Mesenchymal-epithelial interactions in the skin: aiming for site-specific tissue regeneration

Disease modeling of pulmonary fibrosis using human pluripotent stem cell-derived alveolar organoids

Although alveolar epithelial cells play a critical role in the pathogenesis of pulmonary fibrosis, few practical in vitro models exist to study them. Here, we established a novel in vitro pulmonary fibrosis model using alveolar organoids consisting of human pluripotent stem cell-derived alveolar epithelial cells and primary human lung fibroblasts. In this human model, bleomycin treatment induced phenotypes such as epithelial cell-mediated fibroblast activation, cellular senescence, and presence of alveolar epithelial cells in abnormal differentiation states. Chemical screening performed to target these abnormalities showed that inhibition of ALK5 or blocking of integrin αVβ6 ameliorated the fibrogenic changes in the alveolar organoids. Furthermore, organoid contraction and extracellular matrix accumulation in the model recapitulated the pathological changes observed in pulmonary fibrosis. This human model may therefore accelerate the development of highly effective therapeutic agents for otherwise incurable pulmonary fibrosis by targeting alveolar epithelial cells and epithelial-mesenchymal interactions.

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Human pluripotent stem cell-based in vitro pulmonary fibrosis model was established

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Bleomycin-treated alveolar organoids showed epithelium-dependent contraction

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Abnormal differentiation state and cellular senescence in AT2 cells were mimicked

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Inhibition of TGFβ signaling ameliorated the fibrogenic changes of the disease model

Can plantar fibroblast implantation protect amputees from skin injury? A recipe for skin augmentation

Skin injuries remain a persistent problem for users of lower-limb prostheses despite sustained progress in prosthesis design. One factor limiting the prevention of skin injuries is that skin on the residual limb is not suited to bear the mechanical loads of ambulation. One part of the body that is suited to this task is the sole of the foot. Here, we propose a novel strategy to actively augment skin's tolerance to load, increasing its resistance to mechanically induced injuries. We hypothesise that the load tolerance of skin can be augmented by autologous transplantation of plantar fibroblasts into the residual limb dermis. We expect that introducing plantar fibroblasts will induce the overlying keratinocytes to express plantar-specific keratins leading to a tougher epidermis. Using a computational finite element model of a weight-bearing residual limb, we estimate that skin deformation (a key driver of pressure ulcer injuries) could be halved by reprogramming skin to a plantar-like phenotype. We believe this strategy could yield new progress in pressure ulcer prevention for amputees, facilitating rehabilitation and improving quality of life for patients.

Accelerated wound healing process in rat by probiotic Lactobacillus reuteri derived ointment

Background Antioxidant agents have positive effects on wound healing process and on the other hand probiotics also have great antioxidation or oxidation-resistance properties. Methods In this study, we investigated the effects of Lactobacillus reuteri derived ointment as a probiotic bacterium on the wound healing process using a full-thickness rat skin model. The wound diameter and contraction percent measurement, histopathological examination, and myeloperoxidase (MPO) enzyme activity evaluation were carried out during the period of study. Results Amount of deposit collagen was significantly increased; epithelization speed and epidermis production were also observed in the ointment-treated group, while the inflammation rate was also significantly lower than the control group. In addition, a significant reduction in the activity of enzyme MPO was also detected in the ointment-treated group. Conclusions According to the results, probiotic ointment effectively accelerates the wound healing process and it can be used as a promising drug for wound dressing application.

Isolation and Culture of Human Dermal Fibroblasts

Dermal fibroblasts are the main cell type present in skin connective tissue (dermis). Fibroblasts interact with epidermal cells during hair development and in interfollicular skin. Moreover, they play an essential role during cutaneous wound healing and in bioengineering of skin. Hence, culture of primary fibroblast is gaining in importance. In addition, fibroblasts established from skin biopsies provide a powerful tool for investigating normal skin physiology or specific disease states. In this chapter, detailed procedures for establishing and maintaining primary cultures of adult human dermal fibroblasts are described.

Use of homeobox gene expression patterns to determine anatomical regions of origin for body surface tissues derived from adult mice

Anatomical regions of the skin have distinct functions and anatomical characteristics, including thicker or thinner epidermis, more or fewer hair follicles, and lighter or darker skin. For a better therapeutic outcome of skin transplantation, site-specific characteristics of grafted tissues need to be taken into account in terms of their functionality and beauty. However, there is no method for evaluating positional information of epidermal cells. Homeobox genes are expressed along the anterior-posterior axis and direct the body plan in the animal development process. Although the expression of several HOX genes is known to be retained as the positional information in adult tissue, their expression patterns in the body surface tissues in adult mammals are still incompletely understood. In this study, we investigated the expression patterns of 40 homeobox genes, including 39 Hox genes and the paired box 6 (Pax6) gene, in body surface tissues of adult mice. On the basis of the results obtained, we proposed, for the first time, a method for determining anatomical regions of origin for body surface tissues derived from adult mice using Hox genes and Pax6. Evaluation of expression levels of at least 7 Hox genes and Pax6 should be sufficient to distinguish 11 anatomical body surface tissues derived from the adult mouse body. The proposed method may be useful not only for determining the origin of surface tissues from specific anatomical regions of the mammalian body but also for predicting positional information of epithelial cells generated from pluripotent stem cells.

Mesenchymal Cells Affect Salivary Epithelial Cell Morphology on PGS/PLGA Core/Shell Nanofibers

Engineering salivary glands is of interest due to the damaging effects of radiation therapy and the autoimmune disease Sjögren’s syndrome on salivary gland function. One of the current problems in tissue engineering is that in vitro studies often fail to predict in vivo regeneration due to failure of cells to interact with scaffolds and of the single cell types that are typically used for these studies. Although poly (lactic co glycolic acid) (PLGA) nanofiber scaffolds have been used for in vitro growth of epithelial cells, PLGA has low compliance and cells do not penetrate the scaffolds. Using a core-shell electrospinning technique, we incorporated poly (glycerol sebacate) (PGS) into PLGA scaffolds to increase the compliance and decrease hydrophobicity. PGS/PLGA scaffolds promoted epithelial cell penetration into the scaffold and apical localization of tight junction proteins, which is necessary for epithelial cell function. Additionally, co-culture of the salivary epithelial cells with NIH3T3 mesenchymal cells on PGS/PLGA scaffolds facilitated epithelial tissue reorganization and apical localization of tight junction proteins significantly more than in the absence of the mesenchyme. These data demonstrate the applicability of PGS/PLGA nanofibers for epithelial cell self-organization and facilitation of co-culture cell interactions that promote tissue self-organization in vitro.

Scar management in burn injuries using drug delivery and molecular signaling: Current treatments and future directions

In recent decades, there have been tremendous improvements in burn care that have allowed patients to survive severe burn injuries that were once fatal. However, a major limitation of burn care currently is the development of hypertrophic scars in approximately 70% of patients. This significantly decreases the quality of life for patients due to the physical and psychosocial symptoms associated with scarring. Current approaches to manage scarring include surgical techniques and non-surgical methods such as laser therapy, steroid injections, and compression therapy. These treatments are limited in their effectiveness and regularly fail to manage symptoms. As a result, the development of novel treatments that aim to improve outcomes and quality of life is imperative. Drug delivery that targets the molecular cascades of wound healing to attenuate or prevent hypertrophic scarring is a promising approach that has therapeutic potential. In this review, we discuss current treatments for scar management after burn injury, and how drug delivery targeting molecular signaling can lead to new therapeutic strategies.

Human Adipose Mesenchymal Cells Inhibit Melanocyte Differentiation and the Pigmentation of Human Skin via Increased Expression of TGF-β1

There is accumulating evidence that interactions between epidermal melanocytes and stromal cells play an important role in the regulation of skin pigmentation. In this study we established a pigmented dermo-epidermal skin model, melDESS, of human origin to investigate the effects of distinct stromal cells on melanogenesis. melDESS is a complex, clinically relevant skin equivalent composed of an epidermis containing both melanocytes and keratinocytes. Its dermal compartment consists either of adipose tissue-derived stromal cells, dermal fibroblasts (Fbs), or a mixture of both cell types. These skin substitutes were transplanted for 5 weeks on the backs of immuno-incompetent rats and analyzed. Gene expression and Western blot analyses showed a significantly higher expression of transforming growth factor-β1 by adipose tissue-derived stromal cells compared with dermal Fbs. In addition, we showed that melanocytes responded to the increased levels of transforming growth factor-β1 by down-regulating the expression of key melanogenic enzymes such as tyrosinase. This caused decreased melanin synthesis and, consequently, greatly reduced pigmentation of melDESS. The conclusions are of utmost clinical relevance, namely that adipose tissue-derived stromal cells derived from the hypodermis fail to appropriately interact with epidermal melanocytes, thus preventing the sustainable restoration of the patient's native skin color in bioengineered skin grafts.

Reconstitution of full-thickness skin by microcolumn grafting

In addition to providing a physical barrier, skin also serves a diverse range of physiological functions through different specialized resident cell types/structures, including melanocytes (pigmentation and protection against ultraviolet radiation), Langerhans cells (adaptive immunity), fibroblasts (maintaining extracellular matrix, paracrine regulation of keratinocytes), sweat glands (thermoregulation) and hair follicles (hair growth, sensation and a stem cell reservoir). Restoration of these functional elements has been a long-standing challenge in efforts to engineer skin tissue, while autologous skin grafting is limited by the scarcity of donor site skin and morbidity caused by skin harvesting. We demonstrate an alternative approach of harvesting and then implanting μm-scale, full-thickness columns of human skin tissue, which can be removed from a donor site with minimal morbidity and no scarring. Fresh human skin microcolumns were used to reconstitute skin in wounds on immunodeficient mice. The restored skin recapitulated many key features of normal human skin tissue, including epidermal architecture, diverse skin cell populations, adnexal structures and sweat production in response to cholinergic stimulation. These promising preclinical results suggest that harvesting and grafting of microcolumns may be useful for reconstituting fully functional skin in human wounds, without donor site morbidity. © 2016 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Ltd.

Distribution of bioactive lipid mediators in human skin

The skin produces bioactive lipids that participate in physiological and pathological states, including homeostasis, induction, propagation, and resolution of inflammation. However, comprehension of the cutaneous lipid complement, and contribution to differing roles of the epidermal and dermal compartments, remains incomplete. We assessed the profiles of eicosanoids, endocannabinoids, N-acyl ethanolamides, and sphingolipids, in human dermis, epidermis, and suction blister fluid. We identified 18 prostanoids, 12 hydroxy-fatty acids, 9 endocannabinoids and N-acyl ethanolamides, and 21 non-hydroxylated ceramides and sphingoid bases, several demonstrating significantly different expression in the tissues assayed. The array of dermal and epidermal fatty acids was reflected in the lipid mediators produced, whereas similarities between lipid profiles in blister fluid and epidermis indicated a primarily epidermal origin of suction blister fluid. Supplementation with omega-3 fatty acids ex vivo showed that their action is mediated through perturbation of existing species and formation of other anti-inflammatory lipids. These findings demonstrate the diversity of lipid mediators involved in maintaining tissue homeostasis in resting skin and hint at their contribution to signaling, cross-support, and functions of different skin compartments. Profiling lipid mediators in biopsies and suction blister fluid can support studies investigating cutaneous inflammatory responses, dietary manipulation, and skin diseases lacking biomarkers and therapeutic targets.

The influence of stromal cells on the pigmentation of tissue-engineered dermo-epidermal skin grafts

It has been shown in vitro that melanocyte proliferation and function in palmoplantar skin is regulated by mesenchymal factors derived from fibroblasts. In this study, we investigated in vivo the influence of mesenchymal-epithelial interactions in human tissue-engineered skin substitutes reconstructed from palmar- and nonpalmoplantar-derived fibroblasts. Tissue-engineered dermo-epidermal analogs based on collagen type I hydrogels were populated with either human palmar or nonpalmoplantar fibroblasts and seeded with human nonpalmoplantar-derived melanocytes and keratinocytes. These skin substitutes were transplanted onto full-thickness skin wounds of immunoincompetent rats. Four weeks after transplantation the development of skin color was measured and grafts were excised and analyzed with regard to epidermal characteristics, in particular melanocyte number and function. Skin substitutes containing palmar-derived fibroblasts in comparison to nonpalmoplantar-derived fibroblasts showed (a) a significantly lighter pigmentation; (b) a reduced amount of epidermal melanin granules; and (c) a distinct melanosome expression. However, the number of melanocytes in the basal layer remained similar in both transplantation groups. These findings demonstrate that human palmar fibroblasts regulate the function of melanocytes in human pigmented dermo-epidermal skin substitutes after transplantation, whereas the number of melanocytes remains constant. This underscores the influence of site-specific stromal cells and their importance when constructing skin substitutes for clinical application.

Melanocytes and their diseases

Human melanocytes are distributed not only in the epidermis and in hair follicles but also in mucosa, cochlea (ear), iris (eye), and mesencephalon (brain) among other tissues. Melanocytes, which are derived from the neural crest, are unique in that they produce eu-/pheo-melanin pigments in unique membrane-bound organelles termed melanosomes, which can be divided into four stages depending on their degree of maturation. Pigmentation production is determined by three distinct elements: enzymes involved in melanin synthesis, proteins required for melanosome structure, and proteins required for their trafficking and distribution. Many genes are involved in regulating pigmentation at various levels, and mutations in many of them cause pigmentary disorders, which can be classified into three types: hyperpigmentation (including melasma), hypopigmentation (including oculocutaneous albinism [OCA]), and mixed hyper-/hypopigmentation (including dyschromatosis symmetrica hereditaria). We briefly review vitiligo as a representative of an acquired hypopigmentation disorder.

Tissue engineering of skin: human tonsil-derived mesenchymal cells can function as dermal fibroblasts

PURPOSE

It is unclear whether dermal fibroblasts are indispensable key players for tissue engineering of dermo-epidermal skin analogs. In this experimental study, we wanted to test the hypothesis that tonsil-derived mesenchymal cells can assume the role of dermal fibroblasts when culturing pigmented skin analogs for transplantation.

METHODS

Mesenchymal cells from excised tonsils and keratinocytes, melanocytes, and fibroblasts from skin biopsies were isolated, cultured, and expanded. Melanocytes and keratinocytes were seeded in a ratio of 1:5 onto collagen gels previously populated either with tonsil-derived mesenchymal cells or with autologous dermal fibroblasts. These laboratory engineered skin analogs were then transplanted onto full-thickness wounds of immuno-incompetent rats and analyzed after 3 weeks with regard to macroscopic and microscopic epidermal characteristics.

RESULTS

The skin analogs containing tonsil-derived mesenchymal cells showed the same macroscopic appearance as the ones containing dermal fibroblasts. Histologically, features of epidermal stratification, pigmentation, and cornification were identical to those of the controls assembled with autologous dermal fibroblasts. Transmission electron microscopy confirmed these findings.

CONCLUSION

These data suggest that human tonsil-derived mesenchymal cells can assume dermal fibroblast functions, indicating that possibly various types of mesenchymal cells can successfully be employed for "skingineering" purposes. This aspect may have clinical implications when sources for dermal fibroblasts are scarce.

Connective tissue fibroblast properties are position-dependent during mouse digit tip regeneration

A key factor that contributes to the regenerative ability of regeneration-competent animals such as the salamander is their use of innate positional cues that guide the regeneration process. The limbs of mammals has severe regenerative limitations, however the distal most portion of the terminal phalange is regeneration competent. This regenerative ability of the adult mouse digit is level dependent: amputation through the distal half of the terminal phalanx (P3) leads to successful regeneration, whereas amputation through a more proximal location, e.g. the subterminal phalangeal element (P2), fails to regenerate. Do the connective tissue cells of the mammalian digit play a role similar to that of the salamander limb in controlling the regenerative response? To begin to address this question, we isolated and cultured cells of the connective tissue surrounding the phalangeal bones of regeneration competent (P3) and incompetent (P2) levels. Despite their close proximity and localization, these cells show very distinctive profiles when characterized in vitro and in vivo. In vitro studies comparing their proliferation and position-specific interactions reveal that cells isolated from the P3 and P2 are both capable of organizing and differentiating epithelial progenitors, but with different outcomes. The difference in interactions are further characterized with three-dimension cultures, in which P3 regenerative cells are shown to lack a contractile response that is seen in other fibroblast cultures, including the P2 cultures. In in vivo engraftment studies, the difference between these two cell lines is made more apparent. While both P2 and P3 cells participated in the regeneration of the terminal phalanx, their survival and proliferative indices were distinct, thus suggesting a key difference in their ability to interact within a regeneration permissive environment. These studies are the first to demonstrate distinct positional characteristics of connective tissue cells that are associated with their regenerative capabilities.

Cutaneous wound healing: recruiting developmental pathways for regeneration

Following a skin injury, the damaged tissue is repaired through the coordinated biological actions that constitute the cutaneous healing response. In mammals, repaired skin is not identical to intact uninjured skin, however, and this disparity may be caused by differences in the mechanisms that regulate postnatal cutaneous wound repair compared to embryonic skin development. Improving our understanding of the molecular pathways that are involved in these processes is essential to generate new therapies for wound healing complications. Here we focus on the roles of several key developmental signaling pathways (Wnt/β-catenin, TGF-β, Hedgehog, Notch) in mammalian cutaneous wound repair, and compare this to their function in skin development. We discuss the varying responses to cutaneous injury across the taxa, ranging from complete regeneration to scar tissue formation. Finally, we outline how research into the role of developmental pathways during skin repair has contributed to current wound therapies, and holds potential for the development of more effective treatments.

Transforming Growth Factor-β and Endoglin Signaling Orchestrate Wound Healing

Physiological wound healing is a complex process requiring the temporal and spatial co-ordination of various signaling networks, biomechanical forces, and biochemical signaling pathways in both hypoxic and non-hypoxic conditions. Although a plethora of factors are required for successful physiological tissue repair, transforming growth factor beta (TGF-β) expression has been demonstrated throughout wound healing and shown to regulate many processes involved in tissue repair, including production of ECM, proteases, protease inhibitors, migration, chemotaxis, and proliferation of macrophages, fibroblasts of the granulation tissue, epithelial and capillary endothelial cells. TGF-β mediates these effects by stimulating signaling pathways through a receptor complex which contains Endoglin. Endoglin is expressed in a broad spectrum of proliferating and stem cells with elevated expression during hypoxia, and regulates important cellular functions such as proliferation and adhesion via Smad signaling. This review focuses on how the TGF-β family and Endoglin, regulate stem cell availability, and modulate cellular behavior within the wound microenvironment, includes current knowledge of the signaling pathways involved, and explores how this information may be applicable to inflammatory and/or angiogenic diseases such as fibrosis, rheumatoid arthritis and metastatic cancer.

Mesenchymal stromal cells for treatment of steroid-refractory GvHD: a review of the literature and two pediatric cases

Severe acute graft versus host disease (GvHD) is a life-threatening complication after allogeneic hematopoietic stem cell transplantation. Human mesenchymal stromal cells (MSCs) play an important role in endogenous tissue repair and possess strong immune-modulatory properties making them a promising tool for the treatment of steroid-refractory GvHD. To date, a few reports exist on the use of MSCs in treatment of GvHD in children indicating that children tend to respond better than adults, albeit with heterogeneous results.

We here present a review of the literature and the clinical course of two instructive pediatric patients with acute steroid-refractory GvHD after haploidentical stem cell transplantation, which exemplify the beneficial effects of third-party transplanted MSCs in treatment of acute steroid-refractory GvHD. Moreover, we provide a meta-analysis of clinical studies addressing the outcome of patients with steroid-refractory GvHD and treatment with MSCs in adults and in children (n = 183; 122 adults, 61 children). Our meta-analysis demonstrates that the overall response-rate is high (73.8%) and confirms, for the first time, that children indeed respond better to treatment of GvHD with MSCs than adults (complete response 57.4% vs. 45.1%, respectively).

These data emphasize the significance of this therapeutic approach especially in children and indicate that future prospective studies are needed to assess the reasons for the observed differential response-rates in pediatric and adult patients.

Expression of REIC/Dkk-3 in normal and hyperproliferative epidermis

Dickkopf (Dkk) family members are known as Wnt modulators involved in the development, cell growth/differentiation and cancer. REIC/Dkk-3, which does not interfere with Wnt signalling, has been proposed to be a tumor suppressor gene, but its physiological function has remained unclear. In this study, we analysed the expression of REIC/Dkk-3 in normal interfollicular epidermis (IFE) and hyperproliferative epidermis. REIC/Dkk-3 was expressed in human and mouse IFE, being localized at the interface of upper spinous layer and granular layer. Skin cancer cell lines lost REIC/Dkk-3 expression as reported previously. When we analysed patient samples, REIC/Dkk-3 expression was down-regulated in the hyperproliferative epidermis including skin cancers and non-cancerous proliferative diseases. REIC/Dkk-3 expression was also suppressed in the regenerative and inflammative epidermis of model mice. These findings will certainly contribute to the extension of studies on REIC/Dkk-3.

Junctional Adhesion Molecules (JAMs) are Differentially Expressed in Fibroblasts and Co-Localize with ZO-1 to Adherens-Like Junctions

Junctional Adhesion Molecules (JAMs) are components and regulators of the well-characterized epithelial and endothelial tight junction. Since the molecular components of native fibroblast adherens-like junctions remain poorly described we determined JAM expression profiles in fibroblasts. We found JAM-C on human dermal, lung, and corneal primary fibroblast cultures. Within murine lines, JAM-A was found in L-cells, JAM-C in 3T3 L1 cells, and both JAM-A and JAM-C were co-expressed in NIH 3T3 fibroblasts. In primary dermal fibroblasts, JAM-C concentrated at zipper-like junctions that formed between apposing cells. Dual immunostaining showed JAM-C co-localization with the ZO-1 intracellular scaffolding molecule at cell contacts that ranged from 7 microm to over 25 microm in length. JAM-C also labeled similar zipper-like junctions detected with N-Cadherin and Cadherin-11 antibodies. We conclude that endogenous JAM-C is an integral component of the dermal fibroblast adherens-like junction, and our data extend the expression and potential function of JAMs into mesenchymal tissues.

Melanomas display increased cytoprotection to hypericin-mediated cytotoxicity through the induction of autophagy

Photodynamic therapy (PDT) as a regime for melanoma is of limited success due to factors such as the efficacy of the photosensitizer used, penetration depth and the presence of pigment. We characterised a pigmented and an unpigmented melanoma cell line with respect to their phenotypes. Cell viability was assessed after exposure to hypericin, a UVA-activated photosensitizer. Exposure to 3 microM activated hypericin induced a cytoprotective (autophagic) response from both cell lines. However, the pigmented cells accumulated a large amount of glycogen in their cytoplasm. We hypothesise that the treatment induces an initial cytoprotective response through autophagy, but with increased stress results in a different mode of cell death in pigmented melanoma cells from unpigmented cells. These results indicate that hypericin-PDT could be an adjuvant therapy for melanoma.

Physiological factors that regulate skin pigmentation

More than 150 genes have been identified that affect skin color either directly or indirectly, and we review current understanding of physiological factors that regulate skin pigmentation. We focus on melanosome biogenesis, transport and transfer, melanogenic regulators in melanocytes, and factors derived from keratinocytes, fibroblasts, endothelial cells, hormones, inflammatory cells, and nerves. Enzymatic components of melanosomes include tyrosinase, tyrosinase-related protein 1, and dopachrome tautomerase, which depend on the functions of OA1, P, MATP, ATP7A, and BLOC-1 to synthesize eumelanins and pheomelanins. The main structural component of melanosomes is Pmel17/gp100/Silv, whose sorting involves adaptor protein 1A (AP1A), AP1B, AP2, and spectrin, as well as a chaperone-like component, MART-1. During their maturation, melanosomes move from the perinuclear area toward the plasma membrane. Microtubules, dynein, kinesin, actin filaments, Rab27a, melanophilin, myosin Va, and Slp2-a are involved in melanosome transport. Foxn1 and p53 up-regulate skin pigmentation via bFGF and POMC derivatives including alpha-MSH and ACTH, respectively. Other critical factors that affect skin pigmentation include MC1R, CREB, ASP, MITF, PAX3, SOX9/10, LEF-1/TCF, PAR-2, DKK1, SCF, HGF, GM-CSF, endothelin-1, prostaglandins, leukotrienes, thromboxanes, neurotrophins, and neuropeptides. UV radiation up-regulates most factors that increase melanogenesis. Further studies will elucidate the currently unknown functions of many other pigment genes/proteins. (c) 2009 International Union of Biochemistry and Molecular Biology, Inc.

Long-lasting molecular changes in human skin after repetitive in situ UV irradiation

It is known that UV modulates the expression of paracrine factors that regulate melanocyte function in the skin. We investigated the consequences of repetitive UV exposure of human skin in biopsies of 10 subjects with phototypes 2-3.5 taken 1-4 years later. The expression of melanogenic factors (TYR, MART1, MITF), growth factors/receptors (SCF/KIT, bFGF/FGFR1, ET1/EDNRB, HGF, GM-CSF), adhesion molecules (beta-catenin, E-cadherin, N-cadherin), cell cycle proteins (PCNA, cyclins D1, E2) as well as Bcl-2, DKK1, and DKK3, were analyzed by immunohistochemistry. Most of those markers showed no detectable changes at > or = 1 year after the repetitive UV irradiation. Although increased expression of EDNRB protein was detected in 3 of 10 UV-irradiated subjects, there was no detectable change in the expression of ET1 protein or in EDNRB mRNA levels. In summary, only the expression of TYR, MART1, and/or EDNRB, and only in some subjects, was elevated at > or = 1 year after UV irradiation. Thus the long-term effects of repetitive UV irradiation on human skin did not lead to significant changes in skin morphology and there is considerable subject-to-subject variation in responses. The possibility that changes in the expression and function of EDNRB triggers downstream activation of abnormal melanocyte proliferation and differentiation deserves further investigation.

Calmodulin-like protein upregulates myosin-10 in human keratinocytes and is regulated during epidermal wound healing in vivo

Epidermal wound healing is required for normal skin barrier function. Cell motility is a key factor in the ability of keratinocytes to heal epithelial damage. Calmodulin-like protein (CLP) is an epithelial-specific Ca(2+)-binding protein that is regulated during terminal keratinocyte differentiation. CLP is a specific light chain of unconventional myosin-10 (Myo10) and its expression increases filopodial length, filopodial number, and Myo10-dependent cell motility in vitro. However, the effects of CLP expression on keratinocyte motility are unknown. Here we used cultured human keratinocytes to study the role of CLP in regulating Myo10 and the effects of Myo10 and CLP on cell migration. CLP and Myo10 expression were correlated in vitro and required for keratinocyte motility in wound-healing assays. We examined the localization of CLP in wounded skin by immunohistochemistry and found an upregulation and peripheral localization of CLP in the basal and suprabasal cells adjacent to and immediately over the wound bed in vivo. The results suggest that increased CLP expression and CLP-mediated Myo10 function are important for skin differentiation and wound reepithelialization.

Deciphering the function of canonical Wnt signals in development and disease: conditional loss- and gain-of-function mutations of beta-catenin in mice

Wnt signaling is one of a handful of powerful signaling pathways that play crucial roles in the animal life by controlling the genetic programs of embryonic development and adult homeostasis. When disrupted, these signaling pathways cause developmental defects, or diseases, among them cancer. The gateway of the canonical Wnt pathway, which contains >100 genes, is an essential molecule called beta-catenin (Armadillo in Drosophila). Conditional loss- and gain-of-function mutations of beta-catenin in mice provided powerful tools for the functional analysis of canonical Wnt signaling in many tissues and organs. Such studies revealed roles of Wnt signaling that were previously not accessible to genetic analysis due to the early embryonic lethality of conventional beta-catenin knockout mice, as well as the redundancy of Wnt ligands, receptors, and transcription factors. Analysis of conditional beta-catenin loss- and gain-of-function mutant mice demonstrated that canonical Wnt signals control progenitor cell expansion and lineage decisions both in the early embryo and in many organs. Canonical Wnt signaling also plays important roles in the maintenance of various embryonic or adult stem cells, and as recent findings demonstrated, in cancer stem cell types. This has opened new opportunities to model numerous human diseases, which have been associated with deregulated Wnt signaling. Our review summarizes what has been learned from genetic studies of the Wnt pathway by the analysis of conditional beta-catenin loss- and gain-of-function mice.

Interaction of cambial dermal cells (fibroblasts) and epidermis in morphofunctional area of mouse skin

Epidermis and dermis form an integral morphofunctional area, where cambial cells proliferate and their first-division daughter cells differentiate. An important feature of this area is different rates of the development of daughter cells (fibroblasts) in the dermis and epidermis, which is greater in the epidermis. This asymmetry results in the prevalence of first epidermal daughter cells and, hence, their effect on cambial cells, and then of stromal daughter cells and their effects on cambial cells. The regulator factors of epidermal daughter cells promote unblocking of the major polarity axis of cambial (mother) cell, while stromal cells (fibroblasts) induce their polarization along the major axis and the onset of mitosis. In the dermis and epidermis, division of cambial cells is asymmetric; a prominent role in the formation of mother and daughter cells is given to the basal membrane as an elastic support. Mother and daughter cells form ring-like structures generating electric field that can promote differentiation of the daughter cells.

Agent based modelling helps in understanding the rules by which fibroblasts support keratinocyte colony formation

Background

Autologous keratincoytes are routinely expanded using irradiated mouse fibroblasts and bovine serum for clinical use. With growing concerns about the safety of these xenobiotic materials, it is desirable to culture keratinocytes in media without animal derived products. An improved understanding of epithelial/mesenchymal interactions could assist in this.

Methodology/Principal Findings

A keratincyte/fibroblast o-culture model was developed by extending an agent-based keratinocyte colony formation model to include the response of keratinocytes to both fibroblasts and serum. The model was validated by comparison of the in virtuo and in vitro multicellular behaviour of keratinocytes and fibroblasts in single and co-culture in Greens medium. To test the robustness of the model, several properties of the fibroblasts were changed to investigate their influence on the multicellular morphogenesis of keratinocyes and fibroblasts. The model was then used to generate hypotheses to explore the interactions of both proliferative and growth arrested fibroblasts with keratinocytes. The key predictions arising from the model which were confirmed by in vitro experiments were that 1) the ratio of fibroblasts to keratinocytes would critically influence keratinocyte colony expansion, 2) this ratio needed to be optimum at the beginning of the co-culture, 3) proliferative fibroblasts would be more effective than irradiated cells in expanding keratinocytes and 4) in the presence of an adequate number of fibroblasts, keratinocyte expansion would be independent of serum.

Conclusions

A closely associated computational and biological approach is a powerful tool for understanding complex biological systems such as the interactions between keratinocytes and fibroblasts. The key outcome of this study is the finding that the early addition of a critical ratio of proliferative fibroblasts can give rapid keratinocyte expansion without the use of irradiated mouse fibroblasts and bovine serum.

Effects of Wnt3a on proliferation and differentiation of human epidermal stem cells

Epidermal stem cells maintain development and homeostasis of mammalian epidermis throughout life. However, the molecular mechanisms involved in the proliferation and differentiation of epidermal stem cells are far from clear. In this study, we investigated the effects of Wnt3a and Wnt/beta-catenin signaling on proliferation and differentiation of human fetal epidermal stem cells. We found both Wnt3a and active beta-catenin, two key members of the Wnt/beta-catenin signaling, were expressed in human fetal epidermis and epidermal stem cells. In addition, Wnt3a protein can promote proliferation and inhibit differentiation of epidermal stem cells in vitro culture. Our results suggest that Wnt/beta-catenin signaling plays important roles in human fetal skin development and homeostasis, which also provide new insights on the molecular mechanisms of oncogenesis in human epidermis.

In vivo determination of skin near-infrared optical properties using diffuse optical spectroscopy

We develop a superficial diffusing probe with a 3 mm source-detector separation that can be used in combination with diffuse optical spectroscopic (DOS) methods to noninvasively determine full-spectrum optical properties of superficial in vivo skin in the wavelength range from 650 to 1000 nm. This new probe uses a highly scattering layer to diffuse photons emitted from a collimated light source and relies on a two-layer diffusion model to determine tissue absorption coefficient mu a and reduced scattering coefficient mu's. By employing the probe to measure two-layer phantoms that mimic the optical properties of skin, we demonstrate that the probe has an interrogation depth of 1 to 2 mm. We carry out SSFDPM (steady state frequency-domain photon migration) measurements using this new probe on the volar forearm and palm of 15 subjects, including five subjects of African descent, five Asians, and five Caucasians. The optical properties of in vivo skin determined using the superficial diffusing probe show considerable similarity to published optical properties of carefully prepared ex vivo epidermis+dermis.

Does imiquimod histologically rejuvenate ultraviolet radiation-damaged skin?

BACKGROUND

Imiquimod (IMI) 5% is believed by some to result in an improved cosmetic appearance of chronically ultraviolet radiation (UV)-damaged skin.

OBJECTIVE

The objective was to determine what histologic and immunohistologic changes were present in actinically damaged skin after treatment with IMI.

METHODS AND MATERIALS

Pre- and posttherapy biopsies of 12 patients with histories of actinic keratoses were evaluated with routine histology and immunohistochemical stains including p53, p63, proliferating cell nuclear antigen (PCNA), c-kit, and Factor XIIIa.

RESULTS

After IMI therapy there was less compact hyperkeratosis, a more uniform rete ridge pattern with a more ordered proliferation of the epidermis, and a decrease in sun-damaged melanocytes. The papillary dermis showed a more uniform cellularity, and there was increased cellularity within the area of solar elastosis. After therapy, staining for p53, p63, and PCNA was decreased within the epidermis; staining for c-kit was decreased but more uniform in the basal cell; and Factor XIIIa expression was increased within the papillary dermis with a more ordered pattern of staining.

CONCLUSION

These morphologic and immunohistochemical patterns may explain some of the improvement in overall skin appearance after IMI therapy and may be related to the spectrum of signaling pathways induced by the imidazoquinolines.

Dickkopf 1 (DKK1) regulates skin pigmentation and thickness by affecting Wnt/beta-catenin signaling in keratinocytes

The epidermis (containing primarily keratinocytes and melanocytes) overlies the dermis (containing primarily fibroblasts) of human skin. We previously reported that dickkopf 1 (DKK1) secreted by fibroblasts in the dermis elicits the hypopigmented phenotype of palmoplantar skin due to suppression of melanocyte function and growth via the regulation of two important signaling factors, microphthalmia-associated transcription factor (MITF) and beta-catenin. We now report that treatment of keratinocytes with DKK1 increases their proliferation and decreases their uptake of melanin and that treatment of reconstructed skin with DKK1 induces a thicker and less pigmented epidermis. DNA microarray analysis revealed many genes regulated by DKK1, and several with critical expression patterns were validated by reverse transcriptase-polymerase chain reaction and Western blotting. DKK1 induced the expression of keratin 9 and alpha-Kelch-like ECT2 interacting protein (alphaKLEIP) but down-regulated the expression of beta-catenin, glycogen synthase kinase 3beta, protein kinase C, and proteinase-activated receptor-2 (PAR-2), which is consistent with the expression patterns of those proteins in human palmoplantar skin. Treatment of reconstructed skin with DKK1 reproduced the expression patterns of those key proteins observed in palmoplantar skin. These findings further elucidate why human skin is thicker and paler on the palms and soles than on the trunk through topographical and site-specific differences in the secretion of DKK1 by dermal fibroblasts that affects the overlying epidermis.

The role of fibroblasts in tissue engineering and regeneration

Fibroblasts are mesenchymal cells that can be readily cultured in the laboratory and play a significant role in epithelial-mesenchymal interactions, secreting various growth factors and cytokines that have a direct effect on epidermal proliferation, differentiation and formation of extracellular matrix. They have been incorporated into various tissue-engineered products such as Dermagraft (Advanced BioHealing, La Jolla, CA, U.S.A.) and Apligraf (Novartis, Basel, Switzerland) and used for a variety of clinical applications, including the treatment of burns, chronic venous ulcers and several other clinical applications in dermatology and plastic surgery. In this article we review the cell biology of dermal fibroblasts and discuss past and current experience of the clinical use of cultured fibroblasts.

Intractable wounds caused by arteriosclerosis obliterans with end-stage renal disease treated by aggressive debridement and epidermal grafting

BACKGROUND

Patients receiving hemodialysis (HD) need to avoid skin laceration; amputation is common because of intractability of wounds and complications with other diseases, including diabetes mellitus. We have reported the usefulness of aggressive debridement deep enough to expose bone marrow cells, occlusive dressing, and epidermal grafting for diabetic foot ulcers and wounds from rheumatic diseases.

OBJECTIVE

To test whether this experimental protocol is effective to treat intractable wounds in a patient receiving HD accompanied with arteriosclerosis obliterans (ASO).

METHODS AND RESULTS

A 78-year-old patient with chronic renal failure and arteriosclerosis obliterans suffered a wound with exposed bone on the left great toe. Aggressive combination therapy was effective despite methicillin-resistant Staphylococcus aureus infection, and the wound healed in 13 weeks.

LIMITATIONS

This study, reporting a single case, limits the interpretation of results.

CONCLUSION

Aggressive debridement exposing bone marrow cells is useful in preparing a healthy wound bed and epidermal sheet grafting may be accepted more advantageously in an ischemic environment and adopt a site-specific phenotype via mesenchymal-epithelial interactions.

Patterning skin pigmentation via dickkopf

One of the striking regional variations in skin is its pigmentation. Yamaguchi et al. further dissect the mechanism of regional pigmentation by assessing the effects of dickkopf 1 (DKK1), an antagonist of the Wnt pathway produced in lightly pigmented skin, on melanocyte gene expression. The results provide a plethora of candidate genes that may mediate DKK1's inhibitory effects on melanocyte function.

Bronchial epithelial cell growth regulation in fibroblast cocultures: the role of hepatocyte growth factor

Proliferation of bronchial epithelial cells is an important biological process in physiological conditions and various lung diseases. The objective of this study was to determine how bronchial fibroblasts influence bronchial epithelial cell proliferation. The proliferative activity in cocultures was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and direct cells counts. Concentration of cytokines was measured in cell culture supernatants by means of ELISA. In primary cell cocultures, fibroblasts or fibroblast-conditioned medium enhanced 1.85-fold the proliferation of primary bronchial epithelial cells (P < 0.02) compared with bronchial epithelial cells cultured alone. The proliferative activity in cocultures and in fibroblast-conditioned medium was reduced by neutralizing antibody to hepatocyte growth factor (HGF) and HGF receptor c-met. Neutralizing antibodies to FGF-7 and IGF-1 had no effect. Treatment of fibroblast-epithelial cocultures with anti-IL-6 and anti-TNF-alpha neutralizing antibodies and with indomethacin decreased production of HGF. These results indicate that cytokines and PGE(2) may indirectly mediate epithelial cell proliferation via the regulation of HGF in bronchial stromal cells and that HGF plays a crucial role in proinflammatory cytokine-induced proliferation in the experimental system studied.

Immunohistochemistry and in situ hybridization in the study of human skin melanocytes

Although keratinocytes are the most numerous type of cell in the skin, melanocytes are also key players as they produce and distribute melanin that protects the skin from ultraviolet (UV) radiation. In vitro experiments on melanocytic cell lines are useful to study melanogenesis and their progression towards melanoma. However, interactions of melanocytes with keratinocytes and with other types of cells in the skin, such as fibroblasts and Langerhans cells, are also crucial. We describe two techniques, immunohistochemistry (IHC) and tissue in situ hybridization (TISH), that can be used to identify and study melanocytes in the skin and their responses to UV or other stimuli in situ. We describe a practical method to localize melanocytic antigens on formalin-fixed, paraffin-embedded tissue sections and in frozen sections using indirect immunofluorescence with conjugated secondary antibodies. In addition, we detail the use of TISH and its combination with IHC to study mRNA levels of genes expressed in the skin at cellular resolution. This methodology, along with relevant tips and troubleshooting items, are important tools to identify and study melanocytes in the skin.

Hereditary gingival fibromatosis: characteristics and novel putative pathogenic mechanisms

Hereditary gingival fibromatosis (HGF) is a rare condition that can occur as an isolated disease or as part of a syndrome or chromosomal abnormality. In severe cases, the gingival enlargement may cover the crowns of teeth and cause severe functional and esthetic concerns. Histological and cell culture studies have uncovered some of the molecular and cellular changes associated with HGF. However, the pathogenesis of the disease is still largely unknown. Recent studies about the genetic characteristics of HGF have provided novel clues about the potential pathogenic mechanisms. In particular, mutation in the son-of-sevenless (SOS-1) gene has been associated with one form of the disease. However, HGF displays genetic heterogeneity, and mutations in other genes are also likely involved. This review outlines the current knowledge about the histological, cellular, and genetic characteristics of HGF. In addition, the potential role of the SOS-1 molecule and related novel intracellular signaling pathways in the pathogenesis of HGF will be discussed.

The effects of dickkopf 1 on gene expression and Wnt signaling by melanocytes: mechanisms underlying its suppression of melanocyte function and proliferation

Dickkopf 1 (DKK1), which is expressed at high mRNA levels by fibroblasts in the dermis of human skin on the palms and soles, inhibits the function and proliferation of melanocytes in the epidermis of those areas via the suppression of beta-catenin and microphthalmia-associated transcription factor (MITF). In this study, we investigated the protein expression levels of DKK1 between palmoplantar and non-palmoplantar areas and the effects of DKK1 on melanocyte gene expression profiles and on Wnt signaling pathways using DNA microarray technology, reverse transcriptase-PCR, Western blot, 3-dimensional reconstructed skin, immunocytochemistry, and immunohistochemistry. DKK1-responsive genes included those encoding proteins involved in the regulation of melanocyte development, growth, differentiation, and apoptosis (including Kremen 1, G-coupled receptor 51, lipoprotein receptor-related protein 6, low-density lipoprotein receptor, tumor necrosis factor receptor super-family 10, growth arrest and DNA-damage-inducible gene 45beta, and MITF). Of special interest was the rapid decrease in expression of MITF in melanocytes treated with DKK1, which is concurrent with the decreased activities of beta-catenin and of glucose-synthase kinase 3beta via phosphorylation at Ser9 and with the upregulated expression of protein kinase C alpha. These results further clarify the mechanism by which DKK1 suppresses melanocyte density and differentiation, and help explain why DKK1-rich palmoplantar epidermis is paler than non-palmoplantar epidermis via mesenchymal-epithelial interactions.