毛囊干细胞标记物的研究进展

毛囊干细胞是一类位于毛囊隆突区的成体干细胞,对毛囊的周期性生长,表皮和皮脂腺的更新以及皮肤损伤后修复有着至关重要的作用。毛囊干细胞的标记物是对毛囊干细胞进行分离和鉴定的重要依据,对毛囊干细胞的基础研究起着关键作用。因此寻找特异性较高的毛囊干细胞标记物成为了近年的研究热点。本文按毛囊干细胞标记物在细胞中所处部位进行分类,将其分为位于细胞膜、细胞质、细胞核的标记物,综述了目前国内外主要采用的整合素、角蛋白、CD34、CD200等标记物以及新发现的Lgr5、Sox9、Tcf3等基因标记物。     

毛囊干细胞

毛囊干细胞被认为是具慢周期性特点,但特定条件下具有较高增殖能力和克隆形成潜能的细胞。它们在形态学和生物化学上处于较原始的状态,常具有多潜能性。利用干细胞标记技术和克隆形成能力检测手段,人们发现毛囊干细胞主要存在于位于毛囊上半部的隆突部位。毛囊干细胞潜在的分子标记包括β1-整合素、α6-整合素、CD71、角蛋白19、p63和CD34,而在体内和体外它们的分子标记也不尽相同。毛囊隆突部位的干细胞能够分化成表皮、上皮性毛根鞘、发杆和皮脂腺。在个体发育过程中,它们具有分化成其他多种细胞系的能力。对于在毛发形态形成和生长周期中毛囊干细胞的行为,研究者们提出了多种假说,包括隆突激活假说和干细胞迁移假说。如今,毛囊干细胞主要应用于制备皮肤的代替品。     

角蛋白15在大鼠皮肤发育中表达的研究

目的研究角蛋白15(K15)在大鼠皮肤发育中的表达状况,定位表皮干细胞.方法以不同年龄大鼠背部皮肤为标本,用组织学方法,观察出生后大鼠皮肤的形态发育变化;以K15单克隆抗体为一抗,进行免疫组织化学染色,观察K15在大鼠皮肤中的表达状况.结果(1)组织学方法显示,随着年龄的增长,大鼠背部表皮细胞层数逐渐变少;在毛囊的生长周期中,以隆突区为界,毛囊上段为恒定区,下段呈周期性变化(2)免疫组化染色显示,毛囊隆突区细胞胞浆表达K15,随年龄的增长,K15阳性细胞出现在毛母质细胞区、毛囊外根鞘和表皮基底层.结论表皮干细胞位于毛囊隆突区,与表皮的更新和毛囊的周期性变化有关.     

毛囊干细胞研究进展

毛囊干细胞定位在毛囊隆突部,该部位细胞具有其它成体干细胞的共同特性,即慢周期、未分化、自我更新能力及体外增殖能力强等。CD34,K15,K19和Nestin可能作为毛囊干细胞的表面标记。毛囊干细胞在体外可诱导分化为神经元细胞,神经胶质细胞,角化细胞,平滑肌细胞和黑色素细胞等,而在体内（移植后）可分化为神经元、黑色素细胞等。在毛囊干细胞信号调控中涉及到许多的调控信号,主要包括WNT信号、BMP信号和NFATc1等基因的作用。     

皮肤毛囊发育的转录组研究进展

近年来,转录组测序技术在动物重要经济性状受复杂基因网络的调控研究领域取得了显著的成果。作为哺乳动物皮肤的衍生物,毛囊是唯一具有高度自我更新能力、独特的可再生器官,毛囊细胞经增殖分化最终形成毛发。已有的研究表明,诸多生长因子及其受体作为体内分泌协调基因的重要因素,对毛发的生长发育起着重要的调控作用。文章综述了近年来转录组测序技术在人、小鼠及羊等生物的皮肤毛囊发育和再生过程中基因调控方式的研究进展,旨在为今后人工干扰绒毛周期生长发育和分子育种提供理论依据,同时也为皮肤毛囊相关疾病的临床治疗提供新思路。     

干细胞概述

干细胞是存在于胚胎和成体中的一类特殊细胞,它能长期地自我更新,在特定的条件下具有分化形成多种终末细胞的能力,不同来源的干细胞分化潜能各异。从早期胚胎内细胞团分离的胚胎干细胞能分化形成个体所有的细胞类型,并具有在体外无限增殖的能力,是最具有临床应用前景和研究价值的干细胞之一。在成体各种组织和器官中也存在成体干细胞,用于维持机体结构和功能的稳态。近期有关成体干细胞可塑性的研究和成体组织中多能干细胞存在的证据扩大了人们对成体干细胞分化潜能的认识。干细胞具有的多向分化潜能和自我更新能力使其成为未来再生医学的重要种子细胞,并成为研究人类早期胚层特化和器官形成、药物筛选以及基因治疗的最佳工具。     

Edar信号通路调控毛囊发育的研究进展

Edar信号通路最早发现于人少汗型外胚层发育不良综合征(hypohidrotic ectodermal dysplasia,HED)疾病患者,它是调控胚胎发育早期皮肤附属物——头发、指甲、牙齿、外分泌腺等的形态发生、发育过程的重要信号通路。与人类相同,小鼠皮肤内毛囊于胚胎期发生并发育成熟,出生后进入动态变化的毛囊周期性生长。小鼠模型的相关研究表明,Edar信号通路在早期初级毛囊的发生、成体毛囊周期性生长和被毛纤维直径等方面都发挥重要的调控作用。现综述Edar通路中重要信号分子的结构特点、转导途径及其在皮肤和毛囊早期形态发生中的作用;阐述Edar信号通路对毛囊生长周期的调控,对维持皮肤微环境稳态、促进皮肤损伤修复和表皮再生的作用,以及在临床治疗HED相关疾病方面的潜在应用前景。     

小鼠毛囊发育分子遗传学机制研究进展

毛囊作为皮肤的附属器官,具有不断进行组织再生的特点,是研究干细胞的一种理想模型。毛囊发育机制十分复杂,其形态发生与持续终生的再生循环过程涉及表皮(上皮)和真皮(间充质)之间的相互作用。现已有相关的小鼠遗传模型被用于研究毛囊发育及再生的分子机制。该综述介绍最新的小鼠遗传学研究,主要涉及在毛囊发育过程中分别来自表皮和真皮中关键信号分子的敲除或过表达,以描绘一个控制毛囊发育和周期性循环的信号网络,为深入立体地理解毛囊发育机制和临床毛发疾病发病机制提供理论依据。     

潜在的成体肝干/祖细胞

研究者在50年前提出“成体肝组织内存在肝干细胞”这一假说.肝干/祖细胞研究对干细胞基础研究及其临床治疗研究都有着重要的意义.研究者也已从损伤的人类和啮齿动物的肝组织中分离到激活的肝干/祖细胞,并建立了相应的培养体系.目前的研究表明,肝内存在多个具有干细胞特性的细胞,且它们位于肝内不同的区域.另外,潜在的肝干/祖细胞的分子表达谱也已得到一定的阐述.本文结合肝干/祖细胞的研究,对成体肝干/祖细胞的潜在类型、来源与定位作一回顾.     

干细胞核移植效率及核移植胚胎干细胞

干细胞为一类具有无限的或者永生的自我更新能力的细胞,包括胚胎性干细胞和成体干细胞.胚胎性干细胞有胚胎干细胞、畸胎瘤细胞和原始生殖细胞.成体干细胞主要有骨髓间充质干细胞,造血干细胞、神经干细胞、表皮干细胞、脂肪干细胞等.随着体细胞核移植技术与干细胞培养技术的成熟,两者相结合便产生了核移植来源胚胎干细胞(embryonic stem cells via nuclear transfer,ntES细胞),其不仅用于基础的研究,而且也用于临床医学的组织修复和移植的研究.现就干细胞作为核供体时的核移植效率,ntES细胞系的建立、其性质及诱导分化等的研究进展进行综述.     

Glutamate transporter Slc1a3 mediates inter‐niche stem cell activation during skin growth

Tissues contain distinct stem cell niches, but whether cell turnover is coordinated between niches during growth is unknown. Here, we report that in mouse skin, hair growth is accompanied by sebaceous gland and interfollicular epidermis expansion. During hair growth, cells in the bulge and outer root sheath temporarily upregulate the glutamate transporter SLC1A3, and the number of SLC1A3⁺ basal cells in interfollicular epidermis and sebaceous gland increases. Fate mapping of SLC1A3⁺ cells in mice revealed transient expression in proliferating stem/progenitor cells in all three niches. Deletion of slc1a3 delays hair follicle anagen entry, uncouples interfollicular epidermis and sebaceous gland expansion from the hair cycle, and leads to reduced fur density in aged mice, indicating a role of SLC1A3 in stem/progenitor cell activation. Modulation of metabotropic glutamate receptor 5 activity mimics the effects of SLC1A3 deletion or inhibition. These data reveal that stem/progenitor cell activation is synchronized over distinct niches during growth and identify SLC1A3 as a general marker and effector of activated epithelial stem/progenitor cells throughout the skin.     

Distinct stem cell populations regenerate the follicle and interfollicular epidermis

The regeneration of the skin and its appendages is thought to occur by the regulated activation of a dedicated stem cell population. A population of cells in the bulge region of the hair follicle has been identified as the putative stem cell of both the follicle and the interfollicular epidermis. While this assertion is supported by a variety of surrogate assays, there has been no direct confirmation of the normal contribution of these cells to the regeneration of structures other than the cycling portion of the hair follicle. Here, we report lineage analysis revealing that the follicular epithelium is derived from cells in the epidermal placode that express Sonic hedgehog. This analysis also demonstrates that the stem cells resident in the follicular bulge that regenerate the follicle are neither the stem cells of the epidermis nor the source of the stem cells of the epidermis in the absence of trauma.     

Manipulation of stem cell proliferation and lineage commitment: visualisation of label-retaining cells in wholemounts of mouse epidermis

Mammalian epidermis is maintained by stem cells that have the ability to self-renew and generate daughter cells that differentiate along the lineages of the hair follicles, interfollicular epidermis and sebaceous gland. As stem cells divide infrequently in adult mouse epidermis, they can be visualised as DNA label-retaining cells (LRC). With whole-mount labelling, we can examine large areas of interfollicular epidermis and many hair follicles simultaneously, enabling us to evaluate stem cell markers and examine the effects of different stimuli on the LRC population. LRC are not confined to the hair follicle, but also lie in sebaceous glands and interfollicular epidermis. LRC reside throughout the permanent region of the hair follicle, where they express keratin 15 and lie in a region of high alpha6beta4 integrin expression. LRC are not significantly depleted by successive hair growth cycles. They can, nevertheless, be stimulated to divide by treatment with phorbol ester, resulting in near complete loss of LRC within 12 days. Activation of Myc stimulates epidermal proliferation without depleting LRC and induces differentiation of sebocytes within the interfollicular epidermis. Expression of N-terminally truncated Lef1 to block beta-catenin signalling induces transdifferentiation of hair follicles into interfollicular epidermis and sebocytes and causes loss of LRC primarily through proliferation. We conclude that LRC are more sensitive to some proliferative stimuli than others and that changes in lineage can occur with or without recruitment of LRC into cycle.     

Wnt signaling induces differentiation of progenitor cells in organotypic keratinocyte cultures

Background  

Interfollicular skin develops normally only when the activity of the progenitor cells in the basal layer is counterbalanced by the exit of cells into the suprabasal layers, where they differentiate and cornify to establish barrier function. Distinct stem and progenitor compartments have been demonstrated in hair follicles and sebaceous glands, but there are few data to describe the control of interfollicular progenitor cell activity. Wnt signaling has been shown to be an important growth-inducer of stem cell compartments in skin and many other tissues.     

Expression of DeltaNLef1 in mouse epidermis results in differentiation of hair follicles into squamous epidermal cysts and formation of skin tumours.

To examine the consequences of repressing beta-catenin/Lef1 signalling in mouse epidermis, we expressed a DeltaNLef1 transgene, which lacks the beta-catenin binding site, under the control of the keratin 14 promoter. No skin abnormalities were detected before the first postnatal hair cycle. However, from 6 weeks of age, mice underwent progressive hair loss which correlated with the development of dermal cysts. The cysts were derived from the base of the hair follicles and expressed morphological and molecular markers of interfollicular epidermis. Adult mice developed spontaneous skin tumours, most of which exhibited sebaceous differentiation, which could be indicative of an origin in the upper part of the hair follicle. The transgene continued to be expressed in the tumours and beta-catenin signalling was still inhibited, as evidenced by absence of cyclin D1 expression. However, patched mRNA expression was upregulated, suggesting that the sonic hedgehog pathway might play a role in tumour formation. Based on our results and previous data on the consequences of activating beta-catenin/Lef1 signalling in postnatal keratinocytes, we conclude that the level of beta-catenin signalling determines whether keratinocytes differentiate into hair or interfollicular epidermis, and that perturbation of the pathway by overexpression of DeltaNLef1 can lead to skin tumour formation.     

Epidermal stem cells - role in normal, wounded and pathological psoriatic and cancer skin

In this review we focus on epidermal stem cells in the normal regeneration of the skin as well as in wounded and psoriatic skin. Furthermore, we discuss current data supporting the idea of cancer stem cells in the pathogenesis of skin carcinoma and malignant melanoma. Epidermal stem cells present in the basal layer of the interfollicular epidermis and in the bulge region of the hair follicle play a critical role for normal tissue maintenance. In wound healing, multipotent epidermal stem cells contribute to re-epithelization. It is possible that defects in growth control of either epidermal stem cells or transit amplifying cells constitute a primary pathogenetic factor in the epidermal hyperproliferation seen in psoriasis. In cutaneous malignancies mounting evidence supports a stem cell origin in skin carcinoma and malignant melanoma and a possible existence of cancer stem cells.     

Differential response of epithelial stem cell populations in hair follicles to TGF-β signaling

Epidermal stem cells residing in different locations in the skin continuously self-renew and differentiate into distinct cell lineages to maintain skin homeostasis during postnatal life. Murine epidermal stem cells located at the bulge region are responsible for replenishing the hair lineage, while the stem cells at the isthmus regenerate interfollicular epidermis and sebaceous glands. In vitro cell culture and in vivo animal studies have implicated TGF-β signaling in the maintenance of epidermal and hair cycle homeostasis. Here, we employed a triple transgenic animal model that utilizes a combined Cre/loxP and rtTA/TRE system to allow inducible and reversible inhibition of TGF-β signaling in hair follicle lineages and suprabasal layer of the epidermis. Using this animal model, we have analyzed the role of TGF-β signaling in distinct phases of the hair cycle. Transient abrogation of TGF-β signaling does not prevent catagen progression; however, it induces aberrant proliferation and differentiation of isthmus stem cells to epidermis and sebocyte lineages and a blockade in anagen re-entry as well as results in an incomplete hair shaft development. Moreover, ablation of TGF-β signaling during anagen leads to increased apoptosis in the secondary hair germ and bulb matrix cells. Blocking of TGF-β signaling in bulge stem cell cultures abolishes their colony-forming ability, suggesting that TGF-β signaling is required for the maintenance of bulge stem cells. At the molecular level, inhibition of TGF-β signaling results in a decrease in both Lrig1-expressing isthmus stem cells and Lrg5-expressing bulge stem cells, which may account for the phenotypes seen in our animal model. These data strongly suggest that TGF-β signaling plays an important role in regulating the proliferation, differentiation, and apoptosis of distinct epithelial stem cell populations in hair follicles.     

Epithelial stem cells and implications for wound repair

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 interfollicular 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 the cellular and signaling basis of this remarkable adult wound regeneration phenomenon.     

Phospholipase Cdelta1 is required for skin stem cell lineage commitment

Phosphoinositide-specific phospholipase C (PLC) is a key enzyme in phosphoinositide turnover and is involved in a variety of physiological functions. Here we report that PLCdelta(1)-deficient mice undergo progressive hair loss in the first postnatal hair cycle. Epidermal hyperplasia was observed, and many hairs in the skin of PLCdelta(1)-deficient mice failed to penetrate the epidermis and became zigzagged owing to occlusion of the hair canal. Two major downstream signals of PLC, calcium elevation and protein kinase C activation, were impaired in the keratinocytes and skin of PLCdelta(1)-deficient mice. In addition, many cysts that had remarkable similarities to interfollicular epidermis, as well as hyperplasia of sebaceous glands, were observed. Furthermore, PLCdelta(1)-deficient mice developed spontaneous skin tumors that had characteristics of both interfollicular epidermis and sebaceous glands. From these results, we conclude that PLCdelta(1) is required for skin stem cell lineage commitment.