Neonatal Rat Ventricular Cardiac Myocytes Research Articles

Leonurine pretreatment protects the heart from myocardial ischemia-reperfusion injury.

Myocardial ischemia-reperfusion (I/R), an important complication of reperfusion therapy for myocardial infarction, is characterized by hyperactive oxidative stress and inflammatory response. Leonurine (4-guanidino-n-butyl syringate, SCM-198), an alkaloid extracted from Herbaleonuri, was previously found to be highly cardioprotective both in vitro and in vivo. Our current study aimed to investigate the effect of SCM-198 preconditioning on myocardial I/R injury in vitro and in vivo, respectively, as well as to decipher the mechanism involved. Rats were pretreated with SCM-198 before subjected to 45 min of myocardial ischemia, which was followed by 24 h of reperfusion. Primary neonatal rat cardiac ventricular myocytes (NRCMs) were exposed to hypoxia (95% N2 + 5% CO2) for 12 h, and then to 12 h reoxygenation so as to mimic I/R. The enzymatic measurements demonstrated that SCM-198 reduced the release of infarction-related enzymes, and the hemodynamic and echocardiography measurements showed that SCM-198 restored cardiac functions, which suggested that SCM-198 could significantly reduce infarct size, maintaining cardiomyocyte morphology, and that SCM-198 pretreatment could significantly reduce cardiomyocytes apoptosis. Moreover, we demonstrated that SCM-198 could exert a cardioprotective effect by reducing reactive oxygen species (ROS) level and Akt phosphorylation while reducing the phosphorylation of p38 and JNK. In addition, the upregulation of p-Akt, Bcl-2/Bax induced by SCM-198 treatment were blocked by PI3K inhibitor LY294002, and the total protein level of Akt was not affected by SCM-198 pretreatment. Our experimental results indicated that SCM-198 could have a cardioprotective effect on I/R injury, which confirmed the utility of SCM-198 preconditioning as a strategy to prevent I/R injury.

A0876 MiR-21-3p is related to Angiotensin II-induced hypertrophy in cultured neonatal rat ventricular cardiac myocytes

A0876 MiR-21-3p is related to Angiotensin II-induced hypertrophy in cultured neonatal rat ventricular cardiac myocytes

Sulfur dioxide attenuates sepsis-induced cardiac dysfunction via inhibition of NLRP3 inflammasome activation in rats

ObjectiveSulfur dioxide (SO2) plays an important role in maintaining homeostasis of cardiovascular system. This study was aimed to investigate cardioprotective effects of SO2 on in the rat and the underlying mechanism. Methods and resultsSepsis model induced by cecal ligation and puncture (CLP) in rats were used. SO2 donor (NaHSO3/Na2SO3, 1:3 M/M) was administered intraperitoneally at a dose of 85 mg/kg. Primary neonatal rat cardiac ventricular myocytes (NRCMs) were stimulated with LPS (1 mg/mL) in presence or absence of different concentrations of SO2 (10, 50 and 100 μmol/L). SO2 donor could restore the decreased levels of SO2 in plasma and heart of septic rats. SO2 exhibited dramatic improvement in cardiac functions. At 24 h after CLP, SO2 treatments decreased the number of TUNEL-positive cells, Bax/Bcl-2 ratio and activity of caspase-3. Moreover CLP-induced inflammatory response was also relieved by SO2. In NRCMs, SO2 could suppress the LPS-induced myocardial injury, leading to an increase in cell viability, a decrease in LDH and apoptotic rate. Western blot showed that the expression of TLR4, NLRP3, and Caspase-1 were obviously increased in myocardial tissue of CLP group or in NRCMs of LPS group, while SO2 significantly inhibited the CLP-induced or LPS-induced TLR4, NLRP3, and Caspase-1 expression. ConclusionSO2 attenuated sepsis-induced cardiac dysfunction likely in association with the inhibiting inflammation via TLR4/NLRP3 signaling pathway.

G protein-coupled receptor kinase 2 promotes cardiac hypertrophy.

The increase in protein activity and upregulation of G-protein coupled receptor kinase 2 (GRK2) is a hallmark of cardiac stress and heart failure. Inhibition of GRK2 improved cardiac function and survival and diminished cardiac remodeling in various animal heart failure models. The aim of the present study was to investigate the effects of GRK2 on cardiac hypertrophy and dissect potential molecular mechanisms. In mice we observed increased GRK2 mRNA and protein levels following transverse aortic constriction (TAC). Conditional GRK2 knockout mice showed attenuated hypertrophic response with preserved ventricular geometry 6 weeks after TAC operation compared to wild-type animals. In isolated neonatal rat ventricular cardiac myocytes stimulation with angiotensin II and phenylephrine enhanced GRK2 expression leading to enhanced signaling via protein kinase B (PKB or Akt), consecutively inhibiting glycogen synthase kinase 3 beta (GSK3β), such promoting nuclear accumulation and activation of nuclear factor of activated T-cells (NFAT). Cardiac myocyte hypertrophy induced by in vitro GRK2 overexpression increased the cytosolic interaction of GRK2 and phosphoinositide 3-kinase γ (PI3Kγ). Moreover, inhibition of PI3Kγ as well as GRK2 knock down prevented Akt activation resulting in halted NFAT activity and reduced cardiac myocyte hypertrophy. Our data show that enhanced GRK2 expression triggers cardiac hypertrophy by GRK2-PI3Kγ mediated Akt phosphorylation and subsequent inactivation of GSK3β, resulting in enhanced NFAT activity.

Novel protective effects of pulsed electromagnetic field ischemia/reperfusion injury rats.

Extracorporeal pulsed electromagnetic field (PEMF) has shown the ability to regenerate tissue by promoting cell proliferation. In the present study, we investigated for the first time whether PEMF treatment could improve the myocardial ischaemia/reperfusion (I/R) injury and uncovered its underlying mechanisms.In our study, we demonstrated for the first time that extracorporeal PEMF has a novel effect on myocardial I/R injury. The number and function of circulating endothelial progenitor cells (EPCs) were increased in PEMF treating rats. The invivo results showed that per-treatment of PEMF could significantly improve the cardiac function in I/R injury group. In addition, PEMF treatment also reduced the apoptosis of myocardial cells by up-regulating the expression of anti-apoptosis protein B-cell lymphoma 2 (Bcl-2) and down-regulating the expression of pro-apoptosis protein (Bax). Invitro, the results showed that PEMF treatment could significantly reduce the apoptosis and reactive oxygen species (ROS) levels in primary neonatal rat cardiac ventricular myocytes (NRCMs) induced by hypoxia/reoxygenation (H/R). In particular, PEMF increased the phosphorylation of protein kinase B (Akt) and endothelial nitric oxide synthase (eNOS), which might be closely related to attenuated cell apoptosis by increasing the releasing of nitric oxide (NO). Therefore, our data indicated that PEMF could be a potential candidate for I/R injury.

Isolated neonatal rat papillary muscles: a new model to translate neonatal rat myocyte signaling into contractile mechanics.

Isolated cardiac tissue allows investigators to study mechanisms underlying normal and pathological conditions, which would otherwise be difficult or impossible to perform invivo. Cultured neonatal rat ventricular cardiac myocytes (NRVM) are widely used to study signaling and growth mechanisms in the heart, primarily due to the versatility, economy, and convenience of this invitro model. However, the lack of a well-defined longitudinal cellular axis greatly hampers the ability to measure contractile function in these cells, and therefore to associate signaling with mechanical function. In these methods, we demonstrate that this limitation can be overcome by using papillary muscles isolated from neonatal rat hearts. In the methods we describe procedures for isolation of right ventricular papillary muscles from 3-day-old neonatal rats and effects of mechanical and humoral stimuli on contraction and relaxation properties of these tissues.

PI4P Hydrolysis Represents a General Mechanism for DAG Generation and PKC/PKD Activation

Receptor stimulated hydrolysis of phosphatidylinositol 4,5‐bisphosphate (PIP­2­) is critical for many physiological processes, such as neurotransmission and proliferation. Recently our laboratory identified a novel pathway in neonatal rat ventricular cardiac myocytes (NRVMs), where agonist stimulation triggers PLC dependent hydrolysis of the PIP­2­ precursor phosphatidylinositol 4‐phosphate (PI4P) leading to DAG production, nuclear PKD activation and cardiac hypertrophy. We have seen that this newly identified pathway exists in other cell types as well, such as Mouse Embryo Fibroblasts (MEFs) and PANC‐1 cells. To determine if PLC dependent PI4P hydrolysis represents a general mechanism for DAG generation and PKC/PKD activation we examined PI4P depletion and PKD activation in other cell types. In our studies we used a PI 4‐kinase inhibitor, phenylarsine oxide (PAO) or expression of a Golgi specific 4‐phosphatase, Sac1‐K2A (Sac1) to deplete PI4P. PAO treatment or Sac1 expression in NRVMs and MEFs, showed a dramatic reduction of inositol phosphate accumulation after endothelin‐1 (ET‐1) stimulation. PAO treatment completely blocked ET‐1 dependent global PKD activation in NRVMs and MEFs but not neurotensin (NT) dependent PKD activation in PANC‐1 cells. Sac1 expression showed reduced ET‐1 dependent global PKD activation in NRVMs and MEFs but did not change the NT dependent PKD activation in PANC‐1 cells. These results suggest that though Golgi PI4P hydrolysis occurs in multiple cell types, NRVMs and MEFs use PI4P hydrolysis as a source for DAG to promote PKD activation. This shows that PI4P hydrolysis occurs upon receptor stimulation and provides a novel signaling mechanism with numerous implications in physiology and disease.

Abstract 16606: Cardiac Fibroblast-Restricted Enhancement of G q Signaling Prolongs Calcium Transients and Increases Spontaneous Activity in Biomimetic Cardiac Microtissues

Introduction: Enhanced G q signaling in response to hemodynamic stress and injury is well known to induce remodeling in both cardiac myocytes (CMs) and fibroblasts (CFs). However, the effect of CF activation and fibrosis on CMs and integrated myocardial function cannot be easily discerned from concomitant effects on CMs. Hypothesis: Enhanced G q signaling in CFs influences CM function in a 3D microtissue model previously developed in our lab, in which neonatal rat ventricular CMs and CFs are highly interspersed as seen in the myocardium. Methods: CFs infected in suspension (2 hrs, 10 MOI) with empty adenovirus (Ad-Ctr) or Ad encoding wild-type (WT) or constitutively active (Q209L or QL) Gα q were co-seeded with uninfected CMs (CM:CF 1:1) into non-adhesive hydrogels at ~1200 cells per recess (400/800 μm wide/deep). After 2-4 days, we assessed tissue size by microscopy, G q and extracellular matrix proteins proteins by Western Blot analysis, and Ca 2+ transients ([Ca 2+ ] i ) with Rhod 2/AM. Results: Overexpression of Gα q in CFs was associated with a 3-fold (WT) and 7-fold (QL) increase in total inositolphosphate formation, indicating enhanced basal phospholipase β activity. After 4 days, CM:CF QL tissues were larger in size by 30-40% and expressed more laminin and fibronectin. After 3 days, CM:CF CTR paced at 1 Hz had [Ca 2+ ] i duration of 218±3 ms, decay of 141±2 ms, and rise time of 35±4 ms (n=55-69). In CM:CF QL , duration and decay were prolonged by 160 ms and 21 ms, resp., and rise time was decreased by 5 ms (n=10-27). In CM:CF WT with less G q signaling, [Ca 2+ ] i duration and decay were also prolonged but only by 30 ms and 7 ms, resp. (n=46-51). These effects were similar but less pronounced after 2 days and/or at 2 Hz. Spontaneous [Ca 2+ ] i activity was seen in 50% of CM:CF QL , 11% of CM:CF WT , but only 2% of CM:CF CTR microtissues. The gap junction inhibitor carbenoxolone (100 μM) decreased this activity in CM:CF QL by 80% and in CM:CF WT by 15%. Conclusion: We show that enhanced CF-restricted G q signaling in biomimetic cardiac microtissues increases tissue size, prolongs [Ca 2+ ] i duration and decay, and increases spontaneous Ca 2+ activity. Our findings suggest that depending on the CF activation state, CFs can greatly modulate CM calcium handling and potentially influence arrhythmogenesis.

42. Investigation into cardiomyocyte response to cryoablation

Atrial and ventricular tachyarrhythmias represent major cardiovascular diseases that may be treated utilizing thermal therapies. Given this there has been a palpable increase in technologies and approaches of therapeutic intervention, including cryoablation. While increased utilization of cryoablation continues, our fundamental understanding of the response of cardiac cells to the freezing process remains limited. As such we investigated the cellular and molecular response of cardiomyocytes to a range of subfreezing temperatures in an effort to provide further insight to help guide the application of cryoablation for the treatment of cardiac arrhythmias. Primary neonatal rat ventricular cardiac myocytes (NRVCM) and human cardiac myocytes (HCM) were cultured in vitro to study the cellular and molecular effects of thermal excursions. Cells were exposed to a range of temperatures from 37 °C to −40 °C for up to 1 min. Thermal profiles were generated to examine the cooling rates at each target temperature. Samples were then returned to culture and cell survival was measured via metabolic activity, membrane integrity and contractile function. Microfluidic flow cytometry was also conducted to investigate apoptotic involvement and confirm viability assessments of the various populations in a time-course manner. Exposure of NRVCM to temperatures ranging from 37 °C to 0 °C resulted in a minimal reduction in cell viability. Exposure to −5 °C yielded 50% cell death. Temperatures ranging from −10 °C to −20 °C yielded less than 20% survival, whereas exposure to −40 °C resulted in complete cell death. Regardless of the level of cell survival, exposure to temperatures below −5 °C resulted in a loss of spontaneous contraction in surviving cells. HCM demonstrated moderate sensitivity (<30% loss) to temperatures above −10 °C, however a steep decline in cell survival was observed from −12 °C to −25 °C, the point at which all cells were metabolically inactive. Flow cytometric analysis revealed the activation of apoptosis in cardiomyocytes in response to the freezing insult. The level and timing was found to vary with temperature, but not duration of the freeze. Although the utilization of cryoablation for the treatment of arrhythmias is established clinically, there remains a void in our knowledge base of the cellular and molecular responses of cardiac systems to thermal stress. This study, as well as others, are now providing mechanistic answers to the how cryoablation works at the cellular level as well as providing critical characterization data to help guide application and future development of therapeutic application.

D2 dopamine receptor antagonist raclopride induces non‐canonical autophagy in cardiac myocytes

Cell death by autophagy is an important means of maintaining cellular homeostasis in adult cardiac myocytes. Autophagy was previously shown to exert a cardioprotective effect, suggesting that modulation of autophagy pathways is a potential therapeutic strategy in the treatment of heart disease. Although dopamine is known to induce autophagy in neuroblastoma cells, the underlying mechanism and the types of dopamine receptors involved in this process remain unclear. In this study, we used various dopamine receptor antagonists and agonists to identify the specific dopamine receptor that mediates induction of autophagy. We evaluated autophagy induction by the expression of autophagy markers in neonatal rat ventricular cardiac myocytes. We evaluated intracellular calcium levels using Fluo-3/AM and demonstrated autophagy-induced morphological changes in cardiac myocytes using electron microscopy. We also examined the pathway for dopamine-induced autophagy using RNAi-mediated gene knockdown. Raclopride, the well-documented D2 receptor antagonist, significantly upregulated autophagy in cardiac myocytes via an mTOR-independent pathway. There was no difference in intracellular calcium levels between raclopride-treated cells and untreated cells. siRNA-mediated knockdown of Rab9 resulted in decreased expression of autophagy markers in raclopride-treated cells. Interestingly, siRNA-mediated knockdown of Atg7 resulted in a significant increase in Rab9 levels in raclopride-treated cells, suggesting that blocking the classical autophagy pathway results in activation of an alternative pathway. Our study suggests that (1) the D2 dopamine receptor plays a role in autophagy and (2) raclopride mediated a non-canonical autophagy pathway in cardiac myocytes via Rab9.

Abstract 349: Functional Scaffold-Free 3D Cardiac Microtissues: A Novel Model for the Investigation of Heart Cells

To bridge the gap between 2D cell culture and tissue, various 3D cell culture approaches have been developed for the investigation of cardiac myocytes (CM) and fibroblasts (CF), but limitations still exist. The goal of this study was to develop a scaffold-free cardiac culture that could easily and inexpensively create many uniform cardiac microtissues that mimic the cellular distribution and functional behavior of CM and CF in tissue. Using micromolded non-adhesive agarose hydrogels containing 822 concave recesses (800 λm deep x 400 λm wide), we demonstrate that neonatal rat ventricular CM and CF, when seeded alone or in combination, self-assembled into viable (Live/Dead® stain) spherical-shaped microtissues. Importantly, when CM and CF were seeded simultaneously or sequentially, they self-sorted to be highly interspersed, reminiscent of their distribution in ventricular tissue, as shown by cell type-specific CellTracker TM or antibody labeling. Depending on their cellular composition, microtissues expressed extracellular matrix and calcium handling proteins (including SERCA2a), featured typical I K1 and I Ca-L current densities and IV relationships, and formed functional cell-cell connections (as evidenced by spontaneous action potentials, contractions and connexin 43 expression). Microelectrode recordings and optical mapping showed characteristic triangular action potentials (AP) with a resting membrane potential of -66±7 mV (n=4) in spontaneously contracting CM microtissues. Under pacing, optically mapped AP duration at 90% repolarization and conduction velocity were 100±30 ms and 18.0±1.9 cm/s, respectively (n=5 each). The presence of CF led to a prolongation of both AP and calcium transients in CM:CF microtissues (1:1). Furthermore, cell-type-specific adenoviral gene transfer was achieved, with no impact on microtissue formation or cell viability. In conclusion, we have developed a novel scaffold-free cardiac 3D culture model, in which more than 800 homotypic (CM or CF) or heterotypic (CM:CF) microtissues can be formed in a 6-well with ease, analyzed functionally and subjected to cell-type-specific gene transfer, paving the way for future in vitro investigations of CM and CF behavior and their interactions in a 3D environment.

Functional scaffold-free 3-D cardiac microtissues: a novel model for the investigation of heart cells

To bridge the gap between two-dimensional cell culture and tissue, various three-dimensional (3-D) cell culture approaches have been developed for the investigation of cardiac myocytes (CMs) and cardiac fibroblasts (CFs). However, several limitations still exist. This study was designed to develop a cardiac 3-D culture model with a scaffold-free technology that can easily and inexpensively generate large numbers of microtissues with cellular distribution and functional behavior similar to cardiac tissue. Using micromolded nonadhesive agarose hydrogels containing 822 concave recesses (800 μm deep × 400 μm wide), we demonstrated that neonatal rat ventricular CMs and CFs alone or in combination self-assembled into viable (Live/Dead stain) spherical-shaped microtissues. Importantly, when seeded simultaneously or sequentially, CMs and CFs self-sorted to be interspersed, reminiscent of their myocardial distribution, as shown by cell type-specific CellTracker or antibody labeling. Microelectrode recordings and optical mapping revealed characteristic triangular action potentials (APs) with a resting membrane potential of -66 ± 7 mV (n = 4) in spontaneously contracting CM microtissues. Under pacing, optically mapped AP duration at 90% repolarization and conduction velocity were 100 ± 30 ms and 18.0 ± 1.9 cm/s, respectively (n = 5 each). The presence of CFs led to a twofold AP prolongation in heterogenous microtissues (CM-to-CF ratio of 1:1). Importantly, Ba(2+)-sensitive inward rectifier K(+) currents and Ca(2+)-handling proteins, including sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a, were detected in CM-containing microtissues. Furthermore, cell type-specific adenoviral gene transfer was achieved, with no impact on microtissue formation or cell viability. In conclusion, we developed a novel scaffold-free cardiac 3-D culture model with several advancements for the investigation of CM and CF function and cross-regulation.

MicroRNA 21 Inhibits Left Ventricular Remodeling in the Early Phase of Rat Model with Ischemia-reperfusion Injury by Suppressing Cell Apoptosis

Objective: To determine the role of microRNA 21(miR-21) on left ventricular remodeling of rat heart with ischemia-reperfusion (I/R) injury and to investigate the underlying mechanism of miR-21 mediated myocardium protection.Methods: Rats were randomly divided into three groups: an I/R model group with Ad-GFP (Ad-GFP group), an I/R model group with Ad-miR-21 (Ad-miR-21 group) and a sham-surgery group. Changes in hemodynamic parameters were recorded at 1 week after I/R. Histological diagnosis was achieved by hematoxylin and eosin (H&E). Left ventricular (LV) dimensions, myocardial infarct size, LV/BW, collagen type Ⅰ, type Ⅲ and PCNA positive cells were measured. Primary cultures of neonatal rat cardiac ventricular myocytes were performed and cell ischemic injury was induced by hypoxia in a serum- and glucose-free medium, and reoxygenation (H/R).MiR-21 inhibitor and pre-miR-21 were respectively added to the culture medium for the miR-21 knockdown and for the miR-21 up-regulation. qRT-PCR was used to determine the miR-21 levels in cultured cells. Flow cytometry was performed to examine the cell apoptosis.Results: In the Ad-miR-21 group, LV dimensions, myocardial infarct size, LV/BW, collagen type Ⅰ, type Ⅲ and PCNA positive cells all significantly decreased compared with the Ad-GFP group. At 1 week after I/R, the Ad-miR-21 significantly improved LVSP, LV +dp/dtmax, LV − dp/dtmin, and decreased heart rate (HR) and LVEDP compared with the Ad-GFP group. Compared with the Ad-GFP, the cell apoptotic rate significantly decreased in the Ad-miR-21 group. The miR-21 inhibitor exacerbated cardiac myocyte apoptosis and the pre-miR-21 decreased hypoxia/reoxygenation- induced cardiac myocyte apoptosis.Conclusions: Ad-miR-21 improves LV remodeling and decreases the apoptosis of myocardial cells, suggesting the possible mechanism by which Ad-miR-21 functions in protecting against I/R injury.

Abstract P134: Synoviolin Is a Stress-Inducible Endoplasmic/Sarcoplasmic Reticulum E3 Ubiquitin Ligase that Preserves Cardiac Function

We recently reported that synoviolin1 (syvn1) is a novel endoplasmic reticulum stress response (ERSR) protein that is up-regulated in the mouse heart by ATF6, a cardioprotective, nodal transcription factor of the ERSR. Syvn1 is a unique E3 ubiquitin ligase that retrotranslocates misfolded proteins from endoplasmic/sarcoplasmic reticulum (ER/SR) to the cytosol and subsequently polyubiquitinates them, targeting them for degradation. We now report that syvn1 expression is induced with tunicamycin, thapsigargin, and dithiothreitol, ER stressors that activate ATF6. Moreover, adenovirus-mediated syvn1 overexpression in neonatal rat ventricular cardiac myocytes (NRVCMs) increases contractility. Consistent with this finding, syvn1 overexpression increases calcium transient amplitude as well as diastolic calcium. We also find that syvn1 overexpression decreases secretion of MANF, a protective, anti-hypertrophic, ER/SR protein which we find is conditionally secreted when ER/SR calcium is depleted. We also report MANF as the first example of a is protein whose secretion from ventricular myocytes is conditionally dependent on ER/SR calcium. Furthermore, syvn1 reduces the growth of NRVCMs treated with the α-adrenergic agonist, phenylephrine. Moreover, while knockdown of syvn1 in NRVCMs using syvn1-targeted siRNA increases cell death, overexpression of syvn1 promotes cell survival. To investigate the roles of syvn1, in vivo , we examined the effects of syvn1 overexpression in cardiac myocytes in a mouse model of trans-aortic banding. Syvn1 overexpression, in vivo, was achieved by intravenous delivery of recombinant AAV serotype 9 (AAV9; cardiac specific serotype) with MLC2v promoter driving syvn1 expression. Baseline cardiac function, as measured by echocardiography six weeks after gene delivery, shows no difference between AAV9-control and AAV9-syvn1 treated mice. Trans-aortic banding decreases cardiac function in mice injected with AAV9-control. In contrast, cardiac function is preserved in mice injected with AAV9-syvn1. The findings in this study suggest that syvn1 is a novel stress-inducible cardiac E3 ligase with unique functions in regulating protein secretion, maintaining cell viability, and preserving cardiac function.

Tribulosin suppresses apoptosis via PKC epsilon and ERK1/2 signaling pathway during hypoxia/reoxygenation in neonatal rat ventricular cardiac myocytes

Tribulosin (tigogenin 3-O-β-d-xylopyranosyl(1–2)-[β-d-xylopyranosyl (1–3)]-β-d-glucopyranosyl (1–4)-[a-l-rhamnopyranosyl(1–2)]-β-d-galactopyranoside), a component of gross saponins of Tribulus terrestris, has been shown to produce cytoprotective effects in heart. Yet, the precise mechanisms are not fully understood. We examined the mechanisms of tribulosin on myocardial protection. Ventricular myocytes were isolated from the heart of neonatal rats and were exposed to 3 h of hypoxia followed by 2 h reoxygenation. Apoptosis was induced by hypoxia/reoxygenation (H/R), and the expression of protein kinase C epsilon (PKCϵ) and extracellular signal-regulated kinase 1 and 2 (ERK1/2) in cultured neonatal rat cardiac myocytes was detected. The results indicated that treatment with tribulosin in the culture medium protected cardiac myocytes against apoptosis induced by H/R. PKCϵ and ERK1/2 expression increased after pretreated with tribulosin. In the presence of PKCϵ inhibitor co-treated with tribulosin, the expression of ERK1/2 was decreased in H/R cardiac myocytes. While preconditioned with PD98059, ERK1/2 inhibitor, no effects on the expression of PKCϵ were detected. Tribulosin has protective effects on cardiac myocytes against apoptosis induced by H/R injury via PKCϵ and ERK1/2 signaling pathway.

Hierarchical architecture influences calcium dynamics in engineered cardiac muscle

Changes in myocyte cell shape and tissue structure are concurrent with changes in electromechanical function in both the developing and diseased heart. While the anisotropic architecture of cardiac tissue is known to influence the propagation of the action potential, the influence of tissue architecture and its potential role in regulating excitation-contraction coupling (ECC) are less well defined. We hypothesized that changes in the shape and the orientation of cardiac myocytes induced by spatial arrangement of the extracellular matrix (ECM) affects ECC. To test this hypothesis, we isolated and cultured neonatal rat ventricular cardiac myocytes on various micropatterns of fibronectin where they self-organized into tissues with varying degrees of anisotropy. We then measured the morphological features of these engineered myocardial tissues across several hierarchical dimensions by measuring cellular aspect ratio, myocyte area, nuclear density and the degree of cytoskeletal F-actin alignment. We found that when compared with isotropic tissues, anisotropic tissues have increased cellular aspect ratios, increased nuclear densities, decreased myocyte cell areas and smaller variances in actin alignment. To understand how tissue architecture influences cardiac function, we studied the role of anisotropy on intracellular calcium ([Ca(2+)](i)) dynamics by characterizing the [Ca(2+)](i)-frequency relationship of electrically paced tissues. When compared with isotropic tissues, anisotropic tissues displayed significant differences in [Ca(2+)](i) transients, decreased diastolic baseline [Ca(2+)](i) levels and greater [Ca(2+)](i) influx per cardiac cycle. These results suggest that ECM cues influence tissue structure at cellular and subcellular levels and regulate ECC.

Development of a High-throughput Assay for Monitoring cAMP Levels in Cardiac Ventricular Myocytes

G-protein-coupled receptors (GPCRs) represent the largest family of transmembrane receptors involved in cell signal transduction. Many of these GPCRs convey their pharmacological actions by regulating intracellular levels of 3',5'-cyclic adenosine monophosphate (cAMP). Although the heart expresses more than 100 GPCRs, drug agonists for approximately one third of these GPCRs have not been identified. The goal of this project was to initiate the development of a high-throughput screening assay for monitoring cAMP in the heart. Neonatal rat cardiac ventricular myocytes were isolated and cultured on coverslips (whole-cell patch clamp recording) or in 96-well plates (fluorescent imaging plate reader measurements). Cells were infected with adenovirus expressing either beta-galactosidase (AdLacZ) or a mutant cyclic nucleotide-gated (CNG) channel containing the double mutation C460W/E583M (AdCNG). Addition of 2 microM forskolin along with 100 microM 3-isobutyl-1-methylxanthine, to increase intracellular cAMP, activated a cation current in myocytes infected with the AdCNG. In myocytes loaded with the fluorescent Ca indicator Fluo-4, stimulation with forskolin, epinephrine, norepinephrine, or the beta-adrenergic receptor agonist isoproterenol increased the fluorescent signal indicative of Ca influx through the CNG channel. In conclusion, CNG channels are readily expressed in cultured cardiac myocytes and may be utilized in high-throughput screening assays of intracellular cAMP.

Epidermal Growth Factor Receptor activates ERK but not JNK through a Ras independent pathway during cardiomyocyte stretch

We evaluated the Mitogen Activated Protein kinases (MAPK) pathways activated during stretch, a major determinant of ventricular hypertrophy, in neonatal rat ventricular cardiac myocytes in culture. The activations of Ras, ERK and JNK peaked 15 min after the initiation of stretch, suggesting a cause‐effect relationship. A dominant negative form of Ras did not inhibit stretch‐induced ERK and JNK activations showing that Ras was not involved in MAPK stimulation. Among the pathways that activate MAPK, tyrosine kinases were shown to play a major role. Genistein, a tyrosine kinase inhibitor, significantly decreased both ERK and JNK activations during stretch but did not inhibit Ras. The epidermal growth factor receptor (EGFR) is one of the tyrosine kinase receptors. We examined its role using a specific blocker, AG1478. It decreased both basal ERK phosphorylation through the Ras‐Raf1‐MEK cascade and stretch‐induced ERK activation independently of this cascade. In contrast with its effects on ERK, AG1478 did not significantly modify JNK phosphorylation both in basal conditions and during stretch. In addition, our data show that the PI3 kinase‐Akt /PKB pathway is downstream of the EGFR, participating in ERK but not JNK activation. We conclude that the EGFR acts on ERK phosphorylation through 2 different pathways: in basal conditions through the Ras pathway and during stretch through the PI3kinase pathway.

Small molecule phenotypic screen using a MEF2/ HDAC5 mammalian two-hybrid assay

MEF2 is a member of a family of transcription factors necessary for myogenesis. MEF2 appears to be a nodal point in the regulation of myocardial hypertrophy, which is characterized by the expression of many MEF2-dependent genes. In the normal adult heart MEF2 signaling is repressed due to its interaction with class II histone deacetylases 4 and 5 (HDAC4 and HDAC5). Prohypertrophic agents such as CaMKI or CaMKIV cause the dissociation of HDAC4 or HDAC5 from MEF2, a process linked to phosphorylation of HDAC4 or HDAC5 and their nuclear export. Dissociation of HDAC4 or HDAC5 from MEF2 is therefore a potential switch regulating the myocardial hypertrophic response and a potential novel drug discovery target for cardiac hypertrophy and failure. We developed a two-hybrid assay that reports the level of interaction between MEF2 and HDAC5. We used this assay, in a chemical genetic approach, to screen a diverse library of small molecules for compounds that potentially could enhance the interaction between MEF2 and HDAC5. We identified structurally diverse small molecules that cause elevation of the 2-hybrid signal. Some of these molecules are potent inhibitors of in vitro hypertrophic markers in neonatal rat ventricular cardiac myocytes (NRVM). In addition, such molecules inhibited nuclear export of HDAC5 in NRVM, reduced MEF2-dependent gene expression, and inhibited myogenic fusion of C2 myoblasts. Further characterization of these compounds and understanding their mechanism of action, along with additional screening could help elucidate the signaling events leading to cardiac hypertrophy and could serve as starting points in novel drug discovery efforts for compounds with antihypertrophic activity.

Direct and indirect effects of aldosterone on cyclooxygenase-2 and interleukin-6 expression in rat cardiac cells in culture and after myocardial infarction.

Aldosterone contributes to cardiac failure, which is associated with induction of inflammatory mediators. Moreover, aldosterone was shown to induce a vascular inflammatory phenotype in the rat heart. Using Western blotting and/or real-time RT-PCR, we examined the effect of aldosterone on the expression of the proinflammatory molecules, cyclooxygenase-2 (COX-2), and IL-6 in neonatal rat ventricular cardiac myocytes and fibroblasts as well as in adult cardiomyocytes after myocardial infarction. In cardiomyocytes, aldosterone induced COX-2 but not IL-6 expression. After 4-18 h of stimulation with 1 microm aldosterone, a significant increase in COX-2 protein expression was observed, preceded by an increase of COX-2 mRNA levels. After 18 h treatment, 100 nm and 1 microm aldosterone increased COX-2 protein amount by 2- and 4-fold, respectively. Consistently, aldosterone increased by 2.5-fold prostaglandin E(2) secretion in cardiomyocytes. In cardiac fibroblasts, aldosterone increased neither COX-2 nor IL-6 mRNA expression. Interestingly, prostaglandin E(2) (100 nm) strongly induced both proinflammatory molecules in fibroblasts and cardiomyocytes. Our results indicate that aldosterone directly induces COX-2 expression in cardiomyocytes and suggest that the subsequent increase in prostaglandin secretion may act in an autocrine and/or paracrine manner inducing in turn COX-2 and IL-6 expression. In vivo, myocardial infarction strongly increased both COX-2 and IL-6 expression in ventricular cardiomyocytes. Administration of the aldosterone antagonist RU28318 completely prevented COX-2 induction by infarction and partially inhibited the increase in IL-6 mRNA. These data suggest that after myocardial infarction, mineralocorticoid receptor activity is responsible for COX-2 induction and indirectly participates in IL-6 expression in cardiomyocytes.