Mechanical stretch promotes fetal type II epithelial cell differentiation via shedding of HB‐EGF and TGF‐α

• Published in: The Journal of physiology Vol. 587; no. 8; pp. 1739 - 1753
• Main Authors: Wang, Yulian, Maciejewski, Benjamin S., Soto‐Reyes, Dariana, Lee, Hyeon‐Soo, Warburton, David, Sanchez‐Esteban, Juan
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 15-04-2009; Blackwell Science Inc
• Subjects: Animals; Blotting, Northern; Cell Differentiation - drug effects; Cell Differentiation - physiology; Cell Separation; Electroporation; Epithelial Cells - drug effects; Epithelial Cells - physiology; Female; Fibroblasts - physiology; Gestational Age; Heparin-binding EGF-like Growth Factor; Intercellular Signaling Peptides and Proteins - metabolism; Lung - embryology; Lung - physiology; Microscopy, Fluorescence; Physical Stimulation; Pregnancy; Pulmonary Stretch Receptors - drug effects; Pulmonary Stretch Receptors - physiology; Rats; Rats, Sprague-Dawley; Respiratory; Reverse Transcriptase Polymerase Chain Reaction; Transfection; Transforming Growth Factor alpha - metabolism
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2008.163899

The mechanisms by which mechanical forces promote fetal lung development are not fully understood. Here, we investigated differentiation of fetal type II epithelial cells via the epidermal growth factor receptor (EGFR) in response to mechanical strain. First, we showed that incubation of embryonic day (E) 19 fetal type II cells with recombinant heparin‐binding EGF‐like growth factor (HB‐EGF) or transforming growth factor (TGF)‐α, but not with amphiregulin (AR), betacellulin (BTC) or epiregulin (EPR), increased fetal type II cell differentiation, as measured by surfactant protein B/C mRNA and protein levels. Next, we demonstrated that 5% cyclic stretch of E19 monolayers transfected with plasmid encoding alkaline phosphatase (AP)‐tagged ligands shed mature HB‐EGF and TGF‐α into the supernatant and promoted type II cell differentiation. Release of these ligands was also observed in E19 cells subjected to higher degrees of cyclic strain, but not in cells exposed to continuous stretch. Interestingly, the addition of fibroblasts to type II cell cultures did not enhance release of HB‐EGF. Whereas HB‐EGF shedding was also detected in E18 cells exposed to 5% cyclic stretch, release of this ligand after 2.5% sustained stretch was restricted to cells isolated on E18 of gestation. In addition, mechanical stretch released EGF, AR and BTC. We conclude that mechanical stretch promotes fetal type II cell differentiation via ectodomain shedding of HB‐EGF and TGF‐α. The magnitude of shedding varied depending on gestational age, ligand, and strain protocol. These studies provide novel mechanistic information potentially relevant to fetal lung development and to mechanical ventilation‐induced lung injury.