Expression of Smad7 inhibits fibrogenic responses of keratocytes to transforming growth factor β2.

Background: Transforming growth factor β (TGFβ) is one of the most important growth factors in the development of fibrosis and scarring on cornea. Smad7, an inhibitory Smad, can inhibit TGFβ signal transduction. In recent years, effects of lentiviral-mediated Smad7 on inhibition of fibrosis on some organs have been studied, while little is known about the effects on cornea. This study aimed to determine the effects of lentiviral-mediated Smad7 gene expression on keratocyte proliferation and fibrosis induced by TGF β2 in vitro.

Methods: Keratocytes were cultured from corneal tissue isolated from Sprague-Dawley (SD) rats and transfected with Smad7 expressing lentiviral vector (Lv-Smad7) or non-functioning control vector (Lv-blank). Following the exposure to TGFβ2, keratocytes were processed for immunoblotting to assess the phosphorylation of Smad2 as down-stream event of TGFβ/Smad signaling. Expression of fibrotic markers α-smooth muscle actin (α-SMA), type III collagen (collagen III) were measured by Western blotting and quantitative real time polymerase chain reaction (PCR). Overall cell proliferation was determined by 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and the expression of cell cycle-related marker Ki67 at both mRNA and protein levels.

Results: The Smad7 gene transfer suppressed TGFβ/Smad signaling in keratocytes by down-regulating phosphorylation of Smad2. Markers of cell proliferation and fibrosis including Ki67, α-SMA, collagen III were inhibited by introduction of Smad 7 into TGFβ exposed keratocytes. Consequently, the rate of cell proliferation was attenuated.

Conclusion: Smad7 gene transfer inhibited fibrogenic responses of keratocytes to TGFβ2.