Expression and location of phospho-Artemis (Serine516) in hair follicles during induced growth of mouse hair

Artemis has been implicated in having a role in NHEJ, and it is also a multifunctional protein. Previous studies have found Omenn syndrome-like phenotype due to Artemis mutations and associated with alopecia. As Artemis phosphorylation in its c-terminus including Serine516 is prerequisite for the Artemis endonuclease reaction, we postulate that Artemis (Serine516) may be expressed in hair follicle and relate to hair cycling. In this study, hair growth in C57BL/6 mice was induced by plucking the telogen hair on the back. Expression of Artemis (Serine516) in hair follicles during the hair growth cycle was evaluated by immunofluorescence using cryosections and a specific polyclonal anti-Artemis (Serine516) immunoglobulin G (IgG) antibody. It was detected in germ cells, cap, and club hair adjoining the epidermis in telogen. In anagen II, intense staining for Artemis (Serine516) was found in the whole interfollicular epidermis, and in strand keratinocytes. In anagen IV, intense staining for Artemis (Serine516) was detected in basal cells and upper of outer root sheath (ORS) and inner root sheath (IRS). But only upper ORS and lower medulla were stained positive in anagen VI. Upper ORS and lower cortex were positively stained with Artemis (Serine516) in catagen. Based on the phenomenon that the expression of Artemis (Serine516) in mid-anagen and mature anagen was stronger than that in telogen and catagen, we suggest it may take roles in induced growth of mouse hair.     

Betacellulin regulates hair follicle development and hair cycle induction and enhances angiogenesis in wounded skin

Betacellulin (BTC) belongs to the EGF family, whose members play important roles in skin morphogenesis, homeostasis, and repair. However, the role of BTC in skin biology is still unknown. We employed transgenic mice overexpressing BTC ubiquitously to study its role in skin physiology. Immunohistochemistry revealed increased levels of BTC especially in the hair follicles and in the epidermis of transgenic animals. Expression of key markers of epithelial differentiation was unaltered, but keratinocyte proliferation was significantly increased. At post-natal day 1 (P1), transgenic mice displayed a significant retardation of hair follicle morphogenesis. At P17, when most follicles in control mice had initiated hair follicle cycling and had already entered into their first late catagen or telogen phase, all follicles of transgenic mice were still at the mid- to late catagen phases, indicating retarded initiation of hair follicle cycling. Healing of full-thickness excisional wounds and bursting strength of incisional wounds were similar in control and transgenic mice. However, an increase in the area covered by blood vessels at the wound site was detected in transgenic animals. These results provide evidence for a role of BTC in the regulation of epidermal homeostasis, hair follicle morphogenesis and cycling, and wound angiogenesis.     

Keratin 16 expression defines a subset of epithelial cells during skin morphogenesis and the hair cycle

The morphogenesis of skin epithelia and adult hair follicle cycling both require integrated signaling between the epithelium and underlying mesenchyme. Because of their unique regulation, keratin intermediate filaments represent useful markers for the analysis of determination and differentiation processes in complex epithelia, such as the skin. In this study, we analyzed the distribution of mouse type I keratin 16 during skin morphogenesis, in the adult hair cycle, and in challenged epidermis. In mature hair follicles, we find keratin 16 along with its type II keratin partner keratin 6 in the companion layer of the outer root sheath during anagen and in the club hair sheath during catagen and telogen. During embryonic development, the distribution of keratin 16 is uncoupled from its presumed polymerization partner, keratin 6. Keratin 16 initially localizes within early hair germs, but rapidly shifts to a subset of cells at the interface of basal and suprabasal cells above and around the hair germ. The presence of keratin 16 at the transition between mitotically active and differentiating cells is recapitulated in primary keratinocytes cultured in vitro and in phorbol 12-myristate 13-acetate-treated back skin in vivo. We propose that keratin 16 marks cells in an intermediate state of cellular properties in which keratinocytes retain the flexibility required for activities such as cell migration and even mitosis but are resilient enough to provide the structural integrity required of the early suprabasal layers in the context of development, adult hair cycling, and wound repair.     

Molecular mechanisms regulating hair follicle development

Clinical conditions causing hair loss, such as androgenetic alopecia, alopecia areata, and scarring alopecia, can be psychologically devastating to individuals and are the target of a multimillion dollar pharmaceutical industry. The importance of the hair follicle in skin biology, however, does not rest solely with its ability to produce hair. Hair follicles are self-renewing and contain reservoirs of multipotent stem cells that are capable of regenerating the epidermis and are thought to be utilized in wound healing. Hair follicles are also the sites of origin of many neoplasias, including some basal cell carcinomas and pilomatricoma. These diseases result from inappropriate activation of signaling pathways that regulate hair follicle morphogenesis. Identification of the signaling molecules and pathways operating in developing and postnatal, cycling, hair follicles is therefore vital to our understanding of pathogenic states in the skin and may ultimately permit the development of novel therapies for skin tumors as well as for hair loss disease. The purpose of this review is to summarize recent progress in our understanding of the molecular mechanisms regulating hair follicle formation, and to discuss ways in which this information may eventually be utilized in the clinic.     

Cell degeneration in alopecia areata. An ultrastructural study

The morphology and prevalence of different forms of cell degeneration in hair follicles in acute alopecia areata were investigated. In addition to apoptosis and necrosis, a third morphological pattern of cell degeneration, dark-cell transformation, was evident. Fifteen patients with untreated acute alopecia areata and three normal adults without hair loss were studied. Electron microscopy revealed that although apoptosis of outer root sheath keratinocytes produces normal hair follicle involution (catagen), increased levels of apoptosis, necrosis, and dark-cell formation appear to be related to the pathology of alopecia areata. Although cell degeneration was generally restricted to keratinocytes of the lower follicle, melanocytes, Langerhans' and dermal papilla cells were also affected. Keratinocytic degeneration may affect layers of matrix cells in alopecia areata, unlike the apoptosis of scattered outer root sheath cells in normal catagen. The extent of cell death suggests a pathological rather than a physiological event in alopecia areata.     

Stem cells and alopecia: a review of pathogenesis

Recent work has focused on the hair follicle as the main source of multipotent stem cells in the skin. The hair follicle bulge contains multipotent stem cells that can form the epidermis, hair follicles and sebaceous glands and help in repopulation of the epidermis after injury. The localization of these stem cells to the bulge area may explain why some types of inflammatory alopecia cause permanent loss of hair (cicatricial alopecia) (such as lichen planopilaris and discoid lupus erythematosus), while others (such as alopecia areata) are reversible (noncicatricial alopecia). The lack of distinctive bulge morphology in human hair follicles has hampered studies of bulge cells. To date, the best marker for bulge stem cells in human hair is cytokeratin (CK) 15; human bulge cells have been reported to express CK15 selectively throughout all stages of the hair cycle in different types of follicles. There is direct evidence in the mouse, and indirect evidence in the human, that compromising the integrity of the sebaceous gland and/or bulge is important in the development of alopecia. Several interesting studies have been done in the last few years to investigate the role of stem cells in alopecia, especially nonscarring types. This is a review about the role of stem cells in the pathogenesis of alopecia (scarring and nonscarring).     

芳香烃受体在人表皮、毛囊和皮脂腺上的表达及其意义

目的 观察芳香烃受体(AhR)在人表皮、毛囊及皮脂腺细胞上的表达及在二(噁)英作用下的激活情况.方法 采用免疫荧光和免疫组化法观察AhR蛋白在人面部表皮、毛囊、皮脂腺及体外培养的HaCaT细胞和SZ95人皮脂腺细胞上的表达情况;Western印记法观察2,3,7,8-四氯二苯-p-二(噁)英(TCDD)作用HaCaT细胞和SZ95细胞3d后AhR蛋白表达的变化情况.结果 AhR蛋白在人面部皮肤表皮、毛囊、皮脂腺细胞上表达,并且AhR蛋白在表皮棘层和颗粒层的表达强于基底细胞层,在皮脂腺小叶的外周和中央表达强于皮脂腺小叶中间,在毛囊外毛根鞘和近毛小皮细胞上的表达强于内毛根鞘细胞.AhR蛋白在HaCaT细胞和SZ95细胞的细胞核和胞质中高表达.在TCDD作用下,HaCaT细胞和SZ95细胞内AhR蛋白表达明显下降,显示AhR在TCDD作用下被激活.结论 AhR在人表皮、毛囊、皮脂腺、HaCaT细胞及SZ95细胞上高表达,并在TCDD作用下激活,显示二(噁)英有可能通过AhR信号途径引起了人表皮、毛囊和皮脂腺的异常分化.     

Expression of decorin throughout the murine hair follicle cycle: hair cycle dependence and anagen phase prolongation

Decorin is a prototypical member of the small leucine‐rich proteoglycan (SLRP) family, which is involved in numerous biological processes. The role of decorin, as a representative SLRP, in hair follicle morphogenesis has not been elucidated. We present our initial findings on decorin expression patterns during induced murine hair follicle (HF) cycles. It was found that decorin expression is exclusively restricted to the epidermis, outer root sheath and sebaceous glands during the anagen phase, which correlates with the upregulation of decorin mRNA and protein expression in depilated murine dorsal skin. Furthermore, we used a functional approach to investigate the effects of recombinant human decorin (rhDecorin) via cutaneous injection into HFs at various murine hair cycle stages. The local injection of rhDecorin (100 μg/ml) into the hypodermis of depilated C57BL/6 mice at anagen delayed catagen progression. In contrast, rhDecorin injection during the telogen phase caused the premature onset of anagen, as demonstrated by the assessment of the following parameters: (i) hair shaft length, (ii) follicular bulbar diameter, (iii) hair follicle cycling score and (iv) follicular phase percentage. Taken together, our results suggest that decorin may modulate follicular cycling and morphogenesis. In addition, this study also provides insight into the molecular control mechanisms governing hair follicular epithelial–mesenchymal interactions.     

真皮干细胞在毛囊周期中的作用

毛囊由表皮(上皮)及真皮(间充质)组成,它们之间的相互作用在毛囊的形态发生及生长中发挥重要作用,二者之间相互作用是毛囊成功重建的关键因素.在毛发形成过程中,真皮细胞是诱导者,上皮细胞是应答者.真皮鞘和毛乳头内存在毛囊真皮干细胞,属于成体干细胞,具有慢周期、未分化、自我更新和体外增殖能力强的特点.真皮鞘中的真皮干细胞较长寿,可以历经几个毛囊周期,重建真皮鞘.在毛囊周期的生长期,真皮鞘中的干细胞产生新细胞提供给毛乳头;在退行期,真皮干细胞子代移出毛乳头或死亡.毛囊真皮细胞对于损伤和疾病之后的毛囊重建及修复具有重要意义.     

Premature termination of hair follicle morphogenesis and accelerated hair follicle cycling in Iasi congenital atrichia (fzica) mice points to fuzzy as a key element of hair cycle control

Inbred laboratory mice have proven to be useful model systems for studying hair biology and pathomechanisms of hair loss. Fuzzy (fz) is an autosomal recessive mutation that results in hair coat abnormalities. Though this mutant has long been known, its cutaneous abnormalities still await systematic analysis. Here, we provide a systematic skin phenotype analysis of mice that are homozygous for Iasi congenital atrichia (fzica/fzica), which is allelic to fz. Homozygous mice exhibit a sparse hair coat after birth and completely loose their hair at around postnatal day 120. Although early and mid stages of hair follicle morphogenesis are normal, late hair follicle morphogenesis reveals multifocal cell degeneration within the Huxley layer of the inner root sheath (IRS) and a complete lack of the hair shaft medulla. In addition, hair follicle development is prematurely terminated by induction of the first postnatal hair cycle with premature entry into catagen. Subsequently, a dramatically shortened telogen is immediately followed by premature anagen development, resulting in a marked, generalized acceleration of hair follicle cycling. This suggests that fuzzy is not only involved in structural hair shaft integrity and differentiation of the IRS and medulla, but also plays an important role in the control of hair follicle cycling. Our data show that fuzzy is involved in controlling both catagen and anagen initiation, designating fuzzy an exciting target for characterizing the intracutaneous oscillator system that drives hair follicle cycling.     

The expression of stratum corneum chymotryptic enzyme in human anagen hair follicles: further evidence for its involvement in desquamation-like processes

At sites with a continuous formation of cornified epithelia, there is need for continuous cell shedding in order to maintain normal anatomy. Stratum corneum chymotryptic enzyme (SCCE) has been suggested to mediate this process by degrading intercellular cohesive structures in interfollicular epidermis. In the hair follicle, there are several different kinds of cornification processes. With the exception of the formation of the hair shaft, these processes lead to a continuous formation of structures that have to be shed continuously in order to avoid distorting the anatomy of the follicle. In this work, we have investigated the possible involvement of SCCE in the turnover of cornified cells in anagen hair follicles. Using immunohistochemistry, we demonstrated the expression of SCCE in all parts of the follicle where cells are keratinized and eventually shed, i.e. in the uppermost follicle (distal to the opening of the sebaceous duct), in the sebaceous duct and in all parts of the inner root sheath (IRS). SCCE expression was also seen in those cells of the outer root sheath that are believed to move along with the IRS from the bulb and eventually become keratinized and sloughed in the part of the follicle situated between the terminal edge of the IRS and the opening of the sebaceous duct. We could not detect any SCCE in cells forming the hair shaft. Thus, there was a strong correlation between SCCE expression and the continuous formation and shedding of cornified epithelia in anagen hair follicles. This correlation was stronger for SCCE than for a number of common markers of terminal differentiation in keratinocytes. Our results give further support to a part for SCCE in desquamation-like processes. Whether SCCE is involved in diseases affecting hair growth remains to be elucidated.     

Hair loss in autoimmune cutaneous bullous disorders

The expression of the basement membrane zone (BMZ) components in the anagen hair follicles of the human scalp is similar to that of interfollicular epidermis. Expression of the BMZ components varies according to the different follicular portions. Blistering of the scalp, involving lamina lucida and below, usually leads to scarring alopecia secondary to the inflammatory process in the interfollicular epidermis and in the upper portion of the hair follicle. This article discusses the presence of alopecia in the most common acquired forms of bullous disorders.     

Transforming growth factor-beta receptor II is preferentially expressed in the companion layer of the human anagen hair follicle

BACKGROUND: Transforming growth factor (TGF)-beta is a multifunctional growth factor with multiple roles in skin including hair follicle development and cycling, where it regulates cell proliferation, differentiation and apoptosis, as well as in wound healing. While TGF-beta receptor I (TGF-beta RI) and receptor II (TGF-beta RII) expression helps define early human hair follicle morphogenesis, expression in the adult human hair follicle remains to be established. OBJECTIVES: To assess TGF-beta receptor expression in human scalp anagen hair follicles. METHODS: Immunohistochemical and double immunofluorescence analysis of TGF-beta RI and RII was conducted on frozen sections of haired human scalp obtained from 10 healthy individuals. RESULTS: TGF-beta RI expression was detected in the outer root sheath of anagen hair follicles while TGF-beta RII was expressed almost exclusively in the companion layer of inner root sheath and less so in premedulla keratinocytes. Both receptors were colocalized in the companion layer of the proximal and mid follicle. CONCLUSIONS: The well-described role of TGF-beta in keratinocyte apoptosis during catagen is likely to involve anagen-specific hair follicle components including the companion layer, as this layer provides the slippage plane supporting the inner root sheath and hair shaft as they ascend to the skin surface. Results of this study suggest that the colocalization of TGF-beta RI/RII complexes at the companion layer would facilitate TGF-beta signalling at this site to regulate apoptosis of the companion layer keratinocytes, facilitating shrinkage/contraction of this cell layer during hair follicle regression/catagen.     

Epidermal and hair follicle progenitor cells express melanoma-associated chondroitin sulfate proteoglycan core protein

Basal keratinocytes in the epidermis and hair follicle are biologically heterogeneous but must include a stable subpopulation of epidermal stem cells. In animal models these can be identified by their retention of radioactive label due to their slow cycle (label-retaining cells) but human studies largely depend on in vitro characterization of colony forming efficiency and clonogenicity. Differential integrin expression has been used to detect cells of increased proliferative potential but further stem cell markers are urgently required for in vivo and in vitro characterization. Using LHM2, a monoclonal antibody reacting with a high molecular weight melanoma-associated proteoglycan core protein, a subset of basal keratinocytes in both the interfollicular epidermis and the hair follicle has been identified. Coexpression of melanoma-associated chondroitin sulfate proteoglycan with keratins 15 and 19 as well as beta 1 and alpha 6 integrins has been examined in adult and fetal human skin from hair bearing, nonhair bearing, and palmoplantar regions. Although melanoma-associated chondroitin sulfate proteoglycan coexpression with a subset of beta 1 integrin bright basal keratinocytes within the epidermis suggests that melanoma-associated chondroitin sulfate proteoglycan colocalizes with epidermal stem cells, melanoma-associated chondroitin sulfate proteoglycan expression within the hair follicle was more complex and multiple subpopulations of basal outer root sheath keratinocytes are described. These data suggest that epithelial compartmentalization of the outer root sheath is more complex than interfollicular epidermis and further supports the hypothesis that more than one hair follicle stem cell compartment may exist.     

Topical estrogen accelerates hair regrowth in mice after chemotherapy-induced alopecia by favoring the dystrophic catagen response pathway to damage

Estrogen receptor ligands are important modulators of skin physiology and are involved in the control of normal hair follicle cycling. Here, we have studied the effects of topically applied 17-beta-estradiol on pathologic hair follicle cycling as seen during chemotherapy-induced alopecia, one of the major unresolved problems of clinical oncology. For this study we employed a well-established murine model that mimics chemotherapy-induced alopecia in humans. For precisely quantifying the area of hair loss and hair regrowth in this model in vivo, we developed a simple planimetric assay (dotmatrix planimetry). We show that topical 17-beta-estradiol significantly alters the cycling response of murine follicles to cyclophosphamide, whereas the estrogen antagonist ICI 182.780 exerted no such effects. Initially, topical 17-beta-estradiol enhanced chemotherapy-induced alopecia significantly by forcing the follicles into the dystrophic catagen response pathway to hair follicle damage, whereas follicles treated by ICI 182.780 or vehicle shifted into the dystrophic anagen response pathway. Consequently, the regrowth of normally pigmented hair shafts after chemotherapy-induced alopecia was significantly accelerated in the 17-beta-estradiol treated group. Our data encourage one to explore topical estrogens as a potential stimulant for hair re-growth after chemotherapy-induced alopecia.     

Immunohistochemical localization of types 1 and 2 5alpha-reductase in human scalp

The predominant form of 5alpha-reductase (5aR) in human scalp is 5aR1. None the less, clinical studies have shown that finasteride, a selective inhibitor of 5aR2, decreases scalp dihydrotestosterone and promotes hair growth in men with androgenetic alopecia. Immunolocalization studies were thus carried out to examine 5aR isozyme distribution within scalp and, in particular, to determine whether 5aR2 might be associated with hair follicles. 5aR2 was localized using both a rabbit polyclonal and a mouse monoclonal antibody. 5aR1 was detected with a mouse monoclonal antibody. The specificity of these reagents was demonstrated both by immunofluorescence and Western blot analyses of COS cells overexpressing human 5aR1 or 5aR2. When cryosections of scalp from men with androgenetic alopecia were stained with antibody against 5aR2, using immunoperoxidase avidin-biotin complex methodology, immunostaining was observed in the inner layer of the outer root sheath and, in more proximal regions of the follicle, in the inner root sheath. Staining was also prominent in the infundibular region of the follicle, with less intense staining extending throughout the granular layer of the epidermis. Some staining was also seen in sebaceous ducts. Similar results were obtained with both the polyclonal and monoclonal 5aR2 antibodies. In contrast, in scalp cryosections stained with antibody to 5aR1, no immunostaining was observed within hair follicles. Intense staining for the type 1 isozyme was, however, detected within sebaceous glands. Our immunolocalization data suggest that the results seen in clinical trials of men with male pattern hair loss treated with finasteride may be due, at least in part, to local inhibition of 5aR2 within the hair follicle.     

Expression of the hair stem cell-specific marker nestin in epidermal and follicular tumors

Nestin, a marker of neural stem cells, is expressed in the stem cells of the mouse hair follicle. The nestin-expressing hair follicle stem cells give rise to the outer-root sheath. Nestin-expressing hair follicle stem cells that are negative for the keratinocyte marker keratin 15 (K15) can differentiate into neurons, glia, keratinocytes, smooth muscle cells, and melanocytes in vitro. Recent studies suggest that the epithelial stem cells are important in tumorigenesis. In this study, we immunohistochemically examined the expression of three hair follicle stem cell and progenitor cell markers, nestin, K15, and CD34, in normal human epidermis and hair follicles and in epidermal and follicular tumors, trichilemmoma, basal cell carcinoma (BCC), and squamous cell carcinoma (SCC). In normal human skin, the cells in the epidermal basal layer were positive for K15 and negative for nestin and CD34. The hair follicle cells below the sebaceous glands were also positive for nestin and K15 and negative for CD34. The outer-root sheath cells under this area could be divided into three parts: an upper part of the outer-root sheath cells that was partially positive for nestin and positive for K15 and negative for CD34; a middle part that was CD34-positive and K15-negative; and a lower part that was positive for K15 and negative for CD34. In the tumor tissues, nestin immunoreactivity was observed in trichilemmoma but not in BCC. Also, immunoreactivity for K15 was strong in BCC and weak in trichilemmoma, and SCC was negative for nestin and partially positive for K15. No CD34 immunoreactivity was observed in any of the cases. These results suggested that trichilemmoma originates in the nestin-positive/K15-positive/CD34-negative outer-root sheath cells below sebaceous glands, BCC tumor cells from the more mature nestin-negative/K15-positive/CD34-negative outer-root sheath cells, and SCC from the nestin-negative/K15-positive/CD34-negative keratinocytes of the basal cell layer in the epidermis.     

CD10 and CD34 in fetal and adult human hair follicles: dynamic changes in their immunohistochemical expression during embryogenesis and hair cycling

Background  CD10 and CD34 have been detected in both epithelial and mesenchymal components of anagen human hair follicles.
Objectives  To analyse the expression of CD10 and CD34 in human hair follicle development as well as in different phases of the hair cycle.
Methods  Fetal and adult hair follicles at different stages of the hair cycle were examined by immunohistochemistry for CD10 and CD34.
Results  In fetal follicles, CD10 is expressed by the cells of the placodes, and CD34 by the mesenchymal cells of the dermal condensate. As the follicle matures, CD10 can be seen in the matrix cells, inner root sheath and dermal sheath. In adult follicles, the expression of CD10 in the follicular epithelium is present in anagen follicles, but tends to disappear in catagen, and is not detected in telogen. The CD10 positivity of the dermal sheath is more intense in catagen than in anagen follicles. CD34 immunostaining of the external root sheath was seen in adult anagen follicles but not in fetal follicles. This staining of the anagen outer sheath tends to disappear in catagen and is not detected in telogen.
Conclusions  CD10 and CD34 are not proteins constantly present in a specific cell type of the hair follicle, but are proteins that can be expressed by both epithelial and mesenchymal cells depending on the stage of development and hair cycle. The distribution of the immunoreactivity to CD10 in the placode and CD34 in the dermal condensate suggests a role of these proteins in initial stages of hair formation.     

Apoptosis coordinates with proliferation and differentiation during human hair follicle morphogenesis

BACKGROUND: Apoptosis sculptures the most complicated skin appendage, feathers, out of epidermal layers by playing a variety of roles (1). Human hair follicle formation is different from feathers in growth direction and pattern formation of proliferative zone. OBJECTIVE: To delineate the apoptotic events together with proliferation and differentiation in developing human hair follicle and emphasis on the mechanism and biological meaning of epidermal hair canal. METHODS: We used TUNEL to examine apoptosis and Ki-67, involucrin, filaggrin immuno-localization to examine proliferation and differentiation. RESULTS: In hair germs, apoptosis was diffuse in periderm, basal keratinocytes, and mesenchymal cells with high Ki-67 expression, but spared follicular germinative cells with low Ki-67 and high bcl-2 expression. In hair pegs, apoptosis was active in high Ki-67 expression area, like outer root sheath, hair follicle sheath, but spared dermal papilla with low Ki-67 and high bcl-2 expression. In bulbous pegs, apoptosis appeared in companion layer, precortical area, inner root sheath and outer root sheath, but spared bulge area with high bcl-2 expression. Apoptosis resulted in epidermal and subepidermal hair canal formation. Filaggrin and involucrin were expressed in the lining cells of hair canal. CD1a+ cells were densely distributed alone the hair canal before its opening. CONCLUSION: During human hair follicle morphogenesis, apoptosis coordinates with proliferation to shape the growth zone, creates space to free the hair shaft from follicular wall, and directs a driving force on hair shaft extension. Apoptosis accompanies the terminal differentiation of epidermal hair canal. The bottom becomes interfollicular epidermis after roof shedding and hair exposure. Langerhans cells also populate in the hair canal before its opening. The biological meaning of epidermal hair canal is supposed to prepare the barrier when hair perturbing the intact of epidermis.