Photoreceptor renewal and the pigment epithelium - Congratulations to a pioneer in research on the retina

In 1999, a pioneer in retinal cell biology celebrates his seventieth birthd ay: Richard W. Young, Professor of Anatomy at the Dept. of Anatomy and Jule s Stein Eye Institute, University of Southern California, Los Angeles, Cali fornia. USA. Against the current dogma of visual cells as static structures he demonstrated that they undergo continual renewal of their light-sensiti ve outer segments. Entire membranes and/or single molecules are being repla ced, and the tips of outer segments are shed (disk-shedding), and phagocyti zed and degrade by pigment epithelial (PE) cells. About 100 disks are made per rod within 24 hours, and about 30 000 disk membranes from overlying rod s are degradet by one PE cell thus rendering the PE one of the most active phagocytic systems of the body. It is not surprising, therefore, that the a ge pigment lipofuscin accumulates within PE cells, which is mainly composed of undigestible outer segment material. It is generally concludet that lip ofuscin can contribute to the pathogenesis of age related macular degenerat ion (AMD). Early on Young has postulated that light exposure may accelerate AMD and some forms of retinitis pigmentosa (RP). Today we know that indeed in several animal models of RP light exposure can significantly enhance th e disease progression. With a similar insight and intuition he described ap optosis of the retina thus preceding the "apoptotic wave" in eye research. Apoptosis now is considered the final common death pathway of many retinal diseases including degenerations and dystrophies. With his work young has c reated may scientific children, who directly or indirectly were inspired by his pioneering work.