Collagen gel contraction induced by retinal pigment epithelial cells and choroidal fibroblasts involves the protein kinase C pathway

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Abstract
Contraction of intraocular fibrous membranes is an important feature in the pathogenesis of retinal detachment in proliferative vitreoretinopathy (PVR). Collagen gel contraction is a useful in vitro model of membrane contraction in PVR. We studied the role of protein kinase C (PKC) in collagen gel contraction induced by bovine choroidal fibroblasts and retinal pigment epithelial (RPE) cells. Collagen gels embedded with the cells were formed in culture dishes and gel contraction was evaluated. The PKC stimulator, phorbol 12-myristate 13-acetate (PMA), and the protein phosphatase 1 and 2A inhibitor, okadaic acid (OA), were used to evaluate the role of the PKC-mediated phosphorylation system in this gel contraction. Fifteen min incubation with PMA stimulated gel contraction, but 180 min incubation had no effect. Choroidal fibroblast-but not RPE cell-induced gel contraction was stimulated by OA. These effects were inhibited by the broad spectrum protein kinase inhibitor staurosporine and the specific PKC antagonist calphostin C. Transforming growth factor-β (TGF-β)1 and TGF-β2, which are known to be present in eyes with PVR, were evaluated to determine their effect on gel contraction. Both TGF-β1 and 2 had a stimulatory effect on contraction of gels seeded with choroidal fibroblasts and RPE cells, but staurosporine and calphostin C inhibited this TGF-β-induced gel contraction. These results indicate that activation of PKC/protein phosphorylation is an important factor in gel contraction caused by choroidal fibroblasts and RPE cells, and that TGF-β-induced gel contraction is mediated at least in part via the PKC pathway.