Mutations in the gamma(2) subunit of AMP-activated protein kinase cause familial hypertrophic cardiomyopathy: evidence for the central role of energy compromise in disease pathogenesis

Altering Calcium Sensitivity in Heart Failure: A Crossroads of Disease Etiology and Therapeutic Innovation

Heart failure (HF) presents a significant clinical challenge, with current treatments mainly easing symptoms without stopping disease progression. The targeting of calcium (Ca2+) regulation is emerging as a key area for innovative HF treatments that could significantly alter disease outcomes and enhance cardiac function. In this review, we aim to explore the implications of altered Ca2+ sensitivity, a key determinant of cardiac muscle force, in HF, including its roles during systole and diastole and its association with different HF types-HF with preserved and reduced ejection fraction (HFpEF and HFrEF, respectively). We further highlight the role of the two rate constants kon (Ca2+ binding to Troponin C) and koff (its dissociation) to fully comprehend how changes in Ca2+ sensitivity impact heart function. Additionally, we examine how increased Ca2+ sensitivity, while boosting systolic function, also presents diastolic risks, potentially leading to arrhythmias and sudden cardiac death. This suggests that strategies aimed at moderating myofilament Ca2+ sensitivity could revolutionize anti-arrhythmic approaches, reshaping the HF treatment landscape. In conclusion, we emphasize the need for precision in therapeutic approaches targeting Ca2+ sensitivity and call for comprehensive research into the complex interactions between Ca2+ regulation, myofilament sensitivity, and their clinical manifestations in HF.

Emerging Signaling Regulation of Sinoatrial Node Dysfunction

PURPOSE OF REVIEW

The sinoatrial node (SAN), the natural pacemaker of the heart, is responsible for generating electrical impulses and initiating each heartbeat. Sinoatrial node dysfunction (SND) causes various arrhythmias such as sinus arrest, SAN block, and tachycardia/bradycardia syndrome. Unraveling the underlying mechanisms of SND is of paramount importance in the pursuit of developing effective therapeutic strategies for patients with SND. This review provides a concise summary of the most recent progress in the signaling regulation of SND.

RECENT FINDINGS

Recent studies indicate that SND can be caused by abnormal intercellular and intracellular signaling, various forms of heart failure (HF), and diabetes. These discoveries provide novel insights into the underlying mechanisms SND, advancing our understanding of its pathogenesis. SND can cause severe cardiac arrhythmias associated with syncope and an increased risk of sudden death. In addition to ion channels, the SAN is susceptible to the influence of various signalings including Hippo, AMP-activated protein kinase (AMPK), mechanical force, and natriuretic peptide receptors. New cellular and molecular mechanisms related to SND are also deciphered in systemic diseases such as HF and diabetes. Progress in these studies contributes to the development of potential therapeutics for SND.

Metabolic Cardiomyopathies and Cardiac Defects in Inherited Disorders of Carbohydrate Metabolism: A Systematic Review

Heart failure (HF) is a progressive chronic disease that remains a primary cause of death worldwide, affecting over 64 million patients. HF can be caused by cardiomyopathies and congenital cardiac defects with monogenic etiology. The number of genes and monogenic disorders linked to development of cardiac defects is constantly growing and includes inherited metabolic disorders (IMDs). Several IMDs affecting various metabolic pathways have been reported presenting cardiomyopathies and cardiac defects. Considering the pivotal role of sugar metabolism in cardiac tissue, including energy production, nucleic acid synthesis and glycosylation, it is not surprising that an increasing number of IMDs linked to carbohydrate metabolism are described with cardiac manifestations. In this systematic review, we offer a comprehensive overview of IMDs linked to carbohydrate metabolism presenting that present with cardiomyopathies, arrhythmogenic disorders and/or structural cardiac defects. We identified 58 IMDs presenting with cardiac complications: 3 defects of sugar/sugar-linked transporters (GLUT3, GLUT10, THTR1); 2 disorders of the pentose phosphate pathway (G6PDH, TALDO); 9 diseases of glycogen metabolism (GAA, GBE1, GDE, GYG1, GYS1, LAMP2, RBCK1, PRKAG2, G6PT1); 29 congenital disorders of glycosylation (ALG3, ALG6, ALG9, ALG12, ATP6V1A, ATP6V1E1, B3GALTL, B3GAT3, COG1, COG7, DOLK, DPM3, FKRP, FKTN, GMPPB, MPDU1, NPL, PGM1, PIGA, PIGL, PIGN, PIGO, PIGT, PIGV, PMM2, POMT1, POMT2, SRD5A3, XYLT2); 15 carbohydrate-linked lysosomal storage diseases (CTSA, GBA1, GLA, GLB1, HEXB, IDUA, IDS, SGSH, NAGLU, HGSNAT, GNS, GALNS, ARSB, GUSB, ARSK). With this systematic review we aim to raise awareness about the cardiac presentations in carbohydrate-linked IMDs and draw attention to carbohydrate-linked pathogenic mechanisms that may underlie cardiac complications.

QT interval instability and QRS interval dispersion in healthy cats and cats with a hypertrophic cardiomyopathy phenotype

OBJECTIVES

Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats. Electrocardiographic (ECG) analysis can help with the diagnosis of HCM and also in the investigation of the secondary consequences of the disease. This study investigated ECG markers of QT interval variability (total instability [TI], short-term instability [STI], long-term instability [LTI], QT variance [QTv]), mean QT interval (QTa) and QT interval corrected for heart rate (QTac), as well as the duration (QRSd) and dispersion (QRSv) of the QRS interval in healthy cats and in those with HCM.

METHODS

Data were collected from 63 domestic cats: 40 in the control group and 23 in the HCM group. Fifty consecutive QT intervals were recorded for all cats and then QTa, QTac, QTv, TI, LTI and STI were calculated. QRSd and QRSv were also obtained for all animals. A Mann-Whitney U-test was used for group comparison. Receiver operating characteristic curves were plotted to evaluate the sensitivity and specificity of all markers for HCM. Logistic regression analysis was performed to assess the risks of cats having HCM, based on the studied indexes.

RESULTS

QTa (P <0.01), QTac (P <0.01), QRSd (P <0.01) and STI (P = 0.02) were higher in the HCM group. QTa >158.8 ms, QTac >27.4 ms and QRSd >0.045 s had an accuracy of 77.4%, 68.2% and 80.9%, respectively, in detecting HCM. Logistic regression showed that cats with QTa >158 ms, QTac >27.4 ms and QRSd >0.045 s had a 1.58-, 1,23- and 6.5-fold higher risk, respectively, of developing HCM.

CONCLUSIONS AND RELEVANCE

Cats with HCM had higher ventricular instability as assessed by STI and showed a prolongation of the QT and QRS intervals via the QTa, QTac and QRSd markers. These markers show potential as ancillary screening tools for identifying the presence of HCM.

Energy sensor AMPK gamma regulates translation via phosphatase PPP6C independent of AMPK alpha

Maintenance of energy level to drive movements and material exchange with the environment is a basic principle of life. AMP-activated protein kinase (AMPK) senses energy level and is a major regulator of cellular energy responses. The gamma subunit of AMPK senses elevated ratio of AMP to ATP and allosterically activates the alpha catalytic subunit to phosphorylate downstream effectors. Here, we report that knockout of AMPKγ, but not AMPKα, suppressed phosphorylation of eukaryotic translation elongation factor 2 (eEF2) induced by energy starvation. We identified PPP6C as an AMPKγ-regulated phosphatase of eEF2. AMP-bound AMPKγ sequesters PPP6C, thereby blocking dephosphorylation of eEF2 and thus inhibiting translation elongation to preserve energy and to promote cell survival. Further phosphoproteomic analysis identified additional targets of PPP6C regulated by energy stress in an AMPKγ-dependent manner. Thus, AMPKγ senses cellular energy availability to regulate not only AMPKα kinase, but also PPP6C phosphatase and possibly other effectors.

Case report: Genomic screening for inherited cardiac conditions in Ecuadorian mestizo relatives: Improving familial diagnose

INTRODUCTION

Genomic screening is an informative and helpful tool for the clinical management of inherited conditions such as cardiac diseases. Cardiac-inherited diseases are a group of disorders affecting the heart, its system, function, and vasculature. Among the cardiac inherited abnormalities, one of the most common is Wolff-Parkinson-White syndrome. Similarly, hypertrophic cardiomyopathy is another common autosomal dominant inherited cardiac disease. Hypertrophic cardiomyopathy is associated with an increased incidence of Wolff-Parkinson-White syndrome; reports have suggested that it could be caused by a mutation in the protein-coding gene PRKAG2, which encodes a subunit of the AMP-activated protein kinase.

CASE PRESENTATION

A 37-year-old Ecuadorian male (Subject A) with familiar history of bradycardia, cardiac pacemaker implantation, and undiagnosed cardiac conditions began with episodes of tachycardia, dizziness, shortness of breath, and a feeling of fainting. He was diagnosed with hypertrophic myocardiopathy and Wolff Parkinson White preexcitation syndrome. Furthermore, his cousin's son, an 18-year-old Ecuadorian male (Subject B), started suffering from migraine and tachycardia at any time of the day. He was diagnosed with hypertrophic myocardiopathy; his electrocardiogram showed a systolic overload. Next-generation sequencing and ancestry analyses were performed. A c.905G>A p.(Arg302Gln) mutation in the gene PRKAG2 and a mainly European composition were identified in both subjects.

CONCLUSION

Genetic testing is a valuable tool as it can provide important information regarding a disease, including its cause and consequences, not only for single individuals but to identify at-risk relatives. Furthermore, NGS results could guide the physician into targeted therapy. In the present case report, a missense pathogenic Arg302Gln mutation in the PRKAG2 gene has been identified in two related Ecuadorian Subjects diagnosed with hypertrophic myocardiopathy and Wolff-Parkinson-White. The variant has not been reported in Latin America; hence, this is the first report of the Arg302Gln mutation in the PRKAG2 gene in mestizo Ecuadorian subjects with mainly European ancestry components.

AMPK and the Challenge of Treating Hypoxic Pulmonary Hypertension

Hypoxic pulmonary hypertension (HPH) is characterized by sustained elevation of pulmonary artery pressure produced by vasoconstriction and hyperproliferative remodeling of the pulmonary artery and subsequent right ventricular hypertrophy (RVH). The search for therapeutic targets for cardiovascular pathophysiology has extended in many directions. However, studies focused on mitigating high-altitude pulmonary hypertension (HAPH) have been rare. Because AMP-activated protein kinase (AMPK) is involved in cardiovascular and metabolic pathology, AMPK is often studied as a potential therapeutic target. AMPK is best characterized as a sensor of cellular energy that can also restore cellular metabolic homeostasis. However, AMPK has been implicated in other pathways with vasculoprotective effects. Notably, cellular metabolic stress increases the intracellular ADP/ATP or AMP/ATP ratio, and AMPK activation restores ATP levels by activating energy-producing catabolic pathways and inhibiting energy-consuming anabolic pathways, such as cell growth and proliferation pathways, promoting cardiovascular protection. Thus, AMPK activation plays an important role in antiproliferative, antihypertrophic and antioxidant pathways in the pulmonary artery in HPH. However, AMPK plays contradictory roles in promoting HPH development. This review describes the main findings related to AMPK participation in HPH and its potential as a therapeutic target. It also extrapolates known AMPK functions to discuss the less-studied HAPH context.

The mechanics of the heart: zooming in on hypertrophic cardiomyopathy and cMyBP-C

Hypertrophic cardiomyopathy (HCM), a disease characterized by cardiac muscle hypertrophy and hypercontractility, is the most frequently inherited disorder of the heart. HCM is mainly caused by variants in genes encoding proteins of the sarcomere, the basic contractile unit of cardiomyocytes. The most frequently mutated among them is MYBPC3, which encodes cardiac myosin-binding protein C (cMyBP-C), a key regulator of sarcomere contraction. In this review, we summarize clinical and genetic aspects of HCM and provide updated information on the function of the healthy and HCM sarcomere, as well as on emerging therapeutic options targeting sarcomere mechanical activity. Building on what is known about cMyBP-C activity, we examine different pathogenicity drivers by which MYBPC3 variants can cause disease, focussing on protein haploinsufficiency as a common pathomechanism also in nontruncating variants. Finally, we discuss recent evidence correlating altered cMyBP-C mechanical properties with HCM development.

Demystifying the Relationship Between Metformin, AMPK, and Doxorubicin Cardiotoxicity

Doxorubicin (DOX) is an extremely effective and wide-spectrum anticancer drug, but its long-term use can lead to heart failure, which presents a serious problem to millions of cancer survivors who have been treated with DOX. Thus, identifying agents that can reduce DOX cardiotoxicity and concurrently enhance its antitumor efficacy would be of great clinical value. In this respect, the classical antidiabetic drug metformin (MET) has stood out, appearing to have both antitumor and cardioprotective properties. MET is proposed to achieve these beneficial effects through the activation of AMP-activated protein kinase (AMPK), an essential regulator of mitochondrial homeostasis and energy metabolism. AMPK itself has been shown to protect the heart and modulate tumor growth under certain conditions. However, the role and mechanism of the hypothesized MET-AMPK axis in DOX cardiotoxicity and antitumor efficacy remain to be firmly established by in vivo studies using tumor-bearing animal models and large-scale prospective clinical trials. This review summarizes currently available literature for or against a role of AMPK in MET-mediated protection against DOX cardiotoxicity. It also highlights the emerging evidence suggesting distinct roles of the AMPK subunit isoforms in mediating the functions of unique AMPK holoenzymes composed of different combinations of isoforms. Moreover, the review provides a perspective regarding future studies that may help fully elucidate the relationship between MET, AMPK and DOX cardiotoxicity.

Effects of Metformin in Heart Failure: From Pathophysiological Rationale to Clinical Evidence

Type 2 diabetes mellitus (T2DM) is a worldwide major health burden and heart failure (HF) is the most common cardiovascular (CV) complication in affected patients. Therefore, identifying the best pharmacological approach for glycemic control, which is also useful to prevent and ameliorate the prognosis of HF, represents a crucial issue. Currently, the choice is between the new drugs sodium/glucose co-transporter 2 inhibitors that have consistently shown in large CV outcome trials (CVOTs) to reduce the risk of HF-related outcomes in T2DM, and metformin, an old medicament that might end up relegated to the background while exerting interesting protective effects on multiple organs among which include heart failure. When compared with other antihyperglycemic medications, metformin has been demonstrated to be safe and to lower morbidity and mortality for HF, even if these results are difficult to interpret as they emerged mainly from observational studies. Meta-analyses of randomized controlled clinical trials have not produced positive results on the risk or clinical course of HF and sadly, large CV outcome trials are lacking. The point of force of metformin with respect to new diabetic drugs is the amount of data from experimental investigations that, for more than twenty years, still continues to provide mechanistic explanations of the several favorable actions in heart failure such as, the improvement of the myocardial energy metabolic status by modulation of glucose and lipid metabolism, the attenuation of oxidative stress and inflammation, and the inhibition of myocardial cell apoptosis, leading to reduced cardiac remodeling and preserved left ventricular function. In the hope that specific large-scale trials will be carried out to definitively establish the metformin benefit in terms of HF failure outcomes, we reviewed the literature in this field, summarizing the available evidence from experimental and clinical studies reporting on effects in heart metabolism, function, and structure, and the prominent pathophysiological mechanisms involved.

Altered Cardiac Energetics and Mitochondrial Dysfunction in Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is a complex disease partly explained by the effects of individual gene variants on sarcomeric protein biomechanics. At the cellular level, HCM mutations most commonly enhance force production, leading to higher energy demands. Despite significant advances in elucidating sarcomeric structure-function relationships, there is still much to be learned about the mechanisms that link altered cardiac energetics to HCM phenotypes. In this work, we test the hypothesis that changes in cardiac energetics represent a common pathophysiologic pathway in HCM.

METHODS

We performed a comprehensive multiomics profile of the molecular (transcripts, metabolites, and complex lipids), ultrastructural, and functional components of HCM energetics using myocardial samples from 27 HCM patients and 13 normal controls (donor hearts).

RESULTS

Integrated omics analysis revealed alterations in a wide array of biochemical pathways with major dysregulation in fatty acid metabolism, reduction of acylcarnitines, and accumulation of free fatty acids. HCM hearts showed evidence of global energetic decompensation manifested by a decrease in high energy phosphate metabolites (ATP, ADP, and phosphocreatine) and a reduction in mitochondrial genes involved in creatine kinase and ATP synthesis. Accompanying these metabolic derangements, electron microscopy showed an increased fraction of severely damaged mitochondria with reduced cristae density, coinciding with reduced citrate synthase activity and mitochondrial oxidative respiration. These mitochondrial abnormalities were associated with elevated reactive oxygen species and reduced antioxidant defenses. However, despite significant mitochondrial injury, HCM hearts failed to upregulate mitophagic clearance.

CONCLUSIONS

Overall, our findings suggest that perturbed metabolic signaling and mitochondrial dysfunction are common pathogenic mechanisms in patients with HCM. These results highlight potential new drug targets for attenuation of the clinical disease through improving metabolic function and reducing mitochondrial injury.

Dietary Nucleotides Alleviate Hepatic Lipid Deposition via Exogenous AMP-Mediated AMPK Activation in Zebrafish

BACKGROUND

Dietary nucleotides (NTs) have been reported to affect hepatic function and composition. However, the effects on hepatic lipid deposition are less studied.

OBJECTIVES

We aimed to identify the regulatory role of dietary NTs in hepatic lipid deposition of zebrafish and elucidate the underlying mechanisms.

METHODS

Zebrafish (60 ± 1.69 mg; 1 mo old) were fed control diet (16.2% energy as fat) or diet supplemented with 0.1% NTs or 0.02% AMP in feeding experiments 1 and 2. Experiment 3 was conducted with zebrafish larvae. In experiment 4, 1-mo-old zebrafish were fed a high-fat diet (HFD, 38.2% energy as fat) or an HFD supplemented with 0.1% NTs or 0.02% AMP. Hepatic lipid deposition was evaluated by triglyceride (TG) content and staining. Phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) was assayed by immunoblotting. Zebrafish liver (ZFL) cells were treated with exogenous adenosine. Small interfering RNA was used to knock down AMPK or nucleoside transporter SLC28a1 in ZFL cells. Vivo-morpholino was used to knock down AMPK in zebrafish larvae.

RESULTS

Dietary 0.1% NTs or 0.02% AMP reduced hepatic TGs by 62% and 32%, respectively, compared with control (P < 0.05). Dietary AMP enhanced hepatic AMPK and ACC phosphorylation. Consistently, exogenous adenosine enhanced AMPK and ACC phosphorylation by 111% and 53%, respectively, in ZFL cells (P < 0.01) and reduced TG content by 56% (P < 0.05). Knockdown of AMPK and SLC28a1 abolished the effect of adenosine on lipid deposition in ZFL cells, and AMPK morpholino blocked the hepatic lipid-lowering effect of dietary AMP in vivo. Finally, dietary NTs and AMP activated AMPK and attenuated hepatic lipid deposition (28% and 30%, P < 0.05) in fish fed an HFD.

CONCLUSIONS

Dietary NTs and AMP reduce hepatic lipid deposition in zebrafish, which involves exogenous AMP-mediated AMPK activation. Our results suggest that dietary NTs can contribute to alleviation of hepatic steatosis.

Dynamic Regulation of Cysteine Oxidation and Phosphorylation in Myocardial Ischemia-Reperfusion Injury

Myocardial ischemia-reperfusion (I/R) injury significantly alters heart function following infarct and increases the risk of heart failure. Many studies have sought to preserve irreplaceable myocardium, termed cardioprotection, but few, if any, treatments have yielded a substantial reduction in clinical I/R injury. More research is needed to fully understand the molecular pathways that govern cardioprotection. Redox mechanisms, specifically cysteine oxidations, are acute and key regulators of molecular signaling cascades mediated by kinases. Here, we review the role of reactive oxygen species in modifying cysteine residues and how these modifications affect kinase function to impact cardioprotection. This exciting area of research may provide novel insight into mechanisms and likely lead to new treatments for I/R injury.

Genetic basis and molecular biology of cardiac arrhythmias in cardiomyopathies

Cardiac arrhythmias are common, often the first, and sometimes the life-threatening manifestations of hereditary cardiomyopathies. Pathogenic variants in several genes known to cause hereditary cardiac arrhythmias have also been identified in the sporadic cases and small families with cardiomyopathies. These findings suggest a shared genetic aetiology of a subset of hereditary cardiomyopathies and cardiac arrhythmias. The concept of a shared genetic aetiology is in accord with the complex and exquisite interplays that exist between the ion currents and cardiac mechanical function. However, neither the causal role of cardiac arrhythmias genes in cardiomyopathies is well established nor the causal role of cardiomyopathy genes in arrhythmias. On the contrary, secondary changes in ion currents, such as post-translational modifications, are common and contributors to the pathogenesis of arrhythmias in cardiomyopathies through altering biophysical and functional properties of the ion channels. Moreover, structural changes, such as cardiac hypertrophy, dilatation, and fibrosis provide a pro-arrhythmic substrate in hereditary cardiomyopathies. Genetic basis and molecular biology of cardiac arrhythmias in hereditary cardiomyopathies are discussed.

Glycogen storage cardiomyopathy (PRKAG2): diagnostic findings of standard and advanced echocardiography techniques

AIMS

Describe the findings obtained using standard echocardiography (Echo) and deformation indices (2D and 3D speckle tracking strain) in patients (Pts) with PRKAG2 cardiomyopathy. Seek to identify any peculiar characteristics and possible strain patterns that may distinguish this condition from other causes of left ventricular hypertrophy (LVH).

METHODS AND RESULTS

Thirty Pts with genetically proven PRKAG2 (R302Q and H401Q), 16 (53.3%) male, mean age 39.1± 15.4 years old, were examined using standard, speckle tracking (STE), and 3D Echo. Pacemaker (PM) had been implanted in 12 (40%) Pts with a mean age of 38.1 ± 13 years. Hypertrophy was found in varying degrees in 18 (86%) Pts. Seven Pts (24%) presented 3D ejection fraction (EF) below normal limits. Diastolic function was abnormal in 17 (63%) Pts. Global longitudinal strain (GLS) on 2D measured -16.4% ± 5.3%. GLS measured -13.2% ± 4.8%, global radial strain 40.8% ± 13.8%, global circumferential strain (GCS) -16.1% ± 4.4%, and global area strain -26.1% ± 6.7% by 3D Echo offline analyses. Pts with PM presented lower EF and GCS compared with those without PM. EF/GLS measured 3.65 ± 1.00. In the bull's eye map, a strain pattern similar to stripes in 18 (60%) Pts was identified, which might be a differentiating signal among LVH.

CONCLUSION

Echocardiography is a valuable tool in detecting diffuse and focal myocardial abnormalities in PRKAG2 cardiomyopathy. The deformation indices are especially revealing because they may help distinguish this rare infiltrative disease, thereby favouring early diagnosis, enhanced treatment, and improved outcome.

Genetics of Cardiomyopathy: Clinical and Mechanistic Implications for Heart Failure

Genetic cardiomyopathies are an important cause of sudden cardiac death across all age groups. Genetic testing in heart failure clinics is useful for family screening and providing individual prognostic insight. Obtaining a family history of at least three generations, including the creation of a pedigree, is recommended for all patients with primary cardiomyopathy. Additionally, when appropriate, consultation with a genetic counsellor can aid in the success of a genetic evaluation. Clinical screening should be performed on all first-degree relatives of patients with genetic cardiomyopathy.

Genetics has played an important role in the understanding of different cardiomyopathies, and the field of heart failure (HF) genetics is progressing rapidly. Much research has also focused on distinguishing markers of risk in patients with cardiomyopathy using genetic testing. While these efforts currently remain incomplete, new genomic technologies and analytical strategies provide promising opportunities to further explore the genetic architecture of cardiomyopathies, afford insight into the early manifestations of cardiomyopathy, and help define the molecular pathophysiological basis for cardiac remodeling. Cardiovascular physicians should be fully aware of the utility and potential pitfalls of incorporating genetic test results into pre-emptive treatment strategies for patients in the preliminary stages of HF. Future work will need to be directed towards elucidating the biological mechanisms of both rare and common gene variants and environmental determinants of plasticity in the genotype-phenotype relationship. This future research should aim to further our ability to identify, diagnose, and treat disorders that cause HF and sudden cardiac death in young patients, as well as prioritize improving our ability to stratify the risk for these patients prior to the onset of the more severe consequences of their disease.

PRKAG2 Gene Expression Is Elevated and its Protein Levels Are Associated with Increased Amyloid-β Accumulation in the Alzheimer's Disease Brain

Increased amyloid-β (Aβ) accumulation associated with abnormal autophagy-lysosomal activity and nutrient kinase dysregulation are common features in Alzheimer’s disease (AD) brain. Recent studies have identified PRKAG2 and TIPRL genes that control nutrient kinase regulated autophagy, and here we determined if their expression is altered in postmortem AD brains. Gene and protein expression of TIPRL were unchanged. However, gene expression of PRKAG2 was increased 3-fold and its protein levels positively correlated with Aβ accumulation in the AD brain. In summary, our findings suggest that increased PRKAG2 is an important contributing factor to Aβ accumulation in the AD brain.

Hypertrophic Cardiomyopathy and Primary Restrictive Cardiomyopathy: Similarities, Differences and Phenocopies

Hypertrophic cardiomyopathy (HCM) and primary restrictive cardiomyopathy (RCM) have a similar genetic background as they are both caused mainly by variants in sarcomeric genes. These “sarcomeric cardiomyopathies” also share diastolic dysfunction as the prevalent pathophysiological mechanism. Starting from the observation that patients with HCM and primary RCM may coexist in the same family, a characteristic pathophysiological profile of HCM with restrictive physiology has been recently described and supports the hypothesis that familiar forms of primary RCM may represent a part of the phenotypic spectrum of HCM rather than a different genetic cardiomyopathy. To further complicate this scenario some infiltrative (amyloidosis) and storage diseases (Fabry disease and glycogen storage diseases) may show either a hypertrophic or restrictive phenotype according to left ventricular wall thickness and filling pattern. Establishing a correct etiological diagnosis among HCM, primary RCM, and hypertrophic or restrictive phenocopies is of paramount importance for cascade family screening and therapy.

AMPK, metabolism, and vascular function

Adenosine monophosphate-activated protein kinase (AMPK) is a cellular energy sensor activated during energy stress that plays a key role in maintaining energy homeostasis. This ubiquitous signaling pathway has been implicated in multiple functions including mitochondrial biogenesis, redox regulation, cell growth and proliferation, cell autophagy and inflammation. The protective role of AMPK in cardiovascular function and the involvement of dysfunctional AMPK in the pathogenesis of cardiovascular disease have been highlighted in recent years. In this review, we summarize and discuss the role of AMPK in the regulation of blood flow in response to metabolic demand and the basis of the AMPK physiological anticontractile, antioxidant, anti-inflammatory, and antiatherogenic actions in the vascular system. Investigations by others and us have demonstrated the key role of vascular AMPK in the regulation of endothelial function, redox homeostasis, and inflammation, in addition to its protective role in the hypoxia and ischemia/reperfusion injury. The pathophysiological implications of AMPK involvement in vascular function with regard to the vascular complications of metabolic disease and the therapeutic potential of AMPK activators are also discussed.

Genome editing in cardiovascular diseases

Genetic modification at the molecular level in somatic cells, germline, and animal models requires for different purposes, such as introducing desired mutation, deletion of alleles, and insertion of novel genes in the genome. Various genome-editing tools are available to accomplish these alterations, such as zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated (Cas) system. CRISPR-Cas system is an emerging technology, which is being used in biological and medical sciences, including in the cardiovascular field. It assists to identify the mechanism of various cardiovascular disease occurrence, such as hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), and arrhythmogenic cardiomyopathy (ACM). Furthermore, it has been advantages to edit various genes simultaneously and can also be used to treat and prevent several human diseases. This chapter explores the use of the scientific and therapeutic potential of a CRISPR-Cas system to edit the various cardiovascular disease-associated genes to understand the pathways involved in disease progression and treatment.

Cardiometabolism as an Interlocking Puzzle between the Healthy and Diseased Heart: New Frontiers in Therapeutic Applications

Cardiac metabolism represents a crucial and essential connecting bridge between the healthy and diseased heart. The cardiac muscle, which may be considered an omnivore organ with regard to the energy substrate utilization, under physiological conditions mainly draws energy by fatty acids oxidation. Within cardiomyocytes and their mitochondria, through well-concerted enzymatic reactions, substrates converge on the production of ATP, the basic chemical energy that cardiac muscle converts into mechanical energy, i.e., contraction. When a perturbation of homeostasis occurs, such as an ischemic event, the heart is forced to switch its fatty acid-based metabolism to the carbohydrate utilization as a protective mechanism that allows the maintenance of its key role within the whole organism. Consequently, the flexibility of the cardiac metabolic networks deeply influences the ability of the heart to respond, by adapting to pathophysiological changes. The aim of the present review is to summarize the main metabolic changes detectable in the heart under acute and chronic cardiac pathologies, analyzing possible therapeutic targets to be used. On this basis, cardiometabolism can be described as a crucial mechanism in keeping the physiological structure and function of the heart; furthermore, it can be considered a promising goal for future pharmacological agents able to appropriately modulate the rate-limiting steps of heart metabolic pathways.

Post-Translational Modifications of the Energy Guardian AMP-Activated Protein Kinase

Physical exercise elicits physiological metabolic perturbations such as energetic and oxidative stress; however, a diverse range of cellular processes are stimulated in response to combat these challenges and maintain cellular energy homeostasis. AMP-activated protein kinase (AMPK) is a highly conserved enzyme that acts as a metabolic fuel sensor and is central to this adaptive response to exercise. The complexity of AMPK’s role in modulating a range of cellular signalling cascades is well documented, yet aside from its well-characterised regulation by activation loop phosphorylation, AMPK is further subject to a multitude of additional regulatory stimuli. Therefore, in this review we comprehensively outline current knowledge around the post-translational modifications of AMPK, including novel phosphorylation sites, as well as underappreciated roles for ubiquitination, sumoylation, acetylation, methylation and oxidation. We provide insight into the physiological ramifications of these AMPK modifications, which not only affect its activity, but also subcellular localisation, nutrient interactions and protein stability. Lastly, we highlight the current knowledge gaps in this area of AMPK research and provide perspectives on how the field can apply greater rigour to the characterisation of novel AMPK regulatory modifications.

Prenatal detection of distal 1q21.1q21.2 microduplication with abnormal ultrasound findings: Two cases report and literature review

RATIONALE

1q21.1 duplication is an uncommon chromosomal submicroscopic imbalance which is associated with growth/mental retardation, dysmorphic features, autism, multiple congenital and neuropsychiatric disorders.

PATIENT CONCERNS

Two pregnant women underwent amniocentesis for cytogenetic analysis and chromosomal microarray analysis (CMA) following abnormal ultrasound findings. Case 1 presented short nasal bone and case 2 showed absent nasal bone, ventricular septal defect and umbilical cord circling in ultrasonic examination.

DIAGNOSES

G-banding analysis showed that the two fetuses presented normal karyotypic results while CMA detected 1.796 Mb (case 1) and 1.242 Mb (case 2) microduplications in the region of 1q21.1q21.2 separately. Furthermore, the CMA also revealed a 1.2 Mb microdeletion of 8p23.3 in case 1.

INTERVENTIONS

The couple in case 1 chose to terminate the pregnancy, while the couple in case 2 continued the pregnancy and finally delivered a male infant who presented low nasal bridge and ventricular septal defect.

OUTCOMES

The 1q21.1q21.2 duplications in our report were located in the distal 1q21.1 region, overlapping with 1q21.1 duplication syndrome. Case 2 was the first reported live birth with 1q21.1 duplication according to prenatal CMA detection in China.

LESSONS

The genotype-phenotype of 1q21.1 duplication is complicated due to the phenotypic diversity, incomplete penetrance, and lack of obvious characteristics. So it is difficult to predict the postnatal development and health conditions clinically. Hence, long term follow up is necessary for newborn infants with 1q21.1 duplication, irrespective of whether the duplication is de novo or inherited.

Phenotypic expression and clinical outcomes in a South Asian PRKAG2 cardiomyopathy cohort

The PRKAG2 syndrome is a rare autosomal dominant phenocopy of sarcomeric hypertrophic cardiomyopathy (HCM), characterized by ventricular pre-excitation, progressive conduction system disease and left ventricular hypertrophy. This study describes the phenotype, genotype and clinical outcomes of a South-Asian PRKAG2 cardiomyopathy cohort over a 7-year period. Clinical, electrocardiographic, echocardiographic, and cardiac MRI data from 22 individuals with PRKAG2 variants (68% men; mean age 39.5 ± 18.1 years), identified at our HCM centre were studied prospectively. At initial evaluation, all of the patients were in NYHA functional class I or II. The maximum left ventricular wall thickness was 22.9 ± 8.7 mm and left ventricular ejection fraction was 53.4 ± 6.6%. Left ventricular hypertrophy was present in 19 individuals (86%) at baseline. 17 patients had an WPW pattern (77%). After a mean follow-up period of 7 years, 2 patients had undergone accessory pathway ablation, 8 patients (36%) underwent permanent pacemaker implantation (atrio-ventricular blocks-5; sinus node disease-2), 3 patients developed atrial fibrillation, 11 patients (50%) developed progressive worsening in NYHA functional class, and 6 patients (27%) experienced sudden cardiac death or equivalent. PRKAG2 cardiomyopathy must be considered in patients with HCM and progressive conduction system disease.

Exercise adaptations: molecular mechanisms and potential targets for therapeutic benefit

Exercise is fundamental for good health, whereas physical inactivity underpins many chronic diseases of modern society. It is well appreciated that regular exercise improves metabolism and the metabolic phenotype in a number of tissues. The phenotypic alterations observed in skeletal muscle are partly mediated by transcriptional responses that occur following each individual bout of exercise. This adaptive response increases oxidative capacity and influences the function of myokines and extracellular vesicles that signal to other tissues. Our understanding of the epigenetic and transcriptional mechanisms that mediate the skeletal muscle gene expression response to exercise as well as of their upstream signalling pathways has advanced substantially in the past 10 years. With this knowledge also comes the opportunity to design new therapeutic strategies based on the biology of exercise for a variety of chronic conditions where regular exercise might be a challenge. This Review provides an overview of the beneficial adaptive responses to exercise and details the molecular mechanisms involved. The possibility of designing therapeutic interventions based on these molecular mechanisms is addressed, using relevant examples that have exploited this approach.

Genome-wide association study identifies new loci for albuminuria in the Japanese population

BACKGROUND

Urinary albumin excretion (UAE) is a risk factor for cardiovascular diseases, metabolic syndrome, chronic kidney disease, etc. Only a few genome-wide association studies (GWAS) for UAE have been conducted in the European population, but not in the Asian population. Here we conducted GWAS and identified several candidate genes harboring single nucleotide polymorphisms (SNPs) responsible for UAE in the Japanese population.

METHODS

We conducted GWAS for UAE in 7805 individuals of Asian ancestry from health-survey data collected by Tohoku Medical Megabank Organization (ToMMo) and Iwate Tohoku Medical Megabank Organization (IMM). The SNP genotype data were obtained with a SNP microarray. After imputation using a haplotype panel consisting of 2000 genome sequencing, 4,962,728 SNP markers were used for the GWAS.

RESULTS

Eighteen SNPs at 14 loci (GRM7, EXOC1/NMU, LPA, STEAP1B/RAPGEF5, SEMA3D, PRKAG2, TRIQK, SERTM1, TPT1-AS1, OR5AU1, TSHR, FMN1/RYR3, COPRS, and BRD1) were associated with UAE in the Japanese individuals. A locus with particularly strong associations was observed on TSHR, chromosome 14 [rs116622332 (p = 3.99 × 10^-10)].

CONCLUSION

In this study, we successfully identified UAE-associated variant loci in the Japanese population. Further study is required to confirm this association.

Clinical Features and Natural History of PRKAG2 Variant Cardiac Glycogenosis

BACKGROUND

PRKAG2 gene variants cause a syndrome characterized by cardiomyopathy, conduction disease, and ventricular pre-excitation. Only a small number of cases have been reported to date, and the natural history of the disease is poorly understood.

OBJECTIVES

The aim of this study was to describe phenotype and natural history of PRKAG2 variants in a large multicenter European cohort.

METHODS

Clinical, electrocardiographic, and echocardiographic data from 90 subjects with PRKAG2 variants (53% men; median age 33 years; interquartile range [IQR]: 15 to 50 years) recruited from 27 centers were retrospectively studied.

RESULTS

At first evaluation, 93% of patients were in New York Heart Association functional class I or II. Maximum left ventricular wall thickness was 18 ± 8 mm, and left ventricular ejection fraction was 61 ± 12%. Left ventricular hypertrophy (LVH) was present in 60 subjects (67%) at baseline. Thirty patients (33%) had ventricular pre-excitation or had undergone accessory pathway ablation; 17 (19%) had pacemakers (median age at implantation 36 years; IQR: 27 to 46 years), and 16 (18%) had atrial fibrillation (median age 43 years; IQR: 31 to 54 years). After a median follow-up period of 6 years (IQR: 2.3 to 13.9 years), 71% of subjects had LVH, 29% had AF, 21% required de novo pacemakers (median age at implantation 37 years; IQR: 29 to 48 years), 14% required admission for heart failure, 8% experienced sudden cardiac death or equivalent, 4% required heart transplantation, and 13% died.

CONCLUSIONS

PRKAG2 syndrome is a progressive cardiomyopathy characterized by high rates of atrial fibrillation, conduction disease, advanced heart failure, and life-threatening arrhythmias. Classical features of pre-excitation and severe LVH are not uniformly present, and diagnosis should be considered in patients with LVH who develop atrial fibrillation or require permanent pacemakers at a young age.

Wolff-Parkinson-White syndrome: De novo variants and evidence for mutational burden in genes associated with atrial fibrillation

BACKGROUND

Wolff-Parkinson-White (WPW) syndrome is a relatively common arrhythmia affecting ~1-3/1,000 individuals. Mutations in PRKAG2 have been described in rare patients in association with cardiomyopathy. However, the genetic basis of WPW in individuals with a structurally normal heart remains poorly understood. Sudden death due to atrial fibrillation (AF) can also occur in these individuals. Several studies have indicated that despite ablation of an accessory pathway, the risk of AF remains high in patients compared to general population.

METHODS

We applied exome sequencing in 305 subjects, including 65 trios, 80 singletons, and 6 multiple affected families. We used de novo analysis, candidate gene approach, and burden testing to explore the genetic contributions to WPW.

RESULTS

A heterozygous deleterious variant in PRKAG2 was identified in one subject, accounting for 0.6% (1/151) of the genetic basis of WPW in this study. Another individual with WPW and left ventricular hypertrophy carried a known pathogenic variant in MYH7. We found rare de novo variants in genes associated with arrhythmia and cardiomyopathy (ANK2, NEBL, PITX2, and PRDM16) in this cohort. There was an increased burden of rare deleterious variants (MAF ≤ 0.005) with CADD score ≥ 25 in genes linked to AF in cases compared to controls (P = .0023).

CONCLUSIONS

Our findings show an increased burden of rare deleterious variants in genes linked to AF in WPW syndrome, suggesting that genetic factors that determine the development of accessory pathways may be linked to an increased susceptibility of atrial muscle to AF in a subset of patients.

Mutations of the gene FNIP1 associated with a syndromic autosomal recessive immunodeficiency with cardiomyopathy and pre-excitation syndrome

AMPK (adenosine monophosphate-activated protein kinase) is phosphorylated (AMPK-P) in response to low energy through allosteric activation by Adenosine mono- or diphosphate (AMP/ADP). Folliculin (FLCN) and the FLCN-interacting proteins 1 and 2 (FNIP1, 2) modulate AMPK. FNIP1 deficiency patients have a AMPK-P gain of function phenotype with hypertrophic cardiomyopathy, Wolff-Parkinson-White pre-excitation syndrome, myopathy of skeletal muscles and combined immunodeficiency.

Genetic Liver-Specific AMPK Activation Protects against Diet-Induced Obesity and NAFLD

The AMP-activated protein kinase (AMPK) is a highly conserved master regulator of metabolism, whose activation has been proposed to be therapeutically beneficial for the treatment of several metabolic diseases, including nonalcoholic fatty liver disease (NAFLD). NAFLD, characterized by excessive accumulation of hepatic lipids, is the most common chronic liver disease and a major risk factor for development of nonalcoholic steatohepatitis, type 2 diabetes, and other metabolic conditions. To assess the therapeutic potential of AMPK activation, we have generated a genetically engineered mouse model, termed iAMPK^CA, where AMPK can be inducibly activated in vivo in mice in a spatially and temporally restricted manner. Using this model, we show that liver-specific AMPK activation reprograms lipid metabolism, reduces liver steatosis, decreases expression of inflammation and fibrosis genes, and leads to significant therapeutic benefits in the context of diet-induced obesity. These findings further support AMPK as a target for the prevention and treatment of NAFLD.

Garcia et al. present a GEMM, the “iAMPK^CA” mouse, where AMPK is inducibly activated in vivo in a tissue-specific and temporal on and off nature. Liver-specific AMPK activation in these mice protects from diet-induced obesity and reduces liver steatosis, inflammation, and fibrosis. These data further support AMPK as a therapeutic target for NAFLD.

Associations between high blood pressure and DNA methylation

Background

High blood pressure is a major risk factor for cardiovascular disease and is influenced by both environmental and genetic factors. Epigenetic processes including DNA methylation potentially mediate the relationship between genetic factors, the environment and cardiovascular disease. Despite an increased risk of hypertension and cardiovascular disease in individuals of South Asians compared to Europeans, it is not clear whether associations between blood pressure and DNA methylation differ between these groups.

Methods

We performed an epigenome-wide association study and differentially methylated region (DMR) analysis to identify DNA methylation sites and regions that were associated with systolic blood pressure, diastolic blood pressure and hypertension. We analyzed samples from 364 European and 348 South Asian men (first generation migrants to the UK) from the Southall And Brent REvisited cohort, measuring DNA methylation from blood using the Illumina Infinium^® HumanMethylation450 BeadChip.

Results

One CpG site was found to be associated with DBP in trans-ancestry analyses (i.e. both ethnic groups combined), while in Europeans alone seven CpG sites were associated with DBP. No associations were identified between DNA methylation and either SBP or hypertension. Comparison of effect sizes between South Asian and European EWAS for DBP, SBP and hypertension revealed little concordance between analyses. DMR analysis identified several regions with known relationships with CVD and its risk factors.

Conclusion

This study identified differentially methylated sites and regions associated with blood pressure and revealed ethnic differences in these associations. These findings may point to molecular pathways which may explain the elevated cardiovascular disease risk experienced by those of South Asian ancestry when compared to Europeans.

Metabolic Alterations in Inherited Cardiomyopathies

The normal function of the heart relies on a series of complex metabolic processes orchestrating the proper generation and use of energy. In this context, mitochondria serve a crucial role as a platform for energy transduction by supplying ATP to the varying demand of cardiomyocytes, involving an intricate network of pathways regulating the metabolic flux of substrates. The failure of these processes results in structural and functional deficiencies of the cardiac muscle, including inherited cardiomyopathies. These genetic diseases are characterized by cardiac structural and functional anomalies in the absence of abnormal conditions that can explain the observed myocardial abnormality, and are frequently associated with heart failure. Since their original description, major advances have been achieved in the genetic and phenotype knowledge, highlighting the involvement of metabolic abnormalities in their pathogenesis. This review provides a brief overview of the role of mitochondria in the energy metabolism in the heart and focuses on metabolic abnormalities, mitochondrial dysfunction, and storage diseases associated with inherited cardiomyopathies.

Human Induced Pluripotent Stem-Cell-Derived Cardiomyocytes as Models for Genetic Cardiomyopathies

In the last few decades, many pathogenic or likely pathogenic genetic mutations in over hundred different genes have been described for non-ischemic, genetic cardiomyopathies. However, the functional knowledge about most of these mutations is still limited because the generation of adequate animal models is time-consuming and challenging. Therefore, human induced pluripotent stem cells (iPSCs) carrying specific cardiomyopathy-associated mutations are a promising alternative. Since the original discovery that pluripotency can be artificially induced by the expression of different transcription factors, various patient-specific-induced pluripotent stem cell lines have been generated to model non-ischemic, genetic cardiomyopathies in vitro. In this review, we describe the genetic landscape of non-ischemic, genetic cardiomyopathies and give an overview about different human iPSC lines, which have been developed for the disease modeling of inherited cardiomyopathies. We summarize different methods and protocols for the general differentiation of human iPSCs into cardiomyocytes. In addition, we describe methods and technologies to investigate functionally human iPSC-derived cardiomyocytes. Furthermore, we summarize novel genome editing approaches for the genetic manipulation of human iPSCs. This review provides an overview about the genetic landscape of inherited cardiomyopathies with a focus on iPSC technology, which might be of interest for clinicians and basic scientists interested in genetic cardiomyopathies.

A Case Series on Cardiac and Skeletal Involvement in Two Families with PRKAG2 Mutations

Background

PRKAG2 is a rare autosomal dominant syndrome that mainly presents with hypertrophic cardiomyopathy, ventricular preexcitation, and conduction abnormalities. This case report demonstrates that the PRKAG2 mutation presents with various phenotypes already in pediatric patients.

Case Summary

We describe the clinical and investigative findings in two families with a PRKAG2 mutation from the different variants in the gene on chromosome 7q36.1, emphasising that the variability of phenotypes and that presentation in childhood is common. Furthermore, we highlight that skeletal myopathy and hypertrophic cardiomyopathy are significant debilitating characteristics of the PRKAG2 mutation.

Conclusion

In our report of adult and pediatric patients, early presentation in childhood with hypertrophic cardiomyopathy and skeletal muscle involvement was common, demonstrating the challenges of the clinical management of PRKAG2 mutations.

Epigenome-Wide Association Study (EWAS) of Blood Lipids in Healthy Population from STANISLAS Family Study (SFS)

Epigenome-Wide Association Studies (EWAS) are furthering our knowledge of epigenetic modifications involved in the regulation of lipids’ metabolism. Furthermore, epigenetic patterns associated with lipid levels may play an important role in predicting the occurrence of cardiovascular events. To further investigate the relationship between methylation status and lipids, we performed an EWAS in 211 individuals from the STANISLAS Family study (SFS). Methylation at two CpG sites (PRKAG2; p = 1.39 × 10⁻⁸; KREMEN2; p = 5.75 × 10⁻⁹) were significantly associated with lipidomic profiles. Replication was sought in adipose tissue where one probe, cg08897188, was found to be nominally significant (KREMEN2; p = 0.0196). These results could provide new insight in the mechanisms underlying cardiovascular diseases and contribute to new therapeutic interventions.

Infantile Onset Hypertrophic Cardiomyopathy Secondary to PRKAG2 Gene Mutation is Associated with Poor Prognosis

Hypertrophic cardiomyopathy (HCM) is the second most prevalent form of cardiomyopathy in children. The etiology of the HCM is heterogeneous, so is the age of onset of symptoms. The HCM associated with metabolic disorders and genetic syndromes presents early in childhood. There are very few case reports of early-onset infantile HCM secondary to the PRKAG2 gene. Here, we report a case of HCM in a neonate diagnosed prenatally and eventually diagnosed with a missense mutation in the PRKAG2 gene.

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.

Translating emerging molecular genetic insights into clinical practice in inherited cardiomyopathies

Cardiomyopathies are primarily genetic disorders of the myocardium associated with higher risk of life-threatening cardiac arrhythmias, heart failure, and sudden cardiac death. The evolving knowledge in genomic medicine during the last decade has reshaped our understanding of cardiomyopathies as diseases of multifactorial nature and complex pathophysiology. Genetic testing in cardiomyopathies has subsequently grown from primarily a research tool into an essential clinical evaluation piece with important clinical implications for patients and their families. The purpose of this review is to provide with a contemporary insight into the implications of genetic testing in diagnosis, therapy, and prognosis of patients with inherited cardiomyopathies. Here, we summarize the contemporary knowledge on genotype-phenotype correlations in inherited cardiomyopathies and highlight the recent significant achievements in the field of translational cardiovascular genetics.

Emerging pharmacologic and structural therapies for hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is the most common inherited heart disease. Although it was first described over 50 years ago, there has been little in the way of novel disease-specific therapeutic development for these patients. Current treatment practice largely aims at symptomatic control using old drugs made for other diseases and does little to modify the disease course. Septal reduction by surgical myectomy or percutaneous alcohol septal ablation are well-established treatments for pharmacologic-refractory left ventricular outflow tract obstruction in hypertrophic cardiomyopathy patients. In recent years, there has been a relative surge in the development of innovative therapeutics, which aim to target the complex molecular pathophysiology and resulting hemodynamics that underlie hypertrophic cardiomyopathy. Herein, we review the new and emerging therapeutics for hypertrophic cardiomyopathy, which include pharmacologic attenuation of sarcomeric calcium sensitivity, allosteric inhibition of cardiac myosin, myocardial metabolic modulation, and renin-angiotensin-aldosterone system inhibition, as well as structural intervention by percutaneous mitral valve plication and endocardial radiofrequency ablation of septal hypertrophy. In conclusion, while further development of these therapeutic strategies is ongoing, they each mark a significant and promising advancement in treatment for hypertrophic cardiomyopathy patients.

Genome Editing and Induced Pluripotent Stem Cell Technologies for Personalized Study of Cardiovascular Diseases

PURPOSE OF REVIEW

The goal of this review is to highlight the potential of induced pluripotent stem cell (iPSC)-based modeling as a tool for studying human cardiovascular diseases. We present some of the current cardiovascular disease models utilizing genome editing and patient-derived iPSCs.

RECENT FINDINGS

The incorporation of genome-editing and iPSC technologies provides an innovative research platform, providing novel insight into human cardiovascular disease at molecular, cellular, and functional level. In addition, genome editing in diseased iPSC lines holds potential for personalized regenerative therapies. The study of human cardiovascular disease has been revolutionized by cellular reprogramming and genome editing discoveries. These exceptional technologies provide an opportunity to generate human cell cardiovascular disease models and enable therapeutic strategy development in a dish. We anticipate these technologies to improve our understanding of cardiovascular disease pathophysiology leading to optimal treatment for heart diseases in the future.

Allele-specific differences in transcriptome, miRNome, and mitochondrial function in two hypertrophic cardiomyopathy mouse models

Hypertrophic cardiomyopathy (HCM) stems from mutations in sarcomeric proteins that elicit distinct biophysical sequelae, which in turn may yield radically different intracellular signaling and molecular pathologic profiles. These signaling events remain largely unaddressed by clinical trials that have selected patients based on clinical HCM diagnosis, irrespective of genotype. In this study, we determined how two mouse models of HCM differ, with respect to cellular/mitochondrial function and molecular biosignatures, at an early stage of disease. We show that hearts from young R92W-TnT and R403Q-αMyHC mutation-bearing mice differ in their transcriptome, miRNome, intracellular redox environment, mitochondrial antioxidant defense mechanisms, and susceptibility to mitochondrial permeability transition pore opening. Pathway analysis of mRNA-sequencing data and microRNA profiles indicate that R92W-TnT mutants exhibit a biosignature consistent with activation of profibrotic TGF-β signaling. Our results suggest that the oxidative environment and mitochondrial impairment in young R92W-TnT mice promote activation of TGF-β signaling that foreshadows a pernicious phenotype in young individuals. Of the two mutations, R92W-TnT is more likely to benefit from anti-TGF-β signaling effects conferred by angiotensin receptor blockers and may be responsive to mitochondrial antioxidant strategies in the early stage of disease. Molecular and functional profiling may therefore serve as aids to guide precision therapy for HCM.

The C2'- and C3'-endo equilibrium for AMP molecules bound in the cystathionine-beta-synthase domain

The equilibrium between C2'- and C3'-endo conformations of nucleotides in solution, as well as their polymers DNA and RNA, has been well studied in previous work. However, this equilibrium of nucleotides in their binding state remains unclear. We observed two AMP molecules, in C3'- and C2'-endo conformations respectively, simultaneously bound to a cystathionine-beta-synthase (CBS) domain dimer of the magnesium and cobalt efflux protein CorC in the crystallographic study. The C2'-endo AMP molecule assumes the higher sugar pucker energy and one more hydrogen bond with the protein than the C3'-endo molecule does. The balance between the high sugar pucker energy and the low binding energy suggests an equilibrium or switch between C2'- and C3'-endo conformations of the bound nucleotides. Our work challenge the previous hypothesis that the ribose of the bound nucleotides would be locked in a fixed conformation.

Promise and challenges for direct small molecule AMPK activators

AMP-activated protein kinase (AMPK) is an evolutionary conserved and ubiquitously expressed serine/threonine kinase playing a central role in the coordination of energy homeostasis. Based on the beneficial outcomes of its activation on metabolism, AMPK has emerged as an attractive target for the treatment of metabolic diseases. Identification of novel downstream targets of AMPK beyond the regulation of energy metabolism has renewed considerable attention in exploiting AMPK signaling for novel therapeutic targeting strategies including treatment of cancer and inflammatory diseases. The complexity of AMPK system with tissue- and species-specific expression of multiple isoform combination regulated by various inputs, post-traductional modifications and subcellular locations presents unique challenges for drug discovery. Here, we review the most recent advances in the understanding of the mechanism(s) of action of direct small molecule AMPK activators and the potential therapeutic opportunities.

Heterogeneity in a large pedigree with Danon disease: Implications for pathogenesis and management

BACKGROUND

Danon disease is an X-linked disturbance of autophagy manifesting with cognitive impairment and disordered heart and skeletal muscle. After a period of relative stability, patients deteriorate rapidly and may quickly become ineligible for elective heart transplantation - the only life-saving therapy.

METHODS

We report a large pedigree with diverse manifestations of Danon disease in hemizygotes and female heterozygotes.

RESULTS

Malignant cardiac arrhythmias requiring amiodarone treatment induced thyroid disease in two patients; intractable thyrotoxicosis, which enhances autophagy, caused the death of a 21year-old man. Our patients also had striking elevation of serum troponin I during the accelerated phase of their illness (p<0.01) and rising concentrations heralded cardiac decompensation. We argue for changes to cardiac transplantation eligibility criteria.

CONCLUSION

Danon disease causes hypertrophic cardiomyopathy - here we propose a common pathophysiological basis for the metabolic and structural effects of this descriptive class of heart disorders. We also contend that troponin I may have prognostic value and merits exploration for clinical decision-making including health warning bracelets. Rapamycin (Sirolimus®), an approved immunosuppressant which also influences autophagy, may prove beneficial. In the interim, while new treatments are developed, a revaluation of cardiac transplantation eligibility criteria is warranted.

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.

Investigating the cardiac pathology of SCO2-mediated hypertrophic cardiomyopathy using patients induced pluripotent stem cell-derived cardiomyocytes

Mutations in SCO2 are among the most common causes of COX deficiency, resulting in reduced mitochondrial oxidative ATP production capacity, often leading to hypertrophic cardiomyopathy (HCM). To date, none of the recent pertaining reports provide deep understanding of the SCO2 disease pathophysiology. To investigate the cardiac pathology of the disease, we were the first to generate induced pluripotent stem cell (iPSC)-derived cardiomyocytes (iPSC-CMs) from SCO2-mutated patients. For iPSC generation, we reprogrammed skin fibroblasts from two SCO2 patients and healthy controls. The first patient was a compound heterozygote to the common E140K mutation, and the second was homozygote for the less common G193S mutation. iPSC were differentiated into cardiomyocytes through embryoid body (EB) formation. To test the hypothesis that the SCO2 mutation is associated with mitochondrial abnormalities, and intracellular Ca²⁺ -overload resulting in functional derangements and arrhythmias, we investigated in SCO2-mutated iPSC-CMs (compared to control cardiomyocytes): (i) the ultrastructural changes; (ii) the inotropic responsiveness to β-adrenergic stimulation, increased [Ca²⁺ ]_o and angiotensin-II (AT-II); and (iii) the Beat Rate Variability (BRV) characteristics. In support of the hypothesis, we found in the mutated iPSC-CMs major ultrastructural abnormalities and markedly attenuated response to the inotropic interventions and caffeine, as well as delayed afterdepolarizations (DADs) and increased BRV, suggesting impaired SR Ca²⁺ handling due to attenuated SERCA activity caused by ATP shortage. Our novel results show that iPSC-CMs are useful for investigating the pathophysiological mechanisms underlying the SCO2 mutation syndrome.

Mammalian γ2 AMPK regulates intrinsic heart rate

AMPK is a conserved serine/threonine kinase whose activity maintains cellular energy homeostasis. Eukaryotic AMPK exists as αβγ complexes, whose regulatory γ subunit confers energy sensor function by binding adenine nucleotides. Humans bearing activating mutations in the γ2 subunit exhibit a phenotype including unexplained slowing of heart rate (bradycardia). Here, we show that γ2 AMPK activation downregulates fundamental sinoatrial cell pacemaker mechanisms to lower heart rate, including sarcolemmal hyperpolarization-activated current (I f) and ryanodine receptor-derived diastolic local subsarcolemmal Ca2+ release. In contrast, loss of γ2 AMPK induces a reciprocal phenotype of increased heart rate, and prevents the adaptive intrinsic bradycardia of endurance training. Our results reveal that in mammals, for which heart rate is a key determinant of cardiac energy demand, AMPK functions in an organ-specific manner to maintain cardiac energy homeostasis and determines cardiac physiological adaptation to exercise by modulating intrinsic sinoatrial cell behavior.