Preventing Engrailed-1 activation in fibroblasts yields wound regeneration without scarring

Hypoxia reveals a new function of Foxn1 in the keratinocyte antioxidant defense system

Skin exposed to environmental threats, including injuries and oxidative stress, develops an efficient but not fully recognized system of repair and antioxidant protection. Here, using mass spectrometry analysis (LC-MS/MS), followed by in vitro and in vivo experiments, we provided evidence that Foxn1 in keratinocytes regulates elements of the electron transport chain and participates in the thioredoxin system (Txn2, Txnrd3, and Srxn1) induction, particularly in a hypoxic environment. We first showed that Foxn1 in keratinocytes upregulates glutathione thioredoxin reductase 3 (Txnrd3) protein expression, and high levels of Txnrd3 mRNA were detected in injured skin of Foxn1^+/+ mice. We also showed that Foxn1 strongly downregulated the Ccn2 protein expression, participating in epidermal reconstruction after injury. An in vitro assay revealed that Foxn1 controls keratinocyte migration, stimulating it under normoxia and suppressing it under hypoxia. Keratinocytes overexpressing Foxn1 and exposed to hypoxia displayed a reduced ability to promote angiogenesis by downregulating Vegfa expression. In conclusion, this study showed a new mechanism in which Foxn1, along with hypoxia, participates in the activation of antioxidant defense and controls the functional properties of keratinocytes.

Tissue mechanics coevolves with fibrillar matrisomes in healthy and fibrotic tissues

Fibrillar proteins are principal components of extracellular matrix (ECM) that confer mechanical properties to tissues. Fibrosis can result from wound repair in nearly every tissue in adults, and it associates with increased ECM density and crosslinking as well as increased tissue stiffness. Such fibrotic tissues are a major biomedical challenge, and an emerging view posits that the altered mechanical environment supports both synthetic and contractile myofibroblasts in a state of persistent activation. Here, we review the matrisome in several fibrotic diseases, as well as normal tissues, with a focus on physicochemical properties. Stiffness generally increases with the abundance of fibrillar collagens, the major constituent of ECM, with similar mathematical trends for fibrosis as well as adult tissues from soft brain to stiff bone and heart development. Changes in expression of other core matrisome and matrisome-associated proteins or proteoglycans contribute to tissue stiffening in fibrosis by organizing collagen, crosslinking ECM, and facilitating adhesion of myofibroblasts. Understanding how ECM composition and mechanics coevolve during fibrosis can lead to better models and help with antifibrotic therapies.

Down-Regulating Scar Formation by Microneedles Directly via a Mechanical Communication Pathway

Excessive extracellular matrix deposition drives fibroblasts into a state of high mechanical stress, exacerbating pathological fibrosis and hypertrophic scar formation, leading to tissue dysfunction. This study reports a minimally invasive and convenient approach to obtaining scarless tissue using a silk fibroin microneedle patch (SF MNs). We found that by tuning the MN size and density only, the biocompatible MNs significantly decreased the scar elevation index in the rabbit ear hypertrophic scar model and increased ultimate tensile strength close to regular skin. To advance our understanding of this recent approach, we built a fibroblast-populated collagen lattice system and finite element model to study MN-mediated cellular behavior of fibroblasts. We found that the MNs reduced the fibroblasts generated contraction and mechanical stress, as indicated by decreased expression of the mechanical sensitive gene ANKRD1. Specifically, SF MNs attenuated the integrin-FAK signaling and consequently down-regulated the expression of TGF-β1, α-SMA, collagen I, and fibronectin. It resulted in a low-stress microenvironment that helps to reduce scar formation significantly. Microneedles' physical intervention via the mechanotherapeutic strategy is promising for scar-free wound healing.

Hair Follicle Morphogenesis During Embryogenesis, Neogenesis, and Organogenesis

Hair follicles are mini organs that repeat the growth and regression cycle continuously. These dynamic changes are driven by the regulation of stem cells via their multiple niche components. To build the complex structure of hair follicles and surrounding niches, sophisticated morphogenesis is required during embryonic development. This review will explore how hair follicles are formed and maintained through dynamic cellular changes and diverse signaling pathways. In addition, comparison of differences in stem cells and surrounding niche components during embryogenesis, neogenesis, and organogenesis will provide a comprehensive understanding of mechanisms for hair follicle generation and insights into skin regeneration.

Chronic wounds

Chronic wounds are characterized by their inability to heal within an expected time frame and have emerged as an increasingly important clinical problem over the past several decades, owing to their increasing incidence and greater recognition of associated morbidity and socio-economic burden. Even up to a few years ago, the management of chronic wounds relied on standards of care that were outdated. However, the approach to these chronic conditions has improved, with better prevention, diagnosis and treatment. Such improvements are due to major advances in understanding of cellular and molecular aspects of basic science, in innovative and technological breakthroughs in treatment modalities from biomedical engineering, and in our ability to conduct well-controlled and reliable clinical research. The evidence-based approaches resulting from these advances have become the new standard of care. At the same time, these improvements are tempered by the recognition that persistent gaps exist in scientific knowledge of impaired healing and the ability of clinicians to reduce morbidity, loss of limb and mortality. Therefore, taking stock of what is known and what is needed to improve understanding of chronic wounds and their associated failure to heal is crucial to ensuring better treatments and outcomes.

Holy grail of tissue regeneration: Size

Cells and tissue within injured organs undergo a complicated healing process that still remains poorly understood. Interestingly, smaller organisms respond to injury with tissue regeneration and restoration of function, while humans and other large organisms respond to injury by forming dysfunctional, fibrotic scar tissue. Over the past few decades, allometric scaling principles have been well established to show that larger organisms experience exponentially higher tissue forces during movement and locomotion and throughout the organism's lifespan. How these evolutionary adaptations may affect tissue injury has not been thoroughly investigated in humans. We discuss how these adapations may affect healing and demonstrate that blocking the most evolutionary conserved biologic force sensor enables large organisms to heal after injury with true tissue regeneration. Future strategies to disrupt tissue force sensors may unlock the key to regenerating after injury in a wide range of organ systems.

THY1-mediated mechanisms converge to drive YAP activation in skin homeostasis and repair

Anchored cells of the basal epidermis constantly undergo proliferation in an overcrowded environment. An important regulator of epidermal proliferation is YAP, which can be controlled by both cell-matrix and cell-cell interactions. Here, we report that THY1, a GPI-anchored protein, inhibits epidermal YAP activity through converging molecular mechanisms. THY1 deficiency leads to increased adhesion by activating the integrin-β₁-SRC module. Notably, regardless of high cellular densities, the absence of THY1 leads to the dissociation of an adherens junction complex that enables the release and translocation of YAP. Due to increased YAP-dependent proliferation, Thy1^-/- mice display enhanced wound repair and hair follicle regeneration. Taken together, our work reveals THY1 as a crucial regulator of cell-matrix and cell-cell interactions that controls YAP activity in skin homeostasis and regeneration.

Spatiotemporal Dynamics of the Molecular Expression Pattern and Intercellular Interactions in the Glial Scar Response to Spinal Cord Injury

Nerve regeneration in adult mammalian spinal cord is poor because of the lack of intrinsic regeneration of neurons and extrinsic factors - the glial scar is triggered by injury and inhibits or promotes regeneration. Recent technological advances in spatial transcriptomics (ST) provide a unique opportunity to decipher most genes systematically throughout scar formation, which remains poorly understood. Here, we first constructed the tissue-wide gene expression patterns of mouse spinal cords over the course of scar formation using ST after spinal cord injury from 32 samples. Locally, we profiled gene expression gradients from the leading edge to the core of the scar areas to further understand the scar microenvironment, such as neurotransmitter disorders, activation of the pro-inflammatory response, neurotoxic saturated lipids, angiogenesis, obstructed axon extension, and extracellular structure re-organization. In addition, we described 21 cell transcriptional states during scar formation and delineated the origins, functional diversity, and possible trajectories of subpopulations of fibroblasts, glia, and immune cells. Specifically, we found some regulators in special cell types, such as Thbs1 and Col1a2 in macrophages, CD36 and Postn in fibroblasts, Plxnb2 and Nxpe3 in microglia, Clu in astrocytes, and CD74 in oligodendrocytes. Furthermore, salvianolic acid B, a blood-brain barrier permeation and CD36 inhibitor, was administered after surgery and found to remedy fibrosis. Subsequently, we described the extent of the scar boundary and profiled the bidirectional ligand-receptor interactions at the neighboring cluster boundary, contributing to maintain scar architecture during gliosis and fibrosis, and found that GPR37L1_PSAP, and GPR37_PSAP were the most significant gene-pairs among microglia, fibroblasts, and astrocytes. Last, we quantified the fraction of scar-resident cells and proposed four possible phases of scar formation: macrophage infiltration, proliferation and differentiation of scar-resident cells, scar emergence, and scar stationary. Together, these profiles delineated the spatial heterogeneity of the scar, confirmed the previous concepts about scar architecture, provided some new clues for scar formation, and served as a valuable resource for the treatment of central nervous system injury.

Building and Maintaining the Skin

The skin forms a crucial, dynamic barrier between an animal and the external world. In mammals, three stem cell populations possess robust regenerative potential to maintain and repair the body's protective surface: epidermal stem cells, which maintain the stratified epidermis; hair follicle stem cells, which power the cyclic growth of the hair follicle; and melanocyte stem cells, which regenerate pigment-producing melanocytes to color the skin and hair. These stem cells reside in complex microenvironments ("niches") comprising diverse cellular repertoires that enable stem cells to rejuvenate tissues during homeostasis and regenerate them upon injury. Beyond their niches, skin stem cells can also sense and respond to fluctuations in organismal health or changes outside the body. Here, we review these diverse cellular interactions and highlight how far-reaching signals can be transmitted at the local level to enable skin stem cells to tailor their actions to suit the particular occasion and optimize fitness.

Toward Understanding Wound Immunology for High-Fidelity Skin Regeneration

Effective tissue repair is vital for the survival of organisms. Yet, how the immune system coordinates with tissue stem cells (SCs) to effect postnatal tissue restoration remains elusive. This review presents current knowledge surrounding wound-induced SC and immune signaling that favors tissue repair, including wound healing and regeneration. We discuss factors that affect regenerative capacities among organisms and the dynamics of local immune cells and SCs during reepithelialization. We also present recent insights into how immune niches communicate with SCs or other body systems to restore the epithelial architecture. Additionally, we summarize our findings on functional wound regeneration, specifically how alarmin (double-stranded RNA [dsRNA])-activated Toll-like receptor signaling and host-microbe interaction-related immune pathways alter the regenerative property of skin SCs. Last, we touch on mechanisms by which known immunologic cellular and molecular signaling might boost the skin's regenerative property. Overall, this review will provide insights into how therapeutically modulating immune signaling could enhance postnatal tissue regeneration.

The Role of the Extracellular Matrix (ECM) in Wound Healing: A Review

The extracellular matrix (ECM) is a 3-dimensional structure and an essential component in all human tissues. It is comprised of varying proteins, including collagens, elastin, and smaller quantities of structural proteins. Studies have demonstrated the ECM aids in cellular adherence, tissue anchoring, cellular signaling, and recruitment of cells. During times of integumentary injury or damage, either acute or chronic, the ECM is damaged. Through a series of overlapping events called the wound healing phases—hemostasis, inflammation, proliferation, and remodeling—the ECM is synthesized and ideally returned to its native state. This article synthesizes current and historical literature to demonstrate the involvement of the ECM in the varying phases of the wound healing cascade.

Fibroblast Growth Factor 7 Suppresses Fibrosis and Promotes Epithelialization during Wound Healing in Mouse Fetuses

Adult mammalian wounds leave visible scars, whereas skin wounds in developing mouse fetuses are scarless until a certain point in development when complete regeneration occurs, including the structure of the dermis and skin appendages. Analysis of the molecular mechanisms at this transition will provide clues for achieving scarless wound healing. The fibroblast growth factor (FGF) family is a key regulator of inflammation and fibrosis during wound healing. We aimed to determine the expression and role of FGF family members in fetal wound healing. ICR mouse fetuses were surgically wounded at embryonic day 13 (E13), E15, and E17. Expression of FGF family members and FGF receptor (FGFR) in tissue samples from these fetuses was evaluated using in situ hybridization and reverse transcription-quantitative polymerase chain reaction. Fgfr1 was downregulated in E15 and E17 wounds, and its ligand Fgf7 was upregulated in E13 and downregulated in E15 and E17. Recombinant FGF7 administration in E15 wounds suppressed fibrosis and promoted epithelialization at the wound site. Therefore, the expression level of Fgf7 may correlate with scar formation in late mouse embryos, and external administration of FGF7 may represent a therapeutic option to suppress fibrosis and reduce scarring.

The Role of Verteporfin in Prevention of Periprosthetic Capsular Fibrosis: An Experimental Study

BACKGROUND

Capsular contracture (CC) characterized by excessive fibrosis is one of the most common complications after silicone implant surgery. Verteporfin (VP), an inhibitor of Yes-associated protein 1 (YAP1), has recently been found to reduce the fibrotic process.

OBJECTIVES

The aim of this study was to use an in vivo rabbit model to evaluate the efficacy of VP for the prevention of CC.

METHODS

Twenty-four New Zealand rabbits received 10-cc smooth saline silicone implants inserted in the dorsal skin and were randomly divided into 2 groups to receive 2 mL VP (1.5 mg/mL) or 2 mL phosphate-buffered saline solution instillation in the implant pocket. When the animals were killed on Day 60, capsule formation was observed both macroscopically and microscopically. Histologic evaluation included capsule thickness, fibrosis degree, and myofibroblast (α smooth muscle actin positive) content. In addition, the YAP1 expression level was examined by immunofluorescence staining. Transforming growth factor β1, collagen I, and connective tissue growth factor expression were measured by real-time quantitative polymerase chain reaction.

RESULTS

The VP-treated group exhibited thinner, more transparent capsules and less fibrosis than the control group at 60 days postsurgery (P < 0.05). Moreover, the VP treatment significantly reduced α smooth muscle actin, YAP1, transforming growth factor β1, collagen I, and connective tissue growth factor expression levels in the capsular tissues (P < 0.05).

CONCLUSIONS

VP reduced capsule formation after silicone implantation by inhibiting YAP1-mediated mechanical signaling, thereby attenuating excessive collagen deposition in the rabbit model. This preclinical study may provide a feasible strategy to prevent periprosthetic capsular fibrosis in clinical application.

The Contribution of Innervation to Tissue Repair and Regeneration

Animals such as amphibians have an incredible capacity for regeneration with some being able to regrow their tail or appendages. Although some mammalian tissues like the skin and bones can repair following injury, there are only a few examples of true multilineage regeneration, including the distal portion of the digit tip. In both amphibians and mammals, however, to achieve successful repair or regeneration, it is now appreciated that intact nerve innervation is a necessity. Here, we review the current state of literature and discuss recent advances that identify axon-derived signals, Schwann cells, and nerve-derived mesenchymal cells as direct and indirect supporters of adult tissue homeostasis and repair. We posit that understanding how nerves positively influence repair and regeneration could lead to targeted regenerative medicine strategies to enhance tissue repair in humans.

Fibroblast Heterogeneity in Healthy and Wounded Skin

Fibroblasts are the main cell type in the dermis. They are responsible for the synthesis and deposition of structural proteins such as collagen and elastin, which are integrated into the extracellular matrix (ECM). Mouse and human studies using flow cytometry, cell culture, skin reconstitution, and lineage tracing experiments have shown the existence of different subpopulations of fibroblasts, including papillary fibroblasts, reticular fibroblasts, and fibroblasts comprising the dermal papilla at the base of the hair follicle. In recent years, the technological advances in single-cell sequencing have allowed researchers to study the repertoire of cells present in full-thickness skin including the dermis. Multiple groups have confirmed that distinct fibroblast populations can be identified in mouse and human dermis on the basis of differences in the transcriptional profile. Here, we discuss the current state of knowledge regarding dermal fibroblast heterogeneity in healthy mouse and human skin, highlighting the similarities and differences between mouse and human fibroblast subpopulations. We also discuss how fibroblast heterogeneity may provide insights into physiological wound healing and its dysfunction in pathological states such as hypertrophic and keloid scars.

Skin Fibrosis and Recovery Is Dependent on Wnt Activation via DPP4

Fibrosis is the life-threatening, excessive accumulation of the extracellular matrix and is sometimes associated with a loss of lipid-filled cells in the skin and other organs. Understanding the mechanisms of fibrosis and associated lipodystrophy and their reversal may reveal new targets for therapeutic intervention. In vivo genetic models are needed to identify key targets that induce recovery from established fibrosis. Wnt signaling is activated in animal and human fibrotic diseases across organs. Here, we developed a genetically inducible and reversible Wnt activation model and showed that it is sufficient to cause fibrotic dermal remodeling, including extracellular matrix expansion and shrinking of dermal adipocytes. Upon withdrawal from Wnt activation, Wnt-induced fibrotic remodeling was reversed in mouse skin-fully restoring skin architecture. Next, we demonstrated CD26/ DPP4 is a Wnt/β-catenin-responsive gene and a functional mediator of fibrotic transformation. We provide genetic evidence that the Wnt/DPP4 axis is required to drive fibrotic dermal remodeling and is associated with human skin fibrosis severity. Remarkably, DPP4 inhibitors can be repurposed to accelerate recovery from established Wnt-induced fibrosis. Collectively, this study identifies Wnt/DPP4 axis as a key driver of extracellular matrix homeostasis and dermal fat loss, providing therapeutic avenues to manipulate the onset and reversal of tissue fibrosis.

Strategies to Minimize Surgical Scarring: Translation of Lessons Learned from Bedside to Bench and Back

Significance: An understanding of the physiology of wound healing and scarring is necessary to minimize surgical scar formation. By reducing tension across the healing wound, eliminating excess inflammation and infection, and encouraging perfusion to healing areas, surgeons can support healing and minimize scarring. Recent Advances: Preoperatively, newer techniques focused on incision placement to minimize tension, skin sterilization to minimize infection and inflammation, and control of comorbid factors to promote a healing process with minimal scarring are constantly evolving. Intraoperatively, measures like layered closure, undermining, and tissue expansion can be taken to relieve tension across the healing wound. Appropriate suture technique and selection should be considered, and finally, there are new surgical technologies available to reduce tension across the closure. Postoperatively, the healing process can be supported as proliferation and remodeling take place within the wound. A balance of moisture control, tension reduction, and infection prevention can be achieved with dressings, ointments, and silicone. Vitamins and corticosteroids can also affect the scarring process by modulating the cellular factors involved in healing. Critical Issues: Healing with no or minimal scarring is the ultimate goal of wound healing research. Understanding how mechanical tension, inflammation and infection, and perfusion and hypoxia impact profibrotic pathways allows for the development of therapies that can modulate cytokine response and the wound extracellular microenvironment to reduce fibrosis and scarring. Future Directions: New tension-off loading topical treatments, laser, and dermabrasion devices are under development, and small molecule therapeutics have demonstrated scarless wound healing in animal models, providing a promising new direction for future research aimed to minimize surgical scarring.

Standardizing Dimensionless Cutometer Parameters to Determine In Vivo Elasticity of Human Skin

Objective: Skin fibrosis places an enormous burden on patients and society, but disagreement exists over methods to quantify severity of skin scarring. A suction cutometer measures skin elasticity in vivo, but it has not been widely adopted because of inconsistency in data produced. We investigated variability of several dimensionless parameters generated by the cutometer to improve their precision and accuracy. Approach: Twenty adult human subjects underwent suction cutometer measurement of normal skin (NS) and fibrotic scars (FS). Using Mode 1, each subject underwent five trials with each trial containing four curves. R0/2/5/6/7 and Q1/2/3 data were collected. Analyses were performed on these calculated parameters. Results: R0/2/5/6/7 and Q1/2 parameters from curves 1 to 4 demonstrated significant differences, whereas these same parameters were not significantly different when only using curves 2-4. Individual analysis of all parameters between curve 1 and every subsequent curve was statistically significant for R0, R2, R5, R6, R7, Q1, and Q2. No differences were appreciated for parameter Q3. Comparison between NS and FS were significantly different for parameters R5, Q1, and Q3. Innovation: Our study is the first demonstration of accurate comparison between NS and FS using the dimensionless parameters of a suction cutometer. Conclusions: Measured parameters from the first curve of each trial were significantly different from subsequent curves for both NS and FS. Precision and reproducibility of data from dimensionless parameters can therefore be improved by removing the first curve. R5, Q1, and Q3 parameters differentiated NS as more elastic than FS.

Reprograming the immune niche for skin tissue regeneration - From cellular mechanisms to biomaterials applications

Despite the rapid development of therapeutic approaches for skin repair, chronic wounds such as diabetic foot ulcers remain an unaddressed problem that affects millions of people worldwide. Increasing evidence has revealed the crucial and diverse roles of the immune cells in the development and repair of the skin tissue, prompting new research to focus on further understanding and modulating the local immune niche for comprehensive, 'perfect' regeneration. In this review, we first introduce how different immunocytes and certain stromal cells involved in innate and adaptive immunity coordinate to maintain the immune niche and tissue homeostasis, with emphasis on their specific roles in normal and pathological wound healing. We then discuss novel engineering approaches - particularly biomaterials systems and cellular therapies - to target different players of the immune niche, with three major aims to i) overcome 'under-healing', ii) avoid 'over-healing', and iii) promote functional restoration, including appendage development. Finally, we highlight how these strategies strive to manage chronic wounds and achieve full structural and functional skin recovery by creating desirable 'soil' through modulating the immune microenvironment.

Disrupting mechanotransduction decreases fibrosis and contracture in split-thickness skin grafting

Burns and other traumatic injuries represent a substantial biomedical burden. The current standard of care for deep injuries is autologous split-thickness skin grafting (STSG), which frequently results in contractures, abnormal pigmentation, and loss of biomechanical function. Currently, there are no effective therapies that can prevent fibrosis and contracture after STSG. Here, we have developed a clinically relevant porcine model of STSG and comprehensively characterized porcine cell populations involved in healing with single-cell resolution. We identified an up-regulation of proinflammatory and mechanotransduction signaling pathways in standard STSGs. Blocking mechanotransduction with a small-molecule focal adhesion kinase (FAK) inhibitor promoted healing, reduced contracture, mitigated scar formation, restored collagen architecture, and ultimately improved graft biomechanical properties. Acute mechanotransduction blockade up-regulated myeloid CXCL10-mediated anti-inflammation with decreased CXCL14-mediated myeloid and fibroblast recruitment. At later time points, mechanical signaling shifted fibroblasts toward profibrotic differentiation fates, and disruption of mechanotransduction modulated mesenchymal fibroblast differentiation states to block those responses, instead driving fibroblasts toward proregenerative, adipogenic states similar to unwounded skin. We then confirmed these two diverging fibroblast transcriptional trajectories in human skin, human scar, and a three-dimensional organotypic model of human skin. Together, pharmacological blockade of mechanotransduction markedly improved large animal healing after STSG by promoting both early, anti-inflammatory and late, regenerative transcriptional programs, resulting in healed tissue similar to unwounded skin. FAK inhibition could therefore supplement the current standard of care for traumatic and burn injuries.

Fibroblasts in Scar Formation: Biology and Clinical Translation

Scarring, which develops due to fibroblast activation and excessive extracellular matrix deposition, can cause physical, psychological, and cosmetic problems. Fibroblasts are the main type of connective tissue cells and play important roles in wound healing. However, the underlying mechanisms of fibroblast in reaching scarless wound healing require more exploration. Herein, we systematically reviewed how fibroblasts behave in response to skin injuries, as well as their functions in regeneration and scar formation. Several biocompatible materials, including hydrogels and nanoparticles, were also suggested. Moreover, factors that concern transformation from fibroblasts into cancer-associated fibroblasts are mentioned due to a tight association between scar formation and primary skin cancers. These findings will help us better understand skin fibrotic pathogenesis, as well as provide potential targets for scarless wound healing therapies.

A Biomaterial-Based Hedging Immune Strategy for Scarless Tendon Healing

Scarring rather than regeneration, is an inevitable outcome of unbalanced amplifications of inflammation-destructive signals and atresia of the regenerative niche. However, identifying and effectively hedging against the risk of scarring and realizing the conversion of regenerative cues remain difficult. In this work, a hedging immune strategy based microfibrous membrane (Him-MFM), by tethering distearoyl phosphoethanolamine layer-supported copoly(lactic/glycolic acid) electrospun fibers with identified CD11b⁺ /CD68⁺ scarring subpopulation membranes in the immune landscape after tendon injury to counterweigh tissue damage, is reported. Him-MFM, carrying relevant risk receptors is shown to shift high type I biased polarization, alleviate apoptosis and metabolic stress, and mitigate inflammatory tenocyte response. Remarkably, the hedging immune strategy reverses the damaged tendon sheath barrier to the innate IL-33 secretory phenotype by 4.36 times and initiates the mucous-IL-33-Th2 axis, directly supplying a transient but obligate regenerative niche for sheath stem cell proliferation. In murine flexor tendon injury, the wrapping of Him-MFM alleviates pathological responses, protects tenocytes in situ, and restores hierarchically arranged collagen fibers covered with basement membrane, and is structurally and functionally comparable to mature tendons, demonstrating that the hedging immunity is a promising strategy to yield regenerative responses not scarring.

Tetrahedral Framework Nucleic Acids Inhibit Skin Fibrosis via the Pyroptosis Pathway

The skin is the first line of defense for the human body and is vulnerable to injury. Various topical or systemic diseases facilitate skin inflammation, and when the intensity or duration of skin injury exceeds the ability of tissue repair, fibrosis, an outcome of a dysregulated tissue-repair response, begins to dominate the repair process. However, existing methods for reducing skin fibrosis are insufficient and cause side effects, highlighting the need for drugs that effectively inhibit skin fibrosis and reduce immunogenicity, inflammation, apoptosis, and pyroptosis. Tetrahedral framework nucleic acids (tFNAs) are DNA nanomaterials that have a unique spatial structure, demonstrate excellent biosecurity, and promote anti-inflammatory, antioxidative, antifibrotic, angiogenic, and skin-wound-healing activities with almost no toxicity. Here, we explored the potential of tFNAs in skin fibrosis therapy in vitro and in vivo. After incubating cells or injecting mice with profibrogenic molecules and tFNAs, we found that the tFNAs inhibited the epithelial-mesenchymal transition, reduced inflammatory factor levels, decreased skin collagen content, and inhibited the pyroptosis pathway. These findings suggest the potential of tFNAs in treating pyroptosis-related diseases.

Management of non-severe burn wounds in children and adolescents: optimising outcomes through all stages of the patient journey

Paediatric burn injuries are common, especially in children younger than 5 years, and can lead to poor physical and psychosocial outcomes in the long term. In this Review, we aim to summarise the key factors and interventions before hospital admission and following discharge that can improve the long-term outcomes of paediatric burns. Care can be optimised through first aid treatment, correct initial assessment of burn severity, and appropriate patient referral to a burns centre. Scar prevention or treatment and patient follow-up after discharge are also essential. As most burn injuries in children are comparatively small and readily survivable, this Review does not cover the perioperative management associated with severe burns that require fluid resuscitation, or inhalational injury. Burns disproportionately affect children from low socioeconomic backgrounds and those living in low-income and middle-income countries, with ample evidence to suggest that there remains scope for low-cost interventions to improve care for those patients with the greatest burden of burn injury. Current knowledge gaps and future research directions are discussed.

B12-induced reassembly of split photoreceptor protein enables photoresponsive hydrogels with tunable mechanics

Although the tools based on split proteins have found broad applications, ranging from controlled biological signaling to advanced molecular architectures, many of them suffer from drawbacks such as background reassembly, low thermodynamic stability, and static structural features. Here, we present a chemically inducible protein assembly method enabled by the dissection of the carboxyl-terminal domain of a B12-dependent photoreceptor, CarHC. The resulting segments reassemble efficiently upon addition of cobalamin (AdoB12, MeB12, or CNB12). Photolysis of the cofactors such as AdoB12 and MeB12 further leads to stable protein adducts harboring a bis-His-ligated B12. Split CarHC enables the creation of a series of protein hydrogels, of which the mechanics can be either photostrengthened or photoweakened, depending on the type of B12. These materials are also well suited for three dimensional cell culturing. Together, this new protein chemistry, featuring negligible background autoassembly, stable conjugation, and phototunability, has opened up opportunities for designing smart materials.

Urine-Microenvironment-Initiated Composite Hydrogel Patch Reconfiguration Propels Scarless Memory Repair and Reinvigoration of the Urethra

The harsh urine microenvironment (UME), as an inherent hurdle, endangers and renders urethral repair unreachable. Innovatively, the unfavorable UME is utilized as the design source to construct a UME-responsive 3D-printed hydrogel patch for realizing scarless memory repair, wherein laser-excited reactive oxygen species (ROS) production and mechanical strength elevation using chemically crosslinked silicon quantum dots are accessible. Intriguingly, the proposed composite scaffolds can respond to Ca²⁺ in urine, cause structure reconfiguration, and repress swelling to further enhance scaffold stiffness. Systematic experiments validate that ROS birth and unexpected stiffness elevation in such UME-responsive scaffolds can realize scarless memory repair of the urethra in vivo. Comprehensive mechanism explorations uncover that the activations of cell proliferation and collagen-related genes (e.g., MMP-1 and COL3A1) and the dampening of fibrosis-related (e.g., TGF-β/Smad) and mechanosensitive genes (e.g., YAP/TAZ) are responsible for the scarless memory repair of such UME-responsive scaffolds via enhancing collagen deposition, recalling mechanical memory, decreasing fibrosis and inflammation, and accelerating angiogenesis. The design rationales (e.g., UME-initiated structure reconfiguration and antiswelling) can serve as an instructive and general approach for urethra repair.

Fibroblasts Mediate Ectopic Bone Formation of Calcium Phosphate Ceramics

Heterogeneity of fibroblasts directly affects the outcome of tissue regeneration; however, whether bioactive ceramics regulate bone regeneration through fibroblasts is unclear. Ectopic bone formation model with biphasic calcium phosphate (BCP) implantation was used to investigate the temporal and spatial distribution of fibroblasts around ceramics. The effect of BCP on L929 fibroblasts was evaluated by EdU assay, transwell assay, and qRT-PCR. Further, the effect of its conditioned medium on osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) was confirmed by ALP staining. SEM and XRD results showed that BCP contained abundant micro- and macro-pores and consisted of hydrogen-apatite (HA) and β-tricalcium phosphate (β-TCP) phases. Subsequently, BCP implanted into mice muscle successfully induced osteoblasts and bone formation. Fibroblasts labelled by vimentin gathered around BCP at 7 days and peaked at 14 days post implantation. In vitro, BCP inhibited proliferation of L929 fibroblast but promoted its migration. Moreover, expression of Col1a1, Bmp2, and Igf1 in L929 treated by BCP increased significantly while expression of Tgfb1 and Acta did not change. ALP staining further showed conditioned media from L929 fibroblasts treated by BCP could enhance osteogenic differentiation of BMSCs. In conclusion, fibroblasts mediate ectopic bone formation of calcium phosphate ceramics.

A remarkable rodent: Regeneration and reproduction in spiny mice (Acomys)

Although certain organisms are chosen and employed to better understand a specific problem in biology (so-called model organisms), sometimes an animal model reveals its' biomedical importance by happenstance. In many ways, the advent of spiny mice (Acomys) as an emerging model to study regeneration and menstruation stands as a case study in scientific pseudoserendipity (Diaz de Chumaceiro, 1995). As we recount in this chapter, the discovery of these phenotypes, while not entirely accidental, was nonetheless unexpected. In addition to recounting how we uncovered these unusual mammalian traits, we outline recent work by our groups and others that has begun to outline the cellular and genetic mechanisms underlying bonafide mammalian tissue regeneration and a human-like mode of reproduction in spiny mice.

In Situ 3D Bioprinting Living Photosynthetic Scaffolds for Autotrophic Wound Healing

Three-dimensional (3D) bioprinting has been extensively explored for tissue repair and regeneration, while the insufficient nutrient and oxygen availability in the printed constructs, as well as the lack of adaptive dimensions and shapes, compromises the overall therapeutic efficacy and limits their further application. Herein, inspired by the natural symbiotic relationship between salamanders and algae, we present novel living photosynthetic scaffolds by using an in situ microfluidic-assisted 3D bioprinting strategy for adapting irregular-shaped wounds and promoting their healing. As the oxygenic photosynthesis unicellular microalga (Chlorella pyrenoidosa) was incorporated during 3D printing, the generated scaffolds could produce sustainable oxygen under light illumination, which facilitated the cell proliferation, migration, and differentiation even in hypoxic conditions. Thus, when the living microalgae-laden scaffolds were directly printed into diabetic wounds, they could significantly accelerate the chronic wound closure by alleviating local hypoxia, increasing angiogenesis, and promoting extracellular matrix (ECM) synthesis. These results indicate that the in situ bioprinting of living photosynthetic microalgae offers an effective autotrophic biosystem for promoting wound healing, suggesting a promising therapeutic strategy for diverse tissue engineering applications.

Young fibroblast-derived exosomal microRNA-125b transfers beneficial effects on aged cutaneous wound healing

Aged skin wounds heal poorly, resulting in medical, economic, and social burdens posed by nonhealing wounds. Age-related defects in repair are associated with reduced myofibroblasts and dysfunctional extracellular matrix (ECM) deposition. Bidirectional cell-cell communication involving exosome-borne cargo such as micro RNAs (miRs) has emerged as a critical mechanism for wound healing and aged tissue regeneration. Here we report that at the wound edge, aged fibroblasts display reduced migration and differentiation into myofibroblasts, with impaired ECM deposition, when compared with young tissue. Proper activation of fibroblasts to myofibroblasts may alleviate age-related defects in wound healing. Herein, an exosome-guided cell technique was performed to induce effective wound healing. Supplementing wounds with exosomes isolated from young mouse wound-edge fibroblasts (exosomes^Young) significantly improved the abundance of myofibroblasts and wound healing in aged mice and caused fibroblasts to migrate and transition to myofibroblasts in vitro. To determine the underlying mechanism, we found that exosomal transfer of miR-125b to fibroblasts inhibited sirtuin 7 (Sirt7), thus accelerating myofibroblast differentiation and wound healing in aged mice. Notably, after epidermal inhibition of miR-125b or overexpression of Sirt7 in fibroblasts, migration and myofibroblast transition were perturbed. Our findings thus reveal that miR-125b is transferred through exosomes from young fibroblasts to old fibroblasts contributes to promoting fibroblast migration and transition to counteract aging, suggesting a potential avenue for anti-aging interventions in wound healing.

Early and Regular Bronchoscopy Examination on Effect of Diagnosis and Prognosis for Patients With Tracheobronchial Tuberculosis

BACKGROUND

Bronchoscopy is the main method for the diagnosis of tracheobronchial tuberculosis (TBTB). However, it is not well-used in patients with pulmonary tuberculosis (PTB), leading to misdiagnosis. The aim of this study is to verify the value and feasibility of bronchoscopy for an early diagnosis and treatment of TBTB.

MATERIALS AND METHODS

A prospective observational study was performed in patients with active PTB. The ratios of TBTB and tracheobronchial stenosis were analyzed with propensity score matching (PSM) for baseline characteristics, and a Cox regression model was further employed to adjust for residual confounding factors.

RESULTS

A total of 656 patients with active PTB were enrolled in the study that included 307 patients in the active group and 349 patients in the non-active group. The ratio of TBTB was significantly higher in the active group than that in the non-active group [hazard ratio (HR), 2.31; 95% CI, 1.70-3.14; p < 0.001]. With PSM, the proportion of tracheobronchial stenosis in the non-active group was significantly higher than that in the active group (HR, 1.84; 95% CI, 1.15-2.95; p = 0.011). Moreover, the number of patients with moderate to severe stenosis were significantly higher than that in the active group (HR, 4.13; 95% CI, 2.25-7.63; p < 0.001). Similar results were obtained with multivariate analysis. With 12 months of treatment, both therapeutic effective rate (84.7 vs. 68.2%; p = 0.009) and improvement rate of non-fibrotic tracheobronchial stenosis (79.1 vs. 47.4%; p = 0.022) were higher in the active group than that in the non-active group.

CONCLUSION

Active and regular bronchoscopy is conducive to early diagnosis of TBTB, combined with prompt anti-tuberculosis therapy, greatly reducing the occurrence of tracheobronchial stenosis and improving prognosis.

Multifunctional Single-Component Polypeptide Hydrogels: The Gelation Mechanism, Superior Biocompatibility, High Performance Hemostasis, and Scarless Wound Healing

Polymeric hydrogels have been increasingly studied for wound sealants, adhesives, hemostats, and dressings, however, multi-component gelation, adhesion-causing tissue damage, inefficient hemostasis, and skin scarring in wound healing hamper their advances. So it is urgent to develop multifunctional single-component polymeric hydrogels with benign tissue detachment, high performance hemostasis, and scarless wound healing attributes. Herein, a dopamine-modified poly(l-glutamate) hydrogel at an ultralow concentration of 0.1 wt% is serendipitously constructed by physical treatments, in which a gelation mechanism is disclosed via oxidative catechol-crosslinking and sequential dicatechol-carboxyl hydrogen-bonding interactions. The covalent/H-bonding co-crosslinked and highly negative-charged networks enable the polypeptide hydrogels thermo-, salt-, urea-resistant, self-healing, injectable, and adhesive yet detachable. In vitro and in vivo assays demonstrate they have superior biocompatibility with ≈0.5% hemolysis and negligible inflammation. The polypeptide/graphene oxide hybrid hydrogel performs fast and efficient hemostasis of 12 s and 1.4% blood loss, surpassing some hydrogels and commercial counterparts. Remarkably, the polypeptide hydrogels achieve scarless and full wound healing and regenerate thick dermis with some embedded hair follicles within 14 days, presenting superior full-thickness wound healing and skin scar-preventing capabilities. This work provides a simple and practicable method to construct multifunctional polypeptide hemostatic and healing hydrogels that overcome some above-mentioned hurdles.

Recent Advances in Bioengineered Scaffolds for Cutaneous Wound Healing

Wound healing is an evolved dynamic biological process. Though many research and clinical approaches have been explored to restore damaged or diseased skin, the current treatment for deep cutaneous injuries is far from being perfect, and the ideal regenerative therapy remains a significant challenge. Of all treatments, bioengineered scaffolds play a key role and represent great progress in wound repair and skin regeneration. In this review, we focus on the latest advancement in biomaterial scaffolds for wound healing. We discuss the emerging philosophy of designing biomaterial scaffolds, followed by precursor development. We pay particular attention to the therapeutic interventions of bioengineered scaffolds for cutaneous wound healing, and their dual effects while conjugating with bioactive molecules, stem cells, and even immunomodulation. As we review the advancement and the challenges of the current strategies, we also discuss the prospects of scaffold development for wound healing.

Regenerative Approaches for Chronic Wounds

Chronic skin wounds are commonly found in older individuals who have impaired circulation due to diabetes or are immobilized due to physical disability. Chronic wounds pose a severe burden to the health-care system and are likely to become increasingly prevalent in aging populations. Various treatment approaches exist to help the healing process, although the healed tissue does not generally recapitulate intact skin but rather forms a scar that has inferior mechanical properties and that lacks appendages such as hair or sweat glands. This article describes new experimental avenues for attempting to improve the regenerative response of skin using biophysical techniques as well as biochemical methods, in some cases by trying to harness the potential of stem cells, either endogenous to the host or provided exogenously, to regenerate the skin. These approaches primarily address the local wound environment and should likely be combined with other modalities to address regional and systemic disease, as well as social determinants of health. Expected final online publication date for the Annual Review of Biomedical Engineering, Volume 24 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Dermal αSMA+ myofibroblasts orchestrate skin wound repair via β1 integrin and independent of type I collagen production

Skin wound repair is essential for organismal survival and failure of which leads to non-healing wounds, a leading health issue worldwide. However, mechanistic understanding of chronic wounds remains a major challenge due to lack of appropriate genetic mouse models. αSMA⁺ myofibroblasts, a unique class of dermal fibroblasts, are associated with cutaneous wound healing but their precise function remains unknown. We demonstrate that genetic depletion of αSMA⁺ myofibroblasts leads to pleiotropic wound healing defects, including lack of reepithelialization and granulation, dampened angiogenesis, and heightened hypoxia, hallmarks of chronic non-healing wounds. Other wound-associated FAP⁺ and FSP1⁺ fibroblasts do not exhibit such dominant functions. While type I collagen (COL1) expressing cells play a role in the repair process, COL1 produced by αSMA⁺ myofibroblasts is surprisingly dispensable for wound repair. In contrast, we show that β1 integrin from αSMA⁺ myofibroblasts, but not TGFβRII, is essential for wound healing, facilitating contractility, reepithelization, and vascularization. Collectively, our study provides evidence for the functions of myofibroblasts in β1 integrin-mediated wound repair with potential implications for treating chronic non-healing wounds.

Novel insights from a multiomics dissection of the hayflick limit

The process wherein dividing cells exhaust proliferative capacity and enter into replicative senescence has become a prominent model for cellular aging in vitro. Despite decades of study, this cellular state is not fully understood in culture and even much less so during aging. Here, we revisit Leonard Hayflick’s original observation of replicative senescence in WI-38 human lung fibroblasts equipped with a battery of modern techniques including RNA-seq, single-cell RNA-seq, proteomics, metabolomics, and ATAC-seq. We find evidence that the transition to a senescent state manifests early, increases gradually, and corresponds to a concomitant global increase in DNA accessibility in nucleolar and lamin associated domains. Furthermore, we demonstrate that senescent WI-38 cells acquire a striking resemblance to myofibroblasts in a process similar to the epithelial to mesenchymal transition (EMT) that is regulated by t YAP1/TEAD1 and TGF-β2. Lastly, we show that verteporfin inhibition of YAP1/TEAD1 activity in aged WI-38 cells robustly attenuates this gene expression program.

Cut out that YAPping: Mechanisms to reduce scar formation

Tissue repair in adult mammals lacks the regenerative ability of many tissues in other adult organisms like axolotl and newts. In this issue of Cell Stem Cell, Mascharak et al. use multi-omics approaches to identify an essential role for the transcription factor Trps1 in Yap-inhibited fibroblasts' tissue regenerative responses in murine skin.

Mechanogenetics: harnessing mechanobiology for cellular engineering

'Mechanogenetics,' a new field at the convergence of mechanobiology and synthetic biology, presents an innovative strategy to treat, repair, or restore diseased cells and tissues by harnessing mechanical signal transduction pathways to control gene expression. While the role of mechanical forces in regulating development, homeostasis, and disease is well established, only recently have we identified the specific mechanosensors and downstream signaling pathways involved in these processes. Simultaneously, synthetic biological systems are developing increasingly sophisticated approaches of controlling mammalian cellular responses. Continued mechanistic refinement and identification of how cellular mechanosensors respond to homeostatic and pathological mechanical forces, combined with synthetic tools to integrate and respond to these inputs, promises to extend the development of new therapeutic approaches for treating disease.

Head muscle fibro-adipogenic progenitors account for the tilted regeneration towards fibrosis

Branchiomeric head muscle is ontogenetically and phylogenetically distinct from somitic limb muscle, and they exhibit different regenerative capacity. Unique satellite cell property of head muscle could explain the impaired myofiber formation, but the underlying mechanism for fibrosis is still elusive. In this work, we first established a freezing-induced skeletal muscle regeneration model and made comparisons between the regeneration characteristics in tibialis anterior (TA) muscle and masseter (MAS) muscle. The process of myogenesis and fibrogenesis were investigated by histological, immunohistochemical and cellular analysis, to characterize the role of muscle satellite cell (MuSCs) and fibro-adipogenic progenitors (FAPs) in TA and MAS muscle regeneration. Our results revealed that FAPs infiltrated the fibrotic area during MAS muscle regeneration. In contrast to the rapid rise and fall of FAPs number at the early regeneration stages in TA muscle, the number of MAS FAPs increased to a plateau without descending till 14 days after injury. It is the first time that the pivotal role of FAPs in head muscle regeneration was characterized. The persistence of FAPs without timely clearance in the first two weeks of regeneration could be accountable for the head muscle fibrosis.

Chitosan/Gelatin Composite Nonwoven Fabric Scaffold Seeding Minimal Function Unit of Skin for Functional Skin Regeneration

The construction of intact functional skin is a challenging field in tissue engineering. Traditional skin tissue engineering, using "seed cells" as a bioactive source for scaffolding materials maybe not efficient enough. Here a new strategy is shown for constructing functional tissue-engineered skin with Minimal Functional Unit of Skin (MFUS) as the source of bioactivity. Chitosan/gelatin non-woven fabric is used as the scaffold. MFUS is derived from autologous skin with full-thickness skin microstructure and complete functional skin unit harvesting. A mathematical model is used to calculate the MFUS Minimal Harvest Diameter and Angle (MHDA). Chitosan/gelatin non-woven fabric (CS+GEL) is porous and absorbable, with an elastic modulus meeting the requirement of skin engineering. It supports layered and 3D growth of MFUS. The degradation rate of chitosan, including filament diameter and density is evaluated in vivo. MFUS-engineered skin could reduce the density of local nerve fibers in the early stage, potentially reducing pain during wound healing, as well as could limit excessive fibroblast cell migration in the later stage, potentially reducing scar formation. This study proposes a new strategy for the clinical treatment of large full-thickness skin defects by constructing intact functional at minimal cost.

A hybrid hydrogel composed of chitin and β-glucan for effectively management of wound healing and scarring

Non-functional scar commonly forms after the skin injury. At present, most of the clinical treatments for scar eradication are typically with long treatment courses, low curative effects and expensive. In...

Porous MOF Microneedle Array Patch with Photothermal Responsive Nitric Oxide Delivery for Wound Healing

Patches with the capacity of controllable delivering active molecules toward the wound bed to promote wound healing are expectant all along. Herein, a novel porous metal-organic framework (MOF) microneedle (MN) patch enabling photothermal-responsive nitric oxide (NO) delivery for promoting diabetic wound healing is presented. As the NO-loadable copper-benzene-1,3,5-tricarboxylate (HKUST-1) MOF is encapsulated with graphene oxide (GO), the resultant NO@HKUST-1@GO microparticles (NHGs) are imparted with the feature of near-infrared ray (NIR) photothermal response, which facilitate the controlled release of NO molecules. When these NHGs are embedded in a porous PEGDA-MN, the porous structure, larger specific surface area, and sufficient mechanical strength of the integrated MN could promote a more accurate and deeper delivery of NO molecules into the wound site. By applying the resultant NHG-MN to the wound of a type I diabetic rat model, the authors demonstrate that it is capable of accelerating vascularization, tissue regeneration, and collagen deposition, indicating its bright prospect applied in wound healing and other therapeutic scenarios.

Is the future scarless? - Fibroblasts as targets for scarless wound healing: a narrative review

Introduction: Scarless healing is the ideal outcome of wound healing and is exhibited in some species. This narrative review assembles the current understanding of fibroblast heterogenicity along with the latest fibroblast-related targets for scar reduction therapies. Human regenerative wound healing is deemed possible due to the wound regeneration already seen in the early gestation foetus. Methods: This literature narrative review was undertaken by searching PubMed and Web of Science databases and Google Scholar to find articles concerning the fibroblast involvement in wound healing. We evaluated and collated these articles to form a consensus of the current understanding of the field. Discussion: This article describes current understanding of fibroblast heterogenicity and involvement in wound healing, focusing on the role of fibroblasts during physiological scarring. We also present the current most promising targets involving fibroblasts in the reduction of scarring and how we can manipulate the behaviour of fibroblasts to mimic the wound regeneration models in the human foetus. These targets include the pro-fibrotic EN1 positive fibroblast lineage, TGFβ1 inhibition, and genetic therapies utilising miRNAs and siRNAs. Conclusion: No therapies are currently available to eradicate scarring; however, treatment options are available to reduce the appearance of scarring. Further research into the heterogenicity and interactions of fibroblasts in both the foetus and adult is needed, and this may lead to the development of novel treatments against scarring.

All-in-One: Multifunctional Hydrogel Accelerates Oxidative Diabetic Wound Healing through Timed-Release of Exosome and Fibroblast Growth Factor

The treatment of diabetic wounds remains a major challenge in clinical practice, with chronic wounds characterized by multiple drug-resistant bacterial infections, angiopathy, and oxidative damage to the microenvironment. Herein, a novel in situ injectable HA@MnO₂ /FGF-2/Exos hydrogel is introduced for improving diabetic wound healing. Through a simple local injection, this hydrogel is able to form a protective barrier covering the wound, providing rapid hemostasis and long-term antibacterial protection. The MnO₂ /ε-PL nanosheet is able to catalyze the excess H₂ O₂ produced in the wound, converting it to O₂ , thus not only eliminating the harmful effects of H₂ O₂ but also providing O₂ for wound healing. Moreover, the release of M2-derived Exosomes (M2 Exos) and FGF-2 growth factor stimulates angiogenesis and epithelization, respectively. These in vivo and in vitro results demonstrate accelerated healing of diabetic wounds with the use of the HA@MnO₂ /FGF-2/Exos hydrogel, presenting a viable strategy for chronic diabetic wound repair.

Mesenchymal stem cells and COVID-19: the process of discovery and of translation

Mesenchymal stem cells were developed as a cell-based therapeutic in the 1990's. The translation of culture expanded mesenchymal stem cells from a basic science focus into a modern therapeutic has taken 30 years. The current state of the basic science information argues that mesenchymal stem cells may be curative for coronavirus disease 2019 (COVID-19). Indeed, early small-scale clinical trials have shown positive results. The issue raised is how to assemble the resources to get this cell-based therapy approved for clinical use. The technology is complex, the COVID-19 viral infections are life threatening, the cost is high, but human life is precious. What will it take to perfect this potentially curative technology?

The diameter factor of aligned membranes facilitates wound healing by promoting epithelialization in an immune way

Topographical properties, such as pattern and diameter, of biomaterials play important roles in influencing cell activities and manipulating the related immune response during wound healing. We prepared aligned electrospinning membranes with different fiber diameters, including 319 ± 100 nm (A300), 588 ± 132 nm (A600), and 1048 ± 130 nm (A1000), by adjusting the distance from the tip to the collector, the injection rate, and the concentration of the solution. The A300 membranes significantly improved cell proliferation and spreading and facilitated wound healing (epithelization and vascularization) with the regeneration of immature hair follicles compared to the other membranes. Transcriptomics revealed the underlying molecular mechanism that A300 could promote immune-related processes towards a pro-healing direction, significantly promoting keratinocyte migration and skin wound healing. All the results indicated that wound healing requires the active participation of the immune process, and that A300 was a potential candidate for guided skin regeneration applications.

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It is still unclear which diameter interval of aligned membranes is most suitable for tissue regeneration.

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Outstanding performances in the wound healing process was presented by the A300 membranes.

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The transcriptome revealed that A300 could promote immune related processes towards a pro-healing direction.

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A300 promoted keratinocytes migration and final wound healing partially through MMP12.

Parallel single cell multi-omics analysis of neonatal skin reveals transitional fibroblast states that restricts differentiation into distinct fates

One of the keys to achieving skin regeneration lies within understanding the heterogeneity of neonatal fibroblasts, which support skin regeneration. However, the molecular underpinnings regulating the cellular states and fates of these cells are not fully understood. To investigate this, we performed a parallel multi-omics analysis by processing neonatal murine skin for single-cell ATAC-sequencing (scATAC-seq) and single-cell RNA-sequencing (scRNA-seq) separately. Our approach revealed that fibroblast clusters could be sorted into papillary and reticular lineages based on transcriptome profiling, as previously published. However, scATAC-seq analysis of neonatal fibroblast lineage markers, such as, Dpp4/CD26, Corin, and Dlk1 along with markers of myofibroblasts, revealed accessible chromatin in all fibroblast populations despite their lineage-specific transcriptome profiles. These results suggests that accessible chromatin does not always translate to gene expression and that many fibroblast lineage markers reflect a fibroblast state, which includes neonatal papillary, reticular, and myofibroblasts. This analysis also provides a possible explanation as to why these marker genes can be promiscuously expressed in different fibroblast populations under different conditions. Our scATAC-seq analysis also revealed that the functional lineage restriction between dermal papilla and adipocyte fates are regulated by distinct chromatin landscapes. Finally, we have developed a webtool for our multi-omics analysis: https://skinregeneration.org/scatacseq-and-scrnaseq-data-from-thompson-et-al-2021-2/.