Modeling of wound healing processes in human skin using tissue culture

Postbiotic lactobacilli induce cutaneous antimicrobial response and restore the barrier to inhibit the intracellular invasion of Staphylococcus aureus in vitro and ex vivo

Intracellular pathogens including Staphylococcus aureus contribute to the non-healing phenotype of chronic wounds. Lactobacilli, well known as beneficial bacteria, are also reported to modulate the immune system, yet their role in cutaneous immunity remains largely unknown. We explored the therapeutic potential of bacteria-free postbiotics, bioactive lysates of lactobacilli, to reduce intracellular S. aureus colonization and promote healing. Fourteen postbiotics derived from various lactobacilli species were screened, and Latilactobacillus curvatus BGMK2-41 was selected for further analysis based on the most efficient ability to reduce intracellular infection by S. aureus diabetic foot ulcer clinical isolate and S. aureus USA300. Treatment of both infected keratinocytes in vitro and infected human skin ex vivo with BGMK2-41 postbiotic cleared S. aureus. Keratinocytes treated in vitro with BGMK2-41 upregulated expression of antimicrobial response genes, of which DEFB4, ANG, and RNASE7 were also found upregulated in treated ex vivo human skin together with CAMP exclusively upregulated ex vivo. Furthermore, BGMK2-41 postbiotic treatment has a multifaceted impact on the wound healing process. Treatment of keratinocytes stimulated cell migration and the expression of tight junction proteins, while in ex vivo human skin BGMK2-41 increased expression of anti-inflammatory cytokine IL-10, promoted re-epithelialization, and restored the epidermal barrier via upregulation of tight junction proteins. Together, this provides a potential therapeutic approach for persistent intracellular S. aureus infections.

Biodegradable Silk Fibroin Matrices for Wound Closure in a Human 3D Ex Vivo Approach

In this study, the potential of silk fibroin biomaterials for enhancing wound healing is explored, focusing on their integration into a human 3D ex vivo wound model derived from abdominoplasties. For this purpose, cast silk fibroin membranes and electrospun nonwoven matrices from Bombyx mori silk cocoons were compared to untreated controls over 20 days. Keratinocyte behavior and wound healing were analyzed qualitatively and quantitatively by histomorphometric and immune histochemical methods (HE, Ki67, TUNEL). Findings reveal rapid keratinocyte proliferation on both silk fibroin membrane and nonwoven matrices, along with enhanced infiltration in the matrix, suggesting improved early wound closure. Silk fibroin membranes exhibited a significantly improved early regeneration, followed by nonwoven matrices (p < 0.05) compared to untreated wounds, resulting in the formation of multi-layered epidermal structures with complete regeneration. Overall, the materials demonstrated excellent biocompatibility, supporting cell activity with no signs of increased apoptosis or early degradation. These results underscore silk fibroin's potential in clinical wound care, particularly in tissue integration and re-epithelialization, offering valuable insights for advanced and-as a result of the electrospinning technique-individual wound care development. Furthermore, the use of an ex vivo wound model appears to be a viable option for pre-clinical testing.

Guanidinylated/PEGylated chitosan in the bioink promotes the formation of multi-layered keratinocytes in a human skin equivalent

The biological differences of skin between rodent and human beings and the strong appeal to replace the experimental animals have led to the development of alternative models with structures similar to the real human skin. Keratinocytes cultured in vitro on conventional dermal scaffolds tend to form monolayer rather than multi-layer epithelial tissue architectures. How to construct human skin or epidermal equivalents with multi-layered keratinocytes similar to real human epidermis remains one of the greatest challenges. Herein, a human skin equivalent with multi-layered keratinocytes was constructed by 3D bioprinting fibroblasts and subsequent culturing epidermal keratinocytes. Biocompatible guanidinylated/PEGylated chitosan (GPCS) was used as the main component of bioink to 3D bioprint tissue-engineered dermis. The function of GPCS to promote HaCat cell proliferation and connection was confirmed at the genetic, cellular, and histological levels. Compared with the skin tissues with mono-layered keratinocytes engineered with collagen and gelatin, adding GPCS in the bioink generated tissue-engineered human skin equivalents with multi-layered keratinocytes. Such human skin equivalents could be alternative models for biomedical, toxicological, and pharmaceutical research.

Effect of Chitosan-Diosgenin Combination on Wound Healing

The difficult-to-heal wounds continue to be a problem for modern medicine. Chitosan and diosgenin possess anti-inflammatory and antioxidant effects making them relevant substances for wound treatment. That is why this work aimed to study the effect of the combined application of chitosan and diosgenin on a mouse skin wound model. For the purpose, wounds (6 mm diameter) were made on mice's backs and were treated for 9 days with one of the following: 50% ethanol (control), polyethylene glycol (PEG) in 50% ethanol, chitosan and PEG in 50% ethanol (Chs), diosgenin and PEG in 50% ethanol (Dg) and chitosan, diosgenin and PEG in 50% ethanol (ChsDg). Before the first treatment and on the 3rd, 6th and 9th days, the wounds were photographed and their area was determined. On the 9th day, animals were euthanized and wounds' tissues were excised for histological analysis. In addition, the lipid peroxidation (LPO), protein oxidation (POx) and total glutathione (tGSH) levels were measured. The results showed that ChsDg had the most pronounced overall effect on wound area reduction, followed by Chs and PEG. Moreover, the application of ChsDg maintained high levels of tGSH in wound tissues, compared to other substances. It was shown that all tested substances, except ethanol, reduced POx comparable to intact skin levels. Therefore, the combined application of chitosan and diosgenin is a very promising and effective medication for wound healing.

Hyperspectral characterization of re-epithelialization in an in vitro wound model

In vitro wound models are useful for research on wound re-epithelialization. Hyperspectral imaging represents a non-destructive alternative to histology analysis for detection of re-epithelialization. This study aims to characterize the main optical behavior of a wound model in order to enable development of detection algorithms. K-Means clustering and agglomerative analysis were used to group spatial regions based on the spectral behavior, and an inverse photon transport model was used to explain differences in optical properties. Six samples of the wound model were prepared from human tissue and followed over 22 days. Re-epithelialization occurred at a mean rate of 0.24 mm² /day after day 8 to 10. Suppression of wound spectral features was the main feature characterizing re-epithelialized and intact tissue. Modeling the photon transport through a diffuse layer placed on top of wound tissue properties reproduced the spectral behavior. The missing top layer represented by wounds is thus optically detectable using hyperspectral imaging.

Characterization of a Topically Testable Model of Burn Injury on Human Skin Explants

Severe burn injuries remain a major health problem due to high rates of mortality, residual morbidity, and/or aesthetic damages. To find new therapies aimed at promoting a harmonious healing of skin burns, it is important to develop models which take into account the unique properties of the human skin. Based on previously described models of burn injury performed on human skin explants, we hypothesized that maintaining explants under constant tension forces would allow to more closely reproduce the pathophysiological processes of skin remodeling. We thus. Here, we set up and characterized an improved model of deep second-degree burn injury on ex vivo cultured human skin explants at air-liquid interface and maintained under conditions of constant tension forces. A spontaneous re-epithelialization of the lesion was observed 8 to 9 days post burn and was found to rely on the proliferation of basal keratinocytes at the wound edges. Collagen VII at the dermo-epidermal junction reformed along with the progression of re-epithelializatio and a synthesis of procollagen III was observed in the dermis at the wound site. These findings indicate that our model is suitable for the assessment of clinically-relevant therapies aimed at modulating the kinetics of re-epithelialization and/or the activation of fibroblasts following skin burn injuries. In this regard, we evaluated the use of a thermoreversible poloxamer hydrogel as a vehicle for topically-testable therapeutic molecules. Our data showed that, although useful for drug formulation, the p407/p188 poloxamer hydrogel induces a delay of skin re-epithelialization in humans skin explants submitted to experimental burn injury.

Exploiting scale-invariance: a top layer targeted inverse model for hyperspectral images of wounds

Detection of re-epithelialization in wound healing is important, but challenging. Hyperspectral imaging can be used for non-destructive characterization, but efficient techniques are needed to extract and interpret the information. An inverse photon transport model suitable for characterization of re-epithelialization is validated and explored in this study. It exploits scale-invariance to enable fitting of the epidermal skin layer only. Monte Carlo simulations indicate that the fitted layer transmittance and reflectance spectra are unique, and that there exists an infinite number of coupled parameter solutions. The method is used to explain the optical behavior of and detect re-epithelialization in an in vitro wound model.

Death, unity, and the brain

The dead donor rule holds that removing organs from living human beings without their consent is wrongful killing. The rule still prevails in most countries, and I assume it without argument in order to pose the question: is it possible to have a metaphysically correct, clinically relevant analysis of human death that makes organ donation ethically permissible? I argue that the two dominant criteria of death-brain death and circulatory death-are both empirically and metaphysically inadequate as definitions of human death and therefore hold no epistemic value in themselves. I first set out a neo-Aristotelian theory of death as separation of soul (understood as organising principle) and body, which is then fleshed out as loss of organismic integrity. The brain and circulatory criteria are shown to have severe weaknesses as physiological manifestations of loss of integrity. Given the mismatch between what death is, metaphysically speaking, and the dominant criteria accepted by clinicians and philosophers, it turns out that only actual bodily decomposition is a sure sign of death. In this I differ from Alan Shewmon, whose important work I discuss in detail.

Tracking keratinocytes and melanocytes using carboxyfluorescein hydroxysuccinimidyl ester staining

Introduction

The treatment of burn wounds and hypopigmentation conditions often require autologous transplantation of keratinocytes and melanocytes. Tracking transplanted cells to ascertain their contribution to tissue recapitulation presents a challenge. This study demonstrates a methodology based on passive staining with carboxyfluorescein hydroxysuccinimidyl ester (CFSE) that enables localization of cells in tissue sections to investigate the fate of transplanted cells in wound re-epithelialisation.

Methods

Viability and migration of CFSE-stained keratinocytes and melanocytes were investigated using viability staining and scratch assays, while proliferation of cells was measured using flow cytometry. In addition, CFSE-stained keratinocytes and melanocytes were transplanted to a human ex vivo wound model, either in suspension, or with the aid of macroporous gelatine microcarriers. Wounds were analysed seven, 14 and 21 days post transplantation using cryosectioning and fluorescence microscopy. Sections from wounds with transplanted co-cultured keratinocytes and melanocytes were stained for pancytokeratin to distinguish keratinocytes.

Results

CFSE-staining of keratinocytes and melanocytes did not affect the viability, migration or proliferation of the cells. Transplanted cells were tracked in ex vivo wounds for 21 days, illustrating that the staining had no effect on wound re-epithelialisation. In conclusion, this study presents a novel application of CFSE-staining for tacking transplanted primary human keratinocytes and melanocytes.

Optical coherence tomography for assessment of epithelialization in a human ex vivo wound model

The ex vivo human skin wound model is a widely accepted model to study wound epithelialization. Due to a lack of animal models that fully replicate human conditions, the ex vivo model is a valuable tool to study mechanisms of wound reepithelialization, as well as for preclinical testing of novel therapeutics. The current standard for assessment of wound healing in this model is histomorphometric analysis, which is labor intensive, time consuming, and requires multiple biological and technical replicates in addition to assessment of different time points. Optical coherence tomography (OCT) is an emerging noninvasive imaging technology originally developed for noninvasive retinal scans that avoids the deleterious effects of tissue processing. This study investigated OCT as a novel method for assessing reepithelialization in the human ex vivo wound model. Excisional ex vivo wounds were created, maintained at air-liquid interface, and healing progression was assessed at days 4 and 7 with OCT and histology. OCT provided adequate resolution to identify the epidermis, the papillary and reticular dermis, and importantly, migrating epithelium in the wound bed. We have deployed OCT as a noninvasive tool to produce, longitudinal "optical biopsies" of ex vivo human wound healing process, and we established an optimal quantification method of re-epithelialization based on en face OCT images of the total wound area. Pairwise statistical analysis of OCT and histology based quantifications for the rate of epithelialization have shown the feasibility and superiority of OCT technology for noninvasive monitoring of human wound epithelialization. Furthermore, we have utilized OCT to evaluate therapeutic potential of allogeneic adipose stem cells revealing their ability to promote reepithelialization in human ex vivo wounds. OCT technology is promising for its applications in wound healing and evaluation of novel therapeutics in both the laboratory and the clinical settings.

In vitro models for evaluating safety and efficacy of novel technologies for skin drug delivery

For preclinical testing of novel therapeutics, predictive in vitro models of the human skin are required to assess efficacy, absorption and safety. Simple as well as more sophisticated three-dimensional organotypic models of the human skin emerged as versatile and powerful tools simulating healthy as well as diseased skin states. Besides addressing the demands of research and industry, such models serve as valid alternative to animal testing. Recently, the acceptance of several models by regulatory authorities corroborates their role as important building block for preclinical development. However, valid assessment of readout parameters derived from these models requires suitable analytical techniques. Standard analytical methods are mostly destructive and limited regarding in-depth investigation on molecular level. The combination of adequate in vitro models with modern non-invasive analytical modalities bears a great potential to address important skin drug delivery related questions. Topics of interest are for instance the assessment of repeated dosing effects and xenobiotic biotransformation, which cannot be analyzed by destructive techniques. This review provides a comprehensive overview of current in vitro skin models differing in functional complexity and mimicking healthy as well as diseased skin states. Further, benefits and limitations regarding analytical evaluation of efficacy, absorption and safety of novel drug carrier systems applied to such models are discussed along with a prospective view of anticipated future directions. In addition, emerging non-invasive imaging modalities are introduced and their significance and potential to advance current knowledge in the field of skin drug delivery is explored.

UV fluorescence excitation imaging of healing of wounds in skin: Evaluation of wound closure in organ culture model

BACKGROUND AND OBJECTIVE

Molecules native to tissue that fluoresce upon light excitation can serve as reporters of cellular activity and protein structure. In skin, the fluorescence ascribed to tryptophan is a marker of cellular proliferation, whereas the fluorescence ascribed to cross-links of collagen is a structural marker. In this work, we introduce and demonstrate a simple but robust optical method to image the functional process of epithelialization and the exposed dermal collagen in wound healing of human skin in an organ culture model.

MATERIALS AND METHODS

Non-closing non-grafted, partial closing non-grafted, and grafted wounds were created in ex vivo human skin and kept in culture. A wide-field UV fluorescence excitation imaging system was used to visualize epithelialization of the exposed dermis and quantitate wound area, closure, and gap. Histology (H&E staining) was also used to evaluate epithelialization.

RESULTS

The endogenous fluorescence excitation of cross-links of collagen at 335 nm clearly shows the dermis missing epithelium, while the endogenous fluorescence excitation of tryptophan at 295 nm shows keratinocytes in higher proliferating state. The size of the non-closing wound was 11.4 ± 1.8 mm and remained constant during the observation period, while the partial-close wound reached 65.5 ± 4.9% closure by day 16. Evaluations of wound gaps using fluorescence excitation images and histology images are in agreement.

CONCLUSIONS

We have established a fluorescence imaging method for studying epithelialization processes, evaluating keratinocyte proliferation, and quantitating closure during wound healing of skin in an organ culture model: the dermal fluorescence of pepsin-digestible collagen cross-links can be used to quantitate wound size, closure extents, and gaps; and, the epidermal fluorescence ascribed to tryptophan can be used to monitor and quantitate functional states of epithelialization. UV fluorescence excitation imaging has the potential to become a valuable tool for research, diagnostic and educational purposes on evaluating the healing of wounds. Lasers Surg. Med. 48:678-685, 2016. © 2016 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

MALDI MSI analysis of lipid changes in living skin equivalents in response to emollient creams containing palmitoylethanolamide

Mass spectrometry imaging (MSI) is a powerful tool for the study of intact tissue sections. The use of matrix-assisted laser desorption/ionisation (MALDI) MSI for the study of the distribution and effect of emollient treatment on sections of reconstructed living skin equivalents during their development and maturation is described. Living skin equivalent (LSE) samples were obtained at 14days development, re-suspended in maintenance medium and incubated for 24h after delivery. The medium was changed, the LSE treated with either Physiogel A.I.® or Oilatum Junior® emollients and then re-incubated and samples taken at 4, 6 and 24h time points. Mass spectra and mass spectral images were recorded from 12μm sections of the LSE taken at each time point for comparison using MALDI mass spectrometry (MS). It was possible to detect ions characteristic of each emollient in the LSE. In addition a number of lipid species previously reported as being significant in the maturation of the LSE were observable. At the 24h time point, the images revealed what appeared to be differences in the organisation of the skin cells observed across the Physiogel A.I.® treatment group tissue sections when directly compared to the untreated tissue group.

Optimization of an ex vivo wound healing model in the adult human skin: Functional evaluation using photodynamic therapy

Limited utility of in vitro tests and animal models of human repair, create a demand for alternative models of cutaneous healing capable of functional testing. The adult human skin Wound Healing Organ Culture (WHOC) provides a useful model, to study repair and enable evaluation of therapies such as the photodynamic therapy (PDT). Thus, the aim here was to identify the optimal WHOC model and to evaluate the role of PDT in repair. Wound geometry, system of support, and growth media, cellular and matrix biomarkers were investigated in WHOC models. Subsequently, cellular activity, extracellular matrix remodeling, and oxidative stress plus gene and protein levels of makers of wound repair measured the effect of PDT on the optimized WHOC. WHOCs embedded in collagen and supplemented DMEM were better organized showing stratified epidermis and compact dermis with developing neo-epidermis. Post-PDT, the advancing reepithelialization tongue was 3.5 folds longer, and was highly proliferative with CK-14 plus p16 increased (p < 0.05) compared to controls. The neo-epidermis was fully differentiated forming neo-collagen. Proliferating nuclear antigen, p16, COLI, COLIII, MMP3, MMP19, and α-SMA were significantly more expressed (p < 0.05) in dermis surrounding the healing wound. In conclusion, an optimal model of WHOC treated with PDT shows increased reepithelialization and extracellular matrix reconstruction and remodeling, supporting evidence toward development of an optimal ex vivo wound healing model.

Biodegradable Gelatin Microcarriers Facilitate Re-Epithelialization of Human Cutaneous Wounds - An In Vitro Study in Human Skin

The possibility to use a suspended tridimensional matrix as scaffolding for re-epithelialization of in vitro cutaneous wounds was investigated with the aid of a human in vitro wound healing model based on viable full thickness skin. Macroporous gelatin microcarriers, CultiSpher-S, were applied to in vitro wounds and cultured for 21 days. Tissue sections showed incorporation of wound edge keratinocytes into the microcarriers and thicker neoepidermis in wounds treated with microcarriers. Thickness of the neoepidermis was measured digitally, using immunohistochemical staining of keratins as epithelial demarcation. Air-lifting of wounds enhanced stratification in control wounds as well as wounds with CultiSpher-S. Immunohistochemical staining revealed expression of keratin 5, keratin 10, and laminin 5 in the neoepidermal component. We conclude that the CultiSpher-S microcarriers can function as tissue guiding scaffold for re-epithelialization of cutaneous wounds.

Novel in vitro approaches for the simulation and analysis of human skin wounds

Considering the increasing incidence of chronic wounds and severe wound infections, effective drug delivery to wounded skin is of high importance. The rational development of novel therapeutic systems requires appropriate in vitro testing methodologies. In this context, suitable and reliable in vitro models simulating human wounds and advanced analytical techniques for precise wound characterization are urgently needed. In this study, we introduce a novel in vitro model based on excised human skin. In contrast to the established wound models, our novel approach has a coffin-shaped, linear, rectangular geometry with defined wound edges exhibiting consistent appearance along the entire wound bed. In addition, we introduce optical profilometry as a novel technique for nondestructive wound analysis. We successfully demonstrate the applicability of this optical imaging method based on white light reflection for three-dimensional visualization of different wound models. Furthermore, we create virtual noninvasive cross sections of these wounds to assess wound geometry in direct comparison to conventional histological analysis. Imaging analysis of our novel coffin-shaped model resulted in reproducible virtual sections along the entire wound bed. Our findings indicate the potential of our novel in vitro model for improved simulation of human wounds. Further, we successfully overcome the limitations of conventional histological analysis by the employment of optical profilometry for nondestructive three-dimensional wound characterization.

β2-adrenoceptor activation modulates skin wound healing processes to reduce scarring

During wound healing, excessive inflammation, angiogenesis, and differentiated human dermal fibroblast (HDF ) function contribute to scarring, whereas hyperpigmentation negatively affects scar quality. Over 100 million patients heal with a scar every year. To investigate the role of the beta 2 adrenergic receptor (β2AR) in wound scarring, the ability of beta 2 adrenergic receptor agonist (β2ARag) to alter HDF differentiation and function, wound inflammation, angiogenesis, and wound scarring was explored in HDFs, zebrafish, chick chorioallantoic membrane assay (CAM), and a porcine skin wound model, respectively. Here we identify a β2AR-mediated mechanism for scar reduction. β2ARag significantly reduced HDF differentiation, via multiple cAMP and/or fibroblast growth factor 2 or basic FGF (FGF2)-dependent mechanisms, in the presence of transforming growth factor betaβ1, reduced contractile function, and inhibited mRNA expression of a number of profibrotic markers. β2ARag also reduced inflammation and angiogenesis in zebrafish and CAMs in vivo, respectively. In Red Duroc pig full-thickness wounds, β2ARag reduced both scar area and hyperpigmentation by almost 50% and significantly improved scar quality. Indeed, mechanisms delineated in vitro and in other in vivo models were evident in the β2ARag-treated porcine scars in vivo. Both macrophage infiltration and angiogenesis were initially decreased, whereas DF function was impaired in the β2ARag-treated porcine wound bed. These data collectively reveal the potential of β2ARag to improve skin scarring.

Epithelialization in Wound Healing: A Comprehensive Review

Significance: Keratinocytes, a major cellular component of the epidermis, are responsible for restoring the epidermis after injury through a process termed epithelialization. This review will focus on the pivotal role of keratinocytes in epithelialization, including cellular processes and mechanisms of their regulation during re-epithelialization, and their cross talk with other cell types participating in wound healing. Recent Advances: Discoveries in epidermal stem cells, keratinocyte immune function, and the role of the epidermis as an independent neuroendocrine organ will be reviewed. Novel mechanisms of gene expression regulation important for re-epithelialization, including microRNAs and histone modifications, will also be discussed. Critical Issues: Epithelialization is an essential component of wound healing used as a defining parameter of a successful wound closure. A wound cannot be considered healed in the absence of re-epithelialization. The epithelialization process is impaired in all types of chronic wounds. Future Directions: A comprehensive understanding of the epithelialization process will ultimately lead to the development of novel therapeutic approaches to promote wound closure.

Influence of sensory neuropeptides on human cutaneous wound healing process

BACKGROUND

Close interactions exist between primary sensory neurons of the peripheral nervous system (PNS) and skin cells. The PNS may be implicated in the modulation of different skin functions as wound healing.

OBJECTIVE

Study the influence of sensory neurons in human cutaneous wound healing.

METHODS

We incubated injured human skin explants either with rat primary sensory neurons from dorsal root ganglia (DRG) or different neuropeptides (vasoactive intestinal peptide or VIP, calcitonin gene-related peptide or CGRP, substance P or SP) at various concentrations. Then we evaluated their effects on the proliferative and extracellular matrix (ECM) remodeling phases, dermal fibroblasts adhesion and differentiation into myofibroblasts.

RESULTS

Thus, DRG and all studied neuromediators increased fibroblasts and keratinocytes proliferation and act on the expression ratio between collagen type I and type III in favor of collagen I, particularly between the 3rd and 7th day of culture. Furthermore, the enzymatic activities of matrix metalloprotesases (MMP-2 and MMP-9) were increased in the first days of wound healing process. Finally, the adhesion of human dermal fibroblasts and their differentiation into myofibroblasts were promoted after incubation with neuromediators. Interestingly, the most potent concentrations for each tested molecules, were the lowest concentrations, corresponding to physiological concentrations.

CONCLUSION

Sensory neurons and their derived-neuropeptides are able to promote skin wound healing.

Epithelial bridges maintain tissue integrity during collective cell migration

The ability of skin to act as a barrier is primarily determined by the efficiency of skin cells to maintain and restore its continuity and integrity. In fact, during wound healing keratinocytes migrate collectively to maintain their cohesion despite heterogeneities in the extracellular matrix. Here, we show that monolayers of human keratinocytes migrating along functionalized micropatterned surfaces comprising alternating strips of extracellular matrix (fibronectin) and non-adherent polymer form suspended multicellular bridges over the non-adherent areas. The bridges are held together by intercellular adhesion and are subjected to considerable tension, as indicated by the presence of prominent actin bundles. We also show that a model based on force propagation through an elastic material reproduces the main features of bridge maintenance and tension distribution. Our findings suggest that multicellular bridges maintain tissue integrity during wound healing when cell-substrate interactions are weak and may prove helpful in the design of artificial scaffolds for skin regeneration.

Thyrotropin-releasing hormone (TRH) promotes wound re-epithelialisation in frog and human skin

There remains a critical need for new therapeutics that promote wound healing in patients suffering from chronic skin wounds. This is, in part, due to a shortage of simple, physiologically and clinically relevant test systems for investigating candidate agents. The skin of amphibians possesses a remarkable regenerative capacity, which remains insufficiently explored for clinical purposes. Combining comparative biology with a translational medicine approach, we report the development and application of a simple ex vivo frog (Xenopus tropicalis) skin organ culture system that permits exploration of the effects of amphibian skin-derived agents on re-epithelialisation in both frog and human skin. Using this amphibian model, we identify thyrotropin-releasing hormone (TRH) as a novel stimulant of epidermal regeneration. Moving to a complementary human ex vivo wounded skin assay, we demonstrate that the effects of TRH are conserved across the amphibian-mammalian divide: TRH stimulates wound closure and formation of neo-epidermis in organ-cultured human skin, accompanied by increased keratinocyte proliferation and wound healing-associated differentiation (cytokeratin 6 expression). Thus, TRH represents a novel, clinically relevant neuroendocrine wound repair promoter that deserves further exploration. These complementary frog and human skin ex vivo assays encourage a comparative biology approach in future wound healing research so as to facilitate the rapid identification and preclinical testing of novel, evolutionarily conserved, and clinically relevant wound healing promoters.

The epithelial sodium channel mediates the directionality of galvanotaxis in human keratinocytes

Cellular directional migration in an electric field (galvanotaxis) is one of the mechanisms guiding cell movement in embryogenesis and in skin epidermal repair. The epithelial sodium channel (ENaC), in addition to its function of regulating sodium transport in kidney, has recently been found to modulate cell locomotory speed. Here we tested whether ENaC has an additional function of mediating the directional migration of galvanotaxis in keratinocytes. Genetic depletion of ENaC completely blocks only galvanotaxis and does not decrease migration speed. Overexpression of ENaC is sufficient to drive galvanotaxis in otherwise unresponsive cells. Pharmacologic blockade or maintenance of the open state of ENaC also decreases or increases, respectively, galvanotaxis, suggesting that the channel open state is responsible for the response. Stable lamellipodial extensions formed at the cathodal sides of wild-type cells at the start of galvanotaxis; these were absent in the ENaC knockout keratinocytes, suggesting that ENaC mediates galvanotaxis by generating stable lamellipodia that steer cell migration. We provide evidence that ENaC is required for directional migration of keratinocytes in an electric field, supporting a role for ENaC in skin wound healing.

Hyaluronic acid, an important factor in the wound healing properties of amniotic fluid: in vitro studies of re-epithelialisation in human skin wounds

Foetal wounds are unique in their ability to heal rapidly without forming scars. The amniotic fluid, rich in nutrients, growth factors, and hyaluronic acid, surrounds the foetus and is essential to foetal wound healing. The wound healing properties of foetal wounds may be the result of high concentrations of hyaluronic acid. This study aimed to verify that amniotic fluid induces re-epithelialisation in human skin wounds in vitro and to study whether this ability is dependent on hyaluronic acid. Standard deep dermal wounds were produced in vitro in human skin. The skin samples, with a central wound, were incubated in different culture media. Varying concentrations of amniotic fluid and amniotic fluid with added hyaluronidase were tested, and re-epithelialisation was assessed at 3, 7, and 12 days using light microscopy, after staining with haematoxylin and eosin. Amniotic fluid 50% resulted in a significantly higher (p < 0.05) grade of re-epithelialisation than Dulbecco's modified Eagle's medium and 10% amniotic fluid at all time points. When 50% amniotic fluid was compared with 10% foetal calf serum, no significant difference was found in grades of re-epithelialisation on days 3 and 12 and significantly higher grades of re-epithelialisation on day 7 (p < 0.05). Degradation of hyaluronic acid in the medium that contained 50% amniotic fluid gave significantly impaired re-epithelialisation (p < 0.05) on culture days 3 and 7. In conclusion, amniotic fluid promotes accelerated re-epithelialisation and hyaluronic acid is an important ingredient.

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.

Human ex vivo wound healing model

Wound healing is a spatially and temporally regulated process that progresses through sequential, yet overlapping phases and aims to restore barrier breach. To study this complex process scientists use various in vivo and in vitro models. Here we provide step-by-step instructions on how to perform and employ an ex vivo wound healing model to assess epithelization during wound healing in human skin.

β2AR antagonists and β2AR gene deletion both promote skin wound repair processes

Skin wound healing is a complex process requiring the coordinated, temporal orchestration of numerous cell types and biological processes to regenerate damaged tissue. Previous work has demonstrated that a functional β-adrenergic receptor autocrine/paracrine network exists in skin, but the role of β2-adrenergic receptor (β2AR) in wound healing is unknown. A range of in vitro (single-cell migration, immunoblotting, ELISA, enzyme immunoassay), ex vivo (rat aortic ring assay), and in vivo (chick chorioallantoic membrane assay, zebrafish, murine wild-type, and β2AR knockout excisional skin wound models) models were used to demonstrate that blockade or loss of β2AR gene deletion promoted wound repair, a finding that is, to our knowledge, previously unreported. Compared with vehicle-only controls, β2AR antagonism increased angiogenesis, dermal fibroblast function, and re-epithelialization, but had no effect on wound inflammation in vivo. Skin wounds in β2AR knockout mice contracted and re-epithelialized faster in the first few days of wound repair in vivo. β2AR antagonism enhanced cell motility through distinct intracellular signalling mechanisms and increased vascular endothelial growth factor secretion from keratinocytes. β2AR antagonism promoted wound repair processes in the early stages of wound repair, revealing a possible new avenue for therapeutic intervention.

Skin tissue engineering--in vivo and in vitro applications

Significant progress has been made over the years in the development of in vitro-engineered substitutes that mimic human skin, either to be used as grafts for the replacement of lost skin or for the establishment of human-based in vitro skin models. This review summarizes these advances in in vivo and in vitro applications of tissue-engineered skin. We further highlight novel efforts in the design of complex disease-in-a-dish models for studies ranging from disease etiology to drug development and screening.

The linear excisional wound: an improved model for human ex vivo wound epithelialization studies

BACKGROUND/PURPOSE

Wound healing is a complex process that involves multiple intercellular and intracellular processes and extracellular interactions. Explanted human skin has been used as a model for the re-epithelialization phase of human wound healing. The currently used standard technique uses a circular punch biopsy tool to make the initial wound. Despite its wide use, the geometry of round wounds makes it difficult to measure them reliably.

METHODS

Our group has designed a linear wounding tool, and compared the variability in ex vivo human linear and circular wounds.

RESULTS

An F test for differences in variances demonstrated that the linear wounds provided a population of wound size measurements that was 50% less variable than that obtained from a group of matched circular wounds. This reduction in variability would provide substantial advantages for the linear wound technique over the circular wound punch technique, by reducing the sample sizes required for comparative studies of factors that alter healing.

CONCLUSION

This linear wounding tool thus provides a method for wounding that is standardized, provides minimal error in wound gap measurements, and is easily reproducible. We demonstrate its utility in an ex vivo model for the controlled investigation of human skin wounds.

Skin tissue engineering--in vivo and in vitro applications

Significant progress has been made over the years in the development of in vitro-engineered substitutes that mimic human skin, either to be used as grafts for the replacement of lost skin or for the establishment of human-based in vitro skin models. This review summarizes these advances in in vivo and in vitro applications of tissue-engineered skin. We further highlight novel efforts in the design of complex disease-in-a-dish models for studies ranging from disease etiology to drug development and screening.

Development of a three-dimensional human skin equivalent wound model for investigating novel wound healing therapies

Numerous difficulties are associated with the conduct of preclinical studies related to skin and wound repair. Use of small animal models such as rodents is not optimal because of their physiological differences to human skin and mode of wound healing. Although pigs have previously been used because of their human-like mode of healing, the expense and logistics related to their use also renders them suboptimal. In view of this, alternatives are urgently required to advance the field. The experiments reported herein were aimed at developing and validating a simple, reproducible, three-dimensional ex vivo de-epidermised dermis human skin equivalent wound model for the preclinical evaluation of novel wound therapies. Having established that the human skin equivalent wound model does in fact &#x201C;heal," we tested the effect of two novel wound healing therapies. We also examined the utility of the model for studies exploring the mechanisms underpinning these therapies. Taken together the data demonstrate that these new models will have wide-spread application for the generation of fundamental new information on wound healing processes and also hold potential in facilitating preclinical optimization of dosage, duration of therapies, and treatment strategies prior to clinical trials.

Cortisol synthesis in epidermis is induced by IL-1 and tissue injury

Glucocorticoids (GCs) are known inhibitors of wound healing. In this study we report the novel finding that both keratinocytes in vitro and epidermis in vivo synthesize cortisol and how this synthesis regulates wound healing. We show that epidermis expresses enzymes essential for cortisol synthesis, including steroid 11 β-hydroxylase (CYP11B1), and an enzyme that controls negative feedback mechanism, 11β-hydroxysteroid dehydrogenase 2 (11βHSD2). We also found that cortisol synthesis in keratinocytes and skin can be stimulated by ACTH and inhibited by metyrapone (CYP11B1 enzyme inhibitor). Interestingly, IL-1β, the first epidermal signal of tissue injury, induces the expression of CYP11B1 and increases cortisol production by keratinocytes. Additionally, we found induction of CYP11B1 increased production of cortisol and activation of GR pathway during wound healing ex vivo and in vivo using human and porcine wound models, respectively. Conversely, inhibition of cortisol synthesis during wound healing increases IL-1β production, suggesting that cortisol synthesis in epidermis may serve as a local negative feedback to proinflammatory cytokines. Local GCs synthesis, therefore, may provide control of the initial proinflammatory response, preventing excessive inflammation upon tissue injury. Inhibition of GC synthesis accelerated wound closure in vivo, providing the evidence that modulation of cortisol synthesis in epidermis may be an important regulatory mechanism during wound healing.

Infected wound model development of an in vitro biomaterial-protected wound infection model to study microbial activity and antimicrobial treatment through microdialysis

OBJECTIVE

Skin injuries provide a favorable environment for microbial infection if left untreated. This is problematic especially in nosocomial situations having a high prevalence of Staphylococcus aureus that can cause suppuration of wounds, systemic disease, and toxic shock. The objective of this investigation was to use a wound model system to study the interactions between microbial activity, host tissue, therapeutic treatments, and wound biomaterials.

DESIGN

An in vitro wound model was developed using Sykes-Moore chambers filled with 1 of 2 biomaterials used for wound treatment (1% alginate and dialyzed HyFil hydrogel (B. Braun Medical, Inc, Bethlehem, Pennsylvania) and seeded with fibroblasts. The chambers were inoculated with S aureus, and half were later treated with antibiotics through in situ microdialysis tubing.

MAIN OUTCOME MEASURES

The chambers were monitored by obtaining fluid samples and biomaterial samples at specific time intervals (0, 2, 8, and 24 hours) and were analyzed for (1) S aureus protein A (SPA) concentration, (2) viable S aureus numbers, and (3) fibroblast numbers and viability. Chambers containing each biomaterial with and without antibiotics were compared to controls.

MAIN RESULTS

There was an inverse relationship between postinfection S aureus numbers and fibroblast viability. S aureus numbers were usually consistent with SPA concentration, which may have been underestimated because of SPA interactions with the biomaterials.

CONCLUSION

This wound model may be useful to gain an understanding about the interactions between microbial activity, host tissue, therapeutic treatments, and wound biomaterials. Hypotheses about wound treatments derived by means of this model may direct future in vivo studies.

Attenuation of the transforming growth factor beta-signaling pathway in chronic venous ulcers

Transforming growth factor beta (TGFbeta) is important in inflammation, angiogenesis, reepithelialization and connective tissue regeneration during wound healing. We analyzed components of TGFbeta signaling pathway in biopsies from 10 patients with nonhealing venous ulcers (VUs). Using comparative genomics of transcriptional profiles of VUs and TGFbeta-treated keratinocytes, we found deregulation of TGFbeta target genes in VUs. Using quantitative polymerase chain reaction (qPCR) and immunohistochemical analysis, we found suppression of TGFbeta RI, TGFbeta RII and TGFbeta RIII, and complete absence of phosphorylated Smad2 (pSmad2) in VU epidermis. In contrast, pSmad2 was induced in the cells of the migrating epithelial tongue of acute wounds. TGFbeta-inducible transcription factors (GADD45beta , ATF3 and ZFP36L1) were suppressed in VUs. Likewise, genes suppressed by TGFbeta (FABP5, CSTA and S100A8) were induced in nonhealing VUs. An inhibitor of Smad signaling, Smad7 was also downregulated in VUs. We conclude that TGFbeta signaling is functionally blocked in VUs by downregulation of TGFbeta receptors and attenuation of Smad signaling resulting in deregulation of TGFbeta target genes and consequent hyperproliferation. These data suggest that application of exogenous TGFbeta may not be a beneficial treatment for VUs.

The effect of a self-assembling peptide nanofiber scaffold (peptide) when used as a wound dressing for the treatment of deep second degree burns in rats

RADARADARADARADA (RADA16-I) peptide, consisting of 16 alternating hydrophobic and hydrophilic (also alternating negative and positive charges) amino acids, forms extremely stable beta-pleated sheet structure and then self-assembles into nanofibers to produce high-order interwoven nanofiber scaffold hydrogel. To investigate its therapeutic effects, a burn model of partial thickness-deep dermal injury (the deep second degree burns) was performed at the dorsal skin of female Sprague-Dawley rats with an electrical scalding machine. The wounds treated with either RADA16-I or control materials were carefully examined at morphological, histological and cellular levels. We found that RADA16-I can advance the time of eschar appearance and the time of eschar disappearance both by 3-5 days, and speed up wound contraction by 20-30% compared with contrast groups (chitosan, poly(DL)-lactic acid (PDLA), collagen I and the blank) without obvious edema. Immunohistochemical studies showed that both FGF and EGF were obviously expressed in nascent tissue such as epidermis and glands when wounds were treated with the RADA16-I after injury. When peptide stock solution was diluted from 10 to 0.17 mg/mL, atomic force microscopy (AFM) observation showed that the shape of peptide nanofibers changed from the globular-pieces-clustered filaments with 4.8 +/- 0.38 nm in height, 61.6 +/- 6.10 nm in width and 708 +/- 80.2 nm in length, to general filaments with 1.4 +/- 0.36 nm, 17.5 +/- 1.13 nm and 1108 +/- 184 nm. The nanofiber surface porosity gradually decreased from 49-70% to 12-28%. These characteristics contribute to wound healing by offering an "ideal dressing" moist healing microenvironment and a nanofiber 3D scaffold. These results suggest that the self-assembling peptide might be a promising wound dressing with being simple, effective, and affordable.

Treatment with antisense oligonucleotide reduces the expression of type I collagen in a human-skin organ-wound model: implications for antifibrotic gene therapy

Increased collagen expression during wound healing causes scar formation, abnormal contracture, low tensile strength, functional impairment, and disfigurement. A novel ex vivo wound-injury model demonstrated that AS60, an antisense oligonucleotide (ASO) to type I collagen, reduced the mRNA and protein expression of type 1 collagen. Following a cutaneous wound injury in a human-skin organ culture, AS60 injection resulted in a 36% (P < 0.001) and 30% decrease (P < 0.001) in type 1 collagen mRNA and protein expression after 7 days. Similarly, transfection of cultured human fibroblasts with ASO resulted in a 36% decrease (P < 0.001) and a 31% decrease (P < 0.001) in type 1 collagen mRNA and protein expression. Immunofluorescence of human skin organ culture treated with ASO showed a specific reduction in collagen expression. Using AS60 to reduce collagen expression in human skin may have implications for its use as a gene therapy agent to reduce the formation of fibrotic scarring.

Assessment of organ culture for the conservation of human skin allografts

OBJECTIVE

Human skin allografts are used in the treatment of severe burns and their preservation is therefore critical for optimal clinical benefit. Current preservation methods, such as 4 degrees C storage or cryopreservation, cannot prevent the decrease of tissue viability. The aim of this study was to assess viability and function of skin allografts in a new skin organ culture model, allowing conservation parameters as close as possible to physiological conditions: 32 degrees C, air-liquid interface and physiological skin tension.

DESIGN

Twelve skin samples, harvested from 6 living surgical donors, were conserved 35 days in two conditions: conservation at 4 degrees C and organ culture. Viability and function of skin samples were investigated at Day 0, 7, 14, 21, 28 and 35 using cell culture methods (trypan blue exclusion, Colony Forming Efficiency and Growth Rate), histopathological and histoenzymological studies (Ki67 immunostaining).

RESULTS

In the two conditions, fibroblast and keratinocyte viability was progressively affected by storage, with a significant decrease observed after 35 days. No statistical difference could be observed between the two conditions. The two methods were also comparable regarding alterations of fibroblast and keratinocyte culture parameters, which were respectively significantly reduced at Day 7 and 21, compared to fresh skin. By contrast, histopathological and histoenzymological studies revealed a better preservation of skin architecture and proliferative potential at 4 degrees C, as compared to organ culture.

CONCLUSION

These results indicate that skin organ culture does not provide significant advantages for skin allograft preservation. However, its potential use as an experimental model to study skin physiology and wound healing should be further evaluated.

A porcine deep dermal partial thickness burn model with hypertrophic scarring

We developed a reproducible model of deep dermal partial thickness burn injury in juvenile Large White pigs. The contact burn is created using water at 92 degrees C for 15s in a bottle with the bottom replaced with plastic wrap. The depth of injury was determined by a histopathologist who examined tissue sections 2 and 6 days after injury in a blinded manner. Upon creation, the circular wound area developed white eschar and a hyperaemic zone around the wound border. Animals were kept for 6 weeks or 99 days to examine the wound healing process. The wounds took between 3 and 5 weeks for complete re-epithelialisation. Most wounds developed contracted, purple, hypertrophic scars. On measurement, the thickness of the burned skin was approximately 1.8 times that of the control skin at week 6 and approximately 2.2 times thicker than control skin at 99 days after injury. We have developed various methods to assess healing wounds, including digital photographic analysis, depth of organising granulation tissue, immunohistochemistry, electron microscopy and tensiometry. Immunohistochemistry and electron microscopy showed that our porcine hypertrophic scar appears similar to human hypertrophic scarring. The development of this model allows us to test and compare different treatments on burn wounds.

β-Adrenergic Receptor Antagonists Accelerate Skin Wound Healing

The skin is our primary defense against noxious environmental agents. Upon injury, keratinocytes migrate directionally into the wound bed to initiate re-epithelialization, essential for wound repair and restoration of barrier integrity. Keratinocytes express a high level of beta2-adrenergic receptors (beta2-ARs) that appear to play a role in cutaneous homeostasis as aberrations in either keratinocyte beta2-AR function or density are associated with various skin diseases. Here we report the novel finding that beta-AR antagonists promote wound re-epithelialization in a "chronic" human skin wound-healing model. beta-AR antagonists increase ERK phosphorylation, the rate of keratinocyte migration, electric field-directed migration, and ultimately accelerate human skin wound re-epithelialization. We demonstrate that keratinocytes express two key enzymes required for catecholamine (beta-AR agonist) synthesis, tyrosine hydroxylase and phenylethanolamine-N-methyl transferase, both localized within keratinocyte cytoplasmic vesicles. Finally, we confirm the synthesis of epinephrine by measuring the endogenously synthesized catecholamine in keratinocyte extracts. Previously, we have demonstrated that beta-AR agonists delay wound re-epithelialization. Here we report that the mechanism for the beta-AR antagonist-mediated augmentation of wound repair is due to beta2-AR blockade, preventing the binding of endogenously synthesized epinephrine. Our work describes an endogenous beta-AR mediator network in the skin that can temporally regulate skin wound repair. Further investigation of this network will improve our understanding of both the skin repair process and the multiple modes of action of one of the most frequently prescribed class of drugs, hopefully resulting in a new treatment for chronic wounds.

The impact of skin viability on drug metabolism and permeation—BSA toxicity on primary keratinocytes

For testing cutaneous absorption of drugs, ingredients of cosmetics and also for risk assessment of industrial compounds predictable in vitro test protocols are under investigation using excised skin or reconstructed human epidermis. Since the metabolizing enzymes expressed by viable skin can influence the absorption behaviour of substances by changing their structure and thereby their physicochemical characteristics, the metabolic capacity should be considered in the design of the test protocols of compounds susceptible to metabolism. Then data, generated using viable reconstructed epidermis may reflect the in vivo situation. Interestingly, bovine serum albumin (BSA) commonly used in receptor media in permeation studies to facilitate solubility of highly lipophilic substances strongly inhibited the metabolism of topically applied prednicarbate in reconstructed epidermis. Here, we show that 5% BSA is toxic to reconstructed epidermis and keratinocytes which was consistent with the earlier findings. While media toxicity (deficiency media) was at least partly the cause of both apoptotic and necrotic processes in keratinocytes, BSA only slightly increased the rate of necrotic cells. Moreover, caspase inhibitors did not reduce BSA toxicity. Yet, the results show that BSA toxicity on keratinocytes has to be carefully considered if this protein is used in permeation studies with reconstructed epidermis.

β2‐Adrenergic receptor activation delays wound healing

Keratinocytes migrate directionally into the wound bed to initiate re-epithelialization, necessary for wound closure and restoration of barrier function. They solely express the beta2-adrenergic receptor (beta2-AR) subtype of beta-ARs and can also synthesize beta-AR agonists generating a hormonal mediator network in the skin. Emerging studies from our laboratory demonstrate that beta-AR agonists decrease keratinocyte migration via a protein phosphatase (PP) 2A-dependent mechanism. Here we have extended our investigations to observe the effects of beta2-AR activation on keratinocyte polarization, migration, and ERK phosphorylation at the wound edge, cytoskeletal organization, phospho-ERK intracellular localization, proliferation, human skin wound re-epithelialization, wound-induced ERK phosphorylation, and murine skin wound healing. We demonstrate that in keratinocytes, beta2-AR activation is anti-motogenic and anti-mitogenic with both mechanisms being PP2A dependent. beta2-AR activation dramatically alters the organization of the actin cytoskeleton and prevents localization of phospho-ERK to the lamellipodial edge and its colocalization with vinculin. Finally, we demonstrate a beta2-AR-mediated delay in re-epithelialization and decrease in wound-induced epidermal ERK phosphorylation in human skin wounds and a delay in re-epithelialization in murine tail-clip wounds. Our work uncovers novel keratinocyte biology and a previously unrecognized role for the adrenergic hormonal mediator network in the wound repair process.

Induction of Keratinocyte Migration via Transactivation of the Epidermal Growth Factor Receptor by the Antimicrobial Peptide LL-37

The closure of skin wounds is essential for resistance against microbial pathogens, and keratinocyte migration is an important step in skin wound healing. Cathelicidin hCAP18/LL-37 is an innate antimicrobial peptide that is expressed in the skin and acts to eliminate microbial pathogens. Because hCAP18/LL-37 is up-regulated at skin wound sites, we hypothesized that LL-37 induces keratinocyte migration. In this study, we found that 1 microg/ml LL-37 induced the maximum level of keratinocyte migration in the Boyden chamber assay. In addition, LL-37 phosphorylated the epidermal growth factor receptor (EGFR) after 10 min, which suggests that LL-37-induced keratinocyte migration occurs via EGFR transactivation. To test this assumption, we used inhibitors that block the sequential steps of EGFR transactivation, such as OSU8-1, CRM197, anti-EGFR no. 225 Ab, and AG1478. All of these inhibitors completely blocked LL-37-induced keratinocyte migration, which indicates that migration occurs via HB-EGF-mediated EGFR transactivation. Furthermore, CRM197, anti-EGFR no. 225, and AG1478 blocked the LL-37-induced phosphorylation of STAT3, and transfection with a dominant-negative mutant of STAT3 abolished LL-37-induced keratinocyte migration, indicating the involvement of the STAT3 pathway downstream of EGFR transactivation. Finally, we tested whether the suppressor of cytokine signaling (SOCS)/cytokine-inducible Src homology 2-containing protein (CIS) family of negative regulators of STAT3 regulates LL-37-induced keratinocyte migration. Transfection with SOCS1/Jak2 binding protein or SOCS3/CIS3 almost completely abolished LL-37-induced keratinocyte migration. In conclusion, LL-37 induces keratinocyte migration via heparin-binding-EGF-mediated transactivation of EGFR, and SOCS1/Jak 2 binding and SOCS3/CIS3 negatively regulate this migration. The results of this study suggest that LL-37 closes skin wounds by the induction of keratinocyte migration.

Fluorescence imaging of reepithelialization from skin explant cultures on acellular dermis

Reconstituted skin models are valuable tools in studies of cutaneous biology although they are not generally devised to visualize and quantify the time course of reepithelialization. We describe a skin explant culture technique coupled with vital microscopy allowing sequential imaging of epithelial outgrowth while maintaining the tissue in culture. Radial expansion of neo-epidermis was initiated from a 2-mm skin punch biopsy explanted onto acellular human dermis and maintained at the air-liquid interface in serum-containing keratinocyte medium. Microscopic viewings and surface area measurements of newly formed epidermis were performed repeatedly using fluorescein-based cell staining and subsequent image analysis. The labeling and visualization procedures did not interfere with neo-epidermal growth or tissue architecture. In order to appraise the versatility of the model, we studied the effect of epidermal growth factor supplementation on the course of skin resurfacing as related to tissue morphology and proliferative activity over a 10-day cultivation period. Exogenous epidermal growth factor at 10 ng/ml increased the radial outgrowth rate (mean, + 13.3 percent), papillomatosis index (+ 19.2 percent), epithelial thickness (+ 49.8 percent), and fraction of Ki-67 positive basal cells (+ 18.4 percent) in neo-epidermis produced from a biopsy of normal human skin. The contribution of this miniaturized and convenient format for concurrent studies of dynamic and qualitative features of neo-epidermis should be a useful complement to existing assays of epidermalization.