Histone Deacetylase 2 Inhibition Attenuates Downregulation of Hippocampal Plasticity Gene Expression during Aging

Role of histone deacetylases and their inhibitors in neurological diseases

Histone deacetylases (HDACs) are zinc-dependent deacetylases that remove acetyl groups from lysine residues of histones or form protein complexes with other proteins for transcriptional repression, changing chromatin structure tightness, and inhibiting gene expression. Recent in vivo and in vitro studies have amply demonstrated the critical role of HDACs in the cell biology of the nervous system during both physiological and pathological processes and have provided new insights into the conduct of research on neurological disease targets. In addition, in vitro and in vivo studies on HDAC inhibitors show promise for the treatment of various diseases. This review summarizes the regulatory mechanisms of HDAC and the important role of its downstream targets in nervous system diseases, and summarizes the therapeutic mechanisms and efficacy of HDAC inhibitors in various nervous system diseases. Additionally, the current pharmacological situation, problems, and developmental prospects of HDAC inhibitors are described. A better understanding of the pathogenic mechanisms of HDACs in the nervous system may reveal new targets for therapeutic interventions in diseases and help to relieve healthcare pressure through preventive measures.

Class 1 histone deacetylases differentially modulate memory and synaptic genes in a spatial and temporal manner in aged and APP/PS1 mice

Epigenetics plays a vital role in aging and Alzheimer's disease (AD); however, whether epigenetic alterations during aging can initiate AD and exacerbate AD progression remains unclear. In this study, using 3-, 12- and 18- month-old APP/PS1 mice and age matched WT littermates, we conducted a series of memory tests, measured synapse-related gene expression, class 1 histone deacetylases (HDACs) abundance, and H3K9ac levels at target gene promoters in the hippocampus and prefrontal cortex (PFC). Our results showed impaired recognition and long-term spatial memory in 18-month-old WT mice and impaired recognition, short-term working, and long-term spatial reference memory in 12-and 18- month-old APP/PS1 mice. These memory impairments are associated with changes of synapse-related gene (nr2a, glur1, glur2, psd95) expression, HDAC abundance, and H3K9ac levels; more specifically, increased HDAC2 was associated with synapse-related gene expression changes through modulation of H3K9ac at the gene promoters during aging and AD progression in the hippocampus. Conversely, increased HDAC3 was associated with synapse-related gene expression changes through modulation of H3K9ac at the gene promoters during AD progression in the PFC. These findings suggest memory impairments in aging and AD may associated with a differential HDAC modulation of synapse-related gene expression in the brain.

Exercise epigenetics is fueled by cell bioenergetics: Supporting role on brain plasticity and cognition

Exercise has the unique aptitude to benefit overall health of body and brain. Evidence indicates that the effects of exercise can be saved in the epigenome for considerable time to elevate the threshold for various diseases. The action of exercise on epigenetic regulation seems central to building an "epigenetic memory" to influence long-term brain function and behavior. As an intrinsic bioenergetic process, exercise engages the function of the mitochondria and redox pathways to impinge upon molecular mechanisms that regulate synaptic plasticity and learning and memory. We discuss how the action of exercise uses mechanisms of bioenergetics to support a "epigenetic memory" with long-term implications for neural and behavioral plasticity. This information is crucial for directing the power of exercise to reduce the burden of neurological and psychiatric disorders.

Manganese induces oxidative damage in the hippocampus by regulating the expression of oxidative stress-related genes via modulation of H3K18 acetylation

Prolonged exposure to manganese (Mn) contributes to hippocampal Mn accumulation, which leads to neurodegenerative diseases called manganese poisoning. However, the underlying molecular mechanisms remain unclear and there are no ideal biomarkers. Oxidative stress is the essential mechanisms of Mn-related neurotoxicity. Furthermore, histone acetylation has been identified as being engaged in the onset and development of neurodegenerative diseases. Therefore, the work aims to understand the molecular mechanisms of oxidative damage in the hippocampus due to Mn exposure from the aspect of histone acetylation modification and to assess whether H3K18 acetylation (H3K18ac) modification level in peripheral blood reflect Mn-induced oxidative damage in the hippocampus. Here, we randomly divided 60 male rats into four groups and injected them intraperitoneally with sterile pure water and MnCl2 ⋅4H2 O (5, 10, and 15 mg/kg) for 16 weeks, 5 days a week, once a day. The data confirmed that Mn exposure down-regulated superoxide dismutase activity and glutathione level as well as up-regulated malondialdehyde level in the hippocampus and plasma, and that there was a positive correlation between these indicators in the hippocampus and plasma. Besides, we noted that Mn treatment upregulated H3K18ac modification levels in the hippocampus and peripheral blood and that H3K18ac modification levels correlated with oxidative stress. Further studies demonstrated that Mn treatment decreased the amounts of H3K18ac enrichment in the manganese superoxide dismutase (SOD2) and glutathione transferase omega 1 (GSTO1) gene promoter regions, contributing to oxidative damage in the hippocampus. In short, our results demonstrate that Mn induces oxidative damage in the hippocampus by inhibiting the expression of SOD2 and GSTO1 genes via modulation of H3K18ac. In assessing Mn-induced hippocampal neurotoxicity, oxidative damage in plasma may reflect hippocampal oxidative damage in Mn-exposed groups.

An Overview of the Epigenetic Modifications in the Brain under Normal and Pathological Conditions

Epigenetic changes are changes in gene expression that do not involve alterations to the DNA sequence. These changes lead to establishing a so-called epigenetic code that dictates which and when genes are activated, thus orchestrating gene regulation and playing a central role in development, health, and disease. The brain, being mostly formed by cells that do not undergo a renewal process throughout life, is highly prone to the risk of alterations leading to neuronal death and neurodegenerative disorders, mainly at a late age. Here, we review the main epigenetic modifications that have been described in the brain, with particular attention on those related to the onset of developmental anomalies or neurodegenerative conditions and/or occurring in old age. DNA methylation and several types of histone modifications (acetylation, methylation, phosphorylation, ubiquitination, sumoylation, lactylation, and crotonylation) are major players in these processes. They are directly or indirectly involved in the onset of neurodegeneration in Alzheimer's or Parkinson's disease. Therefore, this review briefly describes the roles of these epigenetic changes in the mechanisms of brain development, maturation, and aging and some of the most important factors dynamically regulating or contributing to these changes, such as oxidative stress, inflammation, and mitochondrial dysfunction.

Suv39h1 Silencing Recovers Memory Decline in Scopolamine-Induced Amnesic Mouse Model

Histone post-translational modifications play an important role in the regulation of long-term memory and modulation of expression of neuronal immediate early genes (IEGs). The lysine methyltransferase KMT1A/ Suv39h1 (a mammalian ortholog of the Drosophila melanogaster SU (VAR) 3-9) aids in the methylation of histone H3 at lysine 9. We previously reported that age-related memory decline is associated with an increase in Suv39h1 expression in the hippocampus of male mice. The scopolamine-induced amnesic mouse model is a well-known animal model of memory impairment. In the current study, we have made an attempt to find a link between the changes in the H3K9 trimethylation pattern and memory decline during scopolamine-induced amnesia. It was followed by checking the effect of siRNA-mediated silencing of hippocampal Suv39h1 on memory and expression of neuronal IEGs. Scopolamine treatment significantly increased global levels of H3K9me3 and Suv39h1 in the amnesic hippocampus. Suv39h1 silencing in amnesic mice reduced H3K9me3 levels at the neuronal IEGs (Arc and BDNF) promoter, increased the expression of Arc and BDNF in the hippocampus, and improved recognition memory. Thus, these findings suggest that the silencing of Suv39h1 alone or in combination with other epigenetic drugs might be effective for treating memory decline during amnesia.

Activation of β2-adrenergic receptors prevents AD-type synaptotoxicity via epigenetic mechanisms

We previously reported that prolonged exposure to an enriched environment (EE) enhances hippocampal synaptic plasticity, with one of the significant mechanistic pathways being activation of β2-adrenergic receptor (β2-AR) signaling, thereby mitigating the synaptotoxic effects of soluble oligomers of amyloid β-protein (oAβ). However, the detailed mechanism remained elusive. In this work, we recorded field excitatory postsynaptic potentials (fEPSP) in the CA1 region of mouse hippocampal slices treated with or without toxic Aβ-species. We found that pharmacological activation of β2-AR, but not β1-AR, selectively mimicked the effects of EE in enhancing LTP and preventing oAβ-induced synaptic dysfunction. Mechanistic analyses showed that certain histone deacetylase (HDAC) inhibitors mimicked the benefits of EE, but this was not seen in β2-AR knockout mice, suggesting that activating β2-AR prevents oAβ-mediated synaptic dysfunction via changes in histone acetylation. EE or activation of β-ARs each decreased HDAC2, whereas Aβ oligomers increased HDAC2 levels in the hippocampus. Further, oAβ-induced inflammatory effects and neurite degeneration were prevented by either β2-AR agonists or certain specific HDAC inhibitors. These preclinical results suggest that activation of β2-AR is a novel potential therapeutic strategy to mitigate oAβ-mediated features of AD.

Disruption of histone acetylation homeostasis triggers cognitive dysfunction in experimental diabetes

Epigenetic mechanisms related to diabetes-afflicted CNS complications are largely unknown. The present study investigated the role of histone acetylation mechanisms triggering cognitive dysfunction in the Type 1 and 2 diabetic mice model. Dynamic changes in diabetic parameters like fasting blood glucose levels, glucose tolerance test, and insulin levels were observed after the induction of diabetes. Cognitive performance was significantly diminished in T1D and T2D mice examined by the Morris water maze, novel object recognition test, and Y Maze as compared to controls. Histone profiling revealed a significant reduction in H3K9/14 and H4K12 acetylation in the cortex and hippocampus of T1D and T2D mice vs Controls. While histone deacetylase (HDAC) activity was significantly elevated in brain regions of T1D and T2D mice, the histone acetyltransferase (HAT) activity remain unchanged. Significantly increased HDAC 2, HDAC 3 protein and mRNA expression observed in T1D and T2D brain regions may corroborate for increased HDAC activity. No significant change was observed in protein and mRNA expression of HDAC 1, 5, 6, and 7 in diabetic brains. Reduced H3K9/14 and H4K12 acetylation paralleled transcriptional repression of memory-related markers BDNF, SYP, and PSD-95 in the cortex and hippocampus of T1D and T2D. Pharmacological inhibition of HDAC activity by Trichostatin A enhanced the cognitive changes observed in T1D and T2D by ameliorating BDNF, SYP, Psd-95. The present study provides a better insight into molecular mechanisms related to diabetes-dependent memory changes that can help to generate new advances for therapeutics to be developed in this area.

Tryptophan metabolite norharman secreted by cultivated Lactobacillus attenuates acute pancreatitis as an antagonist of histone deacetylases

BACKGROUND

Patients with acute pancreatitis (AP) exhibit specific phenotypes of gut microbiota associated with severity. Gut microbiota and host interact primarily through metabolites; regrettably, little is known about their roles in AP biological networks. This study examines how enterobacterial metabolites modulate the innate immune system in AP aggravation.

METHODS

In AP, alterations in gut microbiota were detected via microbiomics, and the Lactobacillus metabolites of tryptophan were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). By culturing Lactobacillus with tryptophan, differential metabolites were detected by LC-MS/MS. Lipopolysaccharide (LPS)-stimulated RAW264.7 cells and mice with cerulein plus LPS-induced AP were used to evaluate the biological effect of norharman on M1 macrophages activation in AP development. Further, RNA sequencing and lipid metabolomics were used for screening the therapeutic targets and pathways of norharman. Confocal microscopy assay was used to detect the structure of lipid rafts. Molecular docking was applied to predict the interaction between norharman and HDACs. Luciferase reporter assays and chromatin immunoprecipitation (ChIP) were used to explore the direct mechanism of norharman promoting Rftn1 expression. In addition, myeloid-specific Rftn1 knockout mice were used to verify the role of Rftn1 and the reversed effect of norharman.

RESULTS

AP induced the dysfunction of gut microbiota and their metabolites, resulting in the suppression of Lactobacillus-mediated tryptophan metabolism pathway. The Lactobacillus metabolites of tryptophan, norharman, inhibited the release of inflammatory factor in vitro and in vivo, as a result of its optimal inhibitory action on M1 macrophages. Moreover, norharman blocked multiple inflammatory responses in AP exacerbation due to its ability to maintain the integrity of lipid rafts and restore the dysfunction of lipid metabolism. The mechanism of norharman's activity involved inhibiting the enzyme activity of histone deacetylase (HDACs) to increase histone H3 at lysine 9/14 (H3K9/14) acetylation, which increased the transcription level of Rftn1 (Raftlin 1) to inhibit M1 macrophages' activation.

CONCLUSIONS

The enterobacterial metabolite norharman can decrease HDACs activity to increase H3K9/14 acetylation of Rftn1, which inhibits M1 macrophage activation and restores the balance of lipid metabolism to relieve multiple inflammatory responses. Therefore, norharman may be a promising prodrug to block AP aggravation.

Aging-related histone modification changes in brain function

Aging can be defined as a decline of physiological function that is more difficult to reverse, characterized by the loss of the physiological integrity of tissues, organs, and cells of an organism over time. Normal aging is associated with structural and functional changes in the brain, involving neuronal apoptosis, synaptic structure, neurotransmission, and metabolism alterations, leading to impairment in sleep, cognitive functions, memory, learning, and motor and sensory systems. Histone modification is a significant aging-related epigenetic change that influences synaptic and mitochondrial function and immune and stress responses in the brain. This review discusses the changes in histone modifications that occur during brain aging, specifically methylation and acetylation, and the associated changes in gene transcription and protein expression. We observed that genes related to synaptic and mitochondrial function are downregulated in the aging brain, while genes related to immune response and inflammatory functions are upregulated.

Modulation of Synaptic Plasticity Genes Associated to DNA Damage in a Model of Huntington's Disease

Huntington's disease (HD) is a disease characterized by the progressive degeneration of nerve cells in the brain. DNA damage has been implicated in many neurological disorders; however, the association between this damage and the impaired signaling related to neurodegeneration is still unclear. The transcription factor c-AMP-responsive element binding protein (CREB) has a relevant role in the neuronal plasticity process regulating the expression of several genes, including brain-derived neurotrophic factor (BDNF). Here we analyzed the direct link between DNA damage and the expression of genes involved in neuronal plasticity. The study was performed in model cell lines STHdhQ7 (wild type) and STHdhQ111 (HD model). Treatment with Etoposide (Eto) was used to induce double-strand breaks (DSBs) to evaluate the DNA damage response (DDR) and the expression of synaptic plasticity genes. Eto treatment induced phosphorylation of ATM (p-ATM) and H2AX (γH2AX), markers of DDR, in both cell lines. Interestingly, upon DNA damage, STHdhQ7 cells showed increased expression of activity-regulated cytoskeleton associated protein (Arc) and BDNF when compared to the HD cell line model. Additionally, Eto induced CREB activation with a differential localization of its co-activators in the cell types analyzed. These results suggest that DSBs impact differentially the gene expression patterns of plasticity genes in the normal cell line versus the HD model. This effect is mediated by the impaired localization of CREB-binding protein (CBP) and histone acetylation in the HD model. Our results highlight the role of epigenetics and DNA repair on HD and therefore we suggest that future studies should explore in depth the epigenetic landscape on neuronal pathologies with the goal to further understand molecular mechanisms and pinpoint therapeutic targets.

5-Methylcytosine and 5-Hydroxymethylcytosine in Scrapie-Infected Sheep and Mouse Brain Tissues

Scrapie is a neurodegenerative disorder belonging to the group of transmissible spongiform encephalopathies or prion diseases, which are caused by an infectious isoform of the innocuous cellular prion protein (PrP^C) known as PrP^Sc. DNA methylation, one of the most studied epigenetic mechanisms, is essential for the proper functioning of the central nervous system. Recent findings point to possible involvement of DNA methylation in the pathogenesis of prion diseases, but there is still a lack of knowledge about the behavior of this epigenetic mechanism in such neurodegenerative disorders. Here, we evaluated by immunohistochemistry the 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) levels in sheep and mouse brain tissues infected with scrapie. Expression analysis of different gene coding for epigenetic regulatory enzymes (DNMT1, DNMT3A, DNMT3B, HDAC1, HDAC2, TET1, and TET2) was also carried out. A decrease in 5mC levels was observed in scrapie-affected sheep and mice compared to healthy animals, whereas 5hmC displayed opposite patterns between the two models, demonstrating a decrease in 5hmC in scrapie-infected sheep and an increase in preclinical mice. 5mC correlated with prion-related lesions in mice and sheep, but 5hmC was associated with prion lesions only in sheep. Differences in the expression changes of epigenetic regulatory genes were found between both disease models, being differentially expressed Dnmt3b, Hdac1, and Tet1 in mice and HDAC2 in sheep. Our results support the evidence that DNA methylation in both forms, 5mC and 5hmC, and its associated epigenetic enzymes, take part in the neurodegenerative course of prion diseases.

Epigenetic regulation of aging: implications for interventions of aging and diseases

Aging is accompanied by the decline of organismal functions and a series of prominent hallmarks, including genetic and epigenetic alterations. These aging-associated epigenetic changes include DNA methylation, histone modification, chromatin remodeling, non-coding RNA (ncRNA) regulation, and RNA modification, all of which participate in the regulation of the aging process, and hence contribute to aging-related diseases. Therefore, understanding the epigenetic mechanisms in aging will provide new avenues to develop strategies to delay aging. Indeed, aging interventions based on manipulating epigenetic mechanisms have led to the alleviation of aging or the extension of the lifespan in animal models. Small molecule-based therapies and reprogramming strategies that enable epigenetic rejuvenation have been developed for ameliorating or reversing aging-related conditions. In addition, adopting health-promoting activities, such as caloric restriction, exercise, and calibrating circadian rhythm, has been demonstrated to delay aging. Furthermore, various clinical trials for aging intervention are ongoing, providing more evidence of the safety and efficacy of these therapies. Here, we review recent work on the epigenetic regulation of aging and outline the advances in intervention strategies for aging and age-associated diseases. A better understanding of the critical roles of epigenetics in the aging process will lead to more clinical advances in the prevention of human aging and therapy of aging-related diseases.

'Arc'-hitecture of normal cognitive aging

Arc is an effector immediate-early gene that is critical for forming long-term memories. Since its discovery 25 years ago, it has repeatedly surprised us with a number of intriguing properties, including the transport of its mRNA to recently-activated synapses, its master role in bidirectionally regulating synaptic strength, its evolutionary retroviral origins, its ability to mediate intercellular transfer between neurons via extracellular vesicles (EVs), and its exceptional regulation-both temporally and spatially. The current review discusses how Arc has been used as a tool to identify the neural networks involved in cognitive aging and how Arc itself may contribute to cognitive outcome in aging. In addition, we raise several outstanding questions, including whether Arc-containing EVs in peripheral blood might provide a noninvasive biomarker for memory-related synaptic failure in aging, and whether rectifying Arc dysregulation is likely to be an effective strategy for bending the arc of aging toward successful cognitive outcomes.

Neuromodulating roles of estrogen and phytoestrogens in cognitive therapeutics through epigenetic modifications during aging

Estrogen (E2) plays important role in regulating hippocampal learning and memory. The decline of E2 after menopause affects learning and memory and increases the risk of neurodegenerative diseases like Alzheimer's disease (AD). Additionally, from the estrogen receptor (ER) mediated gene regulation; E2 also regulates gene expression at the transcriptional and posttranscriptional levels through epigenetic modifications. E2 recruits a number of proteins called co-regulators at the promoter region of genes. These co-regulators act as chromatin modifiers, alter DNA and histone modifications and regulate gene expression. Several studies show that E2 regulates learning and memory by altering chromatin at the promoters of memory-linked genes. Due to structural similarities with E2 and low side effects, phytoestrogens are now used as neuroprotective agents to recover learning and memory in animal models as well as human subjects during aging and different neurological disorders. Growing evidence suggests that apart from anti-oxidative and anti-inflammatory properties, phytoestrogens also act as epigenetic modifiers and regulate gene expression through epigenetic modifications. The epigenetic modifying properties of phytoestrogens are mostly studied in cancer cells but very little is known regarding the regulation of synaptic plasticity genes, learning and memory, and neurological disorders. In this article, we discuss the epigenetic modifying properties of E2 and the roles of phytoestrogens as epigenetic modifiers in the brain to recover and maintain cognitive functions.

Gut dysbiosis impairs hippocampal plasticity and behaviors by remodeling serum metabolome

Accumulating evidence suggests that gut microbiota as a critical mediator of gut-brain axis plays an important role in human health. Altered gut microbial profiles have been implicated in increasing the vulnerability of psychiatric disorders, such as autism, depression, and schizophrenia. However, the cellular and molecular mechanisms underlying the association remain unknown. Here, we modified the gut microbiome with antibiotics in newborn mice, and found that gut microbial alteration induced behavioral impairment by decreasing adult neurogenesis and long-term potentiation of synaptic transmission, and altering the gene expression profile in hippocampus. Reconstitution with normal gut flora produced therapeutic effects against both adult neurogenesis and behavioral deficits in the dysbiosis mice. Furthermore, our results show that circulating metabolites changes mediate the effect of gut dysbiosis on hippocampal plasticity and behavior outcomes. Elevating the serum 4-methylphenol, a small aromatic metabolite produced by gut bacteria, was found to induce autism spectrum disorder (ASD)-like behavior impairment and hippocampal dysfunction. Together our finding demonstrates that early-life gut dysbiosis and its correlated metabolites change contribute to hippocampal dysfunction and behavior impairment, hence highlight the potential microbiome-mediated therapies for treating psychiatric disorders.

A Class I HDAC Inhibitor Rescues Synaptic Damage and Neuron Loss in APP-Transfected Cells and APP/PS1 Mice through the GRIP1/AMPA Pathway

As a neurodegenerative disease, Alzheimer’s disease (AD) seriously affects the health of older people. Changes in synapses occur first over the course of the disease, perhaps even before the formation of Aβ plaques. Histone deacetylase (HDAC) mediates the damage of Aβ oligomers to dendritic spines. Therefore, we examined the relationship between HDAC activity and synaptic defects using an HDAC inhibitor (HDACI), BG45, in the human neuroblastoma SH-SY5Y cell line with stable overexpression of Swedish mutant APP (APPsw) and in APP/PS1 transgenic mice during this study. The cells were treated with 15 μM BG45 and the APP/PS1 mice were treated with 30 mg/kg BG45. We detected the levels of synapse-related proteins, HDACs, tau phosphorylation, and amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors using Western blotting and immunohistochemistry. We also measured the expression of cytoskeletal proteins in the cell model. The mRNA levels of the glutamate ion receptor alginate subunit 2 (GRIK2), sodium voltage-gated channel beta subunit (SCN3B), synaptophysin (SYP), Grm2 (the gene encoding glutamate receptor subunit 2 (GluR2)), Grid2IP, glutamate receptor interacting protein 1 (GRIP1), and GRIP2 were detected to explore the effects of the HDACI on regulating the expression of synaptic proteins and AMPA receptors. According to our studies, the expressions of HDAC1, HDAC2, and HDAC3 were increased, which were accompanied by the downregulation of the synapse-related proteins SYP, postsynaptic dendritic protein (PSD-95), and spinophilin as early as 24 h after transfection with the APPsw gene. BG45 upregulated the expression of synapse-related proteins and repaired cytoskeletal damage. In vivo, BG45 alleviated the apoptosis-mediated loss of hippocampal neurons, upregulated synapse-related proteins, reduced Aβ deposition and phosphorylation of tau, and increased the levels of the synapse-related genes GRIK2, SCN3B, SYP, Grm2, and Grid2IP. BG45 increased the expression of the AMPA receptor subunits GluA1, GluA2, and GluA3 on APPsw-transfected cells and increased GRIP1 and GRIP2 expression and AMPA receptor phosphorylation in vivo. Based on these results, HDACs are involved in the early process of synaptic defects in AD models, and BG45 may rescue synaptic damage and the loss of hippocampal neurons by specifically inhibiting HDAC1, HDAC2, and HDAC3, thereby modulating AMPA receptor transduction, increasing synapse-related gene expression, and finally enhancing the function of excitatory synapses. BG45 may be considered a potential drug for the treatment of early AD in further studies.

Long-Term Environmental Enrichment Relieves Dysfunctional Cognition and Synaptic Protein Levels Induced by Prenatal Inflammation in Older CD-1 Mice

A mounting body of evidence suggests that prenatal inflammation may enhance the rate of age-associated cognitive decline and may involve aberrant amounts of synaptic proteins in the hippocampus, including synaptotagmin-1 (Syt1) and activity-regulated cytoskeleton-associated protein (Arc). However, little is known about the specific impact of adolescent environmental enrichment (EE) on age-associated cognitive decline and the changes in synaptic proteins caused by prenatal inflammation. In this study, CD-1 mice in late pregnancy were given intraperitoneal doses of lipopolysaccharide (LPS, 50 μg/kg) or normal saline. Offspring arising from LPS dams were divided into a LPS group and a LPS plus EE (LPS-E) group. The LPS-E mice were exposed to EE from 2 months of age until the end of the experiment (3 or 15 months old). The Morris water maze (MWM) was used to assess the spatial learning and memory capacities of experimental mice, while western blotting and RNA-scope were used to determine the expression levels of Arc and Syt1 in the hippocampus at the protein and mRNA levels, respectively. Analysis revealed that at 15 months of age, the control mice experienced a reduction in cognitive ability and elevated expression levels of Arc and Syt1 genes when compared to control mice at 3 months of age. The LPS-E group exhibited better cognition and lower protein and mRNA levels of Arc and Syt1 than mice in the LPS group of the same age. However, the enriched environment mitigated but did not counteract, the effects of prenatal inflammation on cognitive and synaptic proteins when tested at either 3 or 15 months of age. Our findings revealed that long-term environmental enrichment improved the expression levels of synaptic proteins in CD-1 mice and that this effect was linked to the dysfunctional cognition caused by prenatal inflammation; this process may also be involved in the reduction of hippocampal Arc and Syt1 gene expression.

Methyltransferase-Like 3 Rescues the Amyloid-beta protein-Induced Reduction of Activity-Regulated Cytoskeleton Associated Protein Expression via YTHDF1-Dependent N6-Methyladenosine Modification

Activity-regulated cytoskeleton-associated protein (ARC) is activated by the induction of long-term potentiation and plays an important role in the synaptic plasticity of memory consolidation. Previous studies have shown that abnormal expression of ARC in the brains of patients with Alzheimer’s Disease (AD) leads to the disturbance of synaptic plasticity. ARC expression is mainly regulated by transcriptional and post-translational modification. However, it is unclear whether N6-methyladenosine (m6A) engages in the epigenetic modification of ARC. The AlzData database was used to analyze the brain of AD patients, and Aβ-induced cell models were used. We revealed that ARC expression was reduced in AD patients and Aβ-induced cell models. There were five m6A modification sites of ARC mRNA that were predicted by the SRAMP database, and ARC mRNA was confirmed as the target gene of methyltransferase-like 3 (METTL3) by MeRIP. Amyloid-beta protein (Aβ) repressed the m6A modification. Knockdown of METTL3 decreased ARC mRNA m6A modification and reduced ARC protein expression, while overexpression of METTL3 rescued ARC expression after Aβ treatment. Knockdown of YTH domain family, member 1 (YTHDF1) decreased ARC protein expression, while the overexpression of YTHDF1 could not rescue the loss of ARC protein expression after 3-deazaadenosine treatment or knockdown of METTL3. Our findings identify that METTL3 rescues the Aβ-induced reduction of ARC expression via YTHDF1-Dependent m6A modification, which suggests an important mechanism of epigenetic alteration in AD.

Epigenetic Mechanisms in Memory and Cognitive Decline Associated with Aging and Alzheimer's Disease

Epigenetic mechanisms, which include DNA methylation, a variety of post-translational modifications of histone proteins (acetylation, phosphorylation, methylation, ubiquitination, sumoylation, serotonylation, dopaminylation), chromatin remodeling enzymes, and long non-coding RNAs, are robust regulators of activity-dependent changes in gene transcription. In the brain, many of these epigenetic modifications have been widely implicated in synaptic plasticity and memory formation. Dysregulation of epigenetic mechanisms has been reported in the aged brain and is associated with or contributes to memory decline across the lifespan. Furthermore, alterations in the epigenome have been reported in neurodegenerative disorders, including Alzheimer’s disease. Here, we review the diverse types of epigenetic modifications and their role in activity- and learning-dependent synaptic plasticity. We then discuss how these mechanisms become dysregulated across the lifespan and contribute to memory loss with age and in Alzheimer’s disease. Collectively, the evidence reviewed here strongly supports a role for diverse epigenetic mechanisms in memory formation, aging, and neurodegeneration in the brain.

Human iPSC-Derived Neurons as A Platform for Deciphering the Mechanisms behind Brain Aging

With an increased life expectancy among humans, aging has recently emerged as a major focus in biomedical research. The lack of in vitro aging models-especially for neurological disorders, where access to human brain tissues is limited-has hampered the progress in studies on human brain aging and various age-associated neurodegenerative diseases at the cellular and molecular level. In this review, we provide an overview of age-related changes in the transcriptome, in signaling pathways, and in relation to epigenetic factors that occur in senescent neurons. Moreover, we explore the current cell models used to study neuronal aging in vitro, including immortalized cell lines, primary neuronal culture, neurons directly converted from fibroblasts (Fib-iNs), and iPSC-derived neurons (iPSC-iNs); we also discuss the advantages and limitations of these models. In addition, the key phenotypes associated with cellular senescence that have been observed by these models are compared. Finally, we focus on the potential of combining human iPSC-iNs with genome editing technology in order to further our understanding of brain aging and neurodegenerative diseases, and discuss the future directions and challenges in the field.

Vitamin B12-folic acid supplementation regulates neuronal immediate early gene expression and improves hippocampal dendritic arborization and memory in old male mice

As the relationship among diet, brain aging and memory is complex, it provides ample opportunity for research in multiple directions including behaviour, epigenetics and neuroplasticity. Nutritional deficiencies together with genetic and environmental factors are the major cause of many age-associated pathologies including memory loss. A compromised vitamin B₁₂-folate status in older people is highly prevalent worldwide. Researchers have established a close association between the adequate level of B₁₂-folate and the maintenance of cognitive brain functions. One of the main reasons for age-associated memory loss is downregulation of neuronal immediate early genes (nIEGs). Therefore, we hypothesize here that vitamin B₁₂-folic acid supplementation in old mice can improve memory by altering the expression status of nIEGs. To check this, 72-week-old male Swiss albino mice were orally administered with 2 μg of vitamin B₁₂ and 22 μg of folic acid/mouse/day for eight weeks. Such supplementation improved recognition memory in old and altered the expression of nIEGs. The expression of nIEGs was further found to be regulated by changes in DNA methylation at their promoter regions and CREB phosphorylation (pCREB). In addition, Golgi-Cox staining showed significant improvement in dendritic length, number of branching points and spine density of hippocampal CA1 pyramidal neurons by B₁₂-folic acid supplementation. Taken together, these findings suggest that vitamin B₁₂-folic acid supplementation regulates nIEGs expression and improves dendritic arborization of hippocampal neurons and memory in old male mice.

Histone Deacetylase 2-Mediated Epigenetic Regulation is Involved in the Early Isoflurane Exposure-Related Increase in Susceptibility to Anxiety-Like Behaviour Evoked by Chronic Variable Stress in Mice

Increasing studies report that prolonged or multiple anaesthetic exposures early in life are associated with detrimental effects on brain function. Although studies have evaluated the detrimental effects on neurocognitive function, few have focused on long-term neuropsychiatric effects. In the present study, C57BL/6 mice received either three neonatal isoflurane exposures or control exposure. Starting on postnatal day 45, the mice were either exposed or not to a chronic variable stress (CVS) paradigm, and CVS-related neuropsychiatric performance was evaluated using a series of behavioural tests. The expression levels of histone 3 lysine 9 acetylation (acetyl-H3K9), brain-derived neurotrophic factor (BDNF), cAMP response element-binding protein-binding protein, and histone deacetylases 1-4 in the amygdala were measured by immunoblotting or immunohistochemistry analysis. In mice with neonatal isoflurane exposure, the effects of sodium butyrate (NaB), a commonly used HDAC inhibitor, were examined on CVS-related behavioural and molecular alterations. The results showed that repeated neonatal isoflurane exposure did not affect innate depression-like and anxiety-like behaviours under non-stress conditions but facilitated the CVS-induced anxiety-like behavioural phenotype. Increased HDAC2 expression in the amygdala was associated with an increase in the CVS-induced repression of acetyl-H3K9 and BDNF expression and an enhanced CVS-evoked anxiety-like behavioural phenotype in mice neonatal isoflurane exposure. NaB significantly decreased the CVS-induced anxiety level by elevating acetyl-H3K9 and BDNF expression. These results suggested that early anaesthesia exposure facilitated chronic stress-induced neuropsychiatric outcomes, and the HDAC2-related epigenetic dysregulation of BDNF gene expression is involved in the underlying mechanism.

Histone deacetylase in neuropathology

Neuroepigenetics, a new branch of epigenetics, plays an important role in the regulation of gene expression. Neuroepigenetics is associated with holistic neuronal function and helps in formation and maintenance of memory and learning processes. This includes neurodevelopment and neurodegenerative defects in which histone modification enzymes appear to play a crucial role. These modifications, carried out by acetyltransferases and deacetylases, regulate biologic and cellular processes such as apoptosis and autophagy, inflammatory response, mitochondrial dysfunction, cell-cycle progression and oxidative stress. Alterations in acetylation status of histone as well as non-histone substrates lead to transcriptional deregulation. Histone deacetylase decreases acetylation status and causes transcriptional repression of regulatory genes involved in neural plasticity, synaptogenesis, synaptic and neural plasticity, cognition and memory, and neural differentiation. Transcriptional deactivation in the brain results in development of neurodevelopmental and neurodegenerative disorders. Mounting evidence implicates histone deacetylase inhibitors as potential therapeutic targets to combat neurologic disorders. Recent studies have targeted naturally-occurring biomolecules and micro-RNAs to improve cognitive defects and memory. Multi-target drug ligands targeting HDAC have been developed and used in cell-culture and animal-models of neurologic disorders to ameliorate synaptic and cognitive dysfunction. Herein, we focus on the implications of histone deacetylase enzymes in neuropathology, their regulation of brain function and plausible involvement in the pathogenesis of neurologic defects.

Class I HDAC Inhibitor Improves Synaptic Proteins and Repairs Cytoskeleton Through Regulating Synapse-Related Genes In vitro and In vivo

β-amyloid (Aβ) is an important protein molecule in the pathology of Alzheimer’s disease (AD). Accumulation of Aβ leads to the loss of dendritic spines and synapses. These impairments can be ameliorated by histone deacetylase inhibitors (HDACI). However, the mechanisms of HDACIs underlying the effect on synapse are not fully understood. In this study, we examined the relationship between HDAC activity and synapse-related genes and proteins by the administration of a class I HDAC inhibitor, BG45, in the exogenous Aβ-treated cells and mice. Our studies showed that the treatment of HF-488-Aβ_1–42 to SH-SY5Y cells first increased the expression of the postsynaptic dendritic protein (PSD), then decreased it after 36 h. BG45 can alleviate the reduction of the expression of PSD-95 as well as spinophilin and cytoskeletal protein induced by HF-488-Aβ^1–42 aggregation in SH-SY5Y cells. Similar to the results in vitro, PSD-95 in the hippocampus was temporarily increased in the early days of intravenous injection HF-488-Aβ_1–40 to the mice, followed by the decreased expression of PSD-95 on the 9th day. In further studies, for the mice treated with Aβ for 9 days, we found that BG45 decreased the expression of HDAC1 and 2, increased the expression of PSD-95, spinophilin, and synaptophysin (SYP). Our data also showed that BG45 upregulated levels of three synapse-related genes and proteins GRIK2, SCN3B, and SYNPR. These findings suggest that the exogenous Aβ may stimulate transiently the expression of PSD-95 at an early stage, but subsequently contribute to synaptic defects. HDAC1 and 2 are involved in synaptic defects, and BG45 may improve the expression of synaptic and cytoskeletal proteins and repair cytoskeletal damage by specifically inhibiting HDAC1 and 2, thereby modulating synapse-related genes. BG45 might be a potential therapeutic agent for the treatment of an early stage of Aβ-related neurodegenerative disease.

The effects of early-life growth hormone intervention on tissue specific histone H3 modifications in long-lived Ames dwarf mice

Histone modifications, specifically in the lysine residues of histone H3, have been implicated in lifespan regulation in several model organisms. Our previous studies showed that growth hormone (GH) treatment during early life can dramatically influence lifespan in long-lived Ames dwarf mice. However, the effects of this hormonal intervention on epigenetic modifications have never been examined. In this study, we sought to compare tissue-specific histone H3 lysine methylation and acetylation markers in Ames dwarf and wild type (WT) mice and to determine how these markers are affected by early-life GH intervention. Ames dwarf mice exhibited suppressed H3K4me in both hepatic and brain tissues, while showing elevated H3K27me in the brain. Early-life GH intervention significantly altered the histone H3 markers in those tissues. Furthermore, early GH intervention increased expression of histone H3 acetylation at multiple lysine residues in a tissue-specific manner. This included changes in H3K14ac and H3K18ac in the liver and brain, H3K18ac in visceral adipose tissue and H3K9ac, H3K14ac and H3K27ac in subcutaneous adipose tissue. This study serves as an initial, but important step in elucidating the epigenetic mechanisms by which hormonal signals during early life can influence aging and longevity in mammals.

Effects of Gestational Inflammation with Postpartum Enriched Environment on Age-Related Changes in Cognition and Hippocampal Synaptic Plasticity-Related Proteins

Increasing evidence indicates that exposure to inflammation during pregnancy intensifies the offspring’s cognitive impairment during aging, which might be correlated with changes in some synaptic plasticity-related proteins. In addition, an enriched environment (EE) can significantly exert a beneficial impact on cognition and synaptic plasticity. However, it is unclear whether gestational inflammation combined with postnatal EE affects the changes in cognition and synaptic plasticity-related proteins during aging. In this study, pregnant mice were intraperitoneally injected with lipopolysaccharides (LPS, 50 μg/kg) or normal saline at days 15–17 of pregnancy. At 21 days after delivery, some LPS-treated mice were randomly selected for EE treatment. At the age of 6 and 18 months, Morris water maze (MWM) and western blotting were, respectively, used to evaluate or measure the ability of spatial learning and memory and the levels of postsynaptic plasticity-related proteins in the hippocampus, including postsynaptic density protein 95 (PSD-95), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) GluA1 subunit, and Homer-1b/c. The results showed that 18-month-old control mice had worse spatial learning and memory and lower levels of these synaptic plasticity-related proteins (PSD-95, GluA1, and Homer-1b/c) than the 6-month-old controls. Gestational LPS exposure exacerbated these age-related changes of cognition and synaptic proteins, but EE could alleviate the treatment effect of LPS. In addition, the performance during learning and memory periods in the MWM correlated with the hippocampal levels of PSD-95, GluA1, and Homer-1b/c. Our results suggested that gestational inflammation accelerated age-related cognitive impairment and the decline of PSD-95, GluA1, and Homer-1b/c protein expression, and postpartum EE could alleviate these changes.

Epigenetic Mechanisms of Learning and Memory: Implications for Aging

The neuronal epigenome is highly sensitive to external events and its function is vital for producing stable behavioral outcomes, such as the formation of long-lasting memories. The importance of epigenetic regulation in memory is now well established and growing evidence points to altered epigenome function in the aging brain as a contributing factor to age-related memory decline. In this review, we first summarize the typical role of epigenetic factors in memory processing in a healthy young brain, then discuss the aspects of this system that are altered with aging. There is general agreement that many epigenetic marks are modified with aging, but there are still substantial inconsistencies in the precise nature of these changes and their link with memory decline. Here, we discuss the potential source of age-related changes in the epigenome and their implications for therapeutic intervention in age-related cognitive decline.

Age-related memory decline, dysfunction of the hippocampus and therapeutic opportunities

While the aging of the population is a sign of progress for societies, it also carries its load of negative aspects. Among them, cognitive decline and in particular memory loss is a common feature of non-pathological aging. Autobiographical memories, which rely on the hippocampus, are a primary target of age-related cognitive decline. Here, focusing on the neurobiological mechanisms of memory formation and storage, we describe how hippocampal functions are altered across time in non-pathological mammalian brains. Several hallmarks of aging have been well described over the last decades; among them, we consider altered synaptic communication and plasticity, reduction of adult neurogenesis and epigenetic alterations. Building on the neurobiological processes of cognitive aging that have been identified to date, we review some of the strategies based on lifestyle manupulation allowing to address age-related cognitive deficits.

Poly (I:C) Exposure in Early Life Alters Methylation of DNA and Acetylation of Histone at Synaptic Plasticity Gene Promoter in Developing Rat Brain Leading to Memory Impairment

Background: Exposure to adverse environmental conditions such as toxic chemicals, viral infections, and even stress during pregnancy or early life may disrupt the development of normal brain and its functioning leading to incidence of neurodevelopmental disorders at later stages of life. Recently, we reported that poly (I:C) exposure altered synaptic plasticity protein level and impaired memory through activation of microglia cells.

Purpose: As epigenetic modifications are involved in memory formation, we have studied methylation of DNA and acetylation of histone at promoters of synaptic plasticity genes in the brain of rats exposed to poly (I:C) during early life.

Methods: One dose of poly (I:C) (5 mg/kg bw) was intraperitoneally injected to rat pups on postnatal seventh day. A set of pups exposed to vehicle was included as control. In order to assess methylation of DNA and acetylation of histone at synaptic plasticity gene promoter, we performed qPCR after methylated DNA immunoprecipitation and chromatin immunoprecipitation.

Results: Poly (I:C) exposure reduced the level of 5-methylcytosine (5mC) at synaptic plasticity gene (bdnf, arc, and egr1) promoters in the frontal cortex (FC) and hippocampus of 3-week rats, although increased it later in both regions of 12-week rats as compared to respective controls. On contrary, poly (I:C) exposure enhanced acetylation of histone H3K9 (H3K9Ac) at promoters of these genes in both regions of 3-week rats but decreased in 12-week rats.

Conclusion: Poly (I:C) exposure altered 5mC and H3K9Ac at synaptic plasticity gene promoters resulting in memory impairment of rats at later life.

Effects of Prenatal Exposure to Inflammation Coupled With Stress Exposure During Adolescence on Cognition and Synaptic Protein Levels in Aged CD-1 Mice

Age-associated impairment of spatial learning and memory (AISLM) presents substantial challenges to our health and society. Increasing evidence has indicated that embryonic exposure to inflammation accelerates the AISLM, and this can be attributable, at least partly, to changed synaptic plasticity associated with the activities of various proteins. However, it is still uncertain whether social psychological factors affect this AISLM and/or the expression of synaptic protein-associated genes. Synaptotagmin-1 (Syt1) and activity-regulated cytoskeleton-associated protein (Arc) are two synaptic proteins closely related to cognitive functions. In this study, pregnant CD-1 mice received daily intraperitoneal injections of lipopolysaccharide (LPS) (50 μg/kg) or normal saline at days 15-17 of gestation, and half of the offspring of each group were then subjected to stress for 28 days in adolescence. The Morris water maze (MWM) test was used to separately evaluate spatial learning and memory at 3 and 15 months of age, while western blotting and RNAscope assays were used to measure the protein and mRNA levels of Arc and Syt1 in the hippocampus. The results showed that, at 15 months of age, control mice had worse cognitive ability and higher protein and mRNA levels of Arc and Syt1 than their younger counterparts. Embryonic exposure to inflammation or exposure to stress in adolescence aggravated the AISLM, as well as the age-related increase in Arc and Syt1 expression. Moreover, the hippocampal protein and mRNA levels of Arc and Syt1 were significantly correlated with the performance in the learning and memory periods of the MWM test, especially in the mice that had suffered adverse insults in early life. Our findings indicated that prenatal exposure to inflammation or stress exposure in adolescence exacerbated the AISLM and age-related upregulation of Arc and Syt1 expression, and these effects were linked to cognitive impairments in CD-1 mice exposed to adverse factors in early life.

Genome-Protecting Compounds as Potential Geroprotectors

Throughout life, organisms are exposed to various exogenous and endogenous factors that cause DNA damages and somatic mutations provoking genomic instability. At a young age, compensatory mechanisms of genome protection are activated to prevent phenotypic and functional changes. However, the increasing stress and age-related deterioration in the functioning of these mechanisms result in damage accumulation, overcoming the functional threshold. This leads to aging and the development of age-related diseases. There are several ways to counteract these changes: 1) prevention of DNA damage through stimulation of antioxidant and detoxification systems, as well as transition metal chelation; 2) regulation of DNA methylation, chromatin structure, non-coding RNA activity and prevention of nuclear architecture alterations; 3) improving DNA damage response and repair; 4) selective removal of damaged non-functional and senescent cells. In the article, we have reviewed data about the effects of various trace elements, vitamins, polyphenols, terpenes, and other phytochemicals, as well as a number of synthetic pharmacological substances in these ways. Most of the compounds demonstrate the geroprotective potential and increase the lifespan in model organisms. However, their genome-protecting effects are non-selective and often are conditioned by hormesis. Consequently, the development of selective drugs targeting genome protection is an advanced direction.

Memory and plasticity impairment after binge drinking in adolescent rat hippocampus: GluN2A/GluN2B NMDA receptor subunits imbalance through HDAC2

Ethanol (EtOH) induces cognitive impairment through modulation of synaptic plasticity notably in the hippocampus. The cellular mechanism(s) of these EtOH effects may range from synaptic signaling modulation to alterations of the epigenome. Previously, we reported that two binge-like exposures to EtOH (3 g/kg, ip, 9 h apart) in adolescent rats abolished long-term synaptic depression (LTD) in hippocampus slices, induced learning deficits, and increased N-methyl-d-aspartate (NMDA) receptor signaling through its GluN2B subunit after 48 hours. Here, we tested the hypothesis of EtOH-induced epigenetic alterations leading to modulation of GluN2B and GluN2A NMDA receptor subunits. Forty-two days old rats were treated with EtOH or the histone deacetylase inhibitor (HDACi) sodium butyrate (NaB, 600 mg/kg, ip) injected alone or 30 minutes before EtOH. After 48 hours, learning was tested with novel object recognition while synaptic plasticity and the role of GluN2A and GluN2B subunits in NMDA-fEPSP were measured in CA1 field of hippocampus slices. LTD and memory were impaired 48 hours after EtOH and NMDA-fEPSP analysis unraveled changes in the GluN2A/GluN2B balance. These results were associated with an increase in histone deacetylase (HDAC) activity and HDAC2 mRNA and protein while Ac-H4K12 labelling was decreased. EtOH increases expression of HDAC2 and mRNA level for GluN2B subunit (but not GluN2A), while HDAC2 modulates the promoter of the gene encoding GluN2B. Interestingly, NaB pretreatment prevented all the cellular and memory-impairing effects of EtOH. In conclusion, the memory-impairing effects of two binge-like EtOH exposure involve NMDA receptor-dependent LTD deficits due to a GluN2A/GluN2B imbalance resulting from changes in GluN2B expression induced by HDAC2.

Survey of the Arc Epigenetic Landscape in Normal Cognitive Aging

Aging is accompanied by aberrant gene expression that ultimately affects brain plasticity and the capacity to form long-term memories. Immediate-early genes (IEGs) play an active role in these processes. Using a rat model of normal cognitive aging, we found that the expression of Egr1 and c-Fos was associated with chronological age, whereas Arc was more tightly linked to cognitive outcomes in aging. More specifically, constitutive Arc expression was significantly elevated in aged rats with memory impairment compared to cognitively intact aged rats and young adult animals. Since alterations in the neuroepigenetic mechanisms that gate hippocampal gene expression are also associated with cognitive outcome in aging, we narrowed our focus on examining potential epigenetic mechanisms that may lead to aberrant Arc expression. Employing a multilevel analytical approach using bisulfite sequencing, chromatin immunoprecipitations, and micrococcal nuclease digestion, we identified CpG sites in the Arc promoter that were coupled to poor cognitive outcomes in aging, histone marks that were similarly coupled to spatial memory deficits, and nucleosome positioning that also varied depending on cognitive status. Together, these findings paint a diverse and complex picture of the Arc epigenetic landscape in cognitive aging and bolster a body of work, indicating that dysfunctional epigenetic regulation is associated with memory impairment in the aged brain.

When function follows form: Nuclear compartment structure and the epigenetic landscape of the aging neuron

The human brain is affected by cellular aging. Neurons are primarily generated during embryogenesis and early life with a limited capacity for renewal and replacement, making them some of the oldest cells in the human body. Our present understanding of neurodegenerative diseases points towards advanced neuronal age as a prerequisite for the development of these disorders. While significant progress has been made in understanding the relationship between aging and neurological disease, it will be essential to delve further into the molecular mechanisms of neuronal aging in order to develop therapeutic interventions targeting age-related brain dysfunction. In this mini review, we highlight recent findings on the relationship between the aging of nuclear structures and changes in the epigenetic landscape during neuronal aging and disease.

Suppression of HDAC2 by sodium butyrate alleviates apoptosis of kidney cells in db/db mice and HG‑induced NRK‑52E cells

Butyrate is short-chain fatty acid, which is produced by intestinal microbiota metabolizing dietary fibers. Butyrate participates in various physiological processes predominantly by activating G-coupled-receptors, inhibiting histone deacetylases (HDACs) and serving as an energy substrate. Previous studies have shown that butyrate plays a protective role in diabetic nephropathy (DN); however, the exact mechanism remains unclear. The present study identified that providing sodium butyrate (NaBu) by gavage relieved renal damage and apoptosis in db/db mice, which is a widely used type 2 DN model. In vitro, NaBu suppressed high glucose (HG)-induced apoptosis in normal rat kidney tubular epithelial (NRK-52E) cells. Of the eleven HDACs (HDAC1-11) studied, only the mRNA expression of HDAC2 was attenuated by NaBu in NRK-52E cells under the HG condition. Overexpression of HDAC2 offset the anti-apoptotic effect of NaBu. NaBu also suppressed HG-induced oxidative stress. Additionally, H₂O₂ induced an upregulation of HDAC2 in NRK-52E cells, while NaBu inhibited this process. Mechanistically, NaBu acted as an antioxidant in HG-induced NRK-52E cells and suppressed HG-induced apoptosis of NRK-52E cells through inhibiting HDAC2 by virtue of its anti-oxidative property.

Histone H3K9 Trimethylation Downregulates the Expression of Brain-Derived Neurotrophic Factor in the Dorsal Hippocampus and Impairs Memory Formation During Anaesthesia and Surgery

Brain-derived neurotrophic factor (BDNF) is essential for cognitive and memory functions. Abnormal BDNF expression in the central nervous system may impair these functions. Anaesthesia and surgery can induce perioperative neurocognitive disorders (PND). Clinical studies show that BDNF expression is decreased in patients presenting with cognitive impairment after anaesthesia and surgery. However, the molecular mechanism is still unclear. Epigenetic regulation plays an important role in cognition. The hypermethylation of H3K9 is crucial for transcriptional silencing and the onset of cognitive disorders. Here, we hypothesised that H3K9 trimethylation repressed BDNF expression and impaired memory formation or recall during anaesthesia and surgery. Laparotomy under isoflurane inhalation anaesthesia, behavioural tests, Western blotting, quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR), chromatin immunoprecipitation (ChIP), and immunohistochemistry were used in this study. BDNF expression was decreased in the hippocampus after anaesthesia and surgery. Cognitive impairment affected memory formation but not recall. The trimethylation of H3K9 downregulated BDNF expression. The overexpression of BDNF or use of exogenous BDNF improved the impairment of memory formation caused by anaesthesia and surgery. Therefore, inhibiting H3K9 trimethylation and increasing the expression of BDNF may help prevent PND in the clinical setting.

Neuroepigenetic signatures of age and sex in the living human brain

Age- and sex-related alterations in gene transcription have been demonstrated, however the underlying mechanisms are unresolved. Neuroepigenetic pathways regulate gene transcription in the brain. Here, we measure in vivo expression of the epigenetic enzymes, histone deacetylases (HDACs), across healthy human aging and between sexes using [¹¹C]Martinostat positron emission tomography (PET) neuroimaging (n = 41). Relative HDAC expression increases with age in cerebral white matter, and correlates with age-associated disruptions in white matter microstructure. A post mortem study confirmed that HDAC1 and HDAC2 paralogs are elevated in white matter tissue from elderly donors. There are also sex-specific in vivo HDAC expression differences in brain regions associated with emotion and memory, including the amygdala and hippocampus. Hippocampus and white matter HDAC expression negatively correlates with emotion regulation skills (n = 23). Age and sex are associated with HDAC expression in vivo, which could drive age- and sex-related transcriptional changes and impact human behavior.

Gene transcription is known to vary with age and sex, although the underlying mechanisms are unresolved. Here, the authors show that epigenetic enzymes known as HDACs, which regulate gene transcription, are increasingly expressed with age in the living human brain, with sex differences also observed.

Taking Advantage of the Selectivity of Histone Deacetylases and Phosphodiesterase Inhibitors to Design Better Therapeutic Strategies to Treat Alzheimer's Disease

The discouraging results with therapies for Alzheimer’s disease (AD) in clinical trials, highlights the urgent need to adopt new approaches. Like other complex diseases, it is becoming clear that AD therapies should focus on the simultaneous modulation of several targets implicated in the disease. Recently, using reference compounds and the first-in class CM-414, we demonstrated that the simultaneous inhibition of histone deacetylases [class I histone deacetylases (HDACs) and HDAC6] and phosphodiesterase 5 (PDE5) has a synergistic therapeutic effect in AD models. To identify the best inhibitory balance of HDAC isoforms and PDEs that provides a safe and efficient therapy to combat AD, we tested the compound CM-695 in the Tg2576 mouse model of this disease. CM-695 selectively inhibits HDAC6 over class I HDAC isoforms, which largely overcomes the toxicity associated with HDAC class 1 inhibition. Furthermore, CM-695 inhibits PDE9, which is expressed strongly in the brain and has been proposed as a therapeutic target for AD. Chronic treatment of aged Tg2576 mice with CM-695 ameliorates memory impairment and diminishes brain Aβ, although its therapeutic effect was no longer apparent 4 weeks after the treatment was interrupted. An increase in the presence of 78-KDa glucose regulated protein (GRP78) and heat shock protein 70 (Hsp70) chaperones may underlie the therapeutic effect of CM-695. In summary, chronic treatment with CM-695 appears to reverse the AD phenotype in a safe and effective manner. Taking into account that AD is a multifactorial disorder, the multimodal action of these compounds and the different events they affect may open new avenues to combat AD.

Epigenetic mechanisms related to cognitive decline during aging

Cognitive decline is a hallmark of the aging nervous system, characterized by increasing memory loss and a deterioration of mental capacity, which in turn creates a favorable context for the development of neurodegenerative diseases. One of the most detrimental alterations that occur at the molecular level in the brain during aging is the modification of the epigenetic mechanisms that control gene expression. As a result of these epigenetic-driven changes in the transcriptome most of the functions of the brain including synaptic plasticity, learning, and memory decline with aging. The epigenetic mechanisms altered during aging include DNA methylation, histone modifications, nucleosome remodeling, and microRNA-mediated gene regulation. In this review, we examine the current evidence concerning the changes of epigenetic modifications together with the molecular mechanisms underlying impaired neuronal gene transcription during aging. Herein, we discuss the alterations of DNA methylation pattern that occur in old neurons. We will also describe the most prominent age-related histone posttranslational modifications in the brain since changes in acetylation and methylation of specific lysine residues on H3 and H4 are associated to functional decline in the old. In addition, we discuss the role that changes in the levels of certain miRNAs would play in cognitive decline with aging. Finally, we provide an overview about the mechanisms either extrinsic or intrinsic that would trigger epigenetic changes in the aging brain, and the consequences of these changes, i.e., altered transcriptional profile and reactivation of transposable elements in old brain.

Epigenetic changes during aging and their reprogramming potential

The aging process results in significant epigenetic changes at all levels of chromatin and DNA organization. These include reduced global heterochromatin, nucleosome remodeling and loss, changes in histone marks, global DNA hypomethylation with CpG island hypermethylation, and the relocalization of chromatin modifying factors. Exactly how and why these changes occur is not fully understood, but evidence that these epigenetic changes affect longevity and may cause aging, is growing. Excitingly, new studies show that age-related epigenetic changes can be reversed with interventions such as cyclic expression of the Yamanaka reprogramming factors. This review presents a summary of epigenetic changes that occur in aging, highlights studies indicating that epigenetic changes may contribute to the aging process and outlines the current state of research into interventions to reprogram age-related epigenetic changes.

Distinct Expression Pattern of Epigenetic Machinery Genes in Blood Leucocytes and Brain Cortex of Depressive Patients

In major depressive disorder (MDD), altered gene expression in brain cortex and blood leucocytes may be due to aberrant expression of epigenetic machinery coding genes. Here, we explore the expression of these genes both at the central and peripheral levels. Using real-time quantitative PCR technique, we first measured expression levels of genes encoding DNA and histone modifying enzymes in the dorsolateral prefrontal cortex (DLPFC) and cingulate cortex (CC) of MDD patients (n = 24) and healthy controls (n = 12). For each brain structure, transcripts levels were compared between subject groups. In an exploratory analysis, we then compared the candidate gene expressions between a subgroup of MDD patients with psychotic characteristics (n = 13) and the group of healthy subjects (n = 12). Finally, we compared transcript levels of the candidate genes in blood leucocytes between separate samples of MDD patients (n = 17) and healthy controls (n = 16). In brain and blood leucocytes of MDD patients, we identified an overexpression of genes encoding enzymes which transfer repressive transcriptional marks: HDAC4-5-6-8 and DNMT3B in the DLPFC, HDAC2 in the CC and blood leucocytes. In the DLPFC of patients with psychotic characteristics, two genes (KAT2A and UBE2A) were additionally overexpressed suggesting a shift to a more transcriptionally permissive conformation of chromatin. Aberrant activation of epigenetic repressive systems may be involved in MDD pathogenesis both in brain tissue and blood leucocytes.

Chromatin Changes Associated with Neuronal Maintenance and Their Pharmacological Application

Background:

The transcriptional control of neuronal specification and early development has been intensively stud-ied over the past few decades. However, relatively little is known about transcriptional programs associated with the mainte-nance of terminally differentiated neuronal cells with respect to their functions, structures, and cell type-specific identity features.

Methods:

Notably, largely because of the recent advances in related techniques such as next generation sequencing and chromatin immunoprecipitation sequencing, the physiological implications of system-wide regulation of gene expression through changes in chromatin states have begun to be extensively studied in various contexts and systems, including the nervous system.

Results:

Here, we attempt to review our current understanding of the link between chromatin changes and neuronal mainte-nance in the period of life after the completion of neuronal development. Perturbations involving chromatin changes in the system-wide transcriptional control are believed to be closely associated with diverse aspects of neuronal aging and neuro-degenerative conditions.

Conclusion:

In this review, we focused on heterochromatin and epigenetic dysregulation in neurodegenerative conditions as well as neuronal aging, the most important risk factor leading to neuronal degeneration, in order to highlight the close association between chromatin changes and neuronal maintenance. Lastly, we reviewed the cur-rently available and potential future applications of pharmacological control of the chromatin states associated with neuronal maintenance.

Epigenome Interactions with Patterned Neuronal Activity

The temporal coding of action potential activity is fundamental to nervous system function. Here we consider how gene expression in neurons is regulated by specific patterns of action potential firing, with an emphasis on new information on epigenetic regulation of gene expression. Patterned action potential activity activates intracellular signaling networks selectively in accordance with the kinetics of activation and inactivation of second messengers, phosphorylation and dephosphorylation of protein kinases, and cytoplasmic and nuclear calcium dynamics, which differentially activate specific transcription factors. Increasing evidence also implicates activity-dependent regulation of epigenetic mechanisms to alter chromatin architecture. Changes in three-dimensional chromatin structure, including chromatin compaction, looping, double-stranded DNA breaks, histone and DNA modification, are altered by action potential activity to selectively inhibit or promote transcription of specific genes. These mechanisms of activity-dependent regulation of gene expression are important in neural development, plasticity, and in neurological and psychological disorders.