Effects of keratinocyte-secreted soluble factors on spreading, number of dendrites and cell-cell contacts of human epidermal melanocytes and dermal fibroblasts: a quantitative analysis.

We previously demonstrated that spreading and clustering of in vitro cultured human keratinocytes are autocrine-induced phenomena, mediated by keratinocyte-secreted soluble factor. In this paper, the effects of this factor on spreading, number of dendrites and cell-cell contacts of the two cellular components of skin, melanocytes and fibroblasts have been studied 24 h after plating cells on uncoated plastic surfaces in MCDB153 serum-free medium or in the same medium conditioned by keratinocytes (KCM). Spreading of melanocytes present in the epidermal cell population remained constant at increasing cell density, while that of keratinocytes showed a statistically significant increase. Moreover, time-course experiments showed that the rate of spreading was faster for melanocytes. At increasing epidermal cell density, a statistically significant increase in number of dendrites and cell-cell contacts of melanocytes was observed. Similar results were obtained when melanocytes were plated both in coculture with keratinocytes (as epidermal cell cultures) or as a pure cell population in keratinocyte conditioned medium (KCM), suggesting that the observed phenomena are due to keratinocyte-secreted soluble factors and not to direct keratinocyte-melanocyte interactions. The addition of nerve growth factor (NGF) to fresh medium or addition of an inactivating anti-NGF monoclonal antibody (alpha D11) to KCM did not affect the number of dendrites or cell-cell contacts of melanocytes. Keratinocyte-secreted soluble factor(s) present in KCM also dramatically influenced morphology and cell-cell contacts of human dermal fibroblasts.