Epidermal stem cells and skin tissue engineering in hair follicle regeneration

Abstract

The reconstitution of a fully organized and functional hair follicle from dissociated cells propagated under defined tissue culture conditions is a challenge still pending in tissue engineering. The loss of hair follicles caused by injuries or pathologies such as alopecias not only affects the patients´ psychological well-being, but also endangers certain inherent functions of the skin. It is then of great interest to find different strategies aiming to regenerate or neogenerate the hair follicle under conditions proper of an adult individual. Based upon current knowledge of the epithelial and dermal cells involved in embryonic hair generation and adult hair cycling, and of the epithelial-mesenchymal interactions among them, many researchers have tried to obtain mature hair follicles using different strategies and approaches depending on the causes of hair loss. This review summarizes current advances in the different experimental strategies to regenerate or neogenerate hair follicles, with emphasis on those involving neogenesis of hair follicles in adults from isolated cells and tissue engineering. Most of these experiments were performed using rodent cells, particularly from embryonic or newborn origin. However, no successful strategy to generate human hair follicles from adult cells has yet been reported. This review identifies several issues that should be considered to achieve this objective. Perhaps the most important challenge is to provide the cells with three-dimensional culture conditions mimicking the structure of living tissue. Improving culture conditions that allow the expansion of specific cells without losing their inductive properties, as well as methods of selecting populations of epithelial stem cells should give us the necessary tools to overcome the difficulties that constrain human hair follicle neogenesis. An analysis of patents trends shows that the number of patent applications aiming to hair follicle regeneration and neogenesis has been growing during the last decade, and this field is attractive not only to academic researchers but also to the companies that own almost half of the patents in this field.