APOE and Alzheimer disease: In addition to the role of APOE4 derived from astrocytes and microglia, a growing body of literature also supports a role for APOE4 and pericytes at the blood brain barrier in neurovascular unit dysfunction and AD pathogenesis (Casey et al., 2015; Soto et al., 2015; Halliday et al., 2016; Ma et al., 2018).