Author ORCID Identifier

https://orcid.org/0000-0003-1399-1256

Year of Publication

2022

Degree Name

Master of Science in Medical Sciences (MSMS)

Document Type

Master's Thesis

College

Medicine

Department/School/Program

Medical Sciences

First Advisor

Dr. Steven Estus

Second Advisor

Dr. Melinda Wilson

Abstract

Genetic mutations in the TREM2 gene are highly correlated with risk of Alzheimer’s disease, but alternative splicing patterns of TREM2 transcripts have not been fully described. Characterization of TREM2 alternative splicing will be of significant use to the scientific community as the field of Alzheimer’s disease research progresses. The goal of this study was to fully describe splicing patterns in TREM2, as different splicing isoforms of genes can alter express and/or function of the final protein. Human blood and anterior cingulate cortex brain tissue from 61 individual donors was processed and used for PCR and quantitative PCR as well as western blotting in order to identify and quantify novel TREM2 isoforms. Previously described transcripts of TREM2 which lacked exons 3 or 4, or which retained part of intron 3 were replicated in this study. Additionally, we identified a novel isoform lacking exon 2, D2-TREM2, as well as several novel isoforms lacking multiple exons. D2-TREM2 mRNA in the brain comprised approximately 10% of total TREM2 RNA in the brain. Quantitative expression of TREM2 and frequency D2-TREM2 were compared between subjects with and without Alzheimer’s disease, revealing no significant difference between the two groups. The novel splice isoforms identified in this study were found across multiple tissue types. D2-TREM2 was found with similar frequency in non-brain tissues, ranging from 5.3-13.0%. D2-TREM2 was found to be translated to protein and shares localization and cell trafficking patterns with full-length TREM2. Both D2-TREM2 and full-length TREM2 are predominantly retained in the Golgi complex. Additionally, D2-TREM2 was confirmed to be expressed in the brains of subjects with Alzheimer’s disease as well as those without Alzheimer’s disease. Exon 2 of TREM2 encodes for the ligand-binding domain, which is essential for its function as a receptor and thus function of cells on which it is present, such as microglia in the central nervous system. As D2-TREM2 lacks exon 2, we hypothesize that D2-TREM2 may inhibit full-length TREM2 function and that targeting TREM2 splicing may offer a novel therapeutic approach for Alzheimer’s disease.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2022.312

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