Direct conversion of injury-site myeloid cells to fibroblast-like cells of granulation tissue. Nat Commun. 2018;9:936. [PMID: 29507336 PMCID: PMC5838200 DOI: 10.1038/s41467-018-03208-w]

Interactions at engineered graft-tissue interfaces: A review

The interactions at the graft-tissue interfaces are critical for the results of engraftments post-implantation. To improve the success rate of the implantations, as well as the quality of the patients' life, understanding the possible reactions between artificial materials and the host tissues is helpful in designing new generations of material-based grafts aiming at inducing specific responses from surrounding tissues for their own reparation and regeneration. To help researchers understand the complicated interactions that occur after implantations and to promote the development of better-designed grafts with improved biocompatibility and patient responses, in this review, the topics will be discussed from the basic reactions that occur chronologically at the graft-tissue interfaces after implantations to the existing and potential applications of the mechanisms of such reactions in designing of grafts. It offers a chance to bring up-to-date advances in the field and new strategies of controlling the graft-tissue interfaces.

Fibroblast Heterogeneity in Wound Healing: Hurdles to Clinical Translation

Recent work has revealed that fibroblasts are remarkably heterogeneous cells, but the appropriate lens through which to study this variation (lineage, phenotype, and plasticity) and its relevance to human biology remain unclear. In this opinion article, we comment on recent breakthroughs in our understanding of fibroblast heterogeneity during skin wound healing, and on open questions that must be addressed to clinically translate these findings in order to minimize scarring in patients. We emphasize the need for experimental models of wound healing that better approximate human biology, as well as comparison of scarring and regenerative phenotypes to uncover master regulators of fibrosis.

Extracellular vesicles in Inflammatory Skin Disorders: from Pathophysiology to Treatment

Extracellular vesicles (EVs), naturally secreted by almost all known cell types into extracellular space, can transfer their bioactive cargos of nucleic acids and proteins to recipient cells, mediating cell-cell communication. Thus, they participate in many pathogenic processes including immune regulation, cell proliferation and differentiation, cell death, angiogenesis, among others. Cumulative evidence has shown the important regulatory effects of EVs on the initiation and progression of inflammation, autoimmunity, and cancer. In dermatology, recent studies indicate that EVs play key immunomodulatory roles in inflammatory skin disorders, including psoriasis, atopic dermatitis, lichen planus, bullous pemphigoid, systemic lupus erythematosus, and wound healing. Importantly, EVs can be used as biomarkers of pathophysiological states and/or therapeutic agents, both as carriers of drugs or even as a drug by themselves. In this review, we will summarize current research advances of EVs from different cells and their implications in inflammatory skin disorders, and further discuss their future applications, updated techniques, and challenges in clinical translational medicine.

Adaptive and innate immune mechanisms in cardiac fibrosis complicating pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a syndrome diagnosed by increased mean pulmonary artery (PA) pressure and resistance and normal pulmonary capillary wedge pressure. PAH is characterized pathologically by distal pulmonary artery remodeling, increased pulmonary vascular resistance, and plexiform lesions (PLs). Right ventricular fibrosis and hypertrophy, leading to right ventricular failure, are the main determinants of mortality in PAH. Recent work suggests that right ventricular fibrosis results from resident cardiac fibroblast activation and conversion to myofibroblasts, leading to replacement of contractile cardiomyocytes with nondistensible tissue incapable of conductivity or contractility. However, the origins, triggers, and consequences of myofibroblast expansion and its pathophysiological relationship with PAH are unclear. Recent advances indicate that signals generated by adaptive and innate immune cells may play a role in right ventricular fibrosis and remodeling. This review summarizes recent insights into the mechanisms by which adaptive and innate immune signals participate in the transition of cardiac fibroblasts to activated myofibroblasts and highlights the existing gaps of knowledge as relates to the development of right ventricular fibrosis.

The Role of an IL-10/Hyaluronan Axis in Dermal Wound Healing

Scar formation is the typical endpoint of postnatal dermal wound healing, which affects more than 100 million individuals annually. Not only do scars cause a functional burden by reducing the biomechanical strength of skin at the site of injury, but they also significantly increase healthcare costs and impose psychosocial challenges. Though the mechanisms that dictate how dermal wounds heal are still not completely understood, they are regulated by extracellular matrix (ECM) remodeling, neovascularization, and inflammatory responses. The cytokine interleukin (IL)-10 has emerged as a key mediator of the pro- to anti-inflammatory transition that counters collagen deposition in scarring. In parallel, the high molecular weight (HMW) glycosaminoglycan hyaluronan (HA) is present in the ECM and acts in concert with IL-10 to block pro-inflammatory signals and attenuate fibrotic responses. Notably, high concentrations of both IL-10 and HMW HA are produced in early gestational fetal skin, which heals scarlessly. Since fibroblasts are responsible for collagen deposition, it is critical to determine how the concerted actions of IL-10 and HA drive their function to potentially control fibrogenesis. Beyond their independent actions, an auto-regulatory IL-10/HA axis may exist to modulate the magnitude of CD4⁺ effector T lymphocyte activation and enhance T regulatory cell function in order to reduce scarring. This review underscores the pathophysiological impact of the IL-10/HA axis as a multifaceted molecular mechanism to direct primary cell responders and regulators toward either regenerative dermal tissue repair or scarring.

GM-CSF Calibrates Macrophage Defense and Wound Healing Programs during Intestinal Infection and Inflammation

Macrophages play a central role in intestinal immunity, but inappropriate macrophage activation is associated with inflammatory bowel disease (IBD). Here, we identify granulocyte-macrophage colony stimulating factor (GM-CSF) as a critical regulator of intestinal macrophage activation in patients with IBD and mice with dextran sodium sulfate (DSS)-induced colitis. We find that GM-CSF drives the maturation and polarization of inflammatory intestinal macrophages, promoting anti-microbial functions while suppressing wound-healing transcriptional programs. Group 3 innate lymphoid cells (ILC3s) are a major source of GM-CSF in intestinal inflammation, with a strong positive correlation observed between ILC or CSF2 transcripts and M1 macrophage signatures in IBD mucosal biopsies. Furthermore, GM-CSF-dependent macrophage polarization results in a positive feedback loop that augmented ILC3 activation and type 17 immunity. Together, our data reveal an important role for GM-CSF-mediated ILC-macrophage crosstalk in calibrating intestinal macrophage phenotype to enhance anti-bacterial responses, while inhibiting pro-repair functions associated with fibrosis and stricturing, with important clinical implications.

Novel fibrin-fibronectin matrix accelerates mice skin wound healing

Plasma fibrinogen (F1) and fibronectin (pFN) polymerize to form a fibrin clot that is both a hemostatic and provisional matrix for wound healing. About 90% of plasma F1 has a homodimeric pair of γ chains (γγF1), and 10% has a heterodimeric pair of γ and more acidic γ' chains (γγ'F1). We have synthesized a novel fibrin matrix exclusively from a 1:1 (molar ratio) complex of γγ'F1 and pFN in the presence of highly active thrombin and recombinant Factor XIII (rFXIIIa). In this matrix, the fibrin nanofibers were decorated with pFN nanoclusters (termed γγ'F1:pFN fibrin). In contrast, fibrin made from 1:1 mixture of γγF1 and pFN formed a sporadic distribution of "pFN droplets" (termed γγF1+pFN fibrin). The γγ'F1:pFN fibrin enhanced the adhesion of primary human umbilical vein endothelium cells (HUVECs) relative to the γγF1+FN fibrin. Three dimensional (3D) culturing showed that the γγ'F1:pFN complex fibrin matrix enhanced the proliferation of both HUVECs and primary human fibroblasts. HUVECs in the 3D γγ'F1:pFN fibrin exhibited a starkly enhanced vascular morphogenesis while an apoptotic growth profile was observed in the γγF1+pFN fibrin. Relative to γγF1+pFN fibrin, mouse dermal wounds that were sealed by γγ'F1:pFN fibrin exhibited accelerated and enhanced healing. This study suggests that a 3D pFN presentation on a fibrin matrix promotes wound healing.

Wound healing action of nitric oxide-releasing self-expandable collagen sponge

Mounting evidence showing that local nitric oxide (NO) delivery may significantly improve the wound healing process has stimulated the development of wound dressings capable of releasing NO topically. Herein, we describe the preparation of a self-expandable NO-releasing hydrolyzed collagen sponge (CS), charged with the endogenously found NO donor, S-nitrosoglutathione (GSNO). We show that cold pressed and GSNO-charged CS (CS/GSNO) undergo self-expansion to its original 3D shape upon water absorption to a swelling degree of 2,300 wt%, triggering the release of free NO. Topical application of compressed CS/GSNO on wounds in an animal model showed that exudate absorption by CS/GSNO leads to the release of higher NO doses during the inflammatory phase and progressively lower NO doses at later stages of the healing process. Moreover, treated animals showed significant increase in the mRNA expression levels of monocyte chemoattractant protein-1 (MCP-1), murine macrophage marker (F4/80), transforming growth factor beta (TGF-β), stromal cell-derived factor 1 (SDF-1), insulin-like growth factor-1 (IGF-1), nitric oxide synthase(iNOS), and matrix metalloproteinase(MMP-9). Cluster differentiation 31 (CD31), vascular endothelial growth factor (VEGF), and F4/80 were measured on Days 7 and 12 by immunohistochemistry in the cicatricial tissue. These results indicate that the topical delivery of NO enhances the migration and infiltration of leucocytes, macrophages, and keratinocytes to the wounded tissue, as well as the neovascularization and collagen deposition, which are correlated with an accelerated wound closure. Thus, self-expandable CS/GSNO may represent a novel biocompatible and active wound dress for the topical delivery of NO on wounds.

Reprogramming of human fibroblasts into osteoblasts by insulin-like growth factor-binding protein 7

The induced pluripotent stem cell (iPSC) is a promising cell source for tissue regeneration. However, the therapeutic value of iPSC technology is limited due to the complexity of induction protocols and potential risks of teratoma formation. A trans-differentiation approach employing natural factors may allow better control over reprogramming and improved safety. We report here a novel approach to drive trans-differentiation of human fibroblasts into functional osteoblasts using insulin-like growth factor binding protein 7 (IGFBP7). We initially determined that media conditioned by human osteoblasts can induce reprogramming of human fibroblasts to functional osteoblasts. Proteomic analysis identified IGFBP7 as being significantly elevated in media conditioned with osteoblasts compared with those with fibroblasts. Recombinant IGFBP7 induced a phenotypic switch from fibroblasts to osteoblasts. The switch was associated with senescence and dependent on autocrine IL-6 signaling. Our study supports a novel strategy for regenerating bone by using IGFBP7 to trans-differentiate fibroblasts to osteoblasts.

Engineering Biomaterials with Micro/Nanotechnologies for Cell Reprogramming

Cell reprogramming is a revolutionized biotechnology that offers a powerful tool to engineer cell fate and function for regenerative medicine, disease modeling, drug discovery, and beyond. Leveraging advances in biomaterials and micro/nanotechnologies can enhance the reprogramming performance in vitro and in vivo through the development of delivery strategies and the control of biophysical and biochemical cues. In this review, we present an overview of the state-of-the-art technologies for cell reprogramming and highlight the recent breakthroughs in engineering biomaterials with micro/nanotechnologies to improve reprogramming efficiency and quality. Finally, we discuss future directions and challenges for reprogramming technologies and clinical translation.

Current Approaches Targeting the Wound Healing Phases to Attenuate Fibrosis and Scarring

Cutaneous fibrosis results from suboptimal wound healing following significant tissue injury such as severe burns, trauma, and major surgeries. Pathologic skin fibrosis results in scars that are disfiguring, limit normal movement, and prevent patient recovery and reintegration into society. While various therapeutic strategies have been used to accelerate wound healing and decrease the incidence of scarring, recent studies have targeted the molecular regulators of each phase of wound healing, including the inflammatory, proliferative, and remodeling phases. Here, we reviewed the most recent literature elucidating molecular pathways that can be targeted to reduce fibrosis with a particular focus on post-burn scarring. Current research targeting inflammatory mediators, the epithelial to mesenchymal transition, and regulators of myofibroblast differentiation shows promising results. However, a multimodal approach addressing all three phases of wound healing may provide the best therapeutic outcome.

Scars or Regeneration?-Dermal Fibroblasts as Drivers of Diverse Skin Wound Responses

Scarring and regeneration are two physiologically opposite endpoints to skin injuries, with mammals, including humans, typically healing wounds with fibrotic scars. We aim to provide an updated review on fibroblast heterogeneity as determinants of the scarring-regeneration continuum. We discuss fibroblast-centric mechanisms that dictate scarring-regeneration continua with a focus on intercellular and cell-matrix adhesion. Improved understanding of fibroblast lineage-specific mechanisms and how they determine scar severity will ultimately allow for the development of antiscarring therapies and the promotion of tissue regeneration.

The role of macrophages in the formation of hypertrophic scars and keloids

Numerous studies have shown that macrophages can orchestrate the microenvironment from the early stage of wound healing to the later stages of scar formation. However, few reviews have highlighted the significance of macrophages during the formation of abnormal scars. The purpose of this review was to outline the polarization of macrophages from early to late stage of pathological scar formation, focusing on spatiotemporal diversity of M1 and M2 macrophages. In this review, the role of macrophages in the formation of hypertrophic scars and keloids is summarized in detail. First, an increased number of M2 cells observed before injuries are significantly associated with susceptibility to abnormal scar pathogenesis. Second, decreased expression of M1 at the early stage and delayed expression of M2 at the late stage results in pathological scar formation. Third, M2 cells are highly expressed at both the margin and the superficial region, which is consistent with the invasive property of keloids. Finally, this review helps to characterize strategies for the prediction and prevention of pathological scar formation.

TGF-β1 - A truly transforming growth factor in fibrosis and immunity

'Jack of all trades, master of everything' is a fair label for transforming growth factor β1 (TGF-β) - a cytokine that controls our life at many levels. In the adult organism, TGF-β1 is critical for the development and maturation of immune cells, maintains immune tolerance and homeostasis, and regulates various aspects of immune responses. Following acute tissue damages, TGF-β1 becomes a master regulator of the healing process with impacts on about every cell type involved. Divergence from the tight control of TGF-β1 actions, for instance caused by chronic injury, severe trauma, or infection can tip the balance from regulated physiological to excessive pathological repair. This condition of fibrosis is characterized by accumulation and stiffening of collagenous scar tissue which impairs organ functions to the point of failure. Fibrosis and dysregulated immune responses are also a feature of cancer, in which tumor cells escape immune control partly by manipulating TGF-β1 regulation and where immune cells are excluded from the tumor by fibrotic matrix created during the stroma 'healing' response. Despite the obvious potential of TGF-β-signalling therapies, globally targeting TGF-β1 receptor, downstream pathways, or the active growth factor have proven to be extremely difficult if not impossible in systemic treatment regimes. However, TGF-β1 binding to cell receptors requires prior activation from latent complexes that are extracellularly presented on the surface of immune cells or within the extracellular matrix. These different locations have led to some divergence in the field which is often either seen from the perspective of an immunologists or a fibrosis/matrix researcher. Despite these human boundaries, there is considerable overlap between immune and tissue repair cells with respect to latent TGF-β1 presentation and activation. Moreover, the mechanisms and proteins employed by different cells and spatiotemporal control of latent TGF-β1 activation provide specificity that is amenable to drug development. This review aims at synthesizing the knowledge on TGF-β1 extracellular activation in the immune system and in fibrosis to further stimulate cross talk between the two research communities in solving the TGF-β conundrum.

T Lymphocytes Attenuate Dermal Scarring by Regulating Inflammation, Neovascularization, and Extracellular Matrix Remodeling

Objective: While tissue injury and repair are known to involve adaptive immunity, the profile of lymphocytes involved and their contribution to dermal scarring remain unclear. We hypothesized that restoration of T cell deficiency attenuates dermal scarring. Approach: We assessed the temporal-spatial distribution of T lymphocytes and their subtypes during the physiological dermal wound repair process in mice. Also, we compared the scarring outcomes between wild-type (WT) and severe combined immunodeficient (SCID) mice, which are lymphocyte deficient. Complementary gain-of-function experiments were performed by adoptively transferring lymphocyte subsets to validate their contribution to tissue repair in wounded SCID mice. Results: CD4⁺ T lymphocytes were present within dermal wounds of WT mice beginning on day 1 and remained through day 30. Wounds of SCID mice exhibited accelerated closure, increased inflammation, limited neovascularization, and exacerbated scarring compared with WT mice. Conversely, transfer of either mixed B and T lymphocytes or CD4⁺ lymphocytes alone into SCID mice resulted in moderated healing with less inflammation, collagen deposition, and scarring than control SCID wounds. In contrast, transfer of other lymphocyte subsets, including helper T lymphocytes (CD3⁺CD4⁺CD25^-), CD8⁺ T cells and B cells, or regulatory T lymphocytes (CD4⁺CD25⁺CD127^low), did not reduce scar. Innovation: The finding that lymphocytes delay wound healing but reduce scar is novel and provides new insights into how dermal scarring is regulated. Conclusion: Our data support a suppressive role for CD4⁺ T cells against inflammation and collagen deposition, with protective effects in early-stage dermal wound healing. These data implicate adaptive immunity in the regulation of scarring phenotypes.

Cutaneous Epithelial to Mesenchymal Transition Activator ZEB1 Regulates Wound Angiogenesis and Closure in a Glycemic Status-Dependent Manner

Epithelial to mesenchymal transition (EMT) and wound vascularization are two critical interrelated processes that enable cutaneous wound healing. Zinc finger E-box binding homeobox 1 (ZEB1), primarily studied in the context of tumor biology, is a potent EMT activator. ZEB1 is also known to contribute to endothelial cell survival as well as stimulate tumor angiogenesis. The role of ZEB1 in cutaneous wounds was assessed using Zeb1^+/- mice, as Zeb1^-/- mice are not viable. Quantitative stable isotope labeling by amino acids in cell culture (SILAC) proteomics was used to elucidate the effect of elevated ZEB1, as noted during hyperglycemia. Under different glycemic conditions, ZEB1 binding to E-cadherin promoter was investigated using chromatin immunoprecipitation. Cutaneous wounding resulted in loss of epithelial marker E-cadherin with concomitant gain of ZEB1. The dominant proteins downregulated after ZEB1 overexpression functionally represented adherens junction pathway. Zeb1^+/- mice exhibited compromised wound closure complicated by defective EMT and poor wound angiogenesis. Under hyperglycemic conditions, ZEB1 lost its ability to bind E-cadherin promoter. Keratinocyte E-cadherin, thus upregulated, resisted EMT required for wound healing. Diabetic wound healing was improved in ZEB^+/- as well as in db/db mice subjected to ZEB1 knockdown. This work recognizes ZEB1 as a key regulator of cutaneous wound healing that is of particular relevance to diabetic wound complication.

A Modified Collagen Dressing Induces Transition of Inflammatory to Reparative Phenotype of Wound Macrophages

Collagen containing wound-care dressings are extensively used. However, the mechanism of action of these dressings remain unclear. Earlier studies utilizing a modified collagen gel (MCG) dressing demonstrated improved vascularization of ischemic wounds and better healing outcomes. Wound macrophages are pivotal in facilitating wound angiogenesis and timely healing. The current study was designed to investigate the effect of MCG on wound macrophage phenotype and function. MCG augmented recruitment of macrophage at the wound-site, attenuated pro-inflammatory and promoted anti-inflammatory macrophage polarization. Additionally, MCG increased anti-inflammatory IL-10, IL-4 and pro-angiogenic VEGF production, indicating a direct role of MCG in resolving wound inflammation and improving angiogenesis. At the wound-site, impairment in clearance of apoptotic cell bioburden enables chronic inflammation. Engulfment of apoptotic cells by macrophages (efferocytosis) resolves inflammation via a miR-21-PDCD4-IL-10 pathway. MCG-treated wound macrophages exhibited a significantly bolstered efferocytosis index. Such favorable outcome significantly induced miR-21 expression. MCG-mediated IL-10 production was dampened under conditions of miR-21 knockdown pointing towards miR-21 as a causative factor. Pharmacological inhibition of JNK attenuated IL-10 production by MCG, implicating miR-21-JNK pathway in MCG-mediated IL-10 production by macrophages. This work provides direct evidence demonstrating that a collagen-based wound-care dressing may influence wound macrophage function and therefore modify wound inflammation outcomes.

Direct and Indirect Roles of Macrophages in Hypertrophic Scar Formation

Hypertrophic scars are pathological scars that result from abnormal responses to trauma, and could cause serious functional and cosmetic disability. To date, no optimal treatment method has been established. A variety of cell types are involved in hypertrophic scar formation after wound healing, but the underlying molecular mechanisms and cellular origins of hypertrophic scars are not fully understood. Macrophages are major effector cells in the immune response after tissue injury that orchestrates the process of wound healing. Depending on the local microenvironment, macrophages undergo marked phenotypic and functional changes at different stages during scar pathogenesis. This review intends to summarize the direct and indirect roles of macrophages during hypertrophic scar formation. The in vivo depletion of macrophages or blocking their signaling reduces scar formation in experimental models, thereby establishing macrophages as positive regulatory cells in the skin scar formation. In the future, a significant amount of attention should be given to molecular and cellular mechanisms that cause the phenotypic switch of wound macrophages, which may provide novel therapeutic targets for hypertrophic scars.

Tumorigenic Interplay Between Macrophages and Collagenous Matrix in the Tumor Microenvironment

The tumor microenvironment is a heterogeneous tissue that in addition to tumor cells, contain tumor-associated cell types such as immune cells, fibroblasts, and endothelial cells. Considerably important in the tumor microenvironment is its noncellular component, namely, the extracellular matrix (ECM). In particular, the collagenous matrix is subjected to significant alterations in its composition and structure that create a permissive environment for tumor growth, invasion, and dissemination. Among tumor-infiltrating immune cells, tumor-associated macrophages (TAMs) are numerous in the tumor stroma and are locally educated to mediate important biological functions that profoundly affect tumor initiation, growth, and dissemination. While the influence of TAMs and mechanical properties of the collagenous matrix on tumor invasion and progression have been comprehensively investigated individually, their interaction within the complex tumor microenvironment was overlooked. This review summarizes accumulating evidence that indicate the existence of an intricate tumorigenic crosstalk between TAMs and collagenous matrix. A better mechanistic comprehension of this reciprocal interplay may open a novel arena for cancer therapeutics.

Skin Transcriptome of Middle-Aged Women Supplemented With Natural Herbo-mineral Shilajit Shows Induction of Microvascular and Extracellular Matrix Mechanisms

Objective: Shilajit is a pale-brown to blackish-brown organic mineral substance available from Himalayan rocks. We demonstrated that in type I obese humans, shilajit supplementation significantly upregulated extracellular matrix (ECM)-related genes in the skeletal muscle. Such an effect was highly synergistic with exercise. The present study (clinicaltrials.gov NCT02762032) aimed to evaluate the effects of shilajit supplementation on skin gene expression profile and microperfusion in healthy adult females. Methods: The study design comprised six total study visits including a baseline visit (V1) and a final 14-week visit (V6) following oral shilajit supplementation (125 or 250 mg bid). A skin biopsy of the left inner upper arm of each subject was collected at visit 2 and visit 6 for gene expression profiling using Affymetrix Clariom™ D Assay. Skin perfusion was determined by MATLAB processing of dermascopic images. Transcriptome data were normalized and subjected to statistical analysis. The differentially regulated genes were subjected to Ingenuity Pathway Analysis (IPA®). The expression of the differentially regulated genes identified by IPA® were verified using real-time polymerase chain reaction (RT-PCR). Results: Supplementation with shilajit for 14 weeks was not associated with any reported adverse effect within this period. At a higher dose (250 mg bid), shilajit improved skin perfusion when compared to baseline or the placebo. Pathway analysis identified shilajit-inducible genes relevant to endothelial cell migration, growth of blood vessels, and ECM which were validated by quantitative real-time polymerase chain reaction (RT-PCR) analysis. Conclusions: This work provides maiden evidence demonstrating that oral shilajit supplementation in adult healthy women induced genes relevant to endothelial cell migration and growth of blood vessels. Shilajit supplementation improved skin microperfusion.

Early natural history of neotissue formation in tissue-engineered vascular grafts in a murine model

Aim: To characterize early events in neotissue formation during the first 2 weeks after vascular scaffold implantation. Materials & methods: Biodegradable polymeric scaffolds were implanted as abdominal inferior vena cava interposition grafts in wild-type mice. Results: All scaffolds explanted at day 1 contained a platelet-rich mural thrombus. Within the first few days, the majority of cell infiltration appeared to be from myeloid cells at the peritoneal surface with modest infiltration along the lumen. Host reaction to the graft was distinct between the scaffold and mural thrombus; the scaffold stimulated an escalating foreign body reaction, whereas the thrombus was quickly remodeled into collagen-rich neotissue. Conclusion: Mural thrombi remodel into neotissue that persistently occludes the lumen of vascular grafts.

Fra-2-expressing macrophages promote lung fibrosis in mice

Idiopathic Pulmonary Fibrosis (IPF) is a deadly disease with limited therapies. Tissue fibrosis is associated with Type 2 immune response, although the causal contribution of immune cells is not defined. The AP-1 transcription factor Fra-2 is upregulated in IPF lung sections and Fra-2 transgenic mice (Fra-2tg) exhibit spontaneous lung fibrosis. Here we show that Bleomycin-induced lung fibrosis is attenuated upon myeloid-inactivation of Fra-2 and aggravated in Fra-2tg bone marrow chimeras. Type VI collagen (ColVI), a Fra-2 transcriptional target, is up-regulated in three lung fibrosis models, and macrophages promote myofibroblast activation in vitro in a ColVI- and Fra-2-dependent manner. Fra-2 or ColVI inactivation does not affect macrophage recruitment and alternative activation, suggesting that Fra-2/ColVI specifically controls the paracrine pro-fibrotic activity of macrophages. Importantly, ColVI knock-out mice (KO) and ColVI-KO bone marrow chimeras are protected from Bleomycin-induced lung fibrosis. Therapeutic administration of a Fra-2/AP-1 inhibitor reduces ColVI expression and ameliorates fibrosis in Fra-2tg mice and in the Bleomycin model. Finally, Fra-2 and ColVI positively correlate in IPF patient samples and co-localize in lung macrophages. Therefore, the Fra-2/ColVI pro-fibrotic axis is a promising biomarker and therapeutic target for lung fibrosis, and possibly other fibrotic diseases.

Single-cell analysis reveals fibroblast heterogeneity and myeloid-derived adipocyte progenitors in murine skin wounds

During wound healing in adult mouse skin, hair follicles and then adipocytes regenerate. Adipocytes regenerate from myofibroblasts, a specialized contractile wound fibroblast. Here we study wound fibroblast diversity using single-cell RNA-sequencing. On analysis, wound fibroblasts group into twelve clusters. Pseudotime and RNA velocity analyses reveal that some clusters likely represent consecutive differentiation states toward a contractile phenotype, while others appear to represent distinct fibroblast lineages. One subset of fibroblasts expresses hematopoietic markers, suggesting their myeloid origin. We validate this finding using single-cell western blot and single-cell RNA-sequencing on genetically labeled myofibroblasts. Using bone marrow transplantation and Cre recombinase-based lineage tracing experiments, we rule out cell fusion events and confirm that hematopoietic lineage cells give rise to a subset of myofibroblasts and rare regenerated adipocytes. In conclusion, our study reveals that wounding induces a high degree of heterogeneity among fibroblasts and recruits highly plastic myeloid cells that contribute to adipocyte regeneration.

The diversity of fibroblasts contributing to wound healing is unclear. Here, the authors use single-cell RNA-sequencing to identify heterogeneity among murine fibroblasts in the wound and find that recruited myeloid cells contribute to adipocyte regeneration during healing.

Macrophage and Fibroblast Interactions in Biomaterial-Mediated Fibrosis

Biomaterial-mediated inflammation and fibrosis remain a prominent challenge in designing materials to support tissue repair and regeneration. Despite the many biomaterial technologies that have been designed to evade or suppress inflammation (i.e., delivery of anti-inflammatory drugs, hydrophobic coatings, etc.), many materials are still subject to a foreign body response, resulting in encapsulation of dense, scar-like extracellular matrix. The primary cells involved in biomaterial-mediated fibrosis are macrophages, which modulate inflammation, and fibroblasts, which primarily lay down new extracellular matrix. While macrophages and fibroblasts are implicated in driving biomaterial-mediated fibrosis, the signaling pathways and spatiotemporal crosstalk between these cell types remain loosely defined. In this review, the role of M1 and M2 macrophages (and soluble cues) involved in the fibrous encapsulation of biomaterials in vivo is investigated, with additional focus on fibroblast and macrophage crosstalk in vitro along with in vitro models to study the foreign body response. Lastly, several strategies that have been used to specifically modulate macrophage and fibroblast behavior in vitro and in vivo to control biomaterial-mediated fibrosis are highlighted.

Peptide SIKVAV-modified chitosan hydrogels promote skin wound healing by accelerating angiogenesis and regulating cytokine secretion

Skin wound healing is complex and involves the processes of many factors, among which angiogenesis and inflammatory responses play important roles. New blood vessels provide nutrition and oxygen for skin wound repair. Cytokines in skin wounds, which include pro-inflammatory and anti-inflammatory factors, can modulate the inflammatory response. Therefore, treatment strategies that promote angiogenesis and modulate the inflammatory response in skin wounds can accelerate skin wound healing. This study explored the effects of peptide Ser-Ile-Lys-Val-Ala-Val (SIKVAV)-modified chitosan hydrogels in skin wound healing. General observation demonstrated that SIKVAV-modified chitosan hydrogels promoted the contraction of skin wounds compared with the negative and positive controls. Masson's trichrome staining indicated that peptide-modified chitosan hydrogels accelerated the deposition of more collagen fibers in the skin wounds compared with the negative and positive controls. Immunohistochemistry assays showed that more myofibroblasts were deposited and more angiogenesis was found in skin wounds treated with peptide-modified chitosan hydrogels compared with the negative and positive controls. In addition, qRT-PCR assays showed that peptide-modified chitosan hydrogels promoted the expression of TGF-β1 (transforming growth factor-β1) mRNA and inhibited the expression of TNF-α (tumor necrosis factor-α) mRNA and IL-1β (Interleukin-1β) mRNA and IL-6 (Interleukin-6) mRNA in skin wounds. Taken together, these results indicate the potential of SIKVAV-modified chitosan hydrogels in skin wound healing as complex biomaterials.

Stem cells derived from burned skin - The future of burn care

BACKGROUND

Thermal injuries affect millions of adults and children worldwide and are associated with high morbidity and mortality. The key determinant for the survival of burns is rapid wound healing. Large wounds exceed intrinsic wound-healing capacities, and the currently available coverage materials are insufficient due to lack of cellularity, availability or immunological rejection.

METHODS

Using the surgically debrided tissue, we isolated viable cells from burned skin. The isolated cells cultured in tissue culture dishes and characterized.

FINDINGS

We report here that debrided burned skin, which is routinely excised from patients and otherwise considered medical waste and unconsciously discarded, contains viable, undamaged cells which show characteristics of mesenchymal skin stem cells. Those cells can be extracted, characterized, expanded, and incorporated into created epidermal-dermal substitutes to promote wound healing in immune-compromised mice and Yorkshire pigs without adverse side effects.

INTERPRETATION

These findings are of paramount importance and provide an ideal cell source for autologous skin regeneration. Furthermore, this study highlights that skin contains progenitor cells resistant to thermal stress. FUND: Canadian Institutes of Health Research # 123336. CFI Leader's Opportunity Fund: Project # 25407 National Institutes of Health 2R01GM087285-05A1. EMHSeed: Fund: 500463, A generous donation from Toronto Hydro. Integra© Life Science Company provided the meshed bilayer Integra© for porcine experiments.