Reductions in ApoE and GPx4 highlight the Alzheimer's disease lipid raft vulnerability.

Abstract

AD is associated with increases in lipid peroxidation and decreased antioxidant defense. Little is known about antioxidant defense of brain lipid rafts which are the site of APP processing. Oxidative damage to lipid rafts increases amyloid production. Lipid hydroperoxidases, glutathione peroxidase 4 (GPx4) and peroxiredoxin 6 (Prdx6) are potential detoxifying enzymes capable of reducing oxidized phospholipids and oxysterols within cellular membranes. We hypothesized that lipid hydroperoxidases would be reduced in ApoE4 carriers, which also have deficient cholesterol transport. To determine this, we investigated the status of the AD lipid raft by ApoE isoform in human frontal cortex. Lipid rafts were isolated (Invent Biotechnologies; LR-039) from postmortem AD (ApoE3,3, ApoE3,4, and ApoE4,4) and age-matched controls (ApoE3,3) and were analyzed by western blot and enzymatic assay. Lipid raft ApoE protein level of AD brains showed large decreases: 43% (Ctl vs AD3,3; p<0.01), 53% (Ctl vs AD3,4; p<0.001) and 70% (Ctl vs AD4,4; p<0.0001). Total cholesterol content of lipid rafts decreased 25% (Ctl vs AD; p<0.01). GPx4 protein of lipid rafts decreased 30% (Ctl vs AD3,3; p<0.01), 45% (Ctl vs AD3,4; p<0.0001) and 57% (Ctl vs AD4,4; p<0.001). AD brains from ApoE4,4 carriers had 36%(p<0.01) lower GPx4 localization than ApoE3,3. Prdx6 localization was not detected in the lipid rafts. Reductions in ApoE, total cholesterol, and GPx4 in the AD lipid raft suggests its vulnerability during AD. Furthermore, many of these decreases were ApoE isoform dependent, suggesting that antioxidant defense may differ by ApoE isoform.