Regulation of IL-4 mediated signalling in primary human bronchial fibroblasts by IL-13Rα2

Abstract

Fibroblasts are key effector cells involved in airway inflammation and remodelling in asthma. Interleukin (IL)-4 and IL-13 are important cytokines in the asthma phenotype which act on fibroblasts and other cell types. These cytokines exhibit overlapping functions through use of a common receptor, IL-4Rα:IL-13Rα1. Another receptor, IL 13 Receptor α2 (IL-13Rα2), originally thought to be a decoy receptor for IL-13, has recently been shown to attenuate responses to IL-4 as well as IL-13, by an unknown mechanism. In this thesis, I tested the hypothesis that IL-13Rα2 is responsible for the regulation of IL-4 mediated signalling in bronchial fibroblasts and that regulation by IL-13Rα2 is altered in asthma.

The expression of IL-4 and IL-13 receptors on human bronchial fibroblasts (HBFs) was highly dynamic. IL-13Rα2 expression was significantly increased in response to both IL-4 and IL-13 over 24 hours, requiring de novo protein synthesis. A significant rapid reduction in IL-4Rα expression was also observed in response to either ligand, although levels rapidly returned to normal after removal of the stimulus. Use of a neutralizing antibody showed that induction of IL 13Rα2 suppressed STAT-6 activation and the pro-inflammatory effects of IL-4 and IL-13. No difference was observed in receptor expression levels or the regulatory effects of IL-13Rα2 between healthy and asthmatic subjects.

IL-13Rα2 was also up-regulated by a range of Th1 stimuli including IFNγ and IFNβ, as well as double stranded RNA (dsRNA), with no disease-related differences. The up-regulation of IL 13Rα2 in response to dsRNA hampered attempts to knock down surface expression of IL-13Rα2 using siRNA, but revealed a potential role for IL-13Rα2 in the anti-viral response due to its ability to down-regulate responses to IL-4 and IL-13.

An over expression model of IL-13Rα2 identified the potential for IL-4 to cause activation of STAT3 mediated by IL-13Rα2. In HBFs naturally expressing high levels of IL-13Rα2, addition of IL-4, but not IL-13, significantly increased activation of STAT3, a transcription factor associated with cell survival.

Whilst IL-13Rα2 may have beneficial anti-inflammatory effects by suppressing STAT-6 mediated responses, further work is required to determine potential pro-fibrotic consequences of IL-4/IL-13Rα2 mediated STAT3 activation in HBFs. Since no difference was observed in IL-13Rα2 expression or in its anti-inflammatory efficacy in HBFs from normal or asthmatic donors, these data suggest that the atopic environment is more important than intrinsic differences in the ability of asthma-derived fibroblasts to respond to IL-4 and IL-13.

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Identifiers

ORCID for Donna E. Davies: orcid.org/0000-0002-5117-2991

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