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Silencing mutant ATXN3 expression resolves molecular phenotypes in SCA3 transgenic mice.

ABSTRACT: Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disease caused by a polyglutamine expansion in the deubiquitinating enzyme, Ataxin-3. Currently, there are no effective treatments for this fatal disorder but studies support the hypothesis that reducing mutant Ataxin-3 protein levels might reverse or halt the progression of disease in SCA3. Here, we sought to modulate ATXN3 expression in vivo using RNA interference. We developed artificial microRNA mimics targeting the 3'-untranslated region (3'UTR) of human ATXN3 and then used recombinant adeno-associated virus to deliver them to the cerebellum of transgenic mice expressing the full human disease gene (SCA3/MJD84.2 mice). Anti-ATXN3 microRNA mimics effectively suppressed human ATXN3 expression in SCA3/MJD84.2 mice. Short-term treatment cleared the abnormal nuclear accumulation of mutant Ataxin-3 throughout the transduced SCA3/MJD84.2 cerebellum. Analysis also revealed changes in the steady-state levels of specific microRNAs in the cerebellum of SCA3/MJD84.2 mice, a previously uncharacterized molecular phenotype of SCA3 that appears to be dependent on mutant Ataxin-3 expression. Our findings support the preclinical development of molecular therapies aimed at halting the expression of ATXN3 as a viable approach to SCA3 and point to microRNA deregulation as a potential surrogate marker of SCA3 pathogenesis.

SUBMITTER: Rodriguez-Lebron E

PROVIDER: S-EPMC3808130 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature

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Silencing mutant ATXN3 expression resolves molecular phenotypes in SCA3 transgenic mice.

Rodríguez-Lebrón Edgardo E Costa Maria do Carmo Mdo C Luna-Cancalon Katiuska K Peron Therese M TM Fischer Svetlana S Boudreau Ryan L RL Davidson Beverly L BL Paulson Henry L HL

Molecular therapy : the journal of the American Society of Gene Therapy 20130703 10

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disease caused by a polyglutamine expansion in the deubiquitinating enzyme, Ataxin-3. Currently, there are no effective treatments for this fatal disorder but studies support the hypothesis that reducing mutant Ataxin-3 protein levels might reverse or halt the progression of disease in SCA3. Here, we sought to modulate ATXN3 expression in vivo using RNA interference. We developed artificial microRNA mimics targeting the 3'-untranslated ...[more]

PMID: 23820820

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Project description:Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease (MJD), is an untreatable autosomal dominant neurodegenerative disease, and the most common such inherited ataxia worldwide. The mutation in SCA3 is the expansion of a polymorphic CAG tri-nucleotide repeat sequence in the C-terminal coding region of the ATXN3 gene at chromosomal locus 14q32.1. The mutant ATXN3 protein encoding expanded glutamine (polyQ) sequences interacts with multiple proteins in vivo, and is deposited as aggregates in the SCA3 brain. A large body of literature suggests that the loss of function of the native ATNX3-interacting proteins that are deposited in the polyQ aggregates contributes to cellular toxicity, systemic neurodegeneration and the pathogenic mechanism in SCA3. Nonetheless, a significant understanding of the disease etiology of SCA3, the molecular mechanism by which the polyQ expansions in the mutant ATXN3 induce neurodegeneration in SCA3 has remained elusive. In the present study, we show that the essential DNA strand break repair enzyme PNKP (polynucleotide kinase 3'-phosphatase) interacts with, and is inactivated by, the mutant ATXN3, resulting in inefficient DNA repair, persistent accumulation of DNA damage/strand breaks, and subsequent chronic activation of the DNA damage-response ataxia telangiectasia-mutated (ATM) signaling pathway in SCA3. We report that persistent accumulation of DNA damage/strand breaks and chronic activation of the serine/threonine kinase ATM and the downstream p53 and protein kinase C-δ pro-apoptotic pathways trigger neuronal dysfunction and eventually neuronal death in SCA3. Either PNKP overexpression or pharmacological inhibition of ATM dramatically blocked mutant ATXN3-mediated cell death. Discovery of the mechanism by which mutant ATXN3 induces DNA damage and amplifies the pro-death signaling pathways provides a molecular basis for neurodegeneration due to PNKP inactivation in SCA3, and for the first time offers a possible approach to treatment.

Project description:Machado-Joseph disease (MJD) or spinocerebellar ataxia type 3 (SCA3) is an autosomal dominantly-inherited neurodegenerative disorder caused by the over-repetition of a CAG codon in the MJD1 gene. This expansion translates into a polyglutamine tract that confers a toxic gain-of-function to the mutant protein--ataxin-3, leading to neurodegeneration in specific brain regions, with particular severity in the cerebellum. No treatment able to modify the disease progression is available. However, gene silencing by RNA interference has shown promising results. Therefore, in this study we investigated whether lentiviral-mediated allele-specific silencing of the mutant ataxin-3 gene, after disease onset, would rescue the motor behavior deficits and neuropathological features in a severely impaired transgenic mouse model of MJD. For this purpose, we injected lentiviral vectors encoding allele-specific silencing-sequences (shAtx3) into the cerebellum of diseased transgenic mice expressing the targeted C-variant of mutant ataxin-3 present in 70% of MJD patients. This variation permits to discriminate between the wild-type and mutant forms, maintaining the normal function of the wild-type allele and silencing only the mutant form. Quantitative analysis of rotarod performance, footprint and activity patterns revealed significant and robust alleviation of gait, balance (average 3-fold increase of rotarod test time), locomotor and exploratory activity impairments in shAtx3-injected mice, as compared to control ones injected with shGFP. An important improvement of neuropathology was also observed, regarding the number of intranuclear inclusions, calbindin and DARPP-32 immunoreactivity, fluorojade B and Golgi staining and molecular and granular layers thickness. These data demonstrate for the first time the efficacy of gene silencing in blocking the MJD-associated motor-behavior and neuropathological abnormalities after the onset of the disease, supporting the use of this strategy for therapy of MJD.

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Project description:Abnormal distribution, modification and aggregation of transactivation response DNA-binding protein 43 (TDP-43) are the hallmarks of multiple neurodegenerative diseases, especially frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U) and amyotrophic lateral sclerosis (ALS). Researchers have identified 44 mutations in the TARDBP gene that encode TDP-43 as causative for cases of sporadic and familial ALS http://www.molgen.ua.ac.be/FTDMutations/. Certain mutant forms of TDP-43, such as M337V, are associated with increased low molecular weight (LMW) fragments compared to wild-type (WT) TDP-43 and cause neuronal apoptosis and developmental delay in chick embryos. Such findings support a direct link between altered TDP-43 function and neurodegeneration.To explore the pathogenic properties of the M337V mutation, we generated and characterized two mouse lines expressing human TDP-43 (hTDP-43(M337V)) carrying this mutation. hTDP-43(M337V) was expressed primarily in the nuclei of neurons in the brain and spinal cord, and intranuclear and cytoplasmic phosphorylated TDP-43 aggregates were frequently detected. The levels of TDP-43 LMW products of ~25 kDa and ~35 kDa species were also increased in the transgenic mice. Moreover, overexpression of hTDP-43(M337V) dramatically down regulated the levels of mouse TDP-43 (mTDP-43) protein and RNA, indicating TDP-43 levels are tightly controlled in mammalian systems. TDP-43M337V mice displayed reactive gliosis, widespread ubiquitination, chromatolysis, gait abnormalities, and early lethality. Abnormal cytoplasmic mitochondrial aggregates and abnormal phosphorylated tau were also detected in the mice.Our novel TDP-43M337V mouse model indicates that overexpression of hTDP-43(M337V) alone is toxic in vivo. Because overexpression of hTDP-43 in wild-type TDP-43 and TDP-43M337V mouse models produces similar phenotypes, the mechanisms causing pathogenesis in the mutant model remain unknown. However, our results suggest that overexpression of the hTDP-43(M337V) can cause neuronal dysfunction due to its effect on a number of cell organelles and proteins, such as mitochondria and TDP-43, that are critical for neuronal activity. The mutant model will serve as a valuable tool in the development of future studies designed to uncover pathways associated with TDP-43 neurotoxicity and the precise roles TDP-43 RNA targets play in neurodegeneration.

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Silencing mutant ATXN3 expression resolves molecular phenotypes in SCA3 transgenic mice.

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Silencing mutant ATXN3 expression resolves molecular phenotypes in SCA3 transgenic mice.

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