Tau-RNA crosstalk: Alternative Poly-Adenylation (APA) Regulation in Alzheimer's Disease

Alzheimer's disease (AD) is a devastating degenerative brain disorder and the most prevalent form of dementia, affecting millions worldwide. Given its significant impact on public health, it is crucial to accelerate the development of treatments that would prevent, delay, or reverse the course of the disease and improve early

diagnosis. In neurons, Tau protein is primarily known for its canonical role in assembling and stabilizing microtubules. Moreover, native Tau binds to both DNA and RNA molecules, suggesting a role in RNA transcription, post-transcriptional processing and translation. However, in the AD brain, Tau protein undergoes

misfolding and subsequently forms pathological oligomers. In this context, I propose that misfolded Tau is unable to bind RNA, hampering its function on RNA post-transcriptional processing and altering gene expression. One of the key mechanisms for controlling gene expression in eukaryotic cells is Alternative Poly-

Adenylation (APA). APA can affect the length, stability, translation, localization, and function of mRNAs. In our inducible Tau cell model, wild-type or native (wt) Tau modulates the expression of several APA mRNAs that encode RNA-Binding Proteins (RBPs). Several of these identified RBPs have been observed with altered

function and aggregation in AD and Frontotemporal lobar degeneration (FTLD). These findings underscore the substantial involvement of APA in neuronal degeneration, highlighting its paramount significance in the pathogenesis of AD and AD related disorders (AD/ADRD). However, the mechanism underlying how

Tau modulates APA is unknown. We propose that in AD, Tau oligomerization interferes with APA and hampers short and long 3'-UTR mRNA isoforms of RBPs critical to RNA processing. The primary outcome of this study is to comprehensively profile APA transcripts and gene expression in wild type and mutant Tau-expressing neurons. We seek to build upon our published data, investigating the

effects of pathological Tau (oligomeric and mutant forms) on APA, which is yet to be determined. We will test our hypothesis via two specific aims. In Aim 1, our objective is to identify and compare mRNA isoform libraries from mouse primary hippocampal neurons expressing human wt-Tau (htau) and pathogenic mutant

Tau (rTg5410, MAPT-P301L). We are excited to harness the groundbreaking Poly(A)-ClickSeq (PAC- Seq) technology, an innovative approach that will unlock comprehensive profiles of APA transcripts and gene expression in wt and mutant Tau-expressing neurons. In Aim 2, we propose to identify APA mRNA isoforms in htau and rTg4510 before and after the manifestation of Tau pathology. Additionally, we will use

biochemical and cellular assays to pinpoint changes in Tau oligomer-modulated mRNA isoform levels and expression. Our approach delves deeper into the impact of APA, surpassing the limited evaluation of gene expression offered by previous RNA-Seq methods. By connecting APA with Tau pathology, our study seeks

to advance the field by identifying the mRNA isoforms altered by pathological Tau in AD/ADRD.