Differential leukotriene receptor expression and calcium responses in endothelial cells and macrophages indicate 5-lipoxygenase-dependent circuits of inflammation and atherogenesis

Objective - Inflammatory infiltrates and atherosclerotic lesions emerge when monocytes adhere to endothelial cells (ECs), migrate into the subendothelial space, and become macrophages ( MPhis). Leukotrienes (LTs), products of 5-lipoxygenase, are powerful inflammatory mediators. 5-lipoxygenase(+) MPhis have been shown to increase during atherogenesis, and LT receptor (LT-R) transcripts were identified in diseased arteries. To investigate LT-Rs in cells involved in inflammation and atherogenesis, we used the in vitro models of human umbilical vein ECs (HUVECs) and monocyte-derived MPhis. Methods and Results - HUVECs primarily expressed transcripts of the cysteinyl (cys) LT2-R, which was strongly upregulated by interleukin-4. By contrast, MPhis predominantly expressed transcripts of the cysLT(1)-R. Calcium responses toward LTs revealed differential cysLT-R utilization by both cell types: HUVECs responded to both cysLTs, whereas MPhis preferentially responded to LTD4; HUVECs, but not MPhis, were resistant toward a cysLT(1)-R antagonist, montelukast; cysLTs generated regular calcium oscillations in HUVECs that lasted >60 minutes, resulting in >500 oscillations per cell. By contrast, calcium elevations in MPhis returned to baseline within seconds and were nonoscillatory. Conclusions - Our data raise the possibility that MPhi-derived LTs differentially activate cysLT(2)-Rs via paracrine stimulation and cysLT(1)-Rs via autocrine and paracrine stimulation during inflammation and atherogenesis.