Decreased mechanotransduction prevents nuclear collapse in a Caenorhabditis elegans laminopathy.

The function of the nucleus depends on the integrity of the nuclear lamina, an intermediate filament network associated with the linker of nucleoskeleton and cytoskeleton (LINC) complex. The LINC complex spans the nuclear envelope and mediates nuclear mechanotransduction, the process by which mechanical signals and forces are transmitted across the nuclear envelope. In turn, the AAA+ ATPase torsinA is thought to regulate force transmission from the cytoskeleton to the nucleus. In humans, mutations affecting nuclear envelope-associated proteins cause laminopathies, including progeria, myopathy, and dystonia, though the extent to which endogenous mechanical stresses contribute to these pathologies is unclear. Here, we use the Caenorhabditis elegans germline as a model to investigate mechanisms that maintain nuclear integrity as germ cell nuclei progress through meiotic development and migrate for gametogenesis-processes that require LINC complex function. We report that decreasing the function of the C. elegans torsinA homolog, OOC-5, rescues the sterility and premature aging caused by a null mutation in the single worm lamin homolog. We show that decreasing OOC-5/torsinA activity prevents nuclear collapse in lamin mutants by disrupting the function of the LINC complex. At a mechanistic level, OOC-5/torsinA promotes the assembly or maintenance of the lamin-associated LINC complex and this activity is also important for interphase nuclear pore complex insertion into growing germline nuclei. These results demonstrate that LINC complex-transmitted forces damage nuclei with a compromised nuclear lamina. Thus, the torsinA-LINC complex nexus might comprise a therapeutic target for certain laminopathies by preventing damage from endogenous cellular forces.

Blockade of M4 muscarinic receptors on striatal cholinergic interneurons normalizes striatal dopamine release in a mouse model of TOR1A dystonia.

Trihexyphenidyl (THP), a non-selective muscarinic receptor (mAChR) antagonist, is commonly used for the treatment of dystonia associated with TOR1A, otherwise known as DYT1 dystonia. A better understanding of the mechanism of action of THP is a critical step in the development of better therapeutics with fewer side effects. We previously found that THP normalizes the deficit in striatal dopamine (DA) release in a mouse model of TOR1A dystonia (Tor1a+/ΔE knockin (KI) mice), revealing a plausible mechanism of action for this compound, considering that abnormal DA neurotransmission is consistently associated with many forms of dystonia. However, the mAChR subtype(s) that mediate the rescue of striatal dopamine release remain unclear. In this study we used a combination of pharmacological challenges and cell-type specific mAChR conditional knockout mice of either sex to determine which mAChR subtypes mediate the DA release-enhancing effects of THP. We determined that THP acts in part at M4 mAChR on striatal cholinergic interneurons to enhance DA release in both Tor1a+/+ and Tor1a+/ΔE KI mice. Further, we found that the subtype selective M4 antagonist VU6021625 recapitulates the effects of THP. These data implicate a principal role for M4 mAChR located on striatal cholinergic interneurons in the mechanism of action of THP and suggest that subtype selective M4 mAChR antagonists may be effective therapeutics with fewer side effects than THP for the treatment of TOR1A dystonia.

Transgenic Mice for the Translational Study of Neuropathic Pain and Dystonia.

Murine models are fundamental in the study of clinical conditions and the development of new drugs and treatments. Transgenic technology has started to offer advantages in oncology, encompassing all research fields related to the study of painful syndromes. Knockout mice or mice overexpressing genes encoding for proteins linked to pain development and maintenance can be produced and pain models can be applied to transgenic mice to model the most disabling neurological conditions. Due to the association of movement disorders with sensitivity and pain processing, our group focused for the first time on the role of the torsinA gene GAG deletion-responsible for DYT1 dystonia-in baseline sensitivity and neuropathic responses. The aim of the present report are to review the complex network that exists between the chaperonine-like protein torsinA and the baseline sensitivity pattern-which are fundamental in neuropathic pain-and to point at its possible role in neurodegenerative diseases.

p97/UBXD1 Generate Ubiquitylated Proteins That Are Sequestered into Nuclear Envelope Herniations in Torsin-Deficient Cells.

DYT1 dystonia is a debilitating neurological movement disorder that arises upon Torsin ATPase deficiency. Nuclear envelope (NE) blebs that contain FG-nucleoporins (FG-Nups) and K48-linked ubiquitin are the hallmark phenotype of Torsin manipulation across disease models of DYT1 dystonia. While the aberrant deposition of FG-Nups is caused by defective nuclear pore complex assembly, the source of K48-ubiquitylated proteins inside NE blebs is not known. Here, we demonstrate that the characteristic K48-ubiquitin accumulation inside blebs requires p97 activity. This activity is highly dependent on the p97 adaptor UBXD1. We show that p97 does not significantly depend on the Ufd1/Npl4 heterodimer to generate the K48-ubiquitylated proteins inside blebs, nor does inhibiting translation affect the ubiquitin sequestration in blebs. However, stimulating global ubiquitylation by heat shock greatly increases the amount of K48-ubiquitin sequestered inside blebs. These results suggest that blebs have an extraordinarily high capacity for sequestering ubiquitylated protein generated in a p97-dependent manner. The p97/UBXD1 axis is thus a major factor contributing to cellular DYT1 dystonia pathology and its modulation represents an unexplored potential for therapeutic development.

Alteration of the cholinergic system and motor deficits in cholinergic neuron-specific Dyt1 knockout mice.

Dystonia is a neurological movement disorder characterized by sustained or intermittent muscle contractions, repetitive movement, and sometimes abnormal postures. DYT1 dystonia is one of the most common genetic dystonias, and most patients carry heterozygous DYT1 ∆GAG mutations causing a loss of a glutamic acid of the protein torsinA. Patients can be treated with anticholinergics, such as trihexyphenidyl, suggesting an abnormal cholinergic state. Early work on the cell-autonomous effects of Dyt1 deletion with ChI-specific Dyt1 conditional knockout mice (Dyt1 Ch1KO) revealed abnormal electrophysiological responses of striatal ChIs to muscarine and quinpirole, motor deficits, and no changes in the number or size of the ChIs. However, the Chat-cre line that was used to derive Dyt1 Ch1KO mice contained a neomycin cassette and was reported to have ectopic cre-mediated recombination. In this study, we generated a Dyt1 Ch2KO mouse line by removing the neomycin cassette in Dyt1 Ch1KO mice. The Dyt1 Ch2KO mice showed abnormal paw clenching behavior, motor coordination and balance deficits, impaired motor learning, reduced striatal choline acetyltransferase protein level, and a reduced number of striatal ChIs. Furthermore, the mutant striatal ChIs had a normal muscarinic inhibitory function, impaired quinpirole-mediated inhibition, and altered current density. Our findings demonstrate a cell-autonomous effect of Dyt1 deletion on the striatal ChIs and a critical role for the striatal ChIs and corticostriatal pathway in the pathogenesis of DYT1 dystonia.

Cell-intrinsic effects of TorsinA(ΔE) disrupt dopamine release in a mouse model of TOR1A dystonia.

TOR1A-associated dystonia, otherwise known as DYT1 dystonia, is an inherited dystonia caused by a three base-pair deletion in the TOR1A gene (TOR1AΔE). Although the mechanisms underlying the dystonic movements are largely unknown, abnormalities in striatal dopamine and acetylcholine neurotransmission are consistently implicated whereby dopamine release is reduced while cholinergic tone is increased. Because striatal cholinergic neurotransmission mediates dopamine release, it is not known if the dopamine release deficit is mediated indirectly by abnormal acetylcholine neurotransmission or if Tor1a(ΔE) acts directly within dopaminergic neurons to attenuate release. To dissect the microcircuit that governs the deficit in dopamine release, we conditionally expressed Tor1a(ΔE) in either dopamine neurons or cholinergic interneurons in mice and assessed striatal dopamine release using ex vivo fast scan cyclic voltammetry or dopamine efflux using in vivo microdialysis. Conditional expression of Tor1a(ΔE) in cholinergic neurons did not affect striatal dopamine release. In contrast, conditional expression of Tor1a(ΔE) in dopamine neurons reduced dopamine release to 50% of normal, which is comparable to the deficit in Tor1a+/ΔE knockin mice that express the mutation ubiquitously. Despite the deficit in dopamine release, we found that the Tor1a(ΔE) mutation does not cause obvious nerve terminal dysfunction as other presynaptic mechanisms, including electrical excitability, vesicle recycling/refilling, Ca2+ signaling, D2 dopamine autoreceptor function and GABAB receptor function, are intact. Although the mechanistic link between Tor1a(ΔE) and dopamine release is unclear, these results clearly demonstrate that the defect in dopamine release is caused by the action of the Tor1a(ΔE) mutation within dopamine neurons.

DYT-TOR1A subcellular proteomics reveals selective vulnerability of the nuclear proteome to cell stress.

TorsinA is a AAA+ ATPase that shuttles between the ER lumen and outer nuclear envelope in an ATP-dependent manner and is functionally implicated in nucleocytoplasmic transport. We hypothesized that the DYT-TOR1A dystonia disease-causing variant, ΔE TorsinA, may therefore disrupt the normal subcellular distribution of proteins between the nuclear and cytosolic compartments. To test this hypothesis, we performed proteomic analysis on nuclear and cytosolic subcellular fractions from DYT-TOR1A and wildtype mouse embryonic fibroblasts (MEFs). We further examined the compartmental proteomes following exposure to thapsigargin (Tg), an endoplasmic reticulum (ER) stressor, because DYT-TOR1A dystonia models have previously shown abnormalities in cellular stress responses. Across both subcellular compartments, proteomes of DYT-TOR1A cells showed basal state disruptions consistent with an activated stress response, and in response to thapsigargin, a blunted stress response. However, the DYT-TOR1A nuclear proteome under Tg cell stress showed the most pronounced and disproportionate degree of protein disruptions - 3-fold greater than all other conditions. The affected proteins extended beyond those typically associated with stress responses, including enrichments for processes critical for neuronal synaptic function. These findings highlight the advantage of subcellular proteomics to reveal events that localize to discrete subcellular compartments and refine thinking about the mechanisms and significance of cell stress in DYT-TOR1A pathogenesis.

Decreased number of striatal cholinergic interneurons and motor deficits in dopamine receptor 2-expressing-cell-specific Dyt1 conditional knockout mice.

DYT1 early-onset generalized torsion dystonia is a hereditary movement disorder characterized by abnormal postures and repeated movements. It is caused mainly by a heterozygous trinucleotide deletion in DYT1/TOR1A, coding for torsinA. The mutation may lead to a partial loss of torsinA function. Functional alterations of the basal ganglia circuits have been implicated in this disease. Striatal dopamine receptor 2 (D2R) levels are significantly decreased in DYT1 dystonia patients and in the animal models of DYT1 dystonia. D2R-expressing cells, such as the medium spiny neurons in the indirect pathway, striatal cholinergic interneurons, and dopaminergic neurons in the basal ganglia circuits, contribute to motor performance. However, the function of torsinA in these neurons and its contribution to the motor symptoms is not clear. Here, D2R-expressing-cell-specific Dyt1 conditional knockout (d2KO) mice were generated and in vivo effects of torsinA loss in the corresponding cells were examined. The Dyt1 d2KO mice showed significant reductions of striatal torsinA, acetylcholine metabolic enzymes, Tropomyosin receptor kinase A (TrkA), and cholinergic interneurons. The Dyt1 d2KO mice also showed significant reductions of striatal D2R dimers and tyrosine hydroxylase without significant alteration in striatal monoamine contents or the number of dopaminergic neurons in the substantia nigra. The Dyt1 d2KO male mice showed motor deficits in the accelerated rotarod and beam-walking tests without overt dystonic symptoms. Moreover, the Dyt1 d2KO male mice showed significant correlations between striatal monoamines and locomotion. The results suggest that torsinA in the D2R-expressing cells play a critical role in the development or survival of the striatal cholinergic interneurons, expression of striatal D2R mature form, and motor performance. Medical interventions to compensate for the loss of torsinA function in these neurons may affect the onset and symptoms of this disease.

Impaired differentiation of human induced neural stem cells by TOR1A overexpression.

DYT-TOR1A is the most common inherited dystonia caused by a three nucleotide (GAG) deletion (dE) in the TOR1A gene. Death early after birth and cortical anomalies of the full knockout in rodents underscore its developmental importance. We therefore explored the timed effects of TOR1A-wt and TOR1A-dE during differentiation in a human neural in vitro model. We used lentiviral tet-ON expression of TOR1A-wt and -dE in induced neural stem cells derived from healthy donors. Overexpression was induced during proliferation of neural precursors, during differentiation and after differentiation into mature neurons. Overexpression of both wildtype and mutated protein had no effect on the viability and cell number of neural precursors as well as mature neurons when initiated before or after differentiation. However, if induced during differentiation, overexpression of TOR1A-wt and -dE led to a pronounced reduction of mature neurons in a dose dependent manner. Our data underscores the importance of physiological expression levels of TOR1A as crucial for proper neuronal differentiation. We did not find evidence for a specific impact of the mutated TOR1A on neuronal maturation.

Characterization of the binding mode of JNK-interacting protein 1 (JIP1) to kinesin-light chain 1 (KLC1).

JIP1 was first identified as scaffold protein for the MAP kinase JNK and is a cargo protein for the kinesin1 molecular motor. JIP1 plays significant and broad roles in neurons, mainly as a regulator of kinesin1-dependent transport, and is associated with human pathologies such as cancer and Alzheimer disease. JIP1 is specifically recruited by the kinesin-light chain 1 (KLC1) of kinesin1, but the details of this interaction are not yet fully elucidated. Here, using calorimetry, we extensively biochemically characterized the interaction between KLC1 and JIP1. Using various truncated fragments of the tetratricopeptide repeat (TPR) domain of KLC1, we narrowed down its JIP1-binding region and identified seven KLC1 residues critical for JIP1 binding. These isothermal titration calorimetry (ITC)-based binding data enabled us to footprint the JIP1-binding site on KLC1-TPR. This footprint was used to uncover the structural basis for the marginal inhibition of JIP1 binding by the autoinhibitory LFP-acidic motif of KLC1, as well as for the competition between JIP1 and another cargo protein of kinesin1, the W-acidic motif-containing alcadein-α. Also, we examined the role of each of these critical residues of KLC1 for JIP1 binding in light of the previously reported crystal structure of the KLC1-TPR:JIP1 complex. Finally, sequence search in eukaryotic genomes identified several proteins, among which is SH2D6, that exhibit a motif similar to the KLC1-binding motif of JIP1. Overall, our extensive biochemical characterization of the KLC:JIP1 interaction, as well as identification of potential KLC1-binding partners, improves the understanding of how this growing family of cargos is recruited to kinesin1 by KLC1.

Advances in molecular and cell biology of dystonia: Focus on torsinA.

During the last two decades, our knowledge on the genetic bases of Mendelian forms of dystonia has expanded significantly. This has translated into the generation of multiple cell and animal models to explore the neurobiological bases of this hyperkinetic movement disorder. A majority of these studies have focused on DYT1 dystonia, caused by dominant mutations in the gene encoding for the protein torsinA. Since its discovery, work in multiple laboratories helped identify the subcellular localization of torsinA, key structural features, functionally important physical interactions and biological pathways and physiological events influenced by torsinA. Moreover, recent experimental work indicates potential shared pathogenic pathways between different genetic forms of dystonia. This review will summarize our current knowledge on the molecular and basic biological features of torsinA and its dysfunction when carrying disease-causing mutation, identifying future research priorities and proposing a model of dystonia pathogenesis that might extend beyond DYT1.

TorsinA Is Functionally Associated with Spermatogenesis.

TorsinA is a member of the AAA+ superfamily of adenosine triphosphatases. These AAA+ proteins have numerous biological functions, including vesicle fusion, cytoskeleton dynamics, intracellular trafficking, protein folding, and degradation as well as organelle biogenesis. Of particular interest is torsinA, which is mainly located in the endoplasmic reticulum (ER) and nuclear envelope (NE). Interestingly, mutations in the TOR1A gene (the gene encoding torsinA) are associated with DYT1 dystonia and with the preferential localization of mutated torsinA at the NE, where it is associated with lamina-associated polypeptide 1. A bioinformatics study of the torsinA interactome revealed reproductive processes to be highly relevant, as proteins in this class were found to interact with the former. Interestingly, the torsin protein family had never been previously described to be associated with the mammalian spermatogenic process. Histological staining of torsinA in human testis tissue revealed a granular cytoplasmic localization in mid- and late spermatocytes. We further sought to understand this newly discovered expression of torsinA in the meiotic phase of human spermatogenesis by studying its specific subcellular distribution. TorsinA is not present in the ER as commonly described. The proposal that torsinA might relocate to the pro-acrosomal vesicles in the Golgi apparatus is discussed.

TOR1A variants cause a severe arthrogryposis with developmental delay, strabismus and tremor.

See Ginevrino and Valente (doi:10.1093/brain/awx260) for a scientific commentary on this article. Autosomal dominant torsion dystonia-1 is a disease with incomplete penetrance most often caused by an in-frame GAG deletion (p.Glu303del) in the endoplasmic reticulum luminal protein torsinA encoded by TOR1A. We report an association of the homozygous dominant disease-causing TOR1A p.Glu303del mutation, and a novel homozygous missense variant (p.Gly318Ser) with a severe arthrogryposis phenotype with developmental delay, strabismus and tremor in three unrelated Iranian families. All parents who were carriers of the TOR1A variant showed no evidence of neurological symptoms or signs, indicating decreased penetrance similar to families with autosomal dominant torsion dystonia-1. The results from cell assays demonstrate that the p.Gly318Ser substitution causes a redistribution of torsinA from the endoplasmic reticulum to the nuclear envelope, similar to the hallmark of the p.Glu303del mutation. Our study highlights that TOR1A mutations should be considered in patients with severe arthrogryposis and further expands the phenotypic spectrum associated with TOR1A mutations.

Human TorsinA can function in the yeast cytosol as a molecular chaperone.

TorsinA (TorA) is an AAA+ (ATPases associated with diverse cellular activities) ATPase linked to dystonia type 1 (DYT1), a neurological disorder that leads to uncontrollable muscular movements. Although DYT1 is linked to a 3 bp deletion in the C-terminus of TorA, the biological function of TorA remains to be established. Here, we use the yeast Saccharomyces cerevisiae as a tractable in vivo model to explore TorA function. We demonstrate that TorA can protect yeast cells against different forms of environmental stress and show that in the absence of the molecular disaggregase Hsp104, TorA can refold heat-denatured luciferase in vivo in an ATP-dependent manner. However, this activity requires TorA to be translocated to the cytoplasm from the endoplasmic reticulum in order to access and process cytoplasmic protein aggregates. Furthermore, mutational or chemical inactivation of the ATPase activity of TorA blocks this activity. We also find that TorA can inhibit the propagation of certain conformational variants of [PSI+], the aggregated prion form of the endogenous Sup35 protein. Finally, we show that while cellular localisation remains unchanged in the dystonia-linked TorA mutant ΔE302-303, the ability of this mutant form of TorA to protect against cellular stress and to facilitate protein refolding is impaired, consistent with it being a loss-of-function mutation.

Torsins: not your typical AAA+ ATPases.

Torsin ATPases (Torsins) belong to the widespread AAA+ (ATPases associated with a variety of cellular activities) family of ATPases, which share structural similarity but have diverse cellular functions. Torsins are outliers in this family because they lack many characteristics of typical AAA+ proteins, and they are the only members of the AAA+ family located in the endoplasmic reticulum and contiguous perinuclear space. While it is clear that Torsins have essential roles in many, if not all metazoans, their precise cellular functions remain elusive. Studying Torsins has significant medical relevance since mutations in Torsins or Torsin-associated proteins result in a variety of congenital human disorders, the most frequent of which is early-onset torsion (DYT1) dystonia, a severe movement disorder. A better understanding of the Torsin system is needed to define the molecular etiology of these diseases, potentially enabling corrective therapy. Here, we provide a comprehensive overview of the Torsin system in metazoans, discuss functional clues obtained from various model systems and organisms and provide a phylogenetic and structural analysis of Torsins and their regulatory cofactors in relation to disease-causative mutations. Moreover, we review recent data that have led to a dramatically improved understanding of these machines at a molecular level, providing a foundation for investigating the molecular defects underlying the associated movement disorders. Lastly, we discuss our ideas on how recent progress may be utilized to inform future studies aimed at determining the cellular role(s) of these atypical molecular machines and their implications for dystonia treatment options.

Disruption of Protein Processing in the Endoplasmic Reticulum of DYT1 Knock-in Mice Implicates Novel Pathways in Dystonia Pathogenesis.

Dystonia type 1 (DYT1) is a dominantly inherited neurological disease caused by mutations in TOR1A, the gene encoding the endoplasmic reticulum (ER)-resident protein torsinA. Previous work mostly completed in cell-based systems suggests that mutant torsinA alters protein processing in the secretory pathway. We hypothesized that inducing ER stress in the mammalian brain in vivo would trigger or exacerbate mutant torsinA-induced dysfunction. To test this hypothesis, we crossed DYT1 knock-in with p58(IPK)-null mice. The ER co-chaperone p58(IPK) interacts with BiP and assists in protein maturation by helping to fold ER cargo. Its deletion increases the cellular sensitivity to ER stress. We found a lower generation of DYT1 knock-in/p58 knock-out mice than expected from this cross, suggesting a developmental interaction that influences viability. However, surviving animals did not exhibit abnormal motor function. Analysis of brain tissue uncovered dysregulation of eiF2α and Akt/mTOR translational control pathways in the DYT1 brain, a finding confirmed in a second rodent model and in human brain. Finally, an unbiased proteomic analysis identified relevant changes in the neuronal protein landscape suggesting abnormal ER protein metabolism and calcium dysregulation. Functional studies confirmed the interaction between the DYT1 genotype and neuronal calcium dynamics. Overall, these findings advance our knowledge on dystonia, linking translational control pathways and calcium physiology to dystonia pathogenesis and identifying potential new pharmacological targets. SIGNIFICANCE STATEMENT: Dystonia type 1 (DYT1) is one of the different forms of inherited dystonia, a neurological disorder characterized by involuntary, disabling movements. DYT1 is caused by mutations in the gene that encodes the endoplasmic reticulum (ER)-resident protein torsinA. How mutant torsinA causes neuronal dysfunction remains unknown. Here, we show the behavioral and molecular consequences of stressing the ER in DYT1 mice by increasing the amount of misfolded proteins. This resulted in the generation of a reduced number of animals, evidence of abnormal ER protein processing and dysregulation of translational control pathways. The work described here proposes a shared mechanism for different forms of dystonia, links for the first time known biological pathways to dystonia pathogenesis, and uncovers potential pharmacological targets for its treatment.

Membrane defects and genetic redundancy: Are we at a turning point for DYT1 dystonia?

Heterozygosity for a 3-base pair deletion (ΔGAG) in TOR1A/torsinA is one of the most common causes of hereditary dystonia. In this review, we highlight current understanding of how this mutation causes disease from research spanning structural biochemistry, cell science, neurobiology, and several model organisms. We now know that homozygosity for ΔGAG has the same effects as Tor1aKO , implicating a partial loss of function mechanism in the ΔGAG/+ disease state. In addition, torsinA loss specifically affects neurons in mice, even though the gene is broadly expressed, apparently because of differential expression of homologous torsinB. Furthermore, certain neuronal subtypes are more severely affected by torsinA loss. Interestingly, these include striatal cholinergic interneurons that display abnormal responses to dopamine in several Tor1a animal models. There is also progress on understanding torsinA molecular cell biology. The structural basis of how ΔGAG inhibits torsinA ATPase activity is defined, although mutant torsinAΔGAG protein also displays some characteristics suggesting it contributes to dystonia by a gain-of-function mechanism. Furthermore, a consistent relationship is emerging between torsin dysfunction and membrane biology, including an evolutionarily conserved regulation of lipid metabolism. Considered together, these findings provide major advances toward understanding the molecular, cellular, and neurobiological pathologies of DYT1/TOR1A dystonia that can hopefully be exploited for new approaches to treat this disease. © 2016 International Parkinson and Movement Disorder Society.

Mouse model of rare TOR1A variant found in sporadic focal dystonia impairs domains affected in DYT1 dystonia patients and animal models.

Rare de novo mutations in genes associated with inherited Mendelian disorders are potential contributors to sporadic disease. DYT1 dystonia is an autosomal dominant, early-onset, generalized dystonia associated with an in-frame, trinucleotide deletion (n. delGAG, p. ΔE 302/303) in the Tor1a gene. Here we examine the significance of a rare missense variant in the Tor1a gene (c. 613T>A, p. F205I), previously identified in a patient with sporadic late-onset focal dystonia, by modeling it in mice. Homozygous F205I mice have motor impairment, reduced steady-state levels of TorsinA, altered corticostriatal synaptic plasticity, and prominent brain imaging abnormalities in areas associated with motor function. Thus, the F205I variant causes abnormalities in domains affected in people and/or mouse models with the DYT1 Tor1a mutation (ΔE). Our findings establish the pathological significance of the F205I Tor1a variant and provide a model with both etiological and phenotypic relevance to further investigate dystonia mechanisms.

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.