Cardiomyocyte Inflammasome Signaling in Cardiomyopathies and Atrial Fibrillation: Mechanisms and Potential Therapeutic Implications

Inflammasomes are high molecular weight protein complexes in the cytosol of immune and other cells that play a critical role in the innate immune system in response to cellular stress. NLRP3 inflammasome, the best-understood inflammasome, is known to mediate the maturation (activation) of caspase-1 from pro-caspase-1, causing the maturation and release of cytokines (e.g., interleukin-1β) and potentially leading to a form of inflammatory programmed cell death called pyroptosis. Previous work has shown that the NLRP3 components are expressed in cardiomyocytes and cardiac fibroblasts and recent studies have identified the NLRP3 inflammasome as a key nodal point in the pathogenesis of cardiomyopathies and atrial fibrillation, which may create an opportunity for the development of new therapeutic agents. Here we review the recent evidence for a role of NLRP3 inflammasome in the cardiomyocytes and discuss its potential role in the evolution of cardiac remodeling and arrhythmias and new opportunities created by these very recent developments

Prenatal Genetic Counseling in Congenital Anomalies

The impact of genetic variability on embryogenesis and fetus development established medical genetics as essential for the prevention of congenital anomalies, early detection and appropriate management. Advances in ultrasonography equipment and technique allow early detection of many congenital malformations. In addition, genetic testing can be performed in a prenatal setting on a variety of biological samples obtained by invasive and noninvasive procedures: chorionic villus sampling, amniocentesis, cordocentesis, or maternal blood collection (i.e., cell free fetal DNA). In the past, only a small percentage of congenital anomalies had a readily identifiable etiology; genetic diagnostic procedures can provide at least some of the answers for the remaining unsolved cases. Undoubtedly, the need for appropriate case management and counseling justifies the importance of uncovering the underlying genetic cause of birth defects. In this chapter, we will focus on genetic counseling in congenital anomalies, including isolated congenital anomalies and preimplantation genetic diagnosis. Genetic counseling provides information and support, assisting parents in making informed decisions. Through this process, parents learn about the risk of having a newborn with a congenital malformation and the nature of the disorder and its natural history, are advised on available testing for that particular case, and discuss options for risk management and family planning

Intracellular calcium leak due to FKBP12.6 deficiency in mice facilitates the inducibility of atrial fibrillation

BACKGROUND: Although defective Ca(2+) homeostasis may contribute to arrhythmogenesis in atrial fibrillation (AF), the underlying molecular mechanisms remain poorly understood. Studies in patients with AF revealed that impaired diastolic closure of sarcoplasmic reticulum (SR) Ca(2+)-release channels (ryanodine receptors, RyR2) is associated with reduced levels of the RyR2-inhibitory subunit FKBP12.6. OBJECTIVE: The objective of the present study was to test the hypothesis that Ca(2+) leak from the SR through RyR2 increases the propensity for AF in FKBP12.6-deficient (-/-) mice. METHODS: Surface electrocardiogram and intracardiac electrograms were recorded simultaneously in FKBP12.6-/- mice and wild-type (WT) littermates. Right atrial programmed stimulation was performed before and after injection of RyR2 antagonist tetracaine (0.5 mg/kg). Intracellular Ca(2+) transients were recorded in atrial myocytes from FKBP12.6-/- and WT mice. RESULTS: FKBP12.6-/- mice had structurally normal atria and unaltered expression of key Ca(2+)-handling proteins. AF episodes were inducible in 81% of FKBP12.6-/-, but in only 7% of WT mice (P <.05), and were prevented by tetracaine in all FKBP12.6-/- mice. SR Ca(2+) leak in FKBP12.6-/- myocytes was 53% larger than in WT myocytes, and FKBP12.6-/- myocytes showed increased incidence of spontaneous SR Ca(2+) release events, which could be blocked by tetracaine. CONCLUSION: The increased vulnerability to AF in FKBP12.6-/- mice substantiates the notion that defective SR Ca(2+) release caused by abnormal RyR2 and FKBP12.6 interactions may contribute to the initiation or maintenance of atrial fibrillatio

Brugada Syndrome within Asian Populations: State-of-the-Art Review

Brugada syndrome (BrS) is an inherited cardiac channelopathy with variable expressivity that can lead to sudden cardiac arrest (SCA). Studies worldwide suggest that BrS and Brugada pattern (BrP) have low prevalences in general. However, studies also note that BrS is most prevalent among certain Asian populations. Among the different global regions, the highest prevalence is believed to be in Southeast Asia, followed by the Middle East, South Asia, East Asia, Europe, and North America. It is not only important to recognize such varying degrees of BrS prevalence within Asia but also to understand that there may be significant differences in terms of presenting symptoms, occult risk factors, and the impact on clinical outcomes. The importance of identifying such differences lies in the necessity to develop improved risk assessment strategies to guide secondary prevention and treatment for these patients. Specifically, the decision to pursue placement of an implantable cardiac defibrillator (ICD) can be lifesaving for high-risk BrS patients. However, there remains a significant lack of consensus on how to best risk stratify BrS patients. While the current guidelines recommend ICD implantation in patients with spontaneous Type 1 ECG pattern BrS who present with syncope, there may still exist additional clinical factors that may serve as better predictors or facilitate more refined risk stratification before malignant arrhythmias occur. This carries huge relevance given that BrS patients often do not have any preceding symptoms prior to SCA. This review seeks to delineate the differences in BrS presentation and prevalence within the Asian continent in the hope of identifying potential risk factors to guide better prognostication and management of BrS patients in the future

Sex-specific outcomes of LBBAP versus biventricular pacing : results from I-CLAS

Background: Cardiac resynchronization therapy (CRT) using biventricular pacing (BVP) has been associated with greater clinical improvement in women than men. Recently, left bundle branch area pacing (LBBAP) has been shown to be an alternative form of CRT. Objectives: The purpose of this study was to investigate sex-specific outcomes for death and heart failure events in a large, international, multicenter, cohort of patients undergoing CRT with BVP or LBBAP. Methods: In this international study of 1,778 patients (575 female and 1203 male), sex-specific survival analysis was performed to compare the effect of LBBAP-CRT relative to BVP-CRT on the combined endpoint of death or heart failure hospitalization (HFH), and secondary endpoints of HFH only, and death alone. Results: Female patients were more likely to have nonischemic cardiomyopathy and left bundle branch block (LBBB) and less likely to have hypertension, diabetes, or coronary artery disease than were male patients. Overall, female patients had a better result with LBBAP compared with BVP than did male patients, with a significant 36% reduction in death or HFH (HR: 0.64; 95% CI: 0.43 to 0.97; P = 0.03) and a significant 60% reduction in HFH alone (HR: 0.4; 95% CI: 0.24 to 0.69, P &lt; 0.01). Women had a greater reduction in death or HFH among those with nonischemic cardiomyopathy (HR: 0.45 95% CI: 0.26 to 0.79; P &lt; 0.01) and LBBB (HR: 0.49; 95% CI: 0.27 to 0.87; P &lt; 0.01). Sex-specific echocardiographic outcomes were better in women than in men. Conclusions: Women obtained significantly greater reductions in the combined endpoint of death or HFH (primarily driven by reduction in HFH) with LBBAP compared with BVP among patients requiring CRT than did men

Calmodulin kinase II–mediated sarcoplasmic reticulum Ca2+ leak promotes atrial fibrillation in mice

Atrial fibrillation (AF), the most common human cardiac arrhythmia, is associated with abnormal intracellular Ca2+ handling. Diastolic Ca2+ release from the sarcoplasmic reticulum via “leaky” ryanodine receptors (RyR2s) is hypothesized to contribute to arrhythmogenesis in AF, but the molecular mechanisms are incompletely understood. Here, we have shown that mice with a genetic gain-of-function defect in Ryr2 (which we termed Ryr2R176Q/+ mice) did not exhibit spontaneous AF but that rapid atrial pacing unmasked an increased vulnerability to AF in these mice compared with wild-type mice. Rapid atrial pacing resulted in increased Ca2+/calmodulin-dependent protein kinase II (CaMKII) phosphorylation of RyR2, while both pharmacologic and genetic inhibition of CaMKII prevented AF inducibility in Ryr2R176Q/+ mice. This result suggests that AF requires both an arrhythmogenic substrate (e.g., RyR2 mutation) and enhanced CaMKII activity. Increased CaMKII phosphorylation of RyR2 was observed in atrial biopsies from mice with atrial enlargement and spontaneous AF, goats with lone AF, and patients with chronic AF. Genetic inhibition of CaMKII phosphorylation of RyR2 in Ryr2S2814A knockin mice reduced AF inducibility in a vagotonic AF model. Together, these findings suggest that increased RyR2-dependent Ca2+ leakage due to enhanced CaMKII activity is an important downstream effect of CaMKII in individuals susceptible to AF induction

NLRP3 inflammasome is a key driver of obesity-induced atrial arrhythmias

AIMS: Obesity, an established risk factor of atrial fibrillation (AF), is frequently associated with enhanced inflammatory response. However, whether inflammatory signaling is causally linked to AF pathogenesis in obesity remains elusive. We recently demonstrated that the constitutive activation of the ‘NACHT, LRR, and PYD Domains-containing Protein 3’ (NLRP3) inflammasome promotes AF susceptibility. In this study, we hypothesized that the NLRP3 inflammasome is a key driver of obesity-induced AF. METHODS AND RESULTS: Western blotting was performed to determine the level of NLRP3 inflammasome activation in atrial tissues of obese patients, sheep, and diet-induced obese (DIO) mice. The increased body weight in patients, sheep, and mice was associated with enhanced NLRP3-inflammasome activation. To determine whether NLRP3 contributes to the obesity-induced atrial arrhythmogenesis, wild-type (WT) and NLRP3 homozygous knockout (NLRP3(−/−)) mice were subjected to high-fat-diet (HFD) or normal chow (NC) for 10 weeks. Relative to NC-fed WT mice, HFD-fed WT mice were more susceptible to pacing-induced AF with longer AF duration. In contrast, HFD-fed NLRP3(−/−) mice were resistant to pacing-induced AF. Optical mapping in DIO mice revealed an arrhythmogenic substrate characterized by abbreviated refractoriness and action potential duration (APD), two key determinants of reentry-promoting electrical remodeling. Upregulation of ultra-rapid delayed-rectifier K(+)-channel (Kv1.5) contributed to the shortening of atrial refractoriness. Increased profibrotic signaling and fibrosis along with abnormal Ca(2+) release from sarcoplasmic reticulum (SR) accompanied atrial arrhythmogenesis in DIO mice. Conversely, genetic ablation of Nlrp3 (NLRP3(−/−)) in HFD-fed mice prevented the increases in Kv1.5 and the evolution of electrical remodeling, the upregulation of profibrotic genes, and abnormal SR Ca(2+) release in DIO mice. CONCLUSION: These results demonstrate that the atrial NLRP3 inflammasome is a key driver of obesity-induced atrial arrhythmogenesis and establishes a mechanistic link between obesity-induced AF and NLRP3-inflammasome activation