Apigenin inhibits NLRP3 inflammasome activation in monocytes and macrophages independently of CD38.

Introduction: CD38, a regulator of intracellular calcium signalling, is highly expressed in immune cells. Mice lacking CD38 are very susceptible to acute bacterial infections, implicating CD38 in innate immune responses. The effects of CD38 inhibition on NLRP3 inflammasome activation in human primary monocytes and monocyte-derived macrophages have not been investigated.

Sacubitril/valsartan preserves regional cardiac function following myocardial infarction in rats.

Aims: Sacubitril/valsartan (Sac/Val) is used for treatment of heart failure. The effect of Sac/Val on regional dysfunction following myocardial infarction (MI) remains uncertain. This study aimed at understanding the effects of Sac/Val on regional function after MI.

Electrophysiological tolerance: a new concept for understanding the electrical stability of the heart.

The co-ordinated electrical activity of ∼2 billion cardiac cells ensures stability of the heartbeat. Indeed, the remarkably low incidence (<1%) of ventricular arrhythmias in the healthy heart is only possible when the electrical event across this syncytium is closely controlled. In contrast, the diseased myocardium is associated with increased electrophysiological heterogeneity, unstable rhythm, and increased incidence of lethal arrhythmias.

Exploring Syndecan-4 and MLP and Their Interaction in Primary Cardiomyocytes and H9c2 Cells.

The transmembrane proteoglycan syndecan-4 is known to be involved in the hypertrophic response to pressure overload. Although multiple downstream signaling pathways have been found to be involved in this response in a syndecan-4-dependent manner, there are likely more signaling components involved. As part of a larger syndecan-4 interactome screening, we have previously identified MLP as a binding partner to the cytoplasmic tail of syndecan-4.

Myocardial SERCA2 Protects Against Cardiac Damage and Dysfunction Caused by Inhaled Bromine.

Myocardial sarcoendoplasmic reticulum calcium ATPase 2 (SERCA2) activity is critical for heart function. We have demonstrated that inhaled halogen (chlorine or bromine) gases inactivate SERCA2, impair calcium homeostasis, increase proteolysis, and damage the myocardium ultimately leading to cardiac dysfunction. To further elucidate the mechanistic role of SERCA2 in halogen-induced myocardial damage, we used bromine-exposed cardiac-specific SERCA2 knockout (KO) mice [tamoxifen-administered SERCA2 ( Tg (MHC-MerCreMer) mice] and compared them to the oil-administered controls.

Regulation of cardiomyocyte t-tubule structure by preload and afterload: Roles in cardiac compensation and decompensation.

Mechanical load is a potent regulator of cardiac structure and function. Although high workload during heart failure is associated with disruption of cardiomyocyte t-tubules and Ca homeostasis, it remains unclear whether changes in preload and afterload may promote adaptive t-tubule remodelling. We examined this issue by first investigating isolated effects of stepwise increases in load in cultured rat papillary muscles.

Enhanced Ca2+-Driven Arrhythmias in Female Patients with Atrial Fibrillation: Insights from Computational Modeling.

Background And Aims: Substantial sex-based differences have been reported in atrial fibrillation (AF), with female patients experiencing worse symptoms, increased complications from drug side effects or ablation, and elevated risk of AF-related stroke and mortality. Recent studies revealed sex-specific alterations in AF-associated Ca2+ dysregulation, whereby female cardiomyocytes more frequently exhibit potentially proarrhythmic Ca2+-driven instabilities compared to male cardiomyocytes. In this study, we aim to gain a mechanistic understanding of the Ca2+-handling disturbances and Ca2+-driven arrhythmogenic events in males vs females and establish their responses to Ca2+-targeted interventions.

Polyarginine Cell-Penetrating Peptides Bind and Inhibit SERCA2.

Cell-penetrating peptides (CPPs) are short peptide sequences that have the ability to cross the cell membrane and deliver cargo. Although it is critical that CPPs accomplish this task with minimal off-target effects, such actions have in many cases not been robustly screened. We presently investigated whether the commonly used CPPs TAT and the polyarginines Arg and Arg exert off-target effects on cellular Ca homeostasis.

Cardiomyocytes from female compared to male mice have larger ryanodine receptor clusters and higher calcium spark frequency.

Sex differences in cardiac physiology are receiving increased attention as it has become clear that men and women have different aetiologies of cardiac disease and require different treatments. There are experimental data suggesting that male cardiomyocytes exhibit larger Ca transients due to larger Ca sparks and a higher excitation-contraction coupling gain; in addition, they exhibit a larger response to adrenergic stimulation with isoprenaline (ISO). Here, we studied whether there are sex differences relating to structural organization of the transverse tubular network and ryanodine receptors (RyRs).

Stretch Harmonizes Sarcomere Strain Across the Cardiomyocyte.

Background: Increasing cardiomyocyte contraction during myocardial stretch serves as the basis for the Frank-Starling mechanism in the heart. However, it remains unclear how this phenomenon occurs regionally within cardiomyocytes, at the level of individual sarcomeres. We investigated sarcomere contractile synchrony and how intersarcomere dynamics contribute to increasing contractility during cell lengthening.

BIN1, Myotubularin, and Dynamin-2 Coordinate T-Tubule Growth in Cardiomyocytes.

Background: Transverse tubules (t-tubules) form gradually in the developing heart, critically enabling maturation of cardiomyocyte Ca homeostasis. The membrane bending and scaffolding protein BIN1 (bridging integrator 1) has been implicated in this process. However, it is unclear which of the various reported BIN1 isoforms are involved, and whether BIN1 function is regulated by its putative binding partners MTM1 (myotubularin), a phosphoinositide 3'-phosphatase, and DNM2 (dynamin-2), a GTPase believed to mediate membrane fission.

Augmenting workload drives T-tubule assembly in developing cardiomyocytes.

Contraction of cardiomyocytes is initiated at subcellular elements called dyads, where L-type Ca channels in t-tubules are located within close proximity to ryanodine receptors in the sarcoplasmic reticulum. While evidence from small rodents indicates that dyads are assembled gradually in the developing heart, it is unclear how this process occurs in large mammals. We presently examined dyadic formation in fetal and newborn sheep (Ovis aries), and the regulation of this process by fetal cardiac workload.

Live-cell photo-activated localization microscopy correlates nanoscale ryanodine receptor configuration to calcium sparks in cardiomyocytes.

Ca sparks constitute the fundamental units of Ca release in cardiomyocytes. Here we investigate how ryanodine receptors (RyRs) collectively generate these events by employing a transgenic mouse with a photo-activated label on RyR2. This allowed correlative imaging of RyR localization, by super-resolution Photo-Activated Localization Microscopy, and Ca sparks, by high-speed imaging.

Disruption of Phosphodiesterase 3A Binding to SERCA2 Increases SERCA2 Activity and Reduces Mortality in Mice With Chronic Heart Failure.

Background: Increasing SERCA2 (sarco[endo]-plasmic reticulum Ca ATPase 2) activity is suggested to be beneficial in chronic heart failure, but no selective SERCA2-activating drugs are available. PDE3A (phosphodiesterase 3A) is proposed to be present in the SERCA2 interactome and limit SERCA2 activity. Disruption of PDE3A from SERCA2 might thus be a strategy to develop SERCA2 activators.

A single amino acid deletion in the ER Ca sensor STIM1 reverses the in vitro and in vivo effects of the Stormorken syndrome-causing R304W mutation.

Stormorken syndrome is a multiorgan hereditary disease caused by dysfunction of the endoplasmic reticulum (ER) Ca sensor protein STIM1, which forms the Ca release-activated Ca (CRAC) channel together with the plasma membrane channel Orai1. ER Ca store depletion activates STIM1 by releasing the intramolecular "clamp" formed between the coiled coil 1 (CC1) and CC3 domains of the protein, enabling the C terminus to extend and interact with Orai1. The most frequently occurring mutation in patients with Stormorken syndrome is R304W, which destabilizes and extends the STIM1 C terminus independently of ER Ca store depletion, causing constitutive binding to Orai1 and CRAC channel activation.

ADAMTSL3 knock-out mice develop cardiac dysfunction and dilatation with increased TGFβ signalling after pressure overload.

Heart failure is a major cause of morbidity and mortality worldwide, and can result from pressure overload, where cardiac remodelling is characterized by cardiomyocyte hypertrophy and death, fibrosis, and inflammation. In failing hearts, transforming growth factor (TGF)β drives cardiac fibroblast (CFB) to myofibroblast differentiation causing excessive extracellular matrix production and cardiac remodelling. New strategies to target pathological TGFβ signalling in heart failure are needed.

Lumican accumulates with fibrillar collagen in fibrosis in hypertrophic cardiomyopathy.

Aims: Familial hypertrophic cardiomyopathy (HCM) is the most common form of inherited cardiac disease. It is characterized by myocardial hypertrophy and diastolic dysfunction, and can lead to severe heart failure, arrhythmias, and sudden cardiac death. Cardiac fibrosis, defined by excessive accumulation of extracellular matrix (ECM) components, is central to the pathophysiology of HCM.

: an automated approach to analysis of t-tubule and dyadic organization in cardiomyocytes.

During cardiac disease, t-tubules and dyads are remodelled and disrupted within cardiomyocytes, thereby reducing cardiac performance. Given the pathological implications of such dyadic remodelling, robust and versatile tools for characterizing these sub-cellular structures are needed. While analysis programs for continuous and regular structures such as rodent ventricular t-tubules are available, at least in two dimensions, these approaches are less appropriate for assessment of more irregular structures, such as dyadic proteins and non-rodent t-tubules.

Mechanisms of spontaneous Ca release-mediated arrhythmia in a novel 3D human atrial myocyte model: II. Ca -handling protein variation.

Disruption of the transverse-axial tubule system (TATS) in diseases such as heart failure and atrial fibrillation occurs in combination with changes in the expression and distribution of key Ca -handling proteins. Together this ultrastructural and ionic remodelling is associated with aberrant Ca cycling and electrophysiological instabilities that underlie arrhythmic activity. However, due to the concurrent changes in TATs and Ca -handling protein expression and localization that occur in disease it is difficult to distinguish their individual contributions to the arrhythmogenic state.

Mechanisms of spontaneous Ca release-mediated arrhythmia in a novel 3D human atrial myocyte model: I. Transverse-axial tubule variation.

Intracellular calcium (Ca ) cycling is tightly regulated in the healthy heart ensuring effective contraction. This is achieved by transverse (t)-tubule membrane invaginations that facilitate close coupling of key Ca -handling proteins such as the L-type Ca channel and Na -Ca exchanger (NCX) on the cell surface with ryanodine receptors (RyRs) on the intracellular Ca store. Although less abundant and regular than in the ventricle, t-tubules also exist in atrial myocytes as a network of transverse invaginations with axial extensions known as the transverse-axial tubule system (TATS).

The female syndecan-4 heart has smaller cardiomyocytes, augmented insulin/pSer473-Akt/pSer9-GSK-3β signaling, and lowered SCOP, pThr308-Akt/Akt and GLUT4 levels.

In cardiac muscle, the ubiquitously expressed proteoglycan syndecan-4 is involved in the hypertrophic response to pressure overload. Protein kinase Akt signaling, which is known to regulate hypertrophy, has been found to be reduced in the cardiac muscle of exercised male syndecan-4 mice. In contrast, we have recently found that pSer473-Akt signaling is elevated in the skeletal muscle ( TA) of female syndecan-4 mice.

Prolonged β-adrenergic stimulation disperses ryanodine receptor clusters in cardiomyocytes and has implications for heart failure.

Ryanodine receptors (RyRs) exhibit dynamic arrangements in cardiomyocytes, and we previously showed that 'dispersion' of RyR clusters disrupts Ca homeostasis during heart failure (HF) (Kolstad et al., eLife, 2018). Here, we investigated whether prolonged β-adrenergic stimulation, a hallmark of HF, promotes RyR cluster dispersion and examined the underlying mechanisms.

Nanoscale organization of ryanodine receptor distribution and phosphorylation pattern determines the dynamics of calcium sparks.

Super-resolution imaging techniques have provided a better understanding of the relationship between the nanoscale organization and function of ryanodine receptors (RyRs) in cardiomyocytes. Recent data have indicated that this relationship is disrupted in heart failure (HF), as RyRs are dispersed into smaller and more numerous clusters. However, RyRs are also hyperphosphorylated in this condition, and this is reported to occur preferentially within the cluster centre.