Oxidized Cholesterol Metabolites Found in Human Atherosclerotic Lesions Promote Apolipoprotein C-II Amyloid Fibril Formation

• Published in: Biochemistry (Easton) Vol. 46; no. 18; pp. 5552 - 5561
• Main Authors: Stewart, Cameron R, Wilson, Leanne M, Zhang, Qinghai, Pham, Chi L. L, Waddington, Lynne J, Staples, Maree K, Stapleton, David, Kelly, Jeffery W, Howlett, Geoffrey J
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 08-05-2007
• Subjects: Amino Acid Sequence; Amyloid - biosynthesis; Amyloid - ultrastructure; Apolipoprotein C-II - chemistry; Apolipoprotein C-II - metabolism; Apolipoprotein C-II - ultrastructure; Atherosclerosis - metabolism; Atherosclerosis - pathology; Cholesterol - chemistry; Cholesterol - metabolism; Circular Dichroism; Humans; Lipid Peroxidation; Lipoproteins, LDL - chemistry; Lipoproteins, LDL - metabolism; Molecular Sequence Data; Ozone - metabolism; Protein Conformation
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi602554z

Apolipoprotein amyloid deposits and lipid oxidation products are colocalized in human atherosclerotic tissue. In this study we show that the primary ozonolysis product of cholesterol, 3β-hydroxy-5-oxo-5,6-secocholestan-6-al (KA), rapidly promotes human apolipoprotein (apo) C-II amyloid fibril formation in vitro. Previous studies show that hydrophobic aldehydes, including KA, modify proteins by the formation of a Schiff base with the lysine ε-amino group or N-terminal amino group. High-performance liquid chromatography, mass spectrometry, and proteolysis of KA-modified apoC-II revealed that KA randomly modified six different lysine residues, with primarily one KA attached per apoC-II molecule. Competition experiments showed that an aldehyde scavenging compound partially inhibited the ability of KA to hasten apoC-II fibril formation. Conversely, the acid derivative of KA, lacking the ability to form a Schiff base, accelerated apoC-II fibril formation, albeit to a lesser extent, suggesting that amyloidogenesis triggered by KA involves both covalent and noncovalent mechanisms. The viability of a noncovalent mechanism mediated by KA has been observed previously with α-synuclein aggregation, implicated in Parkinson's disease. Electron microscopy demonstrated that fibrils formed in the presence of KA had a similar morphology to native fibrils; however, the isolated KA−apoC-II covalent adducts in the absence of unmodified apoC-II formed fibrillar structures with altered ropelike morphologies. KA-mediated fibril formation by apoC-II was inhibited by the addition of the amine-containing compound hydralazine and the lipid-binding protein apoA-I. These in vitro studies suggest that the oxidized small molecule pool could trigger or hasten the aggregation of apoC-II to form amyloid deposits.