A cell autonomous torsinA requirement for cholinergic neuron survival and motor control

Cholinergic dysfunction is strongly implicated in dystonia pathophysiology. Previously (Pappas et al., 2015;4:e08352), we reported that Dlx5/6-Cre mediated forebrain deletion of the DYT1 dystonia protein torsinA (Dlx-CKO) causes abnormal twisting and selective degeneration of dorsal striatal cholinergic interneurons (ChI) (Pappas et al., 2015). A central question raised by that work is whether the ChI loss is cell autonomous or requires torsinA loss from neurons synaptically connected to ChIs. Here, we addressed this question by using ChAT-Cre mice to conditionally delete torsinA from cholinergic neurons ('ChAT-CKO'). ChAT-CKO mice phenocopy the Dlx-CKO phenotype of selective dorsal striatal ChI loss and identify an essential requirement for torsinA in brainstem and spinal cholinergic neurons. ChAT-CKO mice are tremulous, weak, and exhibit trunk twisting and postural abnormalities. These findings are the first to demonstrate a cell autonomous requirement for torsinA in specific populations of cholinergic neurons, strengthening the connection between torsinA, cholinergic dysfunction and dystonia pathophysiology.

Inherited dystonias: clinical features and molecular pathways

Recent decades have witnessed dramatic increases in understanding of the genetics of dystonia - a movement disorder characterized by involuntary twisting and abnormal posture. Hampered by a lack of overt neuropathology, researchers are investigating isolated monogenic causes to pinpoint common molecular mechanisms in this heterogeneous disease. Evidence from imaging, cellular, and murine work implicates deficiencies in dopamine neurotransmission, transcriptional dysregulation, and selective vulnerability of distinct neuronal populations to disease mutations. Studies of genetic forms of dystonia are also illuminating the developmental dependence of disease symptoms that is typical of many forms of the disease. As understanding of monogenic forms of dystonia grows, a clearer picture will develop of the abnormal motor circuitry behind this relatively common phenomenology. This chapter focuses on the current data covering the etiology and epidemiology, clinical presentation, and pathogenesis of four monogenic forms of isolated dystonia: DYT-TOR1A, DYT-THAP1, DYT-GCH1, and DYT-GNAL.

Current Opinions and Areas of Consensus on the Role of the Cerebellum in Dystonia

A role for the cerebellum in causing ataxia, a disorder characterized by uncoordinated movement, is widely accepted. Recent work has suggested that alterations in activity, connectivity, and structure of the cerebellum are also associated with dystonia, a neurological disorder characterized by abnormal and sustained muscle contractions often leading to abnormal maintained postures. In this manuscript, the authors discuss their views on how the cerebellum may play a role in dystonia. The following topics are discussed: The relationships between neuronal/network dysfunctions and motor abnormalities in rodent models of dystonia. Data about brain structure, cerebellar metabolism, cerebellar connections, and noninvasive cerebellar stimulation that support (or not) a role for the cerebellum in human dystonia. Connections between the cerebellum and motor cortical and sub-cortical structures that could support a role for the cerebellum in dystonia. Overall points of consensus include: Neuronal dysfunction originating in the cerebellum can drive dystonic movements in rodent model systems. Imaging and neurophysiological studies in humans suggest that the cerebellum plays a role in the pathophysiology of dystonia, but do not provide conclusive evidence that the cerebellum is the primary or sole neuroanatomical site of origin.

Deletion variant rs35153737 in TOR1A is associated with isolated dystonia in a Southwestern Chinese Population

BACKGROUND

TOR1A plays a very important role in early-onset isolated dystonia. Studying the association between the common variants of this gene and dystonia can help us understand the connection between TOR1A mutations and this disease.

METHODS

The TOR1A exon 5 was sequenced in 223 isolated dystonia patients and 210 age-adjusted controls. Patients and controls all came from Southwest China.

RESULTS

The following two common variants were found in the 3'-UTR of TOR1A: NM_000113.2:c.*414delG (rs35153737) and NM_000113.2:c.*824delG (rs3842225). The rs35153737 variant showed a statistically significant association with dystonia using the allele model (P=0.035) and the dominant genetic model (P=0.018); however, no association between rs3842225 and dystonia was found.

CONCLUSION

Our study suggests that there is an association between rs35153737 and dystonia in a southwestern Chinese population, and it may be caused by high linkage disequilibrium between this deletion and potential pathogenic variants in TOR1A.

It's not just the basal ganglia: Cerebellum as a target for dystonia therapeutics

Dystonia is a common movement disorder that devastates the lives of many patients, but the etiology of this disorder remains poorly understood. Dystonia has traditionally been considered a disorder of the basal ganglia. However, growing evidence suggests that the cerebellum may be involved in certain types of dystonia, raising several questions. Can different types of dystonia be classified as either a basal ganglia disorder or a cerebellar disorder? Is dystonia a network disorder that involves the cerebellum and basal ganglia? If dystonia is a network disorder, how can we target treatments to alleviate symptoms in patients? A recent study by Chen et al, using the pharmacological mouse model of rapid-onset dystonia parkinsonism, has provided some insight into these important questions. They showed that the cerebellum can directly modulate basal ganglia activity through a short latency cerebello-thalamo-basal ganglia pathway. Further, this article and others have provided evidence that in some cases, aberrant cerebello-basal ganglia communication can be involved in dystonia. In this review we examine the evidence for the involvement of the cerebellum and cerebello-basal ganglia interactions in dystonia. We conclude that there is ample evidence to suggest that the cerebellum plays a role in some dystonias, including the early-onset primary torsion dystonia DYT1 and that further studies examining the role of this brain region and its interaction with the basal ganglia in dystonia are warranted. © 2017 International Parkinson and Movement Disorder Society.

Evaluation of AZD1446 as a Therapeutic in DYT1 Dystonia

DYT1 dystonia is an early-onset, hyperkinetic movement disorder caused by a deletion in the gene TOR1A, which encodes the protein torsinA. Several lines of evidence show that in animal models of DTY1 dystonia, there is impaired basal dopamine (DA) release and enhanced acetylcholine tone. Clinically, anticholinergic drugs are the most effective pharmacological treatment for DYT1 dystonia, but the currently used agents are non-selective muscarinic antagonists and associated with side effects. We used a DYT1 ∆GAG knock-in mouse model (DYT1 KI) to investigate whether nicotine and/or a non-desensitizing nicotinic agonist, AZD1446, would increase DA output in DYT1 dystonia. Using in vivo microdialysis, we found that DYT1 KI mice showed significantly increased DA output and greater sensitivity to nicotine compared to wild type (WT) littermate controls. In contrast, neither systemic injection (0.25–0.75 mg/kg) or intrastriatal infusion (30 μM–1 mM) of AZD1446 had a significant effect on DA efflux in WT or DYT1 KI mice. In vitro, we found that AZD1446 had no effect on the membrane properties of striatal spiny projection neurons (SPNs) and did not alter the spontaneous firing of ChI interneurons in either WT or DYT1 KI mice. We did observe that the firing frequency of dopaminergic neurons was significantly increased by AZD1446 (10 μM), an effect blocked by dihydro-beta-erythroidine (DHβE 3 μM), but the effect was similar in WT and DYT1 KI mice. Our results support the view that DYT1 models are associated with abnormal striatal cholinergic transmission, and that the DYT1 KI animals have enhanced sensitivity to nicotine. We found little effect of AZD1446 in this model, suggesting that other approaches to nicotinic modulation should be explored.

Strength of cholinergic tone dictates the polarity of dopamine D2 receptor modulation of striatal cholinergic interneuron excitability in DYT1 dystonia

Balance between cholinergic and dopaminergic signaling is central to striatal control of movement and cognition. In dystonia, a common disorder of movement, anticholinergic therapy is often beneficial. This observation suggests there is a pathological increase in cholinergic tone, yet direct confirmation is lacking. In DYT1, an early-onset genetic form of dystonia caused by a mutation in the protein torsinA (TorA), the suspected heightened cholinergic tone is commonly attributed to faulty dopamine D2 receptor (D2R) signaling where D2R agonists cause excitation of striatal cholinergic interneurons (ChIs), rather than the normal inhibition of firing observed in wild-type animals, an effect known as "paradoxical excitation". Here, we provide for the first time direct measurement of elevated striatal extracellular acetylcholine (ACh) in a knock-in mouse model of human DYT1 dystonia (TorA^∆E/+ mice), confirming a striatal hypercholinergic state. We hypothesized that this elevated extracellular ACh might cause chronic over-activation of muscarinic acetylcholine receptors (mAChRs) and disrupt normal D2R function due to their shared coupling to G_i/o-proteins. We tested this concept in vitro first using a broad-spectrum mAChR antagonist, and then using a M2/M4 mAChR selective antagonist to specifically target mAChRs expressed by ChIs. Remarkably, we found that mAChR inhibition reverses the D2R-mediated paradoxical excitation of ChIs recorded in slices from TorA^∆E/+ mice to a typical inhibitory response. Furthermore, we recapitulated the paradoxical D2R excitation of ChIs in striatal slices from wild-type mice within minutes by simply increasing cholinergic tone through pharmacological inhibition of acetylcholinesterase (AChE) or by prolonged agonist activation of mAChRs. Collectively, these results show that enhanced mAChR tone itself is sufficient to rapidly reverse the polarity of D2R regulation of ChI excitability, correcting the previous notion that the D2R mediated paradoxical ChI excitation causes the hypercholinergic state in dystonia. Further, using a combination of genetic and pharmacological approaches, we found evidence that this switch in D2R polarity results from a change in coupling from the preferred G_i/o pathway to non-canonical β-arrestin signaling. These results highlight the need to fully understand how the mutation in TorA leads to pathologically heightened extracellular ACh. Furthermore the discovery of this novel ACh-dopamine interaction and the participation of β-arrestin in regulation of cholinergic interneurons is likely important for other basal ganglia disorders characterized by perturbation of ACh-dopamine balance, including Parkinson and Huntington diseases, l-DOPA-induced dyskinesia and schizophrenia.

Function Identification of the Nucleotides in Key cis-Element of DYSFUNCTIONAL TAPETUM1 (DYT1) Promoter

As a core regulatory gene of the anther development, DYSFUNCTIONAL TAPETUM1 (DYT1) was expressed in tapetum preferentially. Previous study had confirmed that a "CTCC" sequence within DYT1 promoter was indispensable for correct DYT1 expression. However, precise analysis on the function of each nucleotide of this sequence still lacks. Here we employed site mutation assay to identify the function roles of the nucleotides. As a result, the "T" and final "C" of "CTCC" were found essential for the temporal and spatial specificity of DYT1 expression, whereas the other two "C" nucleotides exhibited substitutable somewhat. The substitutes of two flanking nucleotides of "CTCC," however, hardly affected the normal promoter function, suggesting that the "CTCC" sequence as a whole did meet the standard of a canonical cis-element by definition. In addition, it was found that as short as 497 bp DYT1 promoter was sufficient for tissue-specific expression, while longer 505 bp DYT1 promoter sequence was sufficient for species-specific expression.

A role for cerebellum in the hereditary dystonia DYT1

DYT1 is a debilitating movement disorder caused by loss-of-function mutations in torsinA. How these mutations cause dystonia remains unknown. Mouse models which have embryonically targeted torsinA have failed to recapitulate the dystonia seen in patients, possibly due to differential developmental compensation between rodents and humans. To address this issue, torsinA was acutely knocked down in select brain regions of adult mice using shRNAs. TorsinA knockdown in the cerebellum, but not in the basal ganglia, was sufficient to induce dystonia. In agreement with a potential developmental compensation for loss of torsinA in rodents, torsinA knockdown in the immature cerebellum failed to produce dystonia. Abnormal motor symptoms in knockdown animals were associated with irregular cerebellar output caused by changes in the intrinsic activity of both Purkinje cells and neurons of the deep cerebellar nuclei. These data identify the cerebellum as the main site of dysfunction in DYT1, and offer new therapeutic targets.

DOI:http://dx.doi.org/10.7554/eLife.22775.001

Dystonia is the third most common type of movement disorder after Parkinson’s disease and tremor. Patients with dystonia experience prolonged involuntary contractions of their muscles, often causing uncontrollable postures or repetitive movements. Almost thirty years ago, genetic studies revealed that a mutation in the gene that encodes a protein called torsinA causes the most common type of dystonia, called DYT1.

Exactly how mutations that affect the torsinA protein give rise to DYT1 remains unclear, and there are still no effective treatments for the disorder. Part of the problem is that we do not fully understand how torsinA works, or which of its many proposed functions is relevant to dystonia. Moreover, attempts to study DYT1 using genetically modified mice have proved largely unsuccessful. This is because mice that simply express the same genetic mutations that cause dystonia in humans do not show the overt symptoms of dystonia.

Fremont, Tewari et al. have now generated a mouse ‘model’ that does show symptoms of dystonia, and used these model mice to investigate the role of torsinA in the disorder. Acutely reducing the amount of torsinA protein in a region of the brain called the cerebellum induced the symptoms of dystonia in the mice. Conversely, reducing the amount of torsinA in a different brain area known as the basal ganglia had no such effect, even though both the cerebellum and the basal ganglia contribute to movement. Furthermore, neither manipulation had any effect in juvenile mice, which suggests that, in contrast to humans, young mice can compensate for the loss of torsinA.

Fremont, Tewari et al. also found that the loss of torsinA causes the cerebellum to generate incorrect output signals, which in turn trigger the abnormal movements seen in dystonia. In the future, further studies of the model mice could identify the exact changes that occur in neurons following the loss of torsinA from the cerebellum. Understanding these changes could potentially pave the way for developing effective treatments for DYT1 and other dystonias.

DOI:http://dx.doi.org/10.7554/eLife.22775.002

Gene Regulatory Network for Tapetum Development in Arabidopsis thaliana

In flowering plants, male gametophyte development occurs in the anther. Tapetum, the innermost of the four anther somatic layers, surrounds the developing reproductive cells to provide materials for pollen development. A genetic pathway of DYT1-TDF1-AMS-MS188 in regulating tapetum development has been proven. Here we used laser microdissection and pressure catapulting to capture and analyze the transcriptome data for the Arabidopsis tapetum at two stages. With a comprehensive analysis by the microarray data of dyt1, tdf1, ams, and ms188 mutants, we identified possible downstream genes for each transcription factor. These transcription factors regulate many biological processes in addition to activating the expression of the other transcription factor. Briefly, DYT1 may also regulate early tapetum development via E3 ubiquitin ligases and many other transcription factors. TDF1 is likely involved in redox and cell degradation. AMS probably regulates lipid transfer proteins, which are involved in pollen wall formation, and other E3 ubiquitin ligases, functioning in degradating proteins produced in previous processes. MS188 is responsible for most cell wall-related genes, functioning both in tapetum cell wall degradation and pollen wall formation. These results propose a more complex gene regulatory network for tapetum development and function.

Tor1a+/- mice develop dystonia-like movements via a striatal dopaminergic dysregulation triggered by peripheral nerve injury

Isolated generalized dystonia is a central motor network disorder characterized by twisted movements or postures. The most frequent genetic cause is a GAG deletion in the Tor1a (DYT1) gene encoding torsinA with a reduced penetrance of 30-40 % suggesting additional genetic or environmental modifiers. Development of dystonia-like movements after a standardized peripheral nerve crush lesion in wild type (wt) and Tor1a+/- mice, that express 50 % torsinA only, was assessed by scoring of hindlimb movements during tail suspension, by rotarod testing and by computer-assisted gait analysis. Western blot analysis was performed for dopamine transporter (DAT), D1 and D2 receptors from striatal and quantitative RT-PCR analysis for DAT from midbrain dissections. Autoradiography was used to assess the functional DAT binding in striatum. Striatal dopamine and its metabolites were analyzed by high performance liquid chromatography. After nerve crush injury, we found abnormal posturing in the lesioned hindlimb of both mutant and wt mice indicating the profound influence of the nerve lesion (15x vs. 12x relative to control) resembling human peripheral pseudodystonia. In mutant mice the phenotypic abnormalities were increased by about 40 % (p < 0.05). This was accompanied by complex alterations of striatal dopamine homeostasis. Pharmacological blockade of dopamine synthesis reduced severity of dystonia-like movements, whereas treatment with L-Dopa aggravated these but only in mutant mice suggesting a DYT1 related central component relevant to the development of abnormal involuntary movements. Our findings suggest that upon peripheral nerve injury reduced torsinA concentration and environmental stressors may act in concert in causing the central motor network dysfunction of DYT1 dystonia.

Systematic TOR1A non-c.907_909delGAG variant analysis in isolated dystonia and controls

BACKGROUND

An increasing number of rare, functionally relevant non-c.907_909delGAG (non-ΔGAG) variants in TOR1A have been recognized, associated with phenotypic expressions different from classic DYT1 childhood-onset generalized dystonia. Only recently, DYT1 genotype-phenotype correlations have been proposed, awaiting further elucidation in independent cohorts.

METHODS

We screened the entire coding sequence and the 5'-UTR region of TOR1A for rare non-ΔGAG sequence variants in a large series of 940 individuals with various forms of isolated dystonia as well as in 376 ancestry-matched controls. The frequency of rare, predicted deleterious non-ΔGAG TOR1A variants was assessed in the European sample of the Exome Aggregation Consortium (ExAC) dataset.

RESULTS

In the case cohort, we identified a rare 5'-UTR variant (c.-39G > T), a rare splice-region variant (c.445-8T > C), as well as one novel (p.Ile231Asn) and two rare (p.Ala163Val, p.Thr321Met) missense variants, each in a single patient with adult-onset focal/segmental isolated dystonia. Of these variants, only p.Thr321Met qualified as possibly disease-related according to variant interpretation criteria. One novel, predicted deleterious missense substitution (p.Asn208Ser) was detected in the control cohort. Among European ExAC individuals, the carrier rate of rare, predicted deleterious non-ΔGAG variants was 0.4%.

CONCLUSIONS

Our study does not allow the establishment of genotype-specific clinical correlations for DYT1. Further large-scale genetic screening accompanied by comprehensive segregation and functional studies is required to conclusively define the contribution of TOR1A whole-gene variation to the pathogenesis of isolated dystonia.

Functional Connectivity Networks in Asymptomatic and Symptomatic DYT1 Carriers

BACKGROUND

DYT1 mutation is characterized by focal to generalized dystonia and incomplete penetrance. To explore the complex perturbations in the different neural networks and the mutual interactions among them, we studied symptomatic and asymptomatic DTY1 mutation carriers by resting-state functional MRI.

METHODS

A total of 7 symptomatic DYT1, 10 asymptomatic DYT1, and 26 healthy controls were considered. Resting-state functional MRI (Oxford Centre for Functional MRI of the Brain) [FMRIB] Software Library) (FSL) MELODIC, dual regression, (as a toolbox of FSL, with Nets is referred to "networks") (FSLNets) (http://fsl.fmrib.ox.ac.uk/fsl/fslwiki/FSLNets) was performed on 9 resting-state neural networks.

RESULTS

DYT1 mutation signature (symptomatic DYT1 and asymptomatic DYT1) was characterized by increased connectivity in the dorsal attention network and in the left fronto-parietal network. Functional correlates of symptomatic DYT1 patients (symptomatic DYT1 vs healthy controls) showed increased connectivity in the sensorimotor network.

DISCUSSION

This study argues that DYT1 dystonia is a network disorder, with crucial nodes in sensory-motor integration of posterior parietal structures. A better characterization of cortical networks involved in dystonia is crucial for possible neurophysiological therapeutic interventions. © 2016 International Parkinson and Movement Disorder Society.

Electromyographic evidence in support of a knock-in mouse model of DYT1 Dystonia

INTRODUCTION

DYT1 dystonia is an autosomal-dominant movement disorder characterized by abnormal, often repetitive, movements and postures. Its hallmark feature is sustained or intermittent contractions of muscles involving co-contractions of antagonist muscle pairs. The symptoms are relieved with the anticholinergic drug trihexyphenidyl. The primary mutation is a trinucleotide deletion (ΔGAG) in DYT1/TOR1A, which codes for torsinA. Previous studies showed that (1) heterozygous Dyt1 ΔGAG knock-in mice, which have an analogous mutation in the endogenous gene, exhibit motor deficits and altered corticostriatal synaptic plasticity in the brain and (2) these deficits can be rescued by trihexyphenidyl. However, brain imaging studies suggest that the Dyt1 knock-in mouse models nonmanifesting mutation carriers of DYT1 dystonia. The aim of this work was to examine the hallmark features of DYT1 dystonia in the Dyt1 knock-in mice by analyzing muscular activities.

METHODS

Wireless telemetry devices with biopotential channels were implanted to the bicep and the rectus femori muscles in Dyt1 knock-in mice, and muscular activities were recorded before and after trihexyphenidyl administration.

RESULTS

(1) Consistent with DYT1 dystonia patients, Dyt1 knock-in mice showed sustained contractions and co-contractions of the antagonistic bicep femoris and rectus femoris. (2) The abnormal muscle contractions were normalized by trihexyphenidyl.

CONCLUSION

The results suggest that the motor deficits in Dyt1 knock-in mice are likely produced by abnormal muscle contractions, and Dyt1 knock-in mice can potentially be used as a manifesting disease model to study pathophysiology and develop novel therapeutics. © 2016 International Parkinson and Movement Disorder Society.

One novel cis-element is essential for correct DYSFUNCTIONAL TAPETUM 1 (DYT1) expression in Arabidopsis thaliana

We studied the function of DYT1 promoter, found the important sectors controlling specific expression of DYT1 , and identified a new cis -element for further investigation of DYT1 upstream genes. DYT1 is a core regulatory gene for tapetum development in Arabidopsis thaliana. However, the mechanism leading to DYT1 tapetum-preferential expression is still unknown up to date. Here we employed promoter truncation and deletion assay to identify a 'CTCC' cis-element, which was essential for correct DYT1 expression within DYT1 promoter region. Through comparing truncated DYT1 promoter-driven GFP expression, the -481 to -513 bp region from the start point of transcription (SPT) of DYT1 was found indispensable for proper DYT1 expression. Further deletion assay around this region revealed that an approximate -468 bp 'CTCC' sequence deletion abolished normal DYT1 expression completely. Bioinformatics assay suggested that this 'CTCC' motif was potentially a novel DNA-recognition sequence, providing new clue for investigating relationship between DYT1 and its upstream genes.

DYT1 directly regulates the expression of TDF1 for tapetum development and pollen wall formation in Arabidopsis

The tapetum plays a critical role during the development and maturation of microspores. DYSFUNCTIONAL TAPETUM 1 (DYT1) is essential for early tapetal development. Here, we determined that the promoter region (-550 to -463 bp) contains indispensable cis-elements for DYT1 expression. Although DYT1 transcripts can be detected in both meiocytes and tapetal cells, localization of DYT1-GFP demonstrated that DYT1 is strictly located in tapetal cells during microsporogenesis. Chromatin immunoprecipitation (ChIP) analysis revealed that DYT1 directly binds the promoter region of Defective in Tapetal Development and Function 1 (TDF1), a transcription factor essential for tapetum development. When TDF1 driven by the DYT1 promoter is expressed in a dyt1 mutant, the expression of the transcription factors AMS, MS188/MYB80, TEK and MS1 and the pollen wall-related genes are restored. Although the pollen wall is not formed and the microspores are ruptured, DIOC2 staining showed that fatty acids, the precursors of the pollen wall, were synthesized in the transgenic lines. These results indicate that DYT1 regulates the expression of AMS, MS188/MYB80, TEK and MS1 for pollen wall formation, primarily via TDF1.

Decreased dopamine receptor 1 activity and impaired motor-skill transfer in Dyt1 ΔGAG heterozygous knock-in mice

DYT1 dystonia is a movement disorder caused by a trinucleotide deletion (ΔGAG) in DYT1 (TOR1A), corresponding to a glutamic acid loss in the C-terminal region of torsinA. Functional alterations in the basal ganglia circuits have been reported in both DYT1 dystonia patients and rodent models. Dyt1 ΔGAG heterozygous knock-in (KI) mice exhibit motor deficits and decreased striatal dopamine receptor 2 (D2R) binding activity, suggesting a malfunction of the indirect pathway. However, the role of the direct pathway in pathogenesis of dystonia is not yet clear. Here, we report that Dyt1 KI mice exhibit significantly decreased striatal dopamine receptor 1 (D1R) binding activity and D1R protein levels, suggesting the alteration of the direct pathway. The decreased D1R may be caused by translational or post-translational processes since Dyt1 KI mice had normal levels of striatal D1R mRNA and a normal number of striatal neurons expressing D1R. Levels of striatal ionotropic glutamate receptor subunits, dopamine transporter, acetylcholine muscarinic M4 receptor and adenosine A2A receptor were not altered suggesting a specificity of affected polytopic membrane-associated proteins. Contribution of the direct pathway to motor-skill learning has been suggested in another pharmacological rat model injected with a D1R antagonist. In the present study, we developed a novel motor skill transfer test for mice and found deficits in Dyt1 KI mice. Further characterization of both the direct and the indirect pathways in Dyt1 KI mice will aid the development of novel therapeutic drugs.

All in the blink of an eye: new insight into cerebellar and brainstem function in DYT1 and DYT6 dystonia

BACKGROUND AND PURPOSE

Traditionally dystonia has been considered a disorder of basal ganglia dysfunction. However, recent research has advocated a more complex neuroanatomical network. In particular, there is increasing interest in the pathophysiological role of the cerebellum. Patients with cervical and focal hand dystonia have impaired cerebellar associative learning using the paradigm eyeblink conditioning. This is perhaps the most direct evidence to date that the cerebellum is implicated in patients.

METHODS

Eleven patients with DYT1 dystonia and five patients with DYT6 dystonia were examined and rates of eyeblink conditioning were compared with age-matched controls. A marker of brainstem excitability, the blink reflex recovery, was also studied in the same groups.

RESULTS

Patients with DYT1 and DYT6 dystonia have a normal ability to acquire conditioned responses. Blink reflex recovery was enhanced in DYT1 but this effect was not seen in DYT6.

CONCLUSIONS

If the cerebellum is an important driver in DYT1 and DYT6 dystonia our data suggest that there is specific cerebellar dysfunction such that the circuits essential for conditioning function normally. Our data are contrary to observations in focal dystonia and suggest that the cerebellum may have a distinct role in different subsets of dystonia. Evidence of enhanced blink reflex recovery in all patients with dystonia was not found and recent studies calling for the blink recovery reflex to be used as a diagnostic test for dystonic tremor may require further corroboration.

Biochemical and cellular analysis of human variants of the DYT1 dystonia protein, TorsinA/TOR1A

Early-onset dystonia is associated with the deletion of one of a pair of glutamic acid residues (c.904_906delGAG/c.907_909delGAG; p.Glu302del/Glu303del; ΔE 302/303) near the carboxyl-terminus of torsinA, a member of the AAA(+) protein family that localizes to the endoplasmic reticulum lumen and nuclear envelope. This deletion commonly underlies early-onset DYT1 dystonia. While the role of the disease-causing mutation, torsinAΔE, has been established through genetic association studies, it is much less clear whether other rare human variants of torsinA are pathogenic. Two missense variations have been described in single patients: R288Q (c.863G>A; p.Arg288Gln; R288Q) identified in a patient with onset of severe generalized dystonia and myoclonus since infancy and F205I (c.613T>A, p.Phe205Ile; F205I) in a psychiatric patient with late-onset focal dystonia. In this study, we have undertaken a series of analyses comparing the biochemical and cellular effects of these rare variants to torsinAΔE and wild-type (wt) torsinA to reveal whether there are common dysfunctional features. The results revealed that the variants, R288Q and F205I, are more similar in their properties to torsinAΔE protein than to torsinAwt. These findings provide functional evidence for the potential pathogenic nature of these rare sequence variants in the TOR1A gene, thus implicating these pathologies in the development of dystonia.

Unraveling cellular phenotypes of novel TorsinA/TOR1A mutations

A three-nucleotide (GAG) deletion (ΔE) in TorsinA (TOR1A) has been identified as the most common cause of dominantly inherited early-onset torsion dystonia (DYT1). TOR1A encodes a chaperone-like AAA+-protein localized in the endoplasmic reticulum. Currently, only three additional, likely mutations have been reported in single dystonia patients. Here, we report two new, putative TOR1A mutations (p.A14_P15del and p.E121K) that we examined functionally in comparison with wild-type (WT) protein and two known mutations (ΔE and p.R288Q). While inclusion formation is a characteristic feature for ΔE TOR1A, elevated levels of aggregates for other mutations were not observed when compared with WT TOR1A. WT and mutant TOR1A showed preferred degradation through the autophagy-lysosome pathway, which is most pronounced for p.A14_P15del, p.R288Q, and ΔE TOR1A. Notably, blocking of the autophagy pathway with bafilomycin resulted in a significant increase in inclusion formation in p.E121K TOR1A. In addition, all variants had an influence on protein stability. Although the p.A14_P15del mutation affects the proposed oligomerization domain of TOR1A, this mutation did not disturb the ability to dimerize. Our findings demonstrate functional changes for all four mutations on different levels. Thus, both diagnostic and research genetic screening of dystonia patients should not be limited to testing for the ∆E mutation.

Microfluidic platform to evaluate migration of cells from patients with DYT1 dystonia

BACKGROUND

Microfluidic platforms for quantitative evaluation of cell biologic processes allow low cost and time efficient research studies of biological and pathological events, such as monitoring cell migration by real-time imaging. In healthy and disease states, cell migration is crucial in development and wound healing, as well as to maintain the body's homeostasis.

NEW METHOD

The microfluidic chambers allow precise measurements to investigate whether fibroblasts carrying a mutation in the TOR1A gene, underlying the hereditary neurologic disease--DYT1 dystonia, have decreased migration properties when compared to control cells.

RESULTS

We observed that fibroblasts from DYT1 patients showed abnormalities in basic features of cell migration, such as reduced velocity and persistence of movement.

COMPARISON WITH EXISTING METHOD

The microfluidic method enabled us to demonstrate reduced polarization of the nucleus and abnormal orientation of nuclei and Golgi inside the moving DYT1 patient cells compared to control cells, as well as vectorial movement of single cells.

CONCLUSION

We report here different assays useful in determining various parameters of cell migration in DYT1 patient cells as a consequence of the TOR1A gene mutation, including a microfluidic platform, which provides a means to evaluate real-time vectorial movement with single cell resolution in a three-dimensional environment.

The BiP molecular chaperone plays multiple roles during the biogenesis of torsinA, an AAA+ ATPase associated with the neurological disease early-onset torsion dystonia

Early-onset torsion dystonia (EOTD) is a neurological disorder characterized by involuntary and sustained muscle contractions that can lead to paralysis and abnormal posture. EOTD is associated with the deletion of a glutamate (ΔE) in torsinA, an endoplasmic reticulum (ER) resident AAA(+) ATPase. To date, the effect of ΔE on torsinA and the reason that this mutation results in EOTD are unclear. Moreover, there are no specific therapeutic options to treat EOTD. To define the underlying biochemical defects associated with torsinAΔE and to uncover factors that might be targeted to offset defects associated with torsinAΔE, we developed a yeast torsinA expression system and tested the roles of ER chaperones in mediating the folding and stability of torsinA and torsinAΔE. We discovered that the ER lumenal Hsp70, BiP, an associated Hsp40, Scj1, and a nucleotide exchange factor, Lhs1, stabilize torsinA and torsinAΔE. BiP also maintained torsinA and torsinAΔE solubility. Mutations predicted to compromise specific torsinA functional motifs showed a synthetic interaction with the ΔE mutation and destabilized torsinAΔE, suggesting that the ΔE mutation predisposes torsinA to defects in the presence of secondary insults. In this case, BiP was required for torsinAΔE degradation, consistent with data that specific chaperones exhibit either pro-degradative or pro-folding activities. Finally, using two independent approaches, we established that BiP stabilizes torsinA and torsinAΔE in mammalian cells. Together, these data define BiP as the first identified torsinA chaperone, and treatments that modulate BiP might improve symptoms associated with EOTD.

DYT6 in Brazil: Genetic Assessment and Clinical Characteristics of Patients

Background

Several genes associated with dystonia have been identified. A mutation in one of these, THAP1 (DYT6), is linked to isolated dystonia. The aim of this study was to assess the prevalence of THAP1 gene mutations and the clinical characteristics of patients with these mutations in a clinical population in Brazil.

Methods

Seventy-four patients presenting with dystonia involving the cervical muscles and without mutations in the TOR1A (DYT1) gene or any other movement disorders were recruited at a movement disorders clinic between June 2008 and June 2009. All the patients underwent clinical examination and were screened for mutations of the THAP1 gene.

Results

Three patients had the novel p.Gln97Ter THAP1 nonsense mutation in heterozygosis. One of them had no family history of dystonia. Symptoms in this patient first appeared in his right arm, and the condition progressed to the generalized form. The other two patients belonged to the same family (cousins). Symptoms in the first patient started in her right arm at the age of 18 years and the condition progressed to the segmental form. The second patient, who carried the p.Arg169Gln missense mutation, developed dystonia in her left arm at the age of 6 years. The condition progressed to generalized dystonia.

Discussion

We conclude that THAP1 mutations are also a cause, albeit uncommon, of segmental and generalized dystonia in the Brazilian population.