OBJECTIVETo investigate the effect of silicon dioxide (SiO₂) on the expression of E-cadherin, α-smooth muscle actin (α-SMA), and transforming growth factor β₁(TGF-β₁) in human pulmonary epithelial cells (A549) with epithelial-mesenchymal transition (EMT), and to study the roles of epidermal growth factor receptor (EGFR) signaling pathway in SiO₂-induced EMT in A549 cells in vitro.

METHODSAlveolar macrophages (AMs) were stimulated with 50 µg/ml SiO₂for 3, 6, 12, 18, 24, or 36 h, and the supernatants were collected to measure the expression of TGF-β₁protein by ELISA. The AM supernatant in which TGF-β₁reached the highest expression (T=18 h) was used as AM-conditioned supernatant. A549 cells were cultured in AM-conditioned supernatant and stimulated with indicated doses of SiO₂(0, 50, 100, and 200 µg/ml) for 48 h. The cell morphological changes were observed using an inverted microscope. The cells were collected at different times, and the mRNA and protein expression levels of E-cadherin, α-SMA, and EGFR were measured by RT-PCR and immunocytofluorescence, respectively.

RESULTSAfter stimulation by SiO₂, the expression level of TGF-β₁protein at each time point was significantly higher in the presence of AM supernatants than in the absence of AM supernatants (P<0.05). With the action time, the expression level of TGF-β₁protein increased at first and then decreased, and the highest level was reached at 18 h. After exposure to SiO₂, A549 cells exhibited mesenchymal characteristics, such as a spindle shape, pseudopodia change, and fibroblast-like morphology, as observed by inverted microscope, especially in the 200 µg/ml group. With increased concentration of SiO₂, the mRNA and protein expression of E-cadherin was down-regulated gradually, especially in the 200 µg/ml group, whereas the mRNA and protein expression of α-SMA and EGFR was up-regulated gradually, especially in the 200 µg/m1 group. There were significant differences between the SiO₂-treated groups (50, 100, and 200 µg/ml SiO₂) and the control group (P<0.05).

CONCLUSIONAfter being stimulated by SiO₂in vitro, AMs have significantly increased expression level of TGF-β₁protein. The AM supernatant together with SiO₂can induce the transition of pulmonary epithelial cells to mesenchymal cells, and its mechanism may be related to the EGFR signaling pathway.