Affiliations:
Department of Physiology and Sanders-Brown Center on Aging, University of Kentucky, Lexington, KY, USA
Correspondence:
[*]
Correspondence to: Dr. Marcel M. Verbeek, TML, r.830, Department of Neurology, Radboud University Medical Center, P.O. Box 9101, 6500 HB Nijmegen, the Netherlands. Tel.: +31 24 36 14567; Fax: +31 2436 68754; E-mail: steve.estus@uky.edu.
Note: [1] These authors contributed equally to this work.
Abstract: Background: Genetic variants in TREM2 are strongly associated with Alzheimer’s disease (AD) risk but alternative splicing in TREM2 transcripts has not been comprehensively described. Objective:Recognizing that alternative splice variants can result in reduced gene expression and/or altered function, we sought to fully characterize splice variation in TREM2. Methods:Human anterior cingulate autopsy tissue from 61 donors was used for end-point and quantitative PCR and western blotting to identify and quantify novel TREM2 isoforms. Results:In addition to previously described transcripts lacking exon 3 or exon 4, or retaining part of intron 3, we identified novel isoforms lacking exon 2, along with isoforms lacking multiple exons. Isoforms lacking exon 2 were predominant at approximately 10% of TREM2 mRNA in the brain. Expression of TREM2 and frequency of exon 2 skipping did not differ between AD samples and non-AD controls (p = 0.1268 and p = 0.4909, respectively). Further, these novel splice isoforms were also observed across multiple tissues with similar frequency (range 5.3 –13.0%). We found that the exon 2 skipped isoform D2-TREM2 is translated to protein and localizes similarly to full-length TREM2 protein, that both proteins are primarily retained in the Golgi complex, and that D2-TREM2 is expressed in AD and non-AD brain. Conclusion:Since the TREM2 ligand binding domain is encoded by exon 2, and skipping this exon retains reading frame while conserving localization, we hypothesize that D2-TREM2 acts as an inhibitor of TREM2 and targeting TREM2 splicing may be a novel therapeutic pathway for AD.
Keywords: Alternative splicing, Alzheimer’s disease, colocalization, gene expression
