Effect of Class II HDAC inhibition on glutamate transporter expression and survival in SOD1-ALS mice

Current insights in the molecular genetic pathogenesis of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease that leads to the massive loss of motor neurons in cerebrum, brain stem and spinal cord. It affects not only motor neurons but also other neurons and glial cells, resulting in the progressive muscle atrophy, the severe disability and the eventual death due to the respiratory failure. The pathogenesis of ALS is not fully understood. Currently, several factors are considered to be involved in the pathogenesis of ALS, such as genetic factors, imbalances in protein homeostasis, RNA metabolism disorders, mitochondrial dysfunctions, glutamate-mediated excitatory toxicities and intra-neuronal material transport disorders in neurons. The study of genetic mutations related to ALS pathogenesis will link the molecular and cellular mechanisms of the disease, thus enhancing the understanding of its occurrence and progression, thereby providing new insights for the pathogenesis of ALS. This review summarizes the current insights in the molecular genetic pathogenesis of ALS.

Epigenetic regulation of neurotransmitter signaling in neurological disorders

Neurotransmission signaling is a highly conserved system attributed to various regulatory events. The excitatory and inhibitory neurotransmitter systems have been extensively studied, and their role in neuronal cell proliferation, synaptogenesis and dendrite formation in the adult brain is well established. Recent research has shown that epigenetic regulation plays a crucial role in mediating the expression of key genes associated with neurotransmitter pathways, including neurotransmitter receptor and transporter genes. The dysregulation of these genes has been linked to a range of neurological disorders such as attention-deficit/hyperactivity disorder, Parkinson's disease and schizophrenia. This article focuses on epigenetic regulatory mechanisms that control the expression of genes associated with four major chemical carriers in the brain: dopamine (DA), Gamma-aminobutyric acid (GABA), glutamate and serotonin. Additionally, we explore how aberrant epigenetic regulation of these genes can contribute to the pathogenesis of relevant neurological disorders. By targeting the epigenetic mechanisms that control neurotransmitter gene expression, there is a promising opportunity to advance the development of more effective treatments for neurological disorders with the potential to significantly improve the quality of life of individuals impacted by these conditions.

Novel EAAT2 activators improve motor and cognitive impairment in a transgenic model of Huntington's disease

Introduction

Glutamate excitotoxicity is causal in striatal neurodegeneration underlying motor dysfunction and cognitive deficits in Huntington's disease (HD). Excitatory amino acid transporter 2 (EAAT2), the predominant glutamate transporter accounting for >90% of glutamate transport, plays a key role in preventing excitotoxicity by clearing excess glutamate from the intrasynaptic cleft. Accordingly, EAAT2 has emerged as a promising therapeutic target for prevention of neuronal excitotoxicity underlying HD and other neurodegenerative diseases.

Methods

We have previously designed novel EAAT2 positive allosteric modulator GT951, GTS467, and GTS551, with low nanomolar efficacy in glutamate uptake and favorable pharmacokinetic properties. In this study, we test the neuroprotective abilities of these novel EAAT2 activators in vivo using the robust Drosophila HD transgenic model expressing human huntingtin gene with expanded repeats (Htt128Q).

Results

All three compounds significantly restored motor function impaired under HD pathology over a wide dose range. Additionally, treatment with all three compounds significantly improved HD-associated olfactory associative learning and short-term memory defects, while GT951 and GTS551 also improved middle-term memory in low-performing group. Similarly, treatment with GT951 and GTS551 partially protected against early mortality observed in our HD model. Further, treatment with all three EAAT2 activators induced epigenetic expression of EAAT2 Drosophila homolog and several cognition-associated genes.

Conclusion

Together, these results highlight the efficacy of GT951, GTS467 and GTS551 in treating motor and cognitive impairments under HD pathology and support their development for treatment of HD.

Synergistic association of resveratrol and histone deacetylase inhibitors as treatment in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease associated with motor neuron degeneration, progressive paralysis and finally death. Despite the research efforts, currently there is no cure for ALS. In recent years, multiple epigenetic mechanisms have been associated with neurodegenerative diseases. A pathological role for histone hypoacetylation and the abnormal NF-κB/RelA activation involving deacetylation of lysines, with the exclusion of lysine 310, has been established in ALS. Recent findings indicate that the pathological acetylation state of NF-κB/RelA and histone 3 (H3) occurring in the SOD1(G93A) murine model of ALS can be corrected by the synergistic combination of low doses of the AMP-activated kinase (AMPK)-sirtuin 1 pathway activator resveratrol and the histone deacetylase (HDAC) inhibitors MS-275 (entinostat) or valproate. The combination of the epigenetic drugs, by rescuing RelA and the H3 acetylation state, promotes a beneficial and sexually dimorphic effect on disease onset, survival and motor neurons degeneration. In this mini review, we discuss the potential of the epigenetic combination of resveratrol with HDAC inhibitors in the ALS treatment.

Epigenetic Changes in Prion and Prion-like Neurodegenerative Diseases: Recent Advances, Potential as Biomarkers, and Future Perspectives

Prion diseases are transmissible spongiform encephalopathies (TSEs) caused by a conformational conversion of the native cellular prion protein (PrP^C) to an abnormal, infectious isoform called PrP^Sc. Amyotrophic lateral sclerosis, Alzheimer’s, Parkinson’s, and Huntington’s diseases are also known as prion-like diseases because they share common features with prion diseases, including protein misfolding and aggregation, as well as the spread of these misfolded proteins into different brain regions. Increasing evidence proposes the involvement of epigenetic mechanisms, namely DNA methylation, post-translational modifications of histones, and microRNA-mediated post-transcriptional gene regulation in the pathogenesis of prion-like diseases. Little is known about the role of epigenetic modifications in prion diseases, but recent findings also point to a potential regulatory role of epigenetic mechanisms in the pathology of these diseases. This review highlights recent findings on epigenetic modifications in TSEs and prion-like diseases and discusses the potential role of such mechanisms in disease pathology and their use as potential biomarkers.

The NRF2-Dependent Transcriptional Regulation of Antioxidant Defense Pathways: Relevance for Cell Type-Specific Vulnerability to Neurodegeneration and Therapeutic Intervention

Oxidative stress has been implicated in the etiology and pathobiology of various neurodegenerative diseases. At baseline, the cells of the nervous system have the capability to regulate the genes for antioxidant defenses by engaging nuclear factor erythroid 2 (NFE2/NRF)-dependent transcriptional mechanisms, and a number of strategies have been proposed to activate these pathways to promote neuroprotection. Here, we briefly review the biology of the transcription factors of the NFE2/NRF family in the brain and provide evidence for the differential cellular localization of NFE2/NRF family members in the cells of the nervous system. We then discuss these findings in the context of the oxidative stress observed in two neurodegenerative diseases, Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), and present current strategies for activating NFE2/NRF-dependent transcription. Based on the expression of the NFE2/NRF family members in restricted populations of neurons and glia, we propose that, when designing strategies to engage these pathways for neuroprotection, the relative contributions of neuronal and non-neuronal cell types to the overall oxidative state of tissue should be considered, as well as the cell types which have the greatest intrinsic capacity for producing antioxidant enzymes.

Opportunities for histone deacetylase inhibition in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease. ALS patients suffer from a progressive loss of motor neurons, leading to respiratory failure within 3 to 5 years after diagnosis. Available therapies only slow down the disease progression moderately or extend the lifespan by a few months. Epigenetic hallmarks have been linked to the disease, creating an avenue for potential therapeutic approaches. Interference with one class of epigenetic enzymes, histone deacetylases, has been shown to affect neurodegeneration in many preclinical models. Consequently, it is crucial to improve our understanding about histone deacetylases and their inhibitors in (pre)clinical models of ALS. We conclude that selective inhibitors with high tolerability and safety and sufficient blood-brain barrier permeability will be needed to interfere with both epigenetic and non-epigenetic targets of these enzymes. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

Novel Pyridine-Based Hydroxamates and 2'-Aminoanilides as Histone Deacetylase Inhibitors: Biochemical Profile and Anticancer Activity

Starting from the N-hydroxy-3-(4-(2-phenylbutanoyl)amino)phenyl)acrylamide (5 b) previously described by us as a HDAC inhibitor, we prepared four aza-analogues, 6-8, 9 b, as regioisomers containing the pyridine nucleus. Preliminary screening against mHDAC1 highlighted the N-hydroxy-5-(2-(2-phenylbutanoyl)amino)pyridyl)acrylamide (9 b) as the most potent inhibitor. Thus, we further developed both pyridylacrylic- and nicotinic-based hydroxamates (9 a, 9 c-f, and 11 a-f) and 2'-aminoanilides (10 a-f and 12 a-f), related to 9 b, to be tested against HDACs. Among them, the nicotinic hydroxamate 11 d displayed sub-nanomolar potency (IC₅₀ : 0.5 nM) and selectivity up to 34 000 times that of HDAC4 and from 100 to 1300 times that of all the other tested HDAC isoforms. The 2'-aminoanilides were class I-selective HDAC inhibitors, generally more potent against HDAC3, with the nicotinic anilide 12 d being the most effective (IC₅₀ ^HDAC3 =0.113 μM). When tested in U937 leukemia cells, the hydroxamates 9 e, 11 c, and 11 d blocked over 80 % of cells in G2/M phase, whereas the anilides did not alter cell-cycle progress. In the same cell line, the hydroxamate 11 c and the anilide 10 b induced about 30 % apoptosis, and the anilide 12 c displayed about 40 % cytodifferentiation. Finally, the most potent compounds in leukemia cells 9 b, 11 c, 10 b, 10 e, and 12 c were also tested in K562, HCT116, and A549 cancer cells, displaying antiproliferative IC₅₀ values at single-digit to sub-micromolar level.

Ethanol neurotoxicity is mediated by changes in expression, surface localization and functional properties of glutamate AMPA receptors

Modifications in the subunit composition of AMPA receptors (AMPARs) have been linked to the transition from physiological to pathological conditions in a number of contexts, including EtOH-induced neurotoxicity. Previous work from our laboratory showed that EtOH withdrawal causes CA1 pyramidal cell death in organotypic hippocampal slices and changes in the expression of AMPARs. Here, we investigated whether changes in expression and function of AMPARs may be causal for EtOH-induced neurotoxicity. To this aim, we examined the subunit composition, localization and function of AMPARs in hippocampal slices exposed to EtOH by using western blotting, surface expression assay, confocal microscopy and electrophysiology. We found that EtOH withdrawal specifically increases GluA1 protein signal in total homogenates, but not in the post-synaptic density-enriched fraction. This is suggestive of overall increase and redistribution of AMPARs to the extrasynaptic compartment. At functional level, AMPA-induced calcium influx was unexpectedly reduced, whereas AMPA-induced current was enhanced in CA1 pyramidal neurons following EtOH withdrawal, suggesting that increased AMPAR expression may lead to cell death because of elevated excitability, and not for a direct contribution on calcium influx. Finally, the neurotoxicity caused by EtOH withdrawal was attenuated by the non-selective AMPAR antagonist 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide disodium salt as well as by the selective antagonist of GluA2-lacking AMPARs 1-naphthyl acetyl spermine. We conclude that EtOH neurotoxicity involves changes in expression, surface localization and functional properties of AMPARs, and propose GluA2-lacking AMPARs as amenable specific targets for the development of neuroprotective drugs in EtOH-withdrawal syndrome.

Novel therapeutic targets for amyotrophic lateral sclerosis: ribonucleoproteins and cellular autonomy

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is a devastating disease with a lifetime risk of approximately 1:400. It is incurable and invariably fatal. Average survival is between 3 and 5 years and patients become increasingly paralyzed, losing the ability to speak, eat, and breathe. Therapies in development either (i) target specific familial forms of ALS (comprising a minority of around 10% of cases) or ii) emanate from (over)reliance on animal models or non-human/non-neuronal cell models. There is a desperate and unmet clinical need for effective treatments. Deciphering the primacy and relative contributions of defective protein homeostasis and RNA metabolism in ALS across different model systems will facilitate the identification of putative therapeutic targets.

AREAS COVERED

This review examines the putative common primary molecular events that lead to ALS pathogenesis. We focus on deregulated RNA metabolism, protein mislocalization/pathological aggregation and the role of glia in ALS-related motor neuron degeneration. Finally, we describe promising targets for therapeutic evaluation.

EXPERT OPINION

Moving forward, an effective strategy could be achieved by a poly-therapeutic approach which targets both deregulated RNA metabolism and protein dyshomeostasis in the relevant cell types, at the appropriate phase of disease.

Rising Stars: Astrocytes as a Therapeutic Target for ALS Disease

Amyotrophic lateral sclerosis (ALS) is a multifactorial disease, characterized by a progressive loss of motor neurons that eventually leads to paralysis and death. The current ALS-approved drugs modestly change the clinical course of the disease. The mechanism by which motor neurons progressively degenerate remains unclear but entails a non-cell autonomous process. Astrocytes impaired biological functionality were implicated in multiple neurodegenerative diseases, including ALS, frontotemporal dementia (FTD), Parkinson’s disease (PD), and Alzheimer disease (AD). In ALS disease patients, A1 reactive astrocytes were found to play a key role in the pathology of ALS disease and death of motor neurons, via loss or gain of function or acquired toxicity. The contribution of astrocytes to the maintenance of motor neurons by diverse mechanisms makes them a promising therapeutic candidate for the treatment of ALS. Therapeutic approaches targeting at modulating the function of endogenous astrocytes or replacing lost functionality by transplantation of healthy astrocytes, may contribute to the development of therapies which might slow down or even halt the progression ALS diseases. The proposed mechanisms by which astrocytes can potentially ameliorate ALS progression and the status of ALS clinical studies involving astrocytes are discussed.

Mitochondrial Dysfunction, Neurogenesis, and Epigenetics: Putative Implications for Amyotrophic Lateral Sclerosis Neurodegeneration and Treatment

Amyotrophic lateral sclerosis (ALS) is a progressive and devastating multifactorial neurodegenerative disorder. Although the pathogenesis of ALS is still not completely understood, numerous studies suggest that mitochondrial deregulation may be implicated in its onset and progression. Interestingly, mitochondrial deregulation has also been associated with changes in neural stem cells (NSC) proliferation, differentiation, and migration. In this review, we highlight the importance of mitochondrial function for neurogenesis, and how both processes are correlated and may contribute to the pathogenesis of ALS; we have focused primarily on preclinical data from animal models of ALS, since to date no studies have evaluated this link using human samples. As there is currently no cure and no effective therapy to counteract ALS, we have also discussed how improving neurogenic function by epigenetic modulation could benefit ALS. In support of this hypothesis, changes in histone deacetylation can alter mitochondrial function, which in turn might ameliorate cellular proliferation as well as neuronal differentiation and migration. We propose that modulation of epigenetics, mitochondrial function, and neurogenesis might provide new hope for ALS patients, and studies exploring these new territories are warranted in the near future.

Glial Cells-The Strategic Targets in Amyotrophic Lateral Sclerosis Treatment

Amyotrophic lateral sclerosis (ALS) is a fatal neurological disease, which is characterized by the degeneration of motor neurons in the motor cortex and the spinal cord and subsequently by muscle atrophy. To date, numerous gene mutations have been linked to both sporadic and familial ALS, but the effort of many experimental groups to develop a suitable therapy has not, as of yet, proven successful. The original focus was on the degenerating motor neurons, when researchers tried to understand the pathological mechanisms that cause their slow death. However, it was soon discovered that ALS is a complicated and diverse pathology, where not only neurons, but also other cell types, play a crucial role via the so-called non-cell autonomous effect, which strongly deteriorates neuronal conditions. Subsequently, variable glia-based in vitro and in vivo models of ALS were established and used for brand-new experimental and clinical approaches. Such a shift towards glia soon bore its fruit in the form of several clinical studies, which more or less successfully tried to ward the unfavourable prognosis of ALS progression off. In this review, we aimed to summarize current knowledge regarding the involvement of each glial cell type in the progression of ALS, currently available treatments, and to provide an overview of diverse clinical trials covering pharmacological approaches, gene, and cell therapies.

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'.

Epigenetic Regulation of Excitatory Amino Acid Transporter 2 in Neurological Disorders

Excitatory amino acid transporter 2 (EAAT2) is the predominant astrocyte glutamate transporter involved in the reuptake of the majority of the synaptic glutamate in the mammalian central nervous system (CNS). Gene expression can be altered without changing DNA sequences through epigenetic mechanisms. Mechanisms of epigenetic regulation, include DNA methylation, post-translational modifications of histones, chromatin remodeling, and small non-coding RNAs. This review is focused on neurological disorders, such as glioblastoma multiforme (GBM), Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), Parkinson’s disease (PD), bipolar disorder (BD), and neuroHIV where there is evidence that epigenetics plays a role in the reduction of EAAT2 expression. The emerging field of pharmaco-epigenetics provides a novel avenue for epigenetics-based drug therapy. This review highlights findings on the role of epigenetics in the regulation of EAAT2 in different neurological disorders and discusses the current pharmacological approaches used and the potential use of novel therapeutic approaches to induce EAAT2 expression in neurological disorders using CRISPR/Cas9 technology.

Astrocytes in Motor Neuron Diseases

Motor neuron disorders are highly debilitating and mostly fatal conditions for which only limited therapeutic options are available. To overcome this limitation and develop more effective therapeutic strategies, it is critical to discover the pathogenic mechanisms that trigger and sustain motor neuron degeneration with the greatest accuracy and detail. In the case of Amyotrophic Lateral Sclerosis (ALS), several genes have been associated with familial forms of the disease, whilst the vast majority of cases develop sporadically and no defined cause can be held responsible. On the contrary, the huge majority of Spinal Muscular Atrophy (SMA) occurrences are caused by loss-of-function mutations in a single gene, SMN1. Although the typical hallmark of both diseases is the loss of motor neurons, there is increasing awareness that pathological lesions are also present in the neighbouring glia, whose dysfunction clearly contributes to generating a toxic environment in the central nervous system. Here, ALS and SMA are sequentially presented, each disease section having a brief introduction, followed by a focussed discussion on the role of the astrocytes in the disease pathogenesis. Such a dissertation is substantiated by the findings that built awareness on the glial involvement and how the glial-neuronal interplay is perturbed, along with the appraisal of this new cellular site for possible therapeutic intervention.

Sulforaphane triggers a functional elongation of microglial process via the Akt signal

Microglia are a kind of innate immune cells in the nervous system. The amoeboid morphology in microglia indicates a pro-inflammatory status, while their ramified morphologies are associated with anti-neuroinflammation. Recently, we and others have reported that drugs that trigger microglial process elongation may be beneficial for neuroinflammation inhibition. In this study, we found that sulforaphane (SFN), a compound extracted from broccoli sprouts, promotes primary cultured microglial process elongation in both normal and pro-inflammatory conditions in a reversible manner. This pro-elongation effect of SFN was also observed in the prefrontal cortex in vivo and accompanied with an attenuation of pro-inflammatory response as well as an enhancement of anti-inflammatory response in primary cultured microglia. Mechanistic studies revealed that the SFN treatment increased Akt phosphorylation levels in primary cultured microglia and Akt inhibition blocked the effect of SFN on microglial process elongation, suggesting that the regulation of microglial process by SFN is mediated by Akt activation. Functional studies showed that Akt inhibition reversed the effect of SFN on both pro- and anti-inflammatory responses in lipopolysaccharide (LPS)-stimulated microglia. In an inflammation model in vivo, SFN pretreatment not only prevented LPS-induced retractions of microglial process in the prefrontal cortex, but improved LPS-induced behavioral abnormalities in mice, including the increase in immobility time in the tail suspension test and forced swim test as well as the decrease in sucrose preference. These results indicate that the SFN inhibits microglial activation and neuroinflammation-triggered behavioral abnormalities likely through triggering Akt-mediated microglial process elongation.