SIRT1 Mediates Depression-Like Behaviors in the Nucleus Accumbens

CA1 Nampt knockdown recapitulates hippocampal cognitive phenotypes in old mice which nicotinamide mononucleotide improves

Cognitive dysfunction is one of the most concerning outcomes in global population aging. However, the mechanisms by which cognitive functions are impaired during aging remain elusive. It has been established that NAD⁺ levels are reduced in multiple tissues and organs, including the brain. We found that NAD⁺ levels declined in the hippocampus of mice during the course of aging, and whereas we observed minimal age-related effects on spatial learning/memory capabilities in old mice, we discovered that they developed cognitive hypersensitivity in response to aversive stimulation during contextual fear conditioning tests. This cognitive hypersensitivity appears to be associated with alterations in emotionality (fear/anxiety) and sensory processing (shock sensitivity), rather than reflect genuine conditioning/retention effects, during aging. Supplementation of nicotinamide mononucleotide (NMN) improved the sensory processing aspect of the hypersensitivity and possibly other related behaviors. Specific knockdown of nicotinamide phosphoribosyltransferase (Nampt) in the CA1 region, but not in the dentate gyrus, recapitulates this cognitive hypersensitivity observed in old mice. We identified calcium/calmodulin-dependent serine protein kinase (Cask) as a potential downstream effector in response to age-associated NAD⁺ reduction in the hippocampus. Cask expression is responsive to NAD⁺ changes and also reduced in the hippocampus during aging. Short-term NMN supplementation can enhance Cask expression in the hippocampus of old mice. Its promoter activity is regulated in a Sirt1-dependent manner. Taken together, NAD⁺ reduction in the CA1 region contributes to development of age-associated cognitive dysfunction, aspects of which may be prevented or treated by enhancing NAD⁺ availability through supplementation of NAD⁺ intermediates, such as NMN.

Cognitive dysfunction is one of the most concerning outcomes in global population aging. However, the mechanisms of cognitive impairment during aging remain elusive. We found that in old mice, levels of nicotinamide adenine dinucleotide (NAD⁺), an essential chemical for all living organisms, declined in the hippocampus, a critical part of the brain for memory and learning. We also found that age-associated hypersensitivity in cognitive and behavioral functions (cognitive hypersensitivity) was induced by reduced NAD⁺ availability in the hippocampus. Supplementation of nicotinamide mononucleotide (NMN), a critical chemical that is converted to NAD⁺, is able to mitigate the cognitive hypersensitivity observed in old mice. Our findings provide new insights into how NAD⁺ decline affects age-associated anxiety/depression and how such impairments can be prevented or treated by enhancing NAD⁺.

Resilience and immunity

Resilience is the process that allows individuals to adapt to adverse conditions and recover from them. This process is favored by individual qualities that have been amply studied in the field of stress such as personal control, positive affect, optimism, and social support. Biopsychosocial studies on the individual qualities that promote resilience show that these factors help protect against the deleterious influences of stressors on physiology in general and immunity in particular. The reverse is also true as there is evidence that immune processes influence resilience. Most of the data supporting this relationship comes from animal studies on individual differences in the ability to resist situations of chronic stress. These data build on the knowledge that has accumulated on the influence of immune factors on brain and behavior in both animal and human studies. In general, resilient individuals have a different immunophenotype from that of stress susceptible individuals. It is possible to render susceptible individuals resilient and vice versa by changing their inflammatory phenotype. The adaptive immune phenotype also influences the ability to recover from inflammation-induced symptoms. The modulation of these bidirectional relationships between resilience and immunity by the gut microbiota opens the possibility to influence them by probiotics and prebiotics. However, more focused studies on the reciprocal relationship between resilience and immunity will be necessary before this can be put into practice.

Approaching to the Essence of Major Depressive Disorder

Major Depressive Disorder (MDD) is a serious neuropsychic disease. It destroys person’s family relationship and social connections seriously. Latest WHO investigation disclosed nearly 4.4% of the population worldwide (approximately 322 million people) were being affected by MDD extensively [1]. While in China, Dong M, et al. reported the occurrence rate of suicide attempt during hospitalization and after the onset of MDD were 17.3% (95% CI: 12.4-23.7%) and 42.1% (95% CI: 26.1-60.0%) respectively [2]. Another research made by Grupta S, et al. announced MDD in urban China might be under-diagnosed and untreated [3].

SIRT1 mediates obesity- and nutrient-dependent perturbation of pubertal timing by epigenetically controlling Kiss1 expression

Puberty is regulated by epigenetic mechanisms and is highly sensitive to metabolic and nutritional cues. However, the epigenetic pathways mediating the effects of nutrition and obesity on pubertal timing are unknown. Here, we identify Sirtuin 1 (SIRT1), a fuel-sensing deacetylase, as a molecule that restrains female puberty via epigenetic repression of the puberty-activating gene, Kiss1. SIRT1 is expressed in hypothalamic Kiss1 neurons and suppresses Kiss1 expression. SIRT1 interacts with the Polycomb silencing complex to decrease Kiss1 promoter activity. As puberty approaches, SIRT1 is evicted from the Kiss1 promoter facilitating a repressive-to-permissive switch in chromatin landscape. Early-onset overnutrition accelerates these changes, enhances Kiss1 expression and advances puberty. In contrast, undernutrition raises SIRT1 levels, protracts Kiss1 repression and delays puberty. This delay is mimicked by central pharmacological activation of SIRT1 or SIRT1 overexpression, achieved via transgenesis or virogenetic targeting to the ARC. Our results identify SIRT1-mediated inhibition of Kiss1 as key epigenetic mechanism by which nutritional cues and obesity influence mammalian puberty.

The onset of mammalian puberty is sensitive to metabolic changes and nutritional status, but the mechanisms underlying this phenomenon are poorly understood. Here the authors show that the epigenetic regulator of transcription, SIRT1, mediates the effects of under and overnutrition on pubertal timing by controlling the expression of Kiss1 in hypothalamic neurons.

Neuroepigenetics and addictive behaviors: Where do we stand?

Substance use disorders involve long-term changes in the brain that lead to compulsive drug seeking, craving, and a high probability of relapse. Recent findings have highlighted the role of epigenetic regulations in controlling chromatin access and regulation of gene expression following exposure to drugs of abuse. In the present review, we focus on data investigating genome-wide epigenetic modifications in the brain of addicted patients or in rodent models exposed to drugs of abuse, with a particular focus on DNA methylation and histone modifications associated with transcriptional studies. We highlight critical factors for epigenomic studies in addiction. We discuss new findings related to psychostimulants, alcohol, opiate, nicotine and cannabinoids. We examine the possible transmission of these changes across generations. We highlight developing tools, specifically those that allow investigation of structural reorganization of the chromatin. These have the potential to increase our understanding of alteration of chromatin architecture at gene regulatory regions. Neuroepigenetic mechanisms involved in addictive behaviors could explain persistent phenotypic effects of drugs and, in particular, vulnerability to relapse.

Evidence supporting a mechanistic role of sirtuins in mood and metabolic disorders

Sirtuins are NAD⁺-dependent histone deacetylases that play essential roles in cell survival, energy metabolism, inflammation, and aging; therefore, sirtuins are potential therapeutic targets in the treatment of type 2 diabetes, cancer, inflammatory and metabolic disorders, and neurodegenerative diseases. Available evidence provides the basis for hypothesizing that sirtuins 1, 2, and 3 (SIRT1, SIRT2, and SIRT3) may have a mechanistic role subserving mood disorders (i.e. downregulation) and associated co-morbidity (e.g. metabolic disorders). Specifically, the domains of general cognitive processes, as well as cognitive emotional processing may be particularly relevant to sirtuin physiology. Given the role of sirtuins in the perpetuation of circadian rhythmicity, and evidence of dysfunctional circadian cycling in mood disorders, sirtuins may be an underlying etiological factor that links circadian rhythm functionality with mood disorders. Caloric restriction, and caloric restriction mimetics (e.g. resveratrol) are all capable of upregulating sirtuin isoforms implicated in stress response syndromes. Repurposing existing treatments and/or discovery of novel agents capable of modulating sirtuin physiology may represent genuinely novel approaches for trans-diagnostic domains affected in mood disorders and other brain-based illnesses.

SIRT1 is increased in affected brain regions and hypothalamic metabolic pathways are altered in Huntington disease

AIMS

Metabolic dysfunction is involved in modulating the disease process in Huntington disease (HD) but the underlying mechanisms are not known. The aim of this study was to investigate if the metabolic regulators sirtuins are affected in HD.

METHODS

Quantitative real-time polymerase chain reactions were used to assess levels of SIRT1-3 and downstream targets in post mortem brain tissue from HD patients and control cases as well as after selective hypothalamic expression of mutant huntingtin (HTT) using recombinant adeno-associated viral vectors in mice.

RESULTS

We show that mRNA levels of the metabolic regulator SIRT1 are increased in the striatum and the cerebral cortex but not in the less affected cerebellum in post mortem HD brains. Levels of SIRT2 are only increased in the striatum and SIRT3 is not affected in HD. Interestingly, mRNA levels of SIRT1 are selectively increased in the lateral hypothalamic area (LHA) and ventromedial hypothalamus (VMH) in HD. Further analyses of the LHA and VMH confirmed pathological changes in these regions including effects on SIRT1 downstream targets and reduced mRNA levels of orexin (hypocretin), prodynorphin and melanin-concentrating hormone (MCH) in the LHA and of brain-derived neurotrophic factor (BDNF) in the VMH. Analyses after selective hypothalamic expression of mutant HTT suggest that effects on BDNF, orexin, dynorphin and MCH are early and direct, whereas changes in SIRT1 require more widespread expression of mutant HTT.

CONCLUSIONS

We show that SIRT1 expression is increased in HD-affected brain regions and that metabolic pathways are altered in the HD hypothalamus.

Chromatin Regulation in Complex Brain Disorders

Chromatin-related phenomena regulate gene expression by altering the compaction and accessibility of DNA to relevant transcription factors, thus allowing every cell in the body to attain distinct identities and to function properly within a given cellular context. These processes occur not only in the developing central nervous system, but continue throughout the lifetime of a neuron to constantly adapt to changes in the environment. Such changes can be positive or negative, thereby altering the chromatin landscape to influence cellular and synaptic plasticity within relevant neural circuits, and ultimately behavior. Given the importance of epigenetic mechanisms in guiding physiological adaptations, perturbations in these processes in brain have been linked to several neuropsychiatric and neurological disorders. In this review, we cover some of the recent advances linking chromatin dynamics to complex brain disorders and discuss new methodologies that may overcome current limitations in the field.

Social Defeat Stress, Sex, and Addiction-Like Behaviors

Social confrontation is a form of social interaction in animals where two conspecific individuals confront each other in dispute over territory, during the formation of hierarchies, and during breeding seasons. Typically, a social confrontation involves a prevailing individual and a yielding individual. The prevailing individual often exhibits aggressive postures and launches attacks, whereas the yielding individual often adopts postures of defeat. The yielding or defeated animals experience a phenomenon known as social defeat stress, in which they show exaggerated stress as well as autonomic and endocrine responses that cause impairment of both the brain and body. In laboratory settings, one can reliably generate social defeat stress by allowing a naïve (or already defeated) animal to intrude into a home cage in which its resident has already established a territory or is nursing. This resident-intruder paradigm has been widely used in both males and females to study mechanisms in the brain that underlie the stress responses. Stress has profound effects on drug reward for cocaine, methamphetamine, alcohol, and opioids. Particularly, previous experiences with social defeat can exaggerate subsequent addiction-like behaviors. The extent of these addiction-like behaviors depends on the intensity, duration, frequency, and intermittency of the confrontation episodes. This chapter describes four types of social defeat stress: acute, repeated, intermittent, and chronic. Specifically, it focuses on social defeat stress models used in laboratories to study individual, sex, and animal strain differences in addiction-like behaviors.

High-fat Diet Mediates Anxiolytic-like Behaviors in a Time-dependent Manner Through the Regulation of SIRT1 in the Brain

The consumption of a high-fat diet (HFD) and obesity have been associated not only with metabolic diseases but also with neuropsychiatric diseases, such as depression and anxiety. However, results on the effects of an HFD on anxiety are controversial, since both anxiogenic and anxiolytic effects have been reported. In this study, we evaluated the effects of both short- and long-term intake of an HFD on anxiety-like behaviors. To explore the impact of time on the association between an HFD and anxiety, mice were fed with an HFD for 4 weeks or 12 weeks. Compared with control-diet mice, mice given an HFD for 4 weeks displayed anxiolytic-like behaviors. At the same time, we observed decreased SIRT1 expression in the mPFC and the amygdala of HFD-fed mice. Moreover, resveratrol, an activator of SIRT1, reversed the anxiolytic-like behaviors in HFD-fed mice. However, after 12 weeks of consuming a high-fat diet, mice did not exhibit any anti-anxiety behavior or further decreases in SIRT1 expression in the aforementioned brain regions compared with CD-fed mice. When EX-527, a SIRT1 inhibitor, was intraperitoneally injected, we observed anxiolytic effects in the CD-fed mice but not in the 12-week HFD-fed mice. Collectively, our data demonstrate that exposure to a short-term HFD can induce anxiolytic behaviors, which may be associated with decreased SIRT1 in the mPFC and the amygdala. However, this effect is abolished when the high-fat diet is extended to 12 weeks. Together, these results demonstrate that SIRT1 plays an essential role in regulating mood-related behaviors in HFD-fed mice.

NPAS2 Regulation of Anxiety-Like Behavior and GABAA Receptors

Abnormal circadian rhythms and circadian genes are strongly associated with several psychiatric disorders. Neuronal PAS Domain Protein 2 (NPAS2) is a core component of the molecular clock that acts as a transcription factor and is highly expressed in reward- and stress-related brain regions such as the striatum. However, the mechanism by which NPAS2 is involved in mood-related behaviors is still unclear. We measured anxiety-like behaviors in mice with a global null mutation in Npas2 (Npas2 null mutant mice) and found that Npas2 null mutant mice exhibit less anxiety-like behavior than their wild-type (WT) littermates (in elevated plus maze, light/dark box and open field assay). We assessed the effects of acute or chronic stress on striatal Npas2 expression, and found that both stressors increased levels of Npas2. Moreover, knockdown of Npas2 in the ventral striatum resulted in a similar reduction of anxiety-like behaviors as seen in the Npas2 null mutant mouse. Additionally, we identified Gabra genes as transcriptional targets of NPAS2, found that Npas2 null mutant mice exhibit reduced sensitivity to the GABAa positive allosteric modulator, diazepam and that knockdown of Npas2 reduced Gabra1 expression and response to diazepam in the ventral striatum. These results: (1) implicate Npas2 in the response to stress and the development of anxiety; and (2) provide functional evidence for the regulation of GABAergic neurotransmission by NPAS2 in the ventral striatum.

Regulatory Pathways of Monoamine Oxidase A during Social Stress

Social stress has a high impact on many biological systems in the brain, including serotonergic (5-HT) system-a major drug target in the current treatment for depression. Hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis and monoamine oxidase A (MAO-A) are well-known stress responses, which are involved in the central 5-HT system. Although, many MAO-A inhibitors have been developed and used in the therapeutics of depression, effective management of depression by modulating the activity of MAO-A has not been achieved. Identifying the molecular pathways that regulate the activity of MAO-A in the brain is crucial for developing new drug targets for precise control of MAO-A activity. Over the last few decades, several regulatory pathways of MAO-A consisting of Kruppel like factor 11 (KLF11), Sirtuin1, Ring finger protein in neural stem cells (RINES), and Cell division cycle associated 7-like protein (R1) have been identified, and the influence of social stress on these regulatory factors evaluated. This review explores various aspects of these pathways to expand our understanding of the roles of the HPA axis and MAO-A regulatory pathways during social stress. The first part of this review introduces some components of the HPA axis, explains how stress affects them and how they interact with the 5-HT system in the brain. The second part summarizes the novel regulatory pathways of MAO-A, which have high potential as novel therapeutic targets for depression.

Repetitive transcranial magnetic stimulation inhibits Sirt1/MAO-A signaling in the prefrontal cortex in a rat model of depression and cortex-derived astrocytes

Repetitive transcranial magnetic stimulation (rTMS) is a useful monotherapy for depression or adjunctive therapy for resistant depression. However, the anti-depressive effects of different parameters and the underlying mechanisms remain unclear. Here, we aimed to assess the effect of rTMS with different parameters (1/5/10 Hz, 0.84/1.26 T) on the depressive-like behaviors, 5-hydroxytryptamine (5-HT), 5-HIAA (5-hydroxyindoleacetic acid) and DA and NE levels, and monoamine oxidase A (MAO-A) activity in chronic unpredictable stress-treated rats, along with the expression of sirtuin 1 (Sirt1) and MAO-A in the prefrontal cortex (PFC) and cortex-derived astrocytes from new-born rats. Moreover, the depressive-like behaviors were monitored following the transcranial injection of the Sirt1 inhibitor EX527 (1 mM) daily for 1 week. We found that rTMS treatment (5/10 Hz, 0.84/1.26 T) ameliorated depressive-like behaviors, increased 5-HT, DA and NE levels, decreased the 5-HIAA level and Sirt1 and MAO-A expression, and reduced MAO-A activity in the PFC. The depressive-like behaviors were also ameliorated after the transcranial injection of EX527. Importantly, rTMS (5/10 Hz, 0.84/1.26 T) inhibited Sirt1 and MAO-A expressions in astrocytes and Sirt1 knockdown with short hairpin RNA decreased MAO-A expression in astrocytes. These results suggest that the inhibition of Sirt1/MAO-A expression in astrocytes in the PFC may contribute to the different anti-depressive effects of rTMS with different parameters, and may also provide a novel insight into the mechanisms underlying major depressive disorder.

Histone deacetylases (HDACs) as therapeutic target for depressive disorders

Major depressive disorder (MDD) represents approximately 40% of the disability caused by mental illnesses globally. The poorly understood pathophysiology and limited efficiency of pharmacological treatment (based primarily on the principles of the monoaminergic hypothesis) make depression a serious medical, public and socio-economical problem. An increasing number of studies suggest that epigenetic modifications (alterations in gene expression that are not due to changes in DNA sequence) in certain brain regions and neural circuits represent a key mechanism through which environmental factors interact with individual's genetic constitution to affect risk of mental disorders. Accordingly, chromatin-based epigenetic regulation seems to be a promising direction for the development of new, more effective antidepressant drugs. Recently, several inhibitors of histone deacetylases (HDAC) have been extensively studied in the context of antidepressant action. So far, none of them has been used to treat depression in humans due to the low selectivity for specific HDAC isoforms, and consequently, a risk of serious adverse events. In this review, we focus on the HDAC inhibitors (HDACi) with the greatest antidepressant efficacy and their activity in the preclinical studies. Moreover, we discuss their potential therapeutic usefulness in depression and the main limitations.

Abundant collateralization of temporal lobe projections to the accumbens, bed nucleus of stria terminalis, central amygdala and lateral septum

Behavioral flexibility is subserved in part by outputs from the cerebral cortex to telencephalic subcortical structures. In our earlier evaluation of the organization of the cortical-subcortical output system (Reynolds and Zahm, J Neurosci 25:11757-11767, 2005), retrograde double-labeling was evaluated in the prefrontal cortex following tracer injections into pairs of the following subcortical telencephalic structures: caudate-putamen, core and shell of the accumbens (Acb), bed nucleus of stria terminalis (BST) and central nucleus of the amygdala (CeA). The present study was done to assess patterns of retrograde labeling in the temporal lobe after similar paired tracer injections into most of the same telencephalic structures plus the lateral septum (LS). In contrast to the modest double-labeling observed in the prefrontal cortex in the previous study, up to 60-80 % of neurons in the basal and accessory basal amygdaloid nuclei and amygdalopiriform transition area exhibited double-labeling in the present study. The most abundant double-labeling was generated by paired injections into structures affiliated with the extended amygdala, including the CeA, BST and Acb shell. Injections pairing the Acb core with the BST or CeA produced significantly fewer double-labeled neurons. The ventral subiculum exhibited modest amounts of double-labeling associated with paired injections into the Acb, BST, CeA and LS. The results raise the issue of how an extraordinarily collateralized output from the temporal lobe may contribute to behavioral flexibility.

Testing Depression in Mice: a Chronic Social Defeat Stress Model

A vast challenge within neuropsychiatric research has been the development of animal models that accurately reflect symptoms associated with affective disorders. An ethologically valid model that has been shown to be effective in studying depression is the chronic social defeat stress model. In this model, C57BL/6J mice are subjected to chronic social defeat stress induced by CD-1 aggressor mice for 10 consecutive days. Discussed here is a protocol describing the screening process of the CD-1 aggressor mice, the confrontations between the C57BL/6J and CD-1 aggressor mice, and analysis of social avoidance scores as an indication of depression-like behaviors.

The Genetic Architecture of Major Depressive Disorder in Han Chinese Women

IMPORTANCE

Despite the moderate, well-demonstrated heritability of major depressive disorder (MDD), there has been limited success in identifying replicable genetic risk loci, suggesting a complex genetic architecture. Research is needed to quantify the relative contribution of classes of genetic variation across the genome to inform future genetic studies of MDD.

OBJECTIVES

To apply aggregate genetic risk methods to clarify the genetic architecture of MDD by estimating and partitioning heritability by chromosome, minor allele frequency, and functional annotations and to test for enrichment of rare deleterious variants.

DESIGN, SETTING, AND PARTICIPANTS

The CONVERGE (China, Oxford, and Virginia Commonwealth University Experimental Research on Genetic Epidemiology) study collected data on 5278 patients with recurrent MDD from 58 provincial mental health centers and psychiatric departments of general medical hospitals in 45 cities and 23 provinces of China. Screened controls (n = 5196) were recruited from a range of locations, including general hospitals and local community centers. Data were collected from August 1, 2008, to October 31, 2012.

MAIN OUTCOMES AND MEASURES

Genetic risk for liability to recurrent MDD was partitioned using sparse whole-genome sequencing.

RESULTS

In aggregate, common single-nucleotide polymorphisms (SNPs) explained between 20% and 29% of the variance in MDD risk, and the heritability in MDD explained by each chromosome was proportional to its length (r = 0.680; P = .0003), supporting a common polygenic etiology. Partitioning heritability by minor allele frequency indicated that the variance explained was distributed across the allelic frequency spectrum, although relatively common SNPs accounted for a disproportionate fraction of risk. Partitioning by genic annotation indicated a greater contribution of SNPs in protein-coding regions and within 3'-UTR regions of genes. Enrichment of SNPs associated with DNase I-hypersensitive sites was also found in many tissue types, including brain tissue. Examining burden scores from singleton exonic SNPs predicted to be deleterious indicated that cases had significantly more mutations than controls (odds ratio, 1.009; 95% CI, 1.003-1.014; P = .003), including those occurring in genes expressed in the brain (odds ratio, 1.011; 95% CI, 1.003-1.018; P = .004) and within nuclear-encoded genes with mitochondrial gene products (odds ratio, 1.075; 95% CI, 1.018-1.135; P = .009).

CONCLUSIONS AND RELEVANCE

Results support a complex etiology for MDD and highlight the value of analyzing components of heritability to clarify genetic architecture.

Resveratrol ameliorates chronic unpredictable mild stress-induced depression-like behavior: involvement of the HPA axis, inflammatory markers, BDNF, and Wnt/β-catenin pathway in rats

Classic antidepressant drugs are modestly effective across the population and most are associated with intolerable side effects. Recently, numerous lines of evidence suggest that resveratrol (RES), a natural polyphenol, possesses beneficial therapeutic activity for depression. The aim of the present study was to explore whether RES exhibits an antidepressant-like effect in a depression model and to explore the possible mechanism. A depression model was established via chronic unpredictable mild stress (CUMS), after which the model rats in the RES and fluoxetine groups received a daily injection of RES or fluoxetine, respectively. The sucrose preference test, open field test, and forced swimming test were used to explore the antidepressant-like effects of RES. The activity of the hypothalamic-pituitary-adrenal (HPA) axis was evaluated by detecting the plasma corticosterone concentration and hypothalamic mRNA expression of corticotrophin-releasing hormone. The plasma interleukin-6 (IL-6), C-reactive protein (CRP), and tumor necrosis factor-α (TNF-α) concentrations were measured by enzyme-linked immunosorbent assay. Hippocampal protein expression of brain-derived neurotrophic factor (BDNF) and the Wnt/β-catenin pathway were analyzed by western blot. The results showed that RES relieved depression-like behavior of CUMS rats, as indicated by the increased sucrose preference and the decreased immobile time. Rats that received RES treatment exhibited reduced plasma corticosterone levels and corticotrophin-releasing hormone mRNA expression in the hypothalamus, suggesting that the hyperactivity of the HPA axis in CUMS rats was reversed by RES. Moreover, after RES treatment, the rats exhibited increased plasma IL-6, CRP, and TNF-α concentrations. Furthermore, RES treatment upregulated the hippocampal protein levels of BDNF and the relative ratio of p-β-catenin/β-catenin while downregulating the relative ratio of p-GSK-3β/GSK-3β. Our findings suggest that RES improved depressive behavior in CUMS rats by downregulating HPA axis hyperactivity, increasing BDNF expression and plasma IL-6, CRP, and TNF-α concentrations, and regulating the hippocampal Wnt/β-catenin pathway.

AAV-mediated Sirt1 overexpression in skeletal muscle activates oxidative capacity but does not prevent insulin resistance

Type 2 diabetes is characterized by triglyceride accumulation and reduced lipid oxidation capacity in skeletal muscle. SIRT1 is a key protein in the regulation of lipid oxidation and its expression is reduced in the skeletal muscle of insulin resistant mice. In this tissue, Sirt1 up-regulates the expression of genes involved in oxidative metabolism and improves mitochondrial function mainly through PPARGC1 deacetylation. Here we examined whether Sirt1 overexpression mediated by adeno-associated viral vectors of serotype 1 (AAV1) specifically in skeletal muscle can counteract the development of insulin resistance induced by a high fat diet in mice. AAV1-Sirt1-treated mice showed up-regulated expression of key genes related to β-oxidation together with increased levels of phosphorylated AMP protein kinase. Moreover, SIRT1 overexpression in skeletal muscle also increased basal phosphorylated levels of AKT. However, AAV1-Sirt1 treatment was not enough to prevent high fat diet-induced obesity and insulin resistance. Although Sirt1 gene transfer to skeletal muscle induced changes at the muscular level related with lipid and glucose homeostasis, our data indicate that overexpression of SIRT1 in skeletal muscle is not enough to improve whole-body insulin resistance and that suggests that SIRT1 has to be increased in other metabolic tissues to prevent insulin resistance.