A near null variant of 12/15-LOX encoded by a novel SNP in ALOX15 and the risk of coronary artery disease
Introduction
The 12/15-lipoxygenases (12/15-LOXs) are members of a diverse family of lipid peroxidizing enzymes, which catalyze the stereospecific oxygenation of polyunsaturated fatty acids even if these substrates are incorporated in biomembranes or lipoproteins [1], [2]. The human 12/15-LOX is encoded for by a single gene, ALOX15, localized in the LOX gene cluster on chromosome 17 and oxygenates arachidonic acid to 15-S-hydroperoxyeicosatetraenoic acid (15-HpETE) [3]. Although 12/15-LOXs have been previously implicated in the pathogenesis of atherosclerosis, their precise role in this context remains controversial as both in vitro and in vivo experiments have yielded conflicting results. In vitro, 12/15-LOXs may facilitate the oxidation of LDL to a more atherogenic form [4]. In atherosclerotic lesions from rabbits, both the mRNA and the protein have been shown to co-localize with macrophage rich regions and epitopes of oxidized LDL. However, more recent gene expression studies of human atherosclerotic lesions at different stages suggest minimal expression of 12/15-LOX [5]. In vivo, both 12/15-LOX/apoE and the 12/15-LOX/LDL double knockout mice develop significantly less atherosclerosis than the single apoE and LDL knockouts, respectively [6]. Furthermore, over-expression of a human ALOX15 transgene in murine endothelium increased the formation of atherosclerotic lesions in LDL-receptor deficient mice [7]. In contrast, transgenic rabbits over-expressing the human 12/15-LOX in monocyte/macrophages or systemically are protected from development of atherosclerosis [8], [9], [10].
To better define the role of 12/15-LOX in human atherosclerosis, we sought to test the hypothesis that common polymorphisms in the human 12/15-LOX gene (ALOX15) alter the risk of symptomatic CAD.
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Study design
The ADVANCE study (atherosclerotic disease, vascular function, and genetic epidemiology) was approved by the Institutional Review Board at both Stanford University and Kaiser Permanente of Northern California (KPNC).
Between October 28, 2001 and December 31, 2003, we recruited a total of 3179 subjects into five cohorts: a cohort of subjects with clinically significant CAD at a young age (≤45 years for males, ≤55 years for females), a cohort of subjects with incident stable angina at an older
Non-genetic characteristics of the ADVANCE study sample
The ADVANCE study sample consisted of 3546 subjects, whose clinical and other non-genetic characteristics are summarized in Table 1. The older age of controls in the set of older onset cases and controls was a consequence of our stratified sampling design. Stratified sampling and/or preferential participation also led to differences in the prevalence of certain race/ethnic groups by case/control status and to the low prevalence of young cases that were male.
Resequencing and genotyping
We identified 27 polymorphisms by
Discussion
We investigated the effect of specific targeted genetic variation in ALOX15 on the risk of CAD. We found no association between a previously identified SNP in the promoter region and clinical CAD. We also identified a novel SNP in exon 13, ALOX15.18, which produces a near null variant of 12/15-LOX (T560M). In the race/ethnic groups we studied, the minor allele of ALOX15.18 was most common in Hispanics followed by white/Europeans. The minor allele was exceedingly rare in black/African Americans
Disclosures
None.
Acknowledgements
The authors thank the staff and participants of the ADVANCE and ARIC studies for their important contributions.
Sources of funding: The ADVANCE study was supported by a grant from the Donald W. Reynolds Foundation, Las Vegas, NV and the Stanford Cardiovascular Institute, Stanford, CA. The CARDIA study is supported by contracts N01-HC-48047, N01-HC-48048, N01-HC-48049, N01-HC-48050, and N01-HC-95095 from the National Heart, Lung, and Blood Institute. The Atherosclerosis Risk in Communities study
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