Development and cellular functions of the iris pigment epithelium

A number of studies have shown that transplantation of retinal pigment epit helial (RPE) cells to the subretinal space offers a promising treatment mod ality for retinal degenerative diseases. However, it is necessary to transp lant autologous cells to avoid rejection; unfortunately, obtaining autologo us RPE cells necessitates such traumatic surgical intervention as to make t his approach irrelevant. It has been hypothesized that iris pigment epithel ial (IPE) cells may be a possible substitute for RPE cells for transplantat ion into the subretinal space. The iris pigment epithelium, which has the s ame embryonic origin as retinal pigment epithelium, has not received much a ttention from visual scientists. Even though it forms a highly specialized tissue, it is not clear whether the iris pigment epithelium contributes cri tical functions to the health of the visual system. In vivo the IPE does no t appear to have any of the functions characteristic of RPE; however, in vi tro cultured IPE cells do acquire functions, such as specific phagocytosis of rod outer segments, that are characteristic of RPE cells, and have been shown to have the potential to carry out many functions characteristic of R PE cells, e.g., retinol metabolism. The review outlines the development and cellular functions of the IPE with special emphasis on the modulation of t hose functions that can allow the IPE cells to be transplanted to the subre tinal space where they appear to acquire differentiated properties of retin al pigment epithelium (RPE). (C) 2001 Elsevier Science Inc. All rights rese rved.