Through the Lens of Hair Follicle Neogenesis: A New Focus on Mechanisms of Skin Regeneration After Wounding

The 2020 review discussed wound-induced hair follicle neogenesis (WIHN), a process where functional hair follicles regenerate in large wounds in adult mammalian skin. This process, similar to embryonic hair development, requires Wnt signaling in the epidermis. Differences include the critical role of TLR3 mediated double stranded RNA sensing for regeneration, which activates retinoic acid signaling after wounding. Inflammatory cells, such as Fgf9-producing y-8 T cells and macrophages, were identified as important mediators of WIHN. Shh signaling, not necessary in embryonic hair follicle development, plays a major role in WIHN and may redirect cells fated to scarring wounds into a regenerative phenotype. The study suggested that understanding WIHN could lead to new treatments for hair-related disorders or fibrotic scarring.