Htt Protein Research Articles

Genomic Analysis of wig-1 Pathways

BackgroundWig-1 is a transcription factor regulated by p53 that can interact with hnRNP A2/B1, RNA Helicase A, and dsRNAs, which plays an important role in RNA and protein stabilization. in vitro studies have shown that wig-1 binds p53 mRNA and stabilizes it by protecting it from deadenylation. Furthermore, p53 has been implicated as a causal factor in neurodegenerative diseases based in part on its selective regulatory function on gene expression, including genes which, in turn, also possess regulatory functions on gene expression. In this study we focused on the wig-1 transcription factor as a downstream p53 regulated gene and characterized the effects of wig-1 down regulation on gene expression in mouse liver and brain.Methods and ResultsAntisense oligonucleotides (ASOs) were identified that specifically target mouse wig-1 mRNA and produce a dose-dependent reduction in wig-1 mRNA levels in cell culture. These wig-1 ASOs produced marked reductions in wig-1 levels in liver following intraperitoneal administration and in brain tissue following ASO administration through a single striatal bolus injection in FVB and BACHD mice. Wig-1 suppression was well tolerated and resulted in the reduction of mutant Htt protein levels in BACHD mouse brain but had no effect on normal Htt protein levels nor p53 mRNA or protein levels. Expression microarray analysis was employed to determine the effects of wig-1 suppression on genome-wide expression in mouse liver and brain. Reduction of wig-1 caused both down regulation and up regulation of several genes, and a number of wig-1 regulated genes were identified that potentially links wig-1 various signaling pathways and diseases.ConclusionAntisense oligonucleotides can effectively reduce wig-1 levels in mouse liver and brain, which results in specific changes in gene expression for pathways relevant to both the nervous system and cancer.

Amyloid-Mediated Sequestration of Essential Proteins Contributes to Mutant Huntingtin Toxicity in Yeast

BackgroundPolyglutamine expansion is responsible for several neurodegenerative disorders, among which Huntington disease is the most well-known. Studies in the yeast model demonstrated that both aggregation and toxicity of a huntingtin (htt) protein with an expanded polyglutamine region strictly depend on the presence of the prion form of Rnq1 protein ([PIN +]), which has a glutamine/asparagine-rich domain.Principal FindingsHere, we showed that aggregation and toxicity of mutant htt depended on [PIN +] only quantitatively: the presence of [PIN +] elevated the toxicity and the levels of htt detergent-insoluble polymers. In cells lacking [PIN +], toxicity of mutant htt was due to the polymerization and inactivation of the essential glutamine/asparagine-rich Sup35 protein and related inactivation of another essential protein, Sup45, most probably via its sequestration into Sup35 aggregates. However, inhibition of growth of [PIN +] cells depended on Sup35/Sup45 depletion only partially, suggesting that there are other sources of mutant htt toxicity in yeast.ConclusionsThe obtained data suggest that induced polymerization of essential glutamine/asparagine-rich proteins and related sequestration of other proteins which interact with these polymers represent an essential source of htt toxicity.

Transgenic Mouse Model Expressing the Caspase 6 Fragment of Mutant Huntingtin

Huntington's disease (HD) is caused by a polyglutamine expansion in the Huntingtin (Htt) protein. Proteolytic cleavage of Htt into toxic N-terminal fragments is believed to be a key aspect of pathogenesis. The best characterized putative cleavage event is at amino acid 586, hypothesized to be mediated by caspase 6. A corollary of the caspase 6 cleavage hypothesis is that the caspase 6 fragment should be a toxic fragment. To test this hypothesis, and further characterize the role of this fragment, we have generated transgenic mice expressing the N-terminal 586 aa of Htt with a polyglutamine repeat length of 82 (N586-82Q), under the control of the prion promoter. N586-82Q mice show a clear progressive rotarod deficit by 4 months of age, and are hyperactive starting at 5 months, later changing to hypoactivity before early mortality. MRI studies reveal widespread brain atrophy, and histologic studies demonstrate an abundance of Htt aggregates, mostly cytoplasmic, which are predominantly composed of the N586-82Q polypeptide. Smaller soluble N-terminal fragments appear to accumulate over time, peaking at 4 months, and are predominantly found in the nuclear fraction. This model appears to have a phenotype more severe than current full-length Htt models, but less severe than HD mouse models expressing shorter Htt fragments. These studies suggest that the caspase 6 fragment may be a transient intermediate, that fragment size is a factor contributing to the rate of disease progression, and that short soluble nuclear fragments may be most relevant to pathogenesis.

Prothymosin-α Interacts with Mutant Huntingtin and Suppresses Its Cytotoxicity in Cell Culture

Huntington disease (HD), a fatal neurodegenerative disorder, is caused by a lengthening of the polyglutamine tract in the huntingtin (Htt) protein. Despite considerable effort, thus far there is no cure or treatment available for the disorder. Using the approach of tandem affinity purification we recently discovered that prothymosin-α (ProTα), a small highly acidic protein, interacts with mutant Htt (mHtt). This was confirmed by co-immunoprecipitation and a glutathione S-transferase (GST) pull-down assay. Overexpression of ProTα remarkably reduced mHtt-induced cytotoxicity in both non-neuronal and neuronal cell models expressing N-terminal mHtt fragments, whereas knockdown of ProTα expression in the cells enhanced mHtt-caused cell death. Deletion of the central acidic domain of ProTα abolished not only its interaction with mHtt but also its protective effect on mHtt-caused cytotoxicity. Additionally, overexpression of ProTα inhibited caspase-3 activation but enhanced aggregation of mHtt. Furthermore, when added to cultured cells expressing mHtt, the purified recombinant ProTα protein not only entered the cells but it also significantly suppressed the mHtt-caused cytotoxicity. Taken together, these data suggest that ProTα might be a novel therapeutic target for treating HD and other polyglutamine expansion disorders.

Polyglutamine Expanded Huntingtin Dramatically Alters the Genome-Wide Binding of HSF1

In Huntington's disease (HD), polyglutamine expansions in the huntingtin (Htt) protein cause subtle changes in cellular functions that, over-time, lead to neurodegeneration and death. Studies have indicated that activation of the heat shock response can reduce many of the effects of mutant Htt in disease models, suggesting that the heat shock response is impaired in the disease. To understand the basis for this impairment, we have used genome-wide chromatin immunoprecipitation followed by massively parallel sequencing (ChIP-Seq) to examine the effects of mutant Htt on the master regulator of the heat shock response, HSF1. We find that, under normal conditions, HSF1 function is highly similar in cells carrying either wild-type or mutant Htt. However, polyQ-expanded Htt severely blunts the HSF1-mediated stress response. Surprisingly, we find that the HSF1 targets most affected upon stress are not directly associated with proteostasis, but with cytoskeletal binding, focal adhesion and GTPase activity. Our data raise the intriguing hypothesis that the accumulated damage from life-long impairment in these stress responses may contribute significantly to the etiology of Huntington's disease.

The Role of Protein Context in Disease-Related Huntingtin Protein/Lipid Interface Interactions

Huntington's disease (HD) is a neurodegenerative disorder caused by an expansion of a poly-glutamine (poly-Q) region near the N-terminus of the huntingtin (htt) protein. Expansion of the poly-Q region above 35-40 repeats results in the disease that is characterized by inclusion body aggregates of mutated protein. The poly-Q region of htt is flanked by a 17 amino acid N-terminal sequence (N17) and a region of proline repeats (P11). As the cell membrane has been proposed to play a role in mediating htt aggregation, Langmuir trough techniques were used to investigate the effects of flanking regions on the surface activity and insertion of htt peptide constructs into a lipid monolayer. Four peptide constructs were tested: N17-Q35-KK, N17-Q35-P11-KK, KK-Q35-KK and KK-Q35-P11-KK, where the additional lysine residues were attached to improve solubility. Surface activity was measured to determine the affinity of each peptide for the air-water interface. The constructs containing the N-terminal sequence had higher surface activities compared to those without. Inclusion of the polyproline region with the N-terminal sequence contributed to the highest surface activity. To determine peptide association with a cell membrane, insertion of each peptide into a monolayer of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) held at a constant surface pressure was also investigated. Peptides with the flanking N-terminus showed appreciable monolayer insertion. The polyproline region only mediated and increased the degree of insertion when the N-terminus was also present. Rates of insertion of the constructs containing the N-terminus were comparable, while those without this region were markedly slower. Experiments were repeated using monolayers of total brain extract to better model a physiological environment with similar results. The amino acid environment surrounding the poly-Q region dramatically affects peptide association with the cell membrane and this may potentially mediate the aggregation process.

Neuroprotective role of Sirt1 in mammalian models of Huntington's disease through activation of multiple Sirt1 targets

Huntington's disease is a fatal neurodegenerative disorder caused by an expanded polyglutamine repeat in huntingtin (HTT) protein. We previously showed that calorie restriction ameliorated Huntington's disease pathogenesis and slowed disease progression in mice that model Huntington's disease (Huntington's disease mice). We now report that overexpression of sirtuin 1 (Sirt1), a mediator of the beneficial metabolic effects of calorie restriction, protects neurons against mutant HTT toxicity, whereas reduction of Sirt1 exacerbates mutant HTT toxicity. Overexpression of Sirt1 improves motor function, reduces brain atrophy and attenuates mutant-HTT-mediated metabolic abnormalities in Huntington's disease mice. Further mechanistic studies suggested that Sirt1 prevents the mutant-HTT-induced decline in brain-derived neurotrophic factor (BDNF) concentrations and the signaling of its receptor, TrkB, and restores dopamine- and cAMP-regulated phosphoprotein, 32 kDa (DARPP32) concentrations in the striatum. Sirt1 deacetylase activity is required for Sirt1-mediated neuroprotection in Huntington's disease cell models. Notably, we show that mutant HTT interacts with Sirt1 and inhibits Sirt1 deacetylase activity, which results in hyperacetylation of Sirt1 substrates such as forkhead box O3A (Foxo3a), thereby inhibiting its pro-survival function. Overexpression of Sirt1 counteracts the mutant-HTT-induced deacetylase deficit, enhances the deacetylation of Foxo3a and facilitates cell survival. These findings show a neuroprotective role for Sirt1 in mammalian Huntington's disease models and open new avenues for the development of neuroprotective strategies in Huntington's disease.

Potent and Selective Antisense Oligonucleotides Targeting Single-Nucleotide Polymorphisms in the Huntington Disease Gene / Allele-Specific Silencing of Mutant Huntingtin

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by CAG-expansion in the huntingtin gene (HTT) that results in a toxic gain of function in the mutant huntingtin protein (mHTT). Reducing the expression of mHTT is therefore an attractive therapy for HD. However, wild-type HTT protein is essential for development and has critical roles in maintaining neuronal health. Therapies for HD that reduce wild-type HTT may therefore generate unintended negative consequences. We have identified single-nucleotide polymorphism (SNP) targets in the human HD population for the disease-specific targeting of the HTT gene. Using primary cells from patients with HD and the transgenic YAC18 and BACHD mouse lines, we developed antisense oligonucleotide (ASO) molecules that potently and selectively silence mHTT at both exonic and intronic SNP sites. Modification of these ASOs with S-constrained-ethyl (cET) motifs significantly improves potency while maintaining allele selectively in vitro. The developed ASO is potent and selective for mHTT in vivo after delivery to the mouse brain. We demonstrate that potent and selective allele-specific knockdown of the mHTT protein can be achieved at therapeutically relevant SNP sites using ASOs in vitro and in vivo.

A novel target for Huntington's disease: ERK at the crossroads of signaling

Activating the ERK pathway (extracellular signal-regulated kinase pathway) has proven beneficial in several models of Huntington's disease (HD), and drugs that are protective in HD models have recently been found to activate ERK. Thus, the ERK cascade may be a potential target for therapeutic intervention in this currently untreatable disorder. HD is caused by an expanded polyglutamine repeat in the huntingtin (Htt) protein that actuates a diverse set of pathogenic mechanisms. In response to mutant Htt, ERK is activated and directs a protective transcriptional response and inhibits caspase activation. Paradoxically, Htt also interferes with several signaling events of the ERK pathway. Mutant Htt compromises the ERK-dependent transcriptional response to corticostriatal BDNF signaling. Mutant Htt also hinders glutamate uptake from the synaptic cleft by down-regulating ERK-dependent expression of glutamate transporters, leaving cells vulnerable to excitotoxicity. Some of this cellular complexity can be capitalized on to achieve selective activation of ERK, which can be protective.

The long and the short of aberrant ciliogenesis in Huntington disease

Huntington disease (HD) is a dominantly inherited neurodegenerative disorder that is caused by a mutant huntingtin (HTT) gene encoding a version of the Htt protein with an expanded polyglutamine stretch. Although the HTT gene was discovered more than 18 years ago, the functions of normal Htt and the mechanisms by which mutant Htt causes disease are not well defined. In this issue of the JCI, Keryer et al. uncovered a novel function for normal Htt in ciliogenesis and report that mutant Htt causes hypermorphic ciliogenesis and ciliary dysfunction. These observations suggest that it is now critical to understand the extent to which ciliary dysfunction contributes to the different symptoms of HD and to determine whether therapeutic strategies designed to normalize ciliary function can ameliorate the disease.

A Disulfide-Free Single-Domain V L Intrabody with Blocking Activity towards Huntingtin Reveals a Novel Mode of Epitope Recognition

We present the crystal structure and biophysical characterization of a human V L [ variable domain immunoglobulin (Ig) light chain] single-domain intrabody that binds to the huntingtin (Htt) protein and has been engineered for antigen recognition in the absence of its intradomain disulfide bond, otherwise conserved in the Ig fold. Analytical ultracentrifugation demonstrated that the αHtt-V L 12.3 domain is a stable monomer under physiological conditions even at concentrations > 20 μM. Using peptide SPOT arrays, we identified the minimal binding epitope to be EKLMKAFESLKSFQ, comprising the N-terminal residues 5–18 of Htt and including the first residue of the poly-Gln stretch. X-ray structural analysis of αHtt-V L both as apo protein and in the presence of the epitope peptide revealed several interesting insights: first, the role of mutations acquired during the combinatorial selection process of the αHtt-V L 12.3 domain—initially starting from a single-chain Fv fragment—that are responsible for its stability as an individually soluble Ig domain, also lacking the disulfide bridge, and second, a previously unknown mode of antigen recognition, revealing a novel paratope. The Htt epitope peptide adopts a purely α-helical structure in the complex with αHtt-V L and is bound at the base of the complementarity-determining regions (CDRs) at the concave β-sheet that normally gives rise to the interface between the V L domain and its paired V H ( variable domain Ig heavy chain) domain, while only few interactions with CDR-L1 and CDR-L3 are formed. Notably, this noncanonical mode of antigen binding may occur more widely in the area of in vitro selected antibody fragments, including other Ig-like scaffolds, possibly even if a V H domain is present.

Secondary Structures of Native and Pathogenic Huntingtin N-Terminal Fragments

Huntington's disease is a neurodegenerative disorder caused by a polyglutamine (polyQ) expansion in the N-terminal fragment of the Huntingtin (Htt) protein. Structural properties of Htt N-terminal regions and the molecular mechanism leading to protein aggregation have not been fully explained yet. We performed all-atom replica exchange molecular dynamics to investigate the structures of Htt N-terminal parts with polyQ tracts of nonpathogenic and pathogenic lengths. The monomers were composed of the headpiece (17 N-terminal residues), a polyQ tract (polyQ(17) for native and polyQ(55) for pathogenic sequence), and a polyP(11) region, followed by 17 amino acids of mixed sequence. We found that corresponding regions in both fragments fold to similar secondary structures; the headpiece and polyQ stretch adopt mainly α-helical conformations, and polyP(11) forms the PP II-type helix. The native N-terminal fragment is more compact and stabilized by hydrophobic interactions between the surface of polyP(11) and the amphipathic helix of the headpiece. In the pathogenic fragment the headpiece is solvent exposed and does not interact with polyP(11). The predicted structure of the native N-terminal fragment agrees with the X-ray structure of the Htt first exon containing polyQ(17). The structure of the pathogenic fragment adheres to an aggregation model that is mediated by the Htt headpiece.

Characterization of dental pulp stem/stromal cells of Huntington monkey tooth germs

BackgroundDental pulp stem/stromal cells (DPSCs) are categorized as adult stem cells (ASCs) that retain multipotent differentiation capabilities. DPSCs can be isolated from individuals at any age and are considered to be true personal stem cells, making DPSCs one of the potential options for stem cell therapy. However, the properties of DPSCs from individuals with an inherited genetic disorder, such as Huntington's disease (HD), have not been fully investigated.ResultsTo examine if mutant huntingtin (htt) protein impacts DPSC properties, we have established DPSCs from tooth germ of transgenic monkeys that expressed both mutant htt and green fluorescent protein (GFP) genes (rHD/G-DPSCs), and from a monkey that expressed only the GFP gene (rG-DPSCs), which served as a control. Although mutant htt and oligomeric htt aggregates were overtly present in rHD/G-DPSCs, all rHD/G-DPSCs and rG-DPSCs shared similar characteristics, including self-renewal, multipotent differentiation capabilities, expression of stemness and differentiation markers, and cell surface antigen profile.ConclusionsOur results suggest that DPSCs from Huntington monkeys retain ASC properties. Thus DPSCs derived from individuals with genetic disorders such as HD could be a potential source of personal stem cells for therapeutic purposes.

Gastrodia elata prevents huntingtin aggregations through activation of the adenosine A2A receptor and ubiquitin proteasome system

Ethnopharmacological relevanceGastrodia elata Blume (Fam. Orchidaceae) is a traditional Chinese herbal medicine for treating headaches, dizziness, tetanus, epilepsy, and numbness of the limbs, which suggests that it has neuroprotective effect. Aim of the studyTo validate the neuroprotection of Gastrodia elata in preventing neurodegenerations, such as Huntington's disease (HD). Materials and methodsMTT assay was used to validate the protection of Gastrodia elata. In pheochromocytoma (PC12) cell. Transient transfection of mutant huntingtin (Htt) in PC12 cell was used as an in vitro model of HD. Filter retardation assay was used to measure Htt-induced protein aggregations. Proteasome activity was monitored by transfection of pZsProSensor-1 and imaged by a confocal laser scanning microscope. ResultsThis protection of Gastrodia elata could be blocked by an A2A-R antagonist and a protein kinase A (PKA) inhibitor, indicating an A2A-R signaling event. Gastrodia elata could reverse mutant Htt-induced protein aggregations and proteasome de-activation through A2A-R signaling. In addition, activation of PKA tended to activate proteasome activity and reduce mutant Htt protein aggregations. The proteasome inhibitor, MG 132, blocked Gastrodia elata-mediated suppression of mutant Htt aggregations. ConclusionGastrodia elata prevented mutant Htt aggregations and increased proteasomal activity by targeting the A2A-R through PKA-dependent pathway.

Changes in BiP availability reveal hypersensitivity to acute endoplasmic reticulum stress in cells expressing mutant huntingtin

Huntington's disease (HD) is caused by expanded glutamine repeats within the huntingtin (Htt) protein. Mutant Htt (mHtt) in the cytoplasm has been linked to induction of the luminal endoplasmic reticulum (ER) stress pathway, the unfolded protein response (UPR). How mHtt impacts the susceptibility of the ER lumen to stress remains poorly understood. To investigate molecular differences in the ER in cells expressing mHtt, we used live-cell imaging of a sensitive reporter of the misfolded secretory protein burden, GFP fused to the ER chaperone BiP (also known as GRP78), which decreases in mobility as it binds increasing amounts of misfolded proteins. Striatal neurons expressing full-length mHtt showed no differences in BiP-GFP mobility and no evidence of UPR activation compared with wild-type cells at steady state. However, mHtt-expressing cells were acutely sensitive to misfolded secretory proteins. Treatment with ER stressors, tunicamycin or DTT, rapidly decreased BiP-GFP mobility in mHtt striatal cells and accelerated UPR activation compared with wild-type cells. mHtt-expressing cells exhibited decreased misfolded protein flux as a result of ER associated degradation (ERAD) dysfunction. Furthermore, UPR-adapted mHtt cells succumbed to misfolded protein stresses that could be tolerated by adapted wild-type cells. Thus, mHtt expression impairs misfolded secretory protein turnover, decreases the ER stress threshold, and increases cell vulnerability to insults.

PPARgamma rescue of the mitochondrial dysfunction in Huntington's disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by a CAG trinucleotide expansion in the Huntingtin (Htt) gene. The resultant mutant Htt protein (mHtt) forms aggregates in the brain (e.g., cortex and striatum), and causes devastating neuronal degeneration. Transcriptional dysfunction caused by mHtt is critical for HD. We recently demonstrated that a crucial transcription factor peroxisome proliferator-activated receptor-γ (PPARγ) played a major function in the energy homeostasis observed in HD and that PPARγ is a potentially neuroprotective target for this disease. We report here that the transcript level of PPARγ was markedly downregulated in the cortex of a transgenic mouse model of HD (R6/2). Treatment of R6/2 mice with an agonist of PPARγ (thiazolidinedione, TZD) resulted in a beneficial effect on PPARγ. By reducing Htt aggregates and thereby ameliorating the recruitment of PPARγ into Htt aggregates, TZD treatment also elevated the availability of PPARγ level and subsequently normalized the expression of downstream genes (including PGC-1α and several mitochondrial genes) in the cortex. The above protective effects appeared to be exerted by a direct activation of the PPARγ agonist (rosiglitazone) because rosiglitazone protected a neuroblastoma cell line (N2A) from mHtt-evoked mitochondrial deficiency. Our results reveal that TZD and rosiglitazone may play a protective role in HD, and support the view that PPARγ is a potential therapeutic target in HD.

Interaction with Polyglutamine-expanded Huntingtin Alters Cellular Distribution and RNA Processing of Huntingtin Yeast Two-hybrid Protein A (HYPA)

Huntington disease (HD) is an autosomal inherited disorder that causes the deterioration of brain cells. The polyglutamine (polyQ) expansion of huntingtin (Htt) is implicated in the pathogenesis of HD via interaction with an RNA splicing factor, Htt yeast two-hybrid protein A/forming-binding protein 11 (HYPA/FBP11). Besides the pathogenic polyQ expansion, Htt also contains a proline-rich region (PRR) located exactly in the C terminus to the polyQ tract. However, how the polyQ expansion influences the PRR-mediated protein interaction and how this abnormal interaction leads to the biological consequence remain elusive. Our NMR structural analysis indicates that the PRR motif of Htt cooperatively interacts with the tandem WW domains of HYPA through domain chaperoning effect of WW1 on WW2. The polyQ-expanded Htt sequesters HYPA to the cytosolic location and then significantly reduces the efficiency of pre-mRNA splicing. We propose that the toxic gain-of-function of the polyQ-expanded Htt that causes dysfunction of cellular RNA processing contributes to the pathogenesis of HD.

The Kynurenine Pathway Modulates Neurodegeneration in a Drosophila Model of Huntington's Disease

Neuroactive metabolites of the kynurenine pathway (KP) of tryptophan degradation have been implicated in the pathophysiology of neurodegenerative disorders, including Huntington's disease (HD) [1]. A central hallmark of HD is neurodegeneration caused by a polyglutamine expansion in the huntingtin (htt) protein [2]. Here we exploit a transgenic Drosophila melanogaster model of HD to interrogate the therapeutic potential of KP manipulation. We observe that genetic and pharmacological inhibition of kynurenine 3-monooxygenase (KMO) increases levels of the neuroprotective metabolite kynurenic acid (KYNA) relative to the neurotoxic metabolite 3-hydroxykynurenine (3-HK) and ameliorates neurodegeneration. We also find that genetic inhibition of tryptophan 2,3-dioxygenase (TDO), the first and rate-limiting step in the pathway, leads to a similar neuroprotective shift toward KYNA synthesis. Importantly, we demonstrate that the feeding of KYNA and 3-HK to HD model flies directly modulates neurodegeneration, underscoring the causative nature of these metabolites. This study provides the first genetic evidence that inhibition of KMO and TDO activity protects against neurodegenerative disease in an animal model, indicating that strategies targetedattwo key points within the KP may have therapeutic relevance in HD, and possibly other neurodegenerative disorders.

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.

The dysfunction of hepatic transcriptional factors in mice with Huntington's Disease

Huntington's Disease (HD) is an autosomal dominant neurodegenerative disease caused by a CAG trinucleotide expansion in the Huntingtin (Htt) gene. The resultant mutant Htt protein (mHtt) forms aggregates in the brain and several peripheral tissues (e.g., the liver), and causes devastating widespread pathology. Since aggregates of mHtt have been found in the liver, defects in liver function might contribute to peripheral abnormalities in HD mice. We previously reported that two crucial transcription factors PPARγ (peroxisome proliferator-activated receptor-γ) and C/EBPα (CCAAT/enhancer-binding protein α) are potential therapeutic targets of HD. We herein demonstrate that the transcript level of PPARγ was markedly downregulated in the livers of a transgenic mouse model of HD (R6/2). Treatment of R6/2 mice with an agonist of PPARγ (thiazolidinedione, TZD) normalized the reduced PPARγ transcript. By reducing Htt aggregates and thereby ameliorating the recruitment of PPARγ into Htt aggregates, TZD treatment also elevated the availability of the PPARγ level and subsequently normalized the expression of its downstream genes [including PGC-1α (PPAR coactivator-1α) and several mitochondrial genes] and C/EBPα in the liver. The aforementioned protective effects appeared to be exerted by a direct activation of the PPARγ agonist (rosiglitazone) because rosiglitazone reduced mHtt aggregates and rescued energy deficiency in a hepatoma cell line (HepG2). These findings show that the impairment of PPARγ contributes to the liver dysfunction observed in HD. Treatment with PPARγ agents (TZD and rosiglitazone) enhanced the function of PPARγ, and might lead to therapeutic benefits.