Chronic hypoxia down-regulates tight junction protein ZO-2 expression in children with cyanotic congenital heart defect

Adverse remodelling in tetralogy of Fallot: From risk factors to imaging analysis and future perspectives

Although contemporary outcomes of initial surgical repair of tetralogy of Fallot (TOF) are excellent, the survival of adult patients remains significantly lower than that of the normal population due to the high incidence of heart failure, ventricular arrhythmias, and sudden cardiac death. The underlying mechanisms are only partially understood but involve an adverse biventricular response, so-called remodelling, to key stressors such as right ventricular (RV) pressure-and/or volume-overload, myocardial fibrosis, and electro-mechanical dyssynchrony. In this review, we explore risk factors and mechanisms of biventricular remodelling, from histological to electro-mechanical aspects, and the role of imaging in their assessment. We discuss unsolved challenges and future directions to better understand and treat the long-term sequelae of this complex congenital heart disease.

Hypoxia as a potential inducer of immune tolerance, tumor plasticity and a driver of tumor mutational burden: Impact on cancer immunotherapy

In cancer patients, immune cells are often functionally compromised due to the immunosuppressive features of the tumor microenvironment (TME) which contribute to the failures in cancer therapies. Clinical and experimental evidence indicates that developing tumors adapt to the immunological environment and create a local microenvironment that impairs immune function by inducing immune tolerance and invasion. In this context, microenvironmental hypoxia, which is an established hallmark of solid tumors, significantly contributes to tumor aggressiveness and therapy resistance through the induction of tumor plasticity/heterogeneity and, more importantly, through the differentiation and expansion of immune-suppressive stromal cells. We and others have provided evidence indicating that hypoxia also drives genomic instability in cancer cells and interferes with DNA damage response and repair suggesting that hypoxia could be a potential driver of tumor mutational burden. Here, we reviewed the current knowledge on how hypoxic stress in the TME impacts tumor angiogenesis, heterogeneity, plasticity, and immune resistance, with a special interest in tumor immunogenicity and hypoxia targeting. An integrated understanding of the complexity of the effect of hypoxia on the immune and microenvironmental components could lead to the identification of better adapted and more effective combinational strategies in cancer immunotherapy. Clearly, the discovery and validation of therapeutic targets derived from the hypoxic tumor microenvironment is of major importance and the identification of critical hypoxia-associated pathways could generate targets that are undeniably attractive for combined cancer immunotherapy approaches.

Myocardial oedema: pathophysiological basis and implications for the failing heart

Myocardial fluid homeostasis relies on a complex interplay between microvascular filtration, interstitial hydration, cardiomyocyte water uptake and lymphatic removal. Dysregulation of one or more of these mechanisms may result in myocardial oedema. Interstitial and intracellular fluid accumulation disrupts myocardial architecture, intercellular communication, and metabolic pathways, decreasing contractility and increasing myocardial stiffness. The widespread use of cardiac magnetic resonance enabled the identification of myocardial oedema as a clinically relevant imaging finding with prognostic implications in several types of heart failure. Furthermore, growing experimental evidence has contributed to a better understanding of the physical and molecular interactions in the microvascular barrier, myocardial interstitium and lymphatics and how they might be disrupted in heart failure. In this review, we summarize current knowledge on the factors controlling myocardial water balance in the healthy and failing heart and pinpoint the new potential therapeutic avenues.

Persisting and reoccurring cyanosis after Fontan operation is associated with increased late mortality

OBJECTIVES

The Fontan operation aims at reducing cyanosis and cardiac volume overload in patients with complex univentricular heart malformations. However, persisting or reoccurring cyanosis is frequently observed. We sought to systematically determine the prevalence and clinical consequences of persisting and secondary cyanosis after Fontan operation.

METHODS

A total of 331 Fontan patients, operated between 1984 and 2016 with a median postoperative follow-up of 7.9 (interquartile range 2.6-15.8) years, were studied retrospectively. Cyanosis was defined as transcutaneous oxygen saturation ≤93% at rest measured by pulse oximetry. Prevalence of cyanosis was analysed at 3 different time points (t1 = post-Fontan operation, t2 = post-Fontan cardiac catheterization, t3 = last follow-up) and the association of cyanosis with mortality was examined.

RESULTS

Prevalence of cyanosis was 50% at t1 and 39% at t3. Fenestration was patent in 71% and 33% of all cyanotic patients at t1 and t3, respectively. In patients with clinical indication for catheterization (t2; n = 178/331), prevalence of cyanosis was 72%. At t2, patent fenestration (33%), veno-venous collaterals (24%) or both (32%) were present. Thirty-six (11%) patients died during follow-up. In a time-varying multivariable Cox regression analysis, cyanosis was the strongest predictor for late mortality (P < 0.001, hazard ratio 12.2, 95% confidence interval 3.7-40.5).

CONCLUSIONS

Prevalence of cyanosis was considerable during long-term follow-up after Fontan operation and-as a surrogate parameter for unfavourable Fontan haemodynamics-is associated with increased late mortality. Accordingly, particular attention should be directed towards the persistence or reoccurrence of cyanosis during follow-up since it may indicate haemodynamic attrition and development of Fontan failure.

The Interaction Analysis of SNP Variants and DNA Methylation Identifies Novel Methylated Pathogenesis Genes in Congenital Heart Diseases

Congenital heart defect (CHD) is a rare and complicated disease with a high mortality rate. Its etiology remains unclear and includes many aspects. DNA methylation has been indicated to be involved in heart development in the early stage of life, and aberrant methylation level was related to CHDs. This study provides the first evidence of the cross talk of SNP variants and DNA methylation in clarifying CHD underlying genomic cause. We gathered whole exome sequencing (WES) data for Group 1 consisting of patients with PA (n = 78), TOF (n = 20), TAPVC (n = 78), and PDA (n = 40), and 100 healthy children as control group. Rare non-synonymous mutations and novel genes were found and highlighted. Meanwhile, we carried out the second analysis of DNA methylation data from patients with PA (n = 3), TAPVC (n = 3), TOF (n = 3), and PDA (n = 2), and five healthy controls using 850 K array in Group 2. DNA methylation was linked to WES data, and we explored an obvious overlap of hyper/hypomethylated genes. Next, we identified some candidate genes by Fisher’s exact test and Burden analysis; then, those methylated genes were figured out by the criteria of the mutation located in the CpG islands of the genome, differential methylation sites (DMS), and DNA methylation quantitative trait loci (meQTLs) in the database, respectively. Also, the interaction of differentially methylated candidate genes with known CHD pathogenetic genes was depicted in a molecular network. Taken together, our findings show that nine novel genes (ANGPTL4, VEGFA, PAX3, MUC4, HLA-DRB1, TJP2, BCR, PKD1, and HK2) in methylation level are critical to CHD and reveal a new insight into the molecular pathogenesis of CHD.

ZO-2 Is a Master Regulator of Gene Expression, Cell Proliferation, Cytoarchitecture, and Cell Size

ZO-2 is a cytoplasmic protein of tight junctions (TJs). Here, we describe ZO-2 involvement in the formation of the apical junctional complex during early development and in TJ biogenesis in epithelial cultured cells. ZO-2 acts as a scaffold for the polymerization of claudins at TJs and plays a unique role in the blood–testis barrier, as well as at TJs of the human liver and the inner ear. ZO-2 movement between the cytoplasm and nucleus is regulated by nuclear localization and exportation signals and post-translation modifications, while ZO-2 arrival at the cell border is triggered by activation of calcium sensing receptors and corresponding downstream signaling. Depending on its location, ZO-2 associates with junctional proteins and the actomyosin cytoskeleton or a variety of nuclear proteins, playing a role as a transcriptional repressor that leads to inhibition of cell proliferation and transformation. ZO-2 regulates cell architecture through modulation of Rho proteins and its absence induces hypertrophy due to inactivation of the Hippo pathway and activation of mTOR and S6K. The interaction of ZO-2 with viral oncoproteins and kinases and its silencing in diverse carcinomas reinforce the view of ZO-2 as a tumor regulator protein.

ZO-2, a tight junction protein involved in gene expression, proliferation, apoptosis, and cell size regulation

ZO-2 is a peripheral tight junction protein that belongs to the membrane-associated guanylate kinase protein family. Here, we explain the modular and supramodular organization of ZO-2 that allows it to interact with a wide variety of molecules, including cell-cell adhesion proteins, cytoskeletal components, and nuclear factors. We also describe how ZO proteins evolved through metazoan evolution and analyze the intracellular traffic of ZO-2, as well as the roles played by ZO-2 at the plasma membrane and nucleus that translate into the regulation of proliferation, cell size, and apoptosis. In addition, we focus on the impact of ZO-2 expression on male fertility and on maladies like cancer, cholestasis, and hearing loss.

Chronic hypoxia down-regulates tight junction protein ZO-2 expression in children with cyanotic congenital heart defect

Aims

Tight junction protein zonula occludens protein 2 (ZO‐2) is a member of the membrane‐associated guanylate kinases protein family known to be expressed at tight junctions of epithelial and endothelial cells and at adherens junctions (AJs) in cardiomyocytes. Little is known about ZO‐2 expression and function in the human heart. Here, we examined the hypothesis that chronic hypoxia down‐regulates ZO‐2 expression in human myocardium and cultured rat cardiomyocytes.

Methods and results

Patients with a diagnosis of cyanotic (n = 10) or acyanotic (n = 10) Tetralogy of Fallot undergoing surgical repair were used to examine ZO‐2 messenger RNA and protein expression by real time‐PCR, immunohistochemistry, and western blotting. A model of cultured rat cardiomyocytes was used to measure ZO‐2 and AJ proteins levels in response to hypoxia and to investigate ZO‐2 cellular localization. We showed that ZO‐2 is expressed in myocardial tissue in acyanotic and cyanotic children with congenital heart defects. ZO‐2 was specifically down‐regulated in cyanotic myocardium at both the messenger RNA and protein levels when compared with acyanotic patients. This specific down‐regulation can be mimicked in cultured rat cardiomyocytes by treating them with hypoxic conditions confirming that ZO‐2 gene down‐regulation is specifically due to cyanosis. Furthermore, in addition to its cytoplasmic expression, ZO‐2 showed nuclear expression in cultured rat cardiomyocytes suggesting potential role in transcription regulation.

Conclusions

Hypoxia down‐regulates ZO‐2 expression in both cyanotic patient's myocardium and cultured rat cardiomyocytes. This down‐regulation suggest an involvement of ZO‐2 in cardiac remodelling of AJs in cyanotic children and may explain the greater susceptibility of cyanotic patients to corrective heart surgery.