Detailed information about hair follicle stem cells

Hair Follicle Stem Cells

Stem cells

Stem cells which are found in all multi-cellular organisms are truly the building blocks of a living organism. Every single cell in the body “stems” from this kind of cell, hence the name – stem cells. Like actors awaiting a casting call, stem cells wait for a signal to tell them what to become. On receiving the right signal, undifferentiated cells get developed into any of the more than 200 types of cell the adult human body holds.

Since stem cells display such high level of plasticity, they can be used to replace or repair damaged cells, and have the potential to treat cell related diseases such as cancer, Alzheimer's and Parkinson's disease, paralysis, and hair regrowth.

Stem cells can be embryonic as with those stem cells taken from embryos. This source of stem cells is very controversial. However, everyone has stem cells in the tissues of their bodies – they are called “adult” stem cells. Using these cells in research and treatment development may be much less controversial.

Hair follicle stem cells

The epithelial stem cell niche is located in the hair follicle bulge, which is part of the outer root sheath that is in continuity with the interfollicular epidermis and sebaceous Gland. Hair grows from cells located at the base of the hair follicle. Hair follicles continuously cycle through growth, rest, and re-growth phases. Researchers have long suspected that stem cells located within the follicle bulge were responsible for hair growth.

Because of their quiescent nature and strategic location, bulge cells were postulated to be hair follicle stem cells in both mice and men. This hypothesis led to multiple studies that tested the notion that bulge stem cells in adult mice are multipotent and regenerate a lower hair follicle during normal cycling.

Lineage analysis definitively demonstrated that bulge cells give rise to all of the epithelial cell types in the normal regenerating lower follicle during anagen (i.e. the growth phase), in addition the cells also contribute to the sebaceous gland and overlying epidermis.

‘Competence’ of bulge cells

Recently, researchers addressed the therapeutically relevant question of whether isolated hair follicle bulge epithelial cells can generate new hair follicles. This became possible with the identification of bulge cell markers, CD34 and cytokeratin promoter activity.

It was shown that bulge cells do indeed retain their ‘competence’ for generating new hair follicles when removed from their environment or niche. This feat was only possible, however, when bulge cells were combined with ‘inductive’ dermal cells obtained from the skin dermis.

Although hair follicle bulge cells appear to be the only epithelial progenitors of the lower follicle in normal skin, this competence to form follicles is not exclusive to bulge cells.

Interfollicular epidermal cells also retain some capacity to generate new hair follicles both in situ and after isolation; however, the efficiency of bulge cells to form follicles appears greater, suggesting that starting with a pure population of stem cells would increase the effectiveness of cell-based therapies.

Additional studies suggest that other epithelia, cultured epithelial cells, corneal epithelium or amnion also have the capacity to generate hair follicles when juxtaposed with inductive dermal cells.

In fact, numerous types of stem cells, including embryonic, neural, and mesenchymal bone marrow all have the capacity to form skin and hair when introduced into mouse blastocysts. This raises the intriguing possibility that these other types of stem cell could be coaxed into forming hair follicles by the proper inductive cells.

Overall then, it seems that stem cells are very flexible. Stems cells form other parts of the body can form hair follicles thus triggering hair regrowth if given the correct signals. Equally, stem cells in hair follicles can also form other tissues if given the appropriate signals. Other articles on this web site discuss the transformation of hair follicle derived stem cells into adipocytes, blood cells, and even nerve cells.