Hogg, Penelope Ann; (1994) Behavioural characteristics of the cells which form epiretinal membranes. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Epiretinal membranes are contractile cellular proliferations that form on the surfaces of the retina after trauma or insult to the posterior segment of the eye. Key cell types involved in membrane formation are retinal glia, retinal pigment epithelia and fibroblastic cells. A bovine tissue culture test system comprising bovine retinal glia, bovine retinal pigment epithelia and bovine scleral fibroblasts was employed in a series of behavioural studies to investigate the effect of soluble mediators and cell contact on migration, settlement and proliferation of the three key cell types in membrane formation. Migration was assessed in vitro in a modified 48-well Boyden chamber, employing a standard chemoattraction assay. The migration of all three test cell types was stimulated by a glycoprotein found abundantly in epiretinal membranes (fibronectin), samples of subretinal fluid and a retinal crude extract. Cells grown from epiretinal membranes removed during surgery for retinal detachment also migrated to fibronectin. Retinal pigment epithelial cells showed less aptitude for migration to soluble stimuli in a Boyden chamber than the other two cell types and when the cell types were labelled and migrated together, the retinal pigment epithelium still migrated less than the other two cell types. Retinal pigment epithelium were also less responsive to platelet derived growth factor. Static cell settlement studies demonstrated that retinal pigment epithelial cells showed more affinity for settlement onto plastic and in the presence of soluble fibronectin, than the other two cell types but the surface of a retinal glial monolayer appeared to be a less attractive substrate than serum coated plastic for the settlement of all three cell types. Video time-lapse microscopy was employed to monitor the settlement of retinal pigment epithelium onto glial and mixed cell layers. It revealed that the settlement process, in which distinct and reproducible stages could be identified, to be one of invasion and incorporation of the test cell types into the underlying cell layer. The fibroblasts entered a glial monolayer more rapidly than the pigment epithelia but the latter after entry, provoked a wave of glial mitotic activity. The results indicated that within the confines of the test system there was interaction between the cell types, both through cell contact and remotely via soluble mediators and these affected the behavioural responses of migration, settlement and proliferation. The findings when extrapolated to epiretinal membrane formation indicated that: the glia were not a particularly good substrate for either fibroblasts or retinal pigment epithelium. The glia secreted substances attractive for the settlement of the retinal pigment epithelium and for the migration of all three cell types and media collected from cultures of retinal pigment epithelial cells was stimulatory for a whole range of activities and provoked a powerful migratory response from the fibroblasts. So that the retinal pigment epithelium though possibly not the most important cell type in epiretinal membranes have an important role in membrane formation by releasing bioactive substances which attract and modify the behaviour of other cell types.

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