Cell-to-cell interaction prevents cell death in cultured neonatal rat ventricular myocytes

Connexins in the Heart: Regulation, Function and Involvement in Cardiac Disease

Connexins are a family of transmembrane proteins that play a key role in cardiac physiology. Gap junctional channels put into contact the cytoplasms of connected cardiomyocytes, allowing the existence of electrical coupling. However, in addition to this fundamental role, connexins are also involved in cardiomyocyte death and survival. Thus, chemical coupling through gap junctions plays a key role in the spreading of injury between connected cells. Moreover, in addition to their involvement in cell-to-cell communication, mounting evidence indicates that connexins have additional gap junction-independent functions. Opening of unopposed hemichannels, located at the lateral surface of cardiomyocytes, may compromise cell homeostasis and may be involved in ischemia/reperfusion injury. In addition, connexins located at non-canonical cell structures, including mitochondria and the nucleus, have been demonstrated to be involved in cardioprotection and in regulation of cell growth and differentiation. In this review, we will provide, first, an overview on connexin biology, including their synthesis and degradation, their regulation and their interactions. Then, we will conduct an in-depth examination of the role of connexins in cardiac pathophysiology, including new findings regarding their involvement in myocardial ischemia/reperfusion injury, cardiac fibrosis, gene transcription or signaling regulation.

Trauma, a Matter of the Heart-Molecular Mechanism of Post-Traumatic Cardiac Dysfunction

Trauma remains a leading global cause of mortality, particularly in the young population. In the United States, approximately 30,000 patients with blunt cardiac trauma were recorded annually. Cardiac damage is a predictor for poor outcome after multiple trauma, with a poor prognosis and prolonged in-hospitalization. Systemic elevation of cardiac troponins was correlated with survival, injury severity score, and catecholamine consumption of patients after multiple trauma. The clinical features of the so-called "commotio cordis" are dysrhythmias, including ventricular fibrillation and sudden cardiac arrest as well as wall motion disorders. In trauma patients with inappropriate hypotension and inadequate response to fluid resuscitation, cardiac injury should be considered. Therefore, a combination of echocardiography (ECG) measurements, echocardiography, and systemic appearance of cardiomyocyte damage markers such as troponin appears to be an appropriate diagnostic approach to detect cardiac dysfunction after trauma. However, the mechanisms of post-traumatic cardiac dysfunction are still actively being investigated. This review aims to discuss cardiac damage following trauma, focusing on mechanisms of post-traumatic cardiac dysfunction associated with inflammation and complement activation. Herein, a causal relationship of cardiac dysfunction to traumatic brain injury, blunt chest trauma, multiple trauma, burn injury, psychosocial stress, fracture, and hemorrhagic shock are illustrated and therapeutic options are discussed.

Structural alterations and inflammation in the heart after multiple trauma followed by reamed versus non-reamed femoral nailing

BACKGROUND

Approximately 30,000 patients with blunt cardiac trauma are recorded each year in the United States. Blunt cardiac injuries after trauma are associated with a longer hospital stay and a poor overall outcome. Organ damage after trauma is linked to increased systemic release of pro-inflammatory cytokines and damage-associated molecular patterns. However, the interplay between polytrauma and local cardiac injury is unclear. Additionally, the impact of surgical intervention on this process is currently unknown. This study aimed to determine local cardiac immunological and structural alterations after multiple trauma. Furthermore, the impact of the chosen fracture stabilization strategy (reamed versus non-reamed femoral nailing) on cardiac alterations was studied.

EXPERIMENTAL APPROACH

15 male pigs were either exposed to multiple trauma (blunt chest trauma, laparotomy, liver laceration, femur fracture and haemorrhagic shock) or sham conditions. Blood samples as well as cardiac tissue were analysed 4 h and 6 h after trauma. Additionally, murine HL-1 cells were exposed to a defined polytrauma-cocktail, mimicking the pro-inflammatory conditions after multiple trauma in vitro.

RESULTS

After multiple trauma, cardiac structural changes were observed in the left ventricle. More specifically, alterations in the alpha-actinin and desmin protein expression were found. Cardiac structural alterations were accompanied by enhanced local nitrosative stress, increased local inflammation and elevated systemic levels of the high-mobility group box 1 protein. Furthermore, cardiac alterations were observed predominantly in pigs that were treated by non-reamed intramedullary reaming. The polytrauma-cocktail impaired the viability of HL-1 cells in vitro, which was accompanied by a release of troponin I and HFABP.

DISCUSSION

Multiple trauma induced cardiac structural alterations in vivo, which might contribute to the development of early myocardial damage (EMD). This study also revealed that reamed femoral nailing (reamed) is associated with more prominent immunological cardiac alterations compared to nailing without reaming (non-reamed). This suggests that the choice of the initial fracture treatment strategy might be crucial for the overall outcome as well as for any post-traumatic cardiac consequences.

Small G protein signaling modulator 3 (SGSM3) knockdown attenuates apoptosis and cardiogenic differentiation in rat mesenchymal stem cells exposed to hypoxia

Connexin 43 (Cx43) may be important in cell death and survival due to cell-to-cell communication-independent mechanisms. In our previous study, we found that small G protein signaling modulator 3 (SGSM3), a partner of Cx43, contributes to myocardial infarction (MI) in rat hearts. Based on these previous results, we hypothesized that SGSM3 could also play a role in bone marrow-derived rat mesenchymal stem cells (MSCs), which differentiate into cardiomyocytes and/or cells with comparable phenotypes under low oxygen conditions. Cx43 and Cx43-related factor expression profiles were compared between normoxic and hypoxic conditions according to exposure time, and Sgsm3 gene knockdown (KD) using siRNA transfection was performed to validate the interaction between SGSM3 and Cx43 and to determine the roles of SGSM3 in rat MSCs. We identified that SGSM3 interacts with Cx43 in MSCs under different oxygen conditions and that Sgsm3 knockdown inhibits apoptosis and cardiomyocyte differentiation under hypoxic stress. SGSM3/Sgsm3 probably has an effect on MSC survival and thus therapeutic potential in diseased hearts, but SGSM3 may worsen the development of MSC-based therapeutic approaches in regenerative medicine. This study was performed to help us better understand the mechanisms involved in the therapeutic efficacy of MSCs, as well as provide data that could be used pharmacologically.

Substrate Stiffness, Cell Anisotropy, and Cell-Cell Contact Contribute to Enhanced Structural and Calcium Handling Properties of Human Embryonic Stem Cell-Derived Cardiomyocytes

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) can be utilized to understand the mechanisms underlying the development and progression of heart disease, as well as to develop better interventions and treatments for this disease. However, these cells are structurally and functionally immature, which undermines some of their adequacy in modeling adult heart tissue. Previous studies with immature cardiomyocytes have shown that altering substrate stiffness, cell anisotropy, and/or cell-cell contact can enhance the contractile and structural maturation of hPSC-CMs. In this study, the structural and calcium handling properties of human embryonic stem cell-derived cardiomyocytes (hESC-CMs) were enhanced by exposure to a downselected combination of these three maturation stimuli. First, hESC-CMs were seeded onto substrates composed of two commercial formulations of polydimethylsiloxane (PDMS), Sylgard 184 and Sylgard 527, whose stiffness ranged from 5 kPa to 101 kPa. Upon analyzing the morphological and calcium transient properties of these cells, it was concluded that a 21 kPa substrate yielded cells with the highest degree of maturation. Next, these PDMS substrates were microcontact-printed with laminin to force the cultured cells into rod-shaped geometries using line patterns that were 12, 18, or 24 μm in width. We found that cells on the 18 and 24 μm pattern widths had structural and functional properties that were superior to those on the 12 μm pattern. The hESC-CMs were then seeded onto these line-stamped surfaces at a density of 500 000 cells per 25-mm-diameter substrate, to enable the formation of cell-cell contacts at their distal ends. We discovered that this combination of culture conditions resulted in cells that were more structurally and functionally mature than those that were only exposed to one or two stimuli. Our results suggest that downselecting a combination of mechanobiological stimuli could prove to be an effective means of maturing hPSC-CMs in vitro.

Cardiac Depression in Pigs after Multiple Trauma - Characterization of Posttraumatic Structural and Functional Alterations

The purpose of this study was to define the relationship between cardiac depression and morphological and immunological alterations in cardiac tissue after multiple trauma. However, the mechanistic basis of depressed cardiac function after trauma is still elusive. In a porcine polytrauma model including blunt chest trauma, liver laceration, femur fracture and haemorrhage serial trans-thoracic echocardiography was performed and correlated with cellular cardiac injury as well as with the occurrence of extracellular histones in serum. Postmortem analysis of heart tissue was performed 72 h after trauma. Ejection fraction and shortening fraction of the left ventricle were significantly impaired between 4 and 27 h after trauma. H-FABP, troponin I and extracellular histones were elevated early after trauma and returned to baseline after 24 and 48 h, respectively. Furthermore, increased nitrotyrosine and Il-1β generation and apoptosis were identified in cardiac tissue after trauma. Main structural findings revealed alteration of connexin 43 (Cx43) and co-translocation of Cx43 and zonula occludens 1 to the cytosol, reduction of α-actinin and increase of desmin in cardiomyocytes after trauma. The cellular and subcellular events demonstrated in this report may for the first time explain molecular mechanisms associated with cardiac dysfunction after multiple trauma.

Early structural changes of the heart after experimental polytrauma and hemorrhagic shock

Evidence is emerging that systemic inflammation after trauma drives structural and functional impairment of cardiomyocytes and leads to cardiac dysfunction, thus worsening the outcome of polytrauma patients. This study investigates the structural and molecular changes in heart tissue 4 h after multiple injuries with additional hemorrhagic shock using a clinically relevant rodent model of polytrauma. We determined mediators of systemic inflammation (keratinocyte chemoattractant, macrophage chemotactic protein 1), activated complement component C3a and cardiac troponin I in plasma and assessed histological specimen of the mouse heart via standard histomorphology and immunohistochemistry for cellular and subcellular damage and ongoing apoptosis. Further we investigated spatial and quantitative changes of connexin 43 by immunohistochemistry and western blotting. Our results show significantly increased plasma levels of both keratinocyte chemoattractant and cardiac troponin I 4 h after polytrauma and 2 h after induction of hypovolemia. Although we could not detect any morphological changes, immunohistochemical evaluation showed increased level of tissue high-mobility group box 1, which is both a damage-associated molecule and actively released as a danger response signal. Additionally, there was marked lateralization of the cardiac gap-junction protein connexin 43 following combined polytrauma and hemorrhagic shock. These results demonstrate a molecular manifestation of remote injury of cardiac muscle cells in the early phase after polytrauma and hemorrhagic shock with marked disruption of the cardiac gap junction. This disruption of an important component of the electrical conduction system of the heart may lead to arrhythmia and consequently to cardiac dysfunction.

The gap junction modifier ZP1609 decreases cardiomyocyte hypercontracture following ischaemia/reperfusion independent from mitochondrial connexin 43

BACKGROUND AND PURPOSE

Dysregulation of gap junction-mediated cell coupling contributes to development of arrhythmias and myocardial damage after ischaemia/reperfusion (I/R). Connexin 43 (Cx43) is present at ventricular gap junctions and also in the mitochondria of cardiomyocytes. The dipeptide (2S, 4R)-1-(2-aminoacetyl)-4-benzamidopyrrolidine-2-carboxylic acid (ZP1609) has antiarrhythmic properties and reduces infarct size when given at reperfusion. However, it is unclear, whether ZP1609 targets Cx43-containing mitochondria and affects cardiomyocyte hypercontracture following I/R.

EXPERIMENTAL APPROACH

We studied the effects of ZP1609 on the function of murine sub-sarcolemmal mitochondria (SSM, containing Cx43) and interfibrillar mitochondria (IFM, lacking Cx43). Murine isolated cardiomyocytes were subjected to simulated I/R without and with ZP1609 (applied during I/R or at the onset of reperfusion only), and the number of cardiomyocytes undergoing hypercontracture was quantified. Biochemical pathways targeted by ZP1609 in cardiomyocytes were analysed.

KEY RESULTS

ZP1609 inhibited ADP-stimulated respiration and ATP production in SSM and IFM. ROS formation and calcium retention capacities in SSM and IFM were not affected by ZP1609, whereas potassium uptake was enhanced in IFM. The number of rod-shaped cardiomyocytes was increased by ZP1609 (10 μM) when administered either during I/R or reperfusion. ZP1609 altered the phosphorylation of proteins contributing to the protection against I/R injury.

CONCLUSIONS AND IMPLICATIONS

ZP1609 reduced mitochondrial respiration and ATP production, but enhanced potassium uptake of IFM. Additionally, ZP1609 reduced the extent of cardiomyocytes undergoing hypercontracture following I/R. The protective effect was independent of mitochondrial Cx43, as ZP1609 exerts its effects in Cx43-containing SSM and Cx43-lacking IFM.

Mitochondrial Cx43, an important component of cardiac preconditioning

Connexin 43 (Cx43) forms gap junction channels that are essential for the propagation of electrical depolarization in cardiomyocytes, but also with important roles in the pathophysiology of reperfusion injury. However, more recent studies have shown that Cx43 has also important functions independent from intercellular communication between adjacent cardiomyocytes. Some of these actions have been related to the presence of Cx43 in the mitochondria of these cells (mitoCx43). The functions of mitoCx43 have not been completely elucidated, but there is strong evidence indicating that mitoCx43 modulates mitochondrial respiration at respiratory complex I, production of radical oxygen species and ATP synthesis. These functions of mitoCx43 modulate mitochondrial and cellular tolerance to reperfusion after prolonged ischemia and are necessary for the cardioprotective effect of ischemic preconditioning. In the present review article we discuss available knowledge on these functions of mitoCx43 in relation to reperfusion injury, the molecular mechanisms involved and explore the possibility that mitoCx43 may constitute a new pharmacological target in patients with ST-segment elevation myocardial infarction (STEMI). This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Connexin channel and its role in diabetic retinopathy

Diabetic retinopathy is the leading cause of blindness in the working age population. Unfortunately, there is no cure for this devastating ocular complication. The early stage of diabetic retinopathy is characterized by the loss of various cell types in the retina, namely endothelial cells and pericytes. As the disease progresses, vascular leakage, a clinical hallmark of diabetic retinopathy, becomes evident and may eventually lead to diabetic macular edema, the most common cause of vision loss in diabetic retinopathy. Substantial evidence indicates that the disruption of connexin-mediated cellular communication plays a critical role in the pathogenesis of diabetic retinopathy. Yet, it is unclear how altered communication via connexin channel mediated cell-to-cell and cell-to-extracellular microenvironment is linked to the development of diabetic retinopathy. Recent observations suggest the possibility that connexin hemichannels may play a role in the pathogenesis of diabetic retinopathy by allowing communication between cells and the microenvironment. Interestingly, recent studies suggest that connexin channels may be involved in regulating retinal vascular permeability. These cellular events are coordinated at least in part via connexin-mediated intercellular communication and the maintenance of retinal vascular homeostasis. This review highlights the effect of high glucose and diabetic condition on connexin channels and their impact on the development of diabetic retinopathy.

Bioacoustic-enabled patterning of human iPSC-derived cardiomyocytes into 3D cardiac tissue

The creation of physiologically-relevant human cardiac tissue with defined cell structure and function is essential for a wide variety of therapeutic, diagnostic, and drug screening applications. Here we report a new scalable method using Faraday waves to enable rapid aggregation of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) into predefined 3D constructs. At packing densities that approximate native myocardium (10⁸-10⁹ cells/ml), these hiPSC-CM-derived 3D tissues demonstrate significantly improved cell viability, metabolic activity, and intercellular connection when compared to constructs with random cell distribution. Moreover, the patterned hiPSC-CMs within the constructs exhibit significantly greater levels of contractile stress, beat frequency, and contraction-relaxation rates, suggesting their improved maturation. Our results demonstrate a novel application of Faraday waves to create stem cell-derived 3D cardiac tissue that resembles the cellular architecture of a native heart tissue for diverse basic research and clinical applications.

Inhibition of gap junction intercellular communication is involved in silica nanoparticles-induced H9c2 cardiomyocytes apoptosis via the mitochondrial pathway

Gap junction intercellular communication (GJIC) between cardiomyocytes is essential for synchronous heart contraction and relies on connexin-containing channels. Connexin 43 (Cx43) is a major component involved in GJIC in heart tissue, and its abnormal expression is closely associated with various cardiac diseases. Silica nanoparticles (SNPs) are known to induce cardiovascular toxicity. However, the mechanisms through which GJIC plays a role in cardiomyocytes apoptosis induced by SNPs remain unknown. The aim of the present study is to determine whether SNPs-decreased GJIC promotes apoptosis in rat cardiomyocytes cell line (H9c2 cells) via the mitochondrial pathway using CCK-8 Kit, scrape-loading dye transfer technique, Annexin V/PI double-staining assays, and Western blot analysis. The results showed that SNPs elicited cytotoxicity in H9c2 cells in a time- and concentration-dependent manner. SNPs also reduced GJIC in H9c2 cells in a concentration-dependent manner through downregulation of Cx43 and upregulation of P-Cx43. Inhibition of gap junctions by gap junction blocker carbenoxolone disodium resulted in decreased survival and increased apoptosis, whereas enhancement of the gap junctions by retinoic acid led to enhanced survival but decreased apoptosis. Furthermore, SNPs-induced apoptosis through the disrupted functional gap junction was correlated with abnormal expressions of the proteins involved in the mitochondrial pathway-related apoptosis such as Bcl-2/Bax, cytochrome C, Caspase-9, and Caspase-3. Taken together, our results provide the first evidence that SNPs-decreased GJIC promotes apoptosis in cardiomyocytes via the mitochondrial pathway. In addition, downregulation of GJIC by SNPs in cardiomyocytes is mediated through downregulation of Cx43 and upregulation of P-Cx43. These results suggest that in rat cardiomyocytes cell line, GJIC plays a protective role in SNPs-induced apoptosis and that GJIC may be one of the targets for SNPs-induced biological effects.

Gap junction blockage promotes cadmium-induced apoptosis in BRL 3A derived from Buffalo rat liver cells

Gap junctions mediate direct communication between cells; however, toxicological cascade triggered by nonessential metals can abrogate cellular signaling mediated by gap junctions. Although cadmium (Cd) is known to induce apoptosis in organs and tissues, the mechanisms that underlie gap junction activity in Cd-induced apoptosis in BRL 3A rat liver cells has yet to be established. In this study, we showed that Cd treatment decreased the cell index (a measure of cellular electrical impedance) in BRL 3A cells. Mechanistically, we found that Cd exposure decreased expression of connexin 43 (Cx43), increased expression of p-Cx43 and elevated intracellular free Ca²⁺ concentration, corresponding to a decrease in gap junctional intercellular communication. Gap junction blockage pretreatment with 18β-glycyrrhizic acid (GA) promoted Cd-induced apoptosis, involving changes in expression of Bax, Bcl-2, caspase-3 and the mitochondrial transmembrane electrical potential (Δψm). Additionally, GA was found to enhance ERK and p38 activation during Cd-induced activation of mitogen-activated protein kinases, but had no significant effect on JNK activation. Our results indicated the apoptosis-related proteins and the ERK and p38 signaling pathways may participate in gap junction blockage promoting Cd-induced apoptosis in BRL 3A cells.

Concerns in the application of fluorescent probes DCDHF-DA, DHR 123 and DHE to measure reactive oxygen species in vitro

Reactive oxygen species (ROS) are formed in biological systems by partial reduction of molecular oxygen. The essential role of ROS in maintaining physiological health may be corrupted into oxidative stress by their overproduction or the exhaustion of antioxidant mechanisms. Many studies covering a broad range of methodologies have investigated ROS production and their toxic mechanisms of action. Of these methodologies, fluorometry has been among the preferred techniques. Three frequently used fluorescent probes for in vitro studies are 2',7'-dichlorodihydrofluorescein diacetate (DCDHF-DA), Dihydrorhodamine 123 (DHR 123) and Dihydroethidium (DHE). Apart from the unavoidable limitations of auto-oxidation, photo-oxidation and photo-conversion, there are also concerns relating to protocol modification for the improved monitoring of ROS. This paper aims to highlight such contributing factors, including cell culture conditions and the characteristics of individual fluorescent probes in the utilization of these selected probes in in vitro systems.

Connexin 43 is an emerging therapeutic target in ischemia/reperfusion injury, cardioprotection and neuroprotection

Connexins are widely distributed proteins in the body that are crucially important for heart and brain functions. Six connexin subunits form a connexon or hemichannel in the plasma membrane. Interactions between two hemichannels in a head-to-head arrangement result in the formation of a gap junction channel. Gap junctions are necessary to coordinate cell function by passing electrical current flow between heart and nerve cells or by allowing exchange of chemical signals and energy substrates. Apart from its localization at the sarcolemma of cardiomyocytes and brain cells, connexins are also found in the mitochondria where they are involved in the regulation of mitochondrial matrix ion fluxes and respiration. Connexin expression is affected by age and gender as well as several pathophysiological alterations such as hypertension, hypertrophy, diabetes, hypercholesterolemia, ischemia, post-myocardial infarction remodeling or heart failure, and post-translationally connexins are modified by phosphorylation/de-phosphorylation and nitros(yl)ation which can modulate channel activity. Using knockout/knockin technology as well as pharmacological approaches, one of the connexins, namely connexin 43, has been identified to be important for cardiac and brain ischemia/reperfusion injuries as well as protection from it. Therefore, the current review will focus on the importance of connexin 43 for irreversible injury of heart and brain tissues following ischemia/reperfusion and will highlight the importance of connexin 43 as an emerging therapeutic target in cardio- and neuroprotection.

Gene transfection to spheroid culture system on micropatterned culture plate by polyplex nanomicelle: a novel platform of genetically-modified cell transplantation

Three-dimensional (3D) cellular spheroids have attracted much attention as a transplantation procedure because the increased cell-to-cell interaction in spheroids enhances cell survival and its functions after the transplantation into the body. Furthermore, the potency of spheroidal cells may be further improved by introducing transgenes to augment cellular functions as well as enhance the paracrine effects by secreting key proteins involved in the essential cellular signaling cascades. In this study, we organized a new platform for genetically-modified cell transplantation by combining a microfabricated culture system for 3D spheroid formation with a newly developed non-viral transfection system, polyplex nanomicelle. After transfection of Gaussia luciferase using the nanomicelle, the prolonged luciferase expression was obtained for more than a month with continuous albumin secretion from the hepatocyte spheroids to the level comparable with control spheroids receiving no transfection. In contrast, by the transfection using FuGENE HD, a commercially available lipid-based reagent, the luciferase expression was obtained, yet the albumin secretion was significantly decreased with disintegration of the spheroid architecture. To assess the feasibility of the hepatocyte spheroids for in vivo transplantation, the spheroids were recovered by the use of micropatterned culture plate functionalized with thermosensitive polymer and dispersed into Matrigel(TM) Matrix. The luciferase expression as well as albumin secretion was maintained for more than a month from the spheroids in the Matrix. Thus, the combination of spheroid cell culture on micropatterned plates with gene introduction using polyplex nanomicelle is a promising platform for genetically-modified cell transplantation to achieve sustained transgene expression with maintaining innate cell functions.

Neuroprotection in the treatment of glaucoma--A focus on connexin43 gap junction channel blockers

Glaucoma is a form of optic neuropathy and a common cause of blindness, affecting over 60 million people worldwide with an expected rise to 80 million by 2020. Successful treatment is challenging due to the various causes of glaucoma, undetectable symptoms at an early stage and inefficient delivery of drugs to the back of the eye. Conventional glaucoma treatments focus on the reduction of elevated intraocular pressure (IOP) using topical eye drops. However, their efficacy is limited to patients who suffer from high IOP glaucoma and do not address the underlying susceptibility of retinal ganglion cells (RGC) to degeneration. Glaucoma is known as a neurodegenerative disease which starts with RGC death and eventually results in damage of the optic nerve. Neuroprotective strategies therefore offer a novel treatment option for glaucoma by not only preventing neuronal loss but also disease progression. This review firstly gives an overview of the pathophysiology of glaucoma as well as current treatment options including conventional and novel delivery strategies. It then summarizes the rational for neuroprotection as a novel therapy for glaucomatous neuropathies and reviews current potential neuroprotective strategies to preserve RGC, with a focus on connexin43 (Cx43) gap junction channel blockers.

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.

Cx43 in mesenchymal stem cells promotes angiogenesis of the infarcted heart independent of gap junctions

Mesenchymal stem cells (MSCs) with elevated levels of connexin 43 (Cx43) have been shown to exhibit improved protection for ischemic hearts. However, it remains unclear whether Cx43 is involved in the paracrine actions of angiogenesis, the major mechanism of cell therapy. In the present study, an in vitro model with deprivation of oxygen and a murine myocardial infarction model with permanent ligation of the left anterior‑descending (LAD) coronary artery were used to determine whether gap junctions in MSCs promote angiogenesis. It was observed that MSCs that overexpressed Cx43 (MSCs‑Cx43), improve the cardiac function of infarcted myocardium as compared with control MSCs (MSCs‑vector) and MSCs with Cx43 knocked down by small interfering RNA (MSCs‑siCx43), accompanied with a reduction of infarct size and an increase in the vascular density and maturity. Increased levels of representative angiogenic factors [vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF)] were produced by MSCs‑Cx43 compared with MSCs‑siCx43 in vivo and in vitro. However, neither Cx43 formed gap junction specific inhibitor (Cx43 mimetic peptide) or gap junction opener (antiarrhythmic peptide) affected the production of VEGF and bFGF in MSCs under hypoxic stress. These data support the hypothesis that Cx43 in MSCs promotes angiogenesis in the infarcted heart, independent of gap junction formation.

Activation of RISK and SAFE pathways is not involved in the effects of Cx43 deficiency on tolerance to ischemia-reperfusion injury and preconditioning protection

Connexin 43 (Cx43) deficiency increases myocardial tolerance to ischemia-reperfusion injury and abolishes preconditioning protection. It is not known whether modifications in baseline signaling through protective RISK or SAFE pathways or in response to preconditioning may contribute to these effects. To answer this question we used Cx43(Cre-ER(T)/fl) mice, in which Cx43 expression is abolished after 4-hydroxytamoxifen (4-OHT) administration. Isolated hearts from Cx43(Cre-ER(T)/fl) mice, or from Cx43(fl/fl) controls, treated with vehicle or 4-OHT, were submitted to global ischemia (40 min) and reperfusion. Cx43 deficiency was associated with reduced infarct size after ischemia-reperfusion (11.17 ± 3.25 % vs. 65.04 ± 3.79, 59.31 ± 5.36 and 65.40 ± 4.91, in Cx43(fl/fl) animals treated with vehicle, Cx43(fl/fl) mice treated with 4-OHT, and Cx43(Cre-ER(T)/fl) mice treated with vehicle, respectively, n = 8-9, p < 0.001). However, the ratio phosphorylated/total protein expression for Akt, ERK-1/2, GSK3β and STAT3 was not increased in normoxic samples from animals lacking Cx43. Instead, a reduction in the phosphorylation state of GSK3β was observed in Cx43-deficient mice (ratio: 0.15 ± 0.02 vs. 0.56 ± 0.11, 0.77 ± 0.15, and 0.46 ± 0.14, respectively, n = 5-6, p < 0.01). Furthermore, ischemic preconditioning (IPC, 4 cycles of 3.5 min of ischemia and 5 min of reperfusion) increased phosphorylation of ERK-1/2, GSK3β, and STAT3 in all hearts without differences between groups (n = 5-6, p < 0.05), although Cx43 deficient mice were not protected by either IPC or pharmacological preconditioning with diazoxide. Our data demonstrate that modification of RISK and SAFE signaling does not contribute to the role of Cx43 in the increased tolerance to myocardial ischemia-reperfusion injury and in preconditioning protection.

Gap junctional communication promotes apoptosis in a connexin-type-dependent manner

Gap junctions (GJs) have been described to modulate cell death and survival. It still remains unclear whether this effect requires functional GJ channels or depends on channel-independent effects of connexins (Cx), the constituents of GJs. Therefore, we analysed the apoptotic response to streptonigrin (SN, intrinsic apoptotic pathway) or to α-Fas (extrinsic apoptotic pathway) in HeLa cells expressing Cx43 as compared with empty vector-transfected (CTL) cells. Apoptosis assessed by annexin V-fluorescein isothiocyanate/propidium iodide staining was significantly higher in HeLa-Cx43 compared with HeLa-CTL cells. Moreover, the cleavage of caspase-7 or Parp occurred earlier in HeLa-Cx43 than in HeLa-CTL cells. Comparative analysis of the effect of two further (endothelial) Cx (Cx37 and Cx40) on apoptosis revealed that apoptosis was highest in HeLa-Cx43 and lowest in HeLa-Cx37 cells, and correlated with the GJ permeability (assessed by spreading of a GJ-permeable dye and locally induced Ca(2+) signals). Pharmacologic inhibition of GJ formation in HeLa-Cx43 cells reduced apoptosis significantly. The role of GJ communication was further analysed by the expression of truncated Cx43 proteins with and without channel-forming capacity. Activation of caspases was higher in cells expressing the channel-building part (HeLa-Cx43NT-GFP) than in cells expressing the channel-incompetent C-terminal part of Cx43 (HeLa-Cx43CT-GFP) only. A hemichannel-dependent release and, hence, paracrine effect of proapoptotic signals could be excluded since the addition of a peptide (Pep)-blocking Cx43-dependent hemichannels (but not GJs) did not reduce apoptosis in HeLa-Cx43 cells. Treatment with SN resulted in a significant higher increase of the intracellular free Ca(2+) concentration in HeLa-Cx43 and HeLa-Cx43NT-GFP cells compared with HeLa-CTL or HeLa-Cx43CT-GFP cells, suggesting that Ca(2+) or a Ca(2+)-releasing agent could play a signalling role. Blocking of inositol triphosphate receptors reduced the SN-induced Ca(2+) increase as well as the increase in apoptosis. Our observations suggest that Cx43 and Cx40 but not Cx37 promote apoptosis via gap junctional transfer of pro-apoptotic signals between cells.

Calcium and connexin-based intercellular communication, a deadly catch?

Ca(2+) is known as a universal messenger mediating a wide variety of cellular processes, including cell death. In fact, this ion has been proposed as the 'cell death master', not only at the intracellular but also at the intercellular level. The most direct form of intercellular spread of cell death is mediated by gap junction channels. These channels have been shown to propagate cell death as well as cell survival signals between the cytoplasm of neighbouring cells, reflecting the dual role of Ca(2+) signals, i.e. cell death versus survival. Its precursor, the unopposed hemichannel (half of a gap junction channel), has recently joined in as a toxic pore connecting the intracellular with the extracellular environment and allowing the passage of a range of substances. The biochemical nature of the so-called intercellular cell death molecule, transferred through gap junctions or released/taken up via hemichannels, remains elusive but several studies pinpoint Ca(2+) itself or its messenger inositol trisphosphate as the responsible masters in crime. Although direct evidence is still lacking, indirect data including Ca(2+) involvement in intercellular communication and cell death, and effects of intercellular communication on intracellular Ca(2+) homeostasis, support this hypothesis. In addition, hemichannels and their molecular building blocks, connexin or pannexin proteins, may exert their effects on Ca(2+)-dependent cell death at the intracellular level, independently from their channel functions. This review provides a cutting edge overview of the current knowledge and underscores the intimate connection between intercellular communication, Ca(2+) signalling and cell death.

Automaticity and conduction properties of bio-artificial pacemakers assessed in an in vitro monolayer model of neonatal rat ventricular myocytes

AIMS

A better understanding of the ionic mechanisms for cardiac automaticity can lead to better strategies for engineering bio-artificial pacemakers. Here, we attempted to better define the relative contribution of I(f) and I(K1) in the generation of spontaneous action potentials (SAPs) in cardiomyocytes (CMs).

METHODS AND RESULTS

Monolayers of neonatal rat ventricular myocytes (NRVMs) were transduced with a recombinant adenovirus (Ad) to express a gating-engineered HCN1 construct (HCN1-DeltaDeltaDelta) for patch-clamp and multielectrode array (MEA) recordings. Single NRVMs exhibited a bi-phasic response in the generation of SAPs (62.6 +/- 17.4 b.p.m., Days 1-2; 194.3 +/- 12.3 b.p.m., Days 3-4; 73% quiescent, Days 9-10). Although automaticity time-dependently decreased and subsequently ceased, I(f) remained fairly stable (-5.2 +/- 1.1 pA/pF, Days 1-2; -5.1 +/- 1.4 pA/pF, Days 7-8; -4.3 +/- 1.3 pA/pF, Days 13-14). In contrast, I(K1) declined rapidly (from -16.9 +/- 2.7 pA/pF on Days 1-2 to -4.4 +/- 1.6 pA/pF on Days 5-6). Maximum diastolic potential/resting membrane potential (r = 0.89) and action potential duration at 50% (APD(50), r = 0.73) and 90% (APD(90), r = 0.75) but not the firing rate (r = -0.3) were positively correlated to the I(K1). Similarly, monolayer NRVMs ceased to spontaneously fire after long-term culture. Ad-HCN1-DeltaDeltaDelta transduction restored pacing in silenced individual and monolayer NRVMs but with reduced conduction velocity and field potential amplitude.

CONCLUSION

We conclude that the combination of I(K1) and I(f) primes CMs for bio-artificial pacing by determining the threshold. However, I(f) functions as a membrane potential oscillator to determine the basal firing frequency. Future engineering of automaticity in the multicellular setting needs to have conduction taken into consideration.

Connexin43 promotes survival of mesenchymal stem cells in ischaemic heart

The involvement of connexins in regulating cell growth and death has recently been reported. We have investigated whether Cx43 (connexin43) contributes to MSC (mesenchymal stem cell) survival and improves therapeutic efficacy in MI (myocardial infarction). Genetically modified Cx43 MSCs were exposed to hypoxic conditions or injected intramyocardially into a rat MI model. MSCs overexpressing Cx43, with more Bcl-2 and phosphorylated Akt, but less Bax, were relatively tolerant to hypoxic injury. After transplantation, this Cx43 overexpression enhanced cell survival and reduced infarct size, improving contractile performance. Cx43 inhibition by SiRNA reversed the effects of Cx43 overexpression. Therefore, Cx43 may act as a potential target for improving the therapeutic efficacy of MSCs in ischaemic heart disease.

Reduced connexin 43 expression and its effect on the development of vascular lesions in retinas of diabetic mice

PURPOSE. To examine whether diabetes-induced connexin 43 downregulation promotes retinal vascular lesions characteristic of diabetic retinopathy (DR). METHODS. Two animal models, streptozotocin-induced diabetic mice and Cx43 heterozygous knockout (Cx43(+/-)) mice, were studied to directly assess whether diabetes reduces the expression of retinal Cx43, which, in turn, contributes to retinal vascular cell loss by apoptosis. Retinal Cx43 protein levels were assessed in nondiabetic control mice, diabetic mice, and Cx43(+/-) mice by Western blot analysis, and Cx43 localization and distribution in the retinal vascular cells were studied by immunostaining of retinal trypsin digests (RTDs). In parallel, RTDs were stained with hematoxylin and periodic acid Schiff to determine pericyte loss (PL) and acellular capillaries (AC), and TUNEL assays were performed to determine retinal vascular cell apoptosis. RESULTS. Western blot analysis indicated significant reductions in retinal Cx43 protein levels in diabetic mice and Cx43(+/-) mice compared with those of nondiabetic mice. Similarly, a significant reduction in Cx43 immunostaining was observed in the retinal capillaries of diabetic mice and Cx43(+/-) mice compared with those of control mice. Both diabetic and age-matched Cx43(+/-) mice exhibited increased amount of PL, AC, and TUNEL-positive cells compared with control mice. CONCLUSIONS. Diabetes-induced inhibition of Cx43 expression contributes to vascular cell apoptosis in retinas of diabetic mice. This suggests that reduced Cx43 expression plays a critical role in the development of AC and PL associated with DR.

Human cardiac gap-junction coupling: effects of antiarrhythmic peptide AAP10

AIMS

Ventricular arrhythmia is one of the most important causes of death in industrialized countries and often accompanies myocardial infarction and heart failure. In recent years modification of gap-junctional coupling has been proposed as a new antiarrhythmic principle. We wanted to examine whether the gap junction modulator (antiarrhythmic peptide) AAP10 exerts effects on human cardiac gap junctions, whether the effect might be enhanced in uncoupled cells, whether it affects electrical and metabolic coupling, and which of the cardiac connexin isoforms (Cx40, Cx43, Cx45) may be affected.

METHODS AND RESULTS

We determined the influence of 50 nM AAP10 (H(2)N-Gly-Ala-Gly-4Hyp-Pro-Tyr-CONH(2)) on macroscopic gap junction conductance by dual whole-cell voltage clamping in human and rat cardiomyocytes. Cells were partially uncoupled by CO(2)-mediated acidosis (pH 6.3) or kept at 'normal' conditions (pH 7.4, T 36 degrees C). Furthermore, we investigated effects of AAP10 in HeLa cells stably transfected with connexin 40, 43, or 45 and on metabolic coupling determined by dye transfer (Lucifer yellow). AAP10 (50 nM)-enhanced gap-junctional intercellular coupling in human and rat cardiomyocytes, completely prevented CO(2)-acidosis-induced uncoupling and improved metabolic coupling. The coupling effect of AAP10 was significantly enhanced in previously uncoupled cells. Regarding the connexin isoforms, AAP10-enhanced electrical and metabolic coupling in HeLa cells expressing Cx43 or Cx45, but not in HeLa cells expressing Cx40.

CONCLUSION

We conclude that the antiarrhythmic peptide AAP10, which improves gap-junctional intercellular coupling and prevents uncoupling by acidification in human cardiomyocytes, might be useful for antiarrhythmic strategies regarding arrhythmias caused by uncoupling of Cx43 and Cx45, but not Cx40.

Connexin-related signaling in cell death: to live or let die?

Evidence is accumulating that some forms of cell death, like apoptosis, are not only governed by the complex interplay between extracellular and intracellular signals but are also strongly influenced by intercellular communicative networks. The latter is provided by arrays of channels consisting of connexin proteins, with gap junctions directly connecting the cytoplasm of neighboring cells and hemichannels positioned as pores that link the cytoplasm to the extracellular environment. The role of gap junctions in cell death communication has received considerable interest and recently hemichannels have joined in as potentially toxic pores adding their part to the cell death process. However, despite a large body of existing evidence, especially for gap junctions, the exact contribution of the connexin channel family still remains controversial, as both gap junctions and hemichannels may furnish cell death as well as cell survival signals. An additional layer of complexity is formed by the fact that connexin proteins as such, beyond their channel function, may influence the cell death process. We here review the current knowledge on connexins and their channels in cell death and specifically address the molecular mechanisms that underlie connexin-related signaling. We also briefly focus on pannexins, a novel set of connexin-like proteins that have been implicated in cellular responses to pathological insults.

TGF-beta3 inhibits chondrogenesis of cultured chick leg bud mesenchymal cells via downregulation of connexin 43 and integrin beta4

Transforming growth factor beta (TGF-beta) is a multifunctional cytokine that regulates a number of biological responses including chemotaxis, cell cycle progression, differentiation, and apoptosis of cells. Even though temporal and spatial expression of TGF-beta3 suggests its role in chick limb development, it is not well characterized how TGF-beta3 regulates chondrogenic differentiation of limb bud mesenchymal cells. In this study, differential display polymerase chain reaction (DD-PCR) screening and reverse transcription PCR analysis revealed that the mRNA expression of the gap junction protein, connexin 43 (Cx43), was significantly decreased during the first treatment of TGF-beta3 for 24 h in cultured chick leg bud mesenchymal cells. Treatment of these cells with lindane, a general gap junction blocker, or expression of dominant negative Cx43 increased apoptotic cell death and decreased the level of integrin beta4 protein, in a manner similar to that observed when these cells were exposed to TGF-beta3. Similarly, exposure of cultured leg chondroblasts to a functional blocking antibody against integrin-beta4 induced an increase in apoptosis. Treatment of cells with TGF-beta3 decreased the membrane translocation of PKC-alpha, leading to activation of ERK. The increase in apoptotic cell death triggered by TGF-beta3 and dominant negative Cx43 was blocked by inhibition of ERK but increased by inhibition of PKC. Collectively, these data indicate that, in cultured chick leg bud mesenchyme cells, TGF-beta3 treatment downregulates Cx43 and induces apoptotic cell death via downregulation of integrin beta4, activation of ERK and suppression of PKC-alpha activation.

Increasing Gap Junctional Coupling: A Tool for Dissecting the Role of Gap Junctions

Much of our current knowledge about the physiological and pathophysiological role of gap junctions is based on experiments where coupling has been reduced by either chemical agents or genetic modification. This has brought evidence that gap junctions are important in many physiological processes. In a number of cases, gap junctions have been implicated in the initiation and progress of disease, and experimental uncoupling has been used to investigate the exact role of coupling. The inverse approach, i.e., to increase coupling, has become possible in recent years and represents a new way of testing the role of gap junctions. The aim of this review is to summarize the current knowledge obtained with agents that selectively increase gap junctional intercellular coupling. Two approaches will be reviewed: increasing coupling by the use of antiarrhythmic peptide and its synthetic analogs and by interfering with the gating of gap junctional channels.

The modulatory effects of connexin 43 on cell death/survival beyond cell coupling

Connexins form a diverse and ubiquitous family of integral membrane proteins. Characteristically, connexins are assembled into intercellular channels that aggregate into discrete cell-cell contact areas termed gap junctions (GJ), allowing intercellular chemical communication, and are essential for propagation of electrical impulses in excitable tissues, including, prominently, myocardium, where connexin 43 (Cx43) is the most important isoform. Previous studies have shown that GJ-mediated communication has an important role in the cellular response to stress or ischemia. However, recent evidence suggests that connexins, and in particular Cx43, may have additional effects that may be important in cell death and survival by mechanisms independent of cell to cell communication. Connexin hemichannels, located at the plasma membrane, may be important in paracrine signaling that could influence intracellular calcium and cell survival by releasing intracellular mediators as ATP, NAD(+), or glutamate. In addition, recent studies have shown the presence of connexins in cell structures other than the plasma membrane, including the cell nucleus, where it has been suggested that Cx43 influences cell growth and differentiation. In addition, translocation of Cx43 to mitochondria appears to be important for certain forms of cardioprotection. These findings open a new field of research of previously unsuspected roles of Cx43 intracellular signaling.

Changes in gap junction organization and decreased coupling during induced apoptosis in lens epithelial and NIH-3T3 cells

We demonstrate that global induction of apoptosis in primary bovine lens epithelial (LEC) or fibroblastic mouse NIH-3T3 cells by staurosporine, puromycin, cycloheximide, or etoposide is accompanied by a decrease in coupling by gap junctions. Cell coupling as tested by neurobiotin spreading was maintained when the LEC or NIH-3T3 cells were pre-incubated with the pan-caspase inhibitor zVAD or the caspase-3 inhibiting tetrapeptide DEVD. Immunohistochemistry using anti-connexin-43 antibodies showed a reduction of plasma membrane integrated connexin-43 in both cell lines when undergoing apoptosis. Western blotting indicated degradation of connexin-43 that was inhibited by zVAD or DEVD. Cell coupling at single cell level was tested by direct microinjecting into LEC apoptosis-inducing agents of low molecular mass like staurosporine, etoposide and puromycin or the high molecular mass proteins caspase-3 and -8 in activated state. Microinjection of puromycin or etoposide induced apoptotic morphological changes of only the injected cell within 90 or 180 min, but did not affect adjacent cells. In contrast, microinjection of staurosporine led to a rapid induction of apoptosis of the injected and a number of adjacent cells suggesting spreading of staurosporine most probably through gap junction pores held open by dephosphorylation of connexin-43 as verified by immunoblotting and staining using a phospho-serine368-specific anti-connexin-43 antibody. Microinjection of active caspase-8 led after 3 h to morphological apoptotic alterations of only the injected cell, but did not inhibit spreading of co-injected neurobiotin to neighboring cells during the first hour. In contrast, microinjection of active caspase-3-induced apoptosis only of the injected cell after 60 min and rapidly and completely suppressed coupling to neighboring cells.

18β-glycyrrhetinic acid promotes src interaction with connexin43 in rat cardiomyocytes

The mechanism by which 18beta-glycyrrhetinic acid regulates gap junction intercellular communication (GJIC) remains poorly understood. In this study, treatment of cultured rat neonatal cardiomyocytes with 18beta-glycyrrhetinic acid resulted in dose-dependent inhibition of GJIC as assessed by fluorescent dye transfer analysis. 18beta-Glycyrrhetinic acid induced time-dependent serine/threonine dephosphorylation and redistribution of connexin43 (Cx43) in cardiomyocytes and the induced Cx43 dephosphorylation was prevented by the protein phosphatase inhibitor, calyculin A. However, functional analyses showed that the inhibitory effect of 18beta-glycyrrhetinic acid on dye spreading among cardiomyocytes was not blocked by calyculin A, but was blocked by the Src-selective tyrosine kinase inhibitor, PP2. 18beta-Glycyrrhetinic acid also induced an increase in the levels of phosphorylated Src, and this effect was prevented by PP2. Immunoprecipitation using anti-Cx43 and anti-p-Src antibodies showed that 18beta-glycyrrhetinic acid increased the association between p-Src and Cx43 and induced tyrosine phosphorylation of Cx43. We conclude that the inhibitory effect of 18beta-glycyrrhetinic acid on GJIC in cardiomyocytes involves Src-mediated tyrosine phosphorylation of Cx43.

Primordial germ cell deficiency in the connexin 43 knockout mouse arises from apoptosis associated with abnormal p53 activation

Connexin 43 knockout (Cx43alpha1KO) mice exhibit germ cell deficiency, but the underlying cause for the germ cell defect was unknown. Using an Oct4-GFP reporter transgene, we tracked the distribution and migration of primordial germ cells (PGCs) in the Cx43alpha1KO mouse embryo. Analysis with dye injections showed PGCs are gap-junction-communication competent, with dye coupling being markedly reduced in Cx43alpha1-deficient PGCs. Time-lapse videomicroscopy and motion analysis showed that the directionality and speed of cell motility were reduced in the Cx43alpha1KO PGCs. This was observed both in E8.5 and E11.5 embryos. By contrast, PGC abundance did not differ between wild-type and heterozygous/homozygous Cx43alpha1KO embryos until E11.5, when a marked reduction in PGC abundance was detected in the homozygous Cx43alpha1KO embryos. This was accompanied by increased PGC apoptosis and increased expression of activated p53. Injection of alpha-pifithrin, a p53 antagonist, inhibited PGC apoptosis and prevented the loss of PGC. Analysis using a cell adhesion assay indicated a reduction in beta1-integrin function in the Cx43alpha1KO PGCs. Together with the abnormal activation of p53, these findings suggest the possibility of anoikis-mediated apoptosis. Overall, these findings show Cx43alpha1 is essential for PGC survival, with abnormal p53 activation playing a crucial role in the apoptotic loss of PGCs in the Cx43alpha1KO mouse embryos.

Treatment With the Gap Junction Modifier Rotigaptide (ZP123) Reduces Infarct Size in Rats With Chronic Myocardial Infarction

Treatment with non-selective drugs (eg, long-chain alcohols, halothane) that reduce gap junction intercellular communication (GJIC) is associated with reduced infarct size after myocardial infarction (MI). Therefore, it has been suggested that gap junction intercellular communication stimulating compounds may increase infarct size. The antiarrhythmic peptide analogue rotigaptide (ZP123) increases cardiac gap junction intercellular communication and the purpose of the present study was to examine the effects of rotigaptide treatment on infarct size. Myocardial infarction was induced in male rats by ligation of the left anterior descending artery (LAD). Rats (n = 156) were treated with rotigaptide at three dose levels or vehicle from the onset of ischemia and for 3 weeks following LAD occlusion. Infarct size was determined using histomorphometry after 3 weeks treatment. Rotigaptide treatment producing steady state plasma levels of 0.8 +/- 0.1, 5.5 +/- 0.5, and 86 +/- 8 nmol/L had no effect on mortality, but reduced infarct size to 90 +/- 10% (P = 0.41), 67 +/- 7% (P = 0.005), and 82 +/- 7% (P = 0.13), respectively relative to vehicle-treated myocardial infarction rats (100 +/- 12%). In contrast to what was predicted, our data demonstrates that rotigaptide treatment was associated with a significant infarct size reduction. We conclude that whereas treatment with non-selective inhibitors of gap junction intercellular communication cause a reduction in infarct size, this information cannot be extrapolated to the effects of compounds that selectively increase gap junction intercellular communication.

Rotigaptide (ZP123) prevents spontaneous ventricular arrhythmias and reduces infarct size during myocardial ischemia/reperfusion injury in open-chest dogs

The antiarrhythmic and cardioprotective effect of increasing gap junction intercellular communication during ischemia/reperfusion injury has not been studied. The antiarrhythmic peptide rotigaptide (previously ZP123), which maintains gap junction intercellular communication, was tested in dogs subjected to a 60-min coronary artery occlusion and 4 h of reperfusion. Rotigaptide was administered i.v. 10 min before reperfusion as a bolus + i.v. infusion at doses of 1 ng/kg bolus + 10 ng/kg/h infusion (n = 6), 10 ng/kg bolus + 100 ng/kg/h infusion (n = 5), 100 ng/kg bolus + 1000 ng/kg/h infusion (n = 8), 1000 ng/kg bolus + 10 mug/kg/h infusion (n = 6), and vehicle control (n = 5). Premature ventricular complexes (PVCs) were quantified during reperfusion. A series of four or more consecutive PVCs was defined as ventricular tachycardia (VT). The total incidence of VT was reduced significantly with the two highest doses of rotigaptide (20.3 +/- 10.9 and 4.3 +/- 4.1 events; p < 0.05) compared with controls (48.7 +/- 6.0). Total PVCs were reduced significantly from 25.1 +/- 4.2% in control animals to 11.0 +/- 4.4 and 1.7 +/- 1.3% after the two highest doses of rotigaptide. Infarct size, expressed as a percentage of the left ventricle, was reduced significantly from 13.2 +/- 1.9 in controls to 7.1 +/- 1.0 (p < 0.05) at the highest dose of rotigaptide. Ultrastructural evaluation revealed no differences in myocardial injury in the infarct area, area at risk, border zone, or normal zone in vehicle and rotigaptide-treated animals. However, rotigaptide did increase the presence of gap junctions in the area at risk (p = 0.022, Fisher's exact test). Rotigaptide had no effect on heart rate, blood pressure, heart rate-corrected QT interval, or left ventricular end-diastolic pressure. In conclusion, these results demonstrate that rotigaptide is a potent antiarrhythmic compound with cardioprotective effects and desirable safety.

Maternal diabetes adversely affects preovulatory oocyte maturation, development, and granulosa cell apoptosis

Maternal diabetes adversely affects preimplantation embryo development and pregnancy outcomes. The objective of this study was to determine whether diabetes has an impact at an earlier stage of development, the preovulatory oocyte. Models of both acute and chronic insulin-dependent diabetes were used. Acute hyperglycemia was induced by a single streptozotocin injection. Akita mice, which harbor an autosomal dominant mutation causing them to be chronically hypoinsulinemic and hyperglycemic, were used. In both models, preovulatory oocytes were markedly smaller when compared with control animals. A significantly greater number of control oocytes had progressed to meiotic maturation before diabetic oocytes. Both models were found to have smaller, less developed ovarian follicles with a greater number of apoptotic foci by histological evaluation as well as by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling staining. Immunohistochemistry displayed a greater amount of TNF-related apoptosis-inducing ligand (TRAIL) and KILLER, a key murine ligand and receptor involved in the extrinsic pathway, expressed in cumulus cells from hyperglycemic mice compared with controls, suggesting that this apoptotic pathway may be up-regulated under diabetic stress. Elevated KILLER expression was also confirmed through Western blotting. Connexin-43 expression was found to be lower by immunohistochemistry and Western blot analysis in the diabetic samples. Both models of maternal hyperglycemia and hypoinsulinemia may have a detrimental effect on oocyte maturation and development as detailed by the smaller sizes of oocytes and developing ovarian follicles, the lowered percentage reaching germinal vesicle breakdown, and the greater amount of apoptosis. In addition, there may be dysfunctional or decreased communication in diabetic oocytes, as demonstrated by lower expression of connexin-43.

Effects of three-dimensional culturing in a fibrous matrix on cell cycle, apoptosis, and MAb production by hybridoma cells

The effects of culturing hybridoma cells in a three-dimensional (3-D) poly(ethylene terephthalate) (PET) fibrous matrix on cell cycle, apoptosis, metabolism, and monoclonal antibody (MAb) production were evaluated by comparing with two-dimensional (2-D) culturing on microcarrier and multiwell plate surfaces. The percentage of cells in the G1/G0 phase increased during the long-term culturing period of approximately 4 weeks. Compared to the 2-D culture systems, cells grown in 3-D matrices had higher MAb productivity for long-term culture. Decreasing serum content in the culture medium increased both MAb productivity and apoptosis. However, the 3-D culture had a greater increase in MAb productivity and a much lower apoptotic rate than the 2-D culture, especially at 0% serum. Most cells in the 3-D fibrous matrix formed large aggregates and were smaller than cells grown on a 2-D surface or in suspension. The smaller cell size allowed cells to survive better in the high-cell-density environment. The fibrous matrix also selectively retained healthy, nonapoptotic cells. These results suggested that the 3-D fibrous matrix contributed to growth arrest, protected cells to better resist low-serum environments, and reduced apoptosis, all of which contributed to the high viable cell density and volumetric MAb productivity in the long-term 3-D culture.

Adenoviral delivery of human connexin37 induces endothelial cell death through apoptosis

Gap junction channels formed of connexins directly link the cytoplasm of adjacent cells and have been implicated in intercellular signaling that may regulate the functions of vascular cells. To facilitate connexin manipulation and analysis of their roles in adult endothelial cells, we developed adenoviruses containing the vascular connexins (Cx37, Cx40, and Cx43). We infected cultured human umbilical vein endothelial cells with control or connexin adenoviruses. Connexin expression was verified by immunoblotting and immunofluorescence. Infection with the Cx37 adenovirus (but not control or other connexin adenoviruses) led to a dose-dependent death of the endothelial cells that was partially antagonized by the gap junction blocker alpha-glycyrrhetinic acid and altered the intercellular transfer of Lucifer yellow and neurobiotin. Cell morphology, Annexin V and TUNEL staining, and caspase 3 assays all implicated apoptosis in the cell death. These data suggest that connexin-specific alterations of intercellular communication may modulate endothelial cell growth and death.

Cisplatin-induced premature senescence with concomitant reduction of gap junctions in human fibroblasts

To examine the role of gap junctions in cell senescence, the changes of gap junctions in cisplatin-induced premature senescence of primary cultured fibroblasts were studied and compared with the replicative senescent human fibroblasts. Dye transfer assay for gap junction function and immunofluorescent staining for connexin 43 protein distribution were done respectively. Furthermore, cytofluorimetry and DAPI fluorescence staining were performed for cell cycle and apoptosis analysis. p53 gene expression level was detected with indirect immunofluorescence. We found that cisplatin (10 mM) treatment could block cell growth cycle at G1 and induced premature senescence. The premature senescence changes included high frequency of apoptosis, elevation of p53 expression, loss of membranous gap junctions and reduction of dye-transfer capacity. These changes were comparable to the changes of replicative senescence of human fibroblasts. It was also concluded that cisplatin could induce premature senescence concomitant with inhibition of gap junctions in the fibroblasts. Loss of functional gap junctions from the cell membrane may account for the reduced intercellular communication in the premature senescent fibroblasts. The cell system we used may provide a model useful for the study of the gap junction thus promoting agents against premature senescence.

Microfabricated grooves recapitulate neonatal myocyte connexin43 and N-cadherin expression and localization

Our objective is to alter the surface topography on which cardiac myocytes are grown in culture so that they more closely resemble their in vivo counterparts. Microtextured silicone substrata were made using photolithography and microfabrication techniques and then coated with laminin. Primary cardiac myocytes from newborn rats were plated on microgrooved and nontextured substrata. Myocytes were highly oriented on 5 microm grooves (69.8 +/- 2.0%) and significantly different, p < 0.0001, compared with randomly oriented cells grown on nontextured surfaces (2.9 +/- 0.95%; n = 19). Cells on shallower, 2 microm, grooves were slightly less well oriented (46.9 +/- 4.3%, n = 5, p < 0.001). The lateral spacings of the grooves were altered to examine changes in cell-to-cell contact by confocal immunocytochemistry and quantitative protein analysis. Connexin43 and N-cadherin were distributed around the perimeter of the myocytes plated on 10 x 5 x 5 microgrooved surfaces, similar to the localization found in the neonate. Connexin43 expression in cultures on 5 microm deep grooved substrata was equal to the neonatal heart, whereas it differed in nontextured surfaces. We conclude that it is necessary to combine groove depth (5 microm) and lateral ridge dimensions between grooves (5 microm) in order to recapitulate connexin43 and N-cadherin expression levels and subcellular localization to that of the neonate.

Connexin43 as a determinant of myocardial infarct size following coronary occlusion in mice

OBJECTIVES

The purpose of this study was to define the role of cell-cell coupling as an independent determinant of infarct size following coronary occlusion.

BACKGROUND

Electrical uncoupling induced by acute ischemia enhances arrhythmogenesis, but it may also protect the heart by limiting intercellular spread of chemical mediators of injury.

METHODS

The left anterior descending coronary artery was ligated in wild-type (Cx43(+/+)) mice and Cx43-deficient (Cx43(+/-)) mice that are heterozygous for a null allele in the gene encoding the major gap junction channel protein, connexin43 (Cx43). Ventricular remodeling and infarct size were compared in both groups.

RESULTS

Echocardiography at 1 and 10 weeks after infarction showed that left ventricular end-diastolic volume and mass increased and ejection fraction decreased in proportion to infarct size in both Cx43(+/-) and Cx43(+/+) hearts. However, infarct size measured histologically in healing infarcts (eight days after infarction) was 29% smaller in Cx43(+/-) hearts (17 +/- 14% of total left ventricular area, n = 30) than in Cx43(+/+) hearts (24 +/- 15%, n = 23; p = 0.037). Fully healed infarcts were smaller than healing infarcts, owing to resorption of necrotic tissue and maturation of scar, but infarct size at 10 weeks after coronary occlusion was still smaller (by 50%) in Cx43(+/-) hearts (6 +/- 5%, n = 9) compared with Cx43(+/+) hearts (12 +/- 7%, n = 17; p = 0.037).

CONCLUSIONS

Cx43-deficient mice develop smaller infarcts than wild-type mice following coronary ligation. New therapies designed to decrease the risk of arrhythmias by enhancing intercellular communication could lead to larger infarcts caused by persistent coronary occlusion.

The gap junction uncoupler heptanol abrogates infarct size reduction with preconditioning in mouse hearts

BACKGROUND

Emerging evidence suggests that gap junction-mediated intercellular transmission of ions, metabolites and/or second messengers may serve as important determinants of myocyte viability. Our aim was to determine, using isolated buffer-perfused mouse hearts, whether the cardioprotection achieved with ischemic preconditioning (PC) is due in part to: (i) disruption of cell-cell coupling (manifest as a loss in the primary gap junction protein, connexin 43 [Cx43]) and resultant impaired transmission of a 'death' messenger, or conversely, (ii) transfer of a humoral 'survival' factor via existing gap junctions.

METHODS

To explore the first possibility, we employed immunostaining to visualize and quantify Cx43 in hearts subjected to 212 min of PC ischemia or a matched control period. To test the converse corollary, we assessed the effect of heptanol-an agent well recognized to rapidly and reversibly uncouple gap junctions--on the reduction of infarct size (delineated by tetrazolium staining) achieved with PC.

RESULTS

We found no evidence of a deficit in Cx43 immunoreactive signal in response to the PC stimulus. Area of necrosis (AN) was, as expected, reduced in hearts that received PC ischemia vs. controls (31+/-3% vs. 40+/-3% of the left ventricle [LV]; P<.01). However, treatment with heptanol rendered PC ineffective in eliciting protection (AN/LV: 42+/-1%).

CONCLUSIONS

Our results suggest that gap junction-mediated transfer of an as-yet unknown 'survival' factor-rather than disrupted transfer of a 'death messenger'-may play a role in the increased resistance to infarction conferred by antecedent PC ischemia in mouse heart.

Fibroblast growth factors in myocardial ischemia / reperfusion injury and ischemic preconditioning

Angiogenic growth factors such as fibroblast growth factors (FGFs) are currently in clinical trials for accelerating blood vessel formation in myocardial and limb ischemic conditions. However, recent experimental evidence suggests that FGFs can also participate as endogenous cardioprotective agents. In this report, the current knowledge for FGFs implication in myocardial ischemic tolerance will be summarized. Pharmacologic preconditioning with drugs as FGFs that mimic the beneficial effects of ischemic preconditioning could lead to novel therapeutic approaches for the treatment of ischemic disorders including myocardial infarction and stroke.