Differential oxidation of apolipoprotein E isoforms and interaction with phospholipids

Area of Science:

• Neuroscience
• Biochemistry
• Oxidative Stress

Background:

• Oxidized proteins accumulate in Alzheimer's disease (AD) brains.
• Apolipoprotein E (apo E), particularly the apo E4 isoform, is linked to AD and found in amyloid deposits.
• The role of apo E oxidation in AD pathogenesis is not fully understood.

Purpose of the Study:

• To investigate the differential susceptibility of apo E isoforms to oxidation.
• To determine the functional consequences of apo E oxidation on its interaction with lipids and proteolysis.
• To strengthen the link between apo E4, protein oxidation, and Alzheimer's disease.

Main Methods:

• Recombinant apo E isoforms (E2, E3, E4) were oxidized using the myeloperoxidase system.
• Oxidation levels were assessed via immunoblot and high-performance liquid chromatography (HPLC).
• Susceptibility to thrombin proteolysis and incorporation into phospholipid discs were measured.

Main Results:

• Differential oxidation of apo E isoforms was observed: apo E4 > apo E3 > apo E2.
• Oxidation reduced apo E's susceptibility to thrombin proteolysis.
• Oxidation decreased apo E's incorporation into phospholipid discs by approximately 50%.

Conclusions:

• Oxidation of apo E, especially apo E4 and E3, may contribute to impaired lipid recycling in the brain.
• These findings reinforce the association of the apo E4 allele with AD and highlight the role of protein oxidation in AD.
• Further in vivo studies are needed to elucidate the mechanisms of apo E oxidation and myeloperoxidase function in AD.