Sharma, D., S. Sharma, et al. (1999). "Peptide models for inherited neurodegenerative disorders: conformation and aggregation properties of long polyglutamine peptides with and without interruptions." FEBS Lett 456(1): 181-5.
Several neurodegenerative diseases are caused by expansion of polyglutamine repeats in the affected proteins. In spino-cerebellar ataxia type 1 (SCA1), histidine interruptions have been reported to mitigate the pathological effects of long glutamine stretches. To understand this phenomenon, we investigated the conformational preferences of peptides containing both the uninterrupted polyglutamine stretches and those with histidine interruption(s) as seen in SCA1 normals. Our study suggests that substitution of histidines by glutamines induces a conformational change which results in decreased solubility and increased aggregation. Our findings also suggest that all the polyglutamine peptides with and without interruption(s) adopt a beta-structure and not random coil.

Sasaki, H. (1999). "[Unstable expansion of CAG repeat and molecular mechanism of neurodegeneration in SCA1]." Nippon Rinsho 57(4): 801-4.
SCA1 is caused by unstable expansion of CAG repeat in the coding region of a novel gene located on chromosome 6p23. Expansion up to 40-80 repeats develop the disorder, and the repeat length correlates with age at onset, rate of progression, or clinical severity. Expanded SCA1 allele is unstable during meiosis and mitosis, which is related to anticipation phenomenon and somatic mosaicism, respectively. SCA1 gene is expressed ubiquitously. In neurons, its transcript (ataxin-1) localizes mostly in nucleus. Ataxin-1 with expanded glutamine repeat is highly ubiquinated and forms aggregation within nucleus. These findings in clinical genetical, and cell biology are all common in other polyglutamine disorders, highly indicating that common molecular mechanisms underlie in these disorders. Based on these background, recent progress in the research for SCA1 is reviewed.

Sanpei, K. (1999). "[The function of spinocerebellar ataxia type 2 (SCA2) gene product, ataxin-2 and the mechanism of pathogenesis for SCA2]." Nippon Rinsho 57(4): 822-4.
This review summarizes the current progress in the research on the function of ataxin-2 and the mechanism of pathogenesis for SCA2. Recent studies on genomic structure of the human gene for SCA2 and on the mouse homolog of the SCA2 gene have shed light on the molecular mechanism of pathogenesis of SCA2. Analysis of the expression pattern of ataxin-2 in human brain revealed that both wild-type and mutant form of ataxin-2 were expressed and the wild-type ataxin-2 was localized in the cytoplasm with strong labeling of Purkinje cells and that intranuclear inclusions were not seen in SCA2 brain.

Rich, T., E. Assier, et al. (1999). "Disassembly of nuclear inclusions in the dividing cell--a novel insight into neurodegeneration." Hum Mol Genet 8(13): 2451-9.
Spinocerebellar ataxias and Huntington's disease are examples of neurodegenerative diseases caused by a trinucleotide repeat expansion. One hallmark of such diseases is the formation of inclusion bodies (IBs) within neuronal tissue. Although these inclusions may play a pivotal role in the disease process, the reasons underlying their specific accumulation remain obscure. By studying intranuclear IBs in dividing cells we demonstrate for the first time that inclusions such as those of ataxin-1 disperse during mitosis, thus reducing the nuclear aggregate burden. IBs reform in the interphase nucleus. By high-resolution confocal microscopy we also show that inclusions comprise ordered structures capable of homotypic interactions. Unlike those of a non-pathologic protein, ataxin-1 inclusions were shown to be capable of non-specific protein sequestration. Our studies indicate that the specific accumulation of inclusions in terminally differentiated cells such as neurons is a direct consequence of their inability to divide and therefore provides a key to explaining their persistence in neurodegenerative disease.

Pujana, M. A., J. Corral, et al. (1999). "Spinocerebellar ataxias in Spanish patients: genetic analysis of familial and sporadic cases. The Ataxia Study Group." Hum Genet 104(6): 516-22.
Autosomal dominant cerebellar ataxias (ADCA) are a clinically heterogeneous group of neurodegenerative disorders caused by unstable CAG repeat expansions encoding polyglutamine tracts. Five spinocerebellar ataxia genes (SCA1, SCA2, SCA3, SCA6 and SCA7) and another related dominant ataxia gene (DRPLA) have been cloned, allowing the genetic classification of these disorders. We present here the molecular analysis of 87 unrelated familial and 60 sporadic Spanish cases of spinocerebellar ataxia. For ADCA cases 15% were SCA2, 15% SCA3, 6% SCA1, 3% SCA7, 1% SCA6 and 1% DRPLA, an extremely rare mutation in Caucasoid populations. About 58% of ADCA cases remained genetically unclassified. All the SCA1 cases belong to the same geographical area and share a common haplotype for the SCA1 mutation. The expanded alleles ranged from 41 to 59 repeats for SCA1, 35 to 46 [corrected] for SCA2, 67 to 77 for SCA3, and 38 to 113 for SCA7. One SCA6 case had 25 repeats and one DRPLA case had 63 repeats. The highest CAG repeat variation in meiotic transmission of expanded alleles was detected in SCA7, this being of +67 units in one paternal transmission and giving rise to a 113 CAG repeat allele in a patient who died at 3 years of age. Meiotic transmissions have also shown a tendency to more frequent paternal transmission of expanded alleles in SCA1 and maternal in SCA7. All SCA1 and SCA2 expanded alleles analyzed consisted of pure CAG repeats, whereas normal alleles were interrupted by 1-2 CAT trinucleotides in SCA1, except for three alleles of 6, 14 and 21 CAG repeats, and by 1-3 CAA trinucleotides in SCA2. No SCA or DRPLA mutations were detected in the 60 sporadic cases of spinocerebellar ataxia, but one late onset patient was identified as a recessive form due to GAA-repeat expansions in the Friedreich's ataxia gene.

Perez, M. K., H. L. Paulson, et al. (1999). "Ataxin-3 with an altered conformation that exposes the polyglutamine domain is associated with the nuclear matrix." Hum Mol Genet 8(13): 2377-85.
Spinocerebellar ataxia type-3 or Machado-Joseph disease (SCA3/MJD) is a member of the CAG/polyglutamine repeat disease family. In this family of disorders, a normally polymorphic CAG repeat becomes expanded, resulting in expression of an expanded polyglutamine domain in the disease gene product. Experimental models of polyglutamine disease implicate the nucleus in pathogenesis; however, the link between intranuclear expression of expanded polyglutamine and neuronal dysfunction remains unclear. Here we demonstrate that ataxin-3, the disease protein in SCA3/MJD, adopts a unique conformation when expressed within the nucleus of transfected cells. The monoclonal antibody 1C2 is known preferentially to bind expanded polyglutamine, but we find that it also binds a fragment of ataxin-3 containing a normal glutamine repeat. In addition, expression of ataxin-3 within the nucleus exposes the glutamine domain of the full-length non-pathological protein, allowing it to bind the monoclonal antibody 1C2. Fractionation and immunochemical experiments indicate that this novel conformation of intranuclear ataxin-3 is not due to proteolysis, suggesting instead that association with nuclear protein(s) alters the structure of full-length ataxin-3 which exposes the polyglutamine domain. This conformationally altered ataxin-3 is bound to the nuclear matrix. The pathological form of ataxin-3 with an expanded polyglutamine domain also associates with the nuclear matrix. These data suggest that an early event in the pathogenesis of SCA3/MJD may be an altered conformation of ataxin-3 within the nucleus that exposes the polyglutamine domain.

Pang, J., R. Allotey, et al. (1999). "A common disease haplotype segregating in spinocerebellar ataxia 2 (SCA2) pedigrees of diverse ethnic origin." Eur J Hum Genet 7(7): 841-5.
The identification of a CAG trinucleotide repeat expansion, located within the coding sequence of the ataxin-2 gene, as the mutation underlying spinocerebellar ataxia 2 (SCA2) has facilitated direct investigation of pedigrees previously excluded from linkage analysis due to insufficient size or pedigree structure. We have previously described the identification of the ancestral disease haplotype segregating in the Cuban founder population used to assign the disease locus to chromosome 12q23-24.1. We now report evidence for the segregation of the identical core haplotype in pedigrees of diverse ethnic origin from India, Japan and England, established by the analysis of the loci D12S1672 and D12S1333 located 20kb proximal and 200 kb distal to the triplet repeat motif respectively. Interpretation of this data is suggestive that for these pedigrees at least, the mutation has arisen on a single ancestral or predisposing chromosome.

Nasir, J. (1999). "To be or not to be an aggregate." Clin Genet 55(1): 9-10.

Mauger, C., J. Del-Favero, et al. (1999). "Identification and localization of ataxin-7 in brain and retina of a patient with cerebellar ataxia type II using anti-peptide antibody." Brain Res Mol Brain Res 74(1-2): 35-43.
Autosomal dominant cerebellar ataxias (ADCAs) are a complex group of neurodegenerative disorders characterized by progressive degeneration of the cerebellum, brain stem and spinal cord. The spinocerebellar ataxia type 7 (SCA7) is associated with pigmentary macular dystrophy and retinal degeneration leading to blindness caused by a CAG/polyglutamine (polyGln) expansion in the coding region of the SCA7 gene/protein. The SCA7 gene codes for ataxin-7, a protein of unknown function. To investigate its cellular and subcellular localization, we have developed a sequence-specific polyclonal antibody against the N-terminal part of the protein. Immunohistochemical analysis indicated that ataxin-7 accumulates as single nuclear inclusion (NI) in the cells of the brain and retina of a SCA7 patient but not of controls. The 1C2 antibody, directed against expanded polyGln, confirmed the aggregation of mutant ataxin-7 in these NIs. Furthermore, ubiquitin was found in these aggregates, suggesting that mutant ataxin-7 is a target for ubiquitin-dependent proteolysis, but resistant to removal. Electron microscopic studies using immunogold labeling showed that ataxin-7 immunoreactive NIs appear as dense aggregates containing a mixture of granular and filamentary structures. Together, these data confirm the presence of NIs in brain and retina of a SCA7 patient, a common characteristic of disorders caused by expanded CAG/polyGln repeats.

Matsuura, T., H. Sasaki, et al. (1999). "Mosaicism of unstable CAG repeats in the brain of spinocerebellar ataxia type 2." J Neurol 246(9): 835-9.
Spinocerebellar ataxia type 2 (SCA2) is caused by expansion of unstable CAG repeats within the coding region of the novel gene, ataxin-2, on chromosome 12q24.1. We analyzed CAG repeat size of the SCA2 allele in two deceased patients (father and daughter) to investigate the repeat mosaicism in CNS regions. The CAG repeat size was examined using lymphoblastoid cell lines, frozen brain tissues, and paraffin-embedded tissues. In each patient the major repeat size of the expanded allele varied within the brain or spinal cord (father, 39-42; daughter, 39-47 repeats), and was smaller by three to eight repeats in the cerebellum than in other CNS regions. Our results are in agreement with the findings in other polyglutamine disorders showing somatic mosaicism.

Linhartova, I., M. Repitz, et al. (1999). "Conserved domains and lack of evidence for polyglutamine length polymorphism in the chicken homolog of the Machado-Joseph disease gene product ataxin-3." Biochim Biophys Acta 1444(2): 299-305.
Ataxin-3 is a protein of unknown function which is mutated in Machado-Joseph disease by expansion of a genetically unstable CAG repeat encoding polyglutamine. By analysis of chicken ataxin-3 we were able to identify four conserved domains of the protein and detected widespread expression in chicken tissues. In the first such analysis in a non-primate species we found that in contrast to primates, the chicken CAG repeat is short and genetically stable.

Lieberman, A. P., J. Q. Trojanowski, et al. (1999). "Ataxin 1 and ataxin 3 in neuronal intranuclear inclusion disease." Ann Neurol 46(2): 271-3.
Neuronal intranuclear inclusion disease (NIID) is a multisystem neurodegenerative disorder characterized by large intranuclear aggregates in neurons of the central and peripheral nervous system. These ubiquitinated intranuclear inclusions are morphologically similar to the intraneuronal aggregates that have been identified in the CAG/polyglutamine expansion diseases. As rare aggregates in NIID contain a polyglutamine epitope, we further investigated the relationship between this disease and the CAG/polyglutamine expansion diseases. Here, we show that ataxin 1 and ataxin 3 proteins are recruited into aggregates in NIID in the absence of a CAG expansion in the SCA1 and SCA3 genes. These data support an association of NIID with the polyglutamine disorders and provide evidence of in vivo recruitment of proteins with polyglutamine tracts into intraneuronal aggregates.

Li, T., G. Breen, et al. (1999). "No evidence of linkage disequilibrium between a CAG repeat in the SCA1 gene and schizophrenia in Caucasian and Chinese schizophrenic subjects." Psychiatr Genet 9(3): 123-7.
Several recent studies have reported evidence for a schizophrenia locus on chromosome 6p, with a variety of linked markers spanning a approximately 40 cM region between D6S470 and D6S291. However because of the wide region implicated and the difficulty of inferring phenotype from genotype in complex disorders, it is difficult to define its location precisely using linkage data. An alternative approach is to search for linkage disequilibrium. On chromosome 6p, allelic association with a (CAG)29 allele of a triplet repeat marker in the SCA1 gene has been reported, and we have attempted to replicate this finding using a Caucasian case-control sample of 211 affected subjects and 204 controls, and a Han Chinese sample of 100 affected family trios. In the case-control sample, the frequency of the (CAG)29 allele was similar in cases and controls (35%), and no other alleles provided evidence for allelic association. Likewise, there was no evidence for preferential transmission of the (CAG)29 allele to affected offspring in the Chinese sample, although a different allele, (CAG)26, was more often transmitted to the affected offspring. However this data did not reach statistical significance (P = 0.1). We conclude that our data does not support the notion that there is a locus for schizophrenia close to the SCA1 gene. However, since linkage disequilibrium will vary between distinct populations, we cannot exclude this possibility.

Koyano, S., T. Uchihara, et al. (1999). "Neuronal intranuclear inclusions in spinocerebellar ataxia type 2: triple-labeling immunofluorescent study." Neurosci Lett 273(2): 117-20.
Spinocerebellar ataxia type 2 (SCA2) is associated with an expansion of CAG/polyglutamine-repeat of a gene of unknown function. We performed an immunohistochemical study to identify the immunolocalization of the disease protein ataxin-2 in normal and SCA2 patients. Although normal and expanded ataxin-2 were ubiquitously localized to the cytoplasm of neurons, ubiquitinated intranuclear inclusions were observed selectively in 1-2% of neurons of affected brain regions except the cerebellum. Triple-labeling immunofluorescence revealed that ataxin-2, expanded polyglutamine and ubiquitin were colocalized to these neuronal intranuclear inclusions (NIs), indicating that SCA2 shares morphological characteristics common to other neurological disorders associated with an expansion of CAG/polyglutamine-repeat. Lack of NIs in the cerebellar lesion, however, suggests the discrepancy between formation of NIs and neuronal degeneration in SCA2.

Kaytor, M. D., L. A. Duvick, et al. (1999). "Nuclear localization of the spinocerebellar ataxia type 7 protein, ataxin-7." Hum Mol Genet 8(9): 1657-64.
Spinocerebellar ataxia type 7 (SCA7) belongs to a group of neurological disorders caused by a CAG repeat expansion in the coding region of the associated gene. To gain insight into the pathogenesis of SCA7 and possible functions of ataxin-7, we examined the subcellular localization of ataxin-7 in transfected COS-1 cells using SCA7 cDNA clones with different CAG repeat tract lengths. In addition to a diffuse distribution throughout the nucleus, ataxin-7 associated with the nuclear matrix and the nucleolus. The location of the putative SCA7 nuclear localization sequence (NLS) was confirmed by fusing an ataxin-7 fragment with the normally cytoplasmic protein chicken muscle pyruvate kinase. Mutation of this NLS prevented protein from entering the nucleus. Thus, expanded ataxin-7 may carry out its pathogenic effects in the nucleus by altering a matrix-associated nuclear structure and/or by disrupting nucleolar function.

Kaemmerer, W. F. and W. C. Low (1999). "Cerebellar allografts survive and transiently alleviate ataxia in a transgenic model of spinocerebellar ataxia type-1." Exp Neurol 158(2): 301-11.
Spinocerebellar ataxia type 1 (SCA-1) is one of several neurodegenerative diseases, including Huntington's disease, spinobulbar muscular atrophy, dentatorubral-pallidoluysian atrophy, and SCA-2, SCA-3, SCA-6, and SCA-7, each caused by an expanded number of CAG repeats in the coding region of their respective genes. The mechanism by which the resulting proteins are pathogenic is unknown. Clinical trials of neural transplants in Huntington's disease patients are under way. While initial reports are encouraging, definitive evidence of graft survival in patients despite the ongoing disease process is not possible with current imaging techniques. Transplants in primates have shown long-term survival of striatal grafts and recovery of function, but have used lesioning to model Huntington's phenotypically. Studies of striatal grafts in a transgenic mouse model of Huntington's have not yet shown a behavioral benefit. We describe a behavioral benefit of cerebellar grafts in a transgenic model of SCA-1 in which the ataxic phenotype results from expression of an expanded ataxin-1 protein. Mice were transplanted at an age when their ataxic phenotype is just becoming evident. Compared with sham-operated littermates, grafted mice showed better performance on multiple behavioral tests of cerebellar function. Differences persisted for 10 to 12 weeks posttransplant, after which there was a progressive decline in motor performance. At 20 weeks postsurgery, donor Purkinje cell survival was evident in 9 of 12 graft recipients. These results indicate that transplants can have behavioral benefits and grafts can survive long-term despite the ongoing pathological process in a brain actively expressing an expanded polyglutamine protein.

Joo, E. J., J. H. Lee, et al. (1999). "Possible association between schizophrenia and a CAG repeat polymorphism in the spinocerebellar ataxia type 1 (SCA1) gene on human chromosome 6p23." Psychiatr Genet 9(1): 7-11.
The gene for spinocerebellar ataxia type 1 (SCA1) is a potential candidate gene for schizophrenia because of previous positive linkage findings in this region (6p22-24), and because the reported correlation between SCA1 onset and the number of CAG repeats suggests anticipation. To test the involvement of this gene in the development of schizophrenia, we examined genotypes of the SCA1 CAG repeat polymorphism for 49 Caucasian patients with schizophrenia, and 88 Caucasian controls. We found a significant association between the frequencies of alleles of this gene and schizophrenia (chi 2 = 18.40, df = 8, P = 0.018). Among 13 alleles, one allele (31 trinucleotide repeat) was significantly more frequent in patients with schizophrenia than in controls (chi 2 = 9.57, df = 1, P = 0.002). This association was sustained after applying a Bonferroni correction for multiple testing (P = 0.05/13 = 0.004), and the chi-square results were shown to be robust through Monte Carlo simulation. We observed no allelic association with three flanking microsatellite markers (D6S288, D6S1605, and D6S337), suggesting that our result was not due to population stratification. Further studies of this locus are needed to confirm this finding, and to determine a potential role for this gene in the development of schizophrenia.

Huynh, D. P., M. R. Del Bigio, et al. (1999). "Expression of ataxin-2 in brains from normal individuals and patients with Alzheimer's disease and spinocerebellar ataxia 2." Ann Neurol 45(2): 232-41.
Spinocerebellar ataxia type 2 (SCA2) is caused by expansion of a CAG trinucleotide repeat located in the coding region of the human SCA2 gene. The SCA2 gene product, ataxin-2, is a basic protein with two domains (Sm1 and Sm2) implicated in RNA splicing and protein interaction. However, the wild-type function of ataxin-2 is yet to be determined. To help clarify the function of ataxin-2, we produced antibodies to three antigenic peptides of ataxin-2 and analyzed the expression pattern of ataxin-2 in normal and SCA2 adult brains and cerebellum at different developmental stages. These studies revealed that (1) both wild-type and mutant forms of ataxin-2 were synthesized; (2) the wild-type ataxin-2 was localized in the cytoplasm in specific neuronal groups with strong labeling of Purkinje cells; (3) the level of ataxin-2 increased with age in Purkinje cells of normal individuals; and (4) ataxin-2-like immunoreactivity in SCA2 brain tissues was more intense than in normal brain tissues, and intranuclear ubiquitinated inclusions were not seen in SCA2 brain tissues.

Hsieh, M., S. Y. Li, et al. (1999). "Identification of five spinocerebellar ataxia type 2 pedigrees in patients with autosomal dominant cerebellar ataxia in Taiwan." Acta Neurol Scand 100(3): 189-94.
OBJECTIVES: The autosomal dominant cerebellar ataxias (ADCAs) are a group of genetically diverse neurological conditions linked by progressive deterioration in balance and coordination. Spinocerebellar Ataxia Type 2 (SCA2) is one of the ADCAs and also belongs to a special group caused by the expansion of an unstable CAG repeat encoding a polyglutamine tract. We aimed to investigate the frequency of SCA2 mutation in the ataxia patients referred to the clinic. MATERIALS AND METHODS: We screened 58 families with inherent cerebellar ataxia and 57 normal individuals by the use of radioactive genomic polymerase chain reaction (PCR) method. A simple non-radioactive PCR for rapid detection of the expanded SCA2 alleles via agarose gel electrophoresis was also employed. RESULTS: Eight SCA2 affected patients and 1 at-risk individual in 5 unrelated SCA2 families were identified. The CAG repeats of normal alleles in the sample studied range in size from 16 to 30 repeat units, while those of SCA2 chromosomes are expanded to 34 to 49 repeat units. Our results also showed that unlike SCA 1 and SCA3/MJD, the size distribution of the normal alleles showed few polymorphisms, with the 22 repeat allele accounting for 90.1%. Homozygosity in normal individuals was 80.2%. No overlap in ataxin-2 allele size between normal and expanded chromosomes was observed. CONCLUSION: This is the first report of the SCA2 gene distributions in the population of Taiwan. The SCA2 mutation accounts for 8.6% of ADCA type I families referred to us, intermediate between SCA1(1.7%) and SCA3/MJD (24%) of the ADCA type I families in our collection.

Frontali, M., A. Novelletto, et al. (1999). "CAG repeat instability, cryptic sequence variation and pathogeneticity: evidence from different loci." Philos Trans R Soc Lond B Biol Sci 354(1386): 1089-94.
Different aspects of expanded polyglutamine tracts and of their pathogenetic role are taken into consideration here. (i) The (CAG)n length of wild-type alleles of the Huntington disease gene was analysed in instability-prone tumour tissue from colon cancer patients to test whether the process leading to the elongation of alleles towards the expansion range involves single-unit stepwise mutations or larger jumps. The analysis showed that length changes of a single unit had a relatively low frequency. (ii) The observation of an expanded spinocerebellar ataxia (SCA)1 allele with an unusual pattern of multiple CAT interruptions showed that cryptic sequence variations are critical not only for sequence length stability but also for the expression of the disease phenotype. (iii) Small expansions of the (CAG)n sequence at the CACNA1A gene have been reported as causing SCA6. The analysis of families with SCA6 and episodic ataxia type 2 showed that these phenotypes are, in fact, expressions of the same disorder caused either by point mutations or by small (CAG)n expansions. A gain of function has been hypothesized for all proteins containing an expanded polyglutamine stretch, including the alpha 1A subunit of the voltage-gated calcium channel type P/Q coded by the CACNA1A gene. Because point mutations at the same gene with similar phenotypic consequences are highly unlikely to have this effect, an alternative common pathogenetic mechanism for all these mutations, including small expansions, can be hypothesized.

Floyd, J. A. and B. A. Hamilton (1999). "Intranuclear inclusions and the ubiquitin-proteasome pathway: digestion of a red herring?" Neuron 24(4): 765-6.

Evert, B. O., U. Wullner, et al. (1999). "High level expression of expanded full-length ataxin-3 in vitro causes cell death and formation of intranuclear inclusions in neuronal cells." Hum Mol Genet 8(7): 1169-76.
Spinocerebellar ataxia type 3 (SCA3) is caused by a CAG/polyglutamine repeat expansion in the SCA3 gene. To analyse the pathogenic mechanisms in SCA3, we have generated ataxin-3-expressing rat mesencephalic CSM14.1 cells. In these cells, a post-mitotic neuronal phenotype is induced by temperature shift. The isolated stable cell lines provided high level expression of non-expanded (Q23) or expanded (Q70) human full-length ataxin-3. CSM14.1 cells expressing the expanded full-length ataxin-3 developed nuclear inclusion bodies, strong indentations of the nuclear envelope and cytoplasmic vacuolation. These ultrastructural alterations were present prior to a significantly decreased viability of neuronally differentiated cells expressing expanded ataxin-3. The observed spontaneous cell death did not correlate with formation of intranuclear inclusions and was not apoptotic by ultrastructural analysis. No increased susceptibility to staurosporine-induced apoptosis was found for the expanded or non-expanded ataxin-3-expressing cell lines. These data show that high level expression of expanded full-length ataxin-3 in a neuron-like cell line generates ultrastructural alterations of SCA3 pathogenesis and results in increased spontaneous non-apoptotic cell death.

Ellerby, L. M., R. L. Andrusiak, et al. (1999). "Cleavage of atrophin-1 at caspase site aspartic acid 109 modulates cytotoxicity." J Biol Chem 274(13): 8730-6.
Dentatorubropallidoluysian atrophy (DRPLA) is one of eight autosomal dominant neurodegenerative disorders characterized by an abnormal CAG repeat expansion which results in the expression of a protein with a polyglutamine stretch of excessive length. We have reported recently that four of the gene products (huntingtin, atrophin-1 (DRPLA), ataxin-3, and androgen receptor) associated with these open reading frame triplet repeat expansions are substrates for the cysteine protease cell death executioners, the caspases. This led us to hypothesize that caspase cleavage of these proteins may represent a common step in the pathogenesis of each of these four neurodegenerative diseases. Here we present evidence that caspase cleavage of atrophin-1 modulates cytotoxicity and aggregate formation. Cleavage of atrophin-1 at Asp109 by caspases is critical for cytotoxicity because a mutant atrophin-1 that is resistant to caspase cleavage is associated with significantly decreased toxicity. Further, the altered cellular localization within the nucleus and aggregate formation associated with the expanded form of atrophin-1 are completely suppressed by mutation of the caspase cleavage site at Asp109. These results provide support for the toxic fragment hypothesis whereby cleavage of atrophin-1 by caspases may be an important step in the pathogenesis of DRPLA. Therefore, inhibiting caspase cleavage of the polyglutamine-containing proteins may be a feasible therapeutic strategy to prevent cell death.

Duyckaerts, C., A. Durr, et al. (1999). "Nuclear inclusions in spinocerebellar ataxia type 1." Acta Neuropathol (Berl) 97(2): 201-7.
Spinocerebellar ataxia type 1 is due to a CAG repeat expansion in the gene encoding ataxin-1. In a case with an expansion of 56 repeats, intranuclear inclusions were found only in neurons, both in severely affected regions (such as the pons) and in areas where the lesions were inconspicuous (such as the cortex or the striatum). The inclusions were labelled by a monoclonal antibody directed against long polyglutamine stretches (1C2); they were also detected by the anti-ubiquitin antibody. They were faintly eosinophilic, Congo red negative and were not stained by thioflavin S or by ethidium bromide.

Cummings, C. J., H. T. Orr, et al. (1999). "Progress in pathogenesis studies of spinocerebellar ataxia type 1." Philos Trans R Soc Lond B Biol Sci 354(1386): 1079-81.
Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited disorder characterized by progressive loss of coordination, motor impairment and the degeneration of cerebellar Purkinje cells, spinocerebellar tracts and brainstem nuclei. Many dominantly inherited neurodegenerative diseases share the mutational basis of SCA1: the expansion of a translated CAG repeat coding for glutamine. Mice lacking ataxin-1 display learning deficits and altered hippocampal synaptic plasticity but none of the abnormalities seen in human SCA1; mice expressing ataxin-1 with an expanded CAG tract (82 glutamine residues), however, develop Purkinje cell pathology and ataxia. These results suggest that mutant ataxin-1 gains a novel function that leads to neuronal degeneration. This novel function might involve aberrant interaction(s) with cell-specific protein(s), which in turn might explain the selective neuronal pathology. Mutant ataxin-1 interacts preferentially with a leucine-rich acidic nuclear protein that is abundantly expressed in cerebellar Purkinje cells and other brain regions affected in SCA1. Immunolocalization studies in affected neurons of patients and SCA1 transgenic mice showed that mutant ataxin-1 localizes to a single, ubiquitin-positive nuclear inclusion (NI) that alters the distribution of the proteasome and certain chaperones. Further analysis of NIs in transfected HeLa cells established that the proteasome and chaperone proteins co-localize with ataxin-1 aggregates. Moreover, overexpression of the chaperone HDJ-2/HSDJ in HeLa cells decreased ataxin-1 aggregation, suggesting that protein misfolding might underlie NI formation. To assess the importance of the nuclear localization of ataxin-1 and its role in SCA1 pathogenesis, two lines of transgenic mice were generated. In the first line, the nuclear localization signal was mutated so that full-length mutant ataxin-1 would remain in the cytoplasm; mice from this line did not develop any ataxia or pathology. This suggests that mutant ataxin-1 is pathogenic only in the nucleus. To assess the role of the aggregates, transgenic mice were generated with mutant ataxin-1 without the self-association domain (SAD) essential for aggregate formation. These mice developed ataxia and Purkinje cell abnormalities similar to those seen in SCA1 transgenic mice carrying full-length mutant ataxin-1, but lacked NIs. The nuclear milieu is thus a critical factor in SCA1 pathogenesis, but large NIs are not needed to initiate pathogenesis. They might instead be downstream of the primary pathogenic steps. Given the accumulated evidence, we propose the following model for SCA1 pathogenesis: expansion of the polyglutamine tract alters the conformation of ataxin-1, causing it to misfold. This in turn leads to aberrant protein interactions. Cell specificity is determined by the cell-specific proteins interacting with ataxin-1. Submicroscopic protein aggregation might occur because of protein misfolding, and those aggregates become detectable as NIs as the disease advances. Proteasome redistribution to the NI might contribute to disease progression by disturbing proteolysis and subsequent vital cellular functions.

Cummings, C. J., E. Reinstein, et al. (1999). "Mutation of the E6-AP ubiquitin ligase reduces nuclear inclusion frequency while accelerating polyglutamine-induced pathology in SCA1 mice." Neuron 24(4): 879-92.
Mutant ataxin-1, the expanded polyglutamine protein causing spinocerebellar ataxia type 1 (SCA1), aggregates in ubiquitin-positive nuclear inclusions (NI) that alter proteasome distribution in affected SCA1 patient neurons. Here, we observed that ataxin-1 is degraded by the ubiquitin-proteasome pathway. While ataxin-1 [2Q] and mutant ataxin-1 [92Q] are polyubiquitinated equally well in vitro, the mutant form is three times more resistant to degradation. Inhibiting proteasomal degradation promotes ataxin-1 aggregation in transfected cells. And in mice, Purkinje cells that express mutant ataxin-1 but not a ubiquitin-protein ligase have significantly fewer NIs. Nonetheless, the Purkinje cell pathology is markedly worse than that of SCA1 mice. Taken together, NIs are not necessary to induce neurodegeneration, but impaired proteasomal degradation of mutant ataxin-1 may contribute to SCA1 pathogenesis.

Chai, Y., S. L. Koppenhafer, et al. (1999). "Evidence for proteasome involvement in polyglutamine disease: localization to nuclear inclusions in SCA3/MJD and suppression of polyglutamine aggregation in vitro." Hum Mol Genet 8(4): 673-82.
Spinocerebellar ataxia type 3, also known as Machado-Joseph disease (SCA3/MJD), is one of at least eight inherited neurodegenerative diseases caused by expansion of a polyglutamine tract in the disease protein. Here we present two lines of evidence implicating the ubiquitin-proteasome pathway in SCA3/MJD pathogenesis. First, studies of both human disease tissue and in vitro models showed redistribution of the 26S proteasome complex into polyglutamine aggregates. In neurons from SCA3/MJD brain, the proteasome localized to intranuclear inclusions containing the mutant protein, ataxin-3. In transfected cells, the proteasome redistributed into inclusions formed by three expanded polyglutamine proteins: a pathologic ataxin-3 fragment, full-length mutant ataxin-3 and an unrelated GFP-polyglutamine fusion protein. Inclusion formation by the full-length mutant ataxin-3 required nuclear localization of the protein and occurred within specific subnuclear structures recently implicated in the regulation of cell death, promyelocytic leukemia antigen oncogenic domains. In a second set of experiments, inhibitors of the proteasome caused a repeat length-dependent increase in aggregate formation, implying that the proteasome plays a direct role in suppressing polyglutamine aggregation in disease. These results support a central role for protein misfolding in the pathogenesis of SCA3/MJD and suggest that modulating proteasome activity is a potential approach to altering the progression of this and other polyglutamine diseases.

Chai, Y., S. L. Koppenhafer, et al. (1999). "Analysis of the role of heat shock protein (Hsp) molecular chaperones in polyglutamine disease." J Neurosci 19(23): 10338-47.
Polyglutamine (polygln) diseases are a group of inherited neurodegenerative disorders characterized by protein misfolding and aggregation. Here, we investigate the role in polygln disease of heat shock proteins (Hsps), the major class of molecular chaperones responsible for modulating protein folding in the cell. In transfected COS7 and PC12 neural cells, we show that Hsp40 and Hsp70 chaperones localize to intranuclear aggregates formed by either mutant ataxin-3, the disease protein in spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD), or an unrelated green fluorescent protein fusion protein containing expanded polygln. We further demonstrate that expression of expanded polygln protein elicits a stress response in cells as manifested by marked induction of Hsp70. Studies of SCA3/MJD disease brain confirm these findings, showing localization of Hsp40 and, less commonly, Hsp70 chaperones to intranuclear ataxin-3 aggregates. In transfected cells, overexpression of either of two Hsp40 chaperones, the DNAJ protein homologs HDJ-1 and HDJ-2, suppresses aggregation of truncated or full-length mutant ataxin-3. Finally, we extend these studies to a PC12 neural model of polygln toxicity in which we demonstrate that overexpression of HDJ-1 suppresses polygln aggregation with a parallel decrease in toxicity. These results suggest that expanded polygln protein induces a stress response and that specific molecular chaperones may aid the handling of misfolded or aggregated polygln protein in neurons. This study has therapeutic implications because it suggests that efforts to increase chaperone activity may prove beneficial in this class of diseases.

Burk, K., T. Klockgether, et al. (1999). "[New insights in the molecular genetics and pathophysiology of hereditary ataxias]." Nervenarzt 70(6): 491-5.
The hereditary ataxias are a heterogeneous group of inherited neurodegenerative disorders characterised by progressive ataxia that results from degeneration of the cerebellum and its afferent and efferent connections. With respect to the pathogenic mechanisms, the hereditary ataxias may be tentatively divided into three groups: (1) The recessive ataxias are induced by the functional impairment of a protein that is essential for the survival of specific neurons while the autosomal dominant ataxias are either caused by (2) mutations of genes coding for ion channels thus resulting in a channelopathy or by (3) a novel deleterious function of a extended polyglutamine sequence within the proteins encoded by the respective genes.