Differentiation of mouse induced pluripotent stem cells into a multipotent keratinocyte lineage

Astragalus polysaccharide-containing 3D-printed scaffold for traumatized skin repair and proteomic study

Astragalus polysaccharide-containing 3D-printed scaffold shows great potential in traumatic skin repair. This study aimed to investigate its repairing effect and to combine it with proteomic technology to deeply resolve the related protein expression changes. Thirty SD rats were divided randomly into three groups (n = 10 per group): the sham-operated group, the model group and the scaffold group. Subsequently, we conducted a comparative analysis on trauma blood perfusion, trauma healing rate, histological changes, the expression of the YAP/TAZ signalling pathway and angiogenesis-related factors. Additionally, neonatal skin tissues were collected for proteomic analysis. The blood perfusion volume and wound healing recovery in the scaffold group were better than that in the model group (p < 0.05). The protein expression of STAT3, YAP, TAZ and expression of vascular-related factor A (VEGFA) in the scaffold group was higher than that in the model group (p < 0.05). Proteomic analysis showed that there were 207 differential proteins common to the three groups. Mitochondrial function, immune response, redox response, extracellular gap and ATP metabolic process were the main groups of differential protein changes. Oxidative phosphorylation, metabolic pathway, carbon metabolism, calcium signalling pathway, etc. were the main differential metabolic pathway change groups. Astragalus polysaccharide-containing 3D-printed scaffold had certain reversals of protein disorder. The Astragalus polysaccharide-containing 3D-printed scaffold may promote the VEGFs by activating the YAP/TAZ signalling pathway with the help of STAT3 into the nucleus, accelerating early angiogenesis of the trauma, correcting the protein disorder of the trauma and ultimately realizing the repair of the wound.

Periodontitis in Psoriatic Patients: Epidemiological Insights and Putative Etiopathogenic Links

Psoriasis, a systemic autoimmune disorder primarily affecting the skin, manifests through erythematous plaques and scales, impacting approximately 2-3% of the global population. Chronic periodontitis, a prevalent oral disease characterized by the destruction of tooth-supporting tissues, affects roughly 10-15% of adults worldwide. Emerging evidence suggests a bidirectional relationship between psoriasis and chronic periodontitis, supported by epidemiological studies indicating a higher prevalence of periodontitis among individuals with psoriasis and vice versa. Both conditions are chronic inflammatory diseases marked by dysregulated immune responses and altered cytokine profiles, notably involving proinflammatory cytokines such as TNF-α and IL-17. Clinical studies highlight a reciprocal impact of treating one condition on the other, underscoring the necessity of interdisciplinary collaboration between dermatologists and periodontists in managing patients with both conditions. This narrative review provides a comprehensive overview of the relationship between psoriasis and chronic periodontitis, examining epidemiological associations, shared inflammatory pathways, genetic insights, microbial dysbiosis, environmental factors, and clinical implications. The review emphasizes the importance of integrated care approaches and the potential for targeted therapeutic interventions to improve both psoriatic and periodontal patient outcomes, advocating for further research into the molecular and cellular mechanisms underpinning the comorbidity of these diseases.

Development of pluripotent stem cell-derived epidermal organoids that generate effective extracellular vesicles in skin regeneration

Cellular skin substitutes such as epidermal constructs have been developed for various applications, including wound healing and skin regeneration. These cellular models are mostly derived from primary cells such as keratinocytes and fibroblasts in a two-dimensional (2D) state, and further development of three-dimensional (3D) cultured organoids is needed to provide insight into the in vivo epidermal phenotype and physiology. Here, we report the development of epidermal organoids (EpiOs) generated from induced pluripotent stem cells (iPSCs) as a novel epidermal construct and its application as a source of secreted biomolecules recovered by extracellular vesicles (EVs) that can be utilized for cell-free therapy of regenerative medicine. Differentiated iPSC-derived epidermal organoids (iEpiOs) are easily cultured and expanded through multiple organoid passages, while retaining molecular and functional features similar to in vivo epidermis. These mature iEpiOs contain epidermal stem cell populations and retain the ability to further differentiate into other skin compartment lineages, such as hair follicle stem cells. By closely recapitulating the epidermal structure, iEpiOs are expected to provide a more relevant microenvironment to influence cellular processes and therapeutic response. Indeed, iEpiOs can generate high-performance EVs containing high levels of the angiogenic growth factor VEGF and miRNAs predicted to regulate cellular processes such as proliferation, migration, differentiation, and angiogenesis. These EVs contribute to target cell proliferation, migration, and angiogenesis, providing a promising therapeutic tool for in vivo wound healing. Overall, the newly developed iEpiOs strategy as an organoid-based approach provides a powerful model for studying basic and translational skin research and may also lead to future therapeutic applications using iEpiOs-secreted EVs.

Mesenchymal stem cells in craniofacial reconstruction: a comprehensive review

Craniofacial reconstruction faces many challenges, including high complexity, strong specificity, severe injury, irregular and complex wounds, and high risk of bleeding. Traditionally, the "gold standard" for treating craniofacial bone defects has been tissue transplantation, which involves the transplantation of bone, cartilage, skin, and other tissues from other parts of the body. However, the shape of craniofacial bone and cartilage structures varies greatly and is distinctly different from ordinary long bones. Craniofacial bones originate from the neural crest, while long bones originate from the mesoderm. These factors contribute to the poor effectiveness of tissue transplantation in repairing craniofacial defects. Autologous mesenchymal stem cell transplantation exhibits excellent pluripotency, low immunogenicity, and minimally invasive properties, and is considered a potential alternative to tissue transplantation for treating craniofacial defects. Researchers have found that both craniofacial-specific mesenchymal stem cells and mesenchymal stem cells from other parts of the body have significant effects on the restoration and reconstruction of craniofacial bones, cartilage, wounds, and adipose tissue. In addition, the continuous development and application of tissue engineering technology provide new ideas for craniofacial repair. With the continuous exploration of mesenchymal stem cells by researchers and the continuous development of tissue engineering technology, the use of autologous mesenchymal stem cell transplantation for craniofacial reconstruction has gradually been accepted and promoted. This article will review the applications of various types of mesenchymal stem cells and related tissue engineering in craniofacial repair and reconstruction.

Human-Induced Pluripotent Stem Cells in Plastic and Reconstructive Surgery

A hallmark of plastic and reconstructive surgery is restoring form and function. Historically, tissue procured from healthy portions of a patient's body has been used to fill defects, but this is limited by tissue availability. Human-induced pluripotent stem cells (hiPSCs) are stem cells derived from the de-differentiation of mature somatic cells. hiPSCs are of particular interest in plastic surgery as they have the capacity to be re-differentiated into more mature cells, and cultured to grow tissues. This review aims to evaluate the applications of hiPSCs in the plastic surgery context, with a focus on recent advances and limitations. The use of hiPSCs and non-human iPSCs has been researched in the context of skin, nerve, vasculature, skeletal muscle, cartilage, and bone regeneration. hiPSCs offer a future for regenerated autologous skin grafts, flaps comprised of various tissue types, and whole functional units such as the face and limbs. Also, they can be used to model diseases affecting tissues of interest in plastic surgery, such as skin cancers, epidermolysis bullosa, and scleroderma. Tumorigenicity, immunogenicity and pragmatism still pose significant limitations. Further research is required to identify appropriate somatic origin and induction techniques to harness the epigenetic memory of hiPSCs or identify methods to manipulate epigenetic memory.

Advanced function, design and application of skin substitutes for skin regeneration

The development of skin substitutes aims to replace, mimic, or improve the functions of human skin, regenerate damaged skin tissue, and replace or enhance skin function. This includes artificial skin, scaffolds or devices designed for treatment, imitation, or improvement of skin function in wounds and injuries. Therefore, tremendous efforts have been made to develop functional skin substitutes. However, there is still few reports systematically discuss the relationship between the advanced function and design requirements. In this paper, we review the classification, functions, and design requirements of artificial skin or skin substitutes. Different manufacturing strategies for skin substitutes such as hydrogels, 3D/4D printing, electrospinning, microfluidics are summarized. This review also introduces currently available skin substitutes in clinical trials and on the market and the related regulatory requirements. Finally, the prospects and challenges of skin substitutes in the field of tissue engineering are discussed.

A Systematic Review of Stem Cell Differentiation into Keratinocytes for Regenerative Applications

To improve wound healing or treatment of other skin diseases, and provide model cells for skin biology studies, in vitro differentiation of stem cells into keratinocyte-like cells (KLCs) is very desirable in regenerative medicine. This study examined the most recent advancements in in vitro differentiation of stem cells into KLCs, the effect of biofactors, procedures, and preparation for upcoming clinical cases. A range of stem cells with different origins could be differentiated into KLCs under appropriate conditions. The most effective ways of stem cell differentiation into keratinocytes were found to include the co-culture with primary epithelial cells and keratinocytes, and a cocktail of growth factors, cytokines, and small molecules. KLCs should also be supported by biomaterials for the extracellular matrix (ECM), which replicate the composition and functionality of the in vivo extracellular matrix (ECM) and, thus, support their phenotypic and functional characteristics. The detailed efficient characterization of different factors, and their combinations, could make it possible to find the significant inducers for stem cell differentiation into epidermal lineage. Moreover, it allows the development of chemically known media for directing multi-step differentiation procedures.In conclusion, the differentiation of stem cells to KLCs is feasible and KLCs were used in experimental, preclinical, and clinical trials. However, the translation of KLCs from in vitro investigational system to clinically valuable cells is challenging and extremely slow.

Novel Strategies for Angiogenesis in Tissue Injury: Therapeutic Effects of iPSCs-Derived Exosomes

Regeneration after tissue injury is a dynamic and complex process, and angiogenesis is necessary for normal physiological activities and tissue repair. Induced pluripotent stem cells are a new approach in regenerative medicine, which provides good model for the study of difficult-to-obtain human tissues, patient-specific therapy, and tissue repair. As an innovative cell-free therapeutic strategy, the main advantages of the treatment of induced pluripotent stem cells (iPSCs)-derived exosomes are low in tumorigenicity and immunogenicity, which become an important pathway for tissue injury. This review focuses on the mechanism of the angiogenic effect of iPSCs-derived exosomes on wound repair in tissue injury and their potential therapeutic targets, with a view to providing a theoretical basis for the use of iPSCs-derived exosomes in clinical therapy.

A biotin-stabilized HKUST-1/ADM scaffold for facilitating MSC endothelial differentiation and vascularization in diabetic wound healing

Inadequate angiogenesis in diabetic wound healing has been identified as one of the most difficult issues to treat. Copper ions (Cu²⁺) have been confirmed to stimulate angiogenesis; nevertheless, the rapid rise in non-physiological Cu²⁺ concentrations increases the danger of ion poisoning. For the first time, biotin was used to stabilize a copper-based metal-organic framework (HKUST-1) to change its hydrophobicity and achieve sustained release of Cu²⁺. The inability to offer a suitable area for the dynamic interaction between cells and growth factors still restricts the use of nanomaterials for the regeneration of injured skin in diabetes. Acellular dermal matrix (ADM) scaffolds are collagen fibers with natural spatial tissue that can create a biological "niche" for cell attachment and growth. In this study, biotin-stabilized HKUST-1 (B-HKUST-1) nanoparticles were modified with an ADM to form a novel scaffold (ADM-B-HKUST-1). Notably, Cu²⁺ and mesenchymal stem cells (MSCs) released by the composite scaffold may synergistically promote MSC adhesion, proliferation and endothelial differentiation by upregulating the expression of transforming growth factor-β (TGF-β), vascular endothelial growth factor (VEGF) and alpha-smooth muscle actin (α-SMA). Overall, the ADM-B-HKUST1 scaffold combines the dual advantages of the sustained release of Cu²⁺ and creating a biological "niche" can provide a potential strategy for enhancing angiogenesis and promoting diabetic wound healing.

Innovative Treatment Strategies to Accelerate Wound Healing: Trajectory and Recent Advancements

Wound healing is highly specialized dynamic multiple phase process for the repair of damaged/injured tissues through an intricate mechanism. Any failure in the normal wound healing process results in abnormal scar formation, and chronic state which is more susceptible to infections. Chronic wounds affect patients’ quality of life along with increased morbidity and mortality and are huge financial burden to healthcare systems worldwide, and thus requires specialized biomedical intensive treatment for its management. The clinical assessment and management of chronic wounds remains challenging despite the development of various therapeutic regimens owing to its painstakingly long-term treatment requirement and complex wound healing mechanism. Various conventional approaches such as cell therapy, gene therapy, growth factor delivery, wound dressings, and skin grafts etc., are being utilized for promoting wound healing in different types of wounds. However, all these abovementioned therapies are not satisfactory for all wound types, therefore, there is an urgent demand for the development of competitive therapies. Therefore, there is a pertinent requirement to develop newer and innovative treatment modalities for multipart therapeutic regimens for chronic wounds. Recent developments in advanced wound care technology includes nanotherapeutics, stem cells therapy, bioengineered skin grafts, and 3D bioprinting-based strategies for improving therapeutic outcomes with a focus on skin regeneration with minimal side effects. The main objective of this review is to provide an updated overview of progress in therapeutic options in chronic wounds healing and management over the years using next generation innovative approaches. Herein, we have discussed the skin function and anatomy, wounds and wound healing processes, followed by conventional treatment modalities for wound healing and skin regeneration. Furthermore, various emerging and innovative strategies for promoting quality wound healing such as nanotherapeutics, stem cells therapy, 3D bioprinted skin, extracellular matrix-based approaches, platelet-rich plasma-based approaches, and cold plasma treatment therapy have been discussed with their benefits and shortcomings. Finally, challenges of these innovative strategies are reviewed with a note on future prospects.

Vitamin A in Skin and Hair: An Update

Vitamin A is a fat-soluble micronutrient necessary for the growth of healthy skin and hair. However, both too little and too much vitamin A has deleterious effects. Retinoic acid and retinal are the main active metabolites of vitamin A. Retinoic acid dose-dependently regulates hair follicle stem cells, influencing the functioning of the hair cycle, wound healing, and melanocyte stem cells. Retinoic acid also influences melanocyte differentiation and proliferation in a dose-dependent and temporal manner. Levels of retinoids decline when exposed to ultraviolet irradiation in the skin. Retinal is necessary for the phototransduction cascade that initiates melanogenesis but the source of that retinal is currently unknown. This review discusses new research on retinoids and their effects on the skin and hair.

Anti-fibrotic effect of a selective estrogen receptor modulator in systemic sclerosis

Background

The rarity of systemic sclerosis (SSc) has hampered the development of therapies for this intractable autoimmune disease. Induced pluripotent stem cell (iPSC) can be differentiated into the key disease-affected cells in vitro. The generation of patient-derived iPSCs has opened up possibilities for rare disease modeling. Since these cells can recapitulate the disease phenotypes of the cell in question, they are useful high-throughput platforms for screening for drugs that can reverse these abnormal phenotypes.

Methods

SSc iPSC was generated from PBMC by Sendai virus. Human iPSC lines from SSc patients were differentiated into dermal fibroblasts and keratinocytes. The iPSC-derived differentiated cells from the SSc patients were used on high-throughput platforms to screen for FDA-approved drugs that could be effective treatments for SSc.

Results

Skin organoids were generated from these cells exhibited fibrosis that resembled SSc skin. Screening of the 770-FDA-approved drug library showed that the anti-osteoporotic drug raloxifene reduced SSc iPSC-derived fibroblast proliferation and extracellular matrix production and skin fibrosis in organoids and bleomycin-induced SSc-model mice.

Conclusions

This study reveals that a disease model of systemic sclerosis generated using iPSCs-derived skin organoid is a novel tool for in vitro and in vivo dermatologic research. Since raloxifene and bazedoxifene are well-tolerated anti-osteoporotic drugs, our findings suggest that selective estrogen receptor modulator (SERM)-class drugs could treat SSc fibrosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02987-w.

The combined effects of Map3k1 mutation and dioxin on differentiation of keratinocytes derived from mouse embryonic stem cells

Epithelial development starts with stem cell commitment to ectoderm followed by differentiation to the basal keratinocytes. The basal keratinocytes, first committed in embryogenesis, constitute the basal layer of the epidermis. They have robust proliferation and differentiation potential and are responsible for epidermal expansion, maintenance and regeneration. We generated basal epithelial cells in vitro through differentiation of mouse embryonic stem cells (mESCs). Early on in differentiation, the expression of stem cell markers, Oct4 and Nanog, decreased sharply along with increased ectoderm marker keratin (Krt) 18. Later on, Krt 18 expression was subdued when cells displayed basal keratinocyte characteristics, including regular polygonal shape, adherent and tight junctions and Krt 14 expression. These cells additionally expressed abundant Sca-1, Krt15 and p63, suggesting epidermal progenitor characteristics. Using Map3k1 mutant mESCs and environmental dioxin, we examined the gene and environment effects on differentiation. Neither Map3k1 mutation nor dioxin altered mESC differentiation to ectoderm and basal keratinocytes, but they, individually and in combination, potentiated Krt 1 expression and basal to spinous differentiation. Similar gene-environment effects were observed in vivo where dioxin exposure increased Krt 1 more substantially in the epithelium of Map3k1^+/- than wild type embryos. Thus, the in vitro model of epithelial differentiation can be used to investigate the effects of genetic and environmental factors on epidermal development.

Pluripotent Stem Cell Differentiation Toward Functional Basal Stratified Epithelial Cells

In this chapter, an efficient feeder-free protocol of differentiating human pluripotent stem cells (hPSCs) toward the epidermal lineage to generate induced epidermal keratinocytes (iKCs) is described. The iKCs are able to terminally differentiate supra-basally. This hPSC-to-iKC differentiation can serve as a useful model to study epidermal development and disease as well as for therapeutic applications.

Update on Clinically Relevant Genetic Testing in Pediatric Dermatology

Clinical genetic testing enables the detection of specific gene mutations and variants that predispose individuals and their family members to disease. In recent years, tremendous strides have been made in the variety of clinically useful tests. Targeted testing for specific mutations that cause well-known syndromes enables the efficient diagnosis of genetic diseases with cutaneous manifestations. Testing for specific genes, however, may not always reveal a diagnosis. Expanded options are available. This review outlines the major types of available technology with a focus on those tests most useful for pediatric dermatologists.

3D skin models in domestic animals

The skin is a passive and active barrier which protects the body from the environment. Its health is essential for the accomplishment of this role. Since several decades, the skin has aroused a strong interest in various fields (for e.g. cell biology, medicine, toxicology, cosmetology, and pharmacology). In contrast to other organs, 3D models were mostly and directly elaborated in humans due to its architectural simplicity and easy accessibility. The development of these models benefited from the societal pressure to reduce animal experiments. In this review, we first describe human and mouse skin structure and the major differences with other mammals and birds. Next, we describe the different 3D human skin models and their main applications. Finally, we review the available models for domestic animals and discuss the current and potential applications.

3D Organoid Culture Using Skin Keratinocytes Derived from Human Induced Pluripotent Stem Cells

The keratinocytes are predominant cells in the epidermis of the human skin. To assess the cellular response of the keratinocytes to the genotoxic stress, we derived the skin keratinocytes from human induced pluripotent stem cells (iPSCs). Furthermore, three-dimensional (3D) organoid culture method is powerful tool to analyze the organ and tissue response against the genotoxic stress. Here we describe the method of 3D organoid culture using skin keratinocytes derived from human iPSCs.

Cellular therapy options for genetic skin disorders with a focus on recessive dystrophic epidermolysis bullosa

INTRODUCTION

Combinatorial cell and gene therapies for life-threatening inherited skin disorders have shown tremendous potential for preclinical and clinical implementation with significant progress made for recessive dystrophic epidermolysis bullosa (RDEB). To date, various cell lineages including resident skin cells and adult stem cells have been investigated for gene and cell therapy for RDEB reaching the clinical trial stage.

SOURCES OF DATA

Sources of data are key recent literature, ClinicalTrials.gov, Clinicaltrialsregister.eu and pharma press releases.

AREAS OF AGREEMENT

Cell-based gene transfer using autologous patients' cells has demonstrated positive outcomes in preclinical and clinical trials and highlighted the importance of targeting resident skin stem cells to achieve a meaningful long-term effect. Additionally, adult stem cells, such as mesenchymal stromal cells, have the potential to ameliorate systemic manifestations of the disease.

AREAS OF CONTROVERSY

While proven safe, the clinical trials of localized treatment have reported only modest and transient improvements. On the other hand, the risks associated with systemic therapies remain high and should be carefully weighed against the potential benefits. It is unclear to what extent adult stem cells can contribute to skin regeneration/wound healing.

GROWING POINTS

Further research is warranted in order to fulfil the potential of cellular therapies for RDEB. The development of combinatorial gene and cell-based approaches is required to achieve long-term clinical benefits.

AREAS TIMELY FOR DEVELOPING RESEARCH

Induced pluripotent stem cells can potentially provide a valuable source of autologous patient material for cellular therapies. In addition, recent advances in the field of gene editing can overcome hurdles associated with conventional gene addition approaches.

DATA AVAILABILITY STATEMENT

No new data were generated or analysed in support of this review.

Reprogramming of Keratinocytes as Donor or Target Cells Holds Great Promise for Cell Therapy and Regenerative Medicine

One of the most crucial branches of regenerative medicine is cell therapy, in which cellular material is injected into the patient to initiate the regenerative process. Cells obtained by reprogramming of the patient's own cells offer ethical and clinical advantages could provide a new source of material for therapeutic applications. Studies to date have shown that only a subset of differentiated cell types can be reprogrammed. Among these, keratinocytes, which are the most abundant proliferating cell type in the epidermis, have gained increasing attention as both donor and target cells for reprogramming and have become a new focus of regenerative medicine. As target cells for the treatment of skin defects, keratinocytes can be differentiated or reprogrammed from embryonic stem cells, induced pluripotent stem cells, fibroblasts, adipose tissue stem cells, and mesenchymal cells. As donor cells, keratinocytes can be reprogrammed or direct reprogrammed into a number of cell types, including induced pluripotent stem cells, neural cells, and Schwann cells. In this review, we discuss recent advances in keratinocyte reprogramming, focusing on the induction methods, potential molecular mechanisms, conversion efficiency, and safety for clinical applications. Graphical Abstract KCs as target cells can be reprogrammed or differentiated from fibroblasts, iPSCs, ATSCs, and mesenchymal cells. And as donor cells, KCs can be reprogrammed or directly reprogrammded into iPSCs, neural cells, Schwann cells, and epidermal stem cells.

Bioactive Molecules for Skin Repair and Regeneration: Progress and Perspectives

Skin regeneration is a vexing problem in the field of regenerative medicine. A bioactive molecule-based strategy has been frequently used in skin wound healing in recent years. Bioactive molecules are practical tools for regulating cellular processes and have been applied to control cellular differentiation, dedifferentiation, and reprogramming. In this review, we focus on recent progress in the use of bioactive molecules in skin regenerative medicine, by which desired cell types can be generated in vitro for cell therapy and conventional therapeutics can be developed to repair and regenerate skin in vivo through activation of the endogenous repairing potential. We further prospect that the bioactive molecule-base method might be one of the promising strategies to achieve in situ skin regeneration in the future.

Stem cell therapy for chronic skin wounds in the era of personalized medicine: From bench to bedside

With the significant financial burden of chronic cutaneous wounds on the healthcare system, not to the personal burden mention on those individuals afflicted, it has become increasingly essential to improve our clinical treatments. This requires the translation of the most recent benchtop approaches to clinical wound repair as our current treatment modalities have proven insufficient. The most promising potential treatment options rely on stem cell-based therapies. Stem cell proliferation and signaling play crucial roles in every phase of the wound healing process and chronic wounds are often associated with impaired stem cell function. Clinical approaches involving stem cells could thus be utilized in some cases to improve a body's inhibited healing capacity. We aim to present the laboratory research behind the mechanisms and effects of this technology as well as current clinical trials which showcase their therapeutic potential. Given the current problems and complications presented by chronic wounds, we hope to show that developing the clinical applications of stem cell therapies is the rational next step in improving wound care.

Functional Skin Grafts: Where Biomaterials Meet Stem Cells

Skin tissue engineering has attained several clinical milestones making remarkable progress over the past decades. Skin is inhabited by a plethora of cells spatiotemporally arranged in a 3-dimensional (3D) matrix, creating a complex microenvironment of cell-matrix interactions. This complexity makes it difficult to mimic the native skin structure using conventional tissue engineering approaches. With the advent of newer fabrication strategies, the field is evolving rapidly. However, there is still a long way before an artificial skin substitute can fully mimic the functions and anatomical hierarchy of native human skin. The current focus of skin tissue engineers is primarily to develop a 3D construct that maintains the functionality of cultured cells in a guided manner over a period of time. While several natural and synthetic biopolymers have been translated, only partial clinical success is attained so far. Key challenges include the hierarchical complexity of skin anatomy; compositional mismatch in terms of material properties (stiffness, roughness, wettability) and degradation rate; biological complications like varied cell numbers, cell types, matrix gradients in each layer, varied immune responses, and varied methods of fabrication. In addition, with newer biomaterials being adopted for fabricating patient-specific skin substitutes, issues related to escalating processing costs, scalability, and stability of the constructs under in vivo conditions have raised some concerns. This review provides an overview of the field of skin regenerative medicine, existing clinical therapies, and limitations of the current techniques. We have further elaborated on the upcoming tissue engineering strategies that may serve as promising alternatives for generating functional skin substitutes, the pros and cons associated with each technique, and scope of their translational potential in the treatment of chronic skin ailments.

Advanced drug delivery systems and artificial skin grafts for skin wound healing

Cutaneous injuries, especially chronic wounds, burns, and skin wound infection, require painstakingly long-term treatment with an immense financial burden to healthcare systems worldwide. However, clinical management of chronic wounds remains unsatisfactory in many cases. Various strategies including growth factor and gene delivery as well as cell therapy have been used to enhance the healing of non-healing wounds. Drug delivery systems across the nano, micro, and macroscales can extend half-life, improve bioavailability, optimize pharmacokinetics, and decrease dosing frequency of drugs and genes. Replacement of the damaged skin tissue with substitutes comprising cell-laden scaffold can also restore the barrier and regulatory functions of skin at the wound site. This review covers comprehensively the advanced treatment strategies to improve the quality of wound healing.

Feasibility of repairing full-thickness skin defects by iPSC-derived epithelial stem cells seeded on a human acellular amniotic membrane

Background

Induced pluripotent stem cells (iPSCs) can generate epithelial stem cells (EpSCs) as seed cells for skin substitutes to repair skin defects. Here, we investigated the effects of a human acellular amniotic membrane (hAAM) combined with iPSC-derived CD200⁺/ITGA6⁺ EpSCs as a skin substitute on repairing skin defects in nude mice.

Methods

Human urinary cells isolated from a healthy donor were reprogrammed into iPSCs and then induced into CD200⁺/ITGA6⁺ epithelial stem cells. Immunocytochemistry and RT-PCR were used to examine the characteristics of the induced epithelial stem cells. iPSC-derived EpSCs were cultured on a hAAM, and cytocompatibility of the composite was analyzed by CCK8 assays and scanning electron microscopy. Then, hAAMs combined with iPSC-derived EpSCs were transplanted onto skin defects of mice. The effects of this composite on skin repair were evaluated by immunohistochemistry.

Results

The results showed that CD200⁺/ITGA6⁺ epithelial stem cells induced from iPSCs displayed the phenotypes of hair follicle stem cells. After seeding on the hAAM, iPSC-derived epithelial stem cells had the ability to proliferate. After transplantation, CD200⁺/ITGA6⁺ epithelial stem cells on the hAAM promoted the construction of hair follicles and interfollicular epidermis.

Conclusions

These results indicated that transplantation of a hAAM combined with iPS-derived EpSCs is feasible to reconstruct skin and skin appendages, and may be a substantial reference for iPSC-based therapy for skin defects.

DNA Damage Response After Ionizing Radiation Exposure in Skin Keratinocytes Derived from Human-Induced Pluripotent Stem Cells

PURPOSE

Epidermal cells are positioned on the body surface and thus risk being exposed to genotoxic stress, including ionizing radiation (IR), ultraviolet rays, and chemical compounds. The biological effect of IR on the skin tissue is a significant problem for medical applications such as radiation therapy. Keratinocyte stem cells and progenitors are at risk for IR-dependent tumorigenesis during radiation therapy for cancer treatment. To elucidate the molecular mechanism of genome stability in epidermal cells, we derived skin keratinocytes from human-induced pluripotent stem cells (iPSCs) and analyzed their DNA damage response (DDR).

METHODS AND MATERIALS

Skin keratinocytes were derived from iPSCs and designated as first- (P1), second- (P2), and third- (P3) passage cells to compare the differentiation states of DDR. After 2 Gy gamma-ray exposure, cells were immunostained with DNA double-strand break markers γ-H2AX/53BP1 and cell senescence markers p16/p21 for DDR analysis. DDR protein expression level, cell survival, and apoptosis were analyzed by western blotting, WST-8 assay and TUNEL assay, respectively. DDR of constructed 3D organoid modeling was also analyzed.

RESULTS

P1, P2, and P3 keratinocytes were characterized with keratinocyte markers keratin 14 and p63 using immunofluorescence, and all cells were positive to both markers. Derived keratinocytes showed high expression of integrin α6 and CD71 (real-time (qRT)-PCR ratio: iPSCs: integrin α6: 1.12, CD71: 1.25, P1: integrin α6: 7.80, CD71: 0.43, P2: integrin α6: 5.53, CD71: 0.48), suggesting that P1 and P2 keratinocytes have potential as keratinocyte progenitors. Meanwhile, P3 keratinocytes showed low expression of integrin α6 and CD71 (qRT-PCR ratio: P3: integrin α6: 0.55, CD71: 0.10), suggesting differentiated keratinocytes. After IR exposure, the P1 and P2 keratinocytes showed an increase in DNA repair activity by a γ-H2AX/53BP1 focus assay (P1: γ-H2AX: 28.0%, 53BP1: 17.0%, P2: γ-H2AX: 37.7%, 53BP1: 28.3%) but not in P3 keratinocytes (P3: γ-H2AX: 74.7%, 53BP1: 63.7%) compared with iPSCs (γ-H2AX: 57.0%, 53BP1: 55.0%). Furthermore, in derived keratinocytes, expression of the cellular senescence markers p16 and p21 were increased compared with iPSCs (P16: non irradiated, iPSCs: 0%, P1: 12.5%, P2: 14.5%, P3: 29.7%, IR, iPSCs: 0%, P1: 19.5%, P2: 34.8%, P3: 64.5%). DDR protein expression, cellular sensitivity, and apoptosis activity decreased in derived keratinocytes compared with iPSCs.

CONCLUSIONS

We have demonstrated the derivation of keratinocytes from iPSCs and their characterization of differentiated states and DDR. Derived keratinocytes showed progenitors like character as a result of DDR. These results suggest that derived keratinocytes are useful tools for analyzing the effects of IR, such as DDR on the skin tissue from radiation therapy for cancer.

Skin tissue engineering: wound healing based on stem-cell-based therapeutic strategies

Normal wound healing is a dynamic and complex multiple phase process involving coordinated interactions between growth factors, cytokines, chemokines, and various cells. Any failure in these phases may lead wounds to become chronic and have abnormal scar formation. Chronic wounds affect patients' quality of life, since they require repetitive treatments and incur considerable medical costs. Thus, much effort has been focused on developing novel therapeutic approaches for wound treatment. Stem-cell-based therapeutic strategies have been proposed to treat these wounds. They have shown considerable potential for improving the rate and quality of wound healing and regenerating the skin. However, there are many challenges for using stem cells in skin regeneration. In this review, we present some sets of the data published on using embryonic stem cells, induced pluripotent stem cells, and adult stem cells in healing wounds. Additionally, we will discuss the different angles whereby these cells can contribute to their unique features and show the current drawbacks.

Skin tissue regeneration for burn injury

The skin is the largest organ of the body, which meets the environment most directly. Thus, the skin is vulnerable to various damages, particularly burn injury. Skin wound healing is a serious interaction between cell types, cytokines, mediators, the neurovascular system, and matrix remodeling. Tissue regeneration technology remarkably enhances skin repair via re-epidermalization, epidermal-stromal cell interactions, angiogenesis, and inhabitation of hypertrophic scars and keloids. The success rates of skin healing for burn injuries have significantly increased with the use of various skin substitutes. In this review, we discuss skin replacement with cells, growth factors, scaffolds, or cell-seeded scaffolds for skin tissue reconstruction and also compare the high efficacy and cost-effectiveness of each therapy. We describe the essentials, achievements, and challenges of cell-based therapy in reducing scar formation and improving burn injury treatment.

Endowing iPSC-Derived MSCs with Angiogenic and Keratinogenic Differentiation Potential: A Promising Cell Source for Skin Tissue Engineering

Induced pluripotent stem cells (iPSC) hold tremendous potential for personalized cell-based therapy for skin regeneration. Aiming to establish human iPSCs as a potential cell source for skin tissue engineering, we expect to obtain an epidermal-like cell line with angiogenic and keratinogenic differentiation potential via inducing iPSC-derived mesenchymal stem cells (iPSC-MSCs) with basic fibroblast growth factor (bFGF) and/or keratinocyte growth factor (KGF). The results show that iPSC-MSCs were successfully induced with a positive FGFR/KGFR expression on the cell surface. BFGF/KGF induction could significantly increase the expression of vascularization marker CD31 and keratinization marker CK10, respectively, while when combined together, although CD31 and CK10 were still positively expressed, their expressions were lower than that of the single induction group, suggesting that the effects of the two growth factors interfered with each other. This cell line with angiogenic and keratinogenic differentiation potential provides a promising new source of cells for the construction of well vascularized and keratinized tissue engineered skin, furthermore establishing an effective strategy for iPSC-based therapy in skin tissue engineering.

Establishment of a complex skin structure via layered co-culture of keratinocytes and fibroblasts derived from induced pluripotent stem cells

Background

Skin is an organ that plays an important role as a physical barrier and has many other complex functions. Skin mimetics may be useful for studying the pathophysiology of diseases in vitro and for repairing lesions in vivo. Cord blood mononuclear cells (CBMCs) have emerged as a potential cell source for regenerative medicine. Human induced pluripotent stem cells (iPSCs) derived from CBMCs have great potential for allogenic regenerative medicine. Further study is needed on skin differentiation using CBMC-iPSCs.

Methods

Human iPSCs were generated from CBMCs by Sendai virus. CBMC-iPSCs were differentiated to fibroblasts and keratinocytes using embryonic body formation. To generate CBMC-iPSC-derived 3D skin organoid, CBMC-iPSC-derived fibroblasts were added into the insert of a Transwell plate and CBMC-iPSC-derived keratinocytes were seeded onto the fibroblast layer. Transplantation of 3D skin organoid was performed by the tie-over dressing method.

Results

Epidermal and dermal layers were developed using keratinocytes and fibroblasts differentiated from cord blood-derived human iPSCs, respectively. A complex 3D skin organoid was generated by overlaying the epidermal layer onto the dermal layer. A humanized skin model was generated by transplanting this human skin organoid into SCID mice and effectively healed skin lesions.

Conclusions

This study reveals that a human skin organoid generated using CBMC iPSCs is a novel tool for in-vitro and in-vivo dermatologic research.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0958-2) contains supplementary material, which is available to authorized users.

Bilayer Amniotic Membrane/Nano-fibrous Fibroin Scaffold Promotes Differentiation Capability of Menstrual Blood Stem Cells into Keratinocyte-Like Cells

The skin provides a dynamic barrier separating and protecting human body from the exterior world, and then immediate repair and rebuilding of the epidermal barrier is crucial after wound and injury. Wound healing without scars and complete regeneration of skin tissue still remain as a clinical challenge. The demand to engineer scaffolds that actively promote regeneration of damaged areas of the skin has been increased. In this study, menstrual blood-derived stem cells (MenSCs) have been induced to differentiate into keratinocytes-like cells in the presence of human foreskin-derived keratinocytes on a bilayer scaffold based on amniotic membrane and silk fibroin. Based on the findings, newly differentiated keratinocytes from MenSCs successfully expressed the keratinocytes specific markers at both mRNA and protein levels judged by real-time PCR and immunostaining techniques, respectively. We could show that the differentiated cells over bilayer composite scaffolds express the keratinocytes specific markers at higher levels when compared with those cultured in conventional 2D culture system. Based on these findings, bilayer amniotic membrane/nano-fibrous fibroin scaffold represents an efficient natural construct with broad applicability to generate keratinocytes from MenSCs for stem cell-based skin wounds healing and regeneration.

Cell therapy for severe burn wound healing

Cell therapy has emerged as an important component of life-saving procedures in treating burns. Over past decades, advances in stem cells and regenerative medicine have offered exciting opportunities of developing cell-based alternatives and demonstrated the potential and feasibility of various stem cells for burn wound healing. However, there are still scientific and technical issues that should be resolved to facilitate the full potential of the cellular devices. More evidence from large, randomly controlled trials is also needed to understand the clinical impact of cell therapy in burns. This article aims to provide an up-to-date review of the research development and clinical applications of cell therapies in burn wound healing and skin regeneration.

Master regulatory role of p63 in epidermal development and disease

The transcription factor p63 is a master regulator of epidermal development. Mutations in p63 give rise to human developmental diseases that often manifest epidermal defects. In this review, we summarize major p63 isoforms identified so far and p63 mutation-associated human diseases that show epidermal defects. We discuss key roles of p63 in epidermal keratinocyte proliferation and differentiation, emphasizing its master regulatory control of the gene expression pattern and epigenetic landscape that define epidermal fate. We subsequently review the essential function of p63 during epidermal commitment and transdifferentiation towards epithelial lineages, highlighting the notion that p63 is the guardian of the epithelial lineage. Finally, we discuss current therapeutic development strategies for p63 mutation-associated diseases. Our review proposes future directions for dissecting p63-controlled mechanisms in normal and diseased epidermal development and for developing therapeutic options.

Fetal Therapy Model of Myelomeningocele with Three-Dimensional Skin Using Amniotic Fluid Cell-Derived Induced Pluripotent Stem Cells

Myelomeningocele (MMC) is a congenital disease without genetic abnormalities. Neurological symptoms are irreversibly impaired after birth, and no effective treatment has been reported to date. Only surgical repairs have been reported so far. In this study, we performed antenatal treatment of MMC with an artificial skin using induced pluripotent stem cells (iPSCs) generated from a patient with Down syndrome (AF-T21-iPSCs) and twin-twin transfusion syndrome (AF-TTTS-iPSCs) to a rat model. We manufactured three-dimensional skin with epidermis generated from keratinocytes derived from AF-T21-iPSCs and AF-TTTS-iPSCs and dermis of human fibroblasts and collagen type I. For generation of epidermis, we developed a protocol using Y-27632 and epidermal growth factor. The artificial skin was successfully covered over MMC defect sites during pregnancy, implying a possible antenatal surgical treatment with iPSC technology.

Organ-On-A-Chip Platforms: A Convergence of Advanced Materials, Cells, and Microscale Technologies

Significant advances in biomaterials, stem cell biology, and microscale technologies have enabled the fabrication of biologically relevant tissues and organs. Such tissues and organs, referred to as organ-on-a-chip (OOC) platforms, have emerged as a powerful tool in tissue analysis and disease modeling for biological and pharmacological applications. A variety of biomaterials are used in tissue fabrication providing multiple biological, structural, and mechanical cues in the regulation of cell behavior and tissue morphogenesis. Cells derived from humans enable the fabrication of personalized OOC platforms. Microscale technologies are specifically helpful in providing physiological microenvironments for tissues and organs. In this review, biomaterials, cells, and microscale technologies are described as essential components to construct OOC platforms. The latest developments in OOC platforms (e.g., liver, skeletal muscle, cardiac, cancer, lung, skin, bone, and brain) are then discussed as functional tools in simulating human physiology and metabolism. Future perspectives and major challenges in the development of OOC platforms toward accelerating clinical studies of drug discovery are finally highlighted.

Towards topical microRNA-directed therapy for epidermal disorders

There remains an unmet dermatological need for innovative topical agents that achieve better longterm outcomes with fewer side effects. Modulation of the expression and activity of microRNA (miRNAs) represents an emerging translational framework for the development of such innovative therapies because changes in the expression of one miRNA can have wide-ranging effects on diverse cellular processes associated with disease. In this short review, the roles of miRNA in epidermal development, psoriasis, cutaneous squamous cell carcinoma and re-epithelisation are highlighted. Consideration is given to the delivery of oligonucleotides that mimic or inhibit miRNA function using vehicles such as cell penetrating peptides, spherical nucleic acids, deformable liposomes and liquid crystalline nanodispersions. Formulation of miRNA-directed oligonucleotides with such skin-penetrating epidermal agents will drive the development of RNA-based cutaneous therapeutics for deployment as primary or adjuvant therapies for epidermal disorders.

Current and Future Perspectives of Stem Cell Therapy in Dermatology

Stem cells are undifferentiated cells capable of generating, sustaining, and replacing terminally differentiated cells and tissues. They can be isolated from embryonic as well as almost all adult tissues including skin, but are also generated through genetic reprogramming of differentiated cells. Preclinical and clinical research has recently tremendously improved stem cell therapy, being a promising treatment option for various diseases in which current medical therapies fail to cure, prevent progression or relieve symptoms. With the main goal of regeneration or sustained genetic correction of damaged tissue, advanced tissue-engineering techniques are especially applicable for many dermatological diseases including wound healing, genodermatoses (like the severe blistering disorder epidermolysis bullosa) and chronic (auto-)inflammatory diseases. This review summarizes general aspects as well as current and future perspectives of stem cell therapy in dermatology.

Advances of Stem Cell Therapeutics in Cutaneous Wound Healing and Regeneration

Cutaneous wound healing is a complex multiple phase process, which overlaps each other, where several growth factors, cytokines, chemokines, and various cells interact in a well-orchestrated manner. However, an imbalance in any of these phases and factors may lead to disruption in harmony of normal wound healing process, resulting in transformation towards chronic nonhealing wounds and abnormal scar formation. Although various therapeutic interventions are available to treat chronic wounds, current wound-care has met with limited success. Progenitor stem cells possess potential therapeutic ability to overcome limitations of the present treatments as it offers accelerated wound repair with tissue regeneration. A substantial number of stem cell therapies for cutaneous wounds are currently under development as a result of encouraging preliminary findings in both preclinical and clinical studies. However, the mechanisms by which these stem cells contribute to the healing process have yet to be elucidated. In this review, we emphasize on the major treatment modalities currently available for the treatment of the wound, role of various interstitial stem cells and exogenous adult stem cells in cutaneous wound healing, and possible mechanisms involved in the healing process.

Generation of iPS-derived model cells for analyses of hair shaft differentiation

Biological evaluation of hair growth/differentiation activity in vitro has been a formidable challenge, primarily due to the lack of relevant model cell systems. To solve this problem, we generated a stable model cell line in which successive differentiation via epidermal progenitors to hair components is easily inducible and traceable. Mouse induced pluripotent stem (iPS) cell–derived cells were selected to stably express a tetracycline (Tet)-inducible bone morphogenic protein-4 (BMP4) expression cassette and a luciferase reporter driven by a hair-specific keratin 31 gene (krt31) promoter (Tet-BMP4-KRT31-Luc iPS). While Tet- BMP4-KRT31-Luc iPS cells could be maintained as stable iPS cells, the cells differentiated to produce luciferase luminescence in the presence of all-trans retinoic acid (RA) and doxycycline (Dox), and addition of a hair differentiation factor significantly increased luciferase fluorescence. Thus, this cell line may provide a reliable cell-based screening system to evaluate drug candidates for hair differentiation activity.

In vitro differentiation of menstrual blood stem cells into keratinocytes: A potential approach for management of wound healing

The skin wounds caused by insults should be treated immediately to restore the functions and integrity. Recent studies suggest that stem cells-based therapies may be applicable in wound healing. Newly defined menstrual blood-derived stem cells (MenSCs) show high rate of cell proliferation and trans-differentiation potency to various cell types. However, MenSCs potential to generate keratinocyte for future therapeutic use of skin lesions has been remained to investigate. We cultivated MenSCs in the presence of isolated foreskin derived-keratinocytes using an indirect co-culture system and evaluated efficiency of this protocol to generate keratinocytes using immunofluorescent staining and Real Time PCR technique. Our results showed that differentiated keratinocytes express epidermal/keratinocytes lineage specific markers such as K14, p63, and involucrin at both mRNA and protein levels. Immunofluorescent staining showed the expression of involucrin and K14 in differentiated cells in contrast to undifferentiated cells. Moreover, mRNA expression levels of K14 (11.1 folds, p = 0.001), p63 (10.23 folds, p = 0.001), and involucrin (2.94 folds, p = 0.001) were higher in differentiated MenSCs compared to non-cocultured cells. Therefore, we firstly presented evidence about differentiation capability of MenSCs into epidermal/keratinocytes lineage. Considering the advantages of MenSCs such as great accessibility, these stem cells are promising for stem cells-based therapies of skin defects.

Novel and emerging therapies in the treatment of recessive dystrophic epidermolysis bullosa

Epidermolysis bullosa (EB) is a clinically and genetically heterogeneous group of inherited blistering diseases that affects ∼ 500,000 people worldwide. Clinically, individuals with EB have fragile skin and are susceptible to blistering following minimal trauma, with mucous membrane and other organ involvement in some subtypes. Within the spectrum of EB, ∼ 5% of affected individuals have the clinically more severe recessive dystrophic (RDEB) variant with a prevalence of 8 per one million of the population. RDEB is caused by loss-of-function mutations in the type VII collagen gene, COL7A1, which leads to reduced or absent type VII collagen (C7) and a paucity of structurally effective anchoring fibrils at the dermal-epidermal junction (DEJ). Currently, there is no cure for RDEB, although considerable progress has been made in testing novel treatments including gene therapy (lentiviral and gamma retroviral vectors for COL7A1 supplementation in keratinocytes and fibroblasts), as well as cell therapy (use of allogeneic fibroblasts, mesenchymal stromal cells (MSCs), and bone marrow transplantation (BMT)). Here, we review current treatment modalities available as well as novel and emerging therapies in the treatment of RDEB. Clinical trials of new translational therapies in RDEB offer hope for improved clinical management of patients as well as generating broader lessons for regenerative medicine that could be applicable to other inherited or acquired abnormalities of wound healing or scarring.

Skin Diseases Modeling using Combined Tissue Engineering and Microfluidic Technologies

In recent years, both tissue engineering and microfluidics have significantly contributed in engineering of in vitro skin substitutes to test the penetration of chemicals or to replace damaged skins. Organ-on-chip platforms have been recently inspired by the integration of microfluidics and biomaterials in order to develop physiologically relevant disease models. However, the application of organ-on-chip on the development of skin disease models is still limited and needs to be further developed. The impact of tissue engineering, biomaterials and microfluidic platforms on the development of skin grafts and biomimetic in vitro skin models is reviewed. The integration of tissue engineering and microfluidics for the development of biomimetic skin-on-chip platforms is further discussed, not only to improve the performance of present skin models, but also for the development of novel skin disease platforms for drug screening processes.

Direct conversion of mouse embryonic fibroblasts into functional keratinocytes through transient expression of pluripotency-related genes

The insufficient ability of specialized cells such as neurons, cardiac myocytes, and epidermal cells to regenerate after tissue damage poses a great challenge to treat devastating injuries and ailments. Recent studies demonstrated that a diverse array of cell types can be directly derived from embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), or somatic cells by combinations of specific factors. The use of iPSCs and direct somatic cell fate conversion, or transdifferentiation, holds great promise for regenerative medicine as these techniques may circumvent obstacles related to immunological rejection and ethical considerations. However, producing iPSC-derived keratinocytes requires a lengthy two-step process of initially generating iPSCs and subsequently differentiating into skin cells, thereby elevating the risk of cellular damage accumulation and tumor formation. In this study, we describe the reprogramming of mouse embryonic fibroblasts into functional keratinocytes via the transient expression of pluripotency factors coupled with directed differentiation. The isolation of an iPSC intermediate is dispensable when using this method. Cells derived with this approach, termed induced keratinocytes (iKCs), morphologically resemble primary keratinocytes. Furthermore they express keratinocyte-specific markers, downregulate mesenchymal markers as well as the pluripotency factors Oct4, Sox2, and Klf4, and they show important functional characteristics of primary keratinocytes. iKCs can be further differentiated by high calcium administration in vitro and are capable of regenerating a fully stratified epidermis in vivo. Efficient conversion of somatic cells into keratinocytes could have important implications for studying genetic skin diseases and designing regenerative therapies to ameliorate devastating skin conditions.

Generation of folliculogenic human epithelial stem cells from induced pluripotent stem cells

Epithelial stem cells (EpSCs) in the hair follicle bulge are required for hair follicle growth and cycling. The isolation and propagation of human EpSCs for tissue engineering purposes remains a challenge. Here we develop a strategy to differentiate human iPSCs (hiPSCs) into CD200⁺/ITGA6⁺ EpSCs that can reconstitute the epithelial components of the hair follicle and interfollicular epidermis. The hiPSC-derived CD200⁺/ITGA6⁺ cells show a similar gene expression signature as EpSCs directly isolated from human hair follicles. Human iPSC-derived CD200⁺/ITGA6⁺ cells are capable of generating all hair follicle lineages including the hair shaft, and the inner and outer root sheaths in skin reconstitution assays. The regenerated hair follicles possess a KRT15⁺ stem cell population and produce hair shafts expressing hair specific keratins. These results suggest an approach for generating large numbers of human EpSCs for tissue engineering and new treatments for hair loss, wound healing and other degenerative skin disorders.

Progress in corneal wound healing

Corneal wound healing is a complex process involving cell death, migration, proliferation, differentiation, and extracellular matrix remodeling. Many similarities are observed in the healing processes of corneal epithelial, stromal and endothelial cells, as well as cell-specific differences. Corneal epithelial healing largely depends on limbal stem cells and remodeling of the basement membrane. During stromal healing, keratocytes get transformed to motile and contractile myofibroblasts largely due to activation of transforming growth factor-β (TGF-β) system. Endothelial cells heal mostly by migration and spreading, with cell proliferation playing a secondary role. In the last decade, many aspects of wound healing process in different parts of the cornea have been elucidated, and some new therapeutic approaches have emerged. The concept of limbal stem cells received rigorous experimental corroboration, with new markers uncovered and new treatment options including gene and microRNA therapy tested in experimental systems. Transplantation of limbal stem cell-enriched cultures for efficient re-epithelialization in stem cell deficiency and corneal injuries has become reality in clinical setting. Mediators and course of events during stromal healing have been detailed, and new treatment regimens including gene (decorin) and stem cell therapy for excessive healing have been designed. This is a very important advance given the popularity of various refractive surgeries entailing stromal wound healing. Successful surgical ways of replacing the diseased endothelium have been clinically tested, and new approaches to accelerate endothelial healing and suppress endothelial-mesenchymal transformation have been proposed including Rho kinase (ROCK) inhibitor eye drops and gene therapy to activate TGF-β inhibitor SMAD7. Promising new technologies with potential for corneal wound healing manipulation including microRNA, induced pluripotent stem cells to generate corneal epithelium, and nanocarriers for corneal drug delivery are discussed. Attention is also paid to problems in wound healing understanding and treatment, such as lack of specific epithelial stem cell markers, reliable identification of stem cells, efficient prevention of haze and stromal scar formation, lack of data on wound regulating microRNAs in keratocytes and endothelial cells, as well as virtual lack of targeted systems for drug and gene delivery to select corneal cells.

Differentiation of equine induced pluripotent stem cells into a keratinocyte lineage

REASONS FOR PERFORMING STUDY

Skin trauma in horses often leads to the development of chronic nonhealing wounds that lack a keratinocyte cover, vital for healing. Reports in mouse and man confirm the possibility of generating functional keratinocytes from induced pluripotent stem cells (iPSC), thus presenting myriad potential applications for wound management or treatment of skin disease. Similarly, differentiation of equine iPSC (eiPSC) into a keratinocyte lineage should provide opportunities for the advancement of veterinary regenerative medicine.

OBJECTIVES

The purpose of this study was to develop an efficient method for the differentiation of eiPSC into a keratinocyte lineage. It was hypothesised that eiPSC can form differentiated keratinocytes (eiPSC-KC) comparable with primary equine keratinocytes (PEK) in their morphological and functional characteristics.

STUDY DESIGN

Experimental in vitro study.

METHODS

Equine iPSC established using a nonviral system were treated for 30 days with retinoic acid and bone morphogenetic protein-4 to induce directed differentiation into iPSC-KC. Temporospatial gene and protein expression by eiPSC-KC was measured at weekly intervals of differentiation and in response to calcium switch. Proliferative and migratory capacities of eiPSC-KC were compared with those of PEK.

RESULTS

Equine iPSC, upon directed differentiation, showed loss of pluripotency genes and progressive increase in pancytokeratin expression indicating ectodermal specification into keratinocytes. High differentiation efficiency was achieved, with 82.5% of eiPSC expressing keratin 14, a marker of epidermal-specific basal stem cells, after 30 days of directed differentiation. Moreover, the proliferative capacity of eiPSC-KC was superior, while the migratory capacity (measured as the ability to epithelise in vitro wounds) was comparable with that of PEK.

CONCLUSIONS

This proof of concept study suggests that eiPSC can successfully be differentiated into equine keratinocytes (eiPSC-KC) with features that are promising to the development of a stem cell-based skin construct, with the potential to regenerate lost or damaged skin.

Transcriptional profiling of ectoderm specification to keratinocyte fate in human embryonic stem cells

In recent years, several studies have shed light into the processes that regulate epidermal specification and homeostasis. We previously showed that a broad-spectrum γ-secretase inhibitor DAPT promoted early keratinocyte specification in human embryonic stem cells triggered to undergo ectoderm specification. Here, we show that DAPT accelerates human embryonic stem cell differentiation and induces expression of the ectoderm protein AP2. Furthermore, we utilize RNA sequencing to identify several candidate regulators of ectoderm specification including those involved in epithelial and epidermal development in human embryonic stem cells. Genes associated with transcriptional regulation and growth factor activity are significantly enriched upon DAPT treatment during specification of human embryonic stem cells to the ectoderm lineage. The human ectoderm cell signature identified in this study contains several genes expressed in ectodermal and epithelial tissues. Importantly, these genes are also associated with skin disorders and ectodermal defects, providing a platform for understanding the biology of human epidermal keratinocyte development under diseased and homeostatic conditions.

Transdifferentiation of Umbilical Cord–Derived Mesenchymal Stem Cells Into Epidermal-Like Cells by the Mimicking Skin Microenvironment

Human umbilical cord–derived mesenchymal stem cells (UC-MSCs) are multipotent, primitive, and have been widely used for skin tissue engineering. Their transdifferentiation is determined by the local microenvironment. In this study, we investigated the potential epidermal differentiation of UC-MSCs and the formation of epidermis substitutes in a 3-dimensional (3D) microenvironment, which was fabricated by UC-MSCs embedded into collagen–chitosan scaffolds (CCSs) combined with an air–liquid interface (ALI) culture system. Using fluorescence microscope, we observed that UC-MSCs were spindle-shaped and evenly distributed in the scaffold. Methyl thiazolyl blue tetrazolium bromide assay and Live/Dead assay indicated that the CCSs have good biocompatibility with UC-MSCs. Immunohistochemistry and western blotting assay showed that UC-MSCs on the surface of the CCSs were positive for the epidermal markers cytokeratin 19 and involucrin at 14 days. In addition, hematoxylin–eosin staining indicated that multilayered epidermis substitutes were established. The constructed epidermis substitutes were applied to treat full-thickness wounds in rats and proved to promote wound healing. In conclusion, manipulating the 3D microenvironment is a novel method for inducing the epidermal differentiation of MSCs to engineer epidermal substitutes, which provides an alternative strategy for skin tissue engineering.