14-3-3ζ protein prevents formation of GSK3β-phosphorylated Tau protein fibrils

Alzheimer's Disease remains one of the challenges in modern-day medicine, lacking any blockbuster therapy. Despite understanding the pathology and identifying neurofibrillary tangles as a hallmark of the disease, the molecular mechanisms behind it still remain unclear. Understanding post-translational modifications (PTMs) and 14-3-3 protein role can be crucial in uncovering tauopathies progression. Our study was focused on the phosphorylation of recombinant full-length Tau by Glycogen synthase kinase-3 beta (GSK3β). We targeted phosphorylation, particularly at the C terminus and residues identified as AD phospho-biomarkers. Additionally, our study investigated the effect of 14-3-3ζ (highly abundant in the human brain) on the fibrillisation of Tau phosphorylated by GSK3β. Using our optimised fibrillisation conditions, we compared Tau fibril formation both in the presence and absence of 14-3-3ζ protein. Notably, 14-3-3ζ protein significantly inhibited fibril formation under these conditions. This conclusion was supported by both quantitative measurements using the Thioflavin T (ThT) assay and qualitative assessments through visualisation techniques, including negative-stain electron microscopy (NS-EM) and atomic force microscopy (AFM). Besides, chemical cross-linking and nuclear magnetic resonance spectroscopy (NMR) revealed direct interaction between 14-3-3ζ and GSK3β-phosphorylated Tau, proposing the molecular mechanism of inhibition. These findings suggest that 14-3-3ζ may exert a protective role in Alzheimer's Disease by modulating Tau aggregation.