Hypertensive mechanical stretch: A model for monocyte‐derived dendritic cell differentiation

Abstract

Hypertension is a leading cause of mortality in Western society, attributed in part to the oxidative injury and inflammation. Fatty acid oxidation leads to formation of highly reactive isoketals, which adduct to protein lysines and modify proteins. We have shown that dendritic cells (DCs) from hypertensive mice accumulate isoketal‐adducted proteins and act as neoantigens that promote T cell activation. The cellular source of the oxidant responsible for isoketal formation in DCs is not known. Others have shown that human monocytes traversing the endothelium differentiate into monocyte‐derived DCs. In addition, the endothelium is activated in angiotensin‐II induced hypertension to produce reactive oxygen species and to express adhesion molecules and chemokines that attract inflammatory cells. We hypothesized that human endothelial cells exposed to hypertensive mechanical stretch will promote conversion of human monocytes into functional DCs that can activate T cells. We exposed confluent human aortic endothelial cells (HAECs) to either normotensive cyclical stretch of 5% or hypertensive cyclical stretch of 10% using the Flexcell® Tension System for 48 hours. During these exposures to stretch, monocytes from normotensive human volunteers were added to the endothelial cell culture. Following 48 hours of stretch, the monocytes were isolated and mRNA was analyzed. We found that co‐culture with HAECs exposed to hypertensive mechanical stretch markedly increased monocyte mRNA expression of the Th17 polarizing cytokines IL‐6, I‐23A and IL‐1b. In addition, hypertensive stretch of endothelial cells stimulated mRNA expression of the monocyte chemokine CCL4 and the p22phox subunit of the NADPH oxidase. We also found that endothelial cells exposed to hypertensive stretch promoted monocyte differentiation to DCs, as evidenced by the surface expression of DC‐SIGN, CD83 and the co‐stimulatory marker CD86 compared to monocytes co‐cultured with endothelial cells exposed to 5% stretch. The monocyte derived DCs that formed in the presence of hypertensive stretch also contained isoketal‐adducted proteins compared to controls (69.73 ± 5.802 vs 10.79 ± 1.854 respectively, p = 0.0001) as evidenced by intracellular staining and flow cytometry. The effect of endothelial cell stretch on monocyte activation was in part mediated by cell to cell contact, as conditioned media from endothelial cells exposed to hypertensive stretch did not increase IL‐6 and IL‐1b, but did increase p22phox, IL‐23A and TGFb‐1. Monocytes exposed to hypertensive stretch promoted a 1,500‐fold increase in CD4+ T cell proliferation and a 1,300‐fold increase in CD8+ T cells proliferation as monitored by CFSE, compared to monocytes exposed to normotensive 5% stretch. These data show that endothelial cells exposed to hypertensive mechanical stretch promote monocyte differentiation to DCs that express inflammatory cytokines, accumulate isoketal‐adducted proteins and promote T cell proliferation. These findings suggest a new mechanism by which DCs can become activated in hypertension.Support or Funding InformationWilliam Townsend Porter Pre‐doctoral Fellowship from American Physiological Society