Lipopolysaccharide Inhibits Interleukin–13-induced Chemokine (C-C motif) Ligand 26 in Human Airway Epithelial Cells: Possible Role in Eosinophil Chemotaxis in Allergic Asthma

• Author / Creator

  Alotaibi,Dhaifallah S

• Background Allergic asthma is characterized by increased level of Interleukin-13 (IL-13) in the lungs. IL-13 promotes eosinophilic infiltration in the airways by stimulating airway epithelial cells to release eotaxin-3 (CCL26) through the Janus activated kinase-2 (JAK-2)/signal transducer and activator of transcription 6 (STAT6) pathway. Eosinophil accumulation in the airways is a hallmark of allergic asthma. There is also evidence that bacterial products, such as LPS, affect the release of eosinophil chemotactic factors and may alter eosinophil accumulation in peripheral tissues. However, the effects of LPS on airway eosinophilia are incompletely understood. Thus, our aim was to study the effects of LPS on IL-13 -induced CCL26 induction in airway epithelial cells and the mechanisms of these effects. Methods We used LPS to mimic the bacterial insults on the airway epithelium. The human bronchial epithelial cell line BEAS-2B was stimulated with IL-13 (20 ng/ml) alone or in combination with LPS (10 μg/ml) for 24 hr. CCL26 mRNA levels were measured using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and CCL26 protein was measured in the supernatants of these cells using ELISA. STAT6 phosphorylation was measured by western blot. For NF-kB inhibition, BEAS-2B cells were pre-treated with 3 different NF-kB inhibitors, curcumin (10 μM), arctigenin (1 μM), and bengamide B (1 μM), for 2 hr before activation with IL-13 and/or LPS. Results BEAS-2B cell activation with IL-13 for 24 hr strongly induced CCL26 mRNA expression (78.3 ± 3.9 fold over unstimulated cells, n=13, p < 0.001) and the release of CCL26 protein (1462 ± 55.1 pg/ml , while there was no detection of CCL26 protein release in unstimulated cells, n=13, p < 0.001). Simultaneous treatment of BEAS-2B cells with LPS inhibited IL-13 -induced CCL26 expression (n=13, p < 0.001) and CCL26 protein release (n=13, p < 0.001). IL-13 also induced STAT6 phosphorylation in BEAS-2B cells, which peaked at 30 min. STAT6 phosphorylation, was attenuated when cells were activated by IL-13 in the presence of LPS (n=3, p < 0.05). Pre- incubation of the cells with NF-kB inhibitors prevented the LPS effect on IL-13 -induced CCL26 upregulation and STAT6 phosphorylation. Conclusions LPS, a TLR-4 ligand, inhibits the effects of IL-13 on CCL26 expression in airways epithelial cells. This effect may be dependent on LPS interfering with JAK2/STAT6 signaling through NF- kB activation.

• Subjects / Keywords

  • Allergic Asthma
  • Interleukin 13

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R34M91Q8D

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.