Decreased connexin 40 expression of the sinoatrial node mediates ischemic stroke-induced arrhythmia in mice

BACKGROUND

Arrhythmia is the most common cardiac complication after ischemic stroke. Connexin 40 is the staple component of gap junctions, which influences the propagation of cardiac electrical signals in the sinoatrial node. However, the role of connexin 40 in post-stroke arrhythmia remains unclear.

METHODS

In this study, a permanent middle cerebral artery occlusion model was used to simulate the occurrence of an ischemic stroke. Subsequently, an electrocardiogram was utilized to record and assess variations in electrocardiogram measures. In addition, optical tissue clearing and whole-mount immunofluorescence staining were used to confirm the anatomical localization of the sinoatrial node, and the sinoatrial node tissue was collected for RNA sequencing to screen for potential pathological mechanisms. Lastly, the rAAV9-Gja5 virus was injected with ultrasound guidance into the heart to increase Cx40 expression in the sinoatrial node.

RESULTS

We demonstrated that the mice suffering from a permanent middle cerebral artery occlusion displayed significant arrhythmia, including atrial fibrillation, premature ventricular contractions, atrioventricular block, and abnormal electrocardiogram parameters. Of note, we observed a decrease in connexin 40 expression within the sinoatrial node after the ischemic stroke via RNA sequencing and western blot. Furthermore, rAAV9-Gja5 treatment ameliorated the occurrence of arrhythmia following stroke.

CONCLUSIONS

In conclusion, decreased connexin 40 expression in the sinoatrial node contributed to the ischemic stroke-induced cardiac arrhythmia. Therefore, enhancing connexin 40 expression holds promise as a potential therapeutic approach for ischemic stroke-induced arrhythmia.

Cx43 carboxyl terminal domain determines AQP4 and Cx30 endfoot organization and blood brain barrier permeability

The neurovascular unit (NVU) consists of cells intrinsic to the vessel wall, the endothelial cells and pericytes, and astrocyte endfeet that surround the vessel but are separated from it by basement membrane. Endothelial cells are primarily responsible for creating and maintaining blood-brain-barrier (BBB) tightness, but astrocytes contribute to the barrier through paracrine signaling to the endothelial cells and by forming the glia limitans. Gap junctions (GJs) between astrocyte endfeet are composed of connexin 43 (Cx43) and Cx30, which form plaques between cells. GJ plaques formed of Cx43 do not diffuse laterally in the plasma membrane and thus potentially provide stable organizational features to the endfoot domain, whereas GJ plaques formed of other connexins and of Cx43 lacking a large portion of its cytoplasmic carboxyl terminus are quite mobile. In order to examine the organizational features that immobile GJs impose on the endfoot, we have used super-resolution confocal microscopy to map number and sizes of GJ plaques and aquaporin (AQP)-4 channel clusters in the perivascular endfeet of mice in which astrocyte GJs (Cx30, Cx43) were deleted or the carboxyl terminus of Cx43 was truncated. To determine if BBB integrity was compromised in these transgenic mice, we conducted perfusion studies under elevated hydrostatic pressure using horseradish peroxide as a molecular probe enabling detection of micro-hemorrhages in brain sections. These studies revealed that microhemorrhages were more numerous in mice lacking Cx43 or its carboxyl terminus. In perivascular domains of cerebral vessels, we found that density of Cx43 GJs was higher in the truncation mutant, while GJ size was smaller. Density of perivascular particles formed by AQP4 and its extended isoform AQP4ex was inversely related to the presence of full length Cx43, whereas the ratio of sizes of the particles of the AQP4ex isoform to total AQP4 was directly related to the presence of full length Cx43. Confocal analysis showed that Cx43 and Cx30 were substantially colocalized in astrocyte domains near vasculature of truncation mutant mice. These results showing altered distribution of some astrocyte nexus components (AQP4 and Cx30) in Cx43 null mice and in a truncation mutant, together with leakier cerebral vasculature, support the hypothesis that localization and mobility of gap junction proteins and their binding partners influences organization of astrocyte endfeet which in turn impacts BBB integrity of the NVU.

Xanthine oxidase inhibitor febuxostat reduces atrial fibrillation susceptibility by inhibition of oxidized CaMKII in Dahl salt-sensitive rats

Oxidative stress could be a possible mechanism and a therapeutic target of atrial fibrillation (AF). However, the effects of the xanthine oxidase (XO) inhibition for AF remain to be fully elucidated. We investigated the effects of a novel XO inhibitor febuxostat on AF compared with allopurinol in hypertension rat model. Five-week-old Dahl salt-sensitive rats were fed either low-salt (LS) (0.3% NaCl) or high-salt (HS) (8% NaCl) diet. After 4 weeks of diet, HS diet rats were divided into three groups: orally administered to vehicle (HS-C), febuxostat (5 mg/kg/day) (HS-F), or allopurinol (50 mg/kg/day) (HS-A). After 4 weeks of treatment, systolic blood pressure (SBP) was significantly higher in HS-C than LS, and it was slightly but significantly decreased by treatment with each XO inhibitor. AF duration was significantly prolonged in HS-C compared with LS, and significantly suppressed in both HS-F and HS-A (LS; 5.8 ± 3.5 s, HS-C; 33.9 ± 23.7 s, HS-F; 15.0 ± 14.1 s, HS-A; 20.1 ± 11.9 s: P<0.05). Ca2+ spark frequency was obviously increased in HS-C rats and reduced in the XO inhibitor-treated rats, especially in HS-F group. Western blotting revealed that the atrial expression levels of Met281/282-oxidized Ca2+/Calmodulin-dependent kinase II (CaMKII) and Ser2814-phosphorylated ryanodine receptor 2 were significantly increased in HS-C, and those were suppressed in HS-F and HS-A. Decreased expression of gap junction protein connexin 40 in HS-C was partially restored by treatment with each XO inhibitor. In conclusion, XO inhibitor febuxostat, as well as allopurinol, could reduce hypertension-related increase in AF perpetuation by restoring Ca2+ handling and gap junction.

Cis-acting mutation affecting GJA5 transcription is underlying the Melanotic within-feather pigmentation pattern in chickens

Melanotic (Ml) is a mutation in chickens that extends black (eumelanin) pigmentation in normally brown or red (pheomelanin) areas, thus affecting multiple within-feather patterns [J. W. Moore, J. R. Smyth Jr, J. Hered. 62, 215-219 (1971)]. In the present study, linkage mapping using a back-cross between Dark Cornish (Ml/Ml) and Partridge Plymouth Rock (ml+/ml+ ) chickens assigned Ml to an 820-kb region on chromosome 1. Identity-by-descent mapping, via whole-genome sequencing and diagnostic tests using a diverse set of chickens, refined the localization to the genomic region harboring GJA5 encoding gap-junction protein 5 (alias connexin 40) previously associated with pigmentation patterns in zebrafish. An insertion/deletion polymorphism located in the vicinity of the GJA5 promoter region was identified as the candidate causal mutation. Four different GJA5 transcripts were found to be expressed in feather follicles and at least two showed differential expression between genotypes. The results showed that Melanotic constitutes a cis-acting regulatory mutation affecting GJA5 expression. A recent study established the melanocortin-1 receptor (MC1R) locus and the interaction between the MC1R receptor and its antagonist agouti-signaling protein as the primary mechanism underlying variation in within-feather pigmentation patterns in chickens. The present study advances understanding the mechanisms underlying variation in plumage color in birds because it demonstrates that the activity of connexin 40/GJA5 can modulate the periodic pigmentation patterns within individual feathers.

Human model of IRX5 mutations reveals key role for this transcription factor in ventricular conduction

AIMS

Several inherited arrhythmic diseases have been linked to single gene mutations in cardiac ion channels and interacting proteins. However, the mechanisms underlying most arrhythmias, are thought to involve altered regulation of the expression of multiple effectors. In this study, we aimed to examine the role of a transcription factor (TF) belonging to the Iroquois homeobox family, IRX5, in cardiac electrical function.

METHODS AND RESULTS

Using human cardiac tissues, transcriptomic correlative analyses between IRX5 and genes involved in cardiac electrical activity showed that in human ventricular compartment, IRX5 expression strongly correlated to the expression of major actors of cardiac conduction, including the sodium channel, Nav1.5, and Connexin 40 (Cx40). We then generated human-induced pluripotent stem cells (hiPSCs) derived from two Hamamy syndrome-affected patients carrying distinct homozygous loss-of-function mutations in IRX5 gene. Cardiomyocytes derived from these hiPSCs showed impaired cardiac gene expression programme, including misregulation in the control of Nav1.5 and Cx40 expression. In accordance with the prolonged QRS interval observed in Hamamy syndrome patients, a slower ventricular action potential depolarization due to sodium current reduction was observed on electrophysiological analyses performed on patient-derived cardiomyocytes, confirming the functional role of IRX5 in electrical conduction. Finally, a cardiac TF complex was newly identified, composed by IRX5 and GATA4, in which IRX5 potentiated GATA4-induction of SCN5A expression.

CONCLUSION

Altogether, this work unveils a key role for IRX5 in the regulation of human ventricular depolarization and cardiac electrical conduction, providing therefore new insights into our understanding of cardiac diseases.

The novel ginsenoside AD2 prevents angiotensin II-induced connexin 40 and connexin 43 dysregulation by activating AMP kinase signaling in perfused beating rat atria

Connexin-40 (Cx40) and Cx43 are the principal components of gap junctions. Dysregulation of connexin expression is clinically related to cardiac pathologies. 25-Hydroxy protopanaxadiol [25-OH-PPD, 20 (R)-dammarane-3β, 12β, 20, 25-tetrol], known as AD2, is a novel protopanaxadiol extracted from Panax ginseng that exhibits many pharmacological activities, but its effects on cardiac gap junctions are poorly understood. The aim of this study was to evaluate the effects of AD2 on angiotensin II (Ang II)-induced Cx40 and Cx43 dysregulation. In this study, isolated beating rat atria were perfused with Ang II (5 μM) for 1 h to induce Cx40 and Cx43 dysregulation. The effects of AD2 (1.6, 16, and 160 μg/100 g body weight) on Ang II-induced hemodynamics in rats were analyzed by biological recorder, and changes in proteins levels were analyzed by western blotting. The results showed that AD2 ameliorated Ang II-induced hyper hemodynamics and abnormal P-waves, and prevented fibrotic collagen deposition (3.77% ± 1.64%-26.31% ± 1.64% with Ang II, 5.76% ± 0.94% with AD2). Ang II upregulated expression of nuclear factor kappa B, activator protein 1, and transforming growth factor β1, and downregulated of Cx40 and Cx43 expression, which were inhibited by AD2 concomitantly with increased of AMP-activated protein kinase (AMPK) expression via liver kinase B1 activation. The present findings suggest that AD2 inhibited Ang II-induced dysregulation of Cx40 and Cx43 via activation of AMPK signaling, thus highlighting the promise and utility of AD2 for treatment of connexin dysregulation-related heart disease.

Calcium Signal Profiles in Vascular Endothelium from Cdh5-GCaMP8 and Cx40-GCaMP2 Mice

INTRODUCTION

Studies in Cx40-GCaMP2 mice, which express calcium biosensor GCaMP2 in the endothelium under connexin 40 promoter, have identified the unique properties of endothelial calcium signals. However, Cx40-GCaMP2 mouse is associated with a narrow dynamic range and lack of signal in the venous endothelium. Recent studies have proposed many GCaMPs (GCaMP5/6/7/8) with improved properties although their performance in endothelium-specific calcium studies is not known.

METHODS

We characterized a newly developed mouse line that constitutively expresses GCaMP8 in the endothelium under the VE-cadherin (Cdh5-GCaMP8) promoter. Calcium signals through endothelial IP3 receptors and TRP vanilloid 4 (TRPV4) ion channels were recorded in mesenteric arteries (MAs) and veins from Cdh5-GCaMP8 and Cx40-GCaMP2 mice.

RESULTS

Cdh5-GCaMP8 mice showed lower baseline fluorescence intensity, higher dynamic range, and higher amplitudes of individual calcium signals than Cx40-GCaMP2 mice. Importantly, Cdh5-GCaMP8 mice enabled the first recordings of discrete calcium signals in the intact venous endothelium and revealed striking differences in IP3 receptor and TRPV4 channel calcium signals between MAs and mesenteric veins.

CONCLUSION

Our findings suggest that Cdh5-GCaMP8 mice represent significant improvements in dynamic range, sensitivity for low-intensity signals, and the ability to record calcium signals in venous endothelium.

A SPRY1 domain cardiac ryanodine receptor variant associated with short-coupled torsade de pointes

Idiopathic ventricular fibrillation (IVF) causes sudden death in young adult patients without structural or ischemic heart disease. Most IVF cases are sporadic and some patients present with short-coupled torsade de pointes, the genetics of which are poorly understood. A man who had a first syncope at the age of 35 presented with frequent short-coupled premature ventricular beats with bursts of polymorphic ventricular tachycardia and then died suddenly. By exome sequencing, we identified three rare variants: p.I784F in the SPRY1 of the ryanodine receptor 2 (RyR2), p.A96S in connexin 40 (Cx40), reported to affect electrical coupling and cardiac conduction, and a nonsense p.R244X in the cardiac-specific troponin I-interacting kinase (TNNI3K). We assessed intracellular Ca2+ handling in WT and mutant human RYR2 transfected HEK293 cells by fluorescent microscopy and an enhanced store overload-induced Ca2+ release in response to cytosolic Ca2+ was observed in RyR2-I784F cells. In addition, crystal structures and thermal melting temperatures revealed a conformational change in the I784F-SPRY1 domain compared to the WT-domain. The novel RyR2-I784F variant in SPRY1 domain causes a leaky channel under non-stress conditions. The presence of several variants affecting Ca2+ handling and cardiac conduction suggests a possible oligogenic origin for the ectopies originating from Purkinje fibres.

Prolonged duration of repolarization and decreased conduction velocity in the atrial myocardium after hypothermic ischemia-reperfusion may be related to expressions of inward rectifier potassium channel 2.1 protein and connexin 40

OBJECTIVES

The study aimed to determine the role of inward rectifier potassium channel 2.1 protein and connexin 40 expressions in regulating the duration of repolarization and conduction velocity of right atrial myocardium in rats following hypothermic ischemia-reperfusion.

METHODS

The Langendorff isolated rat cardiac perfusion models were divided into control (C) and hypothermic ischemia-reperfusion groups, with 8 models in group C and 16 models in group ischemia-reperfusion. Depending on the incidence of atrial arrhythmia after reperfusion, the models in group ischemia-reperfusion were further divided into reperfusion non-atrial arrhythmia or reperfusion atrial arrhythmia subgroup. Right atrial monophasic action potential duration at 50% and 90% of repolarization after 30 minutes of continuous perfusion in group C and group ischemia-reperfusion (T0), 105 minutes of continuous perfusion in group C or after 15 minutes of reperfusion in group ischemia-reperfusion (T1) and 120 minutes of continuous perfusion in group C or 30 minutes of reperfusion in group ischemia-reperfusion (T2) were recorded. Right atrial conduction velocity and effective refractory period were recorded at T2. Then, the expressions of inward rectifier potassium channel 2.1 protein and connexin 40 in the right atrial myocardium were detected.

RESULTS

Monophasic action potential duration at 50% and 90% were higher at T1 and T2 than those at T0 in subgroup reperfusion atrial arrhythmia (p < 0.05); monophasic action potential duration at 50% in subgroup reperfusion atrial arrhythmia were larger than group C and subgroup reperfusion non-atrial arrhythmia at T1 and T2 (p < 0.05); monophasic action potential duration at 90% in subgroup reperfusion atrial arrhythmia were larger than group C and subgroup reperfusion non-atrial arrhythmia at T1 and T2 (p < 0.05); effective refractory period in subgroup reperfusion atrial arrhythmia was greater than that in group C and subgroup reperfusion non-atrial arrhythmia, and the conduction velocity and the expressions of inward rectifier potassium channel 2.1 protein and connexin 40 were significantly lower than group C and subgroup reperfusion non-atrial arrhythmia (p < 0.05).

CONCLUSIONS

The prolonged duration of repolarization and a decrease in conduction velocity of the atrial myocardium occur in rats after hypothermic ischemia-reperfusion. These observed effects may be related to the downregulated expressions of connexin 40 and inward rectifier potassium channel 2.1.

Human influenza A virus causes myocardial and cardiac-specific conduction system infections associated with early inflammation and premature death

AIMS

Human influenza A virus (hIAV) infection is associated with important cardiovascular complications, although cardiac infection pathophysiology is poorly understood. We aimed to study the ability of hIAV of different pathogenicity to infect the mouse heart, and establish the relationship between the infective capacity and the associated in vivo, cellular and molecular alterations.

METHODS AND RESULTS

We evaluated lung and heart viral titres in mice infected with either one of several hIAV strains inoculated intranasally. 3D reconstructions of infected cardiac tissue were used to identify viral proteins inside mouse cardiomyocytes, Purkinje cells, and cardiac vessels. Viral replication was measured in mouse cultured cardiomyocytes. Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were used to confirm infection and study underlying molecular alterations associated with the in vivo electrophysiological phenotype. Pathogenic and attenuated hIAV strains infected and replicated in cardiomyocytes, Purkinje cells, and hiPSC-CMs. The infection was also present in cardiac endothelial cells. Remarkably, lung viral titres did not statistically correlate with viral titres in the mouse heart. The highly pathogenic human recombinant virus PAmut showed faster replication, higher level of inflammatory cytokines in cardiac tissue and higher viral titres in cardiac HL-1 mouse cells and hiPSC-CMs compared with PB2mut-attenuated virus. Correspondingly, cardiac conduction alterations were especially pronounced in PAmut-infected mice, associated with high mortality rates, compared with PB2mut-infected animals. Consistently, connexin43 and NaV1.5 expression decreased acutely in hiPSC-CMs infected with PAmut virus. YEM1L protease also decreased more rapidly and to lower levels in PAmut-infected hiPSC-CMs compared with PB2mut-infected cells, consistent with mitochondrial dysfunction. Human IAV infection did not increase myocardial fibrosis at 4-day post-infection, although PAmut-infected mice showed an early increase in mRNAs expression of lysyl oxidase.

CONCLUSION

Human IAV can infect the heart and cardiac-specific conduction system, which may contribute to cardiac complications and premature death.

Alteration of Cx37, Cx40, Cx43, Cx45, Panx1, and Renin Expression Patterns in Postnatal Kidneys of Dab1-/- (yotari) Mice

Numerous evidence corroborates roles of gap junctions/hemichannels in proper kidney development. We analyzed how Dab1 gene functional silencing influences expression and localization of Cx37, Cx40, Cx43, Cx45, Panx1 and renin in postnatal kidneys of yotari mice, by using immunohistochemistry and electron microscopy. Dab1 Δ102/221 might lead to the activation of c-Src tyrosine kinase, causing the upregulation of Cx43 in the medulla of yotari mice. The expression of renin was more prominent in yotari mice (p < 0.001). Renin granules were unusually present inside the vascular walls of glomeruli capillaries, in proximal and distal convoluted tubules and in the medulla. Disfunction of Cx40 is likely responsible for increased atypically positioned renin cells which release renin in an uncontrolled fashion, but this doesn't rule out simultaneous involvement of other Cxs, such as Cx45 which was significantly increased in the yotari cortex. The decreased Cx37 expression in yotari medulla might contribute to hypertension reduction provoked by high renin expression. These findings imply the relevance of Cxs/Panx1 as markers of impaired kidney function (high renin) in yotari mice and that they have a role in the preservation of intercellular signaling and implicate connexopathies as the cause of premature death of yotari mice.

BIRC5, GAJ5, and lncRNA NPHP3-AS1 Are Correlated with the Development of Atrial Fibrillation-Valvular Heart Disease

The aim of this study was to explore the pivotal genes or lncRNAs involved in the progression of atrial fibrillation (AF) -valvular heart disease (VHD). The mRNA profiling GSE113013 was obtained from the Gene Expression Omnibus database. The identification of differentially expressed genes (DEGs) and differentially expressed long non-coding RNAs (DElncRNAs) was performed. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were carried out for DEGs. Then, the construction of the protein-protein interaction (PPI) network was conducted. An lncRNA-miRNA-target ceRNA network was constructed after obtaining microRNAs (miRNA) related to DElncRNAs. Ultimately, key disease-related genes were screened. A total of 399 DEGs and 145 DElncRNAs were obtained. There were 283 nodes and 588 interaction pairs in the PPI network, and synaptosome-associated protein 25 (SNAP25) had higher degrees (degree = 22) in the PPI network. There were 65 interaction pairs in the ceRNA network. Here, Baculoviral IAP Repeat Containing 5 (BIRC5) was regulated by hsa-miR-1285-3p, which was regulated by lncRNA NPHP3-AS1. Gap Junction Protein Alpha 5 (GAJ5) was regulated by hsa-miR-4505, hsa-miR-1972, and hsa-miR-1199-5p. In particular, GAJ5 was enriched in the function of ion transmembrane transport regulation, whereas BIRC5 was enriched in the function of apoptosis-multiple species pathway. Similarly, Potassium Inwardly Rectifying Channel Subfamily J Member 6 (KCNJ6) was enriched in the function of an ion channel complex. VENN analysis identified BIRC5 and GJA5 as key AF-related genes. KCNJ6, SNAP25, GJA5, BIRC5, hsa-miR-1285-3p, and lncRNA NPHP3-AS1 were likely to be associated with AF-VHD development.

Chronic Hypoxia Decreases Endothelial Connexin 40, Attenuates Endothelium-Dependent Hyperpolarization-Mediated Relaxation in Small Distal Pulmonary Arteries, and Leads to Pulmonary Hypertension

Background Abnormal endothelial function in the lungs is implicated in the development of pulmonary hypertension; however, there is little information about the difference of endothelial function between small distal pulmonary artery (PA) and large proximal PA and their contribution to the development of pulmonary hypertension. Herein, we investigate endothelium-dependent relaxation in different orders of PAs and examine the molecular mechanisms by which chronic hypoxia attenuates endothelium-dependent pulmonary vasodilation, leading to pulmonary hypertension. Methods and Results Endothelium-dependent relaxation in large proximal PAs (second order) was primarily caused by releasing NO from the endothelium, whereas endothelium-dependent hyperpolarization (EDH)-mediated vasodilation was prominent in small distal PAs (fourth-fifth order). Chronic hypoxia abolished EDH-mediated relaxation in small distal PAs without affecting smooth muscle-dependent relaxation. RNA-sequencing data revealed that, among genes related to EDH, the levels of Cx37, Cx40, Cx43, and IK were altered in mouse pulmonary endothelial cells isolated from chronically hypoxic mice in comparison to mouse pulmonary endothelial cells from normoxic control mice. The protein levels were significantly lower for connexin 40 (Cx40) and higher for connexin 37 in mouse pulmonary endothelial cells from hypoxic mice than normoxic mice. Cx40 knockout mice exhibited significant attenuation of EDH-mediated relaxation and marked increase in right ventricular systolic pressure. Interestingly, chronic hypoxia led to a further increase in right ventricular systolic pressure in Cx40 knockout mice without altering EDH-mediated relaxation. Furthermore, overexpression of Cx40 significantly decreased right ventricular systolic pressure in chronically hypoxic mice. Conclusions These data suggest that chronic hypoxia-induced downregulation of endothelial Cx40 results in impaired EDH-mediated relaxation in small distal PAs and contributes to the development of pulmonary hypertension.

Electrical stimulation applied during differentiation drives the hiPSC-CMs towards a mature cardiac conduction-like cells

Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) resemble fetal cardiomyocytes and electrical stimulation (ES) has been explored to mature the differentiated cells. Here, we hypothesize that ES applied at the beginning of the differentiation process, triggers both differentiation of the hiPSC-CMs into a specialized conduction system (CS) phenotype and cell maturation. We applied ES for 15 days starting on day 0 of the differentiation process and found an increased expression of transcription factors and proteins associated with the development and function of CS including Irx3, Nkx2.5 and contactin 2, Hcn4 and Scn5a, respectively. We also found activation of intercalated disc proteins (Nrap and β-catenin). We detected ES-induced CM maturation as indicated by increased Tnni1 and Tnni3 expression. Confocal micrographs showed a shift towards expression of the gap junction protein connexin 40 in ES hiPSC-CM compared to the more dominant expression of connexin 43 in controls. Finally, analysis of functional parameters revealed that ES hiPSC-CMs exhibited faster action potential (AP) depolarization, longer intracellular Ca2+ transients, and slower AP duration at 90% of repolarization, resembling fast conducting fibers. Altogether, we provided evidence that ES during the differentiation of hiPSC to cardiomyocytes lead to development of cardiac conduction-like cells with more mature cytoarchitecture. Thus, hiPSC-CMs exposed to ES during differentiation can be instrumental to develop CS cells for cardiac disease modelling, screening individual drugs on a precison medicine type platform and support the development of novel therapeutics for arrhythmias.

Structural, Pro-Inflammatory and Calcium Handling Remodeling Underlies Spontaneous Onset of Paroxysmal Atrial Fibrillation in JDP2-Overexpressing Mice

BACKGROUND

Cardiac-specific JDP2 overexpression provokes ventricular dysfunction and atrial dilatation in mice. We performed in vivo studies on JDP2-overexpressing mice to investigate the impact of JDP2 on the predisposition to spontaneous atrial fibrillation (AF).

METHODS

JDP2-overexpression was started by withdrawal of a doxycycline diet in 4-week-old mice. The spontaneous onset of AF was documented by ECG within 4 to 5 weeks of JDP2 overexpression. Gene expression was analyzed by real-time RT-PCR and Western blots.

RESULTS

In atrial tissue of JDP2 mice, besides the 3.6-fold increase of JDP2 mRNA, no changes could be detected within one week of JDP2 overexpression. Atrial dilatation and hypertrophy, combined with elongated cardiomyocytes and fibrosis, became evident after 5 weeks of JDP2 overexpression. Electrocardiogram (ECG) recordings revealed prolonged PQ-intervals and broadened P-waves and QRS-complexes, as well as AV-blocks and paroxysmal AF. Furthermore, reductions were found in the atrial mRNA and protein level of the calcium-handling proteins NCX, Cav1.2 and RyR2, as well as of connexin40 mRNA. mRNA of the hypertrophic marker gene ANP, pro-inflammatory MCP1, as well as markers of immune cell infiltration (CD68, CD20) were increased in JDP2 mice.

CONCLUSION

JDP2 is an important regulator of atrial calcium and immune homeostasis and is involved in the development of atrial conduction defects and arrhythmogenic substrates preceding paroxysmal AF.

Connexin Signaling in the Juxtaglomerular Apparatus (JGA) of Developing, Postnatal Healthy and Nephrotic Human Kidneys

Our study analyzed the expression pattern of different connexins (Cxs) and renin positive cells in the juxtaglomerular apparatus (JGA) of developing, postnatal healthy human kidneys and in nephrotic syndrome of the Finnish type (CNF), by using double immunofluorescence, electron microscopy and statistical measuring. The JGA contained several cell types connected by Cxs, and consisting of macula densa, extraglomerular mesangium (EM) and juxtaglomerular cells (JC), which release renin involved in renin-angiotensin- aldosteron system (RAS) of arterial blood pressure control. During JGA development, strong Cx40 expression gradually decreased, while expression of Cx37, Cx43 and Cx45 increased, postnatally showing more equalized expression patterning. In parallel, initially dispersed renin cells localized to JGA, and greatly increased expression in postnatal kidneys. In CNF kidneys, increased levels of Cx43, Cx37 and Cx45 co-localized with accumulations of renin cells in JGA. Additionally, they reappeared in extraglomerular mesangial cells, indicating association between return to embryonic Cxs patterning and pathologically changed kidney tissue. Based on the described Cxs and renin expression patterning, we suggest involvement of Cx40 primarily in the formation of JGA in developing kidneys, while Cx37, Cx43 and Cx45 might participate in JGA signal transfer important for postnatal maintenance of kidney function and blood pressure control.

NOTCH1 is critical for fibroblast-mediated induction of cardiomyocyte specialization into ventricular conduction system-like cells in vitro

Cardiac fibroblasts are present throughout the myocardium and are enriched in the microenvironment surrounding the ventricular conduction system (VCS). Several forms of arrhythmias are linked to VCS abnormalities, but it is still unclear whether VCS malformations are cardiomyocyte autonomous or could be linked to crosstalk between different cell types. We reasoned that fibroblasts influence cardiomyocyte specialization in VCS cells. We developed 2D and 3D culture models of neonatal rat cardiac cells to assess the influence of cardiac fibroblasts on cardiomyocytes. Cardiomyocytes adjacent to cardiac fibroblasts showed a two-fold increase in expression of VCS markers (NAV1.5 and CONTACTIN 2) and calcium transient duration, displaying a Purkinje-like profile. Fibroblast-conditioned media (fCM) was sufficient to activate VCS-related genes (Irx3, Scn5a, Connexin 40) and to induce action potential prolongation, a hallmark of Purkinge phenotype. fCM-mediated response seemed to be spatially-dependent as cardiomyocyte organoids treated with fCM had increased expression of connexin 40 and NAV1.5 primarily on its outer surface. Finally, NOTCH1 activation in both cardiomyocytes and fibroblasts was required for connexin 40 up-regulation (a proxy of VCS phenotype). Altogether, we provide evidence that cardiac fibroblasts influence cardiomyocyte specialization into VCS-like cells via NOTCH1 signaling in vitro.

ZO-1 Regulates Intercalated Disc Composition and Atrioventricular Node Conduction

RATIONALE

ZO-1 (Zona occludens 1), encoded by the tight junction protein 1 (TJP1) gene, is a regulator of paracellular permeability in epithelia and endothelia. ZO-1 interacts with the actin cytoskeleton, gap, and adherens junction proteins and localizes to intercalated discs in cardiomyocytes. However, the contribution of ZO-1 to cardiac physiology remains poorly defined.

OBJECTIVE

We aim to determine the role of ZO-1 in cardiac function.

METHODS AND RESULTS

Inducible cardiomyocyte-specific Tjp1 deletion mice (Tjp1fl/fl; Myh6Cre/Esr1*) were generated by crossing the Tjp1 floxed mice and Myh6Cre/Esr1* transgenic mice. Tamoxifen-induced loss of ZO-1 led to atrioventricular (AV) block without changes in heart rate, as measured by ECG and ex vivo optical mapping. Mice with tamoxifen-induced conduction system-specific deletion of Tjp1 (Tjp1fl/fl; Hcn4CreERt2) developed AV block while tamoxifen-induced conduction system deletion of Tjp1 distal to the AV node (Tjp1fl/fl; Kcne1CreERt2) did not demonstrate conduction defects. Western blot and immunostaining analyses of AV nodes showed that ZO-1 loss decreased Cx (connexin) 40 expression and intercalated disc localization. Consistent with the mouse model study, immunohistochemical staining showed that ZO-1 is abundantly expressed in the human AV node and colocalizes with Cx40. Ventricular conduction was not altered despite decreased localization of ZO-1 and Cx43 at the ventricular intercalated disc and modestly decreased left ventricular ejection fraction, suggesting ZO-1 is differentially required for AV node and ventricular conduction.

CONCLUSIONS

ZO-1 is a key protein responsible for maintaining appropriate AV node conduction through maintaining gap junction protein localization.

Vascular smooth muscle cell phenotypic transition regulates gap junctions of cardiomyocyte

Atrial fibrillation (AF) is one of the most prevalent arrhythmias. Myocardial sleeves of the pulmonary vein are critical in the occurrence of AF. Our study aims to investigate the effect of synthetic vascular smooth muscle cells (SMCs) on gap junction proteins in cardiomyocytes. (1) Extraction of vascular SMCs from the pulmonary veins of Norway rats. TGF-β1 was used to induce the vascular SMCs switching to the synthetic phenotype and 18-α-GA was used to inhibit gap junctions of SMCs. The contractile and synthetic phenotype vascular SMCs were cocultured with HL-1 cells; (2) Western blotting was used to detect the expression of Cx43, Cx40 and Cx45 in HL-1 cells, and RT-PCR to test microRNA 27b in vascular SMCs or in HL-1 cells; (3) Lucifer yellow dye transfer experiment was used to detect the function of gap junctions. (1) TGF- β1 induced the vascular SMCs switching to synthetic phenotype; (2) Cx43 was significantly increased, and Cx40 and Cx45 were decreased in HL-1 cocultured with synthetic SMCs; (3) The fluorescence intensity of Lucifer yellow was higher in HL-1 cocultured with synthetic SMCs than that in the cells cocultured with contractile SMCs, which was inhibited by18-α-GA; (4) the expression of microRNA 27b was increased in HL-1 cocultured with synthetic SMCs, which was attenuated markedly by 18-α-GA. (5) the expression of ZFHX3 was decreased in HL-1 cocultured with synthetic SMCs, which was reversed by 18-α-GA. The gap junction proteins of HL-1 were regulated by pulmonary venous SMCs undergoing phenotypic transition in this study, accompanied with the up-regulation of microRNA 27b and the down-regulation of ZFHX3 in HL-1 cells, which was associated with heterocellular gap junctions between HL-1 and pulmonary venous SMCs.

Systemic therapy in an RNA toxicity mouse model with an antisense oligonucleotide therapy targeting a non-CUG sequence within the DMPK 3'UTR RNA

Myotonic dystrophy type 1 (DM1), the most common adult muscular dystrophy, is an autosomal dominant disorder caused by an expansion of a (CTG)n tract within the 3' untranslated region (3'UTR) of the dystrophia myotonica protein kinase (DMPK) gene. Mutant DMPK mRNAs are toxic, present in nuclear RNA foci and correlated with a plethora of RNA splicing defects. Cardinal features of DM1 are myotonia and cardiac conduction abnormalities. Using transgenic mice, we have demonstrated that expression of the mutant DMPK 3'UTR is sufficient to elicit these features of DM1. Here, using these mice, we present a study of systemic treatment with an antisense oligonucleotide (ASO) (ISIS 486178) targeted to a non-CUG sequence within the 3'UTR of DMPK. RNA foci and DMPK 3'UTR mRNA levels were reduced in both the heart and skeletal muscles. This correlated with improvements in several splicing defects in skeletal and cardiac muscles. The treatment reduced myotonia and this correlated with increased Clcn1 expression. Furthermore, functional testing showed improvements in treadmill running. Of note, we demonstrate that the ASO treatment reversed the cardiac conduction abnormalities, and this correlated with restoration of Gja5 (connexin 40) expression in the heart. This is the first time that an ASO targeting a non-CUG sequence within the DMPK 3'UTR has demonstrated benefit on the key DM1 phenotypes of myotonia and cardiac conduction defects. Our data also shows for the first time that ASOs may be a viable option for treating cardiac pathology in DM1.

Upregulation of Connexin 40 Mediated by Nitric Oxide Attenuates Cerebral Vasospasm After Subarachnoid Hemorrhage via the Nitric Oxide-Cyclic Guanosine Monophosphate-Protein Kinase G Pathway

OBJECTIVE

The present study was performed to elucidate the role of nitric oxide (NO) and connexin 40 (Cx40) in the induction of cerebral vasospasm after subarachnoid hemorrhage (SAH) in vivo.

METHODS

A SAH rat model was established using the double-bleed method. A total of 108 Sprague-Dawley rats weighing 250-300 g were randomly divided into 6 groups: SAH; SAH plus diethylenetriamine (DETA)/NO (exogenous NO donor); SAH plus 8-bromoadenosine (8-Br)-cyclic guanosine monophosphate (cGMP; protein kinase G [PKG] activator); SAH plus DETA/NO plus KT5823 (PKG inhibitor); SAH plus DETA/NO plus 40Gap27 (Cx40 inhibitor); and sham. The changes in the diameter of the branch microvessels in the middle cerebral artery were recorded. The neurological score was evaluated using the Garcia scoring system. Basilar artery (BA) tension was measured using the Danish Myo Technology myograph system. Cx40 protein expression was analyzed using immunofluorescence and Western blotting. Endothelial NO synthase, soluble guanylate cyclase, and PKG protein expression were measured by Western blotting.

RESULTS

A considerable narrowing of the cerebral vessels was detected in the SAH group compared with that in the sham group. Moreover, compared with the sham group, the SAH group showed a marked decrease in Cx40, endothelial NO synthase, soluble guanylate cyclase, and PKG expression. The expression of Cx40 and PKG were obviously higher in the SAH plus DETA/NO and SAH plus 8-Br-cGMP groups than in the SAH group. However, Cx40 was lower in the SAH plus DETA/NO plus KT5823 and SAH plus DETA/NO plus 40Gap27 groups than in the SAH plus ETA/NO group. The BAs showed significant vasodilation in the SAH plus DETA/NO and SAH plus 8-Br-cGMP groups. However, the vasodilation response of BAs was inhibited in the SAH plus DETA/NO plus KT5823 and SAH plus DETA-NO plus 40Gap27 groups.

CONCLUSIONS

The NO-cGMP-PKG pathway alleviated cerebral vasospasm via Cx40 upregulation.

Intercellular Conduction Optimizes Arterial Network Function and Conserves Blood Flow Homeostasis During Cerebrovascular Challenges

OBJECTIVE

Cerebral arterial networks match blood flow delivery with neural activity. Neurovascular response begins with a stimulus and a focal change in vessel diameter, which by themselves is inconsequential to blood flow magnitude, until they spread and alter the contractile status of neighboring arterial segments. We sought to define the mechanisms underlying integrated vascular behavior and considered the role of intercellular electrical signaling in this phenomenon. Approach and Results: Electron microscopic and histochemical analysis revealed the structural coupling of cerebrovascular cells and the expression of gap junctional subunits at the cell interfaces, enabling intercellular signaling among vascular cells. Indeed, robust vasomotor conduction was detected in human and mice cerebral arteries after focal vessel stimulation: a response attributed to endothelial gap junctional communication, as its genetic alteration attenuated this behavior. Conducted responses were observed to ascend from the penetrating arterioles, influencing the contractile status of cortical surface vessels, in a simulated model of cerebral arterial network. Ascending responses recognized in vivo after whisker stimulation were significantly attenuated in mice with altered endothelial gap junctional signaling confirming that gap junctional communication drives integrated vessel responses. The diminishment in vascular communication also impaired the critical ability of the cerebral vasculature to maintain blood flow homeostasis and hence tissue viability after stroke.

CONCLUSIONS

Our findings highlight the integral role of intercellular electrical signaling in transcribing focal stimuli into coordinated changes in cerebrovascular contractile activity and expose, a hitherto unknown mechanism for flow regulation after stroke.

Molecular basis of arrhythmic substrate in ageing murine peroxisome proliferator-activated receptor γ co-activator deficient hearts modelling mitochondrial dysfunction

INTRODUCTION

Ageing and chronic metabolic disorders are associated with mitochondrial dysfunction and cardiac pro-arrhythmic phenotypes which were recently attributed to slowed atrial and ventricular action potential (AP) conduction in peroxisome proliferator-activated receptor γ co-activator deficient (Pgc-1β-/-) mice.

METHODS

We compared expression levels of voltage-gated Na+ channel (NaV1.5) and gap junction channels, Connexins 40 and 43 (Cx40 and Cx43) in the hearts of young and old, and wild-type (WT) and Pgc-1β-/- mice. This employed Western blotting (WB) for NaV1.5, Cx40 and Cx43 in atrial/ventricular tissue lysates, and immunofluorescence (IF) from Cx43 was explored in tissue sections. Results were analysed using two-way analysis of variance (ANOVA) for independent/interacting effects of age and genotype.

RESULTS

In atria, increased age and Pgc-1β-/- genotype each independently decreased both Cx40 and Cx43 expression without interacting effects. In IF experiments, both age and Pgc-1β deletion independently reduced Cx43 expression. In ventricles, age and genotype exerted interacting effects in WB studies of NaV1.5 expression. Young Pgc-1β-/- then showed greater NaV1.5 expression than young WT ventricles. However, neither age nor Pgc-1β deletion affected Cx43 expression, independently or through interacting effects in both WB and IF studies.

CONCLUSION

Similar pro-arrhythmic atrial/ventricular phenotypes arise in aged/Pgc-1β-/- from differing contributions of altered protein expression and functional effects that may arise from multiple acute mechanisms.

C‑type natriuretic peptide prevents angiotensin II‑induced atrial connexin 40 and 43 dysregulation by activating AMP‑activated kinase signaling

C‑type natriuretic peptide (CNP), from the family of natriuretic peptides (NPs), has been shown to induce antihypertrophic and antifibrotic effects in cardiomyocytes. However, the roles of CNP in the atrial dysregulation of connexin (Cx)40 and Cx43 remain to be elucidated. The present study aimed to investigate the effects of CNP on angiotensin (Ang) II‑induced Cx40 and Cx43 dysregulation in isolated perfused beating rat left atria. A rat isolated perfused beating atrial model was used and the protein levels were determined via western blotting. Ang II significantly upregulated NF‑κB, activator protein‑1, transforming growth factor‑β1 (TGF‑β1), collagen I and matrix metalloproteinase 2, leading to atrial fibrosis, and downregulated expression of Cx40 and Cx43. The changes in Cx40 and Cx43 induced by Ang II were abolished by CNP through upregulation of phosphorylated AMP‑activated kinase a1 (AMPK) and downregulation of TGF‑β1. The effects of CNP on AMPK and TGF‑β1 levels were inhibited by KT5823 and pertussis toxin, inhibitors of protein kinase G (PKG) and NP receptor type C (NPR‑C), respectively. Thus, CNP can prevent Ang II‑induced dysregulation of Cx40 and Cx43 through activation of AMPK via the CNP‑PKG and CNP‑NPR‑C pathways in isolated beating rat atria. The present findings suggested that CNP may be therapeutically useful for clinical conditions involving cardiac dysregulation of Cx expression‑related diseases.

Domain-specific distribution of gap junctions defines cellular coupling to establish a vascular relay in the retina

In the retina, diverse functions of neuronal gap junctions (GJs) have been established. However, the distribution and function of vascular GJs are less clear. Here in the mouse retina whole mounts, we combined structural immunohistochemical analysis and a functional assessment of cellular coupling with a GJ-permeable tracer Neurobiotin to determine distribution patterns of three major vascular connexins. We found that Cx43 was expressed in punctate fashion on astroglia, surrounding all types of blood vessels and in continuous string-like structures along endothelial cell contacts in specialized regions of the vascular tree. Specifically, these Cx43-positive strings originated at the finest capillaries and extended toward the feeding artery. As this structural arrangement promoted strong and exclusive coupling of pericytes and endothelial cells along the corresponding branch, we termed this region a "vascular relay." Cx40 expression was found predominantly along the endothelial cell contacts of the primary arteries and did not overlap with Cx43-positive strings. At their occupied territories, Cx43 and Cx40 clustered with tight junctions and, to a lesser extent, with adhesion contacts, both key elements of the blood-retina barrier. Finally, Cx37 puncta were associated with the entire surface of both mural and endothelial cells across all regions of the vascular tree. This combinatorial analysis of vascular connexins and identification of the vascular relay region will serve as a structural foundation for future studies of neurovascular signaling in health and disease.

Chronic inhibition of the sigma-1 receptor exacerbates atrial fibrillation susceptibility in rats by promoting atrial remodeling

AIMS

This study aimed to evaluate the effects of the sigma-1 receptor (S1R) on atrial fibrillation (AF) susceptibility in rats.

MAIN METHODS

Rats were randomly assigned into three groups for intraperitoneal treatment with saline (CTL group), BD1047 (an antagonist of the S1R, BD group) or BD1047 plus fluvoxamine (an agonist of the S1R, BD + F group) for 4 weeks. The heart rate variability (HRV) and atrial electrophysiological parameters were measured via the PowerLab system and analyzed by LabChart 8.0 software. Atrial histology was determined with Masson staining. The protein levels of connexin (Cx) 40, Cav1.2, S1R, eNOS, p-eNOS, and p-AKT were detected by western blot assays.

KEY FINDINGS

Our results showed that BD1047 significantly shortened the atrial effective refractory period (ERP) and action potential duration (APD), increased AF inducibility and duration, augmented sympathetic activity, depressed parasympathetic activity, and reduced heart rate variability (HRV) compared with the CTL group. Masson staining also showed a significant increase in atrial fibrosis in the BD group. Furthermore, the expressions of S1R, Cx40, Cav1.2, p-eNOS, and p-AKT were dramatically reduced in the BD group compared with the CTL group (all P < 0.01). However, fluvoxamine administration mitigated most of the abovementioned alterations.

SIGNIFICANCE

Our findings indicated that S1R inhibition contributed to atrial electrical remodeling, cardiac autonomic remodeling and atrial fibrosis, which could be attenuated by fluvoxamine, thus providing new insights into the relationship between the S1R and AF.

Systemic Inflammation Rapidly Induces Reversible Atrial Electrical Remodeling: The Role of Interleukin-6-Mediated Changes in Connexin Expression

Background Systemic inflammation is a strong predictor of atrial fibrillation. A key role for electrical remodeling is increasingly recognized, and experimental data suggest that inflammatory cytokines can directly affect connexins resulting in gap-junction dysfunction. We hypothesized that systemic inflammation, regardless of its origin, promotes atrial electric remodeling in vivo, as a result of cytokine-mediated changes in connexin expression. Methods and Results Fifty-four patients with different inflammatory diseases and elevated C-reactive protein were prospectively enrolled, and electrocardiographic P-wave dispersion indices, cytokine levels (interleukin-6, tumor necrosis factor-α, interleukin-1, interleukin-10), and connexin expression (connexin 40, connexin 43) were measured during active disease and after reducing C-reactive protein by >75%. Moreover, peripheral blood mononuclear cells and atrial tissue specimens from an additional sample of 12 patients undergoing cardiac surgery were evaluated for atrial and circulating mRNA levels of connexins. Finally, in vitro effects of interleukin-6 on connexin expression were studied in HL-1 mouse atrial myocytes. In patients with active inflammatory diseases, P-wave dispersion indices were increased but rapidly decreased within days when C-reactive protein normalizes and interleukin-6 levels decline. In inflammatory disease patients, both P-wave dispersion indices and interleukin-6 changes were inversely associated with circulating connexin levels, and a positive correlation between connexin expression in peripheral blood mononuclear cells and atrial tissue was demonstrated. Moreover, interleukin-6 significantly reduced connexin expression in HL-1 cells. Conclusions Our data suggest that regardless of specific etiology and organ localization, systemic inflammation, via interleukin-6 elevation, rapidly induces atrial electrical remodeling by down-regulating cardiac connexins. Although transient, these changes may significantly increase the risk for atrial fibrillation and related complications during active inflammatory processes.

Relationship between Atrial Tissue Remodeling and ECG Features in Atrial Fibrillation

The difference in the atrial organizational structure between patients with atrial fibrillation (AF) and those with sinus rhythm was investigated. In order to analyze the rationality in explaining the electrocardiogram (ECG) characteristics of AF with statistics data or tissue remodeling model, and the logical relationship between the hypothesis of pulmonary veins (PV) muscle sleeves and that of multi wavelets in mechanism of AF, we examined the expression of collagen volume fraction of type I (CVF-I) with picrosirius red staining, connexin 40 (Cx40) by immunohistochemistry, and intercalated disc (ID) using transmission electron microscope in atrial tissue. The results showed that there was significant difference in the expression of CVF-I (t=3.827, P<0.01), Cx40 (t=4.21, P<0.01), and groups of the ID that keeping the electrical transmission and atrial electrical coupling synchronization (t=15.116, P<0.001), but no significant difference was found in total IDs (t=0.611, P=0.543) between patients with AF and those with sinus rhythm. The quantitative differences in the tissue remodeling could not explain the ECG characteristics of AF. The number of normal IDs and abnormal distribution are the structural basis to trigger and maintain atrial electrical remodeling, and induce and maintain AF. Such histological reconstruction supports the hypothesis of multi wavelets and can also explain ECG features.

The research of ion channel-related gene polymorphisms with atrial fibrillation in the Chinese Han population

BACKGROUND

Atrial fibrillation (AF) is one of the common arrhythmia in clinics. Its incidence is high among the elderly. This study aimed to identify a possible connection between ion channel-related gene polymorphisms and the risk of AF.

METHODS

A total of 381 patients with coronary heart disease were recruited. Based on complete cardiac examination, the patients were divided into two subgroups: 185 patients with AF and 196 patients without AF. An association analysis was performed using 13 genotyped SNPs. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated by conditional logistic regression.

RESULTS

In our research, we found that KCNE2 rs8134775 was associated with a decreased AF risk in the allele model (OR = 0.70; 95% CI: 0.50-0.97; p = 0.034). Genetic model analysis shown that the minor allele T of GJA5 rs35594137 was associated with a decreased AF risk under the recessive model (OR = 0.40; 95% CI: 0.19-0.86; p = 0.018) and the minor allele G of KCNJ2 rs8079702 was associated with an increased AF risk in the recessive model (OR = 2.31; 95% CI: 1.20-4.42; p = 0.012).

CONCLUSIONS

Our results suggest that KCNE2, KCNJ2, and GJA5 influence the development of AF.

An in vivo wound healing model for the characterization of the angiogenic process and its modulation by pharmacological interventions

Angiogenesis during wound healing is essential for tissue repair and also affected during cancer treatment by anti-angiogenic drugs. Here, we introduce a minimally invasive wound healing model in the mouse ear to assess angiogenesis with high spatiotemporal resolution in a longitudinal manner in vivo using two-photon microscopy in mice expressing GCaMP2 in arterial endothelial cells. The development of vascular sprouts occurred in a highly orchestrated manner within a time window of 8 days following wounding. Novel sprouts developed exclusively from the distal stump of the transsected arteries, growing towards the proximal arterial stump. This was in line with the incidence of Ca2+ transients in the arterial endothelial cells, most probably a result of VEGF stimulation, which were more numerous on the distal part. Functional analysis revealed perfusion across the wound site via arterial sprouts developed between days 6 and 8 following the incision. At day 8, proximal and distal arteries were structurally and functionally connected, though only 2/3 of all sprouts detected were actually perfused. Treatment with the FDA approved drug, sunitinib, the preclinical drug AZD4547, as well as with the combination of the two agents had significant effects on both structural and functional readouts of neo-angiogenesis. The simplicity and high reproducibility of the model makes it an attractive tool for elucidating migratory activity, phenotype and functionality of endothelial cells during angiogenesis and for evaluating specific anti-angiogenic drug interventions.

Instructive role of melanocytes during pigment pattern formation of the avian skin

Animal skin pigment patterns are excellent models to study the mechanism of biological self-organization. Theoretical approaches developed mathematical models of pigment patterning and molecular genetics have brought progress; however, the responsible cellular mechanism is not fully understood. One long unsolved controversy is whether the patterning information is autonomously determined by melanocytes or nonautonomously determined from the environment. Here, we transplanted purified melanocytes and demonstrated that melanocytes could form periodic pigment patterns cell autonomously. Results of heterospecific transplantation among quail strains are consistent with this finding. Further, we observe that developing melanocytes directly connect with each other via filopodia to form a network in culture and in vivo. This melanocyte network is reminiscent of zebrafish pigment cell networks, where connexin is implicated in stripe formation via genetic studies. Indeed, we found connexin40 (cx40) present on developing melanocytes in birds. Stripe patterns can form in quail skin explant cultures. Several calcium channel modulators can enhance or suppress pigmentation globally, but a gap junction inhibitor can change stripe patterning. Most interestingly, in ovo, misexpression of dominant negative cx40 expands the black region, while overexpression of cx40 expands the yellow region. Subsequently, melanocytes instruct adjacent dermal cells to express agouti signaling protein (ASIP), the regulatory factor for pigment switching, which promotes pheomelanin production. Thus, we demonstrate Japanese quail melanocytes have an autonomous periodic patterning role during body pigment stripe formation. We also show dermal agouti stripes and how the coupling of melanocytes with dermal cells may confer stable and distinct pigment stripe patterns.

Ablation of both Cx40 and Panx1 results in similar cardiovascular phenotypes exhibited in Cx40 knockout mice

Connexins (Cxs) and pannexins (Panxs) are highly regulated large-pore channel-forming proteins that participate in cellular communication via small molecular exchange with the extracellular microenvironment, or in the case of connexins, directly between cells. Given the putative functional overlap between single membrane-spanning connexin hemichannels and Panx channels, and cardiovascular system prevalence, we generated the first Cx40-/-Panx1-/- mouse with the anticipation that this genetic modification would lead to a severe cardiovascular phenotype. Mice null for both Cx40 and Panx1 produced litter sizes and adult growth progression similar to wild-type (WT), Cx40-/- and Panx1-/- mice. Akin to Cx40-/- mice, Cx40-/-Panx1-/- mice exhibited cardiac hypertrophy and elevated systolic, diastolic, and mean arterial blood pressure compared with WT and Panx1-/- mice; however assessment of left ventricular ejection fraction and fractional shortening revealed no evidence of cardiac dysfunction between groups. Furthermore, Cx40-/-, Panx1-/-, and Cx40-/-Panx1-/- mice demonstrated impaired endothelial-mediated vasodilation of aortic segments to increasing concentrations of methacholine (MCh) compared with WT, highlighting roles for both Cx40 and Panx1 in vascular endothelial cell (EC) function. Surprisingly, elevated kidney renin mRNA expression, plasma renin activity, and extraglomerular renin-producing cell populations found in Cx40-/- mice was further exaggerated in double knockout mice. Thus, while gestation and gross development were conserved in Cx40-/-Panx1-/- mice, they exhibit cardiac hypertrophy, hypertension, and impaired endothelial-mediated vasodilation that phenocopies Cx40-/- mice. Nevertheless, the augmented renin homeostasis observed in the double knockout mice suggests that both Cx40 and Panx1 may play an integrative role.

Effects of temperature on transjunctional voltage-dependent gating kinetics in Cx45 and Cx40 gap junction channels

Gap junctions (GJs) are intercellular channels directly linking neighbouring cells and are dodecamers of connexins. In the human heart, connexin40 (Cx40), Cx43, and Cx45 are expressed in different regions of the heart forming GJs ensuring rapid propagation of action potentials in the myocardium. Two of these connexins, Cx40 and Cx45, formed functional GJs with prominent transjunctional voltage-dependent gating (Vj-gating), which can be a mechanism to down regulate coupling conductance (Gj). It is not clear the effects of temperature on Vj-gating properties. We expressed Cx40 or Cx45 in N2A cells to study the Vj-gating extent, the kinetics of deactivation, and the recovery time course from deactivation at 22 °C, 28 °C, and 32 °C. Dynamic uncoupling between cell pairs were evaluated at different temperatures, junctional delays, and/or repeating frequencies. Cx40 or Cx45 GJs showed little changes in the extent of Vj-gating, but in both cases with a faster deactivation kinetics at high temperatures. The recovery from deactivation was faster at higher temperatures for Cx45 GJs, but not for Cx40 GJs. Cx45 GJs, but not Cx40 GJs, were dynamically uncoupled when sufficient junctional delays and/or repeating frequency in all tested temperatures. Gap junction specific dynamic uncoupling could play an important role in regulating action potential propagation speed in Cx45 enriched nodal cells in the heart.

Connexin 40 regulates lung endothelial permeability in acute lung injury via the ROCK1-MYPT1- MLC20 pathway

Increased pulmonary vascular permeability is a hallmark of acute lung injury (ALI). Connexin 40 (Cx40) is a gap junctional protein abundantly present in the lung microvascular endothelium. Yet, the role of Cx40 in the regulation of lung vascular permeability and its underlying mechanisms are unclear. Here, we tested the hypothesis that Cx40 participates in regulation of lung endothelial permeability via a mechanism involving a Rho-associated protein kinase (ROCK) dependent regulation of myosin light chain (MLC). In murine models of intratracheal acid- or LPS-induced lung injury, genetic deficiency of Cx40 attenuated key features of ALI including vascular barrier failure. In human pulmonary microvascular endothelial cells (PMVECs), thrombin-induced loss of transendothelial electrical resistance was attenuated by a Cx40-inhibiting mimetic peptide (40GAP27), Cx40-specific shRNA, or ROCK inhibitor Y27632. In isolated perfused mouse lungs, platelet-activating factor-induced lung weight gain was abrogated by gap junction blocker carbenoxolone, 40GAP27, Y27632, or genetic deficiency of Cx40. Phosphorylation of MLC20 increased drastically in both LPS-treated PMVECs and HCl-treated mouse lungs. Expression of ROCK1 was increased in both LPS-treated PMVECs and HCl-treated mouse lungs, and paralleled by phosphorylation of MLC20. Coimmunoprecipitation experiments revealed protein-protein interaction between ROCK1 and Cx40. LPS-induced upregulation of ROCK1 and phosphorylation of MLC20 were blocked by knockdown of Cx40. LPS caused phosphorylation of myosin phosphatase targeting subunit 1, which could be abrogated by Y27632 or Cx40-shRNA. Our findings reveal a role of Cx40 in regulation of ROCK1 and MLC20 that contributes critically to lung vascular barrier failure in ALI.

Blockade of vascular endothelial growth factor receptor 2 inhibits intraplaque haemorrhage by normalization of plaque neovessels

BACKGROUND

Plaque angiogenesis is associated with atherosclerotic lesion growth, plaque instability and negative clinical outcome. Plaque angiogenesis is a natural occurring process to fulfil the increasing demand of oxygen and nourishment of the vessel wall. However, inadequate formed, immature plaque neovessels are leaky and cause intraplaque haemorrhage.

OBJECTIVE

Blockade of VEGFR2 normalizes the unbridled process of plaque neovessel formation and induces maturation of nascent vessels resulting in prevention of intraplaque haemorrhage and influx of inflammatory cells into the plaque and subsequently increases plaque stability.

METHODS AND RESULTS

In human carotid and vein graft atherosclerotic lesions, leaky plaque neovessels and intraplaque haemorrhage co-localize with VEGF/VEGFR2 and angiopoietins. Using hypercholesterolaemic ApoE3*Leiden mice that received a donor caval vein interposition in the carotid artery, we demonstrate that atherosclerotic vein graft lesions at t28 are associated with hypoxia, Hif1α and Sdf1 up-regulation. Local VEGF administration results in increased plaque angiogenesis. VEGFR2 blockade in this model results in a significant 44% decrease in intraplaque haemorrhage and 80% less extravasated erythrocytes compared to controls. VEGFR2 blockade in vivo results in a 32% of reduction in vein graft size and more stable lesions with significantly reduced macrophage content (30%), and increased collagen (54%) and smooth muscle cell content (123%). Significant decreased VEGF, angiopoietin-2 and increased Connexin 40 expression levels demonstrate increased plaque neovessel maturation in the vein grafts. VEGFR2 blockade in an aortic ring assay showed increased pericyte coverage of the capillary sprouts.

CONCLUSION

Inhibition of intraplaque haemorrhage by controlling neovessels maturation holds promise to improve plaque stability.

Embryonic Tbx3+ cardiomyocytes form the mature cardiac conduction system by progressive fate restriction

A small network of spontaneously active Tbx3+ cardiomyocytes forms the cardiac conduction system (CCS) in adults. Understanding the origin and mechanism of development of the CCS network are important steps towards disease modeling and the development of biological pacemakers to treat arrhythmias. We found that Tbx3 expression in the embryonic mouse heart is associated with automaticity. Genetic inducible fate mapping revealed that Tbx3+ cells in the early heart tube are fated to form the definitive CCS components, except the Purkinje fiber network. At mid-fetal stages, contribution of Tbx3+ cells was restricted to the definitive CCS. We identified a Tbx3+ population in the outflow tract of the early heart tube that formed the atrioventricular bundle. Whereas Tbx3+ cardiomyocytes also contributed to the adjacent Gja5+ atrial and ventricular chamber myocardium, embryonic Gja5+ chamber cardiomyocytes did not contribute to the Tbx3+ sinus node or to atrioventricular ring bundles. In conclusion, the CCS is established by progressive fate restriction of a Tbx3+ cell population in the early developing heart, which implicates Tbx3 as a useful tool for developing strategies to study and treat CCS diseases.

Activin Receptor-Like Kinase 4 Haplodeficiency Mitigates Arrhythmogenic Atrial Remodeling and Vulnerability to Atrial Fibrillation in Cardiac Pathological Hypertrophy

Background Activin receptor-like kinase 4 ( ALK 4) is highly expressed in mammal heart. Atrial fibrillation ( AF ) is closely related to ventricular pressure overload. Because pressure overload increases atrial pressure and leads to atrial remodeling, it would be informative to know whether ALK 4 exerts potential effects on atrial remodeling and AF vulnerability in a pressure-overload model. Methods and Results Wild-type littermates and ALK 4+/- mice were subjected to abdominal aortic constriction or a sham operation. After 4 or 8 weeks, echocardiographic and hemodynamic measurements were performed, and inducibility of AF was tested. The hearts were divided into atria and ventricles and then were fixed in formalin for staining, or they were weighted and snap-frozen for quantitative real-time polymerase chain reaction and Western blot analysis. Compared with wild-type littermates, ALK 4+/- mice demonstrated a similar extent of atrial hypertrophy but significantly suppressed atrial fibrosis at 8 weeks post-abdominal aortic constriction. ALK 4 haplodeficiency partially blocked abdominal aortic constriction-induced upregulation of monocyte chemotactic protein 1 and interleukin-6, and the increased chemotaxin of macrophages. ALK 4 haplodeficiency also blunted a reduction of connexin 40 and redistribution of connexin 43 from the intercalated disk to the lateral membranes, thereby improving localized conduction abnormalities. Meanwhile, ALK 4 haplodeficiency inhibited abdominal aortic constriction-induced decreased INa, ICa-L and IK1 densities as well as the accompanying action potential duration shortening. Mechanistically, ALK 4 haploinsufficiency resulted in the suppression of Smad2/3 activity in this model. Conclusions Our results demonstrate that ALK 4 haplodeficiency ameliorates atrial remodeling and vulnerability to AF in a pressure-overload model through inactivation of the Smad2/3 pathway, suggesting that ALK 4 might be a potential therapeutic target in combating pressure overload-induced AF .

Increased expression and functionality of the gap junction in peripheral blood lymphocytes is associated with hypertension-mediated inflammation in spontaneously hypertensive rats

BACKGROUND

Imbalances in circulating T lymphocytes play critical roles in the pathogenesis of hypertension-mediated inflammation. Connexins (Cxs) in immune cells are involved in the maintenance of homeostasis of T lymphocytes. However, the association between Cxs in peripheral blood T lymphocytes and hypertension-mediated inflammation remains unknown. This study was designed to investigate the role of Cxs in T lymphocytes in hypertension-mediated inflammation in spontaneously hypertensive rats (SHRs).

METHODS

The systolic blood pressure (SBP) in Wistar-Kyoto (WKY) rats and SHRs was monitored using the tail-cuff method. The serum cytokine level was determined using ELISA. The proportions of different T-lymphocyte subtypes in the peripheral blood, the expressions of Cx40/Cx43 in the T-cell subtypes, and the gap junctional intracellular communication (GJIC) of peripheral blood lymphocytes were measured using flow cytometry (FC). The accumulations of Cx40/Cx43 at the plasma membrane and/or in the cytoplasm were determined using immunofluorescence staining. The in vitro mRNA levels of cytokines and GJIC in the peripheral blood lymphocytes were respectively examined using real-time PCR and FC after treatment with Gap27 and/or concanavalin A (Con A).

RESULTS

The percentage of CD4+ T cells and the CD4+/CD8+ ratio were high, and the accumulation or expressions of Cx40/Cx43 in the peripheral blood lymphocytes in SHRs were higher than in those of WKY rats. The percentage of CD8+ and CD4+CD25+ T cells was lower in SHRs. The serum levels of IL-2, IL-4 and IL-6 from SHRs were higher than those from WKY rats, and the serum levels of IL-2 and IL-6 positively correlated with the expression of Cx40/Cx43 in the peripheral blood T lymphocytes from SHRs. The peripheral blood lymphocytes of SHRs exhibited enhanced GJIC. Cx43-based channel inhibition, which was mediated by Gap27, remarkably reduced GJIC in lymphocytes, and suppressed IL-2 and IL-6 mRNA expressions in Con A stimulated peripheral blood lymphocytes.

CONCLUSIONS

Our data suggest that Cxs may be involved in the regulation of T-lymphocyte homeostasis and the production of cytokines. A clear association was found between alterations in Cxs expression or in Cx43-based GJIC and hypertension-mediated inflammation.

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

RATIONALE

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

OBJECTIVE

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

METHODS AND RESULTS

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

CONCLUSIONS

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

[NaHS inhibits the release of TNF-α and IL-6 from peripheral blood lymphocytes in rats and down-regulates the expression of connexin 40 and connexin 43]

Objective To investigate the effect of NaHS on the expression of connexin 40 (Cx40) and Cx43 in peripheral blood lymphocytes and the release of tumor necrosis factor (TNF-α) and interleukin 6 (IL-6). Methods Six Wistar Kyoto (WKY) rats were selected to collect peripheral blood from the abdominal aorta. Lymphocytes were isolated by density gradient centrifugation, and then divided into control group, concanavalin A (ConA) group and ConA combined with NaHS group. The levels of IL-6 and TNF-α were detected by ELISA; the expression and location of Cx40 and Cx43 in lymphocytes were detected by immunofluorescence staining; the expression frequencies of Cx40 and Cx43 in lymphocytes were detected by flow cytometry; and the protein expression of Cx40 and Cx43 in lymphocytes were detected by Western blot analysis. Results The levels of IL-6 and TNF-α were higher in the ConA group than in the control group, but lower in the ConA combined with NaHS group compared with the ConA group. Immunofluorescence showed that Cx40 was mainly expressed in the cytoplasm and nucleus of lymphocytes, while Cx43 was mainly expressed on the cell membrane. The expression frequencies and protein levels of Cx40 and Cx43 in the lymphocytes were higher in ConA group than in the control group, but lower in the ConA combined with NaHS group compared with the ConA group. Conclusion NaHS can inhibit the release of TNF-α and IL-6 from peripheral blood lymphocytes and down-regulate the expression of Cx40 and Cx43 in lymphocytes.

ETV1 activates a rapid conduction transcriptional program in rodent and human cardiomyocytes

Rapid impulse propagation is a defining attribute of the pectinated atrial myocardium and His-Purkinje system (HPS) that safeguards against atrial and ventricular arrhythmias, conduction block, and myocardial dyssynchrony. The complex transcriptional circuitry that dictates rapid conduction remains incompletely understood. Here, we demonstrate that ETV1 (ER81)-dependent gene networks dictate the unique electrophysiological characteristics of atrial and His-Purkinje myocytes. Cardiomyocyte-specific deletion of ETV1 results in cardiac conduction abnormalities, decreased expression of rapid conduction genes (Nkx2-5, Gja5, and Scn5a), HPS hypoplasia, and ventricularization of the unique sodium channel properties that define Purkinje and atrial myocytes in the adult heart. Forced expression of ETV1 in postnatal ventricular myocytes (VMs) reveals that ETV1 promotes a HPS gene signature while diminishing ventricular and nodal gene networks. Remarkably, ETV1 induction in human induced pluripotent stem cell-derived cardiomyocytes increases rapid conduction gene expression and inward sodium currents, converting them towards a HPS phenotype. Our data identify a cardiomyocyte-autonomous, ETV1-dependent pathway that is responsible for specification of rapid conduction zones in the heart and demonstrate that ETV1 is sufficient to promote a HPS transcriptional and functional program upon VMs.

Lack of connexin 40 decreases the calcium sensitivity of renin-secreting juxtaglomerular cells

The so-called calcium paradoxon of renin describes the phenomenon that exocytosis of renin from juxtaglomerular cells of the kidney is stimulated by lowering of the extracellular calcium concentration. The yet poorly understood effect of extracellular calcium on renin secretion appears to depend on the function of the gap junction protein connexin 40 (Cx40) in renin-producing cells. This study aimed to elucidate the role of Cx40 for the calcium dependency of renin secretion in more detail by investigating if Cx40 function is really essential for the influence of extracellular calcium on renin secretion, if and how Cx40 affects intracellular calcium dynamics in renin-secreting cells and if Cx40-mediated gap junctional coupling of renin-secreting cells with the mesangial cell area is relevant for the influence of extracellular calcium on renin secretion. Renin secretion was studied in isolated perfused mouse kidneys. Calcium measurements were performed in renin-producing cells of microdissected glomeruli. The ultrastructure of renin-secreting cells was examined by electron microscopy. We found that Cx40 was not essential for stimulation of renin secretion by lowering of the extracellular calcium concentration. Instead, Cx40 increased the sensitivity of renin secretion response towards lowering of the extracellular calcium concentration. In line, the sensitivity and dynamics of intracellular calcium in response to lowering of extracellular calcium were dampened when renin-secreting cells lacked Cx40. Disruption of gap junctional coupling of renin-secreting cells by selective deletion of Cx40 from mesangial cells, however, did not change the stimulation of renin secretion by lowering of the extracellular calcium concentration. Deletion of Cx40 from renin cells but not from mesangial cells was associated with a shift of renin expression from perivascular cells of afferent arterioles to extraglomerular mesangial cells. Our findings suggest that Cx40 is not directly involved in the regulation of renin secretion by extracellular calcium. Instead, it appears that in renin-secreting cells of the kidney lacking Cx40, intracellular calcium dynamics and therefore also renin secretion are desensitized towards changes of extracellular calcium. Whether the dampened calcium response of renin-secreting cells lacking Cx40 function results from a direct involvement of Cx40 in intracellular calcium regulation or from the cell type shift of renin expression from perivascular to mesangial cells remains to be clarified. In any case, Cx40-mediated gap junctional coupling between renin and mesangial cells is not relevant for the calcium paradoxon of renin secretion.

[Nitric oxide inhibits the release of TNF-α and IL-6 by down-regulating the expression of connexin 40 (Cx40) in rat T lymphocytes]

Objective To investigate the effects of NO on the expression of connexin 40 (Cx40) on peripheral blood lymphocytes and the levels of TNF-α and IL-6 in the supernatant of culture medium. Methods Peripheral blood lymphocytes of Wistar-Kyoto (WKY) rats were isolated from abdominal aorta and cultured in vitro, and then divided into control group, ConA group and ConA combined with NO group. ELISA was performed to test the levels of TNF-α and IL-6 in the supernatant of culture medium. Immunofluorescence technique was used to detect the expression and location of Cx40 on lymphocytes. Flow cytometry was used to determine the expression frequency of Cx40 on lymphocytes. Western blotting was conducted to examine the protein expression of Cx40 on lymphocytes. Results The levels of IL-6 and TNF-α were higher in the ConA group than in the control group, lower in the ConA combined with NO group than in the ConA group. Immunofluorescence showed that Cx40 was mainly expressed in the cytoplasm and the nucleus. The expression of Cx40 on lymphocytes was higher in the ConA group than in the control group, lower in the ConA combined with NO group than in the ConA group. The expression frequency of Cx40 on lymphocytes was higher in the ConA group than in the control group, lower in the ConA combined with NO group than in the ConA group. The protein expressions of Cx40 and Cx43 on lymphocytes were significantly higher in the ConA group than in the control group, lower in the ConA combined with NO group than in the ConA group. Conclusion NO inhibits the release of TNF-α and IL-6 from lymphocytes and down-regulates the expression of Cx40 on lymphocytes, suggesting that Cx40 on lymphocytes may be involved in the anti-inflammatory effect of NO.

Optogenetic termination of atrial fibrillation in mice

Aims

The primary goal in the treatment of symptomatic atrial fibrillation/flutter (AF) is to restore sinus rhythm by cardioversion. Electrical shocks are highly effective, but have to be applied under analgo-sedation and can further harm the heart. In order to develop a novel pain-free and less harmful approach, we explored herein the optogenetic cardioversion by light-induced depolarization.

Methods and results

Hearts from mice expressing Channelrhodopsin-2 (ChR2) and the AF-promoting loss-of-function Connexin 40 Ala96Ser mutation were explanted and perfused with low K+ Tyrode's solution and an atrial KATP-channel activator. This new protocol shortened atrial refractoriness as well as slowed atrial conduction and thereby enabled the induction of sustained AF. AF episodes could be terminated by epicardial illumination of the atria with focussed blue light (470 nm, 0.4 mW/mm2) with an efficacy of ∼97% (n = 17 hearts). In > 80% of cases, light directly terminated the AF episode with onset of illumination. Because similar illumination intensity was able to locally inhibit atrial activity, we propose that a light-induced block of electrical activity is responsible for reliable AF termination. The success rate was strongly depending on the illuminated area, applied light intensity and duration of illumination. Importantly, we were also able to demonstrate optogenetic termination of AF in vivo, using epicardial illumination through the open chest (n = 3 hearts). To point towards a translational potential, we systemically injected an adeno-associated virus to express ChR2 in wild type hearts. After 6-8 months, we found robust ChR2 expression in the atria, enabling light-mediated AF termination in six of seven mice tested.

Conclusion

We provide the first evidence for optogenetic termination of atrial tachyarrhythmia in intact hearts from transgenic as well as wild type mice ex and in vivo. Thus, this report could lay the foundation for the development of implantable devices for pain-free termination of AF.

Functional Characterization of Novel Atrial Fibrillation-Linked GJA5 (Cx40) Mutants

Atrial fibrillation (AF) is the most common form of cardiac arrhythmia. Recently, four novel heterozygous Cx40 mutations-K107R, L223M, Q236H, and I257L-were identified in 4 of 310 unrelated AF patients and a followup genetic analysis of the mutant carriers' families showed that the mutants were present in all the affected members. To study possible alterations associated with these Cx40 mutants, including their cellular localization and gap junction (GJ) function, we expressed GFP-tagged and untagged mutants in connexin-deficient model cells. All four Cx40 mutants showed clustered localization at cell-cell junctions similar to that observed of wildtype Cx40. However, cell pairs expressing Cx40 Q236H, but not the other individual mutants, displayed a significantly lower GJ coupling conductance (Gj) than wildtype Cx40. Similarly, co-expression of Cx40 Q236H with Cx43 resulted in a significantly lower Gj. Transjunctional voltage-dependent gating (Vj gating) properties were also altered in the GJs formed by Q236H. Reduced GJ function and altered Vj gating may play a role in promoting the Q236H carriers to AF.

Differential Association of Cx37 and Cx40 Genetic Variants in Atrial Fibrillation with and without Underlying Structural Heart Disease

Atrial fibrillation (AF) appears in the presence or absence of structural heart disease. The majority of foci causing AF are located near the ostia of pulmonary veins (PVs), where cardiomyocytes and vascular smooth muscle cells interdigitate. Connexins (Cx) form gap junction channels and participate in action potential propagation. Genetic variants in genes encoding Cx40 and Cx37 affect their expression or function and may contribute to PV arrhythmogenicity. DNA was obtained from 196 patients with drug-resistant, symptomatic AF with and without structural heart disease, who were referred for percutaneous catheter ablation. Eighty-nine controls were matched for age, gender, hypertension, and BMI. Genotyping of the Cx40 -44G > A, Cx40 +71A > G, Cx40 -26A > G, and Cx37 1019C > T polymorphisms was performed. The promoter A Cx40 polymorphisms (-44G > A and +71A > G) showed no association with non-structural or structural AF. Distribution of the Cx40 promoter B polymorphism (-26A > G) was different in structural AF when compared to controls (p = 0.03). There was no significant difference with non-structural AF (p = 0.50). The distribution of the Cx37 1019C > T polymorphism was different in non-structural AF (p = 0.03) but not in structural AF (p = 0.08) when compared to controls. Our study describes for the first time an association of drug-resistant non-structural heart disease AF with the Cx37 1019C > T gene polymorphism. We also confirmed the association of the Cx40 - 26G > A polymorphism in patients with AF and structural disease.

Human Connexin40 Mutations Slow Conduction and Increase Propensity for Atrial Fibrillation

BACKGROUND

Patch clamping studies using non-cardiomyocytes revealed that the human connexin40 mutations P88S, G38D, and A96S are associated with reduced gap junction conductances compared to wild type connexin40 (wtCx40). Their effects within myocytes however are unclear. We aimed to characterise P88S, G38D, and A96S after expression in rat hearts and primary cardiomyocyte cultures.

METHODS

Adult Sprague-Dawley rat atria were transduced with a lentivector containing a transgene encoding wtCx40, P88S, G38D, A96S, or eGFP (n=6 per transgene). Electrophysiology studies (EPS) were performed just prior to and 7 days after surgery. Left atria were assessed for connexin expression, mRNA levels, inflammation and fibrosis. Primary cardiomyocyte cultures were also transduced with the abovementioned vectors (n=6 per transgene) and monolayer conduction velocities (CV) and protein expression were assessed at 96hours.

RESULTS

At day 7 EPS, P wave and induced atrial fibrillation (AF) durations were significantly longer in the mutant groups when compared to wtCx40 controls (p<0.05). There were no significant differences in inflammation, fibrosis, or heart to body weight ratios. Monolayer CV's were reduced in the A96S group compared to the wtCx40 group. While similar to wtCx40 controls, P88S velocities were reduced compared to eGFP controls. G38D monolayers possessed spontaneous fibrillatory activity and could not be paced. Immunofluorescence revealed that P88S and G38D reduced native connexin43 myocyte coupling while A96S appeared to co-localise with connexin43 in gap junctions. Connexin43 mRNA levels were similar between groups.

CONCLUSIONS

The A96S, G38D, and P88S Cx40 mutations slow conduction and increased the propensity for inducible AF.

Lipopolysaccharide impairs permeability of pulmonary microvascular endothelial cells via Connexin40

The endotoxin lipopolysaccharide (LPS)-induced pulmonary endothelial barrier disruption is a key pathogenesis of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). However, the molecular mechanisms underlying LPS-impaired permeability of pulmonary microvascular endothelial cells (PMVECs) are not fully understood. Gap junctions, particularly Connexin40 (Cx40), are necessary for the maintenance of normal vascular function. In this study, we for the first time investigated the role of Cx40 in LPS-impaired permeability of PMVECs and provided potential therapeutic approaches based on mechanistic findings of Cx40 regulation by LPS stimuli. Rat PMVECs were isolated, cultured and identified with cell morphology, specific markers, ultrastructural characteristics and functional tests. Western blot analysis demonstrated that Cx40 is the major connexin highly expressed in PMVECs. Furthermore, by inhibiting Cx40 in a time-dependent manner, LPS impaired gap junction function and induced permeability injury of PMVECs. The key role of Cx40 decline in mediating detrimental effects of LPS was further confirmed in rescue experiments through Cx40 overexpression. Mechanistically, LPS stress on PMVECs inhibited the protein kinase C (PKC) pathway, which may synergize with the inflammatory nuclear factor kappaB (NFκB) signaling activation in suppressing Cx40 expression level and phosphorylation. Moreover, through pharmacological PKC activation or NFκB inhibition, Cx40 activity in PMVECs could be restored, leading to maintained barrier function under LPS stress. Our findings uncover a previously unrecognized role of Cx40 and its regulatory mechanisms in impaired endothelial integrity under endotoxin and inflammation, shedding light on intervention approaches to improve pulmonary endothelial barrier function in ALI and ARDS.

Myoendothelial coupling through Cx40 contributes to EDH-induced vasodilation in murine renal arteries: evidence from experiments and modelling

Regulation of renal vascular resistance plays a major role in controlling arterial blood pressure. The endothelium participates in this regulation as endothelial derived hyperpolarization plays a significant role in smaller renal arteries and arterioles, but the exact mechanisms are still unknown.

AIM

To investigate the role of vascular gap junctions and potassium channels in the renal endothelial derived hyperpolarization.

METHODS

In interlobar arteries from wild-type and connexin40 knockout mice, we assessed the role of calcium-activated small (SK) and intermediate (IK) conductance potassium channels. The role of inward rectifier potassium channels (Kir) and Na+ /K+ -ATPases was evaluated as was the contribution from gap junctions. Mathematical models estimating diffusion of ions and electrical coupling in myoendothelial gap junctions were used to interpret the results.

RESULTS

Lack of connexin40 significantly reduces renal endothelial hyperpolarization. Inhibition of SK and IK channels significantly attenuated renal EDH to a similar degree in wild-type and knockout mice. Inhibition of Kir and Na+ /K+ -ATPases affected the response in wild-type and knockout mice but at different levels of stimulation. The model confirms that activation of endothelial SK and IK channels generates a hyperpolarizing current that enters the vascular smooth muscle cells. Also, extracellular potassium increases sufficiently to activate Kir and Na+ /K+ -ATPases.

CONCLUSION

Renal endothelial hyperpolarization is mainly initiated by activation of IK and SK channels. The model shows that hyperpolarization can spread through myoendothelial gap junctions but enough potassium is released to activate Kir and Na+ /K+ -ATPases. Reduced coupling seems to shift the signalling pathway towards release of potassium. However, an alternative pathway also exists and needs to be investigated.

The endothelium in hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) in combination with hypercapnic pulmonary vasoconstriction redistributes pulmonary blood flow from poorly aerated to better ventilated lung regions by an active process of local vasoconstriction. Impairment of HPV results in ventilation-perfusion mismatch and is commonly associated with various lung diseases including pneumonia, sepsis, or cystic fibrosis. Although several regulatory pathways have been identified, considerable knowledge gaps persist, and a unifying concept of the signaling pathways that underlie HPV and their impairment in lung diseases has not yet emerged. In the past, conceptual models of HPV have focused on pulmonary arterial smooth muscle cells (PASMC) acting as sensor and effector of hypoxia in the pulmonary vasculature. In contrast, the endothelium was considered a modulating bystander in this scenario. For an ideal design, however, the oxygen sensor in HPV should be located in the region of gas exchange, i.e., in the alveolar capillary network. This concept requires the retrograde propagation of the hypoxic signal along the endothelial layer of the vascular wall and subsequent contraction of PASMC in upstream arterioles that is elicited via temporospatially tightly controlled endothelial-smooth muscle cell crosstalk. The present review summarizes recent work that provides proof-of-principle for the existence and functional relevance of such signaling pathway in HPV that involves important roles for connexin 40, epoxyeicosatrienoic acids, sphingolipids, and cystic fibrosis transmembrane conductance regulator. Of translational relevance, implication of these molecules provides for novel mechanistic explanations for impaired ventilation/perfusion matching in patients with pneumonia, sepsis, cystic fibrosis, and presumably various other lung diseases.