Differential induction of BLT receptor expression on human endothelial cells by lipopolysacharide, cytokines, and leukotriene B₄

Abstract

Leukotriene (LT) B4 is a powerful chemotactic and immune modulating agent that signals via two receptors denoted BLT1 and BLT2.Here we report that BLT1 and BLT2 are expressed at low levels in an apparently silent state in human umbilical vein endothelial cells (HUVEC). However, treatment with LPS leads to a >10 fold increase in the levels of BLT1 mRNA without any significant effects on BLT2 mRNA. In parallel, LPS also increases the amounts of BLT1 protein.Tumor necrosis factor-␣ (TNF-␣) increases the expression of BLT2 mRNA Ϸ6 times above basal levels with only a modest increase in BLT1 mRNA. Interleukin-1␤ causes variable and parallel increases of both BLT1 and BLT2 mRNA. The natural ligand LTB4 also increases BLT1, but not BLT2, mRNA and protein expression. Along with the induction of BLT1 and͞or BLT2, HUVEC acquire the capacity to respond to LTB4 with increased levels of intracellular calcium and these signals can be blocked by isotype selective BLT antagonists, CP-105696 and LY-255283. In addition, treatment of HUVEC with LTB4 causes increased release of both nitrite, presumably reflecting nitric oxide (NO), and monocyte chemoattractant protein-1. Our data indicate that expression of functional BLT receptors may occur at the surface of endothelial cells in response to LPS, cytokines, and ligand, which in turn may have functional consequences during the early vascular responses to inflammation. Moreover, the results point to BLT receptors as potential targets for pharmacological intervention in LT-dependent inflammatory diseases such as asthma, rheumatoid arthritis, and arteriosclerosis.inflammation ͉ arteriosclerosis ͉ rheumatoid arthritis ͉ asthma ͉ nitric oxide T he leukotrienes (LTs) are a family of lipid mediators that play important roles in a variety of allergic and inflammatory reactions (1, 2). These molecules are divided into two classes, the spasmogenic cysteinyl-LTs (cys-LT) and LTB 4 , which is a classical nM chemotactic agent produced by neutrophils, macrophages, and mast cells. Thus, LTB 4 is a potent chemoattractant for polymorphonuclear leukocytes, comparable to complement peptide C5a and fMet-Leu-Phe (3, 4). Recent data also indicate that LTB 4 is a strong chemoattractant for T cells, creating a functional link between early innate and late adaptive immune responses (5-7). Because of these biological effects, LTB 4 is regarded as an important chemical mediator in a variety of acute and chronic inflammatory diseases and only recently, genetic and biochemical evidence strongly implicate LTB 4 as a mediator of vascular inflammation and arteriosclerosis (8-10). LTB 4 , is synthesized from arachidonic acid via the concerted action of 5-lipoxygenase, assisted by 5-lipoxygenase-activating protein and the terminal LTA 4 hydrolase (11), usually in a single cell or via transcellular routes; this mechanism has been shown to occur in vivo (12,13). LTB 4 signals primarily via a specific, high-affinity, G proteincoupled seven-transmembrane receptor, termed BLT 1 (14). The BLT 1 gene is located on the huma...

Leukotriene B4 Induces Release of Antimicrobial Peptides in Lungs of Virally Infected Mice

“…In this case, LTB 4 would seem to act directly on epithelial, endothelial, or fibroblastic cells leading to secretion of such peptides. The fact that BLT1 mRNA is detectable in lung tissue of mice (43) and that human bronchial fibroblast cells (53), endothelial cells (44), and cells of the alveolar wall (54) express BLT1 at their surface further reinforce this assumption.…”

“…A slight up-regulation in ␤-defensin-3 was also observed in mice that were treated with LTB 4 without viral infection (data not shown). However, when wild-type mice were infected with influenza followed by treatment with LTB 4 , a strong up-regulation in ␤-defensin-3 was observed, mostly in epithelial cells of the airways which correlates with the fact that BLTR is detectable in lungs of mice (43,44). Similarly, up-regulated expression of ␤-defensin-3 was also accompanied by a reduction in viral loads in lungs of infected mice treated with LTB 4 .…”

BLT2 is expressed in PanINs, IPMNs, pancreatic cancer and stimulates tumour cell proliferation

“…BLT2 mRNA expression was demonstrated in murine and human mast cells responsible for recruitment and accumulation of mast cells in areas of inflammation (Lundeen et al, 2006). Another study described a TNFadependent expression of BLT2 in human umbilical vein endothelial cells which may be important during early vascular responses to inflammation (Qiu et al, 2006). In addition, greatly increased BLT2 mRNA levels were found in a variety of human cancers by in situ hybridisation (Yoo et al, 2004).…”

“…In addition, it has been suggested that BLT2 is responsible for LTB 4 -induced generation of reactive oxygen species (ROS) through Rac/ERK and that this receptor is involved in cytokineinduced differentiation and expansion of haematopoietic stem cells (Woo et al, 2002;Chung et al, 2005). Stem cell factor and TNF-a are suggested to regulate BLT2 expression (Lundeen et al, 2006;Qiu et al, 2006).…”

Role of leukotriene B4 receptors in rheumatoid arthritis

“…LTB 4 acting through its receptors (BLT1) can cause chemotaxis, degranulation, adhesion and enhance the survival of neutrophils. Although BLT1 was long known to be a neutrophil chemoattractant receptor, recent studies identified BLT1 expression on macrophages [22], smooth muscle cells [23], endothelial cells [24], activated T-cells [25] and mast cells [26] considerably expanding the potential role of LTB 4 . Recent experiments from our laboratory demonstrated functional expression of BLT1 on both mature and immature dendritic cells and having a direct effect in the control of adaptive immune responses [27].…”