Dystonia is the third most common movement disorder in humans, second only to Parkinson's disease and tremor. The most severe form of dystonia, early onset generalized torsion dystonia, inherited as an autosomal dominant condition, results from a mutation in the coding region of TOR1A. This gene has also been implicated in more prevalent forms of adult onset focal dystonias. TorsinA is an AAA+ protein located primarily in the endoplasmic reticulum(ER) and nuclear envelope(NE). The proposed studies are designed to further characterize torsinA in order to elucidate its functions, as well as dysfunctions caused by the DYT1 mutant form. TorsinA is hypothesized to modulate interactions between NE/ER proteins and the cytoskeleton involved in neurodevelopment, synaptic neurotransmission and response to stress.
Aim 1 - Evaluate the effect of torsinA status on migration of neurons in culture. The effect of torsinA in neuronal migration will be studied using striatal and cortical neurons from homozygous torsinA knock-out, heterozygous knock-in, transgenic and control mouse embryos. Migration will be monitored in microfabricated channels using vital fluorescent dyes and proteins to monitor speed of migration and intracellular movement of cell organelles, with correlative immunocytochemistry.
Aim 2 - Elucidate the ER function of torsinA in processing proteins through the secretory pathway. The focus will be on the function of torsinA in the ER using DTY1 patient and control fibroblasts and mouse neurons with or without torsinA. We will assess secretion of reporter luciferases to monitor release through the secretory and vesicular pathways, as well as processing of normal glycoproteins, the D2 receptor and epsilon-sarcoglycan (mutated in myoclonic dystonia). Immunocytochemistry, cytoskeletal-disrupting drugs and biochemical methods will be used to evaluate potential interactions between torsinA and ER proteins involved in entry into, exit from or movement of the ER.
Aim 3 - Explore involvement of torsinA in the ER stress response. We will evaluate whether mutant torsinA confers hypersensitivity to different forms of ER stress in DYT1 patient as compared to control fibroblasts, and in neurons and neural cells expressing human wild-type or mutant torsinA. ER stress will be monitored using a luciferase reporter to monitor the initial delay in protein synthesis, as well as more traditional methods such as splicing of the XBP-1 message, elevation of BiP levels and cell death. This research will enhance understanding of the molecular etiology of dystonia and provide insights into potential therapeutic intervention.
Current therapies for early onset dystonia are inadequate or intrusive. Understanding the function of torsinA, which is compromised in this movement disorder, will allow rational drug design and provide bioassays to assess the ability of pharmaceuticals to normalize torsinA function in preclinical studies.
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