MAPT and Alzheimer disease: Moreover, Aβ promotes tau cleavage at D421 via caspase-3 and -7, representing an early pathological event in AD, with Δtau-421 facilitating the assembly of tau filaments in vitro, and these filaments in AD brains show immunoreactivity to NFTs (Gamblin et al., 2003; Rissman et al., 2004).