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-α (TNF-α) increases the expression of BLT₂ mRNA ≈6 times above basal levels with only a modest increase in BLT₁ mRNA. Interleukin-1β 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 and/or 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.