Cellular and hormonal regulation of pigmentation in human ocular melanocytes

The purpose of this study was to examine some of the factors that may be re levant to regulating pigmentation in the human eye, specifically whether ch oroidal and iridial melanocytes are sensitive to regulation by epithelial a nd stromal cells and alpha -melanocyte stimulating hormone (alpha -MSH). Hu man choroidal and iridial melanocytes were established in culture and co-cu ltured with epithelial cells and stromal cells derived both from skin and f rom eye in order to determine their influence on choroidal and iridial mela nocyte dopa oxidase activity. In all cases, co-culture of melanocytes with either epithelial cells or fibroblasts led to an increase in dopa oxidase a ctivity during 5 days of co-culture. The extent of the increase ranged from 60% (non-significant) to as much as 185% when both fibroblasts and keratin ocytes were present. The optimal ratio of fibroblasts to melanocytes was 1: 10 (for dermal fibroblasts) or 1:2 (for iridial fibroblasts) and 1:1 for al l epithelial cells to melanocytes. Both choroidal (three out of three cultu res) and iridial (two out of three cultures) melanocytes showed increases i n dopa oxidase activity to alpha -MSH when cultured in Green's media but th e same cells cultured in MCDB153 were unresponsive to alpha -MSH. These in vitro studies suggest that ocular melanocytes have the capacity to be influ enced by adjacent epithelial and stromal cells with respect to pigmentation .