Specific siRNA targeting RORγt inhibits airway inflammation and airway hyperresponsiveness in a mouse model of neutrophilic asthma
Introduction: Epidemiological studies suggest T helper 17 (Th17) cells as important players in the progression of asthma towards a severe phenotype. Regulated by the transcription factor Retinoic acid-related Orphan Receptor gamma (RORγ) t, which is essential for the effector functions and the differentiation and of these cells, Th17 cells appear to act as general promoters of chronic inflammatory responses.
Objective: To evaluate whether the Th17-specific transcription factor RORγt could be a suitable target for a therapeutic intervention of neutrophilic asthma.
Methods: C57BL/6 (WT) and RORγt deficient (RORγt -/-) mice were sensitized to ovalbumin (OVA) by intratracheal instillation of OVA together with LPS and subsequently challenged with an OVA aerosol. In-vitro generated Th17 cells were transfected with several small interfering RNA (siRNA) candidates targeting RORγt. Afterwards, the most active siRNA was selected for testing the in-vivo effects of RORγt downregulation.
Results: RORγt-deficient mice showed reduced lung neutrophilia compared to WT mice in a mouse model of neutrophilic asthma. SiRNA-transfected Th17 cells revealed not only reduced expression of RORγt but also of proinflammatory cytokines such as IL-17A. Intratracheal application of the RORγt-specific siRNA, which was most active in the in vitro setting, prevented airway inflammation characterized by a significantly reduced number of neutrophils, of lymphocytes and decreased bronchoalveolar lavage levels of IL-17A, TNF-α and KC. Moreover, application of the RORγt-specific siRNA inhibited the development of airway hyperresponsiveness (AHR) to methacholine.
Conclusion: Our data indicate that knockdown of RORγt by gene silencing improved airway inflammation in a mouse model of experimental asthma and may have therapeutic potential for the treatment of neutrophilic asthma.