Apoptosis in murine hair follicles during catagen regression

Catagen hair follicle involution has been reported to involve apoptosis, although the precise mechanism has not been satisfactorily resolved. Previous studies have involved solely morphological or electron microscopical methods. We report here studies on murine hair follicles during the first postnatal hair cycle conducted using the terminal deoxy-nucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) method. Electrophoresis of DNA isolated from the hair follicles of the same animals was carried out in order to confirm the systematic fragmentation of DNA that typifies apoptosis. On day 10, when all the follicles were growing, there was no evidence of staining with TUNEL in the hair bulbs. Electrophoresis similarly did not show characteristic DNA ladders. By day 15, a few positive cells were observed in the hair bulbs and the numbers had increased by day 17 when many positive cells were seen, especially in the lower portions of the follicles. Electrophoresis demonstrated DNA ladders on days 15, 16 and 17, although the DNA ladder on day 15 was less prominent than that on day 17. These studies confirmed that apoptosis, as identified by techniques that measure DNA fragmentation, occurs in the lower regions of hair follicles towards the end of catagen. Received: 19 March 1997     

Apoptosis as the mechanism of the involution of hair follicles in catagen transformation

Electron microscopy was performed on mouse skin to study the mechanism of the spontaneous involution of hair follicles during catagen. The reduction in follicles size appears to result from cell deletion by apoptosis, a distinct type of cell death with importance in tissue kinetics. These ultrastructural changes have been misinterpreted in the past as autophagic vacuole formation because of the prominent phagocytosis of the apoptotic fragments by adjacent, surviving cells of the hair follicle.     

A possible role for Langerhans cells in the removal of melanin from early catagen hair follicles

Hair pigmentation is coupled to the hair follicle growth cycle. A common feature of catagen is the translocation of melanin from the matrix to the dermal papilla of the hair follicle. However, the mechanism whereby this pigment, not incorporated into the hair shaft, is removed from the hair bulb during early catagen is poorly understood. Routine ultrastructural examination of four normal scalp specimens revealed a rare hair follicle in early catagen. Close study of the hair bulb of this catagen follicle revealed a Langerhans cell in the process of transferring pigment from the matrix to the dermal papilla. This cell also contained numerous characteristic Langerhans granules (LG) (also known as Birbeck granules). Interestingly, these granules were intimately associated with melanosomes: so intimate, in fact, that melanosomes appeared to have been endocytosed by LG. This unique demonstration of removal of hair follicle melanin by Langerhans cells during early catagen and of pigment uptake by Langerhans cells by endocytosis into LG, suggests one way by which 'unused' pigment can be removed from the hair follicle during catagen.     

Roxithromycin antagonizes catagen induction in murine and human hair follicles: implication of topical roxithromycin as hair restoration reagent

Roxithromycin (RXM) is a 14-member macrolide antibiotics, with a variety of bioregulatory functions including anti-apoptotic activity to keratinocytes. Therefore, RXM has been used for many kinds of skin diseases. In this study, human and murine hair follicles were treated with RXM in order to find the possibility to cure hair loss disease such as androgenetic alopecia (AGA). In AGA, dihydrotestosterone signals apoptosis in dermal papilla cells in susceptible individuals, resting in premature termination of anagen and early entry into catagen. Therefore, anti-apoptotitic drug has a possibility of new candidate for AGA. This study revealed RXM antagonized the in vitro inhibitory effect of IFN-γ on proliferation of keratinocytes and induction of apoptosis in murine and human hair bulb. RXM increases hair elongation and inhibits catagen-like changes induced in vitro with IFN-γ in murine and human hair follicles. Furthermore, topical 5% RXM solution effectively restores hair growth in about half of individuals with AGA without any local and systemic adverse effects. Therefore, RXM is new candidate as a hair restoration drug for AGA.     

Targeting to the hair follicles: Current status and potential

The pilosebaceous unit is a complex structure that undergoes a specific growth cycle and comprises a few important drug targeting sites. For example, drugs can be targeted to the bulge region with stem cells or to the sebaceous glands. Interest in pilosebaceous units is directed towards their utilization as reservoirs for localized therapy and also as a transport pathway for systemic drug delivery. Improved investigative methods, such as differential stripping, are being developed in order to determine follicular penetration. This article reviews relevant aspects of effective follicle-targeting formulations and delivery systems as well as the activity status of hair follicles, and variations in follicle size and distribution throughout various body regions. Each of these factors strongly affects follicular permeation. We provide examples of improved penetration of particle-based formulations and of a size-dependent manner of follicular penetration. Contradictions are also discussed, indicating the need for detailed future investigations.     

毛囊混合细胞在海藻酸钠支架上诱导毛囊重建

目的 探讨原代培养的毛囊外根鞘细胞、毛乳头细胞和成纤维细胞,采用不同接种顺序在体外和体内诱导毛囊形成.方法 将培养的毛囊外根鞘细胞(ORSC)、毛乳头细胞(DPC)和丝裂霉素干预后的成纤维细胞按一定比例制成细胞悬液,并按不同的接种顺序接种于海藻酸钠3D细胞支架上,构建毛囊的体外三维模型并培养8周,行HE染色光镜观察毛囊形成的情况;同时将该三维模型移植入bal/bcl裸鼠皮下体内培养8周,移植部位取材后分别行HE染色、免疫组化和电镜观察毛囊形成的情况.结果 体外构建的毛囊三维模型未见到角化物质及毛囊样结构;裸鼠皮下移植物HE染色可见细胞聚集成团,有呈环状排列的毛囊样结构,CK14,CK15、β1整合素和波形蛋白染色阳性;电镜下模型中可见贴附在支架上的毛囊细胞和红细胞.先接种用丝裂霉素干预的成纤维细胞于海藻酸钠3D细胞支架上培养1周后再接种DPC∶ORSC (1∶5)细胞悬液,裸鼠体内移植物HE染色不仅可见明显的毛囊样结构形成,而且形成毛囊样结构的数目较多.结论 模型中DPC保持了诱导毛囊形成的能力,ORSC保持了毛囊干细胞的特点.并明确了诱导毛囊形成的最佳细胞组合、接种顺序和比例,为体外构建含有毛囊的人工皮肤奠定了一定基础.     

Extracellular histones inhibit hair shaft elongation in cultured human hair follicles and promote regression of hair follicles in mice

Release of histone H4 in rat vibrissa dermal papilla (DP) cells exposed to sub‐toxic dose of colchicines has been recently reported. In addition, exposure to histone H4 has been reported to result in inhibited proliferation and reduced alkaline phosphatase (ALP) activity of cultured vibrissa DP cells. These findings prompted us to investigate the role of extracellular histones in hair growth using cultured human hair follicles and hair cycling using back skin of mice. We report here that exposure of cultured hair follicles to histone H4 and H2A resulted in significant inhibition of elongation of hair shafts, decreased expression of IGF‐1 and decreased expression and activity of ALP. Injection of histones into hypodermis of mice during anagen resulted in premature onset of catagen. Findings of the current study provide strong evidence suggesting the inhibitory role of extracellular histones in hair growth.     

Changes in different melanocyte populations during hair follicle involution (catagen)

Melanin synthesis in the hair follicle (HF) is strictly coupled to the growth stage of the hair cycle and is interrupted during follicle regression (catagen) and resting. Using tyrosine-related protein 2 (Trp)2-LacZ transgenic mice as a model, we show that distinct melanocyte subpopulations of the HF display distinct patterns of apoptosis and survival during catagen. Melanocytes located in the outer root sheath express Bcl-2 and are TUNEL-negative. Part of the pigment-producing melanocytes located above the follicular papilla expresses Fas, TUNEL, and is likely to undergo apoptosis, whereas the other part of these melanocytes expresses c-kit, Bcl-2, and becomes visible in the follicular papilla. During late catagen, TUNEL and Ki-67 negative melanocytes expressing Bcl-2 are seen in the secondary germ of the HF. Lack of proliferation in the follicular melanocytes during catagen suggests that secondary hair germ of late catagen HF is most likely repopulated by melanocytes arising from the outer root sheath or follicular papilla of early/mid-catagen HF. Taken together, these data suggest a possible scenario and mechanisms of the remodeling of the follicular pigmentary unit during HF anagen-catagen-telogen transition and may be used for the establishing in vivo models for pharmacological modulation of melanocyte apoptosis and survival during the hair cycle.     

Apoptosis in wool follicles during mouse epidermal growth factor (mEGF)-induced catagen regression

Depilatory infusions of mouse epidermal growth factor (mEGF) induced regressive involution (catagen) in the wool follicles of Merino sheep. The follicles were examined by transmission electron microscopy prior to infusion and at intervals during catagen regression in order to determine the mechanism(s) involved in follicle involution. Cell deletion by apoptosis occurred in all cell types in the proximal region of catagen follicles between 12 h and 6 days after the beginning of infusion. Apoptosis also occurred in the basal layer of involuting sebaceous glands at 2 and 3 days, following earlier mEGF-induced proliferation. This process involved nuclear chromatin condensation and margination in single, scattered cells which subsequently fragmented and were ultimately phagocytosed and degraded by adjacent unaffected cells. It was concluded that during mEGF-induced catagen, wool follicle involution was accomplished largely through cell death and deletion by apoptosis.     

Morphological changes in the proximal area of the rat's hair follicle during early catagen

Summary This electron-microscopic study of the catagen phase shows that the first alteration of regression of the follicle is localized in the papilla, where the cells withdraw their offshoots and break the contact with the basal lamina. Both at the level of the papilla and of the bulb structures appear that increase the cell cohesion. Under the influence of the outer root sheath an upward migration occurs. This is followed by plication and thickening of the basal lamina. The alterations in the connective tissue sheath occur in a further stage. The first signs of autolysis occur in the center of the epithelial column. At the end of the catagen stage macrophages take care of the clearing-up.     

Cytokeratin expression in pili annulati hair follicles

Pili annulati is a rare autosomal inherited hair shaft abnormality of unknown pathogenesis in which clinical examination reveals alternating light and dark bands leading to a shiny appearance of the hair due to cavities within the cortex of the hair shaft. This is the first investigation of the proposed cytokeratin defect in pili annulati hair follicles. Four cryopreserved pili annulati and four control scalp specimens were analysed using immunohistochemistry for different 'hard' trichocytic and 'soft' epithelial cytokeratins including K1, K6, K10, K14, K16, K17, K18, K19, Ha1 and Hb1. There was no difference in staining intensity and quality of staining pattern seen in pili annulati and control scalp specimens. These results suggest that pili annulati is not caused by a defect of the cytokeratins investigated in this study.     

Prostanoid receptors in anagen human hair follicles

Abstract:  Prostanoid pathway in hair follicle gained closer attention since trichogenic side-effects on hair growth has been observed concomitantly with prostaglandin F_2α receptor (FP) agonist treatment of intraocular pressure. We thus investigated prostanoid receptor distribution in anagen hair follicle and different cell types from hair and skin. Using RT-PCR, Western blot and immunohistochemistry (IHC), we found that all receptors were present in hair follicle. This data shed new light on an underestimated complex network involved in hair growth control. Indeed most of these receptors showed a wide spectrum of expression in cultured cells and the whole hair follicle. Using IHC, we observed that expression of prostaglandin E₂ receptors (EP₂, EP₃, EP₄), prostaglandin D₂ receptor (DP₂), prostanoid thromboxane A₂ receptor (TP) and to a lesser extent EP₁ involved several hair follicle compartments. On the opposite, Prostaglandin I₂ receptor (IP) and DP₁ were more specifically expressed in hair cuticle layer and outer root sheath (ORS) basal layer, respectively. FP expression was essentially restricted to ORS companion layer and dermal papilla ( DP ). Although extracting a clear functional significance from this intricate network remains open challenge, FP labelling, i.e. could explain the biological effect of PGF_{2 α} on hair regrowth, by directly modulating DP function.     

c-Myc expression in human anagen hair follicles

The hair follicle represents a very attractive organ system for studying the precise balance between cell proliferation, growth, differentiation, and death of cells, because it periodically and regularly regenerates, retaining its morphogenetic signals throughout its life. One of the most intriguing oncogenes which is able to induce both cell growth and apoptosis, depending upon the environmental conditions, is c-myc. The aim of the present study was to investigate its presence and localization in human hair follicles by immunohistochemistry and immunofluorescence. Our observations demonstrated the consistent presence of two clusters of c-Myc-expressing cells in anagen follicles, located in two annular regions of the inner root sheath, at the border between cells characterized by putative trichohyalin granules and cells which are keratinized. The lower group belongs to Henle's layer, while the upper group belongs to Huxley's layer. c-Myc oncoprotein seems to favour apoptosis/differentiation and may be a marker for terminal differentiation of trichocytes, at least in the inner root sheath. Our findings agree with the interpretation that the complex morphology of the hair follicle reflects its complex function; the extrusion of a highly organized multicellular structure, the hair shaft, driven by another highly organized multicellular structure, the inner root sheath.