O5-04-01: Molecular mechanisms of Abeta-induced Tau-pathology: Analysis of cross-seeding of Abeta and Tau and its role in prion-like propagation of Tau-pathology in vitro and in vivo

Abstract

tissue homogenates with exogenous Ab1-42 under multiple conditions. Samples were analyzed using acid urea gels followed by Western blotting. Results:The PDAPP mice study revealed Ab42 to Ab40 conversion over time reaching equilibrium by 72hr. Acid urea gel analyses demonstrated that over half of the Ab1-42 peptide administered was converted to Ab1-40. Furthermore, ELISA results from rat studies showed similar conversion rates from Ab42 to Ab40 regardless of the route of administration, centrally or peripherally. Ex-vivo studies using rat tissue homog-enates incubated with exogenous Ab1-42 peptide also exhibited Ab conversion. This conversion was present in all tissues tested, cortex, kidney, liver, pancreas, and spleen, and was exacerbated when the pH was lowered to pH5 from pH7. The rate of conversion to Ab40 was diminished when a c-terminal antibody or pro-tease inhibitor was incorporated into the in-vivo/ex-vivo studies. Conclusions: We have identified in-vivo processing of the carboxyl-terminus of Ab in rodents. The extent of in-vivo processing is exacerbated when an Ab antibody extends the half-life of the peptide. The conversion of Ab1-42 to Ab1-40 occurs both centrally and peripherally. Although the potential for this conversion in human is unknown, these results suggest additional biology after secretase liberation of the Ab from the APP may be important for the overall Ab ratios being measured in CNS and periphery. Background: Combined genetic, pathological and clinical data provided the basis for the amyloid cascade hypothesis, which is further supported by biomarker data and remains the major hypothesis for development of therapeutic strategies. In vitro and preclinical in vivo models have robustly recapitulated amyloid induced Tau-pathology providing support to the amyloid cascade hypothesis and providing tools to understand this event, generally considered to be crucial in the pathogenesis of AD. Methods: We previously reported a preclinical model with robust amyloid induced Tau-pathology , providing an experimental window for analysis of mechanisms of ABeta-induced Tau-pathology in vivo. In this model, we demonstrated the induction of Tau-pathology along functional connections , in regions relatively spared of amyloid pathology. The striking similarity between abeta-induced Tau-pathology in pre-clinical models and in our recently reported Tau-seeding model, provided the basis for our current analysis of Abeta-induced Tau-fi-brillization by cross-seeding and its subsequent propagating potential , in vitro and in vivo. Cell-free assays were used to analyze Tau