Publicação
Insights into pathology and neurodegeneration features in a transgenic mouse model of Machado-Joseph disease
| Resumo: | Machado-Joseph disease (MJD), also known as Spinocerebellar Ataxia 3 (SCA3), is the most common autosomal dominant ataxia worldwide, and is caused by a CAG repeat expansion within the coding region of the ATXN3 gene. The clinical variability of the disease phenotype as well as the age of onset depend on the length of the expanded repeat. The anticipation phenomenon is most frequently associated with repeat expansions in paternal transmission. MJD patients with a repeat expansion above 44 CAGs in the ATXN3 gene present cytoplasmic and/or intranuclear ataxin-3 aggregates and neuronal cell loss in specific areas of the brain. However, some questions remains unanswered in this disease: why only some subpopulations of neurons are affected, although ataxin- 3 is everywhere; what underlies this selective neuronal vulnerability; are these neurons dysfunctional or dying? In an attempt to address these issues, we took advantage of studying a cDNA transgenic mouse model (CMVMJD) expressing the mutant human ataxin-3 under the regulation of the CMV promoter (pCMV), previously generated in our lab. This transgenic mouse model shows an important overlap with genetic and clinical features of MJD, namely genetic instability of the expanded CAG repeat and a motor impairment phenotype. In this work, we performed an extensive pathological analysis of MJD mouse brains, that revealed a significant atrophy in the thalamus and in the dentate neurons. Increased GFAP immunostaining with reactive astrocytes was observed in the vestibular nuclei and substantia nigra of transgenic mice. Regarding cell death, we have searched for evidence of different cell death types (apoptosis and necrosis) by TUNEL assay, caspase-3 analysis and Fluoro-Jade B staining. We did not find any differences between wild-type and MJD transgenic mice, suggesting that probably the affected neurons are not dying, at least by apoptosis or necrosis, instead, they might just be dysfunctional. We also analysed of the somatic mosaicism in neuronal and non-neuronal tissues through aging revealed a significant increase in the mosaicism index of specific brain regions such as the pons, substantia nigra, cerebellar cortex, hipocampus, striatum, deep cerebellar nuclei and hypothalamus with age. However, there was no correlation between the extent of the mosaicism and the pathological involvement of a given region. The results allow us to conclude that the pCMVMJD94 mouse is a good model to study the pathogenic mechanisms of MJD, mimicking an early stage of the disease. |
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| Autores principais: | Silva, Sara Carina Duarte |
| Ano: | 2011 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | Machado-Joseph disease (MJD), also known as Spinocerebellar Ataxia 3 (SCA3), is the most common autosomal dominant ataxia worldwide, and is caused by a CAG repeat expansion within the coding region of the ATXN3 gene. The clinical variability of the disease phenotype as well as the age of onset depend on the length of the expanded repeat. The anticipation phenomenon is most frequently associated with repeat expansions in paternal transmission. MJD patients with a repeat expansion above 44 CAGs in the ATXN3 gene present cytoplasmic and/or intranuclear ataxin-3 aggregates and neuronal cell loss in specific areas of the brain. However, some questions remains unanswered in this disease: why only some subpopulations of neurons are affected, although ataxin- 3 is everywhere; what underlies this selective neuronal vulnerability; are these neurons dysfunctional or dying? In an attempt to address these issues, we took advantage of studying a cDNA transgenic mouse model (CMVMJD) expressing the mutant human ataxin-3 under the regulation of the CMV promoter (pCMV), previously generated in our lab. This transgenic mouse model shows an important overlap with genetic and clinical features of MJD, namely genetic instability of the expanded CAG repeat and a motor impairment phenotype. In this work, we performed an extensive pathological analysis of MJD mouse brains, that revealed a significant atrophy in the thalamus and in the dentate neurons. Increased GFAP immunostaining with reactive astrocytes was observed in the vestibular nuclei and substantia nigra of transgenic mice. Regarding cell death, we have searched for evidence of different cell death types (apoptosis and necrosis) by TUNEL assay, caspase-3 analysis and Fluoro-Jade B staining. We did not find any differences between wild-type and MJD transgenic mice, suggesting that probably the affected neurons are not dying, at least by apoptosis or necrosis, instead, they might just be dysfunctional. We also analysed of the somatic mosaicism in neuronal and non-neuronal tissues through aging revealed a significant increase in the mosaicism index of specific brain regions such as the pons, substantia nigra, cerebellar cortex, hipocampus, striatum, deep cerebellar nuclei and hypothalamus with age. However, there was no correlation between the extent of the mosaicism and the pathological involvement of a given region. The results allow us to conclude that the pCMVMJD94 mouse is a good model to study the pathogenic mechanisms of MJD, mimicking an early stage of the disease. |
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