Effect of titanium dioxide nanoparticles (TiO2 NPs) on the expression of mucin genes in human airway epithelial cells.

OBJECTIVE: Titanium dioxide nanoparticles (TiO2 NPs) are utilized with growing frequency for a wide variety of industrial applications. Recently, acute and chronic exposures to TiO2 NPs have been found to induce inflammatory response in the human respiratory tract. However, the effect and mechanism underlying the induction of major airway mucins by TiO2 NPs have not been elucidated. This study was conducted to characterize the effect of TiO2 NPs, and the mechanism involved, on the expressions of airway mucins in human airway epithelial cells. MATERIALS AND METHODS: In NCI-H292 cells and primary cultures of normal nasal epithelial cells, the effects of TiO2 NPs and signaling pathway for airway mucin genes were investigated by reverse transcriptase-polymerase chain reaction (RT-PCR), real-time PCR, enzyme immunoassays and immunoblot analysis using several specific inhibitors and small interfering RNAs (siRNAs). RESULTS: TiO2 NPs increased MUC5B expression and activated the phosphorylations of extracellular signal-related kinase 1/2 (ERK1/2) and p38 mitogen-activated protein kinase (MAPK). U0126 (an ERK1/2 MAPK inhibitor) and SB203580 (a p38 MAPK inhibitor) inhibited TiO2 NPs-induced MUC5B expression. And knockdown of ERK1, ERK2 and p38 MAPK using siRNAs significantly blocked TiO2 NPs-induced MUC5B mRNA expression. Furthermore, Toll-like receptor 4 (TLR4) mRNA expression was increased by TiO2 NPs, and knockdown by TLR4 siRNA significantly attenuated TiO2 NPs-induced MUC5B mRNA expression and the TiO2 NPs-induced phosphorylations of ERK1/2 and p38 MAPK. DISCUSSION AND CONCLUSIONS: These results demonstrate for the first time that TiO2 NPs induce MUC5B expression via TLR4-dependent ERK1/2 and p38 MAPK signaling pathways in respiratory epithelium.