Novel Conformation Selective Molecular Sensors for Amyloid Aggregates

Misfolding and aggregation of proteins is a central pathogenic event in a myriad of neurodegenerative disorders including Alzheimer's and Parkinson's diseases. Importantly, as protein aggregation is believed to initiate a cascade of events culminating in neurodegeneration and cognitive decline decades before the onset of clinical symptoms, protein aggregates are ideal biomarkers for early disease detection and therapeutic intervention. Currently, there lacks diagnostically useful sensors for detecting protein aggregates involved in disease etiology. To meet this critical need, we are developing novel oligo(p-phenylene ethynylene) electrolytes (OPEs) for the direct sensing of amyloid aggregates and have identified an effective selective sensor, OPE1, for the amyloid conformation of model proteins (lysozyme and insulin) and disease-associate proteins (amyloid-β, tau, and α-synuclein). On the basis of protein binding and photophysical changes observed, keys to the selective detection of the amyloid protein conformation include moderate size, negative charge, and substituents that provide high microenvironment sensitivity to the fluorescence yield. We have further validated the use of OPEs for ex vivo detection of amyloid pathology in brain tissue sections. Confocal fluorescence microscopy combined with co-localization analysis using tau specific antibody AT180 and existing “gold-standard” amyloid dye Thioflavin-T (ThT) showed turn-on OPE1 fluorescence when bound to tau amyloid deposits in transgenic mice and human frontotemporal dementia brain sections with little to no non-specific binding. Importantly, both in vitro and in vivo studies demonstrated that OPEs are superior sensors compared to the conventional dye ThT, exhibiting lower detection limits and higher fluorescence signal. Combined with OPE's versatile and highly tailorable structural and chemical properties, these facile probes have the potential to simultaneously and dynamically track the protein misfolding and aggregation process for both in vitro and in vivo systems, facilitating research into the cause, diagnosis, and treatment of major neurodegenerative disorders.