Asthma is a very frequent airway disease that affects 5 to 20% of the whole population worldwide. Whereas the mortality of asthma has been dramatically decreased within the last 10 years, uncontrolled asthma still induces major consequences on morbidity, quality of life, and economic burden. Asthma control determinants have been associated to indoor allergens sensitization. The most frequent indoor allergen is the house dust mites (HDM), which act in vivo on bronchial epithelial layer. Uncontrolled asthma has also been associated with bronchial remodeling and more specifically to the increased mass of bronchial smooth muscle (BSM). It is now well admitted that, BSM remodeling is related with an increase of asthmatic BSM cell proliferation both in vitro and in vivo. However, the relationship between HDM stimulation of the bronchial epithelial layer and BSM remodeling is unknown.

We have developed an in vitro culture model of epithelium in air liquid interface (ALI) and BSM interaction. We assessed BSM proliferation using BrdU incorporation. We explored the role of leukotrienes in such a proliferation. We assessed the expression of enzymes involved in the leukotrienes synthesis pathway using RT-PCR. Leukotrienes release was assessed by Elisa in vitro on epithelial cell supernatant and in vivo in mouse broncho-alveolar lavage fluid. Finally, leukotrienes receptor expression was assessed both in vitro by flow cytometry and ex vivo by laser microdissection and RT-PCR.

We found that epithelial stimulation by HDM increased the proliferation of asthmatic BSM cells and not that of non-asthmatics. The mechanisms involved an epithelial production of leukotrienes C4 and an over-expression of leukotrienes receptor CysLTR1 by asthmatic BSM cells both in vitro and in vivo.

This work demonstrates the role of HDM on BSM remodeling that occurs only in asthmatic patients and highlights different therapeutic targets at both epithelial and smooth muscle levels.