Characterization of TREM2 Expression in Human Cell lines and Brain Eric Dyne1,2, Yvonne Shao1, Maria Khrestian1, Rumana Akhtar1, Giana D'Aleo1, Shane Formica1, James B. Leverenz3, Lynn Bekris1 1Genomic Medicine Institute, Lerner Research Institute, Cleveland Clinic, Cleveland Ohio; 2School of Biomedical Sciences, Kent State University, Kent Ohio; 3Lou Ruvo Center for Brain Health, Neurological Institute, Cleveland Clinic, Cleveland Ohio
Background: Variation in the protein encoding gene triggering receptor expressed on myeloid cells 2 (TREM2) is associated Alzheimer's disease (AD). In the human brain, TREM2 mRNA is expressed in several regions known to be affected in AD. Given that TREM2 plays a role in in microglial survival and neuroinflammation in AD mouse models, it is important to understand the underlying mechanisms driving changes in TREM2 expression in human tissues. In this investigation, it was hypothesized that trans-acting factors present in certain cell types or brain regions modulate TREM2 regulatory element activity. Therefore, TREM2 expression will differ in glial cells compared to neuronal cell types or in cerebellum compared to hippocampus.
Method: TREM2 expression was evaluated in post-mortem brain using Western Blot. The TREM2 promoter region was PCR amplified from human genomic DNA and cloned into a pGL4.10 luciferase reporter vector. DNA was genotyped for selected promoter SNPs. Three variant combinations (CTCT, CTCG, and AGCT) were identified and cloned into a pGL4.10 luciferase reporter vector promoter only and with the promoter and TREM2 3'UTR. This produced six TREM2 regulatory region haplotype constructs that were transiently transfected into eight human cell lines, including neuronal, glial and hepatocyte cell line. Results: TREM2 protein levels differ between cerebellum and hippocampus. Luciferase activity of TREM2 regulatory element constructs indicate differential regulation that depends on haplotype and cell type. Conclusions: These results suggest that TREM2 expression is specific to certain cell types and implicates the presence of critical cell type specific trans-acting factors that act upon certain regulatory regions of TREM2. Understanding TREM2 regulation provides insight into potential targets for activation or inhibition of TREM2. Further research is warranted to characterize the trans-acting factors that contribute to TREM2 gene regulation.