Blockade of Airway Inflammation and Hyperresponsiveness by Inhibition of BLT2, a Low-Affinity Leukotriene B₄Receptor

Abstract

BLT2 is a low-affinity receptor for leukotriene B(4) (LTB(4)), a potent lipid mediator of inflammation generated from arachidonic acid via the 5-lipoxygenase pathway. Unlike BLT1, a high-affinity receptor for LTB(4), no clear physiological function has yet been identified for BLT2, especially with regard to the pathogenesis of asthma. The aim of this study was to investigate whether BLT2 plays a role in the pathogenesis of asthma. A murine model of allergic asthma was used to evaluate the role of BLT2 in ovalbumin-induced airway inflammation and airway hyperresponsiveness. The levels of BLT2 mRNA and its ligand, LTB(4), in the lung airway were highly elevated after ovalbumin challenge, and down-regulation of BLT2 with antisense BLT2 oligonucleotides markedly attenuated airway inflammation and airway hyperresponsiveness. Further analysis, aimed at identifying mediators downstream of BLT2, revealed that BLT2 activation led to elevation of reactive oxygen species and subsequent activation of NF-kappaB, thus inducing the expression of vascular cell adhesion molecule-1, which is known to be involved in eosinophil infiltration into the lung airway. Together, our results suggest that BLT2 plays a pivotal, mediatory role in the pathogenesis of asthma, acting through a "reactive oxygen species-NF-kappaB"-linked inflammatory signaling pathway.

MyD88–BLT2-dependent cascade contributes to LPS-induced interleukin-6 production in mouse macrophage

“…The primer for BLT2 was described previously. 11,12 The specificity of all primers was confirmed by sequencing of the PCR products. Real-time PCR analysis was performed with the use of LightCycler 480 SYBR Green I Master (Roche Diagnostics, Mannheim, Germany).…”

BLT2 Is Upregulated in Allergen-Stimulated Mast Cells and Mediates the Synthesis of Th2 Cytokines

“…The primers used were 59-AATGCCCAGGATCGAGGT-39 (forward) and 59-GATGGAAGCAAAGGGAGTGA-39 (reverse) for Nox1; 59-CTGTAGGGCTTCCAAGGTGCTTCG-39 (forward) and 59-CCATTTGC-ATGATGCTCTTTAGGC-39 (reverse) for IL-4; and 59-ATCTACAGGAC-CCAGAGGATATTG-39 (forward) and 59-CTGATGTGAGAAAGGAAA-ATGAGT-39 (reverse) for IL-13. The primers for BLT1 and BLT2 have been previously described (24). The specificity of all the primers was confirmed by sequencing the PCR products.…”

“…To test whether BLT2 plays any role in Ag stimulation-induced Th2 cytokine synthesis, we analyzed the effect of BLT2 blockade on Th2 cytokine levels using a BLT2-specific antagonist, LY255283 (24), and siRNA BLT2 knockdown. Treatment of BMMCs with LY255283 resulted in a dramatic attenuation of Ag-induced upregulation of Th2 cytokine transcripts ( Fig.…”

“…Recently, we reported that BLT2 plays a pivotal mediatory role in the pathogenesis of asthma (24). To determine whether BLT2 plays a role in Th2 cytokine production in vivo, we tested the OVA-induced asthma mouse model.…”

“…A previous study from our laboratory has shown that BLT2 plays a critical role in the pathogenesis of asthma, especially with regard to airway inflammation and airway hyperresponsiveness (AHR) (24). However, the role of BLT2 in mast cells in asthmatic pathogenesis has not been elucidated.…”