Contribution of G4 Structure to Alzheimer’s Disease and Tau Pathology
TL;DR
This dissertation explores the hypothesis that G4-forming nucleic acids represent a mechanistic link between cellular stress, RNA biology, and tau aggregation in AD and establishes G-quadruplexes as previously underappreciated regulators of tau biology and implicates RNA structure as an active contributor to AD pathogenesis.
Abstract
The occurrence of Alzheimer’s Disease (AD) is rapidly increasing as our global population ages. With the majority of therapeutic drugs in the last couple of decades failing clinical trials, new molecular targets are needed to combat the expected influx of new AD cases. AD pathogenesis is associated with abnormal protein aggregation, characterized in part by intracellular accumulation of hyperphosphorylated tau (p-tau) in neurofibrillary tangles (NFTs). RNA has been identified as a major non-proteinaceous component of NFTs and has been implicated as an active cofactor in tau aggregation and spread. Recent work has shown that aggregates from AD brains contain almost double the amount of RNA as healthy individuals. This aggregate RNA is significantly enriched in polyguanine stretches with a high likelihood of forming G-quadruplexes (G4s). However, direct interactions between tau protein and G4 structures have been mostly unexplored. In this dissertation, I explore the hypothesis that G4-forming nucleic acids represent a mechanistic link between cellular stress, RNA biology, and tau aggregation in AD. We show that rG4 accumulation increases in the hippocampus with both age and with AD severity. We further observed that neurons exhibiting phospho-tau tangles also contained rG4 structures and that rG4 staining density varied with APOE genotype in the human tissue examined. We then explore the mechanism behind G4 tau interactions with physiological G4s from hippocampal aggregates. We found these G4s to be powerful, sequence-specific modulators of aggregation compared to other RNAs. These G4s induced unique biophysical properties and modulated solubility of associated proteins. They propagated aggregate spread in cells, stabilized distinct tau oligomer populations in the absence of exogenous seeds, and induced fibril formation to vastly differing lengths and morphologies with relatively small changes in nucleotide sequence. These results suggest that the complex systems driving protein aggregation and structural changes in cells could be due to differential enrichment of nucleic acids in aggregates. This work establishes G-quadruplexes as previously underappreciated regulators of tau biology and implicates RNA structure as an active contributor to AD pathogenesis.