Aging, differentiation and apoptosis in human epidermal keratinocytes in culture

Aging of human epidermal keratinocytes was studied by serial passaging them as a monolayer culture in a serum-free medium containing 0.09 M calcium. Under these conditions the cells were constantly kept in a proliferative mode and in an undifferentiated state. Aging characteristics in terms of growth and longevity, cumulative population doubling level, cell yield, protein content, and alterations in morphology and in macromolecular synthesis were studied. Furthermore, the induction of differentiation by raising the calcium concentration in the growth medium has facilitated the use of this system to address the issues of the relationship among aging, differentiation and apoptosis in keratinocytes in culture.