MAB3067 Sigma-AldrichAnti-Connexin 43 Antibody, clone 4E6.2

It has long been held that electrical excitation spreads from cell-to-cell in the heart via low resistance gap junctions (GJ). However, it has also been proposed that myocytes could interact by non-GJ-mediated "ephaptic" mechanisms, facilitating propagation of action potentials in tandem with direct GJ-mediated coupling. We sought evidence that such mechanisms contribute to cardiac conduction. Using super-resolution microscopy, we demonstrate that Nav1.5 is localized within 200 nm of the GJ plaque (a region termed the perinexus). Electron microscopy revealed close apposition of adjacent cell membranes within perinexi suggesting that perinexal sodium channels could function as an ephapse, enabling ephaptic cell-to-cell transfer of electrical excitation. Acute interstitial edema (AIE) increased intermembrane distance at the perinexus and was associated with preferential transverse conduction slowing and increased spontaneous arrhythmia incidence. Inhibiting sodium channels with 0.5 μM flecainide uniformly slowed conduction, but sodium channel inhibition during AIE slowed conduction anisotropically and increased arrhythmia incidence more than AIE alone. Sodium channel inhibition during GJ uncoupling with 25 μM carbenoxolone slowed conduction anisotropically and was also highly proarrhythmic. A computational model of discretized extracellular microdomains (including ephaptic coupling) revealed that conduction trends associated with altered perinexal width, sodium channel conductance, and GJ coupling can be predicted when sodium channel density in the intercalated disk is relatively high. We provide evidence that cardiac conduction depends on a mathematically predicted ephaptic mode of coupling as well as GJ coupling. These data suggest opportunities for novel anti-arrhythmic therapies targeting noncanonical conduction pathways in the heart.

Human adipose tissue-derived mesenchymal stem cells (ADMSCs) are considered eligible candidates for cardiovascular stem cell therapy applications due to their cardiac transdifferentiation potential and immunotolerance. Over the years, the in vitro culture of ADMSCs by platelet lysate (PL), a hemoderivate containing numerous growth factors and cytokines derived from platelet pools, has allowed achieving a safe and reproducible methodology to obtain high cell yield prior to clinical administration. Nevertheless, the biological properties of PL are still to be fully elucidated. In this brief report we show the potential ability of PL to induce a permissive state of cardiac-like transdifferentiation and to cause epigenetic modifications. RTPCR results indicate an upregulation of Cx43, SMA, c-kit, and Thy-1 confirmed by immunofluorescence staining, compared to standard cultures with foetal bovine serum. Moreover, PL-cultured ADMSCs exhibit a remarkable increase of both acetylated histones 3 and 4, with a patient-dependent time trend, and methylation at lysine 9 on histone 3 preceding the acetylation. Expression levels of p300 and SIRT-1, two major regulators of histone 3, are also upregulated after treatment with PL. In conclusion, PL could unravel novel biological properties beyond its routine employment in noncardiac applications, providing new insights into the plasticity of human ADMSCs.

Direct exposure of cardiomyocytes to ethanol causes cardiac damage such as cardiac arrythmias and apoptotic cell death. Cardiomyocytes are connected to each other through intercalated disks (ID), which are composed of a gap junction (GJ), adherens junction, and desmosome. Changes in the content as well as the subcellular localization of connexin43 (Cx43), the main component of the cardiac GJ, are reportedly involved in cardiac arrythmias and subsequent damage. Recently, the hippo-YAP signaling pathway, which links cellular physical status to cell proliferation, differentiation, and apoptosis, has been implicated in cardiac homeostasis under physiological as well as pathological conditions. This study was conducted to explore the possible involvement of junctional intercellular communication, mechanotransduction through cytoskeletal organization, and the hippo-YAP pathway in cardiac damage caused by direct exposure to ethanol. HL-1 murine atrial cardiac cells were used since these cells retain cardiac phenotypes through ID formation and subsequent synchronous contraction. Cells were exposed to 0.5-2% ethanol; significant apoptotic cell death was observed after exposure to 2% ethanol for 48 hours. A decrease in Cx43 levels was already observed after 3 hours exposure to 2% ethanol, suggesting a rapid degradation of this protein. Upon exposure to ethanol, Cx43 translocated into lysosomes. Cellular cytoskeletal organization was also dysregulated by ethanol, as demonstrated by the disruption of myofibrils and intermediate filaments. Coinciding with the loss of cell-cell adherence, decreased phosphorylation of YAP, a hippo pathway effector, was also observed in ethanol-treated cells. Taken together, the results provide evidence that cells exposed directly to ethanol show 1) impaired cell-cell adherence/communication, 2) decreased cellular mechanotransduction by the cytoskeleton, and 3) a suppressed hippo-YAP pathway. Suppression of hippo-YAP pathway signaling should be effective in maintaining cellular homeostasis in cardiomyocytes exposed to ethanol.

Duchenne muscular dystrophy (DMD)-associated cardiac diseases are emerging as a major cause of morbidity and mortality in DMD patients, and many therapies for treatment of skeletal muscle failed to improve cardiac function. The reprogramming of patients' somatic cells into pluripotent stem cells, combined with technologies for correcting the genetic defect, possesses great potential for the development of new treatments for genetic diseases. In this study, we obtained human cardiomyocytes from DMD patient-derived, induced pluripotent stem cells genetically corrected with a human artificial chromosome carrying the whole dystrophin genomic sequence. Stimulation by cytokines was combined with cell culturing on hydrogel with physiological stiffness, allowing an adhesion-dependent maturation and a proper dystrophin expression. The obtained cardiomyocytes showed remarkable sarcomeric organization of cardiac troponin T and α-actinin, expressed cardiac-specific markers, and displayed electrically induced calcium transients lasting less than 1 second. We demonstrated that the human artificial chromosome carrying the whole dystrophin genomic sequence is stably maintained throughout the cardiac differentiation process and that multiple promoters of the dystrophin gene are properly activated, driving expression of different isoforms. These dystrophic cardiomyocytes can be a valuable source for in vitro modeling of DMD-associated cardiac disease. Furthermore, the derivation of genetically corrected, patient-specific cardiomyocytes represents a step toward the development of innovative cell and gene therapy approaches for DMD.

Gap junctional communication (GJC) plays a primordial role in oocyte maturation and meiotic resumption in mammals by directing the transfer of numerous molecules between cumulus cells and the oocyte. Gap junctions are made of connexins (Cx), proteins that regulate GJC in numerous ways. Understanding the dynamic regulation of connexin arrangements during in vitro maturation (IVM) could provide a powerful tool for controlling meiotic resumption and consequently in vitro development of fully competent oocytes. However, physiological events happening during the early hours of IVM may still be elucidated. The present study reports the dynamic regulation of connexin expression, degradation and localization during this stage. Cx43, Cx45 and Cx60 were identified as the main connexins expressed in swine COC. Cx43 and Cx45 transcripts were judged too static to be a regulator of GJC, while Cx43 protein expression was highly responsive to gonadotropins, suggesting that it might be the principal regulator of GJC. In addition, the degradation of Cx43 expressed after 4.5 h of IVM in response to equine chorionic gonadotropin appeared to involve the proteasomal complex. Cx43 localisation appeared to be associated with GJC. Taken together, these results show for the first time that gonadotropins regulate Cx43 protein expression, degradation and localisation in porcine COC during the first several hours of IVM. Regulation of Cx43 may in turn, via GJC, participate in the development of fully competent oocytes.

We examined the neurite outgrowth of sensory neurons on astrocytes following the genetic deletion of N-cadherin (NCAD). Deletion abolished immunostaining for NCAD and the other classical cadherins, indicating that NCAD is likely the only classical cadherin expressed by astrocytes. Only 38% of neurons grown on NCAD-deficient astrocytes for 24 h produced neurites, as compared to 74% of neurons grown on NCAD-expressing astrocytes. Of the neurons that produced neurites, those grown on NCAD-deficient astrocytes had a mean total length of 378 μm, as compared to 1093 μm for neurons grown on NCAD-expressing astrocytes. Thus, the loss of NCAD greatly impairs the formation and extension neurites on astrocytes.

Gap junctions (GJs) are aggregates of channels that provide for direct cytoplasmic connection between cells. Importantly, this connection is thought responsible for cell-to-cell transfer of the cardiac action potential. The GJ channels of ventricular myocytes are composed of connexin43 (Cx43). Interaction of Cx43 with zonula occludens-1 (ZO-1) is localized not only at the GJ plaque, but also to the region surrounding the GJ, the perinexus. Cx43 in the perinexus is not detectable by immunofluorescence, yet localization of Cx43/ZO-1 interaction to this region indicated the presence of Cx43. Therefore, we hypothesized that Cx43 occurs in the perinexus at a lower concentration per unit membrane than in the GJ itself, making it difficult to visualize. To overcome this, the Duolink protein-protein interaction assay was used to detect Cx43. Duolink labeling of cardiomyocytes localized Cx43 to the perinexus. Quantification demonstrated that signal in the perinexus was lower than in the GJ but significantly higher than in nonjunctional regions. Additionally, Duolink of Triton X-100-extracted cultures suggested that perinexal Cx43 is nonjunctional. Importantly, the voltage gated sodium channel Na(v)1.5, which is responsible for initiation of the action potential, was found to interact with perinexal Cx43 but not with ZO-1. This work provides a detailed characterization of the structure of the perinexus at the GJ edge and indicates that one of its potential functions in the heart may be in facilitating conduction of action potential.

A variety of human inherited heart diseases affect the normal functions of cardiomyocytes (CMs), endothelial cells (ECs), or smooth muscle cells (SMCs). To study human heart disease and generate cardiac cells for basic and translational research, an efficient strategy is needed for production of cardiac lineages from human stem cells. In the present study, a highly reproducible method was developed that can simultaneously enrich a large number of CMs and cardiac SMCs and ECs from human induced pluripotent stem (iPS) cells with high purity.

Carbenoxolone (Cbx), a substance from medicinal licorice, is used for antiinflammatory treatments. We investigated the mechanism of action of Cbx on Ca(2+)-induced permeability transition pore (PTP) opening in synaptic and nonsynaptic rat brain mitochondria (RBM), as well as in rat liver mitochondria (RLM), in an attempt to identify the molecular target of Cbx in mitochondria. Exposure to threshold Ca(2+) load induced PTP opening, as seen by sudden Ca(2+) efflux from the mitochondrial matrix and membrane potential collapse. In synaptic RBM, Cbx (1 μM) facilitated the Ca(2+)-induced, cyclosporine A-sensitive PTP opening, while in nonsynaptic mitochondria the Cbx threshold concentration was higher. A well-known molecular target of Cbx is the connexin (Cx) family, gap junction proteins. Moreover, Cx43 was previously found in heart mitochondria and attributed to the preconditioning mechanism of protection. Thus, we hypothesized that Cx43 might be a target for Cbx in brain mitochondria. For the first time, we detected Cx43 by Western blot in RBM, but Cx43 was absent in RLM. Interestingly, two anti-Cx43 antibodies, directed against amino acids 252 to 270 of rat Cx43, abolished the Cbx-induced enhancement of PTP opening in total RBM and in synaptic mitochondria, but not in RLM. In total RBM and in synaptic mitochondria, PTP caused dephosphorylation of Cx43 at serine 368. The phosphorylation level of serine 368 was decreased at threshold calcium concentration and additionally in the combined presence of Cbx in synaptic mitochondria. In conclusion, active mitochondrial Cx43 appears to counteract the Ca(2+)-induced PTP opening and thus might inhibit the PTP-ensuing mitochondrial demise and cell death. Consequently, we suggest that activity of Cx43 in brain mitochondria represents a novel molecular target for protection.

Connexin 43 (Cx43) is a gap junction (GJ) protein widely expressed in mammalian tissues that mediates cell-to-cell coupling. Intercellular channels comprising GJ aggregates form from docking of paired connexons, with one each contributed by apposing cells. Zonula occludens-1 (ZO-1) binds the carboxy terminus of Cx43, and we have previously shown that inhibition of the Cx43/ZO-1 interaction increases GJ size by 48 h. Here we demonstrated that increases in GJ aggregation occur within 2 h (∼Cx43 half-life) following disruption of Cx43/ZO-1. Immunoprecipitation and Duolink protein-protein interaction assays indicated that inhibition targets ZO-1 binding with Cx43 in GJs as well as connexons in an adjacent domain that we term the "perinexus." Consistent with GJ size increases being matched by decreases in connexons, inhibition of Cx43/ZO-1 reduced the extent of perinexal interaction, increased the proportion of connexons docked in GJs relative to undocked connexons in the plasma membrane, and increased GJ intercellular communication while concomitantly decreasing hemichannel-mediated membrane permeance in contacting, but not noncontacting, cells. ZO-1 small interfering RNA and overexpression experiments verified that loss and gain of ZO-1 function govern the transition of connexons into GJs. It is concluded that ZO-1 regulates the rate of undocked connexon aggregation into GJs, enabling dynamic partitioning of Cx43 channel function between junctional and proximal nonjunctional domains of plasma membrane.