Transcriptome analyses reveal tau isoform-driven changes in transposable element and gene expression

Purpose: Overexpression of tau isoforms has been linked to neurodegenerative diseases, and abnormal tau expression is correlated with genomic instability. The purpose of this study is to use RNA-sequencing and molecular biological techniques to determine if there are any unique genomic consequences associated with overexpression of one or more tau isoforms. Methods: SHSY-5Y cells were infected in triplicate with lentiviruses to induce overexpression of 3R and 4R tau isoforms, were treated with amyloid-beta oligomers or DMSO, and were differentiated into neurons using retinoic acid. After RNA collection via TRIzol, poly(A)-selected, 100 bp, paired-end library preparation and sequencing were completed by the IGM Genomics Center, University of California, San Diego, La Jolla, CA, using an Illumina NovaSeq 6000 that was purchased with funding from a National Institutes of Health SIG grant (#S10 OD026929). Trimmed FASTQ files were aligned to GRCH38 using STAR and differential expression of genes and transposable elements was determined using DESeq2 and software from TEToolkit (available from the Hammell Lab at Cold Spring Harbor Laboratory). Results: Our RNA-seq analysis revealed similar gene and transposable element expression patterns between cells overexpressing tau isoforms and patients with Alzheimer's disease or progressive supranuclear palsy. We found widespread differential expression particularly in L1 and Alu transposable elements and upregulation of genes related to extracellular matrix organization, focal adhesions, and cell junctions, among other biological processes. Conclusions: Our study is the first to our knowledge to examine locus-specific transposable element expression in the context of tauopathies, and to our knowledge is the first to specifically examine transposable element expression stemming from overexpression of tau isoforms. Our study provides additional evidence that transposable elements may play a role in tauopathies and provides further insight into the locations of transposable element expression in the genome in the context of neurodegenerative diseases. Overall design: Lentiviral infection to produce tau isoform overexpression in neuronally differentiated SH-SY5Y cells, along with treatment with DMSO or amyloid-beta oligomers to examine transcriptomic effects (N=3).