CROSS-LINKING OF APOLIPOPROTEIN-E BY PRODUCTS OF LIPID-PEROXIDATION

Apolipoprotein E (APOE) genotype and advancing aging are interacting r isk factors in the expression of late-onset and sporadic Alzheimer's d isease (AD). We tested the hypothesis that 2 products of lipid peroxid ation, malondialdehyde (MDA) and 4-hydroxy-2-nonenal (HNE), covalently modify APOE and alter its metabolism. In vitro, both HNE and MDA cros slinked purified APOE3 and APOE4. HNE was a more potent crosslinker th an MDA, and purified APOE3 was more susceptible to crosslinking by HNE than was purified APOE4. In P19 neuroglial cultures, oxidative stress with lipid peroxidation led to increased intracellular accumulation o f anti-HNE and anti-APOE immunoreactive proteins of approximately 50 k Da. Intracellular accumulation of the 50 kDa APOE-immunoreactive prote in (APOE-50) was not prevented by cyclohexamide. suggesting formation by post-translational mechanisms. In CSF, a 50 kDa APOE-immunoreactive protein co-migrated with proteins most immunoreactive for HNE and MDA adducts, and containing (NaBH4)-H-3-reducible bonds. These proteins w ere in CSF from adult subjects (with or without dementia), and in AD p atients homozygous for APOE3 or APOE4 alleles. These data suggest that HNE covalently crosslinks APOE in P19 neuroglial cultures to form a 5 0 kDa protein, and that similar modifications of APOE appear to occur in vivo.