Cyclophilin A differentially activates monocytes and endothelial cells: Role of purity, activity, and endotoxin contamination in commercial preparations

Background Cyclophilin A (CyPA) is a cytoplasmic protein secreted under inflammatory conditions. Extracellular CyPA is detected in atherosclerotic plaques and has been observed to activate endothelial cells as well as monocytes. Methods and results Commercially available recombinant CyPA-induced expression of tissue factor (TF) and vascular cell adhesion molecule-1 (VCAM-1) in human aortic endothelial cells (HAEC). However, CyPA from commercial sources contained lipopolysaccharide at concentrations up to 18.9 ng/ml; moreover, it exhibited low purity as determined by protein spectrum analysis and low activity as assessed by peptidyl prolyl cis–trans isomerase (PPIase) assay. An in-house preparation of pure, active, and uncontaminated CyPA failed to induce endothelial TF or VCAM-1 expression; moreover, it was not chemotactic for HAEC. In contrast, such CyPA exhibited potent chemotactic activity on monocytic THP-1 cells, with a maximal effect on migration occurring at a concentration of 5.5 × 10−9 mol/l. Pretreatment of CyPA with cyclosporine A prevented its effect on THP-1 cell migration; similarly, PPIase-deficient mutant CyPA protein did not induce migration of these cells. In-house prepared CyPA induced the release of Il-6, but not TNF-α, from THP-1 cells. Conclusions Commercially available CyPA exhibits low purity and activity and may be contaminated by endotoxin. Pure, active, and uncontaminated CyPA does not induce endothelial TF or VCAM-1 expression; instead, it acts as a potent monocyte chemoattractant and induces monocyte Il-6 release, implying a role for extracellular CyPA in the pathogenesis of atherosclerosis via activation of monocytes rather than endothelial cells.