Hair follicle bulge: a fascinating reservoir of epithelial stem cells.
Ohyama M.
Source
Department of Dermatology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan.
maboym@sc.itc.keio.ac.jp <maboym@sc.itc.keio.ac.jp>
Abstract
Hair follicles reconstitute themselves though the hair cycle, suggesting the presence of intrinsic stem cells. In contrast to the previous belief that stem cells reside in the bulbar region of hair follicles, stem cells were detected in the bulge area, a contiguous part of outer root sheath, that provides the insertion point for arrector pili muscle and marks the bottom of the permanent portion of hair follicles. The bulge cells are morphologically undifferentiated and slow-cycling under the normal conditions. Later, studies successively demonstrated that bulge cells possess stem cell properties such as high proliferative capacity and multipotency to regenerate not only hair follicles but also sebaceous glands and epidermis. Our knowledge of the bulge cell biology is rapidly increasing because of the identification of novel cell surface markers, the ability to isolate living bulge cells, and microarray analysis of multiple gene expression. Importantly, novel cell surface markers were identified on human bulge cells using precise laser capture microdissection and microarray analyses. Use of these markers enabled the successful enrichment of living human bulge cells, raising the possibility of future treatments of hair disorders using stem cells. Additional clinical relevance of bulge cell biology includes the importance of bulge cells as a gene therapy target and their possible roles in tumorigenesis.
Bald scalp in men with androgenetic alopecia retains hair follicle stem cells but lacks CD200-rich and CD34-positive hair follicle progenitor cells.
Garza LA,
Yang CC,
Zhao T,
Blatt HB,
Lee M,
He H,
Stanton DC,
Carrasco L,
Spiegel JH,
Tobias JW,
Cotsarelis G.
Source
Department of Dermatology, Kligman Laboratories, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Abstract
Androgenetic alopecia (Androgenetic Alopecia), 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 Androgenetic Alopecia 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 Androgenetic Alopecia.
Folliculitis is defined histologically as the presence of inflammatory cells within the wall and ostia of the hair follicle, creating a follicular-based pustule. The actual type of inflammatory cells can vary and may be dependent on the etiology of the folliculitis, the stage at which the biopsy specimen was obtained, or both. The inflammation can be either limited to the superficial aspect of the follicle with primary involvement of the infundibulum or the inflammation can affect both the superficial and deep aspect of the follicle. Deep folliculitis can eventuate from chronic lesions of superficial folliculitis or from lesions that are manipulated, and this may ultimately result in scarring.
Perifolliculitis, on the other hand, is defined as the presence of inflammatory cells in the perifollicular tissues and can involve the adjacent reticular dermis. Folliculitis and perifolliculitis can manifest independently or together as a result of follicular disruption and irritation.
The role of inflammation and immunity in the pathogenesis of androgenetic alopecia.
Magro CM,
Rossi A,
Poe J,
Manhas-Bhutani S,
Sadick N.
Source
Department of Pathology and Laboratory Medicine, Weill Medical College of Cornell University, New York, NY, USA.
Abstract
BACKGROUND:
Female pattern hair loss affects many women; its pathogenetic basis has been held to be similar to men with common baldness.
OBJECTIVE:
The objective of this study was to determine the role of immunity and inflammation in androgenetic alopecia in women and modulate therapy according to inflammatory and immunoreactant profiles.
MATERIALS AND METHODS:
52 women with androgenetic alopecia (AA) underwent scalp biopsies for routine light microscopic assessment and direct immunofluroescent studies. In 18 patients, serologic assessment for antibodies to androgen receptor, estrogen receptor and cytokeratin 15 was conducted.
RESULTS:
A lymphocytic folliculitis targeting the bulge epithelium was observed in many cases. Thirty-three of 52 female patients had significant deposits of IgM within the epidermal basement membrane zone typically accompanied by components of complement activation. The severity of changes light microscopically were more apparent in the positive immunoreactant group.
Biopsies from men with androgenetic alopecia showed a similar pattern of inflammation and immunoreactant deposition. Serologic assessment for antibodies to androgen receptor, estrogen receptor or cytokeratin 15 were negative. Combined modality therapy with minocycline and topical steroids along with red light produced consistent good results in the positive immunoreactant group compared to the negative immunoreactant group.
CONCLUSION:
A lymphocytic microfolliculitis targeting the bulge epithelium along with deposits of epithelial basement membrane zone immunoreactants are frequent findings in androgenetic alopecia and could point toward an immunologically driven trigger. Cases showing a positive immunoreactant profile respond well to combined modality therapy compared to those with a negative result.
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Perifollicular fibrosis: pathogenetic role in androgenetic alopecia.
Yoo HG,
Kim JS,
Lee SR,
Pyo HK,
Moon HI,
Lee JH,
Kwon OS,
Chung JH,
Kim KH,
Eun HC,
Cho KH.
Source
Department of Dermatology, Seoul National University College of Medicine, Laboratory of Cutaneous Aging and Hair Research, Clinical Research Institute, Seoul National University Hospital, and Institute of Dermatological Science, Seoul National University, Seoul, Korea.
Abstract
Androgenetic alopecia (Androgenetic Alopecia) is a dihydrotestosterone (DHT)-mediated process, characterized by continuous miniaturization of androgen reactive hair follicles and accompanied by perifollicular fibrosis of follicular units in histological examination. Testosterone (T: 10(-9)-10(-7) M) treatment increased the expression of type I procollagen at mRNA and protein level. Pretreatment of finasteride (10(-8) M) inhibited the T-induced type I procollagen expression at mRNA (40.2%) and protein levels (24.9%). T treatment increased the expression of transforming growth factor-beta 1 (TGF-beta1) at protein levels by 81.9% in the human scalp dermal fibroblasts (DFs). Pretreatment of finasteride decreased the expression of TGF-beta1 protein induced by an average of T (30.4%). The type I procollagen expression after pretreatment of neutralizing TGF-beta1 antibody (10 microg/ml) was inhibited by an average of 54.3%. Our findings suggest that T-induced TGF-beta1 and type I procollagen expression may contribute to the development of perifollicular fibrosis in the Androgenetic Alopecia, and the inhibitory effects on T-induced procollagen and TGF-beta1 expression may explain another possible mechanism how finasteride works in Androgenetic Alopecia.
Androgenetic alopecia in males: a histopathological and ultrastructural study.
El-Domyati M,
Attia S,
Saleh F,
Abdel-Wahab H.
Source
Department of Dermatology, Al-Minya University, 2 Obour Buildings, Salah Salem St, Apt. 53, Nasr City, Cairo 11371, Egypt.
moetazeldomyati@yahoo.com
Abstract
BACKGROUND:
Androgenetic alopecia is a common cosmetic hair disorder, resulting from interplay of genetic, endocrine, and aging factors leading to a patterned follicular miniaturization. Microinflammation seems to be a potential active player in this process.
AIMS:
To study the histopathological and ultrastructural changes occurring in male androgenetic alopecia (Androgenetic Alopecia). Patients/methods Fifty-five subjects were included in this study (40 with Androgenetic Alopecia and 15 as normal age-matched controls). Skin biopsies from frontal bald area and occipital hairy area were subjected to histopathological examination, immunohistochemical staining for collagen I and ultrastructural study.
RESULTS:
The frontal bald area of patients showed highly significant increase in telogen hairs and decrease in anagen/telogen ratio and terminal/vellus hair ratio (P < 0.001).
Perifollicular inflammation was almost a constant feature in early cases and showed a significant inverse correlation with perifollicular fibrosis (P = 0.048), which was more marked with thickening of the follicular sheath in advanced cases.
CONCLUSION:
Follicular microinflammation plays an integral role in the pathogenesis of Androgenetic Alopecia in early cases.
Over time, thickening of perifollicular sheath takes place due to increased deposition of collagen, resulting in marked perifollicular fibrosis, and sometimes ends by complete destruction of the affected follicles in advanced cases
During the hair cycle the follicle has to be rebuilt from stem cells,” explains Dr Bruno Bernard, director of research for life sciences at L’Oreal. “Stem cells in human hair follicles are localised in two different reservoirs – one is in the upper part of the follicle and the other in the lower part. “The cells in the lower part are required to activate the cells in the upper part and so help to maintain the follicle function. The thickening of collagen in the connective tissue sheath, which sits around the base of the hair follicle, prevents the movement of stem cells from the lower reservoir to the upper reservoir. Bit by bit, the follicle is squeezed and causes the follicles to grow smaller and smaller.” Indeed, research from The Rockefeller University in New York suggests movement between the two groups of stem cells is crucial in normal hair growth.
Another recent study, at the University of Pennsylvania, has shown that bald areas of scalp contain the same number of stem cells as hairy areas. It disproved theories that hair loss in androgenic alopecia was due to a loss of follicle stem cells suggesting that they have just become inactive.