<i>In Situ</i> Labeling of Pathogenic Tau Using Photo-Affinity Chemical Probes

Tau aggregation plays a crucial role in the development of Alzheimer's disease (AD). Developing specific techniques that can isolate pathogenic tau from brain tissue is important for understanding tauopathies and advancing targeted therapies. Here, we develop photoaffinity small molecular probes and a novel method for <i>in situ</i> tissue labeling and investigate their activity in interacting with tau in cells and AD patient brains. Based on the reported chemical structures of tau PET tracers, we designed and synthesized two tau-specific probes, namely, Tau-2 and Tau-4. After validation in cell, mouse model, and patient brain samples, our photolabeling results suggested that Tau-2 effectively labels soluble tau in cell and mouse models, while Tau-4 selectively binds high-molecular-weight tau aggregates in late-stage AD patient brain tissues. Proteomic analysis verified the specific isolation of pathogenic tau from AD brain samples. Collectively, these findings underscore the potential of our photoaffinity probes as powerful tools for investigating tau proteins and neurofibrillary tangles in neurodegenerative diseases.