Huntington's Disease Transgenic Mice Research Articles

Light and electron microscopic characterization of the evolution of cellular pathology in YAC128 Huntington's disease transgenic mice

Huntington's disease (HD) is a progressive neurodegenerative disease caused by the insertion of an expanded polyglutamine sequence within the huntingtin protein. This mutation induces the formation of abnormal protein fragment aggregations and intra-nuclear neuronal inclusions in the brain. The present study aimed to produce a detailed longitudinal characterization of the neuronal pathology in the YAC128 transgenic mouse brain, to determine the similarity of this mouse model to other mouse models and the human condition in the spatial and temporal deposition pattern of the mutant protein fragments. Brain samples were taken from mice aged between 4 and 27 months of age, and assessed using S830 and GFAP immunohistochemistry, stereology and electron microscopy. Four month old mice did not exhibit intra-nuclear or extra-nuclear inclusions using the S830 antibody. Diffuse nuclear staining was present in the cortex, hippocampus and cerebellum from 6 months of age onwards. By 15 months of age, intra-nuclear inclusions were visible in most brain regions including nucleus accumbens, ventral striatum, lateral striatum, motor cortex, sensory cortex and cerebellum. The ventral striatum had a greater density of inclusions than the dorsal striatum. At 15 and 24 months of age, the mice showed increased reactive astrogliosis in the cortex, but no differences were found in the striatum. Necrotic cell death with vacuolation, uneven cell membrane and degenerated Golgi apparatus were detected ultrastructurally at 14 months of age, with some cells showing signs of apoptosis. By 26 months of age, most cells were degenerated in the transgenic animals, with lipofuscin granules being more abundant and larger in these mice than in their wildtype littermates. Our results demonstrate a progressive and widespread neuropathology in the YAC128 mice line that shares some similarity to the human condition. This article is part of a Special Issue entitled 'HD Transgenic Mouse'.

Longitudinal analysis of the behavioural phenotype in YAC128 (C57BL/6J) Huntington's disease transgenic mice

To determine the suitability of mouse models of disease for therapeutic trials, the models must be characterised to determine their similarity to the human condition, and utility for specific therapeutic approaches. The YAC128 mouse model of HD has been bred on to C57BL/6J background in order to provide a mouse model of the disease better suited to behavioural testing, than the visually impaired original line on the FVB background. In the present study, the C57BL/6J YAC128 mice were assessed on several behavioural tasks bi-monthly between 4 and 24 months of age. On the rotarod early and stable deficits were demonstrated in the YAC128 mice from 4 months of age indicating an early abnormality in motor coordination. Early and stable deficits were also found on the balance beam measures of latency to orientate towards the beam and time to traverse it. Measures of fore and hind limb footslips on the balance beam demonstrated early and progressive limb use deficits in the YAC128 mice. On a 3-stage Morris water maze protocol, the YAC128 mice took longer and travelled further to find the hidden platform in each of the 3 locations, indicative of a spatial learning deficit. The YAC128 mice were also less reactive to the primary startle stimuli and the effects of the prepulse which may suggest striatal dysfunction. As a measure of general well being, the body weights of the mice were recorded and demonstrated increased weight in the YAC128 mice until 14 months of age, when they became comparable to that of their wildtype littermates. The YAC128 mouse on the C57BL/6J background has an early, robust and severe behavioural phenotype that shares some similarity to human HD symptomatology.

Inhibition of Lipid Signaling Enzyme Diacylglycerol Kinase ϵ Attenuates Mutant Huntingtin Toxicity

Huntington disease (HD) is a dominantly inherited neurodegenerative disease caused by a polyglutamine expansion in the protein huntingtin (Htt). Striatal and cortical neuronal loss are prominent features of this disease. No disease-modifying treatments have been discovered for HD. To identify new therapeutic targets in HD, we screened a kinase inhibitor library for molecules that block mutant Htt cellular toxicity in a mouse HD striatal cell model, Hdh(111Q/111Q) cells. We found that diacylglycerol kinase (DGK) inhibitor II (R59949) decreased caspase-3/7 activity after serum withdrawal in striatal Hdh(111Q/111Q) cells. In addition, R59949 decreased the accumulation of a 513-amino acid N-terminal Htt fragment processed by caspase-3 and blocked alterations in lipid metabolism during serum withdrawal. To identify the diacylglycerol kinase mediating this effect, we knocked down all four DGK isoforms expressed in the brain (β, γ, ε, and ζ) using siRNA. Only the knockdown of the family member, DGKε, blocked striatal Hdh(111Q/111Q)-mediated toxicity. We also investigated the significance of these findings in vivo. First, we found that reduced function of the Drosophila DGKε homolog significantly improves Htt-induced motor dysfunction in a fly model of HD. In addition, we find that the levels of DGKε are increased in the striatum of R6/2 HD transgenic mice when compared with littermate controls. Together, these findings indicate that increased levels of kinase DGKε contribute to HD pathogenesis and suggest that reducing its levels or activity is a potential therapy for HD.

Transducer of regulated CREB-binding proteins (TORCs) transcription and function is impaired in Huntington's disease

Huntington's disease (HD) is an incurable neurological disorder caused by an abnormal glutamine repeat expansion in the huntingtin (Htt) protein. In the present studies, we investigated the role of Transducers of Regulated cAMP response element-binding (CREB) protein activity (TORCs) in HD, since TORCs play an important role in the expression of the transcriptional co-regulator peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), whose expression is impaired in HD. We found significantly decreased TORC1 expression levels in STHdhQ111 cells expressing mutant Htt, in the striatum of NLS-N171-82Q, R6/2 and HdhQ111 HD transgenic mice and in postmortem striatal tissue from HD patients. TORC1 overexpression in wild-type (WT) and Htt striatal cells increased CREB mRNA and protein levels, PGC-1α promoter activity, mRNA expression of the PGC-1α, NRF-1, Tfam and CytC genes, mitochondrial DNA content, mitochondrial activity and mitochondrial membrane potential. TORC1 overexpression also increased the resistance of striatal cells to 3-nitropropionic (3-NP) acid-mediated toxicity. In cultured WT and mutant Htt striatal cells, small hairpin RNA-mediated TORC1 knockdown resulted in decreased PGC-1α expression and increased susceptibility to 3-NP-induced toxicity. Overexpression of PGC-1α partially prevented TORC1 knockdown-mediated increased susceptibility of Htt striatal cells to 3-NP. Specific knockdown of TORC1 in the striatum of NLS-N171-82Q HD transgenic mice induced neurodegeneration. Lastly, knockdown of Htt prevents transcriptional repression of TORC1 and CREB in Htt striatal cells. These findings show that impaired expression and function of TORC1, which results in a reduction in PGC-1α, plays an important role in mitochondrial dysfunction in HD.

Deregulation of BRCA1 Leads to Impaired Spatiotemporal Dynamics of γ-H2AX and DNA Damage Responses in Huntington’s Disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder of mid-life onset characterized by involuntary movements and progressive cognitive decline caused by a CAG repeat expansion in exon 1 of the Huntingtin (Htt) gene. Neuronal DNA damage is one of the major features of neurodegeneration in HD, but it is not known how it arises or relates to the triplet repeat expansion mutation in the Htt gene. Herein, we found that imbalanced levels of non-phosphorylated and phosphorylated BRCA1 contribute to the DNA damage response in HD. Notably, nuclear foci of γ-H2AX, the molecular component that recruits various DNA damage repair factors to damage sites including BRCA1, were deregulated when DNA was damaged in HD cell lines. BRCA1 specifically interacted with γ-H2AX via the BRCT domain, and this association was reduced in HD. BRCA1 overexpression restored γ-H2AX level in the nucleus of HD cells, while BRCA1 knockdown reduced the spatiotemporal propagation of γ-H2AX foci to the nucleoplasm. The deregulation of BRCA1 correlated with an abnormal nuclear distribution of γ-H2AX in striatal neurons of HD transgenic (R6/2) mice and BRCA1(+/-) mice. Our data indicate that BRCA1 is required for the efficient focal recruitment of γ-H2AX to the sites of neuronal DNA damage. Taken together, our results show that BRCA1 directly modulates the spatiotemporal dynamics of γ-H2AX upon genotoxic stress and serves as a molecular maker for neuronal DNA damage response in HD.

Gene expression analysis on a single cell level in Purkinje cells of Huntington's disease transgenic mice

Ataxia is a clinical feature of most polyglutamine disorders. Cerebellar neurodegeneration of Purkinje cells (PCs) in Huntington's Disease (HD) brain was described in the 1980s. PC death in the R6/2 transgenic model for HD was published by Turmaine et al. [27]. So far, PCs have not been examined on a single cell level. In order to begin to understand PC dysfunction and degeneration in HD we performed a gene expression study on laser-dissected PC based on a DNA microarray screening and quantitative real time PCR (Q-PCR). We demonstrate downregulation of the retinoid acid receptor-related orphan receptor α (RORα) mRNA and RORα-mediated mRNAs, also seen by immunofluorescent staining. As RORα and RORα-dependent transcriptional dysregulation is not only found in the R6/2 model for HD but also in a model for spinocerebellar ataxia type 1 (SCA1) (Serra et al. [24]) the data suggest common pathogenic mechanisms for both polyglutamine diseases.

Huntington's disease: fighting on many fronts

The discovery in 1993 of the genetic abnormality that causes Huntington's disease triggered an explosion in our understanding of this inherited neurodegenerative disorder (The Huntington's Disease Collaborative Research Group, 1993). Since the Huntington's disease mutation is fully penetrant, everyone with the same underlying CAG triplet repeat expansion in the huntingtin ( HTT ) gene will develop a devastating combination of motor, cognitive and psychiatric disturbances. The monogenic nature of Huntington's disease suggests that disease modifying therapies should be within reach. Currently, however, no such treatments exist (Mestre et al. , 2009). Nevertheless, much has been done to characterize the huntingtin (Htt) protein and the effects of its toxic twin, mutant huntingtin. We know that Htt is a large and ubiquitously expressed protein with a range of possible functions, and that Huntington's disease is predominantly caused by the damaging effects of mutant Htt on neurons. A range of animal models recapitulate the molecular, cellular and clinical phenotypes of Huntington's disease, enhancing our understanding and facilitating the search for treatments (Ross and Tabrizi, 2011). Numerous potential pathogenic mechanisms have been identified, leading to promising therapeutic approaches in transgenic Huntington's disease mice and other models. Although none has yet been found effective in human patients, there is optimism in the field that Huntington's disease is a disease for which the goal of effective therapy might be achieved (Munoz-Sanjuan and Bates, 2011). Two articles in this issue of Brain highlight the Huntington's disease research community's multi-faceted approach to developing new treatments for Huntington's disease. Grondin and colleagues report success in a 6-month study of HTT gene silencing using RNA interference in the adult non-human primate brain (Grondin et al. , 2012); while Labbadia et al. (2012) describe the means by which a molecular chaperone can suppress aggregation of disease-associated Htt complexes. Gene silencing is an …

Diced Triplets Expose Neurons to RISC

Diced Triplets Expose Neurons to RISC

Disease-Toxicant Interactions in Manganese Exposed Huntington Disease Mice: Early Changes in Striatal Neuron Morphology and Dopamine Metabolism

YAC128 Huntington's disease (HD) transgenic mice accumulate less manganese (Mn) in the striatum relative to wild-type (WT) littermates. We hypothesized that Mn and mutant Huntingtin (HTT) would exhibit gene-environment interactions at the level of neurochemistry and neuronal morphology. Twelve-week-old WT and YAC128 mice were exposed to MnCl2-4H2O (50 mg/kg) on days 0, 3 and 6. Striatal medium spiny neuron (MSN) morphology, as well as levels of dopamine (DA) and its metabolites (which are known to be sensitive to Mn-exposure), were analyzed at 13 weeks (7 days from initial exposure) and 16 weeks (28 days from initial exposure). No genotype-dependent differences in MSN morphology were apparent at 13 weeks. But at 16 weeks, a genotype effect was observed in YAC128 mice, manifested by an absence of the wild-type age-dependent increase in dendritic length and branching complexity. In addition, genotype-exposure interaction effects were observed for dendritic complexity measures as a function of distance from the soma, where only YAC128 mice were sensitive to Mn exposure. Furthermore, striatal DA levels were unaltered at 13 weeks by genotype or Mn exposure, but at 16 weeks, both Mn exposure and the HD genotype were associated with quantitatively similar reductions in DA and its metabolites. Interestingly, Mn exposure of YAC128 mice did not further decrease DA or its metabolites versus YAC128 vehicle exposed or Mn exposed WT mice. Taken together, these results demonstrate Mn-HD disease-toxicant interactions at the onset of striatal dendritic neuropathology in YAC128 mice. Our results identify the earliest pathological change in striatum of YAC128 mice as being between 13 to 16 weeks. Finally, we show that mutant HTT suppresses some Mn-dependent changes, such as decreased DA levels, while it exacerbates others, such as dendritic pathology.

Histone deacetylase (HDAC) inhibitors targeting HDAC3 and HDAC1 ameliorate polyglutamine-elicited phenotypes in model systems of Huntington's disease

We have previously demonstrated amelioration of Huntington's disease (HD)-related phenotypes in R6/2 transgenic mice in response to treatment with the novel histone deacetylase (HDAC) inhibitor 4b. Here we have measured the selectivity profiles of 4b and related compounds against class I and class II HDACs and have tested their ability to restore altered expression of genes related to HD pathology in mice and to rescue disease effects in cell culture and Drosophila models of HD. R6/2 transgenic and wild-type (wt) mice received daily injections of HDAC inhibitors for 3days followed by real-time PCR analysis to detect expression differences for 13 HD-related genes. We find that HDACi 4b and 136, two compounds showing high potency for inhibiting HDAC3 were most effective in reversing the expression of genes relevant to HD, including Ppp1r1b, which encodes DARPP-32, a marker for medium spiny striatal neurons. In contrast, compounds targeting HDAC1 were less effective at correcting gene expression abnormalities in R6/2 transgenic mice, but did cause significant increases in the expression of selected genes. An additional panel of 4b-related compounds was tested in a Drosophila model of HD and in STHdhQ111 striatal cells to further distinguish HDAC selectivity. Significant improvement in huntingtin-elicited Drosophila eye neurodegeneration in the fly was observed in response to treatment with compounds targeting human HDAC1 and/or HDAC3. In STHdhQ111 striatal cells, the ability of HDAC inhibitors to improve huntingtin-elicited metabolic deficits correlated with the potency at inhibiting HDAC1 and HDAC3, although the IC50 values for HDAC1 inhibition were typically 10-fold higher than for inhibition of HDAC3. Assessment of HDAC protein localization in brain tissue by Western blot analysis revealed accumulation of HDAC1 and HDAC3 in the nucleus of HD transgenic mice compared to wt mice, with a concurrent decrease in cytoplasmic localization, suggesting that these HDACs contribute to a repressive chromatin environment in HD. No differences were detected in the localization of HDAC2, HDAC4 or HDAC7. These results suggest that inhibition of HDACs 1 and 3 can relieve HD-like phenotypes in model systems and that HDAC inhibitors targeting these isotypes might show therapeutic benefit in human HD.

Neuronal aggregates are associated with phenotypic onset in the R6/2 Huntington's disease transgenic mouse

Huntington's disease (HD) is caused by the expansion of the polyglutamine tract expressed in the huntingtin protein. Data from patients show a strong negative correlation between CAG repeat size and age of disease onset. Recent studies in mixed background C57×CBA R6/2 mice suggest the inverse correlation observed in the human disease may not be replicated in some animal models of HD. To further clarify the relationship between repeat length and age of onset, congenic C57BL6/J R6/2 transgenic mice expressing 110, 260 or 310 CAG were tested in a comprehensive behavioral battery at multiple ages. Data confirmed the findings of earlier studies and indicate that on a pure C57BL6/J genetic background, R6/2 mice with larger repeats exhibit a delay in phenotypic onset with increasing polyglutamine size (6 weeks in 110 CAG and 17 weeks in 310 CAG mice). Further analysis confirmed a decrease in transgene transcript expression in 310 CAG mice as well as differential aggregated protein localization in association with repeat length. Mice expressing 110 CAG developed aggregates that localized almost exclusively to the nucleus of neuronal cells in the striatum and cortex. In contrast, tissue from 310 CAG mice exhibited predominantly extranuclear inclusions. Novel mutant protein analysis obtained using time-resolved fluorescence resonance energy transfer (FRET) revealed that soluble protein levels decreased with disease onset in R6/2 mice while aggregated protein levels increased. We believe that these data suggest a role for aggregation and inclusion localization in HD pathogenesis and propose a mechanism for the age of onset delay observed in R6/2 mice.

Enhanced Parasympathetic Nervous Activity in Huntington's Disease Transgenic Mice

Enhanced Parasympathetic Nervous Activity in Huntington's Disease Transgenic Mice

Induced pluripotent stem cell lines from Huntington's disease mice undergo neuronal differentiation while showing alterations in the lysosomal pathway

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by an excessive expansion of a CAG trinucleotide repeat in the gene encoding the protein huntingtin, resulting in an elongated stretch of glutamines near the N-terminus of the protein. Here we report the derivation of a collection of 11 induced pluripotent stem (iPS) cell lines generated through somatic reprogramming of fibroblasts obtained from the R6/2 transgenic HD mouse line. We show that CAG expansion has no effect on reprogramming efficiency, cell proliferation rate, brain-derived neurotrophic factor level, or neurogenic potential. However, genes involved in the cholesterol biosynthesis pathway, which is altered in HD, are also affected in HD-iPS cell lines. Furthermore, we found a lysosomal gene upregulation and an increase in lysosome number in HD-iPS cell lines. These observations suggest that iPS cells from HD mice replicate some but not all of the molecular phenotypes typically observed in the disease; additionally, they do not manifest increased cell death propensity either under self-renewal or differentiated conditions. More studies will be necessary to transform a revolutionary technology into a powerful platform for drug screening approaches.

Dantrolene is neuroprotective in Huntington's disease transgenic mouse model

BackgroundHuntington's disease (HD) is a progressive neurodegenerative disorder caused by a polyglutamine expansion in the Huntingtin protein which results in the selective degeneration of striatal medium spiny neurons (MSNs). Our group has previously demonstrated that calcium (Ca2+) signaling is abnormal in MSNs from the yeast artificial chromosome transgenic mouse model of HD (YAC128). Moreover, we demonstrated that deranged intracellular Ca2+ signaling sensitizes YAC128 MSNs to glutamate-induced excitotoxicity when compared to wild type (WT) MSNs. In previous studies we also observed abnormal neuronal Ca2+ signaling in neurons from spinocerebellar ataxia 2 (SCA2) and spinocerebellar ataxia 3 (SCA3) mouse models and demonstrated that treatment with dantrolene, a ryanodine receptor antagonist and clinically relevant Ca2+ signaling stabilizer, was neuroprotective in experiments with these mouse models. The aim of the current study was to evaluate potential beneficial effects of dantrolene in experiments with YAC128 HD mouse model.ResultsThe application of caffeine and glutamate resulted in increased Ca2+ release from intracellular stores in YAC128 MSN cultures when compared to WT MSN cultures. Pre-treatment with dantrolene protected YAC128 MSNs from glutamate excitotoxicty, with an effective concentration of 100 nM and above. Feeding dantrolene (5 mg/kg) twice a week to YAC128 mice between 2 months and 11.5 months of age resulted in significantly improved performance in the beam-walking and gait-walking assays. Neuropathological analysis revealed that long-term dantrolene feeding to YAC128 mice significantly reduced the loss of NeuN-positive striatal neurons and reduced formation of Httexp nuclear aggregates.ConclusionsOur results support the hypothesis that deranged Ca2+ signaling plays an important role in HD pathology. Our data also implicate the RyanRs as a potential therapeutic target for the treatment of HD and demonstrate that RyanR inhibitors and Ca2+ signaling stabilizers such as dantrolene should be considered as potential therapeutics for the treatment of HD and other polyQ-expansion disorders.

Somatostatin Receptor 1 and 5 Double Knockout Mice Mimic Neurochemical Changes of Huntington's Disease Transgenic Mice

BackgroundSelective degeneration of medium spiny neurons and preservation of medium sized aspiny interneurons in striatum has been implicated in excitotoxicity and pathophysiology of Huntington's disease (HD). However, the molecular mechanism for the selective sparing of medium sized aspiny neurons and vulnerability of projection neurons is still elusive. The pathological characteristic of HD is an extensive reduction of the striatal mass, affecting caudate putamen. Somatostatin (SST) positive neurons are selectively spared in HD and Quinolinic acid/N-methyl-D-aspartic acid induced excitotoxicity, mimic the model of HD. SST plays neuroprotective role in excitotoxicity and the biological effects of SST are mediated by five somatostatin receptor subtypes (SSTR1-5).Methods and FindingsTo delineate subtype selective biological responses we have here investigated changes in SSTR1 and 5 double knockout mice brain and compared with HD transgenic mouse model (R6/2). Our study revealed significant loss of dopamine and cAMP regulated phosphoprotein of 32 kDa (DARPP-32) and comparable changes in SST, N-methyl-D-aspartic acid receptors subtypes, calbindin and brain nitric oxide synthase expression as well as in key signaling proteins including calpain, phospho-extracellular-signal-regulated kinases1/2, synapsin-IIa, protein kinase C-α and calcineurin in SSTR1/5−/− and R6/2 mice. Conversely, the expression of somatostatin receptor subtypes, enkephalin and phosphatidylinositol 3-kinases were strain specific. SSTR1/5 appears to be important in regulating NMDARs, DARPP-32 and signaling molecules in similar fashion as seen in HD transgenic mice.ConclusionsThis is the first comprehensive description of disease related changes upon ablation of G- protein coupled receptor gene. Our results indicate that SST and SSTRs might play an important role in regulation of neurodegeneration and targeting this pathway can provide a novel insight in understanding the pathophysiology of Huntington's disease.

Pathophysiology of Huntington's disease: time-dependent alterations in synaptic and receptor function.

Huntington's disease (HD) is a progressive, fatal neurological condition caused by an expansion of CAG (glutamine) repeats in the coding region of the Huntington gene. To date, there is no cure but great strides have been made to understand pathophysiological mechanisms. In particular, genetic animal models of HD have been instrumental in elucidating the progression of behavioral and physiological alterations, which had not been possible using classic neurotoxin models. Our groups have pioneered the use of transgenic HD mice to examine the excitotoxicity hypothesis of striatal neuronal dysfunction and degeneration, as well as alterations in excitation and inhibition in striatum and cerebral cortex. In this review, we focus on synaptic and receptor alterations of striatal medium-sized spiny (MSNs) and cortical pyramidal neurons in genetic HD mouse models. We demonstrate a complex series of alterations that are region-specific and time-dependent. In particular, many changes are bidirectional depending on the degree of disease progression, that is, early vs. late, and also on the region examined. Early synaptic dysfunction is manifested by dysregulated glutamate release in striatum followed by progressive disconnection between cortex and striatum. The differential effects of altered glutamate release on MSNs originating the direct and indirect pathways is also elucidated, with the unexpected finding that cells of the direct striatal pathway are involved early in the course of the disease. In addition, we review evidence for early N-methyl-D-aspartate receptor (NMDAR) dysfunction leading to enhanced sensitivity of extrasynaptic receptors and a critical role of GluN2B subunits. Some of the alterations in late HD could be compensatory mechanisms designed to cope with early synaptic and receptor dysfunctions. The main findings indicate that HD treatments need to be designed according to the stage of disease progression and should consider regional differences.

Sexually Dimorphic Serotonergic Dysfunction in a Mouse Model of Huntington's Disease and Depression

Depression is the most common psychiatric disorder in Huntington's disease (HD) patients. In the general population, women are more prone to develop depression and such susceptibility might be related to serotonergic dysregulation. There is yet to be a study of sexual dimorphism in the development and presentation of depression in HD patients. We investigated whether 8-week-old male and female R6/1 transgenic HD mice display depressive-like endophenotypes associated with serotonergic impairments. We also studied the behavioral effects of acute treatment with sertraline. We found that only female HD mice exhibited a decreased preference for saccharin as well as impaired emotionality-related behaviors when assessed on the novelty-suppressed feeding test (NSFT) and the forced-swimming test (FST). The exaggerated immobility time displayed by female HD in the FST was reduced by acute administration of sertraline. We also report an increased response to the 5-HT1A receptor agonist 8-OH-DPAT in inducing hypothermia and a decreased 5-HT2A receptor function in HD animals. While tissue levels of serotonin were reduced in both male and female HD mice, we found that serotonin concentration and hydroxylase-2 (TPH2) mRNA levels were higher in the hippocampus of males compared to female animals. Finally, the antidepressant-like effects of sertraline in the FST were blunted in male HD animals. This study reveals sex-specific depressive-related behaviors during an early stage of HD prior to any cognitive and motor deficits. Our data suggest a crucial role for disrupted serotonin signaling in mediating the sexually dimorphic depression-like phenotype in HD mice.

Adenoviral astrocyte-specific expression of BDNF in the striata of mice transgenic for Huntington's disease delays the onset of the motor phenotype.

Huntington's disease (HD) is a neurodegenerative disorder characterized by motor, cognitive, and psychiatric symptoms. The most characteristic structural feature of this disease is neurodegeneration accompanied by gliosis in the striatum. BDNF has been proposed to protect striatal neurons from degeneration, because it is an important survival factor for these neurons from development to adulthood. Considering the extensive gliosis and the survival effects of BDNF, we constructed an adenovirus to express a BDNF cDNA in astrocyte cells using a promoter of the glial fibrillary acidic protein gene. Cells stably transfected in vitro with a BDNF cDNA driven by this promoter expressed BDNF and responded to external stimuli increasing BDNF production. When the vector was applied into the striata of mice transgenic for HD, long-term expression of the transgene was observed, associated with a delay of onset of the motor phenotype of the R6/2 HD transgenic mice. The present data indicate that the striatal expression of BDNF is a potential adjuvant for the treatment of HD.

Neuronal Store-Operated Calcium Entry Pathway as a Novel Therapeutic Target for Huntington's Disease Treatment

Huntington's disease (HD) is a neurodegenerative disorder caused by a polyglutamine expansion within Huntingtin (Htt) protein. In the phenotypic screen we identified a class of quinazoline-derived compounds that delayed a progression of a motor phenotype in transgenic Drosophila HD flies. We found that the store-operated calcium (Ca(2+)) entry (SOC) pathway activity is enhanced in neuronal cells expressing mutant Htt and that the identified compounds inhibit SOC pathway in HD neurons. The same compounds exerted neuroprotective effects in glutamate-toxicity assays with YAC128 medium spiny neurons primary cultures. We demonstrated a key role of TRPC1 channels in supporting SOC pathway in HD neurons. We concluded that the TRPC1-mediated neuronal SOC pathway constitutes a novel target for HD treatment and that the identified compounds represent a novel class of therapeutic agents for treatment of HD and possibly other neurodegenerative disorders.

Light and electron microscopic characterization of the evolution of cellular pathology in the R6/1 Huntington's disease transgenic mice

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by an expansion of CAG repeats in the Htt gene. Examination of the post-mortem brains of HD patients shows the presence of diffuse nuclear htt immunoreactivity and intra-nuclear inclusions. The aim of this study was to produce a detailed characterization of the neuronal pathology in the R6/1 transgenic mouse model. The R6/1 carrier mice demonstrate intra-nuclear and extra-nuclear inclusions with the S830 htt antibody at 2-11 months of age. The distribution pattern of neuronal intra-nuclear inclusions (NIIs) was irregular in several brain regions including the striatum, cortex and hippocampus. A greater number of NIIs were found in the ventral striatum than in the dorsal striatum. In the globus pallidus, cerebellum and thalamus the pattern of inclusion formation was relatively consistent over time. At 4 and 6 months of age, the R6/1 mice showed increased glial fibrillary acid protein (GFAP) immunoreactivity in the cortex compared to their wildtype littermates, yet no difference was found in the striatum. Analysis by electron microscopy found that neurons from the R6/1 carriers contained a densely packed cytoplasm at 1.5 months of age, with some neurons displaying structural abnormalities including vacuolization and nuclear membrane folding. No NIIs were detected at this age, but by 7 months of age, NIIs were present with severe cellular vacuolization. The present study indicates that a decrease in striatal volume with cell loss is present in young (2 months) R6/1 mice, and the distribution of NIIs is robust and widespread, with considerably temporal and spatial variation in NII development between mice.