APOE and type 2 diabetes mellitus: To investigate whether ApoE4 influences cerebral GSK‐3β expression and the insulin signaling pathway in T2DM mice, we first assessed the levels of total GSK‐3β (tGSK‐3β) and phosphorylated GSK‐3β at Tyr216 (pGSK‐3β‐Tyr216, active form) in 6‐month‐old mice (Figure 5a,b).