Impaired Activity of Ryanodine Receptors Contributes to Calcium Mishandling in Cardiomyocytes of Metabolic Syndrome Rats

Establishment and evaluation of targeted molecular screening model for the ryanodine receptor or sarco/endoplasmic reticulum calcium ATPase

BACKGROUD

Endoplasmic reticulum/sarcoplasmic reticulum (ER/SR) is crucial for maintaining intracellular calcium homeostasis due to the calcium-signaling-related proteins on its membrane. While ryanodine receptors (RyR) on insect ER/SR membranes are well-known as targets for diamide insecticides, little is known about other calcium channels. Given the resistance of diamide insecticides, the establishment of molecular screening models targeting RyR or sarco/endoplasmic reticulum calcium ATPase (SERCA) is conducive to the discovery of new insecticidal molecules.

RESULTS

The morphological features of Mythimna separata SR have closed vesicles with integrity and high density. The 282 proteins in the SR component contained RyR and SERCA. A measurement model for the release and uptake of calcium was successfully established by detecting calcium ions outside the SR membrane using a fluorescence spectrophotometer. In vitro testing systems using SR vesicles found that diamide insecticides could activate dose-dependently RyR, with EC50 values of 0.14 μM (Chlorantraniliprole), 0.21 μM (Flubendiamide), and 0.57 μM (Cyantraniliprole), respectively. However, dantrolene inhibited RyR-mediated calcium release with an IC50 value of 353.9 μM, suggesting that dantrolene can weakly antagonize RyR. Moreover, cyclopiazonic acid significantly reduced the enzyme activity and calcium uptake capacity of SERCA. On the contrary, CDN1163 markedly activated the enzyme activity and improved the calcium transport capacity of SERCA.

CONCLUSIONS

SR vesicles can be used to study the function of unknown proteins on the SR membranes, as well as for high-throughput screening of highly active compounds targeting RyR or SERCA. © 2024 Society of Chemical Industry.

Oxidative stress in early metabolic syndrome impairs cardiac RyR2 and SERCA2a activity and modifies the interplay of these proteins during Ca2+ waves

We investigated how oxidative stress (OS) alters Ca2+ handling in ventricular myocytes in early metabolic syndrome (MetS) in sucrose-fed rats. The effects of N-acetyl cysteine (NAC) or dl-Dithiothreitol (DTT) on systolic Ca2+ transients (SCaTs), diastolic Ca2+ sparks (CaS) and Ca2+ waves (CaW), recorded by confocal techniques, and L-type Ca2+ current (ICa), assessed by whole-cell patch clamp, were evaluated in MetS and Control cells. MetS myocytes exhibited decreased SCaTs and CaS frequency but unaffected CaW propagation. In Control cells, NAC/DTT reduced RyR2/SERCA2a activity blunting SCaTs, CaS frequency and CaW propagation, suggesting that basal ROS optimised Ca2+ signalling by maintaining RyR2/SERCA2a function and that these proteins facilitate CaW propagation. Conversely, NAC/DTT in MetS recovered RyR2/SERCA2a function, improving SCaTs and CaS frequency, but unexpectedly decreasing CaW propagation. We hypothesised that OS decreases RyR2/SERCA2a activity at early MetS, and while decreased SERCA2a favours CaW propagation, diminished RyR2 restrains it.

Chronic catestatin treatment reduces atrial fibrillation susceptibility via improving calcium handling in post-infarction heart failure rats

BACKGROUND

Abnormal Ca²⁺ handling is a pivotal element of atrial fibrillation (AF) substrates. Catestatin (CST) modulates intracellular Ca²⁺ handling in cardiomyocytes (CMs). We investigated the effects of CST administration on atrial Ca²⁺ handling and AF susceptibility in rats with post-infarction heart failure (HF).

METHODS

Myocardial infarction (MI) was established by ligation of the left anterior descending coronary artery in rats. Two-week later, rats with post-infarction HF were randomly treated with saline (MI group) or CST (MI + CST group) for 4-week. Cellular Ca²⁺ imaging was performed by incubating atrial CMs with Fura-2 AM. An in vitro electrophysiological study was performed to assess the vulnerability to action potential duration (APD) alternans and AF. Ca²⁺ handling proteins expression was determined using western blotting.

RESULTS

In atrial CMs, compared with the sham group, the sarcoplasmic reticulum (SR) Ca²⁺ load, Ca²⁺ transient (CaT) amplitude, and threshold for Ca²⁺ alternans were significantly decreased, but the diastolic intracellular Ca²⁺ level, SR Ca²⁺ leakage, and spontaneous Ca²⁺ events were markedly increased in the MI group. However, CST attenuated these Ca²⁺-handling abnormalities induced by post-infarction HF. Moreover, vulnerability to atrial APD alternans and AF was significantly increased in isolated hearts from the MI group compared to the sham group, whereas all effects were prevented by CST. CST treatment also preserved SR Ca²⁺-ATPase protein expression but decreased the protein levels of phosphorylated-ryanodine receptor 2 and phosphorylated-Ca²⁺/calmodulin-dependent protein kinase II in atria from post-infarction HF rats.

CONCLUSION

Chronic CST treatment reduces AF vulnerability in rats with MI-induced HF by improving Ca²⁺ handling.

STIM1-Orai1 interaction mediated calcium influx activation contributes to cardiac contractility of insulin-resistant rats

PURPOSE

Metabolic syndrome (MetS) became a tremendous public health burden in the last decades. Store-operated calcium entry (SOCE) is a unique mechanism that causes a calcium influx, which is triggered by calcium store depletion. MetS-induced alterations in cardiac calcium signaling, especially in SOCE are still unclear. Therefore, we aim to examine the possible role of SOCE and its components (STIM1 and Orai1) in the MetS-induced cardiac remodeling.

METHODS

We used male, adult (12 weeks) Wistar albino rats (n = 20). Animals were randomly divided into two groups which were: control (C) and MetS. We gave 33% sucrose solution to animals instead of water for 24 weeks to establish MetS model. In the end, papillary muscle function was evaluated, and various electrophysiological analyses were made in isolated cardiomyocytes. Additionally, STIM1 and Orai1 protein and mRNA expressions were analyzed.

RESULTS

We observed a deterioration in contractility in MetS animals and demonstrated the contribution of SOCE by applying a SOCE inhibitor (BTP2). Calcium spark frequency was increased while its amplitude was decreasing in MetS hearts, which was reversed after SOCE inhibition. The amplitude of transient calcium changes in the MetS group was decreased, and it decreased further BTP2 application. Both protein and mRNA levels of STIM1 and Orai1 were increased significantly in MetS hearts.

CONCLUSION

Current data indicate the significant contribution of SOCE to cardiac calcium handling in the MetS model. We think MetS-induced SOCE activation is a compensation mechanism that is required for the continuum of proper cardiac functioning, although the activation can also cause cardiac hypertrophy.

Cardiac contractility of the African sharptooth catfish, Clarias gariepinus: role of extracellular Ca2+, sarcoplasmic reticulum, and β-adrenergic stimulation

This study investigated the dependence of contraction from extracellular Ca²⁺, the presence of a functional sarcoplasmic reticulum (SR), and the effects of β-adrenergic stimulation using isometric cardiac muscle preparations. Moreover, the expression of Ca²⁺-handling proteins such as SR-Ca²⁺-ATPase (SERCA), phospholamban (PLN), and Na⁺/Ca²⁺ exchanger (NCX) were also evaluated in the ventricular tissue of adult African sharptooth catfish, Clarias gariepinus, a facultative air-breathing fish. In summary, we observed that (1) contractility was strongly regulated by extracellular Ca²⁺; (2) inhibition of SR Ca²⁺-release by application of ryanodine reduced steady-state force production; (3) ventricular myocardium exhibited clear post-rest decay, even in the presence of ryanodine, indicating a decrease in SR Ca²⁺ content and NCX as the main pathway for Ca²⁺ extrusion; (4) a positive force-frequency relationship was observed above 60 bpm (1.0 Hz); (5) ventricular tissue was responsive to β-adrenergic stimulation, which caused significant increases in twitch force, kept a linear force-frequency relationship from 12 to 96 bpm (0.2 to Hz), and improved the cardiac pumping capacity (CPC); and (6) African catfish myocardium exhibited similar expression patterns of NCX, SERCA, and PLN, corroborating our findings that both mechanisms for Ca²⁺ transport across the SR and sarcolemma contribute to Ca²⁺ activator. In conclusion, this fish species displays great physiological plasticity of E-C coupling, able to improve the ability to maintain cardiac performance under physiological conditions to ecological and/or adverse environmental conditions, such as hypoxic air-breathing activity.

Tale of two kinases: Protein kinase A and Ca2+/calmodulin-dependent protein kinase II in pre-diabetic cardiomyopathy

Metabolic syndrome is a pre-diabetic state characterized by several biochemical and physiological alterations, including insulin resistance, visceral fat accumulation, and dyslipidemias, which increase the risk for developing cardiovascular disease. Metabolic syndrome is associated with augmented sympathetic tone, which could account for the etiology of pre-diabetic cardiomyopathy. This review summarizes the current knowledge of the pathophysiological consequences of enhanced and sustained β-adrenergic response in pre-diabetes, focusing on cardiac dysfunction reported in diet-induced experimental models of pre-diabetic cardiomyopathy. The research reviewed indicates that both protein kinase A and Ca²⁺/calmodulin-dependent protein kinase II play important roles in functional responses mediated by β₁-adrenoceptors; therefore, alterations in the expression or function of these kinases can be deleterious. This review also outlines recent information on the role of protein kinase A and Ca²⁺/calmodulin-dependent protein kinase II in abnormal Ca²⁺ handling by cardiomyocytes from diet-induced models of pre-diabetic cardiomyopathy.

Mesenteric Lymph Drainage Improves Cardiac Papillary Contractility and Calcium Sensitivity in Rats with Hemorrhagic Shock

BACKGROUND

Myocardial dysfunction is an important adverse factor of hemorrhagic shock that induces refractory hypotension, and post-hemorrhagic shock mesenteric lymph (PHSML) return is involved in this adverse effect. This study investigated whether mesenteric lymph drainage (MLD) improves PHSML return-induced cardiac contractile dysfunction via the restoration of cardiomyocyte calcium sensitivity.

MATERIALS AND METHODS

A hemorrhage shock model was established by using a controlled hemorrhage through the femoral artery that maintained a mean arterial pressure of 40 ± 2 mmHg for 3 h. MLD and mesenteric lymph duct ligation (MLDL) were performed from 1 to 3 h during hypotension. The papillary muscles of the heart were collected for measurement of calmodulin expression and for determining contractile responses to either isoprenaline or calcium.

RESULTS

The results showed that either MLD or MLDL reversed the hemorrhagic shock-induced downregulation of calmodulin expression, a marker protein of cardiomyocyte calcium sensitization, in papillary muscles. MLD also improved the decreased contractile response and ±df/dt of the papillary muscle strip to gradient isoprenaline or calcium caused by hemorrhagic shock.

CONCLUSION

These findings indicate that increased cardiac contractibility may be associated with the restoration of calcium sensitivity produced by PHSML drainage.

Stress-driven cardiac calcium mishandling via a kinase-to-kinase crosstalk

Calcium homeostasis in the cardiomyocyte is critical to the regulation of normal cardiac function. Abnormal calcium dynamics such as altered uptake by the sarcoplasmic reticulum (SR) Ca²⁺-ATPase and increased diastolic SR calcium leak are involved in the development of maladaptive cardiac remodeling under pathological conditions. Ca²⁺/calmodulin-dependent protein kinase II-δ (CaMKIIδ) is a well-recognized key molecule in calcium dysregulation in cardiomyocytes. Elevated cellular stress is known as a common feature during pathological remodeling, and c-jun N-terminal kinase (JNK) is an important stress kinase that is activated in response to intrinsic and extrinsic stress stimuli. Our lab recently identified specific actions of JNK isoform 2 (JNK2) in CaMKIIδ expression, activation, and CaMKIIδ-dependent SR Ca²⁺ mishandling in the stressed heart. This review focuses on the current understanding of cardiac SR calcium handling under physiological and pathological conditions as well as the newly identified contribution of the stress kinase JNK2 in CaMKIIδ-dependent SR Ca²⁺ abnormal mishandling. The new findings identifying dual roles of JNK2 in CaMKIIδ expression and activation are also discussed in this review.

Diagnostic Criteria for Metabolic Syndrome in Diet-Induced Rodent Models: A Systematic Review

BACKGROUND

Thousands of publications in recent years have addressed the induction of metabolic syndrome (MetS) in rodents. However, the criteria and the reference values for diagnosing this disease have not been defined.

OBJECTIVE

Our main objective was to carry out a systematic review to gather evidence about the criteria for biochemical and anthropometric parameters in which scientific studies have relied on to report that rats developed MetS from a previous dietary manipulation.

METHODS

We compiled characteristics and findings of diet-induced MetS with high-fat, high-carbohydrate, high-fat/high-carbohydrates, and cafeteria diet from PubMed and Science Direct databases published in the last 5 years.

RESULTS

The results on the principal determinants for the syndrome, published in the reviewed articles, were chosen to propose reference values in the rat models of food induction.

CONCLUSION

The values obtained will serve as reference cut-of points in the development of the disease; in addition, the compilation of data will be useful in planning and executing research protocols in animal models.

A combined Langendorff-injection technique for simultaneous isolation of single cardiomyocytes from atria and ventricles of the rat heart

Single cardiomyocytes are widely used for investigations of the cellular and molecular mechanisms of regulation and modulation of cardiac performance. Intact cardiomyocytes allow one to study in detail cell function avoiding the effects of extracellular matrix and neighboring cells. The most established protocols of cardiomyocyte isolation are based on the isolated heart perfusion using a Langendorff-apparatus or on intraventricular perfusion using a syringe. However, the yield of single cardiomyocytes obtained by these methods may be low due to the cell injury following non-uniform enzyme digestion of connective tissue in different heart chambers. Moreover, isolation of atrial cardiomyocytes is challenging because of their small size and complex geometric shape. Here we present a new protocol for simultaneous isolation of high quality cardiomyocytes from the atria, ventricular free walls and interventricular septum. The protocol is based on the combination of the Langendorff perfusion method with the intraventricular and intra-atrial injection technique taking into account the collagen content variation between the different heart chambers. Obtained cells demonstrate rod-shaped morphology, a clear and regular sarcomere striation pattern and rat-specific frequency-dependence of contraction and calcium transient parameters. Our protocol provides gentle cell isolation that increases the yield of single cardiomyocytes suitable for biophysical researches .

FUNDC1 interacts with FBXL2 to govern mitochondrial integrity and cardiac function through an IP3R3-dependent manner in obesity

Defective mitophagy is causally linked to obesity complications. Here, we identified an interaction between mitophagy protein FUNDC1 (FUN14 domain containing 1) and receptor subunit of human SCF (SKP1/cullin/F-box protein) ubiquitin ligase complex FBXL2 as a gatekeeper for mitochondrial Ca²⁺ homeostasis through degradation of IP3R3 (inositol 1,4,5-trisphosphate receptor type 3). Loss of FUNDC1 in FUNDC1^-/- mice accentuated high-fat diet-induced cardiac remodeling, functional and mitochondrial anomalies, cell death, rise in IP3R3, and Ca²⁺ overload. Mass spectrometry and co-immunoprecipitation analyses revealed an interaction between FUNDC1 and FBXL2. Truncated mutants of Fbox (Delta-F-box) disengaged FBXL2 interaction with FUNDC1. Activation or transfection of FBXL2, inhibition of IP3R3 alleviated, whereas disruption of FBXL2 localization sensitized lipotoxicity-induced cardiac damage. FUNDC1 deficiency accelerated and decelerated palmitic acid-induced degradation of FBXL2 and IP3R3, respectively. Our data suggest an essential role for interaction between FUNDC1 and FBXL2 in preserving mitochondrial Ca²⁺ homeostasis and cardiac function in obese hearts.

Autonomous activation of CaMKII exacerbates diastolic calcium leak during beta-adrenergic stimulation in cardiomyocytes of metabolic syndrome rats

Autonomous Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) activation induces abnormal diastolic Ca²⁺ leak, which leads to triggered arrhythmias in a wide range of cardiovascular diseases, including diabetic cardiomyopathy. In hyperglycemia, Ca²⁺ handling alterations can be aggravated under stress conditions via the β-adrenergic signaling pathway, which also involves CaMKII activation. However, little is known about intracellular Ca²⁺ handling disturbances under β-adrenergic stimulation in cardiomyocytes of the prediabetic metabolic syndrome (MetS) model with obesity, and the participation of CaMKII in these alterations. MetS was induced in male Wistar rats by administering 30 % sucrose in drinking water for 16 weeks. Fluo 3-loaded MetS cardiomyocytes exhibited augmented diastolic Ca²⁺ leak (in the form of spontaneous Ca²⁺ waves) under basal conditions and that Ca²⁺ leakage was exacerbated by isoproterenol (ISO, 100 nM). At the molecular level, [³H]-ryanodine binding and basal phosphorylation of cardiac ryanodine receptor (RyR2) at Ser2814, a CaMKII site, were increased in heart homogenates of MetS rats with no changes in RyR2 expression. These alterations were not further augmented by Isoproterenol. SERCA pump activity was augmented 48 % in MetS hearts before β-adrenergic stimuli, which is associated to augmented PLN phosphorylation at T17, a target of CaMKII. In MetS hearts. CaMKII auto-phosphorylation (T287) was increased by 80 %. The augmented diastolic Ca²⁺ leak was prevented by CaMKII inhibition with AIP. In conclusion, CaMKII autonomous activation in cardiomyocytes of MetS rats with central obesity significantly contributes to abnormal diastolic Ca²⁺ leak, increasing the propensity for β-adrenergic receptor-driven lethal arrhythmias.

Antidiabetic Effects of Bisamide Derivative of Dicarboxylic Acid in Metabolic Disorders

In clinical practice, the metabolic syndrome can lead to multiple complications, including diabetes. It remains unclear which component of the metabolic syndrome (obesity, inflammation, hyperglycemia, or insulin resistance) has the strongest inhibitory effect on stem cells involved in beta cell regeneration. This makes it challenging to develop effective treatment options for complications such as diabetes. In our study, experiments were performed on male C57BL/6 mice where metabolic disorders have been introduced experimentally by a combination of streptozotocin-treatment and a high-fat diet. We evaluated the biological effects of Bisamide Derivative of Dicarboxylic Acid (BDDA) and its impact on pancreatic stem cells in vivo. To assess the impact of BDDA, we applied a combination of histological and biochemical methods along with a cytometric analysis of stem cell and progenitor cell markers. We show that in mice with metabolic disorders, BDDA has a positive effect on lipid and glucose metabolism. The pancreatic restoration was associated with a decrease of the inhibitory effects of inflammation and obesity factors on pancreatic stem cells. Our data shows that BDDA increases the number of pancreatic stem cells. Thus, BDDA could be used as a new compound for treating complication of the metabolic syndrome such as diabetes.

Metabolic syndrome diminishes insulin-induced Akt activation and causes a redistribution of Akt-interacting proteins in cardiomyocytes

Metabolic syndrome (MetS) is a cluster of cardiometabolic risk factors, with insulin resistance as a critical component for its development. Insulin signaling in the heart leads to Akt (also known as PKB) activation, a serine/threonine protein kinase, which regulates cardiac glucose metabolism and growth. Cardiac metabolic inflexibility, characterized by impaired insulin-induced glucose uptake and oxidation, has been reported as an early and consistent change in the heart of different models of MetS and diabetes; however, the evaluation of Akt activation has yielded variable results. Here we report in cardiomyocytes of MetS rats, diminished insulin-induced glucose uptake and Akt activation, evaluated by its impaired mobilization towards the plasma membrane and phosphorylation, and reflected in a re-distribution of its interacting proteins, assessed by label-free mass spectrometry (data are available via ProteomeXchange with identifier PXD013260). We report 45 proteins with diminished abundance in Akt complex of MetS cardiomyocytes, mainly represented by energy metabolism-related proteins, and also, 31 Akt-interacting proteins with increased abundance, which were mainly related to contraction, endoplasmic reticulum stress, and Akt negative regulation. These results emphasize the relevance of Akt in the regulation of energy metabolism in the heart and highlight Akt-interacting proteins that could be involved in the detrimental effects of MetS in the heart.

Gender Differences in the Pharmacological Actions of Pegylated Glucagon-Like Peptide-1 on Endothelial Progenitor Cells and Angiogenic Precursor Cells in a Combination of Metabolic Disorders and Lung Emphysema

In clinical practice, the metabolic syndrome (MetS) is often associated with chronic obstructive pulmonary disease (COPD). Although gender differences in MetS are well documented, little is known about sex-specific differences in the pathogenesis of COPD, especially when combined with MetS. Consequently, it is not clear whether the same treatment regime has comparable efficacy in men and women diagnosed with MetS and COPD. In the present study, using sodium glutamate, lipopolysaccharide, and cigarette smoke extract, we simulated lipid metabolism disorders, obesity, hyperglycemia, and pulmonary emphysema (comorbidity) in male and female C57BL/6 mice. We assessed the gender-specific impact of lipid metabolism disorders and pulmonary emphysema on angiogenic precursor cells (endothelial progenitor cells (EPC), pericytes, vascular smooth muscle cells, cells of the lumen of the nascent vessel), as well as the biological effects of pegylated glucagon-like peptide 1 (pegGLP-1) in this experimental paradigm. Simulation of MetS/COPD comorbidity caused an accumulation of EPC (CD45⁻CD31⁺CD34⁺), pericytes, and vascular smooth muscle cells in the lungs of female mice. In contrast, the number of cells involved in the angiogenesis decreased in the lungs of male animals. PegGLP-1 had a positive effect on lipids and area under the curve (AUC), obesity, and prevented the development of pulmonary emphysema. The severity of these effects was stronger in males than in females. Furthermore, PegGLP-1 stimulated regeneration of pulmonary endothelium. At the same time, PegGLP-1 administration caused a mobilization of EPC (CD45⁻CD31⁺CD34⁺) into the bloodstream in females and migration of precursors of angiogenesis and vascular smooth muscle cells to the lungs in male animals. Gender differences in stimulatory action of pegGLP-1 on CD31⁺ endothelial lung cells in vitro were not observed. Based on these findings, we postulated that the cellular mechanism of in vivo regeneration of lung epithelium was at least partly gender-specific. Thus, we concluded that a pegGLP-1-based treatment regime for metabolic disorder and COPD should be further developed primarily for male patients.