Degradation of Fibronectin and Vitronectin and Vitronectin in Chronic Wound Fluid: Analysis by Cell Blotting, Immunoblotting, and Cell Adhesion Assays

Tissue Regeneration and Remodeling in Rat Models after Application of Hypericum perforatum L. Extract-Loaded Bigels

The wound-healing effect of St. John's Wort (SJW) is mainly attributed to hyperforin (HP), but its low stability restricts its topical administration. This study investigates how "free" HP-rich SJW extract (incorporated into a bigel; B/SJW) and extract "protected" by nanostructured lipid carriers (also included in a biphasic semisolid; B/NLC-SJW) affect tissue regeneration in a rat skin excision wound model. Wound diameter, histological changes, and tissue gene expression levels of fibronectin (Fn), matrix metalloproteinase 8 (MMP8), and tumor necrosis factor-alpha (TNF-α) were employed to quantify the healing progress. A significant wound size reduction was achieved after applying both extract-containing semisolids, but after a 21-day application period, the smallest wound size was observed in the B/NLC-SJW-treated animals. However, the inflammatory response was affected more favorably by the bigel containing the "free" SJW extract, as evidenced by histological studies. Moreover, after the application of B/SJW, the expression of Fn, MMP8, and TNF-α was significantly higher than in the positive control. In conclusion, both bigel formulations exhibited beneficial effects on wound healing in rat skin, but B/SJW affected skin restoration processes in a comprehensive and more efficient way.

KRT17 from skin cells with high glucose stimulation promotes keratinocytes proliferation and migration

Impaired diabetic wound healing is an important issue in diabetic complications. Proliferation and migration of keratinocytes are major processes of skin wound repair after injury. However, hyperkeratosis can affect the speed of wound healing. Based on the results of preliminary experiments on increased KRT17 expression after high glucose stimulation of human skin tissue cells, a cell model of human immortalized keratinocyte (HaCaT) stimulation with different concentrations of KRT17 was established in vitro, and the promotion in cell proliferation and migration were discovered. KRT17 silencing promoted diabetic wound healing in the db/db diabetic wound model. Transcriptome sequencing (RNA-seq) was performed on HaCaT cells after KRT17 stimulation, and analysis showed significant enrichment in the PI3K-AKT signaling pathway, in which the regulation of cell c-MYB mRNA, a key molecule regulating cell proliferation and migration, was significantly upregulated. In vitro assays showed increased c-MYB expression and enhanced pAKT activity after HaCaT cell stimulation by KRT17. We speculate that KRT17 is upregulated under high glucose and promotes keratinocyte proliferation and migration caused hyperkeratosis, through the c-MYB/PI3K-AKT pathway, contributing to delayed wound healing.

Evolution of the Chronic Venous Leg Ulcer Microenvironment and Its Impact on Medical Devices and Wound Care Therapies

Studies have reported that the constituents of the wound microenvironment are likely to have critical roles in the degradation and fate of the polymeric matrix and the compounds dissolved in the wound dressing matrix. Thus, chronic wound assessment and the design of effective medical devices and drug products for wound care partly rely on an in-depth understanding of the wound microenvironment. The main aim of this review is to identify and discuss the different stages of chronic wound progression, focusing on the changes in the biochemical composition of the wound microenvironment, with particular attention given to venous leg ulcers (VLUs), as they are one of the most prevalent chronic wound aetiologies. The pathophysiology of venous ulcers is detailed, followed by a thorough review of what is known about the VLU microenvironment and its changes as a function of the evolution of the VLU. Simulating conditions for VLU are then discussed with the view of highlighting potentially relevant simulating media as a function of VLU evolution for a better assessment of biological safety, in particular medical devices intended to be in contact with these wounds.

The basement membrane in epidermal polarity, stemness, and regeneration

The epidermis is a specialized epithelium that constitutes the outermost layer of the skin, and it provides a protective barrier against environmental assaults. Primarily consisting of multilayered keratinocytes, the epidermis is continuously renewed by proliferation of stem cells and the differentiation of their progeny, which undergo terminal differentiation as they leave the basal layer and move upward toward the surface, where they die and slough off. Basal keratinocytes rest on a basement membrane at the dermal-epidermal junction that is composed of specific extracellular matrix proteins organized into interactive and mechanically supportive networks. Firm attachment of basal keratinocytes, and their dynamic regulation via focal adhesions and hemidesmosomes, is essential for maintaining major skin processes, such as self-renewal, barrier function, and resistance to physical and chemical stresses. The adhesive integrin receptors expressed by epidermal cells serve structural, signaling, and mechanosensory roles that are critical for epidermal cell anchorage and tissue homeostasis. More specifically, the basement membrane components play key roles in preserving the stem cell pool, and establishing cell polarity cues enabling asymmetric cell divisions, which result in the transition from a proliferative basal cell layer to suprabasal cells committed to terminal differentiation. Finally, through a well-regulated sequence of synthesis and remodeling, the components of the dermal-epidermal junction play an essential role in regeneration of the epidermis during skin healing. Here too, they provide biological and mechanical signals that are essential to the restoration of barrier function.

Wound fluid sampling methods for proteomic studies: A scoping review

Understanding why some wounds are hard to heal is important for improving care and developing more effective treatments. The method of sample collection used is an integral step in the research process and thus may affect the results obtained. The primary objective of this study was to summarise and map the methods currently used to sample wound fluid for protein profiling and analysis. Eligible studies were those that used a sampling method to collect wound fluid from any human wound for analysis of proteins. A search for eligible studies was performed using MEDLINE, Embase and CINAHL Plus in May 2020. All references were screened for eligibility by one reviewer, followed by discussion and consensus with a second reviewer. Quantitative data were mapped and visualised using appropriate software and summarised via a narrative summary. After screening, 280 studies were included in this review. The most commonly used group of wound fluid collection methods were vacuum, drainage or use of other external devices, with surgical wounds being the most common sample source. Other frequently used collection methods were extraction from absorbent materials, collection beneath an occlusive dressing and direct collection of wound fluid. This scoping review highlights the variety of methods used for wound fluid collection. Many studies had small sample sizes and short sample collection periods; these weaknesses have hampered the discovery and validation of novel biomarkers. Future research should aim to assess the reproducibility and feasibility of sampling and analytical methods for use in larger longitudinal studies.

Hyaluronan, Transforming Growth Factor β, and Extra Domain A-Fibronectin: A Fibrotic Triad

Significance: Inflammation is a critical aspect of injury repair. Nonresolving inflammation, however, is perpetuated by the local generation of extracellular matrix-derived damage-associated molecular pattern molecules (DAMPs), such as the extra domain A (EDA) isoform of fibronectin and hyaluronic acid (HA) that promote the eventual acquisition of a fibrotic response. DAMPs contribute to the inflammatory environment by engaging Toll-like, integrin, and CD44 receptors while stimulating transforming growth factor (TGF)-β signaling to activate a fibroinflammatory genomic program leading to the development of chronic disease. Recent Advances: Signaling through TLR4, CD44, and the TGF-β pathways impact the amplitude and duration of the innate immune response to endogenous DAMPs synthesized in the context of tissue injury. New evidence indicates that crosstalk among these three networks regulates phase transitions as well as the repertoire of expressed genes in the wound healing program determining, thereby, repair outcomes. Clarifying the molecular mechanisms underlying pathway integration is necessary for the development of novel therapeutics to address the spectrum of fibroproliferative diseases that result from maladaptive tissue repair. Critical Issues: There is an increasing appreciation for the role of DAMPs as causative factors in human fibroinflammatory disease regardless of organ site. Defining the involved intermediates essential for the development of targeted therapies is a daunting effort, however, since various classes of DAMPs activate different direct and indirect signaling pathways. Cooperation between two matrix-derived DAMPs, HA, and the EDA isoform of fibronectin, is discussed in this review as is their synergy with the TGF-β network. This information may identify nodes of signal intersection amenable to therapeutic intervention. Future Directions: Clarifying mechanisms underlying the DAMP/growth factor signaling nexus may provide opportunities to engineer the fibroinflammatory response to injury and, thereby, wound healing outcomes. The identification of shared and unique DAMP/growth factor-activated pathways is critical to the design of optimized tissue repair therapies while preserving the host response to bacterial pathogens.

Fibronectin in development and wound healing

Fibronectin structure and composition regulate contextual cell signaling. Recent advances have been made in understanding fibronectin and its role in tissue organization and repair. This review outlines fibronectin splice variants and their functions, evaluates potential therapeutic strategies targeting or utilizing fibronectin, and concludes by discussing potential future directions to modulate fibronectin function in development and wound healing.

Structure-guided design, generation, and biofunction of PEGylated fibroblast growth factor 2 variants for wound healing

Fibroblast growth factor 2 (FGF2) plays an important role in multiple physiological functions such as tissue repair. However, FGF2 has a short half-life in vivo due to protease degradation, thus limiting its clinical application. Traditional PEGylation has typically focused on the N-terminal α-amino group of FGF2. These modifications do not consider potential effects on protein function or structure, and sometimes lead to decreased bioactivity. In this study, we generated three PEGylated FGF2 variants based on the structure of the FGF2-FGFR-heparin ternary complex via gene mutation and PEGylation, and investigated the effects of these PEGylated sites on protein stability and bioactivity. Compared with native FGF2, all PEG-FGF2 conjugates exhibited significantly improved stability. Conjugates PEGylated at a site separated from both binding regions more effectively promoted proliferation, migration and angiogenesis than FGF2 in vitro, and exhibited excellent wound healing activity in vivo, making these conjugates potential therapeutic candidates for wound healing. Computer-assisted modification based on structure reveals the detailed structural characteristics of proteins, allowing efficient protein modification for improved stability and activity. This structure-guided PEGylation offers a more reliable modification strategy and should be applied for the rational design of protein-based therapeutics.

Fibronectin-derived Epiviosamines enhance PDGF-BB-stimulated human dermal fibroblast migration in vitro and granulation tissue formation in vivo

Fibronectin (FN) is a multimodular glycoprotein that is a critical component of the extracellular matrix (ECM) anlage during embryogenesis, morphogenesis, and wound repair. Our laboratory has previously described a family of FN-derived peptides collectively called "epiviosamines" that enhance platelet-derived growth factor-BB (PDGF-BB)-driven tissue cell survival, speed burn healing, and reduce scarring. In this study, we used an agarose drop outmigration assay to report that epiviosamines can enhance PDGF-BB-stimulated adult human dermal fibroblast (AHDF) outmigration in a dose-dependent manner. Furthermore, these peptides can, when delivered topically, stimulate granulation tissue formation in vivo. A thiol-derivatized hyaluronan hydrogel cross-linked with polyethyleneglycol diacrylate (PEGDA) was used to topically deliver a cyclized epiviosamine: cP12 and a cyclized engineered variant of cP12 termed cNP8 to porcine, full-thickness, excisional wounds. Both cP12 and cNP8 exhibited dose-dependent increases in granulation tissue formation at day 4, with 600 μM cNP8 significantly enhancing new granulation tissue compared to vehicle alone. In contrast to previous studies, this study suggests that epiviosamines can be used to increase granulation tissue formation without an exogenous supply of PDGF-BB or any cell-binding peptides. Thus, epiviosamine may be useful topically to increase granulation tissue formation in acute wounds.

Re-epithelialization of adult skin wounds: Cellular mechanisms and therapeutic strategies

Cutaneous wound healing in adult mammals is a complex multi-step process involving overlapping stages of blood clot formation, inflammation, re-epithelialization, granulation tissue formation, neovascularization, and remodelling. Re-epithelialization describes the resurfacing of a wound with new epithelium. The cellular and molecular processes involved in the initiation, maintenance, and completion of epithelialization are essential for successful wound closure. A variety of modulators are involved, including growth factors, cytokines, matrix metalloproteinases, cellular receptors, and extracellular matrix components. Here, we focus on cellular mechanisms underlying keratinocyte migration and proliferation during epidermal closure. Inability to re-epithelialize is a clear indicator of chronic non-healing wounds, which fail to proceed through the normal phases of wound healing in an orderly and timely manner. This review summarizes the current knowledge regarding the management and treatment of acute and chronic wounds, with a focus on re-epithelialization, offering some insights into novel future therapies.

The therapeutic potential of the insect metalloproteinase inhibitor against infections caused by Pseudomonas aeruginosa

OBJECTIVES

The objective of this study was to investigate the therapeutic potential of the insect metalloproteinase inhibitor (IMPI) from Galleria mellonella, the only known specific inhibitor of M4 metalloproteinases.

METHODS

The fusion protein IMPI-GST (glutathione-S-transferase) was produced by fermentation in Escherichia coli and was tested for its ability to inhibit the proteolytic activity of the M4 metalloproteinases thermolysin and Pseudomonas elastase (PE), the latter a key virulence factor of the wound-associated and antibiotic-resistant pathogen Pseudomonas aeruginosa. We also tested the ability of IMPI to inhibit the secretome (Sec) of a P. aeruginosa strain obtained from a wound.

KEY FINDINGS

We found that IMPI-GST inhibited thermolysin and PE in vitro and increased the viability of human keratinocytes exposed to Sec by inhibiting detachment caused by changes in cytoskeletal morphology. IMPI-GST also improved the cell migration rate in an in vitro wound assay and reduced the severity of necrosis caused by Sec in an ex vivo porcine wound model.

CONCLUSIONS

The inhibition of virulence factors is a novel therapeutic approach against antibiotic resistant bacteria. Our results indicate that IMPI is a promising drug candidate for the treatment of P. aeruginosa infections.

Skin-permeable liposome improved stability and permeability of bFGF against skin of mice with deep second degree scald to promote hair follicle neogenesis through inhibition of scar formation

Excessive deposition of extracellular matrix (ECM) usually resulted in scar formation during wound healing, which caused skin dysfunction, such as hair loss. Basic fibroblast growth factor (bFGF) was very helpful for promoting hair follicle neogenesis and regulating the remodeling of ECM during wound healing. Because of its poor stability in wound fluids and low permeability against the dense wound scar, the repairing quality of bFGF on wound was hindered largely in clinical practice. To overcome these drawbacks, herein, a novel liposome with silk fibroin hydrogel core (bFGF-SF-LIP) was firstly prepared to stabilize bFGF, followed by insertion of laurocapam, a permeation enhancer, into the liposomal membrane to construct a skin-permeable liposome (SP-bFGF-SF-LIP). The encapsulated efficiency of bFGF was reaching to nearly 90% when ratio of drug/lipids above 1:300, and it activity was not compromised by laurocapam. SP-bFGF-SF-LIP exhibited a hydrodynamic diameter of 103.3 nm and Zeta potential of -2.31 mV. The stability of the encapsulated bFGF in wound fluid was obviously enhanced. After 24 h of incubation with wound fluid containing MMP-9, the remaining bFGF was as high as 65.4 ± 0.5% for SP-bFGF-SF-LIP, while only 2.1 ± 0.2% of free bFGF was remained. The skin-permeability of bFGF was significantly enhanced by SP-bFGF-SF-LIP and most of the encapsulated bFGF penetrated into the dermis. After treatment with SP-bFGF-SF-LIP, the morphology of hair follicle at wound zone was obviously improved and the hair regrew on the deep second scald mice model. The therapeutic mechanism was highly associated with inhibiting scar formation and promoting vascular growth in dermis. Conclusively, SP-bFGF-SF-LIP may a potential option to improve wound healing with high-quality.

Protease activity as a prognostic factor for wound healing in venous leg ulcers

BACKGROUND

Venous leg ulcers (VLUs) are a common type of complex wound that have a negative impact on people's lives and incur high costs for health services and society. It has been suggested that prolonged high levels of protease activity in the later stages of the healing of chronic wounds may be associated with delayed healing. Protease modulating treatments have been developed which seek to modulate protease activity and thereby promote healing in chronic wounds.

OBJECTIVES

To determine whether protease activity is an independent prognostic factor for the healing of venous leg ulcers.

SEARCH METHODS

In February 2018, we searched the following databases: Cochrane Central Register of Controlled Trials (CENTRAL), Ovid MEDLINE, Ovid Embase and CINAHL.

SELECTION CRITERIA

We included prospective and retrospective longitudinal studies with any follow-up period that recruited people with VLUs and investigated whether protease activity in wound fluid was associated with future healing of VLUs. We included randomised controlled trials (RCTs) analysed as cohort studies, provided interventions were taken into account in the analysis, and case-control studies if there were no available cohort studies. We also included prediction model studies provided they reported separately associations of individual prognostic factors (protease activity) with healing. Studies of any type of protease or combination of proteases were eligible, including proteases from bacteria, and the prognostic factor could be examined as a continuous or categorical variable; any cut-off point was permitted. The primary outcomes were time to healing (survival analysis) and the proportion of people with ulcers completely healed; the secondary outcome was change in ulcer size/rate of wound closure. We extracted unadjusted (simple) and adjusted (multivariable) associations between the prognostic factor and healing.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for inclusion at each stage, and undertook data extraction, assessment of risk of bias and GRADE assessment. We collected association statistics where available. No study reported adjusted analyses: instead we collected unadjusted results or calculated association measures from raw data. We calculated risk ratios when both outcome and prognostic factor were dichotomous variables. When the prognostic factor was reported as continuous data and healing outcomes were dichotomous, we either performed regression analysis or analysed the impact of healing on protease levels, analysing as the standardised mean difference. When both prognostic factor and outcome were continuous data, we reported correlation coefficients or calculated them from individual participant data.We displayed all results on forest plots to give an overall visual representation. We planned to conduct meta-analyses where this was appropriate, otherwise we summarised narratively.

MAIN RESULTS

We included 19 studies comprising 21 cohorts involving 646 participants. Only 11 studies (13 cohorts, 522 participants) had data available for analysis. Of these, five were prospective cohort studies, four were RCTs and two had a type of case-control design. Follow-up time ranged from four to 36 weeks. Studies covered 10 different matrix metalloproteases (MMPs) and two serine proteases (human neutrophil elastase and urokinase-type plasminogen activators). Two studies recorded complete healing as an outcome; other studies recorded partial healing measures. There was clinical and methodological heterogeneity across studies; for example, in the definition of healing, the type of protease and its measurement, the distribution of active and bound protease species, the types of treatment and the reporting of results. Therefore, meta-analysis was not performed. No study had conducted multivariable analyses and all included evidence was of very low certainty because of the lack of adjustment for confounders, the high risk of bias for all studies except one, imprecision around the measures of association and inconsistency in the direction of association. Collectively the research indicated complete uncertainty as to the association between protease activity and VLU healing.

AUTHORS' CONCLUSIONS

This review identified very low validity evidence regarding any association between protease activity and VLU healing and there is complete uncertainty regarding the relationship. The review offers information for both future research and systematic review methodology.

Immune Regulation of Skin Wound Healing: Mechanisms and Novel Therapeutic Targets

Significance: The immune system plays a central role in orchestrating the tissue healing process. Hence, controlling the immune system to promote tissue repair and regeneration is an attractive approach when designing regenerative strategies. This review discusses the pathophysiology of both acute and chronic wounds and possible strategies to control the immune system to accelerate chronic wound closure and promote skin regeneration (scar-less healing) of acute wounds. Recent Advances: Recent studies have revealed the key roles of various immune cells and immune mediators in skin repair. Thus, immune components have been targeted to promote chronic wound repair or skin regeneration and several growth factors, cytokines, and biomaterials have shown promising results in animal models. However, these novel strategies are often struggling to meet efficacy standards in clinical trials, partly due to inadequate drug delivery systems and safety concerns. Critical Issues: Excess inflammation is a major culprit in the dysregulation of normal wound healing, and further limiting inflammation effectively reduces scarring. However, current knowledge is insufficient to efficiently control inflammation and specific immune cells. This is further complicated by inadequate drug delivery methods. Future Directions: Improving our understanding of the molecular pathways through which the immune system controls the wound healing process could facilitate the design of novel regenerative therapies. Additionally, better delivery systems may make current and future therapies more effective. To promote the entry of current regenerative strategies into clinical trials, more evidence on their safety, efficacy, and cost-effectiveness is also needed.

Combined Topical Growth Factor and Protease Inhibitor in Chronic Wound Healing: Protocol for a Randomized Controlled Proof-of-Concept Study

Background

Leg ulcers due to venous disease are chronic wounds that can take 6 or more months to heal. Growth factors have been used to try and improve this healing; however, many such studies have failed, and that is thought to be due to enzymes in the wound that degrade the growth factors and prevent them from working.

Objective

This is a proof-of-concept study that will evaluate the treatment of chronic leg ulcers with topically applied growth factors that are combined with a therapy to prevent their inactivation in the wound. This combined therapy has the potential to speed up the healing of these wounds and thereby improve the quality of life of patients and reduce the costs to the health system.

Methods

This will be a double-blind, placebo-controlled, randomized controlled proof-of-concept study comparing growth factor with protease inhibitor wound dressings to growth factors with standard wound dressings.

Results

The project was funded by the Canadian Institutes for Health Research and enrollment is expected to be initiated in 2018. It is expected that results will be available in 2021.

Conclusions

It is expected that the results of this trial will inform as to whether modifying the wound environment through the use of protease inhibitors increases the effectiveness of topically applied growth factors in the healing of chronic wounds.

Trial Registration

ClinicalTrials.gov NCT02845466; https://clinicaltrials.gov/ct2/show/NCT02845466 (Archived by WebCite at http://www.webcitation.org/6yOPhSBUA)

Xanthine Oxidoreductase: A Novel Therapeutic Target for the Treatment of Chronic Wounds?

Significance: Chronic wounds are a major burden to patients and to healthcare systems worldwide. These wounds are difficult to heal and treatment is often lengthy and expensive. This has led to research efforts focussed on the wound environment attempting to understand the underlying pathological mechanisms of impaired wound healing. While some of this research has translated to advancements in wound therapies and implementation of new treatment options, chronic wounds remain a significant challenge to treat. Thus, identification of effective, low-cost, advanced wound therapies that enhance healing rates of these problematic wounds is still essential. Recent Advances and Critical Issues: Xanthine oxidoreductase (XOR), a molybdoflavin enzyme, is emerging as an important source of reactive oxygen species (ROS) in various pathologies, including diabetes and chronic wounds. XOR has recently been shown to be upregulated in chronic wounds, stimulating the overproduction of ROS during dysfunctional wound healing. XOR-induced ROS can amplify and potentiate inflammation in the wound environment further delaying wound closure. Future Directions: The detrimental role of XOR in impaired healing indicates it may be a therapeutic target. Targeted inhibition of XOR has been shown to reduce the expression and activity of this enzyme in diabetic wound models. In turn, this resulted in a significant decrease in ROS levels in the wound environment and improved wound healing. Therefore, repurposing existing XOR inhibitors that are approved for human use may be able to restore homeostasis at the wound site and enable damaged tissue to return to normal healing.

Epidermal Stem Cells in Skin Wound Healing

Significance: Skin serves as a protective barrier for mammals. Epidermal stem cells are responsible for maintaining skin homeostasis. When cutaneous injuries occur, skin homeostasis and integrity are damaged, leading to dire consequences such as acute, chronic, or infected wounds. Skin wound healing is an intrinsic self-saving chain reaction, which is crucial to facilitating the replacement of damaged or lost tissue. Recent Advances: An immense amount of research has uncovered the underlying mechanisms behind the complex and highly regulated wound healing process. In this review, we will dissect the biological process of adult skin wound healing and emphasize the importance of epidermal stem cells during the wound healing. Critical Issues: We will comprehensively discuss the current clinical practices used on patients with cutaneous wounds, including both traditional skin grafting procedures and advanced grafting techniques with cultured skin stem cells. The majority of these leading techniques still retain some deficiencies during clinical use. Moreover, the regeneration of skin appendages after severe injuries remains a challenge in treatment. Future Directions: Understanding epidermal stem cells and their essential functions during skin wound healing are fundamental components behind the development of clinical treatment on patients with cutaneous wounds. It is important to improve the current standard of care and to develop novel techniques improving patient outcomes and long-term rehabilitation, which should be the goals of future endeavors in the field of skin wound healing.

Oxidative stress and antioxidant strategies in dermatology

Oxidative stress results from a prooxidant-antioxidant imbalance, leading to cellular damage. It is mediated by free radicals, such as reactive oxygen species or reactive nitrogen species, that are generated during physiological aerobic metabolism and pathological inflammatory processes. Skin serves as a protective organ that plays an important role in defending both external and internal toxic stimuli and maintaining homeostasis. It is becoming increasingly evident that oxidative stress is involved in numerous skin diseases and that antioxidative strategies can serve as effective and easy methods for improving these conditions. Herein, we review dysregulated antioxidant systems and antioxidative therapeutic strategies in dermatology.

Altered ECM deposition by diabetic foot ulcer-derived fibroblasts implicates fibronectin in chronic wound repair

Current chronic wound treatments often fail to promote healing of diabetic foot ulcers (DFU), leading to amputation and increased patient morbidity. A critical mediator of proper wound healing is the production, assembly, and remodeling of the extracellular matrix (ECM) by fibroblasts. However, little is known about how these processes are altered in fibroblasts within the DFU microenvironment. Thus, we investigated the capacity of multiple, primary DFU-derived fibroblast strains to express, produce, and assemble ECM proteins compared to diabetic patient-derived fibroblasts and healthy donor-derived fibroblasts. Gene expression microarray analysis showed differential expression of ECM and ECM-regulatory genes by DFU-derived fibroblasts which translated to functional differences in a 3D in vitro ECM tissue model. DFU-derived fibroblasts produced thin, fibronectin-rich matrices, and responded abnormally when challenged with transforming growth factor-beta, a key regulator of matrix production during healing. These results provide novel evidence that DFU-derived fibroblasts contribute to the defective matrices of DFUs and chronic wound pathogenesis.

Self-Assembled Wound Dressings Silence MMP-9 and Improve Diabetic Wound Healing In Vivo

The direct local delivery of short interfering RNA (siRNA) into target tissues presents a real solution to several complex medical conditions that today lack efficacious therapies. The development of an ultrathin polymer coating is described to sustain the delivery of siRNA for up to 2 weeks in vitro and in vivo. This technology successfully reduces the expression of MMP-9 within the wounds of diabetic mice, significantly accelerating the wound healing process and improving the quality of tissue formed.

Retention of Endogenous Viable Cells Enhances the Anti-Inflammatory Activity of Cryopreserved Amnion

Objective: Human amniotic membrane (hAM) has been used to treat wounds for more than 100 years. However, widespread use of fresh hAM has been limited due to its short shelf life and safety concerns. To overcome these concerns, different preservation methods have been introduced. The majority of these methods result in devitalized hAM (dev-hAM). Recently, we developed a cryopreservation method that retains all hAM components intact (int-hAM), including viable endogenous cells. To understand the advantages of retaining viable cells in preserved hAM, we compared the anti-inflammatory properties of int-hAM and dev-hAM.

Approach: The tissue composition of int-hAM and dev-hAM was compared with fresh hAM through histology and cell viability analysis. We also evaluated the ability of int-hAM and dev-hAM to regulate tumor necrosis factor-α (TNF-α), interleukin-1α (IL-1α), and IL-10 release when co-cultured with immune cells; to produce prostaglandin E2 (PGE2) on TNF-α stimulation; and to inhibit proteases.

Results: Int-hAM maintained the structural and cellular integrity of fresh hAM. Int-hAM had >80% cell viability post-thaw and remained viable for at least a week in culture. Viable cells were not detected in dev-hAM. Compared with dev-hAM, int-hAM showed significantly greater downregulation of TNF-α and IL-1α, upregulation of PGE2 and IL-10, and stronger inhibition of collagenase.

Innovation and Conclusion: A new cryopreservation method has been developed to retain all native components of hAM. For the first time, we show that viable endogenous cells significantly augment the anti-inflammatory activity of cryopreserved hAM.

Wound repair: role of immune-epithelial interactions

The epithelium serves as a highly selective barrier at mucosal surfaces. Upon injury, epithelial wound closure is orchestrated by a series of events that emanate from the epithelium itself as well as by the temporal recruitment of immune cells into the wound bed. Epithelial cells adjoining the wound flatten out, migrate, and proliferate to rapidly cover denuded surfaces and re-establish mucosal homeostasis. This process is highly regulated by proteins and lipids, proresolving mediators such as Annexin A1 protein and resolvins released into the epithelial milieu by the epithelium itself and infiltrating innate immune cells including neutrophils and macrophages. Failure to achieve these finely tuned processes is observed in chronic inflammatory diseases that are associated with non-healing wounds. An improved understanding of mechanisms that mediate repair is important in the development of therapeutics aimed to promote mucosal wound repair.

Proteolysis of decellularized extracellular matrices results in loss of fibronectin and cell binding activity

Excessive inflammation in the chronic wound bed is believed to result in increased fibronectin (FN) proteolysis and poor tissue repair. However, FN fragments can prime the immune response and result in higher protease levels. The reciprocity between FN proteolysis and inflammation makes it challenging to determine the specific contribution of FN proteolysis in the extracellular matrix (ECM) on tissue responses. We studied the impact of proteolysis of decellularized extracellular matrices (dECMs) obtained from NIH 3T3 mouse fibroblasts on FN level and activity. The dECMs were treated with α chymotrypsin and proteolysis was stopped at different time points. The protease solution was obtained, the remaining dECM was scrapped and examined by immunoblotting and Bicinchoninic Acid assays. Fibronectin was 9.4 ± 1.8% of the total protein content in the dECM but was more susceptible to proteolysis. After 15 min of protease treatment there was a 67.6% and 11.1% decrease in FN and total protein, respectively, in the dECMs. Fibronectin fragments were present both in the proteolysis solution and in the dECM. Cell adhesion, spreading and actin extensions on dECMs decreased with increasing proteolysis time. Interestingly, the solutions obtained after proteolysis of the dECMs supported cell adhesion and spreading in a time dependent manner, thus demonstrating the presence of FN cell binding activity in the protease solution of dECMs. This study demonstrates the susceptibility of FN in the ECM to proteolysis and the resulting loss of cell adhesion due to the decrease of FN activity and places weight on bioengineering strategies to stabilize FN against proteolysis.

Serpina3n accelerates tissue repair in a diabetic mouse model of delayed wound healing

Chronic, non-healing wounds are a major complication of diabetes and are characterized by chronic inflammation and excessive protease activity. Although once thought to function primarily as a pro-apoptotic serine protease, granzyme B (GzmB) can also accumulate in the extracellular matrix (ECM) during chronic inflammation and cleave ECM proteins that are essential for proper wound healing, including fibronectin. We hypothesized that GzmB contributes to the pathogenesis of impaired diabetic wound healing through excessive ECM degradation. In the present study, the murine serine protease inhibitor, serpina3n (SA3N), was administered to excisional wounds created on the dorsum of genetically induced type-II diabetic mice. Wound closure was monitored and skin wound samples were collected for analyses. Wound closure, including both re-epithelialization and contraction, were significantly increased in SA3N-treated wounds. Histological and immunohistochemical analyses of SA3N-treated wounds revealed a more mature, proliferative granulation tissue phenotype as indicated by increased cell proliferation, vascularization, fibroblast maturation and differentiation, and collagen deposition. Skin homogenates from SA3N-treated wounds also exhibited greater levels of full-length intact fibronectin compared with that of vehicle wounds. In addition, GzmB-induced detachment of mouse embryonic fibroblasts correlated with a rounded and clustered phenotype that was prevented by SA3N. In summary, topical administration of SA3N accelerated wound healing. Our findings suggest that GzmB contributes to the pathogenesis of diabetic wound healing through the proteolytic cleavage of fibronectin that is essential for normal wound closure, and that SA3N promotes granulation tissue maturation and collagen deposition.

Expression and integrity of dermatopontin in chronic cutaneous wounds: a crucial factor in impaired wound healing

Chronic cutaneous wound (CCW) is a major health care burden wherein the healing process is slow or rather static resulting in anatomical and functional restriction of the damaged tissue. Dysregulated expression and degradation of matrix proteins, growth factors and cytokines contribute to the disrupted and uncoordinated healing process of CCW. Therefore, therapeutic approaches for effective management of CCW should be focused towards identifying and manipulating the molecular defects, such as reduced bioavailability of the pro-healing molecules and elevated activity of proteases. This study essentially deals with assessing the expression and integrity of an extracellular matrix protein, Dermatopontin (DPT), in CCW using real-time quantitative reverse transcriptase PCR and immunological techniques. The results indicate that, despite DPT's high mRNA expression, the protein levels are markedly reduced in both CCW tissue and its exudate. To elucidate the cause for this contradiction in mRNA and protein levels, the stability of DPT is analyzed in the presence of wound exudates and various proteases that are naturally elevated in CCW. DPT was observed to be degraded at higher rates when incubated with certain recombinant proteases or chronic wound exudate. In conclusion, the susceptibility of DPT protein to specific proteases present at high levels in the wound milieu resulted in the degradation of DPT, thus leading to impaired healing response in CCW.

Integrin Regulation of Epidermal Functions in Wounds

Significance: Integrins are bidirectional signaling receptors for extracellular matrix that regulate both inside-out signaling that controls keratinocyte-mediated changes to the wound microenvironment and outside-in signaling that controls keratinocyte responses to microenvironmental changes. As such, integrins represent attractive therapeutic targets for treatment of chronic wounds or general promotion of wound healing. Advances in wound management are particularly important as the elderly and diabetic populations within the United States continue to grow. Recent Advances: Although integrins are best known for mediating cell adhesion and migration, integrins in wound epidermis also control cell survival, proliferation, matrix remodeling, and paracrine crosstalk to other cellular compartments of the wound. Importantly, the concept of targeting integrins in the clinic has been established for treatment of certain cancers and other diseases, laying the groundwork for similar exploitation of integrins as targets to treat chronic wounds. Critical Issues: Despite their attractiveness as therapeutic targets, integrins have complex roles in wound healing that are impacted by both their own expression and a highly dynamic wound microenvironment that determines ligand availability. Therefore, identifying relevant integrin ligands in the wound and understanding both distinct and overlapping functions that different integrins play in the epidermis will be critical to determine their precise roles in wound healing. Future Directions: Future research should focus on gaining a thorough understanding of the highly coordinated functions of different integrins in wound epidermis, and on determining which of these functions go awry in pathological wounds. This focus should facilitate development of integrin-targeting therapeutics for treating chronic wounds.

Fibronectin in tissue regeneration: timely disassembly of the scaffold is necessary to complete the build

Tissue injury initiates extracellular matrix molecule expression, including fibronectin production by local cells and fibronectin leakage from plasma. To benefit tissue regeneration, fibronectin promotes opsonization of tissue debris, migration, proliferation, and contraction of cells involved in the healing process, as well as angiogenesis. When regeneration proceeds, the fibronectin matrix is fully degraded. However, in a diseased environment, fibronectin clearance is often disturbed, allowing structural variants to persist and contribute to disease progression and failure of regeneration. Here, we discuss first how fibronectin helps tissue regeneration, with a focus on normal cutaneous wound healing as an example of complete tissue recovery. Then, we continue to argue that, although the fibronectin matrix generated following cartilage and central nervous system white matter (myelin) injury initially benefits regeneration, fibronectin clearance is incomplete in chronic wounds (skin), osteoarthritis (cartilage), and multiple sclerosis (myelin). Fibronectin fragments or aggregates persist, which impair tissue regeneration. The similarities in fibronectin-mediated mechanisms of frustrated regeneration indicate that complete fibronectin clearance is a prerequisite for recovery in any tissue. Also, they provide common targets for developing therapeutic strategies in regenerative medicine.

Proteases and Delayed Wound Healing

SIGNIFICANCE

Proteases and their inhibitors contribute to the balance between extracellular matrix (ECM) degradation and deposition, creating an equilibrium that is essential for the timely and coordinated healing of cutaneous wounds. However, when this balance is disrupted, wounds are led into a state of chronicity characterized by abundant levels of proteases and decreased levels of protease inhibitors.

RECENT ADVANCES

Researchers have sought to investigate the roles of proteases within both acute and chronic wounds and how the manipulation of protease activity may aid healing. Indeed, numerous wound dressings have been developed that target such proteases in an attempt to promote wound healing.

CRITICAL ISSUES

The normal tissue response to injury involves a complex interaction between cells and cellular mediators. In particular, the inflammatory response is augmented in chronic wounds which are characterized by elevated levels of proinflammatory cytokines and proteases. While controlling levels of inflammation and protease expression is a critical part of normal wound healing, elevated and prolonged expression of proteases produced during the inflammatory phase of healing can lead to excessive ECM degradation associated with impaired healing.

FUTURE DIRECTIONS

It seems plausible that future research should aim to investigate the ways in which proteases may be targeted as an alternative therapeutic approach to wound management and to assess the benefits and draw-backs of utilizing wound fluids to assess wound progression in terms of proteolytic activity.

Granzyme B degrades extracellular matrix and contributes to delayed wound closure in apolipoprotein E knockout mice

Chronic inflammation and excessive protease activity have a major role in the persistence of non-healing wounds. Granzyme B (GzmB) is a serine protease expressed during chronic inflammation that, in conjunction with perforin, has a well-established role in initiating apoptotic cell death. GzmB is also capable of acting extracellularly, independent of perforin and can degrade several extracellular matrix (ECM) proteins that are critical during wound healing. We used apolipoprotein E (ApoE) knockout (AKO) mice as a novel model of chronic inflammation and impaired wound healing to investigate the role of GzmB in chronic wounds. Wild-type and AKO mice were grown to 7 weeks (young) or 37 weeks (old) of age on a regular chow or high-fat diet (HFD), given a 1-cm diameter full thickness wound on their mid dorsum and allowed to heal for 16 days. Old AKO mice fed a HFD exhibited reduced wound closure, delayed contraction, chronic inflammation and altered ECM remodeling. Conversely, GzmB/ApoE double knockout mice displayed improved wound closure and contraction rates. In addition, murine GzmB was found to degrade both fibronectin and vitronectin derived from healthy mouse granulation tissue. In addition, GzmB-mediated degradation of fibronectin generated a fragment similar in size to that observed in non-healing mouse wounds. These results provide the first direct evidence that GzmB contributes to chronic wound healing in part through degradation of ECM.

Current understanding of molecular and cellular mechanisms in fibroplasia and angiogenesis during acute wound healing

Cutaneous wound healing ultimately functions to facilitate barrier restoration following injury-induced loss of skin integrity. It is an evolutionarily conserved, multi-cellular, multi-molecular process involving co-ordinated inter-play between complex signalling networks. Cellular proliferation is recognised as the third stage of this sequence. Within this phase, fibroplasia and angiogenesis are co-dependent processes which must be successfully completed in order to form an evolving extracellular matrix and granulation tissue. The resultant structures guide cellular infiltration, differentiation and secretory profile within the wound environment and consequently have major influence on the success or failure of wound healing. This review integrates in vitro, animal and human in vivo studies, to provide up to date descriptions of molecular and cellular interactions involved in fibroplasia and angiogenesis. Significant molecular networks include adhesion molecules, proteinases, cytokines and chemokines as well as a plethora of growth factors. These signals are produced by, and affect behaviour of, cells including fibroblasts, fibrocytes, keratinocytes, endothelial cells and inflammatory cells resulting in significant cellular phenotypic and functional plasticity, as well as controlling composition and remodelling of structural proteins including collagen and fibronectin. The interdependent relationship between angiogenesis and fibroplasia relies on dynamic reciprocity between cellular components, matrix proteins and bioactive molecules. Unbalanced regulation of any one component can have significant consequences resulting in delayed healing, chronic wounds or abnormal scar formation. Greater understanding of angiogenic and fibroplastic mechanisms underlying chronic wound pathogenesis has identified novel therapeutic targets and enabled development of improved treatment strategies including topical growth factors and skin substitutes.

Adipose-derived stem cells and keratinocytes in a chronic wound cell culture model: the role of hydroxyectoine

Chronic wounds represent a major socio-economic problem in developed countries today. Wound healing is a complex biological process. It requires a well-orchestrated interaction of mediators, resident cells and infiltrating cells. In this context, mesenchymal stem cells and keratinocytes play a crucial role in tissue regeneration. In chronic wounds these processes are disturbed and cell viability is reduced. Hydroxyectoine (HyEc) is a membrane protecting osmolyte with protein and macromolecule stabilising properties. Adipose-derived stem cells (ASC) and keratinocytes were cultured with chronic wound fluid (CWF) and treated with HyEc. Proliferation was investigated using MTT test and migration was examined with transwell-migration assay and scratch assay. Gene expression changes of basic fibroblast growth factor (b-FGF), vascular endothelial growth factor (VEGF), matrix metalloproteinases-2 (MMP-2) and MMP-9 were analysed by quantitative real-time polymerase chain reaction (qRT-PCR). CWF significantly inhibited proliferation and migration of keratinocytes. Addition of HyEc did not affect these results. Proliferation capacity of ASC was not influenced by CWF whereas migration was significantly enhanced. HyEc significantly reduced ASC migration. Expression of b-FGF, VEGF, MMP-2 and MMP-9 in ASC, and b-FGF, VEGF and MMP-9 in keratinocytes was strongly induced by chronic wound fluid. HyEc enhanced CWF induced gene expression of VEGF in ASC and MMP-9 in keratinocytes. CWF negatively impaired keratinocyte function, which was not influenced by HyEc. ASC migration was stimulated by CWF, whereas HyEc significantly inhibited migration of ASC. CWF induced gene expression of VEGF in ASC and MMP-9 in keratinocytes was enhanced by HyEc, which might partly be explained by an RNA stabilising effect of HyEc.

A pre-clinical functional assessment of an acellular scaffold intended for the treatment of hard-to-heal wounds

The majority of the population experience successful wound-healing outcomes; however, 1-3% of those aged over 65 years experience delayed wound healing and wound perpetuation. These hard-to-heal wounds contain degraded and dysfunctional extracellular matrix (ECM); yet, the integrity of this structure is critical in the processes of normal wound healing. Here, we evaluated a novel synthetic matrix protein for its ability to act as an acellular scaffold that could replace dysfunctional ECM. In this regard, the synthetic protein was subjected to adsorption and diffusion assays using collagen and human dermal tissues; evaluated for its ability to influence keratinocyte and fibroblast attachment, migration and proliferation and assessed for its ability to influence in vivo wound healing in a porcine model. Critically, these experiments demonstrate that the matrix protein adsorbed to collagen and human dermal tissue but did not diffuse through human dermal tissue within a 24-hour observation period, and facilitated cell attachment, migration and proliferation. In a porcine wound-healing model, significantly smaller wound areas were observed in the test group compared with the control group following the third treatment. These data provide evidence that the synthetic matrix protein has the ability to function as an acellular scaffold for wound-healing purposes.

Chronic wounds - is cellular 'reception' at fault? Examining integrins and intracellular signalling

As with all physiologic processes, chronic wounds are associated with unique intracellular and cellular/extracellular matrix (ECM) receptor types and signalling messages. These cellular receptors mediate responses of the epidermis to provisional wound matrix and change in form and number in cases of impaired wound healing. Integrins are the major cell-surface receptors for cell adhesion and migration and epidermal keratinocytes express several integrins that bind ECM ligands in provisional wound ECM. Integrin receptors and more particularly integrin clusters and focal adhesion points appear to influence epidermal and dermal cell matrix interactions, cell motility, cell phenotype and ultimate healing trajectory. In chronic wounds, a variety of changes in receptors have been identified: decreased integrin α5β1 receptors affect the integration of fibronectin and subsequent keratinocyte migration; integrin αvβ6 stimulate transforming growth factor (TGF)-β and may increase the susceptibility to ulceration and fibrosis; however, TGF-β signal receptors have been found to be dysfunctional in many chronic wounds; additionally receptor interactions result in increased senescent cells including fibroblasts, myofibroblasts and even keratinocytes - this produces a degradative ECM and wound bed and corrosive chronic wound fluid. The activation or inhibition of integrin receptors by various agents may provide an excellent means of influencing wound healing. This process offers an earlier intervention into the wound healing cascade promoting intrinsic healing and elaboration of growth factors and ECM proteins, which may be more cost effective than the traditional attempts at extrinsic addition of these agents.

The role of skin substitutes in the management of chronic cutaneous wounds

Chronic wounds, including diabetic and venous ulcers, represent disruption of normal healing processes resulting in a pathological state of nonhealing cutaneous inflammation. They place an increasingly significant economic burden on healthcare providers as their prevalence is rising in keeping with an aging population. Current treatment modalities are slow acting and resource intensive. Bioengineered skin substitutes from autogenic, allogenic, or xenogenic sources have emerged as a new and alternative therapeutic option. A range of such products is licensed for clinical use, which differ in terms of structure and cellular content. Placed directly onto a prepared wound bed, skin substitutes may stimulate or accelerate healing by promoting revascularization, cellular migration, and repopulation of wound fields through provision of an appropriate scaffold material to facilitate these processes. Products containing fetal or autologous cells also benefit from early release of bioactive molecules including growth factors and cytokines. To date, limited numbers of randomized controlled trials studying skin substitutes have been published but evidence from case series and case-control studies is encouraging. This review discusses chronic wound biology, the influence that skin substitutes can exert on this environment, the products currently available, and examines the evidence for their use in chronic wound management.

Molecular Wound Assessments: Matrix Metalloproteinases

SIGNIFICANCE

The process of wound healing includes the regulated destruction of proteins via enzymes called proteinases. However, when the proteolytic process becomes excessive, pro-healing factors are destroyed and the wound healing process stalls. Matrix metalloproteinases (MMPs) are one key class of proteinases that have been observed to be elevated in many cases of failed wound healing.

RECENT ADVANCES

Two key advances have been made in recent years. First is that, until recently, MMPs were only implicated in impaired healing of chronic wounds. Measurements of MMPs in wound fluids and serum from individuals with acute traumatic wounds have revealed that elevated MMPs are predictive of both impaired healing and of dehiscence of surgically closed wounds. The second advance is in the development of at least three clinically viable methods for measuring MMPs at the point of care.

CRITICAL ISSUES

At present there is no objective method of determining proteinase levels within a wound. Since elevated MMPs have now been shown to be predictive of dehiscence in surgically closed acute wounds, a new clinical utility for measuring MMPs has been established. With the advent of several new technologies to measure MMPs, the translation of this valuable molecular knowledge into improved therapeutic regimens is nearly complete.

FUTURE DIRECTIONS

The clinical utility of measuring MMPs continues to expand and be further validated with each new investigation. The tools that will enable clinicians to leverage this valuable information are nearing maturity and integration into the clinic.

Clinical aspects and molecular diagnostics of skin aging

This contribution will address the effect of aging on skin functions, with a particular focus on skin permeability, wound healing, angiogenesis, lipogenesis, sweat production, immune function, and vitamin D synthesis. With accelerating age, skin functions deteriorate due to structural and morphologic changes. Skin is prone to the development of several diseases, varying from benign to malignant. Because the number of persons aged 80 and older is expected to rise in the next decades, disease prevention will become an important issue. Screening examinations and prevention through public education starting at an early age regarding sun avoidance, the use of sunscreens and the importance of a balanced nutrition are the first steps for successful healthy aging. Although the fundamental mechanisms in the pathogenesis of aged skin are still poorly understood, a growing body of evidence points toward the involvement of multiple pathways. Recent data obtained by expression profiling studies and studies of progeroid syndromes illustrate that among the most important biologic processes involved in skin aging are alterations in DNA repair and stability, mitochondrial function, cell cycle and apoptosis, extracellular matrix, lipid synthesis, ubiquitin-induced proteolysis and cellular metabolism. Among others, a major factor that has been implicated in the initiation of aging is the physiologic decline of hormones occurring with age. However, hormones at age-specific levels may regulate not only age-associated mechanisms but also tumor suppressor pathways that influence carcinogenesis. Understanding the molecular mechanisms of aging may open new strategies to deal with the various diseases accompanying high age, including cancer.