Cell kinetic characterization of cultured human keratinocytes from normal and psoriatic individuals

Psoriasis is a chronic skin disease characterized by epidermal hyperproliferation, disturbed differentiation, and inflammation. It is still a matter of debate whether the pathogenesis of psoriasis is based on immunological mechanisms, on defective growth control mechanisms, or possibly on a combination of both. Several in vivo cell biological differences between psoriatic lesional epidermis and normal epidermis have been reported. However, it is not clear whether these changes are causal or consequential. In case that keratinocytes from psoriatic patients have genetically determined deficiencies or polymorphisms with respect to autocrine growth regulation and the response to inflammatory cytokines, we hypothesize that these differences should be maintained in culture. Here we have started a systematic comparison of first passage keratinocytes cultured from normal skin and uninvolved psoriatic skin to address the question whether there are intrinsic differences in basic cell cycle parameters. In an established, defined culture system using keratinocyte growth medium (KGM) we have determined: (i) cell cycle parameters of exponentially growing keratinocytes, (ii) induction of quiescence by transforming growth factor beta 1 (TGF-beta 1) and (iii) restimulation from the G0-phase of the cell cycle. Bivariate analysis of lodo-deoxyuridine incorporation and relative DNA content was performed by flow cytometry. Within the limitations of this model no gross differences were found between normal and psoriatic keratinocytes with respect to S-phase duration (Ts), total cell cycle duration (Tc), responsiveness to TGF-beta 1 and the kinetics for recruitment from G0. In psoriatic keratinocytes we found a lower amount of cell in S-phase and a shorter duration of G1, compared to normal keratinocytes. The methodology developed here provides us with a model for further studies on differences between normal and psoriatic keratinocytes in their response to immunological and inflammatory mediators.