In vivo and in vitro evidence for the role of elastase shedding of CD163 in human atherothrombosis

Abstract

Aims: CD163 is a macrophage receptor for haptoglogin/hemoglobin (Hp-Hb) complexes, responsible for the clearance of hemoglobin. We hypothesized that production of soluble CD163 may be due to proleolytic shedding of membrane CD163 by neutrophil elastase, reported to be increased in culprit atherosclerotic plaques. We analyzed the relationship between CD163 solubilization and elastase in vitro, in macrophage culture, ex vivo in human atherosclerotic plaque samples, and in vivo plasma of patients with coronary artery disease. Methods and Results: Neutrophil elastase was shown to enhance CD163 shedding and decreased the uptake of hemoglobin-haptoblobin (Hb-Hp) complexes by cultured macrophages. In addition, cultured carotid endarterectomy samples showing features of intra-plaque hemorrhage released more sCD163 and elastase/α1-antitrypsin (α1-AT) complexes than non-hemorrhagic plaques (n=44). Plasma levels of sCD163 and neutrophil elastase (complexed with α1-AT) were measured in patients with an acute coronary syndrome (ACS, n=42), stable angina pectoris (SAP, n=28), or normal coronary angiograms without subclinical atherosclerosis (n=21). ACS patients had higher sCD163 and elastase/α1-AT complexes plasma concentrations than subjects without coronary atherosclerosis. Circulating sCD163 and elastase/α1-AT complexes were positively correlated in patients with ACS (r=0.51, p<0.001) and SAP (r=0.62, p<0.001). Conclusion: Our results suggest that neutrophil elastase promotes CD163 shedding, resulting in a decreased clearance of Hb by macrophages, which may favor plaque destabilization. This may be reflected by increased plasma levels of sCD163 and elastase/α1-AT complexes which are positively correlated in patients with coronary artery disease.