Keratinocyte-Conditioned Media Regulate Collagen Expression in Dermal Fibroblasts

Comparison of three in vitro keratinocytes-fibroblasts wound healing models commonly used in pharmaceutical research

OBJECTIVES

Several common wound healing models have been used to evaluate wound healing agents and formulations, namely: conditioned media (CM), transwell co-cultures (TWCC) and co-cultures (CC) in a monolayer. However, no study has been conducted to compare the relevance of these models in the keratinocytes and fibroblasts interaction physiologically. Therefore, this study aimed to compare these models based on cell migration and proliferation, and matrix metalloproteinase (MMP) expression.

METHODS

Cell migration was analysed by scratch assay and MMP-7, while cell proliferation was analysed by (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium reduction assay.

KEY FINDINGS

Increased cell migration was observed in CM and TWCC models, while varied results were obtained in CC. Cell migration was increased due to upregulation of MMP-7 in CM and TWCC models, while it was downregulated in CC, which might have hindered migration of both cells in monolayers.

CONCLUSIONS

CM and TWCC are more suitable than CC for wound healing research and for evaluating wound healing agents or formulations, as they can better simulate the layered tissue constructs and paracrine interactions in the physiological environment.

Engineering a 3D In Vitro Model of Human Gingival Tissue Equivalent with Genipin/Cytochalasin D

Although three-dimensional (3D) co-culture of gingival keratinocytes and fibroblasts-populated collagen gel can mimic 3D structure of in vivo tissue, the uncontrolled contraction of collagen gel restricts its application in clinical and experimental practices. We here established a stable 3D gingival tissue equivalent (GTE) using hTERT-immortalized gingival fibroblasts (hGFBs)-populated collagen gel directly crosslinked with genipin/cytochalasin D and seeding hTERT-immortalized gingival keratinocytes (TIGKs) on the upper surface for a 2-week air–liquid interface co-culture. MTT assay was used to measure the cell viability of GTEs. GTE size was monitored following culture period, and the contraction was analyzed. Immunohistochemical assay was used to analyze GTE structure. qRT-PCR was conducted to examine the mRNA expression of keratinocyte-specific genes. Fifty µM genipin (G50) or combination (G + C) of G50 and 100 nM cytochalasin D significantly inhibited GTE contraction. Additionally, a higher cell viability appeared in GTEs crosslinked with G50 or G + C. GTEs crosslinked with genipin/cytochalasin D showed a distinct multilayered stratified epithelium that expressed keratinocyte-specific genes similar to native gingiva. Collagen directly crosslinked with G50 or G + C significantly reduced GTE contraction without damaging the epithelium. In summary, the TIGKs and hGFBs can successfully form organotypic multilayered cultures, which can be a valuable tool in the research regarding periodontal disease as well as oral mucosa disease. We conclude that genipin is a promising crosslinker with the ability to reduce collagen contraction while maintaining normal cell function in collagen-based oral tissue engineering.

Collagen gel contraction assays: From modelling wound healing to quantifying cellular interactions with three-dimensional extracellular matrices

Cells respond to and actively remodel the extracellular matrix (ECM). The dynamic and bidirectional interaction between cells and ECM, especially their mechanical interactions, has been found to play an essential role in triggering a series of complex biochemical and biomechanical signal pathways and in regulating cellular functions and behaviours. The collagen gel contraction assay (CGCA) is a widely used method to investigate cell-ECM interactions in 3D environments and provides a mechanically associated readout reflecting 3D cellular contractility. In this review, we summarize various versions of CGCA, with an emphasis on recent high-throughput and low-consumption CGCA techniques. More importantly, we focus on the technique of force monitoring during the contraction of collagen gel, which provides a quantitative characterization of the overall forces generated by all the resident cells in the collagen hydrogel. Accordingly, we present recent biological applications of the CGCA, which have expanded from the initial wound healing model to other studies concerning cell-ECM interactions, including fibrosis, cancer, tissue repair and the preparation of biomimetic microtissues.

Single-Cell Transcriptomics Uncover Key Regulators of Skin Regeneration in Human Long-Term Mechanical Stretch-Mediated Expansion Therapy

Tissue expansion is a commonly performed therapy to grow extra skin invivo for reconstruction. While mechanical stretch-induced epidermal changes have been extensively studied in rodents and cell culture, little is known about the mechanobiology of the human epidermis in vivo. Here, we employed single-cell RNA sequencing to interrogate the changes in the human epidermis during long-term tissue expansion therapy in clinical settings. We also verified the main findings at the protein level by immunofluorescence analysis of independent clinical samples. Our data show that the expanding human skin epidermis maintained a cellular composition and lineage trajectory that are similar to its non-expanding neighbor, suggesting the cellular heterogeneity of long-term expanded samples differs from the early response to the expansion. Also, a decrease in proliferative cells due to the decayed regenerative competency was detected. On the other hand, profound transcriptional changes are detected for epidermal stem cells in the expanding skin versus their non-expanding peers. These include significantly enriched signatures of C-FOS, EMT, and mTOR pathways and upregulation of AREG and SERPINB2 genes. CellChat associated ligand-receptor pairs and signaling pathways were revealed. Together, our data present a single-cell atlas of human epidermal changes in long-term tissue expansion therapy, suggesting that transcriptional change in epidermal stem cells is the major mechanism underlying long-term human skin expansion therapy. We also identified novel therapeutic targets to promote human skin expansion efficiency in the future.

Cell secretomes for wound healing and tissue regeneration: Next generation acellular based tissue engineered products

Wound represents a significant socioeconomic burden for both affected individuals and as a whole healthcare system. Accordingly, stem cells have garnered attention due to their differentiation capacity and ability to aid tissue regeneration by releasing biologically active molecules, found in the cells’ cultivated medium which known as conditioned medium (CM) or secretomes. This acellular approach provides a huge advantage over conventional treatment options, which are mainly used cellular treatment at wound closure. Interestingly, the secretomes contained the cell-secreted proteins such as growth factors, cytokines, chemokines, extracellular matrix (ECM), and small molecules including metabolites, microvesicles, and exosomes. This review aims to provide a general view on secretomes and how it is proven to have great potential in accelerating wound healing. Utilizing the use of secretomes with its secreted proteins and suitable biomaterials for fabrications of acellular skin substitutes can be promising in treating skin loss and accelerate the healing process.

Roles of cutaneous cell-cell communication in wound healing outcome: An emphasis on keratinocyte-fibroblast crosstalk

Tissue repair is a very complex event and involves a continuously orchestrated sequence of signals and responses from platelets, fibroblasts, epithelial, endothelial and immune cells. The details of interaction between these signals, which are mainly growth factors and cytokines, have been widely discussed. However, it is still not clear how activated cells at wound sites lessen their activities after epithelialization is completed. Termination of the wound healing process requires a fine balance between extracellular matrix (ECM) deposition and degradation. Maintaining this balance requires highly accurate epithelial-mesenchymal communication and correct information exchange between keratinocytes and fibroblasts. As it has been reported in the literature, a disruption in epithelialization during the process of wound healing increases the frequency of developing chronic wounds or fibrotic conditions, as seen in a variety of clinical cases. Conversely, the potential stop signal for wound healing should have a regulatory role on both ECM synthesis and degradation to reach a successful wound healing outcome. This review briefly describes the potential roles of growth factors and cytokines in controlling the early phase of wound healing and predominantly explores the role of releasable factors from epithelial-mesenchymal interaction in controlling during and the late stage of the healing process. Emphasis will be given on the crosstalk between keratinocytes and fibroblasts in ECM modulation and the healing outcome following a brief discussion of the wound healing initiation mechanism. In particular, we will review the termination of acute dermal wound healing, which frequently leads to the development of hypertrophic scarring.

Hypertrophic Scarring: Current Knowledge of Predisposing Factors, Cellular and Molecular Mechanisms

Hypertrophic scarring (HSc) is an age-old problem that still affects millions of people physically, psychologically, and economically. Despite advances in surgical techniques and wound care, prevention and treatment of HSc remains a challenge. Elucidation of factors involved in the development of this common fibroproliferative disorder is crucial for further progress in preventive and/or therapeutic measures. Our knowledge about pathophysiology of HSc at the cellular and molecular level has grown considerably in recent decades. In this article, current knowledge of predisposing factors and the cellular and molecular mechanisms of HSc has been reviewed.

Tracing skin aging process: a mini- review of in vitro approaches

Skin is a rather complex, yet useful organ of our body. Besides, skin aging is a complicated process that gains a growing interest as mediates many molecular processes in our body. Thus, an efficient skin model is important to understand skin aging function as well as to develop an effective innovative product for skin aging treatment. In this mini review, we present in vitro methods for assessments of skin aging in an attempt to pinpoint basic molecular mechanisms behind this process achieving both a better understanding of aging function and an effective  evaluation of potential products or ingredients that counteract aging. Specifically, this study presents in vitro assays such as 2D or 3D skin models, to evaluate skin aging-related processes such as skin moisturization, photoaging, wound healing, menopause, and skin microbiome as novel efforts in the designing of efficacy assessments in the development of skincare products.

Secreted Factors from Keloid Keratinocytes Modulate Collagen Deposition by Fibroblasts from Normal and Fibrotic Tissue: A Pilot Study

Interactions between keratinocytes and fibroblasts in the skin layers are crucial in normal tissue development, wound healing, and scarring. This study has investigated the role of keloid keratinocytes in regulating collagen production by primary fibroblasts in vitro. Keloid cells were obtained from removed patients’ tissue whereas normal skin cells were discarded tissue obtained from elective surgery procedures. Fibroblasts and keratinocytes were isolated, cultured, and a transwell co-culture system were used to investigate the effect of keratinocytes on collagen production using a ‘scar-in-a-jar’ model. Keloid fibroblasts produced significantly more collagen than normal skin fibroblasts in monoculture at the RNA, secreted protein, and stable fibrillar protein level. When keloid keratinocytes were added to normal skin fibroblasts, expression of collagen was significantly upregulated in most samples, but when added to keloid fibroblasts, collagen I production was significantly reduced. Interestingly, keloid keratinocytes appear to decrease collagen production by keloid fibroblasts. This suggests that signaling in both keratinocytes and fibroblasts is disrupted in keloid pathology.

Interplay Between Keratinocytes and Fibroblasts: A Systematic Review Providing a New Angle for Understanding Skin Fibrotic Disorders

Background/Objective: Skin fibrosis is the result of aberrant processes leading to abnormal deposition of extracellular matrix (ECM) in the dermis. In healthy skin, keratinocytes participate to maintain skin homeostasis by actively crosstalking with fibroblasts. Within the wide spectrum of fibrotic skin disorders, relatively little attention has been devoted to the role of keratinocytes for their capacity to participate to skin fibrosis. This systematic review aims at summarizing the available knowledge on the reciprocal interplay of keratinocytes with fibroblasts and their soluble mediators in physiological states, mostly wound healing, and conditions associated with skin fibrosis.

Methods: We performed a systematic literature search on PubMed to identify in vitro and ex vivo human studies investigating the keratinocyte characteristics and their interplay with fibroblasts in physiological conditions and within fibrotic skin disorders including hypertrophic scars, keloids, and systemic sclerosis. Studies were selected according to pre-specified eligibility criteria. Data on study methods, models, stimuli and outcomes were retrieved and summarized according to pre-specified criteria.

Results: Among the 6,271 abstracts retrieved, 73 articles were included, of which 14 were specifically dealing with fibrotic skin pathologies. Fifty-six studies investigated how keratinocyte may affect fibroblast responses in terms of ECM-related genes or protein production, phenotype modification, and cytokine production. Most studies in both physiological conditions and fibrosis demonstrated that keratinocytes stimulate fibroblasts through the production of interleukin 1, inducing keratinocyte growth factor (KGF) and metalloproteinases in the fibroblasts. When the potential of keratinocytes to modulate collagen synthesis by healthy fibroblasts was explored, the results were controversial. Nevertheless, studies investigating keratinocytes from fibrotic skin, including keloids, hypertrophic scar, and scleroderma, suggested their potential involvement in enhancing ECM deposition. Twenty-three papers investigated keratinocyte proliferation differentiation and production of soluble mediators in response to interactions with fibroblasts. Most studies showed that fibroblasts modulate keratinocyte viability, proliferation, and differentiation. The production of KGF by fibroblast was identified as key for these functions.

Conclusions: This review condenses evidence for the active interaction between keratinocytes and fibroblasts in maintaining skin homeostasis and the altered homeostatic interplay between keratinocytes and dermal fibroblasts in scleroderma and scleroderma-like disorders.

Rescue of degenerating neurons and cells by stem cell released molecules: using a physiological renormalization strategy

Evidence suggests that adult stem cell types and progenitor cells act collectively in a given tissue to maintain and heal organs, such as muscle, through a release of a multitude of molecules packaged into exosomes from the different cell types. Using this principle for the development of bioinspired therapeutics that induces homeostatic renormalization, here we show that the collection of molecules released from four cell types, including mesenchymal stem cells, fibroblast, neural stem cells, and astrocytes, rescues degenerating neurons and cells. Specifically, oxidative stress induced in a human recombinant TDP‐43‐ or FUS‐tGFP U2OS cell line by exposure to sodium arsenite was shown to be significantly reduced by our collection of molecules using in vitro imaging of FUS and TDP‐43 stress granules. Furthermore, we also show that the collective secretome rescues cortical neurons from glutamate toxicity as evidenced by increased neurite outgrowth, reduced LDH release, and reduced caspase 3/7 activity. These data are the first in a series supporting the development of stem cell‐based exosome systems therapeutics that uses a physiological renormalization strategy to treat neurodegenerative diseases.

Stanniocalcin-1 mediates negative regulatory action of epidermal layer on expression of matrix-related genes in dermal fibroblasts

Dermal-epidermal interaction plays a role in many pathophysiological processes, such as tumor invasion and psoriasis, as well as wound healing, and is mediated at least in part by secretory factors. In this study, we investigated the factor(s) involved. We found that stanniocalcin-1 (STC1), a cytokine, is expressed at the basal layer of epidermis. Knockdown of STC1 with siRNA in HaCaT cells decreased matrix metalloproteinase 1 (MMP1) expression, suggesting that STC1 serves as an autocrine factor, maintaining MMP1 mRNA expression in the epidermal layer. In dermal fibroblasts, STC1 increased MMP1 mRNA expression and decreased collagen1A1 and elastin mRNA expression. These actions were inhibited by SP600125, a jun kinase (JNK) inhibitor. Nuclear translocation of AP-1, a downstream signal of JNK, was implicated in the actions of STC1. In a coculture system of HaCaT cells and fibroblasts, used as a model of dermal-epidermal interaction, knockdown of STC1 in HaCaT cells with siRNA reduced the negative effects (i.e., induction of MMP1 and decrease of collagen1A1 and elastin) of STC1 on fibroblasts. These results suggest that STC1 secreted from the epidermal layer is a mediator of dermal-epidermal interaction.

Experimental models for cutaneous hypertrophic scar research

Human skin wound repair may result in various outcomes with most of them leading to scar formation. Commonly seen in many cutaneous wound healing cases, hypertrophic scars are considered as phenotypes of abnormal wound repair. To prevent the formation of hypertrophic scars, efforts have been made to understand the mechanism of scarring following wound closure. Numerous in vivo and in vitro models have been created to facilitate investigations into cutaneous scarring and the development of antiscarring treatments. To select the best model for a specific study, background knowledge of the current models of hypertrophic scars is necessary. In this review, we describe in vivo and in vitro models for studying hypertrophic scars, as well as the distinct characteristics of these models. The choice of models for a specific study should be based on the characteristics of the model and the goal of the study. In general, in vivo animal models are often used in phenotypical scar formation analysis, development of antiscarring treatment, and functional analyses of individual genes. In contrast, in vitro models are chosen to pathway identification during scar formation as well as in high-throughput analysis in drug development. Besides helping investigators choose the best scarring model for their research, the goal of this review is to provide knowledge for improving the existing models and development of new models. These will contribute to the progress of scarring studies.

Split Thickness Grafts Grow From Bottom Up in Large Skin Injuries

Autologous split thickness skin graft is necessary for the survival of patients with large burns and skin defects. It is not clear how a thin split thickness skin graft becomes remarkably thicker within a few weeks following transplantation. Here, we hypothesized that growth of split thickness graft should be from bottom up probably through conversion of immune cells into collagen producing skin cells. We tested this hypothesis in a preclinical porcine model by grafting split thickness meshed skin (0.508 mm thickness, meshed at 3:1 ratio) on full thickness wounds in pigs. New tissue formation was evaluated on days 10 and 20 postoperation through histological analysis and co-staining for immune cell markers (CD45) and type I collagen. The findings revealed that a split thickness graft grew from bottom up and reached to almost the same level as uninjured skin within 60 days postoperation. The result of immune-staining identified a large number of cells, which co-expressed immune cell marker (CD45) and collagen on day 10 postoperation. Interestingly, as the number of these cells reduced on day 20, most of these cells became positive for collagen production. In another set of experiments, we tested whether immune cells can convert to collagen producing cells in vitro. The results showed that mouse adherent immune cells started to express type 1 procollagen and α-smooth muscle actin when cultured in the presence of fibroblast conditioned media. In conclusion, the early thickening of split thickness graft is likely happening through a major contribution of infiltrated immune cells that convert into mainly collagen producing fibroblasts in large skin injuries.

Human keratinocyte-derived microvesicle miRNA-21 promotes skin wound healing in diabetic rats through facilitating fibroblast function and angiogenesis

Skin wound healing is a complex physiological process that maintains the integrity of the skin tissues, involving a variety of distinct cell types and signaling molecules. The specific signaling pathways or extracellular cues that govern the healing processes remain elusive. Microvesicles (MVs) have recently emerged as critical mediators of cell communication by delivery of genetic materials to target cells. In this study, we found the direct delivery of HEKa-MVs expressing miR-21 mimics significantly promoted the healing of skin wound in diabetic rats. In-depth studies showed that MV miR-21 promoted fibroblast migration, differentiation, and contraction, induced a pro-angiogenic process of endothelial cells and mediated a pro-inflammatory response. Mechanically, MV miR-21 might target specific essential effector mRNA in fibroblasts such as MMP-1, MMP-3, TIMP3, and TIMP4 to increase MMPs expression and enzymatic activities. Moreover, MV miR-21 regulated ɑ-SMA and N-cadherin to induce fibroblast-myofibroblast differentiation. MV miR-21 up-regulated the IL-6 and IL-8 expressions and their secretion to amplify the immune response. Furthermore, MV miR-21 down-regulated PTEN and RECK in protein level, and activate MAPK/ERK signaling cascade, thereby promoting fibroblast functions. Thus, our study has provided for the first time the basis for the potential application of HEKa-MVs, and MV miR-21 in particular for wound healing.

Full Thickness Skin Expansion ex vivo in a Newly Developed Reactor and Evaluation of Auto-Grafting Efficiency of the Expanded Skin Using Yucatan Pig Model

BACKGROUND

Skin grafts are required in numerous clinical procedures, such as reconstruction after skin removal and correction of contracture or scarring after severe skin loss caused by burns, accidents, and trauma. The current standard for skin defect replacement procedures is the use of autologous skin grafts. However, donor-site tissue availability remains a major obstacle for the successful replacement of skin defects and often limits this option. The aim of this study is to effectively expand full thickness skin to clinically useful size using an automated skin reactor and evaluate auto grafting efficiency of the expanded skin using Yucatan female pigs.

METHODS

We developed an automated bioreactor system with the functions of real-time monitoring and remote-control, optimization of grip, and induction of skin porosity for effective tissue expansion. We evaluated the morphological, ultra-structural, and mechanical properties of the expanded skin before and after expansion using histology, immunohistochemistry, and tensile testing. We further carried out in vivo grafting study using Yucatan pigs to investigate the feasibility of this method in clinical application.

RESULTS

The results showed an average expansion rate of 180%. The histological findings indicated that external expansion stimulated cellular activity in the isolated skin and resulted in successful grafting to the transplanted site. Specifically, hyperplasia did not appear at the auto-grafted site, and grafted skin appeared similar to normal skin. Furthermore, mechanical stimuli resulted in an increase in COL1A2 expression in a suitable environment.

CONCLUSIONS

These findings provided insight on the potential of this expansion system in promoting dermal extracellular matrix synthesis in vitro. Conclusively, this newly developed smart skin bioreactor enabled effective skin expansion ex vivo and successful grafting in vivo in a pig model.

Remodeling of dermal collagen in photoaged skin using low-dose 5-aminolevulinic acid photodynamic therapy occurs via the transforming growth factor-β pathway

5-Aminolevulinic acid photodynamic therapy (ALA-PDT) is known to be effective in the treatment of photoaged skin. However, the molecular mechanisms still remain elusive. Protoporphyrin IX (PpIX) fluorescence is primarily located in the epidermis while ALA-PDT affects the dermal collagen, presumably by an indirect mechanism. This study aimed to investigate the molecular communication in low-dose ALA-PDT occurring between epidermal keratinocytes and dermal fibroblasts. Western blotting and enzyme-linked immunosorbent assays were performed to evaluate collagen expression and transforming growth factor-β (TGF-β) signaling in human keratinocytes and dermal fibroblasts. The impact on fibroblast proliferation was assessed by morphology and proliferating cell nuclear antigen immunofluorescence. Skin biopsies from mice were used to analyze the histological changes in dermal collagen and PpIX distribution. When fibroblasts were cocultured with keratinocytes treated with low-dose ALA-PDT, collagen synthesis and fibroblast proliferation were enhanced. Low-dose ALA-PDT stimulated TGF-β1 expression in keratinocytes. Fibroblasts cocultured with low-dose ALA-PDT-treated keratinocytes also showed activation of the TGF-β pathway. In vivo, PpIX fluorescence was densely distributed in photoaged mouse epidermis while collagen in the mouse dermis underwent remodeling. This study suggests that low-dose ALA-PDT can stimulate keratinocytes to release TGF-β1, activating the TGF-β pathway in dermal fibroblasts to remodel collagen in the dermis.

Effect of TGFβ1, TGFβ3 and keratinocyte conditioned media on functional characteristics of dermal fibroblasts derived from reparative (Balb/c) and regenerative (Foxn1 deficient; nude) mouse models

Skin injuries in mammals are healed through repair or regeneration. Our previous studies demonstrated that deficient expression of the transcription factor Foxn1 in epidermis of nude mice accounts for their skin’s pronounced regenerative properties. Since homeostasis within the skin depends on complex interactions between the epidermal and underlying dermal layers, the present study characterizes and compares isolated dermal fibroblasts (DFs) between regenerative nude (Foxn1 deficient) mice and their wild-type Balb/c counterparts. Nude DFs exhibited a higher cumulative number of population doublings (cumulative PD) at low seeding density and increased adipogenic differentiation capacity relative to their Balb/c DF counterparts. Nude DFs displayed reduced migration and gel contraction, functional features associated with wound healing. The comparison of transforming growth factor β family (TGFβ) expression showed significantly higher levels of Tgfβ3 transcript between nude and Balb/c mice but no differences were detected for Tgfβ1. Nude DFs were specifically sensitive to the presence of the pro-regenerative TGFβ3 isoform, showing increased collagen I deposition and alpha smooth muscle actin expression. Viability of Balb/c DFs was stimulated by keratinocyte conditioned media (KCM) from Balb/c (Foxn1 active) but inhibited by nude (Foxn1 deficient) KCM. In contrast, nude DFs did not respond to either KCMs with respect to their metabolic activity. Collectively, the enhanced plasticity and greater sensitivity of nude DFs to TGFβ3 stimulation are indicative of and consistent with their pro-regenerative characteristics. These data support the hypothesis that epidermal Foxn1 plays a critical role in determining the DFs regenerative phenotype.

The molecular pathogenesis of morphoea: from genetics to future treatment targets

A number of immunoinflammatory and profibrotic mechanisms are recognized in the pathogenesis of broad sclerotic skin processes and, more specifically, morphoea. However, the precise aetiopathogenesis is complex and remains unclear. Morphoea is clinically heterogeneous, with variable anatomical patterning, depth of tissue involvement and sclerotic, inflammatory, atrophic and dyspigmented morphology. Underlying mechanisms determining these reproducible clinical subsets are poorly understood but of great clinical and therapeutic relevance. Regional susceptibility mechanisms (e.g. environmental triggers, mosaicism and positional identity) together with distinct pathogenic determinants (including innate, adaptive and imbalanced pro- and antifibrotic signalling pathways) are likely implicated. In the age of genetic profiling and personalized medicine, improved characterization of the environmental, systemic, local, genetic and immunopathological factors underpinning morphoea pathogenesis may open the door to novel targeted therapeutic approaches.

IL-22 capacitates dermal fibroblast responses to TNF in scleroderma

OBJECTIVES

Interleukin (IL) 22 mRNA in systemic sclerosis (SSc) skin and Th22 cells in SSc peripheral blood are increased, but the role of IL-22 in fibrosis development remains poorly understood.

METHODS

Biopsies were obtained from the involved skin of 15 SSc, 4 morphea and 8 healthy donors (HD). The presence of IL-22+ cells in the skin was determined by immunostaining. The in vitro response of HD and SSc fibroblasts to IL-22, IL-22 in conjunction with tumour necrosis factor (TNF) or keratinocyte conditioned medium was assessed by ELISA, radioimmunoassay (RIA), real-time PCR and western blot. The in vivo response in mice was assessed by histomorphometry.

RESULTS

IL-22+ cells were over-represented in the dermis and epidermis of morphea and in the epidermis of SSc compared with HD. The majority of dermal IL-22+ cells were T cells. Dermal fibroblasts expressed both IL-22 receptor subunits IL-10RB and IL-22RA, expression of which was enhanced by TNF and reduced by transforming growth factor (TGF)-β. IL-22 induced rapid phosphorylation of p38 and ERK1/2 in fibroblasts, but failed to induce the synthesis of chemokines and extracellular matrix components. However, IL-22 enhanced the production of monocyte chemotactic protein 1, IL-8 and matrix metalloproteinase 1 induced by TNF. Fibroblast responses were maximal in the presence of conditioned medium from keratinocytes activated by IL-22 in conjunction with TNF. Dermal thickness was maximal in mice injected simultaneously with IL-22 and TNF.

CONCLUSIONS

IL-22 capacitates fibroblast responses to TNF and promotes a proinflammatory fibroblast phenotype by favouring TNF-induced keratinocyte activation. These results define a novel role for keratinocyte-fibroblast interactions in the context of skin fibrosis.

Characterization of A Three-Dimensional Organotypic Co-Culture Skin Model for Epidermal Differentiation of Rat Adipose-Derived Stem Cells

Objective

The organotypic co-culture is a well-known technique to examine cellular interactions and their roles in stem cell proliferation and differentiation. This study aims to evaluate the effects of dermal fibroblasts (DFs) on epidermal differentiation of adipose-derived stem cells (ASCs) using a three-dimensional (3D) organotypic co- culture technique.

Materials and Methods

In this experimental research study, rat DFs and ASCs were isolated and cultured separately on electrospun polycaprolactone (PCL) matrices. The PCL matrices seeded by ASCs were superimposed on to the matrices seeded by DFs in order to create a 3D organotypic co-culture. In the control groups, PCL matrices seeded by ASCs were placed on matrices devoid of DFs. After 10 days, we assessed the expressions of keratinocyte-related genes by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and expression of pan-cytokeratin protein by immunofluorescence in the differentiated keratinocyte-like cells from co- culture and control groups. Keratinocyte-like cell morphologies were also observed by scanning electron microscopy (SEM).

Results

The early, intermediate, and terminal differentiation keratinocyte markers-Cytokeratin14, Filaggrin, and Involucrin significantly expressed in the co-culture groups com- pared to the control ones (P<0.05). We observed pan-cytokeratin in keratinocyte-like cells of both groups by immunofluorescence. SEM observation of the co-culture groups showed that the differentiated keratinocyte-like cells developed a polygonal cobblestone shape, considered characteristic of keratinocytes.

Conclusion

The 3D organotypic co-culture bilayered construct that consisted of DFs and ASCs was an effective technique for epidermal differentiation of ASCs. This co-culture might be useful for epidermal differentiation of stem cells for future applications in skin regeneration.

Keratinocyte-Releasable Factors Stimulate the Expression of Granulocyte Colony-Stimulating Factor in Human Dermal Fibroblasts

Interaction between keratinocytes and fibroblasts plays a critical role in maintaining skin integrity under both normal and pathological conditions. We have previously demonstrated that keratinocyte-releasable factors influence the expression of key extracellular matrix components, such as collagen and matrix metalloproteinases in dermal fibroblasts. In this study, we utilized DNA microarray analysis to examine the effects of keratinocyte-releasable factors on the expression of several cytokines in human dermal fibroblasts. The results revealed significantly higher granulocyte colony-stimulating factor (G-CSF) expression in fibroblasts co-cultured with keratinocytes relative to mono-cultured cells, which was verified by RT-PCR and western blot. G-CSF is an important hematopoietic factor also thought to play a beneficial role in wound healing through stimulating keratinocyte proliferation. To partially characterize the keratinocyte-releasable factors responsible for stimulating G-CSF production, keratinocyte-conditioned medium (KCM) was subjected to thermal treatment and ammonium sulfate precipitation before treating fibroblasts. The results showed that keratinocyte-releasable G-CSF-stimulating factors remain stable at 56°C and upon 50% ammonium sulfate precipitation. Knowing that keratinocytes release IL-1, which stimulates G-CSF expression in various immune cells, several experiments were conducted to ask whether this might also be the case for fibroblasts. The results showed that the addition of recombinant IL-1 markedly increased G-CSF expression in fibroblasts; however, IL-1 receptor antagonist only partially abrogated KCM-stimulated G-CSF expression, indicating the role of additional keratinocyte-releasable factors. These findings underline the importance of cross-talk between keratinocytes and fibroblasts, suggesting that communication between these cells in vivo modulates the production of cytokines required for cutaneous wound healing and maintenance. J. Cell. Biochem. 118: 308-317, 2017. © 2016 Wiley Periodicals, Inc.

Integrin-mediated regulation of epidermal wound functions

During cutaneous wound healing, keratinocyte proliferation and migration are critical for re-epithelialization. In addition the epidermis secretes growth factors, cytokines, proteases, and matricellular proteins into the wound microenvironment that modify the extracellular matrix and stimulate other wound cells that control the inflammatory response, promote angiogenesis and facilitate tissue contraction and remodeling. Wound keratinocytes express at least seven different integrins-the major cell adhesion receptors for the extracellular matrix-that collectively control essential cell-autonomous functions to ensure proper re-epithelialization, including migration, proliferation, survival and basement membrane assembly. Moreover, it has become evident in recent years that some integrins can regulate paracrine signals from wound epidermis that stimulate other wound cells involved in angiogenesis, contraction and inflammation. Importantly, it is likely that abnormal integrin expression or function in the epidermis contributes to wound pathologies such as over-exuberant healing (e.g., hypertrophic scar formation) or diminished healing (e.g., chronic wounds). In this review, we discuss current knowledge of integrin function in the epidermis, which implicates them as attractive therapeutic targets to promote wound healing or treat wound pathologies. We also discuss challenges that arise from the complex roles that multiple integrins play in wound epidermis, which may be regulated through extracellular matrix remodeling that determines ligand availability. Indeed, understanding how different integrin functions are temporally coordinated in wound epidermis and which integrin functions go awry in pathological wounds, will be important to determine how best to target them clinically to achieve maximum therapeutic benefit. Graphical abstract In addition to their well-characterized roles in keratinocyte adhesion, migration and wound re-epithelialization, epidermal integrins play important roles in modifying the wound microenvironment by regulating the expression and secretion of growth factors, extracellular proteases, and matricellular proteins that stimulate other wound cells, including vascular endothelial cells and fibroblasts/myofibroblasts.

On-chip assay of the effect of topographical microenvironment on cell growth and cell-cell interactions during wound healing

Wound healing is an essential physiological process for tissue homeostasis, involving multiple types of cells, extracellular matrices, and growth factor/chemokine interactions. Many in vitro studies have investigated the interactions between cues mentioned above; however, most of them only focused on a single factor. In the present study, we design a wound healing device to recapitulate in vivo complex microenvironments and heterogeneous cell situations to investigate how three types of physiologically related cells interact with their microenvironments around and with each other during a wound healing process. Briefly, a microfluidic device with a micropillar substrate, where diameter and interspacing can be tuned to mimic the topographical features of the 3D extracellular matrix, was designed to perform positional cell loading on the micropillar substrate, co-culture of three types of physiologically related cells, keratinocytes, dermal fibroblasts, and human umbilical vein endothelial cells, as well as an investigation of their interactions during wound healing. The result showed that cell attachment, morphology, cytoskeleton distribution, and nucleus shape were strongly affected by the micropillars, and these cells showed collaborative response to heal the wound. Taken together, these findings highlight the dynamic relationship between cells and their microenvironments. Also, this reproducible device may facilitate the in vitro investigation of numerous physiological and pathological processes such as cancer metastasis, angiogenesis, and tissue engineering.

Roles of Proteoglycans and Glycosaminoglycans in Wound Healing and Fibrosis

A wound is a type of injury that damages living tissues. In this review, we will be referring mainly to healing responses in the organs including skin and the lungs. Fibrosis is a process of dysregulated extracellular matrix (ECM) production that leads to a dense and functionally abnormal connective tissue compartment (dermis). In tissues such as the skin, the repair of the dermis after wounding requires not only the fibroblasts that produce the ECM molecules, but also the overlying epithelial layer (keratinocytes), the endothelial cells, and smooth muscle cells of the blood vessel and white blood cells such as neutrophils and macrophages, which together orchestrate the cytokine-mediated signaling and paracrine interactions that are required to regulate the proper extent and timing of the repair process. This review will focus on the importance of extracellular molecules in the microenvironment, primarily the proteoglycans and glycosaminoglycan hyaluronan, and their roles in wound healing. First, we will briefly summarize the physiological, cellular, and biochemical elements of wound healing, including the importance of cytokine cross-talk between cell types. Second, we will discuss the role of proteoglycans and hyaluronan in regulating these processes. Finally, approaches that utilize these concepts as potential therapies for fibrosis are discussed.

Inhibition of proliferation and migration of stricture fibroblasts by epithelial cell-conditioned media

INTRODUCTION

Urethral stricture is characterized by urethral lumen narrowing due to fibrosis. Urethroplasty of the urethral stricture involves excision of scar, and may be followed by reconstruction of the urethra using split-thickness skin, buccal mucosa, urethral mucosa or, more recently, tissue-engineered grafts. The stricture wound healing process after urethroplasty is known to be mediated by an interaction between keratinocyte and fibroblasts; however, the underlying mechanisms are not studied in detail yet. We investigated the influence of epithelial cell-conditioned medium (ECCM) (obtained from confluent penile skin, buccal mucosa and urethral cell cultures) on the proliferation and migration of stricture fibroblasts using an in vitro scratch assay.

MATERIALS AND METHODS

ECCM was collected from confluent primary epithelial cell cultures of three different human biopsies (penile skin, buccal mucosa and urethral mucosa), whereas stricture fibroblasts were isolated from human urethral stricture biopsies. The effect of ECCM on stricture fibroblasts' proliferation and migration into the scratch was observed using a standard in vitro scratch assay over a period of 3 days. Four experiments were performed independently using four stricture fibroblasts from four patients and ECCM was collected from 12 different patients' primary cell cultures.

RESULTS

ECCM from primary epithelial cells cultures obtained from penile skin, buccal mucosa and urethra inhibited stricture fibroblasts' proliferation and migration in the in vitro scratch assay.

CONCLUSION

These results demonstrate the ability of ECCM to inhibit the proliferation and migration of stricture fibroblasts and present it as an effective adjunct in urethroplasty, which may influence stricture wound healing and inhibit the recurrence of stricture.

Human hypertrophic and keloid scar models: principles, limitations and future challenges from a tissue engineering perspective

Most cutaneous wounds heal with scar formation. Ideally, an inconspicuous normotrophic scar is formed, but an abnormal scar (hypertrophic scar or keloid) can also develop. A major challenge to scientists and physicians is to prevent adverse scar formation after severe trauma (e.g. burn injury) and understand why some individuals will form adverse scars even after relatively minor injury. Currently, many different models exist to study scar formation, ranging from simple monolayer cell culture to 3D tissue-engineered models even to humanized mouse models. Currently, these high-/medium-throughput test models avoid the main questions referring to why an adverse scar forms instead of a normotrophic scar and what causes a hypertrophic scar to form rather than a keloid scar and also, how is the genetic predisposition of the individual and the immune system involved. This information is essential if we are to identify new drug targets and develop optimal strategies in the future to prevent adverse scar formation. This viewpoint review summarizes the progress on in vitro and animal scar models, stresses the limitations in the current models and identifies the future challenges if scar-free healing is to be achieved in the future.

Abnormally differentiating keratinocytes in the epidermis of systemic sclerosis patients show enhanced secretion of CCN2 and S100A9

Skin involvement with dermal fibrosis is a hallmark of systemic sclerosis (SSc), and keratinocytes may be critical regulators of fibroblast function through secretion of chemo-attracting agents, as well as through growth factors and cytokines influencing the phenotype and proliferation rate of fibroblasts. Epithelial-fibroblast interactions have an important role in fibrosis in general. We have characterized the SSc epidermis and asked whether SSc-injured epidermal cells release factors capable of promoting fibrosis. Our results show that the SSc epidermis is hypertrophic, and has altered expression of terminal differentiation markers involucrin, loricrin, and filaggrin. Multiplex profiling revealed that SSc epidermal explants release increased levels of CCN2 and S100A9. CCN2 induction was found to spread into the upper papillary dermis, whereas S100A9 was shown to induce fibroblast proliferation and to enhance fibroblast CCN2 expression via Toll-like receptor 4. These data suggest that the SSc epidermis provides an important source of pro-fibrotic CCN2 and proinflammatory S100A9 in SSc skin, and therefore contributes to the fibrosis and inflammation seen in the disease.

Fibrotic remodeling of tissue-engineered skin with deep dermal fibroblasts is reduced by keratinocytes

Two-thirds of burn patients with deep dermal injuries are affected by hypertrophic scars, and currently, there are no clinically effective therapies. Tissue-engineered skin is a very promising model for the elucidation of the role of matrix microenvironment and biomechanical characteristics and could help in the identification of new therapeutic targets for hypertrophic scars. Conventionally, tissue-engineered skin is made of heterogeneous dermal fibroblasts and keratinocytes; however, recent work has shown that superficial and deep dermal fibroblasts are antifibrotic and profibrotic, respectively. Furthermore, keratinocytes are believed to regulate the development and remodeling of fibrosis in skin. This study aimed to assess the influence of keratinocytes and layered fibroblasts on the characteristics of tissue-engineered skin. Layered fibroblasts and keratinocytes isolated from superficial and deep dermis and epidermis, respectively, of the lower abdominal tissue were independently co-cultured on collagen-glycosaminoglycan scaffolds, and the resulting tissue-engineered skin was assessed for differences in tissue remodeling based on the underlying specific dermal fibroblast subpopulation. Collagen production by deep fibroblasts but not by superficial fibroblasts was significantly reduced upon co-culture with keratinocytes. Also, keratinocytes in the tissue-engineered skin resulted in significantly reduced expression of profibrotic connective tissue growth factor and fibronectin, and increased expression of the antifibrotic matrix metalloproteinase-1 by deep fibroblasts but not by superficial fibroblasts. Tissue-engineered skin made of deep fibroblasts and keratinocytes had lower levels of small proteoglycans, decorin, and fibromodulin, and higher levels of large proteoglycan, versican, compared to tissue-engineered skin made of superficial fibroblasts and keratinocytes. Tissue-engineered skin made of deep fibroblasts and keratinocytes had lower expression of transforming growth factor (TGF)-α, interleukin (IL)-1, and keratinocyte growth factor but higher expression of platelet-derived growth factor and IL-6, compared to tissue-engineered skin made of superficial fibroblasts and keratinocytes. Furthermore, co-culture with keratinocytes reduced TGF-β1 production of deep but not superficial fibroblasts. Additionally, keratinocytes reduced the differentiation of deep fibroblasts to myofibroblasts in tissue-engineered skin constructs, but not that of superficial fibroblasts. Taken together, keratinocytes reduce fibrotic remodeling of the scaffolds by deep dermal fibroblasts. Our results therefore demonstrate that tissue-engineered skin made specifically with a homogeneous population of superficial fibroblasts and keratinocytes is less fibrotic than that with a heterogeneous population of fibroblasts and keratinocytes.

Kynurenine increases matrix metalloproteinase-1 and -3 expression in cultured dermal fibroblasts and improves scarring in vivo

We previously demonstrated that the formation of hypertrophic scarring on the wounds of a rabbit ear fibrotic model was significantly reduced by grafting a bilayer skin substitute expressing indoleamine 2,3-dioxygenase (IDO). Here, we hypothesize that the improved healing quality is due to extracellular matrix modulatory effect of IDO-mediated tryptophan metabolites. To test this hypothesis, a series of in vitro and in vivo experiments were conducted and the findings revealed a significant increase in the expression of matrix metalloproteinase 1 (MMP-1) in fibroblasts either transduced with human IDO gene or cultured with conditioned media obtained from IDO-expressing cells. Consistent with this finding, kynurenine (Kyn) treatment markedly increased the levels of MMP-1 and MMP-3 expression through activation of the MEK (mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase)-ERK1/2 MAPK signaling pathway. On the other hand, Kyn significantly suppressed the expression of type I collagen in fibroblasts as compared with that of control. To test the anti-fibrogenic effect of Kyn in an in vivo model, rabbit ear fibrotic wounds were topically treated with cream containing 50 μg Kyn per l00 μl of cream per wound. The result showed a marked improvement in scar formation relative to the controls. These findings collectively suggest that Kyn can potentially be used as an anti-fibrogenic agent for treating hypertrophic scarring.

Modelling the interaction of keratinocytes and fibroblasts during normal and abnormal wound healing processes

The crosstalk between fibroblasts and keratinocytes is a vital component of the wound healing process, and involves the activity of a number of growth factors and cytokines. In this work, we develop a mathematical model of this crosstalk in order to elucidate the effects of these interactions on the regeneration of collagen in a wound that heals by second intention. We consider the role of four components that strongly affect this process: transforming growth factor-β, platelet-derived growth factor, interleukin-1 and keratinocyte growth factor. The impact of this network of interactions on the degradation of an initial fibrin clot, as well as its subsequent replacement by a matrix that is mainly composed of collagen, is described through an eight-component system of nonlinear partial differential equations. Numerical results, obtained in a two-dimensional domain, highlight key aspects of this multifarious process, such as re-epithelialization. The model is shown to reproduce many of the important features of normal wound healing. In addition, we use the model to simulate the treatment of two pathological cases: chronic hypoxia, which can lead to chronic wounds; and prolonged inflammation, which has been shown to lead to hypertrophic scarring. We find that our model predictions are qualitatively in agreement with previously reported observations and provide an alternative pathway for gaining insight into this complex biological process.

Retinoids suppress cysteine-rich protein 61 (CCN1), a negative regulator of collagen homeostasis, in skin equivalent cultures and aged human skin in vivo

Alterations in connective tissue collagen are prominent features of both chronologically aged and photoaged (ageing because of sun exposure) human skin. These age-related abnormalities are mediated in part by cysteine-rich protein 61 (CCN1). CCN1 is elevated in the dermis of both chronologically aged and photoaged human skin in vivo and promotes aberrant collagen homeostasis by down-regulating type I collagen, the major structural protein in skin, and promoting collagen degradation. Vitamin A and its metabolites have been shown to improve chronologically aged and photoaged skin by promoting deposition of new collagen and preventing its degradation. Here, we investigated regulation of CCN1 expression by retinoids in skin equivalent cultures and chronologically aged and photoaged human skin in vivo. In skin equivalent cultures, all-trans retinoic acid (RA), the major bioactive form of vitamin A in skin, significantly increased type I procollagen and reduced collagenase (matrix metalloproteinases-1, MMP-1). Addition of recombinant human CCN1 to skin equivalent cultures significantly reduced type I procollagen and increased MMP-1. Importantly, RA significantly reduced CCN1 expression in skin equivalent cultures. Topical treatment with retinol (vitamin A, 0.4%) for 7days significantly reduced CCN1 mRNA and protein expression in both chronologically aged (80+years) and photoaged human skin in vivo, compared to vehicle-treated skin. These data indicate that the mechanism by which retinoids improve aged skin, through increased collagen production, involves down-regulation of CCN1.

Detection of RXFP1 receptors in skin biopsies from children with congenital adrenal hyperplasia: a preliminary report

OBJECTIVE

Relaxin may potentiate the effect of topical estrogen treatment to eradicate post-incisional scarring in congenital adrenal hyperplasia (CAH) patients undergoing genitoplasty. The aim of this study was to determine whether CAH skin is capable of responding to relaxin.

PATIENTS AND METHODS

Skin biopsies were obtained from four female CAH patients (aged 2-9 years; Prader 4-5, salt-wasting, 21-hydroxylase deficiency, Caucasian) during routine genitoplasty surgery and screened for relaxin receptors. All received corticosteroid and mineralocorticoid replacement therapy. Specimens were sectioned, mounted and screened for the presence of the putative H2 relaxin receptor using conventional two-antibody immunohistochemistry. Tissue controls were processed concurrently.

RESULTS

Tissue controls evidenced appropriate staining. Biopsies from CAH patients stained positively for RXFP1 expression while some variation between specimens was evident. Staining occurred adjacent to the basement membrane of the epithelium, localized to germinative basal keratinocytes.

CONCLUSION

Based on a limited patient sample, germinative keratinocytes in CAH patients appear competent to respond to relaxin perhaps topically applied. Given that relaxin downregulates collagen accretion and upregulates collagenases, its use may potentiate the effects of estradiol and abrogate post-incisional wound scarring. More research is needed to confirm or refute this thesis.

Mitochondrial turnover and aging of long-lived postmitotic cells: the mitochondrial-lysosomal axis theory of aging

It is now generally accepted that aging and eventual death of multicellular organisms is to a large extent related to macromolecular damage by mitochondrially produced reactive oxygen species, mostly affecting long-lived postmitotic cells, such as neurons and cardiac myocytes. These cells are rarely or not at all replaced during life and can be as old as the whole organism. The inherent inability of autophagy and other cellular-degradation mechanisms to remove damaged structures completely results in the progressive accumulation of garbage, including cytosolic protein aggregates, defective mitochondria, and lipofuscin, an intralysosomal indigestible material. In this review, we stress the importance of crosstalk between mitochondria and lysosomes in aging. The slow accumulation of lipofuscin within lysosomes seems to depress autophagy, resulting in reduced turnover of effective mitochondria. The latter not only are functionally deficient but also produce increased amounts of reactive oxygen species, prompting lipofuscinogenesis. Moreover, defective and enlarged mitochondria are poorly autophagocytosed and constitute a growing population of badly functioning organelles that do not fuse and exchange their contents with normal mitochondria. The progress of these changes seems to result in enhanced oxidative stress, decreased ATP production, and collapse of the cellular catabolic machinery, which eventually is incompatible with survival.

Scar and contracture: biological principles

Dysregulated wound healing and pathologic fibrosis cause abnormal scarring, leading to poor functional and aesthetic results in hand burns. Understanding the underlying biologic mechanisms involved allows the hand surgeon to better address these issues, and suggests new avenues of research to improve patient outcomes. In this article, the authors review the biology of scar and contracture by focusing on potential causes of abnormal wound healing, including depth of injury, cytokines, cells, the immune system, and extracellular matrix, and explore therapeutic measures designed to target the various biologic causes of poor scar.