Effect of TGF-β on ocular surface epithelial cells

Abstract

A role for transforming growth factor (TGF)-β in the pathogenesis of some ocular surface diseases has been proposed. We determined if secretion of TGF-β and expression of TGF-β receptors RI, RII, and RIII by human ocular surface epithelial cells were modified under inflammatory conditions. We also determined how these cells responded to TGF-β. A human corneal epithelial (HCE) cell line and a conjunctival epithelial cell line (IOBA-NHC) were exposed to TGF-β1 and -β2 and to proinflammatory cytokines. TGF-β receptor mRNAs were analyzed by real time reverse transcription polymerase chain reaction (RT-PCR) in both cell lines, and in conjunctival, limbal, and corneal epithelial cells from post-mortem human specimens. Expression of TGF-β receptors and pSMAD2/SMAD2 were determined by Western blot and immunofluorescence assays. Secretion of TGF-β isoforms, cytokine/chemokine, and metalloproteinases (MMPs) were analyzed in cell supernatants by immunobead-based assays. Secretory leukocyte proteinase inhibitor (SLPI) secretion was analyzed by enzyme-linked immunosorbent assay. TGF-β isoform and receptor gene expression was determined by RT-PCR in conjunctival epithelium of dry eye (DE) patients and healthy subjects. Our results showed that TGF-β RI expression was down-regulated with IL-4 exposure, whereas TGF-β RII and TGF-β2 were upregulated by TNF-α in HCE cells. TGF-β RIII receptor expression was upregulated in IOBA-NHC cells by TNF-α and IFN-γ. SMAD2 phosphorylation occurred in HCE and IOBA-NHC cells after TGF-β treatment. TGF-β significantly up- and down-regulated secretion of several cytokines/chemokines by both cell lines and MMP by HCE cells. TGF-β2 and TGF-β3 were upregulated and TGF-β RIII mRNA was down-regulated in DE conjunctival epithelium. These results show that TGF-β plays an important role in directing local inflammatory responses in ocular surface epithelial cells.