Lithium ameliorates altered glycogen synthase kinase-3 and behavior in a mouse model of Fragile X syndrome

Fragile X syndrome (FXS), the most common form of inherited mental retardation and a genetic cause of autism, results from mutated fragile X mental retardation-1 (Fmr1). This study examined the effects on glycogen synthase kinase-3 (GSK3) of treatment with a metabotropic glutamate receptor (mGluR) antagonist, MPEP, and the GSK3 inhibitor, lithium, in C57Bl/6 Fmr1 knockout mice. Increased mGluR signaling may contribute to the pathology of FXS, and the mGluR5 antagonist MPEP increased inhibitory serine-phosphorylation of brain GSK3 selectively in Fmr1 knockout mice but not in wild-type mice. Inhibitory serine-phosphorylation of GSK3 was lower in Fmr1 knockout, than wild-type, mouse brain regions and was increased by acute or chronic lithium treatment, which also increased hippocampal brain-derived neurotrophic factor levels. Fmr1 knockout mice displayed alterations in open-field activity, elevated plus-maze, and passive avoidance, and these differences were ameliorated by chronic lithium treatment. These findings support the hypothesis that impaired inhibition of GSK3 contributes to the pathogenesis of FXS and support GSK3 as a potential therapeutic target.     

Fragile X syndrome: a preclinical review on metabotropic glutamate receptor 5 (mGluR5) antagonists and drug development

Rationale

Fragile X syndrome (FXS) is considered the leading inherited cause of intellectual disability and autism. In FXS, the fragile X mental retardation 1 (FMR1) gene is silenced and the fragile X mental retardation protein (FMRP) is not expressed, resulting in the characteristic features of the syndrome. Despite recent advances in understanding the pathophysiology of FXS, there is still no cure for this condition; current treatment is symptomatic. Preclinical research is essential in the development of potential therapeutic agents.

Objectives

This review provides an overview of the preclinical evidence supporting metabotropic glutamate receptor 5 (mGluR5) antagonists as therapeutic agents for FXS.

Results

According to the mGluR theory of FXS, the absence of FMRP leads to enhanced glutamatergic signaling via mGluR5, which leads to increased protein synthesis and defects in synaptic plasticity including enhanced long-term depression. As such, efforts to develop agents that target the underlying pathophysiology of FXS have focused on mGluR5 modulation. Animal models, particularly the Fmr1 knockout mouse model, have become invaluable in exploring therapeutic approaches on an electrophysiological, behavioral, biochemical, and neuroanatomical level. Two direct approaches are currently being investigated for FXS treatment: reactivating the FMR1 gene and compensating for the lack of FMRP. The latter approach has yielded promising results, with mGluR5 antagonists showing efficacy in clinical trials.

Conclusions

Targeting mGluR5 is a valid approach for the development of therapeutic agents that target the underlying pathophysiology of FXS. Several compounds are currently in development, with encouraging results.     

Group I metabotropic glutamate receptor antagonists alter select behaviors in a mouse model for fragile X syndrome

Rationale  

Studies in the Fmr1 knockout (KO) mouse, a model of fragile X syndrome (FXS), suggest that excessive signaling through group I metabotropic glutamate receptors (mGluRs), comprised of subtypes mGluR1 and mGluR5, may play a role in the pathogenesis of FXS. Currently, no studies have assessed the effect of mGluR1 modulation on Fmr1 KO behavior, and there has not been an extensive behavioral analysis of mGluR5 manipulation in Fmr1 KO mice.     

Glycogen synthase kinase-3β is a functional modulator of serotonin-1B receptors

Glycogen synthase kinase-3 (GSK3) is a constitutively active protein kinase that is involved in neuronal regulation and is a potential pharmacological target of neurological disorders. We found previously that GSK3β selectively interacts with 5-hydroxytryptamine-1B receptors (5-HT1BR) that have important functions in serotonin neurotransmission and behavior. In this study, we provide new information supporting the importance of GSK3β in 5-HT1BR-regulated signaling, physiological function, and behaviors. Using molecular, biochemical, pharmacological, and behavioral approaches, we tested 5-HT1BR's interaction with G(i)α(2) and β-arrestin2 and 5-HT1BR-regulated signaling in cells, serotonin release in mouse cerebral cortical slices, and behaviors in wild-type and β-arrestin2 knockout mice. Molecular ablation of GSK3β and GSK3 inhibitors abolished serotonin-induced change of 5-HT1BR coupling to G(i)α(2) and associated signaling but had no effect on serotonin-induced recruitment of β-arrestin2 to 5-HT1BR. This effect is specific for 5-HT1BR because GSK3 inhibitors did not change the interaction between serotonin 1A receptors and G(i)α(2). Two GSK3 inhibitors, N-(4-methoxybenzyl)-N'-(5-nitro-1,3-thiazol-2-yl)urea (AR-A014418) and 3-(5-bromo-1-methyl-1H-indol-3-yl)-4-(benzofuran-3-yl)pyrrole-2,5-dione (BIP-135), efficiently abolished the inhibitory effect of the 5-HT1BR agonist anpirtoline on serotonin release in mouse cerebral cortical slices. GSK3 inhibitors also facilitated the 5-HT1BR agonist anpirtoline-induced behavioral effect in the tail suspension test but spared anpirtoline-induced locomotor activity. These results suggest that GSK3β is a functional selective modulator of 5-HT1BR-regulated signaling, and GSK3 inhibitors fine-tune the physiological and behavioral actions of 5-HT1BR. Future studies may elucidate the significant roles of GSK3 in serotonin neurotransmission and implications of GSK3 inhibitors as functional selective modulators of 5-HT1BR.     

Suppression of two major Fragile X Syndrome mouse model phenotypes by the mGluR5 antagonist MPEP

Fragile X Syndrome is the most common form of inherited mental retardation worldwide. A Fragile X mouse model, fmr1(tm1Cgr), with a disruption in the X-linked Fmr1 gene, has three substantial deficits observed in several strains: (1) sensitivity to audiogenic seizures (AGS), (2) tendency to spend significantly more time in the center of an open field, and (3) enlarged testes. Alterations in metabotropic glutamate receptor group I signaling were previously identified in the fmr1(tm1Cgr) mouse. In this study, we examined the effect of MPEP, an antagonist of the group I metabotropic glutamate receptor mGluR5, on audiogenic seizures and open field activity of fmr1(tm1Cgr) mice. Genetic analysis revealed synergistic reactions between fmr1(tm1Cgr) and inbred AGS alleles. In addition, AGS sensitivity due to the fmr1(tm1Cgr) allele was restricted during development. Examination of phenotypes combining mGluR5 inhibition and Fmr1 mutation indicated that absence of FMRP may affect mGluR5 signaling through indirect as well as direct pathways. All strains of fmr1(tm1Cgr) mice tested (FVB/NJ, C57BL/6J, and an F1 hybrid of the two) had a more excitable AGS pathway than wild-type, and consequently required more MPEP to achieve seizure suppression. At high doses of mGluR5 antagonists, a Fragile X specific tolerance (loss of drug activity) was observed. The tolerance effect could be overcome by a further increase in drug dose. In open field tests, MPEP reduced fmr1(tm1Cgr) center field behavior to one indistinguishable from wild-type. Therefore, mGluR5 antagonists were able to rescue two of the major phenotypes of the FX mouse. Modulation of mGluR5 signaling may allow amelioration of symptoms of Fragile X Syndrome.     

GSK3 promotes arsenite-induced apoptosis via facilitation of mitochondria disruption

Arsenic is an environmental toxicant that recently has been shown to have anticancer activity against a number of types of cancer cells by inducing apoptosis. Glycogen synthase kinase-3 (GSK3), a serine/threonine kinase, is an important pro-apoptotic signaling enzyme. Although GSK3 has been shown to promote apoptosis caused by a wide variety of insults, a role for GSK3 in arsenic-induced apoptosis has not yet been identified. Investigation of the involvement of GSK3 in arsenite-induced apoptosis demonstrated that arsenite induced apoptosis in SH-SY5Y human neuroblastoma cells, activating the executioner caspase-3 which caused cleavage of poly-ADP ribose-polymerase (PARP). Two selective GSK3 inhibitors, lithium and SB216763, attenuated caspase-3 activation and PARP cleavage induced by arsenite treatment indicating that GSK3 contributed to arsenite-induced apoptosis. Apoptotic signaling following exposure to arsenite involved cytochrome C release from mitochondria, and this was reduced by inhibition of GSK3 indicating that GSK3 promotes arsenite-induced apoptotic signaling upstream of mitochondrial disruption. Moreover, arsenite induced the translocation of Bax and p53 to the mitochondria and the activation-associated oligomerization of Bax, and these crucial events were reduced by inhibition of GSK3, indicating that GSK3 promotes arsenite-induced apoptosis by facilitating signals leading to mitochondrial apoptotic events. Taken together, the findings from this study reveal that GSK3 promotes arsenite-induced apoptosis by facilitating signaling leading to disruption of mitochondria.     

Differential effects of glycogen synthase kinase 3 (GSK3) inhibition by lithium or selective inhibitors in the central nervous system

Glycogen synthase kinase (GSK3) is a constitutively active serine-threonine kinase associated to neurological and psychiatric disorders. GSK3 inhibition is considered a mediator of the efficacy of the mood-stabiliser lithium. This study aimed at comparing the central nervous system effect of lithium with the selective GSK3 inhibitors AZ1080 and compound A in biochemical, cellular, and behavioural tests. Collapsin response mediator protein 2 is a neuron-specific GSK3 substrate. Lithium, AZ1080, and compound A inhibited its phosphorylation in rat primary neurons with different pIC₅₀. After systemic treatments with lithium or GSK3 inhibitors to assess specific functional responses, phosphorylation was unchanged in adult rat brain, while it was strongly inhibited by GSK3 inhibitors in pups, differently from lithium. Lithium may exert neurotrophic effect by increasing brain-derived neurotrophic factor (BDNF) levels: in the present experimental conditions, lithium exerted opposite effects on plasma BDNF levels compared to GSK3 inhibitors, suggesting this effect might not be necessarily mediated by GSK3 inhibition alone. While plasma thyroid-stimulating hormone and luteinising hormone were not affected by lithium, they were decreased by selective inhibitors. GH and prolactin displayed similar responses towards reduction. Follicle-stimulating hormone levels were not altered by treatments, whereas melatonin was specifically increased by AZ1080. Lithium impaired mouse spontaneous locomotion and decreased amphetamine-induced hyper-locomotion. AZ1080 had no effects on locomotion, while compound A reduced spontaneous locomotor activity without effects on amphetamine-induced hyper-locomotion. The present results indicate that a broad correlation between the effects of lithium and selective GSK3 inhibitors could not be devised, suggesting alternative mechanisms, whereas overlapping results could be obtained in specific assays.     

Binge Alcohol Drinking by Mice Requires Intact Group1 Metabotropic Glutamate Receptor Signaling Within the Central Nucleus of the Amygdale

Despite the fact that binge alcohol drinking (intake resulting in blood alcohol concentrations (BACs) ⩾80 mg% within a 2-h period) is the most prevalent form of alcohol-use disorders (AUD), a large knowledge gap exists regarding how this form of AUD influences neural circuits mediating alcohol reinforcement. The present study employed integrative approaches to examine the functional relevance of binge drinking-induced changes in glutamate receptors, their associated scaffolding proteins and certain signaling molecules within the central nucleus of the amygdala (CeA). A 30-day history of binge alcohol drinking (for example, 4–5 g kg⁻¹ per 2 h⁻¹) elevated CeA levels of mGluR1, GluN2B, Homer2a/b and phospholipase C (PLC) β3, without significantly altering protein expression within the adjacent basolateral amygdala. An intra-CeA infusion of mGluR1, mGluR5 and PLC inhibitors all dose-dependently reduced binge intake, without influencing sucrose drinking. The effects of co-infusing mGluR1 and PLC inhibitors were additive, whereas those of coinhibiting mGluR5 and PLC were not, indicating that the efficacy of mGluR1 blockade to lower binge intake involves a pathway independent of PLC activation. The efficacy of mGluR1, mGluR5 and PLC inhibitors to reduce binge intake depended upon intact Homer2 expression as revealed through neuropharmacological studies of Homer2 null mutant mice. Collectively, these data indicate binge alcohol-induced increases in Group1 mGluR signaling within the CeA as a neuroadaptation maintaining excessive alcohol intake, which may contribute to the propensity to binge drink.     

Regulation of Akt and glycogen synthase kinase-3 beta phosphorylation by sodium valproate and lithium

This study tested if sodium valproate or lithium, two agents used to treat bipolar mood disorder, altered the regulatory phosphorylations of Akt or glycogen synthase kinase-3beta (GSK3beta) in human neuroblastoma SH-SY5Y cells. Treatment with sodium valproate caused a gradual but relatively large increase in the activation-associated phosphorylation of Akt on Ser-473, and a similarly gradual but more modest increase in the inhibition-associated phosphorylation of GSK3beta on Ser-9. Two other inhibitors of histone deacetylase, a recently identified target of sodium valproate, also caused gradual increases in the phosphorylation of Akt and GSK3beta. Lithium treatment increased the Ser-9 phosphorylation of GSK3beta both in cells and in mouse brain after chronic administration, but did not alter the phosphorylation of Akt. These results identify novel effects of sodium valproate on the Akt/GSK3beta signaling pathway, indicating that histone deacetylase inhibition is linked to activation of Akt, and show that two anti-bipolar agents have a common action, the increased inhibitory phosphorylation of Ser-9-GSK3beta. The latter finding, along with previous reports that lithium directly inhibits GSK3beta, reveals the possibly unique situation where a single target, GSK3beta, is inhibited by two independent mechanisms, directly and by phosphorylation following lithium administration, and further, that two mood stabilizers have inhibitory effects on GSK3beta.     

Metabotropic glutamate receptor subtype 5 antagonists MPEP and MTEP

Glutamate regulates the function of central nervous system (CNS), in part, through the cAMP and/or IP3/DAG second messenger-associated metabotropic glutamate receptors (mGluRs). The mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) has been extensively used to elucidate potential physiological and pathophysiological functions of mGluR5. Unfortunately, recent evidence indicates significant non-specific actions of MPEP, including inhibition of NMDA receptors. In contrast, in vivo and in vitro characterization of the newer mGluR5 antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) indicates that it is more highly selective for mGluR5 over mGluR1, has no effect on other mGluR subtypes, and has fewer off-target effects than MPEP. This article reviews literature on both of these mGluR5 antagonists, which suggests their possible utility in neurodegeneration, addiction, anxiety and pain management.     

Targeting GSK3 signaling as a potential therapy of neurodegenerative diseases and aging

ABSTRACT

Introduction: Glycogen synthase kinase 3 (GSK3) is at the center of cellular signaling and controls various aspects of brain functions, including development of the nervous system, neuronal plasticity and onset of neurodegenerative disorders.

Areas covered: In this review, recent efforts in elucidating the roles of GSK3 in neuronal plasticity and development of brain pathologies; Alzheimer’s and Parkinson’s disease, schizophrenia, and age-related neurodegeneration are described. The effect of microglia and astrocytes on development of the pathological states is also discussed.

Expert opinion: GSK3β and its signaling pathway partners hold great promise as therapeutic target(s) for a multitude of neurological disorders. Activity of the kinase is often elevated in brain disorders. However, due to the wide range of GSK3 cellular targets, global inhibition of the kinase leads to severe side-effects and GSK3 inhibitors rarely reach Phase-2 clinical trials. Thus, a selective modulation of a specific cellular pool of GSK3 or specific down- or upstream partners of the kinase might provide more efficient anti-neurodegenerative therapies.     

Therapeutic Strategies in Fragile X Syndrome: Dysregulated mGluR Signaling and Beyond

Fragile X syndrome (FXS) is an inherited neurodevelopmental disease caused by loss of function of the fragile X mental retardation protein (FMRP). In the absence of FMRP, signaling through group 1 metabotropic glutamate receptors is elevated and insensitive to stimulation, which may underlie many of the neurological and neuropsychiatric features of FXS. Treatment of FXS animal models with negative allosteric modulators of these receptors and preliminary clinical trials in human patients support the hypothesis that metabotropic glutamate receptor signaling is a valuable therapeutic target in FXS. However, recent research has also shown that FMRP may regulate diverse aspects of neuronal signaling downstream of several cell surface receptors, suggesting a possible new route to more direct disease-targeted therapies. Here, we summarize promising recent advances in basic research identifying and testing novel therapeutic strategies in FXS models, and evaluate their potential therapeutic benefits. We provide an overview of recent and ongoing clinical trials motivated by some of these findings, and discuss the challenges for both basic science and clinical applications in the continued development of effective disease mechanism-targeted therapies for FXS.     

Pharmacological Rescue of Cortical Synaptic and Network Potentiation in a Mouse Model for Fragile X Syndrome

Fragile X syndrome, caused by the mutation of the Fmr1 gene, is characterized by deficits of attention and learning ability. In the hippocampus of Fmr1 knockout mice (KO), long-term depression is enhanced whereas long-term potentiation (LTP) including late-phase LTP (L-LTP) is reduced or unaffected. Here we examined L-LTP in the anterior cingulate cortex (ACC) in Fmr1 KO mice by using a 64-electrode array recording system. In wild-type mice, theta-burst stimulation induced L-LTP that does not occur in all active electrodes/channels within the cingulate circuit and is typically detected in ∼75% of active channels. Furthermore, L-LTP recruited new responses from previous inactive channels. Both L-LTP and the recruitment of inactive responses were blocked in the ACC slices of Fmr1 KO mice. Bath application of metabotropic glutamate receptor 5 (mGluR5) antagonist or glycogen synthase kinase-3 (GSK3) inhibitors rescued the L-LTP and network recruitment. Our results demonstrate that loss of FMRP will greatly impair L-LTP and recruitment of cortical network in the ACC that can be rescued by pharmacological inhibition of mGluR5 or GSK3. This study is the first report of the network properties of L-LTP in the ACC, and provides basic mechanisms for future treatment of cortex-related cognitive defects in fragile X patients.     

A comparative molecular dynamics simulation study to assess the exclusion ability of novel GSK3β inhibitors

The involvement of glycogen synthase kinase 3β (GSK3β) in eukaryotic cell apoptosis and the extensive potency of GSK3β inhibitors to block cell death has made it a potential drug discovery target for many grievous human disorders. GSK3β is phylogenetically related to the CDKs, such as CDK1 and CDK2, which are suggested to be the off-target proteins of GSK3β inhibitors. The present work is focused on delineating the interaction profiles crucial for the exclusion ability of GSK3β inhibitors against CDKs. With this objective in mind, we carried out molecular dynamic simulation studies on previously identified GSK3β inhibitors, docked to the kinase-binding domains of GSK3β, CDK1 and CDK2. The binding mode analysis of these ligands showed all the essential binding interactions required for the selective inhibition of GSK3β. Further, the crucial protein–ligand interactions and GSK3β-selective mechanisms of identified ligands were analyzed and discussed.     

MGS0039: a potent and selective group II metabotropic glutamate receptor antagonist with antidepressant-like activity

The present study describes the pharmacological profile of (1R,2R,3R,5R,6R)-2-Amino-3-(3,4-dichlorobenzyloxy)-6-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (MGS0039), a novel group II mGluR antagonist. MGS0039 showed high affinity for both mGluR2 (Ki = 2.2 nM) and mGluR3 (Ki = 4.5 nM), which are comparable to LY341495, another group II mGluR antagonist. MGS0039 attenuated both glutamate-induced inhibition of forskolin-evoked cyclic AMP formation in CHO cells expressing mGluR2 (IC50 = 20 nM) or mGluR3 (IC50 = 24 nM) and glutamate-increased [35S]GTPgammaS binding to mGluR2 (pA2 = 8.2), which means that MGS0039 acts as an antagonist. MGS0039 shifted the dose-response curve of glutamate-increased [35S]GTPgammaS binding rightward without altering the maximal response, and thereby indicating competitive antagonism. MGS0039 showed no significant effects on other mGluRs as well as the other receptors and transporters we studied. MGS0039 (0.3-3 mg/kg, i.p.) as well as LY341495 (0.1-3 mg/kg, i.p.) had dose-dependent antidepressant-like effects in the rat forced swim test and in the mouse tail suspension test. In contrast, MGS0039 (0.3-3 mg/kg, i.p.) had no apparent effect in the rat social interaction test and in the rat elevated plus-maze. These results indicate that MGS0039 is a potent and selective antagonist of group II mGluR, and that group II mGluR antagonists, like MGS0039, have an antidepressant-like potential in experimental animal models.     

Fusarenon-X induced apoptosis in HL-60 cells depends on caspase activation and cytochrome c release

Fusarenon-X (FX), a trichothecene mycotoxin, is well known to be cytotoxic to mammalian cells. Our previous study revealed that FX induced apoptosis in mouse thymocytes both in vivo and in vitro. We investigated the mode of apoptosis induced by FX using HL-60 cell culture. When FX at a final concentration of 0.5 microg/ml was added, cell degradation was observed 5 h after exposure, and most of the cells had fallen into apoptosis 24 h after exposure. DNA fragmentation into 180-bp multimers was observed 5 h after exposure, and its dose-dependency was clear in the cells treated with 0.1 microg/ml and higher doses. The percentage of apoptotic cells (sub-G(0) population) increased dose- and time-dependently after exposure, when analyzed using flow cytometry. The activities of caspase-3, -8, and -9 were elevated within 2 h by exposure to FX. DNA fragmentation and an increase in the apoptotic population were abrogated by pre-treating the cells with broad-spectrum caspase inhibitors Z-VAD-fmk or Z-Asp-CH(2)-DCB. Cytochrome c release from mitochondria to cytoplasm was observed clearly, and this release occurred caspase-independently. These findings suggest that FX induces apoptosis in HL-60 cells by stimulating cytochrome c release followed by its downstream events including the activation of multiple caspases.     

The challenges of clinical trials in fragile X syndrome

Rationale

Advances in understanding the underlying mechanisms of conditions such as fragile X syndrome (FXS) and autism spectrum disorders have revealed heterogeneous populations. Recent trials of novel FXS therapies have highlighted several challenges including subpopulations with possibly differential therapeutic responses, the lack of specific outcome measures capturing the full range of improvements of patients with FXS, and a lack of biomarkers that can track whether a specific mechanism is responsive to a new drug and whether the response correlates with clinical improvement.

Objectives

We review the phenotypic heterogeneity of FXS and the implications for clinical research in FXS and other neurodevelopmental disorders.

Results

Residual levels of fragile X mental retardation protein (FMRP) expression explain in part the heterogeneity in the FXS phenotype; studies indicate a correlation with both cognitive and behavioral deficits. However, this does not fully explain the extent of phenotypic variance observed or the variability of drug response. Post hoc analyses of studies involving the selective mGluR5 antagonist mavoglurant and the GABA_B agonist arbaclofen have uncovered significant therapeutic responses following patient stratification according to FMR1 promoter methylation patterns or baseline severity of social withdrawal, respectively. Future studies designed to quantify disease modification will need to develop new strategies to track changes effectively over time and in multiple symptom domains.

Conclusion

Appropriate selection of patients and outcome measures is central to optimizing future clinical investigations of these complex disorders.     

Metabotropic glutamate receptor 5 positive allosteric modulators are neuroprotective in a mouse model of Huntington's disease

Background and Purpose

Huntington''s disease (HD) is an autosomal dominant neurodegenerative disorder caused by a polyglutamine expansion in the huntingtin protein. We have previously demonstrated that the cell signalling of the metabotropic glutamate receptor 5 (mGluR5) is altered in a mouse model of HD. Although mGluR5-dependent protective pathways are more activated in HD neurons, intracellular Ca²⁺ release is also more pronounced, which could contribute to excitotoxicity. In the present study, we aim to investigate whether mGluR5 positive allosteric modulators (PAMs) could activate protective pathways without triggering high levels of Ca²⁺ release and be neuroprotective in HD.

Experimental Approach

We performed a neuronal cell death assay to determine which drugs are neuroprotective, Western blot and Ca²⁺ release experiments to investigate the molecular mechanisms involved in this neuroprotection, and object recognition task to determine whether the tested drugs could ameliorate HD memory deficit.

Key Results

We find that mGluR5 PAMs can protect striatal neurons from the excitotoxic neuronal cell death promoted by elevated concentrations of glutamate and NMDA. mGluR5 PAMs are capable of activating Akt without triggering increased intracellular Ca²⁺ concentration ([Ca²⁺]_i); and Akt blockage leads to loss of PAM-mediated neuroprotection. Importantly, PAMs'' potential as drugs that may be used to treat neurodegenerative diseases is highlighted by the neuroprotection exerted by mGluR5 PAMs on striatal neurons from a mouse model of HD, BACHD. Moreover, mGluR5 PAMs can activate neuroprotective pathways more robustly in BACHD mice and ameliorate HD memory deficit.

Conclusions and Implications

mGluR5 PAMs are potential drugs that may be used to treat neurodegenerative diseases, especially HD.