Abstract
Lipopolysaccharide (LPS), a Toll-like receptor (TLR) 4 agonist, causes airway hyperreactivity through nuclear factor-κB (NF-κB). Because NF-κB induces cyclooxygenase-2 (COX-2) to increase synthesis of prostaglandins (PGs), including the potent airway anti-inflammatory and smooth muscle relaxant PGE2, we investigated whether LPS causes short-term PGE2-dependent relaxation of mouse isolated trachea. In rings of trachea contracted submaximally with carbachol, LPS caused slowly developing, epithelium-dependent relaxations that reached a maximum within 60 min. Fluorescence immunohistochemistry revealed TLR4-like immunoreactivity localized predominantly to the epithelium. The LPS antagonist polymixin B; the nonselective COX inhibitor indomethacin; the selective COX-1 and COX-2 inhibitors 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole (SC560) and 4-[5-(4-chlorophenyl)-1-(trifluoromethyl)-1H-pyrazol-1-yl]-benzenesulfonamide (SC236), respectively; the transcription inhibitor actinomycin D; the translation inhibitor cycloheximide; the p38 mitogen-activated protein kinase (p38 MAPK) inhibitor 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imadazole (SB203580); and a combination of the mixed DP/EP1/EP2 receptor antagonist 6-isopropoxy-9-xanthone-2-carboxylic acid (AH6809) and the EP4 receptor antagonist 4′-[3-butyl-5-oxo-1-(2-trifluoromethyl-phenyl)-1-5-dihydro-[1,2,4]triazol-4-ylmethyl]-biphenyl-2-sulfonic acid (3-methyl-thiophene-2-carbonyl)-amide (L-161982) all abolished relaxation to LPS, giving instead slowly developing, small contractions over 60 min. The cytosolic phospholipase A2 (cPLA2) inhibitor 1,1,1-trifluoro-6Z,9Z, 12Z,15Z-heneicosateraen-2-one significantly (p < 0.05) inhibited the relaxation to LPS, whereas the NF-κB proteasomal inhibitor Z-Leu-Leu-Leu-aldehyde (MG-132) had no affect on the relaxation in the first 20 min, after which it reversed the response to a contraction. In conclusion, our data indicate that LPS activates airway epithelial TLR4 to cause release of PGE2 and subsequent EP2 and EP4 receptor-dependent smooth muscle relaxation. Activation of both COX-1 and COX-2 seems to be essential for this novel response to LPS, which also involves cPLA2, p38 MAPK, NF-κB, and an unidentified NF-κB-independent, labile regulatory protein.
Footnotes
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This work was supported by the National Health and Medical Research Council of Australia.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.105.097634.
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ABBREVIATIONS: LPS, lipopolysaccharide; TLR, Toll-like receptor; IL, interleukin; NF-κB, nuclear factor-κB; MAPK, mitogen-activated protein kinase; ERK, extracellular signal-regulated kinase; PG, prostaglandin(s); COX, cyclooxygenase; cPLA2, cytosolic phospholipase A2; Fmax, passive force-stabilized, maximal contractions; ACh, acetylcholine; AACOCF3, 1,1,1-trifluoro-6Z,9Z,12Z,15Z-heneicosateraen-2-one; L-161982, 4-′[3-butyl-5-oxo-1-(2-trifluoromethyl-phenyl)-1-5-dihydro-[1,2,4]triazol-4-ylmethyl]-biphenyl-2-sulfonic acid (3-methyl-thiophene-2-carbonyl)-amide; AH6809, 6-isopropoxy-9-xanthone-2-carboxylic acid; MG-132, Z-Leu-Leu-Leu-aldehyde; SB203580, 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imadazole; SC236, 4-[5-(4-chlorophenyl)-1-(trifluoromethyl)-1H-pyrazol-1-yl]-benzenesulfonamide; SC560, 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole; NK1R, neurokinin-1 receptor; PAR, protease-activated receptor; DMSO, dimethyl sulfoxide; SLIGRL, single-letter amino acid code for the PAR2-peptide agonist Ser-Leu-Isoleu-Gly-Arg-Leu-NH2; L732138, N-acetyl-l-tryptophan 3,5-bis(trifluoromethyl)benzyl ester.
- Received October 23, 2005.
- Accepted February 2, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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