Metabolic Remodeling During H9c2 Myoblast Differentiation: Relevance for In Vitro Toxicity Studies

6PPDQ induces cardiomyocyte senescence via AhR/ROS-mediated autophagic flux blockage

Recently, attention has been drawn to the adverse outcomes of N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPDQ) on human health, but its cardiac toxicity has been relatively understudied. This work aims to investigate the effects of 6PPDQ on differentiated H9c2 cardiomyocytes. Our findings demonstrated that exposure to 6PPDQ altered cellular morphology and disrupted the expression of cardiac-specific markers. Significantly, 6PPDQ exposure led to cardiomyocyte senescence, characterized by elevated β-Galactosidase activity, upregulation of cell cycle inhibitor, induction of DNA double-strand breaks, and remodeling of Lamin B1. Furthermore, 6PPDQ hindered autophagy flux by promoting the formation of autophagosomes while inhibiting the degradation of autolysosomes. Remarkably, restoration of autophagic flux using rapamycin counteracted 6PPDQ-induced cardiomyocyte senescence. Additionally, our study revealed that 6PPDQ significantly increased the ROS production. However, ROS scavenger effectively reduced the blockage of autophagic flux and cardiomyocyte senescence caused by 6PPDQ. Furthermore, we discovered that 6PPDQ activated the Aryl hydrocarbon receptor (AhR) signaling pathway. AhR antagonist was found to reverse the blockage of autophagy and alleviate cardiac senescence, while also reducing ROS levels in 6PPDQ-treated group. In conclusion, our research unveils that exposure to 6PPDQ induces ROS overproduction through AhR activation, leading to disruption of autophagy flux and ultimately contributing to cardiomyocyte senescence.

Systematic cryopreservation study of cardiac myoblasts in suspension

H9c2 myoblasts are a cell line derived from embryonic rat heart tissue and demonstrate the ability to differentiate to cardiac myotubes upon reduction of the serum concentration (from 10% to 1%) and addition of all-trans retinoic acid in the growth medium. H9c2 cells are increasingly being used as an easy-to-culture proxy for some functions of cardiomyocytes. The cryobiology of cardiac cells including H9c2 myoblasts has not been studied as extensively as that of some cell types. Consequently, it is important to characterize the cryobiological response and systematically develop well-optimized cryopreservation protocols for H9c2 cells to have optimal and consistent viability and functionality after thaw for high quality studies with this cell type. In this work, an interrupted slow cooling protocol (graded freezing) was applied to characterize H9c2 response throughout the cooling profile. Important factors that affect the cell response were examined, and final protocols that provided the highest post-thaw viability are reported. One protocol uses the common cryoprotectant dimethyl sulfoxide combined with hydroxyethyl starch, which will be suitable for applications in which the presence of dimethyl sulfoxide is not an issue; and the other protocol uses glycerol as a substitute when there is a desire to avoid dimethyl sulfoxide. Both protocols achieved comparable post-thaw viabilities (higher than 80%) based on SYTO 13/GelRed flow cytometry results. H9c2 cells cryopreserved by either protocol showed ability to differentiate to cardiac myotubes comparable to fresh (unfrozen) H9c2 cells, and their differentiation to cardiac myotubes was confirmed with i) change in cell morphology, ii) expression of cardiac marker troponin I, and iii) increase in mitochondrial mass.

Temperature Dependence of Membrane Permeability Parameters for Five Cell Types Using Nonideal Thermodynamic Assumptions to Mathematically Model Cryopreservation Protocols

Cryopreservation is the process of preserving biological matter at subzero temperatures for long-term storage. During cryopreservation, cells are susceptible to various injuries that can be mitigated by controlling the cooling and warming profiles and cryoprotective agent (CPA) addition and removal procedures. Mathematical modeling of the changing cell volume at different temperatures can greatly reduce the experiments needed to optimize cryopreservation protocols. Such mathematical modeling requires as inputs the cell membrane permeabilities to water and CPA and the osmotically inactive fraction of the cell. Since the intra- and extracellular solutions are generally thermodynamically nonideal, our group has been incorporating the osmotic virial equation to model the solution thermodynamics that underlie the cell volume change equations, adding the second and third osmotic virial coefficients of the grouped intracellular solute to the cell osmotic parameters that must be measured. In our previous work, we reported methods to obtain cell osmotic parameters at room temperature by fitting experimental cell volume kinetic data with equations that incorporated nonideal solution thermodynamics assumptions. Since the relevant cell volume excursions occur at different temperatures, the temperature dependence of the osmotic parameters plays an important role. In this work, we present a new two-part fitting method to obtain five cell-type-specific parameters (water permeability, dimethyl sulfoxide permeability, osmotically inactive fraction, and the second and third osmotic virial coefficients of the intracellular solution) from experimental measurements of equilibrium cell volume and cell volume as a function of time at room temperature and 0 °C for five cell types, namely, human umbilical vein endothelial cells (HUVECs), H9c2 rat myoblasts, porcine corneal endothelial cells (PCECs), the Jurkat T-lymphocyte cell line, and human cerebral microvascular endothelial cells (hCMECs/D3 cell line). The fitting method in this work is based on both equilibrium and kinetic cell volume data, enabling us to solve some technical challenges and expand our previously reported measurement technique to 0 °C. Finally, we use the measured parameters to model the cell volume changes for a HUVEC cryopreservation protocol to demonstrate the impact of the nonideal thermodynamic assumptions on predicting the changing cell volume during freezing and thawing.

Biomimetic cardiac tissue chip and murine arteriovenous fistula models for recapitulating clinically relevant cardiac remodeling under volume overload conditions

Cardiovascular events are the primary cause of death among dialysis patients. While arteriovenous fistulas (AVFs) are the access of choice for hemodialysis patients, AVF creation can lead to a volume overload (VO) state in the heart. We developed a three-dimensional (3D) cardiac tissue chip (CTC) with tunable pressure and stretch to model the acute hemodynamic changes associated with AVF creation to complement our murine AVF model of VO. In this study, we aimed to replicate the hemodynamics of murine AVF models in vitro and hypothesized that if 3D cardiac tissue constructs were subjected to "volume overload" conditions, they would display fibrosis and key gene expression changes seen in AVF mice. Mice underwent either an AVF or sham procedure and were sacrificed at 28 days. Cardiac tissue constructs composed of h9c2 rat cardiac myoblasts and normal adult human dermal fibroblasts in hydrogel were seeded into devices and exposed to 100 mg/10 mmHg pressure (0.4 s/0.6 s) at 1 Hz for 96 h. Controls were exposed to "normal" stretch and experimental group exposed to "volume overload". RT-PCR and histology were performed on the tissue constructs and mice left ventricles (LVs), and transcriptomics of mice LVs were also performed. Our tissue constructs and mice LV both demonstrated cardiac fibrosis as compared to control tissue constructs and sham-operated mice, respectively. Gene expression studies in our tissue constructs and mice LV demonstrated increased expression of genes associated with extracellular matrix production, oxidative stress, inflammation, and fibrosis in the VO conditions vs. control conditions. Our transcriptomics studies demonstrated activated upstream regulators related to fibrosis, inflammation, and oxidative stress such as collagen type 1 complex, TGFB1, CCR2, and VEGFA and inactivated regulators related to mitochondrial biogenesis in LV from mice AVF. In summary, our CTC model yields similar fibrosis-related histology and gene expression profiles as our murine AVF model. Thus, the CTC could potentially play a critical role in understanding cardiac pathobiology of VO states similar to what is present after AVF creation and may prove useful in evaluating therapies.

Noninvasive Diagnosis of the Mitochondrial Function of Doxorubicin-Induced Cardiomyopathy Using In Vivo Dynamic Nuclear Polarization-Magnetic Resonance Imaging

Doxorubicin (DOX) induces dose-dependent cardiotoxicity via oxidative stress and abnormal mitochondrial function in the myocardium. Therefore, a noninvasive in vivo imaging procedure for monitoring the redox status of the heart may aid in monitoring diseases and developing treatments. However, an appropriate technique has yet to be developed. In this study, we demonstrate a technique for detecting and visualizing the redox status of the heart using in vivo dynamic nuclear polarization–magnetic resonance imaging (DNP–MRI) with 3-carbamoyl-PROXYL (CmP) as a molecular imaging probe. Male C57BL/6N mice were administered DOX (20 mg/kg) or saline. DNP–MRI clearly showed a slower DNP signal reduction in the DOX group than in the control group. Importantly, the difference in the DNP signal reduction rate between the two groups occurred earlier than that detected by physiological examination or clinical symptoms. In an in vitro experiment, KCN (an inhibitor of complex IV in the mitochondrial electron transport chain) and DOX inhibited the electron paramagnetic resonance change in H9c2 cardiomyocytes, suggesting that the redox metabolism of CmP in the myocardium is mitochondrion-dependent. Therefore, this molecular imaging technique has the potential to monitor the dynamics of redox metabolic changes in DOX-induced cardiomyopathy and facilitate an early diagnosis of this condition.

Untargeted Metabolomics Studies of H9c2 Cardiac Cells Submitted to Oxidative Stress, β-Adrenergic Stimulation and Doxorubicin Treatment: Investigation of Cardiac Biomarkers

One of the biggest challenges in the search for more effective treatments for diseases is understanding their etiology. Cardiovascular diseases (CVD) are an important example of this, given the high number of deaths annually. Oxidative stress (the imbalance between oxidant and antioxidant species in biological system) is one of the factors responsible for CVD occurrence, demanding extensive investigation. Excess of reactive oxygen species (ROS) are primarily responsible for this condition, and clinical and scientific literature have reported a significant increase in ROS when therapeutic drugs, such as doxorubicin and isoproterenol, are administered. In this context, the aim of this study is the investigation of potential biomarkers that might be associated with oxidative stress in cardiomyocytes. For this purpose, H9c2 cardiomyocytes were submitted to oxidative stress conditions by treatment with doxorubicin (DOX), isoproterenol (ISO) and hydrogen peroxide (PER). Metabolomics analyses of the cell extract and the supernatant obtained from the culture medium were then evaluated by CE-ESI(+)-TOF-MS. Following signal processing, statistical analyses, and molecular features annotations, the results indicate changes in the aspartate, serine, pantothenic acid, glycerophosphocholine and glutathione metabolism in the cell extract.

Comprehending Cardiac Dysfunction by Oxidative Stress: Untargeted Metabolomics of In Vitro Samples

Cardiovascular diseases (CVDs) are noncommunicable diseases known for their complex etiology and high mortality rate. Oxidative stress (OS), a condition in which the release of free radical exceeds endogenous antioxidant capacity, is pivotal in CVC, such as myocardial infarction, ischemia/reperfusion, and heart failure. Due to the lack of information about the implications of OS on cardiovascular conditions, several methodologies have been applied to investigate the causes and consequences, and to find new ways of diagnosis and treatment as well. In the present study, cardiac dysfunction was evaluated by analyzing cells’ alterations with untargeted metabolomics, after simulation of an oxidative stress condition using hydrogen peroxide (H₂O₂) in H9c2 myocytes. Optimizations of H₂O₂ concentration, cell exposure, and cell recovery times were performed through MTT assays. Intracellular metabolites were analyzed right after the oxidative stress (oxidative stress group) and after 48 h of cell recovery (recovery group) by ultra-high-performance liquid chromatography coupled to mass spectrometry (UHPLC-MS) in positive and negative ESI ionization mode. Significant alterations were found in pathways such as “alanine, aspartate and glutamate metabolism”, “glycolysis”, and “glutathione metabolism”, mostly with increased metabolites (upregulated). Furthermore, our results indicated that the LC-MS method is effective for studying metabolism in cardiomyocytes and generated excellent fit (R²Y > 0.987) and predictability (Q² > 0.84) values.

Systematic transcriptomic and phenotypic characterization of human and murine cardiac myocyte cell lines and primary cardiomyocytes reveals serious limitations and low resemblances to adult cardiac phenotype

BACKGROUND

Cardiac cell lines and primary cells are widely used in cardiovascular research. Despite increasing number of publications using these models, comparative characterization of these cell lines has not been performed, therefore, their limitations are undetermined. We aimed to compare cardiac cell lines to primary cardiomyocytes and to mature cardiac tissues in a systematic manner.

METHODS AND RESULTS

Cardiac cell lines (H9C2, AC16, HL-1) were differentiated with widely used protocols. Left ventricular tissue, neonatal primary cardiomyocytes, and human induced pluripotent stem cell-derived cardiomyocytes served as reference tissue or cells. RNA expression of cardiac markers (e.g. Tnnt2, Ryr2) was markedly lower in cell lines compared to references. Differentiation induced increase in cardiac- and decrease in embryonic markers however, the overall transcriptomic profile and annotation to relevant biological processes showed consistently less pronounced cardiac phenotype in all cell lines in comparison to the corresponding references. Immunocytochemistry confirmed low expressions of structural protein sarcomeric alpha-actinin, troponin I and caveolin-3 in cell lines. Susceptibility of cell lines to sI/R injury in terms of viability as well as mitochondrial polarization differed from the primary cells irrespective of their degree of differentiation.

CONCLUSION

Expression patterns of cardiomyocyte markers and whole transcriptomic profile, as well as response to sI/R, and to hypertrophic stimuli indicate low-to-moderate similarity of cell lines to primary cells/cardiac tissues regardless their differentiation. Low resemblance of cell lines to mature adult cardiac tissue limits their potential use. Low translational value should be taken into account while choosing a particular cell line to model cardiomyocytes.

Neutral Re(I) Complex Platform for Live Intracellular Imaging

Luminescent metal complexes are a valuable platform for the generation of cell imaging agents. However, many metal complexes are cationic, a factor that can dominate the intracellular accumulation to specific organelles. Neutral Re(I) complexes offer a more attractive platform for the development of bioconjugated imaging agents, where charge cannot influence their intracellular distribution. Herein, we report the synthesis of a neutral complex (ReAlkyne), which was used as a platform for the generation of four carbohydrate-conjugated imaging agents via Cu(I)-catalyzed azide-alkyne cycloaddition. A comprehensive evaluation of the physical and optical properties of each complex is provided, together with a determination of their utility as live cell imaging agents in H9c2 cardiomyoblasts. Unlike their cationic counterparts, many of which localize within mitochondria, these neutral complexes have localized within the endosomal/lysosomal network, a result consistent with examples of dinuclear carbohydrate-appended neutral Re(I) complexes that have been reported. This further demonstrates the utility of these neutral Re(I) complex imaging platforms as viable imaging platforms for the development of bioconjugated cell imaging agents.

Afrostyrax lepidophyllus Mildbr. and Monodora myristica (Gaertn.) Dunal Extracts Decrease Doxorubicin Cytotoxicity on H9c2 Cardiomyoblasts

Materials and Methods

Bark extracts of these plants (1 and 25 µg/mL) were added 3 hours before coincubating H9c2 cardiomyoblasts with Dox (0.5 and 1 µM) for 24 hours more. We measured cell mass and metabolic viability, mitochondrial transmembrane potential, superoxide anion content, and activity-like of caspase-3 and caspase-9 following treatment with the extracts and/or Dox. Also, selenium and vitamin C contents were measured in the plant extracts.

Results

The results confirmed that Dox treatment decreased cell mass, mitochondrial membrane potential and metabolic viability, increased mitochondrial superoxide anion, and stimulated caspase-3 and caspase-9-like activities. Pretreatment of the cells with the plant extracts significantly inhibited Dox cytotoxicity, with more significant results at the higher concentration. Measurements of selenium and vitamin C in the extracts revealed higher concentration of both when compared with other Cameroonian spices.

Conclusion

Both extracts of A. lepidophyllus and M. myristica were effective against Dox-induced cytotoxicity, most likely due to their content in antioxidants.

Considerations for using isolated cell systems to understand cardiac metabolism and biology

Changes in myocardial metabolic activity are fundamentally linked to cardiac health and remodeling. Primary cardiomyocytes, induced pluripotent stem cell-derived cardiomyocytes, and transformed cardiomyocyte cell lines are common models used to understand how (patho)physiological conditions or stimuli contribute to changes in cardiac metabolism. These cell models are helpful also for defining metabolic mechanisms of cardiac dysfunction and remodeling. Although technical advances have improved our capacity to measure cardiomyocyte metabolism, there is often heterogeneity in metabolic assay protocols and cell models, which could hinder data interpretation and discernment of the mechanisms of cardiac (patho)physiology. In this review, we discuss considerations for integrating cardiomyocyte cell models with techniques that have become relatively common in the field, such as respirometry and extracellular flux analysis. Furthermore, we provide overviews of metabolic assays that complement XF analyses and that provide information on not only catabolic pathway activity, but biosynthetic pathway activity and redox status as well. Cultivating a more widespread understanding of the advantages and limitations of metabolic measurements in cardiomyocyte cell models will continue to be essential for the development of coherent metabolic mechanisms of cardiac health and pathophysiology.

Doxorubicin Cytotoxicity in Differentiated H9c2 Cardiomyocytes: Evidence for Acute Mitochondrial Superoxide Generation

Although a mitochondrial redox-cycling superoxide-generating mechanism for the cardiotoxicity of doxorubicin was suggested from experiments with isolated mitochondria, its occurrence and contribution to cytotoxicity in intact cardiomyocytes is not fully established. Therefore, we determined the immediate and delayed effects of doxorubicin on the generation of reactive oxygen species (ROS) and cytotoxicity in differentiated H9c2 cardiomyocytes. Although relatively short incubations (3 or 6 h) with 1 or 5 µM doxorubicin did not acutely decrease cell survival, exposure to 5 µM doxorubicin for 3 h was sufficient to cause a significant delayed decrease in cell survival after an additional 24 h without doxorubicin. Mitochondrial superoxide generation was observed to increase within 30 min of incubation with 5 µM doxorubicin. Increased intracellular ROS generation, decreased mitochondrial metabolic activity, and decreased mitochondrial membrane potential (MMP) were observed after more extended periods (6-12 h). Overall, these observations support that the toxicity of doxorubicin to differentiated cardiomyocytes involves acute mitochondrial superoxide generation with subsequent intracellular ROS generation, mitochondrial dysfunction, and cell death.

Enhancing Glycolysis Protects against Ischemia-Reperfusion Injury by Reducing ROS Production

After myocardial ischemia-reperfusion, fatty acid oxidation shows fast recovery while glucose oxidation rates remain depressed. A metabolic shift aimed at increasing glucose oxidation has shown to be beneficial in models of myocardial ischemia-reperfusion. However, strategies aimed at increasing glucose consumption in the clinic have provided mixed results and have not yet reached routine clinical practice. A better understanding of the mechanisms underlying the protection afforded by increased glucose oxidation may facilitate the transfer to the clinic. The purpose of this study was to evaluate if the modulation of reactive oxygen species (ROS) was involved in the protection afforded by increased glucose oxidation. Firstly, we characterized an H9C2 cellular model in which the use of glucose or galactose as substrates can modulate glycolysis and oxidative phosphorylation pathways. In this model, there were no differences in morphology, cell number, or ATP and PCr levels. However, galactose-grown cells consumed more oxygen and had an increased Krebs cycle turnover, while cells grown in glucose had increased aerobic glycolysis rate as demonstrated by higher lactate and alanine production. Increased aerobic glycolysis was associated with reduced ROS levels and protected the cells against simulated ischemia-reperfusion injury. Furthermore, ROS scavenger N-acetyl cysteine (NAC) was able to reduce the amount of ROS and to prevent cell death. Lastly, cells grown in galactose showed higher activation of mTOR/Akt signaling pathways. In conclusion, our results provide evidence indicating that metabolic shift towards increased glycolysis reduces mitochondrial ROS production and prevents cell death during ischemia-reperfusion injury.

HIF1α-dependent mitophagy facilitates cardiomyoblast differentiation

Mitophagy is thought to play a key role in eliminating damaged mitochondria, with diseases such as cancer and neurodegeneration exhibiting defects in this process. Mitophagy is also involved in cell differentiation and maturation, potentially through modulating mitochondrial metabolic reprogramming. Here we examined mitophagy that is induced upon iron chelation and found that the transcriptional activity of HIF1α, in part through upregulation of BNIP3 and NIX, is an essential mediator of this pathway in SH-SY5Y cells. In contrast, HIF1α is dispensable for mitophagy occurring upon mitochondrial depolarisation. To examine the role of this pathway in a metabolic reprogramming and differentiation context, we utilised the H9c2 cell line model of cardiomyocyte maturation. During differentiation of these cardiomyoblasts, mitophagy increased and required HIF1α-dependent upregulation of NIX. Though HIF1α was essential for expression of key cardiomyocyte markers, mitophagy was not directly required. However, enhancing mitophagy through NIX overexpression, accelerated marker gene expression. Taken together, our findings provide a molecular link between mitophagy signalling and cardiomyocyte differentiation and suggest that although mitophagy may not be essential per se, it plays a critical role in maintaining mitochondrial integrity during this energy demanding process.

Quantitative proteomic analyses reveal that GPX4 downregulation during myocardial infarction contributes to ferroptosis in cardiomyocytes

Ischaemic heart disease (IHD) is the leading cause of death worldwide. Although myocardial cell death plays a significant role in myocardial infarction (MI), its underlying mechanism remains to be elucidated. To understand the progression of MI and identify potential therapeutic targets, we performed tandem mass tag (TMT)-based quantitative proteomic analysis using an MI mouse model. Gene ontology (GO) analysis and gene set enrichment analysis (GSEA) revealed that the glutathione metabolic pathway and reactive oxygen species (ROS) pathway were significantly downregulated during MI. In particular, glutathione peroxidase 4 (GPX4), which protects cells from ferroptosis (an iron-dependent programme of regulated necrosis), was downregulated in the early and middle stages of MI. RNA-seq and qRT-PCR analyses suggested that GPX4 downregulation occurred at the transcriptional level. Depletion or inhibition of GPX4 using specific siRNA or the chemical inhibitor RSL3, respectively, resulted in the accumulation of lipid peroxide, leading to cell death by ferroptosis in H9c2 cardiomyoblasts. Although neonatal rat ventricular myocytes (NRVMs) were less sensitive to GPX4 inhibition than H9c2 cells, NRVMs rapidly underwent ferroptosis in response to GPX4 inhibition under cysteine deprivation. Our study suggests that downregulation of GPX4 during MI contributes to ferroptotic cell death in cardiomyocytes upon metabolic stress such as cysteine deprivation.

Construction of cardiomyoblast sheets for cardiac tissue repair: comparison of three different approaches

Recently, cell sheet engineering has emerged as one of the most accentuated approaches of tissue engineering and cardiac tissue is the pioneering application area of cell sheets with clinical use. In this study, we cultured rat cardiomyoblasts (H9C2 cell line) to obtain cell sheets by using three different approaches; using (1) thermo-responsive tissue culture plates, (2) high cell seeding density/high serum content and (3) ascorbic acid treatment. To compare the outcomes of three methods, morphologic examination, immunofluorescent stainings and live/dead cell assay were performed and the effects of serum concentration and ascorbic acid treatment on cardiac gene expressions were examined. The results showed that cardiomyoblast sheets were successfully obtained in all approaches without losing their integrity and viability. Also, the results of RT-PCR analysis showed that the types of tissue culture surface, cell seeding density, serum concentration and ascorbic acid treatment affect cardiac gene expressions of cells in cell sheets. Although three methods were succeeded, ascorbic acid treatment was found as the most rapid and effective method to obtain cell sheets with cardiac characteristics.

The Main Metabolites of Fluorouracil + Adriamycin + Cyclophosphamide (FAC) Are Not Major Contributors to FAC Toxicity in H9c2 Cardiac Differentiated Cells

In the clinical practice, the combination of 5-fluorouracil (5-FU) + Adriamycin (also known as doxorubicin, DOX) + cyclophosphamide (CYA) (known as FAC) is used to treat breast cancer. The FAC therapy, however, carries some serious risks, namely potential cardiotoxic effects, although the mechanisms are still unclear. In the present study, the role of the main metabolites regarding FAC-induced cardiotoxicity was assessed at clinical relevant concentrations. Seven-day differentiated H9c2 cells were exposed for 48 h to the main metabolites of FAC, namely the metabolite of 5-FU, α-fluoro-β-alanine (FBAL, 50 or 100 μM), of DOX, doxorubicinol (DOXOL, 0.2 or 1 μM), and of CYA, acrolein (ACRO, 1 or 10 μM), as well as to their combination. The parent drugs (5-FU 50 μM, DOX 1 μM, and CYA 50 μM) were also tested isolated or in combination with the metabolites. Putative cytotoxicity was evaluated through phase contrast microscopy, Hoechst staining, membrane mitochondrial potential, and by two cytotoxicity assays: the reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and the neutral red (NR) lysosomal incorporation. The metabolite DOXOL was more toxic than FBAL and ACRO in the MTT and NR assays. When in combination, neither FBAL nor ACRO increased DOXOL-induced cytotoxicity. No nuclear condensation was observed for any of the tested combinations; however, a significant mitochondrial potential depolarization after FBAL 100 μM + DOXOL 1 μM + ACRO 10 μM or FBAL 100 μM + DOXOL 1 μM exposure was seen at 48 h. When tested alone DOX 1 μM was more cytotoxic than all the parent drugs and metabolites in both the cytotoxicity assays performed. These results demonstrated that DOXOL was the most toxic of all the metabolites tested; nonetheless, the metabolites do not seem to be the major contributors to FAC-induced cardiotoxicity in this cardiac model.

Doxorubicin Is Key for the Cardiotoxicity of FAC (5-Fluorouracil + Adriamycin + Cyclophosphamide) Combination in Differentiated H9c2 Cells

Currently, a common therapeutic approach in cancer treatment encompasses a drug combination to attain an overall better efficacy. Unfortunately, it leads to a higher incidence of severe side effects, namely cardiotoxicity. This work aimed to assess the cytotoxicity of doxorubicin (DOX, also known as Adriamycin), 5-fluorouracil (5-FU), cyclophosphamide (CYA), and their combination (5-Fluorouracil + Adriamycin + Cyclophosphamide, FAC) in H9c2 cardiac cells, for a better understanding of the contribution of each drug to FAC-induced cardiotoxicity. Differentiated H9c2 cells were exposed to pharmacological relevant concentrations of DOX (0.13–5 μM), 5-FU (0.13–5 μM), CYA (0.13–5 μM) for 24 or 48 h. Cells were also exposed to FAC mixtures (0.2, 1 or 5 μM of each drug and 50 μM 5-FU + 1 μM DOX + 50 μM CYA). DOX was the most cytotoxic drug, followed by 5-FU and lastly CYA in both cytotoxicity assays (reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and neutral red (NR) uptake). Concerning the equimolar combination with 1 or 5 μM, FAC caused similar cytotoxicity to DOX alone. Even in the presence of higher concentrations of 5-FU and CYA (50 μM 5-FU + 1 μM DOX + 50 μM CYA), 1 μM DOX was still a determinant for the cardiotoxicity observed in the cytotoxicity assays, phase contrast morphological evaluation, and mitochondrial potential depolarization evaluation. To the best of our knowledge, this was the first in vitro work with this combination regimen, DOX being the most toxic drug and key to the toxicity of FAC.

DHA and 19,20-EDP induce lysosomal-proteolytic-dependent cytotoxicity through de novo ceramide production in H9c2 cells with a glycolytic profile

Docosahexaenoic acid (DHA) and their CYP-derived metabolites, epoxydocosapentaenoic acids (EDPs), are important fatty acids obtained from dietary sources. While it is known that they have significant biological effects, which can differ between cell type and disease state, our understanding of how they work remains limited. Previously, we demonstrated that DHA and 19,20-EDP triggered pronounced cytotoxicity in H9c2 cells correlating with increased ceramide production. In this study, we examine whether DHA- and 19,20-EDP-induced cell death depends on the type of metabolism (glycolysis or OXPHOS). We cultivated H9c2 cells in distinct conditions that result in either glycolytic or oxidative metabolism. Our major findings suggest that DHA and its epoxy metabolite, 19,20-EDP, trigger cytotoxic effects toward H9c2 cells with a glycolytic metabolic profile. Cell death occurred through a mechanism involving activation of a lysosomal-proteolytic degradation pathway. Importantly, accumulation of ceramide played a critical role in the susceptibility of glycolytic H9c2 cells to cytotoxicity. Furthermore, our data suggest that an alteration in the cellular metabolic profile is a major factor determining the type and magnitude of cellular toxic response. Together, the novelty of this study demonstrates that DHA and 19,20-EDP induce cell death in H9c2 cells with a glycolytic metabolicwct 2 profile through a lysosomal-proteolytic mechanism.

p-Coumaric acid mediated protection of H9c2 cells from Doxorubicin-induced cardiotoxicity: Involvement of augmented Nrf2 and autophagy

Doxorubicin (Dox) is a widely administered chemotherapeutic drug and incidences of cardiotoxicity associated with its administration have been of general concern. Extensive research proposes several mechanisms as a cause of Dox induced cardiotoxicity. However, none of these studies have been able to suggest a find one, cure all antidote for the same. To this end, several studies involving plant based compounds or natural products have gained acclaim for their ability to address at least one factor contributing to drug induced pathogenesis. We had previously reported that p-coumaric (pCA) has a protective effect on Dox induced oxidative stress in rat-derived cardiomyoblasts. In this study we investigated the effects of pCA on the regulation of Nrf-2, mitochondrial viability, autophagy and apoptosis in Doxorubicin treated H9c2 cardiomyocytes. ROS induced mitochondrial stress, changes in mitochondrial membrane potential, loss of membrane integrity; nuclear damage as single/double stranded breaks, autophagy and the effects of pre and co-treatment of pCA on Nrf-2 mediated signaling was evaluated by various approaches. The effect of pCA on drug uptake was evaluated through confocal Raman Spectroscopy. We find that nuclear translocation of Nrf-2 is prominently marked by protein-specific antibody conjugated fluorophore in Dox treated cells especially. Cell survival is mediated to a certain extent by the expression of the anti-apoptotic BCl2 in pCA treated cells. However, mRNA levels of autophagy related (Atg) genes suggest that autophagy plays a decisive role in deciding cellular fate. Caspase-3 activation is also observed in pCA treated cells which suggest an alternative function of caspase-3 in pCA mediated cell survival. Expression of antioxidant enzymes confirm the oxidative stress induced by Dox treatment in cells and the modulation of cell redox homeostasis through treatment with pCA.

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.

Cytosolic carnitine acetyltransferase as a source of cytosolic acetyl-CoA: a possible mechanism for regulation of cardiac energy metabolism

The role of carnitine acetyltransferase (CrAT) in regulating cardiac energy metabolism is poorly understood. CrAT modulates mitochondrial acetyl-CoA/CoA (coenzyme A) ratios, thus regulating pyruvate dehydrogenase activity and glucose oxidation. Here, we propose that cardiac CrAT also provides cytosolic acetyl-CoA for the production of malonyl-CoA, a potent inhibitor of fatty acid oxidation. We show that in the murine cardiomyocyte cytosol, reverse CrAT activity (RCrAT, producing acetyl-CoA) is higher compared with the liver, which primarily uses ATP-citrate lyase to produce cytosolic acetyl-CoA for lipogenesis. The heart displayed a lower RCrAT K_m for CoA compared with the liver. Furthermore, cytosolic RCrAT accounted for 4.6 ± 0.7% of total activity in heart tissue and 12.7 ± 0.2% in H9C2 cells, while highly purified heart cytosolic fractions showed significant CrAT protein levels. To investigate the relationship between CrAT and acetyl-CoA carboxylase (ACC), the cytosolic enzyme catalyzing malonyl-CoA production from acetyl-CoA, we studied ACC2-knockout mouse hearts which showed decreased CrAT protein levels and activity, associated with increased palmitate oxidation and acetyl-CoA/CoA ratio compared with controls. Conversely, feeding mice a high-fat diet for 10 weeks increased cardiac CrAT protein levels and activity, associated with a reduced acetyl-CoA/CoA ratio and glucose oxidation. These data support the presence of a cytosolic CrAT with a low K_m for CoA, favoring the formation of cytosolic acetyl-CoA, providing an additional source to the classical ATP-citrate lyase pathway, and that there is an inverse relation between CrAT and the ratio of acetyl-CoA/CoA as evident in conditions affecting the regulation of cardiac energy metabolism.

Mitochondrial CDP-diacylglycerol synthase activity is due to the peripheral protein, TAMM41 and not due to the integral membrane protein, CDP-diacylglycerol synthase 1

CDP diacylglycerol synthase (CDS) catalyses the conversion of phosphatidic acid (PA) to CDP-diacylglycerol, an essential intermediate in the synthesis of phosphatidylglycerol, cardiolipin and phosphatidylinositol (PI). CDS activity has been identified in mitochondria and endoplasmic reticulum of mammalian cells apparently encoded by two highly-related genes, CDS1 and CDS2. Cardiolipin is exclusively synthesised in mitochondria and recent studies in cardiomyocytes suggest that the peroxisome proliferator-activated receptor γ coactivator 1 (PGC-1α and β) serve as transcriptional regulators of mitochondrial biogenesis and up-regulate the transcription of the CDS1 gene. Here we have examined whether CDS1 is responsible for the mitochondrial CDS activity. We report that differentiation of H9c2 cells with retinoic acid towards cardiomyocytes is accompanied by increased expression of mitochondrial proteins, oxygen consumption, and expression of the PA/PI binding protein, PITPNC1, and CDS1 immunoreactivity. Both CDS1 immunoreactivity and CDS activity were found in mitochondria of H9c2 cells as well as in rat heart, liver and brain mitochondria. However, the CDS1 immunoreactivity was traced to a peripheral p55 cross-reactive mitochondrial protein and the mitochondrial CDS activity was due to a peripheral mitochondrial protein, TAMM41, not an integral membrane protein as expected for CDS1. TAMM41 is the mammalian equivalent of the recently identified yeast protein, Tam41. Knockdown of TAMM41 resulted in decreased mitochondrial CDS activity, decreased cardiolipin levels and a decrease in oxygen consumption. We conclude that the CDS activity present in mitochondria is mainly due to TAMM41, which is required for normal mitochondrial function.

Cardiac tissue regeneration: A preliminary study on carbon-based nanotubes gelatin scaffold

The aim of this study was set-up and test of gelatin and carbon nanotubes scaffolds. Gelatin-based (5%) genipin cross-linked (0.2%) scaffolds embedding single-walled carbon nanotubes (SWCNTs, 0.3, 0.5, 0.7, 0.9, and 1.3% w/w) were prepared and mechanically/electrically characterized. For biological evaluation, H9c2 cell line was cultured for 10 days. Cytotoxicity, cell growth and differentiation, immunohistochemistry, and real-time PCR analysis were performed. Myoblast and cardiac differentiation were obtained by serum reduction to 1% (C_1% ) and stimulation with 50 nM all trans-retinoic acid (C_RA ), respectively. Immunohistochemistry showed elongated myotubes in C_1% while round and multinucleated cells in C_RA with also a significantly increased expression of natriuretic peptides (NP) and ET-1 receptors in parallel with a decreased ET-1. On scaffolds, cell viability was similar for Gel-SWCNT_0.3%/0.9% ; NP and ET systems expression decreased in both concentrations with respect to control and CX-43, mainly due to a lacking of complete differentiation in cardiac phenotype during that time. Although further analyses on novel biomaterials are necessary, these results represent a useful starting point to develop new biomaterial-based scaffolds. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2750-2762, 2018.

Naphthoquinoxaline metabolite of mitoxantrone is less cardiotoxic than the parent compound and it can be a more cardiosafe drug in anticancer therapy

Mitoxantrone (MTX) is an antineoplastic agent used to treat several types of cancers and on multiple sclerosis, which shows a high incidence of cardiotoxicity. Still, the underlying mechanisms of MTX cardiotoxicity are poorly understood and the potential toxicity of its metabolites scarcely investigated. Therefore, this work aimed to synthesize the MTX-naphthoquinoxaline metabolite (NAPHT) and to compare its cytotoxicity to the parent compound in 7-day differentiated H9c2 cells using pharmacological relevant concentrations (0.01-5 µM). MTX was more toxic in equivalent concentrations in all cytotoxicity tests performed [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide reduction, neutral red uptake, and lactate dehydrogenase release assays] and times tested (24 and 48 h). Both MTX and NAPHT significantly decreased mitochondrial membrane potential in 7-day differentiated H9c2 cells after a 12-h incubation. However, energetic pathways were affected in a different manner after MTX or NAPHT incubation. ATP increased and lactate levels decreased after a 24-h incubation with MTX, whereas for the same incubation time and concentrations, NAPHT did not cause any significant effect. The increased activity of ATP synthase seems responsible for MTX-induced increases in ATP levels, as oligomycin (an inhibitor of ATP synthase) abrogated this effect on 5 µM MTX-incubated cells. 3-Methyladenine (an autophagy inhibitor) was the only molecule to give a partial protection against the cytotoxicity produced by MTX or NAPHT. To the best of our knowledge, this was the first broad study on NAPHT cardiotoxicity, and it revealed that the parent drug, MTX, caused a higher disruption in the energetic pathways in a cardiac model in vitro, whereas autophagy is involved in the toxicity of both compounds. In conclusion, NAPHT is claimed to largely contribute to MTX-anticancer properties; therefore, this metabolite should be regarded as a good option for a safer anticancer therapy since it is less cardiotoxic than MTX.

Doxorubicin impairs cardiomyocyte viability by suppressing transcription factor EB expression and disrupting autophagy

Doxorubicin (DOX) is an effective anti-cancer agent. However, DOX treatment increases patient susceptibility to dilated cardiomyopathy. DOX predisposes cardiomyocytes to insult by suppressing mitochondrial energy metabolism, altering calcium flux, and disrupting proteolysis and proteostasis. Prior studies have assessed the role of macroautophagy in DOX cardiotoxicity; however, limited studies have examined whether DOX mediates cardiac injury through dysfunctions in inter- and/or intra-lysosomal signaling events. Lysosomal signaling and function is governed by transcription factor EB (TFEB). In the present study, we hypothesized that DOX caused myocyte injury by impairing lysosomal function and signaling through negative regulation of TFEB. Indeed, we found that DOX repressed cellular TFEB expression, which was associated with impaired cathepsin proteolytic activity across in vivo, ex vivo, and in vitro models of DOX cardiotoxicity. Furthermore, we observed that loss of TFEB was associated with reduction in macroautophagy protein expression, inhibition of autophagic flux, impairments in lysosomal cathepsin B activity, and activation of cell death. Restoration and/or activation of TFEB in DOX-treated cardiomyocytes prevented DOX-induced suppression of cathepsin B activity, reduced DOX-mediated reactive oxygen species (ROS) overproduction, attenuated activation of caspase-3, and improved cellular viability. Collectively, loss of TFEB inhibits lysosomal autophagy, rendering cardiomyocytes susceptible to DOX-induced proteotoxicity and injury. Our data reveal a novel mechanism wherein DOX primes cardiomyocytes for cell death by depleting cellular TFEB.

F1FO ATP Synthase Is Expressed at the Surface of Embryonic Rat Heart-Derived H9c2 Cells and Is Affected by Cardiac-Like Differentiation

Taking advantage from the peculiar features of the embryonic rat heart-derived myoblast cell line H9c2, the present study is the first to provide evidence for the expression of F1FO ATP synthase and of ATPase Inhibitory Factor 1 (IF1) on the surface of cells of cardiac origin, together documenting that they were affected through cardiac-like differentiation. Subunits of both the catalytic F1 sector of the complex (ATP synthase-β) and of the peripheral stalk, responsible for the correct F1-FO assembly/coupling, (OSCP, b, F6) were detected by immunofluorescence, together with IF1. The expression of ATP synthase-β, ATP synthase-b and F6 were similar for parental and differentiated H9c2, while the levels of OSCP increased noticeably in differentiated cells, where the results of in situ Proximity Ligation Assay were consistent with OSCP interaction within ecto-F1FO complexes. An opposite trend was shown by IF1 whose ectopic expression appeared greater in the parental H9c2. Here, evidence for the IF1 interaction with ecto-F1FO complexes was provided. Functional analyses corroborate both sets of data. i) An F1FO ATP synthase contribution to the exATP production by differentiated cells suggests an augmented expression of holo-F1FO ATP synthase on plasma membrane, in line with the increase of OSCP expression and interaction considered as a requirement for favoring the F1-FO coupling. ii) The absence of exATP generation by the enzyme, and the finding that exATP hydrolysis was largely oligomycin-insensitive, are in line in parental cells with the deficit of OSCP and suggest the occurrence of sub-assemblies together evoking more regulation by IF1.

Oxidative stress does not play a primary role in the toxicity induced with clinical doses of doxorubicin in myocardial H9c2 cells

The implication of oxidative stress as primary mechanism inducing doxorubicin (DOX) cardiotoxicity is still questionable as many in vitro studies implied supra-clinical drug doses or unreliable methodologies for reactive oxygen species (ROS) detection. The aim of this study was to clarify whether oxidative stress is involved in compliance with the conditions of clinical use of DOX, and using reliable tools for ROS detection. We examined the cytotoxic mechanisms of 2 μM DOX 1 day after the beginning of the treatment in differentiated H9c2 rat embryonic cardiac cells. Cells were exposed for 2 or 24 h with DOX to mimic a single chronic dosage or to favor accumulation, respectively. We found that apoptosis was prevalent in cells exposed for a short period with DOX: cells showed typical hallmarks as loss of anchorage ability, mitochondrial hyperpolarization followed by the collapse of mitochondrial activity, and nuclear condensation. Increasing the exposure period favored a shift to necrosis as the cells preferentially exhibited early DNA impairment and nuclear swelling. In either case, measuring the fluorescence lifetime of 1-pyrenebutyric acid or the intensities of dihydroethidium or amplex red showed a consistent pattern in ROS production which was a slight increased level far from representative of an oxidative stress. Moreover, pre-treatment with dexrazoxane provided a cytoprotective effect although it failed to detoxify ROS. Our data support that oxidative stress is unlikely to be the primary mechanism of DOX cardiac toxicity in vitro.

MicroRNAs mediate the cardioprotective effect of angiotensin-converting enzyme inhibition in acute kidney injury

Cardiovascular disease, including cardiac hypertrophy, is common in patients with kidney disease and can be partially attenuated using blockers of the renin-angiotensin system (RAS). It is unknown whether cardiac microRNAs contribute to the pathogenesis of cardiac hypertrophy or to the protective effect of RAS blockade in kidney disease. Using a subtotal nephrectomy rat model of kidney injury, we investigated changes in cardiac microRNAs that are known to have direct target genes involved in the regulation of apoptosis, fibrosis, and hypertrophy. The effect of treatment with the angiotensin-converting enzyme (ACE) inhibitor ramipril on cardiac microRNAs was also investigated. Kidney injury led to a significant increase in cardiac microRNA-212 and microRNA-132 expression. Ramipril reduced cardiac hypertrophy, attenuated the increase in microRNA-212 and microRNA-132, and significantly increased microRNA-133 and microRNA-1 expression. There was altered expression of caspase-9, B cell lymphoma-2, transforming growth factor-β, fibronectin 1, collagen type 1A1, and forkhead box protein O3, which are all known to be involved in the regulation of apoptosis, fibrosis, and hypertrophy in cardiac cells while being targets for the above microRNAs. ACE inhibitor treatment increased expression of microRNA-133 and microRNA-1. The inhibitory action of ACE inhibitor treatment on increased cardiac NADPH oxidase isoform 1 expression after subtotal nephrectomy surgery suggests that inhibition of oxidative stress is also one of mechanism of ACE inhibitor-mediated cardioprotection. These finding suggests the involvement of microRNAs in the cardioprotective action of ACE inhibition in acute renal injury, which is mediated through an inhibitory action on profibrotic and proapoptotic target genes and stimulatory action on antihypertrophic and antiapoptotic target genes.

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.

BKCa channel activation increases cardiac contractile recovery following hypothermic ischemia/reperfusion

Mitochondrial Ca(2+)-activated large-conductance K(+) (BKCa) channels are thought to provide protection during ischemic insults in the heart. Rottlerin (mallotoxin) has been implicated as a potent BKCa activator. The purpose of this study was twofold: 1) to investigate the efficacy of BKCa channel activation as a cardioprotective strategy during ischemic cardioplegic arrest and reperfusion (CP/R) and 2) to assess the specificity of rottlerin for BKCa channels. Wild-type (WT) and BKCa knockout (KO) mice were subjected to an isolated heart model of ischemic CP/R. A mechanism of rottlerin-induced cardioprotection was also investigated using H9c2 cells subjected to in vitro CP/reoxygenation and assessed for mitochondrial membrane potential and reactive oxygen species (ROS) production. CP/R decreased left ventricular developed pressure, positive and negative first derivatives of left ventricular pressure, and coronary flow (CF) in WT mice. Rottlerin dose dependently increased the recovery of left ventricular function and CF to near baseline levels. BKCa KO hearts treated with or without 500 nM rottlerin were similar to WT CP hearts. H9c2 cells subjected to in vitro CP/R displayed reduced mitochondrial membrane potential and increased ROS generation, both of which were significantly normalized by rottlerin. We conclude that activation of BKCa channels rescues ischemic damage associated with CP/R, likely via effects on improved mitochondrial membrane potential and reduced ROS generation.

Na+/H+ exchanger isoform 1-induced osteopontin expression facilitates cardiomyocyte hypertrophy

Enhanced expression and activity of the Na⁺/H⁺ exchanger isoform 1 (NHE1) has been implicated in cardiomyocyte hypertrophy in various experimental models. The upregulation of NHE1 was correlated with an increase in osteopontin (OPN) expression in models of cardiac hypertrophy (CH), and the mechanism for this remains to be delineated. To determine whether the expression of active NHE1-induces OPN and contributes to the hypertrophic response in vitro, cardiomyocytes were infected with the active form of the NHE1 adenovirus or transfected with OPN silencing RNA (siRNA-OPN) and characterized for cardiomyocyte hypertrophy. Expression of NHE1 in cardiomyocytes resulted in a significant increase in cardiomyocyte hypertrophy markers: cell surface area, protein content, ANP mRNA and expression of phosphorylated-GATA4. NHE1 activity was also significantly increased in cardiomyocytes expressing active NHE1. Interestingly, transfection of cardiomyocytes with siRNA-OPN significantly abolished the NHE1-induced cardiomyocyte hypertrophy. siRNA-OPN also significantly reduced the activity of NHE1 in cardiomyocytes expressing NHE1 (68.5±0.24%; P<0.05), confirming the role of OPN in the NHE1-induced hypertrophic response. The hypertrophic response facilitated by NHE1-induced OPN occurred independent of the extracellular-signal-regulated kinases and Akt, but required p90-ribosomal S6 kinase (RSK). The ability of OPN to facilitate the NHE1-induced hypertrophic response identifies OPN as a potential therapeutic target to reverse the hypertrophic effect induced by the expression of active NHE1.

TGF-β1-mediated differentiation of fibroblasts is associated with increased mitochondrial content and cellular respiration

Objectivs

Cytokine-dependent activation of fibroblasts to myofibroblasts, a key event in fibrosis, is accompanied by phenotypic changes with increased secretory and contractile properties dependent on increased energy utilization, yet changes in the energetic profile of these cells are not fully described. We hypothesize that the TGF-β1-mediated transformation of myofibroblasts is associated with an increase in mitochondrial content and function when compared to naive fibroblasts.

Methods

Cultured NIH/3T3 mouse fibroblasts treated with TGF-β1, a profibrotic cytokine, or vehicle were assessed for transformation to myofibroblasts (appearance of α-smooth muscle actin [α-SMA] stress fibers) and associated changes in mitochondrial content and functions using laser confocal microscopy, Seahorse respirometry, multi-well plate reader and biochemical protocols. Expression of mitochondrial-specific proteins was determined using western blotting, and the mitochondrial DNA quantified using Mitochondrial DNA isolation kit.

Results

Treatment with TGF-β1 (5 ng/mL) induced transformation of naive fibroblasts into myofibroblasts with a threefold increase in the expression of α-SMA (6.85 ± 0.27 RU) compared to cells not treated with TGF-β1 (2.52 ± 0.11 RU). TGF-β1 exposure increased the number of mitochondria in the cells, as monitored by membrane potential sensitive dye tetramethylrhodamine, and expression of mitochondria-specific proteins; voltage-dependent anion channels (0.54 ± 0.05 vs. 0.23 ± 0.05 RU) and adenine nucleotide transporter (0.61 ± 0.11 vs. 0.22 ± 0.05 RU), as well as mitochondrial DNA content (530 ± 12 μg DNA/10⁶ cells vs. 307 ± 9 μg DNA/10⁶ cells in control). TGF-β1 treatment was associated with an increase in mitochondrial function with a twofold increase in baseline oxygen consumption rate (2.25 ± 0.03 vs. 1.13 ± 0.1 nmol O₂/min/10⁶ cells) and FCCP-induced mitochondrial respiration (2.87 ± 0.03 vs. 1.46 ± 0.15 nmol O₂/min/10⁶ cells).

Conclusions

TGF-β1 induced differentiation of fibroblasts is accompanied by energetic remodeling of myofibroblasts with an increase in mitochondrial respiration and mitochondrial content.

Ascribing novel functions to the sarcomeric protein, myosin binding protein H (MyBPH) in cardiac sarcomere contraction

Myosin binding protein H (MyBPH) is a protein of unknown function, which shares sequence and structural similarities with myosin binding protein C (cMyBPC), a protein frequently implicated in hypertrophic cardiomyopathy (HCM). Given the similarity between cMyBPC and MyBPH, we proposed that MyBPH, like cMyBPC, could be involved in HCM pathogenesis and we therefore sought to determine its function. We identified MyBPH-interacting proteins by using yeast two-hybrid (Y2H) analysis. The role of MyBPH and cMyBPC in cardiac cell contractility was analysed by measuring the planar cell surface area of differentiated H9c2 rat cardiomyocytes in response to β-adrenergic stress after siRNA knockdown of MyBPH and cMyBPC. Individual knockdown of either protein had no effect on cardiac contractility, while concurrent knockdowns reduced cardiac contractility. These proteins therefore functionally compensate for one another and are critical for cardiac contractility. We further show that both proteins co-localise with the autophagosomal membrane protein LC3, suggesting that both proteins are involved in autophagosomal membrane maturation processes. The results of this study ascribe novel functions to MyBPH, which may contribute to our understanding of its role in the sarcomere. This study provides evidence for a potential role of MyBPH in HCM, which warrants further investigation.

Metabolic effects of hypoxia in colorectal cancer by 13C NMR isotopomer analysis

¹³C NMR isotopomer analysis was used to characterize intermediary metabolism in three colorectal cancer cell lines (WiDr, LS1034, and C2BBe1) and determine the “metabolic remodeling” that occurs under hypoxia. Under normoxia, the three colorectal cancer cell lines present high rates of lactate production and can be seen as “Warburg” like cancer cells independently of substrate availability, since such profile was dominant at both high and low glucose media contents. The LS1034 was the less glycolytic of the three cell lines and was the most affected by the event of hypoxia, raising abruptly glucose consumption and lactate production. The other two colorectal cell lines, WiDr and C2BBe1, adapted better to hypoxia and were able to maintain their oxidative fluxes even at the very low levels of oxygen. These differential metabolic behaviors of the three colorectal cell lines show how important an adequate knowledge of the “metabolic remodeling” that follows a given cancer treatment is towards the correct (re)design of therapeutic strategies against cancer.

Overexpression of ryanodine receptor type 1 enhances mitochondrial fragmentation and Ca2+-induced ATP production in cardiac H9c2 myoblasts

Ca(+) influx to mitochondria is an important trigger for both mitochondrial dynamics and ATP generation in various cell types, including cardiac cells. Mitochondrial Ca(2+) influx is mainly mediated by the mitochondrial Ca(2+) uniporter (MCU). Growing evidence also indicates that mitochondrial Ca(2+) influx mechanisms are regulated not solely by MCU but also by multiple channels/transporters. We have previously reported that skeletal muscle-type ryanodine receptor (RyR) type 1 (RyR1), which expressed at the mitochondrial inner membrane, serves as an additional Ca(2+) uptake pathway in cardiomyocytes. However, it is still unclear which mitochondrial Ca(2+) influx mechanism is the dominant regulator of mitochondrial morphology/dynamics and energetics in cardiomyocytes. To investigate the role of mitochondrial RyR1 in the regulation of mitochondrial morphology/function in cardiac cells, RyR1 was transiently or stably overexpressed in cardiac H9c2 myoblasts. We found that overexpressed RyR1 was partially localized in mitochondria as observed using both immunoblots of mitochondrial fractionation and confocal microscopy, whereas RyR2, the main RyR isoform in the cardiac sarcoplasmic reticulum, did not show any expression at mitochondria. Interestingly, overexpression of RyR1 but not MCU or RyR2 resulted in mitochondrial fragmentation. These fragmented mitochondria showed bigger and sustained mitochondrial Ca(2+) transients compared with basal tubular mitochondria. In addition, RyR1-overexpressing cells had a higher mitochondrial ATP concentration under basal conditions and showed more ATP production in response to cytosolic Ca(2+) elevation compared with nontransfected cells as observed by a matrix-targeted ATP biosensor. These results indicate that RyR1 possesses a mitochondrial targeting/retention signal and modulates mitochondrial morphology and Ca(2+)-induced ATP production in cardiac H9c2 myoblasts.

Cardiomyocyte culture - an update on the in vitro cardiovascular model and future challenges

The success of any work with isolated cardiomyocytes depends on the reproducibility of cell isolation, because the cells do not divide. To date, there is no suitable in vitro model to study human adult cardiac cell biology. Although embryonic stem cells and induced pluripotent stem cells are able to differentiate into cardiomyocytes in vitro, the efficiency of this process is low. Isolation and expansion of human cardiomyocyte progenitor cells from cardiac surgical waste or, alternatively, from fetal heart tissue is another option. However, to overcome various issues related to human tissue usage, especially ethical concerns, researchers use large- and small-animal models to study cardiac pathophysiology. A simple model to study the changes at the cellular level is cultures of cardiomyocytes. Although primary murine cardiomyocyte cultures have their own advantages and drawbacks, alternative strategies have been developed in the last two decades to minimise animal usage and interspecies differences. This review discusses the use of freshly isolated murine cardiomyocytes and cardiomyocyte alternatives for use in cardiac disease models and other related studies.

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.

Scalable cell alignment on optical media substrates

Cell alignment by underlying topographical cues has been shown to affect important biological processes such as differentiation and functional maturation in vitro. However, the routine use of cell culture substrates with micro- or nano-topographies, such as grooves, is currently hampered by the high cost and specialized facilities required to produce these substrates. Here we present cost-effective commercially available optical media as substrates for aligning cells in culture. These optical media, including CD-R, DVD-R and optical grating, allow different cell types to attach and grow well on them. The physical dimension of the grooves in these optical media allowed cells to be aligned in confluent cell culture with maximal cell-cell interaction and these cell alignment affect the morphology and differentiation of cardiac (H9C2), skeletal muscle (C2C12) and neuronal (PC12) cell lines. The optical media is amenable to various chemical modifications with fibronectin, laminin and gelatin for culturing different cell types. These low-cost commercially available optical media can serve as scalable substrates for research or drug safety screening applications in industry scales.