SAHA decreases HDAC 2 and 4 levels in vivo and improves molecular phenotypes in the R6/2 mouse model of Huntington's disease

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.

Role of histone deacetylases and their inhibitors in neurological diseases

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

Unlocking the epigenetic symphony: histone acetylation's impact on neurobehavioral change in neurodegenerative disorders

Recent genomics and epigenetic advances have empowered the exploration of DNA/RNA methylation and histone modifications crucial for gene expression in response to stress, aging and disease. Interest in understanding neuronal plasticity's epigenetic mechanisms, influencing brain rewiring amid development, aging and neurodegenerative disorders, continues to grow. Histone acetylation dysregulation, a commonality in diverse brain disorders, has become a therapeutic focus. Histone acetyltransferases and histone deacetylases have emerged as promising targets for neurodegenerative disorder treatment. This review delves into histone acetylation regulation, potential therapies and future perspectives for disorders like Alzheimer's, Parkinson's and Huntington's. Exploring genetic-environmental interplay through models and studies reveals molecular changes, behavioral insights and early intervention possibilities targeting the epigenome in at-risk individuals.

Suberoylanilide Hydroxamic Acid (SAHA) Is a Driver Molecule of Neuroplasticity: Implication for Neurological Diseases

Neuroplasticity is a crucial property of the central nervous system to change its activity in response to intrinsic or extrinsic stimuli. This is mainly achieved through the promotion of changes in the epigenome. One of the epi-drivers priming this process is suberoylanilide hydroxamic acid (SAHA or Vorinostat), a pan-histone deacetylase inhibitor that modulates and promotes neuroplasticity in healthy and disease conditions. Knowledge of the specific molecular changes induced by this epidrug is an important area of neuro-epigenetics for the identification of new compounds to treat cognition impairment and/or epilepsy. In this review, we summarize the findings obtained in cellular and animal models of various brain disorders, highlighting the multiple mechanisms activated by SAHA, such as improvement of memory, learning and behavior, and correction of faulty neuronal functioning. Supporting this evidence, in vitro and in vivo data underline how SAHA positively regulates the expression of neuronal genes and microtubule dynamics, induces neurite outgrowth and spine density, and enhances synaptic transmission and potentiation. In particular, we outline studies regarding neurodevelopmental disorders with pharmaco-resistant seizures and/or severe cognitive impairment that to date lack effective drug treatments in which SAHA could ameliorate defective neuroplasticity.

Elaboration of the Effective Multi-Target Therapeutic Platform for the Treatment of Alzheimer's Disease Based on Novel Monoterpene-Derived Hydroxamic Acids

Novel monoterpene-based hydroxamic acids of two structural types were synthesized for the first time. The first type consisted of compounds with a hydroxamate group directly bound to acyclic, monocyclic and bicyclic monoterpene scaffolds. The second type included hydroxamic acids connected with the monoterpene moiety through aliphatic (hexa/heptamethylene) or aromatic linkers. An in vitro analysis of biological activity demonstrated that some of these molecules had powerful HDAC6 inhibitory activity, with the presence of a linker area in the structure of compounds playing a key role. In particular, it was found that hydroxamic acids containing a hexa- and heptamethylene linker and (-)-perill fragment in the Cap group exhibit excellent inhibitory activity against HDAC6 with IC₅₀ in the submicromolar range from 0.56 ± 0.01 µM to 0.74 ± 0.02 µM. The results of the study of antiradical activity demonstrated the presence of moderate ability for some hydroxamic acids to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2ROO^• radicals. The correlation coefficient between the DPPH radical scavenging activity and oxygen radical absorbance capacity (ORAC) value was R² = 0.8400. In addition, compounds with an aromatic linker based on para-substituted cinnamic acids, having a monocyclic para-menthene skeleton as a Cap group, 35a, 38a, 35b and 38b, demonstrated a significant ability to suppress the aggregation of the pathological β-amyloid peptide 1-42. The 35a lead compound with a promising profile of biological activity, discovered in the in vitro experiments, demonstrated neuroprotective effects on in vivo models of Alzheimer's disease using 5xFAD transgenic mice. Together, the results obtained demonstrate a potential strategy for the use of monoterpene-derived hydroxamic acids for treatment of various aspects of Alzheimer's disease.

High-Contrast PET Imaging with [18F]NT160, a Class-IIa Histone Deacetylase Probe for In Vivo Imaging of Epigenetic Machinery in the Central Nervous System

We utilized positron emission tomography (PET) imaging in vivo to map the spatiotemporal biodistribution/expression of class-IIa histone deacetylases (class-IIa HDACs) in the central nervous system (CNS). Herein we report an improved radiosynthesis of [18F]NT160 using 4-hydroxy-TEMPO which led to a significant improvement in radiochemical yield and molar activity. PET imaging with [18F]NT160, a highly potent class-IIa HDAC inhibitor, led to high-quality and high-contrast images of the brain. [18F]NT160 displayed excellent pharmacokinetic and imaging characteristics: brain uptake is high in gray matter regions, tissue kinetics are appropriate for a 18F-tracer, and specific binding for class-IIa HDACs is demonstrated by self-blockade. Higher uptake with [18F]NT160 was observed in the hippocampus, thalamus, and cortex while the uptake in the cerebellum was relatively low. Overall, our current studies with [18F]NT160 will likely facilitate the development and clinical translation of PET tracers for imaging of class-IIa HDACs biodistribution/expression in cancer and the CNS.

Proteomic Analysis of Huntington's Disease Medium Spiny Neurons Identifies Alterations in Lipid Droplets

Huntington's disease (HD) is a neurodegenerative disease caused by a CAG repeat expansion in the Huntingtin (HTT) gene. The resulting polyglutamine (polyQ) tract alters the function of the HTT protein. Although HTT is expressed in different tissues, the medium spiny projection neurons (MSNs) in the striatum are particularly vulnerable in HD. Thus, we sought to define the proteome of human HD patient-derived MSNs. We differentiated HD72 induced pluripotent stem cells and isogenic controls into MSNs and carried out quantitative proteomic analysis. Using data-dependent acquisitions with FAIMS for label-free quantification on the Orbitrap Lumos mass spectrometer, we identified 6,323 proteins with at least two unique peptides. Of these, 901 proteins were altered significantly more in the HD72-MSNs than in isogenic controls. Functional enrichment analysis of upregulated proteins demonstrated extracellular matrix and DNA signaling (DNA replication pathway, double-strand break repair, G1/S transition) with the highest significance. Conversely, processes associated with the downregulated proteins included neurogenesis-axogenesis, the brain-derived neurotrophic factor-signaling pathway, Ephrin-A: EphA pathway, regulation of synaptic plasticity, triglyceride homeostasis cholesterol, plasmid lipoprotein particle immune response, interferon-γ signaling, immune system major histocompatibility complex, lipid metabolism and cellular response to stimulus. Moreover, proteins involved in the formation and maintenance of axons, dendrites, and synapses (e.g., Septin protein members) were dysregulated in HD72-MSNs. Importantly, lipid metabolism pathways were altered, and using quantitative image, we found analysis that lipid droplets accumulated in the HD72-MSN, suggesting a deficit in the turnover of lipids possibly through lipophagy. Our proteomics analysis of HD72-MSNs identified relevant pathways that are altered in MSNs and confirm current and new therapeutic targets for HD.

The role of altered protein acetylation in neurodegenerative disease

Acetylation is a key post-translational modification (PTM) involved in the regulation of both histone and non-histone proteins. It controls cellular processes such as DNA transcription, RNA modifications, proteostasis, aging, autophagy, regulation of cytoskeletal structures, and metabolism. Acetylation is essential to maintain neuronal plasticity and therefore essential for memory and learning. Homeostasis of acetylation is maintained through the activities of histone acetyltransferases (HAT) and histone deacetylase (HDAC) enzymes, with alterations to these tightly regulated processes reported in several neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). Both hyperacetylation and hypoacetylation can impair neuronal physiological homeostasis and increase the accumulation of pathophysiological proteins such as tau, α-synuclein, and Huntingtin protein implicated in AD, PD, and HD, respectively. Additionally, dysregulation of acetylation is linked to impaired axonal transport, a key pathological mechanism in ALS. This review article will discuss the physiological roles of protein acetylation and examine the current literature that describes altered protein acetylation in neurodegenerative disorders.

A minimal region of the HSP90AB1 promoter is suitable for ubiquitous expression in different somatic tissues with applicability for gene therapy

Huntington's disease (HD) is a multi-tissue failure disorder for which there is no cure. We have previously shown an effective therapeutic approach limited mainly to the central nervous system, based on a synthetic zinc finger (ZF) transcription repressor gene therapy, but it would be important to target other tissues as well. In this study, we identify a novel minimal HSP90AB1 promoter region that can efficiently control expression not only in the CNS but also in other affected HD tissues. This promoter-enhancer is effective in driving expression of ZF therapeutic molecules in both HD skeletal muscles and the heart, in the symptomatic R6/1 mouse model. Moreover, for the first time we show that ZF molecules repressing mutant HTT reverse transcriptional pathological remodelling in HD hearts. We conclude that this HSP90AB1 minimal promoter may be used to target multiple HD organs with therapeutic genes. The new promoter has the potential to be added to the portfolio of gene therapy promoters, for use where ubiquitous expression is needed.

The Emerging Landscape of Small-Molecule Therapeutics for the Treatment of Huntington's Disease

Huntington's disease (HD) is a progressive neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin gene (HTT). The new insights into HD's cellular and molecular pathways have led to the identification of numerous potent small-molecule therapeutics for HD therapy. The field of HD-targeting small-molecule therapeutics is accelerating, and the approval of these therapeutics to combat HD may be expected in the near future. For instance, preclinical candidates such as naphthyridine-azaquinolone, AN1, AN2, CHDI-00484077, PRE084, EVP4593, and LOC14 have shown promise for further optimization to enter into HD clinical trials. This perspective aims to summarize the advent of small-molecule therapeutics at various stages of clinical development for HD therapy, emphasizing their structure and design, therapeutic effects, and specific mechanisms of action. Further, we have highlighted the key drivers involved in HD pathogenesis to provide insights into the basic principle for designing promising anti-HD therapeutic leads.

Developing HDAC4-Selective Protein Degraders To Investigate the Role of HDAC4 in Huntington's Disease Pathology

Huntington's disease (HD) is a lethal autosomal dominant neurodegenerative disorder resulting from a CAG repeat expansion in the huntingtin (HTT) gene. The product of translation of this gene is a highly aggregation-prone protein containing a polyglutamine tract >35 repeats (mHTT) that has been shown to colocalize with histone deacetylase 4 (HDAC4) in cytoplasmic inclusions in HD mouse models. Genetic reduction of HDAC4 in an HD mouse model resulted in delayed aggregation of mHTT, along with amelioration of neurological phenotypes and extended lifespan. To further investigate the role of HDAC4 in cellular models of HD, we have developed bifunctional degraders of the protein and report the first potent and selective degraders of HDAC4 that show an effect in multiple cell lines, including HD mouse model-derived cortical neurons. These degraders act via the ubiquitin-proteasomal pathway and selectively degrade HDAC4 over other class IIa HDAC isoforms (HDAC5, HDAC7, and HDAC9).

A comparison of four technologies for detecting p53 aggregates in ovarian cancer

The tumor suppressor protein p53 is mutated in half of all cancers and has been described to form amyloid-like structures, commonly known from key proteins in neurodegenerative diseases. Still, the clinical relevance of p53 aggregates remains largely unknown, which may be due to the lack of sensitive and specific detection methods. The aim of the present study was to compare the suitability of four different methodologies to specifically detect p53 aggregates: co-immunofluorescence (co-IF), proximity ligation assay (PLA), co-immunoprecipitation (co-IP), and the p53-Seprion-ELISA in cancer cell lines and epithelial ovarian cancer tissue samples. In 7 out of 10 (70%) cell lines, all applied techniques showed concordance. For the analysis of the tissue samples co-IF, co-IP, and p53-Seprion-ELISA were compared, resulting in 100% concordance in 23 out of 30 (76.7%) tissue samples. However, Co-IF lacked specificity as there were samples, which did not show p53 staining but abundant staining of amyloid proteins, highlighting that this method demonstrates that proteins share the same subcellular space, but does not specifically detect p53 aggregates. Overall, the PLA and the p53-Seprion-ELISA are the only two methods that allow the quantitative measurement of p53 aggregates. On the one hand, the PLA represents the ideal method for p53 aggregate detection in FFPE tissue, which is the gold-standard preservation method of clinical samples. On the other hand, when fresh-frozen tissue is available the p53-Seprion-ELISA should be preferred because of the shorter turnaround time and the possibility for high-throughput analysis. These methods may add to the understanding of amyloid-like p53 in cancer and could help stratify patients in future clinical trials targeting p53 aggregation.

Identification of the Transcriptional Biomarkers Panel Linked to Pathological Remodelling of the Eye Tissues in Various HD Mouse Models

Ocular abnormalities are becoming associated with a spectrum of pathological events in various neurodegenerative diseases. Huntington's disease (HD) is just such an example of a fatal neurological disorder, where mutated genes (CAG trinucleotide expansions in the Huntingtin gene) have widespread expression, leading to the production of mutant Huntingtin (mHTT) protein. It is well known that mutant HTT protein is prone to form toxic aggregates, which are a typical pathological feature, along with global transcriptome alterations. In this study, we employed well-established quantitative methods such as Affymetrix arrays and quantitative PCR (qPCR) to identify a set of transcriptional biomarkers that will track HD progression in three well-established mouse models: R6/2, R6/1, and HdhQ150. Our array analysis revealed significantly deregulated networks that are related to visual processes and muscle contractions. Furthermore, our targeted quantitative analysis identified a panel of biomarkers with some being dysregulated even at the presymptomatic stage of the disease, e.g., Opn1mw, Opn1sw, and Pfkfb2. Some of the deregulated genes identified in this study have been linked to other genetic ocular disorders such as: GNAT2, a source of achromatopsia, and REEP6, linked to Retinitis pigmentosa. It may thus be a useful platform for preclinical evaluations of therapeutic interventions.

Modifier pathways in polyglutamine (PolyQ) diseases: from genetic screens to drug targets

Polyglutamine (PolyQ) diseases include a group of inherited neurodegenerative disorders caused by unstable expansions of CAG trinucleotide repeats in the coding region of specific genes. Such genetic alterations produce abnormal proteins containing an unusually long PolyQ tract that renders them more prone to aggregate and cause toxicity. Although research in the field in the last years has contributed significantly to the knowledge of the biological mechanisms implicated in these diseases, effective treatments are still lacking. In this review, we revisit work performed in models of PolyQ diseases, namely the yeast Saccharomyces cerevisiae, the nematode worm Caenorhabditis elegans and the fruit fly Drosophila melanogaster, and provide a critical overview of the high-throughput unbiased genetic screens that have been performed using these systems to identify novel genetic modifiers of PolyQ diseases. These approaches have revealed a wide variety of cellular processes that modulate the toxicity and aggregation of mutant PolyQ proteins, reflecting the complexity of these disorders and demonstrating how challenging the development of therapeutic strategies can be. In addition to the unbiased large-scale genetic screenings in non-vertebrate models, complementary studies in mammalian systems, closer to humans, have contributed with novel genetic modifiers of PolyQ diseases, revealing neuronal function and inflammation as key disease modulators. A pathway enrichment analysis, using the human orthologues of genetic modifiers of PolyQ diseases clustered modifier genes into major themes translatable to the human disease context, such as protein folding and transport as well as transcription regulation. Innovative genetic strategies of genetic manipulation, together with significant advances in genomics and bioinformatics, are taking modifier genetic studies to more realistic disease contexts. The characterization of PolyQ disease modifier pathways is of extreme relevance to reveal novel therapeutic possibilities to delay disease onset and progression in patients.

Design, synthesis, biochemical evaluation, radiolabeling and in vivo imaging with high affinity class-IIa histone deacetylase inhibitor for molecular imaging and targeted therapy

Herein, we describe the design, synthesis and deciphering of the key characteristics of the structure activity relationship (SAR) of trifluoromethyloxadiazole (TFMO) bearing class-IIa HDAC inhibitors. Our medicinal chemistry campaign of 23 compounds identified compound 1 as a highly potent inhibitor with sub nM affinity to class-IIa HDAC4 isoform. Therefore, We radiolabeled compound 1 (named thereafter as NT160) with [¹⁸F]fluoride thus producing the identical [¹⁸F]-NT160 as a diagnostic tool for positron emission tomography (PET). [¹⁸F]-NT160 was produced in high radiochemical purity (>95%), moderate radiochemical yield (2−5%) and moderate molar activity in the range of 0.30−0.85 GBq/umol (8.0−23.0 mCi/umol). We also established that [¹⁸F]-NT160 can cross the blood brain barrier and bind to class-IIa HDACs in vivo. The combination of [¹⁸F]-NT160 and 1 represent a novel theranostic pair using the same molecule to enable diagnostic PET imaging with [¹⁸F]-NT160 followed by targeted therapy with NT160.

Histone deacetylase in neuropathology

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

Phase 1/2 Trial of Vorinostat and Radiation and Maintenance Vorinostat in Children with Diffuse Intrinsic Pontine Glioma: A Children's Oncology Group Report

BACKGROUND

A phase 1/2 trial of vorinostat (suberoylanilide hydroxamic acid), an oral histone deacetylase (HDAC) inhibitor, was conducted in children with newly-diagnosed diffuse intrinsic pontine glioma (DIPG) through the Children's Oncology Group (COG) to: 1) determine the recommended phase 2 dose (RP2D) of vorinostat given concurrently with radiation therapy; 2) document the toxicities of continuing vorinostat as maintenance therapy after radiation; and 3) to determine the efficacy of this regimen by comparing the risk of progression or death with an historical model from past COG trials.

METHODS

Vorinostat was given once daily, Monday through Friday, during radiation therapy (54 Gy in 30 fractions), and then continued at 230 mg/m 2 daily for a maximum of twelve 28-day cycles.

RESULTS

Twelve patients enrolled on the phase 1 study; the RP2D of vorinostat given concurrently with radiation was 230 mg/m 2/day, Monday through Friday weekly. The six patients enrolled at the RP2D and an additional 64 patients enrolled onto the phase 2 study contributed to the efficacy assessment. Although vorinostat was well-tolerated, did not interrupt radiation therapy, and was permanently discontinued in only 8.6% of patients due to toxicities, risk for EFS-event was not significantly reduced compared with the target risk derived from historical COG data (p = 0.32; 1-sided). The 1-year EFS was 5.85% (95% CI 1.89 - 13.1%) and 1-year OS was 39.2% (27.8 - 50.5%).

CONCLUSIONS

Vorinostat given concurrently with radiation followed by vorinostat monotherapy was well tolerated in children with newly-diagnosed DIPG but failed to improve outcome.

Inhibition of Histone Deacetylases 1, 2, and 3 Enhances Clearance of Cholesterol Accumulation in Niemann-Pick C1 Fibroblasts

Niemann-Pick disease type C1 (NPC1) is a rare genetic cholesterol storage disorder caused by mutations in the NPC1 gene. Mutations in this transmembrane late endosome protein lead to loss of normal cholesterol efflux from late endosomes and lysosomes. It has been shown that broad spectrum histone deacetylase inhibitors (HDACi's) such as Vorinostat correct the cholesterol accumulation phenotype in the majority of NPC1 mutants tested in cultured cells. In order to determine the optimal specificity for HDACi correction of the mutant NPC1s, we screened 76 HDACi's of varying specificity. We tested the ability of these HDACi's to correct the excess accumulation of cholesterol in patient fibroblast cells that homozygously express NPC1^I1061T, the most common mutation. We determined that inhibition of HDACs 1, 2, and 3 is important for correcting the defect, and combined inhibition of all three is needed to achieve the greatest effect, suggesting a need for multiple effects of the HDACi treatments. Identifying the specific HDACs involved in the process of regulating cholesterol trafficking in NPC1 will help to focus the search for more specific druggable targets.

Epigenetic regulation in Huntington's disease

Huntington's disease (HD) is a devastating and fatal monogenic neurodegenerative disorder characterized by progressive loss of selective neurons in the brain and is caused by an abnormal expansion of CAG trinucleotide repeats in a coding exon of the huntingtin (HTT) gene. Progressive gene expression changes that begin at premanifest stages are a prominent feature of HD and are thought to contribute to disease progression. Increasing evidence suggests the critical involvement of epigenetic mechanisms in abnormal transcription in HD. Genome-wide alterations of a number of epigenetic modifications, including DNA methylation and multiple histone modifications, are associated with HD, suggesting that mutant HTT causes complex epigenetic abnormalities and chromatin structural changes, which may represent an underlying pathogenic mechanism. The causal relationship of specific epigenetic changes to early transcriptional alterations and to disease pathogenesis require further investigation. In this article, we review recent studies on epigenetic regulation in HD with a focus on DNA and histone modifications. We also discuss the contribution of epigenetic modifications to HD pathogenesis as well as potential mechanisms linking mutant HTT and epigenetic alterations. Finally, we discuss the therapeutic potential of epigenetic-based treatments.

Repurposing Vorinostat for the Treatment of Disorders Affecting Brain

Based on the findings in recent years, we summarize the therapeutic potential of vorinostat (VOR), the first approved histone deacetylase (HDAC) inhibitor, in disorders of brain, and strategies to improve drug efficacy and reduce side effects. Scientific evidences provide a strong case for the therapeutic utility of VOR in various disorders affecting brain, including stroke, Alzheimer's disease, frontotemporal dementia, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, spinal muscular atrophy, X-linked adrenoleukodystrophy, epilepsy, Niemann-Pick type C disease, and neuropsychiatric disorders. Further elucidation of the neuroprotective and neurorestorative properties of VOR using proper clinical study designs could provide momentum towards its clinical application. To improve the therapeutic prospect, concerns on systemic toxicity and off-target actions need to be addressed along with the improvement in formulation and delivery aspects, especially with respect to solubility, permeability, and pharmacokinetic properties. Newer approaches in this regard include poly(ethylene glycol)-b-poly(DL-lactic acid) micelles, VOR-pluronic F127 micelles, encapsulation of iron complexes of VOR into PEGylated liposomes, human serum albumin bound VOR nanomedicine, magnetically guided layer-by-layer assembled nanocarriers, as well as convection-enhanced delivery. Even though targeting specific class or isoform of HDAC is projected as advantageous over pan-HDAC inhibitor like VOR, in terms of adverse effects and efficacy, till clinical validation, the idea is debated. As the VOR treatment-related adverse changes are mostly found reversible, further optimization of the therapeutic strategies with respect to dose, dosage regimen, and formulations of VOR could propel its clinical prospects.

HDAC11: a multifaceted histone deacetylase with proficient fatty deacylase activity and its roles in physiological processes

The histone deacetylases (HDACs) family of enzymes possess deacylase activity for histone and nonhistone proteins; HDAC11 is the latest discovered HDAC and the only member of class IV. Besides its shared HDAC family catalytical activity, recent studies underline HDAC11 as a multifaceted enzyme with a very efficient long-chain fatty acid deacylase activity, which has open a whole new field of action for this protein. Here, we summarize the importance of HDAC11 in a vast array of cellular pathways, which has been recently highlighted by discoveries about its subcellular localization, biochemical features, and its regulation by microRNAs and long noncoding RNAs, as well as its new targets and interactors. Additionally, we discuss the recent work showing the consequences of HDAC11 dysregulation in brain, skeletal muscle, and adipose tissue, and during regeneration in response to kidney, skeletal muscle, and vascular injuries, underscoring HDAC11 as an emerging hub protein with physiological functions that are much more extensive than previously thought, and with important implications in human diseases.

Small Non-coding RNAs Are Dysregulated in Huntington's Disease Transgenic Mice Independently of the Therapeutic Effects of an Environmental Intervention

Huntington's disease (HD) is a neurodegenerative disorder caused by a trinucleotide repeat expansion in the huntingtin gene. Transcriptomic dysregulations are well-documented in HD and alterations in small non-coding RNAs (sncRNAs), particularly microRNAs (miRNAs), could underpin that phenomenon. Additionally, environmental enrichment (EE), which is used to model a stimulating lifestyle in pre-clinical research, has been shown to ameliorate HD-related symptoms. However, the mechanisms mediating the therapeutic effects of EE remain largely unknown. This study assessed the effect of EE on sncRNA expression in the striatum of female R6/1 transgenic HD mice at 12 weeks (prior to over motor deficits) and 20 weeks (fully symptomatic) of age. When comparing wild-type and R6/1 mice in the standard housing condition, we found 6 and 64 miRNAs that were differentially expressed at 12 and 20 weeks of age, respectively. The 6 miRNAs (miR-132, miR-212, miR-222, miR-1a, miR-467a, and miR-669c) were commonly dysregulated at both time points. Additionally, genotype had minor effects on the levels of other sncRNAs, in particular, 1 piRNA was dysregulated at 12 weeks of age, and at 20 weeks of age 11 piRNAs, 1 tRNA- and 2 snoRNA-derived fragments were altered in HD mice. No difference in the abundance of other sncRNA subtypes, including rRNA- and snRNA- derived fragments, were observed. While EE improved locomotor symptoms in HD, we found no effect of the housing condition on any of the sncRNA populations examined. Our findings show that HD mainly affects miRNAs and has a minor effect on other sncRNA populations. Furthermore, the therapeutic effects of EE are not associated with the rescue of these dysregulated sncRNAs and may therefore exert these experience-dependent effects via other molecular mechanisms.

Histone deacetylase knockouts modify transcription, CAG instability and nuclear pathology in Huntington disease mice

Somatic expansion of the Huntington’s disease (HD) CAG repeat drives the rate of a pathogenic process ultimately resulting in neuronal cell death. Although mechanisms of toxicity are poorly delineated, transcriptional dysregulation is a likely contributor. To identify modifiers that act at the level of CAG expansion and/or downstream pathogenic processes, we tested the impact of genetic knockout, in Htt^Q111 mice, of Hdac2 or Hdac3 in medium-spiny striatal neurons that exhibit extensive CAG expansion and exquisite disease vulnerability. Both knockouts moderately attenuated CAG expansion, with Hdac2 knockout decreasing nuclear huntingtin pathology. Hdac2 knockout resulted in a substantial transcriptional response that included modification of transcriptional dysregulation elicited by the Htt^Q111 allele, likely via mechanisms unrelated to instability suppression. Our results identify novel modifiers of different aspects of HD pathogenesis in medium-spiny neurons and highlight a complex relationship between the expanded Htt allele and Hdac2 with implications for targeting transcriptional dysregulation in HD.

New Synthetic 3-Benzoyl-5-Hydroxy-2H-Chromen-2-One (LM-031) Inhibits Polyglutamine Aggregation and Promotes Neurite Outgrowth through Enhancement of CREB, NRF2, and Reduction of AMPKα in SCA17 Cell Models

Spinocerebellar ataxia type 17 (SCA17) is caused by a CAG/CAA expansion mutation encoding an expanded polyglutamine (polyQ) tract in TATA-box binding protein (TBP), a general transcription initiation factor. Suppression of cAMP-responsive element binding protein- (CREB-) dependent transcription, impaired nuclear factor erythroid 2-related factor 2 (NRF2) signaling, and interaction of AMP-activated protein kinase (AMPK) with increased oxidative stress have been implicated to be involved in pathogenic mechanisms of polyQ-mediated diseases. In this study, we demonstrated decreased pCREB and NRF2 and activated AMPK contributing to neurotoxicity in SCA17 SH-SY5Y cells. We also showed that licochalcone A and the related in-house derivative compound 3-benzoyl-5-hydroxy-2H-chromen-2-one (LM-031) exhibited antiaggregation, antioxidative, antiapoptosis, and neuroprotective effects in TBP/Q₇₉-GFP-expressing cell models. LM-031 and licochalcone A exerted neuroprotective effects by upregulating pCREB and its downstream genes, BCL2 and GADD45B, and enhancing NRF2. Furthermore, LM-031, but not licochalcone A, reduced activated AMPKα. Knockdown of CREB and NRF2 and treatment of AICAR (5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside), an AMPK activator, attenuated the aggregation-inhibiting and neurite outgrowth promoting effects of LM-031 on TBP/Q₇₉ SH-SY5Y cells. The study results suggest the LM-031 as potential therapeutics for SCA17 and probable other polyQ diseases.

Shaoyao Gancao Tang (SG-Tang), a formulated Chinese medicine, reduces aggregation and exerts neuroprotection in spinocerebellar ataxia type 17 (SCA17) cell and mouse models

Spinocerebellar ataxia (SCA) type 17 is an autosomal dominant ataxia caused by expanded polyglutamine (polyQ) tract in the TATA-box binding protein (TBP). Substantial studies have shown involvement of compromised mitochondria biogenesis regulator peroxisome proliferator-activated receptor gamma-coactivator 1 alpha (PGC-1α), nuclear factor erythroid 2-related factor 2 (NRF2), nuclear factor-Y subunit A (NFYA), and their downstream target genes in the pathogenesis of polyQ-expansion diseases. The extracts of Paeonia lactiflora (P. lactiflora) and Glycyrrhiza uralensis (G. uralensis) have long been used as a Chinese herbal medicine (CHM). Shaoyao Gancao Tang (SG-Tang) is a formulated CHM made of P. lactiflora and G. uralensis at a 1:1 ratio. In the present study, we demonstrated the aggregate-inhibitory and anti-oxidative effect of SG-Tang in 293 TBP/Q₇₉ cells. We then showed that SG-Tang reduced the aggregates and ameliorated the neurite outgrowth deficits in TBP/Q₇₉ SH-SY5Y cells. SG-Tang upregulated expression levels of NFYA, PGC-1α, NRF2, and their downstream target genes in TBP/Q₇₉ SH-SY5Y cells. Knock down of NFYA, PGC-1α, and NRF2 attenuated the neurite outgrowth promoting effect of SG-Tang on TBP/Q₇₉ SH-SY5Y cells. Furthermore, SG-Tang inhibited aggregation and rescued motor-deficits in SCA17 mouse model. The study results suggest the potential of SG-Tang in treating SCA17 and probable other polyQ diseases.

Epigenetics in Neurodegenerative Diseases: The Role of Histone Deacetylases

BACKGROUND & OBJECTIVE

Imbalance in histone acetylation levels and consequently the dysfunction in transcription are associated with a wide variety of neurodegenerative diseases. Histone proteins acetylation and deacetylation is carried out by two opposite acting enzymes, histone acetyltransferases and histone deacetylases (HDACs), respectively. In-vitro and in-vivo animal models of neurodegenerative diseases and post mortem brains of patients have been reported overexpressed level of HDACs. In recent past numerous studies have indicated that HDAC inhibitors (HDACIs) might be a promising class of therapeutic agents for treating these devastating diseases. HDACs being a part of repressive complexes, the outcome of their inhibition has been attributed to enhanced gene expression due to heightened histone acetylation. Beneficial effects of HDACIs has been explored both in preclinical and clinical studies of these diseases. Thus, their screening as future therapeutics for neurodegenerative diseases has been widely explored.

CONCLUSION

In this review, we focus on the putative role of HDACs in neurodegeneration and further discuss their potential as a new therapeutic avenue for treating neurodegenerative diseases.

Hat1 acetylates histone H4 and modulates the transcriptional program in Drosophila embryogenesis

Post-translational modifications of histone proteins play a pivotal role in DNA packaging and regulation of genome functions. Histone acetyltransferase 1 (Hat1) proteins are conserved enzymes that modify histones by acetylating lysine residues. Hat1 is implicated in chromatin assembly and DNA repair but its role in cell functions is not clearly elucidated. We report the generation and characterization of a Hat1 loss-of-function mutant in Drosophila. Hat1 mutants are viable and fertile with a mild sub-lethal phenotype showing that Hat1 is not essential in fruit flies. Lack of Hat1 results in the near complete loss of histone H4 lysine (K) 5 and K12 acetylation in embryos, indicating that Hat1 is the main acetyltransferase specific for these marks in this developmental stage. We found that Hat1 function and the presence of these acetyl marks are not required for the nuclear transport of histone H4 as histone variant His4r retained its nuclear localization both in Hat1 mutants and in His4r-K5R-K12R double point mutants. RNA-seq analysis of embryos indicate that in Hat1 mutants over 2000 genes are dysregulated and the observed transcriptional changes imply a delay in the developmental program of gene expression.

Hdac4 Interactions in Huntington's Disease Viewed Through the Prism of Multiomics

Huntington's disease (HD) is a monogenic disorder, driven by the expansion of a trinucleotide (CAG) repeat within the huntingtin (Htt) gene and culminating in neuronal degeneration in the brain, predominantly in the striatum and cortex. Histone deacetylase 4 (Hdac4) was previously found to contribute to the disease progression, providing a potential therapeutic target. Hdac4 knockdown reduced accumulation of misfolded Htt protein and improved HD phenotypes. However, the underlying mechanism remains unclear, given its independence on deacetylase activity and the predominant cytoplasmic Hdac4 localization in the brain. Here, we undertook a multiomics approach to uncover the function of Hdac4 in the context of HD pathogenesis. We characterized the interactome of endogenous Hdac4 in brains of HD mouse models. Alterations in interactions were investigated in response to Htt polyQ length, comparing mice with normal (Q20) and disease (Q140) Htt, at both pre- and post-symptomatic ages (2 and 10 months, respectively). Parallel analyses for Hdac5, a related class IIa Hdac, highlighted the unique interaction network established by Hdac4. To validate and distinguish interactions specifically enhanced in an HD-vulnerable brain region, we next characterized endogenous Hdac4 interactions in dissected striata from this HD mouse series. Hdac4 associations were polyQ-dependent in the striatum, but not in the whole brain, particularly in symptomatic mice. Hdac5 interactions did not exhibit polyQ dependence. To identify which Hdac4 interactions and functions could participate in HD pathogenesis, we integrated our interactome with proteome and transcriptome data sets generated from the striata. We discovered an overlap in enriched functional classes with the Hdac4 interactome, particularly in vesicular trafficking and synaptic functions, and we further validated the Hdac4 interaction with the Wiskott-Aldrich Syndrome Protein and SCAR Homolog (WASH) complex. This study expands the knowledge of Hdac4 regulation and functions in HD, adding to the understanding of the molecular underpinning of HD phenotypes.

Conformational dynamics and allosteric effect modulated by the unique zinc-binding motif in class IIa HDACs

Class IIa histone deacetylases (HDACs) have been considered as potential targets for the treatment of several diseases. Compared to other HDACs, class IIa HDACs have an additional second zinc binding motif. So far, the function of the unique zinc-binding motif is still not very clear. In this work, extensive classical molecular dynamics (MD) simulations were employed to illuminate the conformational change modulated by the unique zinc-binding motif. It has been revealed that the unique zinc-binding motif is a crucial structural stabilization factor in retaining the catalytic activity of the enzyme and the stability of the multi-protein complex, by remotely modulating the active site pocket in a "closed" conformation. Moreover, it is also revealed that the Loop2 motion in HDAC4 is less flexible than that in HDAC7, which opens a new avenue to design selective inhibitors by utilizing the local conformational dynamics difference between the structurally highly similar HDAC4 and HDAC7. Finally, by comparative studies with class I HDACs (HDAC1-3), it is found that the reversible "in-out" conformational transformation of the binding rail (highly conserved both in class I and IIa HDACs) occurs spontaneously in HDAC1-3, whereas the binding rail is trapped in an "in" conformation owing to the strong metal coordination interaction of the unique CCHC zinc-binding motif in class IIa HDACs. Thus, the CCHC zinc-binding motif may be a feasible allosteric site for the development of class IIa-selective inhibitors.

The complexity of a monogenic neurodegenerative disease: More than two decades of therapeutic driven research into Niemann-Pick type C disease

Niemann-Pick type C (NP-C) disease is a rare and fatal neurodegenerative disease typified by aberrations in intracellular lipid transport. Cholesterol and other lipids accumulate in the late endosome/lysosome of all diseased cells thereby causing neuronal and visceral atrophy. A cure for NP-C remains elusive despite the extensive molecular advances emanating from the identification of the primary genetic defect in 1997. Penetration of the blood-brain barrier and efficacy in the viscera are prerequisites for effective therapy, however the rarity of NP-C disease is the major impediment to progress. Disease diagnosis is challenging and establishment of appropriate test populations for clinical trials difficult. Fortunately, disease models that span the diversity of microbial and metazoan life have been utilized to advance the quest for a therapy. The complexity of lipid storage in this disorder and in the model systems, has led to multiple theories on the primary disease mechanism and consequently numerous and varied proposed interventions. Here, we conduct an evaluation of these studies.

Histone deacetylase inhibitors restore normal hippocampal synaptic plasticity and seizure threshold in a mouse model of Tuberous Sclerosis Complex

Abnormal synaptic plasticity has been implicated in several neurological disorders including epilepsy, dementia and Autism Spectrum Disorder (ASD). Tuberous Sclerosis Complex (TSC) is an autosomal dominant genetic disorder that manifests with seizures, autism, and cognitive deficits. The abnormal intracellular signaling underlying TSC has been the focus of many studies. However, nothing is known about the role of histone modifications in contributing to the neurological manifestations in TSC. Dynamic regulation of chromatin structure via post translational modification of histone tails has been implicated in learning, memory and synaptic plasticity. Histone acetylation and associated gene activation plays a key role in plasticity and so we asked whether histone acetylation might be dysregulated in TSC. In this study, we report a general reduction in hippocampal histone H3 acetylation levels in a mouse model of TSC2. Pharmacological inhibition of Histone Deacetylase (HDAC) activity restores histone H3 acetylation levels and ameliorates the aberrant plasticity in TSC2^+/− mice. We describe a novel seizure phenotype in TSC2^+/− mice that is also normalized with HDAC inhibitors (HDACis). The results from this study suggest an unanticipated role for chromatin modification in TSC and may inform novel therapeutic strategies for TSC patients.

Targeting Ubiquitin Proteasome Pathway with Traditional Chinese Medicine for Treatment of Spinocerebellar Ataxia Type 3

Nine autosomal dominant spinocerebellar ataxias (SCAs) are caused by an abnormal expansion of CAG trinucleotide repeats that encodes a polyglutamine (polyQ) tract within different genes. Accumulation of aggregated mutant proteins is a common feature of polyQ diseases, leading to progressive neuronal dysfunction and degeneration. SCA type 3 (SCA3), the most common form of SCA worldwide, is characterized by a CAG triplet expansion in chromosome 14q32.1 ATXN3 gene. As accumulation of the mutated polyQ protein is a possible initial event in the pathogenic cascade, clearance of aggregated protein by ubiquitin proteasome system (UPS) has been proposed to inhibit downstream detrimental events and suppress neuronal cell death. In this study, Chinese herbal medicine (CHM) extracts were studied for their proteasome-activating, polyQ aggregation-inhibitory and neuroprotective effects in GFP^u and ATXN3/Q 75 -GFP 293/SH-SY5Y cells. Among the 14 tested extracts, 8 displayed increased proteasome activity, which was confirmed by 20S proteasome activity assay and analysis of ubiquitinated and fused GFP proteins in GFP^u cells. All the eight extracts displayed good aggregation-inhibitory potential when tested in ATXN3/Q 75 -GFP 293 cells. Among them, neuroprotective effects of five selected extracts were shown by analyses of polyQ aggregation, neurite outgrowth, caspase 3 and proteasome activities, and ATXN3-GFP, ubiquitin, BCL2 and BAX protein levels in neuronal differentiated ATXN3/Q 75 -GFP SH-SY5Y cells. Finally, enhanced proteasome function, anti-oxidative activity and neuroprotection of catalpol, puerarin and daidzein (active constituents of Rehmannia glutinosa and Pueraria lobata) were demonstrated in GFP^u and/or ATXN3/Q 75 -GFP 293/SH-SY5Y cells. This study may have therapeutic implication in polyQ-mediated disorders.

Roles of Post-translational Modifications in Spinocerebellar Ataxias

Post-translational modifications (PTMs), including phosphorylation, acetylation, ubiquitination, SUMOylation, etc., of proteins can modulate protein properties such as intracellular distribution, activity, stability, aggregation, and interactions. Therefore, PTMs are vital regulatory mechanisms for multiple cellular processes. Spinocerebellar ataxias (SCAs) are hereditary, heterogeneous, neurodegenerative diseases for which the primary manifestation involves ataxia. Because the pathogenesis of most SCAs is correlated with mutant proteins directly or indirectly, the PTMs of disease-related proteins might functionally affect SCA development and represent potential therapeutic interventions. Here, we review multiple PTMs related to disease-causing proteins in SCAs pathogenesis and their effects. Furthermore, we discuss these PTMs as potential targets for treating SCAs and describe translational therapies targeting PTMs that have been published.

Early postnatal behavioral, cellular, and molecular changes in models of Huntington disease are reversible by HDAC inhibition

In Huntington disease (HD) gene carriers the disease-causing mutant Huntingtin (mHTT) is already present during early developmental stages, but, surprisingly, HD patients develop clinical symptoms only many years later. While a developmental role of Huntingtin has been described, so far new therapeutic approaches targeting those early neurodevelopmental processes are lacking. Here, we show that behavioral, cellular, and molecular changes associated with mHTT in the postnatal period of genetic animal models of HD can be reverted using low-dose treatment with a histone deacetylation inhibitor. Our findings support a neurodevelopmental basis for HD and provide proof of concept that pre-HD symptoms, including aberrant neuronal differentiation, are reversible by early therapeutic intervention in vivo.

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by expanded CAG repeats in the huntingtin gene (HTT). Although mutant HTT is expressed during embryonic development and throughout life, clinical HD usually manifests later in adulthood. A number of studies document neurodevelopmental changes associated with mutant HTT, but whether these are reversible under therapy remains unclear. Here, we identify very early behavioral, molecular, and cellular changes in preweaning transgenic HD rats and mice. Reduced ultrasonic vocalization, loss of prepulse inhibition, and increased risk taking are accompanied by disturbances of dopaminergic regulation in vivo, reduced neuronal differentiation capacity in subventricular zone stem/progenitor cells, and impaired neuronal and oligodendrocyte differentiation of mouse embryo-derived neural stem cells in vitro. Interventional treatment of this early phenotype with the histone deacetylase inhibitor (HDACi) LBH589 led to significant improvement in behavioral changes and markers of dopaminergic neurotransmission and complete reversal of aberrant neuronal differentiation in vitro and in vivo. Our data support the notion that neurodevelopmental changes contribute to the prodromal phase of HD and that early, presymptomatic intervention using HDACi may represent a promising novel treatment approach for HD.

Transcriptional Dysregulation and Post-translational Modifications in Polyglutamine Diseases: From Pathogenesis to Potential Therapeutic Strategies

Polyglutamine (polyQ) diseases are hereditary neurodegenerative disorders caused by an abnormal expansion of a trinucleotide CAG repeat in the coding region of their respective associated genes. PolyQ diseases mainly display progressive degeneration of the brain and spinal cord. Nine polyQ diseases are known, including Huntington's disease (HD), spinal and bulbar muscular atrophy (SBMA), dentatorubral-pallidoluysian atrophy (DRPLA), and six forms of spinocerebellar ataxia (SCA). HD is the best characterized polyQ disease. Many studies have reported that transcriptional dysregulation and post-translational disruptions, which may interact with each other, are central features of polyQ diseases. Post-translational modifications, such as the acetylation of histones, are closely associated with the regulation of the transcriptional activity. A number of groups have studied the interactions between the polyQ proteins and transcription factors. Pharmacological drugs or genetic manipulations aimed at correcting the dysregulation have been confirmed to be effective in the treatment of polyQ diseases in many animal and cellular models. For example, histone deaceylase inhibitors have been demonstrated to have beneficial effects in cases of HD, SBMA, DRPLA, and SCA3. In this review, we describe the transcriptional and post-translational dysregulation in polyQ diseases with special focus on HD, and we summarize and comment on potential treatment approaches targeting disruption of transcription and post-translation processes in these diseases.

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.

Complex neuroprotective and neurotoxic effects of histone deacetylases

By their ability to shatter quality of life for both patients and caregivers, neurodegenerative diseases are the most devastating of human disorders. Unfortunately, there are no effective or long-terms treatments capable of slowing down the relentless loss of neurons in any of these diseases. One impediment is the lack of detailed knowledge of the molecular mechanisms underlying the processes of neurodegeneration. While some neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, are mostly sporadic in nature, driven by both environment and genetic susceptibility, many others, including Huntington's disease, spinocerebellar ataxias, and spinal-bulbar muscular atrophy, are genetically inherited disorders. Surprisingly, given their different roots and etiologies, both sporadic and genetic neurodegenerative disorders have been linked to disease mechanisms involving histone deacetylase (HDAC) proteins, which consists of 18 family members with diverse functions. While most studies have implicated certain HDAC subtypes in promoting neurodegeneration, a substantial body of literature suggests that other HDAC proteins can preserve neuronal viability. Of particular interest, however, is the recent realization that a single HDAC subtype can have both neuroprotective and neurotoxic effects. Diverse mechanisms, beyond transcriptional regulation have been linked to these effects, including deacetylation of non-histone proteins, protein-protein interactions, post-translational modifications of the HDAC proteins themselves and direct interactions with disease proteins. The roles of these HDACs in both sporadic and genetic neurodegenerative diseases will be discussed in the current review.

Regulating BMI1 expression via miRNAs promote Mesenchymal to Epithelial Transition (MET) and sensitizes breast cancer cell to chemotherapeutic drug

Polycomb group (PcG) proteinB lymphoma Mo-MLV insertion region 1 homolog (BMI1) is a transcriptional repressor that plays an important role in human carcinogenesis. MicroRNAs (miRNAs) are endogenous small non-coding RNAsthat implicate a negative regulation on gene expression. Deregulation of the expression of miRNAs has been implicated in tumorigenesis. Here, we have shown that knock-down ofBMI1increases theexpression of tumor-suppressivemiRNAs. Elevated levels of expression of miR-200a, miR-200b, miR-15a, miR-429, miR-203were observed upon knock-down of BMI1. Up-regulation of these miRNAsleads to down-regulation ofPRC1 group of proteins i.e. BMI1, RING1A, RING1B and Ub-H2A. Interestingly, overexpression of miR-200a, miR-200b and miR-15aalso produced decreased BMI1 and Ub-H2A protein expression in the CD44+ Cancer Stem Cellpopulation of MDAMB-231cells. Also,elevating the levels of BMI1 regulated miRNAspromoted Mesenchymal to Epithelial transition by regulating the expression of N-Cadherin, Vimentin, β-Catenin, Zeb, Snail thereby resulting in decreased invasion, migration and proliferation. Here, we also report that miR-200a, miR-200b, miR-203 accretes the sensitivity of MDAMB-231 cells to the histone deacetylase inhibitor (HDACi) SAHA and miR-15a sensitized breast cancer cells to the chemotherapeutic drug cisplatin leading to apoptosis. These findings suggest that modulatingspecific miRNAs may serve as a therapeutic approach for the treatment of breast cancer

Divalproex sodium modulates nuclear localization of ataxin-3 and prevents cellular toxicity caused by expanded ataxin-3

BACKGROUND & AIMS

Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease (MJD), is an autosomal dominantly inherited neurodegenerative disorder and the most common form of SCA worldwide. It is caused by the expansion of a polyglutamine (polyQ) tract in the ataxin-3 protein. Nuclear localization of the affected protein is a key event in the pathology of SCA3 via affecting nuclear organization, transcriptional dysfunction, and seeding aggregations, finally causing neurodegeneration and cell death. So far, there is no effective therapy to prevent or slow the progression of SCA3.

METHODS

In this study, we explored the effect of divalproex sodium as an HDACi in SCA3 cell models and explored how divalproex sodium interferes with pathogenetic processes causing SCA3.

RESULTS

We found that divalproex sodium rescues the hypoacetylation levels of histone H3 and attenuates cellular cytotoxicity induced by expanded ataxin-3 partly via preventing nuclear transport of ataxin-3 (particularly heat shock-dependent).

CONCLUSION

Our study provides novel insights into the mechanisms of action of divalproex sodium as a possible treatment for SCA3, beyond the known regulation of transcription.

Nonmammalian Models of Huntington's Disease

Flies, worms, yeast and more recently zebra fish have all been engineered to express expanded polyglutamine repeat versions of Huntingtin with various resulting pathologies including early death, neurodegeneration, and loss of motor function. Each of these models present particular features that make it useful in studying the mechanisms of polyglutamine pathology. However, one particular unbiased readout of mHTT pathology is functional loss of motor control. Loss of motor control is prominent in patients, but it remains unresolved whether pathogenic symptoms in patients result from overt degeneration and loss of neurons or from malfunctioning of surviving neurons as the pathogenic insult builds up. This is why a functional assay such as motor control can be uniquely powerful in revealing early as well as late neurological deficits and does not rely on assumptions such as that the level of inclusions or the degree of neuronal loss can be equated with the level of pathology. Drosophila is well suited for such assays because it contains a functioning nervous system with many parallels to the human condition. In addition, the ability to readily express mHTT transgenes in different tissues and subsets of neurons allows one the possibility of isolating a particular effect to a subset of neurons where one can correlate subcellular events in response to mHTT challenge with pathology at both the cellular and organismal levels. Here we describe methods to monitor the degree of motor function disruption in Drosophila models of HD and we include a brief summary of other nonmammalian models of HD and discussion of their unique strengths.

Experimental and Clinical Strategies for Treating Spinocerebellar Ataxia Type 3

Spinocerebellar ataxia type 3 (SCA3), or Machado-Joseph disease (MJD), is an autosomal dominant neurodegenerative disorder caused by the expansion of a polyglutamine (polyQ) tract in the ataxin-3 protein. To date, there is no effective therapy available to prevent progression of this disease. However, clinical strategies for alleviating various symptoms are imperative to promote a better quality of life for SCA3/MJD patients. Furthermore, experimental therapeutic strategies, including gene silencing or mutant protein clearance, mutant polyQ protein modification, stabilizing the native protein conformation, rescue of cellular dysfunction and neuromodulation to slow the progression of SCA3/MJD, have been developed. In this study, based on the current knowledge, I detail the clinical and experimental therapeutic strategies for treating SCA3/MJD, paying particular attention to drug discovery.

Therapy development in Huntington disease: From current strategies to emerging opportunities

Huntington disease (HD) is a progressive autosomal dominant neurodegenerative disorder in which patients typically present with uncontrolled involuntary movements and subsequent cognitive decline. In 1993, a CAG trinucleotide repeat expansion in the coding region of the huntingtin (HTT) gene was identified as the cause of this disorder. This extended CAG repeat results in production of HTT protein with an expanded polyglutamine tract, leading to pathogenic HTT protein conformers that are resistant to protein turnover, culminating in cellular toxicity and neurodegeneration. Research into the mechanistic basis of HD has highlighted a role for bioenergetics abnormalities stemming from mitochondrial dysfunction, and for synaptic defects, including impaired neurotransmission and excitotoxicity. Interference with transcription regulation may underlie the mitochondrial dysfunction. Current therapies for HD are directed at treating symptoms, as there are no disease-modifying therapies. Commonly prescribed drugs for involuntary movement control include tetrabenazine, a potent and selective inhibitor of vesicular monoamine transporter 2 that depletes synaptic monoamines, and olanzapine, an atypical neuroleptic that blocks the dopamine D2 receptor. Various drugs are used to treat non-motor features. The HD therapeutic pipeline is robust, as numerous efforts are underway to identify disease-modifying treatments, with some small compounds and biological agents moving into clinical trials. Especially encouraging are dosage reduction strategies, including antisense oligonucleotides, and molecules directed at transcription dysregulation. Given the depth and breadth of current HD drug development efforts, there is reason to believe that disease-modifying therapies for HD will emerge, and this achievement will have profound implications for the entire neurotherapeutics field.

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 mechanisms underlying lifespan and age-related effects of dietary restriction and the ketogenic diet

Aging constitutes the central risk factor for major diseases including many forms of cancer, neurodegeneration, and cardiovascular diseases. The aging process is characterized by both global and tissue-specific changes in gene expression across taxonomically diverse species. While aging has historically been thought to entail cell-autonomous, even stochastic changes, recent evidence suggests that modulation of this process can be hierarchal, wherein manipulations of nutrient-sensing neurons (e.g., in the hypothalamus) produce peripheral effects that may modulate the aging process itself. The most robust intervention extending lifespan, plausibly impinging on the aging process, involves different modalities of dietary restriction (DR). Lifespan extension by DR is associated with broad protection against diseases (natural and engineered). Here we review potential epigenetic processes that may link lifespan to age-related diseases, particularly in the context of DR and (other) ketogenic diets, focusing on brain and hypothalamic mechanisms.

Regulating the regulators: Epigenetic, transcriptional, and post-translational regulation of RGS proteins

Regulators of G protein signaling (RGS) are a family of proteins classically known to accelerate the intrinsic GTPase activity of G proteins, which results in accelerated inactivation of heterotrimeric G proteins and inhibition of G protein coupled receptor signaling. RGS proteins play major roles in essential cellular processes, and dysregulation of RGS protein expression is implicated in multiple diseases, including cancer, cardiovascular and neurodegenerative diseases. The expression of RGS proteins is highly dynamic and is regulated by epigenetic, transcriptional and post-translational mechanisms. This review summarizes studies that report dysregulation of RGS protein expression in disease states, and presents examples of drugs that regulate RGS protein expression. Additionally, this review discusses, in detail, the transcriptional and post-transcriptional mechanisms regulating RGS protein expression, and further assesses the therapeutic potential of targeting these mechanisms. Understanding the molecular mechanisms controlling the expression of RGS proteins is essential for the development of therapeutics that indirectly modulate G protein signaling by regulating expression of RGS proteins.