Background Asthma is a chronic airway disease, known to involve several inflammatory mediators. Little is known about how these mediators interact in order to produce or attenuate even basic features of the disease, like airway hyper-reactivity and remodelling. Endothelin-1 (ET-1) and IL-1β are two mediators suggested to play important roles in the induction of airway inflammation.
Objective To investigate the interactions between ET-1 and IL-1β, using a novel in vitro model of asthma, focusing on airway smooth muscle contractility.
Methods Isolated murine tracheal segments were cultured from 1 to 8 days in the absence and presence of IL-1β. The subsequent contractile responses to sarafotoxin 6c (S6c) (selective agonist for ETB receptor) and sarafotoxin 6b (S6b) (ETA and ETB receptor agonist) were recorded by a myographs system. In all experiments, ETB receptors were desensitized before the contractile response to S6b was recorded. Thus, the response to S6b is only mediated by ETA receptors in the present study. The mRNA expressions for ET-1 and endothelin (ET) receptors were quantified by real-time PCR.
Results Organ culture in the presence of IL-1β attenuated the maximal contraction induced by S6c, but not S6b. This reduction was concentration-dependent and was significant after 2, 4 and 8 days of culture. To investigate the mechanisms behind this, inhibitors for endothelin converting enzyme (ECE) phosphoramidon, c-JUN N-terminal kinase (JNK) SP600125, extracellular-signal-regulated kinase 1/2(ERK 1/2) PD98059 and p38 pathway SB203580 were used. Individually, SP600125 and PD98059, but not SB203580, could partly reverse the reduction induced by IL-1β. An additional effect was obtained when SP600125 and PD98059 were combined. The mRNA expressions for ET-1 and ETB receptor were up- and down-regulated, respectively, by IL-1β.
Conclusion Presence of IL-1β in the airways attenuate the contractile response mediated via ETB receptors, an effect dependent on ECE, JNK and ERK 1/2 pathways.