MITOGENESIS AND RETINAL-PIGMENT EPITHELIAL-CELL ANTIGEN EXPRESSION INTHE RAT AFTER KRYPTON LASER PHOTOCOAGULATION

Purpose. Polypeptide growth factors, such as the acidic and basic fibr oblast growth factors (aFGF and bFGF), may be important in the pathoge nesis of subretinal neovascularization. The authors studied the relati onship of aFGF and bFGF expression to retinal pigment epithelial (RPE) cell and choriocapillary endothelial cell proliferation in krypton-la ser-treated regions of the retina, RPE, and choroid of a model of subr etinal neovascularization in the pigmented rat they developed. Methods . Multiple krypton laser burns were applied to the posterior poles of the eyes of pigmented rats according to a protocol described for produ cing subretinal neovascularization in these animals. At intervals up t o 80 days after treatment, the retinas, RPE, and choroid of these anim als were examined by [H-3]-thymidine autoradiography and electron micr oscopic immunocytochemistry, using antibodies to aFGF, bFGF, cytoplasm ic retinaldehyde-binding protein, opsin, and various basement membrane macromolecules. Results. Nuclear radiolabeling became evident in thes e layers when the label was injected as late as 75 days after photocoa gulation, but the number of labeled nuclei was greatest when isotope w as injected 2-5 days after laser treatment. Although there were labele d nuclei in the retina, RPE, and choroid, the frequency of labeling as a fraction of the total number of nuclei appeared to be greatest in t he RPE and choriocapillaris. Non-laser-damaged RPE cells were immunocy tochemically strongly positive for cytoplasmic retinaldehyde-binding p rotein, but were negative for aFGF and bFGF. After laser treatment, ma ny RPE cells lost their cytoplasmic retinaldehyde-binding protein posi tivity but stained strongly for aFGF and bFGF within intracellular str uctures of variable shape and homogeneous appearance. Although these s tructures had an appearance suggestive of basement membrane, they did not stain with antibodies to collagens type IV or V, to laminin, or to heparan sulfate proteoglycan core protein. They also did not stain wi th an antibody to the N-terminal peptide of opsin. Choriocapillary end othelial cells were unreactive with antibodies to aFGF, bFGF, or cytop lasmic retinaldehyde-binding protein either before or after laser trea tment. FGF-positive RPE cells persisted for the 80-day duration of the experiment. Conclusions. Because the presence of FGF-positive RPE cel ls coincides temporally with increased nuclear thymidine labeling in t he RPE and choriocapillaris, aFGF and/or bFGF may be at least partly r esponsible for initiating the process of cell proliferation and subret inal neovascularization in these animals.