Tuning acetylation levels with HAT activators: Therapeutic strategy in neurodegenerative diseases

Transcriptional Expression of Histone Acetyltransferases and Deacetylases During the Recovery of Acute Exercise in Mouse Hippocampus

Protein acetylation, which is dynamically maintained by histone acetyltransferases (HATs) and deacetylases (HDACs), might play essential roles in hippocampal exercise physiology. However, whether HATs/HDACs are imbalanced during the recovery phase following acute exercise has not been determined. Groups of exercised mice with different recovery periods after acute exercise (0 h, 0.5 h, 1 h, 4 h, 7 h, and 24 h) were constructed, and a group of sham-exercised mice was used as the control. The mRNA levels of HATs and HDACs were detected via real-time quantitative polymerase chain reaction. Lysine acetylation on the total proteins and some specific locations on histones were detected via western blotting, as were various acylation modifications on the total proteins. Except for four unaffected genes (Hdac4, Ncoa1, Ncoa2, and Sirt1), the mRNA expression trajectories of 21 other HATs or HDACs affected by exercise could be categorized into three clusters. The genes in Cluster 1 increased quickly following exercise, with a peak at 0.5 h and/or 1 h, and remained at high levels until 24 h. Cluster 2 genes presented a gradual increase with a delayed peak at 4 h or 7 h postexercise before returning to baseline. The expression of Cluster 3 genes decreased at 0.5 h and/or 1 h, with some returning to overexpression (Hdac1 and Sirt3). Although most HATs were upregulated and half of the affected HDACs were downregulated at 0.5 h postexercise, the global or residue-specific histone acetylation levels were unchanged. In contrast, the levels of several metabolism-related acylation products of total proteins, including acetylation, succinylation, 2-hydroxyisobutyryllysine, β-hydroxybutyryllysine, and lactylation, decreased and mainly occurred on nonhistones immediately after exercise. During the 24-h recovery phase after acute exercise, the transcriptional trajectory of HATs or the same class of HDACs in the hippocampus exhibited heterogeneity. Although acute exercise did not affect the selected sites on histone lysine residues, it possibly incurred changes in acetylation and other acylation on nonhistone proteins.

The evolution of small molecule enzyme activators

There is a myriad of enzymes within the body responsible for maintaining homeostasis by providing the means to convert substrates to products as and when required. Physiological enzymes are tightly controlled by many signaling pathways and their products subsequently control other pathways. Traditionally, most drug discovery efforts focus on identifying enzyme inhibitors, due to upregulation being prevalent in many diseases and the existence of endogenous substrates that can be modified to afford inhibitor compounds. As enzyme downregulation and reduction of endogenous activators are observed in multiple diseases, the identification of small molecules with the ability to activate enzymes has recently entered the medicinal chemistry toolbox to afford chemical probes and potential therapeutics as an alternative means to intervene in diseases. In this review we highlight the progress made in the identification and advancement of non-kinase enzyme activators and their potential in treating various disease states.

Neuroepigenetics of ageing and neurodegeneration-associated dementia: An updated review

Gene expression is tremendously altered in the brain during memory acquisition, recall, and forgetfulness. However, non-genetic factors, including environmental elements, epigenetic changes, and lifestyle, have grabbed significant attention in recent years regarding the etiology of neurodegenerative diseases (NDD) and age-associated dementia. Epigenetic modifications are essential in regulating gene expression in all living organisms in a DNA sequence-independent manner. The genes implicated in ageing and NDD-related memory disorders are epigenetically regulated by processes such as DNA methylation, histone acetylation as well as messenger RNA editing machinery. The physiological and optimal state of the epigenome, especially within the CNS of humans, plays an intricate role in helping us adjust to the changing environment, and alterations in it cause many brain disorders, but the mechanisms behind it still need to be well understood. When fully understood, these epigenetic landscapes could act as vital targets for pharmacogenetic rescue strategies for treating several diseases, including neurodegeneration- and age-induced dementia. Keeping this objective in mind, this updated review summarises the epigenetic changes associated with age and neurodegeneration-associated 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.

Epigenetic Modifications by Estrogen and Androgen in Alzheimer's Disease

For the development and maintenance of neuron networks in the brain, epigenetic mechanisms are necessary, as indicated by recent findings. This includes some of the high-order brain processes, such as behavior and cognitive functions. Epigenetic mechanisms could influence the pathophysiology or etiology of some neuronal diseases, altering disease susceptibility and therapy responses. Recent studies support epigenetic dysfunctions in neurodegenerative and psychiatric conditions, such as Alzheimer's disease (AD). These dysfunctions in epigenetic mechanisms also play crucial roles in the transgenerational effects of the environment on the brain and subsequently in the inheritance of pathologies. The possible role of gonadal steroids in the etiology and progression of neurodegenerative diseases, including Alzheimer's disease, has become the subject of a growing body of research over the last 20 years. Recent scientific findings suggest that epigenetic changes, driven by estrogen and androgens, play a vital role in brain functioning. Therefore, exploring the role of estrogen and androgen-based epigenetic changes in the brain is critical for the deeper understanding of AD. This review highlights the epigenetic modifications caused by these two gonadal steroids and the possible therapeutic strategies for AD.

Age-dependent attenuation of spatial memory deficits by the histone acetyltransferase p300/CBP-associated factor (PCAF) in 3xTG Alzheimer's disease mice

Histone acetylation, catalyzed by histone acetyltransferases, has emerged as a promising therapeutic strategy in Alzheimer's disease (AD). By longitudinally characterizing spatial memory at 3, 6, and 9 mo of age, we show that acute activation and inhibition of the histone acetyltransferase PCAF remediated memory impairments in 3xTG-AD mice in an age-related bidirectional manner. At 3 and 6 mo of age, PCAF activation ameliorated memory deficits. At 9 mo of age, PCAF activation had no effect on spatial memory, whereas PCAF inhibition improved memory deficits in females. This work reveals a complex potential therapeutic role for PCAF in AD, initially benefitting memory but becoming detrimental as the disease progresses.

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

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

Histone hypoacetylation contributes to neurotoxicity induced by chronic nickel exposure in vivo and in vitro

Nickel (Ni) is a heavy metal that is both an environmental pollutant and a threat to human health. However, the effects of Ni on the central nervous system in susceptible populations have not been well established. In the present study, the neurotoxicity of Ni and its underlying mechanism were investigated in vivo and in vitro. Ni exposure through drinking water (10 mg Ni/L, 12 weeks) caused learning and memory impairment in mice. Reduced dendrite complexity was observed in both Ni-exposed mouse hippocampi and Ni-treated (200 μM, 72 h) primary cultured hippocampal neurons. The levels of histone acetylation, especially at histone H3 lysine 9 (H3K9ac), were reduced in Ni-exposed mouse hippocampi and cultured neurons. RNA sequencing and chromatin immunoprecipitation (ChIP) sequencing analyses revealed that H3K9ac-modulated gene expression were downregulated. Treatment with sodium butyrate, a histone deacetylase inhibitor, attenuated Ni-induced H3K9 hypoacetylation, neural gene downregulation and dendrite complexity reduction in cultured neurons. Sodium butyrate also restored Ni-induced memory impairment in mice. These results indicate that Ni-induced H3K9 hypoacetylation may be a contributor to the neurotoxicity of Ni. The finding that Ni disturbs histone acetylation in the nervous system may provide new insight into the health risk of chronic Ni exposure.

Mechanistic Exploration of Methionine 274 Acting as a "Switch" of the Selective Pocket Involved in HDAC8 Inhibition: An in Silico Study

The overexpression of histone deacetylase 8 (HDAC8) causes several diseases, and the selective inhibition of HDAC8 has been touted as a promising therapeutic strategy due to its fewer side effects. However, the mechanism of HDAC8 selective inhibition remains unclear. In this study, flexible docking and in silico mutation were used to explore the structural change of methionine (M274) during HDAC8 binding to inhibitors, along with the reason for this change. Meanwhile, steered and conventional molecular dynamics simulations were employed to explore the stability of the structural change. The findings suggest that M274 acts as a "switch" to control the exposure of the HDAC8-selective pocket. The structure of M274 changes from flipped-out to flipped-in only when L-shaped inhibitors bind to HDAC8. This structural change forms a groove that allows these inhibitors to enter the selective pocket. In other HDACs, a leucine residue replaces M274 in situ, and the same structural change is not observed. The findings reveal the mechanism of selective HDAC8 inhibition and provide guidance for the development of novel selective inhibitors.

HAT cofactor TRRAP modulates microtubule dynamics via SP1 signaling to prevent neurodegeneration

Brain homeostasis is regulated by the viability and functionality of neurons. HAT (histone acetyltransferase) and HDAC (histone deacetylase) inhibitors have been applied to treat neurological deficits in humans; yet, the epigenetic regulation in neurodegeneration remains elusive. Mutations of HAT cofactor TRRAP (transformation/transcription domain-associated protein) cause human neuropathies, including psychosis, intellectual disability, autism, and epilepsy, with unknown mechanism. Here we show that Trrap deletion in Purkinje neurons results in neurodegeneration of old mice. Integrated transcriptomics, epigenomics, and proteomics reveal that TRRAP via SP1 conducts a conserved transcriptomic program. TRRAP is required for SP1 binding at the promoter proximity of target genes, especially microtubule dynamics. The ectopic expression of Stathmin3/4 ameliorates defects of TRRAP-deficient neurons, indicating that the microtubule dynamics is particularly vulnerable to the action of SP1 activity. This study unravels a network linking three well-known, but up-to-date unconnected, signaling pathways, namely TRRAP, HAT, and SP1 with microtubule dynamics, in neuroprotection.

TIP60 in aging and neurodegeneration

Epigenetic modification of chromatin, including histone methylation and acetylation, plays critical roles in eukaryotic cells and has a significant impact on chromatin structure/accessibility, gene regulation and, susceptibility to aging, neurodegenerative disease, cancer, and other age-related diseases. This article reviews the current advances on TIP60/KAT5, a major histone acetyltransferase with diverse functions in eukaryotes, with emphasis on its regulation of autophagy, proteasome-dependent protein turnover, RNA transcription, DNA repair, circadian rhythms, learning and memory, and other neurological functions implicated in aging and neurodegeneration. Moreover, the promising therapeutic potential of TIP60 is discussed to target Alzheimer's disease and other neurological diseases.

Disruption of Tip60 HAT mediated neural histone acetylation homeostasis is an early common event in neurodegenerative diseases

Epigenetic dysregulation is a common mechanism shared by molecularly and clinically heterogenous neurodegenerative diseases (NDs). Histone acetylation homeostasis, maintained by the antagonistic activity of histone acetyltransferases (HATs) and histone deacetylases (HDACs), is necessary for appropriate gene expression and neuronal function. Disruption of neural acetylation homeostasis has been implicated in multiple types of NDs including Alzheimer's disease (AD), yet mechanisms underlying alterations remain unclear. We show that like AD, disruption of Tip60 HAT/HDAC2 balance with concomitant epigenetic repression of common Tip60 target neuroplasticity genes occurs early in multiple types of Drosophila ND models such as Parkinson's Disease (PD), Huntington's Disease (HD) and Amyotrophic Lateral Sclerosis (ALS). Repressed neuroplasticity genes show reduced enrichment of Tip60 and epigentic acetylation signatures at all gene loci examined with certain genes showing inappropriate HDAC2 repressor enrichment. Functional neuronal consequences for these disease conditions are reminiscent of human pathology and include locomotion, synapse morphology, and short-term memory deficits. Increasing Tip60 HAT levels specifically in the mushroom body learning and memory center in the Drosophila brain protects against locomotion and short-term memory function deficits in multiple NDs. Together, our results support a model by which Tip60 protects against neurological impairments in different NDs via similar modes of action.

Effect of lysine side chain length on histone lysine acetyltransferase catalysis

Histone lysine acetyltransferase (KAT)-catalyzed acetylation of lysine residues in histone tails plays a key role in regulating gene expression in eukaryotes. Here, we examined the role of lysine side chain length in the catalytic activity of human KATs by incorporating shorter and longer lysine analogs into synthetic histone H3 and H4 peptides. The enzymatic activity of MOF, PCAF and GCN5 acetyltransferases towards histone peptides bearing lysine analogs was evaluated using MALDI-TOF MS assays. Our results demonstrate that human KAT enzymes have an ability to catalyze an efficient acetylation of longer lysine analogs, whereas shorter lysine analogs are not substrates for KATs. Kinetics analyses showed that lysine is a superior KAT substrate to its analogs with altered chain length, implying that lysine has an optimal chain length for KAT-catalyzed acetylation reaction.

The role of astrocytic glutamate transporters GLT-1 and GLAST in neurological disorders: Potential targets for neurotherapeutics

Glutamate is the primary excitatory neurotransmitter in the central nervous system (CNS) which initiates rapid signal transmission in the synapse before its re-uptake into the surrounding glia, specifically astrocytes. The astrocytic glutamate transporters glutamate-aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1) and their human homologs excitatory amino acid transporter 1 (EAAT1) and 2 (EAAT2), respectively, are the major transporters which take up synaptic glutamate to maintain optimal extracellular glutamic levels, thus preventing accumulation in the synaptic cleft and ensuing excitotoxicity. Growing evidence has shown that excitotoxicity is associated with various neurological disorders, including amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), Parkinson's disease (PD), manganism, ischemia, schizophrenia, epilepsy, and autism. While the mechanisms of neurological disorders are not well understood, the dysregulation of GLAST/GLT-1 may play a significant role in excitotoxicity and associated neuropathogenesis. The expression and function of GLAST/GLT-1 may be dysregulated at the genetic, epigenetic, transcriptional or translational levels, leading to high levels of extracellular glutamate and excitotoxicity. Consequently, understanding the regulatory mechanisms of GLAST/GLT-1 has been an area of interest in developing therapeutics for the treatment of neurological disorders. Pharmacological agents including β-lactam antibiotics, estrogen/selective estrogen receptor modulators (SERMs), growth factors, histone deacetylase inhibitors (HDACi), and translational activators have shown significant efficacy in enhancing the expression and function of GLAST/GLT-1 and glutamate uptake both in vitro and in vivo. This comprehensive review will discuss the regulatory mechanisms of GLAST/GLT-1, their association with neurological disorders, and the pharmacological agents which mediate their expression and function. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.

Class I Histone Deacetylase Inhibition by Tianeptinaline Modulates Neuroplasticity and Enhances Memory

Through epigenetic and other regulatory functions, the histone deacetylase (HDAC) family of enzymes has emerged as a promising therapeutic target for central nervous system and other disorders. Here we report on the synthesis and functional characterization of new HDAC inhibitors based structurally on tianeptine, a drug used primarily to treat major depressive disorder (MDD) that has a poorly understood mechanism of action. Since the chemical structure of tianeptine resembles certain HDAC inhibitors, we profiled the in vitro HDAC inhibitory activity of tianeptine and demonstrated its ability to inhibit the lysine deacetylase activity of a subset of class I HDACs. Consistent with a model of active site Zn²⁺ chelation by the carboxylic acid present in tianeptine, newly synthesized analogues containing either a hydroxamic acid or ortho-aminoanilide exhibited increased potency and selectivity among the HDAC family. This in vitro potency translated to improved efficacy in a panel of high-content imaging assays designed to assess HDAC target engagement and functional effects on critical pathways involved in neuroplasticity in both primary mouse neurons and, for the first time, human neurons differentiated from pluripotent stem cells. Most notably, tianeptinaline, a class I HDAC-selective analogue of tianeptine, but not tianeptine itself, increased histone acetylation, and enhanced CREB-mediated transcription and the expression of Arc (activity-regulated cytoskeleton-associated protein). Systemic in vivo administration of tianeptinaline to mice confirmed its brain penetration and was found to enhance contextual fear conditioning, a behavioral test of hippocampal-dependent memory. Tianeptinaline and its derivatives provide new pharmacological tools to dissect chromatin-mediated neuroplasticity underlying memory and other epigenetically related processes implicated in health and disease.

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.

Restoring Tip60 HAT/HDAC2 Balance in the Neurodegenerative Brain Relieves Epigenetic Transcriptional Repression and Reinstates Cognition

Cognitive decline is a debilitating hallmark during preclinical stages of Alzheimer's disease (AD), yet the causes remain unclear. Because histone acetylation homeostasis is critical for mediating epigenetic gene control throughout neuronal development, we postulated that its misregulation contributes to cognitive impairment preceding AD pathology. Here, we show that disruption of Tip60 histone acetlytransferase (HAT)/histone deacetylase 2 (HDAC2) homeostasis occurs early in the brain of an AD-associated amyloid precursor protein (APP) Drosophila model and triggers epigenetic repression of neuroplasticity genes well before Aβ plaques form in male and female larvae. Repressed genes display enhanced HDAC2 binding and reduced Tip60 and histone acetylation enrichment. Increasing Tip60 in the AD-associated APP brain restores Tip60 HAT/HDAC2 balance by decreasing HDAC2 levels, reverses neuroepigenetic alterations to activate synaptic plasticity genes, and reinstates brain morphology and cognition. Such Drosophila neuroplasticity gene epigenetic signatures are conserved in male and female mouse hippocampus and their expression and Tip60 function is compromised in hippocampus from AD patients. We suggest that Tip60 HAT/HDAC2-mediated epigenetic gene disruption is a critical initial step in AD that is reversed by restoring Tip60 in the brain.SIGNIFICANCE STATEMENT Mild cognitive impairment is a debilitating hallmark during preclinical stages of Alzheimer's disease (AD), yet its causes remain unclear. Although recent findings support elevated histone deacetylase 2 (HDAC2) as a cause for epigenetic repression of synaptic genes that contribute to cognitive deficits, whether alterations in histone acetlytransferase (HAT) levels that counterbalance HDAC2 repressor action occur and the identity of these HATs remain unknown. We demonstrate that disruption of Tip60 HAT/HDAC2 homeostasis occurs early in the AD Drosophila brain and triggers epigenetic repression of neuroplasticity genes before Aβ plaques form. Increasing Tip60 in the AD brain restores Tip60 HAT/HDAC2 balance, reverses neuroepigenetic alterations to activate synaptic genes, and reinstates brain morphology and cognition. Our data suggest that disruption of the Tip60 HAT/HDAC2 balance is a critical initial step in AD.

Epigenetic Regulation of Memory-Therapeutic Potential for Disorders

BACKGROUND

Memory is a vital function which declines in different physiological and pathological conditions such as aging and neurodegenerative diseases. Research in the past has reported that memory formation and consolidation require the precise expression of synaptic plasticity genes. However, little is known about the regulation of these genes. Epigenetic modification is now a well established mechanism that regulates synaptic plasticity genes and neuronal functions including memory. Therefore, we have reviewed the epigenetic regulation of memory and its therapeutic potential for memory dysfunction during aging and neurological disorders.

METHOD

Research reports and online contents relevant to epigenetic regulation of memory during physiological and pathological conditions have been compiled and discussed.

RESULTS

Epigenetic modifications include mainly DNA methylation and hydroxymethylation, histone acetylation and methylation which involve chromatin modifying enzymes. These epigenetic marks change during memory formation and impairment due to dementia, aging and neurodegeneration. As the epigenetic modifications are reversible, they can be modulated by enzyme inhibitors leading to the recovery of memory.

CONCLUSION

Epigenetic modifications could be exploited as a potential therapeutic target to recover memory disorders during aging and pathological conditions.

Epigenetic interventions for epileptogenesis: A new frontier for curing epilepsy

This article highlights the emerging therapeutic potential of specific epigenetic modulators as promising antiepileptogenic or disease-modifying agents for curing epilepsy. Currently, there is an unmet need for antiepileptogenic agents that truly prevent the development of epilepsy in people at risk. There is strong evidence that epigenetic signaling, which exerts high fidelity regulation of gene expression, plays a crucial role in the pathophysiology of epileptogenesis and chronic epilepsy. These modifications are not hard-wired into the genome and are constantly reprogrammed by environmental influences. The potential epigenetic mechanisms, including histone modifications, DNA methylation, microRNA-based transcriptional control, and bromodomain reading activity, can drastically alter the neuronal gene expression profile by exerting their summative effects in a coordinated fashion. Such an epigenetic intervention appears more rational strategy for preventing epilepsy because it targets the primary pathway that initially triggers the numerous downstream cellular and molecular events mediating epileptogenesis. Among currently approved epigenetic drugs, the majority are anticancer drugs with well-established profiles in clinical trials and practice. Evidence from preclinical studies supports the premise that these drugs may be applied to a wide range of brain disorders. Targeting histone deacetylation by inhibiting histone deacetylase enzymes appears to be one promising epigenetic therapy since certain inhibitors have been shown to prevent epileptogenesis in animal models. However, developing neuronal specific epigenetic modulators requires rational, pathophysiology-based optimization to efficiently intercept the upstream pathways in epileptogenesis. Overall, epigenetic agents have been well positioned as new frontier tools towards the national goal of curing epilepsy.

Discovery of Therapeutic Approaches for Polyglutamine Diseases: A Summary of Recent Efforts

Polyglutamine (PolyQ) diseases are a group of neurodegenerative disorders caused by the expansion of cytosine-adenine-guanine (CAG) trinucleotide repeats in the coding region of specific genes. This leads to the production of pathogenic proteins containing critically expanded tracts of glutamines. Although polyQ diseases are individually rare, the fact that these nine diseases are irreversibly progressive over 10 to 30 years, severely impairing and ultimately fatal, usually implicating the full-time patient support by a caregiver for long time periods, makes their economic and social impact quite significant. This has led several researchers worldwide to investigate the pathogenic mechanism(s) and therapeutic strategies for polyQ diseases. Although research in the field has grown notably in the last decades, we are still far from having an effective treatment to offer patients, and the decision of which compounds should be translated to the clinics may be very challenging. In this review, we provide a comprehensive and critical overview of the most recent drug discovery efforts in the field of polyQ diseases, including the most relevant findings emerging from two different types of approaches-hypothesis-based candidate molecule testing and hypothesis-free unbiased drug screenings. We hereby summarize and reflect on the preclinical studies as well as all the clinical trials performed to date, aiming to provide a useful framework for increasingly successful future drug discovery and development efforts.

The Many Faces of Elongator in Neurodevelopment and Disease

Development of the nervous system requires a variety of cellular activities, such as proliferation, migration, axonal outgrowth and guidance and synapse formation during the differentiation of neural precursors into mature neurons. Malfunction of these highly regulated and coordinated events results in various neurological diseases. The Elongator complex is a multi-subunit complex highly conserved in eukaryotes whose function has been implicated in the majority of cellular activities underlying neurodevelopment. These activities include cell motility, actin cytoskeleton organization, exocytosis, polarized secretion, intracellular trafficking and the maintenance of neural function. Several studies have associated mutations in Elongator subunits with the neurological disorders familial dysautonomia (FD), intellectual disability (ID), amyotrophic lateral sclerosis (ALS) and rolandic epilepsy (RE). Here, we review the various cellular activities assigned to this complex and discuss the implications for neural development and disease. Further research in this area has the potential to generate new diagnostic tools, better prevention strategies and more effective treatment options for a wide variety of neurological disorders.

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.

Sodium Butyrate, a Histone Deacetylase Inhibitor, Exhibits Neuroprotective/Neurogenic Effects in a Rat Model of Neonatal Hypoxia-Ischemia

Neonatal hypoxic-ischemic (HI) injury still remains an important issue as it is a major cause of neonatal death and neurological dysfunctions. Currently, there are no well-established treatments to reduce brain damage and its long-term sequel in infants. Recently, reported data show that histone deacetylase inhibitors provide neuroprotection in adult stroke models. However, the proof of their relevance in vivo after neonatal HI brain injury remains particularly limited. In the present study, we show neuroprotective/neurogenic effect of sodium butyrate (SB), one of histone deacetylase inhibitors (HDACis), in the dentate gyrus of HI-injured immature rats. Postnatal day 7 (P7) rats underwent left carotid artery ligation followed by 7.6 % O₂ exposure for 1 h. SB (300 mg/kg) was administered in a 5-day regime with the first injection given immediately after the onset of HI. The damage of the ipsilateral hemisphere was evaluated by weight deficit. Newly produced cells were labeled with BrdU, at 50 mg/kg, injected twice daily for 3 consecutive days. Subsequent differentiation of the newborn cells was investigated 2 and 4 weeks after the insult by immunohistochemistry using neuronal and glial cell-lineage markers and BrdU incorporation. Finally, we performed several behavioral tests to evaluate functional outcome. In summary, SB led to a remarkable reduction of the brain damage caused by HI. Moreover, the application of this HDACi protected against HI-induced loss of neuroblasts and oligodendrocyte precursor cells, as well as against neuroinflammation. The observed neuroprotective action suggests that SB may serve as a potential candidate for future treatment of HI-evoked injury in neonates.

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.

Lysine acetyltransferases cyclic adenosine monophosphate response element-binding binding protein and acetyltransferase p300 attenuate transcriptional activity of the mineralocorticoid receptor through its acetylation

Acetylation of the mineralocorticoid receptor (MR) by inhibition of lysine deacetylases attenuates MR's transcriptional activity. However, the specific lysine acetyltransferases that are responsible for acetylation of the MR remain unknown. We hypothesized that the acetyltransferases cyclic adenosine monophosphate response element-binding binding protein (CBP) and acetyltransferase p300 (p300) attenuate transcriptional activity of the MR through its acetylation. Expression of MR target genes was measured by quantitative real-time polymerase chain reaction. Recruitment of MR and RNA polymerase II (Pol II) on promoters of target genes was analysed by chromatin immunoprecipitation. Acetylation of the MR was determined by western blot with an anti-acetyl-lysine antibody after immunoprecipitation with an anti-MR antibody. In human embryonic kidney (HEK) 293 cells, overexpression of CBP or p300, but not p300/CBP-associated factor, increased MR acetylation and decreased expression of MR target genes. The downregulation of target genes coincided with a decrease in the recruitment of MR and Pol II to specific hormone response elements. These results demonstrate that overexpression of CBP or p300 attenuates the transcriptional activity of the MR through its acetylation in HEK 293 cells. Our data provide strong evidence identifying CBP and p300 as lysine acetyltransferases responsible for the regulation of MR that may provide new therapeutic targets for the treatment of hypertension.

Inhibition of different histone acetyltransferases (HATs) uncovers transcription-dependent and -independent acetylation-mediated mechanisms in memory formation

Acetylation of histones changes the efficiency of the transcription processes and thus contributes to the formation of long-term memory (LTM). In our comparative study, we used two inhibitors to characterize the contribution of different histone acetyl transferases (HATs) to appetitive associative learning in the honeybee. For one we applied garcinol, an inhibitor of the HATs of the p300 (EP300 binding protein)/CBP (CREB-binding protein) family, and the HATs of the PCAF (p300/CBP-associated factor) family. As comparative agent we applied C646, a specific inhibitor that selectively blocks HATS of the p300/CBP family. Immunochemical analysis reveals differences in histone H3 acetylation in the honeybee brain, in response to the injection of either C646 or garcinol. Behavioral assessment reveals that the two drugs cause memory impairment of different nature when injected after associative conditioning: processes disturbed by garcinol are annihilated by the established transcription blocker actinomycin D and thus seem to require transcription processes. Actions of C646 are unaltered by actinomycin D, and thus seem to be independent of transcription. The outcome of our different approaches as summarized suggests that distinct HATs contribute to different acetylation-mediated processes in memory formation. We further deduce that the acetylation-mediated processes in memory formation comprise transcription-dependent and transcription-independent mechanisms.

[Epigenetic regulations and cerebral plasticity: towards new therapeutic options in neurodegenerative diseases?]

Although revealed in the 1950's, epigenetics is still a fast-growing field. Its delineations continuously evolve and become clarified. In particular, "neuroepigenetics", a notion that encompasses epigenetic regulations associated with neuronal processes, appears very promising. Indeed, the challenge to be undertaken in this sub-field is double. On the one hand, it should bring molecular comprehension of specific neuronal processes, some of them falling within the long term regulations, such as learning and memory. On the other hand, it could bring therapeutic options for brain diseases, e.g. neurodegenerative diseases such as Alzheimer's or Huntington's diseases.

Epigenetic drugs in Alzheimer's disease

Epigenetic processes, such as DNA methylation and histone acetylation, regulate the genome-environment interactions that may play important roles in a wide range of brain disorders, including Alzheimer's disease (AD). Indeed, the role of epigenetic machinery in learning and memory processes is well documented. In this review, we will focus on the most recent literature on tools that target epigenetic mechanisms, particularly on histone acetylation, and we will discuss the use of chemical probes to validate these targets in therapeutic strategies for AD.

Histone Acetylation Modifiers in the Pathogenesis of Alzheimer's Disease

It is becoming more evident that histone acetylation, as one of the epigenetic modifications or markers, plays a key role in the etiology of Alzheimer’s disease (AD). Histone acetylases and histone deacetylases (HDACs) are the well-known covalent enzymes that modify the reversible acetylation of lysine residues in histone amino-terminal domains. In AD, however, the roles of these enzymes are controversial. Some recent studies indicate that HDAC inhibitors are neuroprotective by regulating memory and synaptic dysfunctions in cellular and animal models of AD; while on the other hand, increase of histone acetylation have been implicated in AD pathology. In this review, we focus on the recent advances on the roles of histone acetylation covalent enzymes in AD and discuss how targeting these enzymes can ultimately lead to therapeutic approaches for treating AD.

A Synthetic DNA-Binding Domain Guides Distinct Chromatin-Modifying Small Molecules to Activate an Identical Gene Network

Synthetic dual-function ligands targeting specific DNA sequences and histone-modifying enzymes were applied to achieve regulatory control over multi-gene networks in living cells. Unlike the broad array of targeting small molecules for histone deacetylases (HDACs), few modulators are known for histone acetyltransferases (HATs), which play a central role in transcriptional control. As a novel chemical approach to induce selective HAT-regulated genes, we conjugated a DNA-binding domain (DBD) "I" to N-(4-chloro-3-trifluoromethyl-phenyl)-2-ethoxy-benzamide (CTB), an artificial HAT activator. In vitro enzyme activity assays and microarray studies were used to demonstrate that distinct functional small molecules could be transformed to have identical bioactivity when conjugated with a targeting DBD. This proof-of-concept synthetic strategy validates the switchable functions of HDACs and HATs in gene regulation and provides a molecular basis for developing versatile bioactive ligands.

Learning and memory: Steroids and epigenetics

Memory formation and utilization is a complex process involving several brain structures in conjunction as the hippocampus, the amygdala and the adjacent cortical areas, usually defined as medial temporal lobe structures (MTL). The memory processes depend on the formation and modulation of synaptic connectivity affecting synaptic strength, synaptic plasticity and synaptic consolidation. The basic neurocognitive mechanisms of learning and memory are shortly recalled in the initial section of this paper. The effect of sex hormones (estrogens, androgens and progesterone) and of adrenocortical steroids on several aspects of memory processes are then analyzed on the basis of animal and human studies. A specific attention has been devoted to the different types of steroid receptors (membrane or nuclear) involved and on local metabolic transformations when required. The review is concluded by a short excursus on the steroid activated epigenetic mechanisms involved in memory formation.

Integrating epigenetic modulators into NanoScript for enhanced chondrogenesis of stem cells

N-(4-Chloro-3-(trifluoromethyl)phenyl)-2-ethoxybenzamide (CTB) is a small molecule that functions by altering the chromatin architecture to modulate gene expression. We report a new CTB derivative with increased solubility and demonstrate CTB's functionality by conjugating it on the recently established NanoScript platform to enhance gene expression and induce stem cell differentiation. NanoScript is a nanoparticle-based artificial transcription factor that emulates the structure and function of transcription factor proteins (TFs) to effectively regulate endogenous gene expression. Modifying NanoScript with CTB will more closely replicate the TF structure and enhance CTB functionality and gene expression. To this end, we first conjugated CTB onto NanoScript and initiated a time-dependent increase in histone acetyltransferase activity. Next, because CTB is known to trigger the pathway involved in regulating Sox9, a master regulator of chondrogenic differentiation, we modifed a Sox9-specific NanoScript with CTB to enhance chondrogenic gene activity and differentiation. Because NanoScript is a tunable and robust platform, it has potential for various gene-regulating applications, such as stem cell differentiation.

Epigenetic upregulation of Cdk5 in the dorsal horn contributes to neuropathic pain in rats

Numerous reports have shown that cyclin-dependent kinase 5 (Cdk5), a proline-directed serine/threonine kinase, critically contributes to the induction and maintenance of chronic pain induced by peripheral inflammation and nerve injury. Recent evidence has also suggested the critical role of an epigenetic mechanism in the setting of chronic pain. The present study aims to elucidate the cyclic AMP response element-binding protein (CREB)-mediated upregulation of Cdk5 and its functional significance in rats with neuropathic pain induced by chronic constriction injury (CCI) in the sciatic nerve. Significantly increased expression of Cdk5 was observed in the dorsal horn of rats with CCI, and intrathecal delivery of Cdk5 inhibitor roscovitine significantly attenuated the mechanical allodynia in these rats. Phosphorylation of CREB and its occupancy in the Cdk5 promoter region was also increased in the dorsal horn, which led to increased histone H4 acetylation in the Cdk5 promoter region and the upregulated transcription of Cdk5. Inhibition of CREB activity attenuated the upregulation of Cdk5 and alleviated the mechanical allodynia in rats with CCI. These results demonstrated a CREB-mediated epigenetic upregulation of Cdk5 in the dorsal horn, which critically contributed to the maintenance of painful behavior in the rats with neuropathic pain.

Assembly and interrogation of Alzheimer's disease genetic networks reveal novel regulators of progression

Alzheimer's disease (AD) is a complex multifactorial disorder with poorly characterized pathogenesis. Our understanding of this disease would thus benefit from an approach that addresses this complexity by elucidating the regulatory networks that are dysregulated in the neural compartment of AD patients, across distinct brain regions. Here, we use a Systems Biology (SB) approach, which has been highly successful in the dissection of cancer related phenotypes, to reverse engineer the transcriptional regulation layer of human neuronal cells and interrogate it to infer candidate Master Regulators (MRs) responsible for disease progression. Analysis of gene expression profiles from laser-captured neurons from AD and controls subjects, using the Algorithm for the Reconstruction of Accurate Cellular Networks (ARACNe), yielded an interactome consisting of 488,353 transcription-factor/target interactions. Interrogation of this interactome, using the Master Regulator INference algorithm (MARINa), identified an unbiased set of candidate MRs causally responsible for regulating the transcriptional signature of AD progression. Experimental assays in autopsy-derived human brain tissue showed that three of the top candidate MRs (YY1, p300 and ZMYM3) are indeed biochemically and histopathologically dysregulated in AD brains compared to controls. Our results additionally implicate p53 and loss of acetylation homeostasis in the neurodegenerative process. This study suggests that an integrative, SB approach can be applied to AD and other neurodegenerative diseases, and provide significant novel insight on the disease progression.

Regulation of object recognition and object placement by ovarian sex steroid hormones

The ovarian hormones 17β-estradiol (E2) and progesterone (P4) are potent modulators of hippocampal memory formation. Both hormones have been demonstrated to enhance hippocampal memory by regulating the cellular and molecular mechanisms thought to underlie memory formation. Behavioral neuroendocrinologists have increasingly used the object recognition and object placement (object location) tasks to investigate the role of E2 and P4 in regulating hippocampal memory formation in rodents. These one-trial learning tasks are ideal for studying acute effects of hormone treatments on different phases of memory because they can be administered during acquisition (pre-training), consolidation (post-training), or retrieval (pre-testing). This review synthesizes the rodent literature testing the effects of E2 and P4 on object recognition (OR) and object placement (OP), and the molecular mechanisms in the hippocampus supporting memory formation in these tasks. Some general trends emerge from the data. Among gonadally intact females, object memory tends to be best when E2 and P4 levels are elevated during the estrous cycle, pregnancy, and in middle age. In ovariectomized females, E2 given before or immediately after testing generally enhances OR and OP in young and middle-aged rats and mice, although effects are mixed in aged rodents. Effects of E2 treatment on OR and OP memory consolidation can be mediated by both classical estrogen receptors (ERα and ERβ), and depend on glutamate receptors (NMDA, mGluR1) and activation of numerous cell signaling cascades (e.g., ERK, PI3K/Akt, mTOR) and epigenetic processes (e.g., histone acetylation, DNA methylation). Acute P4 treatment given immediately after training also enhances OR and OP in young and middle-aged ovariectomized females by activating similar cell signaling pathways as E2 (e.g., ERK, mTOR). The few studies that have administered both hormones in combination suggest that treatment can enhance OR and OP, but that effects are highly dependent on factors such as dose and timing of administration. In addition to providing more detail on these general conclusions, this review will discuss directions for future avenues of research into the hormonal regulation of object memory.

K-Lysine acetyltransferase 2a regulates a hippocampal gene expression network linked to memory formation

Neuronal histone acetylation has been linked to memory consolidation, and targeting histone acetylation has emerged as a promising therapeutic strategy for neuropsychiatric diseases. However, the role of histone-modifying enzymes in the adult brain is still far from being understood. Here we use RNA sequencing to screen the levels of all known histone acetyltransferases (HATs) in the hippocampal CA1 region and find that K-acetyltransferase 2a (Kat2a)--a HAT that has not been studied for its role in memory function so far--shows highest expression. Mice that lack Kat2a show impaired hippocampal synaptic plasticity and long-term memory consolidation. We furthermore show that Kat2a regulates a highly interconnected hippocampal gene expression network linked to neuroactive receptor signaling via a mechanism that involves nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). In conclusion, our data establish Kat2a as a novel and essential regulator of hippocampal memory consolidation.

Histone-acetylation: a link between Alzheimer's disease and post-traumatic stress disorder?

The orchestration of gene-expression programs is essential for cellular homeostasis. Epigenetic processes provide to the cell a key mechanism that allows the regulation of gene-expression networks in response to environmental stimuli. Recently epigenetic mechanisms such as histone-modifications have been implicated with cognitive function and altered epigenome plasticity has been linked to the pathogenesis of neurodegenerative and neuropsychiatric diseases. Thus, key regulators of epigenetic gene-expression have emerged as novel drug targets for brain diseases. Numerous recent review articles discuss in detail the current findings of epigenetic processes in brain diseases. The aim of this article is not to give yet another comprehensive overview of the field but to specifically address the question why the same epigenetic therapies that target histone-acetylation may be suitable to treat seemingly different diseases such as Alzheimer's disease and post-traumatic stress disorder.

Epigenetic memory: the Lamarckian brain

Recent data support the view that epigenetic processes play a role in memory consolidation and help to transmit acquired memories even across generations in a Lamarckian manner. Drugs that target the epigenetic machinery were found to enhance memory function in rodents and ameliorate disease phenotypes in models for brain diseases such as Alzheimer's disease, Chorea Huntington, Depression or Schizophrenia. In this review, I will give an overview on the current knowledge of epigenetic processes in memory function and brain disease with a focus on Morbus Alzheimer as the most common neurodegenerative disease. I will address the question whether an epigenetic therapy could indeed be a suitable therapeutic avenue to treat brain diseases and discuss the necessary steps that should help to take neuroepigenetic research to the next level.

Epigenetic mechanisms in mood disorders: targeting neuroplasticity

Developing novel therapeutics and diagnostic tools based upon an understanding of neuroplasticity is critical in order to improve the treatment and ultimately the prevention of a broad range of nervous system disorders. In the case of mood disorders, such as major depressive disorder (MDD) and bipolar disorder (BPD), where diagnoses are based solely on nosology rather than pathophysiology, there exists a clear unmet medical need to advance our understanding of the underlying molecular mechanisms and to develop fundamentally new mechanism experimental medicines with improved efficacy. In this context, recent preclinical molecular, cellular, and behavioral findings have begun to reveal the importance of epigenetic mechanisms that alter chromatin structure and dynamically regulate patterns of gene expression that may play a critical role in the pathophysiology of mood disorders. Here, we will review recent advances involving the use of animal models in combination with genetic and pharmacological probes to dissect the underlying molecular mechanisms and neurobiological consequence of targeting this chromatin-mediated neuroplasticity. We discuss evidence for the direct and indirect effects of mood stabilizers, antidepressants, and antipsychotics, among their many other effects, on chromatin-modifying enzymes and on the epigenetic state of defined genomic loci, in defined cell types and in specific regions of the brain. These data, as well as findings from patient-derived tissue, have also begun to reveal alterations of epigenetic mechanisms in the pathophysiology and treatment of mood disorders. We summarize growing evidence supporting the notion that selectively targeting chromatin-modifying complexes, including those containing histone deacetylases (HDACs), provides a means to reversibly alter the acetylation state of neuronal chromatin and beneficially impact neuronal activity-regulated gene transcription and mood-related behaviors. Looking beyond current knowledge, we discuss how high-resolution, whole-genome methodologies, such as RNA-sequencing (RNA-Seq) for transcriptome analysis and chromatin immunoprecipitation-sequencing (ChIP-Seq) for analyzing genome-wide occupancy of chromatin-associated factors, are beginning to provide an unprecedented view of both specific genomic loci as well as global properties of chromatin in the nervous system. These methodologies when applied to the characterization of model systems, including those of patient-derived induced pluripotent cell (iPSC) and induced neurons (iNs), will greatly shape our understanding of epigenetic mechanisms and the impact of genetic variation on the regulatory regions of the human genome that can affect neuroplasticity. Finally, we point out critical unanswered questions and areas where additional data are needed in order to better understand the potential to target mechanisms of chromatin-mediated neuroplasticity for novel treatments of mood and other psychiatric disorders.

Lysine acetyltransferases CBP and p300 as therapeutic targets in cognitive and neurodegenerative disorders

Neuropsychiatric pathologies, including neurodegenerative diseases and neurodevelopmental syndromes, are frequently associated with dysregulation of various essential cellular mechanisms, such as transcription, mitochondrial respiration and protein degradation. In these complex scenarios, it is difficult to pinpoint the specific molecular dysfunction that initiated the pathology or that led to the fatal cascade of events that ends with the death of the neuron. Among the possible original factors, epigenetic dysregulation has attracted special attention. This review focuses on two highly related epigenetic factors that are directly involved in a number of neurological disorders, the lysine acetyltransferases CREB-binding protein (CBP) and E1A-associated protein p300 (p300). We first comment on the role of chromatin acetylation and the enzymes that control it, particularly CBP and p300, in neuronal plasticity and cognition. Next, we describe the involvement of these proteins in intellectual disability and in different neurodegenerative diseases. Finally, we discuss the potential of ameliorative strategies targeting CBP/p300 for the treatment of these disorders.

Targeting histone-modifications in Alzheimer's disease. What is the evidence that this is a promising therapeutic avenue?

Alzheimer' s disease (AD) is the most common form of dementia causing an increasing emotional and economical burden to our societies. Although much progress has been made regarding the molecular mechanisms that underlie AD pathogenesis effective therapies are not available yet. The emerging field of neuroepigenetics has provided evidence that de-regulation of epigenetic processes play a role in AD. In this article we will critically review the primary research data that led to the hypothesis that targeting histone-modifying enzymes could be used to treat AD pathogenesis and address the question if the field is ready to translate such findings into clinical application.

The anti-tumor histone deacetylase inhibitor SAHA and the natural flavonoid curcumin exhibit synergistic neuroprotection against amyloid-beta toxicity

With the trend of an increasing aged population worldwide, Alzheimer's disease (AD), an age-related neurodegenerative disorder, as one of the major causes of dementia in elderly people is of growing concern. Despite the many hard efforts attempted during the past several decades in trying to elucidate the pathological mechanisms underlying AD and putting forward potential therapeutic strategies, there is still a lack of effective treatments for AD. The efficacy of many potential therapeutic drugs for AD is of main concern in clinical practice. For example, large bodies of evidence show that the anti-tumor histone deacetylase (HDAC) inhibitor, suberoylanilidehydroxamic acid (SAHA), may be of benefit for the treatment of AD; however, its extensive inhibition of HDACs makes it a poor therapeutic. Moreover, the natural flavonoid, curcumin, may also have a potential therapeutic benefit against AD; however, it is plagued by low bioavailability. Therefore, the integrative effects of SAHA and curcumin were investigated as a protection against amyloid-beta neurotoxicity in vitro. We hypothesized that at low doses their synergistic effect would improve therapeutic selectivity, based on experiments that showed that at low concentrations SAHA and curcumin could provide comprehensive protection against Aβ_25–35-induced neuronal damage in PC12 cells, strongly implying potent synergism. Furthermore, network analysis suggested that the possible mechanism underlying their synergistic action might be derived from restoration of the damaged functional link between Akt and the CBP/p300 pathway, which plays a crucial role in the pathological development of AD. Thus, our findings provided a feasible avenue for the application of a synergistic drug combination, SAHA and curcumin, in the treatment of AD.

Histone deacetylases and their role in motor neuron degeneration

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease, characterized by the progressive loss of motor neurons. The cause of this selective neuronal death is unknown, but transcriptional dysregulation is recently emerging as an important factor. The physical substrate for the regulation of the transcriptional process is chromatin, a complex assembly of histones and DNA. Histones are subject to several post-translational modifications, like acetylation, that are a component of the transcriptional regulation process. Histone acetylation and deacetylation is performed by a group of enzymes (histone acetyltransferases (HATs) and deacetylases, respectively) whose modulation can alter the transcriptional state of many regions of the genome, and thus may be an important target in diseases that share this pathogenic process, as is the case for ALS. This review will discuss the present evidence of transcriptional dysregulation in ALS, the role of histone deacetylases (HDACs) in disease pathogenesis, and the novel pharmacologic strategies that are being comprehensively studied to prevent motor neuron death, with focus on sirtuins (SIRT) and their effectors.

Proteomic analysis reveals differentially regulated protein acetylation in human amyotrophic lateral sclerosis spinal cord

Amyotrophic lateral sclerosis (ALS) is a progressive fatal neurodegenerative disease that primarily affects motor neurons in the brain and spinal cord. Histone deacetylase (HDAC) inhibitors have neuroprotective effects potentially useful for the treatment of neurodegenerative diseases including ALS; however, the molecular mechanisms underlying their potential efficacy is not well understood. Here we report that protein acetylation in urea-soluble proteins is differently regulated in post-mortem ALS spinal cord. Two-dimensional electrophoresis (2-DE) analysis reveals several protein clusters with similar molecular weight but different charge status. Liquid chromatography and tandem mass spectrometry (LC-MS/MS) identifies glial fibrillary acidic protein (GFAP) as the dominant component in the protein clusters. Further analysis indicates six heavily acetylated lysine residues at positions 89, 153, 189, 218, 259 and 331 of GFAP. Immunoprecipitation followed by Western blotting confirms that the larger form of GFAP fragments are acetylated and upregulated in ALS spinal cord. Further studies demonstrate that acetylation of the proteins additional to GFAP is differently regulated, suggesting that acetylation and/or deacetylation play an important role in pathogenesis of ALS.