Use this URL to cite or link to this record in EThOS:
Title: The differentiating and proliferative effects of Transforming Growth Factor beta (TGFβ) and Epidermal Growth Factor (EGF) on asthmatic fibroblasts
Author: Boxall, Christine Barbara
ISNI:       0000 0001 3473 2881
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2004
Availability of Full Text:
Access from EThOS:
Full text unavailable from EThOS. Please try the link below.
Access from Institution:
Rationale: Airway remodelling is a well-characterised component of asthma and is thought to contribute to increased resistance to breathing and persistence of bronchial hyperresponsiveness in asthmatics. It has been proposed that Transfonning Growth Factor beta (TGFβ), a key fibrogenic growth factor released in response to epithelial damage, can promote remodelling by inducing synthesis of extracellular matrix components from (myo)fibroblasts. Epidermal Growth Factor (EGF) is a potent mitogen for epithelial and mesenchymal cells and is also overexpressed in asthma. The balance between EGF driven proliferation and TGFβ mediated differentiation of fibroblasts is of potential importance in the pathogenesis of airway remodelling in asthmatics. Hypothesis 1: Asthmatic bronchial fibroblasts are more responsive to the effects of TGFβ2 induced differentiation and proliferation than normal fibroblasts. Hypothesis 2: EGF antagonises the effects of TGFβ2 induced differentiation and proliferation in bronchial fibroblasts. Methods: Fibroblasts were obtained as outgrowths from bronchial biopsies from normal (n=23) and asthmatic (n=19) subjects. Cultures were treated with TGFβ2 and EGF, alone or in combination to drive proliferation and/or differentiation which was monitored by methylene blue elution assay or αSMA expression. RNA was extracted from the cells for measurement of EGF and TGFβ receptor and ligand expression by Taqman PCR; data were normalised to 18S rRNA. Media were collected for determination of ligand release in response to TGFβ2 and EGF, and measured by ELISA. Binding of TGFβ to its receptors was measured by flow cytometry. Expression and control of amphiregulin (AR) and Hepmin Binding EGF-like Growth Factor (HB-EGF) release by ADAM 12 and 17 were measured by Taqman PCR and ELISA. As there were no commercial ELISAs available to measure HB-EGF I developed an HBEGF and optimised conditions for detection of the growth factor in conditioned media. Results: TGFβ2 caused growth arrest in fibroblasts and initiated their transformation into myofibroblasls, as shown by induction of αSMA. EGF induced fibroblasts to proliferate but did not induce their differentiation. In combination, EGF and TGFβ promoted fibroblast proliferation. Initially αSMA expression was suppressed, suggesting a dominant EGF effect. Upon prolonged culture, TGFβ2 and EGF promoted fibroblast transformation into myofibroblasts indicating a shift towards TGFβ dominance. Changes in TGFβ receptor and ligand expression did not appear to be disease dependent. There was a trend for down regulation of the TGFβ signalling pathway (TGFβ RI, CTGF, αSMA) in quiescent asthmatic fibroblasts, although no difference was seen after TGFβ2 trcatment. EGF induced mRNA expression of AR and HB-EGF in normal and asthmatic fibroblasts. The increase in AR in response to EGF was higher in the asthmatic fibroblasts (p=0.019) compared to the normals. TGFβ had no effect on AR expression but caused a marked dose-dependent induction of HB-EGF expression which was significantly higher in the normal compared with asthmatic cultures (p=0.024). AR was detected in conditioned media and its release was promoted by cellular activation with phorbol ester. HB-EGF was detected in conditioned medium after stimulation with phorbol ester, TGFβ2 and hexadimethrine. There was a trend for lower HB-EGF release from asthmatic fibroblasts. There was also a lower release of AR from asthmatic fibroblasts, although this was attributed to utilisation resulting in a small but significant mitogenic effect apparent only in the asthmatic fibroblasts. Conclusion: The study has revealed novel observations surrounding the complex control of TGFβ and EGF signalling in bronchial fibroblasts. In a TGFβ and EGF rich environment, akin to conditions in inflamed asthmatic airways, fibroblasts can undergo both proliferation and differentiation, potentially contributing to the fibrosis associated with airway remodelling. The suppressed release of AR and HB-EGF, growth factors with potent paracrine activity, lead to a proposal that there is a decline in signalling between the epithelium and asthmatic fibroblasts which may lead to an imbalance in bidirectional communication within the Epithelial-Mesenchymal Trophic Unit (EMTU), leading to decreased epithelial proliferation and an increase in mesenchymal proliferation and differentiation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available