Primary Rat Cardiomyocytes Research Articles

Novel Insights into the Cardio-Protective Effects of FGF21 in Lean and Obese Rat Hearts

AimsFibroblast growth factor 21 (FGF21) is a hepatic metabolic regulator with pleotropic actions. Its plasma concentrations are increased in obesity and diabetes; states associated with an increased incidence of cardiovascular disease. We therefore investigated the direct effect of FGF21 on cardio-protection in obese and lean hearts in response to ischemia.Methods and ResultsFGF21, FGF21-receptor 1 (FGFR1) and beta-Klotho (βKlotho) were expressed in rodent, human hearts and primary rat cardiomyocytes. Cardiac FGF21 was expressed and secreted (real time RT-PCR/western blot and ELISA) in an autocrine-paracrine manner, in response to obesity and hypoxia, involving FGFR1-βKlotho components. Cardiac-FGF21 expression and secretion were increased in response to global ischemia. In contrast βKlotho was reduced in obese hearts. In isolated adult rat cardiomyocytes, FGF21 activated PI3K/Akt (phosphatidylinositol 3-kinase/Akt), ERK1/2(extracellular signal-regulated kinase) and AMPK (AMP-activated protein kinase) pathways. In Langendorff perfused rat [adult male wild-type wistar] hearts, FGF21 administration induced significant cardio-protection and restoration of function following global ischemia. Inhibition of PI3K/Akt, AMPK, ERK1/2 and ROR-α (retinoic-acid receptor alpha) pathway led to significant decrease of FGF21 induced cardio-protection and restoration of cardiac function in response to global ischemia. More importantly, this cardio-protective response induced by FGF21 was reduced in obesity, although the cardiac expression profiles and circulating FGF21 levels were increased.ConclusionIn an ex vivo Langendorff system, we show that FGF21 induced cardiac protection and restoration of cardiac function involving autocrine-paracrine pathways, with reduced effect in obesity. Collectively, our findings provide novel insights into FGF21-induced cardiac effects in obesity and ischemia.

Protein Kinase Cε-Calcineurin Cosignaling Downstream of Toll-Like Receptor 4 Downregulates Fibrosis and Induces Wound Healing Gene Expression in Cardiac Myofibroblasts

The pathways which regulate resolution of inflammation and contribute to positive remodeling of the myocardium following injury are poorly understood. Here we show that protein kinase C epsilon (PKCε) cooperates with the phosphatase calcineurin (CN) to potentiate induction of cardioprotective gene expression while suppressing expression of fibrosis markers. This was achieved by detailed analysis of the regulation of cyclooxygenase 2 (COX-2) expression as a marker gene and by using gene expression profiling to identify genes regulated by coexpression of CN-Aα/PKCε in adult rat cardiac myofibroblasts (ARVFs) on a larger scale. GeneChip analysis of CN-Aα/PKCε-coexpressing ARVFs showed that COX-2 provides a signature for wound healing and is associated with downregulation of fibrosis markers, including connective tissue growth factor (CTGF), fibronectin, and collagens Col1a1, Col3a1, Col6a3, Col11a1, Col12a1, and Col14a1, with concomitant upregulation of cardioprotection markers, including COX-2 itself, lipocalin 2 (LCN2), tissue inhibitor of metalloproteinase 1 (TIMP-1), interleukin-6 (IL-6), and inducible nitric oxide synthase (iNOS). In primary rat cardiomyocyte cultures Toll-like receptor 4 (TLR4) agonist- or PKCε/CN-dependent COX-2 induction occurred in coresident fibroblasts and was blocked by selective inhibition of CN or PKC α/ε or elimination of fibroblasts. Furthermore, ectopic expression of PKCε and CN in ARVFs showed that the effects on COX-2 expression are mediated by specific NFAT sites within the COX-2 promoter as confirmed by site-directed mutagenesis and chromatin immunoprecipitation (ChIP). Therefore, PKCε may negatively regulate adverse myocardial remodeling by cooperating with CN to downregulate fibrosis and induce transcription of cardioprotective wound healing genes, including COX-2.

The Cardioprotective Effect of Protocatechuic Acid on Myocardial Ischemia/Reperfusion Injury

Protocatechuic acid (PCA), a phenolic compound and one of the main metabolites of complex polyphenols, has been found to possess various biological activities, and it may have a potential in the treatment of ischemic heart diseases. This study explored the cardioprotective effect of PCA on myocardial ischemia/reperfusion (MI/R) injury and the underlying mechanisms. In an in vivo rat model of MI/R injury, myocardial infarct size, serum TNF-a level, and platelet aggregation were measured. In a primary neonatal rat cardiomyocyte model of hypoxia/ reoxygenation (H/R) injury, the apoptotic rate, expressions of cleaved caspase-3, and phosphorylated Akt were observed. We found that PCA significantly reduced myocardial infarct size, serum TNF-a level, and platelet aggregation. In vitro experiments revealed that PCA significantly inhibited the apoptotic rate and the expression of cleaved caspase-3, and it upregulated the expression of phosphorylated Akt in cardiomyocytes subjected to H/R injury. Our results suggest that PCA can provide a significant protection against MI/R injury, which may be at least partially attributed to its inhibitions against injury induced by MI/R including the inflammatory response, platelet aggregation, and cardiomyocytes apoptosis.

Abstract 18701: Sildenafil Attenuates Ethanol-Induced Myocardial Dysfunction and Cytotoxicity

Background: Ethanol (EtOH) induces cardiotoxicity by increasing apoptosis, free radical formation and lipid peroxidation. Since sildenafil has potent cardioprotective effects through activation of protein kinase G, we hypothesized that treatment with sildenafil would attenuate cardiotoxicity associated with acute EtOH exposure by reducing apoptosis and preserving function. Methods and Results: Mice were treated with EtOH (3 g/kg/day, ip) ± sildenafil (0.7 mg/kg, ip) for 3 days. Cardiac function was measured in Langendorff mode. EtOH treatment decreased rate-force product (g·bpm) (270 ± 26, P < 0.01) as compared to control (433 ± 23), which was preserved with sildenafil co-treatment (392 ± 38). EtOH increased myocardial apoptosis (1.42 ± 0.16%; P < 0.001 vs. control 0.05 ± 0.03%), which was attenuated with sildenafil (0.05± 0.05%). Sildenafil increased myocardial PKG activity with (2.6 fold) or without EtOH (4.6 fold). To further understand the mechanism of protection of sildenafil against EtOH cardiotoxicity, primary rat cardiomyocytes were treated with 100 mM EtOH ± 10 μM sildenafil. At 18 h, necrosis (trypan blue staining); mitochondrial membrane potential (mΔΨ, JC-1; aggregates/monomer); and ROS (DCF; F488 AU) were measured. At 48 h, apoptosis was assessed by TUNEL. EtOH increased necrosis and apoptosis, which were attenuated with sildenafil (Fig 1). EtOH disrupted mΔΨ (EtOH 1.24 ± 0.17, P < 0.001) and increased ROS production (EtOH 156.73 ± 36.91, P < 0.01) compared to control (13.08 ± 1.78 and 28.09 ± 5.75, respectively). Sildenafil preserved mΔΨ (19.29 ± 3.01) and attenuated ROS production (12.38 ± 5.70). Knockdown of PKG with adenoviral shRNA blocked the protective effect of sildenafil whereas overexpression of PKG1α conferred similar protection against EtOH cytotoxicity (Fig 1). Conclusion: Sildenafil attenuates the EtOH cardiotoxicity through PKG-dependent maintenance of mitochondrial integrity while preserving cardiac function.

Assessing the translatability of In vivo cardiotoxicity mechanisms to In vitro models using causal reasoning

Drug-induced cardiac toxicity has been implicated in 31% of drug withdrawals in the USA. The fact that the risk for cardiac-related adverse events goes undetected in preclinical studies for so many drugs underscores the need for better, more predictive in vitro safety screens to be deployed early in the drug discovery process. Unfortunately, many questions remain about the ability to accurately translate findings from simple cellular systems to the mechanisms that drive toxicity in the complex in vivo environment. In this study, we analyzed translatability of cardiotoxic effects for a diverse set of drugs from rodents to two different cell systems (rat heart tissue-derived cells (H9C2) and primary rat cardiomyocytes (RCM)) based on their transcriptional response. To unravel the altered pathway, we applied a novel computational systems biology approach, the Causal Reasoning Engine (CRE), to infer upstream molecular events causing the observed gene expression changes. By cross-referencing the cardiotoxicity annotations with the pathway analysis, we found evidence of mechanistic convergence towards common molecular mechanisms regardless of the cardiotoxic phenotype. We also experimentally verified two specific molecular hypotheses that translated well from in vivo to in vitro (Kruppel-like factor 4, KLF4 and Transforming growth factor beta 1, TGFB1) supporting the validity of the predictions of the computational pathway analysis. In conclusion, this work demonstrates the use of a novel systems biology approach to predict mechanisms of toxicity such as KLF4 and TGFB1 that translate from in vivo to in vitro. We also show that more complex in vitro models such as primary rat cardiomyocytes may not offer any advantage over simpler models such as immortalized H9C2 cells in terms of translatability to in vivo effects if we consider the right endpoints for the model. Further assessment and validation of the generated molecular hypotheses would greatly enhance our ability to design predictive in vitro cardiotoxicity assays.

Disruption of TAB1/p38α Interaction Using a Cell-permeable Peptide Limits Myocardial Ischemia/Reperfusion Injury

Targeting the adaptor protein (transforming growth factor-β (TGF-β)-activated protein kinase 1 (TAK1)-binding protein 1) (TAB1)-mediated non-canonical activation of p38α to limit ischemia/reperfusion (I/R) injury after an acute myocardial infarction seems to be attractive since TAB1/p38α interaction occurs specifically in very limited circumstances and possesses unique structural basis. However, so far no TAB1/p38α interaction inhibitor has been reported due to the limited knowledge about the interfaces. In this study, we sought to identify key amino acids essential for the unique mode of interaction with computer-guided molecular simulations and molecular docking. After validation of the predicted three-dimensional (3-D) structure of TAB1/p38α complex, we designed several peptides and evaluated whether they could block TAB1/p38α interaction with selectivity. We found that a cell-permeable peptide worked as a selective TAB1/p38α interaction inhibitor and decreased myocardial I/R injury. To our knowledge, this is the first TAB1/p38α interaction inhibitor.

Activin A impairs insulin action in cardiomyocytes via up-regulation of miR-143

Enhanced activin A release from epicardial adipose tissue (EAT) has been linked to the development of cardiac dysfunction in type 2 diabetes (T2D). This study examined whether the inhibition of insulin action induced by epicardial adipokines in cardiomyocytes can be ascribed to alterations in miRNA expression. Expression levels of miRNAs were assessed by real-time PCR in primary adult rat cardiomyocytes (ARC) exposed to conditioned media generated from EAT biopsies (CM-EAT) from patients with and without T2D. CM-EAT-T2D altered the expression of eight miRNAs in ARC vs. CM-EAT from patients without T2D. Of these, only expression of the miR-143/145 cluster was affected by activin A in the same direction as CM-EAT-T2D. Accordingly, activin A neutralizing antibodies prevented the induction of the miR-143/145 cluster by CM-EAT-T2D. Subsequently, the impact of the miR-143/145 cluster on insulin action was investigated. Transfection of HL-1 cells with precursor-miR-143 (pre-miR-143), but not pre-miR-145, blunted the insulin-mediated phosphorylation of Akt and its substrate proline-rich Akt substrate of 40 kDa (PRAS40), and reduced insulin-stimulated glucose uptake. Also lentivirus-mediated expression of pre-miR-143 in ARC reduced insulin-induced Akt phosphorylation. These effects were ascribed to down-regulation of the miR-143 target and regulator of insulin action, the oxysterol-binding protein-related protein 8 (ORP8) in both ARC and HL-1 cells. Finally, LNA-anti-miR-143 protected against the detrimental effects of CM-EAT-T2D on insulin action in ARC. Activin A released from EAT-T2D inhibits insulin action via the induction of miR-143 in cardiomyocytes. This miRNA inhibits the Akt pathway through down-regulation of the novel regulator of insulin action, ORP8.

The effects of quercetin protect cardiomyocytes from A/R injury is related to its capability to increasing expression and activity of PKCε protein

Quercetin is a ubiquitous flavonoid found in vegetable foods. Epidemiological and animal studies have reported an inverse association between quercetin intakes and occurrence and development of various cardiovascular diseases. Some researchers have inferred that the mechanisms of quercetin to protect cardiomyocytes from ischemia/reperfusion injury may be involved in modulation of intracellular signal pathways and regulation of proteins expression beyond its antioxidant activity. The aim of this study was to investigate whether quercetin protect cardiomyocytes from anoxia/reoxygenation injury through PKCε pathway. Neonatal rat primary cardiomyocytes were pretreated with quercetin or quercetin plus εV1-2, a selective PKCε inhibitor, prior to A/R treatment. Western blotting analysis showed that the level of PKCε and phosphor-PKCε Ser297 in the quercetin pretreatment group were all increased significantly compared to the control or A/R group. Subsequent assays showed that pretreated with quercetin could increase the viability of neonatal rat primary cardiomyocytes suffered A/R, decrease the apoptosis and ROS and alleviate the loss of mitochondrial membrane potential induced by A/R injury. However, the protective effects of quercetin disappeared in the group pretreated with εV1-2. Thus, for the first time, we revealed that one of the mechanisms of quercetin protecting cardiomyocytes from A/R injury might be increase the expression of PKCε protein and then enhance the activity of its downstream pathway.

Roles of histone deacetylation and AMP kinase in regulation of cardiomyocyte PGC-1α gene expression in hypoxia

The transcriptional coactivator peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) is a key determinant of cardiac metabolic function by regulating genes governing fatty acid oxidation and mitochondrial biogenesis. PGC-1α expression is reduced in many cardiac diseases, and gene deletion of PGC-1α results in impaired cardiomyocyte metabolism and function. Reduced fuel supply generally induces PGC-1α expression, but the specific role of oxygen deprivation is unclear, and the mechanisms governing PGC-1α gene expression in these situations are poorly understood. During hypoxia of primary rat cardiomyocytes up to 12 h, we found that PGC-1α expression was downregulated via a histone deacetylation-dependent mechanism. Conversely, extended hypoxia to 24 h concomitant with glucose depletion upregulated PGC-1α expression via an AMP-activated protein kinase (AMPK)-mediated mechanism. Our previous work demonstrated that estrogen-related receptor-α (ERRα) regulates PGC-1α expression, and we show here that overexpression of ERRα was sufficient to attenuate PGC-1α downregulation in hypoxia. We confirmed that chronic hypoxia downregulated cardiac PGC-1α expression in a hypoxic but nonischemic hypobaric rat model of pulmonary hypertension. Our data demonstrate that depletion of oxygen or fuel results in repression or induction, respectively, of PGC-1α expression via discrete mechanisms, which may contribute to cardiac energetic derangement during hypoxia, ischemia, and failure.

TWIST1 regulates the activity of ubiquitin proteasome system via the miR-199/214 cluster in human end-stage dilated cardiomyopathy

The transcription factor TWIST1 has been described to regulate the microRNA (miR)-199/214 cluster. Genetic disruption of TWIST1 resulted in a cachectic phenotype and early death of the knock-out mice. This might be connected to the activity of the ubiquitin-proteasome-system (UPS), as miR-199a has been suggested to regulate the ubiquitin E2 ligases Ube2i and Ube2g1. Cardiac tissue from explanted hearts of 42 patients with dilated cardiomyopathy and 20 healthy donor hearts were analysed for protein expression of TWIST1 and its inhibitors Id-1, MuRF-1 and MAFbx, the expression of miR-199a, -199b and -214, as well as the activity of the UPS by using specific fluorogenic substrates. TWIST1 was repressed in patients with dilated cardiomyopathy by 43% (p=0.003), while Id1 expression was unchanged. This was paralleled by a reduced expression of miR-199a by 38 ± 9% (p=0.053), miR-199b by 36 ± 13% (p=0.019) and miR-214 by 41 ± 11% (p=0.0158) compared to donor hearts. An increased peptidylglutamyl-peptide-hydrolysing activity (p<0.0001) was observed in the UPS, while the chymotrypsin-like and trypsin-like activities were unchanged. The protein levels of the rate limiting ubiquitin E3-ligases MuRF-1 and MAFbx were up-regulated (p=0.005 and p=0.0156, respectively). Mechanistically silencing of TWIST1 using siRNA in primary rat cardiomyocytes led to a down-regulation of the miR-199/214 cluster and to a subsequent up-regulation of Ube2i. The TWIST1/miR-199/214 axis is down-regulated in dilated cardiomyopathy, which is likely to play a role in the increased activity of the UPS. This may contribute to the loss of cardiac mass during dilatation of the heart.

Effect of Berberine on PPARα/NO Activation in High Glucose- and Insulin-Induced Cardiomyocyte Hypertrophy

Rhizoma coptidis, the root of Coptis chinensis Franch, has been used in China as a folk medicine in the treatment of diabetes for thousands of years. Berberine, one of the active ingredients of Rhizoma coptidis, has been reported to improve symptoms of diabetes and to treat experimental cardiac hypertrophy, respectively. The objective of this study was to evaluate the potential effect of berberine on cardiomyocyte hypertrophy in diabetes and its possible influence on peroxisome proliferator-activated receptor-α (PPARα)/nitric oxide (NO) signaling pathway. The cardiomyocyte hypertrophy induced by high glucose (25.5 mmol/L) and insulin (0.1 μmol/L) (HGI) was characterized in rat primary cardiomyocyte by measuring the cell surface area, protein content, and atrial natriuretic factor mRNA expression level. Protein and mRNA expression were measured by western blot and real-time RT-PCR, respectively. The enzymatic activity of NO synthase (NOS) was measured using a spectrophotometric assay, and NO concentration was measured using the Griess assay. HGI significantly induced cardiomyocyte hypertrophy and decreased the expression of PPARα and endothelial NOS at the mRNA and protein levels, which occurred in parallel with declining NOS activity and NO concentration. The effect of HGI was inhibited by berberine (0.1 to 100 μmol/L), fenofibrate (0.3 μmol/L), or L-arginine (100 μmol/L). MK886 (0.3 μmol/L), a selective PPARα antagonist, could abolish the effects of berberine and fenofibrate. N G-nitro-L-arginine-methyl ester (100 μmol/L), a NOS inhibitor, could block the effects of L-arginine, but only partially blocked the effects of berberine. These results suggest that berberine can blunt HGI-induced cardiomyocyte hypertrophy in vitro, through the activation of the PPARα/NO signaling pathway.

Characterization of Cardiac Adiponectin Post-Translational Processing and Secretion

Adiponectin (ADN) is primarily secreted from adipocytes, and serum concentrations negatively correlate with obesity, diabetes, and several other metabolic diseases. More recently, secretion and autocrine actions of cardiac ADN have been described. The purpose of this study was to characterize the post-translational modifications undergone by ADN monomers in cardiac and other mammalian, and their association into trimers, hexamers, and larger multimers (>18-mers) during secretory pathway transport. Adiponectin-flag adenovirus (Ad.ADNf) was used to overexpress the protein in mammalian cells and primary adult rat cardiomyocytes. Intracellular and secreted adiponectin were analyzed in cell extracts and 24 h supernatants. Native oligomeric adiponectin within these cellular systems was analyzed by immunofluorescence, while composite monomers and multimers were examined by SDS-PAGE and immunoblotting. Intracellular cardiomyocyte ADN accumulated in junctional SR puncta, an early ER subcompartment, consistent with current views of the cardiac secretory pathway, whereas it co-localized with classical ER markers in HEK and COS cells. Cardiac ADN was secreted as a collection of polymers comprised of a single relatively unmodified protein monomer, similar to that secreted from cultured epididymal fat. Roughly half of the protein was secreted in 24 h. In contrast, ADN from HEK cells secreted polymers comprised of ADN monomers with slightly greater modification. Minor changes in response to treatments with tunicamycin suggest that some portion of both the intracellular and secreted protein monomers undergo N-linked glycosylation. HEK cells alone exhibited significant ability to cleave ADN after its secretion. Among all mammalian cells, both intracellular and secreted ADN were comprised of distinct patterns of protein polymers. Similarities between monomeric and polymeric structures in secreted ADN and effects on adenosine monophosphate-kinase from different mammalian cells support the possibility that ADN serves both endocrine and autocrine actions for fat and heart, respectively.

Myofibril Acquisition from Primary Rat Cardiomyocyte Culture for Mechanical Studies

Introduction: Myofibril based mechanical studies allow targeted evaluation of sarcomeric protein function. Here we describe a novel method of obtaining myofibrils from primary cardiomyocyte culture.Methods: Adult rat ventricular myocytes (ARVMs) were obtained by enzymatic digestion and maintained in serum free environment for 72 hours. ARVMs were homogenized in relaxing solution (pCa 9.0) with 20% sucrose, and myofibril suspension was made. Myofibrils, mounted on a force recording apparatus, were Ca2+-activated and fully relaxed by fast solution switching at 15°C and 2.1 μm initial sarcomere length.Results from ARVM myofibrils were compared to those myofibrils obtained from ventricular tissue with traditional skinning method (0.05% Triton-X100). Results: At maximal Ca2+-activation (pCa 4.5) myofibril mechanical parameters from ARVMs were 8 mN/mm2 (resting tension), 156.4 mN/mm2 (maximal active tension, Po), 5.4 s-1 (rate of force activation, kACT), 5.2 s-1 (rate of force redevelopment following release-restretch, kTR), 41.6 ms (linear relaxation duration), and 13.6 s-1 (exponential relaxation rate). The parameters of the myofibrils isolated from the ventricular tissue were not significantly different. Degree of run-down (decrease in Po and kACT between subsequent activation-relaxation cycles) was evaluated. Between first and third activations, we noted the following % changes in myofibrils from ARVM cultures: −23.6% (Po), −29.6% (kACT). The magnitude of run-down was not statistically different between myofibrils from ARVMs versus the traditional Triton skinned samples. Finally, pCa50 from Triton skinned, ARVM culture day 0, and ARVM culture day 3 myofibrils were 5.76, 5.74, and 5.71, respectively.Conclusion: Myofibrils obtained from ARVMs is a viable method to study myofibril mechanics. This culture based approach to obtaining myofibrils will allow pharmacological and genetic manipulation of the cardiomyocytes to correlate biochemical and biophysical properties.

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Introduction: Previous results suggest maternal gestational under nutrition selectively impairs right ventricular mitochondrial response to acute hypoxia. Hypothesis: After an acute ischemic event, ventricular cardiomyocyte viability in intrauterine growth restricted (IUGR) rat pups is lower than controls (CTR) while mitochondrial reactive oxygen species (ROS) production is increased. RV cardiomyocytes have less viability, and increased ROS, post ischemia compared to left ventricular (LV), and the IUGR RV group with the least. Methods: Pregnant Sprague Dawley rats were subjected to caloric restriction in the 3rd trimester- an established caloric restrictive diet to model IUGR (NR). NR and CTR neonatal hearts were harvested from age 2-3 day pups. RV and LV cardiomyocytes were cultured separately. On day 5 of culture, cells underwent 6 hours of oxygen glucose deprivation (OGD), and cell viability was assessed using an MTT Cell Proliferation Assay 18 hour later. Mitochondrial ROS production was measured by total superoxide production using confocal microscopy. Results: Baseline cell viability in CTR RV was 47% (p?0.01-19) of CTR LV.and NR RV was 30% NR LV (p?0.01-23). Total ROS in CTR RV was 118% of CTR LV (p?0.34) and NR RV was 140% NR LV (p?0.001). A significant increase in ROS production was seen in NR compared to CTR. Total ROS in NR LV was 174% CTR LV (p?0.01) and NR RV was 170% CTR RV (p?0.0001).No difference in cell viability was found following OGD (each group compared to its baseline), CTR LV=56%, CTR RV=61%, NR LV=53% and NR RV=56% (p?0.17). All cells for confocal microscopy died post OGD. Conclusions: Cell viability, using primary neonatal rat cardiomyocyte cultures, is significantly less in RV cardiomyocytes compared to LV. Cell viability was further reduced in cardiomyocytes isolated from NR pups, least in NR RV. OGD, simulating ischemia, decreased cell viability in both NR and CTR. ROS production is greater in mitochondria from cardiomyocytes isolated from NR pups. ROS production was greater NR RV compared to NR LV. Less viability and increased ROS production within the NR group may indicate a defect in bioenergetics as a result of intrauterine nutritional restriction.

Overexpression of AMP-activated protein kinase or protein kinase D prevents lipid-induced insulin resistance in cardiomyocytes

During lipid oversupply, the heart becomes insulin resistant, as exemplified by defective insulin-stimulated glucose uptake, and will develop diastolic dysfunction. In the healthy heart, not only insulin, but also increased contractile activity stimulates glucose uptake. Upon increased contraction both AMP-activated protein kinase (AMPK) and protein kinase D (PKD) are activated, and mediate the stimulation of glucose uptake into cardiomyocytes. Therefore, each of these kinases is a potential therapeutic target in the diabetic heart because they may serve to bypass defective insulin-stimulated glucose uptake. To test the preventive potential of these kinases against loss of insulin-stimulated glucose uptake, AMPK or PKD were adenovirally overexpressed in primary cultures of insulin resistant cardiomyocytes for assaying substrate uptake, insulin responsiveness and lipid accumulation. To induce insulin resistance and lipid loading, rat primary cardiomyocytes were cultured in the presence of high insulin (100nM; HI) or high palmitate (palmitate/BSA: 3/1; HP). HI and HP each reduced insulin responsiveness, and increased basal palmitate uptake and lipid storage. Overexpression of each of the kinases prevented loss of insulin-stimulated glucose uptake. Overexpression of AMPK also prevented loss of insulin signaling in HI- and HP-cultured cardiomyocytes, but did not prevent lipid accumulation. In contrast, overexpression of PKD prevented lipid accumulation, but not loss of insulin signaling in HI- and HP-cultured cardiomyocytes. In conclusion, AMPK and PKD prevent loss of insulin-stimulated glucose uptake into cardiomyocytes cultured under insulin resistance-inducing conditions through different mechanisms. This article is part of a Special Issue entitled "Focus on Cardiac Metabolism".

Secretory Products From Epicardial Adipose Tissue of Patients With Type 2 Diabetes Mellitus Induce Cardiomyocyte Dysfunction

Secreted factors from epicardial adipose tissue (EAT) have been implicated in the development of cardiomyocyte dysfunction. This study aimed to assess whether alterations in the secretory profile of EAT in patients with type 2 diabetes mellitus (DM2) affect contractile function and insulin action in cardiomyocytes. Contractile function and insulin action were analyzed in primary adult rat cardiomyocytes incubated with conditioned media (CM) generated from explants of EAT biopsies obtained from patients without and with DM2. CM from subcutaneous and pericardial adipose tissue biopsies from the same patients served as the control. Cardiomyocytes treated with CM (EAT) from DM2 patients showed reductions in sarcomere shortening, cytosolic Ca(2+) fluxes, expression of sarcoplasmic endoplasmic reticulum ATPase 2a, and decreased insulin-mediated Akt-Ser473-phosphorylation as compared with CM from the other groups. Profiling of the CM showed that activin A, angiopoietin-2, and CD14 selectively accumulated in CM-EAT-DM2 versus CM-EAT in patients without DM2 and CM from the other fat depots. Accordingly, EAT biopsies from DM2 patients were characterized by clusters of CD14-positive monocytes. Furthermore, SMAD2-phosphorylation, a downstream target of activin A signaling, was elevated in cardiomyocytes treated with CM (EAT) from DM2 patients, and the detrimental effects of CM (EAT) from DM2 patients were partially abolished in cardiomyocytes pretreated with a neutralizing antibody against activin A. Finally, both recombinant activin A and angiopoietin-2 reduced cardiomyocyte contractile function, but only activin A reduced the expression of sarcoplasmic endoplasmic reticulum ATPase 2a. Collectively, our data implicate DM2-related alterations in the secretory profile of EAT in the pathogenesis of diabetes mellitus-related heart disease.

Exogenous hydrogen sulfide attenuates diabetic myocardial injury through cardiac mitochondrial protection

In the study, we investigated how exogenous H(2)S (hydrogen sulfide) influenced streptozotocin (STZ)-induced diabetic myocardial injury through cardiac mitochondrial protection and nitric oxide (NO) synthesis in intact rat hearts and primary neonatal rat cardiomyocytes. Diabetes was induced by STZ (50 mg/kg) and the daily administration of 100 μM NaHS (sodium hydrosulfide, an H(2)S donor) in the diabetes + NaHS treatment group. At the end of 4, 8, and 12 weeks, the morphological alterations and functions of the hearts were observed using transmission electron microscopy and echocardiography system. The percentage of apoptotic cardiomyocytes, the mitochondrial membrane potential, the production of reactive oxygen species (ROS) and the level of NO were measured. The expressions of cystathionine-γ-lyase (CSE), caspase-3 and -9, the mitochondrial NOX4 and cytochrome c were analyzed by western blotting. The results showed the cardiac function injured, morphological changes and the apoptotic rate increased in the diabetic rat hearts. In the primary neonatal rat cardiomyocytes of high glucose group, ROS production was increased markedly, whereas the expression of CSE and the level of NO was decreased. However, treatment with NaHS significantly reversed the diabetic rat hearts function, the morphological changes and decreased the levels of ROS and NO in the primary neonatal rat cardiomyocytes administrated with high glucose group. Furthermore, NaHS down-regulated the expression of mitochondrial NOX4 and caspase-3 and -9 and inhibited the release of cytochrome c from mitochondria in the primary neonatal rat cardiomyocytes. In conclusion, H(2)S is involved in the attenuation of diabetic myocardial injury through the protection of cardiac mitochondria.

Exploration of human, rat, and rabbit embryonic cardiomyocytes suggests K-channel block as a common teratogenic mechanism

Several drugs blocking the rapidly activating potassium (K(r)) channel cause malformations (including cardiac defects) and embryonic death in animal teratology studies. In humans, these drugs have an established risk for acquired long-QT syndrome and arrhythmia. Recently, associations between cardiac defects and spontaneous abortions have been reported for drugs widely used in pregnancy (e.g. antidepressants), with long-QT syndrome risk. To investigate whether a common embryonic adverse-effect mechanism exists in the human, rat, and rabbit embryos, we made a comparative study of embryonic cardiomyocytes from all three species. Patch-clamp and quantitative-mRNA measurements of K(r) and slowly activating K (K(s)) channels were performed on human, rat, and rabbit primary cardiomyocytes and cardiac samples from different embryo-foetal stages. The K(r) channel was present when the heart started to beat in all species, but was, in contrast to human and rabbit, lost in rats in late organogenesis. The specific K(r)-channel blocker E-4031 prolonged the action potential in a species- and development-dependent fashion, consistent with the observed K(r)-channel expression pattern and reported sensitive periods of developmental toxicity. E-4031 also increased the QT interval and induced 2:1 atrio-ventricular block in multi-electrode array electrographic recordings of rat embryos. The K(s) channel was expressed in human and rat throughout the embryo-foetal period but not in rabbit. This first comparison of mRNA expression, potassium currents, and action-potential characteristics, with and without a specific K(r)-channel blocker in human, rat, and rabbit embryos provides evidence of K(r)-channel inhibition as a common mechanism for embryonic malformations and death.

Adenoviral Delivery of Angiotensin-(1-7) or Angiotensin-(1-9) Inhibits Cardiomyocyte Hypertrophy via the Mas or Angiotensin Type 2 Receptor

The counter-regulatory axis of the renin angiotensin system peptide angiotensin-(1-7) [Ang-(1-7)] has been identified as a potential therapeutic target in cardiac remodelling, acting via the mas receptor. Furthermore, we recently reported that an alternative peptide, Ang-(1-9) also counteracts cardiac remodelling via the angiotensin type 2 receptor (AT2R). Here, we have engineered adenoviral vectors expressing fusion proteins which release Ang-(1-7) [RAdAng-(1-7)] or Ang-(1-9) [RAdAng-(1-9)] and compared their effects on cardiomyocyte hypertrophy in rat H9c2 cardiomyocytes or primary adult rabbit cardiomyocytes, stimulated with angiotensin II, isoproterenol or arg-vasopressin. RAdAng-(1-7) and RAdAng-(1-9) efficiently transduced cardiomyocytes, expressed fusion proteins and secreted peptides, as demonstrated by western immunoblotting and conditioned media assays. Furthermore, secreted Ang-(1-7) and Ang-(1-9) inhibited cardiomyocyte hypertrophy (Control = 168.7±8.4 µm; AngII = 232.1±10.7 µm; AngII+RAdAng-(1-7) = 186±9.1 µm, RAdAng-(1-9) = 180.5±9 µm; P<0.05) and these effects were selectively reversed by inhibitors of their cognate receptors, the mas antagonist A779 for RAdAng-(1-7) and the AT2R antagonist PD123,319 for RAdAng-(1-9). Thus gene transfer of Ang-(1-7) and Ang-(1-9) produces receptor-specific effects equivalent to those observed with addition of exogenous peptides. These data highlight that Ang-(1-7) and Ang-(1-9) can be expressed via gene transfer and inhibit cardiomyocyte hypertrophy via their respective receptors. This supports applications for this approach for sustained peptide delivery to study molecular effects and potential gene therapeutic actions.

Dual Role for Glucocorticoids in Cardiomyocyte Hypertrophy and Apoptosis

Glucocorticoids and their synthetic derivatives are known to alter cardiac function in vivo; however, the nature of these effects and whether glucocorticoids act directly on cardiomyocytes are poorly understood. To explore the role of glucocorticoid signaling in the heart, we used rat embryonic H9C2 cardiomyocytes and primary cardiomyocytes as model systems. Dexamethasone (100 nm) treatment of cardiomyocytes caused a significant increase in cell size and up-regulated the expression of cardiac hypertrophic markers, including atrial natriuretic factor, β-myosin heavy chain, and skeletal muscle α-actin. In contrast, serum deprivation and TNFα exposure triggered cardiomyocyte apoptosis, and these apoptotic effects were inhibited by dexamethasone. Both the hypertrophic and anti-apoptotic actions of glucocorticoids were abolished by the glucocorticoid receptor (GR) antagonist RU486 and by short hairpin RNA-mediated GR depletion. Blocking the activity of the mineralocorticoid receptor had no effect on these glucocorticoid-dependent cardiomyocyte responses. Aldosterone (1 μm) activation of GR also promoted cardiomyocyte hypertrophy and cell survival. To elucidate the mechanism of the dual glucocorticoid actions, a genome-wide microarray was performed on H9C2 cardiomyocytes treated with vehicle or dexamethasone in the absence or presence of serum. Serum dramatically influenced the transcriptome regulated by GR, revealing potential glucocorticoid signaling mediators in both cardiomyocyte hypertrophy and apoptosis. These studies reveal a direct and dynamic role for glucocorticoids and GR signaling in the modulation of cardiomyocyte function.