The remodeling of connexin in the hypertrophied right ventricular in pulmonary arterial hypertension and the effect of a dual ET receptor antagonist (bosentan)

Hypertension Induces Pro-arrhythmic Cardiac Connexome Disorders: Protective Effects of Treatment

Prolonged population aging and unhealthy lifestyles contribute to the progressive prevalence of arterial hypertension. This is accompanied by low-grade inflammation and over time results in heart dysfunction and failure. Hypertension-induced myocardial structural and ion channel remodeling facilitates the development of both atrial and ventricular fibrillation, and these increase the risk of stroke and sudden death. Herein, we elucidate hypertension-induced impairment of "connexome" cardiomyocyte junctions. This complex ensures cell-to-cell adhesion and coupling for electrical and molecular signal propagation. Connexome dysfunction can be a key factor in promoting the occurrence of both cardiac arrhythmias and heart failure. However, the available literature indicates that arterial hypertension treatment can hamper myocardial structural remodeling, hypertrophy and/or fibrosis, and preserve connexome function. This suggests the pleiotropic effects of antihypertensive agents, including anti-inflammatory. Therefore, further research is required to identify specific molecular targets and pathways that will protect connexomes, and it is also necessary to develop new approaches to maintain heart function in patients suffering from primary or pulmonary arterial hypertension.

New Insights into Pulmonary Hypertension: A Role for Connexin-Mediated Signalling

Pulmonary hypertension is a serious clinical condition characterised by increased pulmonary arterial pressure. This can lead to right ventricular failure which can be fatal. Connexins are gap junction-forming membrane proteins which serve to exchange small molecules of less than 1 kD between cells. Connexins can also form hemi-channels connecting the intracellular and extracellular environments. Hemi-channels can mediate adenosine triphosphate release and are involved in autocrine and paracrine signalling. Recently, our group and others have identified evidence that connexin-mediated signalling may be involved in the pathogenesis of pulmonary hypertension. In this review, we discuss the evidence that dysregulated connexin-mediated signalling is associated with pulmonary hypertension.

Importance of Cx43 for Right Ventricular Function

In the heart, connexins form gap junctions, hemichannels, and are also present within mitochondria, with connexin 43 (Cx43) being the most prominent connexin in the ventricles. Whereas the role of Cx43 is well established for the healthy and diseased left ventricle, less is known about the importance of Cx43 for the development of right ventricular (RV) dysfunction. The present article focusses on the importance of Cx43 for the developing heart. Furthermore, we discuss the expression and localization of Cx43 in the diseased RV, i.e., in the tetralogy of Fallot and in pulmonary hypertension, in which the RV is affected, and RV hypertrophy and failure occur. We will also introduce other Cx molecules that are expressed in RV and surrounding tissues and have been reported to be involved in RV pathophysiology. Finally, we highlight therapeutic strategies aiming to improve RV function in pulmonary hypertension that are associated with alterations of Cx43 expression and function.

The Renal Connexome and Possible Roles of Connexins in Kidney Diseases

Connexins are membrane-spanning proteins that allow for the formation of cell-to-cell channels and cell-to-extracellular space hemichannels. Many connexin subtypes are expressed in kidney cells. Some mutations in connexin genes have been linked to various human pathologies, including cardiovascular, neurodegenerative, lung, and skin diseases, but the exact role of connexins in kidney disease remains unclear. Some hypotheses about a connection between genetic mutations, endoplasmic reticulum (ER) stress, and the unfolded protein response (UPR) in kidney pathology have been explored. The potential relationship of kidney disease to abnormal production of connexin proteins, mutations in their genes together with ER stress, or the UPR is still a matter of debate. In this scenario, it is tantalizing to speculate about a possible role of connexins in the setting of kidney pathologies that are thought to be caused by a deregulated podocyte protein expression, the so-called podocytopathies. In this article, we give examples of the roles of connexins in kidney (patho)physiology and propose avenues for further research concerning connexins, ER stress, and UPR in podocytopathies that may ultimately help refine drug treatment.

All-trans retinoic acid arrests cell cycle in leukemic bone marrow stromal cells by increasing intercellular communication through connexin 43-mediated gap junction

Background

Gap junctional intercellular communication (GJIC) is typically decreased in malignant tumors. Gap junction is not presented between hematopoietic cells but occurred in bone marrow stromal cells (BMSCs). Connexin 43 (Cx43) is the major gap junction (GJ) protein; our previous study revealed that Cx43 expression and GJIC were decreased in acute leukemic BMSCs. All-trans retinoic acid (ATRA) increases GJIC in a variety of cancer cells and has been used to treat acute promyelocytic leukemia, but the effects of ATRA on leukemic BMSCs is unknown. In this study, we evaluated the potential effects of ATRA on cell cycle, proliferation, and apoptosis of leukemic BMSCs. Effects of ATRA on Cx43 expression and GJIC were also examined.

Methods

Human BMSCs obtained from 25 patients with primary acute leukemia, and 10 normal healthy donors were cultured. Effects of ATRA on cell cycle, cell proliferation, and apoptosis were examined with or without co-treatment with amphotericin-B. Cx43 expression was examined at both the mRNA and protein expression levels. GJIC was examined by using a dye transfer assay and measuring the rate of fluorescence recovery after photobleaching (FRAP).

Results

ATRA arrested the cell cycle progression, inhibited cell growth, and increased apoptosis in leukemic BMSCs. Both Cx43 expression and GJIC function were increased by ATRA treatment. Most of the observed effects mediated by ATRA were abolished by amphotericin-B pretreatment.

Conclusions

ATRA arrests cell cycle progression in leukemic BMSCs, likely due to upregulating Cx43 expression and enhancing GJIC function.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-015-0212-7) contains supplementary material, which is available to authorized users.

Stem and progenitor cell therapy for pulmonary arterial hypertension: effects on the right ventricle (2013 Grover Conference Series)

In experimental animals and in patients with pulmonary arterial hypertension (PAH), a wide spectrum of structural and functional conditions is known that may be responsible for the switch of a state of "compensated" right ventricular (RV) hypertrophy to a state of RV failure. In recent years, therapy with differentiated cells, endothelial progenitor cells, and mesenchymal stem cells has been shown to cause partial or complete reversal of pathological characteristics of PAH. The therapeutic effects of stem or progenitor cell therapy are considered to be (1) paracrine effects from stem or progenitor cells that had engrafted in the myocardium (or elsewhere), by compounds that have anti-inflammatory, antiapoptotic, and proangiogenic actions and (2) unloading effects on the right ventricle due to stem or progenitor cell-induced decrease in pulmonary vascular resistance and decrease in pulmonary artery pressure.

Remodeling of mechanical junctions and of microtubule-associated proteins accompany cardiac connexin43 lateralization

BACKGROUND

Desmosomes and adherens junctions provide mechanical continuity between cardiac cells, whereas gap junctions allow for cell-cell electrical/metabolic coupling. These structures reside at the cardiac intercalated disc (ID). Also at the ID is the voltage-gated sodium channel (VGSC) complex. Functional interactions between desmosomes, gap junctions, and VGSC have been demonstrated. Separate studies show, under various conditions, reduced presence of gap junctions at the ID and redistribution of connexin43 (Cx43) to plaques oriented parallel to fiber direction (gap junction "lateralization").

OBJECTIVE

To determine the mechanisms of Cx43 lateralization, and the fate of desmosomal and sodium channel molecules in the setting of Cx43 remodeling.

METHODS

Adult sheep were subjected to right ventricular pressure overload (pulmonary hypertension). Tissue was analyzed by quantitative confocal microscopy and by transmission electron microscopy. Ionic currents were measured using conventional patch clamp.

RESULT

Quantitative confocal microscopy demonstrated lateralization of immunoreactive junctional molecules. Desmosomes and gap junctions in lateral membranes were demonstrable by electron microscopy. Cx43/desmosomal remodeling was accompanied by lateralization of 2 microtubule-associated proteins relevant for Cx43 trafficking: EB1 and kinesin protein Kif5b. In contrast, molecules of the VGSC failed to reorganize in plaques discernable by confocal microscopy. Patch-clamp studies demonstrated change in amplitude and kinetics of sodium current and a small reduction in electrical coupling between cells.

CONCLUSIONS

Cx43 lateralization is part of a complex remodeling that includes mechanical and gap junctions but may exclude components of the VGSC. We speculate that lateralization results from redirectionality of microtubule-mediated forward trafficking. Remodeling of junctional complexes may preserve electrical synchrony under conditions that disrupt ID integrity.

Up-regulation of Cx43 expression and GJIC function in acute leukemia bone marrow stromal cells post-chemotherapy

Gap junction intercellular communication (GJIC) among bone marrow stromal cells (BMSCs) most frequently occurs through a channel composed of connexin43 (Cx43). Dysregulation of connexin expression is believed to have a role in carcinogenesis. In earlier work, we found that in acute leukemia BMSCs, expression of Cx43 and functioning GJIC declined. However, there has been no evaluation of whether GJIC in BMSCs in complete remission (CR) post-chemotherapy is different from GJIC pre-chemotherapy. We studied Cx43 expression and tested GJIC function in human bone marrow cultures under different physiological and pathological conditions. To assay Cx43 expression we used immunocytochemistry, laser scan confocal microscopy (LSCM), flow cytometry and RT-PCR. The results showed that the expression level of Cx43 and its mRNA in acute leukemia BMSCs post-chemotherapy was significantly higher and similar to normal levels than in primary acute leukemia BMSCs (p<0.01). Functional tests in cultures using dye transfer and fluorescence recovery after photobleaching (FRAP) assays showed that the function of GJIC in acute leukemia BMSCs was significantly improved following effective chemotherapy. Our findings suggest Cx43 and GJIC might be involved in the courses of occurrence, development and termination of acute leukemia, and effective chemotherapy could improve Cx43 expression and GJIC function that were dysfunctional prior to treatment.