Long-term exposure to IL-1β enhances Toll-IL-1 receptor-mediated inflammatory signaling in murine airway hyperresponsiveness

Abstract

Toll-interleukin-1 (Toll-IL-1) receptor signaling may play a key role in the development of airway hyperreactivity (AHR) and chronic airway inflammatory diseases such as asthma. Previously, we have demonstrated that pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta), induce AHR. However, the underlying intracellular signaling mechanisms that lead to AHR remain elusive. In order to see if the Toll-IL-1 receptor-mediated inflammatory signal pathways are involved in the development of AHR, the present study was designed to use a real-time PCR array, a sensitive and powerful tool, consisting of 84 genes related to Toll-IL-1 receptor signal pathways. Murine tracheal segments were organ cultured for four days in the presence and absence of IL-1beta. The Toll-IL-1 receptor-mediated inflammatory signal gene profile was studied using the real-time PCR-based cDNA array. The key gene expressions that were altered were verified by immunohistochemistry using confocal microscopy. Tracheal ring segment contractile responsiveness to the inflammatory mediator bradykinin was monitored using a sensitive myograph system. The results showed that after exposed to IL-1beta for four days, the tracheal segments exhibited increased mRNA expression of 67 genes (out of the 84 genes in the array), although expression reached statistical significance for only 16 of these genes. There were 14 genes that showed only a tendency towards a decrease in mRNA expression following IL-1beta treatment. Immunohistochemistry confirmed that protein expression for CD14, RP105, MCP-1 and phosphorylated IkappaB-alpha were increased in both the airway epithelial and smooth muscle cells. In order to link the activation of Toll-IL-1 receptor-mediated inflammatory signal mechanisms to the AHR, the anti-inflammatory drug dexamethasone, was used. Dexamethasone not only completely abolished the IL-1beta-induced AHR to bradykinin, but also abrogated the increased mRNA expression for inflammatory mediators, IL-6, IFN-gamma and Cox-2. In conclusion, long-term exposure of murine airway to IL-1beta induces up- and down-regulation of mRNA expression for Toll-IL-1 receptor signal molecules, with a significant increase in the expression of 16 genes that contribute to the development of airway inflammation and AHR. Understanding cytokine-induced activation of the Toll-IL-1 receptor-mediated inflammatory signaling mechanisms may provide new options for the treatment of airway inflammation and AHR.