Pigment epithelium derived factor, originally identified in conditioned medium of cultured human fetal retinal pigment epithelial (RPE) cells, is a neurotrophic protein that induces extensive neuronal differentiation in human Y79 retinoblastoma cells, a neoplastic counterpart of normal retinoblasts. It has been suggested that PEDF is synthesized by RPE cells and secreted into the retina interphotoreceptor matrix where it may influence development/differentiation of the neural retina. PEDF is a potent inhibitor of angiogenesis. As it does not undergo the S (stressed) to R (relaxed) conformational transition characteristic of active serpins, it exhibits no serine protease inhibitory activity. The PEDF gene is a member of the serpin gene family. Serpins are a group of serine protease inhibitors, some of which have also been reported to exhibit neurotrophic activity.
