Connexins 26, 30, and 43: Differences Among Spontaneous, Chronic, and Accelerated Human Wound Healing

Connexins in epidermal health and diseases: insights into their mutations, implications, and therapeutic solutions

The epidermis, the outermost layer of the skin, serves as a protective barrier against external factors. Epidermal differentiation, a tightly regulated process essential for epidermal homeostasis, epidermal barrier formation and skin integrity maintenance, is orchestrated by several players, including signaling molecules, calcium gradient and junctional complexes such as gap junctions (GJs). GJ proteins, known as connexins facilitate cell-to-cell communication between adjacent keratinocytes. Connexins can function as either hemichannels or GJs, depending on their interaction with other connexons from neighboring keratinocytes. These channels enable the transport of metabolites, cAMP, microRNAs, and ions, including Ca2+, across cell membranes. At least ten distinct connexins are expressed within the epidermis and mutations in at least five of them has been linked to various skin disorders. Connexin mutations may cause aberrant channel activity by altering their synthesis, their gating properties, their intracellular trafficking, and the assembly of hemichannels and GJ channels. In addition to mutations, connexin expression is dysregulated in other skin conditions including psoriasis, chronic wound and skin cancers, indicating the crucial role of connexins in skin homeostasis. Current treatment options for conditions with mutant or altered connexins are limited and primarily focus on symptom management. Several therapeutics, including non-peptide chemicals, antibodies, mimetic peptides and allele-specific small interfering RNAs are promising in treating connexin-related skin disorders. Since connexins play crucial roles in maintaining epidermal homeostasis as shown with linkage to a range of skin disorders and cancer, further investigations are warranted to decipher the molecular and cellular alterations within cells due to mutations or altered expression, leading to abnormal proliferation and differentiation. This would also help characterize the roles of each isoform in skin homeostasis, in addition to the development of innovative therapeutic interventions. This review highlights the critical functions of connexins in the epidermis and the association between connexins and skin disorders, and discusses potential therapeutic options.

PKCμ promotes keratinocyte cell migration through Cx43 phosphorylation-mediated suppression of intercellular communication

Downregulation of intercellular communication through suppression of gap junctional conductance is necessary during wound healing. Connexin 43 (Cx43), a prominent gap junction protein in skin, is downregulated following wounding to restrict communication between keratinocytes. Previous studies found that PKCμ, a novel PKC isozyme, regulates efficient cutaneous wound healing. However, the molecular mechanism by which PKCμ regulates wound healing remains unknown. We have identified that PKCμ suppresses intercellular communication and enhances cell migration in an in vitro wound healing model by regulating Cx43 containing gap junctions. PKCμ can directly interact with and phosphorylate Cx43 at S368, which leads to Cx43 internalization and downregulation. Finally, utilizing phosphomimetic and non-phosphorylatable S368 substitutions and gap junction inhibitors, we confirmed that PKCμ regulates intercellular communication and in vitro wound healing by controlling Cx43-S368 phosphorylation. These results define PKCμ as a critical regulator of Cx43 phosphorylation to control cell migration and wound healing in keratinocytes.

Targeting Cx43 to Reduce the Severity of Pressure Ulcer Progression

In the skin, repeated incidents of ischemia followed by reperfusion can result in the breakdown of the skin and the formation of a pressure ulcer. Here we gently applied paired magnets to the backs of mice to cause ischemia for 1.5 h and then removed them to allow reperfusion. The sterile inflammatory response generated within 4 h causes a stage 1 pressure ulcer with an elevation of the gap junction protein Cx43 in the epidermis. If this process is repeated the insult will result in a more severe stage 2 pressure ulcer with a breakdown of the epidermis 2-3 days later. After a single pinch, the elevation of Cx43 in the epidermis is associated with the inflammatory response with an increased number of neutrophils, HMGB1 (marker of necrosis) and RIP3 (responsible for necroptosis). Delivering Cx43 specific antisense oligonucleotides sub-dermally after a single insult, was able to significantly reduce the elevation of epidermal Cx43 protein expression and reduce the number of neutrophils and prevent the elevation of HMGB1 and RIP3. In a double pinch model, the Cx43 antisense treatment was able to reduce the level of inflammation, necroptosis, and the extent of tissue damage and progression to an open wound. This approach may be useful in reducing the progression of stage 1 pressure ulcers to stage 2.

Melanoma Associated Chitinase 3-Like 1 Promoted Endothelial Cell Activation and Immune Cell Recruitment

Chitinase 3-like 1 (CHI3L1) is an enzymatically inactive mammalian chitinase that is associated with tumor inflammation. Previous research indicated that CHI3L1 is able to interact with different extracellular matrix components, such as heparan sulfate. In the present work, we investigated whether the interaction of CHI3L1 with the extracellular matrix of melanoma cells can trigger an inflammatory activation of endothelial cells. The analysis of the melanoma cell secretome indicated that CHI3L1 increases the abundance of various cytokines, such as CC-chemokine ligand 2 (CCL2), and growth factors, such as vascular endothelial growth factor A (VEGF-A). Using a solid-phase binding assay, we found that heparan sulfate-bound VEGF-A and CCL2 were displaced by recombinant CHI3L1 in a dose-dependent manner. Microfluidic experiments indicated that the CHI3L1 altered melanoma cell secretome promoted immune cell recruitment to the vascular endothelium. In line with the elevated VEGF-A levels, CHI3L1 was also able to promote angiogenesis through the release of extracellular matrix-bound pro-angiogenic factors. In conclusion, we showed that CHI3L1 is able to affect the tumor cell secretome, which in turn can regulate immune cell recruitment and blood vessel formation. Accordingly, our data suggest that the molecular targeting of CHI3L1 in the course of cancer immunotherapies can tune patients’ response and antitumoral inflammation.

Changes in connexin 43 in inflammatory skin disorders: Eczema, psoriasis, and Steven-Johnson syndrome/toxic epidermal necrolysis

BACKGROUND

Connexin 43 (Cx43) plays a central role in the inflammatory response and wound healing. Targeting Cx43 expression reduces inflammation in a variety of injuries. The expression pattern of Cx43 has not been described for many inflammatory skin diseases.

OBJECTIVES

To describe the expression patterns of Cx43 in eczema, psoriasis, Steven-Johnson syndrome/toxic epidermal necrolysis.

METHODS

Archival skin biopsies from patients with eczema, psoriasis, and Steven-Johnson syndrome/toxic epidermal necrosis were identified and examined, with sister sections stained for Cx43 and imaged by confocal microscopy. All samples were compared to age and site-matched normal skin controls.

RESULTS

Epidermal Cx43 is reduced in acute eczema, absent in regions of spongiosis, and is highly elevated in subacute and chronic eczema. In plaque psoriasis, Cx43 is overexpressed in areas with psoriasiform hyperplasia with a fish-scale-like appearance but is lost in regions surrounding neutrophil microabscesses. Cx43 staining is strong in the neutrophils within these microabscesses. In SJS/TEN, Cx43 expression is elevated in areas bordering normal tissue but is rapidly lost in areas of keratinocyte necrosis.

CONCLUSIONS

Dynamic changes in Cx43 levels are seen in inflammatory skin diseases and may represent future potential therapeutic targets.

Staphylococcus aureus impairs cutaneous wound healing by activating the expression of a gap junction protein, connexin-43 in keratinocytes

Chronic wounds have been considered as major medical problems that may result in expensive healthcare. One of the common causes of chronic wounds is bacterial contamination that leads to persistent inflammation and unbalanced host cell immune responses. Among the bacterial strains that have been identified from chronic wounds, Staphylococcus aureus is the most common strain. We previously observed that S. aureus impaired mouse cutaneous wound healing by delaying re-epithelialization. Here, we investigated the mechanism of delayed re-epithelialization caused by S. aureus infection. With the presence of S. aureus exudate, the migration of in vitro cultured human keratinocytes was significantly inhibited and connexin-43 (Cx43) was upregulated. Inhibition of keratinocyte migration by S. aureus exudate disappeared in keratinocytes where the expression of Cx43 knocked down. Protein kinase phosphorylation array showed that phosphorylation of Akt-S473 was upregulated by S. aureus exudate. In vivo study of Cx43 in S. aureus-infected murine splinted cutaneous wound model showed upregulation of Cx43 in the migrating epithelial edge by S. aureus infection. Treatment with a PI3K/Akt inhibitor reduced Cx43 expression and overcame the wound closure impairment by S. aureus infection in the mouse model. This may contribute to the development of treatment to bacterium-infected wounds.

Restraint of Human Skin Fibroblast Motility, Migration, and Cell Surface Actin Dynamics, by Pannexin 1 and P2X7 Receptor Signaling

Wound healing is a dynamic process required to maintain skin integrity and which relies on the precise migration of different cell types. A key molecule that regulates this process is ATP. However, the mechanisms involved in extracellular ATP management are poorly understood, particularly in the human dermis. Here, we explore the role, in human fibroblast migration during wound healing, of Pannexin 1 channels and their relationship with purinergic signals and in vivo cell surface filamentous actin dynamics. Using siRNA against Panx isoforms and different Panx1 channel inhibitors, we demonstrate in cultured human dermal fibroblasts that the absence or inhibition of Panx1 channels accelerates cell migration, increases single-cell motility, and promotes actin redistribution. These changes occur through a mechanism that involves the release of ATP to the extracellular space through a Panx1-dependent mechanism and the activation of the purinergic receptor P2X7. Together, these findings point to a pivotal role of Panx1 channels in skin fibroblast migration and suggest that these channels could be a useful pharmacological target to promote damaged skin healing.

Connexins and the Epithelial Tissue Barrier: A Focus on Connexin 26

Simple Summary

Tissues that face the external environment are known as ‘epithelial tissue’ and form barriers between different body compartments. This includes the outer layer of the skin, linings of the intestine and airways that project into the lumen connecting with the external environment, and the cornea of the eye. These tissues do not have a direct blood supply and are dependent on exchange of regulatory molecules between cells to ensure co-ordination of tissue events. Proteins known as connexins form channels linking cells directly and permit exchange of small regulatory signals. A range of environmental stimuli can dysregulate the level of connexin proteins and or protein function within the epithelia, leading to pathologies including non-healing wounds. Mutations in these proteins are linked with hearing loss, skin and eye disorders of differing severity. As such, connexins emerge as prime therapeutic targets with several agents currently in clinical trials. This review outlines the role of connexins in epithelial tissue and how their dysregulation contributes to pathological pathways.

Abstract

Epithelial tissue responds rapidly to environmental triggers and is constantly renewed. This tissue is also highly accessible for therapeutic targeting. This review highlights the role of connexin mediated communication in avascular epithelial tissue. These proteins form communication conduits with the extracellular space (hemichannels) and between neighboring cells (gap junctions). Regulated exchange of small metabolites less than 1kDa aide the co-ordination of cellular activities and in spatial communication compartments segregating tissue networks. Dysregulation of connexin expression and function has profound impact on physiological processes in epithelial tissue including wound healing. Connexin 26, one of the smallest connexins, is expressed in diverse epithelial tissue and mutations in this protein are associated with hearing loss, skin and eye conditions of differing severity. The functional consequences of dysregulated connexin activity is discussed and the development of connexin targeted therapeutic strategies highlighted.

The molecular and physiological consequences of cold plasma treatment in murine skin and its barrier function

Cold plasma technology is an emerging tool facilitating the spatially controlled delivery of a multitude of reactive species (ROS) to the skin. While the therapeutic efficacy of plasma treatment has been observed in several types of diseases, the fundamental consequences of plasma-derived ROS on skin physiology remain unknown. We aimed to bridge this gap since the epidermal skin barrier and perfusion plays a vital role in health and disease by maintaining homeostasis and protecting from environmental damage. The intact skin of SKH1 mice was plasma-treated in vivo. Gene and protein expression was analyzed utilizing transcriptomics, qPCR, and Western blot. Immunofluorescence aided the analysis of percutaneous skin penetration of curcumin. Tissue oxygenation, perfusion, hemoglobin, and water index was investigated using hyperspectral imaging. Reversed-phase liquid-chromatography/mass spectrometry was performed for the identification of changes in the lipid composition and oxidation. Transcriptomic analysis of plasma-treated skin revealed modulation of genes involved in regulating the junctional network (tight, adherence, and gap junctions), which was confirmed using qPCR, Western blot, and immunofluorescence imaging. Plasma treatment increased the disaggregation of cells in the stratum corneum (SC) concomitant with increased tissue oxygenation, gap junctional intercellular communication, and penetration of the model drug curcumin into the SC preceded by altered oxidation of skin lipids and their composition in vivo. In summary, plasma-derived ROS modify the junctional network, which promoted tissue oxygenation, oxidation of SC-lipids, and restricted penetration of the model drug curcumin, implicating that plasma may provide a novel and sensitive tool of skin barrier regulation.

Advanced Glycation End Products and Receptor (RAGE) Promote Wound Healing of Human Corneal Epithelial Cells

Purpose

We used a human corneal epithelial cell (HCE) line to determine the involvement of the advanced glycation end products (AGEs) / receptor for AGEs (RAGE) couple in corneal epithelium wound healing.

Methods

After wounding, HCE cells were exposed to two major RAGE ligands (HMGB1 and AGEs), and wound healing was evaluated using the in vitro scratch assay. Following wound healing, the HCE cells were used to study the influence of the RAGE ligands on HCE proliferation, invasion, and migration. Activation of the nuclear factor (NF)-κB signaling pathway by the AGEs/RAGE couple was tested using a luciferase reporter assay. Functional transcriptional regulation by this pathway was confirmed by quantification of expression of the connexin 43 target gene. For each experiment, specific RAGE involvement was confirmed by small interfering RNA treatments.

Results

AGEs treatment at a dose of 100 µg/mL significantly improved the wound healing process in a RAGE-dependent manner by promoting cell migration, whereas HMGB1 had no effect. No significant influence of the AGEs/RAGE couple was observed on cell proliferation and invasion. However, this treatment induced an early activation of the NF-κB pathway and positively regulated the expression of the target gene, connexin 43, at both the mRNA and protein levels.

Conclusions

Our results demonstrate that the RAGE pathway is activated by AGEs treatment and is involved in the promotion of corneal epithelial wound healing. This positive action is observed only during the early stages of wound healing, as illustrated by the quick activation of the NF-κB pathway and induction of connexin 43 expression.

ROS from Physical Plasmas: Redox Chemistry for Biomedical Therapy

Physical plasmas generate unique mixes of reactive oxygen and nitrogen species (RONS or ROS). Only a bit more than a decade ago, these plasmas, operating at body temperature, started to be considered for medical therapy with considerably little mechanistic redox chemistry or biomedical research existing on that topic at that time. Today, a vast body of evidence is available on physical plasma-derived ROS, from their spatiotemporal resolution in the plasma gas phase to sophisticated chemical and biochemical analysis of these species once dissolved in liquids. Data from in silico analysis dissected potential reaction pathways of plasma-derived reactive species with biological membranes, and in vitro and in vivo experiments in cell and animal disease models identified molecular mechanisms and potential therapeutic benefits of physical plasmas. In 2013, the first medical plasma systems entered the European market as class IIa devices and have proven to be a valuable resource in dermatology, especially for supporting the healing of chronic wounds. The first results in cancer patients treated with plasma are promising, too. Due to the many potentials of this blooming new field ahead, there is a need to highlight the main concepts distilled from plasma research in chemistry and biology that serve as a mechanistic link between plasma physics (how and which plasma-derived ROS are produced) and therapy (what is the medical benefit). This inevitably puts cellular membranes in focus, as these are the natural interphase between ROS produced by plasmas and translation of their chemical reactivity into distinct biological responses.

[Oral manifestations of KID syndrome: rare clinical case]

The paper presents a rare clinical case of an infant with KID (Keratitis, Ichthyosis, Deafness) syndrome (about 100 patients reported so far) admitted for histological verification of oral mucosa lesions. Disease pathogenesis defines inadequate reparation and skin and mucosa innate immunity defect leading to higher incidence of bacterial and fungal infections, so the 4-years old girl received treatment for vegetating candidiasis of the oral mucosa for several weeks with no clinical improvement. Initial examination showed that the oral lesions resulted from sharp edges of severely affected carious teeth. Histological study of multifocal biopsy revealed pyogenic granulomas and no signs of SCC. Teeth extraction and symptomatic treatment leaded to significant clinical improvement and some remained mucosal changes may be attributed to syndrome manifestations.

Connexin 26 and 43 play a role in regulating proinflammatory events in the epidermis

Dysregulation of Connexin (CX) expression and function is associated with a range of chronic inflammatory conditions including psoriasis and nonhealing wounds. To mimic a proinflammatory environment, HaCaT cells, a model human keratinocyte cell line, were challenged with 10 µg/ml peptidoglycan (PGN) isolated from Staphylococcus aureus for 15 min to 24 hr in the presence or absence of CX blockers and/or following CX26, CX43, PANX1 and TLR2 small interfering RNA (siRNA) knockdown (KD). Expression levels of IL-6, IL-8, CX26, CX43, PANX1, TLR2 and Ki67 were assessed by quantitative real-time polymerase chain reaction, western blot analysis and/or immunocytochemistry. Nuclear factor kappa β (NF-κβ) was blocked with BAY 11-7082, CX-channel function was determined by adenosine 5'-triphosphate (ATP) release assays. Enzyme-linked immunosorbent assay monitored IL6 release following PGN challenge in the presence or absence of siRNA or blockers of CX or purinergic signalling. Exposure to PGN induced IL-6, IL-8, CX26 and TLR2 gene expression but it did not influence CX43, PANX1 or Ki67 messenger RNA expression levels. CX43 protein levels were reduced following 24 hr PGN exposure. PGN-induced CX26 and IL-6 expression were also aborted by TLR2-KD and inhibition of NF-κβ. ATP and IL-6 release were stimulated following 15 min and 1-24 hr challenge with PGN, respectively. Release of both agents was inhibited by coincubation with CX-channel blockers, CX26-, CX43- and TLR2-KD. The IL-6 response was also reduced by purinergic blockers. CX-signalling plays a role in the innate immune response in the epidermis. PGN is detected by TLR2, which via NF-κβ, directly activates CX26 and IL-6 expression. CX43 and CX26 maintain proinflammatory signalling by permitting ATP release, however, PANX1 does not participate.

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.

Redox for Repair: Cold Physical Plasmas and Nrf2 Signaling Promoting Wound Healing

Chronic wounds and ulcers are major public health threats. Being a substantial burden for patients and health care systems alike, better understanding of wound pathophysiology and new avenues in the therapy of chronic wounds are urgently needed. Cold physical plasmas are particularly effective in promoting wound closure, irrespective of its etiology. These partially ionized gases deliver a therapeutic cocktail of reactive oxygen and nitrogen species safely at body temperature and without genotoxic side effects. This field of plasma medicine reanimates the idea of redox repair in physiological healing. This review compiles previous findings of plasma effects in wound healing. It discusses new links between plasma treatment of cells and tissues, and the perception and intracellular translation of plasma-derived reactive species via redox signaling pathways. Specifically, (i) molecular switches governing redox-mediated tissue response; (ii) the activation of the nuclear E2-related factor (Nrf2) signaling, together with antioxidative and immunomodulatory responses; and (iii) the stabilization of the scaffolding function and actin network in dermal fibroblasts are emphasized in the light of wound healing.

Connexin 43-Based Therapeutics for Dermal Wound Healing

The most ubiquitous gap junction protein within the body, connexin 43 (Cx43), is a target of interest for modulating the dermal wound healing response. Observational studies found associations between Cx43 at the wound edge and poor healing response, and subsequent studies utilizing local knockdown of Cx43 found improvements in wound closure rate and final scar appearance. Further preclinical work conducted using Cx43-based peptide therapeutics, including alpha connexin carboxyl terminus 1 (αCT1), a peptide mimetic of the Cx43 carboxyl terminus, reported similar improvements in wound healing and scar formation. Clinical trials and further study into the mode of action have since been conducted on αCT1, and Phase III testing for treatment of diabetic foot ulcers is currently underway. Therapeutics targeting connexin activity show promise in beneficially modulating the human body’s natural healing response for improved patient outcomes across a variety of injuries.

Connexin Communication Compartments and Wound Repair in Epithelial Tissue

Epithelial tissues line the lumen of tracts and ducts connecting to the external environment. They are critical in forming an interface between the internal and external environment and, following assault from environmental factors and pathogens, they must rapidly repair to maintain cellular homeostasis. These tissue networks, that range from a single cell layer, such as in airway epithelium, to highly stratified and differentiated epithelial surfaces, such as the epidermis, are held together by a junctional nexus of proteins including adherens, tight and gap junctions, often forming unique and localised communication compartments activated for localised tissue repair. This review focuses on the dynamic changes that occur in connexins, the constituent proteins of the intercellular gap junction channel, during wound-healing processes and in localised inflammation, with an emphasis on the lung and skin. Current developments in targeting connexins as corrective therapies to improve wound closure and resolve localised inflammation are also discussed. Finally, we consider the emergence of the zebrafish as a concerted whole-animal model to study, visualise and track the events of wound repair and regeneration in real-time living model systems.

Connexins: Synthesis, Post-Translational Modifications, and Trafficking in Health and Disease

Connexins are tetraspan transmembrane proteins that form gap junctions and facilitate direct intercellular communication, a critical feature for the development, function, and homeostasis of tissues and organs. In addition, a growing number of gap junction-independent functions are being ascribed to these proteins. The connexin gene family is under extensive regulation at the transcriptional and post-transcriptional level, and undergoes numerous modifications at the protein level, including phosphorylation, which ultimately affects their trafficking, stability, and function. Here, we summarize these key regulatory events, with emphasis on how these affect connexin multifunctionality in health and disease.

Connexin 43 regulates the expression of wound healing-related genes in human gingival and skin fibroblasts

Fibroblasts are the most abundant connective tissue cells and play an important role in wound healing. It is possible that faster and scarless wound healing in oral mucosal gingiva relative to skin may relate to the distinct phenotype of the fibroblasts residing in these tissues. Connexin 43 (Cx43) is the most ubiquitous Cx in skin (SFBLs) and gingival fibroblasts (GFBLs), and assembles into hemichannels (HCs) and gap junctions (GJs) on the cell membrane. We hypothesized that SFBLs and GFBLs display distinct expression or function of Cx43, and that this may partly underlie the different wound healing outcomes in skin and gingiva. Here we show that Cx43 distinctly formed Cx43 GJs and HCs in human skin and gingiva in vivo. However, in SFBLs, in contrast to GFBLs, only a small proportion of total Cx43 assembled into HC plaques. Using an in vivo-like 3D culture model, we further show that the GJ, HC, and channel-independent functions of Cx43 distinctly regulated wound healing-related gene expression in GFBLs and SFBLs. Therefore, the distinct wound healing outcomes in skin and gingiva may partly relate to the inherently different assembly and function of Cx43 in the resident fibroblasts.

Cartilage regeneration and ageing: Targeting cellular plasticity in osteoarthritis

Ageing processes play a major contributing role for the development of Osteoarthritis (OA). This prototypic degenerative condition of ageing is the most common form of arthritis and is accompanied by a general decline, chronic pain and mobility deficits. The disease is primarily characterized by articular cartilage degradation, followed by subchondral bone thickening, osteophyte formation, synovial inflammation and joint degeneration. In the early stages, osteoarthritic chondrocytes undergo phenotypic changes that increase cell proliferation and cluster formation and enhance the production of matrix-remodelling enzymes. In fact, chondrocytes exhibit differentiation plasticity and undergo phenotypic changes during the healing process. Current studies are focusing on unravelling whether OA is a consequence of an abnormal wound healing response. Recent investigations suggest that alterations in different proteins, such as TGF-ß/BMPs, NF-Kß, Wnt, and Cx43, or SASP factors involved in signalling pathways in wound healing response, could be directly implicated in the initiation of OA. Several findings suggest that osteoarthritic chondrocytes remain in an immature state expressing stemness-associated cell surface markers. In fact, the efficacy of new disease-modifying OA drugs that promote chondrogenic differentiation in animal models indicates that this may be a drug-sensible state. In this review, we highlight the current knowledge regarding cellular plasticity in chondrocytes and OA. A better comprehension of the mechanisms involved in these processes may enable us to understand the molecular pathways that promote abnormal repair and cartilage degradation in OA. This understanding would be advantageous in identifying novel targets and designing therapies to promote effective cartilage repair and successful joint ageing by preventing functional limitations and disability.

A cold plasma jet accelerates wound healing in a murine model of full-thickness skin wounds

Cold plasma has been successfully applied in several fields of medicine that require, for example, pathogen inactivation, implant functionalization or alteration of cellular activity. Previous studies have provided evidence that plasma supports the healing of wounds owing to its beneficial mixtures of reactive species and modulation of inflammation in cells and tissues. To investigate the wound healing activity of an atmospheric pressure plasma jet in vivo, we examined the cold plasma's efficacy on dermal regeneration in a murine model of dermal full-thickness ear wound. Over 14 days, female mice received daily plasma treatment. Quantitative analysis by transmitted light microscopy demonstrated a significantly accelerated wound re-epithelialization at days 3-9 in comparison with untreated controls. In vitro, cold plasma altered keratinocyte and fibroblast migration, while both cell types showed significant stimulation resulting in accelerated closure of gaps in scratch assays. This plasma effect correlated with the downregulation of the gap junctional protein connexin 43 which is thought to be important in the regulation of wound healing. In addition, plasma induced profound changes in adherence junctions and cytoskeletal dynamics as shown by downregulation of E-cadherin and several integrins as well as actin reorganization. Our results theorize cold plasma to be a beneficial treatment option supplementing existing wound therapies.

The Connexin Mimetic Peptide Gap27 and Cx43-Knockdown Reveal Differential Roles for Connexin43 in Wound Closure Events in Skin Model Systems

In the epidermis, remodelling of Connexin43 is a key event in wound closure. However, controversy between the role of connexin channel and non-channel functions exist. We compared the impact of SiRNA targeted to Connexin43 and the connexin mimetic peptide Gap27 on scrape wound closure rates and hemichannel signalling in adult keratinocytes (AK) and fibroblasts sourced from juvenile foreskin (JFF), human neonatal fibroblasts (HNDF) and adult dermal tissue (ADF). The impact of these agents, following 24 h exposure, on GJA1 (encoding Connexin43), Ki67 and TGF-β1 gene expression, and Connexin43 and pSmad3 protein expression levels, were examined by qPCR and Western Blot respectively. In all cell types Gap27 (100 nM–100 μM) attenuated hemichannel activity. In AK and JFF cells, Gap27 (100 nM–100 μM) enhanced scrape wound closure rates by ~50% but did not influence movement in HNDF or ADF cells. In both JF and AK cells, exposure to Gap27 for 24 h reduced the level of Cx43 protein expression but did not affect the level in ADF and HNDF cells. Connexin43-SiRNA enhanced scrape wound closure in all the cell types under investigation. In HDNF and ADF, Connexin43-SiRNA enhanced cell proliferation rates, with enhanced proliferation also observed following exposure of HDNF to Gap27. By contrast, in JFF and AK cells no changes in proliferation occurred. In JFF cells, Connexin43-SiRNA enhanced TGF-β1 levels and in JFF and ADF cells both Connexin43-SiRNA and Gap27 enhanced pSmad3 protein expression levels. We conclude that Connexin43 signalling plays an important role in cell migration in keratinocytes and foreskin derived fibroblasts, however, different pathways are evoked and in dermal derived adult and neonatal fibroblasts, inhibition of Connexin43 signalling plays a more significant role in regulating cell proliferation than cell migration.

Inhibitors of connexin and pannexin channels as potential therapeutics

While gap junctions support the exchange of a number of molecules between neighboring cells, connexin hemichannels provide communication between the cytosol and the extracellular environment of an individual cell. The latter equally holds true for channels composed of pannexin proteins, which display an architecture reminiscent of connexin hemichannels. In physiological conditions, gap junctions are usually open, while connexin hemichannels and, to a lesser extent, pannexin channels are typically closed, yet they can be activated by a number of pathological triggers. Several agents are available to inhibit channels built up by connexin and pannexin proteins, including alcoholic substances, glycyrrhetinic acid, anesthetics and fatty acids. These compounds not always strictly distinguish between gap junctions, connexin hemichannels and pannexin channels, and may have effects on other targets as well. An exception lies with mimetic peptides, which reproduce specific amino acid sequences in connexin or pannexin primary protein structure. In this paper, a state-of-the-art overview is provided on inhibitors of cellular channels consisting of connexins and pannexins with specific focus on their mode-of-action and therapeutic potential.

Disease-linked connexin26 S17F promotes volar skin abnormalities and mild wound healing defects in mice

Several mutant mice have been generated to model connexin (Cx)-linked skin diseases; however, the role of connexins in skin maintenance and during wound healing remains to be fully elucidated. Here we generated a novel, viable, and fertile mouse (Cx26^CK14-S17F/+) with the keratitis-ichthyosis-deafness mutant (Cx26S17F) driven by the cytokeratin 14 promoter. This mutant mouse mirrors several Cx26-linked human skin pathologies suggesting that the etiology of Cx26-linked skin disease indeed stems from epidermal expression of the Cx26 mutant. Cx26^CK14-S17F/+ foot pad epidermis formed severe palmoplantar keratoderma, which expressed elevated levels of Cx26 and filaggrin. Primary keratinocytes isolated from Cx26^CK14-S17F/+ neonates exhibited reduced gap junctional intercellular communication and migration. Furthermore, Cx26^CK14-S17F/+ mouse skin wound closure was normal but repaired epidermis appeared hyperplastic with elevated expression of cytokeratin 6. Taken together, we suggest that the Cx26S17F mutant disturbs keratinocyte differentiation and epidermal remodeling following wound closure. We further posit that Cx26 contributes to epidermal homeostasis by regulating keratinocyte differentiation, and that mice harboring a disease-linked Cx26 mutant display epidermal abnormalities yet retain most wound healing properties.

Epidermal grafting for wound healing: a review on the harvesting systems, the ultrastructure of the graft and the mechanism of wound healing

Epidermal grafting for wound healing involves the transfer of the epidermis from a healthy location to cover a wound. The structural difference of the epidermal graft in comparison to the split-thickness skin graft and full-thickness skin graft contributes to the mechanism of effect. While skin grafting is an epidermal transfer, little is known about the precise mechanism of wound healing by epidermal graft. This paper aims to explore the evolution of the epidermal graft harvesting system over the last five decades, the structural advantages of epidermal graft for wound healing and the current hypotheses on the mechanism of wound healing by epidermal graft. Three mechanisms are proposed: keratinocyte activation, growth factor secretion and reepithelialisation from the wound edge. We evaluate and explain how these processes work and integrate to promote wound healing based on the current in vivo and in vitro evidence. We also review the ongoing clinical trials evaluating the efficacy of epidermal graft for wound healing. The epidermal graft is a promising alternative to the more invasive conventional surgical techniques as it is simple, less expensive and reduces the surgical burden for patients in need of wound coverage.

The Role of Connexins in Wound Healing and Repair: Novel Therapeutic Approaches

Gap junctions are intercellular proteins responsible for mediating both electrical and biochemical coupling through the exchange of ions, second messengers and small metabolites. They consist of two connexons, with (one) connexon supplied by each cell. A connexon is a hexamer of connexins and currently more than 20 connexin isoforms have been described in the literature thus far. Connexins have a short half-life, and therefore gap junction remodeling constantly occurs with a high turnover rate. Post-translational modification, such as phosphorylation, can modify their channel activities. In this article, the roles of connexins in wound healing and repair are reviewed. Novel strategies for modulating the function or expression of connexins, such as the use of antisense technology, synthetic mimetic peptides and bioactive materials for the treatment of skin wounds, diabetic and pressure ulcers as well as cornea wounds, are considered.

Effect of connexin 43 inhibition by the mimetic peptide Gap27 on corneal wound healing, inflammation and neovascularization

Background and Purpose

The connexin 43 (Cx43) mimetic peptide Gap27 was designed to transiently block the function of this gap junction. This study was undertaken to investigate the effect of Gap27 on corneal healing, inflammation and neovascularization.

Experimental Approach

The effect of Gap27 on wound healing, inflammation and vascularization was assessed in primary human corneal epithelial cells (HCEC) in vitro and whole human corneas ex vivo, and in an in vivo rat wound healing model.

Key Results

Gap27 enhanced the wound closure of HCEC in vitro and accelerated wound closure and stratification of epithelium in human corneas ex vivo, but did not suppress the corneal release of inflammatory mediators IL‐6 or TNF‐α in vivo. In human corneas ex vivo, F4/80 positive macrophages were observed around the wound site. In vivo, topical Gap27 treatment enhanced the speed and density of early granulocyte infiltration into rat corneas. After 7 days, the expressions of TNF‐α and TGFβ1 were elevated and correlated with inflammatory cell accumulation in the tissue. Additionally, Gap27 did not suppress VEGF release in organotypic culture, nor did it suppress early or late VEGFA expression or neovascularization in vivo.

Conclusions and Implications

Gap27 can be effective in promoting the healing of superficial epithelial wounds, but in deep stromal wounds it has the potential to promote inflammatory cell migration and accumulation in the tissue and does not suppress the subsequent neovascularization response. These results support the proposal that Gap27 acts as a healing agent in the transient, early stages of corneal epithelial wounding.

Transient suppression of gap junctional intercellular communication after exposure to 100-nanosecond pulsed electric fields

Gap junctional intercellular communication (GJIC) is an important mechanism that is involved and affected in many diseases and injuries. So far, the effect of nanosecond pulsed electric fields (nsPEFs) on the communication between cells was not investigated. An in vitro approach is presented with rat liver epithelial WB-F344 cells grown and exposed in a monolayer. In order to observe sub-lethal effects, cells were exposed to pulsed electric fields with a duration of 100ns and amplitudes between 10 and 20kV/cm. GJIC strongly decreased within 15min after treatment but recovered within 24h. Gene expression of Cx43 was significantly decreased and associated with a reduced total amount of Cx43 protein. In addition, MAP kinases p38 and Erk1/2, involved in Cx43 phosphorylation, were activated and Cx43 became hyperphosphorylated. Immunofluorescent staining of Cx43 displayed the disassembly of gap junctions. Further, a reorganization of the actin cytoskeleton was observed whereas tight junction protein ZO-1 was not significantly affected. All effects were field- and time-dependent and most pronounced within 30 to 60min after treatment. A better understanding of a possible manipulation of GJIC by nsPEFs might eventually offer a possibility to develop and improve treatments.

Connexins and their channels in inflammation

Inflammation may be caused by a variety of factors and is a hallmark of a plethora of acute and chronic diseases. The purpose of inflammation is to eliminate the initial cell injury trigger, to clear out dead cells from damaged tissue and to initiate tissue regeneration. Despite the wealth of knowledge regarding the involvement of cellular communication in inflammation, studies on the role of connexin-based channels in this process have only begun to emerge in the last few years. In this paper, a state-of-the-art overview of the effects of inflammation on connexin signaling is provided. Vice versa, the involvement of connexins and their channels in inflammation will be discussed by relying on studies that use a variety of experimental tools, such as genetically modified animals, small interfering RNA and connexin-based channel blockers. A better understanding of the importance of connexin signaling in inflammation may open up towards clinical perspectives.

Connexins, Pannexins, and Their Channels in Fibroproliferative Diseases

Cellular and molecular mechanisms of wound healing, tissue repair, and fibrogenesis are established in different organs and are essential for the maintenance of function and tissue integrity after cell injury. These mechanisms are also involved in a plethora of fibroproliferative diseases or organ-specific fibrotic disorders, all of which are associated with the excessive deposition of extracellular matrix components. Fibroblasts, which are key cells in tissue repair and fibrogenesis, rely on communicative cellular networks to ensure efficient control of these processes and to prevent abnormal accumulation of extracellular matrix into the tissue. Despite the significant impact on human health, and thus the epidemiologic relevance, there is still no effective treatment for most fibrosis-related diseases. This paper provides an overview of current concepts and mechanisms involved in the participation of cellular communication via connexin-based pores as well as pannexin-based channels in the processes of tissue repair and fibrogenesis in chronic diseases. Understanding these mechanisms may contribute to the development of new therapeutic strategies to clinically manage fibroproliferative diseases and organ-specific fibrotic disorders.

Connexin43 plays diverse roles in co-ordinating cell migration and wound closure events

Chronic wounds are not only debilitating to patients, but also impose a huge financial burden on healthcare providers, as current treatments are not particularly effective. Wound healing is a highly co-ordinated process involving a vast array of signalling molecules and different cell types, therefore a substantial amount of research has been carried out in the quest to develop new therapies. The gap junction (GJ) protein connexin43 (Cx43) is one of the many molecules whose expression has been found to be up-regulated in chronic wounds and as a result targeting it may have therapeutic potential. Two different approaches have been adopted to investigate this: knockdown of Cx43 using antisense oligonucleotides and connexin mimetic peptides (CMPs) which inhibit the function of Cx43 without affecting gene expression. These peptides are targeted to the C-terminal domain or the extracellular loops of Cx43 and thus are likely to function by different means. However, both block channel function and have been shown to enhance cell migration rates. In recent years, non-channel functions have emerged for Cx43, many of which are linked to cytoskeletal dynamics and the extracellular matrix (ECM), showing that Cx43 plays diverse roles in co-ordinating wound closure events. It is clear that both CMPs and antisense oligonucleotides hold therapeutic potential, however maintaining Cx43 expression may be beneficial to the cell by preserving other non-channel functions of Cx43. Recent data in the field will be discussed in this article.

Current and emerging therapies in the management of diabetic foot ulcers

BACKGROUND

Diabetic foot ulcers are one of the major causes of mortality in diabetic patients. Very few drugs and therapies have regulatory approval for this indication and several agents from diverse pharmacological classes are currently in various phases of clinical trials for the management of diabetic foot ulcers.

SCOPE

The purpose of this review is to provide concise information of the drugs and therapies which are approved and present in clinical trials.

REVIEW METHODS

This review was carried out by systematic searches of relevant guidelines, patents, published articles, reviews and abstracts in PubMed/Medline, Web of Science, clinicaltrials.gov, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews and Google Scholar of all English language articles up to 1 March 2015. The following search terms were used: diabetes, diabetic foot, diabetic foot ulcer, diabetic wound, diabetic foot infections, wound management, randomized controlled trials, approved treatments, new treatments and clinical trials.

CONCLUSIONS

The various drugs and therapies for the management of diabetic foot ulcers comprise antibiotics, neuropathic drugs, wound dressings, skin substitutes, growth factors and inflammatory modulators. The majority of these therapies target the treatment of diabetic foot ulcers to address the altered biochemical composition of the diabetic wound. However, no single treatment can be definitively recommended for the treatment of diabetic foot ulcers.

Kinase programs spatiotemporally regulate gap junction assembly and disassembly: Effects on wound repair

Gap junctions are highly ordered plasma membrane domains that are constantly assembled, remodeled and turned over due to the short half-life of connexins, the integral membrane proteins that form gap junctions. Connexin 43 (Cx43), by far the most widely expressed connexin, is phosphorylated at multiple serine residues in the cytoplasmic, C-terminal region allowing for exquisite cellular control over gap junctional communication. This is evident during epidermal wounding where spatiotemporal changes in connexin expression occur as cells are instructed whether to die, proliferate or migrate to promote repair. Early gap junctional communication is required for initiation of keratinocyte migration, but accelerated Cx43 turnover is also critical for proper wound healing at later stages. These events are controlled via a "kinase program" where sequential phosphorylation of Cx43 leads to reductions in Cx43's half-life and significant depletion of gap junctions from the plasma membrane within several hours. The complex regulation of gap junction assembly and turnover affords several steps where intervention might speed wound healing.

Connexins and pannexins in the integumentary system: the skin and appendages

The integumentary system comprises the skin and its appendages, which includes hair, nails, feathers, sebaceous and eccrine glands. In this review, we focus on the expression profile of connexins and pannexins throughout the integumentary system in mammals, birds and fish. We provide a picture of the complexity of the connexin/pannexin network illustrating functional importance of these proteins in maintaining the integrity of the epidermal barrier. The differential regulation and expression of connexins and pannexins during skin renewal, together with a number of epidermal, hair and nail abnormalities associated with mutations in connexins, emphasize that the correct balance of connexin and pannexin expression is critical for maintenance of the skin and its appendages with both channel and non-channel functions playing profound roles. Changes in connexin expression during both hair and feather regeneration provide suggestions of specialized communication compartments. Finally, we discuss the potential use of zebrafish as a model for connexin skin biology, where evidence mounts that differential connexin expression is involved in skin patterning and pigmentation.

Connexin hemichannels influence genetically determined inflammatory and hyperproliferative skin diseases

Connexin mutations underlie numerous human genetic diseases. Several connexin genes have been linked to skin diseases, and mechanistic studies have indicated that a gain of abnormal channel function may be responsible for pathology. The topical accessibility of the epidermal connexins, the existence of several mouse models of human skin disease, and the ongoing identification of pharmacological inhibitors targeting connexins provide an opportunity to test new therapeutic approaches.

An updated review of mechanotransduction in skin disorders: transcriptional regulators, ion channels, and microRNAs

INTRODUCTION

The skin is constantly exposed and responds to a wide range of biomechanical cues. The mechanobiology of skin has already been known and applied by clinicians long before the fundamental molecular mechanisms of mechanotransduction are elucidated.

MATERIALS AND METHODS

Despite increasing knowledge on the mediators of biomechanical signaling such as mitogen-associated protein kinases, Rho GTPases or FAK-ERK pathways, the key elements of mechano-responses transcription factors, and mechano-sensors remain unclear. Recently, canonical biochemical components of Hippo and Wnt signaling pathway YAP and β-catenin were found to exhibit undefined mechanical sensitivity. Mechanical forces were identified to be the dominant regulators of YAP/TAZ activity in a multicellular context. Furthermore, different voltage or ligand sensitive ion channels in the cell membrane exhibited their mechanical sensitivity as mechano-sensors. Additionally, a large number of microRNAs have been confirmed to regulate cellular behavior and contribute to various skin disorders under mechanical stimuli. Mechanosensitive (MS) microRNAs could not only be activated by distinct mechanical force pattern, but also responsively target MS sensors such as e-cadherin and cytoskeleton constituent RhoA.

CONCLUSION

Thus, a comprehensive understanding of this regulatory network of cutaneous mechanotransduction will facilitate the development of novel approaches to wound healing, hypertrophic scar formation, skin regeneration, and the progression or initiation of skin diseases.

Topical administration of a connexin43-based peptide augments healing of chronic neuropathic diabetic foot ulcers: A multicenter, randomized trial

Nonhealing neuropathic foot ulcers remain a significant problem in individuals with diabetes. The gap-junctional protein connexin43 (Cx43) has roles in dermal wound healing and targeting Cx43 signalling accelerates wound reepithelialization. In a prospective, randomized, multicenter clinical trial we evaluated the efficacy and safety of a peptide mimetic of the C-terminus of Cx43, alpha connexin carboxy-terminal (ACT1), in accelerating the healing of chronic diabetic foot ulcers (DFUs) when incorporated into standard of care (SOC) protocols. Adults with DFUs of at least four weeks duration were randomized to receive SOC with or without topical application of ACT1. Primary outcome was mean percent ulcer reepithelialization and safety variables included incidence of treatment related adverse events (AEs) and detection of ACT1 immunogenicity. ACT1 treatment was associated with a significantly greater reduction in mean percent ulcer area from baseline to 12 weeks (72.1% vs. 57.1%; p = 0.03). Analysis of incidence and median time-to-complete-ulcer closure revealed that ACT1 treatment was associated with a greater percentage of participants that reached 100% ulcer reepitheliazation and a reduced median time-to-complete-ulcer closure. No AEs reported were treatment related, and ACT1 was not immunogenic. Treatment protocols that incorporate ACT1 may present a therapeutic strategy that safely augments the reepithelialization of chronic DFUs.

Connexin 43 deficiency accelerates skin wound healing and extracellular matrix remodeling in mice

BACKGROUND

Cellular channels composed of connexin 43 are known to act as key players in the life cycle of the skin and consequently to underlie skin repair.

OBJECTIVE

This study was specifically set up to investigate the suite of molecular mechanisms driven by connexin 43-based channels on wound healing.

METHODS

To this end, a battery of parameters, including re-epithelialization, neovascularization, collagen deposition and extracellular matrix remodeling, was monitored over time during experimentally induced skin repair in heterozygous connexin 43 knockout mice.

RESULTS

It was found that connexin 43 deficiency accelerates re-epithelialization and wound closure, increases proliferation and activation of dermal fibroblasts, and enhances the expression of extracellular matrix remodeling mediators.

CONCLUSION

These data substantiate the notion that connexin 43 may represent an interesting therapeutic target in dermal wound healing.

Bioengineering a human plasma-based epidermal substitute with efficient grafting capacity and high content in clonogenic cells

Cultured epithelial autografts (CEAs) produced from a small, healthy skin biopsy represent a lifesaving surgical technique in cases of full-thickness skin burn covering >50% of total body surface area. CEAs also present numerous drawbacks, among them the use of animal proteins and cells, the high fragility of keratinocyte sheets, and the immaturity of the dermal-epidermal junction, leading to heavy cosmetic and functional sequelae. To overcome these weaknesses, we developed a human plasma-based epidermal substitute (hPBES) for epidermal coverage in cases of massive burn, as an alternative to traditional CEA, and set up critical quality controls for preclinical and clinical studies. In this study, phenotypical analyses in conjunction with functional assays (clonal analysis, long-term culture, or in vivo graft) showed that our new substitute fulfills the biological requirements for epidermal regeneration. hPBES keratinocytes showed high potential for cell proliferation and subsequent differentiation similar to healthy skin compared with a well-known reference material, as ascertained by a combination of quality controls. This work highlights the importance of integrating relevant multiparameter quality controls into the bioengineering of new skin substitutes before they reach clinical development.

SIGNIFICANCE

This work involves the development of a new bioengineered epidermal substitute with pertinent functional quality controls. The novelty of this work is based on this quality approach.

Connexins and skin disease: insights into the role of beta connexins in skin homeostasis

Cell-to-cell communication triggered by connexin channels plays a central role in maintaining epidermal homeostasis. Here, we discuss the role of the beta connexin subgroup, where site-specific mutations in at least 4 of these proteins lead to distinctive non-inflammatory and inflammatory hyperproliferative epidermal disorders. Recent advances in the molecular pathways evoked and correlation with clinical outcome are discussed. The latest data provide increasing evidence that connexins in the epidermis are sensors to environmental stress and that targeting aberrant hemichannel activity holds significant therapeutic potential for inflammatory skin disorders.

Expression and function of connexin 43 in human gingival wound healing and fibroblasts

Connexins (C×s) are a family of transmembrane proteins that form hemichannels and gap junctions (GJs) on the cell membranes, and transfer small signaling molecules between the cytoplasm and extracellular space and between connecting cells, respectively. Among C×s, suppressing C×43 expression or function promotes skin wound closure and granulation tissue formation, and may alleviate scarring, but the mechanisms are not well understood. Oral mucosal gingiva is characterized by faster wound closure and scarless wound healing outcome as compared to skin wounds. Therefore, we hypothesized that C×43 function is down regulated during human gingival wound healing, which in fibroblasts promotes expression of genes conducive for fast and scarless wound healing. Cultured gingival fibroblasts expressed C×43 as their major connexin. Immunostaining of unwounded human gingiva showed that C×43 was abundantly present in the epithelium, and in connective tissue formed large C×43 plaques in fibroblasts. At the early stages of wound healing, C×43 was strongly down regulated in wound epithelial cells and fibroblasts, returning to the level of normal tissue by day 60 post-wounding. Blocking of C×43 function by C×43 mimetic peptide Gap27 suppressed GJ-mediated dye transfer, promoted migration, and caused significant changes in the expression of wound healing-associated genes in gingival fibroblasts. In particular, out of 54 genes analyzed, several MMPs and TGF-β1, involved in regulation of inflammation and extracellular matrix (ECM) turnover, and VEGF-A, involved in angiogenesis, were significantly upregulated while pro-fibrotic ECM molecules, including Collagen type I, and cell contractility-related molecules were significantly down regulated. These responses involved MAPK, GSK3α/β and TGF-β signaling pathways, and AP1 and SP1 transcription factors. Thus, suppressed function of C×43 in fibroblasts promotes their migration, and regulates expression of wound healing-associated genes via AP1, SP1, MAPK, GSK3α/β and TGF-β signaling pathways, and may promote fast and scarless wound healing in human gingiva.

The effect of a connexin43-based Peptide on the healing of chronic venous leg ulcers: a multicenter, randomized trial

The gap junction protein, connexin43 (Cx43), has critical roles in the inflammatory, edematous, and fibrotic processes following dermal injury and during wound healing, and is abnormally upregulated at the epidermal wound margins of venous leg ulcers (VLUs). Targeting Cx43 with ACT1, a peptide mimetic of the carboxyl-terminus of Cx43, accelerates fibroblast migration and proliferation, and wound reepithelialization. In a prospective, multicenter clinical trial conducted in India, adults with chronic VLUs were randomized to treatment with an ACT1 gel formulation plus conventional standard-of-care (SOC) protocols, involving maintaining wound moisture and four-layer compression bandage therapy, or SOC protocols alone. The primary end point was mean percent ulcer reepithelialization from baseline to 12 weeks. A significantly greater reduction in mean percent ulcer area from baseline to 12 weeks was associated with the incorporation of ACT1 therapy (79% (SD 50.4)) as compared with compression bandage therapy alone (36% (SD 179.8); P=0.02). Evaluation of secondary efficacy end points indicated a reduced median time to 50 and 100% ulcer reepithelialization for ACT1-treated ulcers. Incorporation of ACT1 in SOC protocols may represent a well-tolerated, highly effective therapeutic strategy that expedites chronic venous ulcer healing by treating the underlying ulcer pathophysiology through Cx43-mediated pathways.

The use of connexin-based therapeutic approaches to target inflammatory diseases

Alterations in Connexin43 (Cx43) expression levels have been shown to play a role in inflammatory processes including skin wounding and neuroinflammation. Cx43 protein levels increase following a skin wound and can inhibit wound healing. Increased Cx43 has been observed following stroke, epilepsy, ischemia, optic nerve damage, and spinal cord injury with gap junctional communication and hemichannel opening leading to increased secondary damage via the inflammatory response. Connexin43 modulation has been identified as a potential target for protection and repair in neuroinflammation and skin wound repair. This review describes the use of a Cx43 specific antisense oligonucleotide (Cx43 AsODN) and peptide mimetics of the connexin extracellular loop domain to modulate Cx43 expression and/or function in inflammatory disorders of the skin and central nervous system. An overview of the role of connexin43 in inflammatory conditions, how antisense and peptide have allowed us to elucidate the role of Cx43 in these diseases, create models of diseases to test interventions and their potential for use clinically or in current clinical trials is presented. Antisense oligonucleotides are applied topically and have been used to improve wound healing following skin injury. They have also been used to develop ex vivo models of neuroinflammatory diseases that will allow testing of intervention strategies. The connexin mimetic peptides have shown potential in a number of neuroinflammatory disorders in ex vivo models as well as in vivo when delivered directly to the injury site or when delivered systemically.

Immunohistochemical demonstration of connexins in the developing feather follicle of the chicken

Based on immunohistochemistry, the study demonstrates the varying distribution and reaction intensity of connexins (Cx26 [chicken 31sim], 30 [chicken 31], 31, 32, 43, 45) in the developing feather follicle of the chicken (White Leghorn). The different embryonal stages were identified according to the normal table of Hamburger and Hamilton (1951). The development of the feather follicle complex is closely related to skin layer development, making use of the controlling function of connexins. This was evident during feather follicle differentiation, based on communication between ectomesodermal (fibroblasts) and ectodermal cells (developing epidermis), but also by the subsequent separation of the two cell line types related to their connexin-dependent differentiation degree. With the increase in mesenchymal cell numbers during feather placode development, the multiple connexins Cx26 [chicken 31sim] and 43, supported by Cx30 [chicken 31], 31 and 32, were increasingly activating the fibroblast concentrations as related to epidermal follicle buds, the specific follicle structure, the endothelial cells of capillaries and larger blood vessels, as well as the collagen fiber production and the growing feather musculature shortly before hatching; Cx45 could not be demonstrated. In conclusion, it seems that connexin expression is not only coupled to the origin of embryonic cells, but also connected with tissue formation before the follicle system can be formed.

Cardiac to cancer: connecting connexins to clinical opportunity

Gap junctions and their connexin components are indispensable in mediating the cellular coordination required for tissue and organ homeostasis. The critical nature of their existence mandates a connection to disease while at the same time offering therapeutic potential. Therapeutic intervention may be offered through the pharmacological and molecular disruption of the pathways involved in connexin biosynthesis, gap junction assembly, stabilization, or degradation. Chemical inhibitors aimed at closing connexin channels, peptide mimetics corresponding to short connexin sequences, and gene therapy approaches have been incredibly useful molecular tools in deciphering the complexities associated with connexin biology. Recently, therapeutic potential in targeting connexins has evolved from basic research in cell-based models to clinical opportunity in the form of human trials. Clinical promise is particularly evident with regards to targeting connexin43 in the context of wound healing. The following review is aimed at highlighting novel advances where the pharmacological manipulation of connexin biology has proven beneficial in animals or humans.

Connexins: sensors of epidermal integrity that are therapeutic targets

Gap junction proteins (connexins) are differentially expressed throughout the multiple layers of the epidermis. A variety of skin conditions arise with aberrant connexin expression or function and suggest that maintaining the epidermal gap junction network has many important roles in preserving epidermal integrity and homeostasis. Mutations in a number of connexins lead to epidermal dysplasias giving rise to a range of dermatological disorders of differing severity. 'Gain of function' mutations reveal connexin-mediated roles in calcium signalling within the epidermis. Connexins are involved in epidermal innate immunity, inflammation control and in wound repair. The therapeutic potential of targeting connexins to improve wound healing responses is now clear. This review discusses the role of connexins in epidermal integrity, and examines the emerging evidence that connexins act as epidermal sensors to a variety of mechanical, temperature, pathogen-induced and chemical stimuli. Connexins thus act as an integral component of the skin's protective barrier.

Expression of gap junction proteins connexins 26, 30, and 43 in Dupuytren's disease

BACKGROUND AND PURPOSE

Dupuytren's disease (DD) is a benign fibroproliferative process of the palmar aponeurosis showing similarities to wound healing. Communication of cells involved in wound healing is mediated by the composition of gap junction (GJ) proteins. We investigated the expression of 3 GJ proteins, connexins 26, 30, and 43 (Cx26, Cx30, and Cx43) in DD.

PATIENTS AND METHODS

Fragments of Dupuytren's tissue from 31 patients (mean age 56 (30-76) years, 24 male) were analyzed immunohistochemically and compared to control tissue for expression of the GJ proteins Cx26, Cx30, and Cx43 and also alfa-smooth muscle actin (α-SMA).

RESULTS

14 of 31 samples could be attributed to the involutional phase (α-SMA positive) whereas 17 samples had to be considered cords in the residual phase (α-SMA negative). Expression of Cx26 and Cx43 was seen in 12 of the 14 samples from the involutional phase, and Cx30 was seen in 7 of these. Only 4 of the 17 samples from the residual phase showed any Cx, and there was none in the controls.

INTERPRETATION

The high expression of GJ proteins Cx26, Cx30, and Cx43 in α-SMA positive myofibroblast-rich nodules, which are characteristic of the active involutional phase of DD, suggests that connexins could be a novel treatment target for the treatment of DD.