Distinct fibroblast lineages determine dermal architecture in skin development and repair. Nature. 2013;504:277-281. [PMID: 24336287 PMCID: PMC3868929 DOI: 10.1038/nature12783]

The immune function of dermal fibroblasts in skin defence against pathogens

Dermal fibroblasts are the main resident cells of the dermis. They have several significant functions related to wound healing, extracellular matrix production and hair cycling. Dermal fibroblasts can also act as sentinels in defence against infection. They express pattern recognition receptors such as toll-like receptors to sense pathogen components, followed by the synthesis of pro-inflammatory cytokines (including IL-6, IFN-β and TNF-α), chemokines (such as IL-8 and CXCL1) and antimicrobial peptides. Dermal fibroblasts also secrete other molecules-like growth factors and matrix metalloproteinases to benefit tissue repair from infection. Crosstalk between dermal fibroblasts and immune cells may amplify the immune response against infection. Moreover, the transition of a certain adipogenic fibroblasts to adipocytes protects skin from bacterial infection. Together, we discuss the role of dermal fibroblasts in the war against pathogens in this review. Dermal fibroblasts have important immune functions in anti-infection immunity, which should not be overlooked.

Tripterygium wilfordii derivative celastrol, a YAP inhibitor, has antifibrotic effects in systemic sclerosis

OBJECTIVES

Systemic sclerosis (SSc) is characterised by extensive tissue fibrosis maintained by mechanotranductive/proadhesive signalling. Drugs targeting this pathway are therefore of likely therapeutic benefit. The mechanosensitive transcriptional co-activator, yes activated protein-1 (YAP1), is activated in SSc fibroblasts. The terpenoid celastrol is a YAP1 inhibitor; however, if celastrol can alleviate SSc fibrosis is unknown. Moreover, the cell niches required for skin fibrosis are unknown.

METHODS

Human dermal fibroblasts from healthy individuals and patients with diffuse cutaneous SSc were treated with or without transforming growth factor β1 (TGFβ1), with or without celastrol. Mice were subjected to the bleomycin-induced model of skin SSc, in the presence or absence of celastrol. Fibrosis was assessed using RNA Sequencing, real-time PCR, spatial transcriptomic analyses, Western blot, ELISA and histological analyses.

RESULTS

In dermal fibroblasts, celastrol impaired the ability of TGFβ1 to induce an SSc-like pattern of gene expression, including that of cellular communication network factor 2, collagen I and TGFβ1. Celastrol alleviated the persistent fibrotic phenotype of dermal fibroblasts cultured from lesions of SSc patients. In the bleomycin-induced model of skin SSc, increased expression of genes associated with reticular fibroblast and hippo/YAP clusters was observed; conversely, celastrol inhibited these bleomycin-induced changes and blocked nuclear localisation of YAP.

CONCLUSIONS

Our data clarify niches within the skin activated in fibrosis and suggest that compounds, such as celastrol, that antagonise the YAP pathway may be potential treatments for SSc skin fibrosis.

Physical Properties and Cellular Metabolic Characteristics of 3D Spheroids Are Possible Definitive Indices for the Biological Nature of Cancer-Associated Fibroblasts

The current study's objective was to elucidate some currently unknown biological indicators to evaluate the biological nature of cancer-associated fibroblasts (CAFs). For this purpose, four different CAFs, CAFS1, CAFS2, SCC17F and MO-1000, were established using surgical specimens from oral squamous cell carcinomas (OSCC) with different clinical malignant stages (CAFS1 and CAFS2, T2N0M0, stage II; SCC17F and MO-1000, T4aN2bM0, stage IVA). Fibroblasts unrelated to cancer (non-CAFs) were also prepared and used as controls. Initially, confirmation that these four fibroblasts were indeed CAFs was obtained by their mRNA expression using positive and negative markers for the CAF or fibroblasts. To elucidate possible unknown biological indicators, these fibroblasts were subjected to a cellular metabolic analysis by a Seahorse bioanalyzer, in conjugation with 3D spheroid cultures of the cells and co-cultures with a pancreas ductal carcinoma cell line, MIA PaCa-2. The mitochondrial and glycolytic functions of human orbital fibroblasts (HOF) were nearly identical to those of Graves'-disease-related HOF (GOF). In contrast, the characteristics of the metabolic functions of these four CAFs were different from those of human conjunctival fibroblasts (HconF), a representative non-CAF. It is particularly noteworthy that CAFS1 and CAFS2 showed markedly reduced ratios for the rate of oxygen consumption to the extracellular acidification rate, suggesting that glycolysis was enhanced compared to mitochondrial respiration. Similarly, the physical aspects, their appearance and stiffness, of their 3D spheroids and fibroblasts that were induced effects based on the cellular metabolic functions of MIA PaCa-2 were also different between CAFs and non-CAFs, and their levels for CAFS1 or SCC17F were similar to those for CAFS2 or MO-1000 cells, respectively. The findings reported herein indicate that cellular metabolic functions and the physical characteristics of these types of 3D spheroids may be valuable and useful indicators for estimating potential biological diversity among various CAFs.

Morphological, anatomical and histological studies on knob and beak characters of six goose breeds from China

The knob serves as both a sexual indicator of a goose's maturity and a significant packaging attribute that garners consumer attention. However, studies regarding the morphological, anatomical and histological traits of different breeds and ages on the on knob in goose are lacking. In this study, six breeds with typical goose knob types were selected, and their knob size, morphological, anatomical and histological traits were characterized. The results showed that: Knob was more prominent in gander than in female goose, and the difference was the most obvious in Magang goose. Wanxi white goose and Shitou goose had the largest knob bulge, while Magang goose and Sichuan white goose were smaller. The total knob volume of Wanxi White goose and Shitou goose was significantly higher than that of other breeds, regardless of male or female (p < 0.05). The beak volume of Wanxi White goose and gander was significantly higher than that of other goose breeds (p < 0.05). Furthermore, the observation revealed that the "knob" primarily consisted of skin-derived tissue and bony protrusions. As age advances, the knob of both male and female geese undergoes synchronous development, with the knob of male geese typically surpassing that of their female counterparts during the same period. The growth rate of knob in male goose was the fastest from 70 to 120 days of age, and slowed down from 300 to 500 days of age. The growth rate of knob in female goose was slower than that in male goose. There were essential differences in the composition of Yangzhou goose knob and Magang goose knob. The subcutaneous tissue of Magang goose was rich, and the thickness of epidermis, dermis and various layers was significantly smaller than that of Yangzhou goose (p < 0.05). With the growth of goose knob, the cells of the epidermal spinous layer became denser and gradually condensed into an overall structure, and there was a clear boundary between the dermis and epidermis after adult. In adulthood, the fiber fascicle network was staggered and dense, with greater toughness and elasticity, and the stratum corneum, epidermis, reticular layer, dermis and other skin structural layers became thicker.

Calreticulin: a multifunctional protein with potential therapeutic applications for chronic wounds

Calreticulin is recognized as a multifunctional protein that serves an essential role in diverse biological processes that include wound healing, modification and folding of proteins, regulation of the secretory pathway, cell motility, cellular metabolism, protein synthesis, regulation of gene expression, cell cycle regulation and apoptosis. Although the role of calreticulin as an endoplasmic reticulum-chaperone protein has been well described, several studies have demonstrated calreticulin to be a highly versatile protein with an essential role during wound healing. These features make it an ideal molecule for treating a complex, multifactorial diseases that require fine tuning, such as chronic wounds. Indeed, topical application of recombinant calreticulin to wounds in multiple models of wound healing has demonstrated remarkable pro-healing effects. Among them include enhanced keratinocyte and fibroblast migration and proliferation, induction of extracellular matrix proteins, recruitment of macrophages along with increased granulation tissue formation, all of which are important functions in promoting wound healing that are deregulated in chronic wounds. Given the high degree of diverse functions and pro-healing effects, application of exogenous calreticulin warrants further investigation as a potential novel therapeutic option for chronic wound patients. Here, we review and highlight the significant effects of topical application of calreticulin on enhancing wound healing and its potential as a novel therapeutic option to shift chronic wounds into healing, acute-like wounds.

Bioengineered skin organoids: from development to applications

Significant advancements have been made in recent years in the development of highly sophisticated skin organoids. Serving as three-dimensional models that mimic human skin, these organoids have evolved into complex structures and are increasingly recognized as effective alternatives to traditional culture models and human skin due to their ability to overcome the limitations of two-dimensional systems and ethical concerns. The inherent plasticity of skin organoids allows for their construction into physiological and pathological models, enabling the study of skin development and dynamic changes. This review provides an overview of the pivotal work in the progression from 3D layered epidermis to cyst-like skin organoids with appendages. Furthermore, it highlights the latest advancements in organoid construction facilitated by state-of-the-art engineering techniques, such as 3D printing and microfluidic devices. The review also summarizes and discusses the diverse applications of skin organoids in developmental biology, disease modelling, regenerative medicine, and personalized medicine, while considering their prospects and limitations.

Fibroblasts - the cellular choreographers of wound healing

Injuries to our skin trigger a cascade of spatially- and temporally-synchronized healing processes. During such endogenous wound repair, the role of fibroblasts is multifaceted, ranging from the activation and recruitment of innate immune cells through the synthesis and deposition of scar tissue to the conveyor belt-like transport of fascial connective tissue into wounds. A comprehensive understanding of fibroblast diversity and versatility in the healing machinery may help to decipher wound pathologies whilst laying the foundation for novel treatment modalities. In this review, we portray the diversity of fibroblasts and delineate their unique wound healing functions. In addition, we discuss future directions through a clinical-translational lens.

Understanding Fibroblast Heterogeneity in Form and Function

Historically believed to be a homogeneous cell type that is often overlooked, fibroblasts are more and more understood to be heterogeneous in nature. Though the mechanisms behind how fibroblasts participate in homeostasis and pathology are just beginning to be understood, these cells are believed to be highly dynamic and play key roles in fibrosis and remodeling. Focusing primarily on fibroblasts within the skin and during wound healing, we describe the field's current understanding of fibroblast heterogeneity in form and function. From differences due to embryonic origins to anatomical variations, we explore the diverse contributions that fibroblasts have in fibrosis and plasticity. Following this, we describe molecular techniques used in the field to provide deeper insights into subpopulations of fibroblasts and their varied roles in complex processes such as wound healing. Limitations to current work are also discussed, with a focus on future directions that investigators are recommended to take in order to gain a deeper understanding of fibroblast biology and to develop potential targets for translational applications in a clinical setting.

Blank Spots in the Map of Human Skin: The Challenge for Xenotransplantation

Most of the knowledge about human skin homeostasis, development, wound healing, and diseases has been accumulated from human skin biopsy analysis by transferring from animal models and using different culture systems. Human-to-mouse xenografting is one of the fundamental approaches that allows the skin to be studied in vivo and evaluate the ongoing physiological processes in real time. Humanized animals permit the actual techniques for tracing cell fate, clonal analysis, genetic modifications, and drug discovery that could never be employed in humans. This review recapitulates the novel facts about mouse skin self-renewing, regeneration, and pathology, raises issues regarding the gaps in our understanding of the same options in human skin, and postulates the challenges for human skin xenografting.

Skin fibroblast functional heterogeneity in health and disease

Fibroblasts are the major cell population of connective tissue, including the skin dermis, and are best known for their function in depositing and remodelling the extracellular matrix. Besides their role in extracellular matrix homeostasis, fibroblasts have emerged as key players in many biological processes ranging from tissue immunity and wound healing to hair follicle development. Recent advances in single-cell RNA-sequencing technologies have revealed an astonishing transcriptional fibroblast heterogeneity in the skin and other organs. A key challenge in the field is to understand the functional relevance and significance of the identified new cell clusters in health and disease. Here, we discuss the functionally distinct fibroblast subtypes identified in skin homeostasis and repair and how they evolve in fibrotic disease conditions, in particular keloid scars and cancer. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Impact of a Novel Hydrogel with Injectable Platelet-Rich Fibrin in Diabetic Wound Healing

Diabetic wounds are serious complications caused by diabetes mellitus (DM), which are further exacerbated by angiogenesis disorders and prolonged inflammation. Injectable platelet-rich fibrin (i-PRF) is rich in growth factors (GFs) and has been used for the repair and regeneration of diabetic wounds; however, direct application of i-PRF has certain disadvantages, including the instability of the bioactive molecules. Sericin hydrogel, fabricated by silkworm-derived sericin, is a biocompatible material that has anti-inflammatory and healing-promoting properties. Therefore, in this study, we developed a novel hydrogel (named sericin/i-PRF hydrogel) using a simple one-step activation method. The in vitro studies showed that the rapid injectability of the sericin/i-PRF hydrogel allows it to adapt to the irregular shape of the wounds. Additionally, sericin hydrogel could prolong the release of i-PRF-derived bioactive GFs in the sericin/i-PRF hydrogel. Furthermore, sericin/i-PRF hydrogel effectively repaired diabetic wounds, promoted angiogenesis, and reduced inflammation levels in the diabetic wounds of nude mice. These results demonstrate that the sericin/i-PRF hydrogel is a promising agent for diabetic wound healing.

Transcriptomic landscape reveals germline potential of porcine skin-derived multipotent dermal fibroblast progenitors

According to estimations, approximately about 15% of couples worldwide suffer from infertility, in which individuals with azoospermia or oocyte abnormalities cannot be treated with assisted reproductive technology. The skin-derived stem cells (SDSCs) differentiation into primordial germ cell-like cells (PGCLCs) is one of the major breakthroughs in the field of stem cells intervention for infertility treatment in recent years. However, the cellular origin of SDSCs and their dynamic changes in transcription profile during differentiation into PGCLCs in vitro remain largely undissected. Here, the results of single-cell RNA sequencing indicated that porcine SDSCs are mainly derived from multipotent dermal fibroblast progenitors (MDFPs), which are regulated by growth factors (EGF/bFGF). Importantly, porcine SDSCs exhibit pluripotency for differentiating into three germ layers and can effectively differentiate into PGCLCs through complex transcriptional regulation involving histone modification. Moreover, this study also highlights that porcine SDSC-derived PGCLCs specification exhibit conservation with the human primordial germ cells lineage and that its proliferation is mediated by the MAPK signaling pathway. Our findings provide substantial novel insights into the field of regenerative medicine in which stem cells differentiate into germ cells in vitro, as well as potential therapeutic effects in individuals with azoospermia and/or defective oocytes.

Male pattern hair loss: Can developmental origins explain the pattern?

Male pattern hair loss (MPHL), also referred to as male androgenetic alopecia (AGA) is the most common type of non-scarring progressive hair loss, with 80% of men suffering from this condition in their lifetime. In MPHL, the hair line recedes to a specific part of the scalp which cannot be accurately predicted. Hair is lost from the front, vertex, and the crown, yet temporal and occipital follicles remain. The visual effect of hair loss is due to hair follicle miniaturisation, where terminal hair follicles become dimensionally smaller. Miniaturisation is also characterised by a shortening of the growth phase of the hair cycle (anagen), and a prolongation of the dormant phase (kenogen). Together, these changes result in the production of thinner and shorter hair fibres, referred to as miniaturised or vellus hairs. It remains unclear why miniaturisation occurs in this specific pattern, with frontal follicles being susceptible while occipital follicles remain in a terminal state. One main factor we believe to be at play, which will be discussed in this viewpoint, is the developmental origin of the skin and hair follicle dermis on different regions of the scalp.

Dynamic interplay between IL-1 and WNT pathways in regulating dermal adipocyte lineage cells during skin development and wound regeneration

Dermal adipocyte lineage cells are highly plastic and can undergo reversible differentiation and dedifferentiation in response to various stimuli. Using single-cell RNA sequencing of developing or wounded mouse skin, we classify dermal fibroblasts (dFBs) into distinct non-adipogenic and adipogenic cell states. Cell differentiation trajectory analyses identify IL-1-NF-κB and WNT-β-catenin as top signaling pathways that positively and negatively associate with adipogenesis, respectively. Upon wounding, activation of adipocyte progenitors and wound-induced adipogenesis are mediated in part by neutrophils through the IL-1R-NF-κB-CREB signaling axis. In contrast, WNT activation, by WNT ligand and/or ablation of Gsk3, inhibits the adipogenic potential of dFBs but promotes lipolysis and dedifferentiation of mature adipocytes, contributing to myofibroblast formation. Finally, sustained WNT activation and inhibition of adipogenesis is seen in human keloids. These data reveal molecular mechanisms underlying the plasticity of dermal adipocyte lineage cells, defining potential therapeutic targets for defective wound healing and scar formation.

Transcriptomic and in vivo approaches introduced human iPSC-derived microvesicles for skin rejuvenation

The skin undergoes the formation of fine lines and wrinkles through the aging process; also, burns, trauma, and other similar circumstances give rise to various forms of skin ulcers. Induced pluripotent stem cells (iPSCs) have become promising candidates for skin healing and rejuvenation due to not stimulating inflammatory responses, low probability of immune rejection, high metabolic activity, good large-scale production capacity and potentials for personalized medicine. iPSCs can secrete microvesicles (MVs) containing RNA and proteins responsible for the normal repairing process of the skin. This study aimed to evaluate the possibility, safety and effectiveness of applying iPSCs-derived MVs for skin tissue engineering and rejuvenation applications. The possibility was assessed using the evaluation of the mRNA content of iPSC-derived MVs and the behavior of fibroblasts after MV treatment. Investigating the effect of microvesicle on stemness potential of mesenchymal stem cells was performed for safety concerns. In vivo evaluation of MVs was done in order to investigate related immune response, re-epithelialization and blood vessel formation to measure effectiveness. Shedding MVs were round in shape distributed in the range from 100 to 1000 nm in diameter and positive for AQP3, COL2A, FGF2, ITGB, and SEPTIN4 mRNAs. After treating dermal fibroblasts with iPSC-derived MVs, the expressions of collagens Iα1 and III transcripts (as the main fibrous extracellular matrix (ECM) proteins) were upregulated. Meanwhile, the survival and proliferation of MV treated fibroblasts did not change significantly. Evaluation of stemness markers in MV treated MSCs showed negligible alteration. In line with in vitro results, histomorphometry and histopathology findings also confirmed the helpful effect of MVs in skin regeneration in the rat burn wound models. Conducting more investigations on hiPSCs-derived MVs may lead to produce more efficient and safer biopharmaceutics for skin regeneration in the pharmaceutical market.

Unraveling White Adipose Tissue Heterogeneity and Obesity by Adipose Stem/Stromal Cell Biology and 3D Culture Models

The immune and endocrine dysfunctions of white adipose tissue are a hallmark of metabolic disorders such as obesity and type 2 diabetes. In humans, white adipose tissue comprises distinct depots broadly distributed under the skin (hypodermis) and as internal depots (visceral). Depot-specific ASCs could account for visceral and subcutaneous adipose tissue properties, by regulating adipogenesis and immunomodulation. More importantly, visceral and subcutaneous depots account for distinct contributions to obesity and its metabolic comorbidities. Recently, distinct ASCs subpopulations were also described in subcutaneous adipose tissue. Interestingly, the superficial layer closer to the dermis shows hyperplastic and angiogenic capacities, whereas the deep layer is considered as having inflammatory properties similar to visceral. The aim of this focus review is to bring the light of recent discoveries into white adipose tissue heterogeneity together with the biology of distinct ASCs subpopulations and to explore adipose tissue 3D models revealing their advantages, disadvantages, and contributions to elucidate the role of ASCs in obesity development. Recent advances in adipose tissue organoids opened an avenue of possibilities to recreate the main cellular and molecular events of obesity leading to a deep understanding of this inflammatory disease besides contributing to drug discovery. Furthermore, 3D organ-on-a-chip will add reproducibility to these adipose tissue models contributing to their translation to the pharmaceutical industry.

A single-cell transcriptome atlas of pig skin characterizes anatomical positional heterogeneity

Different anatomical locations of the body skin show differences in their gene expression patterns depending on different origins, and the inherent heterogeneous information can be maintained in adults. However, highly resolvable cellular specialization is less well characterized in different anatomical regions of the skin. Pig is regarded as an excellent model animal for human skin research in view of its similar physiology to human. In this study, single-cell RNA sequencing was performed on pig skin tissues from six different anatomical regions of Chenghua (CH) pigs, with a superior skin thickness trait, and the back site of large white (LW) pigs. We obtained 233,715 cells, representing seven cell types, among which we primarily characterized the heterogeneity of the top three cell types, including smooth muscle cells (SMCs), endothelial cells (ECs), and fibroblasts (FBs). Then, we further identified several subtypes of SMCs, ECs, and FBs, and discovered the expression patterns of site-specific genes involved in some important pathways such as the immune response and extracellular matrix (ECM) synthesis in different anatomical regions. By comparing differentially expressed genes of skin FBs among different anatomical regions, we considered TNN, COL11A1, and INHBA as candidate genes for facilitating ECM accumulation. These findings of heterogeneity in the main skin cell types from different anatomical sites will contribute to a better understanding of inherent skin information and place the potential focus on skin generation, transmission, and transplantation, paving the foundation for human skin priming.

Preparation of Apoptotic Extracellular Vesicles from Adipose Tissue and Their Efficacy in Promoting High-Quality Skin Wound Healing

Purpose

A lot of strategies have been attempted to achieve high-quality skin wound healing, among them, fat transplantation has been used for skin wound repair and scar management and has shown beneficial effects. However, the underlying mechanism is still unclear. Recently, studies found that transplanted cells underwent apoptosis within a short period and apoptotic extracellular vesicles (ApoEVs) might play the therapeutic role.

Methods

In this study, we directly isolated apoptotic extracellular vesicles from adipose tissue (ApoEVs-AT) and evaluated their characteristics. In vivo, we investigated the therapeutic role of ApoEVs-AT in full-thickness skin wounds. The rate of wound healing, the quality of granulation tissue, and the area of scars were evaluated here. In vitro, we investigated the cellular behaviors of fibroblasts and endothelial cells induced by ApoEVs-AT, including cellular uptake, proliferation, migration, and differentiation.

Results

ApoEVs-AT could be successfully isolated from adipose tissue and possessed the basic characteristics of ApoEVs. In vivo, ApoEVs-AT could accelerate skin wound healing, improve the quality of granulation tissue, and reduce the area of scars. In vitro, ApoEVs-AT could be engulfed by fibroblasts and endothelial cells, significantly enhancing their proliferation and migration. Moreover, ApoEVs-AT could promote adipogenic differentiation and inhibit the fibrogenic differentiation of fibroblasts.

Conclusion

These findings indicated that ApoEVs could be successfully prepared from adipose tissue and showed the ability to promote high-quality skin wound healing by modulating fibroblasts and endothelial cells.

EGFR marks a subpopulation of dermal mesenchymal cells highly expressing IGF1 which enhances hair follicle regeneration

The skin harbours transcriptionally and functionally heterogeneous mesenchymal cells that participate in various physiological activities by secreting biochemical cues. In this study, we aimed to identify a new subpopulation of dermal mesenchymal cells that enhance hair follicle regeneration through a paracrine mechanism. Integrated single-cell RNA sequencing (scRNA-seq) data analysis revealed epidermal growth factor receptor (EGFR) as a marker of distinct fibroblast subpopulation in the neonatal murine dermis. Immunofluorescence staining and fluorescence-activated cell sorting (FACS) were used to validate the existence of the cell population in Krt14-rtTA-H2BGFP mouse. The difference of gene expression between separated cell subpopulation was examined by real-time PCR. Potential effect of the designated factor on hair follicle regeneration was observed after the application on excisional wounds in Krt14-rtTA-H2BGFP mouse. Immunofluorescence staining demonstrated the existence of dermal EGFR+ cells in neonatal and adult mouse dermis. The EGFR+ mesenchymal population, sorted by FACS, displayed a higher expression level of Igf1 (insulin-like growth factor 1). Co-localisation of IGF1 with EGFR in the mouse dermis and upregulated numbers of hair follicles in healed wounds following the application of exogenous IGF1 illustrated the contribution of EGFR+ cells in promoting wound-induced hair follicle neogenesis. Our results indicate that EGFR identifies a subpopulation of dermal fibroblasts that contribute to IGF1 promotion of hair follicle neogenesis. It broadens the understanding of heterogeneity and the mesenchymal cell function in skin and may facilitate the potential translational application of these cells.

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.

Transcriptional space-time mapping identifies concerted immune and stromal cell patterns and gene programs in wound healing and cancer

Tissue repair responses in metazoans are highly coordinated by different cell types over space and time. However, comprehensive single-cell-based characterization covering this coordination is lacking. Here, we captured transcriptional states of single cells over space and time during skin wound closure, revealing choreographed gene-expression profiles. We identified shared space-time patterns of cellular and gene program enrichment, which we call multicellular "movements" spanning multiple cell types. We validated some of the discovered space-time movements using large-volume imaging of cleared wounds and demonstrated the value of this analysis to predict "sender" and "receiver" gene programs in macrophages and fibroblasts. Finally, we tested the hypothesis that tumors are like "wounds that never heal" and found conserved wound healing movements in mouse melanoma and colorectal tumor models, as well as human tumor samples, revealing fundamental multicellular units of tissue biology for integrative studies.

Mammalian organ regeneration in spiny mice

Fibrosis-driven solid organ failure is a major world-wide health burden with few therapeutic options. Spiny mice (genus: Acomys) are terrestrial mammals that regenerate severe skin wounds without fibrotic scars to evade predators. Recent studies have shown that spiny mice also regenerate acute ischemic and traumatic injuries to kidney, heart, spinal cord, and skeletal muscle. A common feature of this evolved wound healing response is a lack of formation of fibrotic scar tissue that degrades organ function, inhibits regeneration, and leads to organ failure. Complex tissue regeneration is an extremely rare property among mammalian species. In this article, we discuss the evidence that Acomys represents an emerging model organism that offers a unique opportunity for the biomedical community to investigate and clinically translate molecular mechanisms of scarless wound healing and regeneration of organ function in a mammalian species.

PRPF19 modulates morphology and growth behavior in a cell culture model of human skin

The skin provides one of the most visual aging transformations in humans, and premature aging as a consequence of oxidative stress and DNA damage is a frequently seen effect. Cells of the human skin are continuously exposed to endogenous and exogenous DNA damaging factors, which can cause DNA damage in all phases of the cell cycle. Increased levels of DNA damage and/or defective DNA repair can, therefore, accelerate the aging process and/or lead to age-related diseases like cancer. It is not yet clear if enhanced activity of DNA repair factors could increase the life or health span of human skin cells. In previous studies, we identified and characterized the human senescence evasion factor (SNEV)/pre-mRNA-processing factor (PRPF) 19 as a multitalented protein involved in mRNA splicing, DNA repair pathways and lifespan regulation. Here, we show that overexpression of PRPF19 in human dermal fibroblasts leads to a morphological change, reminiscent of juvenile, papillary fibroblasts, despite simultaneous expression of senescence markers. Moreover, conditioned media of this subpopulation showed a positive effect on keratinocyte repopulation of wounded areas. Taken together, these findings indicate that PRPF19 promotes cell viability and slows down the aging process in human skin.

Dermal Fibroblasts as the Main Target for Skin Anti-Age Correction Using a Combination of Regenerative Medicine Methods

This article includes the data from current studies regarding the pathophysiological mechanisms of skin aging and the regenerative processes occurring in the epidermis and dermis at the molecular and cellular level, mainly, the key role of dermal fibroblasts in skin regeneration. Analyzing these data, the authors proposed the concept of skin anti-age therapy that is based on the correction of age-related skin changes by stimulating regenerative processes at the molecular and cellular level. The main target of the skin anti-age therapy is dermal fibroblasts (DFs). A variant of the cosmetological anti-age program using the combination of laser and cellular methods of regenerative medicine is presented in the paper. The program includes three stages of implementation and defines the tasks and methods of each stage. Thus, laser technologies allow one to remodel the collagen matrix and create favorable conditions for DFs functions, whereas the cultivated autologous dermal fibroblasts replenish the pool of mature DFs decreasing with age and are responsible for the synthesis of components of the dermal extracellular matrix. Finally, the use of autological platelet-rich plasma (PRP) enables to maintenance of the achieved results by stimulating DF function. It has been shown that growth factors/cytokines contained in α-granules of platelets injected into the skin bind to the corresponding transmembrane receptors on the surface of DFs and stimulate their synthetic activity. Thus, the consecutive, step-by-step application of the described methods of regenerative medicine amplifies the effect on the molecular and cellular aging processes and thereby allows one to optimize and prolong the clinical results of skin rejuvenation.

An ERK-dependent molecular switch antagonizes fibrosis and promotes regeneration in spiny mice (Acomys)

Although most mammals heal injured tissues and organs with scarring, spiny mice (Acomys) naturally regenerate skin and complex musculoskeletal tissues. Now, the core signaling pathways driving mammalian tissue regeneration are poorly characterized. Here, we show that, while immediate extracellular signal-regulated kinase (ERK) activation is a shared feature of scarring (Mus) and regenerating (Acomys) injuries, ERK activity is only sustained at high levels during complex tissue regeneration. Following ERK inhibition, ear punch regeneration in Acomys shifted toward fibrotic repair. Using single-cell RNA sequencing, we identified ERK-responsive cell types. Loss- and gain-of-function experiments prompted us to uncover fibroblast growth factor and ErbB signaling as upstream ERK regulators of regeneration. The ectopic activation of ERK in scar-prone injuries induced a pro-regenerative response, including cell proliferation, extracellular matrix remodeling, and hair follicle neogenesis. Our data detail an important distinction in ERK activity between regenerating and poorly regenerating adult mammals and open avenues to redirect fibrotic repair toward regenerative healing.

An adhesive gelatin-coated small intestinal submucosa composite hydrogel dressing aids wound healing

It is a challenging clinical task to determine how to repair large-area skin defects better. Traditional wound dressings (e.g., cotton and gauze) can only be used as a dressing; consequently, there is an increasing demand for wound dressings with additional properties (i.e., antibacterial and pro-repair) in clinical practice. In this study, a composite hydrogel with o-nitrobenzene-modified gelatin-coated decellularized small intestinal submucosa (GelNB@SIS) was designed for the repair of skin injuries. SIS is a natural extracellular matrix with a 3D microporous structure and also contains high levels of growth factors and collagen. GelNB provides this material photo-triggering tissue adhesive property. The structure, tissue adhesion, cytotoxicity, and bioactivity to cells were investigated. Based on in vivo study and histological analysis, we found the combination of GelNB and SIS improved the healing process by promoting vascular renewal, dermal remodeling, and epidermal regeneration. Based on our findings, GelNB@SIS is a promising candidate for tissue repair applications.

The Effect of Hybrosome (Umbilical Cord Blood Exosome-Liposome Hybrid Vesicles) on Human Dermal Cells In Vitro

Background

Wound healing is a process that involves multiple physiological steps, and despite the availability of various wound treatment methods, their effectiveness is still limited due to several factors, including cost, efficiency, patient-specific requirements, and side effects. In recent years, nanovesicles called exosomes have gained increasing attention as a potential wound care solution due to their unique cargo components which enable cell-to-cell communication and regulate various biological processes. Umbilical cord blood plasma (UCBP) exosomes have shown promise in triggering beneficial signaling pathways that aid in cell proliferation and wound healing. However, there is still very limited information about the wound-healing effect of UCBP exosomes in the literature.

Objectives

The primary objective of this study was to investigate the "hybrosome" technology generated with calf UCBP-derived exosome-liposome combination.

Methods

The authors developed hybrosome technology by fusing cord blood exosome membranes with liposomes. Nanovesicle characterization, cell proliferation assay, wound-healing scratch assay, immunohistochemistry analysis, anti-inflammation assay, real-time polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay, and cellular uptake studies were performed using the novel hybrid exosomes.

Results

Experimental results showed that hybrosome increases cell proliferation and migration by 40% to 50%, depending on the dose, and induces an anti-inflammatory effect on different cell lines as well as increased wound healing-related gene expression levels in dermal cells in vitro. All in all, this research widens the scope of wound-healing therapeutics to the novel hybrosome technology.

Conclusions

UCBP-based applications have the potential for wound treatments and are promising in the development of novel therapies. This study shows that hybrosomes have outstanding abilities in wound healing using in vitro approaches.

Level of Evidence 3

Comprehensive Characterization of Tissues Derived from Animals at Different Regenerative Stages: A Comparative Analysis between Fetal and Adult Mouse Skin

Tissue regeneration capabilities vary significantly throughout an organism's lifespan. For example, mammals can fully regenerate until they reach specific developmental stages, after which they can only repair the tissue without restoring its original architecture and function. The high regenerative potential of fetal stages has been attributed to various factors, such as stem cells, the immune system, specific growth factors, and the presence of extracellular matrix molecules upon damage. To better understand the local differences between regenerative and reparative tissues, we conducted a comparative analysis of skin derived from mice at regenerative and reparative stages. Our findings show that both types of skin differ in their molecular composition, structure, and functionality. We observed a significant increase in cellular density, nucleic acid content, neutral lipid density, Collagen III, and glycosaminoglycans in regenerative skin compared with reparative skin. Additionally, regenerative skin had significantly higher porosity, metabolic activity, water absorption capacity, and elasticity than reparative skin. Finally, our results also revealed significant differences in lipid distribution, extracellular matrix pore size, and proteoglycans between the two groups. This study provides comprehensive data on the molecular and structural clues that enable full tissue regeneration in fetal stages, which could aid in developing new biomaterials and strategies for tissue engineering and regeneration.

The small and large intestine contain related mesenchymal subsets that derive from embryonic Gli1+ precursors

The intestinal lamina propria contains a diverse network of fibroblasts that provide key support functions to cells within their local environment. Despite this, our understanding of the diversity, location and ontogeny of fibroblasts within and along the length of the intestine remains incomplete. Here we show that the small and large intestinal lamina propria contain similar fibroblast subsets that locate in specific anatomical niches. Nevertheless, we find that the transcriptional profile of similar fibroblast subsets differs markedly between the small intestine and colon suggesting region specific functions. We perform in vivo transplantation and lineage-tracing experiments to demonstrate that adult intestinal fibroblast subsets, smooth muscle cells and pericytes derive from Gli1-expressing precursors present in embryonic day 12.5 intestine. Trajectory analysis of single cell RNA-seq datasets of E12.5 and adult mesenchymal cells suggest that adult smooth muscle cells and fibroblasts derive from distinct embryonic intermediates and that adult fibroblast subsets develop in a linear trajectory from CD81⁺ fibroblasts. Finally, we provide evidence that colonic subepithelial PDGFRα^hi fibroblasts comprise several functionally distinct populations that originate from an Fgfr2-expressing fibroblast intermediate. Our results provide insights into intestinal stromal cell diversity, location, function, and ontogeny, with implications for intestinal development and homeostasis.

Tenascin C+ papillary fibroblasts facilitate neuro-immune interaction in a mouse model of psoriasis

Dermal fibroblasts and cutaneous nerves are important players in skin diseases, while their reciprocal roles during skin inflammation have not been characterized. Here we identify an inflammation-induced subset of papillary fibroblasts that promotes aberrant neurite outgrowth and psoriasiform skin inflammation by secreting the extracellular matrix protein tenascin-C (TNC). Single-cell analysis of fibroblast lineages reveals a Tnc⁺ papillary fibroblast subset with pro-axonogenesis and neuro-regulation transcriptomic hallmarks. TNC overexpression in fibroblasts boosts neurite outgrowth in co-cultured neurons, while fibroblast-specific TNC ablation suppresses hyperinnervation and alleviates skin inflammation in male mice modeling psoriasis. Dermal γδT cells, the main producers of type 17 pathogenic cytokines, frequently contact nerve fibers in mouse psoriasiform lesions and are likely modulated by postsynaptic signals. Overall, our results highlight the role of an inflammation-responsive fibroblast subset in facilitating neuro-immune synapse formation and suggest potential avenues for future therapeutic research.

Piezo inhibition prevents and rescues scarring by targeting the adipocyte to fibroblast transition

While past studies have suggested that plasticity exists between dermal fibroblasts and adipocytes, it remains unknown whether fat actively contributes to fibrosis in scarring. We show that adipocytes convert to scar-forming fibroblasts in response to Piezo -mediated mechanosensing to drive wound fibrosis. We establish that mechanics alone are sufficient to drive adipocyte-to- fibroblast conversion. By leveraging clonal-lineage-tracing in combination with scRNA-seq, Visium, and CODEX, we define a "mechanically naïve" fibroblast-subpopulation that represents a transcriptionally intermediate state between adipocytes and scar-fibroblasts. Finally, we show that Piezo1 or Piezo2 -inhibition yields regenerative healing by preventing adipocytes' activation to fibroblasts, in both mouse-wounds and a novel human-xenograft-wound model. Importantly, Piezo1 -inhibition induced wound regeneration even in pre-existing established scars, a finding that suggests a role for adipocyte-to-fibroblast transition in wound remodeling, the least-understood phase of wound healing. Adipocyte-to-fibroblast transition may thus represent a therapeutic target for minimizing fibrosis via Piezo -inhibition in organs where fat contributes to fibrosis.

The evolving tumor microenvironment: From cancer initiation to metastatic outgrowth

Cancers represent complex ecosystems comprising tumor cells and a multitude of non-cancerous cells, embedded in an altered extracellular matrix. The tumor microenvironment (TME) includes diverse immune cell types, cancer-associated fibroblasts, endothelial cells, pericytes, and various additional tissue-resident cell types. These host cells were once considered bystanders of tumorigenesis but are now known to play critical roles in the pathogenesis of cancer. The cellular composition and functional state of the TME can differ extensively depending on the organ in which the tumor arises, the intrinsic features of cancer cells, the tumor stage, and patient characteristics. Here, we review the importance of the TME in each stage of cancer progression, from tumor initiation, progression, invasion, and intravasation to metastatic dissemination and outgrowth. Understanding the complex interplay between tumor cell-intrinsic, cell-extrinsic, and systemic mediators of disease progression is critical for the rational development of effective anti-cancer treatments.

A double-edged sword of platelet-derived extracellular vesicles in tissues, injury or repair: The current research overview

Extracellular vesicles (EVs) are vesicular bodies with a double-layered membrane structure that are detached from the cell membrane or secreted by the cells. EVs secreted by platelets account for the main part in the blood circulation, which account for about 30% or even more. Many types of cells are regulated by PEVs, including endothelial cells, leukocytes, smooth muscle cells, etc. Nevertheless, despite the growing interest in the study of extracellular vesicles, there are still only a few studies on the role of PEVs. Therefore, this overview mainly focuses on one method of isolation and the functions of PEVs in tissues found so far, including promoting tissue repair and mediating tissue damage, which can be used for researchers to continue to explore the role of PEVs in other fields.

Water from Nitrodi’s Spring Induces Dermal Fibroblast and Keratinocyte Activation, Thus Promoting Wound Repair in the Skin: An In Vitro Study

The Romans knew of Nitrodi’s spring on the island of Ischia more than 2000 years ago. Although the health benefits attributed to Nitrodi’s water are numerous, the underlying mechanisms are still not understood. In this study, we aim to analyze the physicochemical properties and biological effects of Nitrodi’s water on human dermal fibroblasts to determine whether the water exerts in vitro effects that could be relevant to skin wound healing. The results obtained from the study indicate that Nitrodi’s water exerts strong promotional effects on dermal fibroblast viability and a significant stimulatory activity on cell migration. Nitrodi’s water induces alpha-SMA expression in dermal fibroblasts, thus promoting their transition to myofibroblast-protein ECM deposition. Furthermore, Nitrodi’s water reduces intracellular reactive oxygen species (ROS), which play an important role in human skin aging and dermal damage. Unsurprisingly, Nitrodi’s water has significant stimulatory effects on the cell proliferation of epidermal keratinocytes and inhibits the basal ROS production but enhances their response to the oxidative stress caused by external stimuli. Our results will contribute to the development of human clinical trials and further in vitro studies to identify inorganic and/or organic compounds responsible for pharmacological effects.

Lrig1-expressing epidermal progenitors require SCD1 to maintain the dermal papilla niche

Niche cells are widely known to regulate stem/progenitor cells in many mammalian tissues. In the hair, dermal papilla niche cells are well accepted to regulate hair stem/progenitor cells. However, how niche cells themselves are maintained is largely unknown. We present evidence implicating hair matrix progenitors and the lipid modifying enzyme, Stearoyl CoA Desaturase 1, in the regulation of the dermal papilla niche during the anagen-catagen transition of the mouse hair cycle. Our data suggest that this takes place via autocrine Wnt signalling and paracrine Hedgehog signalling. To our knowledge, this is the first report demonstrating a potential role for matrix progenitor cells in maintaining the dermal papilla niche.

Lineage Commitment of Dermal Fibroblast Progenitors is Mediated by Chromatin De-repression

Dermal Fibroblast Progenitors (DFPs) differentiate into distinct fibroblast lineages during skin development. However, the mechanisms that regulate lineage commitment of naive dermal progenitors to form niches around the hair follicle, dermis, and hypodermis, are unknown. In our study, we used multimodal single-cell approaches, epigenetic assays, and allografting techniques to define a DFP state and the mechanisms that govern its differentiation potential. Our results indicate that the overall chromatin profile of DFPs is repressed by H3K27me3 and has inaccessible chromatin at lineage specific genes. Surprisingly, the repressed chromatin profile of DFPs renders them unable to reform skin in allograft assays despite their multipotent potential. Distinct fibroblast lineages, such as the dermal papilla and adipocytes contained specific chromatin profiles that were de-repressed during late embryogenesis by the H3K27-me3 demethylase, Kdm6b/Jmjd3. Tissue-specific deletion of Kdm6b/Jmjd3 resulted in ablating the adipocyte compartment and inhibiting mature dermal papilla functions in single-cell-RNA-seq, ChIPseq, and allografting assays. Altogether our studies reveal a mechanistic multimodal understanding of how DFPs differentiate into distinct fibroblast lineages, and we provide a novel multiomic search-tool within skinregeneration.org.

From gatekeepers to providers: regulation of immune functions by cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs) are major protumorigenic components of the tumor microenvironment in solid cancers. CAFs are heterogeneous, consisting of multiple subsets that display diverse functions. Recently, CAFs have emerged as major promoters of immune evasion. CAFs favor T cell exclusion and exhaustion, promote recruitment of myeloid-derived suppressor cells, and induce protumoral phenotypic shifts in macrophages and neutrophils. With the growing appreciation of CAF heterogeneity came the understanding that different CAF subpopulations may be driving distinct immune-regulatory effects, interacting with different cell types, and perhaps even driving opposing effects on malignancy. In this review we discuss the current understanding of CAF-immune interactions, their effect on tumor progression and therapeutic response, and the possibility of exploiting CAF-immune interactions as potential targets for cancer therapy.

Thermal imprinting during embryogenesis modifies skin repair in juvenile European sea bass (Dicentrarchus labrax)

Fish skin is a multifunctional tissue that develops during embryogenesis, a developmental stage highly susceptible to epigenetic marks. In this study, the impact of egg incubation temperature on the regeneration of a cutaneous wound caused by scale removal in juvenile European sea bass was evaluated. Sea bass eggs were incubated at 11, 13.5 and 16 °C until hatching and then were reared at a common temperature until 9 months when the skin was damaged and sampled at 0, 1 and 3 days after scale removal and compared to the intact skin from the other flank. Skin damage elicited an immediate significant (p < 0.001) up-regulation of pcna in fish from eggs incubated at higher temperatures. In fish from eggs incubated at 11 °C there was a significant (p < 0.001) up-regulation of krt2 compared to fish from higher thermal backgrounds 1 day after skin damage. Damaged epidermis was regenerated after 3 days in all fish irrespective of the thermal background, but in fish from eggs incubated at 11 °C the epidermis was significantly (p < 0.01) thinner compared to other groups, had less goblet cells and less melanomacrophages. The thickness of the dermis increased during regeneration of wounded skin irrespective of the thermal background and by 3 days was significantly (p < 0.01) thicker than the dermis from the intact flank. The expression of genes for ECM remodelling (mmp9, colXα, col1α1, sparc, and angptl2b) and innate immunity (lyg1, lalba, sod1, csf-1r and pparγ) changed during regeneration but were not affected by egg thermal regime. Overall, the results indicate that thermal imprinting of eggs modifies the damage-repair response in juvenile sea bass skin.

Taxonomy of fibroblasts and progenitors in the synovial joint at single-cell resolution

OBJECTIVES

Fibroblasts in synovium include fibroblast-like synoviocytes (FLS) in the lining and Thy1+ connective-tissue fibroblasts in the sublining. We aimed to investigate their developmental origin and relationship with adult progenitors.

METHODS

To discriminate between Gdf5-lineage cells deriving from the embryonic joint interzone and other Pdgfrα-expressing fibroblasts and progenitors, adult Gdf5-Cre;Tom;Pdgfrα-H2BGFP mice were used and cartilage injury was induced to activate progenitors. Cells were isolated from knees, fibroblasts and progenitors were sorted by fluorescence-activated cell-sorting based on developmental origin, and analysed by single-cell RNA-sequencing. Flow cytometry and immunohistochemistry were used for validation. Clonal-lineage mapping was performed using Gdf5-Cre;Confetti mice.

RESULTS

In steady state, Thy1+ sublining fibroblasts were of mixed ontogeny. In contrast, Thy1-Prg4+ lining fibroblasts predominantly derived from the embryonic joint interzone and included Prg4-expressing progenitors distinct from molecularly defined FLS. Clonal-lineage tracing revealed compartmentalisation of Gdf5-lineage fibroblasts between lining and sublining. Following injury, lining hyperplasia resulted from proliferation and differentiation of Prg4-expressing progenitors, with additional recruitment of non-Gdf5-lineage cells, into FLS. Consistent with this, a second population of proliferating cells, enriched near blood vessels in the sublining, supplied activated multipotent cells predicted to give rise to Thy1+ fibroblasts, and to feed into the FLS differentiation trajectory. Transcriptional programmes regulating fibroblast differentiation trajectories were uncovered, identifying Sox5 and Foxo1 as key FLS transcription factors in mice and humans.

CONCLUSIONS

Our findings blueprint a cell atlas of mouse synovial fibroblasts and progenitors in healthy and injured knees, and provide novel insights into the cellular and molecular principles governing the organisation and maintenance of adult synovial joints.

Global trends in research of fibroblasts associated with rheumatoid diseases in the 21st century: A bibliometric analysis

Background

Rheumatoid Diseases (RDs) are a group of systemic auto-immune diseases that are characterized by chronic synovitis, and fibroblast-like synoviocytes (FLSs) play an important role in the occurrence and progression of synovitis. Our study is the first to adopt bibliometric analysis to identify the global scientific production and visualize its current distribution in the 21st century, providing insights for future research through the analysis of themes and keywords.

Methods

We obtained scientific publications from the core collection of the Web of Science (WoS) database, and the bibliometric analysis and visualization were conducted by Biblioshiny software based on R-bibliometrix.

Results

From 2000 to 2022, a total of 3,391 publications were reviewed. China is the most prolific country (n = 2601), and the USA is the most cited country (cited 7225 times). The Center of Experimental Rheumatology at University Hospital Zürich supported the maximum number of articles (n = 40). Steffen Gay published 85 records with 6263 total citations, perhaps making him the most impactful researcher. Arthritis and Rheumatism, Annals of Rheumatic Diseases, and Rheumatology are the top three journals.

Conclusion

The current study revealed that rheumatoid disease (RD)-related fibroblast studies are growing. Based on the bibliometric analysis, we summarized three important topics: activation of different subsets of fibroblasts; regulation of fibroblast function; and in vitro validation of existing discoveries. They are all valuable directions, which provide reference and guidance for researchers and clinicians engaged in the research of RDs and fibroblasts.

Role and mechanism of CD90+ fibroblasts in inflammatory diseases and malignant tumors

Fibroblasts are highly heterogeneous mesenchymal stromal cells, and different fibroblast subpopulations play different roles. A subpopulation of fibroblasts expressing CD90, a 25-37 kDa glycosylphosphatidylinositol anchored protein, plays a dominant role in the fibrotic and pro-inflammatory state. In this review, we focused on CD90⁺ fibroblasts, and their roles and possible mechanisms in disease processes. First, the main biological functions of CD90⁺ fibroblasts in inducing angiogenesis and maintaining tissue homeostasis are described. Second, the role and possible mechanism of CD90⁺ fibroblasts in inducing pulmonary fibrosis, inflammatory arthritis, inflammatory skin diseases, and scar formation are introduced, and we discuss how CD90⁺ cancer-associated fibroblasts might serve as promising cancer biomarkers. Finally, we propose future research directions related to CD90⁺ fibroblasts. This review will provide a theoretical basis for the diagnosis and treatment CD90⁺ fibroblast-related disease.

Murine skin-derived multipotent papillary dermal fibroblast progenitors show germline potential in vitro

BACKGROUND

Many laboratories have described the in vitro isolation of multipotent cells with stem cell properties from the skin of various species termed skin-derived stem cells (SDSCs). However, the cellular origin of these cells and their capability to give rise, among various cell types, to male germ cells, remain largely unexplored.

METHODS

SDSCs were isolated from newborn mice skin, and then differentiated into primordial germ cell-like cells (PGCLCs) in vitro. Single-cell RNA sequencing (scRNA-seq) was then applied to dissect the cellular origin of SDSCs using cells isolated from newborn mouse skin and SDSC colonies. Based on an optimized culture strategy, we successfully generated spermatogonial stem cell-like cells (SSCLCs) in vitro.

RESULTS

Here, using scRNA-seq and analyzing the profile of 7543 single-cell transcriptomes from newborn mouse skin and SDSCs, we discovered that they mainly consist of multipotent papillary dermal fibroblast progenitors (pDFPs) residing in the dermal layer. Moreover, we found that epidermal growth factor (EGF) signaling is pivotal for the capability of these progenitors to proliferate and form large colonies in vitro. Finally, we optimized the protocol to efficiently generate PGCLCs from SDSCs. Furthermore, PGCLCs were induced into SSCLCs and these SSCLCs showed meiotic potential when cultured with testicular organoids.

CONCLUSIONS

Our findings here identify pDFPs as SDSCs derived from newborn skin and show for the first time that such precursors can be induced to generate cells of the male germline.

Fascia Layer-A Novel Target for the Application of Biomaterials in Skin Wound Healing

As the first barrier of the human body, the skin has been of great concern for its wound healing and regeneration. The healing of large, refractory wounds is difficult to be repaired by cell proliferation at the wound edges and usually requires manual intervention for treatment. Therefore, therapeutic tools such as stem cells, biomaterials, and cytokines have been applied to the treatment of skin wounds. Skin microenvironment modulation is a key technology to promote wound repair and skin regeneration. In recent years, a series of novel bioactive materials that modulate the microenvironment and cell behavior have been developed, showing the ability to efficiently facilitate wound repair and skin attachment regeneration. Meanwhile, our lab found that the fascial layer has an indispensable role in wound healing and repair, and this review summarizes the research progress of related bioactive materials and their role in wound healing.

Beyond the Scar: A Basic Science Review of Wound Remodeling

Significance: Increasing development of experimental animal models has allowed for the study of scar formation. However, many pathophysiological unknowns remain in the longest stage of healing, the remodeling stage, which may continue for a year or more. The wound healing process results in different types of scarring classified as normal or pathological depending on failures at each stage. Failures can also occur during wound remodeling, but the molecular mechanisms driving the wound remodeling process have yet to be investigated. Recent Advances: While the current understanding of wound repair is based on investigations of acute healing, these experimental models have informed knowledge of key components of remodeling. This review examines the components that contribute to collagen organization and the final scar, including cell types, their regulation, and signaling pathways. Dysregulation in any one of these components causes pathologic healing. Critical Issues and Future Directions: As wounds continue to remodel months to years after reepithelialization, new models to better understand long-term remodeling will be critical for improving healing outcomes. Further investigation of the contributions of fibroblasts and cell signaling pathways involved during remodeling as well as their potential failures may inform new approaches in promoting regenerative healing beyond reepithelialization.

LEP and LEPR are possibly a double-edged sword for wound healing

Wound healing is a complex and error-prone process. Wound healing in adults often leads to the formation of scars, a type of fibrotic tissue that lacks skin appendages. Hypertrophic scars and keloids can also form when the wound-healing process goes wrong. Leptin (Lep) and leptin receptors (LepRs) have recently been shown to affect multiple stages of wound healing. This effect, however, is paradoxical for scarless wound healing. On the one hand, Lep exerts pro-inflammatory and profibrotic effects; on the other hand, Lep can regulate hair follicle growth. This paper summarises the role of Lep and LepRs on cells in different stages of wound healing, briefly introduces the process of wound healing and Lep and LepRs, and examines the possibility of promoting scarless wound healing through spatiotemporal, systemic, and local regulation of Lep levels and the binding of Lep and LepRs.

Wound-Induced Hair Neogenesis: A Portal to the Development of New Therapies for Hair Loss and Wound Regeneration

Adult mammals retain the remarkable ability to regenerate hair follicles after wounding. Wound-induced hair neogenesis (WIHN) in many ways recapitulates embryogenesis. The origin of the stem cells that give rise to a nascent hair follicle after wounding and the role of mesenchymal cells and signaling pathways responsible for this regenerative phenomenon are slowly being elucidated. WIHN provides a potential therapeutic window for manipulating cell fate by the introduction of factors during the wound healing process to enhance hair follicle formation.

Exploring the Overlooked Roles and Mechanisms of Fibroblasts in the Foreign Body Response

Significance: Foreign body response (FBR), wherein a fibrotic capsule forms around an implanted structure, is a common surgical complication that often leads to pain, discomfort, and eventual revision surgeries. Although believed to have some mechanistic overlap with normal wound healing, much remains to be discovered about the specific mechanism by which this occurs. Recent Advances: Current understanding of FBR has focused on the roles of the immune system and the biomaterial, both major contributors to FBR. However, another key player, the fibroblast, is often overlooked. This review summarizes key contributors of FBR, focusing on the roles of fibroblasts. As much remains to be discovered about fibroblasts' specific roles in FBR, we draw on current knowledge of fibroblast subpopulations and functions during wound healing. We also provide an overview on candidate biomaterials and signaling pathways involved in FBR. Critical Issues and Future Directions: While the global implantable medical devices market is considerable and continues to appreciate in value, FBR remains one of the most common surgical implant complications. In parallel with the continued development of candidate biomaterials, further exploration of potential fibroblast subpopulations at a transcriptional level would provide key insights into further understanding the underlying mechanisms by which fibrous encapsulation occurs, and unveil novel directions for antifibrotic and regenerative therapies in the future.

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.

Role of fibroblast plasticity and heterogeneity in modulating angiogenesis and healing in the diabetic foot ulcer

Chronic diabetic foot ulcers (DFUs) are an important clinical issue faced by clinicians despite the advanced treatment strategies consisting of wound debridement, off-loading, medication, wound dressings, and keeping the ulcer clean. Non-healing DFUs are associated with the risk of amputation, increased morbidity and mortality, and economic stress. Neo-angiogenesis and granulation tissue formation are necessary for physiological DFU healing and acute inflammation play a key role in healing. However, chronic inflammation in association with diabetic complications holds the ulcer in the inflammatory phase without progressing to the resolution phase contributing to non-healing. Fibroblasts acquiring myofibroblasts phenotype contribute to granulation tissue formation and angiogenesis. However, recent studies suggest the presence of five subtypes of fibroblast population and of changing density in non-healing DFUs. Further, the association of fibroblast plasticity and heterogeneity with wound healing suggests that the switch in fibroblast phenotype may affect wound healing. The fibroblast phenotype shift and altered function may be due to the presence of chronic inflammation or a diabetic wound microenvironment. This review focuses on the role of fibroblast plasticity and heterogeneity, the effect of hyperglycemia and inflammatory cytokines on fibroblasts, and the interaction of fibroblasts with other cells in diabetic wound microenvironment in the perspective of DFU healing. Next, we summarize secretory, angiogenic, and angiostatic phenotypes of fibroblast which have been discussed in other organ systems but not in relation to DFUs followed by the perspective on the role of their phenotypes in promoting angiogenesis in DFUs.

Engineering edgeless human skin with enhanced biomechanical properties

Despite the advancements in skin bioengineering, 3D skin constructs are still produced as flat tissues with open edges, disregarding the fully enclosed geometry of human skin. Therefore, they do not effectively cover anatomically complex body sites, e.g., hands. Here, we challenge the prevailing paradigm by engineering the skin as a fully enclosed 3D tissue that can be shaped after a body part and seamlessly transplanted as a biological clothing. Our wearable edgeless skin constructs (WESCs) show enhanced dermal extracellular matrix (ECM) deposition and mechanical properties compared to conventional constructs. WESCs display region-specific cell/ECM alignment, as well as physiologic anisotropic mechanical properties. WESCs replace the skin in full-thickness wounds of challenging body sites (e.g., mouse hindlimbs) with minimal suturing and shorter surgery time. This study provides a compelling technology that may substantially improve wound care and suggests that the recapitulation of the tissue macroanatomy can lead to enhanced biological function.