Interleukin (IL)-13 induces a mucus hypersecretory phenotype in human bronchial epithelial cells (HBECS) thatv is sensitive to PD98059 but not to AG1478 Atherton H.C., Jones G. & Danahay H. Novartis Respiratory Research Centre, Horsham, UK.

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IL-13 is believed to be an important mediator in asthma and other respiratory diseases (Wills-Karp et al., 1998, Zhu et al., 1999). Reported studies have demonstrated a role for IL-13 in inflammation, airway hyper-reactivity and increased mucus secretion. The current study was designed to assess whether IL-13 could induce a change in goblet cell density (GCD), through a direct interaction with human airway epithelium. Subsequently, an initial pharmacological characterisation has been performed using modulators of two pathways potentially involved in both IL-13 signalling and mucin production, namely MEK (MAP kinase kinase) and EGF (epidermal growth factor).

HBECs (Clonetics) were cultured for 21 days on Transwell permeable supports (Costar). For the final 14 days, they were cultured at an air liquid interface (ALI), as previously described (Danahay et al., 2002). All treatments were added as a basolateral media supplement for the final 14 days of differentiation. Initially IL-13 (0.1-10ngmL^-1) was used to determine if there was a concentration-dependent change in GCD. After 14 days of treatment, the cells were fixed and processed for histological determination of GCD by staining with 45M1 (an anti MUC5AC antibody) or alcian blue (AB). In subsequent studies cells were treated with IL-13 (1ngmL^-1) combined with either PD98059 or AG1478 (1-10µM). GCD was measured as the ratio of 45M1 stained area to the length of epithelium (using image analysis software). Data are expressed as mean fold or percentage change in GCD (±s.e.mean), compared to control or IL-13 treated cells and significance assumed when P<0.05 (Student t-test).

Quantification of GCD using either AB or 45M1 staining methods correlated well (R=0.822; P<0.01). 45M1 scoring was chosen for all subsequent studies. IL-13 (1ngmL^-1), induced a maximal 5.5±0.92 (n=7) fold increase in GCD (P<0.01). Paradoxically, there was a 90.1±2.3% (n=9) decrease from this elevated GCD in the IL-13 (10ngmL^-1) treated group (P<0.01). In a subsequent study, IL-13 (1ngmL^-1) induced an 11.4±1.0 (n=6) fold increase in GCD, that was attenuated by PD98059 (44.3±6.5% inhibition at 10µM; P<0.01, n=6). PD98059 had no effect on baseline GCD. In a further study, IL-13 (1ngmL^-1) induced a 4.9±0.6 (n=6) fold increase in GCD that was insensitive to AG1478 (10µM; P>0.05; n=6). However, in this same study, AG1478 (10µM) induced a 70.0±7.2% (n=6) decrease in the basal, non-IL-13 stimulated GCD (P<0.01; n=6).

We demonstrate that IL-13 can act directly on the human airway epithelium to induce a mucus hypersecretory phenotype, assessed as an increase in GCD. We also show involvement of the MEK pathway in the induction of this phenotype, demonstrated using PD98059, a non-selective MEK inhibitor. The effect of AG1478, a potent inhibitor of the EGF receptor tyrosine kinase, demonstrates a role for this pathway in the regulation of basal, but not the IL-13 driven increase in GCD. Further studies will be required to investigate the mechanism for the decrease in GCD observed with IL-13 (10ngmL^-1).

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