Presented at the 8th World Congress for Hair Research (2014) Jeju Island, South Korea.

Understanding molecular mechanisms for regeneration of hair follicles during wound healing provides new opportunities for developing treatments for hair loss and other skin disorders. We show that fibroblast growth factor 9 (fgf9) modulates hair follicle regeneration following wounding of adult mice. Inhibition of fgf9 during wound healing severely impedes this wound-induced hair follicle neogenesis (WIHN). Conversely, overexpression of fgf9 results in a 2-3 fold increase in the number of neogenic hair follicles. Remarkably, gamma-delta T cells in the wound dermis are the initial source of fgf9. Deletion of fgf9 gene in T cells in Lck-Cre;floxed fgf9 results in a marked reduction in WIHN. Similarly, mice lacking gamma-delta T cells demonstrate impaired follicular neogenesis.

We found that fgf9, secreted by gamma-delta T cells, initiates a regenerative response by triggering Wnt expression and subsequent Wnt activation in wound fibroblasts. Employing a unique feedback mechanism, activated fibroblasts then express fgf9, thus amplifying Wnt activity throughout the wound dermis during a critical phase of skin regeneration. Strikingly, humans lack a robust population of resident dermal gamma-delta T cells, potentially explaining their inability to regenerate hair.

These findings which highlight the essential relationship between the immune system and tissue regeneration, establish the importance of fgf9 in hair follicle regeneration and suggests its applicability for therapeutic use in humans.

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Dr George Cotsarelis: Hair Follicle Stem Cells & Skin ...