Phenylene Ethynylene Based Sensors For The Selective Detection Of Tau Pathology

The misfolding and aggregation of the microtubule binding tau protein into β-sheet enriched fibrillar deposits (neurofibrillary tangles NFTs) has been linked to an array of neurodegenerative diseases. As tau aggregation is believed to lead to neurodegeneration and cognitive decline decades before the onset of clinical symptoms, tau aggregates are ideal biomarkers for early disease detection and therapeutic intervention. However, there is a lack of diagnostically useful sensors to detect tau deposits. Herein we have characterized two sensors from a library of oligomeric phenylene ethynylene (OPE)-based conjugated polyelectrolytes, anionic OPE1 and cationic OPE2 as novel fluorescent sensors in the detection of NFTs in brain tissue sections. Previous in vitro studies demonstrated that OPE1 and OPE2 display a conformation selective turn-on fluorescence when bound to pathologically relevant amyloid fibrils. In this study, we characterized and quantified OPE's ex vivo sensing capability through confocal fluorescence microscopy and co-localization analysis using tau specific antibody AT180 and historically used amyloid stain Thioflavin-T. Our results show turn-on OPE1 fluorescence when bound to NFTs in transgenic mice and human frontotemporal dementia brain sections with little to no non-specific binding. While OPE2 also detected NFTs, it exhibited more background staining possibly attributed to interactions with neuropil threads or dystrophic neurites. Importantly, the OPE dyes demonstrated effective sensing at a concentration (5 μM) far lower than Thioflavin-T (1.56 mM and higher). Results from this study thus validated the use of OPEs for the selective sensing of NFTs in brain tissue, laying the groundwork for developing these molecular sensors to into a tool to simultaneously and dynamically track NFT formation for both in vitro and in vivo systems, transforming our ability to study the cause, diagnosis, and treatment of major neurodegenerative disorders.