PRODUCTION OF PLATELET-DERIVED GROWTH-FACTOR BY INTERLEUKIN-1-BETA AND TRANSFORMING GROWTH FACTOR-BETA-STIMULATED RETINAL-PIGMENT EPITHELIAL-CELLS LEADS TO CONTRACTION OF COLLAGEN GELS

Purpose. In an in vitro model of the later contractile stages of proli ferative vitreoretinopathy, interleukin-1 beta (IL-1 beta) and transfo rming growth factor-beta (TGF-beta) stimulate the contraction of colla gen gels by retinal pigment epithelial (RPE) cells. This contraction o ccurs after a lag period and appears not to be a direct effect of the cytokines but is mediated by another factor produced in the presence o f the two cytokines. The nature of this factor has been investigated. Methods. Human RPE cells were seeded onto collagen gels in the presenc e of IL-1 beta and TGF-beta. After 24 hours, the conditioned medium wa s removed and added to new collagen gels seeded with RPE cells, and th e diameter of the collagen gels was measured after various intervals. The ability of the conditioned medium to effect contraction was determ ined after various treatments, including size fractionation, heating, trypsin digestion, and binding to heparin-Sepharose. The involvement o f platelet-derived growth factor (PDGF) as a stimulator of contraction was tested with neutralizing antibodies and by polymerase chain react ion analyses of specific mRNAs. Results. IL-1 beta and TGF-beta cause RPE cells to contract after a delay of up to 24 hours, whereas conditi oned medium from cytokine-treated cells results in immediate contracti on in a manner similar to that of serum. The factor in the conditioned medium causing immediate contraction was found to be heal-stable, try psin-sensitive, and resistant to extremes of pH. It has a size of betw een 30 and 50 kDa and binds heparin. The Factor in conditioned medium from cytokine-treated cells does not act in the presence of C-kinase i nhibitors or cycloheximide, suggesting that signaling is mediated by w ay of protein kinase C and new protein synthesis. Stimulation of contr action by conditioned medium is inhibited by anti-PDGF antibodies, and contraction is stimulated by human PDGF. Conclusions. Contraction in the presence of cytokines is mediated by the production of PDGF; or a PDGF-like molecule. This factor could have implications in the pathoge nesis of proliferative vitreoretinopathy.