Distinct Regulatory Programs Control the Latent Regenerative Potential of Dermal Fibroblasts during Wound Healing

Time-course swRNA-seq uncovers a hierarchical gene regulatory network in controlling the response-repair-remodeling after wounding

Wounding initiates intricate responses crucial for tissue repair and regeneration. Yet, the gene regulatory networks governing wound healing remain poorly understood. Here, employing single-worm RNA sequencing (swRNA-seq) across 12 time-points, we delineated a three-stage wound repair process in C. elegans: response, repair, and remodeling. Integrating diverse datasets, we constructed a dynamic regulatory network comprising 241 transcription regulators and their inferred targets. We identified potentially seven autoregulatory TFs and five cross-autoregulatory loops involving pqm-1 and jun-1. We revealed that TFs might interact with chromatin factors and form TF-TF combinatory modules via intrinsically disordered regions to enhance response robustness. We experimentally validated six regulators functioning in transcriptional and translocation-dependent manners. Notably, nhr-76, daf-16, nhr-84, and oef-1 are potentially required for efficient repair, while elt-2 may act as an inhibitor. These findings elucidate transcriptional responses and hierarchical regulatory networks during C. elegans wound repair, shedding light on mechanisms underlying tissue repair and regeneration.

Single-Cell and Spatial Transcriptome Analysis of Dermal Fibroblast Development in Perinatal Mouse Skin: Dynamic Lineage Differentiation and Key Driver Genes

Several single-cell RNA studies of developing mouse skin have elucidated the molecular and cellular processes involved in skin development. However, they have primarily focused on either the fetal or early postnatal period, leaving a gap in our understanding of skin development. In this study, we conducted a comprehensive time-series analysis by combining single-cell RNA-sequencing datasets collected at different stages of development (embryonic days 13.5, 14.5, and 16.5 and postnatal days 0, 2, and 4) and validated our findings through multipanel in situ spatial transcriptomics. Our analysis indicated that embryonic fibroblasts exhibit heterogeneity from a very early stage and that the rapid determination of each lineage occurs within days after birth. The expression of putative key driver genes, including Hey1, Ebf1, Runx3, and Sox11 for the dermal papilla trajectory; Lrrc15 for the dermal sheath trajectory; Zfp536 and Nrn1 for the papillary fibroblast trajectory; and Lrrn4cl and Mfap5 for the fascia fibroblast trajectory, was detected in the corresponding, spatially identified cell types. Finally, cell-to-cell interaction analysis indicated that the dermal papilla lineage is the primary source of the noncanonical Wnt pathway during skin development. Together, our study provides a transcriptomic reference for future research in the field of skin development and regeneration.

Dermal β-Catenin Is Required for Hedgehog-Driven Hair Follicle Neogenesis

Hair follicle neogenesis (HFN) occurs following large skin excisions in mice, serving as a rare regenerative model in mammalian wound healing. Wound healing typically results in fibrosis in mice and humans. We previously showed small skin excisions in mice result in scarring devoid of HFN, displaying features of non-regenerative healing, and Hedgehog (Hh) activation in the dermis of such wounds can induce HFN. In this study, we sought to verify the role of dermal Wnt/β-catenin signaling in HFN, as this pathway is essential for HF development, but is also paradoxically well-characterized in fibrosis of adult wounds. By deletion of β-catenin in large wound myofibroblasts, we show Wnt/β-catenin signaling is required for endogenous mechanisms of HFN. Through utilizing a combined mouse model that simultaneously induces deletion of β-catenin and constitutive activation of Smoothened (Smo) in myofibroblasts, we also found β-catenin is required for Hh-driven DP formation. Transcriptome analysis confirms Wnt/β-catenin and Hh pathways are activated in dermal papilla (DP) cells. Our results indicate that Wnt-active fibrotic status may also create a permissive state for the regenerative function of Hh, suggesting that activation of both Wnt and Hh pathways in skin wound fibroblasts must be ensured in future strategies to promote HFN.

Skin in the game: a review of single-cell and spatial transcriptomics in dermatological research

Single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics (ST) are two emerging research technologies that uniquely characterize gene expression microenvironments on a cellular or subcellular level. The skin, a clinically accessible tissue composed of diverse, essential cell populations, serves as an ideal target for these high-resolution investigative approaches. Using these tools, researchers are assembling a compendium of data and discoveries in healthy skin as well as a range of dermatologic pathophysiologies, including atopic dermatitis, psoriasis, and cutaneous malignancies. The ongoing advancement of single-cell approaches, coupled with anticipated decreases in cost with increased adoption, will reshape dermatologic research, profoundly influencing disease characterization, prognosis, and ultimately clinical practice.

Fibroblast and myofibroblast activation in normal tissue repair and fibrosis

The term 'fibroblast' often serves as a catch-all for a diverse array of mesenchymal cells, including perivascular cells, stromal progenitor cells and bona fide fibroblasts. Although phenotypically similar, these subpopulations are functionally distinct, maintaining tissue integrity and serving as local progenitor reservoirs. In response to tissue injury, these cells undergo a dynamic fibroblast-myofibroblast transition, marked by extracellular matrix secretion and contraction of actomyosin-based stress fibres. Importantly, whereas transient activation into myofibroblasts aids in tissue repair, persistent activation triggers pathological fibrosis. In this Review, we discuss the roles of mechanical cues, such as tissue stiffness and strain, alongside cell signalling pathways and extracellular matrix ligands in modulating myofibroblast activation and survival. We also highlight the role of epigenetic modifications and myofibroblast memory in physiological and pathological processes. Finally, we discuss potential strategies for therapeutically interfering with these factors and the associated signal transduction pathways to improve the outcome of dysregulated healing.

Single-cell analysis of mesenchymal cells in permeable neural vasculature reveals novel diverse subpopulations of fibroblasts

BACKGROUND

In the choroid plexus and pituitary gland, vasculature is known to have a permeable, fenestrated phenotype which allows for the free passage of molecules in contrast to the blood brain barrier observed in the rest of the CNS. The endothelium of these compartments, along with secretory, neural-lineage cells (choroid epithelium and pituitary endocrine cells) have been studied in detail, but less attention has been given to the perivascular mesenchymal cells of these compartments.

METHODS

The Hic1CreERT2 Rosa26LSL-TdTomato mouse model was used in conjunction with a PdgfraH2B-EGFP mouse model to examine mesenchymal cells, which can be subdivided into Pdgfra+ fibroblasts and Pdgfra- pericytes within the choroid plexus (CP) and pituitary gland (PG), by histological, immunofluorescence staining and single-cell RNA-sequencing analyses.

RESULTS

We found that both CP and PG possess substantial populations of distinct Hic1+ mesenchymal cells, including an abundance of Pdgfra+ fibroblasts. Within the pituitary, we identified distinct subpopulations of Hic1+ fibroblasts in the glandular anterior pituitary and the neurosecretory posterior pituitary. We also identified multiple distinct markers of CP, PG, and the meningeal mesenchymal compartment, including alkaline phosphatase, indole-n-methyltransferase and CD34.

CONCLUSIONS

Novel, distinct subpopulations of mesenchymal cells can be found in permeable vascular interfaces, including the CP, PG, and meninges, and make distinct contributions to both organs through the production of structural proteins, enzymes, transporters, and trophic molecules.

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.

Proteoglycan 4 (PRG4) treatment improves skin wound healing in a porcine model

Proteoglycan 4 (PRG4) is a boundary lubricant originally identified in articular cartilage and has been since shown to have immunomodulation and antifibrotic properties. Previously, we have demonstrated that recombinant human (rh)PRG4 treatment accelerates auricular cartilage injury closure through an inhibition of the fibrotic response, and promotion of tissue regeneration in mice. The purpose of the current study was to examine the effects of rhPRG4 treatment (vs. a DMSO carried control) on full-thickness skin wound healing in a preclinical porcine model. Our findings suggest that while rhPRG4 did not significantly accelerate nor impede full-thickness skin wound closure, it did improve repair quality by decreasing molecular markers of fibrosis and increasing re-vascularization. We also demonstrated that rhPRG4 treatment increased dermal adipose tissue during the healing process specifically by retaining adipocytes in the wound area but did not inhibit lipolysis. Overall, the results of the current study have demonstrated that rhPRG4 acts as antifibrotic agent and regulates dermal adipose tissue during the healing processes resulting in a tissue with a trajectory that more resembles the native skin vs. a fibrotic patch. This study provides strong rationale to examine if rhPRG4 can improve regeneration in human wounds.

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.

Vitamin A resolves lineage plasticity to orchestrate stem cell lineage choices

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

CSMP: A Self-Assembled Plant Polysaccharide-Based Hydrofilm for Enhanced Wound Healing

Wound management remains a critical healthcare issue due to the rising incidence of chronic diseases leading to persistent wounds. Traditional dressings have their limitations, such as potential for further damage during changing and suboptimal healing conditions. Recently, hydrogel-based dressings have gained attention due to their biocompatibility, biodegradability, and ability to fill wounds. Particularly, polysaccharide-based hydrogels have shown potential in various medical applications. This study focuses on the development of a novel hydrofilm wound dressing produced from a blend of chia seed mucilage (CSM) and polyvinyl alcohol (PVA), termed CSMP. While the individual properties of CSM and PVA are well-documented, their combined potential in wound management is largely unexplored. CSMP, coupled with sorbitol and glycerin, and cross-linked using ultraviolet light, results in a flexible, adhesive, and biocompatible hydrofilm demonstrating superior water absorption, moisturizing, and antibacterial properties. This hydrofilm promotes epithelial cell migration, enhanced collagen production, and outperforms existing commercial dressings in animal tests. The innovative CSMP hydrofilm offers a promising, cost-effective approach for improved wound care, bridging existing gaps in dressing performance and preparation simplicity. Future research can unlock further applications of such polysaccharide-based hydrofilm dressings.

[Skin fibrosis : Novel insights in pathophysiology and treatment]

The pathogenesis of fibrosing alterations in the skin and other organ systems is not yet sufficiently understood and current therapeutic options are limited. Fibrosing diseases of the skin lead to a loss of function, which can subsequently be accompanied by serious impairments in quality of life, increased morbidity and ultimately increased mortality. There are currently only a few pharmacological and therapeutic approaches approved to prevent or ameliorate fibrosing diseases. Furthermore, tissue-specific versus common, non-organ-specific pathophysiological cellular and molecular mechanisms are not resolved. The development of new, cause-based and therefore likely more efficient therapeutic approaches is urgently needed. This represents a major challenge, but also opens up the opportunity for special contributions to improve this medically unsolved problem. Here we present important findings from recent years with a focus on the role of the immune response in fibrogenesis.

Cancer-associated Fibroblast-specific Expression of the Matricellular Protein CCN1 Coordinates Neovascularization and Stroma Deposition in Melanoma Metastasis

Melanoma is the leading cause of skin cancer-related death. As prognosis of patients with melanoma remains problematic, identification of new therapeutic targets remains essential. Matricellular proteins are nonstructural extracellular matrix proteins. They are secreted into the tumor microenvironment to coordinate behavior among different cell types, yet their contribution to melanoma is underinvestigated. Examples of matricellular proteins include those comprising the CCN family. The CCN family member, CCN1, is highly proangiogenic. Herein, we show that, in human patients with melanoma, although found in several tumor cell types, CCN1 is highly expressed by a subset of cancer-associated fibroblasts (CAF) in patients with melanoma and this expression correlates positively with expression of proangiogenic genes and progressive disease/resistance to anti-PD1 checkpoint inhibitors. Consistent with these observations, in a syngeneic C57BL6 mouse model of melanoma, loss of CCN1 expression from Col1A2-Cre-, herein identified as "universal," fibroblasts, impaired metastasis of subcutaneously injected B16F10 tumor cells to lung, concomitant with disrupted neovascularization and collagen organization. Disruption of the extracellular matrix in the loss of CCN1 was validated using a novel artificial intelligence-based image analysis platform that revealed significantly decreased phenotypic fibrosis and composite morphometric collagen scores. As drug resistance is linked to matrix deposition and neoangiogenesis, these data suggest that CCN1, due to its multifaceted role, may represent a novel therapeutic target for drug-resistant melanoma. Our data further emphasize the essential role that cancer-associated, (universal) Col1A2-Cre-fibroblasts and extracellular matrix remodeling play in coordinating behavior among different cell types within the tumor microenvironment.

SIGNIFICANCE

In human patients, the expression of proangiogenic matricellular protein CCN1 in CAFs correlates positively with expression of stroma and angiogenic markers and progressive disease/resistance to checkpoint inhibitor therapy. In an animal model, loss of CCN1 from CAFs impaired metastasis of melanoma cells, neovascularization, and collagen deposition, emphasizing that CAFs coordinate cellular behavior in a tumor microenvironment and that CCN1 may be a novel target.

Modulating embryonic signaling pathways paves the way for regeneration in wound healing

Epithelial tissues, including the skin, are highly proliferative tissues with the capability to constant renewal and regeneration, a feature that is essential for survival as the skin forms a protective barrier against external insults and water loss. In adult mammalian skin, every injury will lead to a scar. The scar tissue that is produced to seal the wound efficiently is usually rigid and lacks elasticity and the skin's original resilience to external impacts, but also secondary appendages such as hair follicles and sebaceous glands. While it was long thought that hair follicles develop solely during embryogenesis, it is becoming increasingly clear that hair follicles can also regenerate within a wound. The ability of the skin to induce hair neogenesis following injury however declines with age. As fetal and neonatal skin have the remarkable capacity to heal without scarring, the recapitulation of a neonatal state has been a primary target of recent regenerative research. In this review we highlight how modulating dermal signaling or the abundance of specific fibroblast subsets could be utilized to induce de novo hair follicles within the wound bed, and thus to shift wound repair with a scar to scarless regeneration.

Single-cell analysis of psoriasis resolution demonstrates an inflammatory fibroblast state targeted by IL-23 blockade

Biologic therapies targeting the IL-23/IL-17 axis have transformed the treatment of psoriasis. However, the early mechanisms of action of these drugs remain poorly understood. Here, we perform longitudinal single-cell RNA-sequencing in affected individuals receiving IL-23 inhibitor therapy. By profiling skin at baseline, day 3 and day 14 of treatment, we demonstrate that IL-23 blockade causes marked gene expression shifts, with fibroblast and myeloid populations displaying the most extensive changes at day 3. We also identify a transient WNT5A+/IL24+ fibroblast state, which is only detectable in lesional skin. In-silico and in-vitro studies indicate that signals stemming from these WNT5A+/IL24+ fibroblasts upregulate multiple inflammatory genes in keratinocytes. Importantly, the abundance of WNT5A+/IL24+ fibroblasts is significantly reduced after treatment. This observation is validated in-silico, by deconvolution of multiple transcriptomic datasets, and experimentally, by RNA in-situ hybridization. These findings demonstrate that the evolution of inflammatory fibroblast states is a key feature of resolving psoriasis skin.

Adipose-derived Mesenchymal Stem Cells are Ideal for the Cell-based Treatment of Refractory Wounds: Strong Potential for Angiogenesis

Although Mesenchymal Stem Cells (MSCs)-based therapy has been proposed as a promising strategy for the treatment of chronic lower-extremity ulcers, their optimal sources, amounts, and delivery methods are urgently needed to be determined. In this study, we compared the heterogeneity of the human MSCs derived from bone marrow (BMSCs), umbilical cord (UCMSCs), and adipose tissue (ADSCs) in accelerating wound healing and promoting angiogenesis and explored the underlying mechanism. Briefly, a diabetic rat model with a full-thickness cutaneous wound on the dorsal foot was developed. The wound was topically administered with three types of MSCs. Additionally, we carried out in vitro and in vivo analysis of the angiogenic properties of the MSCs. Moreover, the molecular mechanism of the heterogeneity of the MSCs derived from the three tissues was explored by transcriptome sequencing. When compared with the BMSCs- and UCMSCs-treated groups, the ADSCs-treated group exhibited markedly accelerated healing efficiency, characterized by increased wound closure rates, enhanced angiogenesis, and collagen deposition at the wound site. The three types of MSCs formed three-dimensional capillary-like structures and promoted angiogenesis in vitro and in vivo, with ADSCs exhibiting the highest capacity for tube formation and pro-angiogenesis. Furthermore, transcriptome sequencing revealed that ADSCs had higher expression levels of angiogenesis-associated genes. Our findings indicate that MSCs-based therapy accelerates the healing of ischemia- and diabetes-induced lower-extremity ulcers and that adipose tissue-derived MSCs might be ideal for therapeutic angiogenesis and treatment of chronic ischemic wounds.

Research on evolution process of full-layer incision of skin tissue under different laser incidences

Considering difficulties of achieving vertical incidence of beam in different positions of skin, it is significant to study potential effects of incidence angles of laser on incisions. Surgical platform with a 1064 nm continuous fiber laser was established. Incident angle was adopted and real-time temperature fluctuations in laser operating area could be monitored. The rats were treated with laser at day 0 and day 3 after incision modeling, and H&E, Masson, Sirius Red, and Immuno-histochemical staining and enzyme-linked immunosorbent assay were adopted at day 3, 7, 14 to analyze the performance of healing. Laser with energy density of 67.54 J/mm2 can effectively accelerate wound healing in vivo, in which a laser with incident angle around 60° can effectively avoid scar hyperplasia. Therefore, the use of low energy laser with a small deflection angle has a good clinical application prospect in promoting wound healing.

Spatiotemporal signaling underlies progressive vascular rarefaction in myocardial infarction

Therapeutic angiogenesis represents a promising avenue to revascularize the ischemic heart. Its limited success is partly due to our poor understanding of the cardiac stroma, specifically mural cells, and their response to ischemic injury. Here, we combine single-cell and positional transcriptomics to assess the behavior of mural cells within the healing heart. In response to myocardial infarction, mural cells adopt an altered state closely associated with the infarct and retain a distinct lineage from fibroblasts. This response is concurrent with vascular rarefaction and reduced vascular coverage by mural cells. Positional transcriptomics reveals that the infarcted heart is governed by regional-dependent and temporally regulated programs. While the remote zone acts as an important source of pro-angiogenic signals, the infarct zone is accentuated by chronic activation of anti-angiogenic, pro-fibrotic, and inflammatory cues. Together, our work unveils the spatiotemporal programs underlying cardiac repair and establishes an association between vascular deterioration and mural cell dysfunction.

Targeting DNA methylation and demethylation in diabetic foot ulcers

BACKGROUND

Poor wound healing is a significant complication of diabetes, which is commonly caused by neuropathy, trauma, deformities, plantar hypertension and peripheral arterial disease. Diabetic foot ulcers (DFU) are difficult to heal, which makes patients susceptible to infections and can ultimately conduce to limb amputation or even death in severe cases. An increasing number of studies have found that epigenetic alterations are strongly associated with poor wound healing in diabetes.

AIM OF REVIEW

This work provides significant insights into the development of therapeutics for improving chronic diabetic wound healing, particularly by targeting and regulating DNA methylation and demethylation in DFU. Key scientific concepts of review: DNA methylation and demethylation play an important part in diabetic wound healing, via regulating corresponding signaling pathways in different breeds of cells, including macrophages, vascular endothelial cells and keratinocytes. In this review, we describe the four main phases of wound healing and their abnormality in diabetic patients. Furthermore, we provided an in-depth summary and discussion on how DNA methylation and demethylation regulate diabetic wound healing in different types of cells; and gave a brief summary on recent advances in applying cellular reprogramming techniques for improving diabetic wound healing.

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.

Single-cell analysis reveals distinct fibroblast plasticity during tenocyte regeneration in zebrafish

Despite their importance in tissue maintenance and repair, fibroblast diversity and plasticity remain poorly understood. Using single-cell RNA sequencing, we uncover distinct sclerotome-derived fibroblast populations in zebrafish, including progenitor-like perivascular/interstitial fibroblasts, and specialized fibroblasts such as tenocytes. To determine fibroblast plasticity in vivo, we develop a laser-induced tendon ablation and regeneration model. Lineage tracing reveals that laser-ablated tenocytes are quickly regenerated by preexisting fibroblasts. By combining single-cell clonal analysis and live imaging, we demonstrate that perivascular/interstitial fibroblasts actively migrate to the injury site, where they proliferate and give rise to new tenocytes. By contrast, perivascular fibroblast-derived pericytes or specialized fibroblasts, including tenocytes, exhibit no regenerative plasticity. Active Hedgehog (Hh) signaling is required for the proliferation of activated fibroblasts to ensure efficient tenocyte regeneration. Together, our work highlights the functional diversity of fibroblasts and establishes perivascular/interstitial fibroblasts as tenocyte progenitors that promote tendon regeneration in a Hh signaling-dependent manner.

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.

Repurposing DPP4 Inhibition to Improve Hair Follicle Activation and Regeneration

Skin injury and several diseases elicit fibrosis and induce hair follicle (HF) growth arrest and loss. The resulting alopecia and disfiguration represent a severe burden for patients, both physically and psychologically. Reduction of profibrotic factors such as dipeptidyl peptidase 4 (DPP4) might be a strategy to tackle this issue. We show DPP4 overrepresentation in settings with HF growth arrest (telogen), HF loss, and nonregenerative wound areas in mouse skin and human scalp. Topical DPP4 inhibition with Food and Drug Administration/European Medicines Agency-approved sitagliptin on preclinical models of murine HF activation/regeneration results in accelerated anagen progress, whereas treatment of wounds with sitagliptin results in reduced expression of fibrosis markers, increased induction of anagen around wounds, and HF regeneration in the wound center. These effects are associated with higher expression of Wnt target Lef1, known to be required for HF anagen/HF-activation and regeneration. Sitagliptin treatment decreases profibrotic signaling in the skin, induces a differentiation trajectory of HF cells, and activates Wnt targets related to HF activation/growth but not those supporting fibrosis. Taken together, our study shows a role for DPP4 in HF biology and shows how DPP4 inhibition, currently used as oral medication to treat diabetes, could be repurposed into a topical treatment agent to potentially reverse HF loss in alopecia and after injury.

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.

Genetic vulnerability to Crohn's disease reveals a spatially resolved epithelial restitution program

Effective tissue repair requires coordinated intercellular communication to sense damage, remodel the tissue, and restore function. Here, we dissected the healing response in the intestinal mucosa by mapping intercellular communication at single-cell resolution and integrating with spatial transcriptomics. We demonstrated that a risk variant for Crohn's disease, hepatocyte growth factor activator (HGFAC) Arg509His (R509H), disrupted a damage-sensing pathway connecting the coagulation cascade to growth factors that drive the differentiation of wound-associated epithelial (WAE) cells and production of a localized retinoic acid (RA) gradient to promote fibroblast-mediated tissue remodeling. Specifically, we showed that HGFAC R509H was activated by thrombin protease activity but exhibited impaired proteolytic activation of the growth factor macrophage-stimulating protein (MSP). In Hgfac R509H mice, reduced MSP activation in response to wounding of the colon resulted in impaired WAE cell induction and delayed healing. Through integration of single-cell transcriptomics and spatial transcriptomics, we demonstrated that WAE cells generated RA in a spatially restricted region of the wound site and that mucosal fibroblasts responded to this signal by producing extracellular matrix and growth factors. We further dissected this WAE cell-fibroblast signaling circuit in vitro using a genetically tractable organoid coculture model. Collectively, these studies exploited a genetic perturbation associated with human disease to disrupt a fundamental biological process and then reconstructed a spatially resolved mechanistic model of tissue healing.

Dental Pulp Stem Cells for Bone Tissue Engineering: A Literature Review

Bone tissue engineering (BTE) is a promising approach for repairing and regenerating damaged bone tissue, using stem cells and scaffold structures. Among various stem cell sources, dental pulp stem cells (DPSCs) have emerged as a potential candidate due to their multipotential capabilities, ability to undergo osteogenic differentiation, low immunogenicity, and ease of isolation. This article reviews the biological characteristics of DPSCs, their potential for BTE, and the underlying transcription factors and signaling pathways involved in osteogenic differentiation; it also highlights the application of DPSCs in inducing scaffold tissues for bone regeneration and summarizes animal and clinical studies conducted in this field. This review demonstrates the potential of DPSC-based BTE for effective bone repair and regeneration, with implications for clinical translation.

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.

Tracing immune cells around biomaterials with spatial anchors during large-scale wound regeneration

Skin scarring devoid of dermal appendages after severe trauma has unfavorable effects on aesthetic and physiological functions. Here we present a method for large-area wound regeneration using biodegradable aligned extracellular matrix scaffolds. We show that the implantation of these scaffolds accelerates wound coverage and enhances hair follicle neogenesis. We perform multimodal analysis, in combination with single-cell RNA sequencing and spatial transcriptomics, to explore the immune responses around biomaterials, highlighting the potential role of regulatory T cells in mitigating tissue fibrous by suppressing excessive type 2 inflammation. We find that immunodeficient mice lacking mature T lymphocytes show the typical characteristic of tissue fibrous driven by type 2 macrophage inflammation, validating the potential therapeutic effect of the adaptive immune system activated by biomaterials. These findings contribute to our understanding of the coordination of immune systems in wound regeneration and facilitate the design of immunoregulatory biomaterials in the future.

Prediction and Demonstration of Retinoic Acid Receptor Agonist Ch55 as an Antifibrotic Agent in the Dermis

The prevalence of fibrotic diseases and the lack of pharmacologic modalities to effectively treat them impart particular importance to the discovery of novel antifibrotic therapies. The repurposing of drugs with existing mechanisms of action and/or clinical data is a promising approach for the treatment of fibrotic diseases. One paradigm that pervades all fibrotic diseases is the pathological myofibroblast, a collagen-secreting, contractile mesenchymal cell that is responsible for the deposition of fibrotic tissue. In this study, we use a gene expression paradigm characteristic of activated myofibroblasts in combination with the Connectivity Map to select compounds that are predicted to reverse the pathological gene expression signature associated with the myofibroblast and thus contain the potential for use as antifibrotic compounds. We tested a small list of these compounds in a first-pass screen, applying them to fibroblasts, and identified the retinoic acid receptor agonist Ch55 as a potential hit. Further investigation exhibited and elucidated the antifibrotic effects of Ch55 in vitro as well as showing antiscarring activity upon intradermal application in a preclinical rabbit ear hypertrophic scar model. We hope that similar predictions to uncover antiscarring compounds may yield further preclinical and ultimately clinical success.

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.

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.

COVID-19 Infection May Drive EC-like Myofibroblasts towards Myofibroblasts to Contribute to Pulmonary Fibrosis

COVID-19 has an extensive impact on Homo sapiens globally. Patients with COVID-19 are at an increased risk of developing pulmonary fibrosis. A previous study identified that myofibroblasts could be derived from pulmonary endothelial lineage cells as an important cell source that contributes to pulmonary fibrosis. Here, we analyzed publicly available data and showed that COVID-19 infection drove endothelial lineage cells towards myofibroblasts in pulmonary fibrosis of patients with COVID-19. We also discovered a similar differentiation trajectory in mouse lungs after viral infection. The results suggest that COVID-19 infection leads to the development of pulmonary fibrosis partly through the activation of endothelial cell (EC)-like myofibroblasts.

Exogenously delivered iPSCs disrupt the natural repair response of endogenous MPCs after bone injury

Promoting bone healing including fracture non-unions are promising targets for bone tissue engineering due to the limited success of current clinical treatment methods. There has been significant research on the use of stem cells with and without biomaterial scaffolds to treat bone fractures due to their promising regenerative capabilities. However, the relative roles of exogenous vs. endogenous stem cells and their overall contribution to in vivo fracture repair is not well understood. The purpose of this study was to determine the interaction between exogenous and endogenous stem cells during bone healing. This study was conducted using a standardized burr-hole bone injury model in a mesenchymal progenitor cell (MPC) lineage-tracing mouse under normal homeostatic and osteoporotic conditions. Burr-hole injuries were treated with a collagen-I biomaterial loaded with and without labelled induced pluripotent stem cells (iPSCs). Using lineage-tracing, the roles of exogenous and endogenous stem cells during bone healing were examined. It was observed that treatment with iPSCs resulted in muted healing compared to untreated controls in intact mice post-injury. When the cell populations were examined histologically, iPSC-treated burr-hole defects presented with a dramatic reduction in endogenous MPCs and cell proliferation throughout the injury site. However, when the ovaries were removed and an osteoporotic-like phenotype induced in the mice, iPSCs treatment resulted in increased bone formation relative to untreated controls. In the absence of iPSCs, endogenous MPCs demonstrated robust proliferative and osteogenic capacity to undertake repair and this behaviour was disrupted in the presence of iPSCs which instead took on an osteoblast fate but with little proliferation. This study clearly demonstrates that exogenously delivered cell populations can impact the normal function of endogenous stem/progenitor populations during the normal healing cascade. These interactions need to be better understood to inform cell and biomaterial therapies to treat fractures.

Revealing the Organ-Specific Expression of SPTBN1 using Single-Cell RNA Sequencing Analysis

Despite the recent technological advances in single-cell RNA sequencing, it is still unknown how three marker genes (SPTBN1, EPDR1, and PKDCC), which are associated with bone fractures and highly expressed in the muscle tissue, are contributing to the development of other tissues and organs at the cellular level. This study aims to analyze three marker genes at the single-cell level using 15 organ tissue types of adult human cell atlas (AHCA). The single-cell RNA sequencing analysis used three marker genes and a publicly available AHCA data set. AHCA data set contains more than 84,000 cells from 15 organ tissue types. Quality control filtering, dimensionality reduction, clustering for cells, and data visualization were performed using the Seurat package. A total of 15 organ types are included in the downloaded data sets: Bladder, Blood, Common Bile Duct, Esophagus, Heart, Liver, Lymph Node, Marrow, Muscle, Rectum, Skin, Small Intestine, Spleen, Stomach, and Trachea. In total, 84,363 cells and 228,508 genes were included in the integrated analysis. A marker gene of SPTBN1 is highly expressed across all 15 organ types, particularly in the Fibroblasts, Smooth muscle cells, and Tissue stem cells of the Bladder, Esophagus, Heart, Muscle, Rectum, Skin, and Trachea. In contrast, EPDR1 is highly expressed in the Muscle, Heart, and Trachea, and PKDCC is only expressed in Heart. In conclusion, SPTBN1 is an essential protein gene in physiological development and plays a critical role in the high expression of fibroblasts in multiple organ types. Targeting SPTBN1 may prove beneficial for fracture healing and drug discovery.

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.

Safety and efficacy of autologous skin tissue cells grafting for facial sunken or flat scars

Importance

It is necessary to determine whether safety and efficacy of autologous skin tissue cells grafting for facial sunken or flat scars.

Objective

To identify autologous skin tissue cells grafting can reduce facial sunken or flat scars.

Design setting and participants

In this retrospective cross-sectional study, a total of 128 patients with scar (exclude pathological scar patients), who were receiving autologous skin tissue cells grafting therapy from January 1, 2016, to December 31, 2019.

Interventions

Autologous skin tissue cells grafting.

Main outcomes and measures

Changes in scar severity, color changes in the scar area, infection rate and patient satisfaction.

Results

A total of 128 patients with scar (89 females [69.5%]; mean [SD] age, 30.6 [13.12] years) received autologous skin tissue cells grafting therapy. SCAR (Scar Cosmesis Assessment and Rating), with scores ranging from 0 (best possible scar) to 15 (worst possible scar). After treatment 12 months, the mean [SD] of SCAR score went down from 9.85 [1.33] to 2.67 [1.21]. No infection was observed during treatment or recovery, and the main drawback after autologous skin tissue cells grafting is that the color recovery time is longer. The patient satisfaction 6 months after treatment was 85.2%, furthermore 12 months after treatment patient satisfaction was 94.7%.

Conclusions and relevance

In this study, autologous skin tissue cells grafting was safe and effective to treat facial scars. Therefore, autologous skin tissue cells grafting may be recommended as a reliable treatment for facial scar.

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.

Hic1 identifies a specialized mesenchymal progenitor population in the embryonic limb responsible for bone superstructure formation

The musculoskeletal system relies on the integration of multiple components with diverse physical properties, such as striated muscle, tendon, and bone, that enable locomotion and structural stability. This relies on the emergence of specialized, but poorly characterized, interfaces between these various elements during embryonic development. Within the appendicular skeleton, we show that a subset of mesenchymal progenitors (MPs), identified by Hic1, do not contribute to the primary cartilaginous anlagen but represent the MP population, whose progeny directly contribute to the interfaces that connect bone to tendon (entheses), tendon to muscle (myotendinous junctions), and the associated superstructures. Furthermore, deletion of Hic1 leads to skeletal defects reflective of deficient muscle-bone coupling and, consequently, perturbation of ambulation. Collectively, these findings show that Hic1 identifies a unique MP population that contributes to a secondary wave of bone sculpting critical to skeletal morphogenesis.

Activated fibroblasts in cancer: Perspectives and challenges

Activated fibroblasts in tumors, or cancer-associated fibroblasts (CAFs), have become a popular research area over the past decade. As important players in many aspects of tumor biology, with functions ranging from collagen deposition to immunosuppression, CAFs have been the target of clinical and pre-clinical studies that have revealed their potential pro- and anti-tumorigenic dichotomy. In this review, we describe the important role of CAFs in the tumor microenvironment and the technological advances that made these discoveries possible, and we detail the models that are currently available for CAF investigation. Additionally, we present evidence to support the value of encompassing CAF investigation as a future therapeutic avenue alongside immune and cancer cells while highlighting the challenges that must be addressed for successful clinical translation of new findings.

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.

Screening cell-cell communication in spatial transcriptomics via collective optimal transport

Spatial transcriptomic technologies and spatially annotated single-cell RNA sequencing datasets provide unprecedented opportunities to dissect cell-cell communication (CCC). However, incorporation of the spatial information and complex biochemical processes required in the reconstruction of CCC remains a major challenge. Here, we present COMMOT (COMMunication analysis by Optimal Transport) to infer CCC in spatial transcriptomics, which accounts for the competition between different ligand and receptor species as well as spatial distances between cells. A collective optimal transport method is developed to handle complex molecular interactions and spatial constraints. Furthermore, we introduce downstream analysis tools to infer spatial signaling directionality and genes regulated by signaling using machine learning models. We apply COMMOT to simulation data and eight spatial datasets acquired with five different technologies to show its effectiveness and robustness in identifying spatial CCC in data with varying spatial resolutions and gene coverages. Finally, COMMOT identifies new CCCs during skin morphogenesis in a case study of human epidermal development.

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.

Commensal microbiome promotes hair follicle regeneration by inducing keratinocyte HIF-1α signaling and glutamine metabolism

Tissue injury induces metabolic changes in stem cells, which likely modulate regeneration. Using a model of organ regeneration called wound-induced hair follicle neogenesis (WIHN), we identified skin-resident bacteria as key modulators of keratinocyte metabolism, demonstrating a positive correlation between bacterial load, glutamine metabolism, and regeneration. Specifically, through comprehensive multiomic analysis and single-cell RNA sequencing in murine skin, we show that bacterially induced hypoxia drives increased glutamine metabolism in keratinocytes with attendant enhancement of skin and hair follicle regeneration. In human skin wounds, topical broad-spectrum antibiotics inhibit glutamine production and are partially responsible for reduced healing. These findings reveal a conserved and coherent physiologic context in which bacterially induced metabolic changes improve the tolerance of stem cells to damage and enhance regenerative capacity. This unexpected proregenerative modulation of metabolism by the skin microbiome in both mice and humans suggests important methods for enhancing regeneration after injury.

The Role of Myofibroblasts in Physiological and Pathological Tissue Repair

Myofibroblasts are the construction workers of wound healing and repair damaged tissues by producing and organizing collagen/extracellular matrix (ECM) into scar tissue. Scar tissue effectively and quickly restores the mechanical integrity of lost tissue architecture but comes at the price of lost tissue functionality. Fibrotic diseases caused by excessive or persistent myofibroblast activity can lead to organ failure. This review defines myofibroblast terminology, phenotypic characteristics, and functions. We will focus on the central role of the cell, ECM, and tissue mechanics in regulating tissue repair by controlling myofibroblast action. Additionally, we will discuss how therapies based on mechanical intervention potentially ameliorate wound healing outcomes. Although myofibroblast physiology and pathology affect all organs, we will emphasize cutaneous wound healing and hypertrophic scarring as paradigms for normal tissue repair versus fibrosis. A central message of this review is that myofibroblasts can be activated from multiple cell sources, varying with local environment and type of injury, to either restore tissue integrity and organ function or create an inappropriate mechanical environment.

Fibroblast inflammatory priming determines regenerative versus fibrotic skin repair in reindeer

Adult mammalian skin wounds heal by forming fibrotic scars. We report that full-thickness injuries of reindeer antler skin (velvet) regenerate, whereas back skin forms fibrotic scar. Single-cell multi-omics reveal that uninjured velvet fibroblasts resemble human fetal fibroblasts, whereas back skin fibroblasts express inflammatory mediators mimicking pro-fibrotic adult human and rodent fibroblasts. Consequently, injury elicits site-specific immune responses: back skin fibroblasts amplify myeloid infiltration and maturation during repair, whereas velvet fibroblasts adopt an immunosuppressive phenotype that restricts leukocyte recruitment and hastens immune resolution. Ectopic transplantation of velvet to scar-forming back skin is initially regenerative, but progressively transitions to a fibrotic phenotype akin to the scarless fetal-to-scar-forming transition reported in humans. Skin regeneration is diminished by intensifying, or enhanced by neutralizing, these pathologic fibroblast-immune interactions. Reindeer represent a powerful comparative model for interrogating divergent wound healing outcomes, and our results nominate decoupling of fibroblast-immune interactions as a promising approach to mitigate scar.

A Shape-Adaptive Gallic Acid Driven Multifunctional Adhesive Hydrogel Loaded with Scolopin2 for Wound Repair

Wound healing is one of the major challenges in the biomedical fields. The conventional single drug treatment has unsatisfactory efficacy, and the drug delivery effectiveness is restricted by the short retention on the wound. Herein, we develop a multifunctional adhesive hydrogel that can realize robust adhesion, transdermal delivery, and combination therapy for wound healing. Multifunctional hydrogels (CS-GA-S) are mixed with chitosan-gallic acid (CS-GA), sodium periodate, and centipede peptide-scolopin2, which slowly releases scolopin2 in the layer of the dermis. The released scolopin2 induces the pro-angiogenesis of skin wounds and enables excellent antibacterial effects. Separately, GA as a natural reactive-oxygen-species-scavenger promotes antioxidation, and further enables excellent antibacterial effects and wet tissue adhesion due to a Schiff base and Michael addition reaction for accelerating wound healing. Once adhered to the wound, the precursor solution becomes both a physically and covalently cross-linked network hydrogel, which has potential advantages for wound healing with ease of use, external environment-isolating, and minimal tissue damage. The therapeutic effects of CS-GA-S on wound healing are demonstrated with the full thickness cutaneous wounds of a mouse model. The significant improvement of wound healing is achieved for mice treated with CS-GA-S. This preparation reduces wound system exposure, prolongs local drug residence time, and improves efficacy. Accordingly, with the incorporation of scolopin2 into the shape-adaptive CS-GA hydrogel, the composite hydrogel possesses multi-functions of mechanical adhesion, drug therapy, and skin wound healing. Overall, such an injectable or sprayable hydrogel plays an effective role in emergency wound treatment with the advantage of convenience and portability.