Skin: a promising reservoir for adult stem cell populations.

Plasticity of adult cells has been identified in several post-natal tissues in the past few years and has attracted special attention in regenerative medicine. Skin is the biggest organ in the body. Adult skin consists of epidermis, dermis and appendages such as hairs and glands which are linked to the epidermis but project deep into the dermal layer. Skin stem cell biology has been a focus of increasing interest in current life science. Committed stem cells with limited differentiation potential for regeneration and repair of epidermis have been known for decades. Recent studies further report that adult skin tissues contain cell populations with pluripotent characteristics. Multipotent stem cells from hair follicle and non-follicular skin, both in epidermal and dermal tissues, are found to have the differentiation capacity to generate multiple cell lineages. Basing on the present data, our hypothesis is that skin may serve as a local reservoir of various adult stem cell populations, including committed stem cell populations and pluripotent stem cell populations both in epidermal and dermal tissues. Given its easy accessibility, stem cells in skin will not only provide an experimental model for skin biology, but also may provide an experimental model for studying the epithelial-mesenchymal interactions of several other organs outside of skin. The stem cell populations in skin tissues may also have extensive therapeutic implications in the replacement of skin and may serve as an alternative source of stem cells for several other organs outside of skin. The in situ activation and mobilization of stem cell populations in the skin is an ideal way to renew and repair epidermis and dermis, even appendages.