1,721,027 research outputs found
Intracellular inclusions, pathological markers in diseases caused by expanded polyglutamine tracts?
No full textThe largest group of currently known trinucleotide repeat diseases is caused by (CAG)n repeat expansions. These (CAG)n repeats are translated into polyglutamine tracts from both mutant and wild type alleles. Genetic and transgenic mouse data suggest that the expanded polyglutamines cause disease by conferring a novel deleterious gain of function on the mutant protein. These mutations are associated with the formation of intracellular inclusions. This review will consider findings from necropsy studies of human patients and transgenic mouse models of these diseases, along with in vitro models, in order to try to synthesise the current understanding of these diseases and the evidence for and against inclusion formation as a primary mechanism leading to pathology
Wild type huntingtin reduces the cellular toxicity of mutant huntingtin in mammalian cell models of Huntington's disease
No full textOBJECTIVESRecent data suggest that wild type huntingtin can protect against apoptosis in the testis of mice expressing full length huntingtin transgenes with expanded CAG repeats. It is not clear if this protective effect was confined to particular cell types, or if wild type huntingtin exerted its protective effect in this model by simply reducing the formation of toxic proteolytic fragments from mutant huntingtin.
METHODSWe cotransfected neuronal (SK-N-SH, human neuroblastoma) and non-neuronal (COS-7, monkey kidney) cell lines with HD exon 1 (containing either 21 or 72 CAG repeats) construct DNA and either full length wild type huntingtin or pFLAG (control vector).
RESULTSFull length wild type huntingtin significantly reduced cell death resulting from the mutant HD exon 1 fragments containing 72 CAG repeats in both cell lines. Wild type huntingtin did not significantly modulate cell death caused by transfection of HD exon 1 fragments containing 21 CAG repeats in either cell line.
CONCLUSIONSOur results suggest that wild type huntingtin can significantly reduce the cellular toxicity of mutant HD exon 1 fragments in both neuronal and non-neuronal cell lines. This suggests that wild type huntingtin can be protective in different cell types and that it can act against the toxicity caused by a mutant huntingtin fragment as well as against a full length transgene
Alpha-synuclein overexpression promotes aggregation of mutant huntingtin
No full textProtein aggregates are a neuropathological feature of Huntington's disease and Parkinson's disease. Mutant huntingtin exon 1 with 72 CAG repeats fused to enhanced green fluorescent protein (EGFP) forms hyperfluorescent inclusions in PC12 cells. Inclusion formation is enhanced in cells co-transfected with EGFP-huntingtin-(CAG)(72) and alpha-synuclein, a major component of Parkinson's disease aggregates. However, alpha-synuclein does not form aggregates by itself, nor does it appear in huntingtin inclusions in vitro
Heat shock protein 27 prevents cellular polyglutamine toxicity and suppresses the increase of reactive oxygen species caused by huntingtin
No full textNeuronal loss and intraneuronal protein aggregates are characteristics of Huntington’s disease (HD), which is one of 10 known neurodegenerative disorders caused by an expanded polyglutamine [poly(Q)] tract in the disease protein. N-terminal fragments of mutant huntingtin produce intracellular aggregates and cause toxicity. Several studies have shown that chaperones suppress poly(Q) aggregation and toxicity/cell death, but the mechanisms by which they prevent poly(Q)-mediated cell death remain unclear. In the present study,
we identified heat shock protein 27 (HSP27) as a suppressor of poly(Q) mediated cell death, using a cellular model of HD. In contrast to HSP40/70 chaperones, we showed that HSP27 suppressed poly(Q) death without suppressing poly(Q) aggregation. We tested the hypotheses that HSP27 may reduce poly(Q)-mediated cell death either by binding cytochrome c and inhibiting the mitochondrial death pathway or by protecting gainst reactive oxygen species (ROS). While poly(Q)-induced cell death was reduced by inhibiting cytochrome c (cyt c) release from mitochondria, protection by HSP27 was regulated by its phosphorylation status and was independent of its ability to bind to cyt c. However, we observed that mutant huntingtin caused increased levels of ROS in neuronal and non-neuronal cells. ROS contributed to cell death because both N-acetyl-L-cysteine and glutathione in its reduced form suppressed poly(Q)-mediated cell death. HSP27
decreased ROS in cells expressing mutant huntingtin, suggesting that this chaperone protects cells against oxidative stress. We propose that a poly(Q) mutation can induce ROS that directly contribute to cell death and that HSP27 is an antagonist of this process
Effects of heat shock, heat shock protein 40 (HDJ-2), and proteasome inhibition on protein aggregation in cellular models of Huntington's disease
No full textHuntington's disease (HD), spinocerebellar ataxias types 1 and 3 (SCA1, SCA3), and spinobulbar muscular atrophy (SBMA) are caused by CAG/polyglutamine expansion mutations. A feature of these diseases is ubiquitinated intraneuronal inclusions derived from the mutant proteins, which colocalize with heat shock proteins (HSPs) in SCA1 and SBMA and proteasomal components in SCA1, SCA3, and SBMA. Previous studies suggested that HSPs might protect against inclusion formation, because overexpression of HDJ-2/HSDJ (a human HSP40 homologue) reduced ataxin-1 (SCA1) and androgen receptor (SBMA) aggregate formation in HeLa cells. We investigated these phenomena by transiently transfecting part of huntingtin exon 1 in COS-7, PC12, and SH-SY5Y cells. Inclusion formation was not seen with constructs expressing 23 glutamines but was repeat length and time dependent for mutant constructs with 43–74 repeats. HSP70, HSP40, the 20S proteasome and ubiquitin colocalized with inclusions. Treatment with heat shock and lactacystin, a proteasome inhibitor, increased the proportion of mutant huntingtin exon 1-expressing cells with inclusions. Thus, inclusion formation may be enhanced in polyglutamine diseases, if the pathological process results in proteasome inhibition or a heat-shock response. Overexpression of HDJ-2/HSDJ did not modify inclusion formation in PC12 and SH-SY5Y cells but increased inclusion formation in COS-7 cells. To our knowledge, this is the first report of an HSP increasing aggregation of an abnormally folded protein in mammalian cells and expands the current understanding of the roles of HDJ-2/HSDJ in protein folding. <br/
The deleterious effect of polyglutamine aggregation in cell models of Huntington's disease.
No full textThe molecular biology of Huntington's disease
No full textBackground. Huntington's disease (HD) is a fatal neurodegenerative disorder with an autosomal dominant mode of inheritance. It leads to progressive dementia, psychiatric symptoms and an incapacitating choreiform movement disorder, culminating in premature death. HD is caused by an increased CAG repeat number in a gene coding for a protein with unknown function, called huntingtin. The trinucleotide CAG codes for the amino acid glutamine and the expanded CAG repeats are translated into a series of uninterrupted glutamine residues (a polyglutamine tract).Methods. This review describes the epidemiology, clinical symptomatology, neuropathological features and genetics of HD. The main aim is to examine important findings from animal and cellular models and evaluate how they have enriched our understanding of the pathogenesis of HD and other diseases caused by expanded polyglutamine tracts.Results. Selective death of striatal and cortical neurons occurs. It is likely that the HD mutation confers a deleterious gain of function on the protein. Neuronal intranuclear inclusions containing huntingtin and ubiquitin develop in patients and transgenic mouse models of HD. Other proposed mechanisms contributing to neuropathology include excitotoxicity, oxidative stress, impaired energy metabolism, abnormal protein interactions and apoptosis.Conclusions. Although many interesting findings have accumulated from studies of HD and other polyglutamine diseases, there remain many unresolved issues pertaining to the exact roles of intranuclear inclusions and protein aggregates, the mechanisms of selective neuronal death and delayed onset of illness. Further knowledge in these areas will inspire the development of novel therapeutic strategies
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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