Conformation-specific monoclonal antibodies reveal early Tau structural intermediates in Alzheimer's disease.

Tauopathy, including Alzheimer's disease, is the most prevalent neurodegenerative disorder, yet current therapies fail to halt disease progression, partly because of limited understanding of early tau pathological structures. Cryo-EM has clarified distinct Tau structures tied to disease phenotypes but only in their mature forms and at low throughput. Hence, molecular probes that can recognize early Tau conformations in high throughput and in situ hold the potential to transform our understanding of Tau aggregation. Tau undergoes sequential changes, including hyperphosphorylation and misfolding, with the aggregation-prone paired helical filament 6 region in R3 shown to drive its self-assembly and fibrillar core formation. In this study, we used existing and novel monoclonal antibodies to map the Tau protein in Alzheimer's disease and other tauopathies. The conformation-specific antibody, 16B12, targeting the R1-R3 regions, showed high sensitivity in detecting early Tau structures and inhibited seed-induced aggregation in vitro. Another antibody, 9H6F2, detected P1-P2 interactions and functioned as a pan-biomarker across tauopathies. Our findings underscore the critical role of early P1-P2 and R1-R3 interactions in Tau fibril maturation, and our monoclonal antibodies show promise as early diagnostic markers for Tau-related neurodegeneration.