Résumé
The only recognised genetic determinant of the common forms of Alzheimer's disease (AD) is the ε4 allele of the apolipoprotein E gene (APOE). To identify new candidate genes, we recently performed transcriptomic analysis of 2,741 genes in chromosomal regions of interest using brain tissue of AD cases and controls.
From 82 differentially expressed genes, 1,156 polymorphisms were genotyped in two independent discovery sub-samples (n=945). Seventeen genes exhibited at least one polymorphism associated with AD risk and following correction for multiple testing, we retained the 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 3 polymorphisms within this gene, which we analysed in three independent case-control studies. These polymorphisms and a resulting protective haplotype were systematically associated with AD risk in non-APOE ε4 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 ε4 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 Aβ 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.