Role of Anti-tau Antibodies on Microtubule Polymerization and Stability

Abstract

Tau is an intrinsically disordered protein which in neuronal cells promotes the polymerization and stability of microtubules (MT). In neurodegenerative diseases, tau undergoes post-translational modifications (PTMs), misfolds and forms toxic aggregates. Currently, tauopathies remain without a cure. Immunotherapies targeting tau protein in animal models induced clearance of tau pathology. However, the mechanisms of antibody-based inhibition of neurodegeneration remain mostly unclear. We have previously reported on the inhibition of tau aggregation in vitro by antibodies to non-phosphorylated tau441. We also have shown that phosphorylation of tau441 at Ser199 by GSK-3ß protein kinase may be inhibited by antibodies to phosphorylated tau. Here, we evaluated the polymerization of tubulin in the presence of non-phosphorylated tau and antibodies to non-phosphorylated tau [targeting epitopes in the N-terminus, R4, and C-terminus]. ELISA was used to determine antigen-antibody binding affinities. The microtubules were characterized by transmission electron microscopy. Tubulin fluorescence polymerization assay indicated that the antibodies reduced tubulin polymerization. In the presence of tau441, the tubulin polymerization was rescued even in the presence of antibodies. In addition to MT formation, the stability of paclitaxel-stabilized MT was also evaluated. Data indicate that tau protein and its antibodies play regulatory and/or competitive roles in MT formation/stability.