that SIRT1 is a pro-survival protein that is downregulated under cellular stress.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-017-0364-1) contains supplementary material, which is available to authorized users.

[Autophagy, fitness and longevity]

Autophagy is a key mechanism for the maintenance of intracellular and organismal homeostasis. Accordingly, defects in core components of the autophagic machinery are etiologically associated with a variety of human pathologies, including infectious disorders, cardiovascular diseases, neurodegenerative conditions, and cancer. Intriguingly, several maneuvers that increase the lifespan of model organisms in the laboratory, like caloric restriction, do so in an autophagy-dependent manner. Here, we briefly discuss the intimate relationship between the autophagic preservation of intracellular and organismal fitness and healthy aging.

The age-associated loss of ischemic preconditioning in the kidney is accompanied by mitochondrial dysfunction, increased protein acetylation and decreased autophagy

In young rats, ischemic preconditioning (IPC), which consists of 4 cycles of ischemia and reperfusion alleviated kidney injury caused by 40-min ischemia. However,old rats lost their ability to protect the ischemic kidney by IPC. A similar aged phenotype was demonstrated in 6-month-old OXYS rats having signs of premature aging. In the kidney of old and OXYS rats, the levels of acetylated nuclear proteins were higher than in young rats, however, unlike in young rats, acetylation levels in old and OXYS rats were further increased after IPC. In contrast to Wistar rats, age-matched OXYS demonstrated no increase in lysosome abundance and LC3 content in the kidney after ischemia/reperfusion. The kidney LC3 levels were also lower in OXYS, even under basal conditions, and mitochondrial PINK1 and ubiquitin levels were higher, suggesting impaired mitophagy. The kidney mitochondria from old rats contained a population with diminished membrane potential and this fraction was expanded by IPC. Apparently, oxidative changes with aging result in the appearance of malfunctioning renal mitochondria due to a low efficiency of autophagy. Elevated protein acetylation might be a hallmark of aging which is associated with a decreased autophagy, accumulation of dysfunctional mitochondria, and loss of protection against ischemia by IPC.

Reversible modulation of SIRT1 activity in a mouse strain

The SIRT1 protein deacetylase is reported to have a remarkably wide spectrum of biological functions affecting such varied processes as aging, cancer, metabolism, neurodegeneration and immunity. However, the SIRT1 literature is also full of contradictions. To help establish the role(s) of SIRT1 in these and other biological processes, we set out to create a mouse in which the SIRT1 activity could be toggled between on and off states by fusing the estrogen receptor ligand-binding domain (ER) to the C terminus of the SIRT1 protein. We found that the catalytic activity of the SIRT1-ER fusion protein increased 4–5 fold in cells treated with its ligand, 4-hydroxy-tamoxifen (4OHT). The 4OHT-induced activation of SIRT1-ER was due in large part to a 2 to 4-fold increase in abundance of the SIRT1-ER protein in cells in culture and in tissues in vivo. This increase is reversible and is a consequence of 4OHT-induced stabilization of the SIRT1-ER protein. Since changes in SIRT1 level or activity of 2–4 fold are frequently reported to be sufficient to affect its biological functions, this mouse should be helpful in establishing the causal relationships between SIRT1 and the diseases and processes it affects.

Caloric restriction reduces the systemic progression of mouse AApoAII amyloidosis

In mouse senile amyloidosis, apolipoprotein (Apo) A-II is deposited extracellularly in many organs in the form of amyloid fibrils (AApoAII). Reduction of caloric intake, known as caloric restriction (CR), slows the progress of senescence and age-related disorders in mice. In this study, we intravenously injected 1 μg of isolated AApoAII fibrils into R1.P1-Apoa2c mice to induce experimental amyloidosis and investigated the effects of CR for the next 16 weeks. In the CR group, AApoAII amyloid deposits in the liver, tongue, small intestine and skin were significantly reduced compared to those of the ad libitum feeding group. CR treatment led to obvious reduction in body weight, improvement in glucose metabolism and reduction in the plasma concentration of ApoA-II. Our molecular biological analyses of the liver suggested that CR treatment might improve the symptoms of inflammation, the unfolded protein response induced by amyloid deposits and oxidative stress. Furthermore, we suggest that CR treatment might improve mitochondrial functions via the sirtuin 1-peroxisome proliferator-activated receptor γ coactivator 1α (SIRT1-PGC-1α) pathway. We suggest that CR is a promising approach for treating the onset and/or progression of amyloidosis, especially for systemic amyloidosis such as senile AApoAII amyloidosis. Our analysis of CR treatment for amyloidosis should provide useful information for determining the cause of amyloidosis and developing effective preventive treatments.