Dermal Contributions to Human Interfollicular Epidermal Architecture and Self-Renewal

Human dermal fibroblast-derived secretory proteins for regulating nerve restoration: A bioinformatic approach

BACKGROUND

Human dermal fibroblasts secrete diverse proteins that regulate wound repair and tissue regeneration.

METHODS

In this study, dermal fibroblast-conditioned medium (DFCM) proteins potentially regulating nerve restoration were bioinformatically selected among the 337 protein lists identified by quantitative liquid chromatography-tandem mass spectrometry. Using these proteins, protein-protein interaction network analysis was conducted. In addition, the roles of DFCM proteins were reviewed according to their protein classifications.

RESULTS

Gene Ontology protein classification categorized these 57 DFCM proteins into various classes, including protein-binding activity modulator (N = 11), cytoskeletal protein (N = 8), extracellular matrix protein (N = 6), metabolite interconversion enzyme (N = 5), chaperone (N = 4), scaffold/adapter protein (N = 4), calcium-binding protein (N = 3), cell adhesion molecule (N = 2), intercellular signal molecule (N = 2), protein modifying enzyme (N = 2), transfer/carrier protein (N = 2), membrane traffic protein (N = 1), translational protein (N = 1), and unclassified proteins (N = 6). Further protein-protein interaction network analysis of 57 proteins revealed significant interactions among the proteins that varied according to the settings of confidence score.

CONCLUSIONS

Our bioinformatic analysis demonstrated that DFCM contains many secretory proteins that form significant protein-protein interaction networks crucial for regulating nerve restoration. These findings underscore DFCM proteins' critical roles in various nerve restoration stages during the wound repair process.

Dermal stiffness governs the topography of the epidermis and the underlying basement membrane in young and old human skin

The epidermis is a stratified epithelium that forms the outer layer of the skin. It is composed primarily of keratinocytes and is constantly renewed by the proliferation of stem cells and their progeny that undergo terminal differentiation as they leave the basal layer and migrate to the skin surface. Basal keratinocytes rest on a basement membrane composed of an extracellular matrix that controls their fate via integrin-mediated focal adhesions and hemidesmosomes which are critical elements of the epidermal barrier and promote its regenerative capabilities. The distribution of basal cells with optimal activity provides the basement membrane with its characteristic undulating shape; this configuration disappears with age, leading to epidermal weakness. In this study, we present an in-depth imaging analysis of basal keratinocyte anchorage in samples of human skin from participants across the age spectrum. Our findings reveal that skin aging is associated with the depletion of hemidesmosomes that provide crucial support for stem cell maintenance; their depletion correlates with the loss of the characteristic basement membrane structure. Atomic force microscopy studies of skin and in vitro experiments revealed that the increase in tissue stiffness observed with aging triggers mechanical signals that alter the basement membrane structure and reduce the extent of basal keratinocyte anchorage, forcing them to differentiate. Genomic analysis revealed that epidermal aging was associated with mechanical induction of the transcription factor Krüppel-like factor 4. The altered mechanical properties of tissue being a new hallmark of aging, our work opens new avenues for the development of skin rejuvenation strategies.

Translational frontiers: insight from lymphatics in skin regeneration

The remarkable regenerative ability of the skin, governed by complex molecular mechanisms, offers profound insights into the skin repair processes and the pathogenesis of various dermatological conditions. This understanding, derived from studies in human skin and various model systems, has not only deepened our knowledge of skin regeneration but also facilitated the development of skin substitutes in clinical practice. Recent research highlights the crucial role of lymphatic vessels in skin regeneration. Traditionally associated with fluid dynamics and immune modulation, these vessels are now recognized for interacting with skin stem cells and coordinating regeneration. This Mini Review provides an overview of recent advancements in basic and translational research related to skin regeneration, focusing on the dynamic interplay between lymphatic vessels and skin biology. Key highlights include the critical role of stem cell-lymphatic vessel crosstalk in orchestrating skin regeneration, emerging translational approaches, and their implications for skin diseases. Additionally, the review identifies research gaps and proposes potential future directions, underscoring the significance of this rapidly evolving research arena.

[Histopathological characteristics of peri-implant soft tissue in reconstructed jaws with vascularized bone flaps]

OBJECTIVE

To analyze the histopathological characteristics of peri-implant soft tissue in reconstructed jaws and the changes after keratinized mucosa augmentation (KMA) with free gingival graft (FGG).

METHODS

Twenty patients were enrolled in this study. Five patients of them, who were periodontal and systemic healthy and referred for crown lengthening before restoration with healthy keratinized gingiva collected were enrolled as healthy controls. 15 patients of them were with fibula or iliac bone flaps jaw reconstruction (10 with fibula flap and 5 with iliac flap), who were referred to FGG and implant exposures before restoration. Soft tissue was collected before FGG in reconstructed jaws, and in 5 patients (3 with fibula flap and 2 with iliac flap) 8 weeks after FGG if a second surgery was conducted. Histological analysis with hematoxylin-eosin stain and immunological analysis to interlukin-1 (IL-1), interlukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were performed.

RESULTS

Thickness from the bottom of stratum basale to the top of stratum granulosum and thickness of keratinized layer in reconstructed jaws were significantly lower compared with that of natural healthy keratinized gingiva [0.27 (0.20, 0.30) mm vs. 0.36 (0.35, 0.47) mm, P<0.05; 16.49 (14.90, 23.37) μm vs. 26.37 (24.12, 31.53) μm, P<0.05]. In the reconstructed area, thickness from the bottom of stratum basale to the top of stratum granulosum increased after KMA with FGG [0.19 (0.16, 0.25) mm vs. 0.38 (0.25, 0.39) mm, P=0.059] and the thickness of keratinized layer significantly increased after KMA with FGG [16.42 (14.16, 22.35) μm vs. 28.57 (27.16, 29.14) μm, P<0.05], which was similar to that in the control group. Furthermore, the number of positive cells of IL-1, IL-6 and TNF-α significantly increased after KMA [0.67 (0.17, 8.93) vs. 11.00 (9.16, 18.00); 13.00 (8.50, 14.14) vs. 21.89 (15.00, 28.12); 0.22 (0.04, 0.63) vs. 2.83 (1.68, 5.00), respectively, P<0.05] as well as the average optical density value [0.15 (0.14, 0.17) vs. 0.18 (0.17, 0.21); 0.28 (0.26, 0.33) vs. 0.36 (0.33, 0.37); 0.23 (0.22, 0.29) vs. 0.30 (0.28, 0.42), respectively, P<0.05], which was similar to that in the healthy keratinized gingiva.

CONCLUSION

The lack of rete pegs and inflammatory factors were common in soft tissue with jaw reconstruction. FGG can improve the quality of the epithelium and may improve the stability of the mucosa around implants.

Analyzing secretory proteins in human dermal fibroblast-conditioned medium for angiogenesis: A bioinformatic approach

BACKGROUND

The conditioned medium from human dermal fibroblasts (dermal fibroblast-conditioned medium; DFCM) contains a diverse array of secretory proteins, including growth factors and wound repair-promoting proteins. Angiogenesis, a crucial process that facilitates the infiltration of inflammatory cells during wound repair, is induced by a hypoxic environment and inflammatory cytokines.

METHODS

In this study, we conducted a comprehensive bioinformatic analysis of 337 proteins identified through proteomics analysis of DFCM. We specifically focused on 64 DFCM proteins with potential involvement in angiogenesis. These proteins were further classified based on their characteristics, and we conducted a detailed analysis of their protein-protein interactions.

RESULTS

Gene Ontology protein classification categorized these 64 DFCM proteins into various classes, including metabolite interconversion enzymes (N = 11), protein modifying enzymes (N = 10), protein-binding activity modulators (N = 9), cell adhesion molecules (N = 6), extracellular matrix proteins (N = 6), transfer/carrier proteins (N = 3), calcium-binding proteins (N = 2), chaperones (N = 2), cytoskeletal proteins (N = 2), RNA metabolism proteins (N = 1), intercellular signal molecules (N = 1), transporters (N = 1), scaffold/adaptor proteins (N = 1), and unclassified proteins (N = 9). Furthermore, our protein-protein interaction network analysis of DFCM proteins revealed two distinct networks: one with medium confidence level interaction scores, consisting of 60 proteins with significant connections, and another at a high confidence level, comprising 52 proteins with significant interactions.

CONCLUSIONS

Our bioinformatic analysis highlights the presence of a multitude of secretory proteins in DFCM that form significant protein-protein interaction networks crucial for regulating angiogenesis. These findings underscore the critical roles played by DFCM proteins in various stages of angiogenesis during the wound repair process.

Recent trends and perspectives in reconstruction and regeneration of intra/extra-oral wounds using tissue-engineered oral mucosa equivalents

Many conditions, including cancer, trauma, and congenital anomalies, can damage the oral mucosa. Multiple cultures of oral mucosal cells have been used for biocompatibility tests and oral biology studies. In recent decades, the clinical translation of tissue-engineered products has progressed significantly in developing tangible therapies and inspiring advancements in medical science. However, the reconstruction of an intraoral mucosa defect remains a significant challenge. Despite the drawbacks of donor-site morbidity and limited tissue supply, the use of autologous oral mucosa remains the gold standard for oral mucosa reconstruction and repair. Tissue engineering offers a promising solution for repairing and reconstructing oral mucosa tissues. Cell- and scaffold-based tissue engineering approaches have been employed to treat various soft tissue defects, suggesting the potential clinical use of tissue-engineered oral mucosa (TEOMs). In this review, we first cover the recent trends in the reconstruction and regeneration of extra-/intra-oral wounds using TEOMs. Next, we describe the current status and challenges of TEOMs. Finally, future strategic approaches and potential technologies to support the advancement of TEOMs for clinical use are discussed.

Biomimetic human skin model patterned with rete ridges

Rete ridges consist of undulations between the epidermis and dermis that enhance the mechanical properties and biological function of human skin. However, most human skin models are fabricated with a flat interface between the epidermal and dermal layers. Here, we report a micro-stamping method for producing human skin models patterned with rete ridges of controlled geometry. To mitigate keratinocyte-induced matrix degradation, telocollagen-fibrin matrices with and without crosslinks enable these micropatterned features to persist during longitudinal culture. Our human skin model exhibits an epidermis that includes the following markers: cytokeratin 14, p63, and Ki67 in the basal layer, cytokeratin 10 in the suprabasal layer, and laminin and collagen IV in the basement membrane. We demonstrated that two keratinocyte cell lines, one from a neonatal donor and another from an adult diabetic donor, are compatible with this model. We tested this model using an irritation test and showed that the epidermis prevents rapid penetration of sodium dodecyl sulfate. Gene expression analysis revealed differences in keratinocytes obtained from the two donors as well as between 2D (control) and 3D culture conditions. Our human skin model may find potential application for drug and cosmetic testing, disease and wound healing modeling, and aging studies.

Constructing epidermal rete ridges using a composite hydrogel to enhance multiple signaling pathways for the maintenance of epidermal stem cell niche

The undulating microstructure rete ridge (RR) located at the junction between the dermis and epidermis plays a crucial role in improving skin mechanical properties and maintaining skin homeostasis. However, the investigation of RR microstructures is usually neglected in current tissue engineering for skin regeneration. Here, to create an epidermal model with RR microstructures, keratinocytes were cultured on a patterned GelMA-PEGDA hydrogel constructed using molding technology. Furthermore, grafting acryloylated Arg-Gly-Asp (RGD) peptides on the hydrogel surface significantly improved cell adhesion, fusion, and development. RT-PCR, Western blot, and immunofluorescence staining confirmed that cells on RR microstructures exhibited higher gene and protein expression associated with epidermal stem cells. RNA sequencing analysis of cells on RR microstructure showed higher gene expression profiles related to stem cell maintenance, basement membrane formation, and epidermal development. Furthermore, RT-PCR analysis of epidermal models of various dimensions demonstrated that smaller microstructures were more conducive to epidermal stem cell marker gene expression, which is analogous to human skin. Overall, we have successfully developed a method for integrating RR microstructures into an epidermal model that mimics natural skin to maintain epidermal stem cell niche, providing a valuable reference for researching skin regeneration within the fields of tissue engineering and regenerative medicine. STATEMENT OF SIGNIFICANCE: This study presents a method for precisely fabricating microstructures of skin rete ridges using composite hydrogels, thereby creating a skin model that mimics natural human skin. The findings reveal that this microstructure provides a stem cell niche that regulates the pathways and promotes the expression of proteins related to epidermal stem cells. This work advances the functional properties of tissue engineered skin and holds promise for improving the therapeutic efficacy of artificial skin grafts for the skin wounds.

Proteomic Identification and Quantification of Secretory Proteins in Human Dermal Fibroblast-Conditioned Medium for Wound Repair and Hair Regeneration

Background

Human dermal fibroblasts secrete numerous growth factors and proteins that have been suggested to promote wound repair and hair regeneration.

Methods

Human dermal fibroblast-conditioned medium (DFCM) was prepared, and proteomic analysis was performed. Secretory proteins in DFCM were identified using 1-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis, in-gel trypsin protein digestion, and quantitative liquid chromatography tandem mass spectrometry (LC-MS/MS). Identified proteins were analyzed using bioinformatic methods for the classification and evaluation of protein-protein interactions.

Results

Using LC-MS/MS, 337 proteins were identified in DFCM. Among them, 160 proteins were associated with wound repair, and 57 proteins were associated with hair regeneration. Protein-protein interaction network analysis of 160 DFCM proteins for wound repair at the highest confidence score (0.9) revealed that 110 proteins were grouped into seven distinctive interaction networks. Additionally, protein-protein interaction network analysis of 57 proteins for hair regeneration at the highest confidence score revealed that 29 proteins were grouped into five distinctive interaction networks. The identified DFCM proteins were associated with several pathways for wound repair and hair regeneration, including epidermal growth factor receptor, fibroblast growth factor, integrin, Wnt, cadherin, and transforming growth factor-β signaling pathways.

Conclusion

DFCM contains numerous secretory proteins that comprise groups of protein-protein interaction networks that regulate wound repair and hair regeneration.

Rete ridges: Morphogenesis, function, regulation, and reconstruction

Rete ridges (RRs) are distinct undulating microstructures at the junction of the dermis and epidermis in the skin of humans and certain animals. This structure is essential for enhancing the mechanical characteristics of skin and preserving homeostasis. With the development of tissue engineering and regenerative medicine, artificial skin grafts have made great progress in the field of skin healing. However, the restoration of RRs has been often disregarded or absent in artificial skin grafts, which potentially compromise the efficacy of tissue repair and regeneration. Therefore, this review collates recent research advances in understanding the structural features, function, morphogenesis, influencing factors, and reconstruction strategies pertaining to RRs. In addition, the preparation methods and limitations of tissue-engineered skin with RRs are discussed. STATEMENT OF SIGNIFICANCE: The technology for the development of tissue-engineered skin (TES) is widely studied and reported; however, the preparation of TES containing rete ridges (RRs) is often ignored, with no literature reviews on the structural reconstruction of RRs. This review focuses on the progress pertaining to RRs and focuses on the reconstruction methods for RRs. In addition, it discusses the limitations of existing reconstruction methods. Therefore, this review could be a valuable reference for transferring TES with RR structure from the laboratory to clinical applications in skin repair.

The basement membrane in epidermal polarity, stemness, and regeneration

The epidermis is a specialized epithelium that constitutes the outermost layer of the skin, and it provides a protective barrier against environmental assaults. Primarily consisting of multilayered keratinocytes, the epidermis is continuously renewed by proliferation of stem cells and the differentiation of their progeny, which undergo terminal differentiation as they leave the basal layer and move upward toward the surface, where they die and slough off. Basal keratinocytes rest on a basement membrane at the dermal-epidermal junction that is composed of specific extracellular matrix proteins organized into interactive and mechanically supportive networks. Firm attachment of basal keratinocytes, and their dynamic regulation via focal adhesions and hemidesmosomes, is essential for maintaining major skin processes, such as self-renewal, barrier function, and resistance to physical and chemical stresses. The adhesive integrin receptors expressed by epidermal cells serve structural, signaling, and mechanosensory roles that are critical for epidermal cell anchorage and tissue homeostasis. More specifically, the basement membrane components play key roles in preserving the stem cell pool, and establishing cell polarity cues enabling asymmetric cell divisions, which result in the transition from a proliferative basal cell layer to suprabasal cells committed to terminal differentiation. Finally, through a well-regulated sequence of synthesis and remodeling, the components of the dermal-epidermal junction play an essential role in regeneration of the epidermis during skin healing. Here too, they provide biological and mechanical signals that are essential to the restoration of barrier function.

Effects of Human Fibroblast-Derived Multi-Peptide Factors on the Proliferation and Migration of Nitrogen Plasma-Treated Human Dermal Fibroblasts

Background

Human fibroblast-derived multi-peptide factors (MPFs) promote wound repair by playing crucial roles in cell recruitment, adhesion, attachment, migration, and proliferation.

Methods

Cultured human dermal fibroblasts (HDFs) were directly treated with non-contact low- and high-energy nitrogen plasma and further cultured in various conditioned media. Cell proliferation and wound-healing properties were evaluated.

Results

In Opti-modified Eagle’s medium + GlutaMAX culture, reduced HDF viability was observed 24 h after 2-J/pulse plasma treatment and 12 and 24 h after 3-J/pulse treatment. Meanwhile, in dermal fibroblast-conditioned medium (DFCM) containing MPF culture, reduced HDF viability was observed only 24 h after 3-J/pulse treatment. Under DFCM-MPF culture, the wound area percentage was significantly decreased after 12 and 24 h in untreated HDFs; at 9, 12, and 24 h after 1-J/pulse plasma treatment; at 3, 6, 9, 12, and 24 h after 2-J/pulse plasma treatment; and at 9, 12, and 24 h after 3-J/pulse plasma treatment. Greater migration of HDFs with or without plasma treatment was found in DFCM-MPFs than in other conditioned media.

Conclusion

Low-energy nitrogen plasma treatment promotes HDF proliferation and wound repair. DFCM-MPFs enhanced cell proliferation and improved the wound healing properties of HDFs treated with low- and high-energy plasma.

The potential role of fibroblast-derived multi-peptide factors in activation of growth factors and β-Catenin in hair follicle cells

BACKGROUND

Dermal fibroblasts play a pivotal role in hair follicle regeneration during wound repair. Recently, dermal fibroblast-conditioned medium (DFCM), which contains multi-peptide factors (MPFs), has been used to promote wound repair.

AIM

This study aimed to investigate the stimulatory effects of MPF-containing DFCM on hair growth.

METHODS

MPF-containing DFCM was prepared using human neonatal dermal fibroblasts. Outer root sheath (ORS) and dermal papilla (DP) cells were cultured in MPF-containing DFCM. We examined the expression and secretion of growth factors and cytokines using quantitative polymerase chain reaction and a growth factor array. In addition, the effect of MPFs on β-catenin activity was determined using the TOPflash assay. All experiments were repeated at least three times with separate batches of cells.

RESULTS

MPF-containing DFCM increased keratinocyte growth factor (KGF), vascular endothelial growth factor (VEGF), and epidermal growth factor (EGF) mRNA expression in ORS cells and KGF and VEGF mRNA expression in DP cells. When ORS cells were treated with MPF-containing DFCM, the secretion of several growth factors, including EGF, VEGF, insulin-like growth factor-binding protein (IGFBP)-4, IGFBP-6, and fibroblast growth factor-7, was increased in the cell-cultured medium compared with that in control. Additionally, MPF-containing DFCM increased the transcriptional activation of β-catenin in DP cells.

CONCLUSIONS

These results suggest that MPF-containing DFCM might stimulate hair growth by inducing growth factors in ORS and DP cells and regulating β-catenin in DP cells.

Binary organization of epidermal basal domains highlights robustness to environmental exposure

Adulte interfollicular epidermis (IFE) renewal is likely orchestrated by physiological demands of its complex tissue architecture comprising spatial and cellular heterogeneity. Mouse tail and back skin display two kinds of basal IFE spatial domains that regenerate at different rates. Here, we elucidate the molecular and cellular states of basal IFE domains by marker expression and single-cell transcriptomics in mouse and human skin. We uncover two paths of basal cell differentiation that in part reflect the IFE spatial domain organization. We unravel previously unrecognized similarities between mouse tail IFE basal domains defined as scales and interscales versus human rete ridges and inter-ridges, respectively. Furthermore, our basal IFE transcriptomics and gene targeting in mice provide evidence supporting a physiological role of IFE domains in adaptation to differential UV exposure. We identify Sox6 as a novel UV-induced and interscale/inter-ridge preferred basal IFE-domain transcription factor, important for IFE proliferation and survival. The spatial, cellular, and molecular organization of IFE basal domains underscores skin adaptation to environmental exposure and its unusual robustness in adult homeostasis.

Deciphering the Immune Complexity in Esophageal Adenocarcinoma and Pre-Cancerous Lesions With Sequential Multiplex Immunohistochemistry and Sparse Subspace Clustering Approach

Esophageal adenocarcinoma (EAC) develops from a chronic inflammatory environment across four stages: intestinal metaplasia, known as Barrett's esophagus, low- and high-grade dysplasia, and adenocarcinoma. Although the genomic characteristics of this progression have been well defined via large-scale DNA sequencing, the dynamics of various immune cell subsets and their spatial interactions in their tumor microenvironment remain unclear. Here, we applied a sequential multiplex immunohistochemistry (mIHC) platform with computational image analysis pipelines that allow for the detection of 10 biomarkers in one formalin-fixed paraffin-embedded (FFPE) tissue section. Using this platform and quantitative image analytics, we studied changes in the immune landscape during disease progression based on 40 normal and diseased areas from endoscopic mucosal resection specimens of chemotherapy treatment- naïve patients, including normal esophagus, metaplasia, low- and high-grade dysplasia, and adenocarcinoma. The results revealed a steady increase of FOXP3+ T regulatory cells and a CD163+ myelomonocytic cell subset. In parallel to the manual gating strategy applied for cell phenotyping, we also adopted a sparse subspace clustering (SSC) algorithm allowing the automated cell phenotyping of mIHC-based single-cell data. The algorithm successfully identified comparable cell types, along with significantly enriched FOXP3 T regulatory cells and CD163+ myelomonocytic cells as found in manual gating. In addition, SCC identified a new CSF1R+CD1C+ myeloid lineage, which not only was previously unknown in this disease but also increases with advancing disease stages. This study revealed immune dynamics in EAC progression and highlighted the potential application of a new multiplex imaging platform, combined with computational image analysis on routine clinical FFPE sections, to investigate complex immune populations in tumor ecosystems.

Bifidobacterium infantis strain YLGB-1496 possesses excellent antioxidant and skin barrier-enhancing efficacy in vitro

Atopic dermatitis (AD) is a recurring allergic skin disease that has a high incidence. Orally applied Bifidobacteria ameliorate signs of irritated skin and enhance the skin barrier. The present study investigated the safety and efficacy of a topically used cell-free culture supernatant (CFS) from a Bifidobacterium infantis strain using in vitro evaluation methods. The results showed that CFS had strong free radical scavenging activity on DPPH, ABTS, ·OH and O₂ -radicals. CFS treatment fundamentally reduced the intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) contents and improved the activities of antioxidant enzymes (CAT, SOD and GSH-Px) in H₂ O₂ -treated HaCaT cells. Notably, the upregulation of skin physical barrier gene (FLG, LOR, IVL, AQP3 and TGM1) expression and skin antimicrobial peptide gene (CAMP, hBD-2 and hBD-3) expression by CFS might contribute to skin barrier resistance. CFS was non-irritating to the skin and eyes. CFS from the Bifidobacterium infantis strain had strong antioxidant properties on the skin and strengthened skin barrier function, and it was safe for topical use.

Bioprinting and plastic compression of large pigmented and vascularized human dermo-epidermal skin substitutes by means of a new robotic platform

Extensive availability of engineered autologous dermo-epidermal skin substitutes (DESS) with functional and structural properties of normal human skin represents a goal for the treatment of large skin defects such as severe burns. Recently, a clinical phase I trial with this type of DESS was successfully completed, which included patients own keratinocytes and fibroblasts. Yet, two important features of natural skin were missing: pigmentation and vascularization. The first has important physiological and psychological implications for the patient, the second impacts survival and quality of the graft. Additionally, accurate reproduction of large amounts of patient’s skin in an automated way is essential for upscaling DESS production. Therefore, in the present study, we implemented a new robotic unit (called SkinFactory) for 3D bioprinting of pigmented and pre-vascularized DESS using normal human skin derived fibroblasts, blood- and lymphatic endothelial cells, keratinocytes, and melanocytes. We show the feasibility of our approach by demonstrating the viability of all the cells after printing in vitro, the integrity of the reconstituted capillary network in vivo after transplantation to immunodeficient rats and the anastomosis to the vascular plexus of the host. Our work has to be considered as a proof of concept in view of the implementation of an extended platform, which fully automatize the process of skin substitution: this would be a considerable improvement of the treatment of burn victims and patients with severe skin lesions based on patients own skin derived cells.

Mechanical stretching can modify the papillary dermis pattern and papillary fibroblast characteristics during skin regeneration

Clinical application of mechanical stretching is a reconstructive method for skin repair. Although studies have reported dermal fibroblast heterogeneity, whether stretching affects individual fibroblast subpopulations equally remains unclear. Here, we show the changes in dermal structure and papillary fibroblast (Fp) in regenerated human skin. Exhausted skin regeneration caused dermal-epidermal junction (DEJ) flattening, papillary dermis thinning, and an increase in the type III collagen (COL3)/type I collagen (COL1) ratio with upregulated hallmarks of aging. Well-regenerated skin displayed a notable increase in the Fp population. Consistent changes were observed in the rat expansion model. Moreover, we found that TGFβ1 expression was especially increased in skin showing good regeneration. Activation of the TGFβ1/Smad2/3 pathway improved exhausted skin regeneration and resulted in increased collagen content and Fp proliferation, while pharmacological inhibition of TGFβ1 action impacted well-regenerated skin. Short-term mechanical stretching that promoted skin regeneration enhanced Fp proliferation, extracellular matrix (ECM) synthesis, and increased TGFβ1 expression, leading to good regeneration. Conversely, long-term stretching induced premature Fp senescence, leading to poor regeneration. This work shows the mechanism of mechanical stretching in well skin regeneration that enhances Fp proliferation and ECM synthesis via the TGFβ1/Smad2/3 pathway, and highlights a crucial role of Fps in stretching-induced skin regeneration.

Fabrication of Topographically Controlled Electrospun Scaffolds to Mimic the Stem Cell Microenvironment in the Dermal-Epidermal Junction

The use of microfabrication techniques for the development of innovative constructs for tissue regeneration is a growing area of research. This area comprises both manufacturing and biological approaches for the development of smart materials aiming to control and direct cell behavior to enhance tissue healing. Many groups have focused their efforts on introducing complexity within these innovative constructs via the inclusion of nano- and microtopographical cues mimicking physical and biological aspects of the native stem cell niche. Specifically, in the area of skin tissue engineering, seminal work has reported replicating the microenvironments located in the dermal-epithelial junction, which are known as rete ridges. The rete ridges are key for both stem cell control and the physiological performance of the skin. In this work, we have introduced complexity within electrospun membranes to mimic the morphology of the rete ridges in the skin. We designed and tested three different patterns, characterized them, and explored their performance in vitro, using 3D skin models. One of the studied patterns (pattern B) was shown to aid in the development of an in vitro rite-ridgelike skin model that resulted in the expression of relevant epithelial markers such as collagen IV and integrin β1. In summary, we have developed a new skin model including synthetic rete-ridgelike structures that replicate both morphology and function of the native dermal-epidermal junction and that offer new insights for the development of smart skin tissue engineering constructs.

The Use of Microfabrication Techniques for the Design and Manufacture of Artificial Stem Cell Microenvironments for Tissue Regeneration

The recapitulation of the stem cell microenvironment is an emerging area of research that has grown significantly in the last 10 to 15 years. Being able to understand the underlying mechanisms that relate stem cell behavior to the physical environment in which stem cells reside is currently a challenge that many groups are trying to unravel. Several approaches have attempted to mimic the biological components that constitute the native stem cell niche, however, this is a very intricate environment and, although promising advances have been made recently, it becomes clear that new strategies need to be explored to ensure a better understanding of the stem cell niche behavior. The second strand in stem cell niche research focuses on the use of manufacturing techniques to build simple but functional models; these models aim to mimic the physical features of the niche environment which have also been demonstrated to play a big role in directing cell responses. This second strand has involved a more engineering approach in which a wide set of microfabrication techniques have been explored in detail. This review aims to summarize the use of these microfabrication techniques and how they have approached the challenge of mimicking the native stem cell niche.

Computational flow cytometric analysis to detect epidermal subpopulations in human skin

Background

The detection and dissection of epidermal subgroups could lead to an improved understanding of skin homeostasis and wound healing. Flow cytometric analysis provides an effective method to detect the surface markers of epidermal cells while producing high-dimensional data files.

Methods

A 9-color flow cytometric panel was optimized to reveal the heterogeneous subgroups in the epidermis of human skin. The subsets of epidermal cells were characterized using automated methods based on dimensional reduction approaches (viSNE) and clustering with Spanning-tree Progression Analysis of Density-normalized Events (SPADE).

Results

The manual analysis revealed differences in epidermal distribution between body sites based on a series biaxial gating starting with the expression of CD49f and CD29. The computational analysis divided the whole epidermal cell population into 25 clusters according to the surface marker phenotype with SPADE. This automatic analysis delineated the differences between body sites. The consistency of the results was confirmed with PhenoGraph.

Conclusion

A multicolor flow cytometry panel with a streamlined computational analysis pipeline is a feasible approach to delineate the heterogeneity of the epidermis in human skin.

Structural and ultrastructural studies on the developing vomeronasal sensory epithelium in the grass snake Natrix natrix (Squamata: Colubroidea)

The sensory olfactory epithelium and the vomeronasal sensory epithelium (VSE) are characterized by continuous turnover of the receptor cells during postnatal life and are capable of regeneration after injury. The VSE, like the entire vomeronasal organ, is generally well developed in squamates and is crucial for detection of pheromones and prey odors. Despite the numerous studies on embryonic development of the VSE in squamates, especially in snakes, an ultrastructural analysis, as far as we know, has never been performed. Therefore, we investigated the embryology of the VSE of the grass snake (Natrix natrix) using electron microscopy (SEM and TEM) and light microscopy. As was shown for adult snakes, the hypertrophied ophidian VSE may provide great resolution of changes in neuron morphology located at various epithelial levels. The results of this study suggest that different populations of stem/progenitor cells occur at the base of the ophidian VSE during embryonic development. One of them may be radial glia-like cells, described previously in mouse. The various structure and ultrastructure of neurons located at different parts of the VSE provide evidence for neuronal maturation and aging. Based on these results, a few nonmutually exclusive hypotheses explaining the formation of the peculiar columnar organization of the VSE in snakes were proposed.

Manufacturing micropatterned collagen scaffolds with chemical-crosslinking for development of biomimetic tissue-engineered oral mucosa

The junction between the epithelium and the underlying connective tissue undulates, constituting of rete ridges, which lack currently available soft tissue constructs. In this study, using a micro electro mechanical systems process and soft lithography, fifteen negative molds, with different dimensions and aspect ratios in grid- and pillar-type configurations, were designed and fabricated to create three-dimensional micropatterns and replicated onto fish-scale type I collagen scaffolds treated with chemical crosslinking. Image analyses showed the micropatterns were well-transferred onto the scaffold surfaces, showing the versatility of our manufacturing system. With the help of rheological test, the collagen scaffold manufactured in this study was confirmed to be an ideal gel and have visco-elastic features. As compared with our previous study, its mechanical and handling properties were improved by chemical cross-linking, which is beneficial for grafting and suturing into the complex structures of oral cavity. Histologic evaluation of a tissue-engineered oral mucosa showed the topographical microstructures of grid-type were well-preserved, rather than pillar-type, a well-stratified epithelial layer was regenerated on all scaffolds and the epithelial rete ridge-like structure was developed. As this three-dimensional microstructure is valuable for maintaining epithelial integrity, our micropatterned collagen scaffolds can be used not only intraorally but extraorally as a graft material for human use.

The Human Epidermal Basement Membrane: A Shaped and Cell Instructive Platform That Aging Slowly Alters

One of the most important functions of skin is to act as a protective barrier. To fulfill this role, the structural integrity of the skin depends on the dermal-epidermal junction-a complex network of extracellular matrix macromolecules that connect the outer epidermal layer to the underlying dermis. This junction provides both a structural support to keratinocytes and a specific niche that mediates signals influencing their behavior. It displays a distinctive microarchitecture characterized by an undulating pattern, strengthening dermal-epidermal connectivity and crosstalk. The optimal stiffness arising from the overall molecular organization, together with characteristic anchoring complexes, keeps the dermis and epidermis layers extremely well connected and capable of proper epidermal renewal and regeneration. Due to intrinsic and extrinsic factors, a large number of structural and biological changes accompany skin aging. These changes progressively weaken the dermal-epidermal junction substructure and affect its functions, contributing to the gradual decline in overall skin physiology. Most changes involve reduced turnover or altered enzymatic or non-enzymatic post-translational modifications, compromising the mechanical properties of matrix components and cells. This review combines recent and older data on organization of the dermal-epidermal junction, its mechanical properties and role in mechanotransduction, its involvement in regeneration, and its fate during the aging process.

Cell-specific expression of the transcriptional regulator RHAMM provides a timing mechanism that controls appropriate wound re-epithelialization

Prevention of aberrant cutaneous wound repair and appropriate regeneration of an intact and functional integument require the coordinated timing of fibroblast and keratinocyte migration. Here, we identified a mechanism whereby opposing cell-specific motogenic functions of a multifunctional intracellular and extracellular protein, the receptor for hyaluronan-mediated motility (RHAMM), coordinates fibroblast and keratinocyte migration speed and ensures appropriate timing of excisional wound closure. We found that, unlike in WT mice, in Rhamm-null mice, keratinocyte migration initiates prematurely in the excisional wounds, resulting in wounds that have re-surfaced before the formation of normal granulation tissue, leading to a defective epidermal architecture. We also noted aberrant keratinocyte and fibroblast migration in the Rhamm-null mice, indicating that RHAMM suppresses keratinocyte motility but increases fibroblast motility. This cell context-dependent effect resulted from cell-specific regulation of extracellular signal-regulated kinase 1/2 (ERK1/2) activation and expression of a RHAMM target gene encoding matrix metalloprotease 9 (MMP-9). In fibroblasts, RHAMM promoted ERK1/2 activation and MMP-9 expression, whereas in keratinocytes, RHAMM suppressed these activities. In keratinocytes, loss of RHAMM function or expression promoted epidermal growth factor receptor-regulated MMP-9 expression via ERK1/2, which resulted in cleavage of the ectodomain of the RHAMM partner protein CD44 and thereby increased keratinocyte motility. These results identify RHAMM as a key factor that integrates the timing of wound repair by controlling cell migration.

Histopathology of Oral Submucous Fibrosis in Third Dimension with an Additional note on Hypothesis of Epithelial Atrophy

Oral submucous fibrosis (OSMF) is a potentially malignant disorder, characterized by progressive fibrosis of the lamina propria and underlying connective tissue. It has high chances of malignant transformation. It is caused by betel nut which is very common habit among Indians. Thus, regular monitoring of histopathological changes is mandatory by physicians, private practitioners, and oral pathologists. Therefore, histopathological changes should be understood by everyone who is into health care. This article is a preliminary report on three-dimensional (3D) images and 3D-animation video of histopathological aspect of OSMF designed by author herself, for better understanding of histopathological aspect, which has never been reported so far. Additional hypothesis on epithelial atrophy have also been proposed.

Wild-type and SAMP8 mice show age-dependent changes in distinct stem cell compartments of the interfollicular epidermis

Delayed wound healing and reduced barrier function with an increased risk of cancer are characteristics of aged skin and one possible mechanism is misregulation or dysfunction of epidermal stem cells during aging. Recent studies have identified heterogeneous stem cell populations within the mouse interfollicular epidermis that are defined by territorial distribution and cell division frequency; however, it is unknown whether the individual stem cell populations undergo distinct aging processes. Here we provide comprehensive characterization of age-related changes in the mouse epidermis within the specific territories of slow-cycling and fast-dividing stem cells using old wild-type, senescence-accelerated mouse prone 1 (SAMP1) and SAMP8 mice. During aging, the epidermis exhibits structural changes such as irregular micro-undulations and overall thinning of the tissue. We also find that, in the old epidermis, proliferation is preferentially decreased in the region where fast-dividing stem cells reside whereas the lineage differentiation marker appears to be more affected in the slow-cycling stem cell region. Furthermore, SAMP8, but not SAMP1, exhibits precocious aging similar to that of aged wild-type mice, suggesting a potential use of this model for aging study of the epidermis and its stem cells. Taken together, our study reveals distinct aging processes governing the two epidermal stem cell populations and suggests a potential mechanism in differential responses of compartmentalized stem cells and their niches to aging.

Keratinocyte growth factor (KGF) induces podosome formation via integrin-Erk1/2 signaling in human immortalized oral epithelial cells

Recent study established the role of integrins in keratinocyte growth factor (KGF)-induced oral epithelial adhesion and rete peg elongation. However, how extracellular matrix (ECM) remodeling cooperates with the increased epithelial adhesion during rete peg elongation has yet to be determined. Podosomes are cell-matrix contact structures that combine several abilities, including adhesion and matrix degradation. In the present study, we identified podosome formation at the ventral side of human immortalized oral epithelial cells (HIOECs) upon KGF treatment. Moreover, podosomal components including integrin α6，β4，α3，β1 and MMP14 colocalized with the F-actin-cortactin complex and matrix degradation assays demonstrated the ability of the F-actin-cortactin complex to degrade matrix. Inhibition both of integrin subunits β4 and β1 with specific blocking antibodies and inhibition of Erk1/2 abrogated the KGF-induced podosome formation. Notably, knockdown of integrin subunits β4 and β1 with specific small interfering RNA (siRNA) downregulated the phosphorylation levels of Erk1/2. In contrast, inhibition of both Erk1/2 could upregulate the expression of integrin subunits β4 and β1. These results demonstrate that KGF induces podosome formation via integrin-Erk1/2 signaling in HIOECs, suggesting a novel mechanism by which integrins enhance oral epithelial adhesion and rete peg elongation.

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

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

Treatment of limb wounds of horses with orf virus IL-10 and VEGF-E accelerates resolution of exuberant granulation tissue, but does not prevent its development

Bandaging of limb wounds in horses leads to formation of exuberant granulation tissue (EGT) that retards healing due to protracted inflammation, aberrant vascularisation and delayed epithelialisation. EGT is not observed if wounds are left undressed or when wounds are on the body. A previous study showed that short-term administration of proteins derived from orf virus dampened inflammation and promoted epithelialisation of open wounds in horses. Here, we investigated the impact of orf virus interleukin-10 and vascular endothelial growth factor-E on the development and resolution of EGT. Excisional wounds were created on the forelimb of four horses, and bandages were maintained until full healing to induce EGT formation. Matching body wounds were created to ensure EGT was limited to the limb, and to differentiate the effects of the viral proteins on normal healing and on EGT formation. Viral proteins or the hydrogel vehicle control were administered topically to site-matched wounds at day 1, with repeat administration at day 8. Wound healing and EGT formation were monitored macroscopically. Wound margin samples were harvested at 2, 7 and 14 days, and at full healing, with histology used to observe epithelialisation, immunofluorescence used to detect inflammatory cells, angiogenesis and cell death, and qPCR to measure expression of genes regulating inflammation and angiogenesis. Limb wounds developed EGT, and exhibited slower healing than body wounds. Viral protein treatment did not accelerate healing at either location nor limit EGT formation in limb wounds. Treatment of limb wounds did however increase epithelialisation and angiogenesis, without dampening inflammatory cell infiltration or gene expression. The healed wounds also had less occlusion and death of blood vessels and fewer epidermal rete ridges following viral protein treatment. These findings indicate that the viral protein treatment does not suppress wound inflammation or EGT formation, but does promote vascular and epidermal repair and EGT resolution.

New Proposal to Define the Fascial System

At the beginning of the third millennium, we still do not have a definition of 'fascia' recognized as valid by every researcher. This article attempts to give a new definition of the fascial system, including the epidermis, by comparing the mechanical-metabolic characteristics of the connective tissue and the skin. In fact, according to the latest classification deriving from the Fascia Nomenclature Committee, the outer skin layer is not considered as part of the fascial continuum. This article highlights the reasons for taking the functional characteristics of the tissue into consideration, rather than its mere structure. A brief discussion will address the questions as to what is considered as fascial tissue and from which embryonic germ layer the epidermis is formed. The notion that all the layers intersect will be highlighted, demonstrating that quoting precise definitions of tissue stratification in the living organism probably does not correspond to what happens in vivo. What we propose as a definition is not to be regarded as a point of arrival but as another departure.

Stem cells, niches and scaffolds: Applications to burns and wound care

The importance of skin to survival, and the devastating physical and psychological consequences of scarring following reparative healing of extensive or difficult to heal human wounds, cannot be disputed. We discuss the significant challenges faced by patients and healthcare providers alike in treating these wounds. New state of the art technologies have provided remarkable insights into the role of skin stem and progenitor cells and their niches in maintaining skin homeostasis and in reparative wound healing. Based on this knowledge, we examine different approaches to repair extensive burn injury and chronic wounds, including full and split thickness skin grafts, temporising matrices and scaffolds, and composite cultured skin products. Notable developments include next generation skin substitutes to replace split thickness skin autografts and next generation gene editing coupled with cell therapies to treat genodermatoses. Further refinements are predicted with the advent of bioprinting technologies, and newly defined biomaterials and autologous cell sources that can be engineered to more accurately replicate human skin architecture, function and cosmesis. These advances will undoubtedly improve quality of life for patients with extensive burns and difficult to heal wounds.

A methodology for the production of microfabricated electrospun membranes for the creation of new skin regeneration models

The continual renewal of the epidermis is thought to be related to the presence of populations of epidermal stem cells residing in physically protected microenvironments (rete ridges) directly influenced by the presence of mesenchymal fibroblasts. Current skin in vitro models do acknowledge the influence of stromal fibroblasts in skin reorganisation but the study of the effect of the rete ridge-microenvironment on epidermal renewal still remains a rich topic for exploration. We suggest there is a need for the development of new in vitro models in which to study epithelial stem cell behaviour prior to translating these models into the design of new cell-free biomaterial devices for skin reconstruction. In this study, we aimed to develop new prototype epidermal-like layers containing pseudo-rete ridge structures for studying the effect of topographical cues on epithelial cell behaviour. The models were designed using a range of three-dimensional electrospun microfabricated scaffolds. This was achieved via the utilisation of polyethylene glycol diacrylate to produce a reusable template over which poly(3-hydrroxybutyrate-co-3-hydroxyvalerate) was electrospun. Initial investigations studied the behaviour of keratinocytes cultured on models using plain scaffolds (without the presence of intricate topography) versus keratinocytes cultured on scaffolds containing microfeatures.

Topical Administration of Ibuprofen for Injured Athletes: Considerations, Formulations, and Comparison to Oral Delivery

Non-steroidal anti-inflammatory drugs (NSAIDs) are a class of drugs commonly used to treat both the acute and chronic injuries sustained by athletes during training and competition. In many parts of the world, NSAIDs can be purchased over-the-counter and used without any physician oversight. However, the chronic nature of overuse injuries requires NSAIDs to be taken orally for an extended period of time. As a result, they can have significant adverse effects on athletes, namely gastrointestinal (GI), renal, and cardiovascular damage. Dyspepsia and upper GI ulceration and bleeding are of great concern in chronic NSAID use, and as such oral NSAIDs are generally contraindicated in those with a history of peptic ulcers or irritable bowel disease. In the setting of chronic overuse soft tissue or joint disease, topically administered NSAIDs offer an alternate route of administration that has the potential to deliver a similar level of pain and anti-inflammatory relief while bypassing the harmful side effects associated with oral intake. Topically applied NSAIDs are able to achieve high concentrations within the targeted site of action while simultaneously keeping plasma concentrations low, offering several advantages over oral administration. One commonly used generic NSAID is ibuprofen (2-(4-isobutylphenyl)propanoic acid). First synthesized in the 1960s, ibuprofen has since become widely available as an over-the-counter pharmaceutical. In this review, we outline new and different techniques that have been used to deliver ibuprofen into diseased tissues, including supersaturations, microemulsions, gels, nanosystems, and microneedles. We also review relevant clinical trials comparing transdermally delivered ibuprofen to placebo and orally administered ibuprofen.

Isolating subpopulations of human epidermal basal cells based on polyclonal serum against trypsin-resistant CSPG4 epitopes

Chondroitin sulfate proteoglycan 4 (CSPG4) is highly expressed by human epidermal keratinocytes located at the tip of the dermal papilla where keratinocytes show characteristics of stem cells. However, since available antibodies to CSPG4 are directed against trypsin-sensitive epitopes we have been unable to study these keratinocytes isolated directly from skin samples by flow cytometry. By choosing epitopes of CSPG4 relatively close to the cell membrane we were able to generate a polyclonal antibody that successfully detects CSPG4 on keratinocytes after trypsinization. Although CSPG4-positive basal cells express higher levels of Itgβ1 the colony-forming efficiency is slightly lower than CSPG4-negative basal cells. Sorting the directly isolated keratinocytes based on Itgβ1 did not reveal differences in colony-forming efficiency between keratinocytes expressing high or low levels of Itgβ1. However, after the first passage Itgβ1 could be used to predict colony-forming efficiency whether the culture was established from CSPG4-positive or CSPG4-negative basal cell keratinocytes. Although we were unable to detect differences in the colony-forming assay, global gene expression profiling showed that CSPG4-positive basal cell keratinocytes are distinct from CSPG4-negative basal cell keratinocytes. Our study demonstrates that it is possible to generate antibodies against trypsin-resistant epitopes of CSPG4. Our study also documents a marked change in behaviour upon cell culturing and challenges the way we assess for stemness within the human epidermal basal layer.

Nanoparticle-Enabled Transdermal Drug Delivery Systems for Enhanced Dose Control and Tissue Targeting

Transdermal drug delivery systems have been around for decades, and current technologies (e.g., patches, ointments, and creams) enhance the skin permeation of low molecular weight, lipophilic drugs that are efficacious at low doses. The objective of current transdermal drug delivery research is to discover ways to enhance skin penetration of larger, hydrophilic drugs and macromolecules for disease treatment and vaccination. Nanocarriers made of lipids, metals, or polymers have been successfully used to increase penetration of drugs or vaccines, control drug release, and target drugs to specific areas of skin in vivo. While more research is needed to identify the safety of nanocarriers, this technology has the potential to expand the use of transdermal routes of administration to a wide array of therapeutics. Here, we review the current state of nanoparticle skin delivery systems with special emphasis on targeting skin diseases.