IL-17A Induces Signal Transducers and Activators of Transcription-6-Independent Airway Mucous Cell Metaplasia

Mucous cell metaplasia is a hallmark of asthma, and may be mediated by signal transducers and activators of transcription (STAT)-6 signaling. IL-17A is increased in the bronchoalveolar lavage fluid of patients with severe asthma, and IL-17A also increases mucus production in airway epithelial cells. Asthma therapeutics are being developed that inhibit STAT6 signaling, but the role of IL-17A in inducing mucus production in the absence of STAT6 remains unknown. We hypothesized that IL-17A induces mucous cell metaplasia independent of STAT6, and we tested this hypothesis in two murine models in which increased IL-17A protein expression is evident. In the first model, ovalbumin (OVA)-specific D011.10 Th17 cells were adoptively transferred into wild-type (WT) or STAT6 knockout (KO) mice, and the mice were challenged with OVA or PBS. WT-OVA and STAT6 KO-OVA mice demonstrated increased airway IL-17A and IL-13 protein expression and mucous cell metaplasia, compared with WT-PBS or STAT6 KO-PBS mice. In the second model, WT, STAT1 KO, STAT1/STAT6 double KO (DKO), or STAT1/STAT6/IL-17 receptor A (RA) triple KO(TKO) mice were challenged with respiratory syncytial virus (RSV) or mock viral preparation, and the mucous cells were assessed. STAT1 KO-RSV mice demonstrated increased airway mucous cell metaplasia compared with WT-RSV mice. STAT1 KO-RSV and STAT1/STAT6 DKO-RSV mice also demonstrated increased mucous cell metaplasia, compared with STAT1/STAT6/IL17RA TKO-RSV mice. We also treated primary murine tracheal epithelial cells (mTECs) from WT and STAT6 KO mice. STAT6 KO mTECs showed increased periodic acid-Schiff staining with IL-17A but not with IL-13. Thus, asthma therapies targeting STAT6 may increase IL-17A protein expression, without preventing IL-17A-induced mucus production.