The Connexin43 Carboxyl-Terminal Peptide ACT1 Modulates the Biological Response to Silicone Implants:

Mapping the Anti-Cancer Activity of α-Connexin Carboxyl-Terminal (aCT1) Peptide in Resistant HER2+ Breast Cancer

Connexin 43 (Cx43) is a protein encoded by the GJA1 gene and is a component of cell membrane structures called gap junctions, which facilitate intercellular communication. Prior evidence indicates that elevated GJA1 expression in the HER2-positive (HER2+) subtype of breast cancer is associated with poor prognosis. Prior evidence also suggests that HER2+ breast cancers that have become refractory to HER2-targeted agents have a loss of Cx43 gap junction intercellular communication (GJIC). In this study, a Cx43-targeted agent called alpha-connexin carboxyl-terminal peptide (aCT1) is examined to determine whether GJIC can be rescued in refractory HER2+ breast cancer cells. A proposed mechanism of action for aCT1 is binding to the tight junction protein Zonal Occludens-1 (ZO-1). However, the true scope of activity for aCT1 has not been explored. In this study, mass spectrometry proteomic analysis is used to determine the breadth of aCT1-interacting proteins. The NanoString nCounter Breast Cancer 360 panel is also used to examine the effect of aCT1 on cancer signaling in HER2+ breast cancer cells. Findings from this study show a dynamic range of binding partners for aCT1, many of which regulate gene expression and RNA biology. nCounter analysis shows that a number of pathways are significantly impacted by aCT1, including upregulation of apoptotic factors, leading to the prediction and demonstration that aCT1 can boost the cell death effects of cisplatin and lapatinib in HER2+ breast cancer cells that have become resistant to HER2-targeted agents.

Gap Junctions or Hemichannel-Dependent and Independent Roles of Connexins in Fibrosis, Epithelial-Mesenchymal Transitions, and Wound Healing

Fibrosis initially appears as a normal response to damage, where activated fibroblasts produce large amounts of the extracellular matrix (ECM) during the wound healing process to assist in the repair of injured tissue. However, the excessive accumulation of the ECM, unresolved by remodeling mechanisms, leads to organ dysfunction. Connexins, a family of transmembrane channel proteins, are widely recognized for their major roles in fibrosis, the epithelial-mesenchymal transition (EMT), and wound healing. Efforts have been made in recent years to identify novel mediators and targets for this regulation. Connexins form gap junctions and hemichannels, mediating communications between neighboring cells and inside and outside of cells, respectively. Recent evidence suggests that connexins, beyond forming channels, possess channel-independent functions in fibrosis, the EMT, and wound healing. One crucial channel-independent function is their role as the primary functional component for cell adhesion. Other channel-independent functions of connexins involve their roles in mitochondria and exosomes. This review summarizes the latest advances in the channel-dependent and independent roles of connexins in fibrosis, the EMT, and wound healing, with a particular focus on eye diseases, emphasizing their potential as novel, promising therapeutic targets.

Connexin channels modulation in pathophysiology and treatment of immune and inflammatory disorders

Connexin-mediated intercellular communication mechanisms include bidirectional cell-to-cell coupling by gap junctions and release/influx of molecules by hemichannels. These intercellular communications have relevant roles in numerous immune system activities. Here, we review the current knowledge about the function of connexin channels, mainly those formed by connexin-43, on immunity and inflammation. Focusing on those evidence that support the design and development of therapeutic tools to modulate connexin expression and/or channel activities with treatment potential for infections, wounds, cancer, and other inflammatory conditions.

Mechanisms of Connexin Regulating Peptides

Gap junctions (GJ) and connexins play integral roles in cellular physiology and have been found to be involved in multiple pathophysiological states from cancer to cardiovascular disease. Studies over the last 60 years have demonstrated the utility of altering GJ signaling pathways in experimental models, which has led to them being attractive targets for therapeutic intervention. A number of different mechanisms have been proposed to regulate GJ signaling, including channel blocking, enhancing channel open state, and disrupting protein-protein interactions. The primary mechanism for this has been through the design of numerous peptides as therapeutics, that are either currently in early development or are in various stages of clinical trials. Despite over 25 years of research into connexin targeting peptides, the overall mechanisms of action are still poorly understood. In this overview, we discuss published connexin targeting peptides, their reported mechanisms of action, and the potential for these molecules in the treatment of disease.

Over-activated hemichannels: A possible therapeutic target for human diseases

In our body, all the cells are constantly sharing chemical and electrical information with other cells. This intercellular communication allows them to respond in a concerted way to changes in the extracellular milieu. Connexins are transmembrane proteins that have the particularity of forming two types of channels; hemichannels and gap junction channels. Under normal conditions, hemichannels allow the controlled release of signaling molecules to the extracellular milieu. However, under certain pathological conditions, over-activated hemichannels can induce and/or exacerbate symptoms. In the last decade, great efforts have been put into developing new tools that can modulate these over-activated hemichannels. Small molecules, antibodies and mimetic peptides have shown a potential for the treatment of human diseases. In this review, we summarize recent findings in the field of hemichannel modulation via specific tools, and how these tools could improve patient outcome in certain pathological conditions.

Connexins in Cancer: Jekyll or Hyde?

The expression, localization, and function of connexins, the protein subunits that comprise gap junctions, are often altered in cancer. In addition to cell-cell coupling through gap junction channels, connexins also form hemichannels that allow communication between the cell and the extracellular space and perform non-junctional intracellular activities. Historically, connexins have been considered tumor suppressors; however, they can also serve tumor-promoting functions in some contexts. Here, we review the literature surrounding connexins in cancer cells in terms of specific connexin functions and propose that connexins function upstream of most, if not all, of the hallmarks of cancer. The development of advanced connexin targeting approaches remains an opportunity for the field to further interrogate the role of connexins in cancer phenotypes, particularly through the use of in vivo models. More specific modulators of connexin function will both help elucidate the functions of connexins in cancer and advance connexin-specific therapies in the clinic.

The Effect of Omega-3 Fatty Acids on Capsular Tissue around the Breast Implants

BACKGROUND

One of the most common complications of the use of foreign material, in both reconstructive and cosmetic breast surgery, is capsular contracture. Historically, research on capsular contracture has focused mainly on reducing bacterial contamination through antibiotic solutions. Only secondary studies have focused on pharmacological control of the inflammation process, with particular attention paid to the main inflammation pathway, the arachidonic acid cascade. An important role in the arachidonic acid cascade is played by the omega-3 fatty acids, which are found mainly in oily fish and food supplements. The goal of the present study was to investigate the effects of omega-3 supplements on capsule contraction.

METHODS

Female C57BL/6 mice were implanted with custom-made silicone gel implants and divided into two groups. The treated group received omega-3 oil daily while the control group received water daily by gavage. After mice were euthanized, samples of capsules were collected to evaluate thickness and transforming growth factor (TGF)-β expression.

RESULTS

The results showed that capsules in the omega-3 group were thinner and more transparent than those found in the control group. In addition, a significant downregulation of the TGF-β2 gene transcript was observed in the omega-3 group.

CONCLUSIONS

Omega-3 supplementation seems to be effective in reducing the occurrence of capsular formation, mainly through inhibition of the TGF-β pathway and impairment of collagen deposit. Omega-3 supplementation is a simple and promising method that could be used to prevent or at least reduce capsular contracture after silicone implant surgery.

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.

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.

The Potential for Connexin Hemichannels to Drive Breast Cancer Progression through Regulation of the Inflammatory Response

Over the past few decades, connexin hemichannels have become recognized as major players in modulating the inflammatory response. Chronic inflammation is documented to promote tumorigenesis and is a critical component of tumor progression. Furthermore, inflammation is strongly linked to angiogenesis, immunotolerance, invasiveness, metastasis, and resistance in breast cancers. In this review, the literature on the role of connexin hemichannels in inflammation is summarized, and the potential role for hemichannel-mediated inflammation in driving breast cancer progression is discussed. Lastly, the potential for connexin-based therapeutics to modulate the inflammatory component of the tumor microenvironment as an avenue for the treatment of breast cancer is also discussed.

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.

Role of Non-Myocyte Gap Junctions and Connexin Hemichannels in Cardiovascular Health and Disease: Novel Therapeutic Targets?

The heart is a complex organ composed of multiple cell types, including cardiomyocytes and different non-myocyte populations, all working closely together to determine the hearts properties and maintain normal cardiac function. Connexins are abundantly expressed proteins that form plasma membrane hemichannels and gap junctions between cells. Gap junctions are intracellular channels that allow for communication between cells, and in the heart they play a crucial role in cardiac conduction by coupling adjacent cardiomyocytes. Connexins are expressed in both cardiomyocytes and non-myocytes, including cardiac fibroblasts, endothelial cells, and macrophages. Non-myocytes are the largest population of cells in the heart, and therefore it is important to consider what roles connexins, hemichannels, and gap junctions play in these cell types. The aim of this review is to provide insight into connexin-based signalling in non-myocytes during health and disease, and highlight how targeting these proteins could lead to the development of novel therapies. We conclude that connexins in non-myocytes contribute to arrhythmias and adverse ventricular remodelling following myocardial infarction, and are associated with the initiation and development of atherosclerosis. Therefore, therapeutic interventions targeting these connexins represent an exciting new research avenue with great potential.

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.

Connexin 43 Hemichannels Regulate the Expression of Wound Healing-Associated Genes in Human Gingival Fibroblasts

Connexin 43 (Cx43) is the most ubiquitous connexin in various cells, and presents as hemichannels (HCs) and gap junctions (GJs) on the cell membrane. We have recently shown that Cx43 abundance was strongly reduced in fibroblasts of human gingival wounds, and blocking Cx43 function in cultured human gingival fibroblasts (GFBLs) strongly regulated the expression of wound healing-related genes. However, it is not known whether these responses involved Cx43 HCs or GJs. Here we show that Cx43 assembled into distinct GJ and HC plaques in GFBLs both in vivo and in vitro. Specific blockage of Cx43 HC function by TAT-Gap19, a Cx43 mimetic peptide, significantly upregulated the expression of several MMPs, TGF-β signaling molecules, Tenascin-C, and VEGF-A, while pro-fibrotic molecules, including several extracellular matrix proteins and myofibroblast and cell contractility-related molecules, were significantly downregulated. These changes were linked with TAT-Gap19-induced suppression of ATP signaling and activation of the ERK1/2 signaling pathway. Collectively, our data suggest that reduced Cx43 HC function could promote fast and scarless gingival wound healing. Thus, selective suppression of Cx43 HCs may provide a novel target to modulate wound healing.

Modulation of gap junction-associated Cx43 in neural stem/progenitor cells following traumatic brain injury

Restoration of learning and memory deficits following traumatic brain injury (TBI) is attributed, in part, to enhanced neural stem/progenitor cell (NSPCs) function. Recent findings suggest gap junction (GJ)-associated connexin 43 (Cx43) plays a key role in the cell cycle regulation and function of NSPCs and is modulated following TBI. Here, we demonstrate that Cx43 is up-regulated in the dentate gyrus following TBI and is expressed on vimentin-positive cells in the subgranular zone. To test the role of Cx43 on NSPCs, we exposed primary cultures to the α-connexin Carboxyl Terminal (αCT1) peptide which selectively modulates GJ-associated Cx43. Treatment with αCT1 substantially reduced proliferation and increased caspase 3/7 expression on NSPCs in a dose-dependent manner. αCT1 exposure also reduced overall expression of Cx43 and phospho (p)-Serine368. These findings demonstrate that Cx43 positively regulates adult NPSCs; the modulation of which may influence changes in the dentate gyrus following TBI.

Mechanism of action of the anti-inflammatory connexin43 mimetic peptide JM2

Connexin-based therapeutics have shown the potential for therapeutic efficacy in improving wound healing. Our previous work demonstrated that the connexin43 (Cx43) mimetic peptide juxtamembrane 2 (JM2) reduced the acute inflammatory response to a submuscular implant model by inhibiting purinergic signaling. Given the prospective application in improving tissue-engineered construct tolerance that these results indicated, we sought to determine the mechanism of action for JM2 in the present study. Using confocal microscopy, a gap-FRAP cell communication assay, and an ethidium bromide uptake assay of hemichannel function we found that the peptide reduced cell surface Cx43 levels, Cx43 gap junction (GJ) size, GJ communication, and hemichannel activity. JM2 is based on the sequence of the Cx43 microtubule binding domain, and microtubules have a confirmed role in intracellular trafficking of Cx43 vesicles. Therefore, we tested the effect of JM2 on Cx43-microtubule interaction and microtubule polymerization. We found that JM2 enhanced Cx43-microtubule interaction and that microtubule polymerization was significantly enhanced. Taken together, these data suggest that JM2 inhibits trafficking of Cx43 to the cell surface by promoting irrelevant microtubule polymerization and thereby reduces the number of hemichannels in the plasma membrane available to participate in proinflammatory purinergic signaling. Importantly, this work indicates that JM2 may have therapeutic value in the treatment of proliferative diseases such as cancer. We conclude that the targeted action of JM2 on Cx43 channels may improve the tolerance of implanted tissue-engineered constructs against the innate inflammatory response.

Targeting the tight junction protein, zonula occludens-1, with the connexin43 mimetic peptide, αCT1, reduces VEGF-dependent RPE pathophysiology

A critical target tissue in age-related macular degeneration (AMD) is the retinal pigment epithelium (RPE), which forms the outer blood-retina barrier (BRB). RPE-barrier dysfunction might result from attenuation/disruption of intercellular tight junctions. Zonula occludens-1 (ZO-1) is a major structural protein of intercellular junctions. A connexin43-based peptide mimetic, αCT1, was developed to competitively block interactions at the PDZ2 domain of ZO-1, thereby inhibiting ligands that selectively bind to this domain. We hypothesized that targeting ZO-1 signaling using αCT1 would maintain BRB integrity and reduce RPE pathophysiology by stabilizing gap- and/or tight-junctions. RPE-cell barrier dysfunction was generated in mice using laser photocoagulation triggering choroidal neovascularization (CNV) or bright light exposure leading to morphological damage. αCT1 was delivered via eye drops. αCT1 treatment reduced CNV development and fluid leakage as determined by optical coherence tomography, and damage was correlated with disruption in cellular integrity of surrounding RPE cells. Light damage significantly disrupted RPE cell morphology as determined by ZO-1 and occludin staining and tiling pattern analysis, which was prevented by αCT1 pre-treatment. In vitro experiments using RPE and MDCK monolayers indicated that αCT1 stabilizes tight junctions, independent of its effects on Cx43. Taken together, stabilization of intercellular junctions by αCT1 was effective in ameliorating RPE dysfunction in models of AMD-like pathology.

KEY MESSAGE

The connexin43 mimetic αCT1 accumulates in the mouse retinal pigment epithelium following topical delivery via eye drops. αCT1 eye drops prevented RPE-cell barrier dysfunction in two mouse models. αCT1 stabilizes intercellular tight junctions. Stabilization of cellular junctions via αCT1 may serve as a novel therapeutic approach for both wet and dry age-related macular degeneration.

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.

Connexin-Based Therapeutics and Tissue Engineering Approaches to the Amelioration of Chronic Pancreatitis and Type I Diabetes: Construction and Characterization of a Novel Prevascularized Bioartificial Pancreas

Total pancreatectomy and islet autotransplantation is a cutting-edge technique to treat chronic pancreatitis and postoperative diabetes. A major obstacle has been low islet cell survival due largely to the innate inflammatory response. Connexin43 (Cx43) channels play a key role in early inflammation and have proven to be viable therapeutic targets. Even if cell death due to early inflammation is avoided, insufficient vascularization is a primary obstacle to maintaining the viability of implanted cells. We have invented technologies targeting the inflammatory response and poor vascularization: a Cx43 mimetic peptide that inhibits inflammation and a novel prevascularized tissue engineered construct. We combined these technologies with isolated islets to create a prevascularized bioartificial pancreas that is resistant to the innate inflammatory response. Immunoconfocal microscopy showed that constructs containing islets express insulin and possess a vascular network similar to constructs without islets. Glucose stimulated islet-containing constructs displayed reduced insulin secretion compared to islets alone. However, labeling for insulin post-glucose stimulation revealed that the constructs expressed abundant levels of insulin. This discrepancy was found to be due to the expression of insulin degrading enzyme. These results suggest that the prevascularized bioartificial pancreas is potentially a tool for improving long-term islet cell survival in vivo.

Intracellular Cleavage of the Cx43 C-Terminal Domain by Matrix-Metalloproteases: A Novel Contributor to Inflammation?

The coordination of tissue function is mediated by gap junctions (GJs) that enable direct cell-cell transfer of metabolic and electric signals. GJs are formed by connexin (Cx) proteins of which Cx43 is most widespread in the human body. Beyond its role in direct intercellular communication, Cx43 also forms nonjunctional hemichannels (HCs) in the plasma membrane that mediate the release of paracrine signaling molecules in the extracellular environment. Both HC and GJ channel function are regulated by protein-protein interactions and posttranslational modifications that predominantly take place in the C-terminal domain of Cx43. Matrix metalloproteases (MMPs) are a major group of zinc-dependent proteases, known to regulate not only extracellular matrix remodeling, but also processing of intracellular proteins. Together with Cx43 channels, both GJs and HCs, MMPs contribute to acute inflammation and a small number of studies reports on an MMP-Cx43 link. Here, we build further on these reports and present a novel hypothesis that describes proteolytic cleavage of the Cx43 C-terminal domain by MMPs and explores possibilities of how such cleavage events may affect Cx43 channel function. Finally, we set out how aberrant channel function resulting from cleavage can contribute to the acute inflammatory response during tissue injury.

Biomedical implant capsule formation: lessons learned and the road ahead

Clinicians and investigators have been implanting biomedical devices into patients and experimental animals for centuries. There is a characteristic complex inflammatory response to the presence of the biomedical device with diverse cell signaling, followed by migration of fibroblasts to the implant surface and the eventual walling off of the implant in a collagen capsule. If the device is to interact with the surrounding tissues, the collagen envelope will eventually incapacitate the device or myofibroblasts can cause capsular contracture with resulting distortion, migration, or firmness. This review analyzes the various tactics used in the past to modify or control capsule formation with suggestions for future investigative approaches.

Inhibition of connexin 43 hemichannel-mediated ATP release attenuates early inflammation during the foreign body response

BACKGROUND

In the last 50 years, the use of medical implants has increased dramatically. Failure of implanted devices and biomaterials is a significant source of morbidity and increasing healthcare expenditures. An important cause of implant failure is the host inflammatory response. Recent evidence implicates extracellular ATP as an important inflammatory signaling molecule. A major pathway for release of cytoplasmic ATP into the extracellular space is through connexin hemichannels, which are the unpaired constituents of gap junction intercellular channels. Blockade of hemichannels of the connexin 43 (Cx43) isoform has been shown to reduce inflammation and improve healing. We have developed a Cx43 mimetic peptide (JM2) that targets the microtubule-binding domain of Cx43. The following report investigates the role of the Cx43 microtubule-binding domain in extracellular ATP release by Cx43 hemichannels and how this impacts early inflammatory events of the foreign body reaction.

METHODS

In vitro Cx43 hemichannel-mediated ATP release by cultured human microvascular endothelial cells subjected to hypocalcemic and normocalcemic conditions was measured after application of JM2 and the known hemichannel blocker, flufenamic acid. A submuscular silicone implant model was used to investigate in vivo ATP signaling during the early foreign body response. Implants were coated with control pluronic vehicle or pluronic carrying JM2, ATP, JM2+ATP, or known hemichannel blockers and harvested at 24 h for analysis.

RESULTS

JM2 significantly inhibited connexin hemichannel-mediated ATP release from cultured endothelial cells. Importantly, the early inflammatory response to submuscular silicone implants was inhibited by JM2. The reduction in inflammation by JM2 was reversed by the addition of exogenous ATP to the pluronic vehicle.

CONCLUSIONS

These data indicate that ATP released through Cx43 hemichannels into the vasculature is an important signal driving the early inflammatory response to implanted devices. A vital aspect of this work is that it demonstrates that targeted molecular therapeutics, such as JM2, provide the capacity to regulate inflammation in a clinically relevant system.

Effect of propranolol on capsular reaction around silicone implants in guinea pigs

PURPOSE

To evaluate the effect of propranolol on capsular architecture around silicone implants by measuring the inflammation, capsular thickness, and collagen fiber density, using a guinea pig experimental model.

METHODS

Thirty six adult male guinea pigs randomly divided into two groups (n=18) were used. Each one received a silicone implant with textured-surface. The capsular tissue around implants from untreated or treated animals with the beta-adrenoceptor antagonist propranolol (10 mg/kg, dissolved in daily water) were analyzed for inflammation by histological scoring, capsular thickness by computerized histometry, and collagen fibers type I and Type III density by picrosirius polarization at different time points (7, 14 or 21 days after silicone implantation).

RESULTS

Propranolol treatment reduced inflammation and impaired capsular thickness and delayed collagen maturation around the textured implant.

CONCLUSION

Propranolol reduces the risk of developing capsular contracture around silicone implants with textured surface.

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.

Impact of the controlled release of a connexin 43 peptide on corneal wound closure in an STZ model of type I diabetes

The alpha-carboxy terminus 1 (αCT1) peptide is a synthetically produced mimetic modified from the DDLEI C-terminus sequence of connexin 43 (Cx43). Previous research using various wound healing models have found promising therapeutic effects when applying the drug, resulting in increased wound healing rates and reduced scarring. Previous data suggested a rapid metabolism rate in vitro, creating an interest in long term release. Using a streptozotocin (STZ) type I diabetic rat model with a surgically induced corneal injury, we delivered αCT1 both directly, in a pluronic gel solution, and in a sustained system, using polymeric alginate-poly-l-ornithine (A-PLO) microcapsules (MC). Fluorescent staining of wound area over a 5 day period indicated a significant increase in wound closure rates for both αCT1 and αCT1 MC treated groups, withαCT1 MC groups showing the most rapid wound closure overall. Analysis of inflammatory reaction to the treatment groups indicated significantly lower levels of both Interferon Inducible T-Cell Alpha Chemoattractant (ITAC) and Tumor Necrosis Factor Alpha (TNFα) markers using confocal quantification and ELISA assays. Additional analysis examining genes selected from the EMT pathway using RT-PCR and Western blotting suggested αCT1 modification of Transforming Growth Factor Beta 2 (TGFβ2), Keratin 8 (Krt8), Estrogen Receptor 1 (Esr1), and Glucose Transporter 4 (Glut4) over a 14 day period. Combined, this data indicated a possible suppression of the inflammatory response by αCT1, leading to increased wound healing rates.

Purinergic signaling in early inflammatory events of the foreign body response: modulating extracellular ATP as an enabling technology for engineered implants and tissues

Purinergic signaling is a ubiquitous and vital aspect of mammalian biology in which purines--mainly adenosine triphosphate (ATP)--are released from cells through loss of membrane integrity (cell death), exocytosis, or transport/diffusion across membrane channels, and exert paracrine or autocrine signaling effects through three subclasses of well-characterized receptors: the P1 adenosine receptors, the P2X ionotropic nucleotide receptors, and the P2Y metabotropic receptors. ATP and its metabolites are released by damaged and stressed cells in injured tissues. The early events of wound healing, hemostasis, and inflammation are highly regulated by these signals through activation of purinergic receptors on platelets and neutrophils. Recent data have demonstrated that ATP signaling is of particular importance to targeting leukocytes to sites of injury. This is particularly relevant to the subject of implanted medical devices, engineered tissues, and grafts as all these technologies elicit a wound healing response with varying degrees of encapsulation, rejection, extrusion, or destruction of the tissue or device. Here, we review the biology of purinergic signaling and focus on ATP release and response mechanisms that pertain to the early inflammatory phase of wound healing. Finally, therapeutic options are explored, including a new class of peptidomimetic drugs based on the ATP-conductive channel connexin43.

Gap junctions

Gap junctions are essential to the function of multicellular animals, which require a high degree of coordination between cells. In vertebrates, gap junctions comprise connexins and currently 21 connexins are known in humans. The functions of gap junctions are highly diverse and include exchange of metabolites and electrical signals between cells, as well as functions, which are apparently unrelated to intercellular communication. Given the diversity of gap junction physiology, regulation of gap junction activity is complex. The structure of the various connexins is known to some extent; and structural rearrangements and intramolecular interactions are important for regulation of channel function. Intercellular coupling is further regulated by the number and activity of channels present in gap junctional plaques. The number of connexins in cell-cell channels is regulated by controlling transcription, translation, trafficking, and degradation; and all of these processes are under strict control. Once in the membrane, channel activity is determined by the conductive properties of the connexin involved, which can be regulated by voltage and chemical gating, as well as a large number of posttranslational modifications. The aim of the present article is to review our current knowledge on the structure, regulation, function, and pharmacology of gap junctions. This will be supported by examples of how different connexins and their regulation act in concert to achieve appropriate physiological control, and how disturbances of connexin function can lead to disease.

A synthetic connexin 43 mimetic peptide augments corneal wound healing

The ability to safely and quickly close wounds and lacerations is an area of need in regenerative medicine, with implications toward healing a wide range of tissues and wounds. Using an in vivo corneal injury model, our study applied a newly developed peptide capable of promotion of wound healing and epithelial regeneration. The alpha-carboxy terminus 1 (αCT1) peptide is a 25 amino acid peptide from the C-terminus of connexin 43 (Cx43), modified to promote cellular uptake. Previous studies applying αCT1 to excisional skin wounds in porcine models produced tissues having an overall reduced level of scar tissue and decreased healing time. Rapid metabolism of αCT1 in previous work led to the investigation of extended release on wound healing rate used in this study. Here we delivered αCT1 both directly, in a concentrated pluronic solution, and in a sustained system, using polymeric alginate-poly-l-ornithine (A-PLO) microcapsules. Cell toxicity analysis showed minimal cell-loss with microcapsule treatment. Measurement of wound healing using histology and fluorescence microscopy indicated significant reduction in healing time of αCT1 microcapsule treated rat corneas compared with controls (88% vs. 38%). RT-PCR analysis showed an initial up regulation followed by down regulation of the gene keratin-19 (Krt19). Zonula occludens 1 (ZO-1) showed an opposite down regulation followed by an up regulation whereas Cx43 showed a biphasic response. Inflammatory indexes demonstrated a reduction in the inflammation of corneas treated with αCT1 microcapsules when compared with pluronic gel vehicle. These results suggest αCT1, when applied in a sustained release system, acts as a beneficial wound healing treatment.

The pharmacology of regenerative medicine

Regenerative medicine is a rapidly evolving multidisciplinary, translational research enterprise whose explicit purpose is to advance technologies for the repair and replacement of damaged cells, tissues, and organs. Scientific progress in the field has been steady and expectations for its robust clinical application continue to rise. The major thesis of this review is that the pharmacological sciences will contribute critically to the accelerated translational progress and clinical utility of regenerative medicine technologies. In 2007, we coined the phrase "regenerative pharmacology" to describe the enormous possibilities that could occur at the interface between pharmacology, regenerative medicine, and tissue engineering. The operational definition of regenerative pharmacology is "the application of pharmacological sciences to accelerate, optimize, and characterize (either in vitro or in vivo) the development, maturation, and function of bioengineered and regenerating tissues." As such, regenerative pharmacology seeks to cure disease through restoration of tissue/organ function. This strategy is distinct from standard pharmacotherapy, which is often limited to the amelioration of symptoms. Our goal here is to get pharmacologists more involved in this field of research by exposing them to the tools, opportunities, challenges, and interdisciplinary expertise that will be required to ensure awareness and galvanize involvement. To this end, we illustrate ways in which the pharmacological sciences can drive future innovations in regenerative medicine and tissue engineering and thus help to revolutionize the discovery of curative therapeutics. Hopefully, the broad foundational knowledge provided herein will spark sustained conversations among experts in diverse fields of scientific research to the benefit of all.

Embryonic wound healing: a primer for engineering novel therapies for tissue repair

Scar is the default tissue repair used by the body in response to most injuries-a response that occurs in wounds ranging in seriousness from minor skin cuts to complete severance of the spinal cord. By contrast, before the third trimester of pregnancy embryonic mammals tend to heal without scarring due to a variety of mechanisms and factors that are uniquely in operation during development in utero. The goal of tissue engineering is to develop safe and clinically effective biological substitutes that restore, maintain, or improve tissue function in patients. This review provides a comparative overview of wound healing during development and maturation and seeks to provide a perspective on just how much the embryo may be able teach us in the engineering of new therapies for tissue repair.

A Connexin43 Mimetic Peptide Promotes Regenerative Healing and Improves Mechanical Properties in Skin and Heart

SIGNIFICANCE

Evidence is building that the gap junction protein connexin43 (Cx43) is an important molecule in regenerative healing of skin and heart. Excess scarring from skin wound healing is a continuing clinical problem. Humans generally lack the ability to regenerate tissue following injury, and some degree of fibrotic repair occurs. In the skin, this results in unsightly scars with inferior mechanical properties. In the heart, scarring causes disruption in the contractility of cardiac muscle and increases the risk of deadly arrhythmia. Therapies that tip the balance of wound healing away from scar tissue and toward regeneration would thus represent a significant medical advance.

RECENT ADVANCES

A cell-permeant peptide, αCT1 (alpha connexin carboxyl-terminal peptide), based on the carboxyl-terminus of connexin43, has been shown to elicit changes in gap junction organization and intracellular communication. In the skin, αCT1 applied at acute time points results in decreased inflammatory response, reduced area of scar progenitor tissue, and restoration of more normal dermal structure and mechanical strength. αCT1 application to infarcted hearts improved cardiac contractility, reduced the propensity for arrhythmia, and increased conduction velocity through the injured heart.

CRITICAL ISSUES

Application of therapies like αCT1 could reduce cutaneous scarring and improve mechanical properties of healed skin and the contractile function and electrical stability of the heart following injury or surgery.

FUTURE DIRECTIONS

αCT1 is a potential therapy for cutaneous wounds that could lead to reduced scarring and improvements in the mechanical properties of healed skin. For injured myocardial tissues, this Cx43 mimetic peptide may also provide a therapeutic approach for targeting pathological fibrosis and reducing the likelihood of sudden death from cardiac arrhythmias.

The noncanonical functions of Cx43 in the heart

There is abundant evidence showing that connexins form gap junctions. Yet this does not exclude the possibility that connexins can exert other functions, separate from that of gap junction (or even a permeable hemichannel) formation. Here, we focus on these noncanonical functions of connexin43 (Cx43), particularly in the heart. We describe two specific examples: the importance of Cx43 on intercellular adhesion, and the role of Cx43 in the function of the sodium channel. We propose that these two functions of Cx43 have important repercussions on the propagation of electrical activity in the heart, irrespective of the presence of permeable gap junction channels. Overall, the gap junction-independent functions of Cx43 in cardiac electrophysiology emerge as an exciting area of future research.

Self-organizing tissue-engineered constructs in collagen hydrogels

A novel self-organizing behavior of cellularized gels composed of collagen type 1 that may have utility for tissue engineering is described. Depending on the starting geometry of the tissue culture well, toroidal rings of cells or hollow spheroids were prompted to form autonomously when cells were seeded onto the top of gels and the gels released from attachment to the culture well 12 to 24 h after seeding. Cells within toroids assumed distinct patterns of alignment not seen in control gels in which cells had been mixed in. In control gels, cells formed complex three-dimensional arrangements and assumed relatively higher levels of heterogeneity in expression of the fibronectin splice variant ED-A--a marker of epithelial mesenchymal transformation. The tissue-like constructs resulting from this novel self-organizing behavior may have uses in wound healing and regenerative medicine, as well as building blocks for the iterative assembly of synthetic biological structures.

The pivotal role of fibrocytes and mast cells in mediating fibrotic reactions to biomaterials

Almost all biomaterial implants are surrounded by a fibrotic capsule, although the mechanism of biomaterial-mediated fibrotic reactions is mostly unclear. To search for the types of cells responsible for triggering the tissue responses, we used poly-L glycolic acid polymers capable of releasing various reagents. We first identified that CD45(+)/Collagen 1(+) fibrocytes are recruited and resided within the fibrotic capsule at the implant interface. Interestingly, we found that the recruitment of fibrocytes and the extent of fibrotic tissue formation (collagen type I production) were substantially enhanced and reduced by the localized release of compound 48/80 and cromolyn, respectively. Since it is well established that compound 48/80 and cromolyn alter mast cell reactions, we hypothesized that mast cells are responsible for triggering fibrocyte recruitment and subsequent fibrotic capsule formation surrounding biomaterial implants. To directly test this hypothesis, similar studies were carried out using mast cell deficient mice, WBB6F1/J-Kit(W)/Kit(W-v)/, and their congenic controls. Indeed, mast cell deficient mice prompted substantially less fibrocyte and myofibroblast responses in comparison to C57 wild type mice controls. Most interestingly, subcutaneous mast cell reconstitution of WBB6F1/J-Kit(W)/Kit(W-v)/J mice almost completely restored the fibrocyte response in comparison to the C57 wild type response. These results indicate that the initial biomaterial interaction resulting in the stimulation of mast cells and degranulation byproducts not only stimulates the inflammatory cascade but significantly alters the downstream fibrocyte response and degree of fibrosis.

A peptide mimetic of the connexin43 carboxyl terminus reduces gap junction remodeling and induced arrhythmia following ventricular injury

RATIONALE

Remodeling of connexin (Cx)43 gap junctions (GJs) is linked to ventricular arrhythmia.

OBJECTIVES

A peptide mimetic of the carboxyl terminal (CT) of Cx43, incorporating a postsynaptic density-95/disks-large/ZO-1 (PDZ)-binding domain, reduces Cx43/ZO-1 interaction and GJ size remodeling in vitro. Here, we determined: (1) whether the Cx43-CT mimetic αCT1 altered GJ remodeling following left ventricular (LV) injury in vivo; (2) whether αCT1 affected arrhythmic propensity; and (3) the mechanism of αCT1 effects on arrhythmogenicity and GJ remodeling.

METHODS AND RESULTS

A cryoinjury model generating a reproducible wound and injury border zone (IBZ) in the LV was used. Adherent methylcellulose patches formulated to locally release αCT1 (< 48 hours) were placed on cryoinjuries. Relative to controls, Cx43/ZO-1 colocalization in the IBZ was reduced by αCT1 by 24 hours after injury. Programmed electric stimulation ex vivo and optical mapping of voltage transients indicated that peptide-treated hearts showed reduced inducible arrhythmias and increased ventricular depolarization rates 7 to 9 days after injury. At 24 hours and 1 week after injury, αCT1-treated hearts maintained Cx43 in intercalated disks (IDs) in the IBZ, whereas by 1 week after injury, controls demonstrated Cx43 remodeling from IDs to lateralized distributions. Over a postinjury time course of 1 week, αCT1-treated IBZs showed increased Cx43 phosphorylation at serine368 (Cx43-pS368) relative to control tissues. In biochemical assays, αCT1 promoted phosphorylation of serine368 by protein kinase (PK)C-ε in a dose-dependent manner that was modulated by, but did not require ZO-1 PDZ2.

CONCLUSIONS

αCT1 increases Cx43-pS368 in vitro in a PKC-ε-dependent manner and in the IBZ in vivo acutely following ventricular injury. αCT1-mediated increase in Cx43-pS368 phosphorylation may contribute to reductions in inducible-arrhythmia following injury.

Smooth and textured silicone surfaces of modified gel mammary prostheses cause a different impact on fibroproliferative properties of dermal fibroblasts

Our study addressed the question of whether surface properties of modern standard gel prostheses may have a measurable impact on the fibrogenic properties of cultured human dermal fibroblasts. Fibroblasts were isolated from breast implants by using the explant culture technique and incubated either on smooth or on textured silicone elastomere surfaces. Fibroblast growth was observed 4 weeks following incubation. Expression of transforming growth factor (TGF)-β1 was measured after cell culture. Incubated fibroblasts on textured surfaces showed a fivefold lower growth rate during all experiments. TGF-β1 expression was lowered in smooth surface fibroblasts compared with textured surface cultures. Our results show that smooth and textured silicone surfaces of modified gel breast implants have a different impact on the fibroproliferative properties of dermal fibroblasts. These preliminary results seem promising and we aim to further perform qualitative and quantitative analyses of the inflammatory processes in the environment of the implant and their link to the TGF-β pathway.