[Alzheimer disease and tau protein]

To elucidate involvement of tau protein in neurodegenerative processes in Alzheimer disease and related disorders, self-assembly process and degradative process of tau protein were examined. To understand the mechanisms of the aggregation, binding affinity of tau protein to 14-3-3 protein, which converts tau to a filamentous or aggregated form. was investigated employing a surface plasmon resonance assay. Phosphorylation of tau by protein kinase A increased affinity of tau to 14-3-3, whereas the phosphorylation attenuated formation of filaments or aggregates. FTDP-17 mutation increased affinity of unphosphorlated tau to 14-3-3, compared to wild typed unphosphorylated tau. However the phosphorylation increased its affinity further to the similar level of the affinity of phosphorylated wild typed tau. Similarly the phosphorylation also attenuated formation of filaments or aggreeagates from FTDP-17 mutated tau. To understand the mechanisms of the intracellular accumulation, possible involvement of proteases were studied. Among several proteases, puromycin-sensitive aminopeptidase (PSA) was found as a predominant regulator of degradation of tau protein. In addition FTDP-17 mutation increased phosphorylation of tau proten in cells, and attenuated intracellular degradation of tau protein. These results suggest that self-assembly and accumulation of tau protein are regulated by phosphorylation, and FTDP-17 mutation affects those complexed processes.