Editors' ChoiceBaldness

Stemming Hair Loss

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Science Translational Medicine  23 Feb 2011:
Vol. 3, Issue 71, pp. 71ec24
DOI: 10.1126/scitranslmed.3002276

"A hair in the head is worth two in the brush," quipped writer Oliver Herford. But that statement holds only if hair loss—alopecia—is irreversible. Scarring alopecias caused by such maladies as lupus erythematosus and graft-versus-host disease give rise to permanent hair loss caused by ablation of hair follicle stem cells. In reversible hair-loss conditions caused by inflammation (nonscarring alopecia), follicular progenitor cells are depleted, but their stem cell counterparts are spared. Once inflammation is quelled, follicles can be regenerated from the surviving stem cells and hair can regrow. Now, Garza et al. present evidence that androgenetic alopecia—male pattern baldness—might fall in the reversible category.

Within hair follicles, a structure called the bulge houses a population of small quiescent stem cells that divide when a new hair-growth cycle begins. This division generates progenitor cells that produce new hair shafts. Because male pattern baldness is associated with a reduction in follicle size that can result from the demise of either stem or progenitor cells, the authors looked for both cell types in scalp samples taken from bald and hair-containing regions of the same individuals. Using flow cytometry to compare the size, cell-cycling properties, and protein markers of the cell populations, they found that bald scalp contained a normal-sized population of small quiescent cells (KRT15hi cells) but were deficient in two larger dividing cell types—CD200hiITGA6hi and CD34hi cells. After showing that mice contain a CD200hiITGA6hi cell population that is analogous to the human one, the authors tested the ability of the prospective mouse progenitor cells to regenerate hair follicles in a skin reconstitution assay carried out in a mouse model. When the CD200hiItga6hi cells were combined with neonatal dermal skin cells, hair follicles were produced. Histological analysis revealed that CD200hiItga6hi cells were indeed multipotent in that they gave rise to various types of hair follicle structures, including the outer root sheath, the inner root sheath, and the sebaceous gland.

The observation that follicles from the hairless scalps of subjects with male pattern baldness retain stem-like cells but lack progenitor cells suggests that this kind of alopecia may be reversible. Researchers must now try to decipher the defect that blocks the quiescent-to-dividing cell conversion. A better understanding of the root causes of male pattern baldness may spur the discovery of treatments for this distressing condition—a turn of events that would reduce the stress of frequently finding hairs in the comb, brush, or drain.

L. A. Garza et al., Bald scalp in men with androgenetic alopecia retains hair follicle stem cells but lacks CD200-rich and CD34-positive hair follicle progenitor cells. J. Clin. Invest. 121, 613–622 (2011). [Full Text]

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