The sirtuin-2 inhibitor AK7 is neuroprotective in models of Parkinson's disease but not amyotrophic lateral sclerosis and cerebral ischemia

Acetylation of c-Myc at Lysine 148 Protects Neurons After Ischemia

This study focuses on understanding the role of c-Myc, a cancer-associated transcription factor, in the penumbra following ischemic stroke. While its involvement in cell death and survival is recognized, its post-translational modifications, particularly acetylation, remain understudied in ischemia models. Investigating these modifications could have significant clinical implications for controlling c-Myc activity in the central nervous system. Although previous studies on c-Myc acetylation have been limited to non-neuronal cells, our research examines its expression in perifocal cells during stroke recovery to explore regulatory mechanisms via acetylation. We found that in peri-infarct neurons, c-Myc is upregulated with acetylation at K148 but not K323 during the acute phase of stroke, with SIRT2 deacetylase primarily affecting K148 acetylation. Molecular dynamics simulations suggest that lysine 148 plays a crucial role in stabilizing c-Myc spatial structure. Increased acetylation at K148 reduces c-Myc compaction, potentially limiting its nuclear penetration, promoting calpain-mediated cleavage, and decreasing nuclear localization. Additionally, cytoplasmic acetylation at K148 may alter c-Myc's interaction with unidentified proteins, potentially influencing its pro-apoptotic effects and promoting cytoplasmic accumulation. Targeting SIRT2 with selective inhibitors could be a promising avenue for future stroke therapy strategies.

Current Trends in Sirtuin Activator and Inhibitor Development

Sirtuins are NAD+-dependent protein deacylases and key metabolic regulators, coupling the cellular energy state with selective lysine deacylation to regulate many downstream cellular processes. Humans encode seven sirtuin isoforms (Sirt1-7) with diverse subcellular localization and deacylase targets. Sirtuins are considered protective anti-aging proteins since increased sirtuin activity is canonically associated with lifespan extension and decreased activity with developing aging-related diseases. However, sirtuins can also assume detrimental cellular roles where increased activity contributes to pathophysiology. Modulation of sirtuin activity by activators and inhibitors thus holds substantial potential for defining the cellular roles of sirtuins in health and disease and developing therapeutics. Instead of being comprehensive, this review discusses the well-characterized sirtuin activators and inhibitors available to date, particularly those with demonstrated selectivity, potency, and cellular activity. This review also provides recommendations regarding the best-in-class sirtuin activators and inhibitors for practical research as sirtuin modulator discovery and refinement evolve.

Age-Associated Changes of Sirtuin 2 Expression in CNS and the Periphery

Sirtuin 2 (SIRT2), one of the seven members of the sirtuin family, has emerged as a potential regulator of aging and age-related pathologies since several studies have demonstrated that it shows age-related changes in humans and different animal models. A detailed analysis of the relevant works published to date addressing this topic shows that the changes that occur in SIRT2 with aging seem to be opposite in the brain and in the periphery. On the one hand, aging induces an increase in SIRT2 levels in the brain, which supports the notion that its pharmacological inhibition is beneficial in different neurodegenerative diseases. However, on the other hand, in the periphery, SIRT2 levels are reduced with aging while keeping its expression is protective against age-related peripheral inflammation, insulin resistance, and cardiovascular diseases. Thus, systemic administration of any known modulator of this enzyme would have conflicting outcomes. This review summarizes the currently available information on changes in SIRT2 expression in aging and the underlying mechanisms affected, with the aim of providing evidence to determine whether its pharmacological modulation could be an effective and safe pharmacological strategy for the treatment of age-related diseases.

Cooperative effects of SIRT1 and SIRT2 on APP acetylation

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by amyloid-β (Aβ) deposition and neurofibrillary tangles. Although the NAD+ -dependent deacetylases SIRT1 and SIRT2 play pivotal roles in age-related diseases, their cooperative effects in AD have not yet been elucidated. Here, we report that the SIRT2:SIRT1 ratio is elevated in the brains of aging mice and in the AD mouse models. In HT22 mouse hippocampal neuronal cells, Aβ challenge correlates with decreased SIRT1 expression, while SIRT2 expression is increased. Overexpression of SIRT1 prevents Aβ-induced neurotoxicity. We find that SIRT1 impedes SIRT2-mediated APP deacetylation by inhibiting the binding of SIRT2 to APP. Deletion of SIRT1 reduces APP recycling back to the cell surface and promotes APP transiting toward the endosome, thus contributing to the amyloidogenic processing of APP. Our findings define a mechanism for neuroprotection by SIRT1 through suppression of SIRT2 deacetylation, and provide a promising avenue for therapeutic intervention of AD.

Elevated SIRT2 of serum exosomes is positively correlated with diagnosis of acute ischemic stroke patients

BACKGROUND

Silent Information Regulator 2 (SIRT2) protein inhibition has been shown to play a neuroprotective role in acute ischemic stroke (AIS) in mice. However, its role in AIS patients has not been fully understood. In this study, we aimed to analyze SIRT2 protein expression in serum exosomes of AIS and non-AIS patients, and evaluate its potential role in diagnosis and prognosis of AIS.

METHODS

Serum exosomes from 75 non-AIS subjects and 75 AIS patients were isolated. The SIRT2 protein levels in exosomes were analyzed using enzyme linked immunosorbent assay (ELISA). The National Institutes of Health Stroke Scale (NIHSS) was used to evaluate the severity of the disease. The modified Rankin Scale (mRS) was employed to assess the functional outcomes of the patients at 3-months following stroke onset.

RESULTS

The SIRT2 protein concentration of serum exosomes were higher in AIS patients than non-AIS patients (p < 0.001). Furthermore, the receiver operative characteristic curve (ROC) demonstrated that higher serum exosome SIRT2 could differentiate AIS patients from non-AIS patients with a sensitivity of 81.3% and a specificity of 75.3%. The area under the curve was 0.838 (95% CI: 0.775, 0.902). Additionally, higher SIRT2 concentration of serum exosomes were associated with NIHSS ≥ 4 (p < 0.001) and mRS ≥ 3 (p = 0.025) in AIS patients. The ROC analysis showed SIRT2 could discriminate stroke with NIHSS ≥ 4 from mild stroke (NIHSS < 4) with a sensitivity of 75.0% and a specificity of 69.6%. The area under the curve was 0.771 (95% CI: 0.661,0.881). Similarly, the test showed SIRT2 could differentiate between AIS patients with mRS ≥ 3 from those with mRS < 3 with a sensitivity of 78.3% and a specificity of 51.9%. The area under the curve was 0.663 (95% CI: 0.531,0.796). The logistic regression analysis revealed that SIRT2 concentration in serum exosomes can independently predict the diagnosis of AIS (odd ratio = 1.394, 95%CI 1.231-1.577, p < 0.001) and higher NIHSS scores (≥ 4) (odd ratio = 1.258, 95%CI 1.084-1.460, p = 0.002). However, it could not independently predict the prognosis of AIS (odd ratio = 1.065, 95%CI 0.983-1.154, p = 0.125).

CONCLUSION

The elevation of SIRT2 in serum exosomes may be a valuable biomarker of AIS, which may be a potential diagnostic tool to facilitate decision making for AIS patients.

Microtubule acetylation dyshomeostasis in Parkinson's disease

The inter-neuronal communication occurring in extensively branched neuronal cells is achieved primarily through the microtubule (MT)-mediated axonal transport system. This mechanistically regulated system delivers cargos (proteins, mRNAs and organelles such as mitochondria) back and forth from the soma to the synapse. Motor proteins like kinesins and dynein mechanistically regulate polarized anterograde (from the soma to the synapse) and retrograde (from the synapse to the soma) commute of the cargos, respectively. Proficient axonal transport of such cargos is achieved by altering the microtubule stability via post-translational modifications (PTMs) of α- and β-tubulin heterodimers, core components constructing the MTs. Occurring within the lumen of MTs, K40 acetylation of α-tubulin via α-tubulin acetyl transferase and its subsequent deacetylation by HDAC6 and SIRT2 are widely scrutinized PTMs that make the MTs highly flexible, which in turn promotes their lifespan. The movement of various motor proteins, including kinesin-1 (responsible for axonal mitochondrial commute), is enhanced by this PTM, and dyshomeostasis of neuronal MT acetylation has been observed in a variety of neurodegenerative conditions, including Alzheimer's disease and Parkinson's disease (PD). PD is the second most common neurodegenerative condition and is closely associated with impaired MT dynamics and deregulated tubulin acetylation levels. Although the relationship between status of MT acetylation and progression of PD pathogenesis has become a chicken-and-egg question, our review aims to provide insights into the MT-mediated axonal commute of mitochondria and dyshomeostasis of MT acetylation in PD. The enzymatic regulators of MT acetylation along with their synthetic modulators have also been briefly explored. Moving towards a tubulin-based therapy that enhances MT acetylation could serve as a disease-modifying treatment in neurological conditions that lack it.

SIRT2 plays complex roles in neuroinflammation neuroimmunology-associated disorders

Neuroinflammation and neuroimmunology-associated disorders, including ischemic stroke and neurodegenerative disease, commonly cause severe neurologic function deficits, including bradypragia, hemiplegia, aphasia, and cognitive impairment, and the pathological mechanism is not completely clear. SIRT2, an NAD⁺-dependent deacetylase predominantly localized in the cytoplasm, was proven to play an important and paradoxical role in regulating ischemic stroke and neurodegenerative disease. This review summarizes the comprehensive mechanism of the crucial pathological functions of SIRT2 in apoptosis, necroptosis, autophagy, neuroinflammation, and immune response. Elaborating on the mechanism by which SIRT2 participates in neuroinflammation and neuroimmunology-associated disorders is beneficial to discover novel effective drugs for diseases, varying from vascular disorders to neurodegenerative diseases.

Mass Spectrometry based identification of site-specific proteomic alterations and potential pathways underlying the pathophysiology of schizophrenia

BACKGROUND

Schizophrenia (SZ) is a complex multifactorial disorder that affects 1% of the population worldwide with no available effective treatment. Although proteomic alterations are reported in SZ however proteomic expression aberrations among different brain regions are not fully determined. Therefore, the present study aimed spatial differential protein expression profiling of three distinct regions of SZ brain and identification of associated affected biological pathways in SZ progression.

METHODS AND RESULTS

Comparative protein expression profiling of three distinct autopsied human brain regions (i.e., substantia nigra, hippocampus and prefrontal cortex) of SZ was performed with respective healthy controls. Using two-dimensional electrophoresis (2DE)-based nano liquid chromatography tandem mass spectrometry (Nano-LC MS /MS) analysis, 1443 proteins were identified out of which 58 connote to be significantly dysregulated, representing 26 of substantia nigra,14 of hippocampus and 18 of prefrontal cortex. The 58 differentially expressed proteins were further analyzed using Ingenuity pathway analysis (IPA). The IPA analysis provided protein-protein interaction networks of several proteins including nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kb), extracellular signal regulated kinases 1/2 (ERK1/2), alpha serine / Threonine-protein kinase (AKT1), cellular tumor antigen p53 (TP53) and amyloid precursor protein (APP), holding prime positions in networks and interacts with most of the identified proteins and their closely interacting partners.

CONCLUSION

These findings provide conceptual insights of novel SZ related pathways and the cross talk of co and contra regulated proteins. This spatial proteomic analysis will further broaden the conceptual framework for schizophrenia research in future.

Effect of the Ketone Body, D-β-Hydroxybutyrate, on Sirtuin2-Mediated Regulation of Mitochondrial Quality Control and the Autophagy-Lysosomal Pathway

Mitochondrial activity and quality control are essential for neuronal homeostasis as neurons rely on glucose oxidative metabolism. The ketone body, D-β-hydroxybutyrate (D-BHB), is metabolized to acetyl-CoA in brain mitochondria and used as an energy fuel alternative to glucose. We have previously reported that D-BHB sustains ATP production and stimulates the autophagic flux under glucose deprivation in neurons; however, the effects of D-BHB on mitochondrial turnover under physiological conditions are still unknown. Sirtuins (SIRTs) are NAD⁺-activated protein deacetylases involved in the regulation of mitochondrial biogenesis and mitophagy through the activation of transcription factors FOXO1, FOXO3a, TFEB and PGC1α coactivator. Here, we aimed to investigate the effect of D-BHB on mitochondrial turnover in cultured neurons and the mechanisms involved. Results show that D-BHB increased mitochondrial membrane potential and regulated the NAD⁺/NADH ratio. D-BHB enhanced FOXO1, FOXO3a and PGC1α nuclear levels in an SIRT2-dependent manner and stimulated autophagy, mitophagy and mitochondrial biogenesis. These effects increased neuronal resistance to energy stress. D-BHB also stimulated the autophagic-lysosomal pathway through AMPK activation and TFEB-mediated lysosomal biogenesis. Upregulation of SIRT2, FOXOs, PGC1α and TFEB was confirmed in the brain of ketogenic diet (KD)-treated mice. Altogether, the results identify SIRT2, for the first time, as a target of D-BHB in neurons, which is involved in the regulation of autophagy/mitophagy and mitochondrial quality control.

SIRT2-PFKP interaction dysregulates phagocytosis in macrophages with acute ethanol-exposure

Alcohol abuse, reported by 1/8th critically ill patients, is an independent risk factor for death in sepsis. Sepsis kills over 270,000 patients/year in the US. We reported that the ethanol-exposure suppresses innate-immune response, pathogen clearance, and decreases survival in sepsis-mice via sirtuin 2 (SIRT2). SIRT2 is an NAD+-dependent histone-deacetylase with anti-inflammatory properties. We hypothesized that in ethanol-exposed macrophages, SIRT2 suppresses phagocytosis and pathogen clearance by regulating glycolysis. Immune cells use glycolysis to fuel increased metabolic and energy demand of phagocytosis. Using ethanol-exposed mouse bone marrow- and human blood monocyte-derived macrophages, we found that SIRT2 mutes glycolysis via deacetylating key glycolysis regulating enzyme phosphofructokinase-platelet isoform (PFKP), at mouse lysine 394 (mK394, human: hK395). Acetylation of PFKP at mK394 (hK395) is crucial for PFKP function as a glycolysis regulating enzyme. The PFKP also facilitates phosphorylation and activation of autophagy related protein 4B (Atg4B). Atg4B activates microtubule associated protein 1 light chain-3B (LC3). LC3 is a driver of a subset of phagocytosis, the LC3-associated phagocytosis (LAP), which is crucial for segregation and enhanced clearance of pathogens, in sepsis. We found that in ethanol-exposed cells, the SIRT2-PFKP interaction leads to decreased Atg4B-phosphorylation, decreased LC3 activation, repressed phagocytosis and LAP. Genetic deficiency or pharmacological inhibition of SIRT2 reverse PFKP-deacetylation, suppressed LC3-activation and phagocytosis including LAP, in ethanol-exposed macrophages to improve bacterial clearance and survival in ethanol with sepsis mice.

The Sirtuin 2 Inhibitor AK-7 Leads to an Antidepressant-Like Effect in Mice via Upregulation of CREB1, BDNF, and NTRK2 Pathways

Depression is one of the most important and serious health problems in developing countries which affects millions of people. It is associated with the decrease of the quality of life as well as suicides and mortality. The disease may show recurrent episodes in some patients. Obviously, not all the patients with depression could be treated properly, because some individuals are drug-resistant and the options for the therapy are limited. Therefore, it is crucial to investigate new molecules and pathways that may have possible antidepressant activity. Sirtuin (SIRT), known as a class III histone deacetylase, which is regulated by nicotinamide adenine dinucleotide (NAD +), is one of these molecules. In the current study, we investigated the possible antidepressant-like effect of SIRT2 inhibitor AK-7. For this purpose, behavioral tests were performed in chronic AK-7-treated mice, and the expression levels of BDNF, NGF, NTF3, CREB, NTRK2, ERK1, ERK2, and GAP43 genes were evaluated by qRT-PCR analysis in brain tissues. Protein levels for BDNF, CREB1, and NTRK2 were determined by western blot. Our data showed that AK-7 significantly decreased immobility time and showed antidepressant-like effect. In addition, AK-7 treatment significantly increased mRNA levels of CREB and NTRK2 and protein levels of CREB1, BDNF, and NTRK2. Finally, our results suggest that SIRT2 and AK-7 may have a potential role in the cellular mechanisms of depression.

Mitochondrial dysfunction is a key pathological driver of early stage Parkinson's

BACKGROUND

The molecular drivers of early sporadic Parkinson's disease (PD) remain unclear, and the presence of widespread end stage pathology in late disease masks the distinction between primary or causal disease-specific events and late secondary consequences in stressed or dying cells. However, early and mid-stage Parkinson's brains (Braak stages 3 and 4) exhibit alpha-synuclein inclusions and neuronal loss along a regional gradient of severity, from unaffected-mild-moderate-severe. Here, we exploited this spatial pathological gradient to investigate the molecular drivers of sporadic PD.

METHODS

We combined high precision tissue sampling with unbiased large-scale profiling of protein expression across 9 brain regions in Braak stage 3 and 4 PD brains, and controls, and verified these results using targeted proteomic and functional analyses.

RESULTS

We demonstrate that the spatio-temporal pathology gradient in early-mid PD brains is mirrored by a biochemical gradient of a changing proteome. Importantly, we identify two key events that occur early in the disease, prior to the occurrence of alpha-synuclein inclusions and neuronal loss: (i) a metabolic switch in the utilisation of energy substrates and energy production in the brain, and (ii) perturbation of the mitochondrial redox state. These changes may contribute to the regional vulnerability of developing alpha-synuclein pathology. Later in the disease, mitochondrial function is affected more severely, whilst mitochondrial metabolism, fatty acid oxidation, and mitochondrial respiration are affected across all brain regions.

CONCLUSIONS

Our study provides an in-depth regional profile of the proteome at different stages of PD, and highlights that mitochondrial dysfunction is detectable prior to neuronal loss, and alpha-synuclein fibril deposition, suggesting that mitochondrial dysfunction is one of the key drivers of early disease.

Virtual Screening in the Identification of Sirtuins’ Activity Modulators

Sirtuins are NAD⁺-dependent deac(et)ylases with different subcellular localization. The sirtuins’ family is composed of seven members, named SIRT-1 to SIRT-7. Their substrates include histones and also an increasing number of different proteins. Sirtuins regulate a wide range of different processes, ranging from transcription to metabolism to genome stability. Thus, their dysregulation has been related to the pathogenesis of different diseases. In this review, we discussed the pharmacological approaches based on sirtuins’ modulators (both inhibitors and activators) that have been attempted in in vitro and/or in in vivo experimental settings, to highlight the therapeutic potential of targeting one/more specific sirtuin isoform(s) in cancer, neurodegenerative disorders and type 2 diabetes. Extensive research has already been performed to identify SIRT-1 and -2 modulators, while compounds targeting the other sirtuins have been less studied so far. Beside sections dedicated to each sirtuin, in the present review we also included sections dedicated to pan-sirtuins’ and to parasitic sirtuins’ modulators. A special focus is dedicated to the sirtuins’ modulators identified by the use of virtual screening.

Sirtuins functions in central nervous system cells under neurological disorders

The sirtuins (SIRTs), a class of NAD+ -dependent deacylases, contain seven SIRT family members in mammals, from SIRT1 to SIRT7. Extensive studies have revealed that SIRT proteins regulate virous cell functions. Central nervous system (CNS) decline resulted in progressive cognitive impairment, social and physical abilities dysfunction. Therefore, it is of vital importance to have a better understanding of potential target to promote homeostasis of CNS. SIRTs have merged as the underlying regulating factors of the process of neurological disorders. In this review, we profile multiple functions of SIRT proteins in different cells during brain function and under CNS injury.

Sirtuins promote brain homeostasis, preventing Alzheimer’s disease through targeting neuroinflammation

Both basic pathomechanisms underlying Alzheimer’s disease and some premises for stipulating a possible preventive role of some sirtuins, especially SIRT1 and SIRT3, protective against Alzheimer’s disease-related pathology, are discussed in this article. Sirtuins can inhibit some processes that underlie Alzheimer’s disease-related molecular pathology (e.g., neuroinflammation, neuroinflammation-related oxidative stress, Aβ aggregate deposition, and neurofibrillary tangle formation), thus preventing many of those pathologic alterations at relatively early stages of their development. Subsequently, the authors discuss in details which mechanisms of sirtuin action may prevent the development of Alzheimer’s disease, thus promoting brain homeostasis in the course of aging. In addition, a rationale for boosting sirtuin activity, both with allosteric activators and with NAD+ precursors, has been presented.

Inhibition of SIRT2 promotes APP acetylation and ameliorates cognitive impairment in APP/PS1 transgenic mice

Aging is a primary risk factor for neurodegenerative diseases, such as Alzheimer's disease (AD). SIRT2, an NAD⁺(nicotinamide adenine dinucleotide)-dependent deacetylase, accumulates in the aging brain. Here, we report that, in the amyloid precursor protein (APP)/PS1 transgenic mouse model of AD, genetic deletion of SIRT2 or pharmacological inhibition of SIRT2 ameliorates cognitive impairment. We find that suppression of SIRT2 enhances acetylation of APP, which promotes non-amyloidogenic processing of APP at the cell surface, leading to increased soluble APP-α (sAPPα). We discover that lysines 132 and 134 of the major pathogenic protein β-amyloid (Aβ) precursor are acetylated and that these residues are deacetylated by SIRT2. Strikingly, exogenous expression of wild-type or an acetylation-mimic APP mutant protects cultured primary neurons from Aβ42 challenge. Our study identifies SIRT2-mediated deacetylation of APP on K132 and K134 as a regulated post-translational modification (PTM) and suggests inhibition of SIRT2 as a potential therapeutic strategy for AD.

Histone Deacetylases as Epigenetic Targets for Treating Parkinson’s Disease

Parkinson’s disease (PD) is a chronic progressive neurodegenerative disease that is increasingly becoming a global threat to the health and life of the elderly worldwide. Although there are some drugs clinically available for treating PD, these treatments can only alleviate the symptoms of PD patients but cannot completely cure the disease. Therefore, exploring other potential mechanisms to develop more effective treatments that can modify the course of PD is still highly desirable. Over the last two decades, histone deacetylases, as an important group of epigenetic targets, have attracted much attention in drug discovery. This review focused on the current knowledge about histone deacetylases involved in PD pathophysiology and their inhibitors used in PD studies. Further perspectives related to small molecules that can inhibit or degrade histone deacetylases to treat PD were also discussed.

Regulation of Mitophagy by Sirtuin Family Proteins: A Vital Role in Aging and Age-Related Diseases

Sirtuins are protein factors that can delay aging and alleviate age-related diseases through multiple molecular pathways, mainly by promoting DNA damage repair, delaying telomere shortening, and mediating the longevity effect of caloric restriction. In the last decade, sirtuins have also been suggested to exert mitochondrial quality control by mediating mitophagy, which targets damaged mitochondria and delivers them to lysosomes for degradation. This is especially significant for age-related diseases because dysfunctional mitochondria accumulate in aging organisms. Accordingly, it has been suggested that sirtuins and mitophagy have many common and interactive aspects in the aging process. This article reviews the mechanisms and pathways of sirtuin family-mediated mitophagy and further discusses its role in aging and age-related diseases.

Sirtuins 1 and 2 in the Acute Period After Photothrombotic Stroke: Expression, Localization and Involvement in Apoptosis

Sirtuins (SIRTs) are NAD+- dependent histone deacetylases. They are involved in a variety of biological pathways and are thought to be a promising target for treating several human disorders. Although evidence is piling up to support the neuroprotective role of SIRTs in ischemic stroke, the role of different sirtuin isoforms needs further investigation. We studied the effects of photothrombotic stroke (PTS) on the expression and localization of sirtuins SIRT1 and SIRT2 in neurons and astrocytes of the penumbra and tested the activity of their selective and non-selective inhibitors. SIRT1 levels significantly decreased in the penumbra cells nuclei and increased in their cytoplasm. This indicated a redistribution of SIRT1 from the nucleus to the cytoplasm after PTS. The expression and intracellular distribution of SIRT1 were also observed in astrocytes. Photothrombotic stroke caused a sharp increase in SIRT2 levels in the cytoplasmic fraction of the penumbra neurons. SIRT2 was not expressed in the penumbra astrocytes. SIRT1 and SIRT2 did not co-localize with TUNEL-positive apoptotic cells. Mice were injected with EX-527, a selective SIRT1 inhibitor; SirReal2, selective SIRT2 inhibitor or salermide, a nonspecific inhibitor of SIRT1 and SIRT2. These inhibitors did not demonstrate any change in the infarction volume or the apoptotic index, compared to the control samples. The studies presented indicate the involvement of these sirtuins in the response of brain cells to ischemia in the first 24 h, but the alterations in their expression and change in the localization of SIRT1 are not related to the regulation of penumbra cell apoptosis in the acute period after PTS.

Versatile role of sirtuins in metabolic disorders: From modulation of mitochondrial function to therapeutic interventions

Sirtuins (SIRT1-7) are distinct histone deacetylases (HDACs) whose activity is determined by cellular metabolic status andnicotinamide adenine dinucleotide (NAD⁺ ) levels. HDACs of class III are the members of the SIRT's protein family. SIRTs are the enzymes that modulate mitochondrial activity and energy metabolism. SIRTs have been linked to a number of clinical and physiological operations, such as energy responses to low-calorie availability, aging, stress resistance, inflammation, and apoptosis. Mammalian SIRT2 orthologs have been identified as SIRT1-7 that are found in several subcellular sections, including the cytoplasm (SIRT1, 2), mitochondrial matrix (SIRT3, 4, 5), and the core (SIRT1, 2, 6, 7). For their deacetylase or ADP-ribosyl transferase action, all SIRTs require NAD⁺ and are linked to cellular energy levels. Evolutionarily, SIRT1 is related to yeast's SIRT2 as well as received primary attention in the circulatory system. An endogenous protein, SIRT1 is involved in the development of heart failure and plays a key role in cell death and survival. SIRT2 downregulation protects against ischemic-reperfusion damage. Increase in human longevity is caused by an increase in SIRT3 expression. Cardiomyocytes are also protected by SIRT3 from oxidative damage and aging, as well as suppressing cardiac hypertrophy. SIRT4 and SIRT5 perform their roles in the heart. SIRT6 has also been linked to a reduction in heart hypertrophy. SIRT7 is known to be involved in the regulation of stress responses and apoptosis in the heart.

The Role of Epigenetic Mechanisms in Autoimmune, Neurodegenerative, Cardiovascular, and Imprinting Disorders

Epigenetic mutations like aberrant DNA methylation, histone modifications, or RNA silencing are found in a number of human diseases. This review article discusses the epigenetic mechanisms involved in neurodegenerative disorders, cardiovascular disorders, auto-immune disorder, and genomic imprinting disorders. In addition, emerging epigenetic therapeutic strategies for the treatment of such disorders are presented. Medicinal chemistry campaigns highlighting the efforts of the chemists invested towards the rational design of small molecule inhibitors have also been included. Pleasingly, several classes of epigenetic inhibitors, DNMT, HDAC, BET, HAT, and HMT inhibitors along with RNA based therapies have exhibited the potential to emerge as therapeutics in the longer run. It is quite hopeful that epigenetic modulator-based therapies will advance to clinical stage investigations by leaps and bounds.

Development of a NanoBRET assay to validate dual inhibitors of Sirt2-mediated lysine deacetylation and defatty-acylation that block prostate cancer cell migration

Sirtuin2 (Sirt2) with its NAD⁺-dependent deacetylase and defatty-acylase activities plays a central role in the regulation of specific cellular functions. Dysregulation of Sirt2 activity has been associated with the pathogenesis of many diseases, thus making Sirt2 a promising target for pharmaceutical intervention. Herein, we present new high affinity Sirt2 selective Sirtuin-Rearranging Ligands (SirReals) that inhibit both Sirt2-dependent deacetylation and defatty-acylation in vitro and in cells. We show that simultaneous inhibition of both Sirt2 activities results in strongly reduced levels of the oncoprotein c-Myc and an inhibition of cancer cell migration. Furthermore, we describe the development of a NanoBRET-based assay for Sirt2, thereby providing a method to study cellular target engagement for Sirt2 in a straightforward and accurately quantifiable manner. Applying this assay, we could confirm cellular Sirt2 binding of our new Sirt2 inhibitors and correlate their anticancer effects with their cellular target engagement.

Sirt2 inhibitors that show simultaneous inhibition of Sirt2 deacetylase and defatty-acylase activity block prostate cancer cell migration and their target engagement is shown by a newly developed NanoBRET assay.

Regulation of Hypoxic Signaling and Oxidative Stress via the MicroRNA-SIRT2 Axis and Its Relationship with Aging-Related Diseases

The sirtuin family of nicotinamide adenine dinucleotide-dependent deacetylase and ADP-ribosyl transferases plays key roles in aging, metabolism, stress response, and aging-related diseases. SIRT2 is a unique sirtuin that is expressed in the cytosol and is abundant in neuronal cells. Various microRNAs were recently reported to regulate SIRT2 expression via its 3'-untranslated region (UTR), and single nucleotide polymorphisms in the miRNA-binding sites of SIRT2 3'-UTR were identified in patients with neurodegenerative diseases. The present review highlights recent studies into SIRT2-mediated regulation of the stress response, posttranscriptional regulation of SIRT2 by microRNAs, and the implications of the SIRT2-miRNA axis in aging-related diseases.

SIRT2 and FOXO3a expressions in the cerebral cortex and hippocampus of young and aged male rats: antioxidant and anti-apoptotic effects of melatonin

Melatonin has antioxidant, anti-apoptotic and anti-aging effects in the brain. Sirtuin2 (SIRT2) accumulates in the central nervous system with aging, and its inhibition appears to be protective in aging and aging-related neurodegenerative diseases. Forkhead Box-class O3a (FOXO3a) transcription factor is one of the main targets of SIRT2, and SIRT2-mediated FOXO3a deacetylation is closely related to aging, oxidative stress, and apoptosis. This study aimed to investigate the effects of melatonin on SIRT2 and FOXO3a expressions in the cerebral cortex and hippocampus of aged rats. Young (3 months, n = 18) and aged (22 months, n = 18) male Wistar rats were divided into control (4% DMSO-PBS, sc, for 21 days), melatonin (10 mg/kg, sc, for 21 days) and salermide (1 mM; 25 μl/100 g bw, ip, for 21 days) groups. SIRT2, FOXO3a, Bcl-2, Bax and Bim expressions in the cerebral cortex and hippocampus were demonstrated by Western blotting. SIRT2 and FOXO3a protein levels were also measured by a sandwich ELISA method. Oxidative stress index (OSI) was calculated by measuring total oxidant status (TOS) and total antioxidant status (TAS). Aging increased SIRT2, FOXO3a, Bim (only in the cerebral cortex), Bax (only in the hippocampus), TOS, and OSI, while decreasing Bcl-2, Bcl-2/Bax and TAS in both brain regions. Melatonin decreased SIRT2, FOXO3a, oxidative stress parameters and pro-apoptotic proteins, while increasing TAS, Bcl-2 and Bcl-2/Bax, more specifically in the hippocampus of the aged brain. Our results indicate that inhibition of SIRT2 and FOXO3a expressions appears to be involved in the protective effects of melatonin in the hippocampus of aged rats.

Histone Deacetylases and Their Isoform-Specific Inhibitors in Ischemic Stroke

Cerebral ischemia is the second leading cause of death in the world and multimodal stroke therapy is needed. The ischemic stroke generally reduces the gene expression due to suppression of acetylation of histones H3 and H4. Histone deacetylases inhibitors have been shown to be effective in protecting the brain from ischemic damage. Histone deacetylases inhibitors induce neurogenesis and angiogenesis in damaged brain areas promoting functional recovery after cerebral ischemia. However, the role of different histone deacetylases isoforms in the survival and death of brain cells after stroke is still controversial. This review aims to analyze the data on the neuroprotective activity of nonspecific and selective histone deacetylase inhibitors in ischemic stroke.

Sirtuins as Potential Therapeutic Targets for Mitigating Neuroinflammation Associated With Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder, which is associated with memory deficit and global cognitive decline. Age is the greatest risk factor for AD and, in recent years, it is becoming increasingly appreciated that aging-related neuroinflammation plays a key role in the pathogenesis of AD. The presence of β-amyloid plaques and neurofibrillary tangles are the primary pathological hallmarks of AD; defects which can then activate a cascade of molecular inflammatory pathways in glial cells. Microglia, the resident macrophages in the central nervous system (CNS), are the major triggers of inflammation; a response which is typically intended to prevent further damage to the CNS. However, persistent microglial activation (i.e., neuroinflammation) is toxic to both neurons and glia, which then leads to neurodegeneration. Growing evidence supports a central role for sirtuins in the regulation of neuroinflammation. Sirtuins are NAD+-dependent protein deacetylases that modulate a number of cellular processes associated with inflammation. This review examines the latest findings regarding AD-associated neuroinflammation, mainly focusing on the connections among the microglial molecular pathways of inflammation. Furthermore, we highlight the biology of sirtuins, and their role in neuroinflammation. Suppression of microglial activity through modulation of the sirtuin activity has now become a key area of research, where progress in therapeutic interventions may slow the progression of Alzheimer's disease.

Gene variants and expression changes of SIRT1 and SIRT6 in peripheral blood are associated with Parkinson's disease

Parkinson’s disease (PD) is a neurodegenerative disease caused by complex interaction between genetic and environmental factors. There is a growing body of evidence of the involvement of sirtuins (SIRTs) in disease pathomechanism. SIRTs are NAD+-dependent histone deacetylases which take part in various cellular functions. However, available data of the relationship between SIRT gene polymorphisms and PD is limited. Our aim was to investigate the possible association of 10 SNPs identified within non-mitochondrial SIRTs, SIRT1, -2 and -6 with the risk of PD in Hungarian population, and to compare the expression level of these SIRTs between healthy controls and PD patients. Our results showed that rs3740051 and rs3818292 of SIRT1 and rs350843, rs350844, rs107251, rs350845 and rs350846 of SIRT6 show weak association with PD risk. On the contrary rs12778366 and rs3758391 of SIRT1 and rs10410544 of SIRT2 did not show association with PD. Moreover, we detected that mRNA level of SIRT1 was down-regulated, and mRNA level of SIRT6 was up-regulated, while SIRT2 mRNA level was not altered in the peripheral blood of PD patients as compared to controls. The difference in both cases was more pronounced when comparing the early-onset PD group to the control cohort. Nevertheless, mRNA level changes did not show any association with the presence of any of the investigated SNPs either in the PD or in the control group. In conclusion, our findings suggest that non-mitochondrial sirtuins, SIRT1 and -6 but not SIRT2 might contribute to the pathogenesis of PD in the Hungarian population both via their altered mRNA levels and via gene alterations identified as specific SNPs.

Selective Targeting of Epigenetic Readers and Histone Deacetylases in Autoimmune and Inflammatory Diseases: Recent Advances and Future Perspectives

Histone deacetylases (HDACs) and bromodomain-containing proteins (BCPs) play a key role in chromatin remodeling. Based on their ability to regulate inducible gene expression in the context of inflammation and cancer, HDACs and BCPs have been the focus of drug discovery efforts, and numerous small-molecule inhibitors have been developed. However, dose-limiting toxicities of the first generation of inhibitors, which typically target multiple HDACs or BCPs, have limited translation to the clinic. Over the last decade, an increasing effort has been dedicated to designing class-, isoform-, or domain-specific HDAC or BCP inhibitors, as well as developing strategies for cell-specific targeted drug delivery. Selective inhibition of the epigenetic modulators is helping to elucidate the functions of individual epigenetic proteins and has the potential to yield better and safer therapeutic strategies. In accordance with this idea, several in vitro and in vivo studies have reported the ability of more selective HDAC/BCP inhibitors to recapitulate the beneficial effects of pan-inhibitors with less unwanted adverse events. In this review, we summarize the most recent advances with these strategies, discussing advantages and limitations of these approaches as well as some therapeutic perspectives, focusing on autoimmune and inflammatory diseases.

Sirtuin Acetylation and Deacetylation: a Complex Paradigm in Neurodegenerative Disease

Sirtuins are the class III of histone deacetylases that depend on nicotinamide adenine dinucleotide for their activity. Sirtuins can influence the progression of neurodegenerative disorders by switching between deacetylation and acetylation processes. Histone acetylation occurs when acetyl groups are added to lysine residues on the N-terminal part of histone proteins. Deacetylation, on the other hand, results in the removal of acetyl groups. Pharmacological modulation of sirtuin activity has been shown to influence various neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, Huntington's disease, stroke, and amyotrophic lateral sclerosis. In this review, mechanistic perspective of sirtuins has been discussed in anti-inflammatory, antiapoptotic, and neuroprotective effects in various disorders. We have discussed the structure, neurobiology, and physiology of sirtuins in neurodegenerative disease. Recent preclinical and clinical studies and their outcome have also been elucidated. The aim of this review is to fill in the gaps in our understanding of sirtuins' role in histone acetylation and deacetylation in all neurodegenerative diseases. Here, we emphasized on reviewing all the studies carried out in various labs depicting the role of sirtuin modulators in neuroprotection and highlighted the ideas that can be considered for future perspectives. Taken together, sirtuins may serve as a promising therapeutic target for the treatment of neurodegenerative disorders.

Value of serum and follicular fluid sirtuin (SIRT)1 and SIRT2 protein levels in predicting the outcome of assisted reproduction

Background

To explore whether serum and follicular fluid (FF), sirtuin 1 (SIRT1), and SIRT2 could predict the outcome of assisted reproduction.

Methods

All patients underwent in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) for the first time in the Reproductive Medicine Center of the First Affiliated Hospital of Zhejiang University Medical College from March 2018 to December 2018. According to cumulative clinical pregnancy outcomes, the patients were divided into a pregnancy group and non-pregnancy group. We measured the serum levels of SIRT1, SIRT2, anti-Müllerian hormone (AMH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and estradiol (E2) from the second to the fifth day of menstruation, and the levels of SIRT1 and SIRT2 in serum and FF on the day of human chorionic gonadotropin (HCG) injection and oocyte retrieval.

Results

A total of 125 patients met the inclusion criteria. The pregnancy group comprised 56 cases and non-pregnancy group 69 cases. There were significant differences in basal level SIRT2 (bSIRT2), AMH, antral follicle count (AFC), number of oocytes obtained, number of mature eggs, number of fertilized eggs, number of excellent embryos, number of blastocyst formations, and number of transferred high-quality embryos between the two groups. The area under the curve (AUC) values of bSIRT2, AFC, AMH, and age were significantly different from those under the opportunity reference line (P<0.05). In the subsequent correlation analysis, FFSIRT2, and HCG day serum SIRT2 were negatively correlated with age (r=−0.35, r=−0.19), and positively correlated with AFC (r=0.2, r=0.02). Serum SIRT1 on HCG day was negatively correlated with the number of blastocysts and the number of frozen embryos (r=−0.18, r=−0.21). Levels of FF SIRT1 and FF SIRT2 were significantly lower than those in serum SIRT1 and SIRT2, and there was no significant difference in serum SIRT1 and SIRT2 before and after ovulation promotion.

Conclusions

The results suggest that bSIRT2 has significant statistical significance in predicting the cumulative number of pregnancies. When combined with AMH, AFC, and age, bSIRT2 can predict the cumulative pregnancy outcome. In addition, the level of serum SIRT1 and SIRT2 were not affected by ovulation promotion.

Next-Generation Diamond Electrodes for Neurochemical Sensing: Challenges and Opportunities

Carbon-based electrodes combined with fast-scan cyclic voltammetry (FSCV) enable neurochemical sensing with high spatiotemporal resolution and sensitivity. While their attractive electrochemical and conductive properties have established a long history of use in the detection of neurotransmitters both in vitro and in vivo, carbon fiber microelectrodes (CFMEs) also have limitations in their fabrication, flexibility, and chronic stability. Diamond is a form of carbon with a more rigid bonding structure (sp3-hybridized) which can become conductive when boron-doped. Boron-doped diamond (BDD) is characterized by an extremely wide potential window, low background current, and good biocompatibility. Additionally, methods for processing and patterning diamond allow for high-throughput batch fabrication and customization of electrode arrays with unique architectures. While tradeoffs in sensitivity can undermine the advantages of BDD as a neurochemical sensor, there are numerous untapped opportunities to further improve performance, including anodic pretreatment, or optimization of the FSCV waveform, instrumentation, sp2/sp3 character, doping, surface characteristics, and signal processing. Here, we review the state-of-the-art in diamond electrodes for neurochemical sensing and discuss potential opportunities for future advancements of the technology. We highlight our team's progress with the development of an all-diamond fiber ultramicroelectrode as a novel approach to advance the performance and applications of diamond-based neurochemical sensors.

SIRT1 and SIRT2 Activity Control in Neurodegenerative Diseases

Sirtuins are NAD+ dependent histone deacetylases (HDAC) that play a pivotal role in neuroprotection and cellular senescence. SIRT1-7 are different homologs from sirtuins. They play a prominent role in many aspects of physiology and regulate crucial proteins. Modulation of sirtuins can thus be utilized as a therapeutic target for metabolic disorders. Neurological diseases have distinct clinical manifestations but are mainly age-associated and due to loss of protein homeostasis. Sirtuins mediate several life extension pathways and brain functions that may allow therapeutic intervention for age-related diseases. There is compelling evidence to support the fact that SIRT1 and SIRT2 are shuttled between the nucleus and cytoplasm and perform context-dependent functions in neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). In this review, we highlight the regulation of SIRT1 and SIRT2 in various neurological diseases. This study explores the various modulators that regulate the activity of SIRT1 and SIRT2, which may further assist in the treatment of neurodegenerative disease. Moreover, we analyze the structure and function of various small molecules that have potential significance in modulating sirtuins, as well as the technologies that advance the targeted therapy of neurodegenerative disease.

Sirtuins and Their Implications in Neurodegenerative Diseases from a Drug Discovery Perspective

Sirtuins are class III histone deacetylase (HDAC) enzymes that target both histone and non-histone substrates. They are linked to different brain functions and the regulation of different isoforms of these enzymes is touted to be an emerging therapy for the treatment of neurodegenerative diseases (NDs), including Parkinson's disease (PD), Alzheimer's disease (AD), and amyotrophic lateral sclerosis (ALS). The level of sirtuins affects brain health as many sirtuin-regulated pathways are responsible for the progression of NDs. Certain sirtuins are also implicated in aging, which is a risk factor for many NDs. In addition to SIRT1-3, it has been suggested that the less studied sirtuins (SIRT4-7) also play critical roles in brain health. This review delineates the role of each sirtuin isoform in NDs from a disease centric perspective and provides an up-to-date overview of sirtuin modulators and their potential use as therapeutics in these diseases. Furthermore, the future perspectives for sirtuin modulator development and their therapeutic application in neurodegeneration are outlined in detail, hence providing a research direction for future studies.

Sirtuin3 in Neurological Disorders

Sirtuins are NAD+ dependent enzymes that have a predominant role in neurodegenerative disorders and also regulate the inflammatory process, protein aggregation, etc. The relation between Sirtuins with that of the nervous system and neurodegeneration are widely studied consequently. Sirtuins have a strong role in metabolic syndrome in mitochondria also. The activities of Sirtuins can be altered by using small molecules that would be developed into drugs and it is proven that manipulation of SIRT1 activity influences neurodegenerative disease models. They are especially thrilling since using small molecules, which would be developed into a drug, it is feasible to alter the activities of sirtuins. Different functions of Sirtuins are depended upon their subcellular localization. In this review paper, we are discussing different Sirtuins, differential expression of sirtuins, and expression of sirtuin in the brain and briefly about sirtuin3 (SIRT3).

Microtubule Dysfunction: A Common Feature of Neurodegenerative Diseases

Neurons are particularly susceptible to microtubule (MT) defects and deregulation of the MT cytoskeleton is considered to be a common insult during the pathogenesis of neurodegenerative disorders. Evidence that dysfunctions in the MT system have a direct role in neurodegeneration comes from findings that several forms of neurodegenerative diseases are associated with changes in genes encoding tubulins, the structural units of MTs, MT-associated proteins (MAPs), or additional factors such as MT modifying enzymes which modulating tubulin post-translational modifications (PTMs) regulate MT functions and dynamics. Efforts to use MT-targeting therapeutic agents for the treatment of neurodegenerative diseases are underway. Many of these agents have provided several benefits when tested on both in vitro and in vivo neurodegenerative model systems. Currently, the most frequently addressed therapeutic interventions include drugs that modulate MT stability or that target tubulin PTMs, such as tubulin acetylation. The purpose of this review is to provide an update on the relevance of MT dysfunctions to the process of neurodegeneration and briefly discuss advances in the use of MT-targeting drugs for the treatment of neurodegenerative disorders.

Natural Products as Modulators of Sirtuins

Natural products have been used for the treatment of human diseases since ancient history. Over time, due to the lack of precise tools and techniques for the separation, purification, and structural elucidation of active constituents in natural resources there has been a decline in financial support and efforts in characterization of natural products. Advances in the design of chemical compounds and the understanding of their functions is of pharmacological importance for the biomedical field. However, natural products regained attention as sources of novel drug candidates upon recent developments and progress in technology. Natural compounds were shown to bear an inherent ability to bind to biomacromolecules and cover an unparalleled chemical space in comparison to most libraries used for high-throughput screening. Thus, natural products hold a great potential for the drug discovery of new scaffolds for therapeutic targets such as sirtuins. Sirtuins are Class III histone deacetylases that have been linked to many diseases such as Parkinson`s disease, Alzheimer’s disease, type II diabetes, and cancer linked to aging. In this review, we examine the revitalization of interest in natural products for drug discovery and discuss natural product modulators of sirtuins that could serve as a starting point for the development of isoform selective and highly potent drug-like compounds, as well as the potential application of naturally occurring sirtuin inhibitors in human health and those in clinical trials.

The class II histone deacetylases as therapeutic targets for Parkinson's disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterised by specific motor impairments. The neuropathological hallmarks of PD include progressive degeneration of midbrain dopaminergic neurons, and loss of their axonal projections to the striatum. Additionally, there is progressive accumulation and spread of intracellular aggregates of α-synuclein. Although dopamine-replacement pharmacotherapy can treat PD symptoms in the short-term, there is a critical need for the development of disease-modifying therapies based on an understanding of the underlying disease mechanisms. One such mechanism is histone acetylation, which is a common epigenetic modification that alters gene transcription. A number of studies have described alterations in histone acetylation in the brains of PD patients. Moreover, α-synuclein accumulation has been linked to alterations in histone acetylation and pharmacological strategies aimed at modulating histone acetylation are under investigation as novel approaches to disease modification in PD. Currently, such strategies are focused predominantly on pan-inhibition of histone deacetylase (HDAC) enzymes. Inhibition of specific individual HDAC enzymes is a more targeted strategy that may allow for future clinical translation. However, the most appropriate class of HDACs that should be targeted for neuroprotection in PD is still unclear. Recent work has shed new light on the role of class-II HDACs in dopaminergic degeneration. For this reason, here we describe the regulation of histone acetylation, outline the evidence for alterations in histone acetylation in the PD brain, and focus on the roles of class II HDACs and the potential of class-II HDAC inhibition as a therapeutic approach for neuroprotection in PD.

Microtubule-Associated Proteins with Regulatory Functions by Day and Pathological Potency at Night

The sensing, integrating, and coordinating features of the eukaryotic cells are achieved by the complex ultrastructural arrays and multifarious functions of the cytoskeleton, including the microtubule network. Microtubules play crucial roles achieved by their decoration with proteins/enzymes as well as by posttranslational modifications. This review focuses on the Tubulin Polymerization Promoting Protein (TPPP/p25), a new microtubule associated protein, on its "regulatory functions by day and pathological functions at night". Physiologically, the moonlighting TPPP/p25 modulates the dynamics and stability of the microtubule network by bundling microtubules and enhancing the tubulin acetylation due to the inhibition of tubulin deacetylases. The optimal endogenous TPPP/p25 level is crucial for its physiological functions, to the differentiation of oligodendrocytes, which are the major constituents of the myelin sheath. Pathologically, TPPP/p25 forms toxic oligomers/aggregates with α-synuclein in neurons and oligodendrocytes in Parkinson's disease and Multiple System Atrophy, respectively; and their complex is a potential therapeutic drug target. TPPP/p25-derived microtubule hyperacetylation counteracts uncontrolled cell division. All these issues reveal the anti-mitotic and α-synuclein aggregation-promoting potency of TPPP/p25, consistent with the finding that Parkinson's disease patients have reduced risk for certain cancers.

Emerging Role of Sirtuin 2 in Parkinson's Disease

Parkinson’s disease (PD), the main risk factor of which is age, is one of the most common neurodegenerative diseases, thus presenting a substantial burden on the health of affected individuals as well as an economic burden. Sirtuin 2 (SIRT2), a subtype in the family of sirtuins, belongs to class III histone deacetylases (HDACs). It is known that SIRT2 levels increase with aging, and a growing body of evidence has been accumulating, showing that the activity of SIRT2 mediates various processes involved in PD pathogenesis, including aggregation of α-synuclein (α-syn), microtubule function, oxidative stress, inflammation, and autophagy. There have been conflicting reports about the role of SIRT2 in PD, in that some studies indicate its potential to induce the death of dopaminergic (DA) neurons, and that inhibition of SIRT2 may, therefore, have protective effects in PD. Other studies suggest a protective role of SIRT2 in the context of neuronal damage. As current treatments for PD are directed at alleviating symptoms and are very limited, a comprehensive understanding of the enzymology of SIRT2 in PD may be essential for developing novel therapeutic agents for the treatment of this disease. This review article will provide an update on our knowledge of the structure, distribution, and biological characteristics of SIRT2, and highlight its role in the pathogenesis of PD.

Dichotomous Sirtuins: Implications for Drug Discovery in Neurodegenerative and Cardiometabolic Diseases

Sirtuins (SIRT1-7), a class of NAD⁺-dependent deacylases, are central regulators of metabolic homeostasis and stress responses. While numerous salutary effects associated with sirtuin activation, especially SIRT1, are well documented, other reports show health benefits resulting from sirtuin inhibition. Furthermore, conflicting findings have been obtained regarding the pathophysiological role of specific sirtuin isoforms, suggesting that sirtuins act as 'double-edged swords'. Here, we provide an integrated overview of the different findings on the role of mammalian sirtuins in neurodegenerative and cardiometabolic disorders and attempt to dissect the reasons behind these different effects. Finally, we discuss how addressing these obstacles may provide a better understanding of the complex sirtuin biology and improve the likelihood of identifying effective and selective drug targets for a variety of human disorders.

SIRT2 deacetylates GRASP55 to facilitate post-mitotic Golgi assembly

Sirtuin 2 (SIRT2) is an NAD-dependent sirtuin deacetylase that regulates microtubule and chromatin dynamics, gene expression and cell cycle progression, as well as nuclear envelope reassembly. Recent proteomic analyses have identified Golgi proteins as SIRT2 interactors, indicating that SIRT2 may also play a role in Golgi structure formation. Here, we show that SIRT2 depletion causes Golgi fragmentation and impairs Golgi reassembly at the end of mitosis. SIRT2 interacts with the Golgi reassembly stacking protein GRASP55 (also known as GORASP2) in mitosis when GRASP55 is highly acetylated on K50. Expression of wild-type and the K50R acetylation-deficient mutant of GRASP55, but not the K50Q acetylation-mimetic mutant, in GRASP55 and GRASP65 (also known as GORASP1) double-knockout cells, rescued the Golgi structure and post-mitotic Golgi reassembly. Acetylation-deficient GRASP55 exhibited a higher self-interaction efficiency, a property required for Golgi structure formation. These results demonstrate that SIRT2 regulates Golgi structure by modulating GRASP55 acetylation levels.

Identification of Diketopiperazine-Containing 2-Anilinobenzamides as Potent Sirtuin 2 (SIRT2)-Selective Inhibitors Targeting the "Selectivity Pocket", Substrate-Binding Site, and NAD+-Binding Site

The NAD⁺-dependent deacetylase SIRT2 represents an attractive target for drug development. Here, we designed and synthesized drug-like SIRT2-selective inhibitors based on an analysis of the putative binding modes of recently reported SIRT2-selective inhibitors and evaluated their SIRT2-inhibitory activity. This led us to develop a more drug-like diketopiperazine structure as a "hydrogen bond (H-bond) hunter" to target the substrate-binding site of SIRT2. Thioamide 53, a conjugate of diketopiperazine and 2-anilinobenzamide which is expected to occupy the "selectivity pocket" of SIRT2, exhibited potent SIRT2-selective inhibition. Inhibition of SIRT2 by 53 was mediated by the formation of a 53-ADP-ribose conjugate, suggesting that 53 is a mechanism-based inhibitor targeting the "selectivity pocket", substrate-binding site, and NAD⁺-binding site. Furthermore, 53 showed potent antiproliferative activity toward breast cancer cells and promoted neurite outgrowth of Neuro-2a cells. These findings should pave the way for the discovery of novel therapeutic agents for cancer and neurological disorders.

Elevated Serum SIRT 2 May Differentiate Parkinson's Disease From Atypical Parkinsonian Syndromes

Atypical Parkinson syndromes (APSs) often have symptoms that overlap with those of Parkinson's disease (PD), especially early in the disease, making these disorders difficult to diagnose. Previous studies have demonstrated an association of oligomeric α-synuclein (α-Syn), a key element in the pathogenesis of PD, with Sirtuin (SIRT)2 proteins for modulating PD. We aimed to evaluate SIRT protein expression in serum of PD patients and compare it with APSs and normal elderly control (GC) and to correlate this with α-Syn. SIRT protein expression was evaluated in sera of 68 PD; 34 APS and 68 GC without any neuro-psychiatric illness as controls by surface plasmon resonance (SPR). SIRT2 expression was correlated with α-Syn in PD and GC. Significant (p < 0.0001) differences were observed between serum SIRT2 concentration in PD and APS and GC as well as between APS and GC. Receiver operating characteristic (ROC) analysis revealed the strong cut-off value to differentiate PD from APS and GC and also APS from GC. Significant correlation was observed among SIRT2 levels in early PD patients with Unified Parkinson's Disease Rating Scale (UPDRS), Hoehn & Yahr (H & Y) and increased duration of disease. In addition, a strong positive correlation of SIRT2 with α-Syn (p < 0.0001) was observed. However, no such difference was detected for serum SIRT1 in cases of PD and APS or for GC. The present study is the first to report elevated serum SIRT2 in PD. The study also provided a simple test to distinguish PD from APS and may have translational utility for diagnosis.

Inhibition of SIRT2 by Targeting GSK3β-Mediated Phosphorylation Alleviates SIRT2 Toxicity in SH-SY5Y Cells

Sirtuin 2 (SIRT2) is thought to be important in the pathogenesis of Parkinson’s disease (PD), and the inhibition of SIRT2 rescues α-synuclein toxicity in a cellular model of PD. Recent studies have focused on identifying inhibitors of SIRT2, but little is known about the processes that directly regulate its function. GSK3β is a serine/threonine protein kinase that affects a wide range of biological functions, and it is localized in Lewy bodies (LBs). Therefore, we investigated whether SIRT2 is regulated by GSK3β and enhances cell death in PD. In the present study, Western blot showed that total SIRT2 levels did not change noticeably in a cellular model of PD but that SIRT2 phosphorylation was increased, and GSK3β activity was elevated. In addition, mass spectrometry (MS) studies indicated that SIRT2 was phosphorylated by GSK3β at three specific sites. Phospho- or dephospho-mimicking studies demonstrated that this postmodification (phosphorylation) increased SIRT2 toxicity in SH-SY5Y cells. Collectively, our findings identify a posttranslational mechanism that controls SIRT2 function in PD and provide evidence for a novel regulatory pathway involving GSK3β, SIRT2, and α-synuclein.

Sirtuins in Alzheimer's Disease: SIRT2-Related GenoPhenotypes and Implications for PharmacoEpiGenetics

Sirtuins (SIRT1-7) are NAD⁺-dependent protein deacetylases/ADP ribosyltransferases with important roles in chromatin silencing, cell cycle regulation, cellular differentiation, cellular stress response, metabolism and aging. Sirtuins are components of the epigenetic machinery, which is disturbed in Alzheimer’s disease (AD), contributing to AD pathogenesis. There is an association between the SIRT2-C/T genotype (rs10410544) (50.92%) and AD susceptibility in the APOEε4-negative population (SIRT2-C/C, 34.72%; SIRT2-T/T 14.36%). The integration of SIRT2 and APOE variants in bigenic clusters yields 18 haplotypes. The 5 most frequent bigenic genotypes in AD are 33CT (27.81%), 33CC (21.36%), 34CT (15.29%), 34CC (9.76%) and 33TT (7.18%). There is an accumulation of APOE-3/4 and APOE-4/4 carriers in SIRT2-T/T > SIRT2-C/T > SIRT2-C/C carriers, and also of SIRT2-T/T and SIRT2-C/T carriers in patients who harbor the APOE-4/4 genotype. SIRT2 variants influence biochemical, hematological, metabolic and cardiovascular phenotypes, and modestly affect the pharmacoepigenetic outcome in AD. SIRT2-C/T carriers are the best responders, SIRT2-T/T carriers show an intermediate pattern, and SIRT2-C/C carriers are the worst responders to a multifactorial treatment. In APOE-SIRT2 bigenic clusters, 33CC carriers respond better than 33TT and 34CT carriers, whereas 24CC and 44CC carriers behave as the worst responders. CYP2D6 extensive metabolizers (EM) are the best responders, poor metabolizers (PM) are the worst responders, and ultra-rapid metabolizers (UM) tend to be better responders that intermediate metabolizers (IM). In association with CYP2D6 genophenotypes, SIRT2-C/T-EMs are the best responders. Some Sirtuin modulators might be potential candidates for AD treatment.

Sirt2 Regulates Radiation-Induced Injury

Sirtuin 2 (SIRT2) plays a major role in aging, carcinogenesis and neurodegeneration. While it has been shown that SIRT2 is a mediator of stress-induced cell death, the mechanism remains unclear. In this study, we report the role of SIRT2 in mediating radiation-induced cell death and DNA damage using mouse embryonic fibroblasts (MEFs), progenitor cells and tissues from Sirt2 wild-type and genomic knockout mice, and human tumor and primary cell lines as models. The presence of Sirt2 in cells and tissues significantly enhanced the cell's sensitivity to radiation-induced cytotoxicity by delaying the dispersion of radiation-induced γ-H2AX and 53BP1 foci. This enhanced cellular radiosensitivity correlated with reduced expression of pro-survival and DNA repair proteins, and decreased DNA repair capacities involving both homologous repair and non-homologous end joining DNA repair mechanisms compared to those in Sirt2 knockout (KO) and knockdown (KD) phenotypes. Together, these data suggest SIRT2 plays a critical role in mediating the radiation-induced DNA damage response, thus regulating radiation-induced cell death and survival.

The histone deacetylase inhibitor nicotinamide exacerbates neurodegeneration in the lactacystin rat model of Parkinson's disease

Histone hypoacetylation is associated with dopaminergic neurodegeneration in Parkinson's disease (PD), because of an imbalance in the activities of the enzymes responsible for histone (de)acetylation. Correction of this imbalance, with histone deacetylase (HDAC) inhibiting agents, could be neuroprotective. We therefore hypothesize that nicotinamide, being a selective inhibitor of HDAC class III as well as having modulatory effects on mitochondrial energy metabolism, would be neuroprotective in the lactacystin rat model of PD, which recapitulates the formation of neurotoxic accumulation of altered proteins within the substantia nigra to cause progressive dopaminergic cell death. Rats received nicotinamide for 28 days, starting 7 days after unilateral injection of the irreversible proteasome inhibitor, lactacystin, into the substantia nigra. Longitudinal motor behavioural testing and structural magnetic resonance imaging were used to track changes in this model of PD, and assessment of nigrostriatal integrity, histone acetylation and brain gene expression changes post-mortem used to quantify nicotinamide-induced neuroprotection. Counterintuitively, nicotinamide dose-dependently exacerbated neurodegeneration of dopaminergic neurons, behavioural deficits and structural brain changes in the lactacystin-lesioned rat. Nicotinamide treatment induced histone hyperacetylation and over-expression of numerous neurotrophic and anti-apoptotic factors in the brain, yet failed to result in neuroprotection, rather exacerbated dopaminergic pathology. These findings highlight the importance of inhibitor specificity within HDAC isoforms for therapeutic efficacy in PD, demonstrating the contrasting effects of HDAC class III inhibition upon cell survival in this animal model of the disease. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Salmonella escapes adaptive immune response via SIRT2 mediated modulation of innate immune response in dendritic cells

Salmonella being a successful pathogen, employs a plethora of immune evasion mechanisms. This contributes to pathogenesis, persistence and also limits the efficacy of available treatment. All these contributing factors call upon for new drug targets against Salmonella. For the first time, we have demonstrated that Salmonella upregulates sirtuin 2 (SIRT2), an NAD+ dependent deacetylase in dendritic cells (DC). SIRT2 upregulation results in translocation of NFκB p65 to the nucleus. This further upregulates NOS2 transcription and nitric oxide (NO) production. NO subsequently shows antibacterial activity and suppresses T cell proliferation. NOS2 mediated effect of SIRT2 is further validated by the absence of effect of SIRT2 inhibition in NOS2-/- mice. Inhibition of SIRT2 increases intracellular survival of the pathogen and enhances antigen presentation in vitro. However, in vivo SIRT2 inhibition shows lower bacterial organ burden and reduced tissue damage. SIRT2 knockout mice also demonstrate reduced bacterial organ burden compared to wild-type mice. Collectively, our results prove the role of SIRT2 in Salmonella pathogenesis and the mechanism of action. This can aid in designing of host-targeted therapeutics directed towards inhibition of SIRT2.

Pharmacoepigenomic Interventions as Novel Potential Treatments for Alzheimer's and Parkinson's Diseases

Cerebrovascular and neurodegenerative disorders affect one billion people around the world and result from a combination of genomic, epigenomic, metabolic, and environmental factors. Diagnosis at late stages of disease progression, limited knowledge of gene biomarkers and molecular mechanisms of the pathology, and conventional compounds based on symptomatic rather than mechanistic features, determine the lack of success of current treatments, including current FDA-approved conventional drugs. The epigenetic approach opens new avenues for the detection of early presymptomatic pathological events that would allow the implementation of novel strategies in order to stop or delay the pathological process. The reversibility and potential restoring of epigenetic aberrations along with their potential use as targets for pharmacological and dietary interventions sited the use of epidrugs as potential novel candidates for successful treatments of multifactorial disorders involving neurodegeneration. This manuscript includes a description of the most relevant epigenetic mechanisms involved in the most prevalent neurodegenerative disorders worldwide, as well as the main potential epigenetic-based compounds under investigation for treatment of those disorders and their limitations.

MicroRNA-212-5p Prevents Dopaminergic Neuron Death by Inhibiting SIRT2 in MPTP-Induced Mouse Model of Parkinson's Disease

Recently, emerging evidences show that sirtuins (SIRTs) modulate aging progress and affect neurodegenerative diseases. For example, inhibition of SIRT2 has been recognized to exert neuroprotective effects in Parkinson’s disease (PD). However, current SIRT2 inhibitors are lack of selective property distinguished from its homolog. In this study, we found that SIRT2 protein level was highly increased in PD model, which was negatively regulated by miR-212-5p. In detail, miR-212-5p transfection reduced SIRT2 expression and inhibited SIRT2 activity. In vivo study, miR-212-5p treatment prevented dopaminergic neuron loss and DAT reduction by targeting SIRT2, which means miR-212-5p shows neuroprotective effect in PD. Mechanismly, we found nuclear acetylated p53 was up-regulation according to p53 is a major deacetylation substrate of SIRT2. Furthermore, decreased cytoplasmic p53 promoted autophagy in PD model, which was showed as autophagosomes, autophagic flux, LC3 B and p62 expression. Meanwhile, we also found miR-212-5p treatment somehow alleviated apoptosis in PD model, which might have some underlying mechanisms. In conclusions, our study provides a direct link between miR-212-5p and SIRT2-mediated p53-dependent programmed cell death in the pathogenesis of PD. These findings will give us an insight into the development of highly specifically SIRT2 inhibitor of opening up novel therapeutic avenues for PD.