Impact of hypoxia on immune cells in human atherosclerotic plaques

Abstract

Abstract Background Inflammation plays a major role in atherosclerotic plaques' progression and was shown to be associated with the formation of hypoxic areas within the plaques. However, the data about the impact of hypoxia on atherosclerosis are contradictory, in part due to inadequacy of in vitro and animal models to reproduce faithfully the complexity of human atherosclerotic plaques. Purpose The aim of this study was to investigate the effect of hypoxia on immune status in the ex vivo system of human atherosclerotic plaques. Methods We collected 25 atherosclerotic plaques from patients undergoing carotid endarterectomy, cut plaques into ring-shaped slices and cultured them for 24 hours at the liquid/air interface on collagen sponges under hypoxic (2% O2) and normoxic (12% O2) conditions. After 24 hours we evaluated T-cell activation status within plaques according to the presence of membrane activation markers by means of multiparametric flow cytometry and the activity of cytokine production using xMAP technology. Results We found that CD8 T cells from human atherosclerotic plaques cultured under hypoxic conditions compared to normoxic conditions have a decreased expression of CD69 activation marker (42.7 [34.3; 50.9]% vs 53.8 [33.3; 63.3]%, n=10, p=0.047) and lower level of CD69 and HLA-DR coexpression (16.0 [10.5; 22.3] vs 22.6 [11.3; 28.2], n=10, p=0.02). CD4 T cells did not show any significant changes in expression of activation markers under hypoxia. Hypoxic conditions also resulted in a reduced IL-10 production (104.2 [53.8; 170.9] vs 235.2 [158.5; 335.3] pg/100 mg of tissue, n=20, p=0.0001) and increased VEGF production (116.1 [79.8; 253.5] vs 89.9 [71.1; 148.8] pg/100 mg of tissue, n=20, p=0.033). Conclusions Our results indicate that hypoxia causes a decrease in the activity of cytotoxic T cells and increases stimuli for angiogenesis within the human atherosclerotic plaques. The established ex vivo model of human atherosclerotic plaques culture under hypoxia enables further studies of the hypoxia impact on atherosclerosis. Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): Russian Science Foundation grant