Epithelial-to-mesenchymal transition of human lung alveolar epithelial cells in a microfluidic gradient device

Epithelial-to-mesenchymal transition (EMT), a process in which epithelial cells undergo phenotypic transitions to fibrotic cells, is induced by stimulants including transforming growth factor-beta1 (TGF-β1). In the present study, we developed a microfluidic gradient device to reproduce EMT in A549 human lung alveolar epithelial cells in response to TGF-β1 gradients. The device was directly mounted on the cells that had grown in cell culture plates and produced a stable concentration gradient of TGF-β1 with negligible shear stress, thereby providing a favorable environment for the anchorage-dependent cells. A549 cells elongated with the characteristic spindle-shaped morphological changes with upregulation of alpha-smooth muscle actin, a mesenchyme marker, in a gradient-dependent manner, suggestive of EMT progression. We observed that at higher TGF-β1 concentrations ranging from 5 to 10 ng/mL, the cultures in the microfluidic device allowed to quantitatively pick up subtle differences in the EMT cellular response as compared with plate cultures. These results suggest that the microfluidic gradient device would accurately determine the optimal concentrations of TGF-β1, given that epithelial cells of different tissue origins greatly vary their responses to TGF-β1. Therefore, this microfluidic device could be a powerful tool to monitor EMT induced by a variety of environmental stresses including cigarette smoke with high sensitivity.