Editors' ChoiceRegeneration

Regenerating Hair Follicles

Science's STKE  22 May 2007:
Vol. 2007, Issue 387, pp. tw176
DOI: 10.1126/stke.3872007tw176

Compared with newts and salamanders, adult humans (like other mammals) have a limited ability to regenerate tissues lost to injury, and the loss of adult hair follicles--complex structures comprising at least 10 cell types--has been considered permanent. Ito et al. observed structures that resembled early developing hair follicles in healing skin wounds in mice. Hair follicle neogenesis, which occurred in adult mice after injuries that resulted in healed wounds 0.25 cm2 or larger, was associated with expression of the same genes and proteins found during embryonic follicle development. Lineage analysis indicated that, rather than arising from existing hair follicle stem cells, the newly generated follicles arose from extrafollicular epidermal cells or infundibular cells (cells from the upper portion of the follicle, outside of the follicle stem cell niche). The new follicles proliferated and produced unpigmented hair and appeared to reestablish a hair follicle stem cell population. Wnt signaling has been implicated in hair follicle development, and expression of the Wnt inhibitor Dkk1 prevented hair follicle neogenesis, but not re-epithelialization. Similarly, deletion of epidermal Ctnnb1 (which encodes β-catenin) prior to injury blocked the formation of new hair follicles. In contrast, epidermal overexpression of Wnt7a enhanced wound-dependent hair follicle regeneration. Following injury, the processes of repair and regeneration often appear to compete (see Chuong); thus, the authors suggest that modulating Wnt signaling in wounds could provide a means of decreasing scarring and of treating alopecia.

M. Ito, Z. Yang, T. Andl, C. Cui, N. Kim, S.E. Millar, G. Cotsarelis, Wnt-dependent de novo hair follicle regeneration in adult mouse skin after wounding. Nature 447, 316-320 (2007). [PubMed]

C. M. Chuong, New hair from healing wounds. Nature 447, 265-266 (2007). [PubMed]