Emerging interactions between skin stem cells and their niches

Improving dermal fibroblast-to-epidermis communications and aging wound repair through extracellular vesicle-mediated delivery of Gstm2 mRNA

Skin aging is characterized by the disruption of skin homeostasis and impaired skin injury repair. Treatment of aging skin has long been limited by the unclear intervention targets and delivery techniques. Engineering extracellular vesicles (EVs) as an upgraded version of natural EVs holds great potential in regenerative medicine. In this study, we found that the expression of the critical antioxidant and detoxification gene Gstm2 was significantly reduced in aging skin. Thus, we constructed the skin primary fibroblasts-derived EVs encapsulating Gstm2 mRNA (EVsGstm2), and found that EVsGstm2 could significantly improve skin homeostasis and accelerate wound healing in aged mice. Mechanistically, we found that EVsGstm2 alleviated oxidative stress damage of aging dermal fibroblasts by modulating mitochondrial oxidative phosphorylation, and promoted dermal fibroblasts to regulate skin epidermal cell function by paracrine secretion of Nascent Polypeptide-Associated Complex Alpha subunit (NACA). Furthermore, we confirmed that NACA is a novel skin epidermal cell protective molecule that regulates skin epidermal cell turnover through the ROS-ERK-ETS-Cyclin D pathway. Our findings demonstrate the feasibility and efficacy of EVs-mediated delivery of Gstm2 for aged skin treatment and unveil novel roles of GSTM2 and NACA for improving aging skin.

A new G3BP1-GFP reporter system for assessing skin toxicity by real-time monitoring of stress granules in vitro

The skin, the organ with the largest surface area in the body, is the most susceptible to chemical exposure from the external environment. In this study, we aimed to establish an in vitro skin toxicity monitoring system that utilizes the mechanism of stress granule (SG) formation induced by various cellular stresses. In HaCaT cells, a keratinocyte cell line that comprises the human skin, a green fluorescent protein (GFP) was knocked in at the C-terminal genomic locus of Ras GTPase-activating protein-binding protein 1 (G3BP1), a representative component of SGs. The G3BP1-GFP knock-in HaCaT cells and wild-type (WT) HaCaT cells formed SGs containing G3BP1-GFP upon exposure to arsenite and household chemicals, such as bisphenol A (BPA) and benzalkonium chloride (BAC), in real-time. In addition, the exposure of G3BP1-GFP knock-in HaCaT cells to BPA and BAC promoted the phosphorylation of eukaryotic initiation factor 2 alpha and protein kinase R-like endoplasmic reticulum kinase, which are cell signaling factors involved in SG formation, similar to WT HaCaT cells. In conclusion, this novel G3BP1-GFP knock-in human skin cell system can monitor SG formation in real-time and be utilized to assess skin toxicity to various substances.

Role of umbilical cord mesenchymal stromal cells in skin rejuvenation

Aging is the main cause of many degenerative diseases. The skin is the largest and the most intuitive organ that reflects the aging of the body. Under the interaction of endogenous and exogenous factors, there are cumulative changes in the structure, function, and appearance of the skin, which are characterized by decreased synthesis of collagen and elastin, increased wrinkles, relaxation, pigmentation, and other aging characteristics. skin aging is inevitable, but it can be delayed. The successful isolation of mesenchymal stromal cells (MSC) in 1991 has greatly promoted the progress of cell therapy in human diseases. The International Society for Cellular Therapy (ISCT) points out that the MSC is a kind of pluripotent progenitor cells that have self-renewal ability (limited) in vitro and the potential for mesenchymal cell differentiation. This review mainly introduces the role of perinatal umbilical cord-derived MSC(UC-MSC) in the field of skin rejuvenation. An in-depth and systematic understanding of the mechanism of UC-MSCs against skin aging is of great significance for the early realization of the clinical transformation of UC-MSCs. This paper summarized the characteristics of skin aging and summarized the mechanism of UC-MSCs in skin rejuvenation reported in recent years. In order to provide a reference for further research of UC-MSCs to delay skin aging.

Split-Thickness Skin and Dermal Pixel Grafts Can Be Expanded up to 500 Times to Re-Epithelialize a Full-Thickness Burn Wound

Objective: Autologous skin transplantation is limited by donor site availability for patients with extensive burns. The objective of this study was to demonstrate the feasibility and efficacy of split-thickness skin (STS) and dermal pixel grafts (PG) in the treatment of burns. Approach: The study was divided into three arms of validation, expansion, and combination that all followed the same study design. Sixteen deep partial-thickness burns were created on the dorsum of anesthetized pigs. Three days postinjury the burns were debrided and grafted with STS and dermal PGs. The PGs were prepared by harvesting two skin grafts (split-thickness skin graft [STSG] and dermal graft) from the same donor site going down in depth. The grafts were minced to 0.3 × 0.3 × 0.3 mm PGs and suspended in a small volume of hydrogel. Healing was monitored for 6, 10, 14, or 28 days. In the validation study the PGs at 1:2 expansion ratio were transplanted and compared with STSG and untreated controls. The expansion study investigated the maximum expansion potential of the PGs and the combination of the benefits of transplanting STS and dermal PGs together. Results: The validation study showed that when STS and dermal PGs were transplanted in a 1:2 ratio they fully re-epithelialized the wounds in 14 days. The expansion study demonstrated that using expansion ratios up to 1:500 the wounds were re-epithelialized by day 28. The combination study showed that there was no additional benefit to use STS and dermal PGs together. Innovation: Pixel grafting provides expansion ratios greater than conventional STSG. The possibility to harvest both STS and dermal PGs from the same donor area further reduces the need for healthy skin. Conclusion: STSG and dermal grafts can be minced to PGs with preserved viability and expanded up to 500 times to re-epithelialize a wound.

Vitamin A resolves lineage plasticity to orchestrate stem cell lineage choices

Lineage plasticity-a state of dual fate expression-is required to release stem cells from their niche constraints and redirect them to tissue compartments where they are most needed. In this work, we found that without resolving lineage plasticity, skin stem cells cannot effectively generate each lineage in vitro nor regrow hair and repair wounded epidermis in vivo. A small-molecule screen unearthed retinoic acid as a critical regulator. Combining high-throughput approaches, cell culture, and in vivo mouse genetics, we dissected its roles in tissue regeneration. We found that retinoic acid is made locally in hair follicle stem cell niches, where its levels determine identity and usage. Our findings have therapeutic implications for hair growth as well as chronic wounds and cancers, where lineage plasticity is unresolved.

Epithelial stem cells and niches in lung alveolar regeneration and diseases

Alveoli serve as the functional units of the lungs, responsible for the critical task of blood-gas exchange. Comprising type I (AT1) and type II (AT2) cells, the alveolar epithelium is continuously subject to external aggressors like pathogens and airborne particles. As such, preserving lung function requires both the homeostatic renewal and reparative regeneration of this epithelial layer. Dysfunctions in these processes contribute to various lung diseases. Recent research has pinpointed specific cell subgroups that act as potential stem or progenitor cells for the alveolar epithelium during both homeostasis and regeneration. Additionally, endothelial cells, fibroblasts, and immune cells synergistically establish a nurturing microenvironment-or "niche"-that modulates these epithelial stem cells. This review aims to consolidate the latest findings on the identities of these stem cells and the components of their niche, as well as the molecular mechanisms that govern them. Additionally, this article highlights diseases that arise due to perturbations in stem cell-niche interactions. We also discuss recent technical innovations that have catalyzed these discoveries. Specifically, this review underscores the heterogeneity, plasticity, and dynamic regulation of these stem cell-niche systems. It is our aspiration that a deeper understanding of the fundamental cellular and molecular mechanisms underlying alveolar homeostasis and regeneration will open avenues for identifying novel therapeutic targets for conditions such as chronic obstructive pulmonary disease (COPD), fibrosis, coronavirus disease 2019 (COVID-19), and lung cancer.

Recent progress in hair follicle stem cell markers and their regulatory roles

Hair follicle stem cells (HFSCs) in the bulge are a multipotent adult stem cell population. They can periodically give rise to new HFs and even regenerate the epidermis and sebaceous glands during wound healing. An increasing number of biomarkers have been used to isolate, label, and trace HFSCs in recent years. Considering more detailed data from single-cell transcriptomics technology, we mainly focus on the important HFSC molecular markers and their regulatory roles in this review.

Hair follicle stem cells promote epidermal regeneration under expanded condition

Skin soft tissue expansion is the process of obtaining excess skin mixed with skin development, wound healing, and mechanical stretching. Previous studies have reported that tissue expansion significantly induces epidermal proliferation throughout the skin. However, the mechanisms underlying epidermal regeneration during skin soft tissue expansion are yet to be clarified. Hair follicle stem cells (HFSCs) have been recognized as a promising approach for epidermal regeneration. This study examines HFSC-related epidermal regeneration mechanisms under expanded condition and proposes a potential method for its cellular and molecular regulation.

Cellular senescence and wound healing in aged and diabetic skin

Cellular senescence is a biological mechanism that prevents abnormal cell proliferation during tissue repair, and it is often accompanied by the secretion of various factors, such as cytokines and chemokines, known as the senescence-associated secretory phenotype (SASP). SASP-mediated cell-to-cell communication promotes tissue repair, regeneration, and development. However, senescent cells can accumulate abnormally at injury sites, leading to excessive inflammation, tissue dysfunction, and intractable wounds. The effects of cellular senescence on skin wound healing can be both beneficial and detrimental, depending on the condition. Here, we reviewed the functional differences in cellular senescence that emerge during wound healing, chronic inflammation, and skin aging. We also review the latest mechanisms of wound healing in the epidermis, dermis, and subcutaneous fat, with a focus on cellular senescence, chronic inflammation, and tissue regeneration. Finally, we discuss the potential clinical applications of promoting and inhibiting cellular senescence to maximize benefits and minimize detrimental effects.

Deciphering the molecular mechanisms of stem cell dynamics in hair follicle regeneration

Hair follicles, which are connected to sebaceous glands in the skin, undergo cyclic periods of regeneration, degeneration, and rest throughout adult life in mammals. The crucial function of hair follicle stem cells is to maintain these hair growth cycles. Another vital aspect is the activity of melanocyte stem cells, which differentiate into melanin-producing melanocytes, contributing to skin and hair pigmentation. Sebaceous gland stem cells also have a pivotal role in maintaining the skin barrier by regenerating mature sebocytes. These stem cells are maintained in a specialized microenvironment or niche and are regulated by internal and external signals, determining their dynamic behaviors in homeostasis and hair follicle regeneration. The activity of these stem cells is tightly controlled by various factors secreted by the niche components around the hair follicles, as well as immune-mediated damage signals, aging, metabolic status, and stress. In this study, we review these diverse stem cell regulatory and related molecular mechanisms of hair regeneration and disease conditions. Molecular insights would provide new perspectives on the disease mechanisms as well as hair and skin disorder treatment.

SOX family transcription factors as therapeutic targets in wound healing: A comprehensive review

The SOX family plays a vital role in determining the fate of cells and has garnered attention in the fields of cancer research and regenerative medicine. It also shows promise in the study of wound healing, as it actively participates in the healing processes of various tissues such as skin, fractures, tendons, and the cornea. However, our understanding of the mechanisms behind the SOX family's involvement in wound healing is limited compared to its role in cancer. Gaining insight into its role, distribution, interaction with other factors, and modifications in traumatized tissues could provide valuable new knowledge about wound healing. Based on current research, SOX2, SOX7, and SOX9 are the most promising members of the SOX family for future interventions in wound healing. SOX2 and SOX9 promote the renewal of cells, while SOX7 enhances the microvascular environment. The SOX family holds significant potential for advancing wound healing research. This article provides a comprehensive review of the latest research advancements and therapeutic tools related to the SOX family in wound healing, as well as the potential benefits and challenges of targeting the SOX family for wound treatment.

Wound Microbiota and Its Impact on Wound Healing

Wound healing is a complex process influenced by age, systemic conditions, and local factors. The wound microbiota's crucial role in this process is gaining recognition. This concise review outlines wound microbiota impacts on healing, emphasizing distinct phases like hemostasis, inflammation, and cell proliferation. Inflammatory responses, orchestrated by growth factors and cytokines, recruit neutrophils and monocytes to eliminate pathogens and debris. Notably, microbiota alterations relate to changes in wound healing dynamics. Commensal bacteria influence immune responses, keratinocyte growth, and blood vessel development. For instance, Staphylococcus epidermidis aids keratinocyte progression, while Staphylococcus aureus colonization impedes healing. Other bacteria like Group A Streptococcus spp. And Pseudomonas affect wound healing as well. Clinical applications of microbiota-based wound care are promising, with probiotics and specific bacteria like Acinetobacter baumannii aiding tissue repair through molecule secretion. Understanding microbiota influence on wound healing offers therapeutic avenues. Tailored approaches, including probiotics, prebiotics, and antibiotics, can manipulate the microbiota to enhance immune modulation, tissue repair, and inflammation control. Despite progress, critical questions linger. Determining the ideal microbiota composition for optimal wound healing, elucidating precise influence mechanisms, devising effective manipulation strategies, and comprehending the intricate interplay between the microbiota, host, and other factors require further exploration.

In Vitro Three-Dimensional (3D) Models for Melanoma Immunotherapy

Melanoma is responsible for the majority of skin cancer-related fatalities. Immune checkpoint inhibitor (ICI) treatments have revolutionized the management of the disease by significantly increasing patient survival rates. However, a considerable number of tumors treated with these drugs fail to respond or may develop resistance over time. Tumor growth and its response to therapies are critically influenced by the tumor microenvironment (TME); it directly supports cancer cell growth and influences the behavior of surrounding immune cells, which can become tumor-permissive, thereby rendering immunotherapies ineffective. Ex vivo modeling of melanomas and their response to treatment could significantly advance our understanding and predictions of therapy outcomes. Efforts have been directed toward developing reliable models that accurately mimic melanoma in its appropriate tissue environment, including tumor organoids, bioprinted tissue constructs, and microfluidic devices. However, incorporating and modeling the melanoma TME and immune component remains a significant challenge. Here, we review recent literature regarding the generation of in vitro 3D models of normal skin and melanoma and the approaches used to incorporate the immune compartment in such models. We discuss how these constructs could be combined and used to test immunotherapies and elucidate treatment resistance mechanisms. The development of 3D in vitro melanoma models that faithfully replicate the complexity of the TME and its interaction with the immune system will provide us with the technical tools to better understand ICI resistance and increase its efficacy, thereby improving personalized melanoma therapy.

The frontline of alternatives to animal testing: novel in vitro skin model application in drug development and evaluation

The FDA Modernization Act 2.0 has brought nonclinical drug evaluation into a new era. In vitro models are widely used and play an important role in modern drug development and evaluation, including early candidate drug screening and preclinical drug efficacy and toxicity assessment. Driven by regulatory steering and facilitated by well-defined physiology, novel in vitro skin models are emerging rapidly, becoming the most advanced area in alternative testing research. The revolutionary technologies bring us many in vitro skin models, either laboratory-developed or commercially available, which were all built to emulate the structure of the natural skin to recapitulate the skin's physiological function and particular skin pathology. During the model development, how to achieve balance among complexity, accessibility, capability, and cost-effectiveness remains the core challenge for researchers. This review attempts to introduce the existing in vitro skin models, align them on different dimensions, such as structural complexity, functional maturity, and screening throughput, and provide an update on their current application in various scenarios within the scope of chemical testing and drug development, including testing in genotoxicity, phototoxicity, skin sensitization, corrosion/irritation. Overall, the review will summarize a general strategy for in vitro skin model to enhance future model invention, application, and translation in drug development and evaluation.

The Roles of WNT Signaling Pathways in Skin Development and Mechanical-Stretch-Induced Skin Regeneration

The WNT signaling pathway plays a critical role in a variety of biological processes, including development, adult tissue homeostasis maintenance, and stem cell regulation. Variations in skin conditions can influence the expression of the WNT signaling pathway. In light of the above, a deeper understanding of the specific mechanisms of the WNT signaling pathway in different physiological and pathological states of the skin holds the potential to significantly advance clinical treatments of skin-related diseases. In this review, we present a comprehensive analysis of the molecular and cellular mechanisms of the WNT signaling pathway in skin development, wound healing, and mechanical stretching. Our review sheds new light on the crucial role of the WNT signaling pathway in the regulation of skin physiology and pathology.

Cell Cultures as a Versatile Tool in the Research and Treatment of Autoimmune Connective Tissue Diseases

Cell cultures are an important part of the research and treatment of autoimmune connective tissue diseases. By culturing the various cell types involved in ACTDs, researchers are able to broaden the knowledge about these diseases that, in the near future, may lead to finding cures. Fibroblast cultures and chondrocyte cultures allow scientists to study the behavior, physiology and intracellular interactions of these cells. This helps in understanding the underlying mechanisms of ACTDs, including inflammation, immune dysregulation and tissue damage. Through the analysis of gene expression patterns, surface proteins and cytokine profiles in peripheral blood mononuclear cell cultures and endothelial cell cultures researchers can identify potential biomarkers that can help in diagnosing, monitoring disease activity and predicting patient's response to treatment. Moreover, cell culturing of mesenchymal stem cells and skin modelling in ACTD research and treatment help to evaluate the effects of potential drugs or therapeutics on specific cell types relevant to the disease. Culturing cells in 3D allows us to assess safety, efficacy and the mechanisms of action, thereby aiding in the screening of potential drug candidates and the development of novel therapies. Nowadays, personalized medicine is increasingly mentioned as a future way of dealing with complex diseases such as ACTD. By culturing cells from individual patients and studying patient-specific cells, researchers can gain insights into the unique characteristics of the patient's disease, identify personalized treatment targets, and develop tailored therapeutic strategies for better outcomes. Cell culturing can help in the evaluation of the effects of these therapies on patient-specific cell populations, as well as in predicting overall treatment response. By analyzing changes in response or behavior of patient-derived cells to a treatment, researchers can assess the response effectiveness to specific therapies, thus enabling more informed treatment decisions. This literature review was created as a form of guidance for researchers and clinicians, and it was written with the use of the NCBI database.

Tissue Biology: In Search of a New Paradigm

Animal tissues are made up of multiple cell types that are increasingly well-characterized, yet our understanding of the core principles that govern tissue organization is still incomplete. This is in part because many observable tissue characteristics, such as cellular composition and spatial patterns, are emergent properties, and as such, they cannot be explained through the knowledge of individual cells alone. Here we propose a complex systems theory perspective to address this fundamental gap in our understanding of tissue biology. We introduce the concept of cell categories, which is based on cell relations rather than cell identity. Based on these notions we then discuss common principles of tissue modularity, introducing compositional, structural, and functional tissue modules. Cell diversity and cell relations provide a basis for a new perspective on the underlying principles of tissue organization in health and disease.

Application of mesenchymal stem cells for anti-senescence and clinical challenges

Senescence is a hot topic nowadays, which shows the accumulation of senescent cells and inflammatory factors, leading to the occurrence of various senescence-related diseases. Although some methods have been identified to partly delay senescence, such as strengthening exercise, restricting diet, and some drugs, these only slow down the process of senescence and cannot fundamentally delay or even reverse senescence. Stem cell-based therapy is expected to be a potential effective way to alleviate or cure senescence-related disorders in the coming future. Mesenchymal stromal cells (MSCs) are the most widely used cell type in treating various diseases due to their potentials of self-replication and multidirectional differentiation, paracrine action, and immunoregulatory effects. Some biological characteristics of MSCs can be well targeted at the pathological features of aging. Therefore, MSC-based therapy is also a promising strategy to combat senescence-related diseases. Here we review the recent progresses of MSC-based therapies in the research of age-related diseases and the challenges in clinical application, proving further insight and reference for broad application prospects of MSCs in effectively combating senesce in the future.

Ccrl2-centred immune-related lncRNA-mRNA co-expression network revealed the local skin immune activation mechanism of moxibustion on adjuvant arthritis mice

BACKGROUND

Moxibustion is an important external therapy of traditional medicine that operates on some acupoints on the skin and is usually used for immune-related diseases. However, whether the immune function of the skin, especially the immune-related lncRNAs, contributes to the mechanism of moxibustion remains unclear.

METHODS

Adjuvant arthritis (AA) was induced by injection of Complete Freund's adjuvant (CFA) into the right hind paw of mice. Moxibustion was administered on the Zusanli (ST36) acupoint for 3 weeks. The alteration of foot volume and cytokine concentration in serum was used to evaluate the anti-inflammation effect of moxibustion. CD83 expression in the local skin of ST36 was measured by immunofluorescence staining. Transcriptome RNA sequencing (RNA-seq) and lncRNA-mRNA network analysis were performed to construct a moxibustion-induced Immune-related lncRNA-mRNA co-expression network. qRT-PCR was used to validate the RNA-seq data.

RESULTS

Moxibustion at ST36 relieved the foot swelling, decreased the TNF-α and IL-1β concentrations in serum, and obviously increased the CD83 expression at the local skin of ST36. A total of 548 differentially expressed lncRNAs and 520 linked mRNAs were screened out. The significantly and predominately enriched Go term was inflammatory and immune response, and the main pathways related to inflammatory and immune responses include Toll-like receptor, cytokine-cytokine receptor, and MAPK signaling. The immune-related lncRNA-mRNA co-expression network showed 88 lncRNAs and 36 mRNAs, and Ccrl2 is the central hub of this network.

CONCLUSION

Local immune activation is significantly triggered by moxibustion in ST36 of AA mice. The Ccrl2-centered immune-related lncRNA-mRNA co-expression network would be a promising target for decoding the mechanism of moxibustion for immune-related diseases.

mTOR signaling in hair follicle and hair diseases: recent progress

Mammalian target of rapamycin (mTOR) signaling pathway is a major regulator of cell proliferation and metabolism, playing significant roles in proliferation, apoptosis, inflammation, and illness. More and more evidences showed that the mTOR signaling pathway affects hair follicle circulation and maintains the stability of hair follicle stem cells. mTOR signaling may be a critical cog in Vitamin D receptor (VDR) deficiency-mediated hair follicle damage and degeneration and related alopecia disorders. This review examines the function of mTOR signaling in hair follicles and hair diseases, and talks about the underlying molecular mechanisms that mTOR signaling regulates.

Skin substitutes as treatment for chronic wounds: current and future directions

Chronic wounds such as diabetic foot ulcers and venous leg ulcers place a significant burden on the healthcare system and in some cases, have 5-year mortality rates comparable to cancer. They negatively impact patients' quality of life due to pain, odor, decreased mobility, and social isolation. Skin substitutes are an advanced therapy recommended for wounds that fail to show decrease in size with standard care. The choice of substitute used should be based on evidence, which often differs based on wound etiology. There are more than 75 skin substitutes currently available, and that number is rising. In this review, we discuss current management and future directions of chronic wounds while providing a review of available randomized control trial data for various skin substitutes.

Three-Dimensional Cell Cultures: The Bridge between In Vitro and In Vivo Models

Although historically, the traditional bidimensional in vitro cell system has been widely used in research, providing much fundamental information regarding cellular functions and signaling pathways as well as nuclear activities, the simplicity of this system does not fully reflect the heterogeneity and complexity of the in vivo systems. From this arises the need to use animals for experimental research and in vivo testing. Nevertheless, animal use in experimentation presents various aspects of complexity, such as ethical issues, which led Russell and Burch in 1959 to formulate the 3R (Replacement, Reduction, and Refinement) principle, underlying the urgent need to introduce non-animal-based methods in research. Considering this, three-dimensional (3D) models emerged in the scientific community as a bridge between in vitro and in vivo models, allowing for the achievement of cell differentiation and complexity while avoiding the use of animals in experimental research. The purpose of this review is to provide a general overview of the most common methods to establish 3D cell culture and to discuss their promising applications. Three-dimensional cell cultures have been employed as models to study both organ physiology and diseases; moreover, they represent a valuable tool for studying many aspects of cancer. Finally, the possibility of using 3D models for drug screening and regenerative medicine paves the way for the development of new therapeutic opportunities for many diseases.

A systematic review of natural products for skin applications: Targeting inflammation, wound healing, and photo-aging

BACKGROUND

Every day the skin is constantly exposed to several harmful factors that induce oxidative stress. When the cells are incapable to maintain the balance between antioxidant defenses and reactive oxygen species, the skin no longer can keep its integrity and homeostasis. Chronic inflammation, premature skin aging, tissue damage, and immunosuppression are possible consequences induced by sustained exposure to environmental and endogenous reactive oxygen species. Skin immune and non-immune cells together with the microbiome are essential to efficiently trigger skin immune responses to stress. For this reason, an ever-increasing demand for novel molecules capable of modulating immune functions in the skin has risen the level of their development, particularly in the field of natural product-derived molecules.

PURPOSE

In this review, we explore different classes of molecules that showed evidence in modulate skin immune responses, as well as their target receptors and signaling pathways. Moreover, we describe the role of polyphenols, polysaccharides, fatty acids, peptides, and probiotics as possible treatments for skin conditions, including wound healing, infection, inflammation, allergies, and premature skin aging.

METHODS

Literature was searched, analyzed, and collected using databases, including PubMed, Science Direct, and Google Scholar. The search terms used included "Skin", "wound healing", "natural products", "skin microbiome", "immunomodulation", "anti-inflammatory", "antioxidant", "infection", "UV radiation", "polyphenols", "polysaccharides", "fatty acids", "plant oils", "peptides", "antimicrobial peptides", "probiotics", "atopic dermatitis", "psoriasis", "auto-immunity", "dry skin", "aging", etc., and several combinations of these keywords.

RESULTS

Natural products offer different solutions as possible treatments for several skin conditions. Significant antioxidant and anti-inflammatory activities were reported, followed by the ability to modulate immune functions in the skin. Several membrane-bound immune receptors in the skin recognize diverse types of natural-derived molecules, promoting different immune responses that can improve skin conditions.

CONCLUSION

Despite the increasing progress in drug discovery, several limiting factors need future clarification. Understanding the safety, biological activities, and precise mechanisms of action is a priority as well as the characterization of the active compounds responsible for that. This review provides directions for future studies in the development of new molecules with important pharmaceutical and cosmeceutical value.

Single-cell profiling reveals a potent role of quercetin in promoting hair regeneration

Hair loss affects millions of people at some time in their life, and safe and efficient treatments for hair loss are a significant unmet medical need. We report that topical delivery of quercetin (Que) stimulates resting hair follicles to grow with rapid follicular keratinocyte proliferation and replenishes perifollicular microvasculature in mice. We construct dynamic single-cell transcriptome landscape over the course of hair regrowth and find that Que treatment stimulates the differentiation trajectory in the hair follicles and induces an angiogenic signature in dermal endothelial cells by activating HIF-1α in endothelial cells. Skin administration of a HIF-1α agonist partially recapitulates the pro-angiogenesis and hair-growing effects of Que. Together, these findings provide a molecular understanding for the efficacy of Que in hair regrowth, which underscores the translational potential of targeting the hair follicle niche as a strategy for regenerative medicine, and suggest a route of pharmacological intervention that may promote hair regrowth.

Targeting lymphoid-derived IL-17 signaling to delay skin aging

Skin aging is characterized by structural and functional changes that contribute to age-associated frailty. This probably depends on synergy between alterations in the local niche and stem cell-intrinsic changes, underscored by proinflammatory microenvironments that drive pleotropic changes. The nature of these age-associated inflammatory cues, or how they affect tissue aging, is unknown. Based on single-cell RNA sequencing of the dermal compartment of mouse skin, we show a skew towards an IL-17-expressing phenotype of T helper cells, γδ T cells and innate lymphoid cells in aged skin. Importantly, in vivo blockade of IL-17 signaling during aging reduces the proinflammatory state of the skin, delaying the appearance of age-related traits. Mechanistically, aberrant IL-17 signals through NF-κB in epidermal cells to impair homeostatic functions while promoting an inflammatory state. Our results indicate that aged skin shows signs of chronic inflammation and that increased IL-17 signaling could be targeted to prevent age-associated skin ailments.

Different priming strategies improve distinct therapeutic capabilities of mesenchymal stromal/stem cells: Potential implications for their clinical use

Mesenchymal stromal/stem cells (MSCs) have shown significant therapeutic potential, and have therefore been extensively investigated in preclinical studies of regenerative medicine. However, while MSCs have been shown to be safe as a cellular treatment, they have usually been therapeutically ineffective in human diseases. In fact, in many clinical trials it has been shown that MSCs have moderate or poor efficacy. This inefficacy appears to be ascribable primarily to the heterogeneity of MSCs. Recently, specific priming strategies have been used to improve the therapeutic properties of MSCs. In this review, we explore the literature on the principal priming approaches used to enhance the preclinical inefficacy of MSCs. We found that different priming strategies have been used to direct the therapeutic effects of MSCs toward specific pathological processes. Particularly, while hypoxic priming can be used primarily for the treatment of acute diseases, inflammatory cytokines can be used mainly to prime MSCs in order to treat chronic immune-related disorders. The shift in approach from regeneration to inflammation implies, in MSCs, a shift in the production of functional factors that stimulate regenerative or anti-inflammatory pathways. The opportunity to fine-tune the therapeutic properties of MSCs through different priming strategies could conceivably pave the way for optimizing their therapeutic potential.

Optimization of Surface-Engineered Micropatterns on Bacterial Cellulose for Guided Scar-Free Skin Wound Healing

Bacterial cellulose (BC) has been widely used in tissue engineering due to its unique spatial structure and suitable biological properties. In this study, a small biologically active Arginine-Glycine-Aspartic acid-Serine (RGDS) tetrapeptide was incorporated on the porous BC surface followed by a low-energy CO₂ laser etching operation. As a result, different micropatterns were established on the BC surface with RGDS only anchored on the raised platform surface of the micropatterned BC (MPBC). Material characterization showed that all micropatterned structures exhibited platforms with a width of ~150 μm and grooves with a width of ~100 μm and a depth of ~300 μm, which displayed distinct hydrophilic and hydrophobic properties. The resulting RGDS-MPBC could hold the material integrity, as well as the microstructure morphology under a humid environment. In-vitro and in-vivo assays on cell migration, collagen deposition, and histological analysis revealed that micropatterns led to significant impacts on wound healing progress compared to the BC without surface-engineered micropatterns. Specifically, the basket-woven micropattern etched on the BC surface exhibited the optimal wound healing outcome with the presence of fewer macrophages and the least scar formation. This study further addresses the potential of adopting surface micropatterning strategies to promote skin wounds towards scar-free outcomes.

Immune-Epithelial Cross Talk in Regeneration and Repair

The epithelial tissues that line our body, such as the skin and gut, have remarkable regenerative prowess and continually renew throughout our lifetimes. Owing to their barrier function, these tissues have also evolved sophisticated repair mechanisms to swiftly heal and limit the penetration of harmful agents following injury. Researchers now appreciate that epithelial regeneration and repair are not autonomous processes but rely on a dynamic cross talk with immunity. A wealth of clinical and experimental data point to the functional coupling of reparative and inflammatory responses as two sides of the same coin. Here we bring to the fore the immunological signals that underlie homeostatic epithelial regeneration and restitution following damage. We review our current understanding of how immune cells contribute to distinct phases of repair. When unchecked, immune-mediated repair programs are co-opted to fuel epithelial pathologies such as cancer, psoriasis, and inflammatory bowel diseases. Thus, understanding the reparative functions of immunity may advance therapeutic innovation in regenerative medicine and epithelial inflammatory diseases.

The journey from melanocytes to melanoma

Over the past decade, melanoma has led the field in new cancer treatments, with impressive gains in on-treatment survival but more modest improvements in overall survival. Melanoma presents heterogeneity and transcriptional plasticity that recapitulates distinct melanocyte developmental states and phenotypes, allowing it to adapt to and eventually escape even the most advanced treatments. Despite remarkable advances in our understanding of melanoma biology and genetics, the melanoma cell of origin is still fiercely debated because both melanocyte stem cells and mature melanocytes can be transformed. Animal models and high-throughput single-cell sequencing approaches have opened new opportunities to address this question. Here, we discuss the melanocytic journey from the neural crest, where they emerge as melanoblasts, to the fully mature pigmented melanocytes resident in several tissues. We describe a new understanding of melanocyte biology and the different melanocyte subpopulations and microenvironments they inhabit, and how this provides unique insights into melanoma initiation and progression. We highlight recent findings on melanoma heterogeneity and transcriptional plasticity and their implications for exciting new research areas and treatment opportunities. The lessons from melanocyte biology reveal how cells that are present to protect us from the damaging effects of ultraviolet radiation reach back to their origins to become a potentially deadly cancer.

Plasticity of Dental Cell Types in Development, Regeneration, and Evolution

Recent years have improved our understanding of the plasticity of cell types behind inducing, building, and maintaining different types of teeth. The latest efforts were aided by progress in single-cell transcriptomics, which helped to define not only cell states with mathematical precision but also transitions between them. This includes new aspects of dental epithelial and mesenchymal stem cell niches and beyond. These recent efforts revealed continuous and fluid trajectories connecting cell states during dental development and exposed the natural plasticity of tooth-building progenitors. Such "developmental" plasticity seems to be employed for organizing stem cell niches in adult continuously growing teeth. Furthermore, transitions between mature cell types elicited by trauma might represent a replay of embryonic continuous cell states. Alternatively, they could constitute transitions that evolved de novo, not known from the developmental paradigm. In this review, we discuss and exemplify how dental cell types exhibit plasticity during dynamic processes such as development, self-renewal, repair, and dental replacement. Hypothetically, minor plasticity of cell phenotypes and greater plasticity of transitions between cell subtypes might provide a better response to lifetime challenges, such as damage or dental loss. This plasticity might be additionally harnessed by the evolutionary process during the elaboration of dental cell subtypes in different animal lineages. In turn, the diversification of cell subtypes building teeth brings a diversity of their shape, structural properties, and functions.

MicroRNA-148a Controls Epidermal and Hair Follicle Stem/Progenitor Cells by Modulating the Activities of ROCK1 and ELF5

Skin and hair development is regulated by complex programs of gene activation and silencing and microRNA-dependent modulation of gene expression to maintain normal skin and hair follicle development, homeostasis, and cycling. In this study, we show that miR-148a, through its gene targets, plays an important role in regulating skin homeostasis and hair follicle cycling. RNA and protein analysis of miR-148a and its gene targets were analyzed using a combination of in vitro and in vivo experiments. We show that the expression of miR-148a markedly increases during telogen (bulge and hair germ stem cell compartments). Administration of antisense miR-148a inhibitor into mouse skin during the telogen phases of the postnatal hair cycle results in accelerated anagen development and altered stem cell activity in the skin. We also show that miR-148a can regulate colony-forming abilities of hair follicle bulge stem cells as well as control keratinocyte proliferation/differentiation processes. RNA and protein analysis revealed that miR-148a may control these processes by regulating the expression of Rock1 and Elf5 in vitro and in vivo. These data provide an important foundation for further analyses of miR-148a as a crucial regulator of these genes target in the skin and hair follicles and its importance in maintaining stem/progenitor cell functions during normal tissue homeostasis and regeneration.

Lamprey Wound Healing and Regenerative Effects: The Collaborative Efforts of Diverse Drivers

Skin is a natural barrier between the body and the external environment, and this important multifunctional organ plays roles in body temperature regulation, sensory stimulation, mucus secretion, metabolite excretion and immune defense. Lampreys, as ancient vertebrates, rarely experience infection of damaged skin during farming and efficiently promote skin wound healing. However, the mechanism underlying these wound healing and regenerative effects is unclear. Our histology and transcriptomics results demonstrate that lampreys regenerate a nearly complete skin structure in damaged epidermis, including the secretory glands, and will almost not be infected, even if experiencing full-thickness damage. In addition, ATGL, DGL and MGL participate in the lipolysis process to provide space for infiltrating cells. A large number of red blood cells migrate to the site of injury and exert proinflammatory effects, upregulating the expression of proinflammatory factors such as IL-8 and IL-17. Based on a lamprey skin damage healing model, adipocytes and red blood cells in the subcutaneous fat layer can promote wound healing, which provides a new approach for the study of skin healing mechanisms. Transcriptome data reveal that mechanical signal transduction pathways are mainly regulated by focal adhesion kinase and that the actin cytoskeleton plays an important role in the healing of lamprey skin injuries. We identified RAC1 as a key regulatory gene that is necessary and partially sufficient for wound regeneration. Insights into the mechanisms of lamprey skin injury and healing will provide a theoretical basis for overcoming the challenges associated with chronic healing and scar healing in the clinic.

Robot-assisted in situ bioprinting of gelatin methacrylate hydrogels with stem cells induces hair follicle-inclusive skin regeneration

Large skin defects caused by accidents or disease can cause fluid loss, water and electrolyte disorders, hypoproteinemia and serious infection and remain a difficult problem in clinical practice. In situ bioprinting is a promising, recently developed technology that involves timely, customized, and morphologically adapted bioprinting of bioink into tissue defects to promote the recovery of human tissues or organs. During this process, bioink is a key factor. In this study, we synthesized a biocompatible, photosensitive hydrogel material comprising gelatin methacrylate (GelMA) for robot-assisted in situ bioprinting of skin wounds. The results showed that GelMA demonstrated good printability of that supported the proliferation of skin-derived precursors (SKPs) and maintained their properties. Furthermore, in situ bioprinting of GelMA hydrogels with epidermal stem cells (Epi-SCs) and SKPs onto skin wounds showed complete wound healing and functional tissue skin regeneration. The regenerated skin contains epidermis, dermis, blood vessels, hair follicles, and sebaceous glands and resembling native skin. These results provide an effective strategy for skin repair through the combined application of GelMA hydrogels, Epi-SCs, SKPs and in situ bioprinting and its promising clinical translational potential for further applications.

SCD1 Sustains Homeostasis of Bulge Niche via Maintaining Hemidesmosomes in Basal Keratinocytes

Niche for stem cells profoundly influences their maintenance and fate during tissue homeostasis and pathological disorders; however, the underlying mechanisms and tissue-specific features remain poorly understood. Here, it is reported that fatty acid desaturation catabolized by stearoyl-coenzyme A desaturase 1 (SCD1) regulates hair follicle stem cells (HFSCs) and hair growth by maintaining the bulge, niche for HFSCs. Scd1 deletion in mice results in abnormal hair growth, an effect exerted directly on keratin K14⁺ keratinocytes rather than on HFSCs. Mechanistically, Scd1 deficiency impairs the level of integrin α6β4 complex and thus the assembly of hemidesmosomes (HDs). The disruption of HDs allows the aberrant activation of focal adhesion kinase and PI3K in K14⁺ keratinocytes and subsequently their differentiation and proliferation. The overgrowth of basal keratinocytes results in downward extension of the outer root sheath and interruption of bulge formation. Then, inhibition of PI3K signaling in Scd1^-/- mice normalizes the bulge, HFSCs, and hair growth. Additionally, supplementation of oleic acid to Scd1^-/- mice reestablishes HDs and the homeostasis of bulge niche, and restores hair growth. Thus, SCD1 is critical in regulating hair growth through stabilizing HDs in basal keratinocytes and thus sustaining bulge for HFSC residence and periodic activity.

Apigenin: A Therapeutic Agent for Treatment of Skin Inflammatory Diseases and Cancer

The skin is the main barrier between the body and the environment, protecting it from external oxidative stress induced by ultraviolet rays. It also prevents the entrance of infectious agents such as viruses, external antigens, allergens, and bacteria into our bodies. An overreaction to these agents causes severe skin diseases, including atopic dermatitis, pruritus, psoriasis, skin cancer, and vitiligo. Members of the flavonoid family include apigenin, quercetin, luteolin, and kaempferol. Of these, apigenin has been used as a dietary supplement due to its various biological activities and has been shown to reduce skin inflammation by downregulating various inflammatory markers and molecular targets. In this review, we deal with current knowledge about inflammatory reactions in the skin and the molecular mechanisms by which apigenin reduces skin inflammation.

Distinct bulge stem cell populations maintain the pilosebaceous unit in a β-catenin-dependent manner

The pilosebaceous unit (PSU) is composed of multiple compartments and the self-renewal of PSU depends on distinct hair follicle stem cell (HFSC) populations. However, the differential roles of the HFSCs in sebaceous gland (SG) renewal have not been completely understood. Here, we performed multiple lineage tracing analysis to unveil the contribution of different HFSC populations to PSU regeneration during the hair cycle and wound healing. Our results indicated that the upper bulge stem cells contributed extensively to the SG replenishment during hair cycling, while HFSCs in the lower bugle did not. During skin wound healing, all HFSC populations participated in the SG replenishment. Moreover, β-catenin activation promoted the contribution of HFSCs to SG replenishment, whereas β-catenin deletion substantially repressed the event. Thus, our findings indicated that HFSCs contributed to SG replenishment in a β-catenin-dependent manner.

Thermosensitive Hydrogel Loaded with Nickel-Copper Bimetallic Hollow Nanospheres with SOD and CAT Enzymatic-Like Activity Promotes Acute Wound Healing

Various injury defense and repair functions are performed by the skin. Free radicals secreted after injury cause oxidative stress and inflammatory responses, which make wound healing difficult. However, the current metal nanomaterials for wound repair do not have sufficient catalytic activity or complex material design and cannot properly fit wounds. Therefore, it is imperative to develop more effective therapeutic approaches. This study investigated the effect of Ni₄Cu₂ hollow nanospheres composited with F127 hydrogel on promoting wound healing by applying them to wounds. Ni₄Cu₂ hollow nanospheres exhibited a superior spatial structure, contained many catalytic sites, and could be synthesized in a simple manner. In vitro experiments showed that Ni₄Cu₂ hollow nanospheres had superoxide dismutase-like activity and promoted fibroblast migration, angiogenesis, and macrophage polarization. F127, which is a thermosensitive, nontoxic, phase-change and porous hydrogel material, has proven to be an effective choice for injectable and sprayable medical dressings. Ni₄Cu₂ hollow nanospheres were mixed with F127 hydrogel without significantly affecting its performance. In addition to adapting to the complex, irregular gaps of acute wounds, the mixture lengthened the nanozyme release time, which enhanced healing. Based on the animal experiments, the Ni₄Cu₂/F127 composite hydrogel effectively promoted wound healing, epithelial regeneration, and the formation of skin appendages such as hair follicles in mice. Furthermore, the Ni₄Cu₂/F127 composite hydrogel was nontoxic to animals and had high biological safety. The Ni₄Cu₂/F127 composite hydrogel has provided an innovative strategy to develop composite hydrogels for the treatment of acute skin wounds.

miR-203 represses keratinocyte stemness by targeting survivin

OBJECTIVE

The epidermis possesses the capacity to replace dying cells and to heal wounds, thanks to resident stem cells, which have self-renewal properties. In skin physiology, miRNAs have been shown to be involved in many processes, including skin and hair morphogenesis. Recently, differentiation of epidermal stem cells was shown to be promoted by the miR-203. The miR-203 is upregulated during epidermal differentiation and is of interest because of significant targets.

METHODS

By utilizing a bioinformatic tool, we identified a target site for miR-203 in the survivin mRNA. Silencing miR-203 was managed with the use of antagomir; the silencing of survivin was performed with a siRNA. Survivin expression was determined by qPCR or immunofluorescence in cultured cells, and by immunohistochemistry in skin sections. Involucrin expression was used as marker of keratinocyte differentiation. A rice extract with previously demonstrated anti-aging properties was evaluated on miR-203 modulation.

RESULTS

In this study, we identified a miR-203/survivin axis, important for epidermal homeostasis. We report that differentiation of keratinocyte is dependent on the level of miR-203 expression and that inhibition of miR-203 can increase the expression of survivin, an epidermal marker of stemness.

CONCLUSION

In summary, our findings suggest that miR-203 target 3'UTR region of survivin mRNA and directly represses survivin expression in the epidermis. The rice extract was identified as modulator of miR-203 and pointed out as a promising microRNA-based strategy in treating skin changes occurring with aging.

Investigation of hub genes and immune infiltration in androgenetic alopecia using bioinformatics analysis

Background

Androgenetic alopecia (AGA) is a type of non-scarring hair loss. Current drugs for AGA are accompanied by adverse reactions and a high recurrence rate. Thus, the discovery of diagnostic biomarkers and therapeutic targets for AGA remains imperatively warranted.

Methods

The GSE90594 dataset, which contained scalp skin biopsies from 14 male AGA cases and healthy volunteers, was used to identify the differentially expressed genes (DEGs). Functional enrichment analysis was subsequently performed. Next, the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database combined with the cytoHubba plugin of Cytoscape were used to obtain the key genes of AGA. Thereafter, the Cell-type Identification by Estimating Relative Subsets of RNA Transcripts (CIBERSORT) algorithm was performed to evaluate the relative abundance of immune cells between male AGA patients and healthy controls. The correlation between key genes and infiltrating immune cells was analyzed to obtain the significant immune-cell related genes (IRGs), then intersected with the DEGs between immortalized balding and non-balding human dermal papilla cells (DPCs) of the GSE93766 dataset as well as the DEGs obtained by the GSE90594 dataset, thus obtaining the hub genes of AGA. Finally, the hub genes were validated using GSE36169, which contained expression profiling of tissues biopsied from haired and bald scalps of five individuals with AGA.

Results

A total of 234 DEGs were obtained from the GSE90594 dataset, which were mainly enriched in the extracellular matrix (ECM)-related pathways and immune-related activities. The STRING database and ten algorithms in the cytoHubba plugin of Cytoscape disclosed 21 key DEGs. The results of the CIBERSORT algorithm revealed the relative abundances of 20 kinds of immune cells between diseased and healthy individuals, and yielded 15 IRGs involved in the pathogenesis of AGA. Next, the intersection analysis identified four hub genes of AGA, comprising COL1A2, PCOLCE, ITGAX, and LOX. The GSE36169 dataset validated the expression pattern of hub genes in the haired scalp of AGA patients.

Conclusions

We discovered that the hub genes identified are closely linked with the causative factors of AGA, which could be used as the viable diagnostic and therapeutic target in the clinical applications.

Characteristics of the Skin Microbiome in Selected Dermatological Conditions: A Narrative Review

The skin is the largest and outermost organ of the human body. The microbial diversity of the skin can be influenced by several variable factors such as physiological state, lifestyle, and geographical locations. Recent years have seen increased interest in research aiming at an improved understanding of the relationship between the human microbiota and several diseases. Albeit understudied, interesting correlations between the skin microbiota and several dermatological conditions have been observed. Studies have shown that a decrease or increase in the abundance of certain microbial communities can be implicated in several dermatological pathologies. This narrative review (i) examines the role of the skin microbiota in the maintenance of skin homeostasis and health, (ii) provides examples on how some common skin diseases (acne inversa, candidiasis, psoriasis) are associated with the dysbiosis of microbial communities, and (iii) describes how recent research approaches used in skin microbiome studies may lead to improved, more sensitive diagnostics and individual therapeutics in the foreseeable future.

Isolation of an "Early" Transit Amplifying Keratinocyte Population in Human Epidermis: A Role for the Low Affinity Neurotrophin Receptor CD271

In the interfollicular epidermis (IFE), stem cells (KSC) generate transit amplifying (TA) cells that, after symmetric divisions, produce differentiating daughters. Here, we isolated and characterized the highly proliferative interfollicular epidermal basal cell population "early" TA (ETA) cells, based on their capacity to adhere to type IV collagen. Proliferation and colony-forming efficiency in ETA cells are lower than in KSC but higher than in "late" TA (LTA). Stemness, proliferation, and differentiation markers confirmed that ETA cells display a unique phenotype. Skin reconstructs derived from ETA cells present different features (epidermal thickness, Ki67, and Survivin expression), as compared to skin equivalents generated from either KSC or LTA cells. The low-affinity neurotrophin receptor CD271, which regulates the KSC to TA cell transition in the human epidermis through an on/off switch control mechanism, is predominantly expressed in ETA cells. Skin equivalents generated from siRNA CD271 ETA cells display a more proliferative and less differentiated phenotype, as compared to mock-derived reconstructs. Consistently, CD271 overexpression in LTA cells generates a more proliferative skin equivalent than mock LTA cells. Finally, the CD271 level declines with cellular senescence, while it induces a delay in p16INK4 expression. We conclude that ETA cells represent the first KSC progenitor with exclusive features. CD271 identifies and modulates ETA cells, thus participating in the early differentiation and regenerative capacity of the human epidermis.

Cultured Human Foreskin as a Model System for Evaluating Ionizing Radiation-Induced Skin Injury

Purpose: Precise molecular and cellular mechanisms of radiation-induced dermatitis are incompletely understood. Histone variant H2A.J is associated with cellular senescence and modulates senescence-associated secretory phenotype (SASP) after DNA-damaging insults, such as ionizing radiation (IR). Using ex vivo irradiated cultured foreskin, H2A.J was analyzed as a biomarker of radiation-induced senescence, potentially initiating the inflammatory cascade of radiation-induced skin injury. Methods: Human foreskin explants were collected from young donors, irradiated ex vivo with 10 Gy, and cultured in air-liquid interphase for up to 72 h. At different time-points after ex vivo IR exposure, the foreskin epidermis was analyzed for proliferation and senescence markers by immunofluorescence and immunohistochemical staining of sectioned tissue. Secretion of cytokines was measured in supernatants by ELISA. Using our mouse model with fractionated in vivo irradiation, H2A.J expression was analyzed in epidermal stem/progenitor cell populations localized in different regions of murine hair follicles (HF). Results: Non-vascularized foreskin explants preserved their tissue homeostasis up to 72 h (even after IR exposure), but already non-irradiated foreskin epithelium expressed high levels of H2A.J in all epidermal layers and secreted high amounts of cytokines. Unexpectedly, no further increase in H2A.J expression and no obvious upregulation of cytokine secretion was observed in the foreskin epidermis after ex vivo IR. Undifferentiated keratinocytes in murine HF regions, by contrast, revealed low H2A.J expression in non-irradiated skin and significant radiation-induced H2A.J upregulations at different time-points after IR exposure. Based on its staining characteristics, we presume that H2A.J may have previously underestimated the importance of the epigenetic regulation of keratinocyte maturation. Conclusions: Cultured foreskin characterized by highly keratinized epithelium and specific immunological features is not an appropriate model for studying H2A.J-associated tissue reactions during radiation-induced dermatitis.

A dopamine-methacrylated hyaluronic acid hydrogel as an effective carrier for stem cells in skin regeneration therapy

Adipose-derived stem cells (ADSCs) show potential in skin regeneration research. A previous study reported the failure of full-thickness skin self-repair in an injury area exceeding 4 cm in diameter. Stem cell therapies have shown promise in accelerating skin regeneration; however, the low survival rate of transplanted cells due to the lack of protection during and after transplantation leads to low efficacy. Hence, effective biomaterials for the delivery and retention of ADSCs are urgently needed for skin regeneration purposes. Here, we covalently crosslinked hyaluronic acid with methacrylic anhydride and then covalently crosslinked the product with dopamine to engineer dopamine-methacrylated hyaluronic acid (DA-MeHA). Our experiments suggested that the DA-MeHA hydrogel firmly adhered to the skin wound defect and promoted cell proliferation in vitro and skin defect regeneration in vivo. Mechanistic analyses revealed that the beneficial effect of the DA-MeHA hydrogel combined with ADSCs on skin defect repair may be closely related to the Notch signaling pathway. The ADSCs from the DA-MeHA hydrogel secrete high levels of growth factors and are thus highly efficacious for promoting skin wound healing. This DA-MeHA hydrogel may be used as an effective potential carrier for stem cells as it enhances the efficacy of ADSCs in skin regeneration.

Clinical application of mesenchymal stem cell in regenerative medicine: a narrative review

The multipotency property of mesenchymal stem cells (MSCs) has attained worldwide consideration because of their immense potential for immunomodulation and their therapeutic function in tissue regeneration. MSCs can migrate to tissue injury areas to contribute to immune modulation, secrete anti-inflammatory cytokines and hide themselves from the immune system. Certainly, various investigations have revealed anti-inflammatory, anti-aging, reconstruction, and wound healing potentials of MSCs in many in vitro and in vivo models. Moreover, current progresses in the field of MSCs biology have facilitated the progress of particular guidelines and quality control approaches, which eventually lead to clinical application of MSCs. In this literature, we provided a brief overview of immunoregulatory characteristics and immunosuppressive activities of MSCs. In addition, we discussed the enhancement, utilization, and therapeutic responses of MSCs in neural, liver, kidney, bone, heart diseases, and wound healing.

The regulation of skin homeostasis, repair and the pathogenesis of skin diseases by spatiotemporal activation of epidermal mTOR signaling

The epidermis, the outmost layer of the skin, is a stratified squamous epithelium that protects the body from the external world. The epidermis and its appendages need constantly renew themselves and replace the damaged tissues caused by environmental assaults. The mechanistic target of rapamycin (mTOR) signaling is a central controller of cell growth and metabolism that plays a critical role in development, homeostasis and diseases. Recent findings suggest that mTOR signaling is activated in a spatiotemporal and context-dependent manner in the epidermis, coordinating diverse skin homeostatic processes. Dysregulation of mTOR signaling underlies the pathogenesis of skin diseases, including psoriasis and skin cancer. In this review, we discuss the role of epidermal mTOR signaling activity and function in skin, with a focus on skin barrier formation, hair regeneration, wound repair, as well as skin pathological disorders. We propose that fine-tuned control of mTOR signaling is essential for epidermal structural and functional integrity.

Sox2 in the dermal papilla regulates hair follicle pigmentation

Within the hair follicle (HF) niche, dermal papilla (DP) cells are well known for the hair induction capacity; however, DP cell signaling also regulates HF pigmentation. Here we describe how Sox2 in the DP is a key regulator of melanocyte signaling. To study the largely unknown regulatory role the DP has on hair pigmentation, we characterize leptin receptor (Lepr) expression in the skin and as a genetic tool to target the DP. Sox2 ablation in the DP results in a phenotypic switch from eumelanin to pheomelanin. Mechanistically, we describe a temporal upregulation of Agouti and downregulation of Corin, directly by Sox2 in the DP. We also show that bone morphogenic protein (BMP) signaling regulation by Sox2 is responsible for downregulating MC1R, Dct, and Tyr in melanocytes of Sox2 cKO mice. Thus, we demonstrate that Sox2 in the DP regulates not only the choice of hair pigment but also the overall HF pigment production.

Spatially resolved proteomic map shows that extracellular matrix regulates epidermal growth

Human skin comprises stratified squamous epithelium and dermis with various stromal cells and the extracellular matrix (ECM). The basement membrane (BM), a thin layer at the top of the dermis, serves as a unique niche for determining the fate of epidermal stem cells (EpSCs) by transmitting physical and biochemical signals to establish epidermal cell polarity and maintain the hierarchical structure and function of skin tissue. However, how stem cell niches maintain tissue homeostasis and control wound healing by regulating the behavior of EpSCs is still not completely understood. In this study, a hierarchical skin proteome map is constructed using spatial quantitative proteomics combined with decellularization, laser capture microdissection, and mass spectrometry. The specific functions of different structures of normal native skin tissues or tissues with a dermatologic disease are analyzed in situ. Transforming growth factor-beta (TGFβ)-induced protein ig-h3 (TGFBI), an ECM glycoprotein, in the BM is identified that could enhance the growth and function of EpSCs and promote wound healing. Our results provide insights into the way in which ECM proteins facilitate the growth and function of EpSCs as part of an important niche. The results may benefit the clinical treatment of skin ulcers or diseases with refractory lesions that involve epidermal cell dysfunction and re-epithelialization block in the future.

Ling Leng et al. construct a hierarchical skin proteome map and identify an extracellular matrix glycoprotein TGFBI, which is located in basement membrane and could enhance the growth and function of epidermal stem cells and promote wound healing.

Lymphatics act as a signaling hub to regulate intestinal stem cell activity

Barrier epithelia depend upon resident stem cells for homeostasis, defense, and repair. Epithelial stem cells of small and large intestines (ISCs) respond to their local microenvironments (niches) to fulfill a continuous demand for tissue turnover. The complexity of these niches and underlying communication pathways are not fully known. Here, we report a lymphatic network at the intestinal crypt base that intimately associates with ISCs. Employing in vivo loss of function and lymphatic:organoid cocultures, we show that crypt lymphatics maintain ISCs and inhibit their precocious differentiation. Pairing single-cell and spatial transcriptomics, we apply BayesPrism to deconvolve expression within spatial features and develop SpaceFold to robustly map the niche at high resolution, exposing lymphatics as a central signaling hub for the crypt in general and ISCs in particular. We identify WNT-signaling factors (WNT2, R-SPONDIN-3) and a hitherto unappreciated extracellular matrix protein, REELIN, as crypt lymphatic signals that directly govern the regenerative potential of ISCs.

Analysis and pharmacological modulation of senescence in human epithelial stem cells

Human epithelial stem cells (ESCs) are characterized by long‐term regenerative properties, much dependent on the tissue of origin and varying during their lifespan. We analysed such variables in cultures of ESCs isolated from the skin, conjunctiva, limbus and oral mucosa of healthy donors and patients affected by ectrodactyly‐ectodermal dysplasia‐clefting syndrome, a rare genetic disorder caused by mutations in the p63 gene. We cultured cells until exhaustion in the presence or in the absence of DAPT (γ‐secretase inhibitor; N‐[N‐(3, 5‐difluorophenacetyl)‐L‐alanyl]‐S‐phenylglycine T‐butyl ester). All cells were able to differentiate in vitro but exhibited variable self‐renewal potential. In particular, cells carrying p63 mutations stopped prematurely, compared with controls. Importantly, administration of DAPT significantly extended the replicative properties of all stem cells under examination. RNA sequencing analysis revealed that distinct sets of genes were up‐ or down‐regulated during their lifetime, thus allowing to identify druggable gene networks and off‐the‐shelf compounds potentially dealing with epithelial stem cell senescence. These data will expand our knowledge on the genetic bases of senescence and potentially pave the way to the pharmacological modulation of ageing in epithelial stem cells.