Protective effects and mechanisms of sirtuins in the nervous system

Sirt1 regulates glial progenitor proliferation and regeneration in white matter after neonatal brain injury

Regenerative processes in brain pathologies require the production of distinct neural cell populations from endogenous progenitor cells. We have previously demonstrated that oligodendrocyte progenitor cell (OPC) proliferation is crucial for oligodendrocyte (OL) regeneration in a mouse model of neonatal hypoxia (HX) that reproduces diffuse white matter injury (DWMI) of premature infants. Here we identify the histone deacetylase Sirt1 as a Cdk2 regulator in OPC proliferation and response to HX. HX enhances Sirt1 and Sirt1/Cdk2 complex formation through HIF1α activation. Sirt1 deacetylates retinoblastoma (Rb) in the Rb/E2F1 complex, leading to dissociation of E2F1 and enhanced OPC proliferation. Sirt1 knockdown in culture and its targeted ablation in vivo suppresses basal and HX-induced OPC proliferation. Inhibition of Sirt1 also promotes OPC differentiation after HX. Our results indicate that Sirt1 is an essential regulator of OPC proliferation and OL regeneration after neonatal brain injury. Therefore, enhancing Sirt1 activity may promote OL recovery after DWMI.

Oligodendrocyte progenitor cell (OPC) proliferation is crucial for regeneration after hypoxic lesions in mice, a model of diffuse white matter injury of premature infants. Here, the authors show that the histone deacetylase Sirt1 is a Cdk2-dependent mediator of OPC proliferation and OPC response to hypoxia.

Multiple beneficial effects of melanocortin MC4 receptor agonists in experimental neurodegenerative disorders: Therapeutic perspectives

Melanocortin peptides induce neuroprotection in acute and chronic experimental neurodegenerative conditions. Melanocortins likewise counteract systemic responses to brain injuries. Furthermore, they promote neurogenesis by activating critical signaling pathways. Melanocortin-induced long-lasting improvement in synaptic activity and neurological performance, including learning and memory, sensory-motor orientation and coordinated limb use, has been consistently observed in experimental models of acute and chronic neurodegeneration. Evidence indicates that the neuroprotective and neurogenic effects of melanocortins, as well as the protection against systemic responses to a brain injury, are mediated by brain melanocortin 4 (MC₄) receptors, through an involvement of the vagus nerve. Here we discuss the targets and mechanisms underlying the multiple beneficial effects recently observed in animal models of neurodegeneration. We comment on the potential clinical usefulness of melanocortin MC₄ receptor agonists as neuroprotective and neuroregenerative agents in ischemic stroke, subarachnoid hemorrhage, traumatic brain injury, spinal cord injury, and Alzheimer's disease.

Sirtuin 1 activation protects against early brain injury after experimental subarachnoid hemorrhage in rats

Increasing evidence indicates that sirtuin 1 (SIRT1) is implicated in a wide range of cellular functions, such as oxidative stress, inflammation and apoptosis. The aim of this study was to investigate the change of SIRT1 in the brain after subarachnoid hemorrhage (SAH) and its role on SAH-induced early brain injury (EBI). In the first set of experiments, rats were randomly divided into sham group and SAH groups at 2, 6, 12, 24, 48 and 72 h. The expression of SIRT1 was evaluated by western blot analysis, immunohistochemistry and immunofluorescence. In another set of experiments, SIRT1-specific inhibitor (sirtinol) and activator (activator 3) were exploited to study the role of SIRT1 in SAH-induced EBI. It showed that the protein level of SIRT1 was markedly elevated at the early stage of SAH and peaked at 24 h after SAH. The expression of SIRT1 could be observed in neurons and microglia, and the enhanced SIRT1 was mainly located in neurons after SAH. Administration of sirtinol inhibited the expression and activation of SIRT1 pathways after SAH, while activator 3 enhanced the expression and activation of SIRT1 pathways after SAH. In addition, inhibition of SIRT1 could exacerbate forkhead transcription factors of the O class-, nuclear factor-kappa B- and p53-induced oxidative damage, neuroinflammation and neuronal apoptosis, leading to aggravated brain injury after SAH. In contrast, activator 3 treatment could reduce forkhead transcription factors of the O class-, nuclear factor-kappa B-, and p53-induced oxidative damage, neuroinflammation and neuronal apoptosis to protect against EBI. These results suggest that SIRT1 plays an important role in neuroprotection against EBI after SAH by deacetylation and subsequent inhibition of forkhead transcription factors of the O class-, nuclear factor-kappa B-, and p53-induced oxidative, inflammatory and apoptotic pathways. SIRT1 might be a new promising molecular target for SAH.

Expression Profiles of SIRT1 and APP Genes in Human Neuroblastoma SK-N-SH Cells Treated with Two Epigenetic Agents

In our previous studies, significant hypermethylation of the sirtuin 1 (SIRT1) gene and demethylation of the β-amyloid precursor protein (APP) gene were found in patients with Alzheimer's disease (AD) compared with the normal population. Moreover, the expression of SIRT1 was significantly decreased while that of APP was increased in AD patients. These results indicated a correlation of DNA methylation with gene expression levels in AD patients. To further investigate the epigenetic mechanism of gene modulation in AD, we used two epigenetic drugs, the DNA methylation inhibitor 5-aza-2'-deoxycytidine (DAC) and the histone deacetylase inhibitor trichostatin A (TSA), to treat human neuroblastoma SK-N-SH cells in the presence of amyloid β-peptide Aβ25-35(Aβ25-35). We found that DAC and TSA had different effects on the expression trends of SIRT1 and APP in the cell model of amyloid toxicity. Although other genes, such as microtubule-associated protein τ, presenilin 1, presenilin 2, and apolipoprotein E, were up-regulated after Aβ25-35 treatment, no significant differences were found after DAC and/or TSA treatment. These results support the evidence in AD patients and reveal a strong correlation of SIRT1/APP expression with DNA methylation and/or histone modification, which may help understand the pathogenesis of AD.

Mitochondrial function in hypoxic ischemic injury and influence of aging

Mitochondria are a major target in hypoxic/ischemic injury. Mitochondrial impairment increases with age leading to dysregulation of molecular pathways linked to mitochondria. The perturbation of mitochondrial homeostasis and cellular energetics worsens outcome following hypoxic-ischemic insults in elderly individuals. In response to acute injury conditions, cellular machinery relies on rapid adaptations by modulating posttranslational modifications. Therefore, post-translational regulation of molecular mediators such as hypoxia-inducible factor 1α (HIF-1α), peroxisome proliferator-activated receptor γ coactivator α (PGC-1α), c-MYC, SIRT1 and AMPK play a critical role in the control of the glycolytic-mitochondrial energy axis in response to hypoxic-ischemic conditions. The deficiency of oxygen and nutrients leads to decreased energetic reliance on mitochondria, promoting glycolysis. The combination of pseudohypoxia, declining autophagy, and dysregulation of stress responses with aging adds to impaired host response to hypoxic-ischemic injury. Furthermore, intermitochondrial signal propagation and tissue wide oscillations in mitochondrial metabolism in response to oxidative stress are emerging as vital to cellular energetics. Recently reported intercellular transport of mitochondria through tunneling nanotubes also play a role in the response to and treatments for ischemic injury. In this review we attempt to provide an overview of some of the molecular mechanisms and potential therapies involved in the alteration of cellular energetics with aging and injury with a neurobiological perspective.

Dietary Restriction Affects Neuronal Response Property and GABA Synthesis in the Primary Visual Cortex

Previous studies have reported inconsistent effects of dietary restriction (DR) on cortical inhibition. To clarify this issue, we examined the response properties of neurons in the primary visual cortex (V1) of DR and control groups of cats using in vivo extracellular single-unit recording techniques, and assessed the synthesis of inhibitory neurotransmitter GABA in the V1 of cats from both groups using immunohistochemical and Western blot techniques. Our results showed that the response of V1 neurons to visual stimuli was significantly modified by DR, as indicated by an enhanced selectivity for stimulus orientations and motion directions, decreased visually-evoked response, lowered spontaneous activity and increased signal-to-noise ratio in DR cats relative to control cats. Further, it was shown that, accompanied with these changes of neuronal responsiveness, GABA immunoreactivity and the expression of a key GABA-synthesizing enzyme GAD67 in the V1 were significantly increased by DR. These results demonstrate that DR may retard brain aging by increasing the intracortical inhibition effect and improve the function of visual cortical neurons in visual information processing. This DR-induced elevation of cortical inhibition may favor the brain in modulating energy expenditure based on food availability.

Sirt1 and the Mitochondria

Sirt1 is the most prominent and extensively studied member of sirtuins, the family of mammalian class III histone deacetylases heavily implicated in health span and longevity. Although primarily a nuclear protein, Sirt1's deacetylation of Peroxisome proliferator-activated receptor Gamma Coactivator-1α (PGC-1α) has been extensively implicated in metabolic control and mitochondrial biogenesis, which was proposed to partially underlie Sirt1's role in caloric restriction and impacts on longevity. The notion of Sirt1's regulation of PGC-1α activity and its role in mitochondrial biogenesis has, however, been controversial. Interestingly, Sirt1 also appears to be important for the turnover of defective mitochondria by mitophagy. I discuss here evidences for Sirt1's regulation of mitochondrial biogenesis and turnover, in relation to PGC-1α deacetylation and various aspects of cellular physiology and disease.

The epigenetic regulation of HIF-1α by SIRT1 in MPP(+) treated SH-SY5Y cells

Both silent information regulator 1 (SIRT1) and hypoxia inducible factor 1 (HIF-1) have been found to play important roles in the pathophysiology of Parkinson's disease (PD). However, their mechanisms and their relationship still require further study. In the present study, we focused on the change and relationship of SIRT1 and HIF-1α in PD. PD cell models were established by using methyl-4-phenylpyridinium (MPP(+)), which induced inhibition of cell proliferation, cell cycle arrest and apoptosis. We found that the expression of HIF-1α and its target genes VEGFA and LDHA increased and that SIRT1 expression was inhibited in MPP(+) treated cells. With further analysis, we found that the acetylation of H3K14 combined with the HIF-1α promoter was dramatically increased in cells treated with MPP(+), which resulted in the transcriptional activation of HIF-1α. Moreover, the acetylation of H3K14 and the expression of HIF-1α increased when SIRT1 was knocked down, suggesting that SIRT1 was involved in the epigenetic regulation of HIF-1α. At last, phenformin, another mitochondrial complex1 inhibitor, was used to testify that the increased HIF-1a was not due to off target effects of MPP(+). Therefore, our results support a link between PD and SIRT1/HIF-1α signaling, which may serve as a clue for understanding PD.

Role of SIRT1 in autoimmune demyelination and neurodegeneration

Multiple sclerosis (MS) is a demyelinating disease characterized by chronic inflammation of the central nervous system, in which many factors can act together to influence disease susceptibility and progression. SIRT1 is a member of the histone deacetylase class III family of proteins and is an NAD(+)-dependent histone and protein deacetylase. SIRT1 can induce chromatin silencing through the deacetylation of histones and plays an important role as a key regulator of a wide variety of cellular and physiological processes including DNA damage, cell survival, metabolism, aging, and neurodegeneration. It has gained a lot of attention recently because many studies in animal models of demyelinating and neurodegenerative diseases have shown that SIRT1 induction can ameliorate the course of the disease. SIRT1 expression was found to be decreased in the peripheral blood mononuclear cells of MS patients during relapses. SIRT1 represents a possible biomarker of relapses and a potential new target for therapeutic intervention in MS. Modulation of SIRT1 may be a valuable strategy for treating or preventing MS and neurodegenerative central nervous system disorders.

Sirt1 in cerebral ischemia

Cerebral ischemia is among the leading causes of death worldwide. It is characterized by a lack of blood flow to the brain that results in cell death and damage, ultimately causing motor, sensory, and cognitive impairments. Today, clinical treatment of cerebral ischemia, mostly stroke and cardiac arrest, is limited and new neuroprotective therapies are desperately needed. The Sirtuin family of oxidized nicotinamide adenine dinucleotide (NAD⁺)-dependent deacylases has been shown to govern several processes within the central nervous system as well as to possess neuroprotective properties in a variety of pathological conditions such as Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease, among others. Recently, Sirt1 in particular has been identified as a mediator of cerebral ischemia, with potential as a possible therapeutic target. To gather studies relevant to this topic, we used PubMed and previous reviews to locate, select, and resynthesize the lines of evidence presented here. In this review, we will first describe some functions of Sirt1 in the brain, mainly neurodevelopment, learning and memory, and metabolic regulation. Second, we will discuss the experimental evidence that has implicated Sirt1 as a key protein in the regulation of cerebral ischemia as well as a potential target for the induction of ischemic tolerance.

The role of citicoline in cognitive impairment: pharmacological characteristics, possible advantages, and doubts for an old drug with new perspectives

BACKGROUND

Citicoline is able to potentiate neuroplasticity and is a natural precursor of phospholipid synthesis, or rather serves as a choline source in the metabolic pathways for biosynthesis of acetylcholine. Several studies have shown that it can have beneficial effects both in degenerative and in vascular cognitive decline. The aim of the present study was to review the pharmacokinetics and pharmacodynamics of this drug and its role in cognitive impairment according to the present medical literature.

METHODS

A MEDLINE(®) search was made using the following key words: citicoline, pharmacokinetics, pharmacodynamics, elderly, cognitive impairment, vascular dementia, and Alzheimer's disease. Recent studies on the possible role of citicoline in increasing sirtuin 1 (SIRT1) expression were assessed. Some personal studies were also considered, such as the VITA study and the IDEALE study.

RESULTS

Administered by both oral and intravenous routes, citicoline is converted into two major circulating metabolites, cytidine and choline. It is metabolized in the gut wall and liver. Pharmacokinetic studies suggested that it is well absorbed and highly bioavailable with oral dosing. A number of studies have clearly shown the possible role of citicoline in cognitive impairment of diverse etiology. It can also modulate the activity/expression of some protein kinases involved in neuronal death and increases SIRT1 expression in the central nervous system. The VITA study and the IDEALE study suggested that both parenteral and oral citicoline are effective and safe. Other studies have clearly demonstrated citicoline's effects on several cognitive domains. Conversely, some studies did not point out any evidence of efficacy of this drug.

CONCLUSION

Citicoline appears to be a promising agent to improve cognitive impairment, especially of vascular origin. In fact, so far it appears as a drug with the ability to promote "safe" neuroprotection, capable of enhancing endogenous protective. Large clinical trials are needed to confirm its benefits.

Resveratrol Preconditioning Induces a Novel Extended Window of Ischemic Tolerance in the Mouse Brain

BACKGROUND AND PURPOSE

Prophylactic treatments that afford neuroprotection against stroke may emerge from the field of preconditioning. Resveratrol mimics ischemic preconditioning, reducing ischemic brain injury when administered 2 days before global ischemia in rats. This protection is linked to silent information regulator 2 homologue 1 (Sirt1) and enhanced mitochondrial function possibly through its repression of uncoupling protein 2. Brain-derived neurotrophic factor (BDNF) is another neuroprotective protein associated with Sirt1. In this study, we sought to identify the conditions of resveratrol preconditioning (RPC) that most robustly induce neuroprotection against focal ischemia in mice.

METHODS

We tested 4 different RPC paradigms against a middle cerebral artery occlusion model of stroke. Infarct volume and neurological score were calculated 24 hours after middle cerebral artery occlusion. Sirt1-chromatin binding was evaluated by ChIP-qPCR. Percoll gradients were used to isolate synaptic fractions, and changes in protein expression were determined via Western blot analysis. BDNF concentration was measured using a BDNF-specific ELISA assay.

RESULTS

Although repetitive RPC induced neuroprotection from middle cerebral artery occlusion, strikingly one application of RPC 14 days before middle cerebral artery occlusion showed the most robust protection, reducing infarct volume by 33% and improving neurological score by 28%. Fourteen days after RPC, Sirt1 protein was increased 1.5-fold and differentially bound to the uncoupling protein 2 and BDNF promoter regions. Accordingly, synaptic uncoupling protein 2 level decreased by 23% and cortical BDNF concentration increased 26%.

CONCLUSIONS

RPC induces a novel extended window of ischemic tolerance in the brain that lasts for at least 14 days. Our data suggest that this tolerance may be mediated by Sirt1 through upregulation of BDNF and downregulation of uncoupling protein 2.

Histone Deacetylases Exert Class-Specific Roles in Conditioning the Brain and Heart Against Acute Ischemic Injury

Ischemia-reperfusion (IR) injury comprises a significant portion of morbidity and mortality from heart and brain diseases worldwide. This enduring clinical problem has inspired myriad reports in the scientific literature of experimental interventions seeking to elucidate the pathology of IR injury. Elective cardiac surgery presents perhaps the most viable scenario for protecting the heart and brain from IR injury due to the opportunity to condition the organs prior to insult. The physiological parameters for the preconditioning of vital organs prior to insult through mechanical and pharmacological maneuvers have been heavily examined. These investigations have revealed new insights into how preconditioning alters cellular responses to IR injury. However, the promise of preconditioning remains unfulfilled at the clinical level, and research seeking to implicate cell signals essential to this protection continues. Recent discoveries in molecular biology have revealed that gene expression can be controlled through posttranslational modifications, without altering the chemical structure of the genetic code. In this scenario, gene expression is repressed by enzymes that cause chromatin compaction through catalytic removal of acetyl moieties from lysine residues on histones. These enzymes, called histone deacetylases (HDACs), can be inhibited pharmacologically, leading to the de-repression of protective genes. The discovery that HDACs can also alter the function of non-histone proteins through posttranslational deacetylation has expanded the potential impact of HDAC inhibitors for the treatment of human disease. HDAC inhibitors have been applied in a very small number of experimental models of IR. However, the scientific literature contains an increasing number of reports demonstrating that HDACs converge on preconditioning signals in the cell. This review will describe the influence of HDACs on major preconditioning signaling pathways in the heart and brain.

Parkinson's disease as a result of aging

It is generally considered that Parkinson's disease is induced by specific agents that degenerate a clearly defined population of dopaminergic neurons. Data commented in this review suggest that this assumption is not as clear as is often thought and that aging may be critical for Parkinson's disease. Neurons degenerating in Parkinson's disease also degenerate in normal aging, and the different agents involved in the etiology of this illness are also involved in aging. Senescence is a wider phenomenon affecting cells all over the body, whereas Parkinson's disease seems to be restricted to certain brain centers and cell populations. However, reviewed data suggest that Parkinson's disease may be a local expression of aging on cell populations which, by their characteristics (high number of synaptic terminals and mitochondria, unmyelinated axons, etc.), are highly vulnerable to the agents promoting aging. The development of new knowledge about Parkinson's disease could be accelerated if the research on aging and Parkinson's disease were planned together, and the perspective provided by gerontology gains relevance in this field.

SIRT1 deficiency in microglia contributes to cognitive decline in aging and neurodegeneration via epigenetic regulation of IL-1β

Aging is the predominant risk factor for neurodegenerative diseases. One key phenotype as the brain ages is an aberrant innate immune response characterized by proinflammation. However, the molecular mechanisms underlying aging-associated proinflammation are poorly defined. Whether chronic inflammation plays a causal role in cognitive decline in aging and neurodegeneration has not been established. Here we report a mechanistic link between chronic inflammation and aging microglia and a causal role of aging microglia in neurodegenerative cognitive deficits. We showed that SIRT1 is reduced with the aging of microglia and that microglial SIRT1 deficiency has a causative role in aging- or tau-mediated memory deficits via IL-1β upregulation in mice. Interestingly, the selective activation of IL-1β transcription by SIRT1 deficiency is likely mediated through hypomethylating the specific CpG sites on IL-1β proximal promoter. In humans, hypomethylation of IL-1β is strongly associated with chronological age and with elevated IL-1β transcription. Our findings reveal a novel epigenetic mechanism in aging microglia that contributes to cognitive deficits in aging and neurodegenerative diseases.

Neurohormetic phytochemicals: An evolutionary-bioenergetic perspective

The impact of dietary factors on brain health and vulnerability to disease is increasingly appreciated. The results of epidemiological studies, and intervention trials in animal models suggest that diets rich in phytochemicals can enhance neuroplasticity and resistance to neurodegeneration. Here we describe how interactions of plants and animals during their co-evolution, and resulting reciprocal adaptations, have shaped the remarkable characteristics of phytochemicals and their effects on the physiology of animal cells in general, and neurons in particular. Survival advantages were conferred upon plants capable of producing noxious bitter-tasting chemicals, and on animals able to tolerate the phytochemicals and consume the plants as an energy source. The remarkably diverse array of phytochemicals present in modern fruits, vegetables spices, tea and coffee may have arisen, in part, from the acquisition of adaptive cellular stress responses and detoxification enzymes in animals that enabled them to consume plants containing potentially toxic chemicals. Interestingly, some of the same adaptive stress response mechanisms that protect neurons against noxious phytochemicals are also activated by dietary energy restriction and vigorous physical exertion, two environmental challenges that shaped brain evolution. In this perspective article, we describe some of the signaling pathways relevant to cellular energy metabolism that are modulated by 'neurohormetic phytochemicals' (potentially toxic chemicals produced by plants that have beneficial effects on animals when consumed in moderate amounts). We highlight the cellular bioenergetics-related sirtuin, adenosine monophosphate activated protein kinase (AMPK), mammalian target of rapamycin (mTOR) and insulin-like growth factor 1 (IGF-1) pathways. The inclusion of dietary neurohormetic phytochemicals in an overall program for brain health that also includes exercise and energy restriction may find applications in the prevention and treatment of a range of neurological disorders.

Signaling pathways leading to ischemic mitochondrial neuroprotection

There is extensive evidence that ischemic/reperfusion mediated mitochondrial dysfunction is a major contributor to ischemic damage. However data also indicates that mild ischemic stress induces mitochondrial dependent activation of ischemic preconditioning. Ischemic preconditioning is a neuroprotective mechanism which is activated upon a brief sub-injurious ischemic exposure and is sufficient to provide protection against a subsequent lethal ischemic insult. Current research demonstrates that mitochondria are not only the inducers of but are also an important target of ischemic preconditioning mediated protection. Numerous proteins and signaling pathways are activated by ischemic preconditioning which protect the mitochondria against ischemic damage. In this review we examine some of the proteins activated by ischemic precondition which counteracts the deleterious effects of ischemia/reperfusion thereby maintaining normal mitochondrial activity and lead to ischemic tolerance.

SIRT1 in the brain-connections with aging-associated disorders and lifespan

The silent mating type information regulation 2 proteins (sirtuins) 1 of class III histone deacetylases (HDACs) have been associated with health span and longevity. SIRT1, the best studied member of the mammalian sirtuins, has a myriad of roles in multiple tissues and organs. However, a significant part of SIRT1's role that impinges on aging and lifespan may lie in its activities in the central nervous system (CNS) neurons. Systemically, SIRT1 influences energy metabolism and circadian rhythm through its activity in the hypothalamic nuclei. From a cell biological perspective, SIRT1 is a crucial component of multiple interconnected regulatory networks that modulate dendritic and axonal growth, as well as survival against stress. This neuronal cell autonomous activity of SIRT1 is also important for neuronal plasticity, cognitive functions, as well as protection against aging-associated neuronal degeneration and cognitive decline. We discuss recent findings that have shed light on the various activities of SIRT1 in the brain, which collectively impinge on aging-associated disorders and lifespan.

An exploratory double-blind, randomized clinical trial with selisistat, a SirT1 inhibitor, in patients with Huntington's disease

AIMS

Selisistat, a selective SirT1 inhibitor is being developed as a potentially disease-modifying therapeutic for Huntington's disease (HD). This was the first study of selisistat in HD patients and was primarily aimed at development of pharmacodynamic biomarkers.

METHODS

This was a randomized, double-blind, placebo-controlled, multicentre exploratory study. Fifty-five male and female patients in early stage HD were randomized to receive 10 mg or 100 mg of selisistat or placebo once daily for 14 days. Blood sampling, clinical and safety assessments were conducted throughout the study. Candidate pharmacodynamic markers included circulating soluble huntingtin and innate immune markers.

RESULTS

Selisistat was found to be safe and well tolerated, and systemic exposure parameters showed that the average steady-state plasma concentration achieved at the 10 mg dose level (125 nm) was comparable with the IC50 for SirT1 inhibition. No adverse effects on motor, cognitive or functional readouts were recorded. While circulating levels of soluble huntingtin were not affected by selisistat in this study, the biological samples collected have allowed development of assay technology for use in future studies. No effects on innate immune markers were seen.

CONCLUSIONS

Selisistat was found to be safe and well tolerated in early stage HD patients at plasma concentrations within the anticipated therapeutic concentration range.

Docking and binding free energy calculations of sirtuin inhibitors

Sirtuins form a unique and highly conserved class of NAD(+)-dependent lysine deacylases. Among these the human subtypes Sirt1-3 has been implicated in the pathogenesis of numerous diseases such as cancer, metabolic syndromes, viral diseases and neurological disorders. Most of the sirtuin inhibitors that have been identified so far show limited potency and/or isoform selectivity. Here, we introduce a promising method to generate protein-inhibitor complexes of human Sirt1, Sirt2 and Sirt3 by means of ligand docking and molecular dynamics simulations. This method highly reduces the complexity of such applications and can be applied to other protein targets beside sirtuins. To the best of our knowledge, we present the first binding free energy method developed by using a validated data set of sirtuin inhibitors, where both a fair number of compounds (33 thieno[3,2-d]pyrimidine-6-carboxamide derivatives) was developed and tested in the same laboratory and also crystal structures in complex with the enzyme have been reported. A significant correlation between binding free energies derived from MM-GBSA calculations and in vitro data was found for all three sirtuin subtypes. The developed MM-GBSA protocol is computationally inexpensive and can be applied as a post-docking filter in virtual screening to find novel Sirt1-3 inhibitors as well as to prioritize compounds with similar chemical structures for further biological characterization.

Nutrition facts in multiple sclerosis

The question whether dietary habits and lifestyle have influence on the course of multiple sclerosis (MS) is still a matter of debate, and at present, MS therapy is not associated with any information on diet and lifestyle. Here we show that dietary factors and lifestyle may exacerbate or ameliorate MS symptoms by modulating the inflammatory status of the disease both in relapsing-remitting MS and in primary-progressive MS. This is achieved by controlling both the metabolic and inflammatory pathways in the human cell and the composition of commensal gut microbiota. What increases inflammation are hypercaloric Western-style diets, characterized by high salt, animal fat, red meat, sugar-sweetened drinks, fried food, low fiber, and lack of physical exercise. The persistence of this type of diet upregulates the metabolism of human cells toward biosynthetic pathways including those of proinflammatory molecules and also leads to a dysbiotic gut microbiota, alteration of intestinal immunity, and low-grade systemic inflammation. Conversely, exercise and low-calorie diets based on the assumption of vegetables, fruit, legumes, fish, prebiotics, and probiotics act on nuclear receptors and enzymes that upregulate oxidative metabolism, downregulate the synthesis of proinflammatory molecules, and restore or maintain a healthy symbiotic gut microbiota. Now that we know the molecular mechanisms by which dietary factors and exercise affect the inflammatory status in MS, we can expect that a nutritional intervention with anti-inflammatory food and dietary supplements can alleviate possible side effects of immune-modulatory drugs and the symptoms of chronic fatigue syndrome and thus favor patient wellness.

The promise and perils of HDAC inhibitors in neurodegeneration

Histone deacetylases (HDACs) represent emerging therapeutic targets in the context of neurodegeneration. Indeed, pharmacologic inhibition of HDACs activity in the nervous system has shown beneficial effects in several preclinical models of neurological disorders. However, the translation of such therapeutic approach to clinics has been only marginally successful, mainly due to our still limited knowledge about HDACs physiological role particularly in neurons. Here, we review the potential benefits along with the risks of targeting HDACs in light of what we currently know about HDAC activity in the brain.

Biochemical characterization of sirtuin 6 in the brain and its involvement in oxidative stress response

Sirtuin 6 (SIRT6) is a member of nicotinamide adenine dinucleotide-dependent deacetylase protein family and has been implicated in the control of glucose and lipid metabolism, cancer, genomic stability and DNA repair. Moreover, SIRT6 regulates the expression of a large number of genes involved in stress response and aging. The role of SIRT6 in brain function and neuronal survival is largely unknown. Here, we biochemically characterized SIRT6 in brain tissues and primary neuronal cultures and found that it is highly expressed in cortical and hippocampal regions and enriched in the synaptosomal membrane fraction. Immunoblotting analysis on cortical and hippocampal neurons showed that SIRT6 is downregulated during maturation in vitro, reaching the lowest expression at 11 days in vitro. In addition, SIRT6 overexpression in terminally differentiated cortical and hippocampal neurons, mediated by a neuron-specific recombinant adeno-associated virus, downregulated cell viability under oxidative stress condition. By contrast, under control condition, SIRT6 overexpression had no detrimental effect. Overall these results suggest that SIRT6 may play a role in synaptic function and neuronal maturation and it may be implicated in the regulation of neuronal survival.

Dietary and metabolic control of stem cell function in physiology and cancer

Organismal diet has a profound impact on tissue homeostasis and health in mammals. Adult stem cells are a keystone of tissue homeostasis that alters tissue composition by balancing self-renewal and differentiation divisions. Because somatic stem cells may respond to shifts in organismal physiology to orchestrate tissue remodeling and some cancers are understood to arise from transformed stem cells, there is a likely possibility that organismal diet, stem cell function, and cancer initiation are interconnected. Here we will explore the emerging effects of diet on nutrient-sensing pathways active in mammalian tissue stem cells and their relevance to normal and cancerous growth.

Silent information regulator 2 homolog 1 counters cerebral hypoperfusion injury by deacetylating endothelial nitric oxide synthase

BACKGROUND AND PURPOSE

Silent information regulator 2 homolog 1 (SIRT1) is a protein deacetylase that has been reported to suppress neurodegenerative and cardiovascular diseases in model organisms. We hypothesized that neurovascular protection is one of the diverse actions of SIRT1. This study was designed to determine whether SIRT1 protects against the consequences of cerebral hypoperfusion in vivo.

METHODS

Sirt1-overexpressing (Sirt1-Tg) mice driven by a prion promoter and their wild-type littermates were subjected to bilateral common carotid artery stenosis using external microcoils. Using Sirt1-Tg mice, we assessed the effect of SIRT1 on cerebral blood flow, cerebral angioarchitecture, histological and ultrastructural changes, and spatial working memory at several time points. We also evaluated the effects of preadministration of SIRT1 inhibitors or endothelial nitric oxide synthase inhibitors on cerebral blood flow after bilateral common carotid artery stenosis in Sirt1-Tg mice. Levels of acetylated and nonacetylated endothelial nitric oxide synthase were measured semiquantitatively with immunoblotting.

RESULTS

Cerebral hypoperfusion induced by bilateral common carotid artery stenosis caused memory impairment and histological changes in wild-type littermates. However, these phenotypes were rescued in Sirt1-Tg mice, where cerebral blood flow was maintained even poststenosis. Electron microscopic analyses showed irregularities in the vascular endothelia, such as tight junction openings in wild-type mice, which were absent in Sirt1-Tg littermates. Brain endothelial nitric oxide synthase was acetylated after cerebral hypoperfusion in wild-type littermates but remained unacetylated in Sirt1-Tg mice. Moreover, treatment with SIRT1 inhibitors and endothelial nitric oxide synthase inhibitors abolished the vasculoprotective effects of SIRT1.

CONCLUSIONS

Our results indicate that neurovascular endothelial SIRT1 potentiation upregulates the nitric oxide system and counters cerebral hypoperfusion injury. This novel cerebral blood flow-preserving mechanism offers potential molecular targets for future therapeutic intervention.

Senescence in adipose-derived stem cells and its implications in nerve regeneration

Adult mesenchymal stem cells, specifically adipose-derived stem cells have self-renewal and multiple differentiation potentials and have shown to be the ideal candidate for therapeutic applications in regenerative medicine, particularly in peripheral nerve regeneration. Adipose-derived stem cells are easily harvested, although they may show the effects of aging, hence their potential in nerve repair may be limited by cellular senescence or donor age. Cellular senescence is a complex process whereby stem cells grow old as consequence of intrinsic events (e.g., DNA damage) or environmental cues (e.g., stressful stimuli or diseases), which determine a permanent growth arrest. Several mechanisms are implicated in stem cell senescence, although no one is exclusive of the others. In this review we report some of the most important factors modulating the senescence process, which can influence adipose-derived stem cell morphology and function, and compromise their clinical application for peripheral nerve regenerative cell therapy.

Over-expression of the Sirt3 sirtuin Protects neuronally differentiated PC12 Cells from degeneration induced by oxidative stress and trophic withdrawal

Sirt3 is a mitochondrial sirtuin whose deacetylase activity regulates facets of oxidative metabolic efficiency, anti-oxidative capacity, and intra-mitochondrial signaling. In this study, we tested whether the over-expression of a human Sirt3-myc transgene in differentiated PC12 cells, a model of sympathetic catecholaminergic neurons, would affect the sensitivity of these cells to oxidative stress or trophic withdrawal insults. Expression analysis revealed the Sirt3-myc product was expressed as a 45kDa pro-form, which localized primarily within the cytosol, and a 30kDa processed form that localized predominantly within mitochondria. When subjected to acute glucose deprivation or acute oxygen-glucose deprivation, differentiated PC12 cells over-expressing Sirt3-myc displayed significantly lower levels of cytotoxicity, both at the end of the insult, and at different times following media reperfusion, than cells transfected with a control plasmid. Further, Sirt3-myc over-expression also protected differentiated PC12 cells from apoptosis induced by trophic withdrawal. Collectively, these data indicate that an elevation of Sirt3 is sufficient to protect neuronal PC12 cells from cytotoxic insults, and add to the growing evidence that Sirt3 could be targeted for neuroprotective intervention.

Methamphetamine downregulates striatal glutamate receptors via diverse epigenetic mechanisms

BACKGROUND

Chronic methamphetamine (METH) exposure causes neuroadaptations at glutamatergic synapses.

METHODS

To identify the METH-induced epigenetic underpinnings of these neuroadaptations, we injected increasing METH doses to rats for 2 weeks and measured striatal glutamate receptor expression. We then quantified the effects of METH exposure on histone acetylation. We also measured METH-induced changes in DNA methylation and DNA hydroxymethylation.

RESULTS

Chronic METH decreased transcript and protein expression of GluA1 and GluA2 alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) and GluN1 N-methyl-D-aspartate receptor subunits. These changes were associated with altered electrophysiological glutamatergic responses in striatal neurons. Chromatin immunoprecipitation-polymerase chain reaction revealed that METH decreased enrichment of acetylated histone H4 on GluA1, GluA2, and GluN1 promoters. Methamphetamine exposure also increased repressor element-1 silencing transcription factor (REST) corepressor 1, methylated CpG binding protein 2, and histone deacetylase 2 enrichment, but not of sirtuin 1 or sirtuin 2, onto GluA1 and GluA2 gene sequences. Moreover, METH caused interactions of REST corepressor 1 and methylated CpG binding protein 2 with histone deacetylase 2 and of REST with histone deacetylase 1. Surprisingly, methylated DNA immunoprecipitation and hydroxymethylated DNA immunoprecipitation-polymerase chain reaction revealed METH-induced decreased enrichment of 5-methylcytosine and 5-hydroxymethylcytosine at GluA1 and GluA2 promoter sequences. Importantly, the histone deacetylase inhibitor, valproic acid, blocked METH-induced decreased expression of AMPAR and N-methyl-D-aspartate receptor subunits. Finally, valproic acid also attenuated METH-induced decrease H4K16Ac recruitment on AMPAR gene sequences.

CONCLUSIONS

These observations suggest that histone H4 hypoacetylation may be the main determinant of METH-induced decreased striatal glutamate receptor expression.

Tissue-specific deregulation of selected HDACs characterizes ALS progression in mouse models: pharmacological characterization of SIRT1 and SIRT2 pathways

Acetylation homeostasis is thought to play a role in amyotrophic lateral sclerosis, and treatment with inhibitors of histone deacetylases has been considered a potential and attractive therapeutic approach, despite the lack of a thorough study of this class of proteins. In this study, we have considerably extended previous knowledge on the expression of 13 histone deacetylases in tissues (spinal cord and muscle) from mice carrying two different ALS-linked SOD1 mutations (G93A-SOD1 and G86R-SOD1). We have then focused on class III histone deacetylases SIRT1 and SIRT2 that are considered relevant in neurodegenerative diseases. SIRT1 decreases in the spinal cord, but increases in muscle during the progression of the disease, and a similar expression pattern is observed in the corresponding cell models (neuroblastoma and myoblasts). SIRT2 mRNA expression increases in the spinal cord in both G93A-SOD1 and G86R-SOD1 mice but protein expression is substantially unchanged in all the models examined. At variance with other sirtuin modulators (sirtinol, AGK2 and SRT1720), the well-known SIRT1 inhibitor Ex527 has positive effects on survival of neuronal cells expressing mutant SOD1, but this effect is neither mediated by SIRT1 inhibition nor by SIRT2 inhibition. These data call for caution in proposing sirtuin modulation as a target for treatment.

Activation of SIRT1 by curcumin blocks the neurotoxicity of amyloid-β25-35 in rat cortical neurons

As one of the most important hallmarks of Alzheimer's disease (AD), β-amyloid (Aβ) plays important roles in inducing reactive oxygen species (ROS) generation, mitochondrial dysfunction and apoptotic cell death in neurons. Curcumin extracted from the yellow pigments spice plant turmeric shows multiplied bioactivities such as antioxidant and anti-apoptosis properties in vitro and in vivo. In the present study, the neuroprotective effect of curcumin against Aβ25-35-induced cell death in cultured cortical neurons was investigated. We found that pretreatment of curcumin prevented the cultured cortical neurons from Aβ25-35-induced cell toxicity. In addition, curcumin improved mitochondrial membrane potential (ΔΨm), decreased ROS generation and inhibited apoptotic cell death in Aβ25-35 treated neurons. Furthermore, we found that application of curcumin activated the expression of SIRT1 and subsequently decreased the expression of Bax in the presence of Aβ25-35. The protective effect of curcumin was blocked by SIRT1 siRNA. Taken together, our results suggest that activation of SIRT1 is involved in the neuroprotective action of curcumin.

Sirtuins' modulation of autophagy

The sirtuin family of class III histone deacetylases has been extensively implicated in modulating a myriad of cellular processes, including energy metabolism, stress response, cell/tissue survival and malignancy. Recent studies have also identified multifaceted roles for Sirt1 and Sirt2 in the regulation of autophagy. Sirt1 could influence autophagy directly via its deacetylation of key components of the autophagy induction network, such as the products of autophagy genes (Atg) 5, 7, and 8. Nucleus-localized Sirt1 is also known to induce the expression of autophagy pathway components through the activation of FoxO transcription factor family members. The perception of a linear Sirt1-FoxO axis in autophagy induction is complicated by recent findings that acetylated FoxO1 could bind to Atg7 in the cytoplasm and affect autophagy directly. This occurs with prolonged stress signaling, with FoxO1's continuous dissociation from cytoplasmic Sirt2 and its consequential hyperacetylation. FoxO-mediated nuclear transcription may induce/enhance autophagy in ways that are different compared to cytoplasmic FoxO, thereby leading to contrasting (cell survival versus cell death) outcomes. FoxO and Sirt1 are both subjected to regulation by stress signaling (e.g., through the c-Jun N-terminal kinases (JNK)) in the context of autophagy induction, which are also critical in determining between cell survival and death in a context-dependent manner. We discussed here the emerging molecular intricacies of sirtuins' connections with autophagy. A good understanding of these connections would serve to consolidate a framework of mechanisms underlying Sirt1's protective effects in multiple physiological systems.

Hydrogen sulfide inhibits formaldehyde-induced endoplasmic reticulum stress in PC12 cells by upregulation of SIRT-1

Background

Formaldehyde (FA), a well-known environmental pollutant, has been classified as a neurotoxic molecule. Our recent data demonstrate that hydrogen sulfide (H₂S), the third gaseous transmitter, has a protective effect on the neurotoxicity of FA. However, the exact mechanisms underlying this protection remain largely unknown. Endoplasmic reticulum (ER) stress has been implicated in the neurotoxicity of FA. Silent mating type information regulator 2 homolog 1 (SIRT-1), a histone deacetylases, has various biological activities, including the extension of lifespan, the modulation of ER stress, and the neuroprotective action.

Objective

We hypothesize that the protection of H₂S against FA-induced neurotoxicity involves in inhibiting ER stress by upregulation of SIRT-1. The present study attempted to investigate the protective effect of H₂S on FA-induced ER stress in PC12 cells and the contribution of SIRT-1 to the protection of H₂S against FA-induced injuries, including ER stress, cytotoxicity and apoptosis.

Principal Findings

We found that exogenous application of sodium hydrosulfide (NaHS; an H₂S donor) significantly attenuated FA-induced ER stress responses, including the upregulated levels of glucose-regulated protein 78, C/EBP homologous protein, and cleaved caspase-12 expression. We showed that NaHS upregulates the expression of SIRT-1 in PC12 cells. Moreover, the protective effects of H₂S on FA-elicited ER stress, cytotoxicity and apoptosis were reversed by Sirtinol, a specific inhibitor of SIRT-1.

Conclusion/Significance

These data indicate that H₂S exerts its protection against the neurotoxicity of FA through overcoming ER stress via upregulation of SIRT-1. Our findings provide novel insights into the protective mechanisms of H₂S against FA-induced neurotoxicity.

Role of Sirt1 during the ageing process: relevance to protection of synapses in the brain

Ageing is a stochastic process associated with a progressive decline in physiological functions which predispose to the pathogenesis of several neurodegenerative diseases. The intrinsic complexity of ageing remains a significant challenge to understand the cause of this natural phenomenon. At the molecular level, ageing is thought to be characterized by the accumulation of chronic oxidative damage to lipids, proteins and nucleic acids caused by free radicals. Increased oxidative stress and misfolded protein formations, combined with impaired compensatory mechanisms, may promote neurodegenerative disorders with age. Nutritional modulation through calorie restriction has been shown to be effective as an anti-ageing factor, promoting longevity and protecting against neurodegenerative pathology in yeast, nematodes and murine models. Calorie restriction increases the intracellular levels of the essential pyridine nucleotide, nicotinamide adenine dinucleotide (NAD(+)), a co-substrate for the sirtuin 1 (Sirt1, silent mating-type information regulator 2 homolog 1) activity and a cofactor for oxidative phosphorylation and ATP synthesis. Promotion of intracellular NAD(+) anabolism is speculated to induce neuroprotective effects against amyloid-β-peptide (Aβ) toxicity in some models for Alzheimer's disease (AD). The NAD(+)-dependent histone deacetylase, Sirt1, has been implicated in the ageing process. Sirt1 serves as a deacetylase for numerous proteins involved in several cellular pathways, including stress response and apoptosis, and plays a protective role in neurodegenerative disorders, such as AD.

SIRT1 inhibition by sirtinol aggravates brain edema after experimental subarachnoid hemorrhage

Secondary brain injury following subarachnoid hemorrhage (SAH) is poorly understood. We utilized a rat model of SAH to investigate whether SIRT1 has a protective role against brain edema via the tumor suppressor protein p53 pathway. Experimental SAH was induced in adult male Sprague-Dawley rats by prechiasmatic cistern injection. Brain SIRT1 protein levels were examined in the sham controls and in rats 6, 12, 24, 48, and 72 hr after SAH induction. The SIRT1 inhibitor sirtinol was administered by intracerebroventricular infusion. Neurological functions, blood-brain barrier (BBB) disruption, and brain water content were assessed. Endothelial cell apoptosis, caspase 3 protein expression, p53 acetylation, and matrix metalloproteinase-9 (MMP-9) activity were examined. Compared with the control, SIRT1 protein expression increased remarkably, reaching a maximum at 24 hr after SAH. Sirtinol treatment significantly lowered SIRT1 expression, accompanied by deteriorated neurologic function, BBB disruption, brain edema, increased endothelial cell apoptosis, and increased MMP-9 gelatinase activity compared with the rats treated with vehicle only. Our results suggest that increased expression of endogenous SIRT1 may play a neuroprotective role against brain edema after SAH.

Physical exercise improves synaptic dysfunction and recovers the loss of survival factors in 3xTg-AD mouse brain

Physical exercise has become a potentially beneficial therapy for reducing neurodegeneration symptoms in Alzheimer's disease. Previous studies have shown that cognitive deterioration, anxiety and the startle response observed in 7-month-old 3xTg-AD mice were ameliorated after 6 months of free access to a running wheel. Also, alterations in synaptic response to paired-pulse stimulation were improved. The present study further investigated some molecular mechanisms underlying the beneficial effects of 6 months of voluntary exercise on synaptic plasticity in 7-month-old 3xTg-AD mice. Changes in binding parameters of [(3)H]-flunitrazepam to GABAA receptor and of [(3)H]-MK-801 to NMDA receptor in cerebral cortex of 3xTgAD mice were restored by voluntary exercise. In addition, reduced expression levels of NMDA receptor NR2B subunit were reestablished. The synaptic proteins synaptophysin and PSD-95 and the neuroprotective proteins GDNF and SIRT1 were downregulated in 3xTgAD mice and were recovered by exercise treatment. Overall, in this paper we highlight the fact that different interrelated mechanisms are involved in the beneficial effects of exercise on synaptic plasticity alterations in the 3xTg-AD mouse model.

Interleukin-10 chimeric protein to protect transplanted neural progenitor cells from immune responses

Novel system for protecting transplanted cells from inflammatory responses.

Multiple sclerosis: molecular mechanisms and therapeutic opportunities

The pathophysiology of multiple sclerosis (MS) involves several components: redox, inflammatory/autoimmune, vascular, and neurodegenerative. All of them are supported by the intertwined lines of evidence, and none of them should be written off. However, the exact mechanisms of MS initiation, its development, and progression are still elusive, despite the impressive pace by which the data on MS are accumulating. In this review, we will try to integrate the current facts and concepts, focusing on the role of redox changes and various reactive species in MS. Knowing the schedule of initial changes in pathogenic factors and the key turning points, as well as understanding the redox processes involved in MS pathogenesis is the way to enable MS prevention, early treatment, and the development of therapies that target specific pathophysiological components of the heterogeneous mechanisms of MS, which could alleviate the symptoms and hopefully stop MS. Pertinent to this, we will outline (i) redox processes involved in MS initiation; (ii) the role of reactive species in inflammation; (iii) prooxidative changes responsible for neurodegeneration; and (iv) the potential of antioxidative therapy.

Resveratrol delays Wallerian degeneration in a NAD(+) and DBC1 dependent manner

Axonal degeneration is a central process in the pathogenesis of several neurodegenerative diseases. Understanding the molecular mechanisms that are involved in axonal degeneration is crucial to developing new therapies against diseases involving neuronal damage. Resveratrol is a putative SIRT1 activator that has been shown to delay neurodegenerative diseases, including Amyotrophic Lateral Sclerosis, Alzheimer, and Huntington's disease. However, the effect of resveratrol on axonal degeneration is still controversial. Using an in vitro model of Wallerian degeneration based on cultures of explants of the dorsal root ganglia (DRG), we showed that resveratrol produces a delay in axonal degeneration. Furthermore, the effect of resveratrol on Wallerian degeneration was lost when SIRT1 was pharmacologically inhibited. Interestingly, we found that knocking out Deleted in Breast Cancer-1 (DBC1), an endogenous SIRT1 inhibitor, restores the neuroprotective effect of resveratrol. However, resveratrol did not have an additive protective effect in DBC1 knockout-derived DRGs, suggesting that resveratrol and DBC1 are working through the same signaling pathway. We found biochemical evidence suggesting that resveratrol protects against Wallerian degeneration by promoting the dissociation of SIRT1 and DBC1 in cultured ganglia. Finally, we demonstrated that resveratrol can delay degeneration of crushed nerves in vivo. We propose that resveratrol protects against Wallerian degeneration by activating SIRT1 through dissociation from its inhibitor DBC1.

Effects of Resveratrol and trans-3,5,4'-Trimethoxystilbene on Glutamate-Induced Cytotoxicity, Heme Oxygenase-1, and Sirtuin 1 in HT22 Neuronal Cells

Resveratrol (trans-3,5,4’-trihydroxystilbene) has received considerable attention recently for the potential neuroprotective effects in neurodegenerative disorders where heme oxygenase-1 (HO-1) and sirtuin 1 (SIRT1) represent promising therapeutic targets. Resveratrol has been known to increase HO-1 expression and SIRT1 activity. In this study, the effects of resveratrol and trans-3,5,4’-trimethoxystilbene (TMS), a resveratrol derivative, on cytotoxicity caused by glutamate-induced oxidative stress, HO-1 expression, and SIRT1 activation have been investigated by using murine hippocampal HT22 cells, which have been widely used as an in vitro model for investigating glutamate-induced neurotoxicity. Resveratrol protected HT22 neuronal cells from glutamateinduced cytotoxicity and increased HO-1 expression as well as SIRT1 activity in a concentration-dependent manner. Cytoprotec-tion afforded by resveratrol was partially reversed by the specific inhibition of HO-1 expression by HO-1 small interfering RNA and the nonspecific blockage of HO-1 activity by tin protoporphyrin IX, but not by SIRT1 inhibitors. Surprisingly, TMS, a resveratrol derivative with methoxyl groups in lieu of the hydroxyl groups, and trans-stilbene, a non-hydroxylated analog, failed to protect HT22 cells from glutamate-induced cytotoxicity and to increase HO-1 expression and SIRT1 activity. Taken together, our findings suggest that the cytoprotective effect of resveratrol was at least in part associated with HO-1 expression but not with SIRT1 activation and, importantly, that the presence of hydroxyl groups on the benzene rings of resveratrol appears to be necessary for cytoprotection against glutamate-induced oxidative stress, HO-1 expression, and SIRT1 activation in HT22 neuronal cells.

Neuroprotection in multiple sclerosis: a therapeutic approach

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system that is pathologically characterized by inflammatory demyelination and neurodegeneration. Axonal damage, along with neuronal loss, occurs from disease onset and may lead to progressive and permanent disability. In contrast with the inflammatory pathways, the molecular mechanisms leading to MS neurodegeneration remain largely elusive. With improved understanding of these mechanisms, new potential therapeutic targets for neuroprotection have emerged. We review the current understanding of neurodegenerative processes at play in MS and discuss potential outcome measures and targets for neuroprotection trials.

Ischemic preconditioning alters the epigenetic profile of the brain from ischemic intolerance to ischemic tolerance

Ischemic preconditioning is an innate neuroprotective mechanism in which a sub-injurious ischemic exposure increases the brain's ability to withstand a subsequent, normally injurious ischemic insult. Part of ischemic preconditioning neuroprotection stems from an epigenetic reprogramming of the brain to a phenotype of ischemic tolerance, which results in a gene expression profile different from that observed in the non-injured and ischemia-injured brains. Such neuroprotective reprograming, activated by ischemic preconditioning, requires specific changes in DNA accessibility coordinated with activation of transcriptional activator and repressor proteins, which allows for expression of specific neuroprotective proteins despite a general repression of gene expression. In this review we examine the effects of injurious ischemia and ischemic preconditioning on the regulation of DNA methylation, histone post-translational modifications, and non-coding RNA expression. There is increasing interest in the role of epigenetics in disease pathobiology, and whether and how pharmacological manipulation of epigenetic processes may allow for ischemic neuroprotection. Therefore, a better understanding of the epigenomic determinants underlying the modulation of gene expression that lead to ischemic tolerance or cell death offers the promise of novel neuroprotective therapies that target global reprograming of genomic activity versus individual cellular signaling pathways.

The diversity of histone versus nonhistone sirtuin substrates

The members of the Sir2 family, or sirtuins, are major regulators of the response to different types of stress. The members of the family have adapted to increasing complexities throughout evolution and have become diversified by increasing their number, specificity, and localization and acquiring novel functions. Sirtuins have been consistently implicated in the cross-talk between the genomic information and environment from the prokaryotes onward. Evidence suggests that in the transition to eukaryotes, histones became one of the basic and most conserved targets of the family, to the extent that in yeast and mammals, sirtuins were originally described as NAD(+)-dependent histone deacetylases and classified as class III histone deacetylases. A growing number of studies have determined that sirtuins also target a wide range of nonhistone proteins. Many of these targets are also directly or indirectly related to chromatin regulation. The number of targets has grown considerably in the last decade but has provoked an ill-founded discussion that neglects the importance of histones as sirtuin targets. In this review, we summarize our knowledge regarding the range of sirtuin targets described to date and discuss the different functional implications of histone and nonhistone targets throughout evolution.

Brain response to calorie restriction

Calorie restriction extends longevity and delays ageing in model organisms and mammals, opposing the onset and progression of an array of age-related diseases. These beneficial effects also extend to the maintenance of brain cognitive functions at later age and to the prevention, at least in rodents, of brain senescence and associated neurodegenerative disorders. In recent years, the molecular mechanisms underlying brain response to calorie restriction have begun to be elucidated, revealing the unanticipated role of a number of key nutrient sensors and nutrient-triggered signaling cascades in the translation of metabolic cues into cellular and molecular events that ultimately lead to increased cell resistance to stress, enhanced synaptic plasticity, and improved cognitive performance. Of note, the brain's role in CR also includes the activation of nutrient-sensitive hypothalamic circuitries and the implementation of neuroendocrine responses that impact the entire organism. The present review addresses emerging molecular themes in brain response to dietary restriction, and the implications of this knowledge for the understanding and the prevention of brain disorders associated with ageing and metabolic disease.

Energy metabolism and energy-sensing pathways in mammalian embryonic and adult stem cell fate

Metabolism is influenced by age, food intake, and conditions such as diabetes and obesity. How do physiological or pathological metabolic changes influence stem cells, which are crucial for tissue homeostasis? This Commentary reviews recent evidence that stem cells have different metabolic demands than differentiated cells, and that the molecular mechanisms that control stem cell self-renewal and differentiation are functionally connected to the metabolic state of the cell and the surrounding stem cell niche. Furthermore, we present how energy-sensing signaling molecules and metabolism regulators are implicated in the regulation of stem cell self-renewal and differentiation. Finally, we discuss the emerging literature on the metabolism of induced pluripotent stem cells and how manipulating metabolic pathways might aid cellular reprogramming. Determining how energy metabolism regulates stem cell fate should shed light on the decline in tissue regeneration that occurs during aging and facilitate the development of therapies for degenerative or metabolic diseases.

Towards a 'systems'-level understanding of the nervous system and its disorders

It is becoming clear that nervous system development and adult functioning are highly coupled with other physiological systems. Accordingly, neurological and psychiatric disorders are increasingly being associated with a range of systemic comorbidities including, most prominently, impairments in immunological and bioenergetic parameters as well as in the gut microbiome. Here, we discuss various aspects of the dynamic crosstalk between these systems that underlies nervous system development, homeostasis, and plasticity. We believe a better definition of this underappreciated systems physiology will yield important insights into how nervous system diseases with systemic comorbidities arise and potentially identify novel diagnostic and therapeutic strategies.