Ceramide modulates electrophysiological characteristics and oxidative stress of pulmonary vein cardiomyocytes

Chronic Partial Sleep Deprivation Increased the Incidence of Atrial Fibrillation by Promoting Pulmonary Vein and Atrial Arrhythmogenesis in a Rodent Model

Sleep deprivation (SD) is a recognized risk factor for atrial fibrillation (AF), yet the precise molecular and electrophysiological mechanisms behind SD-induced AF are unclear. This study explores the electrical and structural changes that contribute to AF in chronic partial SD. We induced chronic partial SD in Wistar rats using a modified multiple-platform method. Echocardiography demonstrated impaired systolic and diastolic function in the left ventricle (LV) of the SD rats. The SD rats exhibited an elevated heart rate and a higher low-frequency to high-frequency ratio in a heart-rate variability analysis. Rapid transesophageal atrial pacing led to a higher incidence of AF and longer mean AF durations in the SD rats. Conventional microelectrode recordings showed accelerated pulmonary vein (PV) spontaneous activity in SD rats, along with a heightened occurrence of delayed after-depolarizations in the PV and left atrium (LA) induced by tachypacing and isoproterenol. A Western blot analysis showed reduced expression of G protein-coupled receptor kinase 2 (GRK2) in the LA of the SD rats. Chronic partial SD impairs LV function, promotes AF genesis, and increases PV and LA arrhythmogenesis, potentially attributed to sympathetic overactivity and reduced GRK2 expression. Targeting GRK2 signaling may offer promising therapeutic avenues for managing chronic partial SD-induced AF. Future investigations are mandatory to investigate the dose-response relationship between SD and AF genesis.

GLP-1 receptor agonists and myocardial metabolism in atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Many medical conditions, including hypertension, diabetes, obesity, sleep apnea, and heart failure (HF), increase the risk for AF. Cardiomyocytes have unique metabolic characteristics to maintain adenosine triphosphate production. Significant changes occur in myocardial metabolism in AF. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) have been used to control blood glucose fluctuations and weight in the treatment of type 2 diabetes mellitus (T2DM) and obesity. GLP-1RAs have also been shown to reduce oxidative stress, inflammation, autonomic nervous system modulation, and mitochondrial function. This article reviews the changes in metabolic characteristics in cardiomyocytes in AF. Although the clinical trial outcomes are unsatisfactory, the findings demonstrate that GLP-1 RAs can improve myocardial metabolism in the presence of various risk factors, lowering the incidence of AF.

Neutral sphingomyelinase regulates mechanotransduction in human engineered cardiac tissues and mouse hearts

Cardiovascular disease is the leading cause of death in the USA and is known to be exacerbated by elevated mechanical stress from hypertension. Caveolae are plasma membrane structures that buffer mechanical stress but have been found to be reduced in pathological conditions associated with chronically stretched myocardium. To explore the physiological implications of the loss of caveolae, we used human engineered cardiac tissue (ECT) constructs, composed of human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes and hiPSC-derived cardiac fibroblasts, to develop a long-term cyclic stretch protocol that recapitulates the effects of hypertension on caveolae expression, membrane tension, and the β-adrenergic response. Leveraging this new stretch protocol, we identified neutral sphingomyelinases (nSMase) as mechanoregulated mediators of caveolae loss, ceramide production and the blunted β-adrenergic response in this human cardiac model. Specifically, in our ECT model, nSMase inhibition via GW4869 prevented stretch-induced loss of caveolae-like structures, mitigated nSMase-dependent ceramide production, and maintained the ECT contractile kinetic response to isoprenaline. These findings are correlated with a blood lipidomic analysis in middle-aged and older adults, which revealed an increase of the circulating levels of ceramides in adults with hypertension. Furthermore, we found that conduction slowing from increased pressure loading in mouse left ventricle was abolished in the context of nSMase inhibition. Collectively, these findings identify nSMase as a potent drug target for mitigating stretch-induced effects on cardiac function. KEY POINTS: We have developed a new stretch protocol for human engineered cardiac tissue that recapitulates changes in plasma membrane morphology observed in animal models of pressure/volume overload. Stretch of engineered cardiac tissue induces activation of neutral sphingomyelinase (nSMase), generation of ceramide, and disassembly of caveolae. Activation of nSMase blunts cardiac β-adrenergic contractile kinetics and mediates stretch-induced slowing of conduction and upstroke velocity. Circulating ceramides are increased in adults with hypertension, highlighting the clinical relevance of stretch-induced nSMase activity.

Myocardial Fibrosis and Steatosis in Patients with Aortic Stenosis: Roles of Myostatin and Ceramides

Aortic stenosis (AS) involves progressive valve obstruction and a remodeling response of the left ventriculum (LV) with systolic and diastolic dysfunction. The roles of interstitial fibrosis and myocardial steatosis in LV dysfunction in AS have not been completely characterized. We enrolled 31 patients (19 women and 12 men) with severe AS undergoing elective aortic valve replacement. The subjects were clinically evaluated, and transthoracic echocardiography was performed pre-surgery. LV septal biopsies were obtained to assess fibrosis and apoptosis and fat deposition in myocytes (perilipin 5 (PLIN5)), or in the form of adipocytes within the heart (perilipin 1 (PLIN1)), the presence of ceramides and myostatin were assessed via immunohistochemistry. After BMI adjustment, we found a positive association between fibrosis and apoptotic cardiomyocytes, as well as fibrosis and the area covered by PLIN5. Apoptosis and PLIN5 were also significantly interrelated. LV fibrosis increased with a higher medium gradient (MG) and peak gradient (PG). Ceramides and myostatin levels were higher in patients within the higher MG and PG tertiles. In the linear regression analysis, increased fibrosis correlated with increased apoptosis and myostatin, independent from confounding factors. After adjustment for age and BMI, we found a positive relationship between PLIN5 and E/A and a negative correlation between septal S', global longitudinal strain (GLS), and fibrosis. Myostatin was inversely correlated with GLS and ejection fraction. Fibrosis and myocardial steatosis altogether contribute to ventricular dysfunction in severe AS. The association of myostatin and fibrosis with systolic dysfunction, as well as between myocardial steatosis and diastolic dysfunction, highlights potential therapeutic targets.

Effect of macrophage migration inhibitory factor on pulmonary vein arrhythmogenesis through late sodium current

AIMS

Macrophage migration inhibitory factor (MIF), a pleiotropic inflammatory cytokine, is highly expressed in patients with atrial fibrillation (AF). Inflammation increases the risk of AF and is primarily triggered by pulmonary vein (PV) arrhythmogenesis. This study investigated whether MIF can modulate the electrical activity of the PV and examined the underlying mechanisms of MIF.

METHODS AND RESULTS

A conventional microelectrode, a whole-cell patch clamp, western blotting, and immunofluorescent confocal microscopy were used to investigate electrical activity, calcium (Ca2+) regulation, protein expression, ionic currents, and cytosolic reactive oxygen species (ROS) in rabbit PV tissue and isolated single cardiomyocytes with and without MIF incubation (100 ng/mL, treated for 6 h). The MIF (100 ng/mL)-treated PV tissue (n = 8) demonstrated a faster beating rate (1.8 ± 0.2 vs. 2.6 ± 0.1 Hz, P < 0.05), higher incidence of triggered activity (12.5 vs. 100%, P < 0.05), and premature atrial beat (0 vs. 100%, P < 0.05) than the control PV tissue (n = 8). Compared with the control PV cardiomyocytes, MIF-treated single PV cardiomyocytes had larger Ca2+ transients (0.6 ± 0.1 vs. 1.0 ± 0.1, ΔF/F0, P < 0.05), sarcoplasmic reticulum Ca2+ content (0.9 ± 0.20 vs. 1.7 ± 0.3 mM of cytosol, P < 0.05), and cytosolic ROS (146.8 ± 5.3 vs. 163.7 ± 3.8, ΔF/F0, P < 0.05). Moreover, MIF-treated PV cardiomyocytes exhibited larger late sodium currents (INa-Late), L-type Ca2+ currents, and Na+/Ca2+ exchanger currents than the control PV cardiomyocytes. KN93 [a selective calcium/calmodulin-dependent protein kinase II (CaMKII) blocker, 1 μM], ranolazine (an INa-Late inhibitor, 10 μM), and N-(mercaptopropionyl) glycine (ROS inhibitor, 10 mM) reduced the beating rates and the incidence of triggered activity and premature captures in the MIF-treated PV tissue.

CONCLUSION

Macrophage migration inhibitory factor increased PV arrhythmogenesis through Na+ and Ca2+ dysregulation through the ROS activation of CaMKII signalling, which may contribute to the genesis of AF during inflammation. Anti-CaMKII treatment may reverse PV arrhythmogenesis. Our results clearly reveal a key link between MIF and AF and offer a viable therapeutic target for AF treatment.

Sphingolipid metabolism and signaling in cardiovascular diseases

Sphingolipids are a structural component of the cell membrane, derived from sphingosine, an amino alcohol. Its sphingoid base undergoes various types of enzymatic transformations that lead to the formation of biologically active compounds, which play a crucial role in the essential pathways of cellular signaling, proliferation, maturation, and death. The constantly growing number of experimental and clinical studies emphasizes the pivotal role of sphingolipids in the pathophysiology of cardiovascular diseases, including, in particular, ischemic heart disease, hypertension, heart failure, and stroke. It has also been proven that altering the sphingolipid metabolism has cardioprotective properties in cardiac pathologies, including myocardial infarction. Recent studies suggest that selected sphingolipids may serve as valuable biomarkers useful in the prognosis of cardiovascular disorders in clinical practice. This review aims to provide an overview of the current knowledge of sphingolipid metabolism and signaling in cardiovascular diseases.