Matrix control of scarring

AT2R Activation Improves Wound Healing in a Preclinical Mouse Model

Abnormal skin healing resulting in chronic wounds or hypertrophic scarring remains a major healthcare burden. Here, the antifibrotic angiotensin II type 2 receptor (AT2R) signaling pathway was modulated to determine its impact on cutaneous wound healing. Balb/c mice received two splinted full-thickness wounds. Topical treatments with the selective AT2R agonist compound 21 (C21) and/or selective antagonist PD123319 or saline vehicle were administered until sacrifice on post-wounding days 7 or 10. The rate of wound re-epithelialization was accelerated by PD123319 and combination treatments. In vitro, C21 significantly reduced human fibroblast migration. C21 increased both collagen and vascular densities at days 7 and 10 post-wounding and collagen I:III ratio at day 10, while PD123319 and combination treatments decreased them. Genes associated with regeneration and repair were upregulated by C21, while PD123319 treatment increased the expression of genes associated with inflammation and immune cell chemotaxis. C21 treatment reduced wound total leukocyte and neutrophil staining densities, while PD123319 increased these and macrophage densities. Overall, AT2R activation with C21 yields wounds that mature more quickly with structural, cellular, and gene expression profiles more closely approximating unwounded skin. These findings support AT2R signal modulation as a potential therapeutic target to improve skin quality during wound healing.

Regenerative potential of mesenchymal stromal cells in wound healing: unveiling the influence of normoxic and hypoxic environments

The innate and adaptive immune systems rely on the skin for various purposes, serving as the primary defense against harmful environmental elements. However, skin lesions may lead to undesirable consequences such as scarring, accelerated skin aging, functional impairment, and psychological effects over time. The rising popularity of mesenchymal stromal cells (MSCs) for skin wound treatment is due to their potential as a promising therapeutic option. MSCs offer advantages in terms of differentiation capacity, accessibility, low immunogenicity, and their central role in natural wound-healing processes. To accelerate the healing process, MSCs promote cell migration, angiogenesis, epithelialization, and granulation tissue development. Oxygen plays a critical role in the formation and expansion of mammalian cells. The term "normoxia" refers to the usual oxygen levels, defined at 20.21 percent oxygen (160 mm of mercury), while "hypoxia" denotes oxygen levels of 2.91 percent or less. Notably, the ambient O2 content (20%) in the lab significantly differs from the 2%-9% O2 concentration in their natural habitat. Oxygen regulation of hypoxia-inducible factor-1 (HIF-1) mediated expression of multiple genes plays a crucial role in sustaining stem cell destiny concerning proliferation and differentiation. This study aims to elucidate the impact of normoxia and hypoxia on MSC biology and draw comparisons between the two. The findings suggest that expanding MSC-based regenerative treatments in a hypoxic environment can enhance their growth kinetics, genetic stability, and expression of chemokine receptors, ultimately increasing their effectiveness.

Engineering Cell-ECM-Material Interactions for Musculoskeletal Regeneration

The extracellular microenvironment regulates many of the mechanical and biochemical cues that direct musculoskeletal development and are involved in musculoskeletal disease. The extracellular matrix (ECM) is a main component of this microenvironment. Tissue engineered approaches towards regenerating muscle, cartilage, tendon, and bone target the ECM because it supplies critical signals for regenerating musculoskeletal tissues. Engineered ECM-material scaffolds that mimic key mechanical and biochemical components of the ECM are of particular interest in musculoskeletal tissue engineering. Such materials are biocompatible, can be fabricated to have desirable mechanical and biochemical properties, and can be further chemically or genetically modified to support cell differentiation or halt degenerative disease progression. In this review, we survey how engineered approaches using natural and ECM-derived materials and scaffold systems can harness the unique characteristics of the ECM to support musculoskeletal tissue regeneration, with a focus on skeletal muscle, cartilage, tendon, and bone. We summarize the strengths of current approaches and look towards a future of materials and culture systems with engineered and highly tailored cell-ECM-material interactions to drive musculoskeletal tissue restoration. The works highlighted in this review strongly support the continued exploration of ECM and other engineered materials as tools to control cell fate and make large-scale musculoskeletal regeneration a reality.

How the mechanobiology orchestrates the iterative and reciprocal ECM-cell cross-talk that drives microtissue growth

Controlled tissue growth is essential for multicellular life and requires tight spatiotemporal control over cell proliferation and differentiation until reaching homeostasis. As cells synthesize and remodel extracellular matrix, tissue growth processes can only be understood if the reciprocal feedback between cells and their environment is revealed. Using de novo-grown microtissues, we identified crucial actors of the mechanoregulated events, which iteratively orchestrate a sharp transition from tissue growth to maturation, requiring a myofibroblast-to-fibroblast transition. Cellular decision-making occurs when fibronectin fiber tension switches from highly stretched to relaxed, and it requires the transiently up-regulated appearance of tenascin-C and tissue transglutaminase, matrix metalloprotease activity, as well as a switch from α5β1 to α2β1 integrin engagement and epidermal growth factor receptor signaling. As myofibroblasts are associated with wound healing and inflammatory or fibrotic diseases, crucial knowledge needed to advance regenerative strategies or to counter fibrosis and cancer progression has been gained.

Endogenous Mechanisms of Craniomaxillofacial Repair: Toward Novel Regenerative Therapies

In the fields of oral and craniomaxillofacial surgery, regeneration of multiple tissue types-including bone, skin, teeth, and mucosal soft tissue-is often a desired outcome. However, limited endogenous capacity for regeneration, as well as predisposition of many tissues to fibrotic healing, may prevent recovery of normal form and function for patients. Recent basic science research has advanced our understanding of molecular and cellular pathways of repair in the oral/craniofacial region and how these are influenced by local microenvironment and embryonic origin. Here, we review the current state of knowledge in oral and craniomaxillofacial tissue repair/regeneration in four key areas: bone (in the context of calvarial defects and mandibular regeneration during distraction osteogenesis); skin (in the context of cleft lip/palate surgery); oral mucosa (in the context of minimally scarring repair of mucosal injuries); and teeth (in the context of dental disease/decay). These represent four distinct healing processes and outcomes. We will discuss both divergent and conserved pathways of repair in these contexts, with an eye toward fundamental mechanisms of regeneration vs. fibrosis as well as translational research directions. Ultimately, this knowledge can be leveraged to develop new cell-based and molecular treatment strategies to encourage bone and soft tissue regeneration in oral and craniomaxillofacial surgery.

The Role of Extracellular Matrix in Skin Wound Healing

Impaired wound healing is one of the unsolved problems of modern medicine, affecting patients’ quality of life and causing serious economic losses. Impaired wound healing can manifest itself in the form of chronic skin wounds or hypertrophic scars. Research on the biology and physiology of skin wound healing disorders is actively continuing, but, unfortunately, a single understanding has not been developed. The attention of clinicians to the biological and physiological aspects of wound healing in the skin is necessary for the search for new and effective methods of prevention and treatment of its consequences. In addition, it is important to update knowledge about genetic and non-genetic factors predisposing to impaired wound healing in order to identify risk levels and develop personalized strategies for managing such patients. Wound healing is a very complex process involving several overlapping stages and involving many factors. This thematic review focuses on the extracellular matrix of the skin, in particular its role in wound healing. The authors analyzed the results of fundamental research in recent years, finding promising potential for their transition into real clinical practice.

Fibronectin Molecular Status in Plasma of Women with Endometriosis and Fertility Disorders

The diagnosis of endometriosis and fertility disorders is difficult; therefore, it is necessary to look for reliable biomarkers. Analysis of the molecular status of fibronectin as a key player in repair and wound healing processes, as well as in coagulation and fibrinolysis pathways, is justified. ELISA and SDS-agarose immunoblotting were applied to determine the fibronectin concentration and presence and occurrence of soluble FN-fibrin complexes in the blood plasma of women with endometriosis (n = 38), fertility disorders (n = 28) and the healthy group (n = 25). The concentration of fibronectin in the blood plasma of women with endometriosis (292.61 ± 96.17 mg/L) and fertility disorders (287.53 ± 122.68 mg/L) was significantly higher than in the normal group (226.55 ± 91.98 mg/L). The presence of FN-fibrin complexes of 750, 1000, 1300, 1600 and 1900 kDa in the plasma of women with endometriosis and fertility disorders was shown. The presence of FN-fibrin complexes with a molecular mass of more than 1300 kDa in women with endometriosis and infertility and the complete absence of these complexes in healthy women may indicate an increased and chronic activation of coagulation mechanisms in these patients. The presence of complexes of high molecular mass may be one of the biomarkers of fertility disorders in women.

A story of fibers and stress: Matrix-embedded signals for fibroblast activation in the skin

Our skin is continuously exposed to mechanical challenge, including shear, stretch, and compression. The extracellular matrix of the dermis is perfectly suited to resist these challenges and maintain integrity of normal skin even upon large strains. Fibroblasts are the key cells that interpret mechanical and chemical cues in their environment to turnover matrix and maintain homeostasis in the skin of healthy adults. Upon tissue injury, fibroblasts and an exclusive selection of other cells become activated into myofibroblasts with the task to restore skin integrity by forming structurally imperfect but mechanically stable scar tissue. Failure of myofibroblasts to terminate their actions after successful repair or upon chronic inflammation results in dysregulated myofibroblast activities which can lead to hypertrophic scarring and/or skin fibrosis. After providing an overview on the major fibrillar matrix components in normal skin, we will interrogate the various origins of fibroblasts and myofibroblasts in the skin. We then examine the role of the matrix as signaling hub and how fibroblasts respond to mechanical matrix cues to restore order in the confusing environment of a healing wound.

ECM-regulation of autophagy: The yin and the yang of autophagy during wound healing

Wound healing is a complex sequence of tissue protection, replacement, and reorganization leading to regenerated tissue. Disruption of any of these steps results in the process being incomplete as an ulcer or over-exuberant as a hypertrophic scar. Over the past decade, it has become evident that the extracellular matrix and associated components orchestrate this process. However, the cellular events that are induced by the extracellular matrix to accomplish wound healing remain to be defined. Herein we propose that matrix-regulated cellular macro-autophagy is key to both the tissue replacement and resolution stages of healing by directing cellular function or apoptosis. Further, disruptions in matrix turnover alter autophagic function leading to chronic wounds or scarring. While the literature that directly investigates autophagy during wound healing is sparse, the emerging picture supports our proposing a model of the centrality of the matrix-autophagy modulation as central to physiologic and pathologic healing.

Scar-Free Healing: Current Concepts and Future Perspectives

Every year, millions of people develop scars due to skin injuries after trauma, surgery, or skin burns. From the beginning of wound healing development, scar hyperplasia, and prolonged healing time in wound healing have been severe problems. Based on the difference between adult and fetal wound healing processes, many promising therapies have been developed to decrease scar formation in skin wounds. Currently, there is no good or reliable therapy to cure or prevent scar formation. This work briefly reviews the engineering methods of scarless wound healing, focusing on regenerative biomaterials and different cytokines, growth factors, and extracellular components in regenerative wound healing to minimize skin damage cell types, and scar formation.

Mesenchymal Stem Cell/Multipotent Stromal Cell Augmentation of Wound Healing: Lessons from the Physiology of Matrix and Hypoxia Support

Cutaneous wounds requiring tissue replacement are often challenging to treat and result in substantial economic burden. Many of the challenges inherent to therapy-mediated healing are due to comorbidities of disease and aging that render many wounds as chronic or nonhealing. Repeated failure to resolve chronic wounds compromises the reserve or functioning of localized reparative cells. Transplantation of mesenchymal stem cells/multipotent stromal cells (MSCs) has been proposed to augment the reparative capacity of resident cells within the wound bed to overcome stalled wound healing. However, MSCs face a variety of challenges within the wound micro-environment that curtail their survival after transplantation. MSCs are naturally pro-angiogenic and proreparative, and thus numerous techniques have been attempted to improve their survival and efficacy after transplantation, many with little impact. These setbacks have prompted researchers to re-examine the normal wound bed physiology, resulting in new approaches to MSC transplantation using extracellular matrix proteins and hypoxia preconditioning. These studies have also led to new insights on associated intracellular mechanisms, particularly autophagy, which play key roles in further regulating MSC survival and paracrine signaling. This review provides a brief overview of cutaneous wound healing with discussion on how extracellular matrix proteins and hypoxia can be utilized to improve MSC retention and therapeutic outcome.

The Spectrum of Scarring in Craniofacial Wound Repair

Fibrosis is intimately linked to wound healing and is one of the largest causes of wound-related morbidity. While scar formation is the normal and inevitable outcome of adult mammalian cutaneous wound healing, scarring varies widely between different anatomical sites. The spectrum of craniofacial wound healing spans a particularly diverse range of outcomes. While most craniofacial wounds heal by scarring, which can be functionally and aesthetically devastating, healing of the oral mucosa represents a rare example of nearly scarless postnatal healing in humans. In this review, we describe the typical wound healing process in both skin and the oral cavity. We present clinical correlates and current therapies and discuss the current state of research into mechanisms of scarless healing, toward the ultimate goal of achieving scarless adult skin healing.

Reversing CXCL10 Deficiency Ameliorates Kidney Disease in Diabetic Mice

The excessive accumulation of extracellular matrix material in the kidney is a histopathologic hallmark of diabetic kidney disease that correlates closely with declining function. Although considerable research has focused on the role of profibrotic factors, comparatively little attention has been paid to the possibility that a diminution in endogenous antifibrotic factors may also contribute. Among the latter, the ELR^- CXC chemokines, CXCL9, CXCL10, and CXCL11, have been shown to provide a stop signal to prevent excessive fibrosis. Although the plasma concentrations of CXCL9 and CXCL11 were similar, those of CXCL10 were markedly lower in diabetic db/db mice compared with control db/m mice. In cell culture, CXCL10 inhibited kidney fibroblast collagen production in response to high glucose and the prosclerotic growth factor, transforming growth factor-β. In vivo, recombinant murine CXCL10 reduced mesangial and peritubular matrix expansion, albuminuria, and glomerular hypertrophy in db/db mice. In bone marrow, a major source of circulating chemokines, the concentration of CXCL10 was lower in cells derived from diabetic mice than from their nondiabetic counterparts. Silencing of CXCR3, the cognate receptor for CXCL10, abrogated the antifibrotic effects of bone marrow-derived secretions. In conclusion, experimental diabetes is a state of CXCL10 deficiency and that restoration of CXCL10 abundance prevented fibrosis and the development of diabetic kidney disease in mice.

Mesenchymal Stromal Cell Preconditioning: The Next Step Toward a Customized Treatment For Severe Burn

Over the last century, the clinical management of severe skin burns significantly progressed with the development of burn care units, topical antimicrobials, resuscitation methods, early eschar excision surgeries, and skin grafts. Despite these considerable advances, the present treatment of severe burns remains burdensome, and patients are highly susceptible to skin engraftment failure, infections, organ dysfunction, and hypertrophic scarring. Recent researches have focused on mesenchymal stromal cell (MSC) therapy and hold great promises for tissue repair, as reported in several animal studies and clinical cases. In the present review, we will provide an up-to-date outlook of the pathophysiology of severe skin burns, clinical treatment modalities and current limitations. We will then focus on MSCs and their potential in the burn wound healing both in in vitro and in vivo studies. A specific attention will be paid to the cell preconditioning approach, as a means of improving the MSC efficacy in the treatment of major skin burns. In particular, we will debate how several preconditioning cues would modulate the MSC properties to better match up with the burn pathophysiology in the course of the cell therapy. Finally, we will discuss the clinical interest and feasibility of a MSC-based therapy in comparison to their paracrine derivatives, including microvesicles and conditioned media for the treatment of major skin burn injuries.

Autologous Bone Marrow Mesenchymal Stem Cells Improve the Quality and Stability of Vascularized Flap Surgery of Irradiated Skin in Pigs

Cutaneous radiation syndrome has severe long-term health consequences. Because it causes an unpredictable course of inflammatory waves, conventional surgical treatment is ineffective and often leads to a fibronecrotic process. Data about the long-term stability of healed wounds, with neither inflammation nor resumption of fibrosis, are lacking. In this study, we investigated the effect of injections of local autologous bone marrow-derived mesenchymal stromal cells (BM-MSCs), combined with plastic surgery for skin necrosis, in a large-animal model. Three months after irradiation overexposure to the rump, minipigs were divided into three groups: one group treated by simple excision of the necrotic tissue, the second by vascularized-flap surgery, and the third by vascularized-flap surgery and local autologous BM-MSC injections. Three additional injections of the BM-MSCs were performed weekly for 3 weeks. The quality of cutaneous wound healing was examined 1 year post-treatment. The necrotic tissue excision induced a pathologic scar characterized by myofibroblasts, excessive collagen-1 deposits, and inadequate vascular density. The vascularized-flap surgery alone was accompanied by inadequate production of extracellular matrix (ECM) proteins (decorin, fibronectin); the low col1/col3 ratio, associated with persistent inflammatory nodules, and the loss of vascularization both attested to continued immaturity of the ECM. BM-MSC therapy combined with vascularized-flap surgery provided mature wound healing characterized by a col1/col3 ratio and decorin and fibronectin expression that were all similar to that of nonirradiated skin, with no inflammation, and vascular stability. In this preclinical model, vascularized flap surgery successfully and lastingly remodeled irradiated skin only when combined with BM-MSC therapy. Stem Cells Translational Medicine 2018:569-582.

Delivery-associated presence of supramolecular fibronectin-fibrin complexes in puerperal and cord plasma

Objective: The variable fibronectin (FN) molecular forms are known to be engaged in coagulation and fibrinolysis pathways as well as tissue remodeling and repair processes. Some of them seem to be indispensable molecules within intensive biological processes associated with delivery. The aim of the study was to evaluate the FN molecular status in maternal and cord plasma after vaginal birth and cesarean section (C-section). Materials and methods: The study included nonpregnant women's plasma samples (n = 31) and puerperal and cord plasma samples collected from 49 mothers who delivered healthy newborns at term by vaginal birth (n = 25) and C-section (n = 24). The maternal and cord plasma FN concentrations and presence and relative ratios of different FN-fibrin complexes were determined by ELISA and sodium dodecyl sulfate (SDS) -agarose immunoblotting, respectively. Results: FN concentration in puerperal plasma after vaginal birth (232.08 ± 71.8 mg/L) and C-section (228.17 ± 71.2 mg/L) was significantly higher than in the plasma of nonpregnant women (190.00 ± 48.75 mg/L). In contrast, FN concentration in cord plasma of the C-section group (101.95 ± 30.3 mg/L) was significantly lower than that of the vaginal birth group (121.80 ± 22.2 mg/L). Immunoblotting of puerperal and cord plasma distinguished the most abundant dimeric plasma FN form, the 220-280-kDa FN degradation products and 750-1900-kDa FN-fibrin complexes, which occurred more frequently and in higher amounts in puerperal and cord plasma groups than the nonpregnant women group, although independently of the mode of delivery. Conclusions: Occurrence and relative amount of delivery-associated FN-fibrin complexes in both puerperal and cord plasmas might be bound with the physiological adaptive mechanisms reducing the risk of hemorrhage and intensive remodeling and repair processes after delivery.

Time-dependent changes in extra-domain A-fibronectin concentration and relative amounts of fibronectin-fibrin complexes in plasma of patients with peripheral arterial disease after endovascular revascularisation

Fibronectin (FN) may be involved in time- and stage-dependent and inter-related controlled processes of inflammation, coagulation, and wound healing accompanying peripheral arterial disease (PAD). In the present study, FN and FN-containing extra-domain A (EDA-FN), macromolecular FN-fibrin complexes, and FN monomer were analysed in the plasma of 142 PAD patients, including 37 patients with restenosis, for 37 months after revascularisation. FN concentration increased significantly in the plasma of PAD patients within 7 to 12 months after revascularisation, whereas the high concentration of EDA-FN was maintained up to 24 months, significantly higher in the group 7 to 12 months after revascularisation with recurrence of stenosis and lower in the PAD groups 1 to 3 months and 4 to 6 months after revascularisation with comorbid diabetes and ulceration, respectively. The relative amounts of FN-fibrin complexes up to 1600 kDa and FN monomer were significantly higher, within intervals of 4 to 24 months and 4 to 6 months after revascularisation, respectively. Moreover, the relative amounts of 750 to 1600 kDa FN-fibrin complexes within 13 to 24 months after revascularisation were higher in comparison with those in the group without restenosis. In conclusion, high levels of EDA-FN and FN-fibrin complexes could have potential diagnostic value in the management of PAD patients after revascularisation, predicting restenosis risk.

Embryonic skin development and repair

Fetal cutaneous wounds have the unique ability to completely regenerate wounded skin and heal without scarring. However, adult cutaneous wounds heal via a fibroproliferative response which results in the formation of a scar. Understanding the mechanism(s) of scarless wound healing leads to enormous clinical potential in facilitating an environment conducive to scarless healing in adult cutaneous wounds. This article reviews the embryonic development of the skin and outlines the structural and functional differences in adult and fetal wound healing phenotypes. A review of current developments made towards applying this clinical knowledge to promote scarless healing in adult wounds is addressed.

Black, White, and Gray: Macrophages in Skin Repair and Disease

PURPOSE OF REVIEW

Macrophages alter their responses during the temporal stages of wound healing. During the inflammatory phase macrophages perform phagocytosis. During neovascularization macrophages activate angiogenesis. In the proliferation phase of wound healing, macrophages deposit extracellular matrix and during wound resolution macrophages phagocytize excessive cellular components. This review addresses how these changing phenotypes affect skin repair and disease.

RECENT FINDINGS

Macrophages can determine the outcome of repair and can shift the normal wound healing response into fibrosis or chronic wounds. Emerging single cell technologies for the first time provide us with tools to uncover macrophage origin, heterogeneity and function.

SUMMARY

Macrophages may exist as one population where all cells alter their phenotype in response to signals from the microenvironment. Alternatively, macrophages may exist as distinct subsets that can control wound outcomes. A clarified understanding will strengthen our knowledge of skin biology and aid in the development of wound healing therapies.

Rebooting the collagen gel: Artificial hydrogels for the study of epithelial mesenchymal transformation

The collagen gel has been used to study epithelial-mesenchymal transformation (EMT) for over 30 years. With advances in the field of materials sciences, new options are available to design optically clear, three-dimensional nature-inspired matrix mimetics to study EMT. Here, we review the history of the collagen gel assay, discuss its current use and how newer artificial matrices can be built to simulate in vivo extracellular environments and investigate important current questions in the EMT field. We suggest that further collaborations between materials scientists and biologists will be critical to move the field of EMT forward. Developmental Dynamics 247:332-339, 2018. © 2017 Wiley Periodicals, Inc.

Biocomposite nanofiber matrices to support ECM remodeling by human dermal progenitors and enhanced wound closure

Cell-based therapies have recently been the focus of much research to enhance skin wound healing. An important challenge will be to develop vehicles for cell delivery that promote survival and uniform distribution of cells across the wound bed. These systems should be stiff enough to facilitate handling, whilst soft enough to limit damage to newly synthesized wound tissue and minimize patient discomfort. Herein, we developed several novel modifiable nanofibre scaffolds comprised of Poly (ε-caprolactone) (PCL) and gelatin (GE). We asked whether they could be used as a functional receptacle for adult human Skin-derived Precursor Cells (hSKPs) and how naked scaffolds impact endogenous skin wound healing. PCL and GE were electrospun in a single facile solvent to create composite scaffolds and displayed unique morphological and mechanical properties. After seeding with adult hSKPs, deposition of extracellular matrix proteins and sulphated glycosaminoglycans was found to be enhanced in composite grafts. Moreover, composite scaffolds exhibited significantly higher cell proliferation, greater cell spreading and integration within the nanofiber mats. Transplantation of acellular scaffolds into wounds revealed scaffolds exhibited improvement in dermal-epidermal thickness, axonal density and collagen deposition. These results demonstrate that PCL-based nanofiber scaffolds show promise as a cell delivery system for wound healing.

Tail regeneration and other phenomena of wound healing and tissue restoration in lizards

Wound healing is a fundamental evolutionary adaptation with two possible outcomes: scar formation or reparative regeneration. Scars participate in re-forming the barrier with the external environment and restoring homeostasis to injured tissues, but are well understood to represent dysfunctional replacements. In contrast, reparative regeneration is a tissue-specific program that near-perfectly replicates that which was lost or damaged. Although regeneration is best known from salamanders (including newts and axolotls) and zebrafish, it is unexpectedly widespread among vertebrates. For example, mice and humans can replace their digit tips, while many lizards can spontaneously regenerate almost their entire tail. Whereas the phenomenon of lizard tail regeneration has long been recognized, many details of this process remain poorly understood. All of this is beginning to change. This Review provides a comparative perspective on mechanisms of wound healing and regeneration, with a focus on lizards as an emerging model. Not only are lizards able to regrow cartilage and the spinal cord following tail loss, some species can also regenerate tissues after full-thickness skin wounds to the body, transections of the optic nerve and even lesions to parts of the brain. Current investigations are advancing our understanding of the biological requirements for successful tissue and organ repair, with obvious implications for biomedical sciences and regenerative medicine.

MSCs on an acellular dermal matrix (ADM) sourced from neonatal mouse skin regulate collagen reconstruction of granulation tissue during adult cutaneous wound healing

The novel strategy of MSCs seeded on ADM sourced from neonatal mouse skin promotes full-thickness cutaneous wound healing.

Wnt signaling induces epithelial differentiation during cutaneous wound healing

Cutaneous wound repair in adult mammals typically does not regenerate original dermal architecture. Skin that has undergone repair following injury is not identical to intact uninjured skin. This disparity may be caused by differences in the mechanisms that regulate postnatal cutaneous wound repair compared to embryonic skin development and thus we seek a deeper understanding of the role that Wnt signaling plays in the mechanisms of skin repair in both fetal and adult wounds. The influence of secreted Wnt signaling proteins in tissue homeostasis has galvanized efforts to identify small molecules that target Wnt-mediated cellular responses. Wnt signaling is activated by wounding and participates in every subsequent stage of the healing process from the control of inflammation and programmed cell death, to the mobilization of stem cell reservoirs within the wound site. Endogenous Wnt signaling augmentation represents an attractive option to aid in the restoration of cutaneous wounds, as the complex mechanisms of the Wnt pathway have been increasingly investigated over the years. In this review, we summarize recent data elucidating the roles that Wnt signaling plays in cutaneous wound healing process.

Platelets drive smooth muscle metaplasia and fibrogenesis in endometriosis through epithelial-mesenchymal transition and fibroblast-to-myofibroblast transdifferentiation

Smooth muscle metaplasia (SMM) and fibrotic tissues are frequently seen in endometriotic lesions, yet the mechanisms underlying their formation are poorly understood. In this study, we investigated the roles of activated platelets in driving epithelial-mesenchymal transition (EMT) and fibroblast-to-myofibroblast transdifferentiation (FMT) in endometriosis. Through in vitro experimentations, we found that activated platelets, through the release of TGF-β1 and the induction of TGF-β/Smad signaling pathway, promoted EMT and FMT in endometriosis, resulting in increased cell contractility, collagen production, and ultimately to fibrosis. TGF-β blockade reversed these processes. Prolonged exposure of endometriotic stromal cells to activated platelets induced increased expression of α-SMA as well as markers of differentiated smooth muscle cells. Consequently, endometriotic lesions and their microenvironment contain all the necessary molecular machinery to promote SMM and fibrogenesis. Our results suggest that endometriotic lesions are wounds that undergo repeated injury and healing, highlighting the importance of platelets in the development of endometriosis.

Flagellin preconditioning enhances the efficacy of mesenchymal stem cells in an irradiation-induced proctitis model

The success of mesenchymal stem cell transplantation for proctitis depends not only on cell donors but also on host microenvironmental factors, which play a major role in conditioning mesenchymal stem cell immunosuppressive action and repair. This study sought to determine if flagellin, a TLR5 ligand, can enhance the mesenchymal stem cell treatment efficacy in radiation-induced proctitis. With the use of a colorectal model of 27 Gy irradiation in rats, we investigated and compared the effects on immune capacity and remodeling at 28 d after irradiation of the following: 1) systemic mesenchymal stem cell (5 × 10(6)) administration at d 7 after irradiation, 2) administration of flagellin at d 3 and systemic mesenchymal stem cell administration at d 7, and 3) in vitro preconditioning of mesenchymal stem cells with flagellin, 24 h before their administration on d 7. The mucosal CD8(+) T cell population was normalized after treatment with flagellin-preconditioned mesenchymal stem cells or flagellin plus mesenchymal stem cells, whereas mesenchymal stem cells alone did not alter the radiation-induced elevation of CD8(+) T cell frequency. Mesenchymal stem cell treatment returned the irradiation-elevated frequency of CD25(+) cells in the mucosa-to-control levels, whereas both flagellin-preconditioned mesenchymal stem cell and flagellin-plus-mesenchymal stem cell treatment each significantly increased not only CD25(+) cell frequency but also forkhead box p3 and IL-2Rα expression. Specifically, IL-10 was overexpressed after flagellin-preconditioned mesenchymal stem cell treatment. Analysis of collagen expression showed that the collagen type 1/collagen type 3 ratio, an indicator of wound-healing maturation, was low in the irradiated and mesenchymal stem cell-treated groups and returned to the normal level only after the flagellin-preconditioned mesenchymal stem cell treatment. This was associated with a reduction in myofibroblast accumulation. In a proctitis model, flagellin-preconditioned mesenchymal stem cells improved colonic immune capacity and enhanced tissue remodeling.

Acellular dermal matrix from one-day-old mouse skin on adult scarless cutaneous wound repair by second harmonic generation microscopic imaging

The impacts of two types of acellular dermal matrix (ADM), ADM-1D and ADM-20W (ADM from 1-day-old and 20-week-old mouse skin), are evaluated on collagen density, orientation and the stiffness of new born dermis in adult cutaneous wound healing.

Chemokines in Wound Healing and as Potential Therapeutic Targets for Reducing Cutaneous Scarring

Significance: Cutaneous scarring is an almost inevitable end point of adult human wound healing. It is associated with significant morbidity, both physical and psychological. Pathological scarring, including hypertrophic and keloid scars, can be particularly debilitating. Manipulation of the chemokine system may lead to effective therapies for problematic lesions. Recent Advances: Rapid advancement in the understanding of chemokines and their receptors has led to exciting developments in the world of therapeutics. Modulation of their function has led to clinically effective treatments for conditions as diverse as human immunodeficiency virus and inflammatory bowel disease. Potential methods of targeting chemokines include monoclonal antibodies, small-molecule antagonists, interference with glycosaminoglycan binding and the use of synthetic truncated chemokines. Early work has shown promising results on scar development and appearance when the chemokine system is manipulated. Critical Issues: Chemokines are implicated in all stages of wound healing leading to the development of a cutaneous scar. An understanding of entirely regenerative wound healing in the developing fetus and how the expression of chemokines and their receptors change during the transition to the adult phenotype is central to addressing pathological scarring in adults. Future Directions: As our understanding of chemokine/receptor interactions and scar formation evolves it has become apparent that effective therapies will need to mirror the complexities in these diverse biological processes. It is likely that sophisticated treatments that sequentially influence multiple ligand/receptor interactions throughout all stages of wound healing will be required to deliver viable treatment options.

Skin tissue repair: Matrix microenvironmental influences

The process of repair of wounded skin involves intricate orchestration not only between the epidermal and dermal compartments but also between the resident and immigrant cells and the local microenvironment. Only now are we beginning to appreciate the complex roles played by the matrix in directing the outcome of the repair processes, and how this impacts the signals from the various cells. Recent findings speak of dynamic and reciprocal interactions that occurs among the matrix, growth factors, and cells that underlies this integrated process. Further confounding this integration are the physiologic and pathologic situations that directly alter the matrix to impart at least part of the dysrepair that occurs. These topics will be discussed with a call for innovative model systems of direct relevance to the human situation.

Periostin Is a Key Niche Component for Wound Metastasis of Melanoma

Tissue injury promotes metastasis of several human cancers, although factors associated with wound healing that attract circulating tumor cells have remained unknown. Here, we examined the primary and metastatic lesions that appeared 1 month after trauma in a patient with acral lentiginous melanoma. The levels of mRNA for periostin (POSTN), type 1 collagen, and fibronectin were significantly increased in the metastatic lesion relative to the primary lesion. The increase of these extracellular matrix proteins at the wound site was reproduced in a mouse model of wound healing, with the upregulation of Postn mRNA persisting the longest. POSTN was expressed in the region surrounding melanoma cell nests in metastatic lesions of both wounded mice and the patient. POSTN attenuated the cell adhesion and promoted the migration of melanoma cells without affecting their proliferation in vitro. In the mouse model, the wound site as well as subcutaneously injected osteoblasts that secrete large amounts of POSTN invited the metastasis of remotely-transplanted melanoma cells on the sites. Osteoblasts with suppression of POSTN by shRNA showed a greatly reduced ability to promote such metastasis. Our results suggest that POSTN is a key factor in promoting melanoma cell metastasis to wound sites by providing a premetastatic niche.

The extracellular matrix and transforming growth factor-β1: Tale of a strained relationship

Physiological tissue repair aims at restoring the mechano-protective properties of the extracellular matrix. Consequently, redundant regulatory mechanisms are in place ensuring that tissue remodeling terminates once matrix homeostasis is re-established. If these mechanisms fail, stromal cells become continuously activated, accumulate excessive amounts of stiff matrix, and fibrosis develops. In this mini-review, I develop the hypothesis that the mechanical state of the extracellular matrix and the pro-fibrotic transforming growth factor (TGF)-β1 cooperate to regulate the remodeling activities of stromal cells. TGF-β1 is stored in the matrix as part of a large latent complex and can be activated by cell contractile force that is transmitted by integrins. Matrix straining and stiffening lower the threshold for TGF-β1 activation by increasing the mechanical resistance to cell pulling. Different elements of this mechanism can be pharmacologically targeted to interrupt the mechanical positive feedback loop of fibrosis, including specific integrins and matrix protein interactions.

Therapeutic potential of gingival fibroblasts for cutaneous radiation syndrome: comparison to bone marrow-mesenchymal stem cell grafts

Mesenchymal stem cell (MSC) therapy has recently been investigated as a potential treatment for cutaneous radiation burns. We tested the hypothesis that injection of local gingival fibroblasts (GFs) would promote healing of radiation burn lesions and compared results with those for MSC transplantation. Human clinical- grade GFs or bone marrow-derived MSCs were intradermally injected into mice 21 days after local leg irradiation. Immunostaining and real-time PCR analysis were used to assess the effects of each treatment on extracellular matrix remodeling and inflammation in skin on days 28 and 50 postirradiation. GFs induced the early development of thick, fully regenerated epidermis, skin appendages, and hair follicles, earlier than MSCs did. The acceleration of wound healing by GFs involved rearrangement of the deposited collagen, modification of the Col/MMP/TIMP balance, and modulation of the expression and localization of tenascin-C and of the expression of growth factors (VEGF, EGF, and FGF7). As MSC treatment did, GF injection decreased the irradiation-induced inflammatory response and switched the differentiation of macrophages toward an M2-like phenotype, characterized by CD163(+) macrophage infiltration and strong expression of arginase-1. These findings indicate that GFs are an attractive target for regenerative medicine, for easier to collect, can grow in culture, and promote cutaneous wound healing in irradiation burn lesions.

Regulation of C-X-C chemokine gene expression by keratin 17 and hnRNP K in skin tumor keratinocytes

Interaction between K17 and hnRNP K regulates CXCR3 signaling in an RSK-dependent fashion to promote epithelial tumor cell growth and invasion.

High levels of the intermediate filament keratin 17 (K17) correlate with a poor prognosis for several types of epithelial tumors. However, the causal relationship and underlying mechanisms remain undefined. A recent study suggested that K17 promotes skin tumorigenesis by fostering a specific type of inflammation. We report here that K17 interacts with the RNA-binding protein hnRNP K, which has also been implicated in cancer. K17 is required for the cytoplasmic localization of hnRNP K and for its role in regulating the expression of multiple pro-inflammatory mRNAs. Among these are the CXCR3 ligands CXCL9, CXCL10, and CXCL11, which together form a signaling axis with an established role in tumorigenesis. The K17–hnRNP K partnership is regulated by the ser/thr kinase RSK and required for CXCR3-dependent tumor cell growth and invasion. These findings functionally integrate K17, hnRNP K, and gene expression along with RSK and CXCR3 signaling in a keratinocyte-autonomous axis and provide a potential basis for their implication in tumorigenesis.

Skin wound healing and scarring: fetal wounds and regenerative restitution

The adverse physiological and psychological effects of scars formation after healing of wounds are broad and a major medical problem for patients. In utero, fetal wounds heal in a regenerative manner, though the mechanisms are unknown. Differences in fetal scarless regeneration and adult repair can provide key insight into reduction of scarring therapy. Understanding the cellular and extracellular matrix alterations in excessive adult scarring in comparison to fetal scarless healing may have important implications. Herein, we propose that matrix can be controlled via cellular therapy to resemble a fetal-like matrix that will result in reduced scarring.

Matrikine and matricellular regulators of EGF receptor signaling on cancer cell migration and invasion

Cancer invasion is a complex process requiring, among other events, extensive remodeling of the extracellular matrix including deposition of pro-migratory and pro-proliferative moieties. In recent years, it has been described that while invading through matrices cancer cells can change shape and adapt their migration strategies depending on the microenvironmental context. Although intracellular signaling pathways governing the mesenchymal to amoeboid migration shift and vice versa have been mostly elucidated, the extracellular signals promoting these shifts are largely unknown. In this review, we summarize findings that point to matrikines that bind specifically to the EGF receptor as matricellular molecules that enable cancer cell migrational plasticity and promote invasion.

Mechanoregulation of the Myofibroblast in Wound Contraction, Scarring, and Fibrosis: Opportunities for New Therapeutic Intervention

SIGNIFICANCE

Myofibroblasts are responsible for wound closure that occurs in healed acute wounds. However, their actions can result in disfiguring scar contractures, compromised organ function, and a tumor promoting stroma. Understanding the mechanisms regulating their contractile machinery, gene expression, and lifespan is essential to develop new therapies to control their function.

RECENT ADVANCES

Mechanical stress and transforming growth factor beta-1 (TGF-β1) regulate myofibroblast differentiation from mesenchymal progenitors. As these precursor cells differentiate, they assemble a contractile apparatus to generate the force used to contract wounds. The mechanisms by which mechanical stress promote expression of contractile genes through the TGF-β1 and serum response factor pathways and offer therapeutic targets to limit myofibroblast function are being elucidated.

CRITICAL ISSUES

Emerging evidence suggests that the integration of mechanical cues with intracellular signaling pathways is critical to myofibroblast function via its effects on gene expression, cellular contraction, and paracrine signaling with neighboring cells. In addition, while apoptosis is clearly one pathway that can limit myofibroblast lifespan, recent data suggest that pathogenic myofibroblasts can become senescent and adopt a more beneficial phenotype, or may revert to a quiescent state, thereby limiting their function.

FUTURE DIRECTIONS

Given the important role that myofibroblasts play in pathologies as disparate as cutaneous scarring, organ fibrosis, and tumor progression, knowledge gained in the areas of intracellular signaling networks, mechanical signal transduction, extracellular matrix biology, and cell fate will support efforts to develop new therapies with a wide impact.

SDF-1α mediates wound-promoted tumor growth in a syngeneic orthotopic mouse model of breast cancer

Increased growth of residual tumors in the proximity of acute surgical wounds has been reported; however, the mechanisms of wound-promoted tumor growth remain unknown. Here, we used a syngeneic, orthotopic mouse model of breast cancer to study mechanisms of wound-promoted tumor growth. Our results demonstrate that exposure of metastatic mouse breast cancer cells (4T1) to SDF-1α, which is increased in wound fluid, results in increased tumor growth. Both, wounding and exposure of 4T1 cells to SDF-1α not only increased tumor growth, but also tumor cell proliferation rate and stromal collagen deposition. Conversely, systemic inhibition of SDF-1α signaling with the small molecule AMD 3100 abolished the effect of wounding, and decreased cell proliferation, collagen deposition, and neoangiogenesis to the levels observed in control animals. Furthermore, using different mouse strains we could demonstrate that the effect of wounding on tumor growth and SDF-1α levels is host dependent and varies between mouse strains. Our results show that wound-promoted tumor growth is mediated by elevated SDF-1α levels and indicate that the effect of acute wounds on tumor growth depends on the predetermined wound response of the host background and its predetermined wound response.

The myofibroblast matrix: implications for tissue repair and fibrosis

Myofibroblasts, and the extracellular matrix (ECM) in which they reside, are critical components of wound healing and fibrosis. The ECM, traditionally viewed as the structural elements within which cells reside, is actually a functional tissue whose components possess not only scaffolding characteristics, but also growth factor, mitogenic, and other bioactive properties. Although it has been suggested that tissue fibrosis simply reflects an 'exuberant' wound-healing response, examination of the ECM and the roles of myofibroblasts during fibrogenesis instead suggest that the organism may be attempting to recapitulate developmental programmes designed to regenerate functional tissue. Evidence of this is provided by the temporospatial re-emergence of embryonic ECM proteins by fibroblasts and myofibroblasts that induce cellular programmatic responses intended to produce a functional tissue. In the setting of wound healing (or physiological fibrosis), this occurs in a highly regulated and exquisitely choreographed fashion which results in cessation of haemorrhage, restoration of barrier integrity, and re-establishment of tissue function. However, pathological tissue fibrosis, which oftentimes causes organ dysfunction and significant morbidity or mortality, likely results from dysregulation of normal wound-healing processes or abnormalities of the process itself. This review will focus on the myofibroblast ECM and its role in both physiological and pathological fibrosis, and will discuss the potential for therapeutically targeting ECM proteins for treatment of fibrotic disorders.

An assay to quantify chemotactic properties of degradation products from extracellular matrix

The endogenous chemotaxis of cells toward sites of tissue injury and/or biomaterial implantation is an important component of the host response. Implanted biomaterials capable of recruiting host stem/progenitor cells to a site of interest may obviate challenges associated with cell transplantation. An assay for the identification and quantification of chemotaxis induced by surgically placed biologic scaffolds composed of extracellular matrix is described herein.

The wound-healing response and upregulated embryonic mechanisms: brothers-in-arms forever

The cutaneous wound-healing reaction occurs in overlapping but inter-related phases, which ultimately result in fibrosis. The pathophysiological mechanisms involved in fibrotic diseases, including organ-related and even systemic diseases, such as systemic sclerosis, could represent the successive systemic upregulation of extraembryonic-like phenotypes, that is, amniotic and vitelline phenotypes. These two extraembryonic-like phenotypes act on the injured tissue to induce a process similar to gastrulation, which occurs during the early phases of embryo development. The amniotic-like phenotype plays a leading role in the development of neurogenic responses with significant hydroelectrolytic alterations that essentially represent the development of open microcirculation within the injured tissue. In turn, through the overlapping expression of a vitelline-like phenotype, a bone marrow-related response is produced. Interstitial infiltration by molecular and cellular mediators contributed by amniotic- and vitelline-like functions provides the functional and metabolic autonomy needed for inducing new tissue formation through mechanisms similar to those that act in gastrulation during the early phases of embryonic development. Thus, while a new tissue is formed, it quickly evolves into fibrotic tissue because of premature senescence. Mechanisms related to extraembryonic-like functions have been suggested in the following physiological and pathological processes: embryonic development; wound-healing reactions occurring during adult life; and senescence. The existence of this sort of basic self-organizing fractal-like functional pattern is an essential characteristic of our way of life.

cAMP and Epac in the regulation of tissue fibrosis

Fibrosis, the result of excess deposition of extracellular matrix (ECM), in particular collagen, leads to scarring and loss of function in tissues that include the heart, lung, kidney and liver. The second messenger cAMP can inhibit the formation and extent of ECM during this late phase of inflammation, but the mechanisms for these actions of cAMP and of agents that elevate tissue cAMP levels are not well understood. In this article, we review the fibrotic process and focus on two recently recognized aspects of actions of cAMP and its effector Epac (Exchange protein activated by cAMP): (a) blunting of epithelial-mesenchymal transformation (EMT) and (b) down-regulation of Epac expression by profibrotic agents (e.g. TGF-β, angiotensin II), which may promote tissue fibrosis by decreasing Epac-mediated antifibrotic actions. Pharmacological approaches that raise cAMP or blunt the decrease in Epac expression by profibrotic agents may thus be strategies to block or perhaps reverse tissue fibrosis. LINKED ARTICLES This article is part of a themed section on Novel cAMP Signalling Paradigms. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-2.