RESUMO
Accumulation of oxidative mitochondrial DNA (mtDNA) damage and impaired base excision repair (BER) in brains have been associated with Alzheimer's disease (AD). However, it is still not clear how these affect mtDNA stability, as reported levels of mtDNA mutations in AD are conflicting. Thus, we investigated whether alterations in BER correlate with mtDNA instability in AD using postmortem brain samples from cognitively normal AD subjects and individuals who show neuropathological features of AD, but remained cognitively normal (high-pathology control). To date, no data on DNA repair and mtDNA stability are available for these individuals. BER activities, mtDNA mutations, and mtDNA copy number were measured in the nuclear and mitochondrial extracts. Significantly lower uracil DNA glycosylase activity was detected in nuclear and mitochondrial extracts from AD subjects, while apurinic/apyrimidinic endonuclease activity was similar in all groups. Although mtDNA mutation frequency was similar in all groups, mtDNA copy number was significantly decreased in the temporal cortex of AD brains but not of high-pathology control subjects. Our results show that lower mitochondrial uracil DNA glycosylase activity does not result in increased mutagenesis, but rather in depletion of mtDNA in early-affected brain regions during AD development.
Assuntos
Doença de Alzheimer/genética , Encéfalo/metabolismo , Reparo do DNA/genética , DNA Mitocondrial/genética , DNA Mitocondrial/metabolismo , Idoso , Idoso de 80 Anos ou mais , Doença de Alzheimer/patologia , DNA Liase (Sítios Apurínicos ou Apirimidínicos)/metabolismo , Feminino , Dosagem de Genes , Humanos , Masculino , Pessoa de Meia-Idade , Mutação , Estresse Oxidativo/genética , Lobo Temporal/metabolismo , Uracila-DNA Glicosidase/metabolismoRESUMO
DNA repair mechanisms are responsible for maintaining the integrity of DNA and are essential to life. However, our knowledge of DNA repair mechanisms is based on model organisms such as Escherichia coli, and little is known about free living and uncultured microorganisms. In this study, a functional screening was applied in a metagenomic library with the goal of discovering new genes involved in the maintenance of genomic integrity. One clone was identified and the sequence analysis showed an open reading frame homolog to a hypothetical protein annotated as a member of the Exo_Endo_Phos superfamily. This novel enzyme shows 3'-5' exonuclease activity on single and double strand DNA substrates and it is divalent metal-dependent, EDTA-sensitive and salt resistant. The clone carrying the hypothetical ORF was able to complement strains deficient in recombination or base excision repair, suggesting that the new enzyme may be acting on the repair of single strand breaks with 3' blockers, which are substrates for these repair pathways. Because this is the first report of an enzyme obtained from a metagenomic approach showing exonuclease activity, it was named ExoMeg1. The metagenomic approach has proved to be a useful tool for identifying new genes of uncultured microorganisms.
Assuntos
Exodesoxirribonucleases/química , Exodesoxirribonucleases/genética , Biblioteca Genômica , MetagenomaRESUMO
Cognitive changes in normal aging can be similar to the alterations that take place in the initial stages of a dementia process. Longitudinal studies can provide a better understanding of this progression. Objectives: To evaluate the cognitive and functional evolution of community-dwelling individuals without dementia through a three-year longitudinal study. Methods: 168 individuals were evaluated in 2006. Three years later in 2009, 73 of these subjects were reevaluated as regards cognition and functionality using the Mini Mental State Examination (MMSE), Brief Cognitive Battery (BCB) and the Pfeffer Functional Activities Questionnaire. The statistical analysis included descriptive measurements, the Wilcoxon's test for intra-group comparison, and the Spearman's correlation coefficient test for comparing cognitive and functionality scores. Results: After three years, the Wilcoxon's test showed a discreet yet significant cognitive decline (MMSE: -0.7 points; p=0.02; Z= -2.29; and global score on the BCB: +3.6 points; p=0.02; Z= -2.29), in addition to functional decline (Pfeffer: +0.7 points; p= 0.001; Z= -3.38). Conclusions: After three years of follow-up we observed a discreet yet significant functional and cognitive decline in the subjects. Longitudinal cognitive screening represents an important strategy in the early identification of changes from normal conditions to a dementia process.
Mudanças cognitivas no envelhecimento normal podem se assemelhar às alterações nos períodos iniciais de um processo demencial. Estudos longitudinais possibilitam um entendimento melhor desta progressão. Objetivos: Avaliar, em um estudo longitudinal de três anos, a evolução cognitiva e funcional de sujeitos sem demência da comunidade. Métodos: Após três anos de uma primeira avaliação de 168 sujeitos, em 2006, 73 sujeitos foram reavaliados em 2009 quanto à cognição e funcionalidade, através do Mini-Exame do Estado Mental (Mini-Mental), Bateria Breve de Rastreio Cognitivo (BBRC) e Questionário de Atividades Instrumentais (Pfeffer). A análise estatística constou de medidas descritivas, teste de Wilcoxon para comparação intragrupo e coeficiente de correlação de Spearman para comparação entre escores cognitivos e de funcionalidade. Resultados: Após três anos, o teste de Wilcoxon evidenciou declínio cognitivo discreto, porém significativo (Mini Mental: -0.7 pontos; p=0.02; Z= -2.29; e escore global da BBRC: +3.6 pontos; p=0.02; Z= -2.29), além de declínio funcional (Peffer: +0.7 pontos; p= 0.001; Z= -3,38). Conclusões: Após três anos de seguimento, observou-se discreto, porém significativo, declínio cognitivo e funcional dos sujeitos. A BBRC e o Mini-Mental mostraram-se eficazes para o screening cognitivo. O seguimento cognitivo longitudinal representa uma estratégia importante para a identificação precoce de possível evolução de uma condição de normalidade para um processo demencial.
Assuntos
Humanos , Doença de Alzheimer , Cognição , Demência , Estatísticas não ParamétricasRESUMO
Cognitive changes in normal aging can be similar to the alterations that take place in the initial stages of a dementia process. Longitudinal studies can provide a better understanding of this progression. OBJECTIVES: To evaluate the cognitive and functional evolution of community-dwelling individuals without dementia through a three-year longitudinal study. METHODS: 168 individuals were evaluated in 2006. Three years later in 2009, 73 of these subjects were reevaluated as regards cognition and functionality using the Mini Mental State Examination (MMSE), Brief Cognitive Battery (BCB) and the Pfeffer Functional Activities Questionnaire. The statistical analysis included descriptive measurements, the Wilcoxon's test for intra-group comparison, and the Spearman's correlation coefficient test for comparing cognitive and functionality scores. RESULTS: After three years, the Wilcoxon's test showed a discreet yet significant cognitive decline (MMSE: -0.7 points; p=0.02; Z= -2.29; and global score on the BCB: +3.6 points; p=0.02; Z= -2.29), in addition to functional decline (Pfeffer: +0.7 points; p= 0.001; Z= -3.38). CONCLUSIONS: After three years of follow-up we observed a discreet yet significant functional and cognitive decline in the subjects. Longitudinal cognitive screening represents an important strategy in the early identification of changes from normal conditions to a dementia process.
Mudanças cognitivas no envelhecimento normal podem se assemelhar às alterações nos períodos iniciais de um processo demencial. Estudos longitudinais possibilitam um entendimento melhor desta progressão. OBJETIVOS: Avaliar, em um estudo longitudinal de três anos, a evolução cognitiva e funcional de sujeitos sem demência da comunidade. MÉTODOS: Após três anos de uma primeira avaliação de 168 sujeitos, em 2006, 73 sujeitos foram reavaliados em 2009 quanto à cognição e funcionalidade, através do Mini-Exame do Estado Mental (Mini-Mental), Bateria Breve de Rastreio Cognitivo (BBRC) e Questionário de Atividades Instrumentais (Pfeffer). A análise estatística constou de medidas descritivas, teste de Wilcoxon para comparação intragrupo e coeficiente de correlação de Spearman para comparação entre escores cognitivos e de funcionalidade. RESULTADOS: Após três anos, o teste de Wilcoxon evidenciou declínio cognitivo discreto, porém significativo (Mini Mental: 0.7 pontos; p=0.02; Z= 2.29; e escore global da BBRC: +3.6 pontos; p=0.02; Z= 2.29), além de declínio funcional (Peffer: +0.7 pontos; p= 0.001; Z= 3,38). CONCLUSÕES: Após três anos de seguimento, observou-se discreto, porém significativo, declínio cognitivo e funcional dos sujeitos. A BBRC e o Mini-Mental mostraram-se eficazes para o screening cognitivo. O seguimento cognitivo longitudinal representa uma estratégia importante para a identificação precoce de possível evolução de uma condição de normalidade para um processo demencial.