Interleukin-1 receptor antagonist expression in human endothelial cells and atherosclerosis

The proinflammatory cytokine interleukin (IL)-1 is expressed mainly within the endothelium of atherosclerotic plaques and may be Linked with inflammatory mechanisms of atherogenesis. IL-l action is complex and regulated in part by its naturally occurring inhibitor, the IL-1 receptor antagonist (IL-1ra). Therefore, we studied differential and specific isoform expression of IL-1ra in the endothelium of diseased coronary arteries and in endothelial cells (ECs) stimulated under defined conditions. In view of an association with IL-1ra gene (IL-1RN) polymorphism, the influence of endothelial cell genotype at IL-1RN on IL-1ra protein production was also examined. Secreted IL-1ra and intracellular IL-1ra mRNAs were detected by semiquantitative reverse transcription-polymerase chain reaction in human atherosclerotic and dilated cardiomyopathic coronary arteries; protein expression appeared increased in atherosclerotic compared with dilated cardiomyopathic arteries, where IL-1ra appeared to be confined to the endothelium. Only intracellular IL-1ra,type I mRNA was detected in human umbilical vein ECs (HUVECs) and human coronary artery ECs (HCAECs) when they were stimulated with bacterial lipopolysaccharide/phorbol myristate acetate and transforming growth factor-beta. IL-1 beta and IL-1 alpha were without effect. IL-1ra protein was detected in HUVECs (intracellular IL-1ra), HCAECs (intracellular IL-1ra), and human coronary artery smooth muscle cells (intracellular IL-1ra) by immunoprecipitation,and Western blot. IL Ira was detected in HUVEC cell lysates by ELISA and appeared to be influenced by the genotype of the IL-1RN variable number tandem repeat, an 86-bp repeat polymorphism in intron 2 of the IL-1ra gene, with lower levels of IL Ira produced by IL-1RN allele 2-containing cells (ratio of IL-1ra to total protein: for 1,1 homozygotes, 1.38 +/- 0.28 x 10(-9) [n = 15]; for 1,2 heterozygotes, 0.81 +/- 0.17 x 10(-9) [n = 8]; and for 2,2 homozygotes, 0.6 +/- 0.19 x 10(-9) [n = 5]; P < 0.05 compared with 1,1 homozygotes). This is the first demonstration of IL-1ra in human diseased arteries, stimulated HUVECs, and HCAECs and indicates the endothelial cell as an important source. Endothelial IL-1ra production may be controlled by the endothelial IL-1RN genotype, These data further support the role of the IL-1 system of cytokines in the pathogenesis of atherosclerosis.