Huntington disease: natural history, biomarkers and prospects for therapeutics

Huntington disease (HD) can be seen as a model neurodegenerative disorder, in that it is caused by a single genetic mutation and is amenable to predictive genetic testing, with estimation of years to predicted onset, enabling the entire range of disease natural history to be studied. Structural neuroimaging biomarkers show that progressive regional brain atrophy begins many years before the emergence of diagnosable signs and symptoms of HD, and continues steadily during the symptomatic or 'manifest' period. The continued development of functional, neurochemical and other biomarkers raises hopes that these biomarkers might be useful for future trials of disease-modifying therapeutics to delay the onset and slow the progression of HD. Such advances could herald a new era of personalized preventive therapeutics. We describe the natural history of HD, including the timing of emergence of motor, cognitive and emotional impairments, and the techniques that are used to assess these features. Building on this information, we review recent progress in the development of biomarkers for HD, and potential future roles of these biomarkers in clinical trials.

Protocol for an HTA report: Does therapeutic writing help people with long-term conditions? Systematic review, realist synthesis and economic modelling

INTRODUCTION

Long-term medical conditions (LTCs) cause reduced health-related quality of life and considerable health service expenditure. Writing therapy has potential to improve physical and mental health in people with LTCs, but its effectiveness is not established. This project aims to establish the clinical and cost-effectiveness of therapeutic writing in LTCs by systematic review and economic evaluation, and to evaluate context and mechanisms by which it might work, through realist synthesis.

METHODS

Included are any comparative study of therapeutic writing compared with no writing, waiting list, attention control or placebo writing in patients with any diagnosed LTCs that report at least one of the following: relevant clinical outcomes; quality of life; health service use; psychological, behavioural or social functioning; adherence or adverse events. Searches will be conducted in the main medical databases including MEDLINE, EMBASE, PsycINFO, The Cochrane Library and Science Citation Index. For the realist review, further purposive and iterative searches through snowballing techniques will be undertaken. Inclusions, data extraction and quality assessment will be in duplicate with disagreements resolved through discussion. Quality assessment will include using Grading of Recommendations Assessment, Development and Evaluation (GRADE) criteria. Data synthesis will be narrative and tabular with meta-analysis where appropriate. De novo economic modelling will be attempted in one clinical area if sufficient evidence is available and performed according to the National Institute for Health and Care Excellence (NICE) reference case.

Phosphorylation of mutant huntingtin at serine 116 modulates neuronal toxicity

Phosphorylation has been shown to have a significant impact on expanded huntingtin-mediated cellular toxicity. Several phosphorylation sites have been identified on the huntingtin (Htt) protein. To find new potential therapeutic targets for Huntington's Disease (HD), we used mass spectrometry to identify novel phosphorylation sites on N-terminal Htt, expressed in HEK293 cells. Using site-directed mutagenesis we introduced alterations of phosphorylation sites in a N586 Htt construct containing 82 polyglutamine repeats. The effects of these alterations on expanded Htt toxicity were evaluated in primary neurons using a nuclear condensation assay and a direct time-lapse imaging of neuronal death. As a result of these studies, we identified several novel phosphorylation sites, validated several known sites, and discovered one phospho-null alteration, S116A, that had a protective effect against expanded polyglutamine-mediated cellular toxicity. The results suggest that S116 is a potential therapeutic target, and indicate that our screening method is useful for identifying candidate phosphorylation sites.

Transcriptome-wide discovery of microRNA binding sites in human brain

The orchestration of brain function requires complex gene regulatory networks that are modulated, in part, by microRNAs (miRNAs). These noncoding RNAs associate with argonaute (Ago) proteins in order to direct posttranscriptional gene suppression via base pairing with target transcripts. In order to better understand how miRNAs contribute to human-specialized brain processes and neurological phenotypes, identifying their targets is of paramount importance. Here, we address the latter by profiling Ago2:RNA interactions using HITS-CLIP to generate a transcriptome-wide map of miRNA binding sites in human brain. We uncovered ∼ 7,000 stringent Ago2 binding sites that are highly enriched for conserved sequences corresponding to abundant brain miRNAs. This interactome points to functional miRNA:target pairs across >3,000 genes and represents a valuable resource for accelerating our understanding of miRNA functions in brain. We demonstrate the utility of this map for exploring clinically relevant miRNA binding sites that may facilitate the translation of genetic studies of complex neuropsychiatric diseases into therapeutics.

Solvothermal annealing of block copolymer thin films

A two-stage annealing process for block copolymer films was introduced consisting of a solvent vapor exposure followed by a thermal cycle. By heating the film but not the chamber, changes in the ambient vapor pressure of the solvent were avoided. Films of block copolymers and homopolymers showed transient nonmonotonic swelling behavior immediately after solvent exposure that was dependent on how the thin film was cast before the anneal. Thermal cycling of the solvent-swelled block copolymer films during the solvent vapor anneal (SVA) caused the films to deswell in 1-10 s and produced well-ordered microdomains in templated 45.5 and 51.5 kg/mol polystyrene-block-polydimethylsiloxane films annealed in toluene and n-heptane vapors for total process times of 30 s to 5 min.

Gross feature recognition of Anatomical Images based on Atlas grid (GAIA): Incorporating the local discrepancy between an atlas and a target image to capture the features of anatomic brain MRI

We aimed to develop a new method to convert T1-weighted brain MRIs to feature vectors, which could be used for content-based image retrieval (CBIR). To overcome the wide range of anatomical variability in clinical cases and the inconsistency of imaging protocols, we introduced the Gross feature recognition of Anatomical Images based on Atlas grid (GAIA), in which the local intensity alteration, caused by pathological (e.g., ischemia) or physiological (development and aging) intensity changes, as well as by atlas–image misregistration, is used to capture the anatomical features of target images.

As a proof-of-concept, the GAIA was applied for pattern recognition of the neuroanatomical features of multiple stages of Alzheimer's disease, Huntington's disease, spinocerebellar ataxia type 6, and four subtypes of primary progressive aphasia. For each of these diseases, feature vectors based on a training dataset were applied to a test dataset to evaluate the accuracy of pattern recognition. The feature vectors extracted from the training dataset agreed well with the known pathological hallmarks of the selected neurodegenerative diseases. Overall, discriminant scores of the test images accurately categorized these test images to the correct disease categories. Images without typical disease-related anatomical features were misclassified. The proposed method is a promising method for image feature extraction based on disease-related anatomical features, which should enable users to submit a patient image and search past clinical cases with similar anatomical phenotypes.

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A novel method to convert anatomical brain MRIs to feature vectors is introduced.

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Degree of local atlas–image disagreement is used to capture the anatomical features.

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The method was applied for pattern recognition of various neurodegenerative diseases.

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The feature vectors agreed well with the known pathological hallmarks of diseases.

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The method accurately categorized test images to the correct disease categories.

Elevated arteriolar cerebral blood volume in prodromal Huntington's disease

BACKGROUND

Neurovascular alterations have been implicated in the pathophysiology of Huntington's disease (HD). Because arterioles are most responsive to metabolic alterations, arteriolar cerebral blood volume (CBVa) is an important indicator of cerebrovascular regulation. The objective of this pilot study was to investigate potential neurovascular (CBVa ) abnormality in prodromal-HD patients and compare it with the widely used imaging marker: brain atrophy.

METHODS

CBVa and brain volumes were measured with ultra-high-field (7.0-Telsa) magnetic resonance imaging in seven prodromal-HD patients and nine age-matched controls.

RESULTS

Cortical CBVa was elevated significantly in prodromal-HD patients compared with controls (relative difference, 38.5%; effect size, 1.48). Significant correlations were found between CBVa in the frontal cortex and genetic measures. By contrast, no significant brain atrophy was detected in the prodromal-HD patients.

CONCLUSIONS

CBVa may be abnormal in prodromal-HD, even before substantial brain atrophy occurs. Further investigation with a larger cohort and longitudinal follow-up is merited to determine whether CBVa could be used as a potential biomarker for clinical trials.

Prefrontal executive function associated coupling relates to Huntington's disease stage

Huntington's disease (HD) is a neurodegenerative disease caused by cytosine-adenine-guanine (CAG)-repeat expansion in the huntingtin (HTT) gene. Early changes that may precede clinical manifestation of movement disorder include executive dysfunction. The aim of this study was to identify functional network correlates of impaired higher cognitive functioning in relation to HD stage. Blood-oxygenation-level-dependent (BOLD) functional-magnetic resonance imaging (fMRI) and structural-MRI were performed in 53 subjects with the HD-mutation (41 prodromals, 12 early affected) and 52 controls. Disease stage was estimated for each subject with HD-mutation based on age, length of the CAG-repeat expansion mutation and also putaminal atrophy. The Tower of London test was administered with three levels of complexity during fMRI as a challenge of executive function. Functional brain networks of interest were identified based on cortical gray matter voxel-clusters with significantly enhanced task-related functional coupling to the medial prefrontal cortex (MPFC) area. While prodromal HD-subjects showed similar performance levels as controls, multivariate analysis of task-related functional coupling to the MPFC identified reduced connectivity in prodromal and early manifest HD-subjects for a cluster including mainly parts of the left premotor area. Secondary testing indicated a significant moderator effect for task complexity on group differences and on the degree of correlation to measures of HD stage. Our data suggest that impaired premotor-MPFC coupling reflects HD stage related dysfunction of cognitive systems involved in executive function and may be present in prodromal HD-subjects that are still cognitively normal. Additional longitudinal studies may reveal temporal relationships between impaired task-related premotor-MPFC coupling and other brain changes in HD.

Magnetic entropy change plateau in a geometrically frustrated layered system: FeCrAs-like iron-pnictide structure as a magnetocaloric prototype

Monte Carlo modeling suggests that the magnetothermal features of the Fe2P-structured FeCrAs-like compound offer a promising route for the design of magnetocaloric materials. The prototype structure is modeled as antiferromagnetically coupled layered Heisenberg systems mimicking the distorted Kagome/triangular stacked architecture of FeCrAs iron-pnictide. The magnetic entropy change ΔSm(T) presents a plateau-like behavior which can be tailored by tuning either the JCr-Fe/JCr-Cr exchange energy ratio or the magnetic field. The plateau is defined by cooperative spin ordering within a ferrimagnetic region which exists between two critical temperatures separating at the lower bound (Tac) a canted antiferromagnetic phase and at the upper bound (Tdc) the thermally disordered phase. The refrigerant capacity and adiabatic change of temperature are A(H)(Tdc - Tac) and A(H)Tp/Cm respectively, with Tac < Tp < Tdc, A(H) an increasing positive function of the field defining the height of the plateau and Cm the magnetic specific heat, whose critical behavior is related to the T(a,d)(c) values.

Frontal cortical synaptic communication is abnormal in Disc1 genetic mouse models of schizophrenia

Mouse models carrying Disc1 mutations may provide insights into how Disc1 genetic variations contribute to schizophrenia (SZ) susceptibility. Disc1 mutant mice show behavioral and cognitive disturbances reminiscent of SZ. To dissect the synaptic mechanisms underlying these phenotypes, we examined electrophysiological properties of cortical neurons from two mouse models, the first expressing a truncated mouse Disc1 (mDisc1) protein throughout the entire brain, and the second expressing a truncated human Disc1 (hDisc1) protein in forebrain regions. We obtained whole-cell patch clamp recordings to examine how altered expression of Disc1 protein changes excitatory and inhibitory synaptic transmissions onto cortical pyramidal neurons in the medial prefrontal cortex in 4-7 month-old mDisc1 and hDisc1 mice. In both mDisc1 and hDisc1 mice, the frequency of spontaneous EPSCs was greater than in wild-type littermate controls. Male mice from both lines were more affected by the Disc1 mutation than were females, exhibiting increases in the ratio of excitatory to inhibitory events. Changes in spontaneous IPSCs were only observed in the mDisc1 model and were sex-specific, with diminished cortical GABAergic neurotransmission, a well-documented characteristic of SZ, occurring only in male mDisc1 mice. In contrast, female mDisc1 mice showed an increase in the frequency of small-amplitude sIPSCs. These findings indicate that truncations of Disc1 alter glutamatergic and GABAergic neurotransmission both commonly and differently in the models and some of the effects are sex-specific, revealing how altered Disc1 expression may contribute to behavioral disruptions and cognitive deficits of SZ.

Self-assembled incorporation of modulated block copolymer nanostructures in phase-change memory for switching power reduction

Phase change memory (PCM), which exploits the phase change behavior of chalcogenide materials, affords tremendous advantages over conventional solid-state memory due to its nonvolatility, high speed, and scalability. However, high power consumption of PCM poses a critical challenge and has been the most significant obstacle to its widespread commercialization. Here, we present a novel approach based on the self-assembly of a block copolymer (BCP) to form a thin nanostructured SiOx layer that locally blocks the contact between a heater electrode and a phase change material. The writing current is decreased 5-fold (corresponding to a power reduction by 1/20) as the occupying area fraction of SiOx nanostructures is increased from a fill factor of 9.1% to 63.6%. Simulation results theoretically explain the current reduction mechanism by localized switching of BCP-blocked phase change materials.

Neuroprotective effects of PPAR-γ agonist rosiglitazone in N171-82Q mouse model of Huntington's disease

Huntington's disease (HD) is a devastating genetic neurodegenerative disease caused by CAG trinucleotide expansion in the exon-1 region of the huntingtin gene. Currently, no cure is available. It is becoming increasingly apparent that mutant Huntingtin (HTT) impairs metabolic homeostasis and causes transcriptional dysregulation. The peroxisome proliferator-activated receptor gamma (PPAR-γ) is a transcriptional factor that plays a key role in regulating genes involved in energy metabolism; recent studies demonstrated that PPAR-γ activation prevented mitochondrial depolarization in cells expressing mutant HTT and attenuated neurodegeneration in various models of neurodegenerative diseases. PPAR-γ-coactivator 1α (PGC-1 α) transcription activity is also impaired by mutant HTT. We now report that the PPAR-γ agonist, rosiglitazone (RSG), significantly attenuated mutant HTT-induced toxicity in striatal cells and that the protective effect of RSG is mediated by activation of PPAR-γ. Moreover, chronic administration of RSG (10 mg/kg/day, i.p) significantly improved motor function and attenuated hyperglycemia in N171-82Q HD mice. RSG administration rescued brain derived neurotrophic factor(BDNF) deficiency in the cerebral cortex, and prevented loss of orexin-A-immunopositive neurons in the hypothalamus of N171-82Q HD mice. RSG also prevented PGC-1α reduction and increased Sirt6 protein levels in HD mouse brain. Our results suggest that modifying the PPAR-γ pathway plays a beneficial role in rescuing motor function as well as glucose metabolic abnormalities in HD.

Gene expression alterations in bipolar disorder postmortem brains

OBJECTIVES

  Bipolar disorder (BD) is a mental illness of unknown neuropathology and has several genetic associations. Antipsychotics are effective for the treatment of acute mania, psychosis, or mixed states in individuals with BD. We aimed to identify gene transcripts differentially expressed in postmortem brains from antipsychotics-exposed individuals with BD (hereafter the 'exposed' group), non-exposed individuals with BD (hereafter the 'non-exposed' group), and controls.

METHODS

  We quantified the abundance of gene transcripts in postmortem brains from seven exposed individuals, seven non-exposed individuals, and 12 controls with the Affymetrix U133P2 GeneChip microarrays and technologies. We applied a q-value of ≤0.005 to identify statistically significant transcripts with mean abundance differences between the exposed, non-exposed and control groups.

RESULTS

  We identified 2191 unique genes with significantly altered expression levels in non-exposed brains compared to those in the control and exposed groups. The expression levels of these genes were not significantly different between exposed brains and controls, suggesting a normalization effect of antipsychotics on the expression of these genes. Gene ontology (GO) enrichment analysis showed significant (Bonferroni p ≤ 0.05) clustering of subgroups of the 2191 genes under many GO terms; notably, the protein products of genes enriched are critical to the function of synapses, affecting, for example, intracellular trafficking and synaptic vesicle biogenesis, transport, release and recycling, as well as organization and stabilization of the node of Ranvier.

CONCLUSIONS

  These results support a hypothesis of synaptic and intercellular communication impairment in BD. The apparent normalization of expression patterns with exposure to antipsychotic medication may represent a physiological process that relates both to etiology and improvement patterns of the disorder.

Small-molecule TrkB receptor agonists improve motor function and extend survival in a mouse model of Huntington's disease

Huntington's disease (HD) is a fatal neurodegenerative disease characterized by abnormal motor coordination, cognitive decline and psychiatric disorders. This disease is caused by an expanded CAG trinucleotide repeat in the gene encoding the protein huntingtin. Reduced levels of brain-derived neurotrophic factor (BDNF) in the brain, which results from transcriptional inhibition and axonal transport deficits mediated by mutant huntingtin, have been suggested as critical factors underlying selective neurodegeneration in both HD patients and HD mouse models. BDNF activates its high-affinity receptor TrkB and promotes neuronal survival; restoring BDNF signaling is thus of particular therapeutic interest. In the present study, we evaluated the ability of a small-molecule TrkB agonist 7,8-dihydroxyflavone (7,8-DHF) and its synthetic derivative 4'-dimethylamino-7,8- dihydroxyflavone (4'-DMA-7,8-DHF) to protect neurons in the well-characterized N171-82Q HD mouse model. We found that chronic administration of 7, 8-DHF (5 mg/kg) or 4'-DMA-7,8-DHF (1 mg/kg) significantly improved motor deficits, ameliorated brain atrophy and extended survival in these N171-82Q HD mice. Moreover, 4'-DMA-7,8-DHF preserved DARPP32 levels in the striatum and rescued mutant huntingtin-induced impairment of neurogenesis in the N171-82Q HD mice. These data highlight consideration of TrkB as a therapeutic target in HD and suggest that small-molecule TrkB agonists that penetrate the brain have high potential to be further tested in clinical trials of HD.

Diffuse abnormality of low to moderately organized white matter in schizophrenia

Increasing evidence suggests that abnormal white matter is central to the pathophysiology and, potentially, the pathogenesis of schizophrenia (SCZ). The spatial distribution of observed abnormalities and the type of white matter involved remain to be elucidated. Seventeen chronically ill individuals with SCZ and 17 age- and gender-matched controls were studied using a 3T magnetic resonance imaging diffusion tensor imaging protocol designed to examine the abnormalities of white matter by region and by level of architectural infrastructure as assessed by fractional anisotropy (FA) in native space. After assessing whole-brain FA, FA was divided into quartiles, capturing all brain regions with FA values from 0 to 0.25, 0.25 to 0.5, 0.5 to 0.75, and 0.75 to 1.0. Mean whole-brain FA was 4.6% smaller in the SCZ group than in healthy controls. This difference was largely accounted for by FA values from the second quartile (between 0.25 and 0.5). Second quartile FA was decreased in all 130 brain regions of the template in the SCZ group, with the difference reaching statistical significance in 41 regions. Correspondingly, the amount of brain tissue with an FA of ∼0.4 was significantly reduced in the SCZ group, while the amount of brain tissue falling in the lowest quartile of FA was increased. These findings strongly imply a diffuse loss of white matter integrity in SCZ. Our finding that the loss of integrity disproportionately involves white matter of low to moderate organization suggests an approach to the specificity of white matter abnormalities in SCZ based on microstructure rather than spatial distribution.

Magnetostriction in epitaxial SrTi(1-x)Fe(x)O(3-δ) perovskite films with x = 0.13 and 0.35

The crystal structure, magnetic anisotropy and magnetoelasticity of epitaxial SrTi(0.87)Fe(0.13)O(3-δ) (STF13) and SrTi(0.65)Fe(0.35)O(3-δ) (STF35) films grown on (001), (011), and (111) oriented SrTiO(3) substrates were investigated. The films grew with compressive in-plane strain and underwent tetragonal, monoclinic, and rhombohedral distortions on the (001), (011), and (111) substrates, respectively. All samples showed room temperature magnetic hysteresis loops with strong out-of-plane anisotropy. The resulting magnetoelastic anisotropy was an order of magnitude greater than the magnetocrystalline and shape anisotropies. Magnetoelastic coefficients of B(1) =- 6.7 × 10(6) and B(2) =- 28 to -26 × 10(6) erg cm(-3) for STF13 and B(1) =- 2.0 × 10(6) and B(2) =- 5.4 to -3.9 × 10(6) erg cm(-3) for STF35 were determined from the magnetic anisotropy and lattice strain, corresponding to magnetostriction constants of λ(100) = 2.09 × 10(-6) and λ(111) = 7.68 × 10(-6) for STF13, and λ(100) = 0.62 × 10(-6) and λ(111) = 1.07 × 10(-6) for STF35.

Regionally selective atrophy of subcortical structures in prodromal HD as revealed by statistical shape analysis

Huntington disease (HD) is a neurodegenerative disorder that involves preferential atrophy in the striatal complex and related subcortical nuclei. In this article, which is based on a dataset extracted from the PREDICT-HD study, we use statistical shape analysis with deformation markers obtained through "Large Deformation Diffeomorphic Metric Mapping" of cortical surfaces to highlight specific atrophy patterns in the caudate, putamen, and globus pallidus, at different prodromal stages of the disease. On the basis of the relation to cortico-basal ganglia circuitry, we propose that statistical shape analysis, along with other structural and functional imaging studies, may help expand our understanding of the brain circuitry affected and other aspects of the neurobiology of HD, and also guide the most effective strategies for intervention.

Magneto-optical properties of cerium substituted yttrium iron garnet films with reduced thermal budget for monolithic photonic integrated circuits

Thin films of polycrystalline cerium substituted yttrium iron garnet (CeYIG) were grown on an yttrium iron garnet (YIG) seed layer on Si and Si-on-insulator substrates by pulsed laser deposition, and their optical and magneto-optical properties in the near-IR region were measured. A YIG seed layer of ~30 nm thick processed by rapid thermal anneal at 800°C provided a virtual substrate to promote crystallization of the CeYIG. The effect of the thermal budget of the YIG/CeYIG growth process on the film structure, magnetic and magnetooptical properties was determined.

Seizures in juvenile Huntington's disease: frequency and characterization in a multicenter cohort

Little is known about the epilepsy that often occurs in the juvenile form of Huntington's disease (HD), but is absent from the adult-onset form. The primary aim of this study was to characterize the seizures in juvenile HD (JHD) subjects with regard to frequency, semiology, defining EEG characteristics, and response to antiepileptic agents. A multicenter, retrospective cohort was identified by database query and/or chart review. Data on age of HD onset, primary HD manifestations, number of CAG repeats, the presence or absence of seizures, seizure type(s), antiepileptic drugs used, subjects' response to antiepileptic drugs (AEDs), and EEG results were assembled, where available. Ninety subjects with genetically confirmed JHD were included. Seizures were present in 38% of subjects and were more likely to occur with younger ages of HD onset. Generalized tonic-clonic seizures were the most common seizure type, followed by tonic, myoclonic, and staring spells. Multiple seizure types commonly occurred within the same individual. Data on EEG findings and AED usage are presented. Seizure risk in JHD increases with younger age of HD onset. Our ability to draw firm conclusions about defining EEG characteristics and response to AEDs was limited by the retrospective nature of the study. Future prospective studies are required.

Striatal neuronal loss correlates with clinical motor impairment in Huntington's disease

Huntington's disease (HD) is characterized clinically by chorea, motor impairment, psychiatric manifestations, and dementia. Atrophy of the striatum is the neuropathological hallmark of HD, and previous studies have suggested that striatal atrophy correlates more closely with motor impairment than with chorea. Motor impairment, as measured by motor impairment score, correlates with functional disability in HD patients, but chorea does not. In this study, we investigated the relation between neuronal loss and these motor features. We conducted neuropathological and stereologic assessments of neurons in putamen and subthalamic nuclei in HD patients and age-matched controls. In putamen, we estimated the total number and volume of medium spiny neurons labeled with dopamine- and cAMP-regulated phosphoprotein 32 kDa (DARPP-32). In subthalamic nuclei, we estimated the total number of neurons on hematoxylin & eosin/luxol fast blue stains. In putamen of HD, immunohistochemistry showed DARPP-32 neuronal atrophy with extensive disruption of neurites and neuropil; stereologic studies found significant decreases in both the number and size of DARPP-32 neurons; we also detected a significant reduction of overall putamen volume in HD patients, compared to controls. In subthalamic nuclei, there was a mild, but significant, neuronal loss in the HD group. The loss of neurons in putamen and subthalamic nuclei as well as putaminal atrophy were significantly correlated with severity of motor impairment, but not with chorea. Our findings suggest that neuronal loss and atrophy in striatum and neuronal loss in subthalamic nuclei contribute specifically to the motor impairment of HD, but not to chorea.

TAA repeat variation in the GRIK2 gene does not influence age at onset in Huntington's disease

Huntington's disease is a neurodegenerative disorder caused by an expanded CAG trinucleotide repeat whose length is the major determinant of age at onset but remaining variation appears to be due in part to the effect of genetic modifiers. GRIK2, which encodes GluR6, a mediator of excitatory neurotransmission in the brain, has been suggested in several studies to be a modifier gene based upon a 3' untranslated region TAA trinucleotide repeat polymorphism. Prior to investing in detailed studies of the functional impact of this polymorphism, we sought to confirm its effect on age at onset in a much larger dataset than in previous investigations. We genotyped the HD CAG repeat and the GRIK2 TAA repeat in DNA samples from 2,911 Huntington's disease subjects with known age at onset, and tested for a potential modifier effect of GRIK2 using a variety of statistical approaches. Unlike previous reports, we detected no evidence of an influence of the GRIK2 TAA repeat polymorphism on age at motor onset. Similarly, the GRIK2 polymorphism did not show significant modifier effect on psychiatric and cognitive age at onset in HD. Comprehensive analytical methods applied to a much larger sample than in previous studies do not support a role for GRIK2 as a genetic modifier of age at onset of clinical symptoms in Huntington's disease.

Depressive symptoms in prodromal Huntington's Disease correlate with Stroop-interference related functional connectivity in the ventromedial prefrontal cortex

Huntington's Disease (HD) is a neurodegenerative disorder caused by a cytosine-adenine-guanine (CAG) triplet repeat-expansion in the Huntingtin (HTT) gene. Diagnosis of HD is classically defined by the presence of motor symptoms; however, cognitive and depressive symptoms frequently precede motor manifestations, and may occur early in the prodromal phase. There are sparse data so far on functional brain correlates of depressive symptoms in prodromal HD. A Stroop color-naming test was administered to 32 subjects in the prodromal phase of HD and 52 expansion-negative controls while performing functional magnetic resonance imaging at 3Tesla. Networks of functional connectivity were identified using group independent component analysis, followed by an analysis of functional network interactions. A contrast of temporal regression-based beta-weights was calculated as a reflection of Stroop-interference related activity and correlated with Center for Epidemiologic Studies Depression (CES-D) scores. For secondary analysis, patients were stratified into two subgroups by median split of CAG repeat-length. Stroop performance was independent of HTT mutation-carrier status and CES-D score. Stroop-interference-related activity of the ventromedial prefrontal cortex-node of the default-mode network, calculated by temporal-regression beta-weights, was more highly correlated with depressive symptoms in subjects in the prodromal phase of HD than in controls, differing significantly. The strength of this correlation and its difference from controls increased when a subgroup of patients with longer CAG repeat lengths was analyzed. These findings suggest that depressive symptoms in prodromal HD subjects may reflect altered functional brain network activity in the context of early HD-related brain alterations.

Population stratification may bias analysis of PGC-1α as a modifier of age at Huntington disease motor onset

Huntington’s disease (HD) is an inherited neurodegenerative disorder characterized by motor, cognitive and behavioral disturbances, caused by the expansion of a CAG trinucleotide repeat in the HD gene. The CAG allele size is the major determinant of age at onset (AO) of motor symptoms, although the remaining variance in AO is highly heritable. The rs7665116 SNP in PPARGC1A, encoding the mitochondrial regulator PGC-1α, has been reported to be a significant modifier of AO in three European HD cohorts, perhaps due to affected cases from Italy. We attempted to replicate these findings in a large collection of (1,727) HD patient DNA samples of European origin. In the entire cohort, rs7665116 showed a significant effect in the dominant model (p value = 0.008) and the additive model (p value = 0.009). However, when examined by origin, cases of Southern European origin had an increased rs7665116 minor allele frequency (MAF), consistent with this being an ancestry-tagging SNP. The Southern European cases, despite similar mean CAG allele size, had a significantly older mean AO (p < 0.001), suggesting population-dependent phenotype stratification. When the generalized estimating equations models were adjusted for ancestry, the effect of the rs7665116 genotype on AO decreased dramatically. Our results do not support rs7665116 as a modifier of AO of motor symptoms, as we found evidence for a dramatic effect of phenotypic (AO) and genotypic (MAF) stratification among European cohorts that was not considered in previously reported association studies. A significantly older AO in Southern Europe may reflect population differences in genetic or environmental factors that warrant further investigation.

Brain metabolite alterations and cognitive dysfunction in early Huntington's disease

Huntington's disease (HD) is a neurodegenerative disorder characterized by early cognitive decline that progresses at later stages to dementia and severe movement disorder. HD is caused by a cytosine-adenine-guanine triplet-repeat expansion mutation in the Huntingtin gene, allowing early diagnosis by genetic testing. This study aimed to identify the relationship of N-acetylaspartate and other brain metabolites to cognitive function in HD-mutation carriers by using high-field-strength magnetic resonance spectroscopy (MRS) at 7 Tesla. Twelve individuals with the HD mutation in premanifest or early-stage disease versus 12 healthy controls underwent (1)H magnetic resonance spectroscopy (7.2 mL voxel in the posterior cingulate cortex) at 7 Tesla, and also T1-weighted structural magnetic resonance imaging. All participants received standardized tests of cognitive functioning including the Montreal Cognitive Assessment and standardized quantified neurological examination within an hour before scanning. Individuals with the HD mutation had significantly lower posterior cingulate cortex N-acetylaspartate (-9.6%, P = .02) and glutamate (-10.1%, P = .02) levels than did controls. In contrast, in this small group, measures of brain morphology including striatal and ventricle volumes did not differ significantly. Linear regression with Montreal Cognitive Assessment scores revealed significant correlations with N-acetylaspartate (r(2) = 0.50, P = .01) and glutamate (NAA) (r(2) = 0.64, P = .002) in HD subjects. Our data suggest a relationship between reduced N-acetylaspartate and glutamate levels in the posterior cingulate cortex with cognitive decline in the early stages of HD. N-acetylaspartate and glutamate magnetic resonance spectroscopy signals of the posterior cingulate cortex region may serve as potential biomarkers of disease progression or treatment outcome in HD and other neurodegenerative disorders with early cognitive dysfunction, when structural brain changes are still minor.

trans-(-)-ε-Viniferin increases mitochondrial sirtuin 3 (SIRT3), activates AMP-activated protein kinase (AMPK), and protects cells in models of Huntington Disease

Huntington disease (HD) is an inherited neurodegenerative disorder caused by an abnormal polyglutamine expansion in the protein Huntingtin (Htt). Currently, no cure is available for HD. The mechanisms by which mutant Htt causes neuronal dysfunction and degeneration remain to be fully elucidated. Nevertheless, mitochondrial dysfunction has been suggested as a key event mediating mutant Htt-induced neurotoxicity because neurons are energy-demanding and particularly susceptible to energy deficits and oxidative stress. SIRT3, a member of sirtuin family, is localized to mitochondria and has been implicated in energy metabolism. Notably, we found that cells expressing mutant Htt displayed reduced SIRT3 levels. trans-(-)-ε-Viniferin (viniferin), a natural product among our 22 collected naturally occurring and semisynthetic stilbenic compounds, significantly attenuated mutant Htt-induced depletion of SIRT3 and protected cells from mutant Htt. We demonstrate that viniferin decreases levels of reactive oxygen species and prevents loss of mitochondrial membrane potential in cells expressing mutant Htt. Expression of mutant Htt results in decreased deacetylase activity of SIRT3 and further leads to reduction in cellular NAD(+) levels and mitochondrial biogenesis in cells. Viniferin activates AMP-activated kinase and enhances mitochondrial biogenesis. Knockdown of SIRT3 significantly inhibited viniferin-mediated AMP-activated kinase activation and diminished the neuroprotective effects of viniferin, suggesting that SIRT3 mediates the neuroprotection of viniferin. In conclusion, we establish a novel role for mitochondrial SIRT3 in HD pathogenesis and discovered a natural product that has potent neuroprotection in HD models. Our results suggest that increasing mitochondrial SIRT3 might be considered as a new therapeutic approach to counteract HD, as well as other neurodegenerative diseases with similar mechanisms.

Huntingtin protein interactions altered by polyglutamine expansion as determined by quantitative proteomic analysis

Huntington disease (HD) is a neurodegenerative disorder caused by an expansion of a polyglutamine repeat within the HD gene product, huntingtin. Huntingtin, a large (347 kDa) protein containing multiple HEAT repeats, acts as a scaffold for protein-protein interactions. Huntingtin-induced toxicity is believed to be mediated by a conformational change in expanded huntingtin, leading to protein misfolding and aggregation, aberrant protein interactions and neuronal cell death. While many non-systematic studies of huntingtin interactions have been reported, they were not designed to identify and quantify the changes in the huntingtin interactome induced by polyglutamine expansion. We used tandem affinity purification and quantitative proteomics to compare and quantify interactions of normal or expanded huntingtin isolated from a striatal cell line. We found that proteins preferentially interacting with expanded huntingtin are enriched for intrinsically disordered proteins, consistent with previously suggested roles of such proteins in neurodegenerative disorders. Our functional analysis indicates that proteins related to energy production, protein trafficking, RNA post-transcriptional modifications and cell death were significantly enriched among preferential interactors of expanded huntingtin. Expanded huntingtin interacted with many mitochondrial proteins, including AIFM1, consistent with a role for mitochondrial dysfunction in HD. Furthermore, expanded huntingtin interacted with the stress granule-associated proteins Caprin-1 and G3BP and redistributed to RNA stress granules under ER-stress conditions. These data demonstrate that a number of key cellular functions and networks may be disrupted by abnormal interactions of expanded huntingtin and highlight proteins and pathways that may be involved in HD cellular pathogenesis and that may serve as therapeutic targets.

Striatal volume contributes to the prediction of onset of Huntington disease in incident cases

BACKGROUND

Previous neuroimaging research indicates that brain atrophy in Huntington disease (HD) begins many years before movement abnormalities become severe enough to warrant diagnosis. Most clinical trials being planned for individuals in the prediagnostic stage of HD propose to use delay of disease onset as the primary outcome measure. Although formulas have been developed based on age and CAG repeat length, to predict when HD motor onset will occur, it would be useful to have additional measures that can improve the accuracy of prediction of disease onset.

METHODS

The current study examined magnetic resonance imaging (MRI) measures of striatum and white matter volume in 85 individuals prospectively followed from pre-HD stage through diagnosable motor onset (incident cases) and 85 individuals individually matched with incident cases on CAG repeat length, sex, and age, who were not diagnosed with HD during the course of the study.

RESULTS

Volumes of striatum and white matter were significantly smaller in individuals who would be diagnosed 1 to 4 years following the initial MRI scan, compared with those who would remain in the pre-HD stage. Putamen volume was the measure that best distinguished between the two groups.

CONCLUSIONS

Results suggest that MRI volumetric measures may be helpful in selecting individuals for future clinical trials in pre-HD where HD motor onset is the primary outcome measure. In planning for multisite clinical trials in pre-HD, investigators may also want to consider using more objective measures, such as MRI volumes, in addition to onset of diagnosable movement disorder, as major outcome measures.

Loss of junctophilin-3 contributes to Huntington disease-like 2 pathogenesis

OBJECTIVE

Huntington disease-like 2 (HDL2) is a progressive, late onset autosomal dominant neurodegenerative disorder, with remarkable similarities to Huntington disease (HD). HDL2 is caused by a CTG/CAG repeat expansion. In the CTG orientation, the repeat is located within the alternatively spliced exon 2A of junctophilin-3 (JPH3), potentially encoding polyleucine and polyalanine, whereas on the strand antisense to JPH3, the repeat is in frame to encode polyglutamine. The JPH3 protein product serves to stabilize junctional membrane complexes and regulate neuronal calcium flux. We have previously demonstrated the potential pathogenic properties of JPH3 transcripts containing expanded CUG repeats. The aim of this study was to test the possibility that loss of JPH3 expression or expanded amino acid tracts also contribute to HDL2 pathogenesis.

METHODS

Transcripts from the HDL2 locus, and their protein products, were examined in HDL2, HD, and control frontal cortex. The effect of loss of Jph3 was examined in mice with partial or complete loss of Jph3.

RESULTS

Bidirectional transcription occurs at the HDL2 locus, although expression of antisense transcripts with expanded CAG repeats is limited. Protein products with expanded amino acid tracts were not detected in HDL2 brain. However, JPH3 transcripts and full-length JPH3 protein are decreased in HDL2 brain, and Jph3 hemizygous and null mice exhibit abnormal motor function.

INTERPRETATION

Our results suggest that the pathogenic mechanism of HDL2 is multifactorial, involving both a toxic gain of function of JPH3 RNA and a toxic loss of JPH3 expression.

Identification of novel potentially toxic oligomers formed in vitro from mammalian-derived expanded huntingtin exon-1 protein

Huntington disease is a genetic neurodegenerative disorder that arises from an expanded polyglutamine region in the N terminus of the HD gene product, huntingtin. Protein inclusions comprised of N-terminal fragments of mutant huntingtin are a characteristic feature of disease, though are likely to play a protective role rather than a causative one in neurodegeneration. Soluble oligomeric assemblies of huntingtin formed early in the aggregation process are candidate toxic species in HD. In the present study, we established an in vitro system to generate recombinant huntingtin in mammalian cells. Using both denaturing and native gel analysis, we have identified novel oligomeric forms of mammalian-derived expanded huntingtin exon-1 N-terminal fragment. These species are transient and were not previously detected using bacterially expressed exon-1 protein. Importantly, these species are recognized by 3B5H10, an antibody that recognizes a two-stranded hairpin conformation of expanded polyglutamine believed to be associated with a toxic form of huntingtin. Interestingly, comparable oligomeric species were not observed for expanded huntingtin shortstop, a 117-amino acid fragment of huntingtin shown previously in mammalian cell lines and transgenic mice, and here in primary cortical neurons, to be non-toxic. Further, we demonstrate that expanded huntingtin shortstop has a reduced ability to form amyloid-like fibrils characteristic of the aggregation pathway for toxic expanded polyglutamine proteins. Taken together, these data provide a possible candidate toxic species in HD. In addition, these studies demonstrate the fundamental differences in early aggregation events between mutant huntingtin exon-1 and shortstop proteins that may underlie the differences in toxicity.

Impaired cortico-striatal functional connectivity in prodromal Huntington's Disease

Huntington's Disease (HD) is a neurodegenerative disease caused by a CAG triplet-repeat expansion-mutation in the Huntingtin gene. Subjects at risk for HD can be identified by genetic testing in the prodromal phase. Structural changes of basal-ganglia nuclei such as the caudate nucleus are well-replicated findings observable early in prodromal-HD subjects and may be preceded by distinct functional alterations of cortico-striatal circuits. This study aims to assess functional integrity of the motor system as a cortico-striatal circuit with particular clinical relevance in HD. Ten subjects in the prodromal phase of HD and ten matched controls were administered blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) at rest (3T). Functional connectivity was measured as synchrony of BOLD activity between the caudate nucleus and thirteen cortical brain regions (seeds). Basal-ganglia volumes were assessed as established markers of disease progression in prodromal-HD. Linear regression analysis was performed to test for a relationship between structural changes and group differences in functional connectivity. Prodromal-HD subjects showed reduced BOLD synchrony between two seeds in the premotor cortex (BA6) and the caudate nucleus. While similar effect sizes could be observed for reduced basal-ganglia volumes and differences in functional connectivity, coefficients of determination indicate a moderate relationship between functional connectivity and striatal atrophy. Our data show reduced cortico-striatal functional connectivity at rest in prodromal-HD and suggest a relation to early structural brain changes. Additional longitudinal studies are necessary to elucidate the temporal relationship between functional alterations and earliest structural brain changes in prodromal-HD.

Spatiotemporal mapping of brain atrophy in mouse models of Huntington's disease using longitudinal in vivo magnetic resonance imaging

Mouse models of Huntington's disease (HD) that recapitulate some of the phenotypic features of human HD, play a crucial role in investigating disease mechanisms and testing potential therapeutic approaches. Longitudinal studies of these models can yield valuable insights into the temporal course of disease progression and the effect of drug treatments on the progressive phenotypes. Atrophy of the brain, particularly the striatum, is a characteristic phenotype of human HD, is known to begin long before the onset of motor symptoms, and correlates strongly with clinical features. Elucidating the spatial and temporal patterns of atrophy in HD mouse models is important to characterize the phenotypes of these models, as well as evaluate the effects of neuroprotective treatments at specific time frames during disease progression. In this study, three dimensional in vivo magnetic resonance imaging (MRI) and automated longitudinal deformation-based morphological analysis was used to elucidate the spatial and temporal patterns of brain atrophy in the R6/2 and N171-82Q mouse models of HD. Using an established MRI-based brain atlas and mixed-effects modeling of deformation-based metrics, we report the rates of progression and region-specificity of brain atrophy in the two models. Further, the longitudinal analysis approach was used to evaluate the effects of sertraline and coenzyme Q(10) (CoQ(10)) treatments on progressive atrophy in the N171-82Q model. Sertraline treatment resulted in significant slowing of atrophy, especially in the striatum and frontal cortex regions, while no significant effects of CoQ(10) treatment were observed. Progressive cortical and striatal atrophy in the N171-82Q mice showed significant positive correlations with measured functional deficits. The findings of this report can be used for future testing and comparison of potential therapeutics in mouse models of HD.

CAG repeat expansion in Huntington disease determines age at onset in a fully dominant fashion

OBJECTIVE

Age at onset of diagnostic motor manifestations in Huntington disease (HD) is strongly correlated with an expanded CAG trinucleotide repeat. The length of the normal CAG repeat allele has been reported also to influence age at onset, in interaction with the expanded allele. Due to profound implications for disease mechanism and modification, we tested whether the normal allele, interaction between the expanded and normal alleles, or presence of a second expanded allele affects age at onset of HD motor signs.

METHODS

We modeled natural log-transformed age at onset as a function of CAG repeat lengths of expanded and normal alleles and their interaction by linear regression.

RESULTS

An apparently significant effect of interaction on age at motor onset among 4,068 subjects was dependent on a single outlier data point. A rigorous statistical analysis with a well-behaved dataset that conformed to the fundamental assumptions of linear regression (e.g., constant variance and normally distributed error) revealed significance only for the expanded CAG repeat, with no effect of the normal CAG repeat. Ten subjects with 2 expanded alleles showed an age at motor onset consistent with the length of the larger expanded allele.

CONCLUSIONS

Normal allele CAG length, interaction between expanded and normal alleles, and presence of a second expanded allele do not influence age at onset of motor manifestations, indicating that the rate of HD pathogenesis leading to motor diagnosis is determined by a completely dominant action of the longest expanded allele and as yet unidentified genetic or environmental factors.

The role of deprivation, abuse, and trauma in pediatric catatonia without a clear medical cause

OBJECTIVE

Catatonia is considered a unique syndrome of motor signs, at times life-threatening when aggravated by autonomic dysfunction and fever, but eminently treatable with specific medical treatments, if recognized early. Catatonia commonly occurs in children and adolescents with a wide range of associated disorders. The role of deprivation, abuse, or trauma in the development of pediatric catatonia is examined.

METHOD

Reports considering deprivation, abuse, or trauma as precipitants of catatonia in pediatric cases are culled from the classic writings on catatonia and from a selective review of modern contributions.

RESULTS

Kahlbaum gave trauma a central role in catatonia in many young adult cases. Kanner described children with psychogenic catalepsy. Anaclitic depression, a condition found by Spitz in deprived institutionalized children, strongly resembles stuporous catatonia. Leonhard considered lack of communication with the mother or substitute mother as an important risk factor for childhood catatonia. Children including those with autism who experience emotional and physical trauma sometimes develop catatonia. The clinical descriptions of children with classic catatonic syndromes and those of contemporary refugee children with a syndrome labeled Pervasive Refusal Syndrome are similar.

CONCLUSION

The literature supports the view that deprivation, abuse, and trauma can precipitate catatonia in children and adolescents.

Age, CAG repeat length, and clinical progression in Huntington's disease

The objective of this study was to further explore the effect of CAG repeat length on the rate of clinical progression in patients with Huntington's disease. The dataset included records for 569 subjects followed prospectively at the Baltimore Huntington's Disease Center. Participants were seen for a mean of 7.1 visits, with a mean follow-up of 8.2 years. Subjects were evaluated using the Quantified Neurologic Examination and its Motor Impairment subscale, the Mini-Mental State Examination, and the Huntington's disease Activities of Daily Living Scale. By itself, CAG repeat length showed a statistically significant but small effect on the progression of all clinical measures. Contrary to our previous expectations, controlling for age of onset increased the correlation between CAG repeat length and progression of all variables by 69% to 159%. Graphical models further supported the idea that individuals with smaller triplet expansions experience a more gradual decline. CAG repeat length becomes an important determinant of clinical prognosis when accounting for age of onset. This suggests that the aging process itself influences clinical outcomes in Huntington's disease. Inconsistent results in prior studies examining CAG repeat length and progression may indeed reflect a lack of age adjustment.

A novel obesity model: synphilin-1-induced hyperphagia and obesity in mice

Aims

The pathogenesis of obesity remains incompletely understood and the exploration of the role of novel proteins in obesity may provide important insights into its causes and treatments. Here we report a previously unidentified role for synphilin-1 in the controls of food intake and body weight. Synphilin-1, a cytoplasmic protein, was initially identified as an interaction partner of alpha-synuclein, and has implications in Parkinson's disease pathogenesis related to protein aggregation.

Subjects and methods

To study the in vivo role of synphilin-1, we characterized a human synphilin-1 transgenic mouse (SP1) by assessing synphilin-1 expression, plasma parameters, food intake and spontaneous activity to determine the major behavioral changes and their consequences in the development of the obesity phenotype.

Results

Expression of human synphilin-1 in brain neurons in SP1 mice resulted in increased food intake, body weight and body fat. SP1 mice also displayed hyperinsulinemia, hyperleptinemia and impaired glucose tolerance. Pair-feeding SP1 mice to amounts consumed by non-transgenic mice prevented the increased body weight, adiposity, hyperinsulinemia and hyperleptinemia demonstrating that these were all the consequences of increased food intake. Transgenic expression of synphilin-1 was enriched in hypothalamic nuclei involved in feeding control, and fasting induced elevated endogenous synphilin-1 levels at these sites, suggesting that synphilin-1 is an important player in the hypothalamic energy balance regulatory system.

Conclusion

These studies identify a novel function of synphilin-1 in controlling food intake and body weight, and may provide a unique obesity model for future studies of obesity pathogenesis and therapeutics.

Highly tunable self-assembled nanostructures from a poly(2-vinylpyridine-b-dimethylsiloxane) block copolymer

An extraordinarily large degree of tunability in geometry and dimension is demonstrated in films of a self-assembled block copolymer. A poly(2-vinylpyridine-b-dimethylsiloxane) block copolymer with highly incompatible blocks was spun-cast on patterned substrates and treated with various solvent vapors. The degree of selective swelling in the poly(2-vinylpyridine) matrix block could be controlled over an extensive range, leading to the formation of various microdomain morphologies such as spheres, cylinders, hexagonally perforated lamellae, and lamellae from the same block copolymer. The systematic control of swelling ratio and the choice of solvent vapors offer the unusual ability to control the width of very well-ordered linear features within a range between 6 and 31 nm. This methodology is particularly useful for nanolithography based on directed self-assembly in that a single block copolymer film can form microdomains with a broad range of geometries and sizes without the need to change molecular weight or volume fraction.

Association between Age and Striatal Volume Stratified by CAG Repeat Length in Prodromal Huntington Disease

Background: Longer CAG repeat length is associated with faster clinical progression in Huntington disease, although the effect of higher repeat length on brain atrophy is not well documented. Method: Striatal volumes were obtained from MRI scans of 720 individuals with prodromal Huntington disease. Striatal volume was plotted against age separately for groups with CAG repeat lengths of 38–39, 40, 41, 42, 43, 44, 45, 46, and 47–54. Results: Slopes representing the association between age and striatal volume were significantly steeper as CAG repeat length increased. Discussion: Although cross-sectional, these data suggest that striatal atrophy, like clinical progression, may occur faster with higher CAG repeat lengths.

Dictyostelium huntingtin controls chemotaxis and cytokinesis through the regulation of myosin II phosphorylation

This work shows that huntingtin protein (Htt) regulates the phosphorylation status of myosin II during chemotaxis and cytokinesis through protein phosphatase 2A (PP2A). Our findings provide novel insights into the physiological function of Htt and the pathogenesis of Huntington's disease.

Abnormalities in the huntingtin protein (Htt) are associated with Huntington's disease. Despite its importance, the function of Htt is largely unknown. We show that Htt is required for normal chemotaxis and cytokinesis in Dictyostelium discoideum. Cells lacking Htt showed slower migration toward the chemoattractant cAMP and contained lower levels of cortical myosin II, which is likely due to defects in dephosphorylation of myosin II mediated by protein phosphatase 2A (PP2A). htt⁻ cells also failed to maintain myosin II in the cortex of the cleavage furrow, generating unseparated daughter cells connected through a thin cytoplasmic bridge. Furthermore, similar to Dictyostelium htt⁻ cells, siRNA-mediated knockdown of human HTT also decreased the PP2A activity in HeLa cells. Our data indicate that Htt regulates the phosphorylation status of myosin II during chemotaxis and cytokinesis through PP2A.

Longitudinal change in regional brain volumes in prodromal Huntington disease

OBJECTIVE

As therapeutics are being developed to target the underlying neuropathology of Huntington disease, interest is increasing in methodologies for conducting clinical trials in the prodromal phase. This study was designed to examine the potential utility of structural MRI measures as outcome measures for such trials.

METHODS

Data are presented from 211 prodromal individuals and 60 controls, scanned both at baseline and at the 2-year follow-up. Prodromal participants were divided into groups based on proximity to estimated onset of diagnosable clinical disease: far (>15 years from estimated onset), mid (9-15 years) and near (<9 years). Volumetric measurements of caudate, putamen, total striatum, globus pallidus, thalamus, total grey and white matter and cerebrospinal fluid were performed.

RESULTS

All prodromal groups showed a faster rate of atrophy than controls in striatum, total brain and cerebral white matter (especially in the frontal lobe). Neither prodromal participants nor controls showed any significant longitudinal change in cortex (either total cortical grey or within individual lobes). When normal age-related atrophy (ie, change observed in the control group) was taken into account, there was more statistically significant disease-related atrophy in white matter than in striatum.

CONCLUSION

Measures of volume change in striatum and white-matter volume, particularly in the frontal lobe, may serve as excellent outcome measures for future clinical trials in prodromal Huntington disease. Clinical trials using white matter or striatal volume change as an outcome measure will be most efficient if the sample is restricted to individuals who are within 15 years of estimated onset of diagnosable disease.

A compact beta model of huntingtin toxicity

Huntington disease results from an expanded polyglutamine region in the N terminus of the huntingtin protein. HD pathology is characterized by neuronal degeneration and protein inclusions containing N-terminal fragments of mutant huntingtin. Structural information is minimal, though it is believed that mutant huntingtin polyglutamine adopts β structure upon conversion to a toxic form. To this end, we designed mammalian cell expression constructs encoding compact β variants of Htt exon 1 N-terminal fragment and tested their ability to aggregate and induce toxicity in cultured neuronal cells. In parallel, we performed molecular dynamics simulations, which indicate that constructs with expanded polyglutamine β-strands are stabilized by main-chain hydrogen bonding. Finally, we found a correlation between the reactivity to 3B5H10, an expanded polyglutamine antibody that recognizes a compact β rich hairpin structure, and the ability to induce cell toxicity. These data are consistent with an important role for a compact β structure in mutant huntingtin-induced cell toxicity.

Structural MRI detects progressive regional brain atrophy and neuroprotective effects in N171-82Q Huntington's disease mouse model

Huntington's disease (HD) displays progressive striatal atrophy that occurs long before the onset of clinical motor symptoms. As there is no treatment for the disease once overt symptoms appear, it has been suggested that neuroprotective therapy given during this presymptomatic period might slow progression of the disease. This requires biomarkers that can reliably detect early changes and are sensitive to treatment response. In mouse models of HD, structural MRI measures have been shown to detect disease onset. To determine whether such measures could also be suitable biomarkers for following responses to treatment, we used T2-weighted MR imaging combined with automated morphological analyses and characterized changes in regional brain volumes longitudinally in the N171-82Q HD mouse model in a preclinical trial. We report here that N171-82Q HD mice exhibit adult-onset and progressive brain atrophy in the striatum and neocortex as well as in whole brain; the progressive atrophy in striatum and neocortex is positively correlated with motor deficits. Most notably, MRI also detected neuroprotective effects of sertraline treatment, a neuroprotective agent confirmed in our previous studies. Our present studies provide the first evidence that longitudinal structural MRI measures can detect the therapeutic effect in HD mice, suggesting that such measures in brain could be valuable biomarkers in HD clinical trials.

Cysteine proteases bleomycin hydrolase and cathepsin Z mediate N-terminal proteolysis and toxicity of mutant huntingtin

N-terminal proteolysis of huntingtin is thought to be an important mediator of HD pathogenesis. The formation of short N-terminal fragments of huntingtin (cp-1/cp-2, cp-A/cp-B) has been demonstrated in cells and in vivo. We previously mapped the cp-2 cleavage site by mass spectrometry to position Arg167 of huntingtin. The proteolytic enzymes generating short N-terminal fragments of huntingtin remain unknown. To search for such proteases, we conducted a genome-wide screen using an RNA-silencing approach and an assay for huntingtin proteolysis based on the detection of cp-1 and cp-2 fragments by Western blotting. The primary screen was carried out in HEK293 cells, and the secondary screen was carried out in neuronal HT22 cells, transfected in both cases with a construct encoding the N-terminal 511 amino acids of mutant huntingtin. For additional validation of the hits, we employed a complementary assay for proteolysis of huntingtin involving overexpression of individual proteases with huntingtin in two cell lines. The screen identified 11 enzymes, with two major candidates to carry out the cp-2 cleavage, bleomycin hydrolase (BLMH) and cathepsin Z, which are both cysteine proteases of a papain-like structure. Knockdown of either protease reduced cp-2 cleavage, and ameliorated mutant huntingtin induced toxicity, whereas their overexpression increased the cp-2 cleavage. Both proteases partially co-localized with Htt in the cytoplasm and within or in association with early and late endosomes, with some nuclear co-localization observed for cathepsin Z. BLMH and cathepsin Z are expressed in the brain and have been associated previously with neurodegeneration. Our findings further validate the cysteine protease family, and BLMH and cathepsin Z in particular, as potential novel targets for HD therapeutics.

Huntington's disease: from molecular pathogenesis to clinical treatment

Huntington's disease is a progressive, fatal, neurodegenerative disorder caused by an expanded CAG repeat in the huntingtin gene, which encodes an abnormally long polyglutamine repeat in the huntingtin protein. Huntington's disease has served as a model for the study of other more common neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease. These disorders all share features including: delayed onset; selective neuronal vulnerability, despite widespread expression of disease-related proteins during the whole lifetime; abnormal protein processing and aggregation; and cellular toxic effects involving both cell autonomous and cell-cell interaction mechanisms. Pathogenic pathways of Huntington's disease are beginning to be unravelled, offering targets for treatments. Additionally, predictive genetic testing and findings of neuroimaging studies show that, as in some other neurodegenerative disorders, neurodegeneration in affected individuals begins many years before onset of diagnosable signs and symptoms of Huntington's disease, and it is accompanied by subtle cognitive, motor, and psychiatric changes (so-called prodromal disease). Thus, Huntington's disease is also emerging as a model for strategies to develop therapeutic interventions, not only to slow progression of manifest disease but also to delay, or ideally prevent, its onset.

Smaller intracranial volume in prodromal Huntington's disease: evidence for abnormal neurodevelopment

Huntington's disease is an autosomal dominant brain disease. Although conceptualized as a neurodegenerative disease of the striatum, a growing number of studies challenge this classic concept of Huntington's disease aetiology. Intracranial volume is the tissue and fluid within the calvarium and is a representation of the maximal brain growth obtained during development. The current study reports intracranial volume obtained from an magnetic resonance imaging brain scan in a sample of subjects (n = 707) who have undergone presymptomatic gene testing. Participants who are gene-expanded but not yet manifesting the disease (prodromal Huntington's disease) are compared with subjects who are non-gene expanded. The prodromal males had significantly smaller intracranial volume measures with a mean volume that was 4% lower compared with controls. Although the prodromal females had smaller intracranial volume measures compared with their controls, this was not significant. The current findings suggest that mutant huntingtin can cause abnormal development, which may contribute to the pathogenesis of Huntington's disease.