Understanding fibroblast heterogeneity in the skin

Effect of amniotic fluid on hair follicle growth

Purpose: Human amniotic fluid stem cells (hAFSCs) have shown significant regenerative potential in treating hair loss, wound healing, and tissue repair. This study aims to evaluate the effects of human amniotic fluid (hAF) on hair follicle (HF) regeneration and immune system modulation.

Materials and Methods: The hAF used was pooled, acellular, and gamma-irradiated to standardize its contents and enhance its stability. Both irradiated (FAFI) and non-irradiated (FAF) hAF were assessed for their efficacy and safety in promoting hair growth and modulating immune responses in a rat model of hair loss. The study examined HF regeneration, transition to the anagen phase, and macrophage polarization from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype.

Results: Both FAF and FAFI treatments significantly increased HF density, with FAFI exhibiting enhanced effects. Histological analysis demonstrated improved HF regeneration, increased M2 macrophages, and reduced collagen fiber deposition in treated areas. Gamma irradiation likely improved the efficacy of FAFI by stabilizing active components and inhibiting protease activity.

Conclusions: Irradiated hAF is a safe and effective therapeutic candidate for alopecia and HF growth disorders. These findings support further evaluation of hAF in clinical trials to validate its potential for hair regeneration therapies.

Stiffness regulates extracellular matrix synthesis in fibroblasts by DDR1-TGF-β/STAT3 mechanotransduction axis

For a long time, research on atherosclerosis (AS) has mainly focused on endothelial cells (ECs) and smooth muscle cells (SMCs) in blood vessels. Fibroblasts, however, being the major component in adventitia, little is known about their role. Fibroblasts are highly plastic cells, capable of undergoing phenotypic changes in response to various extracellular signals. Once activated, fibroblasts can promote fibrosis by altering the secretion of extracellular matrix (ECM). In this study, the effect of ECM stiffness on fibroblasts was investigated. Polyacrylamide (PA) gels with varying elastic moduli (1 kPa, 20 kPa and 100 kPa) were used as models for matrix stiffness. Human fibroblasts were cultured on these substrates, and their phenotypic and functional changes were examined. The data revealed that a collagen-binding receptor, Discoidin Domain Receptor 1 (DDR1), plays a central role in sensing mechanical stimuli from ECM. Matrix stiffness-induced phosphorylation of DDR1 suppresses the synthesis of ECM proteins in fibroblasts. The expression of ECM proteins on the 1 kPa substrate was significantly higher than that on the 20 kPa and 100 kPa substrates, while the phosphorylation level of DDR1 was notably reduced. After knocking out DDR1, the difference in ECM proteins expression among the three substrates with different stiffness levels disappeared. The signal transduction from DDR1 to ECM synthesis is mediated by the TGF-β/STAT3 signaling axis. Our study reveals how matrix stiffness regulates the synthesis of ECM in fibroblasts and paves the way for understanding the regulation of fibrotic process in the pathogenesis of AS.

Imbalanced redox dynamics induce fibroblast senescence leading to impaired stem cell pools and skin aging

Skin function depends on a meticulously regulated dynamic interaction of distinct skin compartments such as the epidermis and dermis. Adaptive responses at the molecular and cellular level are essential for these interactions - and if dysregulated - drive skin aging and other pathologies. After defining the role of redox homeodynamics in physiology and aging pathology, we focus on the redox distress-dependent aging of dermal fibroblasts including their progenitors. We here discuss the prime role of senescent fibroblasts in the control of their own endogenous niche and stem cell niches for epidermal stem cells, hair follicle stem cells, adipocyte precursors and muscle stem cells. We here review that redox imbalance induced reduction in Insulin-like Growth Factor-1 drives skin aging by the depletion of stem cell pools. This IGF-1 reduction is mediated via the redox-sensitive transcription factor JunB and also by the redox-dependent changes in sphingolipid-metabolism, among others. In addition, we will discuss the changes in the extracellular matrix of the skin affecting cellular senescence and the skin integrity and function in aging. The aim is a deeper understanding of the two main redox-dependent hubs such as JunB-induced depletion of IGF-1, and the sphingolipid-mediated remodeling of the cell membrane with its impact on IGF-1, fibroblast heterogeneity, function, senescence and plasticity in skin aging.

Fibroblasts fluctuating between mesenchyme and epithelium are involved in hair follicle mesenchyme development

The transition between the mesenchyme and epithelium contributes to the development of various tissues. During skin development, epithelial-mesenchymal transition in the ectodermal epithelia is involved in the development of the dermal mesenchyme in early embryos. However, the precise roles and functions of epithelial-mesenchymal/mesenchymal-epithelial transition in cutaneous development have not been fully elucidated. In this study, we aimed to elucidate these roles and functions in the neonatal mouse skin. We conducted single-cell RNA sequencing and immunohistochemical analyses to search for Pdgfra-expressing (Pα +) fibroblasts with transition activities to/from Krt5-expressing keratinocytes. We determined that the Pα +/Krt5-lineage (K5 lin+) fibroblasts significantly contributed to developing hair follicle dermal stem cells to generate lower dermal papilla cells and lower dermal sheath cells. In the developing mouse skin, K5 lin + fibroblasts appeared concurrently with hair follicle development and formed outer edge cells in the early dermal papilla on embryonic day 16.5. K5 lin + hair follicle mesenchymal cells were also maintained in aged mouse skin. These results provide insights into the role and function of the transition between the mesenchyme and epithelium in hair follicle development and maintenance.

Distinguishing the Metabolic Effect of Fetal and Adult Fibrinogen on Human Fibroblast Cell Culture by IR-MALDESI Mass Spectrometry Imaging

Mass spectrometry imaging (MSI) of cells can elucidate metabolic changes with cellular and molecular specificity. Fibroblasts are mesenchymal cells that are important in tissue homeostasis and wound healing. During early wound healing, fibroblasts adhere to fibrinogen and migrate into fibrin clots, which are important interactions to stabilize early blood clots and promote subsequent tissue remodeling. It is understood that fibrinogen exists in distinct forms, fetal and adult, which have differing glycosylation and morphological effects on fibroblasts. Despite their importance to wound healing and the extracellular environment, fibroblasts are not commonly studied by MSI. While many MSI studies are conducted at the single-cell or subcellular level, there is still utility in accessing a broad view of the metabolic changes in a cell culture above single-cell spatial resolution. This enables imaging a wider area and larger number of cells directly from cell culture. In this work, dermal fibroblasts were imaged directly from cell culture chamber slides by infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI). This method enabled treating the chambers with adult or fetal fibrinogen prior to cell culture and reduced sample preparation prior to MSI. Many metabolic effects of serum and fibrinogen type were elucidated, with changes in many membrane lipids such as cholesterol and ceramides potentially contributing to the observed morphological effects of fibrinogen types on fibroblasts.

Fetal Fibroblast Heterogeneity Defines Dermal Architecture during Human Embryonic Skin Development

To investigate the heterogeneity of fibroblasts in human fetal skin, we analyzed published single-cell RNA-sequencing data (7 and 16 weeks after conception) and performed single-molecule FISH to map their spatial distribution and predicted dynamic interactions. Clustering revealed 8 fibroblast populations with changes in developmental stage-specific abundance. Proliferative cells (MKI67+) were present at all stages. The appearance of dermal papilla (PRDM1+) and hair follicle (SLC26A7+) fibroblasts coincided with hair follicle maturation, whereas fibroblasts (apolipoprotein E positive) specifically associated with blood vessels increased in abundance as the vessels developed. HOXC5 was a marker of the most abundant fibroblasts 7-8 weeks after conception; this cluster was diminished 9-13 weeks after conception and undetectable subsequently. A second population (PLAT+) decreased in abundance with the same kinetics. Fibroblasts corresponding to papillary dermis (GRP+) were predominant 9-13 weeks after conception, whereas reticular dermal fibroblasts (ASPN+) were the major cluster 14-16 weeks after conception. Partition-based graph abstraction and pseudotime analysis indicated that the HOXC5+ fibroblasts were closely connected with the papillary and hair follicle fibroblasts, whereas the PLAT+ fibroblasts were connected with reticular and vascular fibroblasts. Dermal papilla fibroblasts were the most highly differentiated. Integration of fetal and adult datasets distinguished the adult and fetal papillary clusters from the reticular clusters.

Hidradenitis Suppurativa Tunnels: Unveiling a Unique Disease Entity

Hidradenitis suppurativa tunnel structures lined with epithelium within the dermis are unique features of advanced disease stages that significantly impair patients' QOL. The presence of hidradenitis suppurativa tunnels is associated with a decreased likelihood of achieving a clinical response, even when receiving biological therapy. The cellular and molecular mechanisms underlying tunnel formation and pathology are only partially understood, which hampers the development of more effective targeted therapies. Tunnels create a unique microenvironment that drives a vicious cycle of hidradenitis suppurativa inflammation, with tunnel keratinocytes exhibiting an activated phenotype characterized by distinct gene expression signatures. In this review, we summarize the current literature and discuss aspects of the pathophysiology of tunnels, including the role of hair follicle epidermal stem cells in tunnel formation, potential role of fibroblast-mediated epithelial-mesenchymal transition, role of dermal papilla fibroblasts, and aberrant proinflammatory repair response contributing to the observed fibrosis and scarring. Finally, tunnel structures are characterized by unique microbial dysbiosis and an overabundance of Gram-negative anaerobes that are not targeted by current therapeutics. In addition to outlining the possible mechanisms of tunnel formation, we provide perspectives on the translation of current knowledge into more effective treatment approaches for patients with hidradenitis suppurativa tunnels.

Lactobacillus reuteri NCHBL-005 improves wound healing by promoting the activation of fibroblasts through TLR2/MAPK signaling

BACKGROUND

Wound healing is a complex physiological process essential for restoring tissue integrity following various injuries, ranging from minor, everyday incidents to post-surgical complications. Emerging studies have demonstrated that lactic acid bacteria (LAB) can offer benefits beyond gut health, extending their positive effects on skin health. This study investigated the potential of Lactobacillus reuteri NCHBL-005, a honeybee-derived probiotic strain, to enhance fibroblast-mediated wound healing.

METHOD

L929 cells and mouse embryonic fibroblasts (MEFs) were utilized as models to specifically target fibroblasts. To assess the wound healing potential in vitro, a scratch assay was performed, providing insights into wound closure. Additionally, we created wound models in mice to evaluate the in vivo effects of the treatment.

RESULTS

Our results showed that L. reuteri NCHBL-005 significantly accelerated wound closure in L929 fibroblast compared to other lactobacilli and exhibited superior efficacy in activating the mitogen-activated protein kinase (MAPK) pathway. Through MAPK inhibition assays, we confirmed that the wound healing effects of L. reuteri NCHBL-005 were MAPK-dependent, promoting fibroblast proliferation and differentiation. Notably, L. reuteri NCHBL-005 treatment did not facilitate wound healing in MEF cells derived from Toll-like-receptor 2 knockout (TLR2-/-) mice, highlighting the critical role of TLR2 in this mechanism. In vivo studies further corroborated these findings, in which topical administration of L. reuteri NCHBL-005 enhanced wound healing and stimulated fibroblast proliferation and activation, as confirmed by histopathological analysis.

CONCLUSION

These findings revealed that L. reuteri NCHBL-005 activates fibroblasts through TLR2 stimulation and subsequent MAPK pathway activation, suggesting its potential as a promising therapeutic candidate for wound management.

Cancer-associated fibroblasts in breast cancer in the single-cell era: Opportunities and challenges

Breast cancer is a leading cause of morbidity and mortality in women, and its progression is closely linked to the tumor microenvironment (TME). Cancer-associated fibroblasts (CAFs), key components of the TME, play a crucial role in promoting tumor growth by driving cancer cell proliferation, invasion, extracellular matrix (ECM) remodeling, inflammation, chemoresistance, and immunosuppression. CAFs exhibit considerable heterogeneity and are classified into subgroups based on different combinations of biomarkers. Single-cell RNA sequencing (scRNA-seq) enables high-throughput and high-resolution analysis of individual cells. Relying on this technology, it is possible to cluster complex CAFs according to different biomarkers to analyze the specific phenotypes and functions of different subpopulations. This review explores CAF clusters in breast cancer and their associated biomarkers, highlighting their roles in disease progression and potential for targeted therapies.

The HOX code of human adult fibroblasts reflects their ectomesenchymal or mesodermal origin

Fibroblasts, the most abundant cell type in the human body, play crucial roles in biological processes such as inflammation and cancer progression. They originate from the mesoderm or neural-crest-derived ectomesenchyme. Ectomesenchyme-derived fibroblasts contribute to facial formation and do not express HOX genes during development. The expression and role of the HOX genes in adult fibroblasts is not known. We investigated whether the developmental pattern persists into adulthood and under pathological conditions, such as cancer. We collected adult fibroblasts of ectomesenchymal and mesodermal origins from distinct body parts. The isolated fibroblasts were characterised by immunocytochemistry, and their transcriptome was analysed by whole genome profiling. Significant differences were observed between normal fibroblasts from the face (ectomesenchyme) and upper limb (mesoderm), particularly in genes associated with limb development, including HOX genes, e.g., HOXA9 and HOXD9. Notably, the pattern of HOX gene expression remained consistent postnatally, even in fibroblasts from pathological tissues, including inflammatory states and cancer-associated fibroblasts from primary and metastatic tumours. Therefore, the distinctive HOX gene expression pattern can serve as an indicator of the topological origin of fibroblasts. The influence of cell position and HOX gene expression in fibroblasts on disease progression warrants further investigation.

Efficacy of an Autologous Dermal Fibroblast Injection in Reducing the Retear Rate After Arthroscopic Rotator Cuff Repair: A Prospective Randomized Controlled Trial

BACKGROUND

Interest in biological augmentation for improving bone-tendon interface (BTI) healing after arthroscopic rotator cuff repair (ARCR) is growing. Dermal fibroblasts, known for collagen synthesis similar to tenocytes, have shown effectiveness in BTI healing in chronic rotator cuff tear (RCT) models in rabbits. However, no human clinical trials have been conducted.

PURPOSE

To evaluate the clinical efficacy of autologous dermal fibroblasts (ADFs) for BTI healing after ARCR in patients with full-thickness RCTs >2 cm.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 2.

METHODS

A total of 86 patients were prospectively enrolled and randomized into 2 groups: an additional ADF injection between the bone and tendon during ARCR (ADF group) or ARCR alone (control group). A skin biopsy from the buttock was performed to obtain ADFs, which were cultured for approximately 4 weeks before surgery. ARCR was standardized to the double-row suture bridge technique to reduce the heterogeneity in different repair methods. The primary variable for evaluating ADF efficacy was the retear rate using magnetic resonance imaging at 6 months postoperatively. Secondary variables included range of motion, the American Shoulder and Elbow Surgeons score, the Constant score, and the Simple Shoulder Test score at baseline and at 6 and 12 months postoperatively.

RESULTS

Overall, 13 patients dropped out because of a subscapularis tendon tear, loss to follow-up, or the withdrawal of consent (7 in the ADF group and 6 in the control group). The retear rate was significantly lower in the ADF group (5.6% [2/36]) than in the control group (24.3% [9/37]) (P = .025). The American Shoulder and Elbow Surgeons, Constant, and Simple Shoulder Test scores showed significant improvement after surgery in both groups (all P values <.001). Functional scores and range of motion did not significantly differ between the 2 groups at 6 and 12 months (all P values >.05).

CONCLUSION

ADF application into the BTI during ARCR significantly decreased the retear rate in patients with full-thickness RCTs >2 cm. Therefore, an ADF injection could be a promising biological supplement to enhance BTI healing in these patients. However, clinical outcomes showed no significant difference between the 2 groups at 6 months and 1 year postoperatively.

Safety and efficacy of hairy scalp donors in thick split-thickness skin grafting: Healing and complications at donor sites

Background

We aimed to investigate how the thickness of removed skin grafts affects the healing time at the donor site, with a focus on the depth of the donor wound and the normal thickness of the scalp.

Methods

We examined the outcomes of the donor sites of thick split-thickness skin grafts using hairy scalp skin in 102 Korean patients. We measured the thickness of the scalp donor skin using preoperative ultrasonography, histometric thickness of normal scalp skin in 61 patients, and histometric thickness of the thickest part of the grafted skin after surgery.

Results

The mean normal ultrasound thickness of the scalp donors was 1.711 mm, with a mean histometric normal scalp thickness of 1.926 mm (61 cases), mean dermatome depth set of 0.569 mm (22/1000 inches, 22 mils), and mean histometric harvested skin thickness of 0.677 mm. The relationship between healing time and percentage of histometric graft thickness per ultrasonographic normal scalp skin thickness was statistically significant and correlated positively. Healing of the partial portion of the scalp was delayed in 9 donors due to infection and folliculitis. Scalp donor wounds healed during postoperative days 6 and 15, except for the ones with infected portions.

Conclusion

Patients in this study successfully achieved scarless regenerative healing of their scalp donor wounds. Furthermore, adequate wound dressing can prevent alopecia and scarring of infected donor wounds. The results of this study offer valuable insights into the advantages of using scalp skin in grafts, underscoring its potential as a preferred option for achieving optimal regenerative healing.

Spiny mice (Acomys) have evolved cellular features to support regenerative healing

Spiny mice (Acomys spp.) are warm-blooded (homeothermic) vertebrates whose ability to restore missing tissue through regenerative healing has coincided with the evolution of unique cellular and physiological adaptations across different tissue types. This review seeks to explore how these bizarre rodents deploy unique or altered injury response mechanisms to either enhance tissue repair or fully regenerate excised tissue compared to closely related, scar-forming mammals. First, we examine overall trends in healing Acomys tissues, including the cellular stress response, the ability to activate and maintain cell cycle progression, and the expression of certain features in reproductive adults that are normally associated with embryos. Second, we focus on specific cell types that exhibit precisely regulated proliferation to restore missing tissue. While Acomys utilize many of the same cell types involved in scar formation, these cells exhibit divergent activation profiles during regenerative healing. Considered together, current lines of evidence support sustained deployment of proregenerative pathways in conjunction with transient activation of fibrotic pathways to facilitate regeneration and improve tissue repair in Acomys.

Isolation and Culture of Human Dermal Fibroblasts

Dermal fibroblasts are the main cell type present in skin connective tissue (dermis). They are responsible for the synthesis of dermal extracellular matrix (ECM), providing mechanical stability for the dermal layer. In addition, fibroblasts interact with epidermal cells during hair development and in interfollicular skin cells through bidirectional interactions and secretion of growth factors and cytokines. The changes in the fibroblast population correlate with structural, compositional, quantitative, and qualitative transformations of the main ECM proteins in the dermis, as well as with the age-related disorders, and the state and proliferative activity of basal keratinocytes that are the main cells in the epidermis. Moreover, fibroblasts play an essential role during cutaneous wound healing and in bio-engineering of skin. Hence, culture of primary fibroblast is gaining in importance. In addition, fibroblast cultures established from skin biopsies provide a powerful tool for investigating normal skin physiology or specific disease states. In this chapter, detailed procedures for the establishing and maintaining primary cultures of adult human dermal fibroblasts are described.

Mindin regulates fibroblast subpopulations through distinct Src family kinases during fibrogenesis

Fibrosis results from excessive extracellular matrix (ECM) deposition, which causes tissue stiffening and organ dysfunction. Activated fibroblasts, central to fibrosis, exhibit increased migration, proliferation, contraction, and ECM production. However, it remains unclear if the same fibroblast performs all of the processes that fall under the umbrella term of "activation." Owing to fibroblast heterogeneity in connective tissues, subpopulations with specific functions may operate under distinct regulatory controls. Using a transgenic mouse model of skin fibrosis, we found that Mindin (also known as spondin-2), secreted by Snail-transgenic keratinocytes, differentially regulates fibroblast subpopulations. Mindin promotes migration and inflammatory gene expression in SCA1+ dermal fibroblasts via Fyn kinase. In contrast, it enhances contractility and collagen production in papillary CD26+ fibroblasts through c-Src signaling. Moreover, in the context of the fibrotic microenvironment of the tumor stroma, we found that differential responses of resident fibroblast subpopulations to Mindin extend to the generation of functionally heterogeneous cancer-associated fibroblasts. This study identifies Mindin as a key orchestrator of dermal fibroblast heterogeneity, reshaping cellular dynamics and signaling diversity in the complex landscapes of skin fibrosis and cancer.

Quercetin rescues dihydrotestosterone-treated human dermal papilla cells via SHP2/AKT signaling to suppress autophagy and apoptosis

The management of hair loss is vital in clinical dermatology due to its prevalence and impact on patients' quality of life. Quercetin is recognized for its diverse activities, including anti-inflammatory, anti-cancer, and immune regulation. However, its effects on human hair follicles and mechanisms remain unclear. This study explored quercetin's impact on countering DHT-induced cell damage, emphasizing apoptosis, cell cycle, mitochondria, and autophagy. Quercetin mitigated DHT's harm, restoring dermal papilla cell function and modulating cell cycle proteins. It restrained DHT-induced ROS and ATP loss, preserving mitochondrial integrity. Through network pharmacology analysis, it was discovered that quercetin targets SHP2, thereby regulating AKT signaling. Additionally, in mice, quercetin was found to promote hair growth. These significant insights highlight the potential of quercetin as a promising solution for hair loss and hair regeneration.

Skin immune-mesenchymal interplay within tertiary lymphoid structures promotes autoimmune pathogenesis in hidradenitis suppurativa

Hidradenitis suppurativa (HS) is a chronic, debilitating inflammatory skin disease characterized by keratinized epithelial tunnels that grow deeply into the dermis. Here, we examined the immune microenvironment within human HS lesions. Multi-omics profiling and multiplexed imaging identified tertiary lymphoid structures (TLSs) near HS tunnels. These TLSs were enriched with proliferative T cells, including follicular helper (Tfh), regulatory (Treg), and pathogenic T cells (IL17A+ and IFNG+), alongside extensive clonal expansion of plasma cells producing antibodies reactive to keratinocytes. HS fibroblasts express CXCL13 or CCL19 in response to immune cytokines. Using a microfluidic system to mimic TLS on a chip, we found that HS fibroblasts critically orchestrated lymphocyte aggregation via tumor necrosis factor alpha (TNF-α)-CXCL13 and TNF-α-CCL19 feedback loops with B and T cells, respectively; early TNF-α blockade suppressed aggregate initiation. Our findings provide insights into TLS formation in the skin, suggest therapeutic avenues for HS, and reveal mechanisms that may apply to other autoimmune settings, including Crohn's disease.

Comparison of Culturing Methods of Primary Vaginal Fibroblasts

IMPORTANCE

Vaginal fibroblast function is altered in people with pelvic organ prolapse. Thus, it is important to study vaginal fibroblasts to better understand the pathophysiology of prolapse.

OBJECTIVE

This study aimed to compare 3 culturing methods of primary vaginal fibroblasts.

STUDY DESIGN

This was an in vitro study. Patients who were undergoing surgery for vaginal prolapse were recruited. Excess vaginal epithelial tissue that would have otherwise been discarded was collected. The vaginal fibroblasts from each participant were cultured via (1) 3-hour digest, (2) coverslip, and (3) gelatin-coat methods. Differences in the efficiency of cell isolation, expression of known fibroblast-associated genes, and cellular function were compared between the 3 methods using one-way analysis of variance and Tukey test for post hoc pairwise comparisons (P < 0.05).

RESULTS

Five patients with pelvic organ prolapse were recruited. Fibroblasts cultured via the 3-hour digest method became confluent within 3-5 days in a 100-mm dish compared to 2-3 weeks in a 6-well dish for the coverslip and gelatin-coat methods. Cells from all culture methods expressed similar amounts of vimentin and α smooth muscle actin. There were no significant differences in morphology; gene expression levels of MMP1, MMP2, ACTA2, COL1A1, COL3A1, and LOXL1 on qPCR; cell viability; proliferation; and migration between the 3 culturing methods.

CONCLUSION

Culturing primary vaginal fibroblasts via the 3-hour digest, coverslip, and gelatin-coat methods similarly resulted in reliable primary vaginal fibroblast growth and function.

Umbelliferone alleviates impaired wound healing and skin barrier dysfunction in high glucose-exposed dermal fibroblasts and diabetic skins

Skin wound healing is a complex process involving various cellular and molecular events. However, chronic wounds, particularly in individuals with diabetes, often experience delayed wound healing, potentially leading to diabetic skin complications. In this study, we examined the effects of umbelliferone on skin wound healing using dermal fibroblasts and skin tissues from a type 2 diabetic mouse model. Our results demonstrate that umbelliferone enhances several crucial aspects of wound healing. It increases the synthesis of key extracellular matrix components such as collagen I and fibronectin, as well as proteins involved in cell migration like EVL and Fascin-1. Additionally, umbelliferone boosts the secretion of angiogenesis factors VEGF and HIF-1α, enhances the expression of cell adhesion proteins including E-cadherin, ZO-1, and Occludin, and elevates levels of skin hydration-related proteins like HAS2 and AQP3. Notably, umbelliferone reduces the expression of HYAL, thereby potentially decreasing tissue permeability. As a result, it promotes extracellular matrix deposition, activates cell migration and proliferation, and stimulates pro-angiogenic factors while maintaining skin barrier functions. In summary, these findings underscore the therapeutic potential of umbelliferone in diabetic wound care, suggesting its promise as a treatment for diabetic skin complications. KEY MESSAGES: Umbelliferone suppressed the breakdown of extracellular matrix components in the skin dermis while promoting their synthesis. Umbelliferone augmented the migratory and proliferative capacities of fibroblasts. Umbelliferone activated the release of angiogenic factors in diabetic wounds, leading to accelerated wound healing. Umbelliferone bolstered intercellular adhesion and reinforced the skin barrier by preventing moisture loss and preserving skin hydration.

Neural crest precursors from the skin are the primary source of directly reprogrammed neurons

Direct reprogramming involves the conversion of differentiated cell types without returning to an earlier developmental state. Here, we explore how heterogeneity in developmental lineage and maturity of the starting cell population contributes to direct reprogramming using the conversion of murine fibroblasts into neurons. Our hypothesis is that a single lineage of cells contributes to most reprogramming and that a rare elite precursor with intrinsic bias is the source of reprogrammed neurons. We find that nearly all reprogrammed neurons are derived from the neural crest (NC) lineage. Moreover, when rare proliferating NC precursors are selectively ablated, there is a large reduction in the number of reprogrammed neurons. Previous interpretations of this paradigm are that it demonstrates a cell fate conversion across embryonic germ layers (mesoderm to ectoderm). Our interpretation is that this is actually directed differentiation of a neural lineage stem cell in the skin that has intrinsic bias to produce neuronal progeny.

Characterizing Fibroblast Heterogeneity in Diabetic Wounds Through Single-Cell RNA-Sequencing

Diabetes mellitus is an increasingly prevalent chronic metabolic disorder characterized by physiologic hyperglycemia that, when left uncontrolled, can lead to significant complications in multiple organs. Diabetic wounds are common in the general population, yet the underlying mechanism of impaired healing in such wounds remains unclear. Single-cell RNA-sequencing (scRNAseq) has recently emerged as a tool to study the gene expression of heterogeneous cell populations in skin wounds. Herein, we review the history of scRNAseq and its application to the study of diabetic wound healing, focusing on how innovations in single-cell sequencing have transformed strategies for fibroblast analysis. We summarize recent research on the role of fibroblasts in diabetic wound healing and describe the functional and cellular heterogeneity of skin fibroblasts. Moreover, we highlight future opportunities in diabetic wound fibroblast research, with a focus on characterizing distinct fibroblast subpopulations and their lineages. Leveraging single-cell technologies to explore fibroblast heterogeneity and the complex biology of diabetic wounds may reveal new therapeutic targets for improving wound healing and ultimately alleviate the clinical burden of chronic wounds.

Accelerated Closure of Diabetic Wounds by Efficient Recruitment of Fibroblasts upon Inhibiting a 14-3-3/ROCK Regulatory Axis

Chronic non-healing wounds negatively impact quality of life and are a significant financial drain on health systems. The risk of infection that exacerbates comorbidities in patients necessitates regular application of wound care. Understanding the mechanisms underlying impaired wound healing are therefore a key priority to inform effective new-generation treatments. In this study, we demonstrate that 14-3-3-mediated suppression of signaling through ROCK is a critical mechanism that inhibits the healing of diabetic wounds. Accordingly, pharmacological inhibition of 14-3-3 by topical application of the sphingo-mimetic drug RB-11 to diabetic wounds on a mouse model of type II diabetes accelerated wound closure more than 2-fold than vehicle control, phenocopying our previous observations in 14-3-3ζ-knockout mice. We also demonstrate that accelerated closure of the wounded epidermis by 14-3-3 inhibition causes enhanced signaling through the Rho-ROCK pathway and that the underlying cellular mechanism involves the efficient recruitment of dermal fibroblasts into the wound and the rapid production of extracellular matrix proteins to re-establish the injured dermis. Our observations that the 14-3-3/ROCK inhibitory axis characterizes impaired wound healing and that its suppression facilitates fibroblast recruitment and accelerated re-epithelialization suggest new possibilities for treating diabetic wounds by pharmacologically targeting this axis.

An Update on Molecular Mechanisms of Scarring-A Narrative Review

Fibroblasts, the principal cellular mediators of connective tissue remodeling, play a crucial role in the formation of physiological and pathological scars. Understanding the intricate interplay between fibroblasts and other cellular and molecular components is essential for elucidating the underlying mechanisms driving scar formation. Hypertrophic scars, keloids and atrophic scars arise from dysregulated wound healing processes characterized by persistent inflammation, aberrant collagen deposition, and impaired extracellular matrix remodeling. Fibroblasts play a central role in the pathogenesis of such pathological scars, driving aberrant extracellular matrix remodeling, subsequently contributing to the formation of raised or depressed fibrotic lesions. The investigation of complex interactions between fibroblasts and the microenvironment is crucial for developing targeted therapeutic interventions aimed at modulating fibroblast activity and improving clinical outcomes in patients with pathological scars. Further research into the molecular pathways governing fibroblast behavior and their heterogeneity holds promise for advancing scar management strategies. This narrative review was performed to shed light on the mechanisms behind scar formation, with a special focus on the role of fibroblasts in the formation of different types of scars, providing insights into the pathophysiology of these conditions. Through the analysis of current knowledge, this review seeks to identify the key cellular and molecular mechanisms involved in fibroblast activation, collagen synthesis, and extracellular matrix remodeling in hypertrophic scar, keloid, or atrophic scar formation.

Characterization and Physiological Differences of Two Primary Cultures of Human Normal and Hypertrophic Scar Dermal Fibroblasts: A Pilot Study

Background/Objectives: Dermal fibroblasts (DFs) are key participants in skin hypertrophic scarring, and their properties are being studied to identify the molecular and cellular mechanisms underlying the pathogenesis of skin scarring. Methods: In the present work, we performed a comparative analysis of DFs isolated from normal skin (normal dermal fibroblasts, NDFs), and hypertrophic scar skin (hypertrophic scar fibroblasts, HTSFs). The fibroblasts were karyotyped and phenotyped, and experiments on growth rate, wound healing, and single-cell motility were conducted. Results: Comparative analysis revealed a minor karyotype difference between cells. However, HTSFs are characterized by higher proliferation level and motility compared to NDFs. These significant differences may be associated with quantitative and qualitative differences in the cell secretome. A proteomic comparison of NDF and HTSF found that differences were associated with metabolic proteins reflecting physiological differences between the two cells lines. Numerous unique proteins were found only in the vesicular phase of vHTSFs. Some proteins involved in cell proliferation (protein-glutamine gamma-glutamyltransferase K) and cell motility (catenin delta-1), which regulate gene transcription and the activity of Rho family GTPases and downstream cytoskeletal dynamics, were identified. A number of proteins which potentially play a role in fibrosis and inflammation (mucin-5B, CD97, adhesion G protein-coupled receptor E2, antileukoproteinase, protein S100-A8 and S100-A9, protein caspase recruitment domain-containing protein 14) were detected in vHTSFs. Conclusions: A comparative analysis of primary cell cultures revealed their various properties, especially in the cell secretome. These proteins may be considered promising target molecules for developing treatment or prevention strategies for pathological skin scarring.

Unraveling the Functional Heterogeneity of Human Skin at Single-Cell Resolution

The skin consists of several cell populations, including epithelial, immune, and stromal cells. Recently, there has been a significant increase in single-cell RNA-sequencing studies, contributing to the development of a consensus Human Skin Cell Atlas. The aim is to understand skin biology better and identify potential therapeutic targets. The present review utilized previously published single-cell RNA-sequencing datasets to explore human skin's cellular and functional heterogeneity. Additionally, it summarizes the functional significance of newly identified cell subpopulations in processes such as wound healing and aging.

A recent update on the connection between dietary phytochemicals and skin cancer: emerging understanding of the molecular mechanism

Constant exposure to harmful substances from both inside and outside the body can mess up the body's natural ways of keeping itself in balance. This can cause severe skin damage, including basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and melanoma. However, plant-derived compounds found in fruits and vegetables have been shown to protect against skin cancer-causing free radicals and other harmful substances. It has been determined that these dietary phytochemicals are effective in preventing skin cancer and are widely available, inexpensive, and well-tolerated. Studies have shown that these phytochemicals possess anti-inflammatory, antioxidant, and antiangiogenic properties that can aid in the prevention of skin cancers. In addition, they influence crucial cellular processes such as angiogenesis and cell cycle control, which can halt the progression of skin cancer. The present paper discusses the benefits of specific dietary phytochemicals found in fruits and vegetables, as well as the signaling pathways they regulate, the molecular mechanisms involved in the prevention of skin cancer, and their drawbacks.

Enzymatic activity of fibroblast activation protein-α is essential for TGF-β1-induced fibroblastic differentiation of human periodontal ligament cells

Human periodontal ligament cells (hPDLCs) contain multipotent postnatal stem cells that can differentiate into PDL fibroblasts, osteoblasts, and cementoblasts. Interaction between the extracellular environment and stem cells is an important factor for differentiation into other progenitor cells. To identify cell surface molecules that induce PDL fibroblastic differentiation, we developed a series of monoclonal antibodies against membrane/ECM molecules. One of these antibodies, an anti-PDL25 antibody, recognizes approximately a 100 kDa protein, and this antigenic molecule accumulates in the periodontal ligament region of tooth roots. By mass spectrometric analysis, we found that the antigenic molecule recognized by the anti-PDL25 antibody is fibroblast activation protein α (FAPα). The expression level of FAPα/PDL25 increased in TGF-β1-induced PDL fibroblasts, and this protein was localized in the cell boundaries and elongated processes of the fibroblastic cells. Ectopic expression of FAPα induced fibroblastic differentiation. In contrast, expression of representative markers for PDL differentiation was decreased by knock down and antibody blocking of FAPα/PDL25. Inhibition of dipeptidyl peptidase activity by a potent FAPα inhibitor dramatically inhibited PDL fibroblastic marker expression but did not affect in cell proliferation and migration.

Mmp14-dependent remodeling of the pericellular-dermal collagen interface governs fibroblast survival

Dermal fibroblasts deposit type I collagen, the dominant extracellular matrix molecule found in skin, during early postnatal development. Coincident with this biosynthetic program, fibroblasts proteolytically remodel pericellular collagen fibrils by mobilizing the membrane-anchored matrix metalloproteinase, Mmp14. Unexpectedly, dermal fibroblasts in Mmp14-/- mice commit to a large-scale apoptotic program that leaves skin tissues replete with dying cells. A requirement for Mmp14 in dermal fibroblast survival is recapitulated in vitro when cells are embedded within, but not cultured atop, three-dimensional hydrogels of crosslinked type I collagen. In the absence of Mmp14-dependent pericellular proteolysis, dermal fibroblasts fail to trigger β1 integrin activation and instead actuate a TGF-β1/phospho-JNK stress response that leads to apoptotic cell death in vitro as well as in vivo. Taken together, these studies identify Mmp14 as a requisite cell survival factor that maintains dermal fibroblast viability in postnatal dermal tissues.

The Human Neonatal Skin Fibroblast, an Available Cell Source for Tissue Production and Transplantation, Exhibits Low Risk of Immunogenicity In Vitro

The immunogenicity of allogeneic skin fibroblasts in transplantation has been controversial. Whether this controversy comes from a natural heterogeneity among fibroblast subsets or species-specific differences between human and mouse remains to be addressed. In this study, we sought to investigate whether fibroblasts derived from either adult or neonatal human skin tissues could induce different immune responses toward phagocytosis and T cell activation using in vitro co-culture models. Our results indicate that both phagocytosis and T cell proliferation are reduced in the presence of neonatal skin fibroblasts compared to adult skin fibroblasts. We also show that neonatal skin fibroblasts secrete paracrine factors that are responsible for reduced T cell proliferation. In addition, we show that neonatal skin fibroblasts express less class II human leukocyte antigen (HLA) molecules than adult skin fibroblasts after interferon gamma priming, which might also contribute to reduced T cell proliferation. In conclusion, this study supports the use of allogeneic neonatal skin fibroblasts as a readily available cell source for tissue production and transplantation to treat patients with severe injuries.

scHolography: a computational method for single-cell spatial neighborhood reconstruction and analysis

Spatial transcriptomics has transformed our ability to study tissue complexity. However, it remains challenging to accurately dissect tissue organization at single-cell resolution. Here we introduce scHolography, a machine learning-based method designed to reconstruct single-cell spatial neighborhoods and facilitate 3D tissue visualization using spatial and single-cell RNA sequencing data. scHolography employs a high-dimensional transcriptome-to-space projection that infers spatial relationships among cells, defining spatial neighborhoods and enhancing analyses of cell-cell communication. When applied to both human and mouse datasets, scHolography enables quantitative assessments of spatial cell neighborhoods, cell-cell interactions, and tumor-immune microenvironment. Together, scHolography offers a robust computational framework for elucidating 3D tissue organization and analyzing spatial dynamics at the cellular level.

Integration mapping of cardiac fibroblast single-cell transcriptomes elucidates cellular principles of fibrosis in diverse pathologies

Single-cell technology has allowed researchers to probe tissue complexity and dynamics at unprecedented depth in health and disease. However, the generation of high-dimensionality single-cell atlases and virtual three-dimensional tissues requires integrated reference maps that harmonize disparate experimental designs, analytical pipelines, and taxonomies. Here, we present a comprehensive single-cell transcriptome integration map of cardiac fibrosis, which underpins pathophysiology in most cardiovascular diseases. Our findings reveal similarity between cardiac fibroblast (CF) identities and dynamics in ischemic versus pressure overload models of cardiomyopathy. We also describe timelines for commitment of activated CFs to proliferation and myofibrogenesis, profibrotic and antifibrotic polarization of myofibroblasts and matrifibrocytes, and CF conservation across mouse and human healthy and diseased hearts. These insights have the potential to inform knowledge-based therapies.

Subpopulations of fibroblasts derived from human iPS cells

Organ fibrosis causes collagen fiber overgrowth and impairs organ function. Cardiac fibrosis after myocardial infarction impairs cardiac function significantly, pulmonary fibrosis reduces gas exchange efficiency, and liver fibrosis disturbs the natural function of the liver. Its development is associated with the differentiation of fibroblasts into myofibroblasts and increased collagen synthesis. Fibrosis has organ specificity, defined by the heterogeneity of fibroblasts. Although this heterogeneity is established during embryonic development, it has not been defined yet. Fibroblastic differentiation of induced pluripotent stem cells (iPSCs) recapitulates the process by which fibroblasts acquire diversity. Here, we differentiated iPSCs into cardiac, hepatic, and dermal fibroblasts and analyzed their properties using single-cell RNA sequencing. We observed characteristic subpopulations with different ratios in each organ-type fibroblast group, which contained both resting and distinct ACTA2+ myofibroblasts. These findings provide crucial information on the ontogeny-based heterogeneity of fibroblasts, leading to the development of therapeutic strategies to control fibrosis.

miR-125b-5p delivered by adipose-derived stem cell exosomes alleviates hypertrophic scarring by suppressing Smad2

Background

Hypertrophic scarring is the most serious and unmet challenge following burn and trauma injury and often leads to pain, itching and even loss of function. However, the demand for ideal scar prevention and treatment is difficult to satisfy. We aimed to discover the effects and mechanisms of adipose-derived stem cell (ADSC) exosomes in hypertrophic scarring.

Methods

ADSC exosomes were isolated from the culture supernatant of ADSCs and identified by nanoparticle tracking analysis, transmission electron microscopy and western blotting. The effect of ADSC exosomes on wound healing and scar formation was detected by the wound model of BALB/c mice. We isolated myofibroblasts from hypertrophic scar tissue and detected the cell viability, proliferation and migration of myofibroblasts. In addition, collagen formation and fibrosis-related molecules were also detected. To further disclose the mechanism of ADSC exosomes on fibrosis in myofibroblasts, we detected the expression of Smad2 in hypertrophic scar tissue and normal skin and the regulatory mechanism of ADSC exosomes on Smad2. Injection of bleomycin was performed in male BALB/c mice to establish an in vivo fibrosis model while ADSC exosomes were administered to observe their protective effect. The tissue injury of mice was observed via hematoxylin and eosin and Masson staining and related testing.

Results

In this study, we found that ADSC exosomes could not only speed up wound healing and improve healing quality but also prevent scar formation. ADSC exosomes inhibited expression of fibrosis-related molecules such as α-smooth muscle actin, collagen I (COL1) and COL3 and inhibited the transdifferentiation of myofibroblasts. In addition, we verified that Smad2 is highly expressed in both hypertrophic scar tissue and hypertrophic fibroblasts, while ADSC exosomes downregulated the expression of Smad2 in hypertrophic fibroblasts. Further regulatory mechanism analysis revealed that microRNA-125b-5p (miR-125b-5p) is highly expressed in ADSC exosomes and binds to the 3' untranslated region of Smad2, thus inhibiting its expression. In vivo experiments also revealed that ADSC exosomes could alleviate bleomycin-induced skin fibrosis and downregulate the expression of Smad2.

Conclusions

We found that ADSC exosomes could alleviate hypertrophic scars via the suppression of Smad2 by the specific delivery of miR-125b-5p.

The role of positional information in determining dermal fibroblast diversity

The largest mammalian organ, skin, consisting of a dermal connective tissue layer that underlies and supports the epidermis, acts as a protective barrier that excludes external pathogens and disseminates sensory signals emanating from the local microenvironment. Dermal connective tissue is comprised of a collagen-rich extracellular matrix (ECM) that is produced by connective tissue fibroblasts resident within the dermis. When wounded, a tissue repair program is induced whereby fibroblasts, in response to alterations in the microenvironment, produce new ECM components, resulting in the formation of a scar. Failure to terminate the normal tissue repair program causes fibrotic conditions including: hypertrophic scars, keloids, and the systemic autoimmune connective tissue disease scleroderma (systemic sclerosis, SSc). Histological and single-cell RNA sequencing (scRNAseq) studies have revealed that fibroblasts are heterogeneous and highly plastic. Understanding how this diversity contributes to dermal homeostasis, wounding, fibrosis, and cancer may ultimately result in novel anti-fibrotic therapies and personalized medicine. This review summarizes studies supporting this concept.

Biomaterials for immunomodulation in wound healing

The substantial economic impact of non-healing wounds, scarring, and burns stemming from skin injuries is evident, resulting in a financial burden on both patients and the healthcare system. This review paper provides an overview of the skin's vital role in guarding against various environmental challenges as the body's largest protective organ and associated developments in biomaterials for wound healing. We first introduce the composition of skin tissue and the intricate processes of wound healing, with special attention to the crucial role of immunomodulation in both acute and chronic wounds. This highlights how the imbalance in the immune response, particularly in chronic wounds associated with underlying health conditions such as diabetes and immunosuppression, hinders normal healing stages. Then, this review distinguishes between traditional wound-healing strategies that create an optimal microenvironment and recent peptide-based biomaterials that modulate cellular processes and immune responses to facilitate wound closure. Additionally, we highlight the importance of considering the stages of wounds in the healing process. By integrating advanced materials engineering with an in-depth understanding of wound biology, this approach holds promise for reshaping the field of wound management and ultimately offering improved outcomes for patients with acute and chronic wounds.

The role of dermal fibroblasts in autoimmune skin diseases

Fibroblasts are an important subset of mesenchymal cells in maintaining skin homeostasis and resisting harmful stimuli. Meanwhile, fibroblasts modulate immune cell function by secreting cytokines, thereby implicating their involvement in various dermatological conditions such as psoriasis, vitiligo, and atopic dermatitis. Recently, variations in the subtypes of fibroblasts and their expression profiles have been identified in these prevalent autoimmune skin diseases, implying that fibroblasts may exhibit distinct functionalities across different diseases. In this review, from the perspective of their fundamental functions and remarkable heterogeneity, we have comprehensively collected evidence on the role of fibroblasts and their distinct subpopulations in psoriasis, vitiligo, atopic dermatitis, and scleroderma. Importantly, these findings hold promise for guiding future research directions and identifying novel therapeutic targets for treating these diseases.

Assessing the fate and contribution of Foxd1-expressing embryonic precursors and their progeny in palatal development, homeostasis and excisional repair

Oral mucosal tissues heal rapidly with minimal scarring, although palatal mucosa can be associated with excessive fibrosis in response to injury. Investigations on the balance between neovascularization and tissue repair suggests regulation of angiogenesis is an important determinant of repair versus scarring. Associated with pericyte mediated fibrosis in kidney injury, FoxD1 is implicated in growth centres during cranio-facial development, although which cell lineages are derived from these embryonic populations in development and in adult animals is unknown. Using a lineage tracing approach, we assessed the fate of embryonic Foxd1-expressing progenitor cells and their progeny in palatal development and during wound healing in adult mice. During palatal development as well as in post-natal tissues, Foxd1-lineage progeny were associated with the vasculature and the epineurium. Post-injury, de novo expression of FoxD1 was not detectable, although Foxd1-lineage progeny expanded while exhibiting low association with the fibroblast/myofibroblast markers PDGFα, PDGFβ, vimentin, α-smooth muscle actin, as well as the neuronal associated markers S100β and p75NTR. Foxd1-lineage progeny were primarily associated with CD146, CD31, and to a lesser extent CD105, remaining in close proximity to developing neovascular structures. Our findings demonstrate that FoxD1 derived cells are predominantly associated with the palatal vasculature and provide strong evidence that FoxD1 derived cells do not give rise to populations involved directly in the scarring of the palate.

Light Sheet-Based Laser Patterning Bioprinting Produces Long-Term Viable Full-Thickness Skin Constructs

Tissue engineering holds great promise for biomedical research and healthcare, offering alternatives to animal models and enabling tissue regeneration and organ transplantation. 3D bioprinting stands out for its design flexibility and reproducibility. Here, an integrated fluorescent light sheet bioprinting and imaging system is presented that combines high printing speed (0.66 mm3 /s) and resolution (9 µm) with light sheet-based imaging. This approach employs direct laser patterning and a static light sheet for confined voxel crosslinking in photocrosslinkable materials. The developed bioprinter enables real-time monitoring of hydrogel crosslinking using fluorescent recovery after photobleaching (FRAP) and brightfield imaging as well as in situ light sheet imaging of cells. Human fibroblasts encapsulated in a thiol-ene click chemistry-based hydrogel exhibited high viability (83% ± 4.34%) and functionality. Furthermore, full-thickness skin constructs displayed characteristics of both epidermal and dermal layers and remained viable for 41 days. The integrated approach demonstrates the capabilities of light sheet bioprinting, offering high speed, resolution, and real-time characterization. Future enhancements involving solid-state laser scanning devices such as acousto-optic deflectors and modulators will further enhance resolution and speed, opening new opportunities in light-based bioprinting and advancing tissue engineering.

Engineered Extracellular Vesicles in Wound Healing: Design, Paradigms, and Clinical Application

The severe quality of life and economic burden imposed by non-healing skin wounds, infection risks, and treatment costs are affecting millions of patients worldwide. To mitigate these challenges, scientists are relentlessly seeking effective treatment measures. In recent years, extracellular vesicles (EVs) have emerged as a promising cell-free therapy strategy, attracting extensive attention from researchers. EVs mediate intercellular communication, possessing excellent biocompatibility and stability. These features make EVs a potential tool for treating a plethora of diseases, including those related to wound repair. However, there is a growing focus on the engineering of EVs to overcome inherent limitations such as low production, relatively fixed content, and targeting capabilities of natural EVs. This engineering could improve both the effectiveness and specificity of EVs in wound repair treatments. In light of this, the present review will introduce the latest progress in the design methods and experimental paradigms of engineered EVs applied in wound repair. Furthermore, it will comprehensively analyze the current clinical research status and prospects of engineered EVs within this field.

Local and systemic mechanisms that control the hair follicle stem cell niche

Hair follicles are essential appendages of the mammalian skin, as hair performs vital functions of protection, thermoregulation and sensation. Hair follicles harbour exceptional regenerative abilities as they contain multiple somatic stem cell populations such as hair follicle stem cells (HFSCs) and melanocyte stem cells. Surrounding the stem cells and their progeny, diverse groups of cells and extracellular matrix proteins are organized to form a microenvironment (called 'niche') that serves to promote and maintain the optimal functioning of these stem cell populations. Recent studies have shed light on the intricate nature of the HFSC niche and its crucial role in regulating hair follicle regeneration. In this Review, we describe how the niche serves as a signalling hub, communicating, deciphering and integrating both local signals within the skin and systemic inputs from the body and environment to modulate HFSC activity. We delve into the recent advancements in identifying the cellular and molecular nature of the niche, providing a holistic perspective on its essential functions in hair follicle morphogenesis, regeneration and ageing.

Scarring Skin: Mechanisms and Therapies

Skin injury always results in fibrotic, non-functional scars in adults. Although multiple factors are well-known contributors to scar formation, the precise underlying mechanisms remain elusive. This review aims to elucidate the intricacies of the wound healing process, summarize the known factors driving skin cells in wounds toward a scarring fate, and particularly to discuss the impact of fibroblast heterogeneity on scar formation. To the end, we explore potential therapeutic interventions used in the treatment of scarring wounds.

Multiscale spatial mapping of cell populations across anatomical sites in healthy human skin and basal cell carcinoma

Our understanding of how human skin cells differ according to anatomical site and tumour formation is limited. To address this, we have created a multiscale spatial atlas of healthy skin and basal cell carcinoma (BCC), incorporating in vivo optical coherence tomography, single-cell RNA sequencing, spatial global transcriptional profiling, and in situ sequencing. Computational spatial deconvolution and projection revealed the localisation of distinct cell populations to specific tissue contexts. Although cell populations were conserved between healthy anatomical sites and in BCC, mesenchymal cell populations including fibroblasts and pericytes retained signatures of developmental origin. Spatial profiling and in silico lineage tracing support a hair follicle origin for BCC and demonstrate that cancer-associated fibroblasts are an expansion of a POSTN+ subpopulation associated with hair follicles in healthy skin. RGS5+ pericytes are also expanded in BCC suggesting a role in vascular remodelling. We propose that the identity of mesenchymal cell populations is regulated by signals emanating from adjacent structures and that these signals are repurposed to promote the expansion of skin cancer stroma. The resource we have created is publicly available in an interactive format for the research community.

Particulate matter 10 induces oxidative stress and apoptosis in rhesus macaques skin fibroblast

Background

Particulate matter (PM) is a major air pollutant that affects human health worldwide. PM can pass through the skin barrier, thus causing skin diseases such as heat rash, allergic reaction, infection, or inflammation. However, only a few studies have been conducted on the cytotoxic effects of PM exposure on large-scale animals. Therefore, herein, we investigated whether and how PM affects rhesus macaque skin fibroblasts.

Methods

Rhesus macaque skin fibroblasts were treated with various concentrations of PM10 (1, 5, 10, 50, and 100 μg/mL) and incubated for 24, 48, and 72 h. Then, cell viability assay, TUNEL assay, and qRT-PCR were performed on the treated cells. Further, the reactive oxygen species, glutathione, and cathepsin B levels were determined. The MTT assay revealed that PM10 (>50 μg/mL) proportionately reduced the cell proliferation rate.

Results

PM10 treatment increased TUNEL-positive cell numbers, following the pro-apoptosis-associated genes (CASP3 and BAX) and tumor suppressor gene TP53 were significantly upregulated. PM10 treatment induced reactive oxidative stress. Cathepsin B intensity was increased, whereas GSH intensity was decreased. The mRNA expression levels of antioxidant enzyme-related genes (CAT, GPX1 and GPX3) were significantly upregulated. Furthermore, PM10 reduced the mitochondrial membrane potential. The mRNA expression of mitochondrial complex genes, such as NDUFA1, NDUFA2, NDUFAC2, NDUFS4, and ATP5H were also significantly upregulated. In conclusion, these results showed that PM10 triggers apoptosis and mitochondrial damage, thus inducing ROS accumulation. These findings provide potential information on the cytotoxic effects of PM10 treatment and help to understand the mechanism of air pollution-induced skin diseases.

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.

Identifying characteristics of dermal fibroblasts in skin homeostasis and disease

Heterogeneous dermal fibroblasts are the main components that constitute the dermis. Distinct fibroblast subgroups show specific characteristics and functional plasticity that determine dermal structure during skin development and wound healing. Although researchers have described the roles of fibroblast subsets, this is not completely understood. We review recent evidence supporting understanding about the heterogeneity of fibroblasts. We summarize the origins and the identified profiles of fibroblast subpopulations. The characteristics of fibroblast subpopulations in both healthy and diseased states are highlighted, and the potential of subpopulations to be involved in wound healing in different ways was discussed. Additionally, we review the plasticity of subpopulations and the underlying signalling mechanisms. This review may provide greater insights into potential novel therapeutic targets and tissue regeneration strategies for the future.

CD201+ fascia progenitors choreograph injury repair

Optimal tissue recovery and organismal survival are achieved by spatiotemporal tuning of tissue inflammation, contraction and scar formation1. Here we identify a multipotent fibroblast progenitor marked by CD201 expression in the fascia, the deepest connective tissue layer of the skin. Using skin injury models in mice, single-cell transcriptomics and genetic lineage tracing, ablation and gene deletion models, we demonstrate that CD201+ progenitors control the pace of wound healing by generating multiple specialized cell types, from proinflammatory fibroblasts to myofibroblasts, in a spatiotemporally tuned sequence. We identified retinoic acid and hypoxia signalling as the entry checkpoints into proinflammatory and myofibroblast states. Modulating CD201+ progenitor differentiation impaired the spatiotemporal appearances of fibroblasts and chronically delayed wound healing. The discovery of proinflammatory and myofibroblast progenitors and their differentiation pathways provide a new roadmap to understand and clinically treat impaired wound healing.

Mesenchymal stem cells paracrine proteins from three-dimensional dynamic culture system promoted wound healing in third-degree burn models

Recovery of skin function remains a significant clinical challenge for deep burns owing to the severe scar formation and poor appendage regeneration, and stem cell therapy has shown great potential for injured tissue regeneration. Here, a cell-free therapy system for deep burn skin was explored using mesenchymal stem cell paracrine proteins (MSC-PP) and polyethylene glycol (PEG) temperature-sensitive hydrogels. A three-dimensional (3D) dynamic culture system for MSCs' large-scale expansion was established using a porous gelatin microcarrier crosslinked with hyaluronic acid (PGM-HA), and the purified MSC-PP from culture supernatant was characterized by mass spectrometric analysis. The results showed the 3D dynamic culture system regulated MSCs cell cycle, reduced apoptosis, and decreased lactic acid content, and the MSC-PP produced in 3D group can promote cell proliferation, migration, and adhesion. The MSC-PP + PEG system maintained stable release in 28 days of observation in vitro. The in vivo therapeutic efficacy was investigated in the rabbit's third-degree burn model, and saline, PEG, MSC-PP, and MSC-PP + PEG treatments groups were set. The in vivo results showed that the MSC-PP + PEG group significantly improved wound healing, inhibited scar formation, and facilitated skin appendage regeneration. In conclusion, the MSC-PP + PEG sustained-release system provides a potentially effective treatment for deep burn skin healing.

Integrated single-cell and spatial transcriptomics reveals heterogeneity of fibroblast and pivotal genes in psoriasis

Psoriasis, which is one of the most common skin diseases, involves an array of complex immune constituents including T cells, dendritic cells and monocytes. Particularly, the cytokine IL17A, primarily generated by TH17 cells, assumes a crucial function in the etiology of psoriasis. In this study, a comprehensive investigation utilizing bulk RNA analysis, single-cell RNA sequencing, and spatial transcriptomics was employed to elucidate the underlying mechanisms of psoriasis. Our study revealed that there is an overlap between the genes that are differentially expressed in psoriasis patients receiving three anti-IL17A monoclonal antibody drugs and the genes that are differentially expressed in lesion versus non-lesion samples in these patients. Further analysis using single-cell and spatial data from psoriasis samples confirmed the expression of hub genes that had low expressions in psoriasis tissue but were up-regulated after anti-IL17A treatments. These genes were found to be associated with the treatment effects of brodalumab and methotrexate, but not adalimumab, etanercept, and ustekinumab. Additionally, these genes were predominantly expressed in fibroblasts. In our study, fibroblasts were categorized into five clusters. Notably, hub genes exhibited predominant expression in cluster 3 fibroblasts, which were primarily engaged in the regulation of the extracellular matrix and were predominantly located in the reticular dermis. Subsequent analysis unveiled that cluster 3 fibroblasts also established communication with epithelial cells and monocytes via the ANGPTL-SDC4 ligand-receptor configuration, and their regulation was governed by the transcription factor TWIST1. Conversely, cluster 4 fibroblasts, responsible for vascular endothelial regulation, were predominantly distributed in the papillary dermis. Cluster 4 predominantly engaged in interactions with endothelial cells via MDK signals and was governed by the distinctive transcription factor, ERG. By means of an integrated analysis encompassing bulk transcriptomics, single-cell RNA sequencing, and spatial transcriptomics, we have discerned genes and clusters of fibroblasts that potentially contribute to the pathogenesis of psoriasis.

Lineage commitment of dermal fibroblast progenitors is controlled by Kdm6b-mediated chromatin demethylation

Dermal Fibroblast Progenitors (DFPs) differentiate into distinct fibroblast lineages during skin development. However, the epigenetic mechanisms that regulate DFP differentiation are not known. Our objective was to use multimodal single-cell approaches, epigenetic assays, and allografting techniques to define a DFP state and the mechanism that governs its differentiation potential. Our initial results indicated that the overall transcription profile of DFPs is repressed by H3K27me3 and has inaccessible chromatin at lineage-specific genes. Surprisingly, the repressive chromatin profile of DFPs renders them unable to reform the skin in allograft assays despite their multipotent potential. We hypothesized that chromatin derepression was modulated by the H3K27me3 demethylase, Kdm6b/Jmjd3. Dermal fibroblast-specific deletion of Kdm6b/Jmjd3 in mice resulted in adipocyte compartment ablation and inhibition of mature dermal papilla functions, confirmed by additional single-cell RNA-seq, ChIP-seq, and allografting assays. We conclude that DFPs are functionally derepressed during murine skin development by Kdm6b/Jmjd3. Our studies therefore reveal a multimodal understanding of how DFPs differentiate into distinct fibroblast lineages and provide a novel publicly available multiomics search tool.

DeepCCI: a deep learning framework for identifying cell-cell interactions from single-cell RNA sequencing data

MOTIVATION

Cell-cell interactions (CCIs) play critical roles in many biological processes such as cellular differentiation, tissue homeostasis, and immune response. With the rapid development of high throughput single-cell RNA sequencing (scRNA-seq) technologies, it is of high importance to identify CCIs from the ever-increasing scRNA-seq data. However, limited by the algorithmic constraints, current computational methods based on statistical strategies ignore some key latent information contained in scRNA-seq data with high sparsity and heterogeneity.

RESULTS

Here, we developed a deep learning framework named DeepCCI to identify meaningful CCIs from scRNA-seq data. Applications of DeepCCI to a wide range of publicly available datasets from diverse technologies and platforms demonstrate its ability to predict significant CCIs accurately and effectively. Powered by the flexible and easy-to-use software, DeepCCI can provide the one-stop solution to discover meaningful intercellular interactions and build CCI networks from scRNA-seq data.

AVAILABILITY AND IMPLEMENTATION

The source code of DeepCCI is available online at https://github.com/JiangBioLab/DeepCCI.