Association Study of the <b><i>TREM2 </i></b>Gene and Identification of a Novel Variant in Exon 2 in Iranian Patients with Late-Onset Alzheimer's Disease

ABSTRACTA single nucleotide polymorphism (SNP) in exon 2 of the CD33 gene is associated with reduced susceptibility to late-onset Alzheimer’s disease (AD) and causal for elevated mRNA lacking exon 2. In contrast to full-length CD33, transcripts lacking exon 2 result in CD33 protein unable to suppress activation responses in myeloid cells, including microglia. Currently, little is known about the regulation of CD33 exon 2 splicing. Using functional genomics and proteomic approaches, we found that SRSF1 and PTBP1 act as splicing enhancers to increase CD33 exon 2 inclusion in mRNA. Binding of PTBP1 to RNA sequences proximal to the intron 1-exon 2 splice junction is altered by the SNP and represents a potential mechanism behind the SNP-genotype dependent alternative splicing. Our studies also reveal that binding of SRSF1 to the CD33 RNA is not altered by the SNP genotype. Instead, a putative SRSF1 binding sequence at the 3′ end of exon 2 directs CD33 exon 2 inclusion into the mRNA, indicating that PTBP1 and SRSF1 promote full-length isoform expression through different mechanisms. Our findings shed light on molecular interactions that regulate CD33 exon 2 splicing, ultimately impacting receptor expression on the cell surface. These data aid in the understanding of CD33’s regulation of microglial signaling underpinning the AD genetic associations.

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Genetic Analysis of TREM2 Variants in Tunisian Patients with Alzheimer's Disease

Medical Principles and Practice ◽

10.1159/000489779 ◽

2018 ◽

Vol 27 (4) ◽

pp. 317-322 ◽

Cited By ~ 1

Author(s):

Zied Landoulsi ◽

Mouna Ben Djebara ◽

Imen Kacem ◽

Youssef Sidhom ◽

Rym Kefi ◽

...

Keyword(s):

Alzheimer’S Disease ◽

Alzheimer's Disease ◽

Rare Variants ◽

Late Onset ◽

Tunisian Population ◽

Fisher Exact Test ◽

Exon 2 ◽

Exact Test ◽

Tunisian Patients ◽

Synonymous Variant

Objective: Rare variants in the TREM2 gene have been reported to significantly increase the risk of Alzheimer’s disease in Caucasian populations. Hitherto, this association was not studied in North African populations. In this work, we aimed to study the association between TREM2 exon 2 variants and the risk of late-onset Alzheimer’s disease (LOAD) in a Tunisian population. Subjects and Methods: We sequenced exon 2 of TREM2 in a Tunisian cohort of 172 LOAD patients and 158 control subjects. We used the Fisher exact test to compare the distribution of allelic frequencies between the two groups. Results: We identified 4 previously reported nonsynonymous variants (p.Asp39Glu, p.Arg62His, p.Thr96Lys, and p.Val126Gly) and 1 novel synonymous variant (p.Gln109Gln), none of which was significantly associated with the risk of Alzheimer’s disease. Moreover, the rare TREM2 variant (p.Arg47His), which was considered to be a risk factor for Alzheimer’s disease in European descent populations, was not detected in our cohort. Conclusion: These findings do not support a major role for TREM2 in the pathogenesis of LOAD in the Tunisian population.

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