Primary Neonatal Rat Ventricular Myocytes Research Articles

Letter by Li and Nie Regarding Article, “Inflammatory Glycoprotein 130 Signaling Links Changes in Microtubules and Junctophilin-2 to Altered Mitochondrial Metabolism and Right Ventricular Contractility”

HomeCirculation: Heart FailureVol. 15, No. 8Letter by Li and Nie Regarding Article, “Inflammatory Glycoprotein 130 Signaling Links Changes in Microtubules and Junctophilin-2 to Altered Mitochondrial Metabolism and Right Ventricular Contractility” Free AccessLetterPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessLetterPDF/EPUBLetter by Li and Nie Regarding Article, “Inflammatory Glycoprotein 130 Signaling Links Changes in Microtubules and Junctophilin-2 to Altered Mitochondrial Metabolism and Right Ventricular Contractility” Ruopu Li, MD, PhD and Yu Nie, PhD Ruopu LiRuopu Li https://orcid.org/0000-0002-7724-018X State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China. Search for more papers by this author and Yu NieYu Nie https://orcid.org/0000-0002-8744-0046 State Key Laboratory of Cardiovascular Disease, Fuwai Hospital, National Center for Cardiovascular Disease, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China. Search for more papers by this author Originally published27 Jun 2022https://doi.org/10.1161/CIRCHEARTFAILURE.122.009531Circulation: Heart Failure. 2022;15Other version(s) of this articleYou are viewing the most recent version of this article. Previous versions: June 27, 2022: Ahead of Print To the Editor:We read with great interest the recent article by Prisco et al1 regarding the cardiac-protective role of gp130 blockade in monocrotaline induced pulmonary artery hypertension reflected by the antihypertrophy, antifibrotic effect, and the mitigated right ventricle function after gp130 antagonist SC-144 administration. The study expanded our consideration of gp130’s downstream signal to right heart function and its connecting role of inflammation, cytoskeleton organization and energy metabolism. However, here are some questions we would like to raise regarding the findings in the original article.Regenerative repair after myocardial injury requires gp130-induced STAT3 and Src-YAP pathways.2,3 And it has been reported that the loss of gp130 signaling in heart lead to adaption incapacity under biomechanical stress of pressure overload.4 We would like to respectfully ask what is the authors’ perspective on the opposite biological effect of gp130 concerning cardiac tissue response toward stress between left and right ventricle.Although major, there are different pathways downstream of gp130 other than Jak-STAT3. Did the author also detect other signaling pathways, including Erk-MAPK (extracellular regulated protein kinases-mitogen activated protein kinase pathway), PI3K-Akt (phosphoinositide-3 kinase-serine/threonine kinase Akt [also known as protein kinase B or PKB] pathway), and Src-YAP (pathway of proto-oncogene tyrosine-protein kinase Src and its downstream protein Yes associated protein [YAP]) pathways, in the pulmonary artery hypertension model before and after SC-144 administration? And did the author confirm the similar effect with SC-144 treatment under STAT3 antagonized model? SC-144 was adopted for the construction of gp130 depletion model. But the agent triggers different gp130 downstream signaling alteration including STAT3 inhibition and Erk activation.5The author treated immortalized H9c2 cell line with cytoskeleton stabilizer paclitaxel and detected an impaired mitochondrial metabolic activity. Here, we expected whether cytoskeleton interference would result in the same outcome in mitochondrial metabolism in primary neonatal rat ventricular myocytes (primary cardiomyocytes isolated form neonatal Rattus norvegicus). Paclitaxel has cytotoxicity on proliferative cells by inhibiting spindle formation, and cell mitosis is an energy-consuming process. So, the impair of cell cycle results in metabolic dysfunction. It is confusing whether it was due to the cell cycle toxicity or the cytoskeleton stabilizing that causes the alteration of mitochondrial metabolism.Article InformationSources of FundingThis work was supported by the National Natural Science Foundation of China (grant 81970243) and the Chinese Academy of Medical Sciences Innovation Fund for Medical Sciences (grant 2021-I2M-1-008).Disclosures None.FootnotesFor Sources of Funding and Disclosures, see page 823.

Nobiletin Attenuates Pathological Cardiac Remodeling after Myocardial Infarction via Activating PPARγ and PGC1α.

Materials and Methods C57BL/6 mice were treated with coronary artery ligation to generate an MI model, followed by treatment for 3 weeks with NOB (50 mg/kg/d) or vehicle (50 mg/kg/d), with or without the peroxisome proliferator-activated receptor gamma (PPARγ) inhibitor T0070907 (1 mg/kg/d). Cardiac function (echocardiography, survival rate, Evans blue, and triphenyl tetrazolium chloride staining), fibrosis (Masson's trichrome staining, quantitative real-time polymerase chain reaction (qRT-PCR), and western blot (WB)), hypertrophy (haematoxylin-eosin staining, wheat germ agglutinin staining, and qRT-PCR), and apoptosis (WB and terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) staining) were evaluated. Hypoxia-induced apoptosis (TUNEL, WB) and phenylephrine- (PE-) induced pathological hypertrophy (immunofluorescence staining, qRT-PCR) models were established in primary neonatal rat ventricular myocytes (NRVMs). The effects of NOB with or without T0070907 were examined for the expression of PPARγ and PPARγ coactivator 1α (PGC1α) by WB in mice and NRVMs. The potential downstream effectors of PPARγ were further analyzed by WB in mice. Results Following MI in mice, NOB intervention enhanced cardiac function across three predominant dimensions of pathological cardiac remodeling, which reflected in decreasing cardiac fibrosis, apoptosis, and hypertrophy decompensation. NOB intervention also alleviated apoptosis and hypertrophy in NRVMs. NOB intervention upregulated PPARγ and PGC1α in vivo and in vitro. Furthermore, the PPARγ inhibitor abolished the protective effects of NOB against pathological cardiac remodeling during the progression from MI to CHF. The potential downstream effectors of PPARγ were nuclear factor erythroid 2-related factor 2 (Nrf-2) and heme oxygenase 1 (HO-1). Conclusions Our findings suggested that NOB alleviates pathological cardiac remodeling after MI via PPARγ and PGC1α upregulation.

PKM1 Exerts Critical Roles in Cardiac Remodeling Under Pressure Overload in the Heart.

Metabolic remodeling precedes most alterations during cardiac hypertrophic growth under hemodynamic stress. The elevation of glucose utilization has been recognized as a hallmark of metabolic remodeling. However, its role in cardiac hypertrophic growth and heart failure in response to pressure overload remains to be fully illustrated. Here, we aimed to dissect the role of cardiac PKM1 (pyruvate kinase muscle isozyme 1) in glucose metabolic regulation and cardiac response under pressure overload. Cardiac-specific deletion of PKM1 was achieved by crossing the floxed PKM1 mouse model with the cardiomyocyte-specific Cre transgenic mouse. PKM1 transgenic mice were generated under the control of tetracycline response elements, and cardiac-specific overexpression of PKM1 was induced by doxycycline administration in adult mice. Pressure overload was triggered by transverse aortic constriction. Primary neonatal rat ventricular myocytes were used to dissect molecular mechanisms. Moreover, metabolomics and nuclear magnetic resonance spectroscopy analyses were conducted to determine cardiac metabolic flux in response to pressure overload. We found that PKM1 expression is reduced in failing human and mouse hearts. It is important to note that cardiomyocyte-specific deletion of PKM1 exacerbates cardiac dysfunction and fibrosis in response to pressure overload. Inducible overexpression of PKM1 in cardiomyocytes protects the heart against transverse aortic constriction-induced cardiomyopathy and heart failure. At the mechanistic level, PKM1 is required for the augmentation of glycolytic flux, mitochondrial respiration, and ATP production under pressure overload. Furthermore, deficiency of PKM1 causes a defect in cardiomyocyte growth and a decrease in pyruvate dehydrogenase complex activity at both in vitro and in vivo levels. These findings suggest that PKM1 plays an essential role in maintaining a homeostatic response in the heart under hemodynamic stress.

Evidence for synergy between sarcomeres and fibroblasts in an in vitro model of myocardial reverse remodeling

We have created a novel in-vitro platform to study reverse remodeling of engineered heart tissue (EHT) after mechanical unloading. EHTs were created by seeding decellularized porcine myocardial sections with a mixture of primary neonatal rat ventricular myocytes and cardiac fibroblasts. Each end of the ribbon-like constructs was fixed to a plastic clip, allowing the tissues to be statically stretched or slackened. Inelastic deformation was introduced by stretching tissues by 20% of their original length. EHTs were subsequently unloaded by returning tissues to their original, shorter length. Mechanical characterization of EHTs immediately after unloading and at subsequent time points confirmed the presence of a reverse-remodeling process, through which stress-free tissue length was increased after chronic stretch but gradually decreased back to its original value within 9 days. When a cardiac myosin inhibitor was applied to tissues after unloading, EHTs failed to completely recover their passive and active mechanical properties, suggesting a role for actomyosin contraction in reverse remodeling. Selectively inhibiting cardiomyocyte contraction or fibroblast activity after mechanical unloading showed that contractile activity of both cell types was required to achieve full remodeling. Similar tests with EHTs formed from human induced pluripotent stem cell-derived cardiomyocytes also showed reverse remodeling that was enhanced when treated with omecamtiv mecarbil, a myosin activator. These experiments suggest essential roles for active sarcomeric contraction and fibroblast activity in reverse remodeling of myocardium after mechanical unloading. Our findings provide a mechanistic rationale for designing potential therapies to encourage reverse remodeling in patient hearts.

RIP1/RIP3/MLKL-mediated necroptosis contributes to vinblastine-induced myocardial damage

Vinblastine (VBL) has been considered as a first-line anti-tumor drug for many years. However, vinblastine-caused myocardial damage has been continually reported. The underlying molecular mechanism of the myocardial damage remains unknown. Here, we show that vinblastine induces myocardial damage and necroptosis is involved in the vinblastine-induced myocardial damage both in vitro and in vivo. The results of WST-8 and flow cytometry analysis show that vinblastine causes damage to H9c2 cells, and the results of animal experiments show that vinblastine causes myocardial cell damage. The necrosome components, receptor-interacting protein 1 (RIP1) receptor-interacting protein 3 (RIP3), are significantly increased in vinblastine-treated H9c2 cells, primary neonatal rat ventricular myocytes and rat heart tissues. And the downstream substrate of RIP3, mixed lineage kinase domain like protein (MLKL) was also increased. Pre-treatment with necroptosis inhibitors partially inhibits the necrosome components and MLKL levels and alleviates vinblastine-induced myocardial injury both in vitro and in vivo. This study indicates that necroptosis participated in vinblastine-evoked myocardial cell death partially, which would be a potential target for relieving the chemotherapy-related myocardial damage.

Abstract 17473: GRK2 in the Mitochondria: Uncovering Novel Mechanisms in Heart Failure

Introduction: During heart failure, levels and activity of G protein-coupled receptor kinase 2 (GRK2) increase. GRK2 is canonically studied in the phosphorylation of GPCRs and β-adrenergic desensitization. Noncanonical activities of GRK2 are being uncovered, however. Our lab has recently discovered that in cardiac myocytes, GRK2 translocates to the mitochondria ( mtGRK2 ) following injury and is associated with negative effects on metabolism and cell survival. Hypothesis: GRK2 plays a role in regulating mitochondrial function following cardiac stress and contributes to HF pathogenesis in a novel manner, by interacting with a novel group of mitochondrial proteins involved in pro-death signaling, bioenergetics and substrate utilization. Methods: Mitochondrial translocation of GRK2 was validated with either protein kinase C inhibitor (chelerythine) administration or hypoxia/reoxygenation stress in primary neonatal rat ventricular myocytes or a cardiac-like cell line. Immunoprecipitation of the GRK2 interactome basally and under stress conditions was conducted endogenously in vitro, in vivo , and with purified recombinant GRK2 peptides. Proteins were separated via SDS-PAGE and potential binding partners were identified by mass spectroscopy (LCMS) and proteomics analysis conducted with Ingenuity Pathway (IPA; Qiagen) software to determine which partners in the GRK2 interactome were potentially involved in mitochondrial dysfunction. Results: Subunits of Complexes I, II, IV and V of the electron transport chain were identified as potential mtGRK2 interacting partners. Several mtGRK2-ETC interactions were increased following oxidative stress-induced translocation of GRK2. Finally, mtGRK2 appears to phosphorylate some of the interactome partners identified in mitochondrial dysfunction. Conclusions: The phosphorylation of subunits of the ATP synthesis machinery by mtGRK2, or other mechanisms of interaction between these proteins, may be regulating some of the phenotypic effects of HF previously observed by our lab, such as increased ROS production and reduced fatty acid metabolism. Further research is essential to elucidate the novel role of GRK2 in regulating mitochondrial bioenergetics and cell death in failing hearts.

ATF6β is an Adaptive Transcription Factor in Cardiac Myocyte.

RationaleATF6 is an endoplasmic reticulum (ER) transmembrane protein, which is activated in response to the accumulation of misfolded proteins in the ER, a phenomenon known as ER stress. During ER stress, ATF6 is activated through proteolytic cleavage in the Golgi, which releases the N‐terminal active form that will translocate to the nucleus and act as a transcription factor, regulating a widespan of adaptive genes in an attempt to restore proteostasis in the ER, thus resolving ER stress and promoting cell survival. If ER proteostasis is terminally impaired, a maladaptive response will be activated and cell death will occur. There exist two isoforms of ATF6, ATF6α and ATF6β, which have high sequential and structural homology in their ER transmembrane and DNA binding domains. Our previous studies have shown that acute activation of ATF6α is protective in cardiac myocytes under different simulated pathologies in the heart, such as ischemic injury and pressure overload. On the other hand, the precise role of ATF6β in cardiac myocyte gene regulation and viability has yet to be determined.HypothesisATF6β is an adaptive transcription factor that is critical to cardiac myocyte viability.MethodWe used cultured primary neonatal rat ventricular myocytes (NRVM) as a model to study the role of ATF6β, in a loss‐of‐function or gain‐of‐function approach. To study the impact of ATF6β loss‐of‐function, we used small interfering RNA targeted to ATF6β to knockdown its expression. To study the impact of ATF6β gain‐of‐function, we overexpressed ATF6β by infection of NRVMs with ATF6β‐encoding adenovirus. Thereafter, in both models, we assessed cell viability by MTT assay over a period of four days after treatment with or without the chemical ER‐stress inducer tunicamycin (TM). We also determined the adaptive and maladaptive gene profiles of NRVMs in both loss‐of‐function and gain‐of‐function models using real‐time quantitative PCR.ResultsOur results showed that ATF6β knockdown significantly decreased cardiac myocyte viability over time without TM, and TM‐induced ER‐stress exacerbated this loss in viability. ATF6β overexpression maintained cell viability throughout the time course compared to cells treated with control adenovirus, both with and without TM. Gene expression analysis in the ATF6β loss‐of‐function model showed a downregulation of adaptive genes, such as the chaperone Hsp90b1 and anti‐apoptotic gene Bcl2, and an upregulation of the maladaptive, pro‐apoptotic gene Bbc3. Consistent with the loss‐of‐function model, in the gain‐of‐function model, gene expression analysis showed an upregulation of chaperone gene Hspa5 and a downregulation of Bbc3.ConclusionThe effect of ATF6β loss‐ and gain‐of‐function on cell viability and Bbc3 gene expression demonstrate that ATF6β has an adaptive role in cardiac myocyte viability and suggest a regulatory role of ATF6β on Bbc3 gene expression to achieve its effect on viability.Support or Funding InformationAmerican Heart Association, National Institute of Health

Spexin protects cardiomyocytes from hypoxia-induced metabolic and mitochondrial dysfunction.

Spexin (SPX) is a novel peptide with pleiotropic functions in adipose tissue including energy balance adjustment, fatty acid uptake, and glucose homeostasis. SPX level is closely associated with cardiovascular risk factors such as age, obesity, hypertension, and diabetes; however, its physiological significance in the cardiovascular system remains mostly undefined. We therefore here investigated the roles of SPX in regulating hypoxia-induced alterations in energy metabolism and mitochondrial function. We firstly confirmed that SPX is expressed in human and mouse cardiac tissue and documented that exposure to hypoxia in vitro reduces SPX level in rat H9C2 cardiomyocytes and primary neonatal rat ventricular myocytes (NRVMs). We then treated primary NRVMs with SPX before exposure to hypoxia, which (1) promoted fatty acid metabolism by enhancing expression of FAT/CD36, CPT1, ACADM, and PPAR-a and PGC1-a; (2) did not improve impaired glucose uptake; and (3) significantly prevented the downregulation of TFAM and mitochondrial electron transport chain complex and restrained UCP2 level and reactive oxygen species (ROS) production, thus enhancing ATP level in cardiomyocytes. In summary, SPX protects energy and mitochondrial homeostasis of cardiomyocytes during hypoxia, thereby highlighting the potential importance of SPX in the treatment of cardiovascular diseases.

Abstract 371: Chromatin Remodeling Mechanisms by Bromodomain PHD Finger Transcription Factor in Cardiac Hypertrophy and Heart Failure

Alteration of chromatin conformation has a profound effect on gene expression, and can lead to heart failure, which remains a major cause of death worldwide. ATP-dependent chromatin remodelers utilize the energy of ATP to remodel chromatin in specific regions of the genome. However, the mechanisms of ATP-dependent chromatin remodeling and how they connect to the genome remain poorly understood. We have discovered that the nucleosome remodeler Bromodomain PHD-finger Transcription Factor (BPTF), the largest subunit of the Nucleosome Remodeling Factor (NURF), plays an important role in cardiac hypertrophy. Our preliminary data show that BPTF is enriched in failing human hearts, a phenomenon similarly observed in mouse hearts subjected to pressure overload hypertrophy (TAC). BPTF is up-regulated in primary neonatal rat ventricular myocytes (NRVM) and human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) stimulated with the hypertrophic agonist phenylephrine (PE). Strikingly, specific silencing of BPTF in NRVM and hiPSC-CMs, inhibits the expression of the atrial natriuretic peptide (ANP), a marker of cardiac hypertrophy. Chromatin immunoprecipitation performed in NRVM show that BPTF binds to the ANP promoter, but not to GAPDH. Proteomics experiments performed in failing human hearts revealed a multi-protein complex formed between BPTF and novel chromatin regulators. At the level of the nucleosome, BPTF in combination with one of its partners, remodels chromatin by facilitating nucleosomes “sliding” along the DNA. This mechanism is mediated by the binding of BPTF to histone H3 trimethylated at Lysine-4 (H3K4me3), an “active” mark of transcription also up-regulated in the early phase of cardiac hypertrophy in NRVM and in mouse TAC hearts. Our study suggests a novel chromatin signature controlled by BPTF, that dictates specific gene patterns implicated in pathological cardiac hypertrophy. Our study uncovers a new epigenetic mechanism controlling pathological cardiac remodeling and heart failure.

Inhibition of miR-23a attenuates doxorubicin-induced mitochondria-dependent cardiomyocyte apoptosis by targeting the PGC-1α/Drp1 pathway

Background and purposeDoxorubicin (Dox)-induced cardiotoxicity limits its clinical use. A number of microRNAs (miRs) have been found essential in Dox-induced cardiotoxicity. The aim of the present study was to elucidate the effects of miR-23a on Dox-induced cardiomyocyte apoptosis and underlying mechanisms. Experimental approachDox-induced cardiotoxicity model was established in primary neonatal rat ventricular myocytes (NRVMs). MTT assay, Live/Dead staining was employed to examine the viability and cell death of NRVMs. Mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) were measured. Protein levels of mitochondria biogenesis and fission/fusion associated factors including peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), dynamin-related protein-1 (Drp1) and mitofusin 2 (Mfn2) were detected. Meanwhile, apoptosis-related cytochrome c (Cyt c) and caspase-3 expression were examined by western blot. PGC-1α siRNA was employed to validate the role of miR-23a in Dox-induced cardiotoxicity. Key resultsMiR-23a expression was significantly increased by Dox concentration-dependently. Inhibition of miR-23a markedly increased viability and MMP, reduced cell death and ROS production of NRVMs. MiR-23a mimic significantly inhibited expression of its target PGC-1α. MiR-23a inhibitor significantly diminished phosphorylation of Drp1 without affecting Mfn2 expression. Protein expression of Cyt c and cleaved caspase-3 were markedly inhibited by miR-23a inhibitor. The protective effects of miR-23a inhibitor were reversed by PGC-1α siRNA. Conclusions and implicationsIncreased miR-23a promoted mitochondrial injury in the Dox-induced cellular model. Inhibition of miR-23a attenuated cardiomyocyte damage by directly targeting PGC-1α/p-Drp1, thereby inhibiting mitochondria-dependent apoptosis. These findings may provide a new potential target for the treatment of Dox-induced cardiotoxicity.

Protein S -Nitrosylation Controls Glycogen Synthase Kinase 3β Function Independent of Its Phosphorylation State

GSK-3β (glycogen synthase kinase 3β) is a multifunctional and constitutively active kinase known to regulate a myriad of cellular processes. The primary mechanism to regulate its function is through phosphorylation-dependent inhibition at serine-9 residue. Emerging evidence indicates that there may be alternative mechanisms that control GSK-3β for certain functions. Here, we sought to understand the role of protein S-nitrosylation (SNO) on the function of GSK-3β. SNO-dependent modulation of the localization of GSK-3β and its ability to phosphorylate downstream targets was investigated in vitro, and the network of proteins differentially impacted by phospho- or SNO-dependent GSK-3β regulation and in vivo SNO modification of key signaling kinases during the development of heart failure was also studied. We found that GSK-3β undergoes site-specific SNO both in vitro, in HEK293 cells, H9C2 myoblasts, and primary neonatal rat ventricular myocytes, as well as in vivo, in hearts from an animal model of heart failure and sudden cardiac death. S-nitrosylation of GSK-3β significantly inhibits its kinase activity independent of the canonical phospho-inhibition pathway. S-nitrosylation of GSK-3β promotes its nuclear translocation and access to novel downstream phosphosubstrates which are enriched for a novel amino acid consensus sequence motif. Quantitative phosphoproteomics pathway analysis reveals that nuclear GSK-3β plays a central role in cell cycle control, RNA splicing, and DNA damage response. The results indicate that SNO has a differential effect on the location and activity of GSK-3β in the cytoplasm versus the nucleus. SNO modification of GSK-3β occurs in vivo and could contribute to the pathobiology of heart failure and sudden cardiac death.

Protective role and mechanism of snakegourd peel against myocardial infarction in rats

BackgroundInjection of snakegourd peel (SP), an herb used in traditional Chinese medicine, is used to treat coronary artery disease and stable angina in China. However, its therapeutic role and mechanism of action for the treatment of myocardial infarction (MI) is not fully understood. PurposeThe present study was designed to investigate the effect of SP on MI-induced cardiac injury and elucidate its underlying molecular mechanisms. MethodsTo create an in vivo model of MI, we ligated the left coronary artery of Wistar rats. For our in vitro model of MI, we treated primary neonatal rat ventricular myocytes with hypoxia. Myocardial infarct size was measured by triphenyltetrazolium chloride (TTC) staining. Intracellular calcium concentration (Ca2+) was measured by confocal microscopy, and cardiomyocyte apoptosis was assessed by TUNEL assay. Western blot was applied to determine protein levels. ResultsThree days post-MI, SP significantly improved MI-induced impairment of cardiac function, as indicated by increased left ventricular systolic pressure (LVSP), maximum rate of left ventricular pressure rise and fall (± dp/dt max), and decreased left ventricular end-diastolic pressure (LVEDP). In addition, SP treatment markedly reduced the infarct size and serum lactate dehydrogenase (LDH) activity; inhibited cardiomyocyte apoptosis and Caspase-3 activation both in vivo and in vitro; and decreased intracellular calcium overload, Cav1.2, phosphorylated JNK (p-JNK), and p38 MAPK (p-p38 MAPK) levels in ischemic myocardium. ConclusionSP alleviated cardiac ischemic injury and inhibited cardiomyocyte apoptosis by attenuating intracellular calcium overload, suppressing Caspase-3 activation, and downregulating protein expression of p-JNK and p-p38MAPK. These results suggest that SP may serve as a potential novel therapeutic drug for MI.

Astragalus polysaccharide restores autophagic flux and improves cardiomyocyte function in doxorubicin-induced cardiotoxicity.

Doxorubicin (adriamycin), an anthracycline antibiotic, is commonly used to treat many types of solid and hematological malignancies. Unfortunately, clinical usage of doxorubicin is limited due to the associated acute and chronic cardiotoxicity. Previous studies demonstrated that Astragalus polysaccharide (APS), the extracts of Astragalus membranaceus, had strong anti-tumor activities and anti-inflammatory effects. However, whether APS could mitigate chemotherapy-induced cardiotoxicity is unclear thus far. We used a doxorubicin-induced neonatal rat cardiomyocyte injury model and a mouse heart failure model to explore the function of APS. GFP-LC3 adenovirus-mediated autophagic vesicle assays, GFP and RFP tandemly tagged LC3 (tfLC3) assays and Western blot analyses were performed to analyze the cell function and cell signaling changes following APS treatment in cardiomyocytes. First, doxorubicin treatment led to C57BL/6J mouse heart failure and increased cardiomyocyte apoptosis, with a disturbed cell autophagic flux. Second, APS restored autophagy in doxorubicin-treated primary neonatal rat ventricular myocytes and in the doxorubicin-induced heart failure mouse model. Third, APS attenuated doxorubicin-induced heart injury by regulating the AMPK/mTOR pathway. The mTOR inhibitor rapamycin significantly abrogated the protective effect of APS. These results suggest that doxorubicin could induce heart failure by disturbing cardiomyocyte autophagic flux, which may cause excessive cell apoptosis. APS could restore normal autophagic flux, ameliorating doxorubicin-induced cardiotoxicity by regulating the AMPK/mTOR pathway.

Hypertrophy changes 3D shape of hiPSC-cardiomyocytes: Implications for cellular maturation in regenerative medicine.

Advances in the use of human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes for heart regeneration and in vitro disease models demand a greater understanding of how these cells grow and mature in 3-dimensional space. In this study, we developed an analysis methodology of single cardiomyocytes plated on 2D surfaces to assess their 3D myofilament volume and its z-height distribution, or shape, upon hypertrophic stimulation via phenylephrine (PE) treatment or long-term culture ("aging"). Cardiomyocytes were fixed and labeled with α-actinin for confocal microscopy imaging to obtain z-stacks for 3D myofilament volume analysis. In primary neonatal rat ventricular myocytes (NRVMs), area increased 72% with PE, while volume increased 31%. In hiPSC-cardiomyocytes, area increased 70% with PE and 4-fold with aging; however, volume increased significantly only with aging by 2.3-fold. Analysis of z-height myofilament volume distribution in hiPSC-cardiomyocytes revealed a shift from a fairly uniform distribution in control cells to a basally located volume in a more flat and spread morphology with PE and even more so with aging, a shape that was akin to all NRVMs analyzed. These results suggest that 2D area is not a sufficient measure of hiPSC-cardiomyocyte growth and maturation, and that changes in 3D volume and its distribution are essential for understanding hiPSC-cardiomyocyte biology for disease modeling and regenerative medicine applications.

Discovery of novel small molecule inhibitors of cardiac hypertrophy using high throughput, high content imaging

Chronic cardiac hypertrophy is maladaptive and contributes to the pathogenesis of heart failure. The objective of this study was to identify small molecule inhibitors of pathological cardiomyocyte hypertrophy. High content screening was performed with primary neonatal rat ventricular myocytes (NRVMs) cultured on 96-well plates and treated with a library of 3241 distinct small molecules. Non-toxic hit compounds that blocked hypertrophy in response to phenylephrine (PE) and phorbol myristate acetate (PMA) were identified based on their ability to reduce cell size and inhibit expression of atrial natriuretic factor (ANF), which is a biomarker of pathological cardiac hypertrophy. Many of the hit compounds are existing drugs that have not previously been evaluated for benefit in the setting of cardiovascular disease. One such compound, the anti-malarial drug artesunate, blocked left ventricular hypertrophy (LVH) and improved cardiac function in adult mice subjected to transverse aortic constriction (TAC). These findings demonstrate that phenotypic screening with primary cardiomyocytes can be used to discover anti-hypertrophic lead compounds for heart failure drug discovery. Using annotated libraries of compounds with known selectivity profiles, this screening methodology also facilitates chemical biological dissection of signaling networks that control pathological growth of the heart.

BDNF-mediates Down-regulation of MicroRNA-195 Inhibits Ischemic Cardiac Apoptosis in Rats.

Background: Our previous studies suggested that brain-derived neurotrophic factor (BDNF)/tropomyosin-related kinase B (TrkB) axis inhibited cardiomyocyte apoptosis in myocardial infarction (MI). However, the relationship between BDNF and microRNA (miRNA) in cardiomyocytes are unclear. The present study was performed to investigate the role of miR-195 and the interplay between BDNF and miR-195 in ischemic cardiomyocyte apoptosis.Methods: Male Wistar rats were subjected to coronary artery ligation, and primary neonatal rat ventricular myocytes were treated with hypoxia or hydrogen peroxide (H2O2). BDNF level in rat ventricles was measured by enzyme linked immunosorbent assay (ELISA). miR-195 mimic, inhibitor or negative control was transfected into the cardiomyocytes. Cell viability and apoptosis were detected by MTT assay and TdT-mediated dUTP nick end labeling (TUNEL) staining, respectively. Cardiac function and apoptosis were detected in MI rats intravenously injected with antagomiR-195. Luciferase assay, Western blot and Real-time RT-PCR were employed to clarify the interplay between miR-195 and BDNF.Results: miR-195 level was dynamically regulated in response to MI and significantly increased in ischemic regions 24 h post-MI as well as in hypoxic or H2O2-treated cardiomyocytes. Meanwhile, BDNF protein level was rapidly increased in MI rats and H2O2-treated cardiomyocytes. Apoptosis in both hypoxic and H2O2-treated cardiomyocytes were markedly reduced and cell viability was increased by miR-195 inhibitor. Moreover, inhibition of miR-195 significantly improved cardiac function of MI rats. Bcl-2 but not BDNF was validated as the direct target of miR-195. Furthermore, BDNF abolished the pro-apoptotic role of miR-195, which was reversed by its scavenger TrkB-Fc.Conclusion: Up-regulation of miR-195 in ischemic cardiomyocytes promotes ischemic apoptosis by targeting Bcl-2. BDNF mitigated the pro-apoptotic effect of miR-195 in rat cardiomyocytes. These findings may provide better understanding of the pro-apoptotic role of miR-195 in MI and suggest that BDNF/miR-195/Bcl-2 axis may be beneficial for limiting myocardial ischemic injury.

Higenamine protects ischemia/reperfusion induced cardiac injury and myocyte apoptosis through activation of β2-AR/PI3K/AKT signaling pathway

Cardiomyocyte apoptosis contributes to ischemic cardiac injury and the development of heart failure. Higenamine is a key component of the Chinese herb aconite root that has been prescribed for treating symptoms of heart failure for thousands of years in the oriental Asian countries. It has been shown that higenamine has anti-apoptotic effects in a few cell types including cardiomyocytes. However, the pharmacological target and molecular mechanism of higenamine in the heart are still not fully illustrated. Herein, we report that higenamine protected myocyte apoptosis and ischemia/reperfusion (I/R) injury through selective activation of beta2-adrenergic receptor (β2-AR). In particular, we show that higenamine significantly reduced I/R-induced myocardial infarction in mice. In both primary neonatal rat and adult mouse ventricular myocytes, we show higenamine inhibited cell apoptosis and also reduced biochemical markers of apoptosis such as cleaved caspase 3 and 9. More importantly, we show that the anti-apoptotic effects of higenamine in cardiomyocytes were completely abolished by β2-AR but not β1-AR antagonism. Furthermore, we confirmed that higenamine attenuated I/R-induced myocardial injury and reduced cleaved caspases in a β2-AR dependent manner in intact mouse hearts. Higenamine stimulated AKT phosphorylation and required PI3K activation for the anti-apoptotic effect in cardiomyocytes. These findings together suggest that anti-apoptotic and cardiac protective effects of higenamine are mediated by the β2-AR/PI3K/AKT cascade.

Upstream open reading frame in 5′-untranslated region reduces titin mRNA translational efficiency

Titin is the largest known protein and a critical determinant of myofibril elasticity and sarcomere structure in striated muscle. Accumulating evidence that mRNA transcripts are post-transcriptionally regulated by specific motifs located in the flanking untranslated regions (UTRs) led us to consider the role of titin 5′-UTR in regulating its translational efficiency. Titin 5′-UTR is highly homologous between human, mouse, and rat, and sequence analysis revealed the presence of a stem-loop and two upstream AUG codons (uAUGs) converging on a shared in frame stop codon. We generated a mouse titin 5′-UTR luciferase reporter construct and targeted the stem-loop and each uAUG for mutation. The wild-type and mutated constructs were transfected into the cardiac HL-1 cell line and primary neonatal rat ventricular myocytes (NRVM). SV40 driven 5′-UTR luciferase activity was significantly suppressed by wild-type titin 5′-UTR (∼70% in HL-1 cells and ∼60% in NRVM). Mutating both uAUGs was found to alleviate titin 5′-UTR suppression, while eliminating the stem-loop had no effect. Treatment with various growth stimuli: pacing, PMA or neuregulin had no effect on titin 5′-UTR luciferase activity. Doxorubicin stress stimuli reduced titin 5′-UTR suppression, while H2O2 had no effect. A reported single nucleotide polymorphism (SNP) rs13422986 at position -4 of the uAUG2 was introduced and found to further repress titin 5′-UTR luciferase activity. We conclude that the uAUG motifs in titin 5′-UTR serve as translational repressors in the control of titin gene expression, and that mutations/SNPs of the uAUGs or doxorubicin stress could alter titin translational efficiency.

Phosphatidylinositol 4,5-bisphosphate regulates CapZβ1 and actin dynamics in response to mechanical strain

Mechanical stress causes filament remodeling leading to myocyte hypertrophy and heart failure. The actin capping protein Z (CapZ) tightly binds to the barbed end of actin filaments, thus regulating actin assembly. The hypothesis is that the binding between CapZ and the actin filament is modulated through phosphatidylinositol 4,5-bisphosphate (PIP2) and how the COOH-terminus of CapZβ1 regulates this binding. Primary neonatal rat ventricular myocytes (NRVMs) were strained at 10% amplitude and 1-Hz frequency. Dot blotting measured the PIP2 amount, and affinity precipitation assay assessed the direct interaction between PIP2 and CapZβ1. Fluorescence recovery after photobleaching of green fluorescent protein-CapZβ1 and actin-green fluorescent protein after 1 h of strain shows the dynamics significantly increased above the unstrained group. The increases in CapZ and actin dynamics were blunted by neomycin, suggesting PIP2 signaling is involved. The amount of PIP2 dramatically increased in NRVMs strained for 1 h. With a ROCK or RhoA inhibitor, changes were markedly reduced. Subcellular fractionation and antibody localization showed PIP2 distributed to the sarcomeres. More PIP2-bound CapZβ1 was found in strained NRVMs. Less PIP2 bound to the CapZβ1 with its COOH-terminus intact than in the COOH-terminal mutant of CapZβ1, suggesting some inhibitory role for the COOH-terminus. Myocyte hypertrophy normally induced by 48 h of cyclic strain was blunted by dominant negative RhoA or neomycin. This suggests that after many hours of cyclic strain, a possible mechanism for cell hypertrophy is the accumulation of thin filament assembly triggered partially by the increased PIP2 level and its binding to CapZ.

Implications of the O-GlcNAc modification in the regulation of nuclear apoptosis in T cells

BackgroundO-linked β-N-acetylglucosamine (O-GlcNAc) is a nutrient-/stress-sensitive post-translational modification that affects nucleocytoplasmic proteins. The enzyme O-N-acetylglucosamine transferase (OGT) catalyzes the addition of O-GlcNAc, whereas O-N-acetylglucosaminidase (OGA) removes it. O-GlcNAcylation plays a role in fundamental regulatory mechanisms through the modification of proteins involved in cell division, metabolism, transcription, cell signaling and apoptosis. The effects of O-GlcNAcylation on apoptosis appear to be cell-dependent, as elevated levels played a protective role in primary neonatal rat ventricular myocytes but had a cytotoxic effect in rat pancreatic β-cells. The aim of the current study was to determine the implications of the O-GlcNAc modification on T cell apoptosis. MethodsHuman T lymphoblastic HPB-ALL cells were treated with the OGA inhibitor O-(2-acetamido-2-deoxy-d-glucopyranosylidene) amino-N-phenylcarbamate (PUGNAc), or with glucosamine (GlcN), to increase O-GlcNAcylation. Apoptosis was induced in the presence of tributyltin (TBT). DNA fragmentation was observed by cell cycle analysis and corresponded to the sub G0/G1 population. O-GlcNAcylated proteins were detected by immunoblot using a specific antibody (ctd110.6) and were precipitated using succinylated wheat germ agglutinin (sWGA). ResultsHPB-ALL cells treated with PUGNAc displayed a significant reduction in DNA fragmentation after TBT-induced apoptosis. DFF45, the protein that inhibits the endonuclease DFF40, was identified to be O-GlcNAc modified. O-GlcNAcylated DFF45 appeared to be more resistant to caspase cleavage during apoptosis. Our results suggest that a decrease in the O-GlcNAc modification on DFF45 occurs before its cleavage by caspase. General significanceOur results indicate that the O-GlcNAcylation of DFF45 may represent a mechanism to control the accidental activation of DFF.