Cytokine induced airway hyperreactivity characterized in an in-vitro model of asthma

Abstract: Asthma is a chronic disorder of the lower airways, characterized by inflammation and hyperreactivity. Pro-inflammatory cytokines like tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) are known to play important roles in the pathogenesis, but our knowledge how these cytokines contribute to the development of airway hyperreactivity is limited. The aims of the present study were to investigate relationships between TNF-alpha and IL-1beta, and airway smooth muscle contractility, focusing on the mechanism behind the development of airway hyperreactivity. To that end an in-vitro model for assessment of long-term effects of inflammatory mediators on the airway smooth muscle was developed. The model was based on the organ culture of murine tracheal segments in combination with subsequent evaluation in a myograph system, along with mRNA quantification and histology. Tissues were shown to maintain their contractile phenotype and morphological organization during a culture period up to 16 days. Presence of TNF-alpha and IL-1beta, during 1, 2, 4 or 8 days of culture, increased the contractile response induced by 5-hydroxytryptamine (5-HT), des-Arg9-bradykinin and bradykinin in a time- and concentration-dependent manner, whereas the contractile response to sarafotoxin 6c (S6c) was decreased by the long-term presence of IL-1beta. Pharmacological analysis revealed that contractions induced by 5-HT, des-Arg9-bradykinin and bradykinin were mediated by 5HT2A, and bradykinin B1 and B2 receptors, respectively. Real-time PCR showed that TNF-alpha and IL-1beta induced an up-regulation of the bradykinin B1 and B2 receptors. In addition, IL-1beta caused a down-regulation of the endothelin B receptor (ETB). Experiments with actinomycin D, a general transcriptional inhibitor and dexamethasone, a NF-kappaB / AP-1 inhibitor, along with analysis of the receptor mRNA expression revealed that the up-regulation of bradykinin B1 and B2 receptors was dependent on intact transcriptional mechanisms, whereas the increased 5-HT2A contraction appeared unaffected by transcriptional interference. 5-HT2A receptor-mediated contractions induced by IL-1beta involved the JNK and p38 mitogen-activated protein kinase (MAPK) pathways. Experiments with the JNK inhibitor SP600125, the ERK 1/2 inhibitor PD98059 and the p38 inhibitor SB203580 suggested that JNK was a key molecule of vital importance for both TNF-alpha and IL-1beta induced bradykinin B1 and B2 receptor up-regulation, whereas both the ERK1/2 and JNK pathways were required for the IL-1beta induced down-regulation of the ETB receptors. Remicade(registered), an anti-TNF-alpha antibody, inhibited IL-1beta-induced increases of the airway contractions, via inhibition of TNF-alpha and subsequent synthesis of the new receptors. The present findings that pro-inflammatory cytokines, like TNF-alpha and IL-1beta, can induce airway hyperreactivity via interference with the intracellular MAPK signal transduction pathways might contribute to new concepts for the treatment of asthma.