Multiple connexin expression in regenerating arterial endothelial gap junctions

Relationship between SNP rs1764391 and Susceptibility, Risk Factors, Gene-environment Interactions of Acute Myocardial Infarction in Guangxi Han Chinese Population

BACKGROUND

Large-scale population studies showed that the SNP rs1764391 of Connexin37 gene also known as Cx37 gene may play a pivotal role in the occurrence and development of acute myocardial infarction (AMI). Published results, however, are highly controversial.

OBJECTIVE

This study aimed to examine the association between SNP rs1764391 of Cx37 and diseasesusceptibility, several risk factors, and gene-environment interactions of AMI in Guangxi Han Chinese population.

METHODS

In this study, 344 healthy controls and 344 AMI patients of Han Chinese population were enrolled. The TaqMan assay was implemented to identify genotypes of Cx37 and allele frequencies of SNP rs1764391 in both the AMI and control groups.

RESULTS

Significant differences were detected in TT genotype frequencies of SNP rs1764391 between the AMI and control groups (P < 0.05). In the context of gender stratification, the result was also statistically different in women (P < 0.05). Each variable such as age, BMI, diabetes, high blood pressure, smoking and TC was a risk factor and correlated significantly (P < 0.05) with the development of AMI. HDL-C correlated negatively with the risk of AMI (P < 0.001). BMI, smoking or alcohol consumed interacts significantly (P < 0.017) with the presence of the SNP rs1764391 CC genotype.

CONCLUSION

Evidences were presented that Cx37 rs1764391 variation may contribute to the risk for AMI, especially in women and this genetic variant may prove to be a potential biomarker for AMI risk stratification and may prove to be a useful target for therapeutic intervention to further improve prognosis in high-risk patients.

Large-Scale Single-Cell RNA-Seq Reveals Molecular Signatures of Heterogeneous Populations of Human Induced Pluripotent Stem Cell-Derived Endothelial Cells

RATIONALE

Human-induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) have risen as a useful tool in cardiovascular research, offering a wide gamut of translational and clinical applications. However, inefficiency of the currently available iPSC-EC differentiation protocol and underlying heterogeneity of derived iPSC-ECs remain as major limitations of iPSC-EC technology.

OBJECTIVE

Here, we performed droplet-based single-cell RNA sequencing (scRNA-seq) of the human iPSCs after iPSC-EC differentiation. Droplet-based scRNA-seq enables analysis of thousands of cells in parallel, allowing comprehensive analysis of transcriptional heterogeneity.

METHODS AND RESULTS

Bona fide iPSC-EC cluster was identified by scRNA-seq, which expressed high levels of endothelial-specific genes. iPSC-ECs, sorted by CD144 antibody-conjugated magnetic sorting, exhibited standard endothelial morphology and function including tube formation, response to inflammatory signals, and production of NO. Nonendothelial cell populations resulting from the differentiation protocol were identified, which included immature cardiomyocytes, hepatic-like cells, and vascular smooth muscle cells. Furthermore, scRNA-seq analysis of purified iPSC-ECs revealed transcriptional heterogeneity with 4 major subpopulations, marked by robust enrichment of CLDN5, APLNR, GJA5, and ESM1 genes, respectively.

CONCLUSIONS

Massively parallel, droplet-based scRNA-seq allowed meticulous analysis of thousands of human iPSCs subjected to iPSC-EC differentiation. Results showed inefficiency of the differentiation technique, which can be improved with further studies based on identification of molecular signatures that inhibit expansion of nonendothelial cell types. Subtypes of bona fide human iPSC-ECs were also identified, allowing us to sort for iPSC-ECs with specific biological function and identity.

Morphine Induces Fibroblast Activation through Up-regulation of Connexin 43 Expression: Implication of Fibrosis in Wound Healing

Morphine is the most effective drugs for attenuating various types of severe pain, but morphine abuse carries a high risk of systemic fibrosis. Our previous have indicated that systemic administration of morphine hinders angiogenesis and delays wound healing. Here we have explained the pathological mechanism underlying the effect of morphine on wound healing. To determine how morphine affects wound healing, we first created a wound in mice treated them with a combination of a low doses (5 mg/kg/day) and high doses (20 or 30 mg/kg/day) of morphine. An In vivo study revealed that high-dose morphine-induced abnormal myofibroblasts persist after the end of wound healing because of connexin 43 (Cx43) upregulation. High-dose morphine-induced Cx43 increased the expression levels of focal adhesion molecules, namely fibronectin and alpha-smooth muscle actin (α-SMA) through the activation of transforming growth factor (TGF)-β1 signaling. In addition, we found that Cx43 contributed to TGF-βRII/ Smad2/3 signaling for regulating the differentiation of fibroblasts into myofibroblasts during high-dose morphine exposure. In conclusion, the abnormal regulation of Cx43 by morphine may induce systemic fibrosis because of abnormal myofibroblast function.

VEGF promotes endothelial progenitor cell differentiation and vascular repair through connexin 43

Background

Endothelial progenitor cell (EPC) differentiation is considered crucial for vascular repair. Vascular endothelial growth factor (VEGF) induces EPC differentiation, but the underlying mechanism of this phenomenon remains unclear. Connexin 43 (Cx43) is reported to be involved in the regulation of stem cell differentiation. Therefore, we sought to determine whether Cx43 is involved in VEGF-induced EPC differentiation and vascular repair.

Methods

Rat spleen-derived EPCs were cultured and treated with various concentrations of VEGF (0, 10, or 50 ng/mL), and the relationship between EPC differentiation and Cx43 expression was evaluated. Thereafter, fluorescence redistribution after photobleaching was performed to assess the relationship between adjacent EPC differentiation and Cx43-induced gap junction intercellular communication (GJIC). After carotid artery injury, EPCs pretreated with VEGF were injected into the tail veins, and the effects of Cx43 on vascular repair were evaluated.

Results

EPCs cultured with VEGF exhibited accelerated differentiation and increased expression of Cx43. However, inhibition of Cx43 expression using short interfering RNA (siRNA) attenuated EPC GJIC and consequent EPC differentiation. VEGF-pretreated EPC transplantation promoted EPC homing and reendothelialization, and inhibited neointimal formation. These effects were attenuated by siRNA inhibition of Cx43.

Conclusions

Our results from in vivo and in vitro experiments indicated that VEGF promotes EPC differentiation and vascular repair through Cx43.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0684-1) contains supplementary material, which is available to authorized users.

Gap junction proteins and their role in spinal cord injury

Gap junctions are specialized intercellular communication channels that are formed by two hexameric connexin hemichannels, one provided by each of the two adjacent cells. Gap junctions and hemichannels play an important role in regulating cellular metabolism, signaling, and functions in both normal and pathological conditions. Following spinal cord injury (SCI), there is damage and disturbance to the neuronal elements of the spinal cord including severing of axon tracts and rapid cell death. The initial mechanical disruption is followed by multiple secondary cascades that cause further tissue loss and dysfunction. Recent studies have implicated connexin proteins as playing a critical role in the secondary phase of SCI by propagating death signals through extensive glial networks. In this review, we bring together past and current studies to outline the distribution, changes and roles of various connexins found in neurons and glial cells, before and in response to SCI. We discuss the contribution of pathologically activated connexin proteins, in particular connexin 43, to functional recovery and neuropathic pain, as well as providing an update on potential connexin specific pharmacological agents to treat SCI.

Association of Connexin37 C1019T with myocardial infarction and coronary artery disease: a meta-analysis

BACKGROUND

Several studies have reported that Connexin37 (Cx37) gene C1019T polymorphism is associated with myocardial infarction (MI) and coronary artery disease (CAD). However, the results remain contradictory.

METHODS AND RESULTS

Pubmed, Embase, and Cochrane library databases were systemically searched. Data were extracted by two independent reviewers and pooled odds ratio (OR) with 95% confidence interval (CI) was calculated. A total of 3498 MI cases and 3986 controls, as well as 1808 CAD cases and 1197 controls were enrolled in this meta-analysis. For MI, the overall ORs and 95% CIs of 1019T were 1.04, 0.95-1.15; and 1.02, 0.85-1.22 in dominant and recessive models, respectively. For CAD, the overall ORs and 95% CIs of 1019T were 0.61, 0.51-0.72; and 0.52, 0.43-0.62 in dominant and recessive models, respectively. No publication bias was found in this meta-analysis.

CONCLUSIONS

This meta-analysis showed that Cx37 C1019T was a risk factor for MI and a protective factor for CAD.

Lack of association between the connexin 37 C1019T gene polymorphism and coronary artery disease in a Chinese population: Meta-analysis of 2,206 subjects

The connexin 37 (Cx37) C1019T gene polymorphism has been suggested to be correlated with increased coronary artery disease (CAD) risk, but research results remain inconsistent. To explore the relationship between the Cx37 C1019T gene polymorphism and CAD in a Chinese population, the current meta-analysis of 6 individual studies involving 1,244 CAD patients and 962 controls was conducted. The pooled odds ratios (ORs) as well as the corresponding 95% confidence intervals (CIs) were estimated using a random- or fixed-effect model. No significant association was found between Cx37 C1019T gene polymorphism and CAD in the Chinese population under the allelic (OR=0.96; 95% CI=0.59-1.56, P=0.87), recessive (OR=0.77, 95% CI=0.28-2.08, P=0.60), dominant (OR=0.990, 95% CI=0.773-1.266, P=0.934), additive (OR=1.000, 95% CI=0.736-1.359, P=1.000), homozygous (OR=1.062, 95% CI=0.598-1.887, P=0.836) or heterozygous (OR=1.017, 95% CI=0.802-1.291, P=0.888) genetic models. Cx37 C1019T gene polymorphism was not suggested to be associated with CAD susceptibility in the Chinese population. In conclusion, no association was found between Cx37 C1019T gene polymorphism and CAD in the Chinese population.

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.

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.

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.

Oxidized phospholipid species promote in vivo differential cx43 phosphorylation and vascular smooth muscle cell proliferation

Regulation of both the expression and function of connexins in the vascular wall is important during atherosclerosis. Progression of the disease state is marked by vascular smooth muscle cell (VSMC) proliferation, which coincides with the reduced expression levels of connexin 43 (Cx43). However, nothing is currently known about the factors that regulate post-translational modifications of Cx43 in atherogenesis, which could be of particular importance, due to the association between site-specific Cx43 phosphorylation and cellular proliferation. We compared the effects of direct carotid applications of two oxidized phospholipid derivatives, 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphorylcholine (POVPC) and 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphorylcholine (PGPC), on Cx43 expression and phosphorylation, and on cell proliferation. Since both POVPC and PGPC have been shown to act through different intracellular pathways, we hypothesized that each oxidized phospholipid species could induce differential Cx43 phosphorylation events in the cytoplasmically located carboxyl-terminal region of the protein, which could potentially enhance cell proliferation. Application of POVPC caused a reduction in VSMC Cx43 levels, enhanced its phosphorylation at serine (pS) 279/282, and increased VSMC proliferation both in vivo and in vitro. Treatment with PGPC enhanced VSMC pS368 levels with no associated change in proliferation. These oxidized phospholipid-induced Cx43 post-translational changes in VSMCs were consistent with those identified in ApoE(-/-) mice. Taken together, these results demonstrate that post-translational phosphorylation of Cx43 could be a key factor in the pathogenesis of atherosclerosis.

Intercellular Communication in Atherosclerosis

Cell-to-cell communication is a process necessary for physiological tissue homeostasis and appears often altered during disease. Gap junction channels, formed by connexins, allow the direct intercellular communication between adjacent cells. After a brief review of the pathophysiology of atherosclerosis, we will discuss the role of connexins throughout the different stages of the disease.

Biological and biophysical properties of vascular connexin channels

Intercellular channels formed by connexin proteins play a pivotal role in the direct movement of ions and larger cytoplasmic solutes between vascular endothelial cells, between vascular smooth muscle cells, and between endothelial and smooth muscle cells. Multiple genetic and epigenetic factors modulate connexin expression levels and/or channel function, including cell-type-independent and cell-type-specific transcription factors, posttranslational modifications, and localized membrane targeting. Additionally, differences in protein-protein interactions, including those between connexins, significantly contribute to both vascular homeostasis and disease progression. The biophysical properties of the connexin channels identified in the vasculature, those formed by Cx37, Cx40, Cx43 and/or Cx45 proteins, are discussed in this chapter in the physiological and pathophysiological context of vessel function.

Diabetes reduces aortic endothelial gap junctions in ApoE-deficient mice: simvastatin exacerbates the reduction

We examined the endothelial gap junctions in diabetic hyperlipidemic mice. Male apolipoprotein E (apoE)-deficient mice were made diabetic by streptozotocin. Three weeks later, the animals were treated with simvastatin for 2 weeks. The expression of aortic gap junctions in the non-diabetic (n=10), untreated diabetic (n=10), and simvastatin-treated diabetic animals (n=6) was analyzed. There was a >4-fold increase in serum cholesterol level and >50% increase in plaque areas in the diabetic mice, regardless of simvastatin treatment. Western blotting of aortae showed reduced expression of connexin37 (Cx37) and Cx40 in the diabetic mice, which were further decreased in the simvastatin-treated diabetic mice. Immunoconfocal microscopy showed that endothelial gap junctions made of Cx37 and Cx40 were both reduced in the untreated diabetic mice compared with the non-diabetic mice (decrease: Cx37, 41%; Cx40, 42%; both p<0.01). The reduction was greater in the simvastatin-treated mice (decrease in treated diabetic vs non-diabetic: Cx37, 61%; Cx40, 79%; both p<0.01; decrease in treated diabetic vs untreated diabetic: Cx37, 34%; Cx40, 63%; both p<0.01). Cx37 and Cx40 were decreased in the endothelium of plaque surface. Cx43 appeared in the medial layer and inner layer of the intima. All three connexins were rarely expressed in monocytes/macrophages inside the plaques. In conclusion, in apoE-deficient mice, streptozotocin-induced diabetes is associated with downregulation of endothelial Cx37 and Cx40 gap junctions. Short-term treatment with simvastatin exacerbates the downregulation.

Blocking connexin43 expression reduces inflammation and improves functional recovery after spinal cord injury

After traumatic CNS injury, a cascade of secondary events expands the initial lesion. The gap-junction protein connexin43 (Cx43), which is transiently up-regulated, has been implicated in the spread of 'bystander' damage. We have used an antisense oligodeoxynucleotide (asODN) to suppress Cx43 up-regulation in two rat models of spinal cord injury. Within 24 h of compression injury, rats treated with Cx43-asODN scored higher than sense-ODN and vehicle-treated controls on behavioural tests of locomotion. Their spinal cords showed less swelling and tissue disruption, less up-regulation of astrocytic GFAP, and less extravasation of fluorescently-labelled bovine serum albumin and neutrophils. The locomotor improvement was sustained over at least 4 weeks. Following partial spinal cord transection, Cx43-asODN treatment reduced GFAP immunoreactivity, neutrophil recruitment, and the activity of OX42(+) microglia in and around the lesion site. Cx43 has many potential roles in the pathophysiology of CNS injury and may be a valuable target for therapeutic intervention.

The influence of smoking and homocysteine on subclinical atherosclerosis is modified by the connexin37 C1019T polymorphism - The Cardiovascular Risk in Young Finns Study

BACKGROUND

A polymorphism C1019T on the connexin37 (Cx37) gene has been found to associate with coronary artery disease. There are conflicting results on which allele confers risk, and the possibility of interactions between the polymorphism and risk factors has been raised. In this study, we examined interactions between the Cx37 polymorphism and common risk factors and their associations to early vascular parameters of atherosclerosis: carotid artery intima-media thickness (IMT), and carotid artery compliance (CAC) and brachial artery flow mediated dilatation (FMD).

METHODS

A population of 1440 healthy young adults from the Cardiovascular Risk in Young Finns Study was studied. The subjects were genotyped and their cardiovascular risk factor and ultrasound data gathered in 2001 were used for the statistical analyses.

RESULTS

In the whole population, homocysteine in subjects with the TT genotype was found to be associated with higher FMD values (p for interaction 0.038) and remained so in three different adjusted models (p for interaction 0.022-0.038). In women with the CC genotype, smoking was found to be associated with higher FMD values and the smoking-by-genotype interaction remained significant in three adjusted models (p for interaction 0.001-0.041). In women with TT genotype, the effect of smoking was opposite, i.e., FMD values for smokers were lower compared to non-smokers. In men, physical activity interacted with Cx37 on CAC in the CT and TT genotypes (p for interaction 0.011). No significant interactions were found to predict IMT.

CONCLUSIONS

The effect of smoking and homocysteine levels on arterial endothelial functions and elasticity were modified by the allelic variation of the Cx37 gene. These data suggest that variation in the connexin gene may modify effects risk factors have on vascular function.

Associations between connexin37 gene polymorphism and markers of subclinical atherosclerosis: the Cardiovascular Risk in Young Finns study

OBJECTIVE

Connexin37 (cx37) C1019T polymorphism has been shown to associate with coronary artery disease in different populations. We investigated whether this polymorphism associates with carotid artery intima-media thickness (IMT), carotid artery compliance (CAC) and brachial artery flow mediated dilatation (FMD) - i.e., early ultrasound markers of subclinical atherosclerosis - in a clinically healthy population of young Finnish adults.

METHODS AND RESULTS

1440 individuals from the Cardiovascular Risk in Young Finns study were genotyped and studied using cardiovascular risk factor and ultrasound data obtained in 2001. In linear regression models, no significant association between the cx37 polymorphism and carotid IMT, CAC or brachial artery FMD (ANOVA, p=0.159, 0.151 and 0.547), respectively, was found in the whole population or in women and men separately.

CONCLUSIONS

The connexin37 C1019T polymorphism is not related with markers of subclinical atherosclerosis in young adults.

Roles of Gap Junctions and Connexins in Non-Neoplastic Pathological Processes in which Cell Proliferation Is Involved

Cell proliferation is an important process for reproduction, growth and renewal of living cells and occurs in several situations during life. Cell proliferation is present in all the steps of carcinogenesis, initiation, promotion and progression. Gap junctions are the only specialization of cell membranes that allows communication between adjacent cells. They are known to contribute to tissue homeostasis and are composed of transmembrane proteins called "connexins." These junctions are also known to be involved in cell proliferation control. The roles of gap junctions and connexins in cell proliferation are complex and still under investigation. Since pioneer studies by Loewenstein, it is known that neoplastic cells lack communicating junctions. They do not communicate with their neighbors or with non-neoplastic cells from the surrounding area. There are many studies and review articles dedicated to neoplastic tissues. The aim of this review is to present evidence on the roles of gap junctions and connexins in non-neoplastic processes in which cell proliferation is involved.

Endothelial gap junctions are down-regulated by arsenic trioxide

We investigated the effect of As(2)O(3), an anti-cancer drug, on endothelial gap junctions. Human aortic endothelial cells (HAEC) were treated with As(2)O(3) at 1, 10, 100, and 1000 ng/ml and the cells were examined to evaluate the expression of connexin43 (Cx43) and to assess gap-junction communication. Endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) were measured to assess for endothelial dysfunction. Male Sprague-Dawley rats were given intravenous As(2)O(3) (200 mug/kg/day) or saline for 4 weeks, after which aortic endothelial gap junctions, eNOS, and circulating NO levels were evaluated. We found that HAEC Cx43 transcripts and gap junctions were reduced and gap-junction communication was attenuated by As(2)O(3). This decrease of Cx43 gap junctions was prevented by the addition of protease inhibitors. At a dose of 100 ng/ml of As(2)O(3), eNOS was reduced at 48 h, but NO was markedly reduced by 1 h. In animals treated with As(2)O(3), endothelial gap junctions comprising Cx37, Cx40, or Cx43 were all reduced in amount, while eNOS and circulating NO levels remained unchanged. In both in vitro and in vivo rat experiments, endothelial gap junctions were consistently reduced by As(2)O(3), unlike the response of eNOS and NO, which were decreased in cells but not in the rat aortic endothelium. The reduction in Cx43 involved both down-regulation at the transcriptional level and increased degradation. These findings indicate that gap-junction communication in the vascular endothelium is inhibited by treatment with As(2)O(3).

Comparison of endothelial cells grown on different stent materials

We compared the behavior of endothelial cells grown on stent materials. Human umbilical vein endothelial cells (HUVEC) were seeded (200 or 800 cells/mm(2)) onto different metallic sheets, including 316 stainless steel (low carbon; 316LSS), nitinol, and 316LSS coated with TiN or TiO(2). Cells seeded onto tissue culture-treated polystyrene dish coated with gelatin were used as controls. Forty-eight hours later, the cells were examined by Western blotting, immunofluorescence microscopy, and scanning electron microscopy (SEM). The results showed that for either seeding values, the levels of cellularity on TiN and TiO(2) are comparable or higher, and those on 316LSS and nitinol are lower compared to the controls (p < 0.05). SEM demonstrated that cells are well-attached on the metallic surface with various amount of cellular processes. In metals seeded with 800 cells/mm(2), Western blotting showed that the overlying cells expressed less amounts of endothelial nitric oxide synthase (eNOS), Von Willebrand factor (VWF), and connexin43 protein compared to the controls (p < 0.05). Immunofluorescence microscopy confirmed the results of immunoblotting. In conclusion, stent materials affect HUVEC's growth and protein expression profile. Down-regulation of eNOS, VWF, and connexin43 gap junctions is a common phenomenon in the cells growing on the examined metallic materials, suggesting the existence of endothelial dysfunction in the arterial segments containing the stents made of such materials.

The phosphorylated form of connexin43 is up-regulated in breast hyperplasias and carcinomas and in their neoformed capillaries

We applied an antiserum (SA226P) specifically recognizing the phosphorylated form of connexin43 (P-Cx43) to human breast samples including normal breast samples, with fibrocystic disease (FCD), fibroadenomas (FA), in situ and infiltrating carcinomas of all major types, and miscellaneous extramammary tumors. The findings were compared with those obtained with commercial antisera recognizing all Cx43 forms (pan-Cx43). A subset of samples was stained for Her2-neu and p44/42 to mitogen-activated protein kinase. Paraffin step sections were used. Immunoblots were performed on frozen samples of a representative subset of cases. In the normal breast, FCD, and FA, SA226P stained strongly and extensively most myoepithelial cells (MECs); luminal cells remained unstained. In proliferative FCD and some cellular FA, SA226P stained MEC and the capillary endothelium (CE). In ductal and lobular in situ carcinomas, SA226P reacted strongly and diffusely with the remaining MEC, the CE, and the transformed luminal cells. SA226P stained all infiltrating carcinomas except the tubular variant. In all breast carcinomas, the CE within and adjacent to tumors and some myofibroblasts stained with SA226P. By contrast, pan-Cx43 stained weakly and sporadically the MEC and rare samples of invasive carcinomas. Notably, Mab p44/42 reacted in parallel with the samples stained with SA226P, whereas reactions with Her2 were negative. Immunoblot findings paralleled those obtained immunohistochemically. We conclude that P-Cx43, restricted to MEC in the normal breast, is up-regulated in the same cells in hyperplasias and dysplasias and FA and is strongly up-regulated in invasive carcinomas. Notably, in some proliferative FCD and in most in situ and infiltrating carcinomas, P-Cx43 is strongly expressed in CE within and adjacent to the lesions but not away from them. These findings were paralleled by the strong nuclear reactions noted with Mab p44/42. These phenomena, although not exclusive to malignancy, are particularly conspicuous in breast carcinomas and seemingly reflect active proliferation associated with abnormal gap junctional intercellular communication.

Gap junctional communication in tissue inflammation and repair

Local injury induces a complex orchestrated response to stimulate healing of injured tissues, cellular regeneration and phagocytosis. Practically, inflammation is defined as a defense process whereby fluid and white blood cells accumulate at a site of injury. The balance of cytokines, chemokines, and growth factors is likely to play a key role in regulating important cell functions such as migration, proliferation, and matrix synthesis during the process of inflammation. Hence, the initiation, maintenance, and resolution of innate responses depend upon cellular communication. A process similar to tissue repair and subsequent scarring is found in a variety of fibrotic diseases. This may occur in a single organ such as liver, kidneys, pancreas, lung, skin, and heart, but fibrosis may also have a more generalized distribution such as in atherosclerosis. The purpose of this review is to summarize recent advances on the contribution of gap junction-mediated intercellular communication in the modulation of the inflammatory response and tissue repair.

Connexin 43 mediated gap junctional communication enhances breast tumor cell diapedesis in culture

Introduction

Metastasis involves the emigration of tumor cells through the vascular endothelium, a process also known as diapedesis. The molecular mechanisms regulating tumor cell diapedesis are poorly understood, but may involve heterocellular gap junctional intercellular communication (GJIC) between tumor cells and endothelial cells.

Method

To test this hypothesis we expressed connexin 43 (Cx43) in GJIC-deficient mammary epithelial tumor cells (HBL100) and examined their ability to form gap junctions, establish heterocellular GJIC and migrate through monolayers of human microvascular endothelial cells (HMVEC) grown on matrigel-coated coverslips.

Results

HBL100 cells expressing Cx43 formed functional heterocellular gap junctions with HMVEC monolayers within 30 minutes. In addition, immunocytochemistry revealed Cx43 localized to contact sites between Cx43 expressing tumor cells and endothelial cells. Quantitative analysis of diapedesis revealed a two-fold increase in diapedesis of Cx43 expressing cells compared to empty vector control cells. The expression of a functionally inactive Cx43 chimeric protein in HBL100 cells failed to increase migration efficiency, suggesting that the observed up-regulation of diapedesis in Cx43 expressing cells required heterocellular GJIC. This finding is further supported by the observation that blocking homocellular and heterocellular GJIC with carbenoxolone in co-cultures also reduced diapedesis of Cx43 expressing HBL100 tumor cells.

Conclusion

Collectively, our results suggest that heterocellular GJIC between breast tumor cells and endothelial cells may be an important regulatory step during metastasis.

Down-regulating effect of nicotine on connexin43 gap junctions in human umbilical vein endothelial cells is attenuated by statins

We investigated the effect of nicotine on connexin43 (Cx43) expression and gap-junctional communication in human umbilical vein endothelial cells (HUVEC). We also evaluated whether the effect requires activation of acetyl choline receptors sensitive to nicotine (nAChRs) and is altered by statins. The results showed that expression of Cx43 protein is reduced by nicotine in a dose-dependent manner (6 x 10(-4) M nicotine vs control, 33% reduction, p < 0.01), though Cx43 mRNA is up-regulated (6 x 10(-4) M nicotine vs control, 36% increase, p < 0.01). Concomitantly, the communication function, determined by fluorescence recovery after photobleaching, is decreased (6 x 10(-4) M nicotine vs control, 38% reduction, p < 0.05). Such a down-regulation of Cx43 gap junctions by nicotine disappears in the presence of the nAChRs antagonist, dihydro-beta-erythroidine, and protease inhibitors leupeptin plus N-acetyl-Leu-Leu-Norleu-al (ALLN). Similarly, the effect of nicotine is attenuated by statins, including fluvastatin, lovastatin, pravastatin, and simvastatin, even at the presence of mevalonate. We concluded that i) nicotine down-regulates Cx43 expression and gap-junctional communication in HUVEC via post-transcriptional modification, which involves enhancement of Cx43 proteolysis; ii) the effect of nicotine is mediated via activation of nAChRs; and iii) the effect of nicotine is attenuated by statins through mechanisms outside the hypolipidemic pathway.

Time course of vascular reactivity to contracting and relaxing agents after endothelial denudation by balloon angioplasty in rat carotid artery

Endothelial injuries induced by different stimuli lead to proliferation of intimal vascular smooth muscle cells with formation of neointima. In this functional study, we evaluated the reactivity to contracting and vasorelaxing agents in Wistar rat carotid artery at different times (1, 7, 14, 21 and 28 days) after endothelial denudation with angioplastic balloon technique. Injured (IC) and uninjured carotid artery rings (UC) were placed in an isolated organ bath for isometric force displacement. IC collected at 1, 7, 14, 21 and 28 days showed a reduction in contraction to phenylephrine (0.3 microM), angiotensin II (0.1 microM), U46619 (0.1 microM), KCl (60 mM) and A23187 (1microM) at any experimental time compared to rings obtained from UC. The evaluation of endothelial-derived relaxing or hyperpolarizing factor (EDRF or EDHF), induced by acetylcholine (0.001-1 microM) in presence of indomethacin (10 microM) or indomethacin and Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME) (10 and 100 microM, respectively), was carried out at 14, 21 and 28 days. The EDRF-induced relaxation was significantly (P < 0.0001) reduced at 14 days and it improved through out the observation time, indeed at 28 days it was indistinguishable from UC relaxation curve. In contrast, the EDHF-induced relaxation was significantly (P < 0.0001) reduced at all experimental time. A significant reduction in nitric oxide-induced relaxation, sodium nitroprusside (0.001-10 microM), was observed at 7, 14 and 21 days, but not at 28 days. The relaxation induced by diazoxide (3-300 microM), an opener of KATP channels, was significantly reduced only at 7 days but not at 14, 21 and 28 days. Western blot analysis of myosin heavy chain revealed that up to 28 days the re-differentiation (maturity state) of smooth muscle cells was not yet reached. In conclusion, our data showed that hyporeactivity to contracting and relaxing agents in endothelial denuded carotid of rats could be linked to a multifactorial condition in which reduction of receptors and alterations in post-receptor transductions in neointima may produce modification of protein expression and/or variation in ion flux where calcium could have a pivotal role.

Regulation of connexin biosynthesis, assembly, gap junction formation, and removal

Gap junctions (GJs) are the only known cellular structures that allow a direct transfer of signaling molecules from cell-to-cell by forming hydrophilic channels that bridge the opposing membranes of neighboring cells. The crucial role of GJ-mediated intercellular communication (GJIC) for coordination of development, tissue function, and cell homeostasis is now well documented. In addition, recent findings have fueled the novel concepts that connexins, although redundant, have unique and specific functions, that GJIC may play a significant role in unstable, transient cell-cell contacts, and that GJ hemi-channels by themselves may function in intra-/extracellular signaling. Assembly of these channels is a complicated, highly regulated process that includes biosynthesis of the connexin subunit proteins on endoplasmic reticulum membranes, oligomerization of compatible subunits into hexameric hemi-channels (connexons), delivery of the connexons to the plasma membrane, head-on docking of compatible connexons in the extracellular space at distinct locations, arrangement of channels into dynamic, spatially and temporally organized GJ channel aggregates (so-called plaques), and coordinated removal of channels into the cytoplasm followed by their degradation. Here we review the current knowledge of the processes that lead to GJ biosynthesis and degradation, draw comparisons to other membrane proteins, highlight novel findings, point out contradictory observations, and provide some provocative suggestive solutions.

Genetic risk for coronary artery disease in individuals with or without type 2 diabetes

Given that a substantial proportion of individuals with coronary artery disease (CAD) also have type 2 diabetes, it is important to identify genes that confer susceptibility to CAD independently in subjects with type 2 diabetes and in those without this condition. A large-scale association study was performed to identify genes that confer susceptibility to CAD in either the absence or presence of type 2 diabetes. The study population comprised 5207 unrelated Japanese individuals, including 3085 subjects with CAD and 2122 controls. Among all subjects, 1704 individuals had type 2 diabetes and 3503 individuals did not have this condition. The genotypes for 33 polymorphisms of 27 candidate genes were determined with a fluorescence- or colorimetry-based allele-specific DNA primer-probe assay system. Multivariate logistic regression analysis with adjustment for age, body mass index, and the prevalence of smoking, hypertension, hypercholesterolemia, and hyperuricemia revealed that the following polymorphisms were significantly (P < 0.005) associated with CAD: the 1019C -->T of the connexin 37 gene for men with type 2 diabetes; the 2445G -->A in the fatty acid-binding protein 2 gene for women with this condition; the -863C-->A in the tumor necrosis factor-alpha gene, the -219G-->T in the apolipoprotein E gene, the 1019C-->T in the connexin 37 gene for men without type 2 diabetes; and the -482C-->T in the apolipoprotein C-III gene for women without this condition. Genotyping of these polymorphisms may prove informative for assessment of the genetic risk for CAD in the absence or presence of type 2 diabetes.

Premature myocardial infarction novel susceptibility locus on chromosome 1P34-36 identified by genomewide linkage analysis

The most frequent causes of death and disability in the Western world are atherosclerotic coronary artery disease (CAD) and acute myocardial infarction (MI). This common disease is thought to have a polygenic basis with a complex interaction with environmental factors. Here, we report results of a genomewide search for susceptibility genes for MI in a well-characterized U.S. cohort consisting of 1,613 individuals in 428 multiplex families with familial premature CAD and MI: 712 with MI, 974 with CAD, and average age of onset of 44.4+/-9.7 years. Genotyping was performed at the National Heart, Lung, and Blood Institute Mammalian Genotyping Facility through use of 408 markers that span the entire human genome every 10 cM. Linkage analysis was performed with the modified Haseman-Elston regression model through use of the SIBPAL program. Three genomewide scans were conducted: single-point, multipoint, and multipoint performed on of white pedigrees only (92% of the cohort). One novel significant susceptibility locus was detected for MI on chromosomal region 1p34-36, with a multipoint allele-sharing P value of <10(-12) (LOD=11.68). Validation by use of a permutation test yielded a pointwise empirical P value of.00011 at this locus, which corresponds to a genomewide significance of P<.05. For the less restrictive phenotype of CAD, no genetic locus was detected, suggesting that CAD and MI may not share all susceptibility genes. The present study thus identifies a novel genetic-susceptibility locus for MI and provides a framework for the ultimate cloning of a gene for the complex disease MI.

Association of gene polymorphisms with coronary artery disease in low- or high-risk subjects defined by conventional risk factors

OBJECTIVES

The aim of the study was to identify genes that confer susceptibility to coronary artery disease (CAD) in low- or high-risk men or women separately and thereby to assess the genetic risk of CAD in such individuals.

BACKGROUND

The prevention of CAD would be facilitated by the identification of genes that confer susceptibility to this condition independently in low- or high-risk individuals, as defined by conventional risk factors.

METHODS

The study population comprised 1661 unrelated Japanese individuals, including 1011 patients with CAD and 650 control subjects. Among all study subjects, 601 individuals (high-risk subjects) had hypertension, diabetes mellitus, and hypercholesterolemia, and 1060 individuals (low-risk subjects) had none of these risk factors for CAD. The genotypes for 37 polymorphisms of 31 candidate genes were determined by a fluorescence- or colorimetry-based allele-specific DNA primer-probe assay system.

RESULTS

Multivariate logistic regression analysis, with adjustment for age, body mass index, and the prevalence of smoking and hyperuricemia, revealed that the -219G-->T polymorphism of the apolipoprotein E gene in low-risk men, the -1171/5A-->6A polymorphism of the stromelysin-1 gene in low-risk women, the 1019C-->T polymorphism of the connexin 37 gene in high-risk men, and the 3932T-->C polymorphism of the apolipoprotein E gene in high-risk women were significantly associated with CAD. A stepwise forward selection procedure revealed that the effects of these polymorphisms on CAD were statistically independent of age or conventional risk factors.

CONCLUSIONS

Genotyping of these polymorphisms may prove informative for assessment of the genetic risk of CAD in low- or high-risk men or women.

Expression of connexins in the normal and obstructed developing kidney

Connections between cells are achieved by proteins called connexins that comprise the gap junction. Connexins play a major role in organ development. Our reverse transcription-polymerase chain reaction (RT-PCR) studies demonstrate that Cx30, Cx36, Cx37, Cx40, Cx45, Cx46, and Cx50 are expressed in the kidney. Quantitative RT-PCR indicates that Cx37, Cx45, and Cx46 are preferentially expressed during early renal development. We also explored the expression of connexins in neonatal unilateral ureteral obstruction (UUO). After 12 days of neonatal UUO, the renal mRNA expression of Cx30, Cx37, and Cx40 was significantly elevated. In contrast, there was no change in connexin renal mRNA levels in adult UUO. We conclude that multiple connexins are expressed in the rat kidney and several are aberrantly expressed in neonatal UUO.

Epithelial cells of nasal mucosa express functional gap junctions of connexin 43

OBJECTIVE

Recent studies have suggested that inositol triphosphate is transmitted through the gap junction of adjacent epithelial cells and communicates the intracellular calcium wave that controls the beating of cilia. Therefore, gap junction-mediated intercellular communication may modulate the metachronal ciliary beating of respiratory mucosa.

MATERIAL AND METHODS

The expression and function of gap junctions were evaluated in nasal mucosa using immunofluorescent staining, Western blotting and Lucifer Yellow dye coupling in both whole nasal mucosa and cultured nasal epithelial cells.

RESULTS

Among connexins (Cxs) 26, 32 and 43, only Cx43 was found in the nasal mucosa, in both the epithelial cells and submucosa tissue. Using Western blotting, Cx43 protein was found in protein extracts of both whole mucosa and cultured epithelial cells. The Cx43 protein content increased twofold between the 3rd and 6th days of culture. Lucifer Yellow dye, microinjected into single cultured epithelial cells, had spread to the adjacent cells.

CONCLUSION

Cx43 is present in nasal mucosa. The expression of Cx43 on epithelial cells increases after culture. The dye-coupling study in epithelial cells indicated that the signal may be transmitted to neighboring cells via a gap junction composed of Cx43. Thus, Cx43 may be involved in the regulation of metachronal ciliary beating in ciliated epithelial cells and growth or differentiation in nasal tissue.

2',5'-Dihydroxychalcone down-regulates endothelial connexin43 gap junctions and affects MAP kinase activation

We examined the effect of 2',5'-dihydroxychalcone on connexin43 (Cx43) expression and gap-junctional communication in human umbilical vein endothelial cells (HUVEC). The result showed that expression of Cx43 is rapidly reduced by 2',5'-dihydroxychalcone in a dose-dependent manner, Concomitantly, the communication function, determined by fluorescence recovery after photobleaching (FRAP), is decreased. We further investigated whether the mitogen-activated protein (MAP) kinase and the degradation pathway of gap junctions are involved in these processes. Although the change of Cx43 is not affected by the level of fetal calf serum (FCS) used in the medium, activation of MAP kinase varies, depending on the FCS level. At a low level (0.5%), the chalcone inhibits the activation, like PD98059, a specific inhibitor of MAP kinase kinase. However, at a high level (20%), MAP kinase is activated. On the other hand, the chalcone's down-regulating effect on Cx43, while is totally blocked by protease inhibitors leupeptin and N-acetyl-leucyl-norleucinal (ALLN), persists in the presence of PD98059, We concluded that 2',5'-dihydroxychalcone down-regulates Cx43 expression and gap-junctional communication in the HUVEC via enhancement of the proteolysis pathway, and this compound possesses dual effects on MAP kinase activation.

ADP-induced pial arteriolar dilation in ovariectomized rats involves gap junctional communication

It was previously shown that, despite the loss of nitric oxide (NO) dependence, ADP-induced pial arteriolar dilation was not attenuated in estrogen-depleted [i.e., ovariectomized (Ovx)] rats. Additional evidence suggested that the NO was replaced by an endothelium-dependent hyperpolarizing factor (EDHF)-like mechanism. To further characterize the nascent EDHF role in Ovx females, the current study was undertaken to test whether, in Ovx rats, ADP-induced pial arteriolar dilation retained its endothelial dependence and whether gap junctions are involved in that response. A closed cranial window and intravital microscopy system was used to monitor pial arteriolar diameter changes in anesthetized rats. The endothelial portion of the ADP-induced dilation was evaluated using light dye endothelial injury (L/D). The study was organized around three experimental approaches. First, the responses of pial arterioles to ADP before and after L/D exposure in intact and Ovx female rats were tested. L/D reduced the ADP response by 50-70% in both groups, thereby indicating that the endothelium dependence of ADP-induced vasodilation is not altered by chronic estrogen depletion. Second, the NO synthase inhibitor N(omega)-nitro-L-arginine (L-NNA) and the prostanoid synthesis inhibitor indomethacin (Indo) were coapplied. In intact females, L-NNA-Indo attenuated the response to ADP by 50%, with no further changes upon the addition of L/D. On the other hand, L-NNA-Indo did not affect ADP reactivity in Ovx rats, but subsequent L/D exposure reduced the ADP response by >50%. The NO-prostanoid-independent, but endothelium-dependent, nature of the response in Ovx females is a hallmark of EDHF participation. Third, gap junctional inhibition strategies were applied. A selective inhibitor of gap junctional function, Gap 27, did not affect ADP reactivity in intact females but reduced the the ADP response by 50% in Ovx females. A similar result was obtained following application of a connexin43 antisense oligonucleotide. These findings suggest that the nascent EDHF dependency of ADP-induced pial arteriolar dilation in Ovx females involves connexin43-related gap junctional communication.

Cx40 and Cx43 expression ratio influences heteromeric/ heterotypic gap junction channel properties

In cells that coexpress connexin (Cx)40 and Cx43, the ratio of expression can vary depending on the cellular environment. We examined the effect of changing Cx40:Cx43 expression ratio on functional gap junction properties. Rin cells transfected with Cx40 or Cx43 (Rin40, Rin43) were cocultured with 6B5n, A7r5, A7r540C1, or A7r540C3 cells for electrophysiological and dye coupling analysis. Cx40:Cx43 expression ratio in 6B5n, A7r5, A7r540C1, and A7r540C3 cells was ~1:1, 3:1, 5:1, and 10:1, respectively. When Rin43 cells were paired with coexpressing cells, there was an increasing asymmetry of voltage-dependent gating and a shift toward smaller conductance events as Cx40:Cx43 ratio increased in the coexpressing cell. These observations could not be predicted by linear combinations of Cx40 and Cx43 properties in proportion to the expressed ratios of the two Cxs. When Rin40 cells were paired with coexpressing cells, the net voltage gating and single-channel conductance behavior were similar to those of Rin40/Rin40 cell pairs. Dye permeability properties of cell monolayers demonstrated that as Cx40:Cx43 expression ratio increased in coexpressing cells the charge and size selectivity of dye transfer reflected that of Rin40 cells, as would be predicted. These data indicate that the electrophysiological properties of heteromeric/heterotypic channels are not directly related to the proportions of Cx constituents expressed in the cell; however, the dye permeability of these same channels can be predicted by the relative Cx contributions.

Differential expression of connexin43 in foetal, adult and tumour-associated human brain endothelial cells

Connexin43 (Cx43), the main protein constituting the gap junctions between astrocytes, has previously been demonstrated in endothelial cells of somatic vessels where the intercellular coupling that it provides plays a role in endothelial proliferation and migration. In this study, Cx43 expression was analysed in human brain microvascular endothelial cells of the cortical plate of 18-week foetal telencephalon, in adult cerebral cortex and glioma (astrocytomas). The study was carried out by immunocytochemistry utilizing a Cx43 monoclonal antibody and a polyclonal antibody anti-GLUT1 (glucose transporter isoform 1) to identify the endothelial cells and to localize Cx43. Endothelial Cx43 is differently expressed in the cortical plate, cerebral cortex and astrocytoma. Within the cortical plate and tumour, Cx43 is highly expressed in microvascular endothelial cells whereas it is virtually absent in the cerebral cortex microvessels. The high expression of the gap junction protein in developing brain, as well as in brain tumours, may be related to the growth status of the microvessels during brain and tumour angiogenesis. The lack of endothelial Cx43 in the cerebral cortex is in agreement with the characteristics of the mature brain endothelial cells that are sealed by tight junctions. In conclusion, the results indicate that endothelial Cx43 expression is developmentally regulated in the normal human brain and suggest that it is controlled by the microenvironment in both normal and tumour-related conditions.

Gap junctions, homeostasis, and injury

Gap junctions (Gj) play an important role in the communication between cells of many tissues. They are composed of channels that permit the passage of ions and low molecular weight metabolites between adjacent cells, without exposure to the extracellular environment. These pathways are formed by the interaction between two hemichannels on the surface of opposing cells. These hemichannels are formed by the association of six identical subunits, named connexins (Cx), which are integral membrane proteins. Cell coupling via Gj is dependent on the specific pattern of Cx gene expression. This pattern of gene expression is altered during several pathological conditions resulting in changes of cell coupling. The regulation of Cx gene expression is affected at different levels from transcription to post translational processes during injury. In addition, Gj cellular communication is regulated by gating mechanisms. The alteration of Gj communication during injury could be rationalized by two opposite theories. One hypothesis proposes that the alteration of Gj communication attenuates the spread of toxic metabolites from the injured area to healthy organ regions. The alternative proposition is that a reduction of cellular communication reduces the loss of important cellular metabolisms, such as ATP and glucose.

Paradoxical overexpression and translocation of connexin43 in homocysteine-treated endothelial cells

Hyperhomocysteinemia is an established cause of defective vasorelaxation. Gene expression screening of human umbilical vein endothelial cells (HUVEC) treated with homocysteine (Hcy) revealed that connexin43 (Cx43) was upregulated. Expression of Cx43 was increased more than twofold in Hcy-treated HUVEC. Gap junctional communication (Lucifer yellow and whole cell patch clamp) was not enhanced in Hcy-treated HUVEC. HUVEC expressing chimeric Cx43-green fluorescent protein exhibited it at cell-cell contacts in control but showed redistribution to the intracellular compartment(s) in Hcy-treated cells. Confocal microscopy of HUVEC stained with anti-Cx43, mitochondrial, and endoplasmic reticulum fluorescent markers showed the localization of Cx43 to the plasma membrane of control cells and its colocalization with the mitochondrial marker in Hcy-treated HUVEC. Studies of isolated mitochondria confirmed overexpression of Cx43 in the mitochondria of Hcy-treated HUVEC. Microdissected renal interlobar arteries, which normally exhibit endothelium-derived hyperpolarizing factor-induced vasorelaxation, showed reduced nitric oxide synthase- and cyclooxygenase-independent vasorelaxation to acetylcholine after pretreatment with Hcy. In summary, Hcy-induced upregulation of Cx43 transcript and protein expression are associated with unaltered intercellular communication, redistribution of Cx43 in HUVEC, and reduced nitric oxide- and prostanoid-independent vascular responses to acetylcholine in Hcy-treated arteries.

Downregulation of connexin 43 expression by high glucose reduces gap junction activity in microvascular endothelial cells

Impairment of retinal vascular homeostasis is associated with the development and progression of diabetic retinopathy involving gap junction intercellular communication (GJIC) activity. The principal gap junction protein of intercellular communication, connexin, was investigated to determine the effects of high glucose concentrations on the expression of endothelial-specific connexins (Cx37, Cx40, and Cx43), connexin phosphorylation pattern, and GJIC activity. Rat microvascular endothelial (RME) cells grown in high (30 mmol/l)-glucose medium for 9 days had reduced Cx43 expression: Cx43 mRNA (68 +/- 13% of control; P = 0.019, n = 5) and protein (55.6 +/- 16% of control; P = 0.003, n = 5) levels were reduced; however, Cx37 and Cx40 expression was not affected. Using alkaline phosphatase and Western blot analyses, we identified three forms of Cx43: a nonphosphorylated form (P0) and two phosphorylated forms (P1 and P2). Expression of all three forms was decreased in cells grown in high-glucose medium: PO, 73 +/- 15% of control (P = 0.04); P1, 57 +/- 16% of control (P = 0.01); and P2, 42 +/- 22% of control (P = 0.006). Using immunofluorescence microscopy, we observed Cx43 localization at specific sites of contact (plaques) between adjacent cells. In cells grown in high-glucose medium, we observed reduced plaque counts (63 +/- 6% of control; P = 0.009) and decreased intensity of Cx43 immunofluorescence compared with cells grown in normal medium. Furthermore, using scrape load dye transfer (SLDT) technique, we found that these cells exhibited reduced GJIC activity (60% of control; P = 0.01, n = 5). The reduction in GJIC activity correlated with the decreased Cx43 protein levels (r = 0.9). These results indicate that high glucose concentrations inhibited GJIC activity by reducing Cx43 synthesis in RME cells. Impaired intercellular communication may contribute to breakdown of homeostatic balance in diabetic microangiopathy.

Connexin37 gene polymorphism and coronary artery disease in Taiwan

BACKGROUND

A recent study shows that a C1019T polymorphism of the gene encoding the gap junction protein connexin37 contributes to the genesis of atherosclerotic plaques in human carotid artery. However, whether such a polymorphism can be used as a prognostic marker in atherosclerotic disease of other arterial sites, such as coronary artery disease, is not known.

METHODS

We analyzed the allelic status in 177 subjects with coronary artery disease (age, 61+/-11 years; male/female, 120/57) and 102 controls (60+/-11 years; male/female, 70/32). Both groups were matched, before genotype analysis, for a variety of other traditional risk factors, including body mass index, smoking status, levels of blood pressure, sugar, creatinine, and lipid profiles, in addition to age and sex.

RESULTS

The T allele was less frequently seen in the control group, compared to the disease group (10.7 vs. 20.1%, TT+TC vs. CC, P<0.01). Subsequent analysis demonstrated that a significant difference existed in the male (9.2 vs. 22.8%, TT+TC vs. CC, P<0.005), but not in the female. Another finding was that the T allele frequency in all participants was less than 15%, markedly lower than that reported in non-Taiwanese.

CONCLUSIONS

The observation indicates that the polymorphism in the connexin37 gene potentially plays a role in the manifestation of coronary atherosclerosis in Taiwan.

Immunocytochemical analysis of connexin expression in the healthy and diseased cardiovascular system

Gap junctions play essential roles in the normal function of the heart and arteries, mediating the spread of the electrical impulse that stimulates synchronized contraction of the cardiac chambers, and contributing to co-ordination of activities between cells of the arterial wall. In common with other multicellular systems, cardiovascular tissues express multiple connexin isotypes that confer distinctive channel properties. This review highlights how state-of-the-art immunocytochemical and cellular imaging techniques, as part of a multidisciplinary approach in gap junction research, have advanced our understanding of connexin diversity in cardiovascular cell function in health and disease. In the heart, spatially defined patterns of expression of three connexin isotypes-connexin43, connexin40, and connexin45-underlie the precisely orchestrated patterns of current flow governing the normal cardiac rhythm. Derangement of gap junction organization and/or reduced expression of connexin43 are associated with arrhythmic tendency in the diseased human ventricle, and high levels of connexin40 in the atrium are associated with increased risk of developing atrial fibrillation after coronary by-pass surgery. In the major arteries, endothelial gap junctions may simultaneously express three connexin isotypes, connexin40, connexin37, and connexin43; underlying medial smooth muscle, by contrast, predominantly expresses connexin43, with connexin45 additionally expressed at restricted sites. In normal arterial smooth muscle, the abundance of connexin43 gap junctions varies according to vascular site, and shows an inverse relationship with desmin expression and positive correlation with the quantity of extracellular matrix. Increased connexin43 expression between smooth muscle cells is closely linked to phenotypic transformation in early human coronary atherosclerosis and in the response of the arterial wall to injury. Current evidence thus suggests that gap junctions in both their guises, as pathways for cell-to-cell signaling in the vessel wall and as pathways for impulse conduction in the heart, contribute to the initial pathogenesis and eventual clinical manifestation of human cardiovascular disease.