Background Although epithelial-mesenchymal transition (EMT) has been well described in other organs, eg, the kidney, it has only recently been described in the lung. Using the rat alveolar type II (ATII) cell line, RLE-6TN and adult rat ATIIs, Willis et al (Am J Pathol 2005;166:1321-32) have recently demonstrated that ATII cells when chronically exposed to transforming growth factor (TGF)-β undergo EMT, raising the possibility that epithelial cells can serve as a source of myofibroblasts in chronic fibrotic conditions. Whether EMT occurs in chronic lung disease of the premature infant, a condition characterized by myofibroblast proliferation, is not known.
Objective To determine whether cultured fetal rat ATII cells undergo EMT upon treatment with cytokines that are known to be associated with CLD of the newborn.
Design/Methods Sprague-Dawley fetal rat lung ATII cells were isolated at embryonic (e) day 19 and cultured in Dulbecco's Minimum Essential Medium + 10% FBS at 37°C in 6-well plates, 60 mm, and 100 mm dishes, as needed. At near confluence, the cells were maintained in culture with and without recombinant human TGF-β1 (2.5 ng/mL), tumor necrosis factor (TNF)-α (1 ng/mL), and TGF-β1 (2.5 ng/mL) + TNF-α (1 ng/mL) up to 10 days. EMT was examined by determining the expression of well-established markers of the alveolar epithelial (surfactant protein-B and -C, CTP:cholinephosphate cytidylyltransferase α, and aquaporin-5) and mesenchymal (α-smooth muscle actin, calponin, type I collagen) phenotypes on day 1, 6, and 10 at mRNA (RT-PCR) and protein (Western hybridization) levels. ATII cell function was also simultaneously determined through [3 H]choline incorporation into saturated phosphatidylcholine.
Results Based on the expression of well-established alveolar epithelial and mesenchymal markers, there was no evidence of either spontaneous or cytokine-stimulated EMT up to 10 days in culture in e19 rat ATII cells.
Conclusions Unlike the pathogenesis of the pulmonary fibrosis in the adult, EMT is not a prominent feature of the CLD of the premature infant. We speculate that premature ATII cells are resistant to EMT, and fibroblast-to-myofibroblast transdifferentiation rather than EMT is crucial in the pathogenesis of the CLD of the premature infant.
Supported in part by NIH grants HL75405A (V.K.R. and J.S.T.) and HL55268 (J.S.T. and V.K.R.), Philip Morris USA Inc. and Philip Morris International, Tobacco-Related Disease Research Program (14RT-0073), and March of Dimes.
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