An improved and rapid method to construct skin equivalents from human hair follicles and fibroblasts

Skin microbiota analysis in human 3D skin models-"Free your mice"

In the May issue of Experimental Dermatology 2018, we published a review article focusing on human 3D skin models in the context of microbiota research. The principal intention was to provide an overview of present and future concepts to use skin models in microbiota analyses. With the present viewpoint, we would like to draw the reader's attention again to the use of human skin models in microbiota research with the aim to highlight the benefits and necessity of human skin models to analyse the human skin-microbiota interaction. This is accompanied by a critical view on mice models that often are not suitable to analyse the functional impact of the human skin microbiota. In addition, we present novel and future concepts highlighting the benefits of human 3D skin models in microbiota research.

Utilizing Organoid and Air-Liquid Interface Models as a Screening Method in the Development of New Host Defense Peptides

Host defense peptides (HDPs), also known as antimicrobial peptides, are naturally occurring polypeptides (~12–50 residues) composed of cationic and hydrophobic amino acids that adopt an amphipathic conformation upon folding usually after contact with membranes. HDPs have a variety of biological activities including immunomodulatory, anti-inflammatory, anti-bacterial, and anti-biofilm functions. Although HDPs have the potential to address the global threat of antibiotic resistance and to treat immune and inflammatory disorders, they have yet to achieve this promise. Indeed, there are several challenges associated with bringing peptide-based drug candidates from the lab bench to clinical practice, including identifying appropriate indications, stability, toxicity, and cost. These challenges can be addressed in part by the development of innate defense regulator (IDR) peptides and peptidomimetics, which are synthetic derivatives of HDPs with similar or better efficacy, increased stability, and reduced toxicity and cost of the original HDP. However, one of the largest gaps between basic research and clinical application is the validity and translatability of conventional model systems, such as cell lines and animal models, for screening HDPs and their derivatives as potential drug therapies. Indeed, such translation has often relied on animal models, which have only limited validity. Here we discuss the recent development of human organoids for disease modeling and drug screening, assisted by the use of omics analyses. Organoids, developed from primary cells, cell lines, or human pluripotent stem cells, are three-dimensional, self-organizing structures that closely resemble their corresponding in vivo organs with regards to immune responses, tissue organization, and physiological properties; thus, organoids represent a reliable method for studying efficacy, formulation, toxicity and to some extent drug stability and pharmacodynamics. The use of patient-derived organoids enables the study of patient-specific efficacy, toxicogenomics and drug response predictions. We outline how organoids and omics data analysis can be leveraged to aid in the clinical translation of IDR peptides.

3D-Organotypic Cultures to Unravel Molecular and Cellular Abnormalities in Atopic Dermatitis and Ichthyosis Vulgaris

Atopic dermatitis (AD) is characterized by dry and itchy skin evolving into disseminated skin lesions. AD is believed to result from a primary acquired or a genetically-induced epidermal barrier defect leading to immune hyper-responsiveness. Filaggrin (FLG) is a protein found in the cornified envelope of fully differentiated keratinocytes, referred to as corneocytes. Although FLG null mutations are strongly associated with AD, they are not sufficient to induce the disease. Moreover, most patients with ichthyosis vulgaris (IV), a monogenetic skin disease characterized by FLG homozygous, heterozygous, or compound heterozygous null mutations, display non-inflamed dry and scaly skin. Thus, all causes of epidermal barrier impairment in AD have not yet been identified, including those leading to the Th2-predominant inflammation observed in AD. Three dimensional organotypic cultures have emerged as valuable tools in skin research, replacing animal experimentation in many cases and precluding the need for repeated patient biopsies. Here, we review the results on IV and AD obtained with epidermal or skin equivalents and consider these findings in the context of human in vivo data. Further research utilizing complex models including immune cells and cutaneous innervation will enable finer dissection of the pathogenesis of AD and deepen our knowledge of epidermal biology.

3D bioprinting of skin tissue: From pre-processing to final product evaluation

Bioprinted skin tissue has the potential for aiding drug screening, formulation development, clinical transplantation, chemical and cosmetic testing, as well as basic research. Limitations of conventional skin tissue engineering approaches have driven the development of biomimetic skin equivalent via 3D bioprinting. A key hope for bioprinting skin is the improved tissue authenticity over conventional skin equivalent construction, enabling the precise localization of multiple cell types and appendages within a construct. The printing of skin faces challenges broadly associated with general 3D bioprinting, including the selection of cell types and biomaterials, and additionally requires in vitro culture formats that allow for growth at an air-liquid interface. This paper provides a thorough review of current 3D bioprinting technologies used to engineer human skin constructs and presents the overall pipelines of designing a biomimetic artificial skin via 3D bioprinting from the design phase (i.e. pre-processing phase) through the tissue maturation phase (i.e. post-processing) and into final product evaluation for drug screening, development, and drug delivery applications.

Multifaceted role of hair follicle dermal cells in bioengineered skins

BACKGROUND

The method of generating bioengineered skin constructs was pioneered several decades ago; nowadays these constructs are used regularly for the treatment of severe burns and nonhealing wounds. Commonly, these constructs are comprised of skin fibroblasts within a collagen scaffold, forming the skin dermis, and stratified keratinocytes overlying this, forming the skin epidermis. In the past decade there has been a surge of interest in bioengineered skins, with researchers seeking alternative cell sources, or scaffolds, from which constructs can be established, and for more biomimetic equivalents with skin appendages.

OBJECTIVES

To evaluate whether human hair follicle dermal cells can act as an alternative cell source for engineering the dermal component of engineered skin constructs.

METHODS

We established in vitro skin constructs by incorporating into the collagenous dermal compartment: (i) primary interfollicular dermal fibroblasts, (ii) hair follicle dermal papilla cells or (iii) hair follicle dermal sheath cells. In vivo skins were established by mixing dermal cells and keratinocytes in chambers on top of immunologically compromised mice.

RESULTS

All fibroblast subtypes were capable of supporting growth of overlying epithelial cells, both in vitro and in vivo. However, we found hair follicle dermal sheath cells to be superior to fibroblasts in their capacity to influence the establishment of a basal lamina.

CONCLUSIONS

Human hair follicle dermal cells can be readily interchanged with interfollicular fibroblasts and used as an alternative cell source for establishing the dermal component of engineered skin both in vitro and in vivo.

The use of skin models in drug development

Three dimensional (3D) tissue models of the human skin are probably the most developed and understood in vitro engineered constructs. The motivation to accomplish organotypic structures was driven by the clinics to enable transplantation of in vitro grown tissue substitutes and by the cosmetics industry as alternative test substrates in order to replace animal models. Today a huge variety of 3D human skin models exist, covering a multitude of scientific and/or technical demands. This review summarizes and discusses different approaches of skin model development and sets them into the context of drug development. Although human skin models have become indispensable for the cosmetics industry, they have not yet started their triumphal procession in pharmaceutical research and development. For drug development these tissue models may be of particular interest for a) systemically acting drugs applied on the skin, and b) drugs acting at the site of application in the case of skin diseases or disorders. Although quite a broad spectrum of models covering different aspects of the skin as a biologically acting surface exists, these are most often single stand-alone approaches. In order to enable the comprehensive application into drug development processes, the approaches have to be synchronized to allow a cross-over comparison. Besides the development of biological relevant models, other issues are not less important in the context of drug development: standardized production procedures, process automation, establishment of significant analytical methods, and data correlation. For the successful routine use of engineered human skin models in drug development, major requirements were defined. If these requirements can be accomplished in the next few years, human organotypic skin models will become indispensable for drug development, too.

Improving topical non-melanoma skin cancer treatment: In vitro efficacy of a novel guanosine-analog phosphonate

Actinic keratosis, a frequent carcinoma in situ of non-melanoma skin cancer (NMSC), can transform into life-threatening cutaneous squamous cell carcinoma. Current treatment is limited due to low complete clearance rates and asks for novel therapeutic concepts; the novel purine nucleotide analogue OxBu may be an option. In order to enhance skin penetration, solid lipid nanoparticles (SLN, 136-156 nm) were produced with an OxBu entrapment efficiency of 96.5 ± 0.1%. For improved preclinical evaluation, we combined tissue engineering with clinically used keratin-18 quantification. Three doses of 10(-3) mol/l OxBu, dissolved in phosphate-buffered saline as well as loaded to SLN, were effective on reconstructed NMSC. Tumour response and apoptosis induction were evaluated by an increase in caspase-cleaved fragment of keratin-18, caspase-7 activation as well as by reduced expression of matrix metallopeptidase-2 and Ki-67. OxBu efficacy was superior to equimolar 5-fluorouracil solution, and thus the drug should be subjected to the next step in preclinical evaluation.

Plucked human hair shafts and biomolecular medical research

The hair follicle is a skin integument at the boundary between an organism and its immediate environment. The biological role of the human hair follicle has lost some of its ancestral importance. However, an indepth investigation of this miniorgan reveals hidden complexity with huge research potential. An essential consideration when dealing with human research is the awareness of potential harm and thus the absolute need not to harm—a rule aptly qualified by the Latin term “primum non nocere” (first do no harm). The plucked hair shaft offers such advantages. The use of stem cells found in hair follicles cells is gaining momentum in the field of regenerative medicine. Furthermore, current diagnostic and clinical applications of plucked hair follicles include their use as autologous and/or three-dimensional epidermal equivalents, together with their utilization as surrogate tissue in pharmacokinetic and pharmacodynamics studies. Consequently, the use of noninvasive diagnostic procedures on hair follicle shafts, posing as a surrogate molecular model for internal organs in the individual patient for a spectrum of human disease conditions, can possibly become a reality in the near future.

Hair follicle: a novel source of multipotent stem cells for tissue engineering and regenerative medicine

The adult body harbors powerful reservoirs of stem cells that enable tissue regeneration under homeostatic conditions or in response to disease or injury. The hair follicle (HF) is a readily accessible mini organ within the skin and contains stem cells from diverse developmental origins that were shown to have surprisingly broad differentiation potential. In this review, we discuss the biology of the HF with particular emphasis on the various stem cell populations residing within the tissue. We summarize the existing knowledge on putative HF stem cell markers, the differentiation potential, and technologies to isolate and expand distinct stem cell populations. We also discuss the potential of HF stem cells for drug and gene delivery, tissue engineering, and regenerative medicine. We propose that the abundance of stem cells with broad differentiation potential and the ease of accessibility makes the HF an ideal source of stem cells for gene and cell therapies.

Alternatives for animal wound model systems

In this chapter a review of animal model systems already being utilized to study normal and pathologic wound healing is provided. We also go into details on alternatives for animal wound model systems. The case is made for limitations in the various approaches. We also discuss the benefits/limitations of in vitro/ex vivo systems bringing everything up to date with our current work on developing a cell-based reporter system for diabetic wound healing.

Epithelial morphogenesis of germline-derived pluripotent stem cells on organotypic skin equivalents in vitro

For tissue engineering, cultivation of pluripotent stem cells on three-dimensional scaffolds allows the generation of organ-like structures. Previously, we have established an organotypic culture system of skin to induce epidermal differentiation in adult stem cells. Multipotent stem cells are not able to differentiate across germinal boundaries. In contrast, pluripotent stem cells readily differentiate into tissues of all three germ layers. Germline-derived pluripotent stem cells (gPS cells) can be generated by induction of pluripotency in mouse unipotent germline stem cells without the introduction of exogenous transcription factors. In the current study, we analyzed the influence of organotypic culture conditions of skin on the epithelial differentiation of gPS cells in comparison to the well-established HM1 ES cell line. Quantitative RT-PCR data of the pluripotency gene Oct4 showed that gPS cells are characterized by an accelerated Oct4-downregulation compared to HM1 ES cells. When subjected to the organotypic culture conditions of skin, gPS cells formed tubulocystic structures lined by stratified (CK5/6(+), CK14(+), CK8/18(-)) epithelia. HM1 ES cells formed only small tubulocystic structures lined by simple, CK8/18(+) epithelia. BMP-4, an epidermal morphogen, significantly enhanced the expression of epithelial markers in HM1 ES cells, but did not significantly affect the formation of complex (squamous) epithelia in gPS cells. In HM1 ES cells the differentiation into squamous epithelium was only inducible in the presence of mature dermal fibroblasts. Both pluripotent stem cell types spontaneously differentiated into mesodermal, endodermal and into neuroectodermal cells at low frequency, underlining their pluripotent differentiation capacity. Concluding, the organotypic culture conditions of skin induce a multilayered, stratified epithelium in gPS cells, in HM1 ES cells only in the presence of dermal fibroblasts. Thus, our data show that differentiation protocols strongly depend on the stem cell type and have to be modified for each specific stem cell type.

Establishment and characterization of outer root sheath (ORS) cell line from Jining grey goat

A new line of outer root sheath (ORS) cells was established from hair follicles of Jining grey goat by using a mechanical separation combined with enzyme digestion. Cell morphology is described at different phases. The chromosome analysis of ORS cells, identification of the ORS cells and morphological reversion test were detected at the 4th and 40th passages. The ORS cells were healthy and the growth characteristics were stable with a population doubling time of 52 h. Chromosome analysis showed that >58% of cells were diploid. Test for ORS cell line CK19 expression was positive. This newly established ORS cell line not only lays the foundation for further studying on the growth, regeneration, development law of goat hair follicle but also provides a mirror for the research of human hair in medical field.

Epithelial stem cells

It is likely that adult epithelial stem cells will be useful in the treatment of diseases, such as ectodermal dysplasias, monilethrix, Netherton syndrome, Menkes disease, hereditary epidermolysis bullosa, and alopecias. Additionally, other skin problems such as burn wounds, chronic wounds, and ulcers will benefit from stem cell-related therapies. However, there are many questions that need to be answered before this goal can be realized. The most important of these questions is what regulates the adhesion of stem cells to the niche versus migration to the site of injury. We have started to identify the mechanisms involved in this decision-making process.

Isolation and culture of adult epithelial stem cells from human skin

The homeostasis of all self-renewing tissues is dependent on adult stem cells. As undifferentiated stem cells undergo asymmetric divisions, they generate daughter cells that retain the stem cell phenotype and transit-amplifying cells (TA cells) that migrate from the stem cell niche, undergo rapid proliferation and terminally differentiate to repopulate the tissue. Epithelial stem cells have been identified in the epidermis, hair follicle, and intestine as cells with a high in vitro proliferative potential and as slow-cycling label-retaining cells in vivo (1-3). Adult, tissue-specific stem cells are responsible for the regeneration of the tissues in which they reside during normal physiologic turnover as well as during times of stress (4-5). Moreover, stem cells are generally considered to be multi-potent, possessing the capacity to give rise to multiple cell types within the tissue (6). For example, rodent hair follicle stem cells can generate epidermis, sebaceous glands, and hair follicles (7-9). We have shown that stem cells from the human hair follicle bulge region exhibit multi-potentiality (10). Stem cells have become a valuable tool in biomedical research, due to their utility as an in vitro system for studying developmental biology, differentiation, tumorigenesis and for their possible therapeutic utility. It is likely that adult epithelial stem cells will be useful in the treatment of diseases such as ectodermal dysplasias, monilethrix, Netherton syndrome, Menkes disease, hereditary epidermolysis bullosa and alopecias (11-13). Additionally, other skin problems such as burn wounds, chronic wounds and ulcers will benefit from stem cell related therapies (14,15). Given the potential for reprogramming of adult cells into a pluripotent state (iPS cells)(16,17), the readily accessible and expandable adult stem cells in human skin may provide a valuable source of cells for induction and downstream therapy for a wide range of disease including diabetes and Parkinson's disease.

The role of biomaterials in the direction of mesenchymal stem cell properties and extracellular matrix remodelling in dermal tissue engineering

Recently, a new generation of dermal equivalents (DE) was presented which are solely generated on a human fibroblast-derived dermal matrix. Since human mesenchymal stem cells from bone marrow (BM-MSC) and Wharton's Jelly of the umbilical cord (UC-MSC) are characterised by a distinct biosynthetic and paracrine activity, they are an appealing alternative approach for generating cell-based DE. This study compares the epithelial-mesenchymal interaction and extracellular matrix (ECM) remodelling of cell-based and collagen-based DE using fibroblasts, BM-MSC or UC-MSC, respectively, in co-culture with the keratinocyte cell line HaCaT. While fibroblast-based DE exhibit normal matrix synthesis, proliferation and differentiation of keratinocytes, mesenchymal stem cell-based DE resulted in excessive production of inhomogenous matrix aggregates, loss of polarisation of the epidermal cell layer and an inconstant paracrine activity. In contrast, collagen-embedded MSC revealed a homogenous growth pattern as well as a constant expression of growth factors and ECM proteins without a negative influence on the epidermal layer as shown by histology, electron microscopy, immunohistochemistry and realtime-RT-PCR. These results indicate the necessity of an instructive biomaterial-based scaffold to direct stem cell differentiation, proliferation, paracrine activity as well as regulation of ECM deposition.

Immunoarchitectural characterization of a human skin model reconstructed in vitro

CONTEXT AND OBJECTIVE

Over the last few years, different models for human skin equivalent reconstructed in vitro (HSERIV) have been reported for clinical usage and applications in research for the pharmaceutical industry. Before release for routine use as human skin replacements, HSERIV models need to be tested regarding their similarity with in vivo skin, using morphological (architectural) and immunohistochemical (functional) analyses. A model for HSERIV has been developed in our hospital, and our aim here was to further characterize its immunoarchitectural features by comparing them with human skin, before it can be tested for clinical use, e.g. for severe burns or wounds, whenever ancillary methods are not indicated.

DESIGN AND SETTING

Experimental laboratory study, in the Skin Cell Culture Laboratory, School of Medical Sciences, Universidade Estadual de Campinas.

METHODS

Histological sections were stained with hematoxylin-eosin, Masson's trichrome for collagen fibers, periodic acid-Schiff reagent for basement membrane and glycogen, Weigert-Van Gieson for elastic fibers and Fontana-Masson for melanocytes. Immunohistochemistry was used to localize cytokeratins (broad spectrum of molecular weight, AE1/AE3), high molecular weight cytokeratins (34betaE12), low molecular weight cytokeratins (35betaH11), cytokeratins 7 and 20, vimentin, S-100 protein (for melanocytic and dendritic cells), CD68 (KP1, histiocytes) and CD34 (QBend, endothelium).

RESULTS

Histology revealed satisfactory similarity between HSERIV and in vivo skin. Immunohistochemical analysis on HSERIV demonstrated that the marker pattern was similar to what is generally present in human skin in vivo.

CONCLUSION

HSERIV is morphologically and functionally compatible with human skin observed in vivo.

Isolation and culture of different epidermal and dermal cell types from human scalp suitable for the development of a therapeutical cell spray

BACKGROUND

Previous studies demonstrated, that cultured epithelial autografts (CEA) can be isolated and skin cell sprays can be produced for application on different types of wounds. The purpose of the present study was to determine which cell types can be isolated from the human scalp and whether these cells can be used for spray transplantation.

METHODS

Outer root sheath cells (ORS), keratinocytes, melanocytes, dermal papilla cells (DP), and dermal sheath cells (DSC) were isolated from human scalp tissue. Isolated cells were characterized, expanded and sprayed in an in vitro model. Growth behaviour, morphology and cell counts were compared with non-sprayed cells.

RESULTS

With acceptable time, equipment and laboratory personnel a sufficient amount of keratinocytes, ORS, melanocytes, DP cells and DSC cells could be achieved. The cells are sufficient for application as a cell spray. Cells, positive for Integrin alpha6, Cytokeratin 19, CD73 and CD105 were identified within the cultures.

CONCLUSIONS

Human scalp is suitable to gain epidermal and dermal cells for the development of therapeutic cell spray transplantation. Further studies have to determine, whether these cells can be combined to produce wound specific skin substitutes.

Three-dimensional epidermis-like growth of human mesenchymal stem cells on dermal equivalents: contribution to tissue organization by adaptation of myofibroblastic phenotype and function

Human mesenchymal stem cells (hMSC) are able to differentiate into mature cells of various mesenchymal tissues. Recent studies have reported that hMSC may even give rise to cells of ectodermal origin. This indication of plasticity makes hMSC a promising donor source for cell-based therapies. This study explores the differentiation potential of hMSC in a tissue-specific microenvironment simulated in vitro. HMSC were cultured air-exposed on dermal equivalents (DEs) consisting of collagen types I and III with dermal fibroblasts and subjected to conditions similar to those used for tissue engineering of skin with keratinocytes. Culture conditions were additionally modified by pre-treating the cells with 5-azacytidine or supplementing the medium with all trans retinoic acid (RA). HMSC were capable of adaptation to epidermis-specific conditions without losing their mesenchymal multipotency. However, despite the viability and evident three-dimensional epidermis-like growth pattern, hMSC showed a persistent expression of mesenchymal but not of epithelial markers, thus indicating a lack of epidermal (trans) differentiation. Further, electron microscopy and immunohistochemical analyses demonstrated that hMSC cultured under epidermis-specific conditions adopted a myofibroblastic phenotype and function, promoted in particular by air exposure. In conclusion, multipotent hMSC failed to differentiate into E-cadherin- or cytokeratin-expressing cells under optimized organotypic culture conditions for keratinocytes but differentiated into myofibroblast-like cells contracting the extracellular matrix, a phenomenon that was enhanced by RA and 5-azacytidine. These results indicate that hMSC might contribute to wound-healing processes by extracellular matrix reorganization and wound contraction but not by differentiation into keratinocytes.

Regulation of cellular zinc balance as a potential mechanism of EVER-mediated protection against pathogenesis by cutaneous oncogenic human papillomaviruses

Epidermodysplasia verruciformis (EV) is a genodermatosis associated with skin cancers that results from a selective susceptibility to related human papillomaviruses (EV HPV). Invalidating mutations in either of two genes (EVER1 and EVER2) with unknown functions cause most EV cases. We report that EVER1 and EVER2 proteins form a complex and interact with the zinc transporter 1 (ZnT-1), as shown by yeast two-hybrid screening, GST pull-down, and immunoprecipitation experiments. In keratinocytes, EVER and ZnT-1 proteins do not influence intracellular zinc concentration, but do affect intracellular zinc distribution. EVER2 was found to inhibit free zinc influx to nucleoli. Keratinocytes with a mutated EVER2 grew faster than wild-type keratinocytes. In transiently and stably transfected HaCaT cells, EVER and ZnT-1 down-regulated transcription factors stimulated by zinc (MTF-1) or cytokines (c-Jun and Elk), as detected with luciferase assays. To get some insight into the control of EV HPV infection, we searched for interaction between EVER and ZnT-1 and oncoproteins of cutaneous (HPV5) and genital (HPV16) genotypes. HPV16 E5 protein binds to EVER and ZnT-1 and blocks their negative regulation. The lack of a functional E5 protein encoded by EV HPV genome may account for host restriction of these viruses.

High-resolution optical coherence tomography as a non-destructive monitoring tool for the engineering of skin equivalents

BACKGROUND

Three dimensional skin equivalents are widely used in dermatopharmacological and toxicological studies and as autologous transplants in wound healing. In pharmacology, there is tremendous need for monitoring the response of engineered skin equivalents to external treatment. Transplantation of skin equivalents for wound healing requires careful verification of their quality prior to transplantation. Optical coherence tomography (OCT) is a non-contact, non-destructive imaging technique for living tissues offering the potential to fulfill these needs. This work presents an analysis of OCT for high-resolution monitoring of skin equivalents at different stages during the culture process.

METHODS

We developed a high-resolution OCT imaging setup based on a commercially available OCT system. A broadband femtosecond laser light source replaces the original superluminescence diode. Tomograms of living skin equivalents were recorded with an axial resolution of 3 mum and correlated with histology and immunofluorescence images. Comparison with standard low-resolution OCT is presented to emphasize the advantages of high-resolution OCT for this application.

RESULTS

OCT is particularly able to distinguish between different layers of skin equivalents including stratum corneum, epidermal and dermal layer as well as the basement membrane zone. The high-resolution OCT scans correlate closely with two key benchmarks, histology and immunofluorescence imaging.

CONCLUSIONS

This study clearly demonstrates the benefits of high-resolution OCT for identifying living tissue structure and morphology. Compared with the current gold standard histology, OCT offers non-destructive tissue imaging, enabling high-resolution evaluation of living tissue morphology and structure as it evolves.

Cutaneous gene therapy

Possibilities of using the skin for somatic gene therapy have been investigated for more than 20 years. Strategies have included both direct gene transfer into the skin and indirect gene transfer utilizing cultured cells as an intermediate step for gene manipulation. Viral as well as nonviral vectors have been used, and both gene addition and gene editing have been performed. Although cutaneous gene therapy has now begun translating into clinical medicine (as seen by the first clinical gene therapy project of an inherited skin disorder) further developments are still required.

Skin Retinoid Concentrations Are Modulated by CYP26AI Expression Restricted to Basal Keratinocytes in Normal Human Skin and Differentiated 3D Skin Models

Cellular levels of all-trans retinoic acid (RA) are meticulously regulated utilizing an array of systems to balance uptake, biosynthesis, catabolism, and efflux transport. Metabolic transformation of all-trans RA to 4-hydroxylated RA appears to be primarily catalyzed by the cytochrome P450 (CYP) 26AI. Analysis of monolayer cultures of normal human epidermal keratinocytes (NHEKs) and dermal fibroblasts by quantitative real-time PCR and reverse transcription-PCR revealed no basal levels of CYP26AI mRNA expression, whereas specific transcripts were detectable following addition of 10(-6) M all-trans RA. Immunofluorescence and Western blot analysis showed a weak expression of CYP26AI in NHEK, which was increased by stimulation with all-trans RA. Using a newly developed peptide antibody, we further examined the localization of CYP26AI expression in normal skin and three-dimensional (3D) skin models. In contrast to cell culture monolayers where CYP26AI was only weakly detectable, strong constitutive expression of CYP26AI in vivo and in organotypic culture was found to be restricted to basal epidermal keratinocytes, as well as eccrine sweat glands and sebaceous glands. These studies verify the capacity of human skin to metabolize RA, although substantial differences exist in CYP expression between normal skin and 3D skin models compared to monolayer cultures. Complex metabolic processes that maintain retinoid homeostasis may therefore be better studied in model systems more closely resembling in vivo skin. In light of our prior studies documenting the functional activity of RA metabolites, expression of CYP26 in the sebaceous gland epithelium supports the suggestion that altered RA metabolism may be involved in the pathogenesis of acne.

Model for human skin reconstructed in vitro composed of associated dermis and epidermis

CONTEXT AND OBJECTIVE

The technique of obtaining human skin with dermis and epidermis reconstructed from cells isolated from patients can enable autologous skin grafting on patients with few donor sites. It also enables in vitro trials on chemicals and drugs. The objective of this work was to demonstrate a method for obtaining human skin composed of associated dermis and epidermis, reconstructed in vitro.

DESIGN AND SETTING

Experimental laboratory study, in the Skin Cell Culture Laboratory of Faculdade de Ciências Médicas, Universidade Estadual de Campinas.

METHODS

Cells from human fibroblast cultures are injected into bovine collagen type I matrix and kept immersed in specific culturing medium for fibroblasts. This enables human dermis reconstruction in vitro. On this, by culturing human keratinocytes and melanocytes, differentiated epidermis is formed, leading to the creation of human skin composed of associated dermis and epidermis, reconstructed in vitro.

RESULTS

We showed that human skin composed of associated dermis and epidermis can be successfully reconstructed in vitro. It is histologically formed in the same way as human skin in vivo. Collagen tissue can be identified in the dermis, with cells and extracellular matrix organized in parallel to multilayer epidermis.

CONCLUSIONS

It is possible to obtain completely differentiated human skin composed of associated dermis and epidermis, reconstructed in vitro, from injection of human fibroblasts into bovine collagen type I matrix and culturing of human keratinocytes and melanocytes on this matrix.

An Improved Organ Culture for Regeneration of Pure Autologous Keratinocytes from Small Split-Thickness Skin Specimens

BACKGROUND

Failure of autologous keratinocyte culture from small split-thickness skin specimens or contamination of the keratinocyte culture by melanocytes represents practical problems in basic medical research and clinical studies.

PURPOSE

To establish a simple and reliable method of harvesting pure autologous keratinocytes from a small split-thickness skin specimen.

METHODS

Split-thickness (0.3 mm) skin explants (1 x 2 mm) were firstly cultured in DMEM containing 10% FCS till formation of keratinocyte strips, then cultured in serum-free keratinocyte growth medium or cocultured with lethally irradiated 3T3 fibroblasts (J2) in a mixture of DMEM and Ham's F12 (DF) medium.

RESULTS

Pure autologous keratinocyte culture is easily and reliably established by this organ culture technique.

CONCLUSION

Culturing of skin explants in serum-free keratinocyte growth medium or coculturing of the skin explants with lethally irradiated 3T3 cells in DF medium is proved to be a useful, simple and reliable method of harvesting pure autologous keratinocytes from a small split-thickness skin biopsy.

Allelic loss underlies type 2 segmental Hailey-Hailey disease, providing molecular confirmation of a novel genetic concept

Hailey-Hailey disease (HHD) is an autosomal dominant trait characterized by erythematous and oozing skin lesions preponderantly involving the body folds. In the present unusual case, however, unilateral segmental areas along the lines of Blaschko showing a rather severe involvement were superimposed on the ordinary symmetrical phenotype. Based on this observation and similar forms of mosaicism as reported in other autosomal dominant skin disorders, we postulated that in such cases, 2 different types of segmental involvement can be distinguished. Accordingly, the linear lesions as noted in the present case would exemplify type 2 segmental HHD. In the heterozygous embryo, loss of heterozygosity occurring at an early developmental stage would have given rise to pronounced linear lesions reflecting homozygosity or hemizygosity for the mutation. By analyzing DNA and RNA derived from blood and skin samples as well as keratinocytes of the index patient with various molecular techniques including RT-PCR, real-time PCR, and microsatellite analysis, we found a consistent loss of the paternal wild-type allele in more severely affected segmental skin regions, confirming this hypothesis for the first time, to our knowledge, at the molecular and cellular level.

Xenobiotic bioconversion in human epidermis models

There is a great need for alternative experimental methods for measuring percutaneous xenobiotic biotransformation. Animal testing and excised human skin studies have been the historical standards for confirmation of therapeutic and toxic effects that occur in the skin as a result of drug and other chemical metabolism. Human skin epidermal bioequivalents have become progressively more used for these types of pharmacological/toxicological studies in recent years. These epidermal models have been used in the form of cell culture, tissue sheets, and highly differentiated epidermal and epidermal/dermal systems. This review highlights the existing published data on the utility of these skin bioequivalent models for various types of metabolism and toxicology studies that should be of interest to the dermatopharmaceutical scientist.