No / Several lines of evidence support an autoimmune basis for alopecia areata (AA), a common putative autoimmune hair loss disorder. However, definitive support is lacking largely because the identity of hair follicle (HF) autoantigen(s) involved in its pathogenesis remains unknown. Here, we isolated AA-reactive HF-specific antigens from normal human scalp anagen HF extracts by immunoprecipitation using serum antibodies from 10 AA patients. Samples were analyzed by LC-MALDI-TOF/TOF mass spectrometry, which indicated strong reactivity to the hair growth phase-specific structural protein trichohyalin in all AA sera. Keratin 16 (K16) was also identified as another potential AA-relevant target HF antigen. Double immunofluorescence studies using AA (and control sera) together with a monoclonal antibody to trichohyalin revealed that AA sera contained immunoreactivity that colocalized with trichohyalin in the growth phase-specific inner root sheath of HF. Furthermore, a partial colocalization of AA serum reactivity with anti-K16 antibody was observed in the outer root sheath of the HF. In summary, this study supports the involvement of an immune response to anagen-specific HFs antigens in AA and specifically suggests that an immune response to trichohyalin and K16 may have a role in the pathogenesis of the enigmatic disorder.

No / The Rho family GTPases Cdc42 and Rac1 are critical regulators of the actin cytoskeleton and are essential for skin and hair function. Wiskott-Aldrich syndrome family proteins act downstream of these GTPases, controlling actin assembly and cytoskeletal reorganization, but their role in epithelial cells has not been characterized in vivo. Here, we used a conditional knockout approach to assess the role of neural Wiskott-Aldrich syndrome protein (N-WASP), the ubiquitously expressed Wiskott-Aldrich syndrome-like (WASL) protein, in mouse skin. We found that N-WASP deficiency in mouse skin led to severe alopecia, epidermal hyperproliferation, and ulceration, without obvious effects on epidermal differentiation and wound healing. Further analysis revealed that the observed alopecia was likely the result of a progressive and ultimately nearly complete block in hair follicle (HF) cycling by 5 months of age. N-WASP deficiency also led to abnormal proliferation of skin progenitor cells, resulting in their depletion over time. Furthermore, N-WASP deficiency in vitro and in vivo correlated with decreased GSK-3beta phosphorylation, decreased nuclear localization of beta-catenin in follicular keratinocytes, and decreased Wnt-dependent transcription. Our results indicate a critical role for N-WASP in skin function and HF cycling and identify a link between N-WASP and Wnt signaling. We therefore propose that N-WASP acts as a positive regulator of beta-catenin-dependent transcription, modulating differentiation of HF progenitor cells.

No / Androgens stimulate many hair follicles to alter hair colour and size via the hair growth cycle; in androgenetic alopecia tiny, pale hairs gradually replace large, pigmented ones. Since stem cell factor (SCF) is important in embryonic melanocyte migration and maintaining adult rodent pigmentation, we investigated SCF/c-Kit signalling in human hair follicles to determine whether this was altered in androgenetic alopecia. Quantitative immunohistochemistry detected three melanocyte-lineage markers and c-Kit in four focus areas: the epidermis, infundibulum, hair bulb (where pigment is formed) and mid-follicle outer root sheath (ORS). Colocalisation confirmed melanocyte c-Kit expression; cultured follicular melanocytes also exhibited c-Kit. Few ORS cells expressed differentiated melanocyte markers or c-Kit, but NKI/beteb antibody, which also recognises early melanocyte-lineage antigens, identified fourfold more cells, confirmed by colocalisation. Occasional similar bulbar cells were seen. Melanocyte distribution, concentration and c-Kit expression were unaltered in balding follicles. Androgenetic alopecia cultured dermal papilla cells secreted less SCF, measured by ELISA, than normal cells. This identifies three types of melanocyte-lineage cells in human follicles. The c-Kit expression by dendritic, pigmenting, bulbar melanocytes and rounded, differentiated, non-pigmenting ORS melanocytes implicate SCF in maintaining pigmentation and migration into regenerating hair bulbs. Less differentiated, c-Kit-independent cells in the mid-follicle ORS stem cell niche and occasionally in the bulb, presumably a local reserve for long scalp hair growth, implicate other factors in activating stem cells. Androgens appear to reduce alopecia hair colour by inhibiting dermal papilla SCF production, impeding bulbar melanocyte pigmentation. These results may facilitate new treatments for hair colour changes in hirsutism, alopecia or greying.

Balding causes widespread psychological distress but is poorly controlled. The commonest treatment, minoxidil, was originally an antihypertensive drug that promoted unwanted hair. We hypothesized that another serendipitous discovery, increased eyelash growth side-effects of prostamide F(2alpha)-related eyedrops for glaucoma, may be relevant for scalp alopecias. Eyelash hairs and follicles are highly specialized and remain unaffected by androgens that inhibit scalp follicles and stimulate many others. Therefore, we investigated whether non-eyelash follicles could respond to bimatoprost, a prostamide F(2alpha) analog recently licensed for eyelash hypotrichosis. Bimatoprost, at pharmacologically selective concentrations, increased hair synthesis in scalp follicle organ culture and advanced mouse pelage hair regrowth in vivo compared to vehicle alone. A prostamide receptor antagonist blocked isolated follicle growth, confirming a direct, receptor-mediated mechanism within follicles; RT-PCR analysis identified 3 relevant receptor genes in scalp follicles in vivo. Receptors were located in the key follicle regulator, the dermal papilla, by analyzing individual follicular structures and immunohistochemistry. Thus, bimatoprost stimulates human scalp follicles in culture and rodent pelage follicles in vivo, mirroring eyelash behavior, and scalp follicles contain bimatoprost-sensitive prostamide receptors in vivo. This highlights a new follicular signaling system and confirms that bimatoprost offers a novel, low-risk therapeutic approach for scalp alopecias.