Gene expression profile of tissue engineered skin subjected to acute barrier disruption

Epidermal Potentiation of Dermal Fibrosis: Lessons from Occlusion and Mucosal Healing

Fibrotic skin conditions, such as hypertrophic and keloid scars, frequently result from injury to the skin and as sequelae to surgical procedures. The development of skin fibrosis may lead to patient discomfort, limitation in range of motion, and cosmetic disfigurement. Despite the frequency of skin fibrosis, treatments that seek to address the root causes of fibrosis are lacking. Much research into fibrotic pathophysiology has focused on dermal pathology, but less research has been performed to understand aberrations in fibrotic epidermis, leading to an incomplete understanding of dermal fibrosis. The literature on occlusion, a treatment modality known to reduce dermal fibrosis, in part through accelerating wound healing and regulating aberrant epidermal inflammation that otherwise drives fibrosis in the dermis, is reviewed. There is a focus on epidermal-dermal crosstalk, which contributes to the development and maintenance of dermal fibrosis, an underemphasized interplay that may yield novel strategies for treatment if understood in more detail.

Modulation of Photoaging-Induced Cutaneous Elastin: Evaluation of Gene and Protein Expression of Markers Related to Elastogenesis Under Different Photoexposure Conditions

INTRODUCTION

Photoaging is the process by which ultraviolet rays gradually induce clinical and histological changes in the skin through the production and organization of biological molecules, such as elastin, which is critical to skin strength and elasticity. After exposure to radiation, elastin may undergo alternative mRNA splicing, resulting in modified proteins that contribute to the formation of aging characteristics, such as solar elastosis. The present work aimed to study two different forms of elastin under these conditions: normal elastin and elastin that had been altered in exon 26A.

METHODS

These different forms of elastin were characterized for gene expression by quantitative real-time polymerase chain reaction (qPCR) and for protein expression by immunohistochemistry of ex vivo skins (from photoexposed and non-photoexposed areas) and in vitro reconstituted skin. In addition, up- and downstream molecules in the elastin signaling cascade were evaluated.

RESULTS

As a result, a significant increase in the gene expression of elastin 26A was observed in both ex vivo photoexposed skin tissues and the in vitro photoexposed reconstituted skins. Additionally, significant increases in the gene expression levels of matrix metalloproteinase-12 (MMP12) and lysyl oxidase (LOX) were observed in the ex vivo skin model. The evaluation of protein expression levels of some photoaging markers on the reconstituted skin revealed increased tropoelastin and fibrillin-1 expression after photoexposure.

CONCLUSION

This work contributes to a better understanding of the biological mechanisms involved in photoaging, making it possible to obtain new strategies for the development of dermocosmetic active ingredients to prevent and treat skin aging.

Proteomic characterization of skin and epidermis in response to environmental agents

The skin and its outer epidermis layer in particular, prevent access of various environmental agents including potential allergens, irritants, carcinogens, ultraviolet radiation and microbes. Cells in the epidermis make a significant contribution to innate as well as adaptive immune reactions in skin. The skin immunity thus provides a biologic defense in response to hazardous environmental agents. Although proteomics has been utilized to establish skin proteomes and investigate skin responses to some environmental agents, it has not been extensively used to address the complexity of skin responses to various environments. This review summarizes cutaneous genes and proteins that have been characterized as related to skin exposure to environmental agents. In parallel, this review emphasizes functional proteomics and systems biology, which are believed to be an important future direction toward characterizing the skin proteome-environmental interaction and developing successful therapeutic strategies for skin diseases caused by environmental insults.

Nanog reverses the effects of organismal aging on mesenchymal stem cell proliferation and myogenic differentiation potential

Although the therapeutic potential of mesenchymal stem cells (MSCs) is widely accepted, loss of cell function due to donor aging or culture senescence are major limiting factors hampering their clinical application. Our laboratory recently showed that MSCs originating from older donors suffer from limited proliferative capacity and significantly reduced myogenic differentiation potential. This is a major concern, as the patients most likely to suffer from cardiovascular disease are elderly. Here we tested the hypothesis that a single pluripotency-associated transcription factor, namely Nanog, may reverse the proliferation and differentiation potential of bone marrow-derived MSC (BM-MSC) from adult donors. Microarray analysis showed that adult (a)BM-MSC expressing Nanog clustered close to Nanog-expressing neonatal cells. Nanog markedly upregulated genes involved in cell cycle, DNA replication, and DNA damage repair and enhanced the proliferation rate and clonogenic capacity of aBM-MSC. Notably, Nanog reversed the myogenic differentiation potential and restored the contractile function of aBM-MSC to a similar level as that of neonatal (n)BM-MSC. The effect of Nanog on contractility was mediated--at least in part--through activation of the TGF-β pathway by diffusible factors secreted in the conditioned medium of Nanog-expressing BM-MSC. Overall, our results suggest that Nanog may be used to overcome the effects of organismal aging on aBM-MSC, thereby increasing the potential of MSC from aged donors for cellular therapy and tissue regeneration.

Risk factor-dependent dynamics of atopic dermatitis: modelling multi-scale regulation of epithelium homeostasis

Epithelial tissue provides the body with its first layer of protection against harmful environmental stimuli by enacting the regulatory interplay between a physical barrier preventing the influx of external stimuli and an inflammatory response to the infiltrating stimuli. Importantly, this interdependent regulation occurs on different time scales: the tissue-level barrier permeability is regulated over the course of hours, whereas the cellular-level enzymatic reactions leading to inflammation take place within minutes. This multi-scale regulation is key to the epithelium's function and its dysfunction leads to various diseases. This paper presents a mathematical model of regulatory mechanisms in the epidermal epithelium that includes processes on two different time scales at the cellular and tissue levels. We use this model to investigate the essential regulatory interactions between epidermal barrier integrity and skin inflammation and how their dysfunction leads to atopic dermatitis (AD). Our model exhibits a structure of dual (positive and negative) control at both cellular and tissue levels. We also determined how the variation induced by well-known risk factors for AD can break the balance of the dual control. Our model analysis based on time-scale separation suggests that each risk factor leads to qualitatively different dynamic behaviours of different severity for AD, and that the coincidence of multiple risk factors dramatically increases the fragility of the epithelium's function. The proposed mathematical framework should also be applicable to other inflammatory diseases that have similar time-scale separation and control architectures.

Epidermal morphogenesis during progressive in vitro 3D reconstruction at the air-liquid interface

Keratinocyte monolayers, cultured in immersed conditions, constitute a frequently used in vitro model system to study keratinocytes behaviour in response to environmental assaults. However, monolayers lack the keratinocyte terminal differentiation and the organization of the epidermal tissue, which are observed in vivo. Advancements of in vitro techniques were used to reconstruct three-dimensional equivalents that mimic human epidermis in terms of layering, differentiation and barrier function. Here, we update a published method and illustrate the progressive morphogenesis responsible for in vitro reconstruction. The analysis of cell proliferation, expression of differentiation markers and barrier efficacy demonstrate the excellent similarity of the reconstructed tissue with normal human epidermis. Availability of epidermal tissue during its reconstruction phase in culture appears crucial for studies intending to challenge the barrier function.

Human keratinocytes' response to injury upregulates CCL20 and other genes linking innate and adaptive immunity

In the early stages of wound healing, keratinocytes become “activated” and release inflammatory molecules such as interleukin-1 and interleukin-8 that are linked to innate immune responses and neutrophil recruitment. It is unclear, however, whether keratinocytes release molecules linked to adaptive immune responses, e.g. CCL20, in their early state of activation without signals from infiltrating T cells. This study aims to isolate the immediate alterations in protective and inflammatory gene expression that occur in epidermal keratinocytes, with a particular focus on molecules associated with cell-mediated immunity. We used dispase-separated epidermis, followed by intercellular disassociation by trypsinization, as a model for epidermal injury. We obtained a pure population of keratinocytes using flow cytometry. As a control for uninjured epidermis, we performed laser capture microdissection on normal human skin. Sorted keratinocytes had an early burst of upregulated gene expression, which included CCL20, IL-15, IL-23A, IFN-κ, and several antimicrobial peptides. Our results provide insight into the potential role of keratinocytes as contributors to cell-mediated inflammation, and expand knowledge about gene modulation that occurs during early wound healing. Our findings may be relevant to cutaneous diseases such as psoriasis, where micro-injury can trigger the formation of psoriatic plaques at the site of trauma.

Molecular and functional effects of organismal ageing on smooth muscle cells derived from bone marrow mesenchymal stem cells

AIMS

Bone marrow-derived smooth muscle cells (BM-SMCs) have high potential as an autologous cell source of vascular progenitors but normal cell function and turnover frequency may decline with age. In this study we set out to study the effects of organismal ageing on the molecular and functional properties of BM-SMCs.

METHODS AND RESULTS

To address this issue, we employed a smooth muscle alpha-actin promoter (alphaSMA) driving expression of enhanced green fluorescence protein (EGFP) to isolate SMCs from bone marrow of neonatal (nBM-SMCs) or adult (aBM-SMCs) sheep and examined their proliferation potential and contractility. Compared with nBM-SMCs, aBM-SMCs exhibited lower clonogenicity and proliferation potential that could be improved significantly by addition of basic fibroblast growth factor. Vascular constructs from aBM-SMCs showed reduced ability to generate force and contract fibrin hydrogels and this function could be partially restored by addition of transforming growth factor-beta1. They also exhibited lower receptor- and non-receptor-mediated vascular contractility and mechanical strength, which was comparable to that of tissue constructs prepared with vascular SMCs from neonatal umbilical veins. In agreement with the contractile properties and mechanical strength of vascular constructs, aBM-SMCs displayed significantly lower expression of alphaSMA, smoothelin, desmin, type I collagen, and tropoelastin transcripts compared with nBM-SMCs.

CONCLUSION

Understanding the effects of organismal ageing on BM-SMCs and the properties of the resulting vascular constructs may lead to innovative ways to facilitate application of these cells in the treatment of cardiovascular disease which is especially prevalent in the elderly.

Large scale study of epidermal recovery after stratum corneum removal: dynamics of genomic response

The stratum corneum (SC) is a superficial skin compartment that protects the body from the outside environment. Any disturbance of this function induces cascading steps of molecular and cellular repair in the whole epidermis. The aim of this study was to investigate epidermal gene expression following SC removal by tape stripping. Twenty-nine healthy male volunteers were included (27 +/- 4 years old). Tape stripping was processed on one inner forearm, the other unstripped forearm served as a control. Epidermis samples were collected at 2, 6, 19, 30 and 72 h after tape stripping. Trans-epidermal water loss measurements were performed at each step to monitor barrier restoration. Total RNA was extracted from collected epidermis samples and analysed by using DermArray cDNA microarrays. Among 4000 genes under investigation, we found that the expression of 370 genes varied significantly at least once during the time following stripping. Using an original clustering method, the modulated genes were gathered into eight groups. A functional characterization of the clusters enabled us to get a dynamic and global view of the main molecular processes taking place during epidermal recovery.

An integrated reaction-transport model for DNA surface hybridization: implications for DNA microarrays

DNA microarrays have the potential to revolutionize medical diagnostics and development of individualized medical treatments. However, accurate quantification of scantily expressed genes and precise measurement of small differences between different treatments is not currently feasible. A major challenge remains the understanding of physicochemical processes and rate-limiting steps of hybridization of complex mixtures of DNA targets on immobilized DNA probes. To this end, we developed a mathematical model to describe the effects of molecular orientation and transport on the kinetics and efficiency of hybridization. First, we calculated the hybridization rate constant based on the distance between the complementary nucleotides of the target and probe DNA. The surface reaction rate was then integrated with translational and rotational transport of target DNA to the surface to calculate the kinetics of hybridization. Our model predicts that hybridization of short DNA targets is diffusion limited but long targets are kinetically limited. In addition, for DNA targets with wide size distribution, it may be difficult to distinguish between specific binding of long targets from nonspecific binding of short ones. Our model provides novel insight into the process of DNA hybridization and suggests operating conditions to improve the sensitivity and accuracy of microarray experiments.

Reconstructing protein networks of epithelial differentiation from histological sections

MOTIVATION

For systems biology of complex stratified epithelia like human epidermis, it will be of particular importance to reconstruct the spatiotemporal gene and protein networks regulating keratinocyte differentiation and homeostasis.

RESULTS

Inside the epidermis, the differentiation state of individual keratinocytes is correlated with their respective distance from the connective tissue. We here present a novel method to profile this correlation for multiple epithelial protein biomarkers in the form of quantitative spatial profiles. Profiles were computed by applying image processing algorithms to histological sections stained with tri-color indirect immunofluorescence. From the quantitative spatial profiles, reflecting the spatiotemporal changes of protein expression during cellular differentiation, graphs of protein networks were reconstructed.

CONCLUSION

Spatiotemporal networks can be used as a means for comparing and interpreting quantitative spatial protein expression profiles obtained from different tissue samples. In combination with automated microscopes, our new method supports the large-scale systems biological analysis of stratified epithelial tissues.

KGF promotes integrin alpha5 expression through CCAAT/enhancer-binding protein-beta

Keratinocyte growth factor (KGF) and alpha(5)beta(1)-integrin are not expressed in normal skin but they are both highly upregulated in the migrating epidermis during wound healing. Here we report that KGF increased alpha(5) mRNA and protein levels in epidermoid carcinoma cells and stratified bioengineered epidermis. Interestingly, KGF increased integrin alpha(5) in the basal as well as suprabasal cell epidermal layers. Promoter studies indicated that KGF-induced integrin alpha(5) promoter activation was dependent on the C/EBP transcription factor binding site. Accordingly, KGF induced sustained phosphorylation of C/EBP-beta that was dependent on activation of ERK1/2. In addition, a dominant negative form of C/EBP-beta inhibited alpha(5) promoter activity and blocking C/EBP-beta with siRNA diminished integrin alpha(5) expression. Taken together, our data indicate that KGF increased integrin alpha(5) expression by phosphorylating C/EBP-beta. Interestingly, KGF-induced upregulation of integrin alpha(5) was more pronounced in three-dimensional tissue analogues than in conventional two-dimensional culture suggesting that stratified epidermis may be useful in understanding the effects of growth factors in the local tissue microenvironment.

Cellular responses to disruption of the permeability barrier in a three-dimensional organotypic epidermal model

Repeated injury to the stratum corneum of mammalian skin (caused by friction, soaps, or organic solvents) elicits hyperkeratosis and epidermal thickening. Functionally, these changes serve to restore the cutaneous barrier and protect the organism. To better understand the molecular and cellular basis of this response, we have engineered an in vitro model of acetone-induced injury using organotypic epidermal cultures. Rat epidermal keratinocytes (REKs), grown on a collagen raft in the absence of any feeder fibroblasts, developed all the hallmarks of a true epidermis including a well-formed cornified layer. To induce barrier injury, REK cultures were treated with intermittent 30-s exposures to acetone then were fixed and paraffin-sectioned. After two exposures, increased proliferation (Ki67 and BrdU staining) was observed in basal and suprabasal layers. After three exposures, proliferation became confined to localized buds in the basal layer and increased terminal differentiation was observed (compact hyperkeratosis of the stratum corneum, elevated levels of K10 and filaggrin, and heightened transglutaminase activity). Thus, barrier disruption causes epidermal hyperplasia and/or enhances differentiation, depending upon the extent and duration of injury. Given that no fibroblasts are present in the model, the ability to mount a hyperplastic response to barrier injury is an inherent property of keratinocytes.

DNA microarrays in dermatology and skin biology

Because of its accessibility, skin has been among the first organs analyzed using DNA microarrays. Skin cancers, melanomas, and basal and squamous cell carcinomas have been intensely investigated because they are very frequent and can be fatal. Psoriasis, one of the most common human inflammatory diseases, has been studied comprehensively using DNA microarrays. In addition, epidermal keratinocytes have been the target of many studies because they respond to a rich variety of inflammatory and immunomodulating cytokines, hormones, vitamins, ultraviolet (UV) light, toxins, and physical injury. Because of the ethical considerations, the effects of harmful or dangerous agents on skin have been studied using artificial skin substitutes. Transcriptional mechanisms that regulate epidermal differentiation and cornification have begun to yield their mysteries, and very exciting recent studies identified the genes specifically expressed in epidermal stem cells. Thus, skin has everything: stem cells, differentiation, signaling, inflammation, diseases, and cancer. All these exciting facets of skin have been explored using DNA microarrays. Researchers in skin biology and dermatology were among the first to implement this technology and we expect that they will continue to generate exciting and useful new knowledge.

Experimental models and high-throughput diagnostics for tissue regeneration

During wound healing, cells recreate functional structures to regenerate the injured tissue. Understanding the healing process is essential for the development of new concepts and the design of novel biomimetic approaches for delivery of cells, genes and growth factors to accelerate tissue regeneration. To this end, realistic experimental models and high-throughput diagnostics are necessary to understand the molecular mechanisms of healing and reveal the genetic networks that determine tissue repair versus regeneration. Following a brief overview of the biology of wound healing, this review covers the in vitro and in vivo models that are employed at present to study the healing process. Discussion then covers the application of high-throughput genomic and proteomic technologies in epithelial development, living skin substitutes and wound healing. Finally, this review provides a perspective on novel technologies that should be developed to facilitate the understanding of wound healing complications and the design of therapeutics that target the underlying deficiencies.

Gene-modified tissue-engineered skin: the next generation of skin substitutes

Tissue engineering combines the principles of cell biology, engineering and materials science to develop three-dimensional tissues to replace or restore tissue function. Tissue engineered skin is one of most advanced tissue constructs, yet it lacks several important functions including those provided by hair follicles, sebaceous glands, sweat glands and dendritic cells. Although the complexity of skin may be difficult to recapitulate entirely, new or improved functions can be provided by genetic modification of the cells that make up the tissues. Gene therapy can also be used in wound healing to promote tissue regeneration or prevent healing abnormalities such as formation of scars and keloids. Finally, gene-enhanced skin substitutes have great potential as cell-based devices to deliver therapeutics locally or systemically. Although significant progress has been made in the development of gene transfer technologies, several challenges have to be met before clinical application of genetically modified skin tissue. Engineering challenges include methods for improved efficiency and targeted gene delivery; efficient gene transfer to the stem cells that constantly regenerate the dynamic epidermal tissue; and development of novel biomaterials for controlled gene delivery. In addition, advances in regulatable vectors to achieve spatially and temporally controlled gene expression by physiological or exogenous signals may facilitate pharmacological administration of therapeutics through genetically engineered skin. Gene modified skin substitutes are also employed as biological models to understand tissue development or disease progression in a realistic three-dimensional context. In summary, gene therapy has the potential to generate the next generation of skin substitutes with enhanced capacity for treatment of burns, chronic wounds and even systemic diseases.

In vitro and in vivo comparison of dermal irritancy of jet fuel exposure using EpiDerm (EPI-200) cultured human skin and hairless rats

The purpose of this study was to evaluate an in vitro EpiDerm human skin model (EPI-200) to study the irritation potential of jet fuels (JP-8 and JP-8+100). Parallel in vivo studies on hairless rats on the dermal irritancy of jet fuels were also conducted. Cytokines are an important part of an irritation and inflammatory cascade, which are expressed in upon dermal exposures of irritant chemicals even when there are no obvious visible marks of irritation on the skin. We have chosen two primary cytokines (IL-1alpha and TNF-1alpha) as markers of irritation response of jet fuels. Initially, the EPI-200 was treated with different quantities of JP-8 and JP-8+100 to determine quantities which did not cause significant cytotoxicity, as monitored using the MTT assay and paraffin embedded histological cross-sections. Volumes of 2.5-50 microl/tissue (approximately 4.0-78 microl/cm2) of JP-8 and JP-8+100 showed a dose dependent loss of tissue viability and morphological alterations of the tissue. At a quantity of 1.25 microl/tissue (approximately 2.0 microl/cm2), no significant change in tissue viability or morphology was observed for exposure time extending to 48 h. Nonetheless, this dose induced significant increase in IL-1alpha and TNF-alpha release versus non-treated controls after 24 and 48 h. In addition, IL-1alpha release for JP-8+100 was significantly higher than that observed for JP-8, but TNF-alpha release after 48 h exposure to these two jet fuels was the same. These findings parallel in vivo studies on hairless rats, which indicated higher irritation levels due to JP-8+100 versus JP-8. In vivo, transepidermal water loss (TEWL) and IL-1alpha expression levels followed the order JP-8+100 > JP-8 > control. Further, in vivo TNF-alpha levels for JP-8 and JP-8+100 were also elevated but not significantly different from one another. In aggregate, these findings indicate that EPI-200 tissue model can be utilized as an alternative to the use of animals in evaluating dermal irritation.

Epidermal Morphogenesis: The Transcriptional Program of Human Keratinocytes during Stratification

The epidermis serves to protect the body against environmental assaults and at the same time is able to survive and replenish itself under harsh conditions. The epidermis accomplishes this feat via a well-orchestrated program of stratification and terminal differentiation that provides barrier against infection, radiation, and water loss. Despite significant progress in skin biology, many molecules and pathways that are involved in stratification and barrier formation remain unknown. Here, we employed tissue-engineered models of complete versus impaired epidermal stratification to discover the genes that may be important in this process. Transcriptional profiling at different stages of development showed significant differences in transcription, signaling, and most important metabolism-associated genes between fully stratified and poorly stratified epithelia. These transcriptional changes correlated well with functional data on cell proliferation, expression of adhesion molecules, and utilization of metabolic pathways, ultimately leading to different phenotypes. Our data identified genes that were not previously known to play a role in epidermis and established a link between metabolism and morphogenesis in skin epithelium.

Gene expression profiling of mouse postnatal cerebellar development using oligonucleotide microarrays designed to detect differences in glycoconjugate expression

Differences in gene expression patterns between adult and postnatal day 7 (P7) mouse cerebellum, at the peak of granule neuron migration, were analyzed by hybridization to the GLYCOv2 glycogene array. This custom designed oligonucleotide array focuses on glycosyl transferases, carbohydrate-binding proteins, proteoglycans and related genes, and 173 genes were identified as being differentially expressed with statistical confidence. Expression levels for 11 of these genes were compared by RT-PCR, and their differential expression between P7 and adult cerebellum confirmed. Within the group of genes showing differential expression, the sialyltransferases (SiaTs) and GalNAc-Ts that were elevated at P7 prefer glycoprotein substrates, whilst the SiaTs and GalNAc-Ts that were elevated in the adult preferentially modify glycolipids, consistent with a role for gangliosides in maintaining neuronal function in the adult. Also within this group, three proteoglycans--versican, bamacan and glypican-2--were elevated at P7, along with growth factor midkine, which is known to bind to multiple types of proteoglycans, and fibroblast growth factor receptor 1, whose activity is known to be influenced by heparan sulfate proteoglycans. Two sulfotransferases that can modify the extent of proteoglycan sulfation were also differentially regulated, and may modify the interaction of a subset of proteoglycans with their binding partners during cerebellar development. Bamacan, glypican-2 and midkine were shown to be expressed in different cell types, and their roles in cerebellar development during granule neuron migration and maturation are discussed.

Gene transfer to epidermal stem cells: implications for tissue engineering

The skin is an attractive target for gene therapy because it is easily accessible and shows great potential as an ectopic site for protein delivery in vivo. Genetically modified epidermal cells can be used to engineer three-dimensional skin substitutes, which when transplanted can act as in vivo 'bioreactors' for delivery of therapeutic proteins locally or systemically. Although some gene transfer technologies have the potential to afford permanent genetic modification, differentiation and eventual loss of genetically modified cells from the epidermis results in temporary transgene expression. Therefore, to achieve stable long-term gene expression, it is critical to deliver genes to epidermal stem cells, which possess unlimited growth potential and self-renewal capacity. This review discusses the recent advances in epidermal stem cell isolation, gene transfer and engineering of skin substitutes. Recent efforts that employ gene therapy and tissue engineering for the treatment of genetic diseases, chronic wounds and systemic disorders, such as leptin deficiency or diabetes, are reviewed. Finally, the use of gene-modified tissue-engineered skin as a biological model for understanding tissue development, wound healing and epithelial carcinogenesis is also discussed.