[show abstract][hide abstract] ABSTRACT: Epithelial stem cells (EpSCs) in the hair follicle bulge are required for hair follicle growth and cycling. The isolation and propagation of human EpSCs for tissue engineering purposes remains a challenge. Here we develop a strategy to differentiate human iPSCs (hiPSCs) into CD200(+)/ITGA6(+) EpSCs that can reconstitute the epithelial components of the hair follicle and interfollicular epidermis. The hiPSC-derived CD200(+)/ITGA6(+) cells show a similar gene expression signature as EpSCs directly isolated from human hair follicles. Human iPSC-derived CD200(+)/ITGA6(+) cells are capable of generating all hair follicle lineages including the hair shaft, and the inner and outer root sheaths in skin reconstitution assays. The regenerated hair follicles possess a KRT15(+) stem cell population and produce hair shafts expressing hair-specific keratins. These results suggest an approach for generating large numbers of human EpSCs for tissue engineering and new treatments for hair loss, wound healing and other degenerative skin disorders.
[show abstract][hide abstract] ABSTRACT: Wnt/β-catenin signaling is a central regulator of adult stem cells. Variable sensitivity of Wnt reporter transgenes, β-catenin's dual roles in adhesion and signaling, and hair follicle degradation and inflammation resulting from broad deletion of epithelial β-catenin have precluded clear understanding of Wnt/β-catenin's functions in adult skin stem cells. By inducibly deleting β-catenin globally in skin epithelia, only in hair follicle stem cells, or only in interfollicular epidermis and comparing the phenotypes with those caused by ectopic expression of the Wnt/β-catenin inhibitor Dkk1, we show that this pathway is necessary for hair follicle stem cell proliferation. However, β-catenin is not required within hair follicle stem cells for their maintenance, and follicles resume proliferating after ectopic Dkk1 has been removed, indicating persistence of functional progenitors. We further unexpectedly discovered a broader role for Wnt/β-catenin signaling in contributing to progenitor cell proliferation in nonhairy epithelia and interfollicular epidermis under homeostatic, but not inflammatory, conditions.
[show abstract][hide abstract] ABSTRACT: Understanding molecular mechanisms for regeneration of hair follicles provides new opportunities for developing treatments for hair loss and other skin disorders. Here we show that fibroblast growth factor 9 (Fgf9), initially secreted by γδ T cells, modulates hair follicle regeneration after wounding the skin of adult mice. Reducing Fgf9 expression decreases this wound-induced hair neogenesis (WIHN). Conversely, overexpression of Fgf9 results in a two- to threefold increase in the number of neogenic hair follicles. We found that Fgf9 from γδ T cells triggers Wnt expression and subsequent Wnt activation in wound fibroblasts. Through a unique feedback mechanism, activated fibroblasts then express Fgf9, thus amplifying Wnt activity throughout the wound dermis during a crucial phase of skin regeneration. Notably, humans lack a robust population of resident dermal γδ T cells, potentially explaining their inability to regenerate hair after wounding. These findings highlight the essential relationship between the immune system and tissue regeneration. The importance of Fgf9 in hair follicle regeneration suggests that it could be used therapeutically in humans.
[show abstract][hide abstract] ABSTRACT: Vitamin A (vitA) has many roles in human biology. With respect to hair, knockout mice for vitA receptor, hairless, and vitamin D genes have similar phenotypes, and follicle loss occurs during catagen. Hypovitaminosis A from inadequate vitA intake causes hair loss. This work suggests that dietary vitA may have a role in precipitating and maintaining alopecias as well.
Journal of Investigative Dermatology 02/2013; 133(2):285-6. · 6.19 Impact Factor
[show abstract][hide abstract] ABSTRACT: Activation of epithelial stem cells and efficient recruitment of their proliferating progeny plays a critical role in cutaneous wound healing. The reepithelialized wound epidermis has a mosaic composition consisting of progeny that can be traced back both to epidermal and several types of hair follicle stem cells. The contribution of hair follicle stem cells to wound epidermis is particularly intriguing as it involves lineage identity change from follicular to epidermal. Studies from our laboratory show that hair follicle-fated bulge stem cells commit only transient amplifying epidermal progeny that participate in the initial wound re-epithelialization, but eventually are outcompeted by other epidermal clones and largely disappear after a few months. Conversely, recently described stem cell populations residing in the isthmus portion of hair follicle contribute long-lasting progeny toward wound epidermis and, arguably, give rise to new inter-follicular epidermal stem cells. The role of epithelial stem cells during wound healing is not limited to regenerating stratified epidermis. By studying regenerative response in large cutaneous wounds, our laboratory uncovered that epithelial cells in the center of the wound can acquire greater morphogenetic plasticity and, together with the underlying wound dermis, can engage in an embryonic-like process of hair follicle neogenesis. Future studies should uncover cellular and signaling basis of this remarkable adult wound regeneration phenomenon.
Seminars in Cell and Developmental Biology 10/2012; · 6.20 Impact Factor
[show abstract][hide abstract] ABSTRACT: Testosterone is necessary for the development of male pattern baldness, known as androgenetic alopecia (AGA); yet, the mechanisms for decreased hair growth in this disorder are unclear. We show that prostaglandin D(2) synthase (PTGDS) is elevated at the mRNA and protein levels in bald scalp compared to haired scalp of men with AGA. The product of PTGDS enzyme activity, prostaglandin D(2) (PGD(2)), is similarly elevated in bald scalp. During normal follicle cycling in mice, Ptgds and PGD(2) levels increase immediately preceding the regression phase, suggesting an inhibitory effect on hair growth. We show that PGD(2) inhibits hair growth in explanted human hair follicles and when applied topically to mice. Hair growth inhibition requires the PGD(2) receptor G protein (heterotrimeric guanine nucleotide)-coupled receptor 44 (GPR44), but not the PGD(2) receptor 1 (PTGDR). Furthermore, we find that a transgenic mouse, K14-Ptgs2, which targets prostaglandin-endoperoxide synthase 2 expression to the skin, demonstrates elevated levels of PGD(2) in the skin and develops alopecia, follicular miniaturization, and sebaceous gland hyperplasia, which are all hallmarks of human AGA. These results define PGD(2) as an inhibitor of hair growth in AGA and suggest the PGD(2)-GPR44 pathway as a potential target for treatment.
Science translational medicine 03/2012; 4(126):126ra34. · 10.76 Impact Factor
[show abstract][hide abstract] ABSTRACT: Fox-Fordyce disease (FFD) is a relatively rare entity with a typical clinical presentation. Numerous studies have described unifying histopathological features of FFD, which together suggest a defect in the follicular infundibulum resulting in follicular dilation with keratin plugging, subsequent apocrine duct obstruction, and apocrine gland dilation, with eventual extravasation of the apocrine secretions as the primary histopathogenic events in the evolution of the disease.
We describe a case of FFD that developed in a 41-year-old woman 3 months after completing a series of axillary laser hair removal treatments, and we detail the clinical and histopathological changes typical for FFD.
Because defective infundibular maturation has been suggested to play a central role in the evolution of FFD, the close temporal relationship of laser hair therapy with the development of FFD suggests a causal role, which we continue to explore.
Archives of dermatology 05/2011; 147(5):573-6. · 4.76 Impact Factor
[show abstract][hide abstract] ABSTRACT: In vivo confocal scanning laser microscopy (CSLM) is a recently developed non-invasive technique for visualizing microscopic structures with the skin. CSLM has been used to characterize proliferative and inflammatory skin diseases, neoplastic skin lesions and pigmented lesions.
Here, we assessed the ability of CSLM to evaluate the formation of neogenic hair follicles after a full-thickness wound in mice.
Full-thickness wounds were made on the dorsal skin of 3-week-old mice. After scab detachment (SD), the number, width, length, space and volume of neogenic hair follicles were analyzed using CSLM. The results were compared with those from conventional methods, including staining for alkaline phosphatase (AP) and keratin 17 (K17) as well as histology.
Quantification of neogenic hair follicles using CSLM compared favorably with the results from direct measurements on isolated epidermal tissue after immunostaining for K17, a marker for the epithelial portion of new hair follicles. CSLM detected 89% of K17-stained follicles. CSLM more accurately quantified the number of new follicles compared with AP staining, which detects the dermal portion of the new follicle. The width and length measurement from CSLM and histology were very close and correlated with each other. The minimum length of a neogenic hair follicle that could be detected by CSLM was 21 μm. The space between neogenic hair follicles was decreased in histological sections compared with CSLM.
CSLM is an accurate and valuable method for counting and measuring neogenic hair follicles non-invasively. CSLM produces images similar to histology in mice. Measurements of microstructures using CSLM more accurately reflect actual sizes as this technique avoids fixation artifacts. In vivo visualization of developing follicles with CSLM allows the detection of serial changes in hair follicle formation, thus conserving the numbers of mice required for studies and improving the detection of temporal changes in developing hair follicles.
Skin Research and Technology 04/2011; 17(4):387-97. · 1.41 Impact Factor
[show abstract][hide abstract] ABSTRACT: Androgenetic alopecia (AGA), also known as common baldness, is characterized by a marked decrease in hair follicle size, which could be related to the loss of hair follicle stem or progenitor cells. To test this hypothesis, we analyzed bald and non-bald scalp from AGA individuals for the presence of hair follicle stem and progenitor cells. Cells expressing cytokeratin15 (KRT15), CD200, CD34, and integrin, α6 (ITGA6) were quantitated via flow cytometry. High levels of KRT15 expression correlated with stem cell properties of small cell size and quiescence. These KRT15(hi) stem cells were maintained in bald scalp samples. However, CD200(hi)ITGA6(hi) and CD34(hi) cell populations--which both possessed a progenitor phenotype, in that they localized closely to the stem cell-rich bulge area but were larger and more proliferative than the KRT15(hi) stem cells--were markedly diminished. In functional assays, analogous CD200(hi)Itga6(hi) cells from murine hair follicles were multipotent and generated new hair follicles in skin reconstitution assays. These findings support the notion that a defect in conversion of hair follicle stem cells to progenitor cells plays a role in the pathogenesis of AGA.
The Journal of clinical investigation 02/2011; 121(2):613-22. · 15.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: The cell of origin for basal cell carcinoma (BCC) remains controversial. In this issue of Cancer Cell, Wang et al. provide strong evidence that BCC arise from hair follicle stem cells.
Cancer cell 01/2011; 19(1):5-6. · 25.29 Impact Factor
[show abstract][hide abstract] ABSTRACT: Hair follicle stem cells in the epithelial bulge are responsible for the continual regeneration of the hair follicle during cycling. The bulge cells reside in a niche composed of dermal cells. The dermal compartment of the hair follicle consists of the dermal papilla and dermal sheath. Interactions between hair follicle epithelial and dermal cells are necessary for hair follicle morphogenesis during development and in hair reconstitution assays. Dermal papilla and dermal sheath cells express specific markers and possess distinctive morphology and behavior in culture. These cells can induce hair follicle differentiation in epithelial cells and are required in hair reconstitution assays either in the form of intact tissue, dissociated freshly prepared cells or cultured cells. This review will focus on hair follicle dermal cells since most therapeutic efforts to date have concentrated on this aspect of the hair follicle, with the idea that enriching hair-inductive dermal cell populations and expanding their number by culture while maintaining their properties, will establish an efficient hair reconstitution assay that could eventually have therapeutic implications.
Journal of dermatological science 12/2009; 57(1):2-11. · 3.71 Impact Factor
[show abstract][hide abstract] ABSTRACT: The hair follicle contributes cells to the interfollicular epidermis after wounding, but the functional role of these cells has not been resolved. To address this question, Langton et al. (this issue, 2008) take advantage of the Edaradd mutant mouse, which lacks hair follicles on its tail. They discover an initial sluggish response of the hairless tail epidermis to wounding that is rapidly compensated for by recruitment of epidermal cells from outside the normally responsive area. This suggests that the hair follicle is important but not necessary for normal wound healing.
Journal of Investigative Dermatology 06/2008; 128(5):1059-61. · 6.19 Impact Factor
[show abstract][hide abstract] ABSTRACT: Identification of adult stem cells and their location (niches) is of great relevance for regenerative medicine. However, stem cell niches are still poorly defined in most adult tissues. Here, we show that the longest telomeres are a general feature of adult stem cell compartments. Using confocal telomere quantitative fluorescence in situ hybridization (telomapping), we find gradients of telomere length within tissues, with the longest telomeres mapping to the known stem cell compartments. In mouse hair follicles, we show that cells with the longest telomeres map to the known stem cell compartments, colocalize with stem cell markers, and behave as stem cells upon treatment with mitogenic stimuli. Using K15-EGFP reporter mice, which mark hair follicle stem cells, we show that GFP-positive cells have the longest telomeres. The stem cell compartments in small intestine, testis, cornea, and brain of the mouse are also enriched in cells with the longest telomeres. This constitutes the description of a novel general property of adult stem cell compartments. Finally, we make the novel finding that telomeres shorten with age in different mouse stem cell compartments, which parallels a decline in stem cell functionality, suggesting that telomere loss may contribute to stem cell dysfunction with age.
Genes & Development 04/2008; 22(5):654-67. · 12.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: At the present time, no efficient in vivo method for gene transfer to skin stem cells exists. In this study, we hypothesized that early in gestation, specific epidermal stem cell populations may be accessible for gene transfer. To test this hypothesis, we injected lentiviral vectors encoding the green fluorescence protein marker gene driven by either the cytomegalovirus promoter or the keratin 5 (K5) promoter into the murine amniotic space at early developmental stages between embryonic days 8 and 12. This resulted in sustained green fluorescent protein (GFP) expression in both basal epidermal stem cells and bulge cells in the hair follicles of the skin. Transduction of stem cell populations was dependent on the developmental stage, and confirmed by the prolonged duration of GFP expression in all skin elements into adulthood. In addition, transduced stem cell populations responded to regenerative signals after wounding and actively participated in wound healing. Finally, we quantified the fraction of epidermal stem cells transduced, and the distribution of transduction related to the promoters utilized, confirming improved efficiency with the K5 promoter. This simple approach has possible biological applications in our study of gene functions in skin, and perhaps future clinical applications for treatment of skin based disorders.
[show abstract][hide abstract] ABSTRACT: One challenge faced by stem cell biologists is the bioengineering of an organ. Ehama et al. (2007, this issue) used cells derived from human and rodent epidermis and dermal papilla to reconstitute hair-follicle mini-organs. Some result in hair follicles; others are hair follicle-like. The challenge calls for the development of a set of criteria to define a hair follicle so that bioengineered products in the future can be evaluated.
Journal of Investigative Dermatology 10/2007; 127(9):2098-100. · 6.19 Impact Factor
[show abstract][hide abstract] ABSTRACT: Developmental abnormalities, cancer, and premature aging each have been linked to defects in the DNA damage response (DDR). Mutations in the ATR checkpoint regulator cause developmental defects in mice (pregastrulation lethality) and humans (Seckel syndrome). Here we show that eliminating ATR in adult mice leads to defects in tissue homeostasis and the rapid appearance of age-related phenotypes, such as hair graying, alopecia, kyphosis, osteoporosis, thymic involution, fibrosis, and other abnormalities. Histological and genetic analyses indicate that ATR deletion causes acute cellular loss in tissues in which continuous cell proliferation is required for maintenance. Importantly, thymic involution, alopecia, and hair graying in ATR knockout mice were associated with dramatic reductions in tissue-specific stem and progenitor cells and exhaustion of tissue renewal and homeostatic capacity. In aggregate, these studies suggest that reduced regenerative capacity in adults via deletion of a developmentally essential DDR gene is sufficient to cause the premature appearance of age-related phenotypes.
[show abstract][hide abstract] ABSTRACT: The cell surface marker CD34 marks mouse hair follicle bulge cells, which have attributes of stem cells, including quiescence and multipotency. Using a CD34 knockout (KO) mouse, we tested the hypothesis that CD34 may participate in tumor development in mice because hair follicle stem cells are thought to be a major target of carcinogens in the two-stage model of mouse skin carcinogenesis. Following initiation with 200 nmol 7,12-dimethylbenz(a)anthracene (DMBA), mice were promoted with 12-O-tetradecanoylphorbol-13-acetate (TPA) for 20 weeks. Under these conditions, CD34KO mice failed to develop papillomas. Increasing the initiating dose of DMBA to 400 nmol resulted in tumor development in the CD34KO mice, albeit with an increased latency and lower tumor yield compared with the wild-type (WT) strain. DNA adduct analysis of keratinocytes from DMBA-initiated CD34KO mice revealed that DMBA was metabolically activated into carcinogenic diol epoxides at both 200 and 400 nmol. Chronic exposure to TPA revealed that CD34KO skin developed and sustained epidermal hyperplasia. However, CD34KO hair follicles typically remained in telogen rather than transitioning into anagen growth, confirmed by retention of bromodeoxyuridine-labeled bulge stem cells within the hair follicle. Unique localization of the hair follicle progenitor cell marker MTS24 was found in interfollicular basal cells in TPA-treated WT mice, whereas staining remained restricted to the hair follicles of CD34KO mice, suggesting that progenitor cells migrate into epidermis differently between strains. These data show that CD34 is required for TPA-induced hair follicle stem cell activation and tumor formation in mice.
Cancer Research 06/2007; 67(9):4173-81. · 8.65 Impact Factor