Connexin 43 overexpression induces lung cancer angiogenesis in vitro following phosphorylation at Ser279 in its C‑terminus

Blocking angiogenesis can inhibit tumor growth and metastasis. However, the mechanism underlying regulation of lung cancer angiogenesis remains unclear. The gap junction protein connexin 43 (Cx43) is implicated in angiogenesis. The aim of the present study was to determine the role of Cx43 in angiogenesis in vitro and its signaling pathways. Human pulmonary microvascular endothelial cells were transfected with Cx43-targeting siRNA or Cx43-overexpressing recombinant plasmid vector. Reverse transcription-quantitative polymerase chain reaction and western blotting were performed to determine Cx43, zonula occludens-1 (ZO-1), E-cadherin, β-catenin, von Willebrand factor (vWF), and plasminogen activator inhibitor-1 (PAI-1) mRNA and protein expression levels, respectively. Tyr265, Ser279, Ser368, and Ser373 phosphorylation levels in the C-terminus of Cx43 and intracellular and membranal Cx43 contents were determined using western blotting. Additionally, immunofluorescence, tube formation, Cell Counting Kit-8, and Transwell migration assays were performed. The results revealed that compared with that in the control samples, Cx43, ZO-1, E-cadherin, β-catenin, vWF, and PAI-1 mRNA and protein expression were significantly increased in the Cx43 overexpression group and significantly decreased in the Cx43-knockdown group. Moreover, the phosphorylation level of Ser279 as well as cell proliferation and migration rates were markedly increased in the Cx43 overexpression group, and tube formation revealed that the potential of angiogenesis was also increased. Conversely, in the Cx43-knockdown group, the phosphorylation level of Ser279 and cell proliferation and migration rates were reduced, and the potential of angiogenesis was greatly impaired. Under Cx43 overexpression, membranal Cx43 content was significantly increased, whereas under Cx43 knockdown, it was significantly reduced. Therefore, Cx43 overexpression could induce pulmonary angiogenesis in vitro by promoting cell proliferation and migration and activating ZO-1, E-cadherin, β-catenin, vWF, and PAI-1. This may be achieved by promoting phosphorylation and activation of the intracellular signal site Ser279 at the C-terminus of Cx43.

Connexins may play a critical role in cigarette smoke-induced pulmonary hypertension

Pulmonary hypertension (PH) is a chronic progressive disease characterized by pulmonary vasoconstriction and remodeling. It causes a gradual increase in pulmonary vascular resistance leading to right-sided heart failure, and may be fatal. Chronic exposure to cigarette smoke (CS) is an essential risk factor for PH group 3; however, smoking continues to be prevalent and smoking cessation is reported to be difficult. A majority of smokers exhibit PH, which leads to a concomitant increase in the risk of mortality. The current treatments for PH group 3 focus on vasodilation and long-term oxygen supplementation, and fail to stop or reverse PH-associated continuous vascular remodeling. Recent studies have suggested that pulmonary vascular endothelial dysfunction induced by CS exposure may be an initial event in the natural history of PH, which in turn may be associated with abnormal alterations in connexin (Cx) expression. The relationship between Cx and CS-induced PH development has not yet been directly investigated. Therefore, this review will describe the roles of CS and Cx in the development of PH and discuss the related downstream pathways. We also discuss the possible role of Cx in CS-induced PH. It is hoped that this review may provide new perspectives for early intervention.

Cx43 Promotes Endothelial Cell Migration and Angiogenesis via the Tyrosine Phosphatase SHP-2

The gap junction protein connexin 43 (Cx43) is associated with increased cell migration and to related changes of the actin cytoskeleton, which is mediated via its C-terminal cytoplasmic tail and is independent of its channel function. Cx43 has been shown to possess an angiogenic potential, however, the role of Cx43 in endothelial cell migration has not yet been investigated. Here, we found that the knock-down of Cx43 by siRNA in human microvascular endothelial cells (HMEC) reduces migration, as assessed by a wound assay in vitro and impaired aortic vessel sprouting ex vivo. Immunoprecipitation of Cx43 revealed an interaction with the tyrosine phosphatase SHP-2, which enhanced its phosphatase activity, as observed in Cx43 expressing HeLa cells compared to cells treated with an empty vector. Interestingly, the expression of a dominant negative substrate trapping mutant SHP-2 (CS) in HMEC, via lentiviral transduction, also impaired endothelial migration to a similar extent as Cx43 siRNA compared to SHP-2 WT. Moreover, the reduction in endothelial migration upon Cx43 siRNA could not be rescued by the introduction of a constitutively active SHP-2 construct (EA). Our data demonstrate that Cx43 and SHP-2 mediate endothelial cell migration, revealing a novel interaction between Cx43 and SHP-2, which is essential for this process.

Expression of Connexin43 Stimulates Endothelial Angiogenesis Independently of Gap Junctional Communication In Vitro

Connexins (Cx) form gap junctions (GJ) and allow for intercellular communication. However, these proteins also modulate gene expression, growth, and cell migration. The downregulation of Cx43 impairs endothelial cell migration and angiogenetic potential. Conversely, endothelial Cx43 expression is upregulated in an in vivo angiogenesis model relying on hemodynamic forces. We studied the effects of Cx43 expression on tube formation and proliferation in HUVECs and examined its dependency on GJ communication. Expectedly, intercellular communication assessed by dye transfer was linked to Cx43 expression levels in HUVECs and was sensitive to a GJ blockade by the Cx43 mimetic peptide Gap27. The proliferation of HUVECs was not affected by Cx43 overexpression using Cx43 cDNA transfection, siRNA-mediated knockdown of Cx43, or the inhibition of GJ compared to the controls (transfection of an empty vector, scrambled siRNA, and the solvent). In contrast, endothelial tube and sprout formation in HUVECs was minimized after Cx43 knockdown and significantly enhanced after Cx43 overexpression. This was not affected by a GJ blockade (Gap27). We conclude that Cx43 expression positively modulates the angiogenic potential of endothelial cells independent of GJ communication. Since proliferation remained unaffected, we suggest that Cx43 protein may modulate endothelial cell migration, thereby supporting angiogenesis. The modulation of Cx43 expression may represent an exploitable principle for angiogenesis induction in clinical therapy.

Reduction of Connexin 43 Attenuates Angiogenic Effects of Human Smooth Muscle Progenitor Cells via Inactivation of Akt and NF-κB Pathway

OBJECTIVE

Circulating progenitor cells possess vasculogenesis property and participate in repair of vascular injury. Cx (connexin) 43-a transmembrane protein constituting gap junctions-is involved in vascular pathology. However, the role of Cx43 in smooth muscle progenitor cells (SPCs) remained unclear. Approach and Results: Human SPCs cultured from CD34+ peripheral blood mononuclear cells expressed smooth muscle cell markers, such as smooth muscle MHC (myosin heavy chain), nonmuscle MHC, calponin, and CD140B, and Cx43 was the most abundant Cx isoform. To evaluate the role of Cx43 in SPCs, short interference RNA was used to knock down Cx43 expression. Cellular activities of SPCs were reduced by Cx43 downregulation. In addition, Cx43 downregulation attenuated angiogenic potential of SPCs in hind limb ischemia mice. Protein array and ELISA of the supernatant from SPCs showed that IL (interleukin)-6, IL-8, and HGF (hepatocyte growth factor) were reduced by Cx43 downregulation. Simultaneously, Cx43 downregulation reduced the phosphorylation of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) and Akt (protein kinase B) pathway and reactivation of NF-κB and Akt using betulinic acid, and SC79 could restore the secretion of growth factors and cytokines. Moreover, FAK (focal adhesion kinase)-Src (proto-oncogene tyrosine-protein kinase Src) activation was increased by Cx43 downregulation, and inactivation of Akt-NF-κB could be restored by Src inhibitor (PP2), indicating that Akt-NF-κB inactivated by Cx43 downregulation arose from FAK-Src activation. Finally, the depressed cellular activities and secretion of SPCs after Cx43 downregulation were restored by FAK inhibitor PF-562271 or PP2.

CONCLUSIONS

SPCs possess angiogenic potential to repair ischemic tissue mainly through paracrine effects. Gap junction protein Cx43 plays an important role in regulating cellular function and paracrine effects of SPCs through FAK-Src axis.

Association of vascular endothelial growth factor A polymorphisms and aberrant expression of connexin 43 and VEGFA with idiopathic recurrent spontaneous miscarriage

AIM

Idiopathic recurrent spontaneous miscarriage (IRSM) is one of the pregnancy outcomes that affects 1-2% of women trying to conceive. Specific genotype or aberrant expression of vascular endothelial growth factor A (VEGFA) and connexin 43 (Cx43) as two important genes for embryonic development are deemed to increase the risk of IRSM.

METHODS

To investigate any possible association of VEGFA polymorphisms and aberrant expression of Cx43 and VEGFA with IRSM, we carried out a case-control study including embryo chorionic villus tissues of 100 pregnant women with IRSM and 100 embryo chorionic villus tissues of healthy pregnant women without history of miscarriage. Restriction fragment length polymorphism was used for genotyping of rs699947 (-2578C/A) and rs2010963 (-634G/C) polymorphisms in VEGFA. Besides, quantitative real-time PCR was performed for VEGFA and Cx43 expression analysis.

RESULTS

The results showed that the frequency of -634G/C and C/C genotypes was significantly higher in aborted fetuses (P = 0.001 and P < 0.001, respectively) compared to the control group's. However, the frequency of -2578C/A genotypes was not significantly different between the cases and controls. Moreover, a significant higher expression of VEGF (P = 0.0005) and Cx43 (P = 0.0011) was observed in chorionic villus tissues of women with IRSM.

CONCLUSION

The finding demonstrated that IRSM frequency may depend on GC and CC genotypes of rs2010963 VEGF polymorphism and expression level of VEGF and Cx43 in IRSM patients was increased.

The Functional Implications of Endothelial Gap Junctions and Cellular Mechanics in Vascular Angiogenesis

Angiogenesis—the sprouting and growth of new blood vessels from the existing vasculature—is an important contributor to tumor development, since it facilitates the supply of oxygen and nutrients to cancer cells. Endothelial cells are critically affected during the angiogenic process as their proliferation, motility, and morphology are modulated by pro-angiogenic and environmental factors associated with tumor tissues and cancer cells. Recent in vivo and in vitro studies have revealed that the gap junctions of endothelial cells also participate in the promotion of angiogenesis. Pro-angiogenic factors modulate gap junction function and connexin expression in endothelial cells, whereas endothelial connexins are involved in angiogenic tube formation and in the cell migration of endothelial cells. Several mechanisms, including gap junction function-dependent or -independent pathways, have been proposed. In particular, connexins might have the potential to regulate cell mechanics such as cell morphology, cell migration, and cellular stiffness that are dynamically changed during the angiogenic processes. Here, we review the implication for endothelial gap junctions and cellular mechanics in vascular angiogenesis.

Inhibition of Cx43 attenuates ERK1/2 activation, enhances the expression of Cav‑1 and suppresses cell proliferation

In addition to being an important component of the gap junction, connexin 43 (Cx43) has been shown to regulate other cellular functions, including cell proliferation. This regulatory role of Cx43 may be important in therapeutic situations, including wound healing or ischemic injuries. Caveolin‑1 (Cav‑1) has been shown to regulate angiogenesis. The aim of the present study was to analyze whether Cx43 counter‑regulates Cav‑1 in controlling the proliferation and migration of endothelial cells. The inhibition of Cx43 with niflumic acid, flufenamic acid and 18‑α‑glycyrrhetinic acid in cultured human umbilical vein endothelial cells resulted in decreased phosphorylation of extracellular signal‑regulated kinase (ERK)1/2 and increased expression of Cav‑1, as shown by western blot analysis. Furthermore, the inhibition of Cx43 resulted in a 50±7% decrease in cell proliferation, determined using a crystal violet assay, a 48±5% decrease in migration, determined using a migration assay, and a 49±6% decrease in endothelial tube formation, determined using a Matrigel assay, compared with the control. Similar results were obtained following specific inhibition of Cx43 by mimetic peptides (Gap26 and Gap27). Inhibition of the mitogen‑activated protein kinase kinase/ERK pathway with PD‑98059 resulted in an increased expression of Cav‑1 and a reduction in the expression of Cx43. Furthermore, cell proliferation, migration and tube formation in endothelial cells were impaired. By contrast, downregulation of the protein expression of Cav‑1 by small interference RNA resulted in increased expression of Cx43 and phosphorylation of ERK1/2. Accordingly, the number of cells in the Cav‑1 treated‑group increased by 35±5% compared with the controls. The data of the present study showed that Cav‑1 suppressed cell proliferation by inhibiting the activity of Cx43, which is upstream of ERK1/2. The downregulation of Cav‑1 protein resulted in loss of the inhibitory activity of Cav‑1 on cell proliferation and led to increased cell proliferation. This counter‑regulatory effect of Cx43 may be of importance in therapeutic angiogenesis.

Targeted therapy of chronic liver diseases with the inhibitors of angiogenesis

Angiogenesis appears to be intrinsically associated with the progression of chronic liver diseases, which eventually leads to the development of cirrhosis and related complications, including hepatocellular carcinoma. Several studies have suggested that this association is relevant for chronic liver disease (CLD) progression, with angiogenesis. The fact that angiogenesis plays a pivotal role in CLDs gives rise to new opportunities for treating CLDs. Inhibitor of angiogenesis has proved effective for the treatment of patients suffering from CLD. However, it is limited in diagnosis. The last decade has witnessed a plethora of publications which elucidate the potential of angiogenesis inhibitors for the therapy of CLD. The close relationship between the progression of CLDs and angiogenesis emphasizes the need for anti-angiogenic therapy to block/slow down CLD progression. The present review summarizes all these discussions, the results of the related studies carried out to date and the future prospects in this field. We discuss liver angiogenesis in normal and pathophysiologic conditions with a focus on the role and future use of angiogenic factors as second-line treatment of CLD. This review compiles relevant findings and offers opinions that have emerged in last few years relating liver angiogenesis and its treatment using anti-angiogenic factors.

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.

Upregulation of connexin43 by glucose deprivation in H9c2 cells via the extracellular signal‑regulated kinase/mitogen‑activated protein kinase signaling pathway

Cardiac connexin43 (Cx43) serves an essential role in maintaining the functional integrity of the heart. The present study investigated the effect of glucose deprivation (GD) on Cx43 protein expression levels in H9c2 cells, and demonstrated that following 2 h GD, Cx43 protein expression levels in H9c2 cells increased by ~68%. In addition, GD activated the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) signaling pathway, which regulated the expression levels of cardiac Cx43. A MAPK inhibitor and U0126, an ERK inhibitor, abolished the effects of GD on Cx43 expression levels. Under GD, the protein expression levels of Beclin-1, p62 and LC3 were augmented, and were decreased in the presence of ERK inhibitor or siRNA-ERK. In addition, H9c2 cells exposed to GD exhibited marked increase in LDH release and decreased MTT reduction activity, all of which were not significantly reversed by U0126 treatment. Therefore, the ERK/MAPK signaling pathway may be involved in elevating cardiac Cx43 expression levels under GD in H9c2 cells.

Electronic Cigarette Smoke Impairs Normal Mesenchymal Stem Cell Differentiation

Electronic cigarettes (e-cigarettes) are promoted as low-risk alternatives to combustible cigarettes. However, the effects of chronic inhalation of potential toxicants emitted by ecigarettes remain largely unexamined. It is conceivable that smoking-induced chronic diseases result in cellular injury, in the absence of effective repair by stem cells. This study evaluates the effect of cigarette and e-cigarette aerosol extracts on the survival and differentiation of bone marrow-derived mesenchymal stem cells (MSCs). MSC growth and osteogenic differentiation were examined after exposure to smoke extracts. Data revealed detrimental effects of both cigarette and e-cigarette extracts on MSC morphology and growth. Levels and activity of alkaline phosphatase, an osteogenic marker, decreased and induction of osteoblastic differentiation was impaired. Both smoke extracts prevented osteogenic differentiation from progressing, evident by decreased expression of terminal osteogenic markers and mineralization. Elevated levels of reactive oxygen species (ROS) were detected in cells exposed to smoke extracts. Moreover, decreased differentiation potential was concomitant with severe down-regulation of Connexin 43 expression, leading to the loss of gap junction-mediated communication, which together with elevated ROS levels, could explain decreased proliferation and loss of differentiation potential. Hence, e-cigarettes present similar risk as combustible cigarettes with respect to tissue repair impairment.

Haemodynamically stimulated and in vivo generated axially vascularized soft-tissue free flaps for closure of complex defects: Evaluation in a small animal model

The arteriovenous (AV) loop model permits the creation of significant volumes of axially vascularized tissue that represents an alternative to conventional free flaps, circumventing their common limitations. However, such AV loop-based flaps have never before been examined in standardized animal models with respect to their suitability for reconstruction of critical bone-exposing defects. In the course of our preliminary studies, we implemented a novel defect model in rats that provides standardized and critical wound conditions and evaluated whether AV loop-generated flaps are suitable for free microsurgical transfer and closure of composite defects. We compared three groups of rodents with similar scapular defects: one received the AV flap, whereas controls were left to heal by secondary intention or with supplementary acellular matrix alone. To create the flaps, AV loops were placed into subcutaneous Teflon chambers filled with acellular matrix and transferred to the thigh region. Flap maturation was evaluated by histological analysis of angiogenesis and cell migration at days 14 and 28 after loop creation. Flap transfer to the scapular region and microsurgical anastomoses were performed after 14 days. Postoperative defect closure and perfusion were continually compared between groups. Within the AV flap chamber, the mean vessel number, cell count and the proportion of proliferating cells increased significantly over time. The novel defect model revealed that stable wound coverage with homogeneous vascular integration was achieved by AV loop-vascularized soft-tissue free flaps compared with controls. In summary, our study indicates for the first time that complex composite defects in rats can successfully be treated with AV loop-based free flaps.

The pivotal role of extracellular signal-regulated kinase in gap junction-mediated regulation of TXNIP

Gap junctions (GJs) play a major role in the control of cell structure, function, and metabolism. However, the molecular mechanisms involved are still poorly understood. Given that thioredoxin-interacting protein (TXNIP) regulates a broad range of cellular processes, we tested the possible involvement of TXNIP. Disruption of GJs with several chemical GJ inhibitors or connexin43 (Cx43) siRNA potently suppressed TXNIP, which was preceded by an activation of extracellular signal-regulated kinase (ERK). Inhibition of ERK or its upstream kinase with chemical inhibitors prevented the reduction of TXNIP. On the contrary, activation of ERK with mitogens or phosphatase inhibitors reproduced the suppressive effects of GJs. Further analysis revealed that dysfunction of GJs promoted TXNIP phosphorylation, ubiquitination, and degradation, whereas inhibition of ERK exerted the opposite effects. Moreover, inhibition of GJs elevated Glut1 and enhanced cell resistance to ER stress in a similar way to TXNIP downregulation. Collectively, our study thus characterizes ERK-mediated suppression of TXNIP as a presently unreported mechanism by which GJs regulate cell behaviors.

Endosulfan poisoning: An overview

Endosulfan, an organochlorine (OC) insecticide, is a widely used agricultural pesticide, despite its life threatening toxic effects. In this review, the pharmacokinetics of endosulfan, mechanism of endosulfan toxicity, clinical presentations and management, histopathological findings, and toxicological analysis are described, in addition to its environmental toxicity. The toxic effects of endosulfan can affect many organs and systems presenting in a wide array of signs and symptoms. Although termed a restricted OC-classed pesticide, it continues to be used, especially in the developing world, owing to its beneficial effects on agriculture. Several cases of endosulfan poisoning have been reported from different regions of the world. Whether accidental or intentional, endosulfan ingestion proves to be fatal unless immediate, aggressive treatment is initiated. Management is mainly supportive as no antidote exists for endosulfan poisoning as yet. The use of endosulfan needs to be strictly regulated and eventually banned worldwide altogether to lower the current morbidity and mortality resulting from this pesticide. Additionally, monitoring biological samples, using non-invasive techniques such as breast milk sampling, can provide an effective method of observing the elimination of this environmentally persistent organic pollutant from the general population.

Connexin Channels at the Glio-Vascular Interface: Gatekeepers of the Brain

Neuronal survival, electrical signaling and synaptic activity require a well-balanced micro-environment in the central nervous system. This is achieved by the blood-brain barrier (BBB), an endothelial barrier situated in the brain capillaries, that controls near-to-all passage in and out of the brain. The endothelial barrier function is highly dependent on signaling interactions with surrounding glial, neuronal and vascular cells, together forming the neuro-glio-vascular unit. Within this functional unit, connexin (Cx) channels are of utmost importance for intercellular communication between the different cellular compartments. Connexins are best known as the building blocks of gap junction (GJ) channels that enable direct cell-cell transfer of metabolic, biochemical and electric signals. In addition, beyond their role in direct intercellular communication, Cxs also form unapposed, non-junctional hemichannels in the plasma membrane that allow the passage of several paracrine messengers, complementing direct GJ communication. Within the NGVU, Cxs are expressed in vascular endothelial cells, including those that form the BBB, and are eminent in astrocytes, especially at their endfoot processes that wrap around cerebral vessels. However, despite the density of Cx channels at this so-called gliovascular interface, it remains unclear as to how Cx-based signaling between astrocytes and BBB endothelial cells may converge control over BBB permeability in health and disease. In this review we describe available evidence that supports a role for astroglial as well as endothelial Cxs in the regulation of BBB permeability during development as well as in disease states.

Flow-Induced Axial Vascularization: The Arteriovenous Loop in Angiogenesis and Tissue Engineering

Fabrication of a viable vascular network providing oxygen supply is identified as one crucial limiting factor to generate more complex three-dimensional constructs. The arteriovenous loop model provides initial blood supply and has a high angioinductive potency, making it suitable for vascularization of larger, tissue-engineered constructs. Also because of its angiogenic capabilities the arteriovenous loop is recently also used as a model to evaluate angiogenesis in vivo. This review summarizes the history of the arteriovenous loop model in research and its technical and surgical aspects. Through modifications of the isolation chamber and its containing matrices, tissue generation can be enhanced. In addition, matrices can be used as release systems for local application of growth factors, such as vascular endothelial growth factor and basic fibroblast growth factor, to affect vascular network formation. A special focus in this review is set on the assessment of angiogenesis in the arteriovenous loop model. This model provides good conditions for assessment of angiogenesis with the initial cell-free environment of the isolation chamber, which is vascularized by the arteriovenous loop. Because of the angiogenic capabilities of the arteriovenous loop model, different attempts were performed to create functional tissue in the isolation chamber for potential clinical application. Arteriovenous loops in combination with autologous bone marrow aspirate were already used to reconstruct large bone defects in humans.

Exposure to endosulfan increases endothelial permeability by transcellular and paracellular pathways in relation to cardiovascular diseases

Exposure to environmental pollutants results in out-of-balance of vascular homeostasis. Endothelial dysfunction leads to a disruption of the endothelial permeability characteristics, associated with cardiovascular diseases. We previously reported that endosulfan could cause endothelial dysfunction, but the role of endosulfan in permeability of endothelial cells has been unexplored. To elucidate molecular mechanism of endosulfan-induced changes in endothelial permeability, human umbilical vein endothelial cells (HUVECs) were exposed to endosulfan, followed by endothelial permeability analysis. The results showed that permeability of HUVECs was enhanced at 48 h after exposure to endosulfan in a dose-dependent manner. Immunofluorescence analysis demonstrated the disruptions of actin cytoskeleton and focal adhesion in endosulfan-exposed cells. Endosulfan activated MMP3/LAMC1/FAK signaling pathway, and downregulated ROCK and PXN in transcellular pathway. Endosulfan affected adherens junctions via E-cadherin and β-catenin, and impaired gap junctions through downregulation of Cx43 in paracellular pathway. We predicted four closely related human cardiovascular diseases in Nextbio, including shock, coronary arteriosclerosis, disorder of cardiac function and hypertensive disorder in relation to endosulfan exposure. Some genes such as ROCK2 and PXN were predicted to be key genes in these diseases. These findings suggest that endosulfan increased endothelial permeability by paracellular and transcellular pathways, implicating the potential correlation between endosulfan and cardiovascular diseases.

Enhanced generation of human induced pluripotent stem cells by ectopic expression of Connexin 45

Somatic cells can be successfully reprogrammed into pluripotent stem cells by the ectopic expression of defined transcriptional factors. However, improved efficiency and better understanding the molecular mechanism underlying reprogramming are still required. In the present study, a scrape loading/dye transfer assay showed that human induced pluripotent stem cells (hiPSCs) contained functional gap junctions partially contributed by Connexin 45 (CX45). We then found CX45 was expressed in human embryonic stem cells (hESCs) and human dermal fibroblasts (hDFs) derived hiPSCs. Then we showed that CX45 was dramatically upregulated during the reprogramming process. Most importantly, the ectopic expression of CX45 significantly enhanced the reprogramming efficiency together with the Yamanaka factors (OCT4, SOX2, KLF4, cMYC - OSKM), whereas knockdown of endogenous CX45 expression significantly blocked cellular reprogramming and reduced the efficiency. Our further study demonstrated that CX45 overexpression or knockdown modulated the cell proliferation rate which was associated with the reprogramming efficiency. In conclusion, our data highlighted the critical role of CX45 in reprogramming and may increase the cell division rate and result in an accelerated kinetics of iPSCs production.

Reduced expressions of connexin 43 and VEGF in the first-trimester tissues from women with recurrent pregnancy loss

BACKGROUND

Approximately 45-50 % of the recurrent pregnancy loss (RPL) remain(s) unexplained that challenges its clinical management. Formation and development of placenta as well as angiogenesis are critical for successful pregnancy. Vascular endothelial growth factor (VEGF) and connexin 43 (Cx43) play important roles in angiogenesis and placenta development and aberration of these have been linked to RPL. We aimed to investigate whether the expressions of VEGF and Cx43 were altered in the first-trimester tissues (chorionic villi and decidua) collected from women with RPL compared to those from healthy early pregnant women.

METHODS

First-trimester chorionic villi and decidua were collected from pregnant women diagnosed RPL who ended up with surgical intervention (n = 28) in comparison to those collected from women requesting surgical termination of their unwanted normal first-trimester pregnancies (n = 28). These two groups of women were matched in age and gestational weeks. Tissues were analyzed for the protein and messenger ribonucleic acid (mRNA) expressions of Cx43 and VEGF by immunohistochemistry, western blot, and quantitative reverse transcription polymerase chain reaction (qRT-PCR).

RESULTS

The expressions of both Cx43 and VEGF at the level of mRNA and protein in the villi and decidua from women with RPL were significantly decreased compared with those from women with normal early pregnancy.

CONCLUSIONS

Reduction of Cx43 and VEGF expressed in the first-trimester tissues might indicate their important roles involved in RPL and thus holds the potential to develop pharmaceutical therapies for treatment of RPL.

Tumor-induced loss of mural Connexin 43 gap junction activity promotes endothelial proliferation

Background

Proper functional association between mural cells and endothelial cells (EC) causes EC of blood vessels to become quiescent. Mural cells on tumor vessels exhibit decreased attachment to EC, which allows vessels to be unstable and proliferative. The mechanisms by which tumors prevent proper association between mural cells and EC are not well understood. Since gap junctions (GJ) play an important role in cell-cell contact and communication, we investigated whether loss of GJ plays a role in tumor-induced mural cell dissociation.

Methods

Mural cell regulation of endothelial proliferation was assessed by direct co-culture assays of fluorescently labeled cells quantified by flow cytometry or plate reader. Gap junction function was assessed by parachute assay. Connexin 43 (Cx43) protein in mural cells exposed to conditioned media from cancer cells was assessed by Western and confocal microscopy; mRNA levels were assessed by quantitative real-time PCR. Expression vectors or siRNA were utilized to overexpress or knock down Cx43. Tumor growth and angiogenesis was assessed in mouse hosts deficient for Cx43.

Results

Using parachute dye transfer assay, we demonstrate that media conditioned by MDA-MB-231 breast cancer cells diminishes GJ communication between mural cells (vascular smooth muscle cells, vSMC) and EC. Both protein and mRNA of the GJ component Connexin 43 (Cx43) are downregulated in mural cells by tumor-conditioned media; media from non-tumorigenic MCF10A cells had no effect. Loss of GJ communication by Cx43 siRNA knockdown, treatment with blocking peptide, or exposure to tumor-conditioned media diminishes the ability of mural cells to inhibit EC proliferation in co-culture assays, while overexpression of Cx43 in vSMC restores GJ and endothelial inhibition. Breast tumor cells implanted into mice heterozygous for Cx43 show no changes in tumor growth, but exhibit significantly increased tumor vascularization determined by CD31 staining, along with decreased mural cell support detected by NG2 staining.

Conclusions

Our data indicate that i) functional Cx43 is required for mural cell-induced endothelial quiescence, and ii) downregulation of Cx43 GJ by tumors frees endothelium to respond to angiogenic cues. These data define a novel and important role for maintained Cx43 function in regulation of vessel quiescence, and suggest its loss may contribute to pathological tumor angiogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1420-9) contains supplementary material, which is available to authorized users.

Flow increase is decisive to initiate angiogenesis in veins exposed to altered hemodynamics

Exposing a vein to altered hemodynamics by creating an arteriovenous (AV) shunt evokes considerable vessel formation that may be of therapeutic potential. However, it is unclear whether the introduction of oscillatory flow and/or flow increase is decisive. To distinguish between these mechanical stimuli we grafted a femoral vein into the arterial flow pathway of the contralateral limb in rats creating an arterioarterial (AA) loop (n = 7). Alternatively, we connected the femoral artery and vein using the vein graft, whereby we created an AV-loop (n = 27). Vessel loops were embedded in a fibrin filled chamber and blood flow was measured by means of flow probes immediately after surgery (day 0) and 15 days after loop creation. On day 15, animals were sacrificed and angiogenesis was evaluated using μCT and histological analysis. Mean flow increased from 0.5 to 2.4 mL/min and was elevated throughout the cardiac cycle at day 0 in AV-loops whereas, as expected, it remained unchanged in AA-loops. Flow in AV-loops decreased with time, and was at day 15 not different from untreated femoral vessels or AA-loop grafts. Pulsatile flow oscillations were similar in AV-and AA-loops at day 0. The flow amplitude amounted to ~1.3 mL/min which was comparable to values in untreated arteries. Flow amplitude remained constant in AA-loops, whereas it decreased in AV-loops (day 15: 0.4 mL/min). A large number of newly formed vessels were present in AV-loops at day 15 arising from the grafted vein. In marked contrast, angiogenesis originating from the grafted vein was absent in AA-loops. We conclude that exposure to substantially increased flow is required to initiate angiogenesis in grafted veins, whereas selective enhancement of pulsatile flow is unable to do so. This suggests that indeed flow and most likely wall shear stress is decisive to initiate formation of vessels in this hemodynamically driven angiogenesis model.

Ganoderma lucidum inhibits proliferation of human ovarian cancer cells by suppressing VEGF expression and up-regulating the expression of connexin 43

Background

Ganoderma lucidum (G. lucidum, Reishimax) is an herbal mushroom known to have inhibitory effect on tumor cell growth. However, the molecular mechanisms responsible for its anti-proliferative effects on the ovarian cancer have not been fully elucidated.

Methods

Human ovarian cancer cells HO 8910 (HOCC) and human primary ovarian cells (HPOC) were treated with G. lucidum. Effects of G. lucidum treatment on cell proliferation were studied by MTT assay. The expression of vascular endothelial growth factor (VEGF) and connexin 43 (Cx43) were measured by immunohistochemistry and real time polymerase chain reaction. To study the molecular mechanism of CX43 mediated anti-tumor activity, small interference RNA (siRNA) was used to knockdown Cx43 expression in HOCC.

Results

G. lucidum treatment resulted in reduced proliferation of HOCC. Inhibition of proliferation was accompanied by a decrease in VEGF expression and increase in Cx43 expression in the cancer cells. The extent of immune-reactivity of Cx43 or VEGF in cancer cells were correlated with the concentrations of G. lucidum used for treatment. Furthermore, knockdown of Cx43 expression in HOCC abrogated the effect of G. lucidum on cell proliferation without alteration of G. lucidum-induced attenuation of VEGF expression.

Conclusions

G. lucidum inhibits ovarian cancer by down-regulating the expression of VEGF and up-regulating the downstream Cx43 expression. G. lucidum may be a promising therapeutic agent for the treatment of ovarian cancer.

Regulation of cellular communication by signaling microdomains in the blood vessel wall

It has become increasingly clear that the accumulation of proteins in specific regions of the plasma membrane can facilitate cellular communication. These regions, termed signaling microdomains, are found throughout the blood vessel wall where cellular communication, both within and between cell types, must be tightly regulated to maintain proper vascular function. We will define a cellular signaling microdomain and apply this definition to the plethora of means by which cellular communication has been hypothesized to occur in the blood vessel wall. To that end, we make a case for three broad areas of cellular communication where signaling microdomains could play an important role: 1) paracrine release of free radicals and gaseous molecules such as nitric oxide and reactive oxygen species; 2) role of ion channels including gap junctions and potassium channels, especially those associated with the endothelium-derived hyperpolarization mediated signaling, and lastly, 3) mechanism of exocytosis that has considerable oversight by signaling microdomains, especially those associated with the release of von Willebrand factor. When summed, we believe that it is clear that the organization and regulation of signaling microdomains is an essential component to vessel wall function.

Endothelial connexin32 enhances angiogenesis by positively regulating tube formation and cell migration

The gap junction proteins connexin32 (Cx32), Cx37, Cx40, and Cx43 are expressed in endothelial cells, and regulate vascular functions involving inflammation, vasculogenesis and vascular remodeling. Aberrant Cxs expression promotes the development of atherosclerosis which is modulated by angiogenesis; however the role played by endothelial Cxs in angiogenesis remains unclear. In this study, we determined the effects of endothelial Cxs, particularly Cx32, on angiogenesis. EA.hy926 cells that had been transfected to overexpress Cx32 significantly increased capillary length and the number on branches compared to Cx-transfectant cells over-expressing Cx37, Cx40, and Cx43 or mock-treated cells. Treatment via intracellular transfer of anti-Cx32 antibody suppressed tube formation of human umbilical vein endothelial cells (HUVECs) compared to controls. In vitro wound healing assays revealed that Cx32-transfectant cells significantly increased the repaired area while anti-Cx32 antibody-treated HUVECs reduced it. Ex vivo aorta ring assays and in vivo matrigel plaque assays showed that Cx32-deficient mice impaired both vascular sprouting from the aorta and cell migration into the implanted matrigel. Therefore endothelial Cx32 facilitates tube formation, wound healing, vascular sprouting, and cell migration. Our results suggest that endothelial Cx32 positively regulates angiogenesis by enhancing endothelial cell tube formation and cell migration.

Role of asymmetric methylarginine and connexin 43 in the regulation of pulmonary endothelial function

Abstract Circulating levels of asymmetric dimethylarginine (ADMA), a nitric oxide synthase inhibitor, are increased in patients with idiopathic pulmonary hypertension (IPAH). We hypothesized that ADMA abrogates gap junctional communication, required for the coordinated regulation of endothelial barrier function and angiogenesis, and so contributes to pulmonary endothelial dysfunction. The effects of ADMA on expression and function of gap junctional proteins were studied in human pulmonary artery endothelial cells; pulmonary endothelial microvascular cells from mice deficient in an enzyme metabolizing ADMA, dimethylarginine dimethylaminohydrolase I (DDAHI); and blood-derived endothelial-like cells from patients with IPAH. Exogenous and endogenous ADMA inhibited protein expression and membrane localization of connexin 43 (Cx43) in a nitric oxide/soluble guanosine monophosphate/c-jun-dependent manner in pulmonary endothelial cells, resulting in the inhibition of gap junctional communication, increased permeability, and decreased angiogenesis. The effects of ADMA were prevented by overexpression of DDAHI or Cx43 and by treatment with rotigaptide. Blood-derived endothelial-like cells from IPAH patients displayed a distinct disease-related phenotype compared to cells from healthy controls, characterized by reduced DDAHI expression, increased ADMA production, and abnormal angiogenesis. In summary, we show that ADMA induces pulmonary endothelial dysfunction via changes in expression and activity of Cx43. Cells from IPAH patients exhibit abnormal DDAHI/Cx43 signaling as well as differences in gap junctional communication, barrier function, and angiogenesis. Strategies that promote DDAHI/Cx43 signaling may have an endothelium-protective effect and be beneficial in pulmonary vascular disease.

High flow conditions increase connexin43 expression in a rat arteriovenous and angioinductive loop model

Gap junctions are involved in vascular growth and their expression pattern is modulated in response to hemodynamic conditions. They are clusters of intercellular channels formed by connexins (Cx) of which four subtypes are expressed in the cardiovascular system, namely Cx37, Cx40, Cx43 and Cx45. We hypothesize that high flow conditions affect vascular expression of Cx in vivo. To test this hypothesis, flow hemodynamics and subsequent changes in vascular expression of Cx were studied in an angioinductive rat arteriovenous (AV) loop model. Fifteen days after interposition of a femoral vein graft between femoral artery and vein encased in a fibrin-filled chamber strong neovascularization was evident that emerged predominantly from the graft. Blood flow through the grafted vessel was enhanced ∼4.5-fold accompanied by increased pulsatility exceeding arterial levels. Whereas Cx43 protein expression in the femoral vein is negligible at physiologic flow conditions as judged by immunostaining its expression was enhanced in the endothelium of the venous graft exposed to these hemodynamic changes for 5 days. This was most likely due to enhanced transcription since Cx43 mRNA increased likewise, whereas Cx37 mRNA expression remained unaffected and Cx40 mRNA was reduced. Although enhanced Cx43 expression in regions of high flow in vivo has already been demonstrated, the arteriovenous graft used in the present study provides a reliable model to verify an association between Cx43 expression and high flow conditions in vivo that was selective for this Cx. We conclude that enhancement of blood flow and its oscillation possibly associated with the transition from laminar to more turbulent flow induces Cx43 expression in a vein serving as an AV loop. It is tempting to speculate that this upregulation is involved in the vessel formation occuring in this model as Cx43 was suggested to be involved in angiogenesis.

Connexin 43 is involved in the generation of human-induced pluripotent stem cells

Although somatic cells can be successfully programmed to create pluripotent stem cells by ectopically expressing defined transcriptional factors, reprogramming efficiency is low and the reprogramming mechanism remains unclear. Previous reports have shown that almost all human connexin (CX) isoforms are expressed by human embryonic stem (hES) cells and that gap junctional intercellular communication (GJIC) is important for ES cell survival and differentiation. However, the CX expression profiles in human induced pluripotent stem (iPS) cells and the role of CXs in the process of reprogramming back to iPS cells remains unknown. Here, we determined the expression levels of most forms of CX in human embryonic fibroblasts (hEFs) and in the hEF-derived iPS cells. A scrape loading/dye transfer assay showed that human iPS cells contained functional gap junctions (GJs) that could be affected by pharmacological inhibitors of GJ function. We found that CX43 was the most dramatically upregulated CX following reprogramming. Most importantly, the ectopic expression of CX43 significantly enhanced the reprogramming efficiency, whereas shRNA-mediated knockdown of endogenous CX43 expression greatly reduced the efficiency. In addition, we found that CX43 overexpression or knockdown affected the expression of E-CADHERIN, a marker of the mesenchymal-to-epithelial transition (MET), during reprogramming. In conclusion, our data indicate that CX43 expression is important for reprogramming and may mediate the MET that is associated with the acquisition of pluripotency.

Reduction of connexin43 in human endothelial progenitor cells impairs the angiogenic potential

Our previous work showed that arsenic trioxide down-regulated Cx43 and attenuated the angiogenic potential of human late endothelial progenitor cells (EPC). However, the relation between Cx43 and angiogenic activity of the EPC remained unclear. In the study, human late EPC were treated with siRNA specific to Cx43 (Cx43siRNA). The expression profiles as well as activity of the treated cells were examined. In parallel, the angiogenic potential of human EPC treated with Cx43siRNA was evaluated using murine hind limb ischemic model. The results showed that, in the EPC treated with Cx43siRNA, the activity of migration, proliferation, and angiogenic potential were attenuated, accompanied by reduction in vascular endothelial growth factor (VEGF) expression. In hind limb ischemia mice, EPC treated with Cx43siRNA lost the therapeutic angiogenic potential. VEGF supplementation partially recovered the activity impaired by Cx43 down-regulation. In conclusion, reduced Cx43 expression per se in the EPC causes decreased expression of VEGF and impaired angiogenic potential of the cells. Prevention of Cx43 reduction is a potential target to maintain the angiogenic potential of the EPC.

Expression of connexin 32 and connexin 43 in acute myeloid leukemia and their roles in proliferation

Connexins (Cxs), a conserved family of trans-membrane proteins, function in the organization of cell-cell communicatin via gap junctions in multicellular organisms. However, the role of Cxs in acute myeloid leukemia (AML) is poorly understood. In this study, we investigated the relationship between cell proliferation and expression of connexin 43 (Cx43) and connexin 32 (Cx32) mRNA and proteins in acute myeloid leukemia in vitro. Proliferation was observed using a growth curve and the rate of proliferation was detected by MTT assay in the acute myeloid leukemia cell lines OCI-AML3 and OCIM2. Cell cycle and cell proliferation index were assessed by flow cytometry analysis. The mRNA expression of the gap junction genes Cx43 and Cx32 was detected by RT-PCR. The expression of Cx43 and Cx32 proteins in the cell lines was analyzed by western blot analysis and immunofluorescence. The doubling time of OCI-AML3 and OCIM2 was 48 h and 36 h, respectively. In OCIM2, the percentage of cells in the S phase fraction was 59.47±9.6%, and the proliferation rate was 78.12±8.9%; however, in OCI-AML3, the percentage of cells in the S phase was 24.95±5.8%, and the proliferation rate was 35.21±6.7%. At the mRNA level, both cell lines expressed Cx43 and Cx32, and there was no significant difference in the expression of Cx43 and Cx32 mRNA in the two cell lines. At the protein level, there was a significant difference in the expression of Cx43, but not of Cx32. The proliferation ability of OCIM2 was higher than OCI-AML3, and OCIM2 exhibited higher Cx43 western blot and fluorescence intensities compared with OCI-AML3. The results suggest that a higher expression of Cx43 in AML cells may play a significant role in the proliferation ability.

Knock-down of endothelial connexins impairs angiogenesis

Connexins (Cx) are suggested to play important roles in growth and differentiation. Aim of our study was to investigate the role of endothelial Cx in the angiogenic process. Several parameters of angiogenesis were assessed in 18 h Matrigel in vitro angiogenesis assays with human umbilical vein endothelial cells (HUVEC). Prior to culture on Matrigel cells were treated with nicotine or the gap junction inhibitor palmitoleic acid (PA), or siRNA-knock-down of either Cx37, Cx40 or Cx43 was performed. Changes in Cx expression and their effects on gap-junctional communication were investigated using immunofluorescence microscopy, Western blot and Lucifer Yellow dye transfer. Knock-down of each Cx-isoform significantly reduced the amount of specific Cx protein in HUVEC. Cx-knock-down as well as treatment with PA impaired intercellular communication via gap junctions and diminished significantly the number of capillary branches. Knock-down of Cx43 and Cx40 or treatment with PA reduced complexity pattern in the angiogenesis assay. Nicotine significantly reduced expression of Cx43 and Cx37 as well as average length of capillary branches, number of branches and pattern in the Matrigel assay. We can conclude that connexins are involved in angiogenesis, in particular in branch formation. This can partly explain the changes in angiogenesis seen under nicotine treatment.

Effects of carbenoxolone on flow-mediated vasodilatation in healthy adults

Gap junctions play a key role in maintaining the functional integrity of the vascular wall. Using carbenoxolone (CBX) as a gap junction blocker, we aimed to assess the contribution of gap junctions in the vascular wall to flow-mediated vasodilatation (FMD) in healthy adults. Percentage FMD (%FMD) and circulating vasoactive molecules/activity, including atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), aldosterone, cortisol, plasma renin activity (PRA), and endothelin (ET-1), were measured in 25 healthy volunteers (mean age: 30.1 ± 5.4 yr; 14 males) before and after oral administration of CBX (100 mg). %FMD decreased after ingestion of CBX (9.71 ± 3.1 vs. 3.40 ± 2.0%; P < 0.0001). The levels of ANP, BNP, cortisol, and ET-1 remained stationary, while both PRA and aldosterone decreased ( P < 0.005) after CBX ingestion. Blood pressure and heart rate were minimally changed by CBX. Inhibition of gap junctional communication by CBX impairs FMD in healthy persons, suggesting that physiologically, vascular gap junctions participate in the maintenance of FMD. CBX does not induce the release of vasoconstricting molecules or enhance vasoconstriction, suggesting that inhibition of gap junctional communication by CBX underlies the impairment of FMD. Therefore, administering CBX in FMD examination can be a way to follow the effect of gap junctions on endothelial function, but further work remains to verify the specificity of CBX effect.

Fluorescent gold nanoclusters as a biocompatible marker for in vitro and in vivo tracking of endothelial cells

We have been investigating the fluorescent property and biocompatibility of novel fluorescent gold nanoclusters (FANC) in human aortic endothelial cells (HAEC) and endothelial progenitor cells (EPC). FANC (50-1000 nmol/L) was delivered into cells via the liposome complex. The fluorescence lasted for at least 28 days with a half-life of 9 days in vitro. Examination of 12 transcripts regulating the essential function of endothelial cells after a 72 h delivery showed that only the vascular cell adhesion molecule 1 and the vascular endothelial cadherin were down-regulated at high concentration (500 nmol/L). In addition, no activation of caspase 3 or proliferating cell nuclear antigens was detected. 3-[4,5-Dimethylthiazol-2-yl]-2,5- diphenyltetrazolium bromide (MTT) assay demonstrated that, unlike the markedly suppressed viability in cells treated with quantum dots, FANC had minimal effect on the viability, unless above 500 nmol/L, at which level a minor reduction of viability mainly caused by liposome was found. Tube formation assay showed no impaired angiogenesis in the EPC treated with FANC. In vivo study using hindlimb ischemic mice with an intramuscular injection of FANC-labeled human EPC showed that the cells preserved an angiogenic potential and exhibited traceable signals after 21 days. These findings demonstrated that FANC is a promising biocompatible fluorescent probe.

Non-channel functions of connexins in cell growth and cell death

Cellular communication mediated by gap junction channels and hemichannels, both composed of connexin proteins, constitutes two acknowledged regulatory platforms in the accomplishment of tissue homeostasis. In recent years, an abundance of reports has been published indicating functions for connexin proteins in the control of the cellular life cycle that occur independently of their channel activities. This has yet been most exemplified in the context of cell growth and cell death, and is therefore as such addressed in the current paper. Specific attention is hereby paid to the molecular mechanisms that underpin the cellular non-channel roles of connexin proteins, namely the alteration of the expression of tissue homeostasis determinants and the physical interaction with cell growth and cell death regulators. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

AGE-BSA down-regulates endothelial connexin43 gap junctions

Background

Advanced glycation end products generated in the circulation of diabetic patients were reported to affect the function of vascular wall. We examined the effects of advanced glycation end products-bovine serum albumin (AGE-BSA) on endothelial connexin43 (Cx43) expression and gap-junction communication.

Results

In human aortic endothelial cells (HAEC) treated with a series concentrations of AGE-BSA (0-500 μg/ml) for 24 and 48 hours, Cx43 transcript and Cx43 protein were reduced in a dose dependent manner. In addition, gap-junction communication was reduced. To clarify the mechanisms underlying the down-regulation, MAPKs pathways in HAEC were examined. Both a MEK1 inhibitor (PD98059) and a p38 MAPK inhibitor (SB203580) significantly reversed the reductions of Cx43 mRNA and protein induced by AGE-BSA. Consistently, phosphorylation of ERK and p38 MAPK was enhanced in response to exposure to AGE-BSA. However, all reversions of down-regulated Cx43 by inhibitors did not restore the functional gap-junction communication.

Conclusions

AGE-BSA down-regulated Cx43 expression in HAEC, mainly through reduced Cx43 transcription, and the process involved activation of ERK and p38 MAPK.

Down-regulation of connexin43 gap junction by serum deprivation in human endothelial cells was improved by (-)-Epigallocatechin gallate via ERK MAP kinase pathway

Intercellular communication through gap junctions (GJIC) plays an essential role in maintaining the functional integrity of vascular endothelium. Despite emerging evidence suggests that (-)-Epigallocatechin gallate (EGCG) may improve endothelial function. However, its effect on Cx43 gap junction in endothelial cells remains unexplored. Here we investigated the effect of EGCG on connexin43 (Cx43) gap junction in endothelial cells. The levels of Cx43 protein in human umbilical vein endothelial cells (HUVECs) cultured under serum-deprivation 48 h decreased about 50%, accompanied by decreased GJIC. This reduction can be reversed by treatments with EGCG. In addition, EGCG activated ERK, P38, and JNK mitogen-activated protein kinases (MAPKs), which were supposed to participate in the regulation of Cx43. A MEK inhibitor PD98059, but not SB203580 (a p38 kinase inhibitor) or SP600125 (a JNK kinase inhibitor), abolished the effects of EGCG on Cx43 expression and GJIC. Moreover, although both Akt and eNOS phosphorylation were time-dependently augmented by EGCG, neither PI3K inhibitor LY294002 nor eNOS inhibitor L-NAME blocked the effects of EGCG on Cx43 gap junctions. Thus, EGCG attenuated Cx43 down-regulation and impaired GJIC induced by serum deprivation, ERK MAPK Signal transduction pathway appears to be involved in these processes.

Connexins: sensors and regulators of cell cycling

It is nowadays well established that gap junctions are critical gatekeepers of cell proliferation, by controlling the intercellular exchange of essential growth regulators. In recent years, however, it has become clear that the picture is not as simple as originally anticipated, as structural precursors of gap junctions can affect cell cycling by performing actions not related to gap junctional intercellular communication. Indeed, connexin hemichannels also foresee a pathway for cell growth communication, albeit between the intracellular compartment and the extracellular environment, while connexin proteins as such can directly or indirectly influence the production of cell cycle regulators independently of their channel activities. Furthermore, a novel set of connexin-like proteins, the pannexins, have lately joined in as regulators of the cell proliferation process, which they can affect as either single units or as channel entities. In the current paper, these multifaceted aspects of connexin-related signalling in cell cycling are reviewed.

Classical swine fever virus down-regulates endothelial connexin 43 gap junctions

Classical swine fever is a contagious disease of pigs characterized by fatal hemorrhagic fever. Classical swine fever virus (CSFV) induces the expression of pro-inflammatory and pro-coagulant factors of vascular endothelial cells and establishes a long-term infection. This study aimed to understand the effect of CSFV on endothelial connexin 43 (Cx43) expression and gap junctional intercellular coupling (GJIC). Porcine aortic endothelial cells were infected with CSFV at different multiplicity of infection for 48 h. Semi-quantitative RT-PCR, immunoconfocal microscopy, and Western blotting showed that the transcription and translation of Cx43 were reduced, and this was associated with an attenuation of GJIC. This decrease occurred in a time-dependent manner. An ERK inhibitor (PD98059), a JNK inhibitor (SP600125), and proteasome/lysosome inhibitors all significantly reversed the reduction in Cx43 protein levels without any influence on the titer of progeny virus. In addition, CSFV activated ERK and JNK in a time-dependent manner and down-regulated Cx43 promoter activity, mainly through decreased AP2 binding. This effect was primarily caused by the replication of CSFV rather than a consequence of cytokines being induced by CSFV infection of endothelial cells.

Development of the endothelium: an emphasis on heterogeneity

The endothelium is composed of specialized epithelial cells that line the vasculature, the lymph vessels, and the heart. These endothelial cells are characterized by their stratification and are connected via intercellular junctions that confer specific permeability. Although all endothelium acts as a barrier, considerable heterogeneity exists among different organs and even within vessels. During development, the endothelial cells are specified before they migrate to their final destination, and then they commit to an arterial or venous fate. From the venous endothelial cell population, a subset of cells is further specified as lymphatic endothelium. The endothelium can be highly permeable, as in the lymph vessels, or impenetrable, as in the blood-brain barrier. These differences arise during development and are orchestrated through a series of signaling pathways. This review details how endothelial cells arise and are directed to their specific fate, specifically targeting what differentiates endothelial populations.

Ultrasonic microbubble-mediated gene delivery causes phenotypic changes of human aortic endothelial cells

Ultrasound, in combination with microbubbles, serves as a feasible nonviral method in vascular gene delivery. However, the effects of ultrasonic microbubble transfection (UMT) on vascular endothelial cells remained unclear. We therefore investigated whether UMT itself causes phenotypic changes of the human aortic endothelial cells (HAEC) in vitro. HAEC were cultured with solution containing luciferase reporter gene and microbubbles followed by exposure to ultrasound of selected parameters. Thereafter, the proliferation and migration activities of HAEC were investigated. Real-time RT-PCR and/or western blotting were performed to assess expression profile of HAEC, including growth-related factors (vascular endothelial growth factor, fins-like tyrosine kinase-1 [Flt-1] and kinase insert domain-containing receptor [KDR]), coagulatory factor (von Willebrand factor), vasodilatory enzyme (endothelial nitric oxide synthase), gap junctional protein connexin43 and adhesion molecules (P-selectin, intercellular adhesion molecule 1 and vascular cell adhesion molecule 1). The results showed that in conditions where UMT lead to expression of luciferase, proliferation capacity is enhanced (p<0.001), partly attributable to the effect of ultrasound (p<0.05), after excluding the effect of contact inhibition. In addition, the expression of KDR and Flt-1 were found increased at either the mRNA level, protein level, or both (p<0.05). Other markers did not have significant changes (all p>0.2). Similarly, the migration capacity was minimally changed (p>0.3). In conclusion, UMT causes phenotypic changes of HAEC by enhancing proliferation and upregulating KDR and Flt-1, while possesses no obvious adverse effect on viable transfected cells. Further investigation is required to clarify the impact of these changes by UMT in vivo.

Silencing TRPM7 promotes growth/proliferation and nitric oxide production of vascular endothelial cells via the ERK pathway

AIMS

The presence and potential function of transient receptor potential melastatin 7 (TRPM7), a Ca2+-permeable non-selective cation channel of the TRP channel superfamily in human vascular endothelial cells, were examined.

METHODS AND RESULTS

Whole-cell patch-clamp recordings showed outward-rectifying currents in human umbilical vein endothelial cells (HUVECs), which was potentiated by removing the extracellular Ca2+ and Mg2+, but inhibited by non-specific TRPM7 blocker Gd3+ or 2-aminoethoxydiphenyl borate (2-APB). TRPM7 mRNA was detected in HUVECs by RT-PCR, but TRPM6, its closest homologue, was not. Silencing TRPM7 by small interfering RNA (siRNA) decreased the level of TRPM7 mRNA and the TRPM7-like current. Interestingly, knockdown of TRPM7 with siRNA or inhibition of TRPM7 function with 2-APB increased the phosphorylation of extracellular signal-regulated kinase (ERK) and enhanced growth/proliferation of HUVECs. This enhanced cell growth/proliferation was abolished by an inhibitor of the ERK signalling pathway. In addition to cell growth/proliferation, silencing TRPM7 also increased expression of nitric oxide synthase and nitric oxide production in an ERK pathway-dependent manner.

CONCLUSION

These observations suggest that TRPM7 channels may play an important role in the function of vascular endothelial cells.

C-reactive protein, sodium azide, and endothelial connexin43 gap junctions

We investigated the effect of C-reactive protein (CRP) and sodium azide (NaN(3)) on endothelial Cx43 gap junctions. Human aortic endothelial cells (HAEC) were treated with (a) detoxified CRP, (b) detoxified dialyzed CRP, (c) detoxified dialyzed CRP plus NaN(3), (d) NaN(3), or (e) dialyzed NaN(3). The concentration of CRP in all preparations was fixed to 25 microg/ml and that of NaN(3) in the preparations of (c) to (e) was equivalent to that contained in the 25 microg/ml CRP purchased commercially. The results showed that both the expression of Cx43 protein and gap junctional communication function post-48-h incubation were reduced and inhibited by the detoxified CRP, NaN(3), or detoxified dialyzed CRP plus NaN(3), but not by the detoxified dialyzed CRP or dialyzed NaN(3). Reverse transcription-polymerase chain reaction analysis of cells treated for 72 h also showed a pattern of transcriptional regulation essentially the same as that for the proteins. We concluded that CRP does not have a significant effect on Cx43 gap junctions of HAEC, but NaN(3) inhibited the viability of cells and downregulate their junctions.