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J. Swaney, G. Hansen, W. Garland, R. Sabbadini, G. Stoller; Sphingosine-1-Phosphate Is a Novel Lysolipid Mediator of Epithelial-to-Mesenchymal Transition by Human Retinal Pigmented Epithelial (RPE) Cells. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5727.
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Proliferative vitreoretinopathy (PVR) is a retinal disorder characterized by the formation of abnormal vitreal, preretinal and subretinal fibrotic membranes and bands following retinal detachment and is often associated with a poor visual outcome. RPE cells are one of the key players in PVR and contribute to the formation of fibrocontractile sheets of scar tissue that promote retinal folding and tractional, recurrent retinal detachments. Previously, PVR was believed to result, at least in part, from increased concentrations of protein growth factors within the vitreous humor of the eye. In a process referred to as epithelial-to-mesenchymal transition (EMT), these growth factors promote transformation of normal RPE cells into fibrocontractile, myofibroblasts-like cells that exhibit prominent, α-smooth muscle actin (α-SMA)-containing stress fibers. Here we demonstrate for the first time that a previously unrecognized factor, the bioactive lysolipid sphingosine-1-phosphate (S1P), promotes EMT, profibrotic protein expression and collagen gel contraction by human RPE cells in a manner that may promote PVR.
S1P was detected in rabbit vitreous fluid (n=10) using ELISA and intracellular localization of S1P was examined in human RPE cells using immunohistochemistry. RNA expression of S1P receptors and sphingosine kinases (proteins responsible for S1P production) were analyzed using RT-PCR and α-SMA (a myofibroblast marker) and plasminogen activator inhibitor-1 (PAI-1; a fibrotic marker) protein expression were measured using immunoblot. Gel contraction was analyzed using RPE-embedded collagen gels.
S1P is present in normal rabbit vitreous fluid at approximately 120 nM (N=10). Human RPE cells exhibited intracellular localization of S1P and prominent S1P receptor and sphingosine kinase RNA expression. S1P stimulated α-SMA and PAI-1 protein expression by 66 % and 21%, respectively, by human RPE cells in culture and promoted gel contraction by 16% in RPE-embedded collagen gels.
Combined these data provide evidence that human RPE cells have the molecular ability to produce and respond to S1P and that this novel lysolipid regulatory factor, promotes EMT of human RPE cells. This data suggests that S1P may play a previously unrecognized role in the fibrocontractive ocular disorder PVR
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