APOE and tauopathy: Elevated levels of cholesterol observed in neural cells of APOE ε4 carriers (Heeren et al., 2004; Chen et al., 2014; Mahley, 2016b; Lin et al., 2018), in tandem with increased tauopathy due to defects in cholesterol metabolism (Distl et al., 2001; Rahman et al., 2005), suggest heightened cholesterol levels may promote tau propagation.