Isoproterenol cytotoxicity is dependent on the differentiation state of the cardiomyoblast H9c2 cell line

In vitro characterization of Trypanosoma cruzi infection dynamics in skeletal and cardiac myotubes models suggests a potential cell-to-cell transmission in mediating cardiac pathology

Chagas disease predominantly affects the heart, esophagus, and colon in its chronic phase. However, the precise infection mechanisms of the causal agent Trypanosoma cruzi in these tissue types remain incompletely understood. This study investigated T. cruzi infection dynamics in skeletal (SM) and cardiac myotubes (CM) differentiated from H9c2(2-1) myoblasts (control). SM and CM were generated using 1% fetal bovine serum (FBS) without or with retinoic acid, respectively. Initial invasion efficiencies and numbers of released parasites were equivalent between undifferentiated and differentiated cells (~0.3-0.6%). Concomitantly, parasite motility patterns were similar across cell lines. However, CM demonstrated significantly higher infection kinetics over time, reaching 13.26% infected cells versus 3.12% for SM and 3.70% for myoblasts at later stages. Cellular automata modeling suggested an enhanced role for cell-to-cell transmission in driving the heightened parasitism observed in CM. The increased late-stage susceptibility of CM, potentially mediated by cell-to-cell transfer mechanisms of the parasite, aligns with reported clinical tropism patterns. The myotube infection models provide novel insights into Chagas disease pathogenesis that are not fully attainable through in vivo examination alone. Expanding knowledge in this area could aid therapeutic development for this neglected illness.

Pannexin 1 Channels Control Cardiomyocyte Metabolism and Neutrophil Recruitment During Non-Ischemic Heart Failure

Pannexin 1 (PANX1), a ubiquitously expressed ATP release membrane channel, has been shown to play a role in inflammation, blood pressure regulation, and myocardial infarction. However, a possible role of PANX1 in cardiomyocytes in the progression of heart failure has not yet been investigated. We generated a novel mouse line with constitutive deletion of PANX1 in cardiomyocytes (Panx1 MyHC6 ). PANX1 deletion in cardiomyocytes had no effect on unstressed heart function but increased the glycolytic metabolism both in vivo and in vitro . In vitro , treatment of H9c2 cardiomyocytes with isoproterenol led to PANX1-dependent release of ATP and Yo-Pro-1 uptake, as assessed by pharmacological blockade with spironolactone and siRNA-mediated knock-down of PANX1. To investigate non-ischemic heart failure and the preceding cardiac hypertrophy we administered isoproterenol, and we demonstrate that Panx1 MyHC6 mice were protected from systolic and diastolic left ventricle volume increases and cardiomyocyte hypertrophy. Moreover, we found that Panx1 MyHC6 mice showed decreased isoproterenol-induced recruitment of immune cells (CD45 + ), particularly neutrophils (CD11b + , Ly6g + ), to the myocardium. Together these data demonstrate that PANX1 deficiency in cardiomyocytes impacts glycolytic metabolism and protects against cardiac hypertrophy in non-ischemic heart failure at least in part by reducing immune cell recruitment. Our study implies PANX1 channel inhibition as a therapeutic approach to ameliorate cardiac dysfunction in heart failure patients.

LncRNA H19 inhibition impairs endoplasmic reticulum-mitochondria contact in hepatic cells and augments gluconeogenesis by increasing VDAC1 levels

Inspite of exerting independent cellular functions, the endoplasmic-reticulum (ER) and the mitochondria also physically connect at specific sites termed mitochondria-associated ER membranes (MAMs) and these sites consist of several tethering proteins that play varied roles in diverse cellular processes. However, the regulation of these tethering proteins within the cell is relatively less studied. Here, we show that several MAM proteins are significantly altered in the liver during diabetes and among these, the lncRNA, H19 regulates the levels of VDAC1. Inhibition of H19 expression using H19 specific siRNA altered VDAC1, mitochondrial Ca2+ and oxygen consumption rate, ATP and ROS levels and enhanced ER and mitochondria coupling in Hepa 1-6 cells. While H19 inhibition did not impact lipid accumulation, levels of gluconeogenic genes were significantly increased. JNK-phosphorylation and IRS1-Ser307-phosphorylation were increased by H19 inhibition and this was associated with abrogation of insulin-stimulated AKT (Ser-473) phosphorylation and glucose uptake in Hepa 1-6 cells. While inhibition of VDAC1 expression using siRNAs and with metformin significantly rescued the effects of H19 inhibition, VDAC1 overexpression alone exerted effects similar to H19 inhibition, suggesting that VDAC1 increase mediates the adverse effects of H19. In-vivo H19 inhibition using specific siRNAs increased hepatic VDAC1, pJNK and pIRS1 (Ser307) levels and decreased AKT (Ser-473) phosphorylation in mice. These suggest an important role of the H19-VDAC1 axis in ER-mitochondria coupling and regulation of gluconeogenesis in the liver during diabetes.

Identification and validation of voltage-dependent anion channel 1-related genes and immune cell infiltration in diabetic nephropathy

AIMS/INTRODUCTION

This study investigated the roles of voltage-dependent anion channel 1-related differentially expressed genes (VRDEGs) in diabetic nephropathy (DN).

MATERIALS AND METHODS

We downloaded two datasets from patients with DN, namely, GSE30122 and GSE30529, from the Gene Expression Omnibus database. VRDEGs associated with DN were obtained from the intersection of voltage-dependent anion channel 1-related genes from the GeneCards database, and differentially expressed genes were screened according to group (DN/healthy) in the two datasets. The enriched pathways of the VRDEGs were analyzed. Hub genes were selected using a protein-protein interaction network, and their predictive value was verified through receiver operating characteristic curve analysis. The CIBERSORTx software examined hub genes and immune cell infiltration associations. The protein expression of hub genes was verified through immunohistochemistry in 16-week-old db/db mice for experimentation as a model of type 2 DN. Finally, potential drugs targeting hub genes that inhibit DN development were identified.

RESULTS

A total of 57 VRDEGs were identified. The two datasets showed high expression of the PI3K, Notch, transforming growth factor-β, interleukin-10 and interleukin-17 pathways in DN. Five hub genes (ITGAM, B2M, LYZ, C3 and CASP1) associated with DN were identified and verified. Immunohistochemistry showed that the five hub genes were highly expressed in db/db mice, compared with db/m mice. The infiltration of immune cells was significantly correlated with the five hub genes.

CONCLUSIONS

Five hub genes were significantly correlated with immune cell infiltration and might be crucial to DN development. This study provides insight into the mechanisms involved in the pathogenesis of DN.

The retinoic acid response is a minor component of the cardiac phenotype in H9c2 myoblast differentiation

The H9c2 myoblast cell line, isolated from the left ventricular tissue of rat, is currently used in vitro as a mimetic for skeletal and cardiac muscle due to its biochemical, morphological, and electrical/hormonal signaling properties. During culture, H9c2 cells acquire a myotube phenotype, where a critical component is the inclusion of retinoic acid (RA). The results from some authors on H9c2 suggested that thousands of genes respond to RA stimuli, while others report hundreds of genes responding to RA over different cell types. In this article, using a more appropriate experimental design, we first confirm the H9c2 cardiac phenotype with and without RA and report transcriptomic and physiological changes regarding calcium handling, bioenergetics, and other biological concepts. Interestingly, of the 2360 genes showing a transcriptional change, 622 genes were statistically associated with the RA response. Of these genes, only 305 were RA-specific, and the rest also showed a culture-time component. Thus, the major expression changes (from 74 to 87%) were indeed due to culture conditions over time. Unexpectedly, only a few components of the retinol pathway in KEGG responded to RA. Our results show the role of RA in the H9c2 cultures impacting the interpretation using H9c2 as an in vitro model.

Age-Dependent Changes in Calcium Regulation after Myocardial Ischemia-Reperfusion Injury

During aging, heart structure and function gradually deteriorate, which subsequently increases susceptibility to ischemia-reperfusion (IR). Maintenance of Ca²⁺ homeostasis is critical for cardiac contractility. We used Langendorff's model to monitor the susceptibility of aging (6-, 15-, and 24-month-old) hearts to IR, with a specific focus on Ca²⁺-handling proteins. IR, but not aging itself, triggered left ventricular changes when the maximum rate of pressure development decreased in 24-month-olds, and the maximum rate of relaxation was most affected in 6-month-old hearts. Aging caused a deprivation of Ca²⁺-ATPase (SERCA2a), Na⁺/Ca²⁺ exchanger, mitochondrial Ca²⁺ uniporter, and ryanodine receptor contents. IR-induced damage to ryanodine receptor stimulates Ca²⁺ leakage in 6-month-old hearts and elevated phospholamban (PLN)-to-SERCA2a ratio can slow down Ca²⁺ reuptake seen at 2-5 μM Ca²⁺. Total and monomeric PLN mirrored the response of overexpressed SERCA2a after IR in 24-month-old hearts, resulting in stable Ca²⁺-ATPase activity. Upregulated PLN accelerated inhibition of Ca²⁺-ATPase activity at low free Ca²⁺ in 15-month-old after IR, and reduced SERCA2a content subsequently impairs the Ca²⁺-sequestering capacity. In conclusion, our study suggests that aging is associated with a significant decrease in the abundance and function of Ca²⁺-handling proteins. However, the IR-induced damage was not increased during aging.

Cardioprotective potential of the antioxidant-rich bioactive fraction of Garcinia pedunculata Roxb. ex Buch.-Ham. against isoproterenol-induced myocardial infarction in Wistar rats

This Study aimed to characterise the phenolic compounds in Garcinia pedunculata extract and assess their potential antioxidant activity as well as its cardioprotective potential in isoproterenol-induced cardiac hypertrophy in an experimental animal model. In vitro antioxidant properties were determined using DPPH, ABTS, FRAP, PMD assays. In vitro lipid peroxidation experiment was also performed with heart tissues. Cardioprotective and cardiotoxicity effects were determined using the cell line studies. The cardioprotective effect of GP was assessed in a rat model of isoproterenol-(ISO-) induced cardiac hypertrophy by subcutaneous administration. Heart weight/tail length ratio and cardiac hypertrophy indicators were reduced after oral administration of GP. Additionally, GP reduced oxidative stress and heart inflammation brought on by ISO. In H9c2 cells, the antihypertrophic and anti-inflammatory effects of the extract of GP were seen in the presence of ISO, which were further supported by the in vivo observations. This study makes a compelling case for the possibility that supplementing with dried GP fruit can prevent heart hypertrophy by reducing oxidative stress and inflammation.

Inhibition of mitochondrial respiration has fundamentally different effects on proliferation, cell survival and stress response in immature versus differentiated cardiomyocyte cell lines

Myocardial tissue homeostasis is critically important for heart development, growth and function throughout the life course. The loss of cardiomyocytes under pathological conditions ultimately leads to cardiovascular disease due to the limited regenerative capacity of the postnatal mammalian heart. Inhibition of electron transport along the mitochondrial respiratory chain causes cellular stress characterized by ATP depletion as well as excessive generation of reactive oxygen species. Adult cardiomyocytes are highly susceptible to mitochondrial dysfunction whereas embryonic cardiomyocytes in the mouse heart have been shown to be resistant towards mitochondrial complex III inhibition. To functionally characterize the molecular mechanisms mediating this stress tolerance, we used H9c2 cells as an in vitro model for immature cardiomyoblasts and treated them with various inhibitors of mitochondrial respiration. The complex I inhibitor rotenone rapidly induced cell cycle arrest and apoptosis whereas the complex III inhibitor antimycin A (AMA) had no effect on proliferation and only mildly increased cell death. HL-1 cells, a differentiated and contractile cardiomyocyte cell line from mouse atrium, were highly susceptible to AMA treatment evident by cell cycle arrest and death. AMA induced various stress response mechanisms in H9c2 cells, such as the mitochondrial unfolded protein response (UPR^mt), integrated stress response (ISR), heat shock response (HSR) and antioxidative defense. Inhibition of the UPR, ISR and HSR by siRNA mediated knock down of key components does not impair growth of H9c2 cells upon AMA treatment. In contrast, knock down of NRF2, an important transcriptional regulator of genes involved in detoxification of reactive oxygen species, reduces growth of H9c2 cells upon AMA treatment. Various approaches to activate cell protective mechanisms and alleviate oxidative stress in HL-1 cells failed to rescue them from AMA induced growth arrest and death. In summary, these data show that the site of electron transport interruption along the mitochondrial respiratory chain determines cell fate in immature cardiomyoblasts. The study furthermore points to fundamental differences in stress tolerance and cell survival between immature and differentiated cardiomyocytes which may underlie the growth plasticity of embryonic cardiomyocytes during heart development but also highlight the obstacles of cardioprotective therapies in the adult heart.

Cardiomyocyte-specific knockout of ADAM17 ameliorates left ventricular remodeling and function in diabetic cardiomyopathy of mice

Angiotensin-converting enzyme 2 (ACE2) has proven beneficial in attenuating diabetic cardiomyopathy (DCM) but has been found to be a substrate of a disintegrin and metalloprotease protein-17 (ADAM17). However, whether ADAM17 plays a role in the pathogenesis and intervention of DCM is obscure. In this study, we created cardiomyocyte-specific knockout of ADAM17 (A17^α-MHCKO) mice, and left ventricular dimension, function, pathology and molecular biology were assessed in ADAM17^fl/fl control, A17^α-MHCKO control, ADAM17^fl/fl diabetic and A17^α-MHCKO diabetic mice. Both differentiated H9c2 cells and neonatal rat cardiomyocytes (NRCMs) were used to explore the molecular mechanisms underlying the effect of ADAM17 on DCM. The results showed that protein expression and activity of ADAM17 were upregulated whereas the protein expression of ACE2 was downregulated in the myocardium of diabetic mice. Cardiomyocyte-specific knockout of ADAM17 mitigated cardiac fibrosis and cardiomyocyte apoptosis and ameliorated cardiac dysfunction in mice with DCM. Bioinformatic analyses detected a number of genes enriched in metabolic pathways, in particular the AMPK signaling pathway, expressed differentially between the hearts of A17^α-MHCKO and ADAM17^fl/fl diabetic mice. The mechanism may involve activated AMPK pathway, increased autophagosome formation and improved autophagic flux, which reduced the apoptotic response in cardiomyocytes. In addition, hypoxia-inducible factor-1α (HIF-1α) might act as an upstream mediator of upregulated ADAM17 and ADAM17 might affect AMPK signaling via α1 A-adrenergic receptor (ADRA1A). These results indicated that ADAM17 activity and ACE2 shedding were enhanced in DCM, which was reversed by cardiomyocyte-specific ADAM17 knockout. Thus, inhibition of ADAM17 may provide a promising approach to the treatment of DCM.

Proposed mechanisms underlying the salutary effects of ADAM17 deficiency on diabetic cardiomyopathy. ADAM17 deficiency increases autophagosome formation and improves autophagic flux via reducing ACE2 shedding, activating AMPK pathway, and promoting TFEB nuclear translocation, which reduces the apoptotic response in cardiomyocytes and attenuates left ventricular remodeling and dysfunction in DCM of mice.

D-pinitol attenuates isoproterenol induced myocardial infarction by alleviating cardiac inflammation, oxidative stress and ultrastructural changes in Swiss Albino mice

Cardiovascular diseases are the most disturbing problems throughout the world. The side effects of existing drugs are continuously compelling the scientist to look for better options in terms of safety, efficacy and cost-effectiveness. Our study is also a move in this direction. We have chosen D-pinitol to see its cardioprotective role in isoproterenol-induced myocardial infarction in Swiss Albino mice. Grouping was made by dividing mice into eight groups (n = 6). Group I - control; Group II - Isoproterenol (ISO) (150 mg/kg, i.p.); Group III - D-pinitol (PIN) (25 mg), Group IV - PIN (50 mg), Group V - PIN (100 mg) per kg per oral, respectively with ISO; Group VI - PIN _{per se} (100 mg D-pinitol only); Group VII - Propranolol (PRO) (20 mg/kg/oral) with ISO; and Group VIII - PRO _{per se} (20 mg/kg, p.o.). After 24 hrs of the last dose, the blood sample was collected for biochemical parameters, then mice were, euthanised through cervical dislocation under anesthesia and cardiac tissue was collected for biochemical, histopathological and ultrastructural evaluation. Administration of ISO in mice altered the level of antioxidant markers, cardiac injury markers and inflammatory markers, which were significantly restored towards normal by D-pinitol at the dose of 50 and 100 mg. 25 mg of D-pinitol dosage, did not produce significant cardio protection. The histopathological and ultrastructural analysis further confirmed these findings. Our study showed that D-pinitol significantly protected myocardial damage which was induced by ISO and reverted oxidative stress and inflammation considerably.

Assessing Drug-Induced Mitochondrial Toxicity in Cardiomyocytes: Implications for Preclinical Cardiac Safety Evaluation

Drug-induced cardiotoxicity not only leads to the attrition of drugs during development, but also contributes to the high morbidity and mortality rates of cardiovascular diseases. Comprehensive testing for proarrhythmic risks of drugs has been applied in preclinical cardiac safety assessment for over 15 years. However, other mechanisms of cardiac toxicity have not received such attention. Of them, mitochondrial impairment is a common form of cardiotoxicity and is known to account for over half of cardiovascular adverse-event-related black box warnings imposed by the U.S. Food and Drug Administration. Although it has been studied in great depth, mitochondrial toxicity assessment has not yet been incorporated into routine safety tests for cardiotoxicity at the preclinical stage. This review discusses the main characteristics of mitochondria in cardiomyocytes, drug-induced mitochondrial toxicities, and high-throughput screening strategies for cardiomyocytes, as well as their proposed integration into preclinical safety pharmacology. We emphasize the advantages of using adult human primary cardiomyocytes for the evaluation of mitochondrial morphology and function, and the need for a novel cardiac safety testing platform integrating mitochondrial toxicity and proarrhythmic risk assessments in cardiac safety evaluation.

The Effects of Mechanical Loading Variations on the Hypertrophic, Anti-Apoptotic, and Anti-Inflammatory Responses of Differentiated Cardiomyocyte-like H9C2 Cells

Cardiomyocytes possess the ability to respond to mechanical stimuli by adapting their biological functions. This study investigated cellular and molecular events in cardiomyocyte-like H9C2 cells during differentiation as well as the signalling and gene expression responses of the differentiated cells under various mechanical stretching protocols in vitro. Immunofluorescence was used to monitor MyHC expression and structural changes during cardiomyoblast differentiation. Moreover, alterations in the expression of cardiac-specific markers, cell cycle regulatory factors, MRFs, hypertrophic, apoptotic, atrophy and inflammatory factors, as well as the activation of major intracellular signalling pathways were evaluated during differentiation and under mechanical stretching of the differentiated H9C2 cells. Compared to undifferentiated cells, advanced-differentiation cardiomyoblasts exhibited increased expression of cardiac-specific markers, MyHC, MRFs, and IGF-1 isoforms. Moreover, differentiated cells that underwent a low strain/frequency mechanical loading protocol of intermediate duration showed enhanced expression of MRFs and hypertrophic factors, along with a decreased expression of apoptotic, atrophy, and inflammatory factors compared to both high-strain/frequency loading protocols and to unloaded cells. These findings suggest that altering the strain and frequency of mechanical loading applied on differentiated H9C2 cardiomyoblasts can regulate their anabolic/survival program, with a low-strain/frequency stretching being, overall, most effective at inducing beneficial responses.

Propranolol and low-dose isoproterenol ameliorate insulin resistance, enhance β-arrestin2 signaling, and reduce cardiac remodeling in high-fructose, high-fat diet-fed mice: Comparative study with metformin

AIMS

β-Arrestin2 signaling has emerged as a promising therapeutic target for the management of insulin resistance and related complications. Moreover, recent studies have shown that certain G protein-coupled receptor (GPCR) ligands can modulate β-arrestin2 signaling. The current study examined the effects of the β-blocker propranolol and a low dose of the agonist isoproterenol (L-D-ISOPROT) on β-arrestin2 signaling, insulin resistance, and cardiac remodeling in high-fructose, high-fat diet (HFrHFD)-fed mice. In addition, the effects of these agents were compared to those of the clinical antidiabetic agent, metformin.

MATERIALS AND METHODS

Insulin resistance was induced by HFrHFD feeding for 16 weeks. Mice were then randomly allocated to groups receiving propranolol, L-D-ISOPROT, metformin, or vehicle (control) for 4 weeks starting on week 13 of HFrHFD feeding. Survival rate, body weight, visceral fat weight, blood glucose, serum insulin, insulin resistance index, hepatic β-arrestin2 signaling, heart weight, left and right ventricular thicknesses, cardiac fibrosis severity, serum endothelin-1, cardiac cardiotrophin-1, and cardiac β-arrestin2 signaling were then compared among groups.

KEY FINDINGS

HFrHFD for 16 weeks significantly increased insulin resistance index, cardiac fibrosis area, and serum endothelin-1, and reduced hepatic β-arrestin2 signaling, cardiac cardiotrophin-1, and cardiac β-arrestin2 signaling without significant changes in survival rate, body weight, visceral fat weight, heart weight, or left and right ventricular thicknesses. All three drugs reduced insulin resistance and cardiac remodeling parameters and enhanced β-arrestin2 signaling with variable efficacies.

SIGNIFICANCE

Propranolol and L-D-ISOPROT, like metformin, can reduce insulin-resistance and cardiac remodeling in HFrHFD-fed mice, possibly by upregulating β-arrestin2 signaling activity. Therefore, β-arrestin2-signaling modulation might be a promising strategy for insulin-resistance treatment.

Nuciferine Attenuates Doxorubicin-Induced Cardiotoxicity: An In Vitro and In Vivo Study

Chemotherapeutic drugs are a known factor that impairs the system of life due to their severe side effects. A more worrying fact is that the patients administered with doxorubicin fall under the risk of cardiotoxicity. The evolution of exploring plant-derived compounds is a possible way to combat health issues in therapeutic applications. Hence, this study focuses on the protective effect of plant-based compound nuciferine (NFN) against doxorubicin-induced cardiotoxicity in both in vitro and in vivo models. In this investigation, nuciferine significantly reduces DOX-mediated cardiotoxicity by mitigating reactive oxygen species, thereby preventing DNA fragmentation, regulating apoptosis genes and reducing the caspase 3/7 levels in vitro. Besides, nuciferine has shown significant protection against DOX-induced cardiac impairment and the upregulation of cardiogenic markers in vivo. The DOX-induced oxidative stress can be mitigated via enhancing the endogenous antioxidants, thereby controlling ROS-mediated apoptosis. In virtue of these potential features, nuciferine can be a budding candidate to address therapeutic needs.

Mitochondrial OPA1 cleavage is reversibly activated by differentiation of H9c2 cardiomyoblasts

Optic atrophy-1 (OPA1) is a dynamin-like GTPase localized to the mitochondrial inner membrane, playing key roles in inner membrane fusion and cristae maintenance. OPA1 is regulated by the mitochondrial transmembrane potential (Δψ_m): when Δψ_m is intact, long OPA1 isoforms (L-OPA1) carry out inner membrane fusion. Upon loss of Δψ_m, L-OPA1 isoforms are proteolytically cleaved to short (S-OPA1) isoforms by the stress-inducible OMA1 metalloprotease, causing collapse of the mitochondrial network and promoting apoptosis. Here, we show that L-OPA1 isoforms of H9c2 cardiomyoblasts are retained under loss of Δψ_m, despite the presence of OMA1. However, when H9c2s are differentiated to a more cardiac-like phenotype via treatment with retinoic acid (RA) in low serum media, loss of Δ ψ_m induces robust, and reversible, cleavage of L-OPA1 and subsequent OMA1 degradation. These findings indicate that a potent developmental switch regulates Δ ψ_m-sensitive OPA1 cleavage, suggesting novel developmental and regulatory mechanisms for OPA1 homeostasis.

Context-specific network modeling identifies new crosstalk in β-adrenergic cardiac hypertrophy

Cardiac hypertrophy is a context-dependent phenomenon wherein a myriad of biochemical and biomechanical factors regulate myocardial growth through a complex large-scale signaling network. Although numerous studies have investigated hypertrophic signaling pathways, less is known about hypertrophy signaling as a whole network and how this network acts in a context-dependent manner. Here, we developed a systematic approach, CLASSED (Context-specific Logic-bASed Signaling nEtwork Development), to revise a large-scale signaling model based on context-specific data and identify main reactions and new crosstalks regulating context-specific response. CLASSED involves four sequential stages with an automated validation module as a core which builds a logic-based ODE model from the interaction graph and outputs the model validation percent. The context-specific model is developed by estimation of default parameters, classified qualitative validation, hybrid Morris-Sobol global sensitivity analysis, and discovery of missing context-dependent crosstalks. Applying this pipeline to our prior-knowledge hypertrophy network with context-specific data revealed key signaling reactions which distinctly regulate cell response to isoproterenol, phenylephrine, angiotensin II and stretch. Furthermore, with CLASSED we developed a context-specific model of β-adrenergic cardiac hypertrophy. The model predicted new crosstalks between calcium/calmodulin-dependent pathways and upstream signaling of Ras in the ISO-specific context. Experiments in cardiomyocytes validated the model’s predictions on the role of CaMKII-Gβγ and CaN-Gβγ interactions in mediating hypertrophic signals in ISO-specific context and revealed a difference in the phosphorylation magnitude and translocation of ERK1/2 between cardiac myocytes and fibroblasts. CLASSED is a systematic approach for developing context-specific large-scale signaling networks, yielding insights into new-found crosstalks in β-adrenergic cardiac hypertrophy.

Pathological cardiac hypertrophy is a disease in which the heart grows abnormally in response to different motivators such as high blood pressure or variations in hormones and growth factors. The shape of the heart after its growth depends on the context in which it grows. Since cell signaling in the cardiac cells plays a key role in the determination of heart shape, a thorough understanding of cardiac cells signaling in each context enlightens the mechanisms which control response of cardiac cells. However, cell signaling in cardiac hypertrophy comprises a complex web of pathways with numerous interactions, and predicting how these interactions control the hypertrophic signal in each context is not achievable by only experiments or general computational models. To address this need, we developed an approach to bring together the experimental data of each context with a signaling network curated from literature to identify the main players of cardiac cells response in each context and attain the context-specific models of cardiac hypertrophy. By utilizing our approach, we identified the main regulators of cardiac hypertrophy in four important contexts. We developed a network model of β-adrenergic cardiac hypertrophy, and predicted and validated new interactions that regulate cardiac cells response in this context.

VDAC1 at the Intersection of Cell Metabolism, Apoptosis, and Diseases

The voltage-dependent anion channel 1 (VDAC1) protein, is an important regulator of mitochondrial function, and serves as a mitochondrial gatekeeper, with responsibility for cellular fate. In addition to control over energy sources and metabolism, the protein also regulates epigenomic elements and apoptosis via mediating the release of apoptotic proteins from the mitochondria. Apoptotic and pathological conditions, as well as certain viruses, induce cell death by inducing VDAC1 overexpression leading to oligomerization, and the formation of a large channel within the VDAC1 homo-oligomer. This then permits the release of pro-apoptotic proteins from the mitochondria and subsequent apoptosis. Mitochondrial DNA can also be released through this channel, which triggers type-Ι interferon responses. VDAC1 also participates in endoplasmic reticulum (ER)-mitochondria cross-talk, and in the regulation of autophagy, and inflammation. Its location in the outer mitochondrial membrane, makes VDAC1 ideally placed to interact with over 100 proteins, and to orchestrate the interaction of mitochondrial and cellular activities through a number of signaling pathways. Here, we provide insights into the multiple functions of VDAC1 and describe its involvement in several diseases, which demonstrate the potential of this protein as a druggable target in a wide variety of pathologies, including cancer.

Lotusine, an alkaloid from Nelumbo nucifera (Gaertn.), attenuates doxorubicin-induced toxicity in embryonically derived H9c2 cells

Cardiotoxicity is the major challenge in chemotherapy with doxorubicin (DOX) or adriamycin. Doxorubicin manifests oxidative stress via an uncontrolled progression of reactive oxygen species in cardiomyocytes; thereby, dysregulation and dysfunction of myocardium thus lead to apoptosis. Several attempts have been made to overcome this side effect in patients with antioxidant-rich supplements to control the free radicals. Plant-based or plant-derived compounds pay more attention to cure such complications in patients for supporting the treatment, revitalizing or regulating the normal metabolism. Hence, our study focused on pretreatment of embryonically derived rat cardiomyocytes (H9c2) with phytocompound lotusine to prevent DOX-mediated oxidative stress. From the experiment, the DOX-exposed cells have shown morphological abnormalities such as reduced cell size, shrinkage, blebbing, and chromatin condensation, whereas no such deformities were observed in lotusine-pretreated cells even after the exposure to DOX. Increased endogenous antioxidants with reduced lipid peroxidation were observed in lotusine-pretreated cells, whereas the antioxidants were reduced along with increased lipid peroxidation in doxorubicin-exposed cells. A decreased reactive oxygen species generation was evidenced with the 2',7'-dichlorofluorescein diacetate (DCF-DA) staining method. In qPCR analysis, the lotusine-pretreated cells have mitigated doxorubicin-mediated apoptosis by downregulating the pro-apoptotic gene Bax and apoptotic executor caspase-3. It was further confirmed with the luminometric assay, which resulted in lesser luminescence in lotusine-pretreated cells, whereas higher luminescence was recorded in doxorubicin-alone-treated cells. In conclusion, the present study revealed that the lotusine pretreatment has exhibited potential cardioprotective activity against DOX-induced oxidative stress by increasing the intracellular antioxidant defense.

Experimental models of cardiac physiology and pathology

Experimental models of cardiac disease play a key role in understanding the pathophysiology of the disease and developing new therapies. The features of the experimental models should reflect the clinical phenotype, which can have a wide spectrum of underlying mechanisms. We review characteristics of commonly used experimental models of cardiac physiology and pathophysiology in all translational steps including in vitro, small animal, and large animal models. Understanding their characteristics and relevance to clinical disease is the key for successful translation to effective therapies.

Bcl-2-Protein Family as Modulators of IP3 Receptors and Other Organellar Ca2+ Channels

The pro- and antiapoptotic proteins belonging to the B-cell lymphoma-2 (Bcl-2) family exert a critical control over cell-death processes by enabling or counteracting mitochondrial outer membrane permeabilization. Beyond this mitochondrial function, several Bcl-2 family members have emerged as critical modulators of intracellular Ca²⁺ homeostasis and dynamics, showing proapoptotic and antiapoptotic functions. Bcl-2 family proteins specifically target several intracellular Ca²⁺-transport systems, including organellar Ca²⁺ channels: inositol 1,4,5-trisphosphate receptors (IP₃Rs) and ryanodine receptors (RyRs), Ca²⁺-release channels mediating Ca²⁺ flux from the endoplasmic reticulum, as well as voltage-dependent anion channels (VDACs), which mediate Ca²⁺ flux across the mitochondrial outer membrane into the mitochondria. Although the formation of protein complexes between Bcl-2 proteins and these channels has been extensively studied, a major advance during recent years has been elucidating the complex interaction of Bcl-2 proteins with IP₃Rs. Distinct interaction sites for different Bcl-2 family members were identified in the primary structure of IP₃Rs. The unique molecular profiles of these Bcl-2 proteins may account for their distinct functional outcomes when bound to IP₃Rs. Furthermore, Bcl-2 inhibitors used in cancer therapy may affect IP₃R function as part of their proapoptotic effect and/or as an adverse effect in healthy cells.

Protective effect of Nelumbo nucifera (Gaertn.) against H2O2-induced oxidative stress on H9c2 cardiomyocytes

Ischemic heart disease (IHD), a severe condition of myocardium facing impediment in the supply of basic needs for cellular metabolism is caused by atherosclerosis. Though statin drugs could control the use of surgery on IHD patients, the complete rehabilitation or prophylaxis can be achieved through herbal-based medicines viz. either in the form of crude extract or pure phytocompounds. In the present study, pretreatment with leaf extract of Nelumbo nucifera Gaertn. was investigated for cardioprotective activity-in vitro by mitigating H₂O₂-induced oxidative stress. Analysis such as estimation of antioxidants, lipid peroxidation, and DNA fragmentation assay revealed significant protective effect of plant extract on cardiomyocytes. Reactive oxygen species detection was done by using 2',7'-dichlorofluorescein diacetate, apoptosis detection with Acridine Orange/Ethidium Bromide and nuclear damage detection by diamidino-2-phenylindole which confirmed the protective effect of N. nucifera extract. In addition, gene expression studies of apoptotic regulatory genes (Bcl2 and Cas-9) resulted in significant protection of nucifera extract pretreated and maintained cells. To conclude, in vitro cardioprotective activity of N. nucifera against H₂O₂ induced oxidative stress was achieved at the concentration of 50 µg/ml. Therefore, major phytocompounds present in extract could be beneficial in managing cardiac complications in the future.

Sulfated polysaccharides from the edible marine algae Padina tetrastromatica attenuates isoproterenol-induced oxidative damage via activation of PI3K/Akt/Nrf2 signaling pathway - An in vitro and in vivo approach

The reactive oxygen species (ROS) induced oxidative stress is an inevitable factor for the pathogenesis of cardiovascular diseases. The edible marine algae-derived sulfated polysaccharides gained special attention as novel bioactive compounds having potential pharmacological activities. The present study evaluated in vitro and in vivo cardioprotective properties of sulfated polysaccharides from the edible brown marine algae Padina tetrastromatica (PSPS) against isoproterenol (ISO) induced cardiac damage. The cardioprotective properties of PSPS were first evaluated in H9c2 cardiac myoblasts and the results were confirmed by in vivo studies conducted in male Sprague-Dawley rats. The biochemical parameters, histopathological analysis, mRNA expressions, and ELISA studies indicated that PSPS significantly decreased (p < 0.05) the cardiac damage induced by ISO by reducing lipid peroxidation and improving antioxidant status, both in vitro and in vivo, via modulating PI3k/Akt/Nrf2 signaling pathway. The histopathological evidence further reinforced our findings and highlighted the promising cardioprotective activities offered by PSPS.

Phenolic Metabolites Modulate Cardiomyocyte Beating in Response to Isoproterenol

Cardiovascular disease (CVD) is a public health concern, and the third cause of death worldwide. Several epidemiological studies and experimental approaches have demonstrated that consumption of polyphenol-enriched fruits and vegetables can promote cardioprotection. Thus, diet plays a key role in CVD development and/or prevention. Physiological β-adrenergic stimulation promotes beneficial inotropic effects by increasing heart rate, contractility and relaxation speed of cardiomyocytes. Nevertheless, chronic activation of β-adrenergic receptors can cause arrhythmias, oxidative stress and cell death. Herein the cardioprotective effect of human metabolites derived from polyphenols present in berries was assessed in cardiomyocytes, in response to chronic β-adrenergic stimulation, to disclose some of the underlying molecular mechanisms. Ventricular cardiomyocytes derived from neonate rats were treated with three human bioavailable phenolic metabolites found in circulating human plasma, following berries' ingestion (catechol-O-sulphate, pyrogallol-O-sulphate, and 1-methylpyrogallol-O-sulphate). The experimental conditions mimic the physiological concentrations and circulating time of these metabolites in the human plasma (2 h). Cardiomyocytes were then challenged with the β-adrenergic agonist isoproterenol (ISO) for 24 h. The presence of phenolic metabolites limited ISO-induced mitochondrial oxidative stress. Likewise, phenolic metabolites increased cell beating rate and synchronized cardiomyocyte beating population, following prolonged β-adrenergic receptor activation. Finally, phenolic metabolites also prevented ISO-increased activation of PKA-cAMP pathway, modulating Ca²⁺ signalling and rescuing cells from an arrhythmogenic Ca²⁺ transients' phenotype. Unexpected cardioprotective properties of the recently identified human-circulating berry-derived polyphenol metabolites were identified. These metabolites modulate cardiomyocyte beating and Ca²⁺ transients following β-adrenergic prolonged stimulation.

Dronedarone-Induced Cardiac Mitochondrial Dysfunction and Its Mitigation by Epoxyeicosatrienoic Acids

Dronedarone and amiodarone are structurally similar antiarrhythmic drugs. Dronedarone worsens cardiac adverse effects with unknown causes while amiodarone has no cardiac adversity. Dronedarone induces preclinical mitochondrial toxicity in rat liver and exhibits clinical hepatotoxicity. Here, we further investigated the relative potential of the antiarrhythmic drugs in causing mitochondrial injury in cardiomyocytes. Differentiated rat H9c2 cardiomyocytes were treated with dronedarone, amiodarone, and their respective metabolites namely N-desbutyldronedarone (NDBD) and N-desethylamiodarone (NDEA). Intracellular ATP content, mitochondrial membrane potential (Δψm), and inhibition of carnitine palmitoyltransferase I (CPT1) activity and arachidonic acid (AA) metabolism were measured in H9c2 cells. Inhibition of electron transport chain (ETC) activities and uncoupling of ETC were further studied in isolated rat heart mitochondria. Dronedarone, amiodarone, NDBD and NDEA decreased intracellular ATP content significantly (IC50 = 0.49, 1.84, 1.07, and 0.63 µM, respectively) and dissipated Δψm potently (IC50 = 0.5, 2.94, 12.8, and 7.38 µM, respectively). Dronedarone, NDBD, and NDEA weakly inhibited CPT1 activity while amiodarone (IC50 > 100 µM) yielded negligible inhibition. Only dronedarone inhibited AA metabolism to its regioisomeric epoxyeicosatrienoic acids (EETs) consistently and potently. NADH-supplemented ETC activity was inhibited by dronedarone, amiodarone, NDBD and NDEA (IC50 = 3.07, 5.24, 11.94, and 16.16 µM, respectively). Cytotoxicity, ATP decrease and Δψm disruption were ameliorated via exogenous pre-treatment of H9c2 cells with 11, 12-EET and 14, 15-EET. Our study confirmed that dronedarone causes mitochondrial injury in cardiomyocytes by perturbing Δψm, inhibiting mitochondrial complex I, uncoupling ETC and dysregulating AA-EET metabolism. We postulate that cardiac mitochondrial injury is one potential contributing factor to dronedarone-induced cardiac failure exacerbation.

Three-dimensional spherical gelatin bubble-based scaffold improves the myotube formation of H9c2 myoblasts

Microenvironmental factors including physical and chemical cues can regulate stem cells as well as terminally differentiated cells to modulate their biological function and differentiation. However, one of the physical cues, the substrate's dimensionality, has not been studied extensively. In this study, the flow-focusing method with a microfluidic device was used to generate gelatin bubbles to fabricate highly ordered three-dimensional (3D) scaffolds. Rat H9c2 myoblasts were seeded into the 3D gelatin bubble-based scaffolds and compared to those grown on 2D gelatin-coating substrates to demonstrate the influences of spatial cues on cell behaviors. Relative to cells on the 2D substrates, the H9c2 myoblasts were featured by a good survival and normal mitochondrial activity but slower cell proliferation within the 3D scaffolds. The cortical actin filaments of H9c2 cells were localized close to the cell membrane when cultured on the 2D substrates, while the F-actins distributed uniformly and occupied most of the cell cytoplasm within the 3D scaffolds. H9c2 myoblasts fused as multinuclear myotubes within the 3D scaffolds without any induction but cells cultured on the 2D substrates had a relatively lower fusion index even differentiation medium was provided. Although there was no difference in actin α 1 and myosin heavy chain 1, H9c2 cells had a higher myogenin messenger RNA level in the 3D scaffolds than those of on the 2D substrates. This study reveals that the dimensionality influences differentiation and fusion of myoblasts.

Catalytic activation of β-arrestin by GPCRs

β-arrestins are critical regulator and transducer proteins for G-protein-coupled receptors (GPCRs). β-arrestin is widely believed to be activated by forming a stable and stoichiometric GPCR-β-arrestin scaffold complex, which requires and is driven by the phosphorylated tail of the GPCR. Here we demonstrate a distinct and additional mechanism of β-arrestin activation that does not require stable GPCR-β-arrestin scaffolding or the GPCR tail. Instead, it occurs through transient engagement of the GPCR core, which destabilizes a conserved inter-domain charge network in β-arrestin. This promotes capture of β-arrestin at the plasma membrane and its accumulation in clathrin-coated endocytic structures (CCSs) after dissociation from the GPCR, requiring a series of interactions with membrane phosphoinositides and CCS-lattice proteins. β-arrestin clustering in CCSs in the absence of the upstream activating GPCR is associated with a β-arrestin-dependent component of the cellular ERK (extracellular signal-regulated kinase) response. These results delineate a discrete mechanism of cellular β-arrestin function that is activated catalytically by GPCRs.

Reduced oxygen tension culturing conditionally alters toxicogenic response of differentiated H9c2 cardiomyoblasts to acrolein

Acrolein is a reactive electrophilic aldehyde known to cause mitochondrial dysfunction, oxidative stress, and dysregulation of signaling transduction in vitro. Most in vitro systems employ standard cell culture maintenance conditions of 95% air/5% CO₂, translating to a culture oxygen tension of approximately 20%, far above most physiological tissues. The purpose of this investigation was to examine whether low-serum, retinoic acid differentiated H9c2 cells were less sensitive to acrolein insult when cultured under reduced oxygen tension. H9c2 cells were maintained separately in 20% and 5% oxygen, differentiated for 5 d, and then exposed to acrolein for 30 min in media containing varying concentrations of tricarboxylic acid and glycolytic substrates, followed by fresh medium replacement. Cells were then assessed for MTT reduction at 2 h and 24 h after acrolein insult. We showed that pyruvate supplementation in combination with lowered oxygen culturing significantly attenuated acrolein-induced viability loss at 24 h. Poly(ADP-ribose) polymerase inhibition and EGTA preferentially provided partial rescue to low oxygen cultures, but not for standard cultures. Collectively, these results offer evidence supporting altered toxicogenic response of H9c2 during physiologically relevant oxygen tension culturing.

Disruption of mitochondrial function as mechanism for anti-cancer activity of a novel mitochondriotropic menadione derivative

Menadione, also known as vitamin K₃, is a 2-methyl-1,4 naphthoquinone with a potent cytotoxic activity mainly resulting from its quinone redox-cycling with production of reactive oxygen species (ROS). Although increased ROS generation is considered a relevant mechanism in cancer cell death, it may not be sufficiently effective to kill cancer cells due to phenotypic adaptations. Therefore, combining ROS-generating agents with other molecules targeting important cancer cell phenotypes can be an effective therapeutic strategy. As mitochondrial dysfunction has been implicated in many human diseases, including cancer, we describe here the discovery of a mitochondrial-directed agent (MitoK₃), which was developed by conjugating a TPP cation to the C3 position of the menadione's naphthoquinone ring, increasing its selective accumulation in mitochondria, as well as led to alterations of its redox properties and consequent biological outcome. MitoK₃ disturbed the mitochondrial bioenergetic apparatus, with subsequent loss of mitochondrial ATP production. The combinatory strategy of MitoK₃ with anticancer agent doxorubicin (DOX) resulted in a degree of cytotoxicity higher than those of the individual molecules, as the combination triggered tumour apoptotic cell death evident by caspase 3/9 activities, probably through mitochondrial destabilization or by interference with mitochondrial redox processes. The results of this investigation support the importance of drug discovery process in developing molecules that can be use as adjuvant therapy in patients with specific cancer subtypes.

VDAC1 at the crossroads of cell metabolism, apoptosis and cell stress

This review presents current knowledge related to VDAC1 as a multi-functional mitochondrial protein acting on both sides of the coin, regulating cell life and death, and highlighting these functions in relation to disease. It is now recognized that VDAC1 plays a crucial role in regulating the metabolic and energetic functions of mitochondria. The location of VDAC1 at the outer mitochondrial membrane (OMM) allows the control of metabolic cross-talk between mitochondria and the rest of the cell and also enables interaction of VDAC1 with proteins involved in metabolic and survival pathways. Along with regulating cellular energy production and metabolism, VDAC1 is also involved in the process of mitochondria-mediated apoptosis by mediating the release of apoptotic proteins and interacting with anti-apoptotic proteins. VDAC1 functions in the release of apoptotic proteins located in the mitochondrial intermembrane space via oligomerization to form a large channel that allows passage of cytochrome c and AIF and their release to the cytosol, subsequently resulting in apoptotic cell death. VDAC1 also regulates apoptosis via interactions with apoptosis regulatory proteins, such as hexokinase, Bcl2 and Bcl-xL, some of which are also highly expressed in many cancers. This review also provides insight into VDAC1 function in Ca²⁺ homeostasis, oxidative stress, and presents VDAC1 as a hub protein interacting with over 100 proteins. Such interactions enable VDAC1 to mediate and regulate the integration of mitochondrial functions with cellular activities. VDAC1 can thus be considered as standing at the crossroads between mitochondrial metabolite transport and apoptosis and hence represents an emerging cancer drug target.

Voltage-Dependent Anion Channel 1 As an Emerging Drug Target for Novel Anti-Cancer Therapeutics

Cancer cells share several properties, high proliferation potential, reprogramed metabolism, and resistance to apoptotic cues. Acquiring these hallmarks involves changes in key oncogenes and non-oncogenes essential for cancer cell survival and prosperity, and is accompanied by the increased energy requirements of proliferating cells. Mitochondria occupy a central position in cell life and death with mitochondrial bioenergetics, biosynthesis, and signaling are critical for tumorigenesis. Voltage-dependent anion channel 1 (VDAC1) is situated in the outer mitochondrial membrane (OMM) and serving as a mitochondrial gatekeeper. VDAC1 allowing the transfer of metabolites, fatty acid ions, Ca²⁺, reactive oxygen species, and cholesterol across the OMM and is a key player in mitochondrial-mediate apoptosis. Moreover, VDAC1 serves as a hub protein, interacting with diverse sets of proteins from the cytosol, endoplasmic reticulum, and mitochondria that together regulate metabolic and signaling pathways. The observation that VDAC1 is over-expressed in many cancers suggests that the protein may play a pivotal role in cancer cell survival. However, VDAC1 is also important in mitochondria-mediated apoptosis, mediating release of apoptotic proteins and interacting with anti-apoptotic proteins, such as B-cell lymphoma 2 (Bcl-2), Bcl-xL, and hexokinase (HK), which are also highly expressed in many cancers. Strategically located in a “bottleneck” position, controlling metabolic homeostasis and apoptosis, VDAC1 thus represents an emerging target for anti-cancer drugs. This review presents an overview on the multi-functional mitochondrial protein VDAC1 performing several functions and interacting with distinct sets of partners to regulate both cell life and death, and highlights the importance of the protein for cancer cell survival. We address recent results related to the mechanisms of VDAC1-mediated apoptosis and the potential of associated proteins to modulate of VDAC1 activity, with the aim of developing VDAC1-based approaches. The first strategy involves modification of cell metabolism using VDAC1-specific small interfering RNA leading to inhibition of cancer cell and tumor growth and reversed oncogenic properties. The second strategy involves activation of cancer cell death using VDAC1-based peptides that prevent cell death induction by anti-apoptotic proteins. Finally, we discuss the potential therapeutic benefits of treatments and drugs leading to enhanced VDAC1 expression or targeting VDAC1 to induce apoptosis.

The role of β-adrenergic receptors and p38MAPK signaling pathways in physiological processes of cardiosphere-derived cells

The effects of β adrenergic receptors (β-ARs) and p38 mitogen-activated protein kinases (MAPK) pathways on cardiosphere-derived cells (CDCs) are largely unknown. This study aimed to investigate the roles of β-ARs and p38MAPK pathways on the proliferation, apoptosis, and differentiation capacity of CDCs. The CDCs were treated with β1-AR blocker (Met group), β2-AR antagonist (ICI group), and p38MAPK inhibitor (SB group), non-selective β-AR blocker (PRO group), and β-AR agonist (ISO group). The viability, apoptotic rate and differentiation status of CDCs were determined by MST-1 assay, flow cytometery, and Western blot, respectively. The CDCs viability significantly reduced in ICI group (all P < 0.05), and SB group had a significant high viability after 48 h treatment (P < 0.05). Compared with control group, all treated groups had a low apoptotic rate. After treatment for 72 h, ISO treatment elevated the expression of Nkx2.5, and could partially or fully attenuate the inhibitory effects of β-AR antagonists and/or p38MAPK inhibitor. A similar overall trend of protein expression levels among all groups could be observed between protein pairs of cTnT and β1-AR as well as c-Kit and β2-AR, respectively. These results suggested that β-ARs and p38MAPK signaling pathways play crucial roles in the proliferation and differentiation of CDCs. Our findings should be helpful for better understanding the molecular mechanism underlying the physiological processes of CDCs.

VDAC1 functions in Ca2+ homeostasis and cell life and death in health and disease

In the outer mitochondrial membrane (OMM), the voltage-dependent anion channel 1 (VDAC1) serves as a mitochondrial gatekeeper, controlling the metabolic and energy cross-talk between mitochondria and the rest of the cell. VDAC1 also functions in cellular Ca²⁺ homeostasis by transporting Ca²⁺ in and out of mitochondria. VDAC1 has also been recognized as a key protein in mitochondria-mediated apoptosis, contributing to the release of apoptotic proteins located in the inter-membranal space (IMS) and regulating apoptosis via association with pro- and anti-apoptotic members of the Bcl-2 family of proteins and hexokinase. VDAC1 is highly Ca²⁺-permeable, transporting Ca²⁺ to the IMS and thus modulating Ca²⁺ access to Ca²⁺ transporters in the inner mitochondrial membrane. Intra-mitochondrial Ca²⁺ controls energy metabolism via modulating critical enzymes in the tricarboxylic acid cycle and in fatty acid oxidation. Ca²⁺ also determines cell sensitivity to apoptotic stimuli and promotes the release of pro-apoptotic proteins. However, the precise mechanism by which intracellular Ca²⁺ mediates apoptosis is not known. Here, the roles of VDAC1 in mitochondrial Ca²⁺ homeostasis are presented while emphasizing a new proposed mechanism for the mode of action of pro-apoptotic drugs. This view, proposing that Ca²⁺-dependent enhancement of VDAC1 expression levels is a major mechanism by which apoptotic stimuli induce apoptosis, position VDAC1 oligomerization at a molecular focal point in apoptosis regulation. The interactions of VDAC1 with many proteins involved in Ca²⁺ homeostasis or regulated by Ca²⁺, as well as VDAC-mediated control of cell life and death and the association of VDAC with disease, are also presented.

Functional selectivity of GPCR-directed drug action through location bias

G protein-coupled receptors (GPCRs) are increasingly recognized to operate from intracellular membranes as well as the plasma membrane. The β₂-adrenergic GPCR can activate Gs-linkedcyclic AMP (cAMP) signaling from endosomes. We show here that the homologous human β₁-adrenergic receptor initiates an internal Gs-cAMP signal from the Golgi apparatus. By developing a chemical method to acutely squelch G protein coupling at defined membrane locations, we demonstrate that Golgi activation contributes significantly to the overall cellular cAMP response. Golgi signalling utilizes a pre-existing receptor pool rather than receptors delivered from the cell surface, requiring separate access of extracellular ligands. Epinephrine, a hydrophilic endogenous ligand, accesses the Golgi-localized receptor pool by facilitated transport requiring the organic cation transporter 3 (OCT3) whereas drugs can access the Golgi pool by passive diffusion according to hydrophobicity. We demonstrate marked differences among both agonist and antagonist drugs in Golgi-localized receptor access, and show that β-blocker drugs presently used in the clinic differ markedly in ability to antagonize the Golgi signal. We propose ’location bias’ as a new principle for achieving functional selectivity of GPCR-directed drug action.

Surface-modified particles loaded with CaMKII inhibitor protect cardiac cells against mitochondrial injury

An excess of calcium (Ca²⁺) influx into mitochondria during mitochondrial re-energization is one of the causes of myocardial cell death during ischemic/reperfusion injury. This overload of Ca²⁺ triggers the mitochondrial permeability transition pore (mPTP) opening which leads to programmed cell death. During the ischemic/reperfusion stage, the activated Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) enzyme is responsible for Ca²⁺ influx. To reduce CaMKII-related cell death, sub-micron particles composed of poly(lactic-co-glycolic acid) (PLGA), loaded with a CaMKII inhibitor peptide were fabricated. The CaMKII inhibitor peptide-loaded (CIP) particles were coated with a mitochondria targeting moiety, triphenylphosphonium cation (TPP), which allowed the particles to accumulate and release the peptide inside mitochondria to inhibit CaMKII activity. The fluorescently labeled TPP-CIP was taken up by mitochondria and successfully reduced reactive oxygen species (ROS) caused by Isoprenaline (ISO) in a differentiated rat cardiomyocyte-like cell line. When cells were treated with TPP-CIP prior to ISO exposure, they maintained mitochondrial membrane potential. The TPP-CIP protected cells from ISO-induced ROS production and decreased mitochondrial membrane potential. Thus, TPP-CIP has the potential to be used in protection against ischemia/reperfusion injury.

Novel Platform of Cardiomyocyte Culture and Coculture via Fibroblast-Derived Matrix-Coupled Aligned Electrospun Nanofiber

For cardiac tissue engineering, much attention has been given to the artificial cardiac microenvironment in which anisotropic design of scaffold and extracellular matrix (ECM) are the major cues. Here we propose poly(l-lactide-co-caprolactone) and fibroblast-derived ECM (PLCL/FDM), a hybrid scaffold that combines aligned electrospun PLCL fibers and FDM. Fibroblasts were grown on the PLCL fibers for 5-7 days and subsequently decellularized to produce PLCL/FDM. Various analyses confirmed aligned, FDM-deposited PLCL fibers. Compared to fibronectin (FN)-coated electrospun PLCL fibers (control), H9c2 cardiomyoblast differentiation was significantly effective, and neonatal rat cardiomyocyte (CM) phenotype and maturation was improved on PLCL/FDM. Moreover, a coculture platform was created using multilayer PLCL/FDM in which two different cells make indirect or direct cell-cell contacts. Such coculture platforms demonstrate their feasibility in terms of higher cell viability, efficiency of target cell harvest (>95% in noncontact; 85% in contact mode), and molecular diffusion through the PLCL/FDM layer. Coculture of primary CMs and fibroblasts exhibited much better CM phenotype and improvement of CM maturity upon either direct or indirect interactions, compared to the conventional coculture systems (transwell insert and tissue culture plate (TCP)). Taken together, our platform should be very useful and have significant contributions in investigating some scientific or practical issues of crosstalks between multiple cell types.

Novel Compounds Targeting the Mitochondrial Protein VDAC1 Inhibit Apoptosis and Protect against Mitochondrial Dysfunction

Apoptosis is thought to play a critical role in several pathological processes, such as neurodegenerative diseases (i.e. Parkinson's and Alzheimer's diseases) and various cardiovascular diseases. Despite the fact that apoptotic mechanisms are well defined, there is still no substantial therapeutic strategy to stop or even slow this process. Thus, there is an unmet need for therapeutic agents that are able to block or slow apoptosis in neurodegenerative and cardiovascular diseases. The outer mitochondrial membrane protein voltage-dependent anion channel 1 (VDAC1) is a convergence point for a variety of cell survival and death signals, including apoptosis. Recently, we demonstrated that VDAC1 oligomerization is involved in mitochondrion-mediated apoptosis. Thus, VDAC1 oligomerization represents a prime target for agents designed to modulate apoptosis. Here, high-throughput compound screening and medicinal chemistry were employed to develop compounds that directly interact with VDAC1 and prevent VDAC1 oligomerization, concomitant with an inhibition of apoptosis as induced by various means and in various cell lines. The compounds protected against apoptosis-associated mitochondrial dysfunction, restoring dissipated mitochondrial membrane potential, and thus cell energy and metabolism, decreasing reactive oxidative species production, and preventing detachment of hexokinase bound to mitochondria and disruption of intracellular Ca²⁺ levels. Thus, this study describes novel drug candidates with a defined mechanism of action that involves inhibition of VDAC1 oligomerization, apoptosis, and mitochondrial dysfunction. The compounds VBIT-3 and VBIT-4 offer a therapeutic strategy for treating different diseases associated with enhanced apoptosis and point to VDAC1 as a promising target for therapeutic intervention.

Endocytosis‒Mediated Invasion and Pathogenicity of Streptococcus agalactiae in Rat Cardiomyocyte (H9C2)

Streptococcus agalactiae infection causes high mortality in cardiovascular disease (CVD) patients, especially in case of setting prosthetic valve during cardiac surgery. However, the pathogenesis mechanism of S. agalactiae associate with CVD has not been well studied. Here, we have demonstrated the pathogenicity of S. agalactiae in rat cardiomyocytes (H9C2). Interestingly, both live and dead cells of S. agalactiae were uptaken by H9C2 cells. To further dissect the process of S. agalactiae internalization, we chemically inhibited discrete parts of cellular uptake system in H9C2 cells using genistein, chlorpromazine, nocodazole and cytochalasin B. Chemical inhibition of microtubule and actin formation by nocodazole and cytochalasin B impaired S. agalactiae internalization into H9C2 cells. Consistently, reverse‒ transcription PCR (RT‒PCR) and quantitative real time‒PCR (RT-qPCR) analyses also detected higher levels of transcripts for cytoskeleton forming genes, Acta1 and Tubb5 in S. agalactiae‒infected H9C2 cells, suggesting the requirement of functional cytoskeleton in pathogenesis. Host survival assay demonstrated that S. agalactiae internalization induced cytotoxicity in H9C2 cells. S. agalactiae cells grown with benzyl penicillin reduced its ability to internalize and induce cytotoxicity in H9C2 cells, which could be attributed with the removal of surface lipoteichoic acid (LTA) from S. agalactiae. Further, the LTA extracted from S. agalactiae also exhibited dose‒dependent cytotoxicity in H9C2 cells. Taken together, our data suggest that S. agalactiae cells internalized H9C2 cells through energy‒dependent endocytic processes and the LTA of S. agalactiae play major role in host cell internalization and cytotoxicity induction.

Design, Synthesis, and Cardioprotective Effects of N-Mercapto-Based Hydrogen Sulfide Donors

Hydrogen sulfide (H2S) is a signaling molecule which plays regulatory roles in many physiological and/or pathological processes. Therefore, regulation of H2S levels could have great potential therapeutic value. In this work, we report the design, synthesis, and evaluation of a class of N-mercapto (N-SH)-based H2S donors. Thirty-three donors were synthesized and tested. Our results indicated that controllable H2S release from these donors could be achieved upon structural modifications. Selected donors (NSHD-1, NSHD-2, and NSHD-6) were tested in cellular models of oxidative damage and showed significant cytoprotective effects. Moreover, NSHD-1 and NSHD-2 were also found to exhibit potent protective effects in a murine model of myocardial ischemia reperfusion (MI/R) injury.

Dichloroacetate, the Pyruvate Dehydrogenase Complex and the Modulation of mESC Pluripotency

Introduction

The pyruvate dehydrogenase (PDH) complex is localized in the mitochondrial matrix catalyzing the irreversible decarboxylation of pyruvate to acetyl-CoA and NADH. For proper complex regulation the E1-α subunit functions as an on/off switch regulated by phosphorylation/dephosphorylation. In different cell types one of the four-pyruvate dehydrogenase kinase isoforms (PDHK1-4) can phosphorylate this subunit leading to PDH inactivation. Our previous results with human Embryonic Stem Cells (hESC), suggested that PDHK could be a key regulator in the metabolic profile of pluripotent cells, as it is upregulated in pluripotent stem cells. Therefore, we wondered if metabolic modulation, via inexpensive pharmacological inhibition of PDHK, could impact metabolism and pluripotency.

Methods/Results

In order to assess the importance of the PDH cycle in mouse Embryonic Stem Cells (mESC), we incubated cells with the PDHK inhibitor dichloroacetate (DCA) and observed that in its presence ESC started to differentiate. Changes in mitochondrial function and proliferation potential were also found and protein levels for PDH (both phosphorylated and non-phosphorylated) and PDHK1 were monitored. Interestingly, we were also able to describe a possible pathway that involves Hif-1α and p53 during DCA-induced loss of pluripotency. Results with ESCs treated with DCA were comparable to those obtained for cells grown without Leukemia Inhibitor Factor (LIF), used in this case as a positive control for differentiation.

Conclusions

DCA negatively affects ESC pluripotency by changing cell metabolism and elements related to the PDH cycle, suggesting that PDHK could function as a possible metabolic gatekeeper in ESC, and may be a good target to modulate metabolism and differentiation. Although further molecular biology-based experiments are required, our data suggests that inactive PDH favors pluripotency and that ESC have similar strategies as cancer cells to maintain a glycolytic profile, by using some of the signaling pathways found in the latter cells.

Gene Expression Profiling of H9c2 Myoblast Differentiation towards a Cardiac-Like Phenotype

H9c2 myoblasts are a cell model used as an alternative for cardiomyocytes. H9c2 cells have the ability to differentiate towards a cardiac phenotype when the media serum is reduced in the presence of all-trans-retinoic acid (RA), creating multinucleated cells with low proliferative capacity. In the present study, we performed for the first time a transcriptional analysis of the H9c2 cell line in two differentiation states, i.e. embryonic cells and differentiated cardiac-like cells. The results show that RA-induced H9c2 differentiation increased the expression of genes encoding for cardiac sarcomeric proteins such as troponin T, or calcium transporters and associated machinery, including SERCA2, ryanodine receptor and phospholamban as well as genes associated with mitochondrial energy production including respiratory chain complexes subunits, mitochondrial creatine kinase, carnitine palmitoyltransferase I and uncoupling proteins. Undifferentiated myoblasts showed increased gene expression of pro-survival proteins such as Bcl-2 as well as cell cycle-regulating proteins. The results indicate that the differentiation of H9c2 cells lead to an increase of transcripts and protein levels involved in calcium handling, glycolytic and mitochondrial metabolism, confirming that H9c2 cell differentiation induced by RA towards a more cardiac-like phenotype involves remodeled mitochondrial function. PI3K, PDK1 and p-CREB also appear to be involved on H9c2 differentiation. Furthermore, complex analysis of differently expressed transcripts revealed significant up-regulation of gene expression related to cardiac muscle contraction, dilated cardiomyopathy and other pathways specific for the cardiac tissue. Metabolic and gene expression remodeling impacts cell responses to different stimuli and determine how these cells are used for biochemical assays.

Pseudomonas aeruginosa PAO1 induces distinct cell death mechanisms in H9C2 cells and its differentiated form

Bacterial infections in myocardium may lead to the myocardial damage, which may progress to dilated cardiomyopathy and cardiac arrest. Pseudomonas aeruginosa has been reported to cause myocarditis and other systemic infections especially in immunocompromised patients. To understand the cellular responses during the establishment of infection in myocardium, we challenged differentiated H9C2 cells with P. aeruginosa PAO1. We also did comparison studies with infected undifferentiated form of H9C2 cells. Invasion studies revealed that PAO1 can invade both forms of cells and is able to survive and replicate within the host. Internalization of PAO1 was confirmed by live cell imaging and flow cytometry analysis. Though invasion of the pathogen triggered an increased ROS production in the host cells at earlier post-infection periods, it was decreased at later post-infection periods. Invasion of PAO1 induced cell death through apoptosis in differentiated H9C2 cells. Significant decrease in cell size, formation of polarized mitochondria, and nuclear fragmentation were observed in the infected differentiated cells. On the contrary, cell death preceded by multinucleation was observed in infected undifferentiated H9C2 cells. Morphological markers such as multinuclei and micro nuclei were observed. Cell cycle arrest in G2/M phase corroborates that the undifferentiated H9C2 cells experienced cell death preceded by multinucleation.

Hydrogen gas protects against serum and glucose deprivation‑induced myocardial injury in H9c2 cells through activation of the NF‑E2‑related factor 2/heme oxygenase 1 signaling pathway

Ischemia or hypoxia‑induced myocardial injury is closely associated with oxidative stress. Scavenging free radicals and/or enhancing endogenous antioxidative defense systems may be beneficial for the impediment of myocardial ischemic injury. Hydrogen (H2) gas, as a water‑ and lipid‑soluble small molecule, is not only able to selectively eliminate hydroxyl (·OH) free radicals, but also to enhance endogenous antioxidative defense systems in rat lungs and arabidopsis plants. However, thus far, it has remained elusive whether H2 gas protects cardiomyocytes through enhancement of endogenous antioxidative defense systems. In the present study, the cardioprotective effect of H2 gas against ischemic or hypoxic injury was investigated, along with the underlying molecular mechanisms. H9c2 cardiomyoblasts (H9c2 cells) were treated in vitro with a chemical hypoxia inducer, cobalt chloride (CoCl2), to imitate hypoxia, or by serum and glucose deprivation (SGD) to imitate ischemia. Cell viability and intracellular ·OH free radicals were assessed. The role of an endogenous antioxidative defense system, the NF‑E2‑related factor 2 (Nrf2)/heme oxygenase 1 (HO‑1) signaling pathway, was evaluated. The findings revealed that treatment with CoCl2 or SGD markedly reduced cell viability in H9c2 cells. H2 gas‑rich medium protected against cell injury induced by SGD, but not that induced by CoCl2. When the cells were exposed to SGD, levels of intracellular ·OH free radicals were markedly increased; this was mitigated by H2 gas‑rich medium. Exposure of the cells to SGD also resulted in significant increases in HO‑1 expression and nuclear Nrf2 levels, and the HO‑1 inhibitor ZnPP IX and the Nrf2 inhibitor brusatol aggravated SGD‑induced cellular injury. H2 gas‑rich medium enhanced SGD‑induced upregulation of HO‑1 and Nrf2, and the HO‑1 or Nrf2 inhibition partially suppressed H2 gas‑induced cardioprotection. Furthermore, following genetic silencing of Nrf2 by RNA interference, the effects of H2 gas on the induction of HO‑1 and cardioprotection were markedly reduced. In conclusion, H2 gas protected cardiomyocytes from ischemia‑induced myocardial injury through elimination of ·OH free radicals and also through activation of the Nrf2/HO‑1 signaling pathway.

A systematic review of fetal genes as biomarkers of cardiac hypertrophy in rodent models of diabetes

Pathological cardiac hypertrophy activates a suite of genes called the fetal gene program (FGP). Pathological hypertrophy occurs in diabetic cardiomyopathy (DCM); therefore, the FGP is widely used as a biomarker of DCM in animal studies. However, it is unknown whether the FGP is a consistent marker of hypertrophy in rodent models of diabetes. Therefore, we analyzed this relationship in 94 systematically selected studies. Results showed that diabetes induced with cytotoxic glucose analogs such as streptozotocin was associated with decreased cardiac weight, but genetic or diet-induced models of diabetes were significantly more likely to show cardiac hypertrophy (P<0.05). Animal strain, sex, age, and duration of diabetes did not moderate this effect. There were no correlations between the heart weight:body weight index and mRNA or protein levels of the fetal genes α-myosin heavy chain (α-MHC) or β-MHC, sarco/endoplasmic reticulum Ca²⁺-ATPase, atrial natriuretic peptide (ANP), or brain natriuretic peptide. The only correlates of non-indexed heart weight were the protein levels of α-MHC (Spearman's ρ = 1, P<0.05) and ANP (ρ = −0.73, P<0.05). These results indicate that most commonly measured genes in the FGP are confounded by diabetogenic methods, and are not associated with cardiac hypertrophy in rodent models of diabetes.

Inhibition of mitochondrial complex III blocks neuronal differentiation and maintains embryonic stem cell pluripotency

The mitochondrion is emerging as a key organelle in stem cell biology, acting as a regulator of stem cell pluripotency and differentiation. In this study we sought to understand the effect of mitochondrial complex III inhibition during neuronal differentiation of mouse embryonic stem cells. When exposed to antimycin A, a specific complex III inhibitor, embryonic stem cells failed to differentiate into dopaminergic neurons, maintaining high Oct4 levels even when subjected to a specific differentiation protocol. Mitochondrial inhibition affected distinct populations of cells present in culture, inducing cell loss in differentiated cells, but not inducing apoptosis in mouse embryonic stem cells. A reduction in overall proliferation rate was observed, corresponding to a slight arrest in S phase. Moreover, antimycin A treatment induced a consistent increase in HIF-1α protein levels. The present work demonstrates that mitochondrial metabolism is critical for neuronal differentiation and emphasizes that modulation of mitochondrial functions through pharmacological approaches can be useful in the context of controlling stem cell maintenance/differentiation.

Mitochondrial disruption occurs downstream from β-adrenergic overactivation by isoproterenol in differentiated, but not undifferentiated H9c2 cardiomyoblasts: differential activation of stress and survival pathways

β-Adrenergic receptor stimulation plays an important role in cardiomyocyte stress responses, which may result in apoptosis and cardiovascular degeneration. We previously demonstrated that toxicity of the β-adrenergic agonist isoproterenol on H9c2 cardiomyoblasts depends on the stage of cell differentiation. We now investigate β-adrenergic receptor downstream signaling pathways and stress responses that explain the impact of muscle cell differentiation on hyper-β-adrenergic stimulation-induced cytotoxicity. When incubated with isoproterenol, differentiated H9c2 muscle cells have increased cytosolic calcium, cyclic-adenosine monophosphate content and oxidative stress, as well as mitochondrial depolarization, increased superoxide anion, loss of subunits from the mitochondrial respiratory chain, decreased Bcl-xL content, increased p53 and phosphorylated-p66Shc as well as activated caspase-3. Undifferentiated H9c2 cells incubated with isoproterenol showed increased Bcl-xL protein and increased superoxide dismutase 2 which may act as protective mechanisms. We conclude that the differentiation of H9c2 is associated with differential regulation of stress responses, which impact the toxicity of several agents, namely those acting through β-adrenergic receptors and resulting in mitochondrial disruption in differentiated cells only.

Berberine improves insulin resistance in cardiomyocytes via activation of 5'-adenosine monophosphate-activated protein kinase

OBJECTIVE

Insulin resistance plays an important role in the pathogenesis of diabetic cardiomyopathy. Berberine (BBR) is a plant alkaloid which promotes hypoglycemia via increasing insulin sensitivity in peripheral tissues. Little is known of BBR's role in regulating glucose metabolism in heart.

MATERIALS/METHODS

We examined the effect and mechanism of BBR on glucose consumption and glucose uptake in insulin sensitive or insulin resistant rat H9c2 cardiomyocyte cells. H9c2 myoblast cells were differentiated into cardiomyocytes and incubated with insulin for 24h to induce insulin resistance.

RESULTS

BBR-treatment of H9c2 cells increased glucose consumption and glucose uptake compared to controls. In addition, BBR-treatment attenuated the reduction in glucose consumption and glucose uptake in insulin resistant H9c2 cells. Compound C, an inhibitor of AMP-activated protein kinase (AMPK), abolished the enhancement of glucose consumption and glucose uptake mediated by BBR in both insulin sensitive and insulin resistant H9c2 cells compared to controls.

CONCLUSION

BBR significantly increased AMPK activity, but had little effect on the activity of protein kinase B (AKT) in insulin resistant H9c2 cells, suggesting that berberine improves insulin resistance in H9c2 cardiomyocytes at least in part via stimulation of AMPK activity.

Short term exercise induces PGC-1α, ameliorates inflammation and increases mitochondrial membrane proteins but fails to increase respiratory enzymes in aging diabetic hearts

PGC-1α, a transcriptional coactivator, controls inflammation and mitochondrial gene expression in insulin-sensitive tissues following exercise intervention. However, attributing such effects to PGC-1α is counfounded by exercise-induced fluctuations in blood glucose, insulin or bodyweight in diabetic patients. The goal of this study was to investigate the role of PGC-1α on inflammation and mitochondrial protein expressions in aging db/db mice hearts, independent of changes in glycemic parameters. In 8-month-old db/db mice hearts with diabetes lasting over 22 weeks, short-term, moderate-intensity exercise upregulated PGC-1α without altering body weight or glycemic parameters. Nonetheless, such a regimen lowered both cardiac (macrophage infiltration, iNOS and TNFα) and systemic (circulating chemokines and cytokines) inflammation. Curiously, such an anti-inflammatory effect was also linked to attenuated expression of downstream transcription factors of PGC-1α such as NRF-1 and several respiratory genes. Such mismatch between PGC-1α and its downstream targets was associated with elevated mitochondrial membrane proteins like Tom70 but a concurrent reduction in oxidative phosphorylation protein expressions in exercised db/db hearts. As mitochondrial oxidative stress was predominant in these hearts, in support of our in vivo data, increasing concentrations of H₂O₂ dose-dependently increased PGC-1α expression while inhibiting expression of inflammatory genes and downstream transcription factors in H9c2 cardiomyocytes in vitro. We conclude that short-term exercise-induced oxidative stress may be key in attenuating cardiac inflammatory genes and impairing PGC-1α mediated gene transcription of downstream transcription factors in type 2 diabetic hearts at an advanced age.