Toll‐like receptor stimulation induces airway hyper‐responsiveness to bradykinin, an effect mediated by JNK and NF‐κB signaling pathways

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Abstract
Airway infections induce hyper-responsiveness in asthmatic patients. Toll-like receptors (TLR) mediate inflammatory responses to microbes. Occurrence and effects of TLR2, TLR3 and TLR4 were examined in a mouse organ culture model of asthma focusing on the smooth muscle responses to bradykinin. TLR2, TLR3 and TLR4 mRNA, and TLR2 and TLR4 immunoreactivity were detected in the tracheal muscle layer. Tracheal organ culture for 1 or 4 days with lipopolysaccharide (LPS; TLR2/4 agonist) or polyinosinic polycytidylic acid (poly-I-C; TLR3 agonist) enhanced bradykinin- and [des-Arg9]-bradykinin-induced contractions. Simultaneous LPS and poly-I-C treatment resulted in synergistic enhancement of bradykinin-induced contraction. In carbachol-pre-contracted segments TLR stimulationinduced less potent relaxations to bradykinin and [des-Arg9]-bradykinin. The LPS and poly-I-C enhancement of bradykinin-induced contraction was inhibited by the transcriptional inhibitor actinomycin-D, dexamethasone, the proteasome inhibitor MG-132 and the c-Jun N-terminal kinase (JNK) inhibitor SP600125. LPS and poly-I-C induced translocation of NF-κB p65 to the nucleus and up-regulation of kinin B1 and B2 receptor mRNA. In summary, TLR2, TLR3 and TLR4 are expressed in the mouse tracheal smooth muscle. Costimulation of these receptors results in NF-κB- and JNK-mediated transcription of B1 and B2 receptor, inducing hyper-responsiveness to bradykinin.