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Life Sci. 2004 Nov 19;76(1):29-37.

TGF-beta1 induces alveolar epithelial to mesenchymal transition in vitro.

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Zhejiang Respiratory Drugs Research Laboratory of State Food Drugs Administration of China, School of Medicine, Zhejiang University, Hangzhou 310031, China.


The aim of this study was to investigate whether transforming growth factor-beta1 (TGF-beta1) could induce alveolar epithelial to mesenchymal transition (EMT) in vitro. Alveolar epithelial cells (AECs) from SD rats were isolated by elastase cell dispersion and IgG panning. Expression of alpha-smooth muscle actin (alpha-SMA) was assayed using Western blotting and immunostaining analysis. Morphological changes, the markers of epithelial cell (E-cadherin), and stress fiber by actin reorganization were detected by an indirect immunostaining. The contents of collagen I were determined by spectrophotometry. The levels of endogenous TGF-beta1 were measured with ELISA. Incubation of AECs with TGF-beta1 (0.1 approximately 10 ng/mL) induced abundant expression of alpha-SMA protein, and alpha-SMA expression in AECs reached a plateau when TGF-beta1 was > 3 ng/mL. Furthermore, we found that TGF-beta1 (3 ng/mL) exposure of AECs induced an authentic EMT characterized by abundant expression of alpha-smooth muscle actin, transformation of myofibroblastic morphology, increased formation of stress fiber by actin reorganization, and loss of epithelial marker E-cadherin. Meanwhile, significant increase in the levels of collagen I from 32.0 +/- 6.6 mg/g in control to 98 +/- 10.8 mg/g in TGF-beta1-treated group was found over a 72 h incubation period. Moreover, following stimulated by TGF-beta1 (3 ng/mL), a marked and time-dependent increase in endogenous TGF-beta1 released from AECs was observed. At time points 72 h, TGF-beta1 release mounted to 3451 pg/ml, which was much enough to induce EMT in vitro. These results demonstrated that AECs, under stimulation of TGF-beta1, underwent a conversion process into myofibroblasts in vitro.

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