Transforming Growth Factor-β Signaling Cascade Induced by Mechanical Stimulation of Fluid Shear Stress in Cultured Corneal Epithelial Cells

PURPOSE. Because blinking is regarded as mechanical stimulation of fluid shear stress on the corneal epithelial cells, we investigated the effects of fluid shear stress on cultured human corneal epithelial cells (HCECs). METHODS. The HCECs were exposed to shear stress (0, 1.2, 12 dyne/cm(2)) with the parallel-plate type of flow chamber. Wound healing, cellular proliferation, growth factor expression, TGF-beta 1 concentration in the culture supernatant, and phosphorylation of SMAD2 were investigated. RESULTS. Monolayers of HCECs exposed to shear stress had delayed wound healing and decreased proliferation compared with those of the static control (0 dyne/cm(2)). With increasing shear stress, TGF-beta 1 expression and phosphorylation of SMAD2 increased significantly, but the levels of total TGF-beta 1 in the culture supernatant decreased significantly. Delayed wound healing, decreased proliferation, and phosphorylation of the SMAD2 by shear stress were canceled out with a TGF-beta receptor inhibitor. CONCLUSIONS. Fluid shear stress on the HCECs affected TGF-beta signaling, which was associated with delayed wound healing. Mechanical stress by blinking might involve TGF-beta signaling, and activation of TGF-beta might be a key factor in wound healing of the corneal epithelium. Further studies should investigate the molecular mechanism of shear stress-induced activation of TGF-beta.