CELF2 regulates the species-specific alternative splicing of TREM2

Motoaki Yanaizu,Jun-Ichi Satoh,Yoshihiro Kino,Nobuyuki Nukina,Chika Washizu

doi:10.1038/s41598-020-75057-x

Motoaki Yanaizu, Jun-Ichi Satoh + Show 3 more

Open Access

https://doi.org/10.1038/s41598-020-75057-x

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Abstract

Genetic variations of TREM2 have been implicated as a risk factor of Alzheimer’s disease (AD). Recent studies suggest that the loss of TREM2 function compromises microglial responses to the accumulation of amyloid beta. Previously, we found that exon 3 of TREM2 is an alternative exon whose skipping leads to a reduction in full-length TREM2 protein by inducing nonsense-mediated mRNA decay. Here, we aimed to identify factors regulating TREM2 splicing. Using a panel of RNA-binding proteins, we found that exon 3 skipping of TREM2 was promoted by two paralogous proteins, CELF1 and CELF2, which were both linked previously with risk loci of AD. Although the overexpression of both CELF1 and CELF2 enhanced exon 3 skipping, only CELF2 reduced the expression of full-length TREM2 protein. Notably, the TREM2 ortholog in the green monkey, but not in the mouse, showed alternative splicing of exon 3 like human TREM2. Similarly, splicing regulation of exon 3 by CELF1/2 was found to be common to humans and monkeys. Using chimeric minigenes of human and mouse TREM2, we mapped a CELF-responsive sequence within intron 3 of human TREM2. Collectively, our results revealed a novel regulatory factor of TREM2 expression and highlighted a species-dependent difference of its regulation.

Highlights

Genetic variations of TREM2 have been implicated as a risk factor of Alzheimer’s disease (AD)
A chimeric minigene assay and RNA immunoprecipitation (RIP) suggested that intron 3 of human TREM2 mediates the effect of CELF2
To identify the factors regulating the alternative splicing of TREM2 exon 3, we selected 34 RNA-binding proteins (RBPs) derived from murine cDNA and expressed them as EGFP-fused proteins

Summary

Introduction

Genetic variations of TREM2 have been implicated as a risk factor of Alzheimer’s disease (AD). We identified a regulatory mechanism associated with TREM2 expression through an attempt to develop a therapeutic strategy for a TREM2 mutation (c.482 + 2T>C) that causes N HD27 This splice-site mutation results in the skipping of TREM2 exon 3, which produces a premature termination codon (PTC) on exon 4 that, in turn, induces the destabilization of mRNA through nonsense-mediated mRNA decay (NMD). CELF1 and CELF2 belong to the CELF family and have been shown to regulate RNA processing, including mRNA stability, splicing, and translation[31,32,33,34] Both CELF1 and CELF2 have been suggested to be genes conferring susceptibility to AD in genome-wide association studies (GWAS)[35,36]. Our results provide a novel molecular link between TREM2 and CELF proteins and reveal a species-specific difference of TREM2 that may be important for the disease modeling of AD and other neurological diseases involving microglia and TREM2

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