Microarray analysis reveals induction of heat shock proteins mRNAs by the torsion dystonia protein, TorsinA

DYT-TOR1A dystonia: an update on pathogenesis and treatment

DYT-TOR1A dystonia is a neurological disorder characterized by involuntary muscle contractions and abnormal movements. It is a severe genetic form of dystonia caused by mutations in the TOR1A gene. TorsinA is a member of the AAA + family of adenosine triphosphatases (ATPases) involved in a variety of cellular functions, including protein folding, lipid metabolism, cytoskeletal organization, and nucleocytoskeletal coupling. Almost all patients with TOR1A-related dystonia harbor the same mutation, an in-frame GAG deletion (ΔGAG) in the last of its 5 exons. This recurrent variant results in the deletion of one of two tandem glutamic acid residues (i.e., E302/303) in a protein named torsinA [torsinA(△E)]. Although the mutation is hereditary, not all carriers will develop DYT-TOR1A dystonia, indicating the involvement of other factors in the disease process. The current understanding of the pathophysiology of DYT-TOR1A dystonia involves multiple factors, including abnormal protein folding, signaling between neurons and glial cells, and dysfunction of the protein quality control system. As there are currently no curative treatments for DYT-TOR1A dystonia, progress in research provides insight into its pathogenesis, leading to potential therapeutic and preventative strategies. This review summarizes the latest research advances in the pathogenesis, diagnosis, and treatment of DYT-TOR1A dystonia.

Loss of the dystonia gene Thap1 leads to transcriptional deficits that converge on common pathogenic pathways in dystonic syndromes

Dystonia is a movement disorder characterized by involuntary and repetitive co-contractions of agonist and antagonist muscles. Dystonia 6 (DYT6) is an autosomal dominant dystonia caused by loss-of-function mutations in the zinc finger transcription factor THAP1. We have generated Thap1 knock-out mice with a view to understanding its transcriptional role. While germ-line deletion of Thap1 is embryonic lethal, mice lacking one Thap1 allele-which in principle should recapitulate the haploinsufficiency of the human syndrome-do not show a discernable phenotype. This is because mice show autoregulation of Thap1 mRNA levels with upregulation at the non-affected locus. We then deleted Thap1 in glial and neuronal precursors using a nestin-conditional approach. Although these mice do not exhibit dystonia, they show pronounced locomotor deficits reflecting derangements in the cerebellar and basal ganglia circuitry. These behavioral features are associated with alterations in the expression of genes involved in nervous system development, synaptic transmission, cytoskeleton, gliosis and dopamine signaling that link DYT6 to other primary and secondary dystonic syndromes.

Emerging common molecular pathways for primary dystonia

The dystonias are a group of hyperkinetic movement disorders whose principal cause is neuron dysfunction at 1 or more interconnected nodes of the motor system. The study of genes and proteins that cause familial dystonia provides critical information about the cellular pathways involved in this dysfunction, which disrupts the motor pathways at the systems level. In recent years study of the increasing number of DYT genes has implicated a number of cell functions that appear to be involved in the pathogenesis of dystonia. A review of the literature published in English-language publications available on PubMed relating to the genetics and cellular pathology of dystonia was performed. Numerous potential pathogenetic mechanisms have been identified. We describe those that fall into 3 emerging thematic groups: cell-cycle and transcriptional regulation in the nucleus, endoplasmic reticulum and nuclear envelope function, and control of synaptic function. © 2013 Movement Disorder Society.

Prolonged generalized dystonia after chronic cerebellar application of kainic acid

Dystonia has traditionally been considered as a basal ganglia disorder, but there is growing evidence that impaired function of the cerebellum may also play a crucial part in the pathogenesis of this disorder. We now demonstrate that chronic application of kainic acid into the cerebellar vermis of rats results in a prolonged and generalized dystonic motor phenotype and provide detailed characterization of this new animal model for dystonia. c-fos expression, as a marker of neuronal activation, was increased not only in the cerebellum itself, but also in the ventro-anterior thalamus, further supporting the assumption of a disturbed neuronal network underlying the pathogenesis of this disorder. Preproenkephalin expression in the striatum was reduced, but prodynorphin expression remained unaltered, suggesting secondary changes in the indirect, but not in the direct basal ganglia pathway in our model system. Hsp70 expression was specifically increased in the Purkinje cell layer and the red nucleus. This new rat model of dystonia may be useful not only for further studies investigating the role of the cerebellum in the pathogenesis of dystonia, but also to assess compounds for their beneficial effect on dystonia in a rodent model of prolonged, generalized dystonia.

Untethering the nuclear envelope and cytoskeleton: biologically distinct dystonias arising from a common cellular dysfunction

Most cases of early onset DYT1 dystonia in humans are caused by a GAG deletion in the TOR1A gene leading to loss of a glutamic acid (ΔE) in the torsinA protein, which underlies a movement disorder associated with neuronal dysfunction without apparent neurodegeneration. Mutation/deletion of the gene (Dst) encoding dystonin in mice results in a dystonic movement disorder termed dystonia musculorum, which resembles aspects of dystonia in humans. While torsinA and dystonin proteins do not share modular domain architecture, they participate in a similar function by modulating a structural link between the nuclear envelope and the cytoskeleton in neuronal cells. We suggest that through a shared interaction with the nuclear envelope protein nesprin-3α, torsinA and the neuronal dystonin-a2 isoform comprise a bridge complex between the outer nuclear membrane and the cytoskeleton, which is critical for some aspects of neuronal development and function. Elucidation of the overlapping roles of torsinA and dystonin-a2 in nuclear/endoplasmic reticulum dynamics should provide insights into the cellular mechanisms underlying the dystonic phenotype.

Molecular pathways in dystonia

The hereditary dystonias comprise a set of diseases defined by a common constellation of motor deficits. These disorders are most likely associated with different molecular etiologies, many of which have yet to be elucidated. Here we discuss recent advances in three forms of hereditary dystonia, DYT1, DYT6 and DYT16, which share a similar clinical picture: onset in childhood or adolescence, progressive spread of symptoms with generalized involvement of body regions and a steady state affliction without treatment. Unlike DYT1, the genes responsible for DYT6 and DYT16 have only recently been identified, with relatively little information about the function of the encoded proteins. Nevertheless, recent data suggest that these proteins may fit together within interacting pathways involved in dopaminergic signaling, transcriptional regulation, and cellular stress responses. This review focuses on these molecular pathways, highlighting potential common themes among these dystonias which may serve as areas for future research. This article is part of a Special Issue entitled "Advances in dystonia".

Expression profiling in peripheral blood reveals signature for penetrance in DYT1 dystonia

DYT1 dystonia is an autosomal-dominantly inherited movement disorder, which is usually caused by a GAG deletion in the TOR1A gene. Due to the reduced penetrance of approximately 30-40%, the determination of the mutation in a subject is of limited use with regard to actual manifestation of symptoms. In the present study, we used Affymetrix oligonucleotide microarrays to analyze global gene expression in blood samples of 15 manifesting and 15 non-manifesting mutation carriers in order to identify a susceptibility profile beyond the GAG deletion which is associated with the manifestation of symptoms in DYT1 dystonia. We identified a genetic signature which distinguished between asymptomatic mutation carriers and symptomatic DYT1 patients with 86.7% sensitivity and 100% specificity. This genetic signature could correctly predict the disease state in an independent test set with a sensitivity of 87.5% and a specificity of 85.7%. Conclusively, this genetic signature might provide a possibility to distinguish DYT1 patients from asymptomatic mutation carriers.

Transcriptional and proteomic profiling in a cellular model of DYT1 dystonia

DYT1, the most common inherited dystonia, is caused by a common dominant mutation in the TOR1A gene that leads to a glutamic acid deletion in the protein torsinA. Wild-type torsinA locates preferentially in the endoplasmic reticulum while the disease-linked mutant accumulates in the nuclear envelope. As a result, it has been proposed that DYT1 pathogenesis could result either from transcriptional dysregulation caused by abnormal interactions of mutant torsinA with nuclear envelope proteins, or from a loss of torsinA function in the endoplasmic reticulum that would impair specific neurobiological pathways. Aiming to determine whether one or both of these potential mechanisms are implicated in DYT1 pathogenesis, we completed unbiased transcriptional and proteomic profiling in well-characterized neural cell lines that inducibly express wild-type or mutant torsinA. These experiments demonstrated that the accumulation of mutant torsinA in the nuclear envelope is not sufficient to cause transcriptional dysregulation. However, we detected expression changes at the protein level that, together with other reports, suggest a potential implication of torsinA on energy metabolism and regulation of the redox state. Furthermore, several proteins identified in this study have been previously linked to other forms of dystonia. In conclusion, our results argue against the hypothesis of transcriptional dysregulation in DYT1 dystonia, suggesting potential alternative pathogenic pathways.

Biochemical characterization of torsinB

Mutations in torsinA, a member of the AAA+ family of ATPases, are associated with early onset-dystonia. A closely related homologue, torsinB, has also been described but the significance of this second form is not clear. Here, we demonstrate that in transfected cells, torsinB has similar electrophoretic mobility to torsinA but is more basic consistent with predictions from the cDNA sequence. Like torsinA, torsinB is glycosylated and localized to PDI-positive structures in cells. However, torsinB unlike torsinA has a tendency to form intracellular inclusions when expressed at similar levels. We were able to confirm previous reports that torsinA is present in brainstem Lewy bodies, but we saw no torsinB-like immunoreactivity in the same structures. These results show that torsins A and B are similar proteins, although there are differences in the abundance of the two homologues and in their recruitment into Lewy bodies.

Brainstem pathology in DYT1 primary torsion dystonia

DYT1 dystonia is a severe form of young-onset dystonia caused by a mutation in the gene that encodes for the protein torsinA, which is thought to play a role in protein transport and degradation. We describe, for the first time to our knowledge, perinuclear inclusion bodies in the midbrain reticular formation and periaqueductal gray in four clinically documented and genetically confirmed DYT1 patients but not in controls. The inclusions were located within cholinergic and other neurons in the pedunculopontine nucleus, cuneiform nucleus, and griseum centrale mesencephali and stained positively for ubiquitin, torsinA, and the nuclear envelope protein lamin A/C. No evidence of inclusion body formation was detected in the substantia nigra pars compacta, striatum, hippocampus, or selected regions of the cerebral cortex. We also noted tau/ubiquitin-immunoreactive aggregates in pigmented neurons of the substantia nigra pars compacta and locus coeruleus in all four DYT1 dystonia cases, but not in controls. This study supports the notion that DYT1 dystonia is associated with impaired protein handling and the nuclear envelope. The role of the pedunculopontine and cuneiform nuclei, and related brainstem brainstem structures, in mediating motor activity and controlling muscle tone suggests that alterations in these structures could underlie the pathophysiology of DYT1 dystonia [corrected]