Myeloid Cells in Cutaneous Wound Repair

IL-4 and IL-13: Regulators and Effectors of Wound Repair

Type 2 immunity mediates protective responses to helminths and pathological responses to allergens, but it also has broad roles in the maintenance of tissue integrity, including wound repair. Type 2 cytokines are known to promote fibrosis, an overzealous repair response, but their contribution to healthy wound repair is less well understood. This review discusses the evidence that the canonical type 2 cytokines, IL-4 and IL-13, are integral to the tissue repair process through two main pathways. First, essential for the progression of effective tissue repair, IL-4 and IL-13 suppress the initial inflammatory response to injury. Second, these cytokines regulate how the extracellular matrix is modified, broken down, and rebuilt for effective repair. IL-4 and/or IL-13 amplifies multiple aspects of the tissue repair response, but many of these pathways are highly redundant and can be induced by other signals. Therefore, the exact contribution of IL-4Rα signaling remains difficult to unravel.

Exosomal IRF1-loaded rat adipose-derived stem cell sheet contributes to wound healing in the diabetic foot ulcers

BACKGROUND

Cell-based therapy has been recognized as a novel technique for the management of diabetic foot ulcers, and cell-sheet engineering leads to improved efficacy in cell transplantation. This study aims to explore the possible molecular mechanism of the rat adipose-derived stem cell (ASC) sheet loaded with exosomal interferon regulatory factor 1 (IRF1) in foot wound healing.

METHODS

Rats were rendered diabetic with streptozotocin, followed by measurement of miR-16-5p expression in wound tissues. Relationship between IRF1, microRNA (miR)-16-5p, and trans-acting transcription factor 5 (SP5) was analyzed using luciferase activity, RNA pull-down, and chromatin immunoprecipitation assays. IRF1 was overexpressed in rat ASCs (rASCs) or loaded onto the rASC sheet, and then exosomes were extracted from rASCs. Accordingly, we assessed the effects of IRF1-exosome or IRF1-rASC sheet on the proliferation and migration of the fibroblasts along with endothelial cell angiogenesis.

RESULTS

miR-16-5p was poorly expressed in the wound tissues of diabetic rats. Overexpression of miR-16-5p promoted fibroblast proliferation and migration as well as endothelial cell angiogenesis, thus expediting wound healing. IRF1 was an upstream transcription factor that could bind to the miR-16-5p promoter and increase its expression. In addition, SP5 was a downstream target gene of miR-16-5p. IRF1-exosome from rASCs or the IRF1-rASC sheet facilitated the foot wound healing in diabetic rats through miR-16-5p-dependent inhibition of SP5.

CONCLUSION

The present study demonstrates that exosomal IRF1-loaded rASC sheet regulates miR-16-5p/SP5 axis to facilitate wound healing in diabetic rats, which aids in development of stem cell-based therapeutic strategies for diabetic foot wounds.

Immune Cells in Cutaneous Wound Healing: A Review of Functional Data from Animal Models

The healing of skin wounds involves the activation and recruitment of various immune cell types, many of which are believed to contribute significantly to different aspects of the repair process. Roles for immune cells have been described in practically all stages of wound healing, including hemostasis, inflammation, proliferation and scar formation/remodeling. Over the last decade, tools to deplete immune cell populations in animal models have become more advanced, leading to a surge in the number of studies examining the function of specific immune cell types in skin repair. In this review, we will summarize what is known about distinct immune cell types in cutaneous wound healing, with an emphasis on data from animal studies in which specific cell types have been targeted.

A Dual-Acting Nitric Oxide Donor and Phosphodiesterase 5 Inhibitor Promotes Wound Healing in Normal Mice and Mice with Diabetes

Chronic wounds affect a large percentage of the population worldwide and cause significant morbidity. Unfortunately, efficient compounds for the treatment of chronic wounds are yet not available. Endothelial dysfunction, which is at least in part a result of compromised nitric oxide production and concomitant reduction in cGMP levels, is a major pathologic feature of chronic wounds. Therefore, we designed and synthesized a compound with a unique dual-acting activity (TOP-N53), acting as a nitric oxide donor and phosphodiesterase 5 inhibitor, and applied it locally to full-thickness skin wounds in healthy and healing-impaired mice with diabetes. TOP-N53 promoted keratinocyte proliferation, angiogenesis, and collagen maturation in healthy mice without accelerating the wound inflammatory response or scar formation. Most importantly, it partially rescued the healing impairment of mice with genetically determined type II diabetes (db/db) by stimulating re-epithelialization and granulation tissue formation, including angiogenesis. In vitro studies with human and murine primary cells showed a positive effect of TOP-N53 on keratinocyte and fibroblast migration, keratinocyte proliferation, and endothelial cell migration and tube formation. These results demonstrate a remarkable healing-promoting activity of TOP-N53 by targeting the major resident cells in the wound tissue.

Bioactive borate glass triggers phenotypic changes in adipose stem cells

A bioactive borate glass, 13-93B3 (B3), has been used successfully in the clinic to treat chronic, nonhealing wounds without scarring. However, the mechanism by which B3 stimulates wound healing is poorly understood. Because adipose stem cells (ASCs) have been shown to have multiple roles in wound repair, we hypothesized that B3 triggers ASCs. In this study, we evaluate the effects of B3 on ASC survival, migration, differentiation, and protein secretion in vitro. In concentrations ≤10 mg/ml, B3 did not affect ASC viability under static conditions. B3 promoted the migration of ASCs but did not increase differentiation into bone or fat. B3 also decreased ASCs secretion of collagen I, PAI-1, MCP-1, DR6, DKK-1, angiogenin, IL-1, IGFBP-6, VEGF, and TIMP-2; increased expression of IL-1R and E-selectin; had a transient decrease in IL-6 secretion; and had a transient increase in bFGF secretion. Together, these results show that B3 alters the protein secretion of ASCs.

Live imaging the foreign body response in zebrafish reveals how dampening inflammation reduces fibrosis

Implanting biomaterials in tissues leads to inflammation and a foreign body response (FBR), which can result in rejection. Here, we live image the FBR triggered by surgical suture implantation in a translucent zebrafish model and compare with an acute wound response. We observe inflammation extending from the suture margins, correlating with subsequent avascular and fibrotic encapsulation zones: sutures that induce more inflammation result in increased zones of avascularity and fibrosis. Moreover, we capture macrophages as they fuse to become multinucleate foreign body giant cells (FBGCs) adjacent to the most pro-inflammatory sutures. Genetic and pharmacological dampening of the inflammatory response minimises the FBR (including FBGC generation) and normalises the status of the tissue surrounding these sutures. This model of FBR in adult zebrafish allows us to live image the process and to modulate it in ways that may lead us towards new strategies to ameliorate and circumvent FBR in humans.This article has an associated First Person interview with the first author of the paper.

Live imaging of wound angiogenesis reveals macrophage orchestrated vessel sprouting and regression

Wound angiogenesis is an integral part of tissue repair and is impaired in many pathologies of healing. Here, we investigate the cellular interactions between innate immune cells and endothelial cells at wounds that drive neoangiogenic sprouting in real time and in vivo. Our studies in mouse and zebrafish wounds indicate that macrophages are drawn to wound blood vessels soon after injury and are intimately associated throughout the repair process and that macrophage ablation results in impaired neoangiogenesis. Macrophages also positively influence wound angiogenesis by driving resolution of anti‐angiogenic wound neutrophils. Experimental manipulation of the wound environment to specifically alter macrophage activation state dramatically influences subsequent blood vessel sprouting, with premature dampening of tumour necrosis factor‐α expression leading to impaired neoangiogenesis. Complementary human tissue culture studies indicate that inflammatory macrophages associate with endothelial cells and are sufficient to drive vessel sprouting via vascular endothelial growth factor signalling. Subsequently, macrophages also play a role in blood vessel regression during the resolution phase of wound repair, and their absence, or shifted activation state, impairs appropriate vessel clearance.

Impact of repeated abdominal surgery on wound healing and myeloid cell dynamics

BACKGROUND

Even though wound dehiscence is a surgical complication, under certain medical conditions, repetition of the laparotomy (LT) (relaparotomy) can become inevitable. In addition to the risks associated with this surgical operation, relaparotomy can interfere with the tissue healing and contribute to the development of chronic wounds.

METHODS

In an experimental relaparotomy wounding model, this study investigated the impact of repeated surgery on wound healing and on the immune cells of myeloid origin.

RESULTS

The first repeat of the LT triggered fibrosis and marginally interfered with the wound healing; however, the second operation completely abrogated the healing process. Splenomegaly was observed as an indicator of the chronic inflammation and the systemic effect of repeated laparotomies. In the blood stream, the spleen, and the liver, these repeated surgeries exhibited a major impact on the CD11b⁺Ly6C⁺Ly6G^- monocytes. On the other hand, especially, whespecially the second relaparotomy resulted in a massive purging of neutrophil granulocytes into the circulation. These CD11b⁺Ly6C⁺Ly6G⁺ neutrophils that were disseminated on repeated abdominal laparotomies had a proinflammatory character that positively influenced T cell proliferation and displayed a high capacity for production of reactive oxygen species.

CONCLUSIONS

The repetition of abdominal LT not only interferes with the wound healing but also contributes to the development of imperfectly healing wounds which have systemic impact on immune compartments.

Élie Metchnikoff (1845-1916): celebrating 100 years of cellular immunology and beyond

The year 2016 marks 100 years since the death of Élie Metchnikoff (1845-1916), the Russian zoologist who pioneered the study of cellular immunology and who is widely credited with the discovery of phagocytosis, for which he was jointly awarded the Nobel Prize in Physiology or Medicine in 1908. However, his long scientific career spanned many disciplines and has had far-reaching effects on modern immunology beyond the study of phagocytosis. In this Viewpoint article, five leading immunologists from the fields of phagocytosis, macrophage biology, leukocyte migration, the microbiota and intravital imaging tell Nature Reviews Immunology how Metchnikoff's work has influenced past, present and future research in their respective fields.