MAPT and proteostasis deficiencies: Emerging clinical and experimental results support the hypothesis that pathological α-syn, Aβ, and tau are prion-like peptides/proteins that can induce the propagation of endogenous monomers, and cause proteinopathy spreading from cell-to-cell (Braak et al., 2003; Kordower et al., 2008; Li et al., 2008; Luk et al., 2012; Guo et al., 2016; Mao et al., 2016; Tyson et al., 2016; He et al., 2018; Kam et al., 2018; Kim et al., 2019).