ABSTRACT
Asthma is a chronic inflammatory disease in which airway epithelial cells are the first line of defense against exposure of the airway to infectious agents. Src homology protein (SHP)-1, a protein tyrosine phosphatase, is a negative regulator of signaling pathways that are critical to the development of asthma and host defense. We hypothesize that SHP-1 function is defective in asthma, contributing to the increased inflammatory response induced by Mycoplasma pneumoniae, a pathogen known to exacerbate asthma. M. pneumoniae significantly activated SHP-1 in airway epithelial cells collected from nonasthmatic subjects by bronchoscopy with airway brushing but not in cells from asthmatic subjects. In asthmatic airway epithelial cells, M. pneumoniae induced significant PI3K/Akt phosphorylation, NF-κB activation, and IL-8 production compared with nonasthmatic cells, which were reversed by SHP-1 overexpression. Conversely, SHP-1 knockdown significantly increased IL-8 production and PI3K/Akt and NF-κB activation in the setting of M. pneumoniae infection in nonasthmatic cells, but it did not exacerbate these three parameters already activated in asthmatic cells. Thus, SHP-1 plays a critical role in abrogating M. pneumoniae-induced IL-8 production in nonasthmatic airway epithelial cells through inhibition of PI3K/Akt and NF-κB activity, but it is defective in asthma, resulting in an enhanced inflammatory response to infection.
Subject(s)
Asthma/enzymology , Epithelial Cells/immunology , Mycoplasma pneumoniae/immunology , Protein Tyrosine Phosphatase, Non-Receptor Type 6/physiology , Adult , Asthma/immunology , Asthma/physiopathology , Bronchoalveolar Lavage Fluid/cytology , Cell Nucleus/enzymology , Cells, Cultured/enzymology , Cells, Cultured/immunology , Epithelial Cells/enzymology , Female , Humans , In Vitro Techniques , Inflammation , Interleukin-8/biosynthesis , Interleukin-8/genetics , Male , NF-kappa B/metabolism , Phosphatidylinositol 3-Kinases/metabolism , Phosphorylation , Protein Processing, Post-Translational , Protein Tyrosine Phosphatase, Non-Receptor Type 6/antagonists & inhibitors , Protein Tyrosine Phosphatase, Non-Receptor Type 6/genetics , Proto-Oncogene Proteins c-akt/metabolism , RNA Interference , RNA, Small Interfering/pharmacology , Transcription, Genetic , Young AdultABSTRACT
RATIONALE: Invasive cell phenotypes have been demonstrated in malignant transformation, but not in other diseases, such as asthma. Cellular invasiveness is thought to be mediated by transforming growth factor (TGF)-ß1 and matrix metalloproteinases (MMPs). IL-13 is a key T(H)2 cytokine that directs many features of airway remodeling through TGF-ß1 and MMPs. OBJECTIVES: We hypothesized that, in human asthma, IL-13 stimulates increased airway fibroblast invasiveness via TGF-ß1 and MMPs in asthma compared with normal controls. METHODS: Fibroblasts were cultured from endobronchial biopsies in 20 subjects with mild asthma (FEV(1): 90 ± 3.6% pred) and 17 normal control subjects (FEV(1): 102 ± 2.9% pred) who underwent bronchoscopy. Airway fibroblast invasiveness was investigated using Matrigel chambers. IL-13 or IL-13 with TGF-ß1 neutralizing antibody or pan-MMP inhibitor (GM6001) was added to the lower chamber as a chemoattractant. Flow cytometry and immunohistochemistry were performed in a subset of subjects to evaluate IL-13 receptor levels. MEASUREMENTS AND MAIN RESULTS: IL-13 significantly stimulated invasion in asthmatic airway fibroblasts, compared with normal control subjects. Inhibitors of both TGF-ß1 and MMPs blocked IL-13-induced invasion in asthma, but had no effect in normal control subjects. At baseline, in airway tissue, IL-13 receptors were expressed in significantly higher levels in asthma, compared with normal control subjects. In airway fibroblasts, baseline IL-13Rα2 was reduced in asthma compared with normal control subjects. CONCLUSIONS: IL-13 potentiates airway fibroblast invasion through a mechanism involving TGF-ß1 and MMPs. IL-13 receptor subunits are differentially expressed in asthma. These effects may result in IL-13-directed airway remodeling in asthma.
