**2. Tau in tauopathies**

The main roles of tau protein are stimulating microtubule assembly and maintaining microtubule stability; these are regulated by its phosphorylation level. The preeminent activity of tau is maintained by its regular phosphorylation level, that is, 2–3 mol phosphate/mol of the protein [28]. The unusual functions of tau protein might be defined by this phosphorylation as well. Tau hyperphosphorylation reduces the microtubule binding and microtubule assemblyforming activity of tau [29, 30]. In case of in vitro experiments, cleaved tau has a high tendency to unfasten from microtubules and subsequently, to aggregate [31].
