Targeting of Rac1 prevents bronchoconstriction and airway hyperresponsiveness

Publication date: Available online 16 November 2017
Source:Journal of Allergy and Clinical Immunology
Author(s): Gwennan André-Grégoire, Florian Dilasser, Julie Chesné, Faouzi Braza, Antoine Magnan, Gervaise Loirand, Vincent Sauzeau
BackgroundThe molecular mechanisms responsible for airway smooth muscle cells (aSMC) contraction and proliferation in airway hyperresponsiveness (AHR) associated with asthma are still largely unknown. The small GTPases of the Rho family (RhoA, Rac1 and Cdc42) play a central role in SMC functions including migration, proliferation and contraction.ObjectiveThe objective of this study is to identify the role of Rac1 in aSMC contraction and to investigate its involvement in AHR associated with allergic asthma.MethodsTo define the role of Rac1 in aSMC, ex- and in vitro analyses of bronchial reactivity were performed on bronchi from smooth muscle (SM)-specific Rac1 knockout mice (SM-Rac1-KO) and human individuals. In addition, this murine model was exposed to allergens (ovalbumin or house dust mite extract) to decipher in vivo the implication of Rac1 in AHR.ResultsThe specific SMC deletion or pharmacological inhibition of Rac1 in mice prevented the bronchoconstrictor response to methacholine. In human bronchi a similar role of Rac1 was observed during bronchoconstriction. We further demonstrated that Rac1 activation is responsible for bronchoconstrictor-induced increase in intracellular Ca²⁺ concentration and contraction both in murine and human bronchial aSMC, through its association with phospholipase C β2 and the stimulation of inositol 1,4,5-trisphosphate production. In vivo, Rac1 deletion in SMC or pharmacological Rac1 inhibition by nebulization of NSC23766 prevented AHR in murine models of allergic asthma. Moreover, nebulization of NSC23766 decreased eosinophil and neutrophil populations in bronchoalveolar lavages from asthmatic mice.ConclusionOur data reveal an unexpected and essential role of Rac1 in the regulation of intracellular Ca²⁺ and contraction of aSMC, and the development of AHR. Rac1 thus appears as an attractive therapeutic target in asthma, with a combined beneficial action on both bronchoconstriction and pulmonary inflammation.

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