Mice lacking beta6 integrin in skin show accelerated wound repair in dexamethasone impaired wound healing model

Decoding the complexity of delayed wound healing following Enterococcus faecalis infection

Wound infections are highly prevalent and can lead to delayed or failed healing, causing significant morbidity and adverse economic impacts. These infections occur in various contexts, including diabetic foot ulcers, burns, and surgical sites. Enterococcus faecalis is often found in persistent non-healing wounds, but its contribution to chronic wounds remains understudied. To address this, we employed single-cell RNA sequencing (scRNA-seq) on infected wounds in comparison to uninfected wounds in a mouse model. Examining over 23,000 cells, we created a comprehensive single-cell atlas that captures the cellular and transcriptomic landscape of these wounds. Our analysis revealed unique transcriptional and metabolic alterations in infected wounds, elucidating the distinct molecular changes associated with bacterial infection compared to the normal wound healing process. We identified dysregulated keratinocyte and fibroblast transcriptomes in response to infection, jointly contributing to an anti-inflammatory environment. Notably, E. faecalis infection prompted a premature, incomplete epithelial-mesenchymal transition in keratinocytes. Additionally, E. faecalis infection modulated M2-like macrophage polarization by inhibiting pro-inflammatory resolution in vitro, in vivo, and in our scRNA-seq atlas. Furthermore, we discovered macrophage crosstalk with neutrophils, which regulates chemokine signaling pathways, while promoting anti-inflammatory interactions with endothelial cells. Overall, our findings offer new insights into the immunosuppressive role of E. faecalis in wound infections.

Targeting integrin pathways: mechanisms and advances in therapy

Integrins are considered the main cell-adhesion transmembrane receptors that play multifaceted roles as extracellular matrix (ECM)-cytoskeletal linkers and transducers in biochemical and mechanical signals between cells and their environment in a wide range of states in health and diseases. Integrin functions are dependable on a delicate balance between active and inactive status via multiple mechanisms, including protein-protein interactions, conformational changes, and trafficking. Due to their exposure on the cell surface and sensitivity to the molecular blockade, integrins have been investigated as pharmacological targets for nearly 40 years, but given the complexity of integrins and sometimes opposite characteristics, targeting integrin therapeutics has been a challenge. To date, only seven drugs targeting integrins have been successfully marketed, including abciximab, eptifibatide, tirofiban, natalizumab, vedolizumab, lifitegrast, and carotegrast. Currently, there are approximately 90 kinds of integrin-based therapeutic drugs or imaging agents in clinical studies, including small molecules, antibodies, synthetic mimic peptides, antibody-drug conjugates (ADCs), chimeric antigen receptor (CAR) T-cell therapy, imaging agents, etc. A serious lesson from past integrin drug discovery and research efforts is that successes rely on both a deep understanding of integrin-regulatory mechanisms and unmet clinical needs. Herein, we provide a systematic and complete review of all integrin family members and integrin-mediated downstream signal transduction to highlight ongoing efforts to develop new therapies/diagnoses from bench to clinic. In addition, we further discuss the trend of drug development, how to improve the success rate of clinical trials targeting integrin therapies, and the key points for clinical research, basic research, and translational research.

Development and evaluation of drug delivery patch for topical wound healing application

Wound treatment remains a challenge to many clinicians because of the complexities of the wound healing process. With the astonishing progress of biomedical engineering during the past few decades, conventional drug delivery systems have been evolved into smart drug delivery systems with stimuli-responsive characteristics. The objective of this study was to develop and evaluate an electromechanically actuated drug dispensation device which can release active pharmaceutical compound in a controlled fashion. Additive manufacturing was employed to design and fabricate the device. Haptic technology was used to provide stimulation for drug release, and Cicatrin was used to evaluate the drug release patterns of device. Drug release study was comprised of in vitro drug release, static study, and the purpose of this study was to develop a compliance chart for different wound conditions. The effectiveness of shortlisted drug regimen from compliance chart was validated through microbial study and animal studies. The results of animal studies were compared with commercially available drug release systems. The results of drug release studies gave different dose regimens for different wound conditions. The effective dose regimen was able to create 1-cm-wide microbial zone of inhibitions. The wound healing rate of mice for commercially available release system for five consecutive days was 10%, 10%, 20%, 40% and 50% and for test device was 10%, 30%, 60%, 90% and 100%. Hence, the device proved its effectiveness and efficacy of dosage regimen for wound healing applications through in vitro, microbial and in vivo studies. In conclusion, this device proved to be an accurate and specific drug delivery system with improved medication and therapeutic outcomes for personalized medication.

Role of TGF-β in Skin Chronic Wounds: A Keratinocyte Perspective

Chronic wounds are characterized for their incapacity to heal within an expected time frame. Potential mechanisms driving this impairment are poorly understood and current hypotheses point to the development of an unbalanced milieu of growth factor and cytokines. Among them, TGF-β is considered to promote the broadest spectrum of effects. Although it is known to contribute to healthy skin homeostasis, the highly context-dependent nature of TGF-β signaling restricts the understanding of its roles in healing and wound chronification. Historically, low TGF-β levels have been suggested as a pattern in chronic wounds. However, a revision of the available evidence in humans indicates that this could constitute a questionable argument. Thus, in chronic wounds, divergences regarding skin tissue compartments seem to be characterized by elevated TGF-β levels only in the epidermis. Understanding how this aspect affects keratinocyte activities and their capacity to re-epithelialize might offer an opportunity to gain comprehensive knowledge of the involvement of TGF-β in chronic wounds. In this review, we compile existing evidence on the roles played by TGF-β during skin wound healing, with special emphasis on keratinocyte responses. Current limitations and future perspectives of TGF-β research in chronic wounds are discussed.

Integrin αvβ6: Structure, function and role in health and disease

Integrins are cell surface receptors that traditionally mediate cell-to-extracellular matrix and cell-to-cell adhesion. They can, however, also bind a large repertoire of other molecules. Integrin αvβ6 is exclusively expressed in epithelial cells where it can, for example, serve as a fibronectin receptor. However, its hallmark function is to activate transforming growth factor-β1 (TGF-β1) to modulate innate immune surveillance in lungs and skin and along the gastrointestinal tract, and to maintain epithelial stem cell quiescence. The loss of αvβ6 integrin function in mice and humans leads to an altered immune response in lungs and skin, amelogenesis imperfecta, periodontal disease and, in some cases, alopecia. Elevated αvβ6 integrin expression and aberrant TGF-β1 activation and function are associated with organ fibrosis and cancer. Therefore, αvβ6 integrin serves as an attractive target for cancer imaging and for fibrosis and cancer therapy.

Reduced transforming growth factor β1 (TGF-β1) in the repair of airway epithelial cells of children with asthma

BACKGROUND AND OBJECTIVE

Evidence into the role of TGF-β1 in airway epithelial repair in asthma is still controversial. This study tested the hypothesis that the reduced TGF-β1 levels previously observed in paediatric asthmatic airway epithelial cells directly contribute to the dysregulated repair seen in these cells.

METHODS

Primary airway epithelial cells (pAEC) from children with asthma (n = 16) and non-asthmatic subjects (n = 20) were isolated, and subcultured for investigation of TGF-β1 gene and protein via quantitative polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Expression of other associated genes such as integrins αvβ6, αvβ8 and MT1-MMP were also tested. Small interfering RNA (siRNA) was employed to assess the role of TGF-β1 during wound repair.

RESULTS

TGF-β1 gene and protein expression were significantly downregulated in asthmatic pAEC over the course of repair, compared with cells from non-asthmatic children. Messenger RNA (mRNA) expression of TGF-β1 was also directly implicated in non-asthmatic and asthmatic pAEC proliferation over their quiescent counterparts. Small interfering RNA-mediated knockdown of TGF-β1 compromised repair in non-asthmatic pAEC and exacerbated the dysregulated repair seen in asthmatic pAEC. Expression of major TGF-β1 activators of epithelial cells, integrin αvβ6 and αvβ8 was also measured and there was no difference in αvβ6 gene expression between the two cohorts. Although integrin αvβ8 gene expression was significantly higher in asthmatic pAEC, the expression of MT1-MMP (MMP14) which facilitates the αvβ8 mediated TGF-β1 activation was significantly downregulated.

CONCLUSION

Our data has highlighted the importance of TGF-β1 in pAEC wound repair in vitro. The significantly lower levels seen in asthmatic pAEC subsequently contributes to the dysregulated repair observed in these cells.

Transcriptome and ultrastructural changes in dystrophic Epidermolysis bullosa resemble skin aging

The aging process of skin has been investigated recently with respect to mitochondrial function and oxidative stress. We have here observed striking phenotypic and clinical similarity between skin aging and recessive dystrophic Epidermolysis bullosa (RDEB), which is caused by recessive mutations in the gene coding for collagen VII, COL7A1. Ultrastructural changes, defects in wound healing, and inflammation markers are in part shared with aged skin. We have here compared the skin transcriptomes of young adults suffering from RDEB with that of sex‐ and age‐matched healthy probands. In parallel we have compared the skin transcriptome of healthy young adults with that of elderly healthy donors. Quite surprisingly, there was a large overlap of the two gene lists that concerned a limited number of functional protein families. Most prominent among the proteins found are a number of proteins of the cornified envelope or proteins mechanistically involved in cornification and other skin proteins. Further, the overlap list contains a large number of genes with a known role in inflammation. We are documenting some of the most prominent ultrastructural and protein changes by immunofluorescence analysis of skin sections from patients, old individuals, and healthy controls.

Integrin αvβ6 sustains and promotes tumor invasive growth in colon cancer progression

AIM: To detect the mechanism by which colon tumor escapes the growth constraints imposed on normal cells by cell crowding and dense pericellular matrices.

METHODS: An immunohistochemical study of integrin αvβ6 and matrix metalloproteinase-9 (MMP-9) was performed on tissue microarrays of 200 spots, including 100 cases of colon tumors.

RESULTS: High immunoreactivity for αvβ6 (73.7%; 28/38) and MMP-9 (76.5%; 52/68) was observed in invasive tumor portions. Furthermore, the effects of integrin αvβ6 on tumor invasive growth in nude mice were detected. Tumor invasive growth and high expression of both αvβ6 and MMP-9 were only seen in tumors resulting from WiDr cells expressing αvβ6 in the tumorigenicity assay. Flow cytometry was applied to analyze αvβ6 expression in colon cancer WiDr and SW480 cells. The effects of cell density on αvβ6 expression and MMP-9 secretion were also detected by Biotrak MMP-9 activity assay and gelatin zymography assay. High cell density evidently enhanced αvβ6 expression and promoted MMP-9 secretion compared with low density.

CONCLUSION: Integrin αvβ6 sustains and promotes tumor invasive growth in tumor progression via a self-perpetuating mechanism. Integrin ανβ6-mediated MMP-9 secretion facilitates pericellular matrix degradation at high cell density, which provides the basis of invasive growth.

The inflammatory actions of coagulant and fibrinolytic proteases in disease

Aside from their role in hemostasis, coagulant and fibrinolytic proteases are important mediators of inflammation in diseases such as asthma, atherosclerosis, rheumatoid arthritis, and cancer. The blood circulating zymogens of these proteases enter damaged tissue as a consequence of vascular leak or rupture to become activated and contribute to extravascular coagulation or fibrinolysis. The coagulants, factor Xa (FXa), factor VIIa (FVIIa), tissue factor, and thrombin, also evoke cell-mediated actions on structural cells (e.g., fibroblasts and smooth muscle cells) or inflammatory cells (e.g., macrophages) via the proteolytic activation of protease-activated receptors (PARs). Plasmin, the principle enzymatic mediator of fibrinolysis, also forms toll-like receptor-4 (TLR-4) activating fibrin degradation products (FDPs) and can release latent-matrix bound growth factors such as transforming growth factor-β (TGF-β). Furthermore, the proteases that convert plasminogen into plasmin (e.g., urokinase plasminogen activator) evoke plasmin-independent proinflammatory actions involving coreceptor activation. Selectively targeting the receptor-mediated actions of hemostatic proteases is a strategy that may be used to treat inflammatory disease without the bleeding complications of conventional anticoagulant therapies. The mechanisms by which proteases of the coagulant and fibrinolytic systems contribute to extravascular inflammation in disease will be considered in this review.

The Role of TGFβ Signaling in Wound Epithelialization

Significance: Transforming growth factor β (TGFβ) has a crucial role in maintaining skin homeostasis. TGFβ signaling is important for re-epithelialization, inflammation, angiogenesis, and granulation tissue formation during wound healing. This review will discuss the most important findings regarding the role of TGFβ in epidermal maintenance and its restoration after injury. Recent Advances: Latest findings on the role of TGFβ signaling in normal and impaired wound healing, including the role of TGFβ pathway in tissue regeneration observed in super-healer animal models, will be reviewed. Critical Issues: The TGFβ pathway is attenuated in nonhealing wounds. Observed suppression of TGFβ signaling in chronic ulcers may contribute to the loss of tissue homeostasis and the inability of keratinocytes to migrate and close a wound. Future Directions: A better understanding of TGFβ signaling may provide new insights not only in the normal epithelialization process, but also in tissue regeneration. Future studies focused on TGFβ-mediated crosstalk between multiple cell types involved in wound healing may lead to development of novel therapeutic advances for chronic wounds.

G protein coupled receptor transactivation: extending the paradigm to include serine/threonine kinase receptors

The current paradigm of G protein coupled receptor signaling involves a classical pathway being the activation of phospholipase C and the generation of 1,4,5-inositol trisphosphate, signaling through β-arrestin scaffold molecules and the transactivation of tyrosine kinase growth factor receptors. Transactivation greatly expands the range of signaling pathways and responses attributable to the receptor. Recently it has been revealed that G protein coupled receptor agonists can also transactivate the serine/threonine kinase cell surface receptor for transforming growth factor-β (Alk5). This leads to the generation of carboxyl terminal phosphorylated Smad2 which is the immediate downstream product of the activated Alk5. Thus, the current paradigm of G protein coupled signaling can be expanded to include the transactivation of the serine kinase receptor Alk5. These insights expand the possibilities for outcomes of therapeutically targeting GPCRs where more substantive and prolonged actions such as the synthesis of extracellular matrix may be affected.

Effect of propolis on mast cells in wound healing

Wound healing is divided into three phases: inflammatory, proliferative and remodeling. Mast cells participate in all these phases. The aim of the present study was to determine the effects of propolis on the population of mast cells in oral surgical wounds in comparison to the results obtained with dexamethasone. This study was prospective, in vivo, randomized, semiexperimental, quantitative and comparative animal. A circular surgical wound was made on the dorsum of the tongue of 90 hamsters divided into three experimental groups: topical application of 30% propolis alcoholic extract (Group 1); 0.1% dexamethasone in orabase cream (Group 2); and orabase cream alone (Group 3). Applications were performed every 12 h throughout the experiment. The postoperative times for killing of the animals were 1, 3, 7, 14 and 28 days. The Student's t test for independent samples was employed in the statistical analysis. In the inflammatory phase of healing, propolis caused a greater reduction in the number of mast cells on the edge and in the central region of the surgical wound in comparison to dexamethasone. Moreover, the number of mast cells on day 1 was lower in the central region of the wounds treated with the orabase cream alone in comparison to dexamethasone. In conclusion, the anti-inflammatory action of propolis mediated by mast cells was more effective than dexamethasone in the inflammatory phase of healing.

Epithelial integrins with special reference to oral epithelia

Adhesion of epithelium to the extracellular matrix is crucial for the maintenance of systemic and oral health. In the oral cavity, teeth or artificial dental implants penetrate the soft tissue of the gingiva. In this interface, gingival soft tissue needs to be well attached via the epithelial seal to the tooth or implant surface to maintain health. After injury or wounding, epithelial tissue rapidly migrates to form the initial epithelial cover to restore the barrier against infection. These events are crucially dependent on deposition of extracellular matrix and proper activation and function of integrin receptors in the epithelial cells. Recent experimental evidence suggests that epithelial integrins also participate in the regulation of periodontal inflammation. In this review, we will discuss the structure and function of epithelial integrins and their extracellular ligands and elaborate on their potential role in disease and repair processes in the oral cavity.

Integrin β6-deficient mice show enhanced keratinocyte proliferation and retarded hair follicle regression after depilation

Integrin αvβ6 is an epithelial-specific receptor that binds and activates latent transforming growth factor-β1 (TGF-β1). TGF-β1 has been implicated as an endogenous inducer of hair follicle (HF) regression during hair cycling. We hypothesized that αvβ6 integrin-mediated TGF-β1 signaling regulates hair regeneration and HF involution. In wild-type (WT) mice, the expression of integrin αvβ6 was strongly upregulated in the outer root sheath (ORS) during early hair regeneration, and was specifically enhanced in the HF bulge region. Expression gradually decreased in late anagen and remained restricted to the bulge region in the catagen and telogen stage HFs. The first spontaneous hair cycle was not altered in β6 integrin knockout (β6(-/-)) mice. However, after depilation, β6(-/-) mice exhibited retarded HF regression compared with WT controls. β6(-/-) follicles contained significantly higher numbers of proliferating Ki67-positive keratinocytes than WT follicles at an identical cycle stage. The β6(-/-) follicles also demonstrated significantly reduced levels of TGF-β1 expression and Smad2 phosphorylation during early anagen and anagen-catagen transition. Our study indicates that αvβ6 integrin has an important inhibitory role in keratinocyte proliferation in both HFs and interfollicular epidermis. Thus, downregulated TGF-β1 signaling in β6(-/-) mice may affect bulge niche stem cell behavior.

Wound healing activity of the human antimicrobial peptide LL37

Antimicrobial peptides (AMPs) are part of the innate immune system and are generally defined as cationic, amphipathic peptides, with less than 50 amino acids, including multiple arginine and lysine residues. The human cathelicidin antimicrobial peptide LL37 can be found at different concentrations in many different cells, tissues and body fluids and has a broad spectrum of antimicrobial and immunomodulatory activities. The healing of wound is a complex process that involves different steps: hemostasis, inflammation, remodeling/granulation tissue formation and re-epithelialization. Inflammation and angiogenesis are two fundamental physiological conditions implicated in this process. We have recently developed a new method for the expression and purification of recombinant LL37. In this work, we show that the recombinant peptide P-LL37 with a N-terminus proline preserves its immunophysiological properties in vitro and in vivo. P-LL37 neutralized the activation of macrophages by lipopolysaccharide (LPS). Besides, the peptide induced proliferation, migration and tubule-like structures formation by endothelial cells. Wound healing experiments were performed in dexamethasone-treated mice to study the effect of LL37 on angiogenesis and wound regeneration. The topical application of synthetic and recombinant LL37 increased vascularization and re-epithelialization. Taken together, these results clearly demonstrate that LL37 may have a key role in wound regeneration through vascularization.

Skin wound healing in diabetic β6 integrin-deficient mice

Integrin αvβ6 is a heterodimeric cell surface receptor, which is absent from the normal epithelium, but is expressed in wound-edge keratinocytes during re-epithelialization. However, the function of the αvβ6 integrin in wound repair remains unclear. Impaired wound healing in patients with diabetes constitutes a major clinical problem worldwide and has been associated with the accumulation of advanced glycated endproducts (AGEs) in the tissues. AGEs may account for aberrant interactions between integrin receptors and their extracellular matrix ligands such as fibronectin (FN). In this study, we compared healing of experimental excisional skin wounds in wild-type (WT) and β6-knockout (β6(-/-) ) mice with streptozotocin-induced diabetes. Results showed that diabetic β6(-/-) mice had a significant delay in early wound closure rate compared with diabetic WT mice, suggesting that αvβ6 integrin may serve as a protective role in re-epithelialization of diabetic wounds. To mimic the glycosylated wound matrix, we generated a methylglyoxal (MG)-glycated variant of FN. Keratinocytes utilized αvβ6 and β1 integrins for spreading on both non-glycated and FN-MG, but their spreading was reduced on FN-MG. These findings indicated that glycation of FN and possibly other integrin ligands could hamper keratinocyte interactions with the provisional matrix proteins during re-epithelialization of diabetic wounds.

The effect of incorporation of SDF-1alpha into PLGA scaffolds on stem cell recruitment and the inflammatory response

Despite significant advances in the understanding of tissue responses to biomaterials, most implants are still plagued by inflammatory responses which can lead to fibrotic encapsulation. This is of dire consequence in tissue engineering, where seeded cells and bioactive components are separated from the native tissue, limiting the regenerative potential of the design. Additionally, these interactions prevent desired tissue integration and angiogenesis, preventing functionality of the design. Recent evidence supports that mesenchymal stem cells (MSC) and hematopoietic stem cells (HSC) can have beneficial effects which alter the inflammatory responses and improve healing. The purpose of this study was to examine whether stem cells could be targeted to the site of biomaterial implantation and whether increasing local stem cell responses could improve the tissue response to PLGA scaffold implants. Through incorporation of SDF-1alpha through factor adsorption and mini-osmotic pump delivery, the host-derived stem cell response can be improved resulting in 3X increase in stem cell populations at the interface for up to 2 weeks. These interactions were found to significantly alter the acute mast cell responses, reducing the number of mast cells and degranulated mast cells near the scaffold implants. This led to subsequent downstream reduction in the inflammatory cell responses, and through altered mast cell activation and stem cell participation, increased angiogenesis and decreased fibrotic responses to the scaffold implants. These results support that enhanced recruitment of autologous stem cells can improve the tissue responses to biomaterial implants through modifying/bypassing inflammatory cell responses and jumpstarting stem cell participation in healing at the implant interface.

Integrin-TGF-beta crosstalk in fibrosis, cancer and wound healing

Accumulating evidence indicates that there is extensive crosstalk between integrins and TGF-beta signalling. TGF-beta affects integrin-mediated cell adhesion and migration by regulating the expression of integrins, their ligands and integrin-associated proteins. Conversely, several integrins directly control TGF-beta activation. In addition, a number of integrins can interfere with both Smad-dependent and Smad-independent TGF-beta signalling in different ways, including the regulation of the expression of TGF-beta signalling pathway components, the physical association of integrins with TGF-beta receptors and the modulation of downstream effectors. Reciprocal TGF-beta-integrin signalling is implicated in normal physiology, as well as in a variety of pathological processes including systemic sclerosis, idiopathic pulmonary fibrosis, chronic obstructive pulmonary disease and cancer; thus, integrins could provide attractive therapeutic targets to interfere with TGF-beta signalling in these processes.