UV-INDUCED APOPTOSIS IN SKIN EQUIVALENTS - INHIBITION BY PHORBOL ESTER AND BCL-2 OVEREXPRESSION

To determine the role of apoptosis in epidermal homeostasis and to ide ntify its regulators in skin, we have developed and characterised a ph ysiologically relevant in vitro model of epidermal apoptosis. First, w e show that keratinocyte cell death can be induced by ultraviolet irra diation within the stratified epidermis of the skin equivalent in an i n vivo-like manner. DNA fragmentation and changes in the patterns of e xpression of p53 and Bcl-2 suggest that the mechanisms operating in UV -induced apoptosis in the skin equivalent are controlled by these fact ors. Secondly, we demonstrate that apoptosis in this model is amenable to modulation by exogenous factors present in the culture medium, suc h as phorbol ester, and by tranfected genes, as shown by overexpressio n of bcl-2. These studies show that the skin equivalent is a valuable model in which to determine the controllable steps of the apoptotic pa thway independently of the immune system and to correlate apoptosis to the physiologic state of the keratinocyte.