Mouse Model Of Huntington's Disease Research Articles

Focused Ultrasound-Mediated Disruption of the Blood–Brain Barrier for AAV9 Delivery in a Mouse Model of Huntington’s Disease

Huntington’s disease (HD) is a monogenic neurodegenerative disorder caused by a cytosine–adenine–guanine (CAG) trinucleotide repeat expansion in the HTT gene. There are no cures for HD, but the genetic basis of this disorder makes gene therapy a viable approach. Adeno-associated virus (AAV)-miRNA-based therapies have been demonstrated to be effective in lowering HTT mRNA; however, the blood–brain barrier (BBB) poses a significant challenge for gene delivery to the brain. Delivery strategies include direct injections into the central nervous system, which are invasive and can result in poor diffusion of viral particles through the brain parenchyma. Focused ultrasound (FUS) is an alternative approach that can be used to non-invasively deliver AAVs by temporarily disrupting the BBB. Here, we investigate FUS-mediated delivery of a single-stranded AAV9 bearing a cDNA for GFP in 2-month-old wild-type mice and the zQ175 HD mouse model at 2-, 6-, and 12-months. FUS treatment improved AAV9 delivery for all mouse groups. The delivery efficacy was similar for all WT and HD groups, with the exception of the zQ175 12-month cohort, where we observed decreased GFP expression. Astrocytosis did not increase after FUS treatment, even within the zQ175 12-month group exhibiting higher baseline levels of GFAP expression. These findings demonstrate that FUS can be used to non-invasively deliver an AAV9-based gene therapy to targeted brain regions in a mouse model of Huntington’s disease.

Deep behavioural phenotyping of the Q175 Huntington disease mouse model: effects of age, sex, and weight

BackgroundHuntington disease (HD) is a neurodegenerative disorder with complex motor and behavioural manifestations. The Q175 knock-in mouse model of HD has gained recent popularity as a genetically accurate model of the human disease. However, behavioural phenotypes are often subtle and progress slowly in this model. Here, we have implemented machine-learning algorithms to investigate behaviour in the Q175 model and compare differences between sexes and disease stages. We explore distinct behavioural patterns and motor functions in open field, rotarod, water T-maze, and home cage lever-pulling tasks.ResultsIn the open field, we observed habituation deficits in two versions of the Q175 model (zQ175dn and Q175FDN, on two different background strains), and using B-SOiD, an advanced machine learning approach, we found altered performance of rearing in male manifest zQ175dn mice. Notably, we found that weight had a considerable effect on performance of accelerating rotarod and water T-maze tasks and controlled for this by normalizing for weight. Manifest zQ175dn mice displayed a deficit in accelerating rotarod (after weight normalization), as well as changes to paw kinematics specific to males. Our water T-maze experiments revealed response learning deficits in manifest zQ175dn mice and reversal learning deficits in premanifest male zQ175dn mice; further analysis using PyMouseTracks software allowed us to characterize new behavioural features in this task, including time at decision point and number of accelerations. In a home cage-based lever-pulling assessment, we found significant learning deficits in male manifest zQ175dn mice. A subset of mice also underwent electrophysiology slice experiments, revealing a reduced spontaneous excitatory event frequency in male manifest zQ175dn mice.ConclusionsOur study uncovered several behavioural changes in Q175 mice that differed by sex, age, and strain. Our results highlight the impact of weight and experimental protocol on behavioural results, and the utility of machine learning tools to examine behaviour in more detailed ways than was previously possible. Specifically, this work provides the field with an updated overview of behavioural impairments in this model of HD, as well as novel techniques for dissecting behaviour in the open field, accelerating rotarod, and T-maze tasks.

Mechanisms of synapse-to-nucleus calcium signalling in striatal neurons and impairments in Huntington's disease.

Huntington's disease (HD) is a monogenic disorder with autosomal dominant inheritance. In HD patients, neurons in the striatum and cortex degenerate, leading to motor, psychiatric and cognitive disorders. Dysregulated synaptic function and calcium handling are common in many neurodegenerative diseases, including HD. N-methyl-D-aspartate (NMDA) receptor function is enhanced in HD at extrasynaptic sites, altering the balance of calcium-dependent neuronal survival versus death signalling pathways. Endoplasmic reticulum (ER) calcium handling is also abnormal in HD. The ER, which is continuous with the nuclear envelope, is purportedly involved in nuclear calcium signalling; based on this, we hypothesised that nuclear calcium signalling is altered in HD. We explored this hypothesis with calcium imaging techniques, including simultaneous epifluorescent imaging of cytosolic and nuclear calcium using jRCaMP1b and GCaMP3 sensors, respectively, in striatal spiny projection neurons in cortical-striatal co-cultures from the YAC128 mouse model of HD. Our data show contributions from a variety of calcium channels to nuclear calcium signalling. NMDA receptors (NMDARs) play an essential role in initiating action potential-dependent calcium signalling to the nucleus, and ryanodine receptors (RyR) contribute to both cytosolic and nuclear calcium signals. Unlike previous reports in glutamatergic hippocampal and cortical neurons, we found that in GABAergic striatal neurons, L-type voltage-gated calcium channels (CaV) contribute to cytosolic, but not nuclear calcium signalling. Calcium imaging also suggests impairments in nuclear calcium signalling in HD striatal neurons, where spontaneous action potential-dependent calcium transients in the nucleus were smaller in YAC128 striatal neurons compared to those of wild-type (WT). Our results elucidate mechanisms involved in action potential-dependent nuclear calcium signalling in GABAergic striatal neurons, and have revealed a clear deficit in this signalling in HD.

Altered mitochondrial Ca2+ uptake in presynaptic terminals of cultured striatal and cortical neurons from the zQ175 knock-in mouse model of Huntington's disease

Calcium (Ca2+) in mitochondria plays crucial roles in neurons including modulating metabolic processes. Moreover, excessive Ca2+ in mitochondria can lead to cell death. Thus, altered mitochondrial Ca2+ regulation has been implicated in several neurodegenerative diseases including Huntington's disease (HD). HD is a progressive hereditary neurodegenerative disorder that results from abnormally expanded cytosine-adenine-guanine trinucleotide repeats in the huntingtin gene. One neuropathological hallmark of HD is neuronal loss in the striatum and cortex. However, mechanisms underlying selective loss of striatal and cortical neurons in HD remain elusive. Here, we measured the basal Ca2+ levels and Ca2+ uptake in single presynaptic mitochondria during 100 external electrical stimuli using highly sensitive mitochondria-targeted Ca2+ indicators in cultured cortical and striatal neurons of a knock-in mouse model of HD (zQ175 mice). We observed elevated presynaptic mitochondrial Ca2+ uptake during 100 electrical stimuli in HD cortical neurons compared with wild-type (WT) cortical neurons. We also found the highly elevated presynaptic mitochondrial basal Ca2+ level and Ca2+ uptake during 100 stimuli in HD striatal neurons. The elevated presynaptic mitochondrial basal Ca2+ level in HD striatal neurons and Ca2+ uptake during stimulation in HD striatal and cortical neurons can disrupt neurotransmission and induce mitochondrial Ca2+ overload, eventually leading to neuronal death in the striatum and cortex of HD.

A Fast-Binding, Functionally Reversible, COX-2 Radiotracer for CNS PET Imaging.

Cyclooxygenase-2 (COX-2) is an enzyme that plays a pivotal role in peripheral inflammation and pain via the prostaglandin pathway. In the central nervous system (CNS), COX-2 is implicated in neurodegenerative and psychiatric disorders as a potential therapeutic target and biomarker. However, clinical studies with COX-2 have yielded inconsistent results, partly due to limited mechanistic understanding of how COX-2 activity relates to CNS pathology. Therefore, developing COX-2 positron emission tomography (PET) radiotracers for human neuroimaging is of interest. This study introduces [11C]BRD1158, which is a potent and uniquely fast-binding, selective COX-2 PET radiotracer. [11C]BRD1158 was developed by prioritizing potency at COX-2, isoform selectivity over COX-1, fast binding kinetics, and free fraction in the brain. Evaluated through in vivo PET neuroimaging in rodent models with human COX-2 overexpression, [11C]BRD1158 demonstrated high brain uptake, fast target-engagement, functional reversibility, and excellent specific binding, which is advantageous for human imaging applications. Lastly, post-mortem samples from Huntington's disease (HD) patients and preclinical HD mouse models showed that COX-2 levels were elevated specifically in disease-affected brain regions, primarily from increased expression in microglia. These findings indicate that COX-2 holds promise as a novel clinical marker of HD onset and progression, one of many potential applications of [11C]BRD1158 human PET.

Progressive alterations in polysomal architecture and activation of ribosome stalling relief factors in a mouse model of Huntington's disease

Given their highly polarized morphology and functional singularity, neurons require precise spatial and temporal control of protein synthesis. Alterations in protein translation have been implicated in the development and progression of a wide range of neurological and neurodegenerative disorders, including Huntington's disease (HD). In this study we examined the architecture of polysomes in their native brain context in striatal tissue from the zQ175 knock-in mouse model of HD. We performed 3D electron tomography of high-pressure frozen and freeze-substituted striatal tissue from HD models and corresponding controls at different ages. Electron tomography results revealed progressive remodelling towards a more compacted polysomal architecture in the mouse model, an effect that coincided with the emergence and progression of HD related symptoms. The aberrant polysomal architecture is compatible with ribosome stalling phenomena. In fact, we also detected in the zQ175 model an increase in the striatal expression of the stalling relief factor EIF5A2 and an increase in the accumulation of eIF5A1, eIF5A2 and hypusinated eIF5A1, the active form of eIF5A1. Polysomal sedimentation gradients showed differences in the relative accumulation of 40S ribosomal subunits and in polysomal distribution in striatal samples of the zQ175 model. These findings indicate that changes in the architecture of the protein synthesis machinery may underlie translational alterations associated with HD, opening new avenues for understanding the progression of the disease.

Huntingtin HTT1a is generated in a CAG repeat-length-dependent manner in human tissues

BackgroundThe disease-causing mutation in Huntington disease (HD) is a CAG trinucleotide expansion in the huntingtin (HTT) gene. The mutated CAG tract results in the production of a small RNA, HTT1a, coding for only exon 1 of HTT. HTT1a is generated by a block in the splicing reaction of HTT exon 1 to exon 2 followed by cleavage in intron 1 and polyadenylation. Translation of HTT1a leads to the expression of the highly toxic HTT exon 1 protein fragment. We have previously shown that the levels of HTT1a expression in mouse models of HD is dependent on the CAG repeat length. However, these data are lacking for human tissues.MethodsTo answer this question, we developed highly sensitive digital PCR assays to determine HTT1a levels in human samples. These assays allow the absolute quantification of transcript numbers and thus also facilitate the comparison of HTT1a levels between tissues, cell types and across different studies. Furthermore, we measured CAG repeat sizes for every sample used in the study. Finally, we analysed our data with ANOVA and linear modelling to determine the correlation of HTT1a expression levels with CAG repeat sizes.ResultsIn summary, we show that HTT1a is indeed expressed in a CAG repeat-length-dependent manner in human post mortem brain tissues as well as in several peripheral cell types. In particular, PBMCs show a statistically significant positive correlation of HTT1a expression with CAG repeat length, and elevated HTT1a expression levels even in the adult-onset CAG repeat range.ConclusionsOur results show that HTT1a expression occurs throughout a wide range of tissues and likely with all CAG lengths. Our data from peripheral sample sources demonstrate that HTT1a is indeed generated throughout the body in a CAG repeat-length-dependent manner. Therefore, the levels of HTT1a might be a sensitive marker of disease state and/or progression and should be monitored over time, especially in clinical trials targeting HTT expression.

Retinal dysfunction in Huntington’s disease mouse models concurs with local gliosis and microglia activation

Huntington’s disease (HD) is caused by an aberrant expansion of CAG repeats in the HTT gene that mainly affects basal ganglia. Although striatal dysfunction has been widely studied in HD mouse models, other brain areas can also be relevant to the pathology. In this sense, we have special interest on the retina as this is the most exposed part of the central nervous system that enable health monitoring of patients using noninvasive techniques. To establish the retina as an appropriate tissue for HD studies, we need to correlate the retinal alterations with those in the inner brain, i.e., striatum. We confirmed the malfunction of the transgenic R6/1 retinas, which underwent a rearrangement of their transcriptome as extensive as in the striatum. Although tissue-enriched genes were downregulated in both areas, a neuroinflammation signature was only clearly induced in the R6/1 retina in which the observed glial activation was reminiscent of the situation in HD patient’s brains. The retinal neuroinflammation was confirmed in the slow progressive knock-in zQ175 strain. Overall, these results demonstrated the suitability of the mouse retina as a research model for HD and its associated glial activation.

Efficacy of therapy by MK-28 PERK activation in the Huntington's disease R6/2 mouse model

There is currently no disease-modifying therapy for Huntington's disease (HD). We recently described a small molecule, MK-28, which restored homeostasis in HD models by specifically activating PKR-like ER kinase (PERK). This activation boosts the unfolded protein response (UPR), thereby reducing endoplasmic reticulum (ER) stress, a central cytotoxic mechanism in HD and other neurodegenerative diseases. Here, we have tested the long-term effects of MK-28 in HD model mice. R6/2 CAG (160) mice were treated by lifetime intraperitoneal injections 3 times a week. CatWalk measurements of motor function showed strong improvement compared to untreated mice after only two weeks of MK-28 treatment and continued with time, most significantly at 1 ​mg/kg MK-28, approaching WT values. Seven weeks treatment significantly improved paw grip strength. Body weight recovered and glucose levels, which are elevated in HD mice, were significantly reduced. Treatment with another PERK activator, CCT020312 at 1 ​mg/kg, also caused amelioration, consistent with PERK activation. Lifespan, measured in more resilient R6/2 CAG (120) mice with daily IP injection, was much extended by 16 days (20%) with 0.3 ​mg/kg MK-28, and by 38 days (46%) with 1 ​mg/kg MK-28. No toxicity, measured by weight, blood glucose levels and blood liver function markers, was detectable in WT mice treated for 6 weeks with 6 ​mg/kg MK-28. Boosting of PERK activity by long-term treatment with MK-28 could be a safe and promising therapeutic approach for HD.

Deregulated Transcriptome as a Platform for Adrenal Huntington's Disease-Related Pathology.

Huntington's disease (HD) is a neurodegenerative disorder that affects mainly the central nervous system (CNS) by inducing progressive deterioration in both its structure and function. In recent years, there has been growing interest in the impact of HD on peripheral tissue function. Herein, we used the R6/2 mouse model of HD to investigate the influence of the disease on adrenal gland functioning. A transcriptomic analysis conducted using a well-established quantitative method, an Affymetrix array, revealed changes in gene expression in the R6/2 model compared to genetic background controls. For the first time, we identified disruptions in cholesterol and sterol metabolism, blood coagulation, and xenobiotic metabolism in HD adrenal glands. This study showed that the disrupted expression of these genes may contribute to the underlying mechanisms of Huntington's disease. Our findings may contribute to developing a better understanding of Huntington's disease progression and aid in the development of novel diagnostic or therapeutic approaches.

Systemic delivery of mutant huntingtin lowering antisense oligonucleotides to the brain using apolipoprotein A-I nanodisks for Huntington disease

Efficient delivery of therapeutics to the central nervous system (CNS) remains a major challenge for the treatment of neurological diseases. Huntington disease (HD) is a dominantly inherited neurodegenerative disorder caused by a CAG trinucleotide expansion mutation in the HTT gene which codes for a toxic mutant huntingtin (mHTT) protein. Pharmacological reduction of mHTT in the CNS using antisense oligonucleotides (ASO) ameliorates HD-like phenotypes in rodent models of HD, with such therapies being investigated in clinical trials for HD.In this study, we report the optimization of apolipoprotein A-I nanodisks (apoA-I NDs) as vehicles for delivery of a HTT-targeted ASO (HTT ASO) to the brain and peripheral organs for HD. We demonstrate that apoA-I wild type (WT) and the apoA-I K133C mutant incubated with a synthetic lipid, 1,2-dimyristoyl-sn-glycero-3-phosphocholine, can self-assemble into monodisperse discoidal particles with diameters <20 nm that transmigrate across an in vitro blood-brain barrier model of HD. We demonstrate that apoA-I NDs are well tolerated in vivo, and that apoA-I K133C NDs show enhanced distribution to the CNS and peripheral organs compared to apoA-I WT NDs following systemic administration. ApoA-I K133C conjugated with HTT ASO forms NDs (HTT ASO NDs) that induce significant mHTT lowering in the liver, skeletal muscle and heart as well as in the brain when delivered intravenously in the BACHD mouse model of HD. Furthermore, HTT ASO NDs increase the magnitude of mHTT lowering in the striatum and cortex compared to HTT ASO alone following intracerebroventricular administration. These findings demonstrate the potential utility of apoA-I NDs as biocompatible vehicles for enhancing delivery of mutant HTT lowering ASOs to the CNS and peripheral organs for HD.

Glucocorticoid receptor antagonist CORT113176 attenuates motor and neuropathological symptoms of Huntington's disease in R6/2 mice

Huntington's Disease (HD) is a progressive neurodegenerative disease caused by a mutation in the huntingtin gene. The mutation leads to a toxic gain of function of the mutant huntingtin (mHtt) protein resulting in cellular malfunction, aberrant huntingtin aggregation and eventually neuronal cell death. Patients with HD show impaired motor functions and cognitive decline. Elevated levels of glucocorticoids have been found in HD patients and in HD mouse models, and there is a positive correlation between increased glucocorticoid levels and the progression of HD. Therefore, antagonism of the glucocorticoid receptor (GR) may be an interesting strategy for the treatment of HD. In this study, we evaluated the efficacy of the selective GR antagonist CORT113176 in the commonly used R6/2 mouse model. In male mice, CORT113176 treatment significantly delayed the loss of grip strength, the development of hindlimb clasping, gait abnormalities, and the occurrence of epileptic seizures. CORT113176 treatment delayed loss of DARPP-32 immunoreactivity in the dorsolateral striatum. It also restored HD-related parameters including astrocyte markers in both the dorsolateral striatum and the hippocampus, and microglia markers in the hippocampus. This suggests that CORT113176 has both cell-type and brain region-specific effects. CORT113176 delayed the formation of mHtt aggregates in the striatum and the hippocampus. In female mice, we did not observe major effects of CORT113176 treatment on HD-related symptoms, with the exception of the anti-epileptic effects. We conclude that CORT113176 effectively delays several key symptoms related to the HD phenotype in male R6/2 mice and believe that GR antagonism may be a possible treatment option.

Reducing huntingtin by immunotherapy delays disease progression in a mouse model of Huntington disease

In Huntington disease (HD), the mutant huntingtin (mtHTT) protein is the principal cause of pathological changes that initiate primarily along the cortico-striatal axis. mtHTT is ubiquitously expressed and there is, accordingly, growing recognition that HD is a systemic disorder with functional interplay between the brain and the periphery. We have developed a monoclonal antibody, C6–17, targeting an exposed region of HTT near the aa586 Caspase 6 cleavage site. As recently published, mAB C6–17 can block cell-to-cell propagation of mtHTT in vitro. In order to reduce the burden of the mutant protein in vivo, we queried whether extracellular mtHTT could be therapeutically targeted in YAC128 HD mice. In a series of proof of concept experiments, we found that systemic mAB C6–17 treatment resulted in the distribution of the mAB C6–17 to peripheral and CNS tissues and led to the reduction of HTT protein levels. Compared to CTRL mAB or vehicle treated mice, the mAB C6–17 treated YAC128 animals showed improved body weight and motor behaviors, a delayed progression in motor deficits and reduced striatal EM48 immunoreactivity. These results provide the first proof of concept for the feasibility and therapeutic efficacy of an antibody-based anti-HTT passive immunization approach and suggest this modality as a potential new HD treatment strategy.

Sex differences in sleep architecture in a mouse model of Huntington's disease.

Sleep and circadian rhythm disturbances are common features of Huntington's disease (HD). HD is an autosomal dominant neurodegenerative disorder that affects men and women in equal numbers, but some epidemiological studies as well as preclinical work indicate there may be sex differences in disease presentation and progression. Since sex differences in HD could provide important insights to understand cellular and molecular mechanism(s), we used the bacterial artificial chromosome transgenic mouse model of HD (BACHD) to examine whether sex differences in sleep/wake cycles are detectable in an animal model of the disease. Electroencephalography/electromyography (EEG/EMG) was used to measure sleep/wake states and polysomnographic patterns in young adult (12-week-old) male and female wild-type and BACHD mice. Our findings show that male, but not female, BACHD mice exhibited increased variation in phases of the rhythms as compared to age- and sex-matched wild-types. For both rapid-eye movement (REM) and non-rapid eye movement (NREM) sleep, genotypic and sex differences were detected. In particular, the BACHD males spent less time in NREM sleep and exhibited a more fragmented sleep than the other groups. Finally, in response to 6 h of sleep deprivation, both genotypes and sexes displayed the predicted homeostatic responses to sleep loss. These findings suggest that females are relatively protected early in disease progression in this HD model.

Dietary fibre confers therapeutic effects in a preclinical model of Huntington’s disease

Huntington’s disease (HD) is a neurodegenerative disorder involving psychiatric, cognitive and motor deficits, as well as peripheral symptoms, including gastrointestinal dysfunction. The R6/1 HD mouse model expresses a mutant human huntingtin transgene and has been shown to provide an accurate disease model. Recent evidence of gut microbiome disruption was shown in preclinical and clinical HD. Therefore, we aimed to assess the potential role of gut microbial modulation in the treatment of HD. The R6/1 HD mice and wild-type littermate controls were randomised to receive diets containing different amounts of fibre: high-fibre (10 % fibre), control (5 % fibre), or zero-fibre (0 % fibre), from 6 to 20 weeks of age. We characterized the onset and progression of motor, cognitive and affective deficits, as well as gastrointestinal function and gut morphological changes. Faeces were collected for gut microbiome profiling using 16S rRNA sequencing, at 14 and 20 weeks of age. When compared to the control diet, high-fibre diet improved the performance of HD mice in behavioral tests of cognitive and affective function, as well as the gastrointestinal function of both HD and wild-type mice. While the diets changed the beta diversity of wild-type mice, no statistical significance was observed at 14 or 20 weeks of age within the HD mice. Analysis of Composition of Microbiomes with Bias Correction (ANCOM-BC) models were performed to evaluate microbiota composition, which identified differences, including a decreased relative abundance of the phyla Actinobacteriota, Campylobacterota and Proteobacteria and an increased relative abundance of the families Bacteroidaceae, Oscillospiraceae and Ruminococcaceae in HD mice when compared to wild-type mice after receiving high-fibre diet. PICRUSt2 revealed that high-fibre diet also decreased potentially pathogenic functional pathways in HD. In conclusion, high-fibre intake was effective in enhancing gastrointestinal function, cognition and affective behaviors in HD mice. These findings indicate that dietary fibre interventions may have therapeutic potential in Huntington’s disease to delay clinical onset, and have implications for related disorders exhibiting dysfunction of the gut-brain axis.

A cutting-edge approach based on UHPLC-MS to simultaneously investigate oxysterols and cholesterol precursors in biological samples: Validation in Huntington's disease mouse model

Brain is most cholesterol-rich organ in the body. Since cholesterol does not cross the blood brain barrier, its metabolism is provided in situ by astrocytes and neurons, and it is crucial for maintaining sterol levels and neuronal integrity and function. Recent studies have shown that the levels of cholesterol precursors and metabolites are lower in the brains of animal models of Huntington's disease (HD) while reduced levels of its catabolite are detected in the plasma of patients. In this study, we introduce a novel analytical method designed to fulfill the complex analytical requirements associated with cholesterol metabolites detection in neurodegenerative disorders. The method allows for the simultaneous quantification of a specific set of oxysterols along with cholesterol precursors in biological samples.The proposed method uses an Ultra-High-Performance Liquid Chromatography-Mass Spectrometry (UHPLC-MS) system operating in multiple reaction monitoring (MRM). Since sterols can be found in biological matrices in either free form or esterified to various fatty acids, a three-step extraction procedure was devised, consisting of alkaline hydrolysis, liquid-liquid extraction and final concentration omitting the need for a solid-phase extraction (SPE) step.The validated method achieved a detection limit of 10 ng/mL in plasma and 1 ng/mg in brain tissue, reaching a comparable sensitivity to previously published LC-MS and GC–MS methods. All target analytes were separated on a reverse-phase column employing a segmented gradient and a temperature ramp. This strategy enabled the elution and separation of all selected metabolites within a 30-minutes timeframe. This innovative approach was employed to quantify cholesterol metabolites in both plasma and brain samples from wild-type (WT) and R6/2 mice, a mouse model of HD. The results obtained from the sample analysis highlighted a significant reduction in desmosterol levels in the R6/2 brain at 12 weeks.In conclusion, the proposed method paves the way for further development of high-sensitive and reproducible protocols to comprehensively investigate simultaneous alterations in both cholesterol biosynthesis and catabolism in HD samples.

Activin A targets extrasynaptic NMDA receptors to ameliorate neuronal and behavioral deficits in a mouse model of Huntington disease

Cortical-striatal synaptic dysfunction, including enhanced toxic signaling by extrasynaptic N-methyl-d-aspartate receptors (eNMDARs), precedes neurodegeneration in Huntington disease (HD). A previous study showed Activin A, whose transcription is upregulated by calcium influx via synaptic NMDARs, suppresses eNMDAR signaling. Therefore, we examined the role of Activin A in the YAC128 HD mouse model, comparing it to wild-type controls. We found decreased Activin A secretion in YAC128 cortical-striatal co-cultures, while Activin A overexpression in this model rescued altered eNMDAR expression. Striatal overexpression of Activin A in vivo improved motor learning on the rotarod task, and normalized striatal neuronal eNMDAR-mediated currents, membrane capacitance and spontaneous excitatory postsynaptic current frequency in the YAC128 mice. These results support the therapeutic potential of Activin A signaling and targeting eNMDARs to restore striatal neuronal health and ameliorate behavioral deficits in HD.

Altered anterograde axonal transport of mitochondria in cultured striatal neurons of a knock-in mouse model of Huntington's disease

Huntington's disease (HD) is a progressive genetic neurodegenerative disease caused by an abnormal expansion of a cytosine-adenine-guanine trinucleotide repeat in the huntingtin gene. One pathological feature of HD is neuronal loss in the striatum. Despite many efforts, mechanisms underlying neuronal loss in HD striatum remain elusive. It was suggested that the mutant huntingtin protein interacts mitochondrial proteins and causes mitochondrial dysfunction in striatal neurons. However, whether axonal transport of mitochondria is altered in HD striatal neurons remains controversial. Here, we examined axonal transport of single mitochondria labelled with Mito-DsRed2 in cultured striatal neurons of zQ175 knock-in mice (a knock-in mouse model of HD). We observed decreased anterograde axonal transport of proximal mitochondria in HD striatal neurons compared with wild-type (WT) striatal neurons. Decreased anterograde transport in HD striatal neurons was prevented by overexpressing mitochondrial Rho GTPase 1 (Miro1). Our results offer a new insight into mechanisms underlying neuronal loss in the striatum in HD.

A cyclic pyrrole-imidazole polyamide reduces pathogenic RNA in CAG/CTG triplet repeat neurological disease models.

Expansion of CAG and CTG (CWG) triplet repeats causes several inherited neurological diseases. The CWG repeat diseases are thought to involve complex pathogenic mechanisms through expanded CWG repeat-derived RNAs in a noncoding region and polypeptides in a coding region, respectively. However, an effective therapeutic approach has not been established for the CWG repeat diseases. Here, we show that a CWG repeat DNA-targeting compound, cyclic pyrrole-imidazole polyamide (CWG-cPIP), suppressed the pathogenesis of coding and noncoding CWG repeat diseases. CWG-cPIP bound to the hairpin form of mismatched CWG DNA, interfering with transcription elongation by RNA polymerase through a preferential activity toward repeat-expanded DNA. We found that CWG-cPIP selectively inhibited pathogenic mRNA transcripts from expanded CWG repeats, reducing CUG RNA foci and polyglutamine accumulation in cells from patients with myotonic dystrophy type 1 (DM1) and Huntington's disease (HD). Treatment with CWG-cPIP ameliorated behavioral deficits in adeno-associated virus-mediated CWG repeat-expressing mice and in a genetic mouse model of HD, without cytotoxicity or off-target effects. Together, we present a candidate compound that targets expanded CWG repeat DNA independently of its genomic location and reduces both pathogenic RNA and protein levels. CWG-cPIP may be used for the treatment of CWG repeat diseases and improvement of clinical outcomes.

Age- and region-dependent cortical excitability in the zQ175 Huntington disease mouse model.

The neurodegenerative disorder, Huntington disease (HD), manifests as disorders of movement, cognition and mood. Although studies report abnormal corticostriatal synaptic function early in HD mouse models, less is known about cortical-cortical activity across brain regions and disease stages. Recently, we reported enhanced mesoscale spread of cortical responses to sensory stimulation in vivo at early-manifest stages of two HD mouse models. Here, we investigated cortical excitability of zQ175 HD-model mice compared to their wild-type littermates across different cell types, ages and/or cortical regions using ex vivo electrophysiology. Cortical pyramidal neurons (CPNs) in somatosensory cortex of zQ175 mice showed intrinsic hyper-excitability at 3-4months, but hypo-excitability at early-manifest stage (8-9months); reduced frequency of spontaneous excitatory postsynaptic currents (sEPSCs) was seen at both ages. In contrast, motor cortex CPNs in early-manifest zQ175 mice showed increased intrinsic excitability and sEPSC frequency. Large-amplitude excitatory discharges recorded from CPNs in early-manifest zQ175 mice showed increased frequency only in somatosensory cortex, suggesting the intrinsic hypo-excitability of these CPNs may be compensatory against cortical network hyper-excitability. Similarly, in early-manifest zQ175 mice, region-dependent differences were seen in fast-spiking interneurons (FSIs): somatosensory but not motor FSIs from early-manifest zQ175 mice had reduced intrinsic excitability. Moreover, CPNs showed decreased frequency of spontaneous inhibitory postsynaptic currents and increased excitatory-inhibitory (E-I) balance of evoked synaptic currents in somatosensory cortex. Aberrant large-amplitude discharges and reduced inhibitory drive may therefore underlie E-I imbalances that result in circuit changes and synaptic dysfunction in early-manifest HD.