IL-13 induces a bronchial epithelial phenotype that is profibrotic.
BACKGROUND
Inflammatory cytokines (e.g. IL-13) and mechanical perturbations (e.g. scrape injury) to the epithelium release profibrotic factors such as TGF-beta2, which may, in turn, stimulate subepithelial fibrosis in asthma. We hypothesized that prolonged IL-13 exposure creates a plastic epithelial phenotype that is profibrotic through continuous secretion of soluble mediators at levels that stimulate subepithelial fibrosis.


METHODS
Normal human bronchial epithelial cells (NHBE) were treated with IL-13 (0, 0.1, 1, or 10 ng/ml) for 14 days (day 7 to day 21 following seeding) at an air-liquid interface during differentiation, and then withdrawn for 1 or 7 days. Pre-treated and untreated NHBE were co-cultured for 3 days with normal human lung fibroblasts (NHLF) embedded in rat-tail collagen gels during days 22-25 or days 28-31.


RESULTS
IL-13 induced increasing levels of MUC5AC protein, and TGF-beta2, while decreasing beta-Tubulin IV at day 22 and 28 in the NHBE. TGF-beta2, soluble collagen in the media, salt soluble collagen in the matrix, and second harmonic generation (SHG) signal from fibrillar collagen in the matrix were elevated in the IL-13 pre-treated NHBE co-cultures at day 25, but not at day 31. A TGF-beta2 neutralizing antibody reversed the increase in collagen content and SHG signal.


CONCLUSIONS
Prolonged IL-13 exposure followed by withdrawal creates an epithelial phenotype, which continuously secretes TGF-beta2 at levels that increase collagen secretion and alters the bulk optical properties of an underlying fibroblast-embedded collagen matrix. Extended withdrawal of IL-13 from the epithelium followed by co-culture does not stimulate fibrosis, indicating plasticity of the cultured airway epithelium and an ability to return to a baseline. Hence, IL-13 may contribute to subepithelial fibrosis in asthma by stimulating biologically significant TGF-beta2 secretion from the airway epithelium.
Malavia
Nikita K
NK
Department of Chemical Engineering and Materials Science, University of California - Irvine, Irvine, CA, USA. nmalavia@uci.edu
Mih
Justin D
JD
Raub
Christopher B
CB
Dinh
Bao T
BT
George
Steven C
SC
D001980:Bronchi / Q000187:drug effects* / Q000378:metabolism*; D002478:Cells, Cultured; D003094:Collagen / Q000378:metabolism; D015536:Down-Regulation; D004334:Drug Administration Schedule; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D018793:Interleukin-13 / Q000008:administration & dosage / Q000494:pharmacology*; D055271:Mucin 5AC; D009077:Mucins / Q000378:metabolism; D010641:Phenotype; D011658:Pulmonary Fibrosis / Q000209:etiology*; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000494:pharmacology; D013997:Time Factors; D053781:Transforming Growth Factor beta2 / Q000378:metabolism*; D014404:Tubulin / Q000378:metabolism
D018793:Interleukin-13; C524678:MUC5AC protein, human; C524680:Muc5ac protein, rat; D055271:Mucin 5AC; D009077:Mucins; D011994:Recombinant Proteins; D053781:Transforming Growth Factor beta2; D014404:Tubulin; D003094:Collagen