Side population cells in human and mouse epidermis lack stem cell characteristics

Area of Science:

• Cell biology
• Dermatology
• Stem cell research

Background:

• Side population (sp) cells, identified by Hoechst 33342 exclusion via flow fluorimetry, are found in various tissues and can function as multipotent stem cells.
• The presence and function of sp cells within the epidermis, termed epidermal sp (Esp) cells, remain largely uncharacterized.

Purpose of the Study:

• To investigate the existence of Esp cells in mouse and human epidermis.
• To determine if Esp cells represent epidermal stem cells.
• To characterize the molecular markers and location of Esp cells.

Main Methods:

• Flow fluorimetry analysis using Hoechst 33342 dye to identify sp cells.
• Immunohistochemical analysis of marker gene expression (alpha6 integrin, sca-1, MHC class II, Flk1, beta1 integrin, ABCG2) in mouse and human skin samples.
• Analysis of label-retaining cells and cell cycling status.

Main Results:

• Esp cells were identified in both mouse and human epidermis.
• In mice, Esp cells are a subpopulation of alpha6 integrin-positive basal cells, expressing sca-1 and negative for MHC class II and Flk1. They are cycling cells but distinct from label-retaining cells.
• Human Esp cells express the transporter ABCG2, with high expression in sweat gland duct epithelium and low expression in the epidermal basal layer. Beta1 integrin levels were not significantly high.

Conclusions:

• Epidermal side population cells (Esp cells) exist in both mouse and human skin.
• Esp cells represent a distinct subpopulation of basal keratinocytes with potential stem cell characteristics.
• The transporter ABCG2 is a key marker for human Esp cells, suggesting its role in their function or identification.