Isolation of a retinal pigment epithelial cell-derived fraction which promotes Muller cell proliferation

Retinal pigment epithelial cells (RPE) secrete a factor(s) in vitro which p romotes Muller cell proliferation. To begin the isolation of the active fac tor, medium conditioned by cultured RPE (RPE-CM) was fractionated by fast p rotein liquid chromatography. The fractions were tested in an assay for Mul ler cell proliferation and it was found that one fraction contained biologi cal activity comparable to that of complete RPE-CM. Gel electrophoresis dem onstrated that this fraction consisted of proteins with approximate molecul ar masses of 35-88 kDa. An affinity assay revealed that only an 88-kDa prot ein in the RPE-CM binds to Muller cells. This protein was also present in t he active fraction; therefore, it is the most likely source of the mitogeni c activity of RPE-CM. (C) 2000 Elsevier Science B.V. All rights reserved.