Functional characterization of beta1-integrin-positive epidermal cell populations.

Epidermal keratinocytes are heterogeneous and can be divided into stem cells (strong beta1-integrin expression) with unlimited clonogenic potential, transient amplifying cells (weaker beta1-integrin expression) with restricted proliferative capacity and terminally differentiated cells (no beta1-integrin expression) that have lost the capacity to divide. We tested the hypothesis that cell kinetic characteristics of the epidermal subpopulations differ. Single cell suspensions from small human skin punch biopsies were sorted flow cytometrically into a beta1-integrin weakly positive (dim) and strongly positive (bright) subpopulation and the clonogenic potential was compared in cell culture experiments. Image analysis was used to determine growth characteristics of the colonies. We found that cell size in the beta1-integrin bright subpopulation increased when colonies aged, whereas this was constant in the dim subpopulation. The total number of colonies formed and the growth rate of the colonies were higher in the beta1-integrin dim cells than in the bright subpopulation. Experimental data from this study confirm the hypothesis that cell kinetic characteristics of beta1-integrin dim and bright cells are different. Combining flow cytometric sorting, cell culture and image analysis provides powerful means for phenotypical and functional characterization of epidermal subpopulations.