Targeting specific HATs for neurodegenerative disease treatment: translating basic biology to therapeutic possibilities

HAT and HDAC: Enzyme with Contradictory Action in Neurodegenerative Diseases

In view of the increasing risk of neurodegenerative diseases, epigenetics plays a fundamental role in the field of neuroscience. Several modifications have been studied including DNA methylation, histone acetylation, histone phosphorylation, etc. Histone acetylation and deacetylation regulate gene expression, and the regular activity of histone acetyltransferases (HATs) and histone deacetylases (HDACs) provides regulatory stages for gene expression and cell cycle. Imbalanced homeostasis in these enzymes causes a detrimental effect on neurophysiological function. Intriguingly, epigenetic remodelling via histone acetylation in certain brain areas has been found to play a key role in the neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease. It has been demonstrated that a number of HATs have a role in crucial brain processes such regulating neuronal plasticity and memory formation. The most recent therapeutic methods involve the use of small molecules known as histone deacetylase (HDAC) inhibitors that antagonize HDAC activity thereby increase acetylation levels in order to prevent the loss of HAT function in neurodegenerative disorders. The target specificity of the HDAC inhibitors now in use raises concerns about their applicability, despite the fact that this strategy has demonstrated promising therapeutic outcomes. The aim of this review is to summarize the cross-linking between histone modification and its regulation in the pathogenesis of neurological disorders. Furthermore, these findings also support the notion of new pharmacotherapies that target particular areas of the brain using histone deacetylase inhibitors.

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.

Epidrugs in the Therapy of Central Nervous System Disorders: A Way to Drive on?

The polygenic nature of neurological and psychiatric syndromes and the significant impact of environmental factors on the underlying developmental, homeostatic, and neuroplastic mechanisms suggest that an efficient therapy for these disorders should be a complex one. Pharmacological interventions with drugs selectively influencing the epigenetic landscape (epidrugs) allow one to hit multiple targets, therefore, assumably addressing a wide spectrum of genetic and environmental mechanisms of central nervous system (CNS) disorders. The aim of this review is to understand what fundamental pathological mechanisms would be optimal to target with epidrugs in the treatment of neurological or psychiatric complications. To date, the use of histone deacetylases and DNA methyltransferase inhibitors (HDACis and DNMTis) in the clinic is focused on the treatment of neoplasms (mainly of a glial origin) and is based on the cytostatic and cytotoxic actions of these compounds. Preclinical data show that besides this activity, inhibitors of histone deacetylases, DNA methyltransferases, bromodomains, and ten-eleven translocation (TET) proteins impact the expression of neuroimmune inflammation mediators (cytokines and pro-apoptotic factors), neurotrophins (brain-derived neurotropic factor (BDNF) and nerve growth factor (NGF)), ion channels, ionotropic receptors, as well as pathoproteins (β-amyloid, tau protein, and α-synuclein). Based on this profile of activities, epidrugs may be favorable as a treatment for neurodegenerative diseases. For the treatment of neurodevelopmental disorders, drug addiction, as well as anxiety disorders, depression, schizophrenia, and epilepsy, contemporary epidrugs still require further development concerning a tuning of pharmacological effects, reduction in toxicity, and development of efficient treatment protocols. A promising strategy to further clarify the potential targets of epidrugs as therapeutic means to cure neurological and psychiatric syndromes is the profiling of the epigenetic mechanisms, which have evolved upon actions of complex physiological lifestyle factors, such as diet and physical exercise, and which are effective in the management of neurodegenerative diseases and dementia.

Tip60's Novel RNA-Binding Function Modulates Alternative Splicing of Pre-mRNA Targets Implicated in Alzheimer's Disease

The severity of Alzheimer's disease (AD) progression involves a complex interplay of genetics, age, and environmental factors orchestrated by histone acetyltransferase (HAT)-mediated neuroepigenetic mechanisms. While disruption of Tip60 HAT action in neural gene control is implicated in AD, alternative mechanisms underlying Tip60 function remain unexplored. Here, we report a novel RNA binding function for Tip60 in addition to its HAT function. We show that Tip60 preferentially interacts with pre-mRNAs emanating from its chromatin neural gene targets in the Drosophila brain and this RNA binding function is conserved in human hippocampus and disrupted in Drosophila brains that model AD pathology and in AD patient hippocampus of either sex. Since RNA splicing occurs co-transcriptionally and alternative splicing (AS) defects are implicated in AD, we investigated whether Tip60-RNA targeting modulates splicing decisions and whether this function is altered in AD. Replicate multivariate analysis of transcript splicing (rMATS) analysis of RNA-Seq datasets from wild-type and AD fly brains revealed a multitude of mammalian-like AS defects. Strikingly, over half of these altered RNAs are identified as bona-fide Tip60-RNA targets that are enriched for in the AD-gene curated database, with some of these AS alterations prevented against by increasing Tip60 in the fly brain. Further, human orthologs of several Tip60-modulated splicing genes in Drosophila are well characterized aberrantly spliced genes in human AD brains, implicating disruption of Tip60's splicing function in AD pathogenesis. Our results support a novel RNA interaction and splicing regulatory function for Tip60 that may underly AS impairments that hallmark AD etiology.SIGNIFICANCE STATEMENT Alzheimer's disease (AD) has recently emerged as a hotbed for RNA alternative splicing (AS) defects that alter protein function in the brain yet causes remain unclear. Although recent findings suggest convergence of epigenetics with co-transcriptional AS, whether epigenetic dysregulation in AD pathology underlies AS defects remains unknown. Here, we identify a novel RNA interaction and splicing regulatory function for Tip60 histone acetyltransferase (HAT) that is disrupted in Drosophila brains modeling AD pathology and in human AD hippocampus. Importantly, mammalian orthologs of several Tip60-modulated splicing genes in Drosophila are well characterized aberrantly spliced genes in human AD brain. We propose that Tip60-mediated AS modulation is a conserved critical posttranscriptional step that may underlie AS defects now characterized as hallmarks of AD.

Plasticity, genetics, and epigenetics in l-dopa-induced dyskinesias

l-Dopa-induced dyskinesias (LIDs) are a frequent complication in l-dopa-treated patients affected by Parkinson's disease (PD). In the last years, several progresses in the knowledge of LIDs mechanisms have led to the identification of several molecular and electrophysiologic events. A complex cascade of intracellular events underlies the pathophysiology of LIDs, and, among these, aberrant plasticity in the cortico-basal ganglia system, at striatal and cortical level, plays a key role. Furthermore, several recent studies have investigated genetic susceptibility and epigenetic modifications in LIDs pathophysiology that might have future relevance in clinical practice and pharmacologic research. These progresses might lead to the development of specific strategies not only to treat, but also to prevent or delay the development of LIDs in PD.

Understanding the role of histone deacetylase and their inhibitors in neurodegenerative disorders: Current targets and future perspective

Neurodegenerative diseases are a group of pathological conditions that cause motor inc-ordination (jerking movements), cognitive and memory impairments result from degeneration of neurons in a specific area of the brain. Oxidative stress, mitochondrial dysfunction, excitotoxicity, neuroinflammation, neurochemical imbalance and histone deacetylase enzymes (HDAC) are known to play a crucial role in neurodegeneration. HDAC is classified into four categories (class I, II, III and class IV) depending upon their location and functions. HDAC1 and 2 are involved in neurodegeneration, while HDAC3-11 and class III HDACs are beneficial as neuroprotective. HDACs are localized in different parts of the brain- HDAC1 (hippocampus and cortex), HDAC2 (nucleus), HDAC3, 4, 5, 7 and 9 (nucleus and cytoplasm), HDAC6 & HDAC7 (cytoplasm) and HDAC11 (Nucleus, cornus ammonis 1 and spinal cord). In pathological conditions, HDAC up-regulates glutamate, phosphorylation of tau, and glial fibrillary acidic proteins while down-regulating BDNF, Heat shock protein 70 and Gelsolin. Class III HDACs are divided into seven sub-classes (SIRT1-SIRT7). Sirtuins are localized in the different parts of the brain and neuron -Sirt1 (nucleus), Sirt2 (cortex, striatum, hippocampus and spinal cord), Sirt3 (mitochondria and cytoplasm), Sirt4, Sirt5 & Sirt6 (mitochondria), Sirt7 (nucleus) and Sirt8 (nucleolus). SIRTs (1, 3, 4, and 6) are involved in neuronal survival, proliferation and modulating stress response, and SIRT2 is associated with Parkinsonism, Huntington’s disease and Alzheimer’s disease, whereas SIRT6 is only associated with Alzheimer’s disease. In this critical review, we have discussed the mechanisms and therapeutic targets of HDACs that would be beneficial for the management of neurodegenerative disorders.

SVA insertion in X-linked Dystonia Parkinsonism alters histone H3 acetylation associated with TAF1 gene

X-linked Dystonia-Parkinsonism (XDP) is a neurodegenerative disease linked to an insertion of a SINE-VNTR-Alu (SVA)-type retrotransposon within an intron of TAF1. This SVA insertion induces aberrant TAF1 splicing and partial intron retention, thereby decreasing levels of the full-length transcript. Here we sought to determine if these altered transcriptional dynamics caused by the SVA are also accompanied by local changes in histone acetylation, given that these modifications influence gene expression. Because TAF1 protein may itself exhibit histone acetyltransferase activity, we also examined whether decreased TAF1 expression in XDP cell lines and post-mortem brain affects global levels of acetylated histone H3 (AcH3). The results demonstrate that total AcH3 are not altered in XDP post-mortem prefrontal cortex or cell lines. We also did not detect local differences in AcH3 associated with TAF1 exons or intronic sites flanking the SVA insertion. There was, however, a decrease in AcH3 association with the exon immediately proximal to the intronic SVA, and this decrease was normalized by CRISPR/Cas-excision of the SVA. Collectively, these data suggest that the SVA insertion alters histone status in this region, which may contribute to the dysregulation of TAF1 expression.

New insights of poly(ADP-ribosylation) in neurodegenerative diseases: A focus on protein phase separation and pathologic aggregation

Abnormal protein aggregation is a common pathological feature of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and amyotrophic lateral sclerosis (ALS). Protein posttranslational modifications (PTMs) play a crucial regulatory role in the formation of pathologic aggregation. Among the known PTMs involved in neurodegeneration, poly(ADP-ribosylation) (PARylation) has emerged with promising therapeutic potentials of the use of poly(ADP-ribose) (PAR) polymerase (PARP) inhibitors. In this review, we describe the mounting evidence that abnormal PARP activation is involved in various neurodegenerative diseases, and discuss the underpinning mechanisms with a focus on the recent findings that PARylation affects liquid-liquid phase separation and aggregation of amyloid proteins. We hope this review will stimulate further investigation of the unknown functions of PARylation and promote the development of more effective therapeutic agents in treating neurodegeneration.

Neuronal susceptibility to beta-amyloid toxicity and ischemic injury involves histone deacetylase-2 regulation of endophilin-B1

Histone deacetylases (HDACs) catalyze acetyl group removal from histone proteins, leading to altered chromatin structure and gene expression. HDAC2 is highly expressed in adult brain, and HDAC2 levels are elevated in Alzheimer's disease (AD) brain. We previously reported that neuron-specific splice isoforms of Endophilin-B1 (Endo-B1) promote neuronal survival, but are reduced in human AD brain and mouse models of AD and stroke. Here, we demonstrate that HDAC2 suppresses Endo-B1 expression. HDAC2 knockdown or knockout enhances expression of Endo-B1. Conversely, HDAC2 overexpression decreases Endo-B1 expression. We also demonstrate that neurons exposed to beta-amyloid increase HDAC2 and reduce histone H3 acetylation while HDAC2 knockdown prevents Aβ induced loss of histone H3 acetylation, mitochondrial dysfunction, caspase-3 activation, and neuronal death. The protective effect of HDAC2 knockdown was abrogated by Endo-B1 shRNA and in Endo-B1-null neurons, suggesting that HDAC2-induced neurotoxicity is mediated through suppression of Endo-B1. HDAC2 overexpression also modulates neuronal expression of mitofusin2 (Mfn2) and mitochondrial fission factor (MFF), recapitulating the pattern of change observed in AD. HDAC2 knockout mice demonstrate reduced injury in the middle cerebral artery occlusion with reperfusion (MCAO/R) model of cerebral ischemia demonstrating enhanced neuronal survival, minimized loss of Endo-B1, and normalized expression of Mfn2. These findings support the hypothesis that HDAC2 represses Endo-B1, sensitizing neurons to mitochondrial dysfunction and cell death in stroke and AD.

Upregulation of Znf179 acetylation by SAHA protects cells against oxidative stress

The accumulation of reactive oxygen species (ROS) commonly occurs during normal aging and during some acute/chronic progressive disorders. In order to avoid oxidative damage, scavenging of these radicals is important. Previously, we identified zinc finger protein 179 (Znf179) as a neuroprotector that increases antioxidant enzymes against superoxide radicals. However, the molecular mechanisms involved in the activation and regulation of Znf179 remain unresolved. Here, by performing sequence alignment, bioinformatics analysis, immunoprecipitation using two specific acetyl-lysine antibodies, and treatment with the histone deacetylase (HDAC) inhibitor SAHA, we determined the lysine-specific acetylation of Znf179. Furthermore, we investigated Znf179 interaction with HDACs and revealed that peroxide insult induced a dissociation of Znf179-HDAC1/HDAC6, causing an increase in Znf179 acetylation. Importantly, HDAC inhibition by SAHA further prompted Znf179 hyperacetylation, which promoted Znf179 to form a transcriptional complex with Sp1 and increased antioxidant gene expression against oxidative attack. In summary, the results obtained in this study showed that Znf179 was regulated by HDACs and that Znf179 acetylation was a critical mechanism in the induction of antioxidant defense systems. Additionally, HDAC inhibitors may have therapeutic potential for induction of Znf179 acetylation, strengthening the Znf179 protective functions against neurodegenerative processes.

Environmental Enrichment Induces Changes in Long-Term Memory for Social Transmission of Food Preference in Aged Mice through a Mechanism Associated with Epigenetic Processes

Decline in declarative learning and memory performance is a typical feature of normal aging processes. Exposure of aged animals to an enriched environment (EE) counteracts this decline, an effect correlated with reduction of age-related changes in hippocampal dendritic branching, spine density, neurogenesis, gliogenesis, and neural plasticity, including its epigenetic underpinnings. Declarative memories depend on the medial temporal lobe system, including the hippocampus, for their formation, but, over days to weeks, they become increasingly dependent on other brain regions such as the neocortex and in particular the prefrontal cortex (PFC), a process known as system consolidation. Recently, it has been shown that early tagging of cortical networks is a crucial neurobiological process for remote memory formation and that this tagging involves epigenetic mechanisms in the recipient orbitofrontal (OFC) areas. Whether EE can enhance system consolidation in aged animals has not been tested; in particular, whether the early tagging mechanisms in OFC areas are deficient in aged animals and whether EE can ameliorate them is not known. This study aimed at testing whether EE could affect system consolidation in aged mice using the social transmission of food preference paradigm, which involves an ethologically based form of associative olfactory memory. We found that only EE mice successfully performed the remote memory recall task, showed neuronal activation in OFC, assessed with c-fos immunohistochemistry and early tagging of OFC, assessed with histone H3 acetylation, suggesting a defective system consolidation and early OFC tagging in aged mice which are ameliorated by EE.

Effects of histone acetyltransferase inhibitors on L-DOPA-induced dyskinesia in a murine model of Parkinson's disease

Histone acetylation is a key regulatory factor for gene expression in cells. Modulation of histone acetylation by targeting of histone acetyltransferases (HATs) effectively alters many gene expression profiles and synaptic plasticity in the brain. However, the role of HATs on L-DOPA-induced dyskinesia of Parkinson's disease (PD) has not been reported. Our aim was to determine whether HAT inhibitors such as anacardic acid, garcinol, and curcumin from natural plants reduce severity of L-DOPA-induced dyskinesia using a unilaterally 6-hydroxydopamine (6-OHDA)-lesioned PD mouse model. Anacardic acid 2 mg/kg, garcinol 5 mg/kg, or curcumin 100 mg/kg co-treatment with L-DOPA significantly reduced the axial, limb, and orofacial (ALO) score indicating less dyskinesia with administration of HAT inhibitors in 6-OHDA-lesioned mice. Additionally, L-DOPA's efficacy was not altered by the compounds in the early stage of treatment. The expression levels of c-Fos, Fra-2, and Arc were effectively decreased by administration of HAT inhibitors in the ipsilateral striatum. Our findings indicate that HAT inhibitor co-treatment with L-DOPA may have therapeutic potential for management of L-DOPA-induced dyskinesia in patients with PD.

Epigenetic regulatory modifications in genetic and sporadic frontotemporal dementia

INTRODUCTION

Epigenetic modifications have recently been linked to neurodegenerative diseases, such as frontotemporal dementia (FTD), which represents the second most common form of dementia in adulthood after Alzheimer's disease (AD). Epigenetic regulation occurs at different cellular levels and serve as a way to alter genetic information not only in aging but also following environmental signals. Thus, epigenetics mechanisms could exert their function at early stage of the disease, especially in sporadic cases. Areas covered: Herein, the available evidence supporting the concept that epigenetic-driven changes might shed the light into the pathogenic mechanisms of FTD will be summarized, with particular regard to their influence in underlying sporadic/familiar FTD onset and/or severity, and to the possibility to open a new scenario to facilitate early diagnosis and the identification of novel therapeutic targets. Bibliographic search through PubMed was used to find the studies included in this review. Expert commentary: Although epigenetic investigation in neurodegenerative disorders is in its infancy, recent advances in the technology of epigenetic change determination has led to novel, challenging findings. In particular, the knowledge and the characterization of epigenetic events could result in novel therapeutic strategies.

Epigenetic modulation by small molecule compounds for neurodegenerative disorders

The accumulation of somatic and genetic mutations which altered the structure and coding information of the DNA are the major cause of neurological disorders. However, our recent understanding of molecular mechanisms of 'epigenetic' phenomenon reveals that the modifications of chromatin play a significant role in the development and severity of neurological disorders. These epigenetic processes are dynamic and reversible as compared to genetic ablations which are stable and irreversible. Therefore, targeting these epigenetic processes through small molecule modulators are of great therapeutic potential. To date, large number of small molecule modulators have been discovered which are capable of altering the brain pathology by targeting epigenetic enzymes. In this review, we shall put forward the key studies supporting the role of altered epigenetic processes in neurological disorders with especial emphasis on neurodegenerative disorders. A few small molecule modulators which have been shown to possess promising results in the animal model system of neurological disorders will also be discussed with future perspectives.

Dissociable roles for histone acetyltransferases p300 and PCAF in hippocampus and perirhinal cortex-mediated object memory

The importance of histone acetylation for certain types of memory is now well established. However, the specific contributions of the various histone acetyltransferases to distinct memory functions remain to be determined; therefore, we employed selective histone acetyltransferase protein inhibitors and short-interference RNAs to evaluate the roles of CREB-binding protein (CBP), E1A-binding protein (p300) and p300/CBP-associated factor (PCAF) in hippocampus and perirhinal cortex (PRh)-mediated object memory. Rats were tested for short- (STM) and long-term memory (LTM) in the object-in-place task, which relies on the hippocampus and PRh for spatial memory and object identity processing, respectively. Selective inhibition of these histone acetyltransferases by small-interfering RNA and pharmacological inhibitors targeting the HAT domain produced dissociable effects. In the hippocampus, CBP or p300 inhibition impaired long-term but not short-term object memory, while inhibition of PCAF impaired memory at both delays. In PRh, HAT inhibition did not impair STM, and only CBP and PCAF inhibition disrupted LTM; p300 inhibition had no effects. Messenger RNA analyses revealed findings consistent with the pattern of behavioral effects, as all three enzymes were upregulated in the hippocampus (dentate gyrus) following learning, whereas only CBP and PCAF were upregulated in PRh. These results demonstrate, for the first time, the necessity of histone acetyltransferase activity for PRh-mediated object memory and indicate that the specific mnemonic roles of distinctive histone acetyltransferases can be dissociated according to specific brain regions and memory timeframe.

Neuroprotective effects of artemisinin against isoflurane-induced cognitive impairments and neuronal cell death involve JNK/ERK1/2 signalling and improved hippocampal histone acetylation in neonatal rats

OBJECTIVE

This study was performed to assess the effect of artemisinin against isoflurane-induced neuronal apoptosis and cognitive impairment in neonatal rats.

METHODS

Artemisinin (50, 100 or 200 mg/kg b.wt/day; oral gavage) was administered to separate groups of neonatal rats starting from postnatal day 3 (P3) to postnatal day 21 (P21). On postnatal day 7 (P7), animals were exposed to inhalation anaesthetic isoflurane (0.75%) for 6 h.

KEY FINDINGS

Neuronal apoptosis following anaesthetic exposure was significantly reduced by artemisinin. Isoflurane-induced upregulated cleaved caspase-3, Bax and Bad expression were downregulated. Western blotting analysis revealed that treatment with artemisinin significantly enhanced the expression of anti-apoptotic proteins (Bcl-2, Bcl-xL, c-IAP-1, c-IAP-2, xIAP and survivin). Artemisinin increased the acetylation of H3K9 and H4K12 while reducing the expression of histone deacetlyases (HDACs) - HDAC-2 and HDAC-3. Isoflurane-induced activation of JNK signalling and downregulated ERK1/2 expression was effectively modulated by artemisinin. General behaviour of the animals in open-field and T-maze test were improved. Morris water maze test and object recognition test revealed better learning, working memory and also better memory retention on artemisinin treatment.

CONCLUSIONS

Artemisinin effectively inhibited neuronal apoptosis and improved cognition and memory via regulating histone acetylation and JNK/ERK1/2 signalling.

Emerging Role of Epigenetic Mechanisms in Alcohol Addiction

Alcohol use disorder (AUD) is a complex brain disorder with an array of persistent behavioral and neurochemical manifestations. Both genetic and environmental factors are known to contribute to the development of AUD, and recent studies on alcohol exposure and subsequent changes in gene expression suggest the importance of epigenetic mechanisms. In particular, histone modifications and DNA methylation have emerged as important regulators of gene expression and associated phenotypes of AUD. Given the therapeutic potential of epigenetic targets, this review aims to summarize the role of epigenetic regulation in our current understanding of AUD by evaluating known epigenetic signatures of brain regions critical to addictive behaviors in both animal and human studies throughout various stages of AUD. More specifically, the effects of acute and chronic alcohol exposure, tolerance, and postexposure withdrawal on epigenetically induced changes to gene expression and synaptic plasticity within key brain regions and the associated behavioral phenotypes have been discussed. Understanding the contribution of epigenetic regulation to crucial signaling pathways may prove vital for future development of novel biomarkers and treatment agents in ameliorating or preventing AUD.

Anti-aging pharmacology: Promises and pitfalls

Life expectancy has grown dramatically in modern times. This increase, however, is not accompanied by the same increase in healthspan. Efforts to extend healthspan through pharmacological agents targeting aging-related pathological changes are now in the spotlight of geroscience, the main idea of which is that delaying of aging is far more effective than preventing the particular chronic disorders. Currently, anti-aging pharmacology is a rapidly developing discipline. It is a preventive field of health care, as opposed to conventional medicine which focuses on treating symptoms rather than root causes of illness. A number of pharmacological agents targeting basic aging pathways (i.e., calorie restriction mimetics, autophagy inducers, senolytics etc.) are now under investigation. This review summarizes the literature related to advances, perspectives and challenges in the field of anti-aging pharmacology.

REM sleep and its Loss-Associated Epigenetic Regulation with Reference to Noradrenaline in Particular

Sleep is an essential physiological process, which has been divided into rapid eye movement sleep (REMS) and non-REMS (NREMS) in higher animals. REMS is a unique phenomenon that unlike other sleep-waking states is not under voluntary control. Directly or indirectly it influences or gets influenced by most of the physiological processes controlled by the brain. It has been proposed that REMS serves housekeeping function of the brain. Extensive research has shown that during REMS at least noradrenaline (NA) -ergic neurons must cease activity and upon REMS loss, there are increased levels of NA in the brain, which then induces many of the REMS loss associated acute and chronic effects. The NA level is controlled by many bio-molecules that are regulated at the molecular and transcriptional levels. Similarly, NA can also directly or indirectly modulate the synthesis and levels of many molecules, which in turn may affect physiological processes. The burgeoning field of behavioral neuroepigenetics has gained importance in recent years and explains the regulatory mechanisms underlying several behavioral phenomena. As REMS and its loss associated changes in NA modulate several pathophysiological processes, in this review we have attempted to explain on one hand how the epigenetic mechanisms regulating the gene expression of factors like tyrosine hydroxylase (TH), monoamine oxidase (MAO), noradrenaline transporter (NAT) control NA levels and on the other hand, how NA per se can affect other molecules in neural circuitry at the epigenetic level resulting in behavioral changes in health and diseases. An understanding of these events will expose the molecular basis of REMS and its loss-associated pathophysiological changes; which are presented as a testable hypothesis for confirmation.

Tip60 HAT Action Mediates Environmental Enrichment Induced Cognitive Restoration

Environmental enrichment (EE) conditions have beneficial effects for reinstating cognitive ability in neuropathological disorders like Alzheimer's disease (AD). While EE benefits involve epigenetic gene control mechanisms that comprise histone acetylation, the histone acetyltransferases (HATs) involved remain largely unknown. Here, we examine a role for Tip60 HAT action in mediating activity- dependent beneficial neuroadaptations to EE using the Drosophila CNS mushroom body (MB) as a well-characterized cognition model. We show that flies raised under EE conditions display enhanced MB axonal outgrowth, synaptic marker protein production, histone acetylation induction and transcriptional activation of cognition linked genes when compared to their genotypically identical siblings raised under isolated conditions. Further, these beneficial changes are impaired in both Tip60 HAT mutant flies and APP neurodegenerative flies. While EE conditions provide some beneficial neuroadaptive changes in the APP neurodegenerative fly MB, such positive changes are significantly enhanced by increasing MB Tip60 HAT levels. Our results implicate Tip60 as a critical mediator of EE-induced benefits, and provide broad insights into synergistic behavioral and epigenetic based therapeutic approaches for treatment of cognitive disorder.

Tip off the HAT- Epigenetic control of learning and memory by Drosophila Tip60

Disruption of epigenetic gene control mechanisms involving histone acetylation in the brain causes cognitive impairment, a debilitating hallmark of most neurodegenerative disorders. Histone acetylation regulates cognitive gene expression via chromatin packaging control in neurons. Unfortunately, the histone acetyltransferases (HATs) that generate such neural epigenetic signatures and their mechanisms of action remain unclear. Our recent findings provide insight into this question by demonstrating that Tip60 HAT action is critical for morphology and function of the mushroom body (MB), the learning and memory center in the Drosophila brain. We show that Tip60 is robustly produced in MB Kenyon cells and extending axonal lobes and that targeted MB Tip60 HAT loss results in axonal outgrowth disruption. Functional consequences of loss and gain of Tip60 HAT levels in the MB are evidenced by defects in memory. Tip60 ChIP-Seq analysis reveals enrichment for genes that function in cognitive processes and accordingly, key genes representing these pathways are misregulated in the Tip60 HAT mutant fly brain. Remarkably, increasing levels of Tip60 in the MB rescues learning and memory deficits resulting from Alzheimer's disease associated amyloid precursor protein (APP) induced neurodegeneration. Our studies highlight the potential of HAT activators as a therapeutic option for cognitive disorders.

Epigenetic Mechanisms in Developmental Alcohol-Induced Neurobehavioral Deficits

Alcohol consumption during pregnancy and its damaging consequences on the developing infant brain are significant public health, social, and economic issues. The major distinctive features of prenatal alcohol exposure in humans are cognitive and behavioral dysfunction due to damage to the central nervous system (CNS), which results in a continuum of disarray that is collectively called fetal alcohol spectrum disorder (FASD). Many rodent models have been developed to understand the mechanisms of and to reproduce the human FASD phenotypes. These animal FASD studies have provided several molecular pathways that are likely responsible for the neurobehavioral abnormalities that are associated with prenatal alcohol exposure of the developing CNS. Recently, many laboratories have identified several immediate, as well as long-lasting, epigenetic modifications of DNA methylation, DNA-associated histone proteins and microRNA (miRNA) biogenesis by using a variety of epigenetic approaches in rodent FASD models. Because DNA methylation patterns, DNA-associated histone protein modifications and miRNA-regulated gene expression are crucial for synaptic plasticity and learning and memory, they can therefore offer an answer to many of the neurobehavioral abnormalities that are found in FASD. In this review, we briefly discuss the current literature of DNA methylation, DNA-associated histone proteins modification and miRNA and review recent developments concerning epigenetic changes in FASD.

Role of histone acetylation in long-term neurobehavioral effects of neonatal Exposure to sevoflurane in rats

Human studies, and especially laboratory studies, provide evidence that early life exposure to general anesthesia may affect neurocognitive development via largely unknown mechanisms. We explored whether hippocampal histone acetylation had a role in neurodevelopmental effects of sevoflurane administered to neonatal rats. Male Sprague-Dawley rats were exposed to 3% sevoflurane or were subjected to maternal separation only for 2h daily at postnatal days 6, 7, and 8. The histone deacetylase inhibitor, sodium butyrate (250mg/kg, intraperitoneally), or saline was administered starting 2h prior to anesthesia or maternal separation and continued daily until the end of behavioral tests, which were performed between postnatal days 33 and 50. Upon completion of the behavioral tests, the brain tissues were harvested for further analysis. Rats neonatally exposed to sevoflurane exhibited decreased freezing time in the fear conditioning contextual test and increased escape latency, decreased time in target quadrant, and number of platform crossings in the Morris water maze test. The sevoflurane-exposed rats had lower hippocampal density of dendritic spines, reduced levels of the brain-derived neurotrophic factor, c-fos protein, microtubule-associated protein 2, synapsin1, postsynaptic density protein 95, pCREB/CREB, CREB binding protein, and acetylated histones H3 and H4, and increased levels of histone deacetylases 3 and 8. These neurobehavioral abnormalities were normalized in the sevoflurane-exposed rats treated with sodium butyrate. Our findings provide evidence that neonatal exposure to sevoflurane induces neurobehavioral abnormalities and long-lasting alterations in histone acetylation; normalization of histone acetylation may alleviate the neurodevelopmental side effects of the anesthetic.

Epigenetic Research of Neurodegenerative Disorders Using Patient iPSC-Based Models

Epigenetic mechanisms play a role in human disease but their involvement in pathologies from the central nervous system has been hampered by the complexity of the brain together with its unique cellular architecture and diversity. Until recently, disease targeted neural types were only available as postmortem materials after many years of disease evolution. Current in vitro systems of induced pluripotent stem cells (iPSCs) generated by cell reprogramming of somatic cells from patients have provided valuable disease models recapitulating key pathological molecular events. Yet whether cell reprogramming on itself implies a truly epigenetic reprogramming, the epigenetic mechanisms governing this process are only partially understood. Moreover, elucidating epigenetic regulation using patient-specific iPSC-derived neural models is expected to have a great impact to unravel the pathophysiology of neurodegenerative diseases and to hopefully expand future therapeutic possibilities. Here we will critically review current knowledge of epigenetic involvement in neurodegenerative disorders focusing on the potential of iPSCs as a promising tool for epigenetic research of these diseases.

Mating and memory: an educational primer for use with "epigenetic control of learning and memory in Drosophila by Tip60 HAT action"

An article by Xu et al. in the December 2014 issue of GENETICS can be used to illustrate epigenetic modification of gene expression, reverse genetic manipulation, genetic/epigenetic influence on behavioral studies, and studies using the Drosophila model organism applied to human disease. This Primer provides background information; technical explanations of genetic, biochemical, and behavioral approaches from the study; and an example of an approach for classroom use with discussion questions to aid in student comprehension of the research article.

Epigenetic pathway targets for the treatment of disease: accelerating progress in the development of pharmacological tools: IUPHAR Review 11

The properties of a cell are determined both genetically by the DNA sequence of its genes and epigenetically through processes that regulate the pattern, timing and magnitude of expression of its genes. While the genetic basis of disease has been a topic of intense study for decades, recent years have seen a dramatic increase in the understanding of epigenetic regulatory mechanisms and a growing appreciation that epigenetic misregulation makes a significant contribution to human disease. Several large protein families have been identified that act in different ways to control the expression of genes through epigenetic mechanisms. Many of these protein families are finally proving tractable for the development of small molecules that modulate their function and represent new target classes for drug discovery. Here, we provide an overview of some of the key epigenetic regulatory proteins and discuss progress towards the development of pharmacological tools for use in research and therapy.

The role of epigenetics in cognitive ageing

OBJECTIVE

As the population is ageing, a better understanding of the underlying causes of age-related cognitive decline (cognitive ageing) is required. Epigenetic dysregulation is proposed as one of the underlying mechanisms for cognitive ageing. We review the current knowledge on epigenetics and cognitive ageing and appraise the potential of epigenetic preventative and therapeutic interventions.

DESIGN

Articles on cognitive ageing and epigenetics in English were identified.

RESULTS

Epigenetic dysregulation occurs with cognitive ageing, with changes in histone post-translational modifications, DNA methylation and non-coding RNA reported. However, human studies are lacking, with most being cross-sectional using peripheral blood samples. Pharmacological and lifestyle factors have the potential to change aberrant epigenetic profiles; but few studies have examined this in relation to cognitive ageing.

CONCLUSIONS

The relationship between epigenetic modifications and cognitive ageing is only beginning to be investigated. Epigenetic dysregulation appears to be an important feature in cognitive ageing, but whether it is an epiphenomenon or a causal factor remains to be elucidated. Clarification of the relationship between epigenetic profiles of different cell types is essential and would determine whether epigenetic marks of peripheral tissues can be used as a proxy for changes occurring in the brain. The use of lifestyle and pharmacological interventions to improve cognitive performance and quality of life of older adults needs more investigation.

Histone hyperacetylation up-regulates protein kinase Cδ in dopaminergic neurons to induce cell death: relevance to epigenetic mechanisms of neurodegeneration in Parkinson disease

The oxidative stress-sensitive protein kinase Cδ (PKCδ) has been implicated in dopaminergic neuronal cell death. However, little is known about the epigenetic mechanisms regulating PKCδ expression in neurons. Here, we report a novel mechanism by which the PKCδ gene can be regulated by histone acetylation. Treatment with histone deacetylase (HDAC) inhibitor sodium butyrate (NaBu) induced PKCδ expression in cultured neurons, brain slices, and animal models. Several other HDAC inhibitors also mimicked NaBu. The chromatin immunoprecipitation analysis revealed that hyperacetylation of histone H4 by NaBu is associated with the PKCδ promoter. Deletion analysis of the PKCδ promoter mapped the NaBu-responsive element to an 81-bp minimal promoter region. Detailed mutagenesis studies within this region revealed that four GC boxes conferred hyperacetylation-induced PKCδ promoter activation. Cotransfection experiments and Sp inhibitor studies demonstrated that Sp1, Sp3, and Sp4 regulated NaBu-induced PKCδ up-regulation. However, NaBu did not alter the DNA binding activities of Sp proteins or their expression. Interestingly, a one-hybrid analysis revealed that NaBu enhanced transcriptional activity of Sp1/Sp3. Overexpression of the p300/cAMP-response element-binding protein-binding protein (CBP) potentiated the NaBu-mediated transactivation potential of Sp1/Sp3, but expressing several HDACs attenuated this effect, suggesting that p300/CBP and HDACs act as coactivators or corepressors in histone acetylation-induced PKCδ up-regulation. Finally, using genetic and pharmacological approaches, we showed that NaBu up-regulation of PKCδ sensitizes neurons to cell death in a human dopaminergic cell model and brain slice cultures. Together, these results indicate that histone acetylation regulates PKCδ expression to augment nigrostriatal dopaminergic cell death, which could contribute to the progressive neuropathogenesis of Parkinson disease.

Epigenetic control of learning and memory in Drosophila by Tip60 HAT action

Disruption of epigenetic gene control mechanisms in the brain causes significant cognitive impairment that is a debilitating hallmark of most neurodegenerative disorders, including Alzheimer's disease (AD). Histone acetylation is one of the best characterized of these epigenetic mechanisms that is critical for regulating learning- and memory- associated gene expression profiles, yet the specific histone acetyltransferases (HATs) that mediate these effects have yet to be fully characterized. Here, we investigate an epigenetic role for the HAT Tip60 in learning and memory formation using the Drosophila CNS mushroom body (MB) as a well-characterized cognition model. We show that Tip60 is endogenously expressed in the Kenyon cells, the intrinsic neurons of the MB, and in the MB axonal lobes. Targeted loss of Tip60 HAT activity in the MB causes thinner and shorter axonal lobes while increasing Tip60 HAT levels cause no morphological defects. Functional consequences of both loss and gain of Tip60 HAT levels in the MB are evidenced by defects in immediate-recall memory. Our ChIP-Seq analysis reveals that Tip60 target genes are enriched for functions in cognitive processes, and, accordingly, key genes representing these pathways are misregulated in the Tip60 HAT mutant fly brain. Remarkably, we find that both learning and immediate-recall memory deficits that occur under AD-associated, amyloid precursor protein (APP)-induced neurodegenerative conditions can be effectively rescued by increasing Tip60 HAT levels specifically in the MB. Together, our findings uncover an epigenetic transcriptional regulatory role for Tip60 in cognitive function and highlight the potential of HAT activators as a therapeutic option for neurodegenerative disorders.

Vitamin A deficiency impairs spatial learning and memory: the mechanism of abnormal CBP-dependent histone acetylation regulated by retinoic acid receptor alpha

Vitamin A (VA) is an essential micronutrient. Numerous studies have confirmed that VA deficiency (VAD) leads to a decline in learning and memory function. Our previous studies have demonstrated that retinoic acid nuclear receptor α (RARα) in the hippocampus plays a crucial role in learning and memory, but the exact mechanism for this process is unclear. Epigenetic modifications, particularly histone acetylation, are involved in nervous system development, learning and memory function, and the pathogenesis of neurodegenerative diseases. Histone acetyltransferases (HATs), such as CREB-binding protein (CBP), E1A-binding protein p300 (p300), and p300/CBP-associated factor (PCAF), are critical for regulating memory function. The current study uses RARα and CBP as examples to study the connections between the RA signaling pathway and histone acetylation modification and to reveal the epigenetic mechanism in VAD-induced learning and memory impairment. This study examined the expression of RARα, HATs, acetylated histone H3/H4, and memory-related genes (Zif268, cFos, FosB), as well as the interaction of RARα and CBP in the hippocampus of 8-week-old rats. Additionally, the changes shown in vivo were further assessed in primary cultured neurons with the inhibition or overexpression of RARα. We found significantly lower levels of histone acetylation in the VAD rats. Furthermore, this downregulation, which impairs learning and memory, is induced by the dysregulation of CBP-dependent histone acetylation that is mediated by RARα. This work provides a solid theoretical foundation and experimental basis for the importance of ensuring sufficient nutritional VA during pregnancy and early life to prevent impairments of learning and memory in adulthood.

HDAC signaling in neuronal development and axon regeneration

The development and repair of the nervous system requires the coordinated expression of a large number of specific genes. Epigenetic modifications of histones represent an essential principle by which neurons regulate transcriptional responses and adapt to environmental cues. The post-translational modification of histones by chromatin-modifying enzymes histone acetyltransferases (HATs) and histone deacetylases (HDACs) shapes chromatin to adjust transcriptional profiles during neuronal development. Recent observations also point to a critical role for histone acetylation and deacetylation in the response of neurons to injury. While HDACs are mostly known to attenuate transcription through their deacetylase activity and their interaction with co-repressors, these enzymes are also found in the cytoplasm where they display transcription-independent activities by regulating the function of diverse proteins. Here we discuss recent studies that go beyond the traditional use of HDAC inhibitors and have begun to dissect the roles of individual HDAC isoforms in neuronal development and repair after injury.

Epigenetics, fragile X syndrome and transcriptional therapy

Epigenetics refers to the study of heritable changes in gene expression that occur without a change in DNA sequence. Epigenetic mechanisms therefore include all transcriptional controls that determine how genes are expressed during development and differentiation, but also in individual cells responding to environmental stimuli. The purpose of this review is to examine the basic principles of epigenetic mechanisms and their contribution to human disorders with a particular focus on fragile X syndrome (FXS), the most common monogenic form of developmental cognitive impairment. FXS represents a prototype of the so-called repeat expansion disorders due to "dynamic" mutations, namely the expansion (known as "full mutation") of a CGG repeat in the 5'UTR of the FMR1 gene. This genetic anomaly is accompanied by epigenetic modifications (mainly DNA methylation and histone deacetylation), resulting in the inactivation of the FMR1 gene. The presence of an intact FMR1 coding sequence allowed pharmacological reactivation of gene transcription, particularly through the use of the DNA demethylating agent 5'-aza-2'-deoxycytydine and/or inhibitors of histone deacetylases. These treatments suggested that DNA methylation is dominant over histone acetylation in silencing the FMR1 gene. The importance of DNA methylation in repressing FMR1 transcription is confirmed by the existence of rare unaffected males carrying unmethylated full mutations. Finally, we address the potential use of epigenetic approaches to targeted treatment of other genetic conditions.

Epigenetics components of aging in the central nervous system

This review highlights recent discoveries that have shaped the emerging viewpoints in the field of epigenetic influences in the central nervous system (CNS), focusing on the following questions: (i) How is the CNS shaped during development when precursor cells transition into morphologically and molecularly distinct cell types, and is this event driven by epigenetic alterations?; ii) How do epigenetic pathways control CNS function?; (iii) What happens to "epigenetic memory" during aging processes, and do these alterations cause CNS dysfunction?; (iv) Can one restore normal CNS function by manipulating the epigenome using pharmacologic agents, and will this ameliorate aging-related neurodegeneration? These and other still unanswered questions remain critical to understanding the impact of multifaceted epigenetic machinery on the age-related dysfunction of CNS.

Epigenetics and ncRNAs in brain function and disease: mechanisms and prospects for therapy

The most fundamental roles of non-coding RNAs (ncRNAs) and epigenetic mechanisms are the guidance of cellular differentiation in development and the regulation of gene expression in adult tissues. In brain, both ncRNAs and the various epigenetic gene regulatory mechanisms play a fundamental role in neurogenesis and normal neuronal function. Thus, epigenetic chromatin remodelling can render coding sites transcriptionally inactive by DNA methylation, histone modifications or antisense RNA interactions. On the other hand, microRNAs (miRNAs) are ncRNA molecules that can regulate the expression of hundreds of genes post-transcriptionally, typically recognising binding sites in the 3' untranslated region (UTR) of mRNA transcripts. Furthermore, there are a myriad of interactions in the interface of miRNAs and epigenetics. For example, epigenetic mechanisms can silence miRNA coding sites, and miRNAs can be the effectors of transcriptional gene silencing, targeting complementary promoters or silencing the expression of epigenetic modifier genes like MECP2 and EZH2 leading to global changes in the epigenome. Alterations in this regulatory machinery play a key role in the pathology of complex disorders including cancer and neurological diseases. For example, miRNA genes are frequently inactivated by epimutations in gliomas. Here we describe the interactions between epigenetic and ncRNA regulatory systems and discuss therapeutic potential, with an emphasis on tumors, cognitive disorders and neurodegenerative diseases.

Epigenetic changes: a common theme in acute myelogenous leukemogenesis

Acute myeloid leukemia (AML) is a rather common disease, characterized by the presence of a clonal population of hematopoietic progenitor cells with impaired differentiation. Although traditionally AML has been considered the result of genetic alterations, more recently experimental evidence have demonstrated that epigenetic modifications are important in development and maintenance of leukemia cells. In this review we summarize current scientific knowledge of epigenetic alterations involved in leukemogenesis. We also highlight the developing of new technological strategies that are based on epigenetic processes and have been registered as Patents of Inventions in the United Nations dependent World Intellectual Property Office (WIPO) and the main Patent offices worldwide.