RESUMO
To more rapidly identify candidate genes located within chromosomal regions of interest defined by genome scan studies in Alzheimer's disease (AD), we have developed a customized microarray containing all the ORFs (n=2741) located within nine of these regions. Levels of gene expression were assessed in total RNA from brain tissue of 12 controls and 12 AD patients. Of all genes showing differential expression, we focused on the ornithine transcarbamylase (OTC) gene on Xp21.1., a key enzyme of the urea cycle which we found to be expressed in AD brains but not in controls, as confirmed by RT-PCR. We also detected mRNA expression of all the other urea cycle enzymes in AD brains. Immunochemistry experiments revealed that the OTC expression was strictly restricted to vascular endothelial cells in brain. Furthermore, OTC activity was 880% increased in the CSF of probable AD cases compared with controls. We analysed the association of the OTC -389 G/A and -241 A/G promoter polymorphisms with the risk of developing AD. We observed that rare haplotypes may be associated with the risk of AD through a possible modulation of the methylation of the OTC promoter. In conclusion, our results suggest the involvement of a new pathway in AD brains involving the urea cycle.
Assuntos
Doença de Alzheimer/enzimologia , Expressão Gênica/fisiologia , Ornitina Carbamoiltransferase/metabolismo , Polimorfismo de Nucleotídeo Único , Idoso , Idoso de 80 Anos ou mais , Doença de Alzheimer/patologia , Doença de Alzheimer/fisiopatologia , Encéfalo/metabolismo , Análise Mutacional de DNA/métodos , Feminino , Genótipo , Humanos , Masculino , Análise em Microsséries/métodos , Ornitina Carbamoiltransferase/genética , Fatores SexuaisRESUMO
The only recognized genetic determinant of the common forms of Alzheimer's disease (AD) is the epsilon 4 allele of the apolipoprotein E gene (APOE). To identify new candidate genes, we recently performed transcriptomic analysis of 2741 genes in chromosomal regions of interest using brain tissue of AD cases and controls. From 82 differentially expressed genes, 1156 polymorphisms were genotyped in two independent discovery subsamples (n=945). Seventeen genes exhibited at least one polymorphism associated with AD risk, and following correction for multiple testing, we retained the interleukin (IL)-33 gene. We first confirmed that the IL-33 expression was decreased in the brain of AD cases compared with that of controls. Further genetic analysis led us to select three polymorphisms within this gene, which we analyzed in three independent case-control studies. These polymorphisms and a resulting protective haplotype were systematically associated with AD risk in non-APOE epsilon 4 carriers. Using a large prospective study, these associations were also detected when analyzing the prevalent and incident AD cases together or the incident AD cases alone. These polymorphisms were also associated with less cerebral amyloid angiopathy (CAA) in the brain of non-APOE epsilon 4 AD cases. Immunohistochemistry experiments finally indicated that the IL-33 expression was consistently restricted to vascular capillaries in the brain. Moreover, IL-33 overexpression in cellular models led to a specific decrease in secretion of the A beta(40) peptides, the main CAA component. In conclusion, our data suggest that genetic variants in IL-33 gene may be associated with a decrease in AD risk potentially in modulating CAA formation.
Assuntos
Doença de Alzheimer/diagnóstico , Doença de Alzheimer/genética , Interleucinas/genética , Interleucinas/metabolismo , Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/metabolismo , Animais , Apolipoproteína E4/genética , Encéfalo/metabolismo , Células COS , Estudos de Casos e Controles , Linhagem Celular Transformada , Angiopatia Amiloide Cerebral/genética , Angiopatia Amiloide Cerebral/metabolismo , Angiopatia Amiloide Cerebral/patologia , Chlorocebus aethiops , Feminino , Seguimentos , Carga Genética , Predisposição Genética para Doença , Estudo de Associação Genômica Ampla , Genótipo , Humanos , Interleucina-33 , Cooperação Internacional , Masculino , Neuroblastoma , Análise de Sequência com Séries de Oligonucleotídeos/métodos , Fragmentos de Peptídeos/metabolismo , Polimorfismo de Nucleotídeo Único , Modelos de Riscos Proporcionais , RNA Mensageiro/metabolismo , Estudos Retrospectivos , Transfecção/métodosRESUMO
Fibrodysplasia ossificans progressiva (FOP) is a rare but very severe disease, characterised by congenital malformations of the toes and by progressive heterotopic ossification of muscles and joints. Two genes, the noggin (NOG) gene and the activin A type I receptor (ACVRI) gene, are involved in FOP. In this study we have searched for the NOG and the 617G>A (ACVR1) mutations in a well characterized series of twenty-seven French FOP patients. Five NOG mutations (delta 42, 274G>C, 275G>A, 276G>A, and 283G>A) have been found in seven (26%) of our FOP patients. The 617G>A mutation in the ACVR1 gene is found in fourteen (52%) of the patients. With one exception (patient number 22), 617G>A and NOG mutations are mutually exclusive in patients. Mutations 274G>C, 283G>A and 617G>A segregate with the trait in five different FOP families, some members of them being partially affected by the disease.