| 1. |
- Smith, Ruben, et al.
(författare)
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Mutant huntingtin interacts with {beta}-tubulin and disrupts vesicular transport and insulin secretion.
- 2009
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Ingår i: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 18:20, s. 3942-3954
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Tidskriftsartikel (refereegranskat)abstract
- Huntington's disease is a severe progressive neurodegenerative disorder caused by a CAG-expansion in the IT15 gene, which encodes huntingtin. The disease primarily affects the neostriatum and cerebral cortex and also associates with increased incidence of diabetes. Here, we show that mutant huntingtin disrupts intracellular transport and insulin secretion by direct interference with microtubular beta-tubulin. We demonstrate that mutant huntingtin impairs glucose-stimulated insulin secretion in insulin-producing beta-cells, without altering stored levels of insulin. Using VSVG-YFP, we show that mutant huntingtin retards post-Golgi transport. Moreover, we demonstrate that the speed of insulin vesicle trafficking is reduced. Using immunoprecipitation of mutant and wild-type huntingtin in combination with mass spectrometry, we reveal an enhanced and aberrant interaction between mutant huntingtin and beta-tubulin, implying the underlying mechanism of impaired intracellular transport. Thus, our findings have revealed a novel pathogenetic process by which mutant huntingtin may disrupt hormone exocytosis from beta-cells and possibly impair vesicular transport in any cell that expresses the pathogenic protein.
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| 2. |
- Maynard, Christa J., et al.
(författare)
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Accumulation of ubiquitin conjugates in a polyglutamine disease model occurs without global ubiquitin/proteasome system impairment
- 2009
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Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 106:33, s. 13986-13991
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Tidskriftsartikel (refereegranskat)abstract
- Aggregation-prone proteins have been suggested to overwhelm and impair the ubiquitin/proteasome system (UPS) in polyglutamine (polyQ) disorders, such as Huntington's disease (HD). Overexpression of an N-terminal fragment of mutant huntingtin (N-mutHtt), an aggregation-prone polyQ protein responsible for HD, obstructs the UPS in cellular models. Furthermore, based on the accumulation of polyubiquitin conjugates in brains of R6/2 mice, which express human N-mutHtt and are one of the most severe polyQ disorder models, it has been proposed that UPS dysfunction is a consistent feature of this pathology, occurring in both in vitro and in vivo models. Here, we have exploited transgenic mice that ubiquitously express a ubiquitin fusion degradation proteasome substrate to directly assess the functionality of the UPS in R6/2 mice or the slower onset R6/1 mice. Although expression of N-mutHtt caused a general inhibition of the UPS in PC12 cells, we did not observe an increase in the levels of proteasome reporter substrate in the brains of R6/2 and R6/1 mice. We show that the increase in ubiquitin conjugates in R6/2 mice can be primarily attributed to an accumulation of large ubiquitin conjugates that are different from the conjugates observed upon UPS inhibition. Together our data show that polyubiquitylated proteins accumulate in R6/2 brain despite a largely operative UPS, and suggest that neurons are able to avoid or compensate for the inhibitory effects of N-mutHtt.
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| 3. |
- Paul-Visse, Gesine, et al.
(författare)
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Tyrosine hydroxylase expression is unstable in a human immortalized mesencephalic cell line - Studies in vitro and after intracerebral grafting in vivo
- 2007
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Ingår i: Molecular and Cellular Neuroscience. - : Elsevier BV. - 1044-7431. ; 34:3, s. 390-399
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the stability of the dopaminergic phenotype in a conditionally immortalized human mesencephalic cell line, NIESC2.10. Even though MESC2.10 cells exhibit features of dopaminergic neurons in vitro, none of the cells expressed tyrosine hydroxylase (TH) after transplantation into a rat model of Parkinson's disease. We examined whether this is caused by cell death or loss of transmitter phenotype. Cells were cultured in differentiation medium, then harvested and replated into the same medium where they continued to express TH, whereas replated cells fed medium lacking differentiation factors (dibutyryl cAMP and glial cell line-derived neurotrophic factor) did not. Interestingly, cultures grown in the absence of differentiation factors could regain TH expression once exposed to differentiation medium. Our data suggest that TH expression in vitro is inducible in neurons derived from the NIESC2.10 cell line and that the dopaminergic phenotype of these cells in vivo might be unstable. (c) 2006 Elsevier Inc. All rights reserved.
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| 4. |
- Petersén, Åsa, et al.
(författare)
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Orexin loss in Huntington's disease.
- 2005
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Ingår i: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 14:1, s. 39-47
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Tidskriftsartikel (refereegranskat)abstract
- Huntington's disease (HD) is a devastating neurodegenerative disorder caused by an expanded CAG repeat in the gene encoding huntingtin, a protein of unknown function. Mutant huntingtin forms intracellular aggregates and is associated with neuronal death in select brain regions. The most studied mouse model (R6/2) of HD replicates many features of the disease, but has been reported to exhibit only very little neuronal death. We describe for the first time a dramatic atrophy and loss of orexin neurons in the lateral hypothalamus of R6/2 mice. Importantly, we also found a significant atrophy and loss of orexin neurons in Huntington patients. Like animal models and patients with impaired orexin function, the R6/2 mice were narcoleptic. Both the number of orexin neurons in the lateral hypothalamus and the levels of orexin in the cerebrospinal fluid were reduced by 72% in end-stage R6/2 mice compared with wild-type littermates, suggesting that orexin could be used as a biomarker reflecting neurodegeneration. Our results show that the loss of orexin is a novel and potentially very important pathology in HD.
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| 5. |
- Smith, Ruben, et al.
(författare)
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Cholinergic neuronal defect without cell loss in Huntington's disease.
- 2006
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Ingår i: Human Molecular Genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 15:21, s. 3119-3131
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Tidskriftsartikel (refereegranskat)abstract
- Huntington's disease (HD) is a neurodegenerative disorder caused by a CAG-repeat expansion in the huntingtin (IT15) gene. The striatum is one of the regions most affected by neurodegeneration, resulting in the loss of the medium-sized spiny neurons. Traditionally, the large cholinergic striatal interneurons are believed to be spared. Recent studies demonstrate that neuronal dysfunction without cell death also plays an important role in early and mid-stages of the disease. Here, we report that cholinergic transmission is affected in a HD transgenic mouse model (R6/1) and in tissues from HD patients. Stereological analysis shows no loss of cholinergic neurons in the striatum or septum in R6/1 mice. In contrast, the levels of mRNA and protein for vesicular acetylcholine transporter (VAChT) and choline acetyltransferase (ChAT) are decreased in the striatum and cortex, and acetylcholine esterase activity is lowered in the striatum of R6/1 mice already at young ages. Accordingly, VAChT is also reduced in striatal tissue from patients with HD. The decrease of VAChT in the patient samples studied is restricted to the striatum and does not occur in the hippocampus or the spinal cord. The expression and localization of REST/NRSF, a transcriptional regulator for the VAChT and ChAT genes, are not altered in cholinergic neurons. We show that the R6/1 mice exhibit severe deficits in learning and reference memory. Taken together, our data show that the cholinergic system is dysfunctional in R6/1 and HD patients. Consequently, they provide a rationale for testing of pro-cholinergic drugs in this disease.
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| 6. |
- Smith, Ruben, et al.
(författare)
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Depletion of rabphilin 3A in a transgenic mouse model (R6/1) of Huntington's disease, a possible culprit in synaptic dysfunction.
- 2005
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Ingår i: Neurobiology of Disease. - : Elsevier BV. - 0969-9961. ; 20:3, s. 673-684
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Tidskriftsartikel (refereegranskat)abstract
- Huntington's disease (HD) is a hereditary neurodegenerative disorder characterized by progressive psychiatric, cognitive, and motor disturbances. We studied the expression of synaptic vesicle proteins in the R6/1 transgenic mouse model of HD. We observed that the levels of rabphilin 3A, a protein involved in exocytosis, is substantially decreased in synapses of most brain regions in R6/1 mice. The appearance of the reduction coincides with the onset of motor deficits and behavioral disturbances. Double immunohistochemistry did not show colocalization between rabphilin 3A and huntingtin aggregates in the HD mice. Using in situ hybridization, we demonstrated that rabphilin 3A mRNA expression was substantially reduced in the R6/1 mouse cortex compared to wild-type mice. Our results indicate that a decrease in mRNA levels underlie the depletion of protein levels of rabphilin 3A, and we suggest that this reduction may be involved in causing impaired synaptic transmission in R6/1 mice.
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| 7. |
- Smith, Ruben, et al.
(författare)
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Fria radikaler och sjuka proteiner - bovarna bakom Parkinsons sjukdom?[Free radicals and ailing proteins - the culprits behind Parkinson’s disease?]
- 2003
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Ingår i: Läkartidningen. - 0023-7205. ; 100:15, s. 6-1329
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Tidskriftsartikel (refereegranskat)abstract
- Parkinson’s disease is one of the most common neurodegenerative diseases, and affects approximately 1% of the population over 65 years of age. Many different insults appear to be involved in the etiology of the disease, among them environmental toxins and mitochondrial dysfunction. During the past five years, mutations in five different genes have been linked to rare, familial forms of Parkinson’s disease. One of the mutated proteins, a-synuclein is normally implicated in synaptic plasticity and vesicle function. Dysfunction of this protein might lead to increased cytoplasmic dopamine levels. Since cytoplasmic dopamine is readily prone to autooxidation and enzymatic degradation - processes which generate reactive oxygen species - failure to properly store dopamine into vesicles might lead to oxidative stress. Indeed, nigral tissue from idiopathic Parkinson’s disease patients shows signs of oxidative damage. In this article we propose that dopamine-induced oxidative stress might be a common final pathway in the pathogenesis of the disease.
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| 8. |
- Smith, Ruben, et al.
(författare)
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Loss of SNAP-25 and rabphilin 3a in sensory-motor cortex in Huntington's disease.
- 2007
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Ingår i: Journal of Neurochemistry. - : Wiley. - 1471-4159 .- 0022-3042. ; 103:1, s. 115-123
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Tidskriftsartikel (refereegranskat)abstract
- Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder caused by a CAG-expansion in the gene encoding the protein huntingtin. The disease is characterized by progressive motor disturbances, cognitive defects, dementia, and weight loss. Using western blotting and immunohistochemistry we have assessed the expression levels and patterns of a number of proteins involved in neurotransmitter release in post-mortem frontal cortex samples from 10 HD cases with different disease grades. We report a loss of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein, synaptosome-associated protein 25 (SNAP 25) in HD brains of grades I–IV. Moreover, in brains of grade III and IV we found a reduction in rabphilin 3a, a protein involved in vesicle docking and recycling. These losses appear to be specific and not due to a general loss of synapses in the HD cortex. Thus, levels of synaptobrevin II, syntaxin 1, rab3a or synaptophysin are unaltered in the same patient samples. SNAP 25 and rabphilin 3a are crucial for neurotransmitter release. Therefore, we suggest that a deficient pre-synaptic transmitter release may underlie some of the symptoms of HD.
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| 9. |
- Smith, Ruben, et al.
(författare)
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Synaptic dysfunction in Huntington's disease: a new perspective
- 2005
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Ingår i: Cellular and Molecular Life Sciences. - : Springer Science and Business Media LLC. - 1420-9071 .- 1420-682X. ; 62:17, s. 1901-1912
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Forskningsöversikt (refereegranskat)abstract
- Huntington's disease (HD) is caused by a polyglutamine expansion in the protein huntingtin and is characterized by intraneuronal inclusions and widespread neuronal death at the late stage of the disease. In research, most of the emphasis has been on understanding the cell death and its mechanisms. Until recently, it was believed that the vast majority, if not all, of the symptoms in HD are a direct consequence of neurodegeneration. However, increasing evidence shows that subtle alterations in synaptic function could underlie the early symptoms. It is of particular interest to understand the nature of this neuronal dysfunction. Normal huntingtin interacts with various cytoskeletal and synaptic vesicle proteins that are essential for exocytosis and endocytosis. Altered interactions of mutant huntingtin with its associated partners could contribute to abnormal synaptic transmission in HD. This review describes recent advances in understanding synaptic dysfunction in HD.
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| 10. |
- van der Burg, Jorien m, et al.
(författare)
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Increased metabolism in the R6/2 mouse model of Huntington's disease.
- 2008
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Ingår i: Neurobiology of Disease. - : Elsevier BV. - 0969-9961. ; 29:1, s. 41-51
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Tidskriftsartikel (refereegranskat)abstract
- Huntington’s disease (HD) is a hereditary disorder characterized by personality changes, chorea, dementia and weight loss. The cause of this weight loss is unknown. The aim of this study was to examine body weight changes and weight-regulating factors in HD using the R6/2 mouse model as a tool. We found that R6/2 mice started losing weight at 9 weeks of age. Total locomotor activity was unaltered and caloric intake was not decreased until 11 weeks of age, which led us to hypothesize that increased metabolism might underlie the weight loss. Indeed, oxygen consumption in R6/2 mice was elevated from 6 weeks of age, indicative of an increased metabolism. Several organ systems that regulate weight and metabolism, including the hypothalamus, the stomach and adipose tissue displayed abnormalities in R6/2 mice. Together, these data demonstrate that weight loss in R6/2 mice is associated with increased metabolism and changes in several weight-regulating factors.
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