MicroRNA 181b Regulates Decorin Production by Dermal Fibroblasts and May Be a Potential Therapy for Hypertrophic Scar

Hypertrophic scarring is a frequent fibroproliferative complication following deep dermal burns leading to impaired function and lifelong disfigurement. Decorin reduces fibrosis and induces regeneration in many tissues, and is significantly downregulated in hypertrophic scar and normal deep dermal fibroblasts. It was hypothesized that microRNAs in these fibroblasts downregulate decorin and blocking them would increase decorin and may prevent hypertrophic scarring. Lower decorin levels were found in hypertrophic scar as compared to normal skin, and in deep as compared to superficial dermis. A decorin 3’ un-translated region reporter assay demonstrated microRNA decreased decorin in deep dermal fibroblasts, and microRNA screening predicted miR- 24, 181b, 421, 526b, or 543 as candidates. After finding increased levels of mir-181b in deep dermal fibroblasts, it was demonstrated that TGF-β₁ stimulation decreased miR-24 but increased miR-181b and that hypertrophic scar and deep dermis contained increased levels of miR-181b. By blocking miR-181b with an antagomiR, it was possible to increase decorin protein expression in dermal fibroblasts. This suggests miR-181b is involved in the differential expression of decorin in skin and wound healing. Furthermore, blocking miR-181b reversed TGF-β₁ induced decorin downregulation and myofibroblast differentiation in hypertrophic scar fibroblasts, suggesting a potential therapy for hypertrophic scar.     

Skin aging: a role for telomerase and telomere dynamics?

Skin is a complex tissue composed of two very different compartments -- the continuously renewing epidermis made up mostly by keratinocytes and the underlying matrix-rich dermis with the resting fibroblasts as its major cellular components. Both compartments are tightly interconnected and a paracrine mutual interaction is essential for epidermal growth, differentiation, and tissue homeostasis. Skin aging is commonly viewed as wrinkle formation, hair greying, and impaired wound healing. Nevertheless, the epidermis as the outermost shield needs to remain intact in order to guarantee an inside-out and outside-in barrier function throughout life time of a human being. Furthermore, the epidermis is one of the few regenerative tissues that express telomerase, the ribonucleoprotein complex that can counteract telomere erosion, one of the presently mostly favoured potential mechanisms causing cellular aging. This raises the question whether in the epidermis telomerase is able to counteract telomere erosion and thereby to prevents a telomere-dependent aging process and consequently which part of the skin is responsible for the most obvious changes associated with skin aging.     

Clonal characterization of fibroblasts in the superficial layer of the adult human dermis

The dermis of adult human skin contains a physiologically heterogeneous population of fibroblasts that interact to produce its unique architecture and that participate in inflammatory and wound repair functions in vivo. This heterogeneity has been well documented for fibroblasts located in the superficial papillary dermis and the deep reticular dermis. However, the existence of diverse fibroblast subpopulations within a given region of the dermis has not been explored. In this study, fibroblast cultures have been established from the superficial dermis following enzymatic dissociation of the tissue. These fibroblasts have been cloned by limiting dilution and initially selected on the basis of morphology and proliferation kinetics. Fibroblasts in some of the clones selected for study express α-smooth muscle actin, a myofibroblast characteristic. Significant differences for fibroblast clones obtained from the same piece of skin have been observed with regard to their rate of collagen lattice contraction, their ability to organize a fibronectin matrix, their release of specific growth factors/cytokines into culture medium, and their response to interleukin-1α. These differences in both morphological and physiological characteristics indicate that the superficial papillary dermis contains a heterogeneous population of fibroblasts. This heterogeneity might indicate that diverse subpopulations of fibroblasts are required to interact in both homeostatic and pathological situations in skin. We thank L’Oréal Life Sciences for providing funding for these studies.     

Roles for PDGF-A and sonic hedgehog in development of mesenchymal components of the hair follicle.

Skin appendages, such as hair, develop as a result of complex reciprocal signaling between epithelial and mesenchymal cells. These interactions are not well understood at the molecular level. Platelet-derived growth factor-A (PDGF-A) is expressed in the developing epidermis and hair follicle epithelium, and its receptor PDGF-Ralpha is expressed in associated mesenchymal structures. Here we have characterized the skin and hair phenotypes of mice carrying a null mutation in the PDGF-A gene. Postnatal PDGF-A-/- mice developed thinner dermis, misshapen hair follicles, smaller dermal papillae, abnormal dermal sheaths and thinner hair, compared with wild-type siblings. BrdU labeling showed reduced cell proliferation in the dermis and in the dermal sheaths of PDGF-A-/- skin. PDGF-A-/- skin transplantation to nude mice led to abnormal hair formation, reproducing some of the features of the skin phenotype of PDGF-A-/- mice. Taken together, expression patterns and mutant phenotypes suggest that epidermal PDGF-A has a role in stimulating the proliferation of dermal mesenchymal cells that may contribute to the formation of dermal papillae, mesenchymal sheaths and dermal fibroblasts. Finally, we show that sonic hedgehog (shh)-/- mouse embryos have disrupted formation of dermal papillae. Such embryos fail to form pre-papilla aggregates of postmitotic PDGF-Ralpha-positive cells, suggesting that shh has a critical role in the assembly of the dermal papilla.     

Xanthophore migration from the dermis to the epidermis and dermal remodeling during Salamandra salamandra salamandra (L.) larval development

During larval development of Salamandra salamandra salamandra chromatophores organize to form the definitive pigment pattern constituted by a black background with yellow patches that are characterized by epidermal xanthophores and dermal iridophores. Simultaneously the dermis undergoes remodeling from the larval stage to that typical of the adult. In the present study we ultrastucturally and immunocytochemically examined skin fragments of S. s. salamandra larvae and juveniles in order to investigate the modalities of xanthophore migration and differentiation in the context of dermal remodeling from the larval to adult stage. Semithin and thin sections showed that the dermis in newly born larvae consists of a compact connective tissue (basement lamella), to which fibroblasts and xanthophores adhere, and of a loose deep collagen layer. As larval development proceeds, fibroblasts and xanthophores invade the basement lamella, skin glands develop and the adult dermis forms. At metamorphosis, xanthophores reach the epidermis crossing through the basal lamina. We examined immunocytochemically the expression of signal molecules, such as fibronectin, vitronectin, beta1-integrin, chondroitin sulfate, E-cadherin, N-cadherin and plasminogen activator, which are known to be involved in regulating morphogenetic events. Their role in dermal remodeling and in pigment pattern formation is discussed.     

松江鲈鱼皮肤的显微和亚显微结构

采用光学显微镜、扫描电镜和透射电镜,对松江鲈鱼(Trachidermus fasciatus)成体皮肤的显微和亚显微结构进行了观察。结果表明,松江鲈鱼体表不同部位皮肤的厚薄不一,但基本结构相似。皮肤由表皮和真皮层构成。松江鲈鱼的皮肤裸露无鳞,表皮层较薄,由约4～8层细胞构成,主要由复层上皮细胞和黏液细胞及基底细胞组成。表层细胞呈扁平、多边形,细胞之间主要靠桥粒紧密连接,连接处形成增厚的边缘嵴状突起。表皮细胞游离面向内凹陷,表面形成指纹状微嵴。黏液细胞呈圆形或卵圆形,散布在上皮细胞之间。黏液细胞内的黏原颗粒具有椭圆颗粒状、均匀致密的块状和疏松丝状3种不同形态。真皮通过基膜与表皮相连,由稀疏层和致密层构成。真皮结缔组织在腹部较厚而在其他部位较薄。表皮与真皮连接处有色素层,头部、背部、尾柄和体侧皮肤色素细胞分布多,色素层明显,而腹部和颏部皮肤缺少色素。松江鲈鱼黄河群体真皮层中有角质棘状突起,而滦河群体则无。头部、体侧和尾柄处皮肤上还分布有侧线孔和表面神经丘等感觉器官。     

UVA exposure of human skin reconstructed in vitro induces apoptosis of dermal fibroblasts: subsequent connective tissue repair and implications in photoaging

The skin reconstructed in vitro has been previously shown to be a useful model to investigate the effects of UVB exposure (Bernerd and Asselineau, 1997). The present study describes the response to UVA irradiation. Major alterations were observed within the dermal compartment. Apoptosis of fibroblasts located in the superficial area of the dermal equivalent was observed as soon as 6 h after irradiation, leading to their disappearance after 48 h. This effect was obtained without major alterations of epidermal keratinocytes suggesting a differential cell type sensitivity to UVA radiations. In addition, collagenase I was secreted by dermal fibroblasts. The UVA dermal effects could be observed even after removal of the epidermis during the post irradiation period, demonstrating that they were independent of the keratinocyte response. The analysis of the tissue regeneration during the following 2 weeks revealed a connective tissue repair via fibroblasts proliferation, migration and active synthesis of extracellular matrix proteins such as fibronectin and procollagen I. This cellular recolonization of the superficial part of the dermal equivalent was due to activation of surviving fibroblasts located deeply in the dermal equivalent. The direct damage in the dermis and the subsequent connective tissue repair may contribute to the formation of UVA-induced dermal alterations.     

Scale morphogenesis and ultrastructure of dermis during embryonic development in the alligator (Alligator mississippiensis, Crocodilia, Reptilia)

Formation of scales in different body regions of embryonic alligators is described using light and electron microscopy. Transformation of the skin surface to produce scales takes place between stages 19 and 23, after which the shape of scales is complete over most of the embryonic surface. Scalation is not synchronous; different regions develop scales at different rates. Initially scales are formed on the back and dorsal side of the proximal tail and appear as undulations of the epidermis which form symmetrical (bumps) or asymmetrical (serrated) scale anlagen. No dermal condensations are apparent beneath the epidermis, although in some areas of the skin (belly, limbs) mesenchymal cells are more numerous within the bumps than in other areas. At stage 21, scalation has spread to the neck and belly but is absent or poorly developed over most areas of the flank, gular, jaw, limb and head regions. Grooves form between the outer edges of adjacent scales or interbump regions. A superficial denser dermis and a reticulated deep subdermis are visible in many scales from stage 21. The dermis forms a superficial loose and a deep dense layer from stage 22. Both loose and deep dermis, and sometimes the deep reticulate subdermis, move towards the surface to form the dermal core of scales, although the mechanism of this movement is not known. Bundles of collagen fibrils, with almost no elastic fibrils, are progressively deposited, especially in the denser dermis. At stage 22, the flank, gular and proximal areas of limbs form scales, but the head, jaw, distal limbs and digits still lack scales. The digits become scaled at stage 23 when scalation is well advanced in the other regions. By stage 24 most of the body is scaled and subsequent scale modifications occur only by growth. Five main types of scales are recognized by their shape: symmetrical scutes, asymmetrical scutes, overlapping scutes, tuberculate scales, and elevated asymmetrical scutes (tail verticils). Pigmentation, mainly due to epidermal melanocytes, is visible at embryonic stage 23 and progresses through stages 24 and 25.     

Expression of high molecular weight (67K) keratin in human keratinocytes cultured on dead de-epidermized dermis

The influence of living dermal tissue upon epidermal differentiation during embryonic development as well as in vitro culture has been documented. Living dermal tissue contains both cellular and matricial elements. In the present study, third-passage subcultured adult human keratinocytes were either seeded on plastic dishes or recombined with dead de-epidermized dermis and further cultured for 3 weeks. After this time, keratins were extracted and analysed by one- and two-dimensional gel electrophoresis. The 67K keratin subunit, which is thought to be involved in the process of in vivo type skin differentiation, was absent in ordinary cultures; however, it was expressed in air-exposed cultures on dead de-epidermized dermis. Quantitatively, however, it did not reach the in vivo level. This suggests that in principle, the induction of the expression of this protein does not require the presence of living dermal cells.     

Aging Alters Functionally Human Dermal Papillary Fibroblasts but Not Reticular Fibroblasts: A New View of Skin Morphogenesis and Aging

Understanding the contribution of the dermis in skin aging is a key question, since this tissue is particularly important for skin integrity, and because its properties can affect the epidermis. Characteristics of matched pairs of dermal papillary and reticular fibroblasts (Fp and Fr) were investigated throughout aging, comparing morphology, secretion of cytokines, MMPs/TIMPs, growth potential, and interaction with epidermal keratinocytes. We observed that Fp populations were characterized by a higher proportion of small cells with low granularity and a higher growth potential than Fr populations. However, these differences became less marked with increasing age of donors. Aging was also associated with changes in the secretion activity of both Fp and Fr. Using a reconstructed skin model, we evidenced that Fp and Fr cells do not possess equivalent capacities to sustain keratinopoiesis. Comparing Fp and Fr from young donors, we noticed that dermal equivalents containing Fp were more potent to promote epidermal morphogenesis than those containing Fr. These data emphasize the complexity of dermal fibroblast biology and document the specific functional properties of Fp and Fr. Our results suggest a new model of skin aging in which marked alterations of Fp may affect the histological characteristics of skin.     

SD大鼠与巴马小型猪的皮肤组织学比较

目的研究及观察SD大鼠和巴马小型猪皮肤的正常比较组织学。方法取SD大鼠和巴马小型猪不同部位的皮肤进行石蜡切片、HE染色,光学显微镜观察。结果两种动物的皮肤组织学结构在以下方面存在着显著差异：1.SD大鼠的毛囊成簇分布,平均3～9成群,而巴马小型猪的毛囊较稀少;2.SD大鼠表皮较薄,没有透明层,基底细胞缺乏异质性,真皮与表皮连接面平坦,没有皮钉;而在巴马小型猪皮肤表皮和真皮连接区,有上下交错的表皮皮钉和真皮乳头;3.SD大鼠的真皮结构相对松散,真皮血管系统不发达,而巴马小型猪皮肤的真皮网织层和乳头层交界的地方,水平分布着很多的浅表小静脉和小动脉丛,这种血管分布的方式与人类皮肤中的血管分布极为类似;4.SD大鼠的汗腺只局限于足垫的皮肤,汗腺上皮只有一种细胞类型,腺细胞呈立方形或矮柱状,胞核圆形,导管短而弯曲,由两层上皮细胞组成。而巴马小型猪皮肤的汗腺是顶泌汗腺,分布于真皮和脂肪相接的真皮深层,分泌部为粗管,管腔大,盘曲成团。腺细胞呈立方形或扁平,胞核圆形或长梭形。腺细胞与基膜之间也有肌上皮细胞。导管较细而直,开口于毛囊上段。     

Collagen XII and XIV, new partners of cartilage oligomeric matrix protein in the skin extracellular matrix suprastructure

The tensile and scaffolding properties of skin rely on the complex extracellular matrix (ECM) that surrounds cells, vasculature, nerves, and adnexus structures and supports the epidermis. In the skin, collagen I fibrils are the major structural component of the dermal ECM, decorated by proteoglycans and by fibril-associated collagens with interrupted triple helices such as collagens XII and XIV. Here we show that the cartilage oligomeric matrix protein (COMP), an abundant component of cartilage ECM, is expressed in healthy human skin. COMP expression is detected in the dermal compartment of skin and in cultured fibroblasts, whereas epidermis and HaCaT cells are negative. In addition to binding collagen I, COMP binds to collagens XII and XIV via their C-terminal collagenous domains. All three proteins codistribute in a characteristic narrow zone in the superficial papillary dermis of healthy human skin. Ultrastructural analysis by immunogold labeling confirmed colocalization and further revealed the presence of COMP along with collagens XII and XIV in anchoring plaques. On the basis of these observations, we postulate that COMP functions as an adapter protein in human skin, similar to its function in cartilage ECM, by organizing collagen I fibrils into a suprastructure, mainly in the vicinity of anchoring plaques that stabilize the cohesion between the upper dermis and the basement membrane zone.     

Atmospheric oxygen accelerates the induction of a post-mitotic phenotype in human dermal fibroblasts: the key protective role of glutathione

It has been proposed that ageing of human dermal fibroblasts occurs as a multi-stage process during which cells progress from a mitotic to a post-mitotic state. We describe the development of a simple and novel cell-cloning model for identifying and quantifying the different fibroblast morphotypes associated with the induction of post mitotic behaviour. We have found that under atmospheric (20%) oxygen tension a significant proportion of human dermal fibroblasts are rapidly induced to switch from a mitotic to a post-mitotic phenotype. In contrast, under more physiological (4%) oxygen conditions, the induction of a post-mitotic phenotype is largely prevented. Increasing oxidative stress by addition of hydrogen peroxide or depletion of glutathione also induced a switch from a mitotic to a post-mitotic phenotype in these cells, whereas addition of the anti-oxidant N-acetylcysteine under atmospheric (20%) oxygen tension potently inhibited this process. In addition, a statistically significant correlation was observed between the magnitude of intracellular glutathione depletion and the reduction in the population of mitotic cells in this model. We propose that the switch from a mitotic to a post-mitotic phenotype represents a process of cellular ageing and that standard atmospheric oxygen tension imposes a substantial oxidative stress on dermal fibroblasts which accelerates this process in culture. The data also suggest that intracellular glutathione levels strongly influence the induction of a post-mitotic phenotype and that, by implication, depletion of glutathione may play a significant role in the progression of cellular ageing in human skin.     

Reprogramming adult dermis to a neonatal state through epidermal activation of β-catenin

Hair follicle formation depends on reciprocal epidermal-dermal interactions and occurs during skin development, but not in adult life. This suggests that the properties of dermal fibroblasts change during postnatal development. To examine this, we used a PdgfraEGFP mouse line to isolate GFP-positive fibroblasts from neonatal skin, adult telogen and anagen skin and adult skin in which ectopic hair follicles had been induced by transgenic epidermal activation of β-catenin (EF skin). We also isolated epidermal cells from each mouse. The gene expression profile of EF epidermis was most similar to that of anagen epidermis, consistent with activation of β-catenin signalling. By contrast, adult dermis with ectopic hair follicles more closely resembled neonatal dermis than adult telogen or anagen dermis. In particular, genes associated with mitosis were upregulated and extracellular matrix-associated genes were downregulated in neonatal and EF fibroblasts. We confirmed that sustained epidermal β-catenin activation stimulated fibroblasts to proliferate to reach the high cell density of neonatal skin. In addition, the extracellular matrix was comprehensively remodelled, with mature collagen being replaced by collagen subtypes normally present only in developing skin. The changes in proliferation and extracellular matrix composition originated from a specific subpopulation of fibroblasts located beneath the sebaceous gland. Our results show that adult dermis is an unexpectedly plastic tissue that can be reprogrammed to acquire the molecular, cellular and structural characteristics of neonatal dermis in response to cues from the overlying epidermis.     

Distinct roles of JNK-1 and ERK-2 isoforms in permeability barrier repair and wound healing

c-Jun N-terminal kinases (JNKs, also called stress activated protein kinases) and the extra-cellular signal responsive kinases (ERKs) exert different functions in mitogenesis, maturation and differentiation of immune and epithelial cells. We investigated specific functions of individual JNK and ERK isoforms in skin permeability barrier repair and in wound healing. JNK1, but not JNK2 or JNK3, deficient mice revealed a delay in the permeability barrier repair after superficial injury to the skin (tape-stripping) as well as a delay in the healing of full skin thickness wounds. Skin barrier injury induced an increase in epidermal JNK1 enzyme activity in mouse skin in vivo, and JNK1 activity correlated with the degree of differentiation in organotypic keratinocyte cultures. Skin injury activated epidermal ERK2 enzyme activity with biphasic maxima after 30 min and 3h, and the activity was independent from the differentiation state in keratinocyte culture. In summary, superficial and deep wound healing depends on the differential activity of MAP kinases such as JNK1 in epidermal differentiation and ERK2 in proliferation.     

Induction of Mucous Metaplasia in Chick Embryonic Skin by Retinol-Pretreated Embryonic Chick or Quail Dermal Fibroblasts through Cell-Cell Interaction: Correlation of a Transient Increase in Retinoic Acid Receptor β mRNA in Retinol-Treated Dermal Fibroblasts with Their Competence to Induce Epidermal Mucous Metaplasia

Epidermal mucous metaplasia of 13-day-old chick embryonic tarsometatarsal skin can be induced by culture in medium containing 20 μM retinol for only 8 hr and then in a chemically defined medium without retinol for 2 days. Retinol primarily affects the dermal cells, which then transform the epithelial cells into mucus-secreting cells. In this study, we developed a system using a combination of retinol-pretreated chick or quail dermal fibroblasts and chick skin, and showed that retinol-pretreated quail embryonic dermal fibroblasts invaded the dermis of chick embryonic skin to beneath the epidermal basal cells within 1 day of culture and induced metaplasia, suggesting that epidermal mucous metaplasia of the skin was induced by the direct interaction of retinol-pretreated dermal fibroblasts with the epidermal cells or by low diffusible paracrine factor produced by the fibroblasts.
Increase in retinoic acid receptor β (RARβ) mRNA in dermal fibroblasts was observed after 8 hr-treatment with retinol which preceded morphological changes induced by retinol and this increase was correlated with the competence of the dermal fibroblasts to induce epidermal mucous metaplasia. Thus some gene product(s) controlled by RARβ in dermal fibroblasts may be an essential signal for induction of epidermal mucous metaplasia.     

Distinct Wnt members regulate the hierarchical morphogenesis of skin regions (spinal tract) and individual feathers

Skin morphogenesis occurs in successive stages. First, the skin forms distinct regions (macropatterning). Then skin appendages with particular shapes and sizes form within each region (micropatterning). Ectopic DKK expression inhibited dermis formation in feather tracts and individual buds, implying the importance of Wnts, and prompted the assessment of individual Wnt functions at different morphogenetic levels using the feather model. Wnt 1, 3a, 5a and 11 initially were expressed moderately throughout the feather tract then were up-regulated in restricted regions following two modes: Wnt 1 and 3a became restricted to the placodal epithelium, then to the elongated distal bud epidermis; Wnt 5a and 11 intensified in the inter-tract region and interprimordia epidermis or dermis, respectively, then appeared in the elongated distal bud dermis. Their role in feather tract formation was determined using RCAS mediated misexpression in ovo at E2/E3. Their function in periodic feather patterning was examined by misexpression in vitro using reconstituted E7 skin explant cultures. Wnt 1 reduced spinal tract size, but enhanced feather primordia size. Wnt 3a increased dermal thickness, expanded the spinal tract size, reduced interbud domain spacing, and produced non-tapering "giant buds". Wnt 11 and dominant negative Wnt 1 enhanced interbud spacing, and generated thinner buds. In cultured dermal fibroblasts, Wnt 1 and 3a stimulated cell proliferation and activated the canonical beta-catenin pathway. Wnt 11 inhibited proliferation but stimulated migration. Wnt 5a and 11 triggered the JNK pathway. Thus distinctive Wnts have positive and negative roles in forming the dermis, tracts, interbud spacing and the growth and shaping of individual buds.     

The mutant form of lamin A that causes Hutchinson-Gilford progeria is a biomarker of cellular aging in human skin

Hutchinson-Gilford progeria syndrome (HGPS, OMIM 176670) is a rare disorder characterized by accelerated aging and early death, frequently from stroke or coronary artery disease. 90% of HGPS cases carry the LMNA G608G (GGC>GGT) mutation within exon 11 of LMNA, activating a splice donor site that results in production of a dominant negative form of lamin A protein, denoted progerin. Screening 150 skin biopsies from unaffected individuals (newborn to 97 years) showed that a similar splicing event occurs in vivo at a low level in the skin at all ages. While progerin mRNA remains low, the protein accumulates in the skin with age in a subset of dermal fibroblasts and in a few terminally differentiated keratinocytes. Progerin-positive fibroblasts localize near the basement membrane and in the papillary dermis of young adult skin; however, their numbers increase and their distribution reaches the deep reticular dermis in elderly skin. Our findings demonstrate that progerin expression is a biomarker of normal cellular aging and may potentially be linked to terminal differentiation and senescence in elderly individuals.     

Fibroblasts play a regulatory role in the control of pigmentation in reconstructed human skin from skin types I and II

Human melanocytes in monolayer culture are extremely dependent on a wide range of soluble signals for their proliferation and melanogenesis. The advent of three-dimensional models of reconstructed skin allows one to ask questions of how these cells are regulated within a setting which more closely approximates normal skin. The purpose of this study was to investigate to what extent melanocytes within a reconstructed skin model are sensitive to regulation by dermal fibroblasts, basement membrane (BM) proteins and the addition of alpha-melanocyte-stimulating hormone (alpha-MSH). Sterilized acellular de-epidermized dermis (prepared to retain BM proteins or deliberately denuded of BM by enzymatic treatment) from skin type I or II was reconstituted with fibroblasts, melanocytes and keratinocytes. In all but one case (9/10), cell donors were skin type I or II. The presence of BM antigens was found to be necessary for positional orientation of the melanocytes; in the absence of BM, melanocytes moved into the upper keratinocyte layer pigmenting spontaneously. Addition of fibroblasts suppressed the extent of spontaneous pigmentation of melanocytes within this model. Neither alpha-MSH nor cholera toxin induced pigmentation in this model despite the fact that melanocytes clearly had the ability to synthesize pigment.     

Cell technologies and the development of skin substitutes

Large skin lesions might be of different cause and sometime resistant to the conventional and surgical treatment. For many years, skin grafting used to serve one of the most important methods to treat large and deep skin lesions. However, a limited availability of the substrate for transplantation restricts wider application of the approach. Utilization of wound covers and skin replacements of various types (including synthetic, biological and biosynthetic ones) provides an alternative. Skin substitutes--biosynthetic covers of the complex structure--constitute the most important niche in a wide spectrum of wound covers developed and actively utilized by today. Cell substrates used in the former include dermal fibroblasts, neonatal foreskin fibroblasts and keratinocytes. In the current review, key properties of the modern skin substitutes, structure features of the most widespread types. and principle of the work with the particular cell types are analyzed. Comparative analysis of the efficiency of wound covers is provided.