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A5963 - IgE Stimulates Airway Mesenchymal Cells by Two Independent Signaling Pathways: STAT3 and MicroRNA21-5p and PI3K-AKT-mTOR Signaling Pathway
Author Block: L. Fang1, M. Tamm2, D. Stolz3, M. Roth1; 1Pneumology / Biomedicine, University Hospital of Basel, Basel, Switzerland, 2Univ Hosp Basel, 4031 Basel, Switzerland, 3University hospital of basel, Clinic of Pneumology and Respiratory Cell Research, 4031 Basel, Switzerland.
RATIONALE: Airway remodeling is an irreversible pathology in allergic asthma, which is often linked to increased serum IgE level. Airway wall remodeling results from activated sub-epithelial mesenchymal cells, which express both high and low affinitive IgE receptors, FcεR-I and CD23. Interestingly, mesenchymal cells respond to non-antigen specific IgE in the absence of allergens. This study investigated by which molecular mechanisms IgE contributes to airway wall remodeling.
METHODS: Human airway mesenchymal cells were isolated and expanded from endoscopic bronchial tissue biopsies from asthma patients (n=15). IgE receptor expression by airway mesenchymal cells was determined by immunofluorescence microscopy and western blot. For signaling studies, the cells were exposed to non-antigen specific human IgE (1ug/ml) for up to 48 hours. The production of collagen-type I and fibronectin was evaluated by determined by cell based ELISA. Cellular mitochondria performance was determined by quantitative confocal microscopy as mitochondria mass, and by real-time PCR for two mitochondria regulating proteins PGC1α and PPARγ. The activation of STAT3 and PI3K-AKT-mTOR signaling pathways was confirmed by applying specific inhibitors. MicroRNA21-5p was determined by quantitative real-time PCR and its effects on signaling by overexpression of either microRNA21-5p mimics or inhibitors
RESULTS: The expression of FcεR-I by bronchial mesenchymal cells was high compared to that of CD23 and showed a donor specific variability. IgE activated both the STAT3 and PI3K-AKT-mTOR signaling pathways within 48hours, as demonstrated by increased phosphorylation of STAT3 and p70S6 kinase. IgE significantly increased the mitochondria content and activity shown by increased gene expressions, and production of collagen type I and fibronectin. IgE induced the phosphorylation of -STAT3 which promoted microR21-5p transcription. In parallel, PTEN, an inhibitor of AKT signaling, was significantly down-regulated. Selective mTOR pathway inhibitors (LY294002, S3I-201, rapamycin) blocked the IgE induced mesenchymal cell remodeling. Furthermore, when cells were treated with
microRNA21-5p mimics or inhibitors the expression of its target PTEN was accordingly modified.
CONCLUSIONS: IgE promoted airway mesenchymal cell activity through two independent signaling pathways, which merged at the level of mTOR signaling and subsequently up regulated mitochondrial activity and ECM production. This in vitro data describes a novel mechanism by which non-allergic IgE contributes to mesenchyme cell activity and airway remodeling. (356/400 words)