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Purpose: To examine the role of retinoic acid receptor (RAR) isoforms in interleukin-1β (IL-1β)-induced collagen degradation by corneal fibroblasts., Methods: Primary rabbit corneal fibroblasts embedded in a three-dimensional collagen gel were incubated with or without all-trans retinoic acid (ATRA), the RAR-α agonist Am580, the RAR-β agonist AC55649, or the RAR-γ agonist R667. Collagen degradation was determined by measurement of hydroxyproline produced in acid hydrolysates of culture supernatants. Matrix metalloproteinase (MMP) expression was evaluated by immunoblot analysis and gelatin zymography. The phosphorylation of mitogen-activated protein kinases (MAPKs) and the endogenous nuclear factor (NF)-κB inhibitor IκB-α was examined by immunoblot analysis. Cell proliferation was measured with a bromodeoxyuridine incorporation assay, and cell viability was determined by measurement of the release of lactate dehydrogenase., Results: Interleukin-1β-induced collagen degradation by corneal fibroblasts was inhibited by ATRA, Am580, and R667 in a concentration-dependent manner but was unaffected by AC55649, with the inhibitory effects of ATRA and R667 being markedly greater than that of Am580. The IL-1β-induced production of MMP-1, MMP-2, MMP-3, and MMP-9 by corneal fibroblasts was also inhibited by R667 in a concentration-dependent manner. R667 inhibited the IL-1β-induced phosphorylation of IκB-α but not that of MAPKs. R667 had no effect on the proliferation or viability of corneal fibroblasts., Conclusions: The RAR-γ agonist R667 suppressed MMP production and thereby inhibited collagen degradation by corneal fibroblasts exposed to the proinflammatory cytokine IL-1β. These effects of R667 may be mediated by the NF-κB signaling pathway.

Purpose: Excessive wound contraction can lead to scar formation in the conjunctiva. The effects of all-trans-retinoic acid (ATRA) on the contractility of human Tenon fibroblasts (HTFs) cultured in three-dimensional (3D) collagen gels were investigated., Methods: Human Tenon fibroblasts were cultured in 3D gels of type I collagen and in the absence or presence of TGF-β, ATRA, or various inhibitors. Collagen gel contraction was evaluated by measurement of gel diameter. Phosphorylation of various signaling molecules was examined by immunoblot analysis. The formation of actin stress fibers and focal adhesions was detected by laser confocal microscopy., Results: All-trans-retinoic acid inhibited TGF-β-induced collagen gel contraction mediated by HTFs in a concentration- and time-dependent manner. The TGF-β-induced phosphorylation of focal adhesion kinase (FAK) and formation of stress fibers and focal adhesions in HTFs were attenuated by ATRA. All-trans-retinoic acid also inhibited the TGF-β-induced phosphorylation of the mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase (ERK), p38, and c-Jun NH2-terminal kinase (JNK) as well as that of c-Jun and Smad2/3. Furthermore, TGF-β-induced collagen gel contraction was blocked by inhibitors of ERK, p38, or JNK signaling., Conclusions: All-trans-retinoic acid inhibited TGF-β-induced collagen gel contraction mediated by HTFs, most likely by attenuating the formation of actin stress fibers and focal adhesions as well as signaling by MAPKs, c-Jun, and Smads. All-trans-retinoic acid may therefore prove effective for inhibition of conjunctival scarring through attenuation of the contractility of Tenon fibroblasts., (Copyright 2014 The Association for Research in Vision and Ophthalmology, Inc.)

Purpose: Collagen contraction mediated by retinal pigment epithelial (RPE) cells contributes to the pathogenesis of proliferative vitreoretinopathy (PVR). We examined the effects of sex hormones on this process., Methods: Mouse RPE cells were cultured in a type I collagen gel and exposed to 17β-estradiol, progesterone, or dehydro-epiandrosterone. Collagen contraction induced by transforming growth factor-β2 (TGF-β2) was determined by measurement of gel diameter. Expression of α-smooth muscle actin (α-SMA), as well as phosphorylation of Smad2 and myosin light chain (MLC), was examined by immunoblot analysis. Matrix metalloproteinase (MMP) release was evaluated by gelatin zymography. Fibronectin and interleukin-6 secretion was measured with immunoassays., Results: The female sex hormones 17β-estradiol and progesterone inhibited TGF-β2-induced collagen contraction mediated by RPE cells, whereas the male sex hormone dehydro-epiandrosterone had no such effect. The TGF-β2-induced release of MMP-2 and MMP-9 from RPE cells was also inhibited by 17β-estradiol and progesterone, and the MMP inhibitor GM6001 attenuated TGF-β2-induced collagen contraction. Expression of the mesenchymal markers α-SMA and fibronectin, interleukin-6 release, and Smad2 and MLC phosphorylation induced by TGF-β2 were all inhibited by 17β-estradiol and progesterone. Immunohistochemical analysis also detected nuclear immunoreactivity for estrogen and progesterone receptors in proliferative fibrocellular membranes of PVR patients., Conclusions: Female sex hormones inhibited TGF-β2-induced collagen contraction mediated by RPE cells. This action appeared to be mediated through inhibition both of MMP, α-SMA, and fibronectin expression as well as of Smad2 and MLC phosphorylation. Female sex hormones might thus prove effective for the treatment of PVR.

Purpose: TNF-α disrupts the barrier function of cultured human corneal epithelial (HCE) cells. We investigated the effects of the cytoprotective drug rebamipide on this barrier disruption by TNF-α as well as on corneal epithelial damage in a rat model of dry eye., Methods: The barrier function of HCE cells was evaluated by measurement of transepithelial electrical resistance. The distribution of tight-junction (ZO-1, occludin) and adherens-junction (E-cadherin, β-catenin) proteins, and the p65 subunit of nuclear factor-κB (NF-κB) was determined by immunofluorescence microscopy. Expression of junctional proteins as well as phosphorylation of the NF-κB inhibitor IκB-α and myosin light chain (MLC) were examined by immunoblot analysis. A rat model of dry eye was developed by surgical removal of exorbital lacrimal glands., Results: Rebamipide inhibited the disruption of barrier function as well as the downregulation of ZO-1 expression, and the disappearance of ZO-1 from the interfaces of neighboring HCE cells induced by TNF-α. It also inhibited the phosphorylation and downregulation of IκB-α, the translocation of p65 to the nucleus, the formation of actin stress fibers, and the phosphorylation of MLC induced by TNF-α in HCE cells. Treatment with rebamipide eyedrops promoted the healing of corneal epithelial defects as well as attenuated the loss of ZO-1 from the surface of corneal epithelial cells in rats., Conclusions: Rebamipide protects corneal epithelial cells from the TNF-α-induced disruption of barrier function by maintaining the distribution and expression of ZO-1 as well as the organization of the actin cytoskeleton. Rebamipide is, thus, a potential drug for preventing or ameliorating the loss of corneal epithelial barrier function associated with ocular inflammation.

Purpose: To examine the effect of medroxyprogesterone 17-acetate (MPA) on interleukin-1β (IL-1β)-induced collagen degradation by corneal fibroblasts., Methods: Rabbit corneal fibroblasts were cultured in three-dimensional collagen gels with or without MPA. Collagen degradation was determined by measurement of hydroxyproline after acid hydrolysis. The expression or activity of matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs) was evaluated by immunoblot analysis or gelatin zymography. The phosphorylation of mitogen-activated protein kinases (MAPKs) in corneal fibroblasts was examined by immunoblot analysis. Cell proliferation and viability were evaluated by measurement of bromodeoxyuridine incorporation and the release of lactate dehydrogenase, respectively., Results: MPA inhibited IL-1β-induced collagen degradation by corneal fibroblasts in a concentration- and time-dependent manner. MMP expression and activation as well as TIMP expression in corneal fibroblasts exposed to IL-1β were also inhibited by MPA. MPA had no effect on cell proliferation or viability. MPA inhibited the IL-1β-induced phosphorylation of p38 MAPK without affecting that of the MAPKs ERK or JNK. IL-1β-induced MMP expression and activation as well as collagen degradation were also blocked by the p38 MAPK inhibitor SB203580., Conclusions: MPA inhibited MMP expression and thereby suppressed collagen degradation by corneal fibroblasts induced by IL-1β. Furthermore, inhibition of p38 MAPK phosphorylation by MPA may contribute to its inhibition of collagen degradation.

Purpose: Corneal epithelial migration during wound healing is important for maintenance of corneal transparency, and fibronectin plays a key role in regulation of the adhesion and migration of corneal epithelial cells. The role of β-Pix in intracellular signaling that underlies the stimulatory effects of fibronectin on the adhesion and migration of corneal epithelial cells was examined., Methods: Simian virus 40-transformed human corneal epithelial (HCE) cells were cultured on fibronectin or on bovine serum albumin as a control. The localization and tyrosine phosphorylation of β-Pix were examined by immunofluorescence and immunoprecipitation analyses, respectively. The actin cytoskeleton and focal adhesions were detected by staining of cells with rhodamine-phalloidin and antibodies to phosphotyrosine, respectively. The effects of depletion of β-Pix on HCE cell adhesion and migration on fibronectin were investigated by cell transfection with a small interfering RNA specific for β-Pix mRNA., Results: Fibronectin induced the tyrosine phosphorylation of β-Pix as well as its apparent accumulation at focal adhesions in HCE cells. Depletion of β-Pix inhibited the effects of fibronectin on remodeling of the actin cytoskeleton and the formation of focal adhesions. It also inhibited the migration of HCE cells on fibronectin in an in vitro model of wound healing, but it did not affect cell adhesion to fibronectin., Conclusions: β-Pix contributes to the regulation of the formation of focal adhesions as well as that of cell migration by fibronectin in HCE cells. This protein therefore likely plays an important role in signal transduction underlying corneal epithelial wound healing.

Purpose: Viral infection at the ocular surface can lead to the chronic condition of viral stromal keratitis. Polyinosinic-polycytidylic acid [poly(I:C)], an analog of viral double-stranded RNA, induces the expression of adhesion molecules in cultured corneal fibroblasts. The authors investigated the roles of nuclear factor (NF)-κB and phosphoinositide 3-kinase (PI3K)-Akt signaling pathways in the poly(I:C)-induced expression of adhesion molecules in corneal fibroblasts., Methods: Human corneal fibroblasts were cultured with poly(I:C) in the absence or presence of IκB kinase 2 (IKK2) inhibitor (an inhibitor of NF-κB activation) or the PI3K inhibitor LY294002. The expression of vascular cell adhesion molecule (VCAM)-1, intercellular adhesion molecule (ICAM)-1, ICAM-2, and E-selectin, as well as the phosphorylation of the NF-κB inhibitory protein IκB-α and Akt, were examined by immunoblot analysis. The subcellular localization of adhesion molecules was determined by immunofluorescence analysis., Results: Poly(I:C) increased the expression of VCAM-1 and ICAM-1 but not that of ICAM-2 or E-selectin in corneal fibroblasts. Poly(I:C) also induced the phosphorylation of IκB-α and Akt. The poly(I:C)-induced expression of VCAM-1 and ICAM-1 was attenuated by both IKK2 inhibitor and LY294002., Conclusions: The NF-κB and PI3K-Akt signaling pathways mediate the poly(I:C)-induced upregulation of VCAM-1 and ICAM-1 in corneal fibroblasts, with PI3K acting upstream of NF-κB activation. These pathways thus likely modulate local immune and inflammatory responses to viral infection in the corneal stroma.

Purpose: To characterize the mechanism of corneal ulceration associated with viral keratitis, the authors investigated the effects of polyinosinic-polycytidylic acid [poly(I:C)], a synthetic analog of viral double-stranded RNA, on the expression of matrix metalloproteinases (MMPs) in human corneal fibroblasts., Methods: The expression of MMPs in human corneal fibroblasts cultured in the absence or presence of poly(I:C) was examined by immunoblot analysis, gelatin zymography, and quantitative reverse transcription-polymerase chain reaction analysis. The phosphorylation of the NF-κB inhibitor protein IκB-α was assessed by immunoblot analysis, and the concentration of interleukin (IL)-1β in culture supernatants was measured by enzyme-linked immunosorbent assay., Results: Poly(I:C) increased the expression of MMP-1 and MMP-3 in corneal fibroblasts at the mRNA and protein levels. It also induced the phosphorylation of IκB-α and the secretion of IL-1β in these cells. The poly(I:C)-induced expression of MMP-1 and MMP-3 was attenuated by a synthetic inhibitor of NF-κB signaling and by IL-1 receptor antagonist; the latter also inhibited poly(I:C)-induced phosphorylation of IκB-α., Conclusions: Poly(I:C) induces the expression of MMP-1 and MMP-3 in human corneal fibroblasts in a manner dependent on activation of the transcription factor NF-κB and on IL-1β secretion. These effects may play an important role in corneal ulceration associated with viral keratitis.