Integrative Analysis of PRKAG2 Cardiomyopathy iPS and Microtissue Models Identifies AMPK as a Regulator of Metabolism, Survival, and Fibrosis

Functional Prediction of Chronic Kidney Disease Susceptibility Gene PRKAG2 by Comprehensively Bioinformatics Analysis

The genetic predisposition to chronic kidney disease (CKD) has been widely evaluated especially using the genome-wide association studies, which highlighted some novel genetic susceptibility variants in many genes, and estimated glomerular filtration rate to diagnose and stage CKD. Of these variants, rs7805747 in PRKAG2 was identified to be significantly associated with both serum creatinine and CKD with genome wide significance level. Until now, the potential mechanism by which rs7805747 affects CKD risk is still unclear. Here, we performed a functional analysis of rs7805747 variant using multiple bioinformatics software and databases. Using RegulomeDB and HaploReg (version 4.1), rs7805747 was predicated to locate in enhancer histone marks (Liver, Duodenum Mucosa, Fetal Intestine Large, Fetal Intestine Small, and Right Ventricle tissues). Using GWAS analysis in PhenoScanner, we showed that rs7805747 is not only associated with CKD, but also is significantly associated with other diseases or phenotypes. Using metabolite analysis in PhenoScanner, rs7805747 is identified to be significantly associated with not only the serum creatinine, but also with other 16 metabolites. Using eQTL analysis in PhenoScanner, rs7805747 is identified to be significantly associated with gene expression in multiple human tissues and multiple genes including PRKAG2. The gene expression analysis of PRKAG2 using 53 tissues from GTEx RNA-Seq of 8555 samples (570 donors) in GTEx showed that PRKAG2 had the highest median expression in Heart-Atrial Appendage. Using the gene expression profiles in human CKD, we further identified different expression of PRKAG2 gene in CKD cases compared with control samples. In summary, our findings provide new insight into the underlying susceptibility of PRKAG2 gene to CKD.

Sudden cardiac death due to the Wolff-Parkinson-White syndrome: A case report with genetic analysis

RATIONALE

The Wolff-Parkinson-White syndrome (WPW) is a benign heart disease with accessory pathways, which can result in cardiac arrhythmias. The purpose of this case report is to introduce a rare case of sudden cardiac death (SCD) with a mild myocardial bridge and a history of WPW.

PATIENT CONCERNS

A 25-year-old man with known WPW syndrome died at night while sleeping.

DIAGNOSES

Diagnosis of WPW syndrome is based on typical electrocardiogram findings with a documented dysrhythmia before the victim's death.

INTERVENTIONS

At autopsy, no traumatic injury or common poisons were found, only a slight myocardial bridge was detected. We performed whole exome sequencing and identified several genetic variations related to SCD.

OUTCOMES

We considered that the cause of death in this case was SCD in which arrhythmia might play an important role.

LESSONS

This case highlights SCD can occur in WPW patients with mild or unrecognized structural abnormality. Postmortem genetic examination can assist the diagnosis of sudden cardiac death, especially when no lethal structural abnormality is found in the decedent.

Molecular Pathogenesis of Familial Wolff-Parkinson-White Syndrome

Familial Wolff-Parkinson-White (WPW) syndrome is an autosomal dominant inherited disease and consists of a small percentage of WPW syndrome which exhibits ventricular pre-excitation by development of accessory atrioventricular pathway. A series of mutations in PRKAG2 gene encoding gamma2 subunit of 5'AMP-activated protein kinase (AMPK) has been identified as the cause of familial WPW syndrome. AMPK is one of the most important metabolic regulators of carbohydrates and lipids in many types of tissues including cardiac and skeletal muscles. Patients and animals with the mutation in PRKAG2 gene exhibit aberrant atrioventricular conduction associated with cardiac glycogen overload. Recent studies have revealed "novel" significance of canonical pathways leading to glycogen synthesis and provided us profound insights into molecular mechanism of the regulation of glycogen metabolism by AMPK. This review focuses on the molecular basis of the pathogenesis of cardiac abnormality due to PRKAG2 mutation and will provide current overviews of the mechanism of glycogen regulation by AMPK. J. Med. Invest. 65:1-8, February, 2018.

Human γ2-AMPK Mutations

In humans, dominant mutations in the gene encoding the regulatory γ2-subunit of AMP-activated protein kinase (PRKAG2) result in a highly penetrant phenotype dominated by cardiac features: left ventricular hypertrophy, ventricular pre-excitation, atrial tachyarrhythmia, cardiac conduction disease, and myocardial glycogen storage. The discovery of a link between the cell's fundamental energy sensor, AMPK, and inherited cardiac disease catalyzed intense interest into the biological role of AMPK in the heart. In this chapter, we provide an introduction to the spectrum of human disease resulting from pathogenic variants in PRKAG2, outlining its discovery, clinical genetics, and current perspectives on its pathogenesis and highlighting mechanistic insights derived through the evaluation of disease models. We also present a clinical perspective on the major components of the cardiomyopathy associated with mutations in PRKAG2, together with less commonly described extracardiac features, its prognosis, and principles of management.

Fibrosis-Related Gene Expression in Single Ventricle Heart Disease

OBJECTIVE

To evaluate fibrosis and fibrosis-related gene expression in the myocardium of pediatric subjects with single ventricle with right ventricular failure.

STUDY DESIGN

Real-time quantitative polymerase chain reaction was performed on explanted right ventricular myocardium of pediatric subjects with single ventricle disease and controls with nonfailing heart disease. Subjects were divided into 3 groups: single ventricle failing (right ventricular failure before or after stage I palliation), single ventricle nonfailing (infants listed for primary transplantation with normal right ventricular function), and stage III (Fontan or right ventricular failure after stage III). To evaluate subjects of similar age and right ventricular volume loading, single ventricle disease with failure was compared with single ventricle without failure and stage III was compared with nonfailing right ventricular disease. Histologic fibrosis was assessed in all hearts. Mann-Whitney tests were performed to identify differences in gene expression.

RESULTS

Collagen (Col1α, Col3) expression is decreased in single ventricle congenital heart disease with failure compared with nonfailing single ventricle congenital heart disease (P = .019 and P = .035, respectively), and is equivalent in stage III compared with nonfailing right ventricular heart disease. Tissue inhibitors of metalloproteinase (TIMP-1, TIMP-3, and TIMP-4) are downregulated in stage III compared with nonfailing right ventricular heart disease (P = .0047, P = .013 and P = .013, respectively). Matrix metalloproteinases (MMP-2, MMP-9) are similar between nonfailing single ventricular heart disease and failing single ventricular heart disease, and between stage III heart disease and nonfailing right ventricular heart disease. There is no difference in the prevalence of right ventricular fibrosis by histology in subjects with single ventricular failure heart disease with right ventricular failure (18%) compared with those with normal right ventricular function (38%).

CONCLUSIONS

Fibrosis is not a primary contributor to right ventricular failure in infants and young children with single ventricular heart disease. Additional studies are required to understand whether antifibrotic therapies are beneficial in this population.

Human heart disease: lessons from human pluripotent stem cell-derived cardiomyocytes

Technical advances in generating and phenotyping cardiomyocytes from human pluripotent stem cells (hPSC-CMs) are now driving their wider acceptance as in vitro models to understand human heart disease and discover therapeutic targets that may lead to new compounds for clinical use. Current literature clearly shows that hPSC-CMs recapitulate many molecular, cellular, and functional aspects of human heart pathophysiology and their responses to cardioactive drugs. Here, we provide a comprehensive overview of hPSC-CMs models that have been described to date and highlight their most recent and remarkable contributions to research on cardiovascular diseases and disorders with cardiac traits. We conclude discussing immediate challenges, limitations, and emerging solutions.

Deconvoluting AMP-activated protein kinase (AMPK) adenine nucleotide binding and sensing

AMP-activated protein kinase (AMPK) is a central cellular energy sensor that adapts metabolism and growth to the energy state of the cell. AMPK senses the ratio of adenine nucleotides (adenylate energy charge) by competitive binding of AMP, ADP, and ATP to three sites (CBS1, CBS3, and CBS4) in its γ-subunit. Because these three binding sites are functionally interconnected, it remains unclear how nucleotides bind to individual sites, which nucleotides occupy each site under physiological conditions, and how binding to one site affects binding to the other sites. Here, we comprehensively analyze nucleotide binding to wild-type and mutant AMPK protein complexes by quantitative competition assays and by hydrogen-deuterium exchange MS. We also demonstrate that NADPH, in addition to the known AMPK ligand NADH, directly and competitively binds AMPK at the AMP-sensing CBS3 site. Our findings reveal how AMP binding to one site affects the conformation and adenine nucleotide binding at the other two sites and establish CBS3, and not CBS1, as the high affinity exchangeable AMP/ADP/ATP-binding site. We further show that AMP binding at CBS4 increases AMP binding at CBS3 by 2 orders of magnitude and reverses the AMP/ATP preference of CBS3. Together, these results illustrate how the three CBS sites collaborate to enable highly sensitive detection of cellular energy states to maintain the tight ATP homeostastis required for cellular metabolism.