Down-regulation of ATBF1 activates STAT3 signaling via PIAS3 in pacing-induced HL-1 atrial myocytes

A potential role of human esophageal cancer-related gene-4 in cardiovascular homeostasis

Human esophageal cancer related gene-4 (ECRG-4) encodes a 148-aminoacid pre-pro-peptide that can be processed tissue-dependently into multiple small peptides possessing multiple functions distinct from, similar to, or opposite to the tumor suppressor function of the full-length Ecrg4. Ecrg-4 is covalently bound to the cell surface through its signal peptide, colocalized with the innate immunity complex (TLR4-CD14-MD2), and functions as a 'sentinel' molecule in the maintenance of epithelium and leukocyte homeostasis, meaning that the presence of Ecrg-4 on the cell surface signals the maintained homeostasis, whereas the loss of Ecrg-4 due to tissue injury activates pro-inflammatory and tissue proliferative responses, and the level of Ecrg-4 gradually returns to its pre-injury level upon wound healing. Interestingly, Ecrg-4 is also highly expressed in the heart and its conduction system, endothelial cells, and vascular smooth muscle cells. Accumulating evidence has shown that Ecrg-4 is involved in cardiac rate/rhythm control, the development of atrial fibrillation, doxorubicin-induced cardiotoxicity, the ischemic response of the heart and hypoxic response in the carotid body, the pathogenesis of atherosclerosis, and likely the endemic incidence of idiopathic dilated cardiomyopathy. These preliminary discoveries suggest that Ecrg-4 may function as a 'sentinel' molecule in cardiovascular system as well. Here, we briefly review the basic characteristics of ECRG-4 as a tumor suppressor gene and its regulatory functions on inflammation and apoptosis; summarize the discoveries about its distribution in cardiovascular system and involvement in the development of CVDs, and discuss its potential as a novel therapeutic target for the maintenance of cardiovascular system homeostasis.

Exosomal Cargo: Pro-angiogeneic, anti-inflammatory, and regenerative effects in ischemic and non-ischemic heart diseases - A comprehensive review

Heart diseases are the primary cause of mortality and morbidity worldwide which inflict a heavy social and economic burden. Among heart diseases, most deaths are due to myocardial infarction (MI) or heart attack, which occurs when a decrement in blood flow to the heart causes injury to cardiac tissue. Despite several available diagnostic, therapeutic, and prognostic approaches, heart disease remains a significant concern. Exosomes are a kind of small extracellular vesicles released by different types of cells that play a part in intercellular communication by transferring bioactive molecules important in regenerative medicine. Many studies have reported the diagnostic, therapeutic, and prognostic role of exosomes in various heart diseases. Herein, we reviewed the roles of exosomes as new emerging agents in various types of heart diseases, including ischemic heart disease, cardiomyopathy, arrhythmia, and valvular disease, focusing on pathogenesis, therapeutic, diagnostic, and prognostic roles in different areas. We have also mentioned different routes of exosome delivery to target tissues, the effects of preconditioning and modification on exosome's capability, exosome production in compliance with good manufacturing practice (GMP), and their ongoing clinical applications in various medical contexts to shed light on possible clinical translation.

Loss of the Atrial Fibrillation-Related Gene, Zfhx3, Results in Atrial Dilation and Arrhythmias

BACKGROUND

ZFHX3 (zinc finger homeobox 3), a gene that encodes a large transcription factor, is at the second-most significantly associated locus with atrial fibrillation (AF), but its function in the heart is unknown. This study aims to identify causative genetic variation related to AF at the ZFHX3 locus and examine the impact of Zfhx3 loss on cardiac function in mice.

METHODS

CRISPR-Cas9 genome editing, chromatin immunoprecipitation, and luciferase assays in pluripotent stem cell-derived cardiomyocytes were used to identify causative genetic variation related to AF at the ZFHX3 locus. Cardiac function was assessed by echocardiography, magnetic resonance imaging, electrophysiology studies, calcium imaging, and RNA sequencing in mice with heterozygous and homozygous cardiomyocyte-restricted Zfhx3 loss (Zfhx3 Het and knockout, respectively). Human cardiac single-nucleus ATAC (assay for transposase-accessible chromatin)-sequencing data was analyzed to determine which genes in atrial cardiomyocytes are directly regulated by ZFHX3.

RESULTS

We found single-nucleotide polymorphism (SNP) rs12931021 modulates an enhancer regulating ZFHX3 expression, and the AF risk allele is associated with decreased ZFHX3 transcription. We observed a gene-dose response in AF susceptibility with Zfhx3 knockout mice having higher incidence, frequency, and burden of AF than Zfhx3 Het and wild-type mice, with alterations in conduction velocity, atrial action potential duration, calcium handling and the development of atrial enlargement and thrombus, and dilated cardiomyopathy. Zfhx3 loss results in atrial-specific differential effects on genes and signaling pathways involved in cardiac pathophysiology and AF.

CONCLUSIONS

Our findings implicate ZFHX3 as the causative gene at the 16q22 locus for AF, and cardiac abnormalities caused by loss of cardiac Zfhx3 are due to atrial-specific dysregulation of pathways involved in AF susceptibility. Together, these data reveal a novel and important role for Zfhx3 in the control of cardiac genes and signaling pathways essential for normal atrial function.

miR-135a Regulates Atrial Fibrillation by Targeting Smad3

Background

Atrial fibrillation (AF) is the most common arrhythmia in clinical. Atrial fibrosis is a hallmark feature of atrial structural remodeling in AF, which is regulated by the TGF-β1/Smad3 pathway. Recent studies have implicated that miRNAs are involved in the process of AF. However, the regulatory mechanisms of miRNAs remain largely unknown. This study is aimed at investigating the function and regulatory network of miR-135a in AF.

Methods

In vivo, the plasma was collected from patients with AF and non-AF subjects. Adult SD rats were induced by acetylcholine (ACh) (66 μg/ml)-CaCl₂ (10 mg/ml) to establish an AF rat model. In vitro, atrial fibroblasts (AFs), isolated from adult SD rats, were treated with high-frequency electrical stimulation (HES) (12 h) and hypoxia (24 h) to mimic the AF and atrial fibrosis, respectively. miR-135a expression was detected through quantitative real-time polymerase chain reaction (qRT-PCR). The association between miR-135a and Smad3 was speculated by the TargetScan database and confirmed by the luciferase reporter assay. Fibrosis-related genes, Smad3, and TRPM7 were all assessed.

Results

The expression of miR-135a was markedly decreased in the plasma of AF patients and AF rats, which was consistent with that in HES-treated and hypoxia-treated AFs. Smad3 was identified as a target of miR-135a. the downregulation of miR-135a was associated with the enhancement of Smad3/TRPM7 expressions in AFs. Additionally, the knockdown of Smad3 significantly reduced the expression of TRPM7 and further inhibited atrial fibrosis.

Conclusions

Our study demonstrates that miR-135a regulates AF via Smad3/TRPM7, which is a potential therapeutic target for AF.

Comparative Analysis of Non-Coding RNA Transcriptomics in Heart Failure

Heart failure constitutes a clinical complex syndrome with different symptomatic characteristics depending on age, sex, race and ethnicity, among others, which has become a major public health issue with an increasing prevalence. One of the most interesting tools seeking to improve prevention, diagnosis, treatment and prognosis of this pathology has focused on finding new molecular biomarkers since heart failure relies on deficient cardiac homeostasis, which is regulated by a strict gene expression. Therefore, currently, analyses of non-coding RNA transcriptomics have been oriented towards human samples. The present review develops a comparative study emphasizing the relevance of microRNAs, long non-coding RNAs and circular RNAs as potential biomarkers in heart failure. Significantly, further studies in this field of research are fundamental to supporting their widespread clinical use. In this sense, the various methodologies used by the authors should be standardized, including larger cohorts, homogeneity of the samples and uniformity of the bioinformatic pipelines used to reach stratification and statistical significance of the results. These basic adjustments could provide promising steps to designing novel strategies for clinical management of patients with heart failure.

Genetics of atrial fibrillation-an update of recent findings

Atrial fibrillation (AF) is a common cardiac arrhythmia and a major risk factor for stroke, heart failure, and premature death. AF has a strong genetic predisposition. This review highlights the recent findings on the genetics of AF from genome-wide association studies (GWAS) and high-throughput sequencing studies. The consensus from GWAS implies that AF is both polygenic and pleiotropic in nature. With the advent of whole-genome sequencing and whole-exome sequencing, rare variants associated with AF pathogenesis have been identified. The recent studies have contributed towards better understanding of AF pathogenesis.

Transcriptional factors in calcium mishandling and atrial fibrillation development

Healthy cardiac conduction relies on the coordinated electrical activity of distinct populations of cardiomyocytes. Disruption of cell-cell conduction results in cardiac arrhythmias, a leading cause of morbidity and mortality worldwide. Recent genetic studies have highlighted a major heritable component and identified numerous loci associated with risk of atrial fibrillation, including transcription factor genes, particularly those important in cardiac development, microRNAs, and long noncoding RNAs. Identification of such genetic factors has prompted the search to understand the mechanisms that underlie the genetic component of AF. Recent studies have found several mechanisms by which genetic alterations can result in AF formation via disruption of calcium handling. Loss of developmental transcription factors in adult cardiomyocytes can result in disruption of SR calcium ATPase, sodium calcium exchanger, calcium channels, among other ion channels, which underlie action potential abnormalities and triggered activity that can contribute to AF. This review aims to summarize the complex network of transcription factors and their roles in calcium handling.

ZFHX3 knockdown dysregulates mitochondrial adaptations to tachypacing in atrial myocytes through enhanced oxidative stress and calcium overload

AIM

To investigate the role of zinc finger homeobox 3 gene (ZFHX3) in tachypacing-induced mitochondrial dysfunction and explore its molecular mechanisms and potential as a therapeutic target in atrial fibrillation (AF).

METHODS

Through a bioluminescent assay, a patch clamp, confocal fluorescence and fluorescence microscopy, microplate enzyme activity assays and Western blotting, we studied ATP and ADP production, mitochondrial electron transfer chain complex activities, ATP-sensitive potassium channels (I_KATP ), mitochondrial oxidative stress, Ca²⁺ content, and protein expression in control and ZFHX3 knockdown (KD) HL-1 cells subjected to 1 and 5-Hz pacing for 24 hours.

RESULTS

Compared with 1-Hz pacing, 5-Hz pacing increased ATP and ADP production, I_KATP , phosphorylated adenosine monophosphate-activated protein kinase and inositol 1,4,5-triphosphate (IP₃ ) receptor (IP₃ R) protein expression. Tachypacing induced mitochondrial oxidative stress and Ca²⁺ overload in both cell types. Furthermore, under 1- and 5-Hz pacing, ZFHX3 KD cells showed higher I_KATP , ATP and ADP production, mitochondrial oxidative stress and Ca²⁺ content than control cells. Under 5-Hz pacing, 2-aminoethoxydiphenyl borate (2-APB; 3 μmol/L, an IP₃ R inhibitor) and MitoTEMPO (10 µmol/L, a mitochondria-targeted antioxidant) reduced ADP and increased ATP production in both cell types; however, only 2-APB significantly reduced mitochondrial Ca²⁺ overload in control cells. Under 5-Hz pacing, mitochondrial oxidative stress was significantly reduced by both MitoTEMPO and 2-APB and only by 2-APB in control and ZFHX3 KD cells respectively.

CONCLUSION

ZFHX3 KD cells modulate mitochondrial adaptations to tachypacing in HL-1 cardiomyocytes through Ca²⁺ overload, oxidative stress and metabolic disorder. Targeting IP₃ R signalling or oxidative stress could reduce AF.

Exosomal miR-320d derived from adipose tissue-derived MSCs inhibits apoptosis in cardiomyocytes with atrial fibrillation (AF)

MicroRNAs (miRNAs) play a key role in various pathological processes like atrial fibrillation (AF), which is a common cardiac arrhythmia. Exosomes are essential information carrier in the intercellular communication. Therefore, this study aimed to investigate the effects of exosomal miR-320d on cardiomyocytes with AF and related mechanisms. To do this, AMSCs were transfected with miR-320d mimics, AMSCs-derived exosomes were co-cultured with cardiomyocytes with AF. MTT, TUNEL staining, flow cytometry, real-time PCR, western blots, and luciferase reporter assays were performed. The results revealed that miR-320d expression was decreased in AF cardiomyocytes. AF increased apoptosis and reduced cell viability in cardiomyocytes. By transfection with miR-320d mimics, the miR-320d level was increased in AMSCs, exosomes and cardiomyocytes, which reversed the effect of AF on cardiomyocytes. STAT3 was down-regulated in AF cardiomyocytes and was a direct target gene of miR-320d. Inhibition of STAT3 abolished the effect of modified exosomes in cardiomyocytes, causing decreased apoptosis and increased cell viability. Taken together, the results suggested that exosomal miR-320d was associated with AF cardiomyocytes apoptosis and cell viability and that the effect of miR-320d on cardiomyocytes is STAT3-dependent. Therefore, this study provides a novel understanding of the molecular basis of AF and provides insight into therapeutic strategies for AF.

Genetics of Atrial Fibrilation: In Search of Novel Therapeutic Targets

Atrial fibrillation (AF) is the most frequent arrhythmogenic disease in humans, ranging from 2% in the general population and rising up to 10-12% in 80+ years. Genetic analyses of AF familiar cases have identified a series of point mutations in distinct ion channels, supporting a causative link. However, these genetic defects only explain a minority of AF patients. Genomewide association studies identified single nucleotide polymorphisms (SNPs), close to PITX2 on 4q25 chromosome, that are highly associated to AF. Subsequent GWAS studies have identified several new loci, involving additional transcription and growth factors. Furthermore, these risk 4q25 SNPs serve as surrogate biomarkers to identify AF recurrence in distinct surgical and pharmacological interventions. Experimental studies have demonstrated an intricate signalling pathway supporting a key role of the homeobox transcription factor PITX2 as a transcriptional regulator. Furthermore, cardiovascular risk factors such as hyperthyroidism, hypertension and redox homeostasis have been identified to modulate PITX2 driven gene regulatory networks. We provide herein a state-of-the-art review of the genetic bases of atrial fibrillation, our current understanding of the genetic regulatory networks involved in AF and its plausible usage for searching novel therapeutic targets.

Evaluation of novel SNPs and haplotypes within the <i>ATBF1</i> gene and their effects on economically important production traits in cattle

Abstract. AT motif binding factor 1 (ATBF1) gene can promote the expression level of the growth hormone 1 (GH1) gene by binding to the enhancers of the POU1F1 and PROP1 genes; thus, it affects the growth and development of livestock. Considering that the ATBF1 gene also has a close relationship with the Janus kinase–signal transductor and activator of transcription (JAK–STAT) pathway, the objective of this work was to identify novel single-nucleotide polymorphism (SNP) variations and their association with growth traits in native Chinese cattle breeds. Five novel SNPs within the ATBF1 gene were found in 644 Qinchuan and Jinnan cattle for first time using 25 pairs of screening and genotyping primers. The five novel SNPs were named as AC_000175:g.140344C>G (SNP1), g.146573T>C (SNP2), g.205468C>T (SNP3), g.205575A>G (SNP4) and g.297690C<T (SNP5). Among them, SNP1 and SNP2 were synonymous coding SNPs, while SNP5 was a missense coding SNP, and the other SNPs were intronic. Haplotype analysis found 18 haplotypes in the two breeds, and three and five closely linked loci were revealed in Qinchuan and Jinnan breeds, respectively. Association analysis revealed that SNP1 was significantly associated with the height across the hip in Qinchuan cattle. SNP2 was found to be significantly related to chest circumference and body side length traits in Jinnan cattle. SNP3 was found to have significant associations with four growth traits in Qinchuan cattle. Moreover, the different combined genotypes, SNP1–SNP3, SNP1–SNP4 and SNP2–SNP5 were significantly associated with the growth traits in cattle. These findings indicated that the bovine ATBF1 gene had marked effects on growth traits, and the growth-trait-related loci can be used as DNA markers for maker-assisted selection (MAS) breeding programs in cattle.

Graphene Sheet-Induced Global Maturation of Cardiomyocytes Derived from Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (hiPSCs) can proliferate infinitely. Their ability to differentiate into cardiomyocytes provides abundant sources for disease modeling, drug screening and regenerative medicine. However, hiPSC-derived cardiomyocytes (hiPSC-CMs) display a low degree of maturation and fetal-like properties. Current in vitro differentiation methods do not mimic the structural, mechanical, or physiological properties of the cardiogenesis niche. Recently, we present an efficient cardiac maturation platform that combines hiPSCs monolayer cardiac differentiation with graphene substrate, which is a biocompatible and superconductive material. The hiPSCs lines were successfully maintained on the graphene sheets and were able to differentiate into functional cardiomyocytes. This strategy markedly increased the myofibril ultrastructural organization, elevated the conduction velocity, and enhanced both the Ca²⁺ handling and electrophysiological properties in the absence of electrical stimulation. On the graphene substrate, the expression of connexin 43 increased along with the conduction velocity. Interestingly, the bone morphogenetic proteins signaling was also significantly activated during early cardiogenesis, confirmed by RNA sequencing analysis. Here, we reasoned that graphene substrate as a conductive biomimetic surface could facilitate the intrinsic electrical propagation, mimicking the microenvironment of the native heart, to further promote the global maturation of hiPSC-CMs. Our findings highlight the capability of electrically active substrates to influence cardiomyocyte development. We believe that application of graphene sheets will be useful for simple, fast, and scalable maturation of regenerated cardiomyocytes.

A Potential Role of Esophageal Cancer Related Gene-4 for Atrial Fibrillation

Epidemiological studies have shown a strong correlation between tumor and AF. However, the molecular link between tumor and AF remains unknown. ECRG4, a tumor suppressor gene that is expressed in the A-V node and in sporadic ventricular myocytes, inhibits tumorigenesis and monitors tissue homeostasis by functioning as a ‘sentinel’ molecule gauging inflammatory and cell proliferative responses. To explore the potential physiological function of Ecrg4 in heart, we evaluated its distribution in heart, analyzed its expression in patients with persistent AF and in a canine AF model, and dissected the molecular events downstream of Ecrg4. The results showed that the level of Ecrg4 expression is homogenously high in atria and the conduction systems and in sporadic ventricular myocytes. Importantly, the expression of Ecrg4 was significantly decreased in atrial appendages of AF patients than patients with SR. Moreover, in rapid pacing canine AF models, the expression of ECRG4 in atria was significantly decreased compared to that of the controls. Mechanistically, knockdown ECRG4 in atrial myocytes significantly shortened the APDs, inhibited the expression of Gja1, and activated pro-inflammatory cascades and genes involved in cardiac remodeling. These results suggest that Ecrg4 may play a critical role in the pathogenesis of AF.

Structural and electrophysiological dysfunctions due to increased endoplasmic reticulum stress in a long-term pacing model using human induced pluripotent stem cell-derived ventricular cardiomyocytes

Background

Long-term ventricular pacing has deleterious effects and becomes more significant when cumulative percent ventricular pacing (Cum%VP) exceeds 40% of time. However, cellular disturbances and pathways by which pacing leads to myocardial disorders are not well understood. Attempts to resolve these questions have been hampered by difficulties in obtaining human cardiac tissue and the inability to build a longer-lasting (lasting longer than weeks) pacing model in vitro.

Methods

Human induced pluripotent stem cell-derived ventricular cardiomyocytes (VCMs) were cultured in the presence of electrical stimulation for 2 weeks. Quantitative structural and electrophysiological analyses were used to define the functional disturbances of pacing.

Results

Compared to controls, paced VCMs exhibited a remarkable reduction in the contractile protein expression, an increased apoptosis ratio and electrophysiological remodelling in a Cum%VP-dependent manner. Investigation of the protein expression levels revealed that long-term pacing universally activated both ER stress and downstream calpain. Moreover, the inhibition of calpain attenuated the adverse effects on the structural remodelling and increased the I_{Ca, L} in paced VCMs.

Conclusions

The results demonstrated that pacing VCMs for 2 weeks in vitro led to a series of structural and electrophysiological dysfunctions. The increased ER stress and downstream calpain could be a central mechanism underlying the disease pathogenesis. This finding could represent a new therapeutic target in the management of long-term pacing patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0566-6) contains supplementary material, which is available to authorized users.

Association of atrial fibrillation susceptibility genes, atrial fibrillation phenotypes and response to catheter ablation: a gene-based analysis of GWAS data

Background

Previous studies have suggested PITX2, KCNN3 and ZFHX3 as atrial fibrillation (AF) susceptibility genes. Single common genetic polymorphisms of those genes have been linked with AF phenotypes and rhythm outcome of AF catheter ablation although their mechanisms remain elusive. New gene-based association tests may help clarifying genotype–phenotype correlations. Therefore, we hypothesized that PITX2, KCNN3 and ZFHX3 associate with left atrial enlargement and persistent AF and subsequently with ablation outcome.

Methods and results

Samples from 660 patients with paroxysmal (n = 370) or persistent AF (n = 290) undergoing AF catheter ablation were genotyped for ~1,000,000 SNPs. Gene-based association was investigated using two different gene-based association tests (VEGAS, minSNP). Among the three candidate genes, only ZFHX3 associated with left atrial dilatation and AF recurrence after catheter ablation.

Conclusion

This study suggests a contribution of ZFHX3 to AF remodeling and response to therapy. Future and larger studies are necessary to replicate and apply these findings with an emphasis on designing AF pathophysiology-based multi-locus risk scores.

Gene regulatory networks in atrial fibrillation

Atrial fibrillation (AF) is the most frequent arrhythmogenic syndrome in humans. With an estimate incidence of 1%-2% in the general population, AF raises up to almost 10%-12% in 80+ years. Thus, AF represents nowadays a highly prevalent medical problem generating a large economic burden. At the electrophysiological level, distinct mechanisms have been elucidated. Yet, despite its prevalence, the genetic and molecular culprits of this pandemic cardiac electrophysiological abnormality have remained largely obscure. Molecular genetics of AF familiar cases have demonstrated that single nucleotide mutations in distinct genes encoding for ion channels underlie the onset of AF, albeit such alterations only explain a minor subset of patients with AF. In recent years, analyses by means of genome-wide association studies have unraveled a more complex picture of the etiology of AF, pointing out to distinct cardiac-enriched transcription factors, as well as to other regulatory genes. Furthermore a new layer of regulatory mechanisms have emerged, i.e., post-transcriptional regulation mediated by non-coding RNA, which have been demonstrated to exert pivotal roles in cardiac electrophysiology. In this manuscript, we aim to provide a comprehensive review of the genetic regulatory networks that if impaired exert electrophysiological abnormalities that contribute to the onset, and subsequently, on self-perpetuation of AF.

Novel Nucleotide Variations, Haplotypes Structure and Associations with Growth Related Traits of Goat AT Motif-Binding Factor (ATBF1) Gene

The AT motif-binding factor (ATBF1) not only interacts with protein inhibitor of activated signal transducer and activator of transcription 3 (STAT3) (PIAS3) to suppress STAT3 signaling regulating embryo early development and cell differentiation, but is required for early activation of the pituitary specific transcription factor 1 (Pit1) gene (also known as POU1F1) critically affecting mammalian growth and development. The goal of this study was to detect novel nucleotide variations and haplotypes structure of the ATBF1 gene, as well as to test their associations with growth-related traits in goats. Herein, a total of seven novel single nucleotide polymorphisms (SNPs) (SNP 1-7) within this gene were found in two well-known Chinese native goat breeds. Haplotypes structure analysis demonstrated that there were four haplotypes in Hainan black goat while seventeen haplotypes in Xinong Saanen dairy goat, and both breeds only shared one haplotype (hap1). Association testing revealed that the SNP2, SNP5, SNP6, and SNP7 loci were also found to significantly associate with growth-related traits in goats, respectively. Moreover, one diplotype in Xinong Saanen dairy goats significantly linked to growth related traits. These preliminary findings not only would extend the spectrum of genetic variations of the goat ATBF1 gene, but also would contribute to implementing marker-assisted selection in genetics and breeding in goats.

Acetylation mediates Cx43 reduction caused by electrical stimulation

Communication between cardiomyocytes depends upon gap junctions (GJ). Previous studies have demonstrated that electrical stimulation induces GJ remodeling and modifies histone acetylase (HAT) and deacetylase (HDAC) activities, although these two results have not been linked. The aim of this work was to establish whether electrical stimulation modulates GJ-mediated cardiac cell-cell communication by acetylation-dependent mechanisms. Field stimulation of HL-1 cardiomyocytes at 0.5 Hz for 24 h significantly reduced connexin43 (Cx43) expression and cell-cell communication. HDAC activity was down-regulated whereas HAT activity was not modified resulting in increased acetylation of Cx43. Consistent with a post-translational mechanism, we did not observe a reduction in Cx43 mRNA in electrically stimulated cells, while the proteasomal inhibitor MG132 maintained Cx43 expression. Further, the treatment of paced cells with the HAT inhibitor Anacardic Acid maintained both the levels of Cx43 and cell-cell communication. Finally, we observed increased acetylation of Cx43 in the left ventricles of dogs subjected to chronic tachypacing as a model of abnormal ventricular activation. In conclusion, our findings suggest that altered electrical activity can regulate cardiomyocyte communication by influencing the acetylation status of Cx43.

The CAA repeat polymorphism in the ZFHX3 gene is associated with risk of coronary heart disease in a Chinese population

Coronary heart disease (CHD) is a disease resulting from the interaction between genetic variations and environmental factors. Zinc finger homeobox 3 (ZFHX3) is a transcription factor and contains a poly-glutamine tract in a compositionally biased region that is encoded by exon 9, containing a cluster of CAG and CAA triplets followed by the polymorphic CAA repeats: (CAG)2(CAA)2(CAG)3CAACAG(CAA)nGCA. Thus, nine successive glutamine residues precede the poly-glutamine tract, encoded by the polymorphic CAA repeats. The aim of this study was to investigate the association of the CAA repeat polymorphism in exon 9 of the ZFHX3 gene with the risk of CHD in a Chinese population. The CAA repeat polymorphism was determined by polymerase chain reaction followed by DNA sequencing in 321 CHD patients. Genotype frequencies were compared using the non-parametric mood median test. Four alleles of CAG(CAA)10GCA, CAG(CAA)8GCA, CAG(CAA)9GCA, and CAG(CAA)11GCA were found in Chinese CHD patients in exon 9 of the ZFHX3 gene. The CAG(CAA)10GCA was a major allele (95.95%), and the CAG(CAA)8GCA was a minor allele (3.58%). The CAG(CAA)9GCA and CAG(CAA)11GCA were rare alleles (0.31% and 0.16%). The CAG(CAA)10GCA allele encodes a poly-glutamine tract of 19 residues. Importantly, the CHD patients homozygous for the CAG(CAA)10GCA allele had a higher risk of CHD, compared to the heterozygous patients carrying a CAG(CAA)8GCA allele. Moreover, the CAG(CAA)10GCA allele was significantly associated with hypertension, diabetes mellitus, or dyslipidemia (P < 0.05). Thus, the CAA repeat polymorphism in exon 9 of the ZFHX3 gene contributes to the CHD susceptibility in the Chinese population.

Deletion of PDK1 causes cardiac sodium current reduction in mice

Background

The AGC protein kinase family regulates multiple cellular functions. 3-phosphoinositide-dependent protein kinase-1 (PDK1) is involved in the pathogenesis of arrhythmia, and its downstream factor, Forkhead box O1 (Foxo1), negatively regulates the expression of the cardiac sodium channel, Nav1.5. Mice are known to die suddenly after PDK1 deletion within 11 weeks, but the underlying electrophysiological bases are unclear. Thus, the aim of this study was to investigate the potential mechanisms between PDK1 signaling pathway and cardiac sodium current.

Methods and Results

Using patch clamp and western blotting techniques, we investigated the role of the PDK1-Foxo1 pathway in PDK1 knockout mice and cultured cardiomyocytes. We found that PDK1 knockout mice undergo slower heart rate, prolonged QRS and QTc intervals and abnormal conduction within the first few weeks of birth. Furthermore, the peak sodium current is decreased by 33% in cells lacking PDK1. The phosphorylation of Akt (308T) and Foxo1 (24T) and the expression of Nav1.5 in the myocardium of PDK1-knockout mice are decreased, while the nuclear localization of Foxo1 is increased. The role of the PDK1-Foxo1 pathway in regulating Nav1.5 levels and sodium current density was verified using selective PDK1, Akt and Foxo1 inhibitors and isolated neonatal rat cardiomyocytes.

Conclusion

These results indicate that PDK1 participates in the dysregulation of electrophysiological basis by regulating the PDK1-Foxo1 pathway, which in turn regulates the expression of Nav1.5 and cardiac sodium channel function.

The role of transcription factors in atrial fibrillation

Atrial fibrillation (AF) is a complex disease that results from genetic and environmental factors and their interactions. In recent years, genome-wide association studies (GWAS) and family-based linkage analysis have found amounts of genetic variants associated with AF. Some of them lie in coding sequences and thus mediate the encoded proteins, some in non-coding regions and influence the expression of adjacent genes. These variants exert influence on the development of cardiovascular system and normal cardiac electrical activity in different levels, and eventually contribute to the occurrence of AF. Among these affected genes, as a crucial means of transcriptional regulation, several transcription factors play important roles in the pathogenesis of AF. In this review, we will focus on the potential role of PITX2, PRRX1, ZHFX3, TBX5, and NKX2.5 in AF.

The ER stress-mediated mitochondrial apoptotic pathway and MAPKs modulate tachypacing-induced apoptosis in HL-1 atrial myocytes

Background and Object

Cell apoptosis is a contributing factor in the initiation, progression and relapse of atrial fibrillation (AF), a life-threatening illness accompanied with stroke and heart failure. However, the regulatory cascade of apoptosis is intricate and remains unidentified, especially in the setting of AF. The aim of this study was to explore the roles of endoplasmic reticulum (ER) stress, mitochondrial apoptotic pathway (MAP), mitogen-activated protein kinases (MAPKs), and their cross-talking in tachypacing-induced apoptosis.

Methods and Results

HL-1 cells were cultured in the presence of tachypacing for 24 h to simulate atrial tachycardia remodeling. Results showed that tachypacing reduced cell viability measured by the cell counting kit-8, dissipated mitochondrial membrane potential detected by JC-1 staining and resulted in approximately 50% apoptosis examined by Hoechst staining and annexin V/propidium iodide staining. In addition, the proteins involved in ER stress, MAP and MAPKs were universally up-regulated or activated via phosphorylation, as confirmed by western blotting; and reversely silencing of ER stress, caspase-3 (the ultimate executor of MAP) and MAPKs with specific inhibitors prior to pacing partially alleviated apoptosis. An inhibitor of ER stress was applied to further investigate the responses of mitochondria and MAPKs to ER stress, and results indicated that suppression of ER stress comprehensively but incompletely attenuated the activation of MAP and MAPKs aroused by tachypacing, with the exception of ERK1/2, one branch of MAPKs.

Conclusions

Our study suggested tachypacing-induced apoptosis is regulated by ER stress-mediated MAP and MAPKs. Thus, the above three components are all promising anti-apoptotic targets in AF patients and ER stress appears to play a dominant role due to its comprehensive effects.