Leukotriene B ₄ signaling through NF-κB-dependent BLT ₁ receptors on vascular smooth muscle cells in atherosclerosis and intimal hyperplasia

Abstract

Leukotriene B4 (LTB4), a potent leukocyte chemoattractant derived from the 5-lipoxygenase metabolism of arachidonic acid, exerts its action by means of specific cell surface receptors, denoted BLT1 and BLT2. In this study, BLT1 receptor proteins were detected in human carotid artery atherosclerotic plaques, colocalizing with markers for macrophages, endothelial cells, and vascular smooth muscle cells (SMC). Challenge of human coronary artery SMC with either LTB 4 or U75302, a partial agonist that is selective for the BLT1 receptor, induced an Ϸ4-fold increase of whole-cell currents by using the patch-clamp technique, indicating that these cells express functional BLT1 receptors. LTB4 induced migration and proliferation of SMC in vitro, and treatment with the BLT receptor antagonist BIIL 284 (10 mg͞kg, once daily) for 14 days after carotid artery balloon injury in vivo inhibited intimal hyperplasia in rats. In the latter model, SMC derived from the intima exhibited increased levels of BLT 1 receptor mRNA compared with medial SMC. BLT receptor up-regulation in the intima in vivo, as well as that induced by IL-1␤ in vitro, were prevented by transfection with a dominantnegative form of I kinase ␤ carried by adenovirus, indicating that BLT1 receptor expression depends on NF-〉. These results show that LTB4 activates functional BLT1 receptors on vascular SMC, inducing chemotaxis and proliferation, and that BLT1 receptors were up-regulated through an I kinase ␤͞NF-B-dependent pathway. Inhibition of LTB4͞BLT1 signaling during the response to vascular injury reduced intimal hyperplasia, suggesting this pathway as a possible target for therapy.restenosis ͉ cell proliferation ͉ chemotaxis ͉ lipoxygenase ͉ eicosanoids L eukotrienes (LTs) are inflammatory mediators that are derived from the 5-lipoxygenase (5-LO) pathway of arachidonic acid metabolism (1). Leukotrienes exert their actions by means of membrane-bound G protein-coupled receptors; CysLT receptors, which are activated by leukotrienes C 4 , D 4 , and E 4 ; and BLT receptors, which are activated by leukotriene B 4 (LTB 4 ) (2, 3). The last class consists of two receptor subtypes, BLT 1 and BLT 2 , representing the high-and low-affinity receptors for LTB 4 , respectively (4, 5). BLT receptors are expressed on leukocytes; neutrophils, eosinophils, and T lymphocytes all migrate in response to LTB 4 (6, 8-11).A major role for the leukotriene pathway in vascular disease was suggested by studies of a congenic mouse strain demonstrating resistance to atherosclerosis linked to a locus on chromosome 6, within which the gene for 5-LO was mapped subsequently (12). Also, expression of the enzymes and receptors of the 5-LO pathway has been demonstrated in human atherosclerotic plaques (13), and genetic studies have revealed that polymorphism in the 5-LO promoter is associated with an increased carotid artery intima thickness (14) and that the gene encoding the 5-LO-activating protein (FLAP) is associated with an increased risk of stroke and myocardial infarction (15).Although the...

Leukotriene Signaling in Atherosclerosis and Ischemia

“…The important signaling through these receptors has been supported by findings in ApoE −/− mice with a targeted BLT 1 receptor, which have fewer SMCs in their lesions [38]. Furthermore, BLT receptor antagonism reduces intimal hyperplasia after vascular injury in rats [5,40]. Taken together, the LTinduced stimulation of SMCs suggests their involvement in the intimal hyperplasia associated both with early atherosclerosis and in-stent restenosis after coronary interventions [5].…”

“…1) inhibits intimal hyperplasia after vascular injury in different animal models [5,39]. Recently, it was discovered that SMCs within human atherosclerotic lesions also express receptors for LTB 4 [38,40], mediating proliferation and migration of coronary artery SMCs [40]. The important signaling through these receptors has been supported by findings in ApoE −/− mice with a targeted BLT 1 receptor, which have fewer SMCs in their lesions [38].…”

“…Although healthy human arteries may not express receptors for LTB 4 , an endothelial BLT 1 receptor expression is induced in atherosclerotic lesions [40]. Findings in animal models have in addition suggested that LTB 4 -signaling through the BLT 1 receptor may also be associated with an endotheliumdependent release of vasoactive factors [49,50].…”

Platelets stimulate airway smooth muscle cell proliferation through mechanisms involving 5-lipoxygenase and reactive oxygen species

“…Many studies in vitro have shown that arachidonic acid metabolites influence on cell proliferation although the effects are cell-type specific [14][15][16][17]35]. Cysteinyl leukotrienes, products of the 5-LOX pathway, have been implicated in various stages of airway inflammation, in the present study, we found that inhibition of PLA 2 and 5-LOX significantly reduced the ASMC proliferation caused by platelets.…”

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].…”