Endothelial gap junctions are down-regulated by arsenic trioxide

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.

GJA1 reverses arsenic-induced EMT via modulating MAPK/ERK signaling pathway

Arsenic is known as a well-established human carcinogen. Gap Junction Protein Alpha 1 (GJA1) is a multifunction protein that forms gap junction channels and is important for intercellular communication. Recently, its aberrant expression has been shown to associate with cancer recurrence and metastatic spread. However, whether GJA1 plays a role in arsenic carcinogenesis remains unknown. Here, we demonstrated that chronic exposure of human bronchial epithelial BEAS-2B cells to sodium arsenite promoted epithelial-mesenchymal transition (EMT) via increasing the expression of EMT inducer S100A4 and activation of MAPK/ERK signaling. In vitro and in vivo experiments showed that chronic exposure to sodium arsenite reduced GJA1 expression. Forced expression of GJA1 inhibited sodium arsenite-induced EMT via suppressing MAPK/ERK signaling whereas GJA1 knockdown produced an opposite effect. Intriguingly, chronic exposure to sodium arsenite increased autophagy flux. Inhibition of autophagy by pharmacological intervention or genetic deletion of autophagy core gene Beclin-1 upregulated GJA1 expression. These results suggested that GJA1 restrained the carcinogenic effect of sodium arsenite by limiting MAPK/ERK signaling, and GJA1 expression was decreased by arsenic-activated autophagy. In addition, interventions directed at enhancing the level or functional activity of GJA1 could be of preventive and therapeutic interest.

Heavy Metal-Induced Cerebral Small Vessel Disease: Insights into Molecular Mechanisms and Possible Reversal Strategies

Heavy metals are considered a continuous threat to humanity, as they cannot be eradicated. Prolonged exposure to heavy metals/metalloids in humans has been associated with several health risks, including neurodegeneration, vascular dysfunction, metabolic disorders, cancer, etc. Small blood vessels are highly vulnerable to heavy metals as they are directly exposed to the blood circulatory system, which has comparatively higher concentration of heavy metals than other organs. Cerebral small vessel disease (CSVD) is an umbrella term used to describe various pathological processes that affect the cerebral small blood vessels and is accepted as a primary contributor in associated disorders, such as dementia, cognitive disabilities, mood disorder, and ischemic, as well as a hemorrhagic stroke. In this review, we discuss the possible implication of heavy metals/metalloid exposure in CSVD and its associated disorders based on in-vitro, preclinical, and clinical evidences. We briefly discuss the CSVD, prevalence, epidemiology, and risk factors for development such as genetic, traditional, and environmental factors. Toxic effects of specific heavy metal/metalloid intoxication (As, Cd, Pb, Hg, and Cu) in the small vessel associated endothelium and vascular dysfunction too have been reviewed. An attempt has been made to highlight the possible molecular mechanism involved in the pathophysiology, such as oxidative stress, inflammatory pathway, matrix metalloproteinases (MMPs) expression, and amyloid angiopathy in the CSVD and related disorders. Finally, we discussed the role of cellular antioxidant defense enzymes to neutralize the toxic effect, and also highlighted the potential reversal strategies to combat heavy metal-induced vascular changes. In conclusion, heavy metals in small vessels are strongly associated with the development as well as the progression of CSVD. Chelation therapy may be an effective strategy to reduce the toxic metal load and the associated complications.

Interaction of arsenic with gap junction protein connexin 43 alters gap junctional intercellular communication

Chronic exposure to Arsenic pollution in ground water is one of the largest environmental health disasters in the world. The toxicity of trivalent Arsenicals primarily happens due to its interaction with sulfhydryl groups in proteins. Arsenic binding to the protein can change the conformation of the protein and alter its interactions with other proteins leading to tissue damage. Therefore, much importance has been given to the studies of Arsenic bound proteins, for the purpose of understanding the origins of toxicity and to explore therapeutics. Here we study the dynamic effect of Arsenic on Connexin 43 (Cx43), a protein that forms the gap junctions, whose alteration deeply perturbs the cell-to-cell communication vital for maintaining tissue homeostasis. In silico molecular modelling and in vitro studies comparing Arsenic treated and untreated conditions show distinct results. Gap junction communication is severely disrupted by Arsenic due to reduced availability of unaltered Cx43 in the membrane bound form. In silico and Inductively Coupled Plasma Mass Spectrometry studies revealed the interaction of Arsenic to the Cx43 preferably occurs through surface exposed cysteines, thereby capping the thiol groups that form disulfide bonds in the tertiary structure. This leads to disruption of Cx43 oligomerization, and altered Cx43 is incompetent for transportation to the membrane surface, often forming aggregates primarily localizing in the endoplasmic reticulum. Loss of functional Cx43 on the cell surface have a deleterious effect on cellular homeostasis leading to selective vulnerability to cell death and tissue damage.

The ADMA/DDAH/NO pathway in human vein endothelial cells exposed to arsenite

Inorganic arsenic (iAs) exposure is related to cardiovascular disease, which is characterized by endothelial dysfunction and nitric oxide (NO) depletion. The mechanisms underlying NO depletion as related to iAs exposure are not fully understood. The endogenous inhibitor of nitric oxide synthase, asymmetric dimethylarginine (ADMA), might be a molecular target of iAs. ADMA concentrations are regulated by proteins involved in its synthesis (arginine methyl transferase 1 [PRMT-1]) and degradation (dimethylarginine dimethylaminohydrolase [DDAH]). Both, ADMA and NO are susceptible to oxidative stress. We aimed to determine the ADMA/DDAH/NO pathway in human vein endothelial cells (HUVEC-CS) exposed to arsenite. We exposed HUVEC-CS cells to 1, 2.5 and 5μM of arsenite for 24h. We proved that arsenite at 5μM was able to decrease NO levels with an associated increase in ADMA and depletion of l-arginine in HUVEC-CS cells. We also found a decrease in DDAH-1 protein expression with 5μM of arsenite compared to the control group. However, we did not observe significant differences in PRMT-1 protein expression at any of the concentrations of arsenite employed. Finally, arsenite (2.5 and 5μM) increased NADPH oxidase 4 protein levels compared with the control group. We conclude that ADMA, l-arginine and DDAH are involved in NO depletion produced by arsenite, and that the mechanism is related to oxidative stress.

Arsenic Exposure and Predicted 10-Year Atherosclerotic Cardiovascular Risk Using the Pooled Cohort Equations in U.S. Hypertensive Adults

This study was to evaluate the association of urine arsenic with predicted 10-year atherosclerotic cardiovascular disease (ASCVD) risk in U.S. adults with hypertension. Cross-sectional analysis was conducted in 1570 hypertensive adults aged 40-79 years in the 2003-2012 National Health and Nutrition Examination Survey (NHANES) with determinations of urine arsenic. Predicted 10-year ASCVD risk was estimated by the Pooled Cohort Equations, developed by the American College of Cardiology/American Heart Association in 2013. For men, after adjustment for sociodemographic factors, urine dilution, ASCVD risk factors and organic arsenic intake from seafood, participants in the highest quartiles of urine arsenic had higher 10-year predicted ASCVD risk than in the lowest quartiles; the increases were 24% (95% confidence interval (CI): 2%, 53%) for total arsenic, 13% (95% CI: 2%, 25%) for dimethylarsinate and 22% (95% CI: 5%, 40%) for total arsenic minus arsenobetaine separately. For women, the corresponding increases were 5% (95% CI: -15%, 29%), 10% (95% CI: -8%, 30%) and 0% (95% CI: -15%, 19%), respectively. Arsenic exposure, even at low levels, may contribute to increased ASCVD risk in men with hypertension. Furthermore, our findings suggest that particular circumstances need urgently to be considered while elucidating cardiovascular effects of low inorganic arsenic levels.

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.

Arsenic trioxide alters the differentiation of mouse embryonic stem cell into cardiomyocytes

Chronic arsenic exposure is associated with increased morbidity and mortality for cardiovascular diseases. Arsenic increases myocardial infarction mortality in young adulthood, suggesting that exposure during foetal life correlates with cardiac alterations emerging later. Here, we investigated the mechanisms of arsenic trioxide (ATO) cardiomyocytes disruption during their differentiation from mouse embryonic stem cells. Throughout 15 days of differentiation in the presence of ATO (0.1, 0.5, 1.0 μM) we analysed: the expression of i) marker genes of mesoderm (day 4), myofibrillogenic commitment (day 7) and post-natal-like cardiomyocytes (day 15); ii) sarcomeric proteins and their organisation; iii) Connexin 43 and iv) the kinematics contractile properties of syncytia. The higher the dose used, the earlier the stage of differentiation affected (mesoderm commitment, 1.0 μM). At 0.5 or 1.0 μM the expression of cardiomyocyte marker genes is altered. Even at 0.1 μM, ATO leads to reduction and skewed ratio of sarcomeric proteins and to a rarefied distribution of Connexin 43 cardiac junctions. These alterations contribute to the dysruption of the sarcomere and syncytium organisation and to the impairment of kinematic parameters of cardiomyocyte function. This study contributes insights into the mechanistic comprehension of cardiac diseases caused by in utero arsenic exposure.

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.

The effects of 2-aminoethoxydiphenyl borate and diphenylboronic anhydride on gap junctions composed of Connexin43 in TM₄ sertoli cells

2-Aminoethoxydiphenyl borate (2-APB) has recently been demonstrated to inhibit gap junction (GJ) channels, whereas the underlying mechanisms are still unknown. Using mouse TM₄ Sertoli cell which expresses connexin43 (Cx43), we explored the effects of 2-APB and its analogues on dye-coupling through junctional channels formed by Cx43 and on expression of Cx43. Exposure of the cells to 2-APB (1-50 µM) and one of its analogues diphenylboronic anhydride (DPBA) (1-30 µM) for 4 h leads to a significant decrease in dye coupling of GJ in a concentration-dependent manner. The inhibitory effects of 2-APB and DPBA are reversible since decreased GJ coupling resumes after the two compounds are washed out. The disfunction of GJ induced by 2-APB and DPBA is associated with a decrease in total amount of Cx43 protein and number of GJs on the cell membrane. 2-APB and DPBA do not alter Cx43 phosphorylation state and the level of Cx43 mRNA expression. The loss of Cx43 protein is prevented by either lysosomal or proteasomal inhibitor, suggesting that the decrease in Cx43 results from a 2-APB or DPBA-enhanced degradation of Cx43. The present results indicate that 2-APB and DPBA inhibit GJ communication through decreasing Cx43 expression in TM₄ cells.

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.

Connexin-based signaling in acute myelogenous leukemia (AML)

Normal and malignant hematopoiesis are regulated by intercellular communication in the hematopoietic microenvironments, and both soluble mediators as well as direct cell-cell contact play important functional roles. Gap junctions are complex membrane structures that transfer molecules between neighboring cells and thereby alter intracellular signaling and metabolism. The gap junction building blocks, the connexins, are also involved in gap junction-independent intercellular communication by forming hemichannels that transfer substances between the intra- and extracellular spaces. Connexins are furthermore involved in cell regulation as single molecules by modulating intracellular pathways and possibly gene transcription. The role of connexins in leukemogenesis and leukemic cell functions are not well characterized. In this review, we describe the known effects of gap junctions and connexins in acute myelogenous leukemia and the diverse potential of connexins in acute myelogenous leukemia chemosensitivity, intracellular signaling and cell death regulation.