GROWTH-CHARACTERISTICS AND ULTRASTRUCTURE OF HUMAN RETINAL-PIGMENT EPITHELIUM INVITRO

Abstract

The in vitro growth characteristics and morphology of human retinal pigment epithelium (RPE) cells from adult donor eyes (15-100 yr old) were studied. RPE cells are viable in culture for several months, but only a fraction of the cells actually divide. Rapid cell proliferation and confluency of a culture occur from 10-30 days after seeding. The time for confluency is age- and media-dependent; the number of cells that are potential dividers and contribute to confluency decreases with increasing donor age. Since melanolipofuscin granules do not form in vitro and are diluted by cell division, stationary (nondividing) cells are distinguished from the dividing cells by the presence of dense clusters of melanolipofuscin granules in the stationary cells. Confluent cultures contain a monolayer of relatively clear polygonal cells with density pigmented stationary cells scattered throughout. Stationary cells often represent up to 95% of the original RPE cell population. Ultrastructurally all cells appear epithelioid with apical-basal polarity, junctional complexes and cytoplasmic organization characteristic of RPE cells in vivo. Stationary cells are extremely large with melanolipofuscin granules clustered around the nucleus. Melanolipofuscin is a unique marker for nondividing cells and may elucidate the age-dependent loss of replicability of human RPE.