Oxidized cholesterol metabolites found in human atherosclerotic lesions promote apolipoprotein C-II amyloid fibril formation.
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, 3beta-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 epsilon-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 alpha-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.
Stewart
Cameron R
CR
Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville, Victoria 3010, Australia.
Wilson
Leanne M
LM
Zhang
Qinghai
Q
Pham
Chi L L
CL
Waddington
Lynne J
LJ
Staples
Maree K
MK
Stapleton
David
D
Kelly
Jeffery W
JW
Howlett
Geoffrey J
GJ
D000595:Amino Acid Sequence; D000682:Amyloid / Q000096:biosynthesis* / Q000648:ultrastructure; D053304:Apolipoprotein C-II / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D050197:Atherosclerosis / Q000378:metabolism* / Q000473:pathology; D002784:Cholesterol / Q000737:chemistry* / Q000378:metabolism; D002942:Circular Dichroism; D006801:Humans; D015227:Lipid Peroxidation; D008077:Lipoproteins, LDL / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D010126:Ozone / Q000378:metabolism; D011487:Protein Conformation
D000682:Amyloid; D053304:Apolipoprotein C-II; D008077:Lipoproteins, LDL; C099252:oxidized low density lipoprotein; D010126:Ozone; D002784:Cholesterol