CD133 Is a Marker for Long-Term Repopulating Murine Epidermal Stem Cells

Maintenance, repair, and renewal of the epidermis are thought to depend on a pool of dedicated epidermal stem cells (EpiSCs). Like for many somatic tissues, isolation of a nearly pure population of stem cells is a primary goal in cutaneous biology. We used a quantitative transplantation assay, using injection of keratinocytes into subcutis combined with limiting dilution analysis, to assess the long-term repopulating ability of putative murine EpiSC populations. Putative EpiSC populations were isolated by FACS sorting. The CD133+ population and the subpopulation of CD133+ cells that exhibits high mitochondrial membrane potential (DΨmhi) were enriched for long-term repopulating EpiSCs versus unfractionated cells (3.9- and 5.2-fold, respectively). Evidence for self-renewal capacity was obtained by serial transplantation of long-term epidermal repopulating units derived from CD133+ and CD133+ΔΨmhi keratinocytes. CD133+ keratinocytes were multipotent and produced significantly more hair follicles than CD133− cells. CD133+ cells were a subset of the previously described integrin α6+CD34+ bulge cell population, and 28.9±8.6% were label-retaining cells. Thus, murine keratinocytes within the CD133+ and CD133+ΔΨmhi populations contain EpiSCs that regenerate the epidermis for the long term, are self-renewing, multipotent, and label-retaining cells.