Atmospheric oxygen accelerates the induction of a post-mitotic phenotype in human dermal fibroblasts: the key protective role of glutathione

It has been proposed that ageing of human dermal fibroblasts occurs as a mu lti-stage process during which cells pl-ogress from a mitotic to a post-mit otic state. We describe the development of a simple and novel cell-cloning model for identifying and quantifying the different fibroblast morphotypes associated with the induction of post mitotic behaviour. We have found that under atmospheric (20%) oxygen tension a significant proportion of human d ermal fibroblasts are rapidly induced to switch from a mitotic to a post-mi totic phenotype. In contrast, under more physiological (4%) oxygen conditio ns, the induction of a post-mitotic phenotype is largely prevented. Increas ing oxidative stress by addition of hydrogen peroxide or depletion of gluta thione also induced a switch from a mitotic to a post-mitotic phenotype in these cells, whereas addition of the anti-oxidant N-acetylcysteine under at mospheric (20%) oxygen tension potently inhibited this process. In addition , a statistically significant correlation was observed between the magnitud e of intracellular glutathione depletion and the reduction in the populatio n of mitotic cells in this model. We propose that the switch from a mitotic to a post-mitotic phenotype represents a process of cellular ageing and th at standard atmospheric oxygen tension imposes a substantial oxidative stre ss on dermal fibroblasts which accelerates this process in culture. The dat a also suggest that intracellular glutathione levels strongly influence the induction of a post-mitotic phenotype and that, by implication, depletion of glutathione may play a significant role in the progression of cellular a geing in human skin.