β-Adrenergic stimulation activates protein kinase Cε and induces extracellular signal-regulated kinase phosphorylation and cardiomyocyte hypertrophy

Abnormal phosphorylation / dephosphorylation and Ca2+ dysfunction in heart failure

Heart failure (HF) can be caused by a variety of causes characterized by abnormal myocardial systole and diastole. Ca2+ current through the L-type calcium channel (LTCC) on the membrane is the initial trigger signal for a cardiac cycle. Declined systole and diastole in HF are associated with dysfunction of myocardial Ca2+ function. This disorder can be correlated with unbalanced levels of phosphorylation / dephosphorylation of LTCC, endoplasmic reticulum (ER), and myofilament. Kinase and phosphatase activity changes along with HF progress, resulting in phased changes in the degree of phosphorylation / dephosphorylation. It is important to realize the phosphorylation / dephosphorylation differences between a normal and a failing heart. This review focuses on phosphorylation / dephosphorylation changes in the progression of HF and summarizes the effects of phosphorylation / dephosphorylation of LTCC, ER function, and myofilament function in normal conditions and HF based on previous experiments and clinical research. Also, we summarize current therapeutic methods based on abnormal phosphorylation / dephosphorylation and clarify potential therapeutic directions.

Signalling of Adrenoceptors: Canonical Pathways and New Paradigms

The concept of G protein-coupled receptors initially arose from studies of the β-adrenoceptor, adenylyl cyclase, and cAMP signalling pathway. Since then both canonical G protein-coupled receptor signalling pathways and emerging paradigms in receptor signalling have been defined by experiments focused on adrenoceptors. Here, we discuss the evidence for G protein coupling specificity of the nine adrenoceptor subtypes. We summarise the ability of each of the adrenoceptors to activate proximal signalling mediators including cAMP, calcium, mitogen-activated protein kinases, and protein kinase C pathways. Finally, we highlight the importance of precise spatial and temporal control of adrenoceptor signalling that is controlled by the localisation of receptors at intracellular membranes and in larger protein complexes.

Effects of exposure to sediment-associated fipronil on cardiac function of Neotropical armored catfish Hypostomus regani

Fipronil is widely used as a broad-spectrum insecticide in agriculture, urban environments, and veterinary medicine. Fipronil can enter aquatic ecosystems and spread to sediment and organic matter, representing a risk to non-target species. This study aimed to evaluate the effects of short-term (96 h) exposure to a low and realistic concentration of sediment-associated fipronil (4.2 µg.kg^-1 of Regent® 800 WG) on myocardial contractility of armored catfish Hypostomus regain, a benthic fish species. Fipronil exposure induced increased inotropism and acceleration of contractile kinetics, although no alterations in the relative ventricular mass were observed. This better cardiac function was associated with an elevated expression and/or function of the Na⁺/Ca²⁺ exchanger and its marked contribution to contraction and relaxation, probably due to a stress-induced adrenergic stimulation. Ventricle strips of exposed fish also exhibited a faster relaxation and a higher cardiac pumping capacity, indicating that armored catfish were able to perform cardiac adjustments to face the exposure. However, a high energetic cost to maintain an increased cardiac performance can make fish more susceptible to other stressors, impairing developmental processes and/or survival. These findings highlight the need for regulations of emerging contaminants, such as fipronil, to ensure adequate protection of the aquatic system.

Puerarin attenuates isoproterenol‑induced myocardial hypertrophy via inhibition of the Wnt/β‑catenin signaling pathway

Myocardial hypertrophy (MH) is an independent risk factor for cardiovascular disease, which in turn lead to arrhythmia or heart failure. Therefore, attention must be paid to formulation of therapeutic strategies for MH. Puerarin is a key bioactive ingredient isolated from Pueraria genera of plants that is beneficial for the treatment of MH. However, its molecular mechanism of action has not been fully determined. In the present study, 40 µM puerarin was demonstrated to be a safe dose for human AC16 cells using Cell Counting Kit‑8 assay. The protective effects of puerarin against MH were demonstrated in AC16 cells stimulated with isoproterenol (ISO). These effects were characterized by a significant decrease in surface area of cells (assessed using fluorescence staining) and mRNA and protein expression levels of MH‑associated biomarkers, including atrial and brain natriuretic peptide, assessed using reverse transcription‑quantitative PCR and western blotting, as well as β‑myosin heavy chain mRNA expression levels. Mechanistically, western blotting demonstrated that puerarin inhibited activation of the Wnt signaling pathway. Puerarin also significantly decreased phosphorylation of p65; this was mediated via crosstalk between the Wnt and NF‑κB signaling pathways. An inhibitor (Dickkopf‑1) and activator (IM‑12) of the Wnt signaling pathway were used to demonstrate that puerarin‑mediated effects alleviated ISO‑induced MH via the Wnt signaling pathway. The results of the present study demonstrated that puerarin pre‑treatment may be a potential therapeutic strategy for preventing ISO‑induced MH and managing MH in the future.

Cardioprotection of Immature Heart by Simultaneous Activation of PKA and Epac: A Role for the Mitochondrial Permeability Transition Pore

Metabolic and ionic changes during ischaemia predispose the heart to the damaging effects of reperfusion. Such changes and the resulting injury differ between immature and adult hearts. Therefore, cardioprotective strategies for adults must be tested in immature hearts. We have recently shown that the simultaneous activation of protein kinase A (PKA) and exchange protein activated by cAMP (Epac) confers marked cardioprotection in adult hearts. The aim of this study is to investigate the efficacy of this intervention in immature hearts and determine whether the mitochondrial permeability transition pore (MPTP) is involved. Isolated perfused Langendorff hearts from both adult and immature rats were exposed to global ischaemia and reperfusion injury (I/R) following control perfusion or perfusion after an equilibration period with activators of PKA and/or Epac. Functional outcome and reperfusion injury were measured and in parallel, mitochondria were isolated following 5 min of reperfusion to determine whether cardioprotective interventions involved changes in MPTP opening behaviour. Perfusion for 5 min preceding ischaemia of injury-matched adult and immature hearts with 5 µM 8-Br (8-Br-cAMP-AM), an activator of both PKA and Epac, led to significant reduction in post-reperfusion CK release and infarct size. Perfusion with this agent also led to a reduction in MPTP opening propensity in both adult and immature hearts. These data show that immature hearts are innately more resistant to I/R injury than adults, and that this is due to a reduced tendency of MPTP opening following reperfusion. Furthermore, simultaneous stimulation of PKA and Epac causes cardioprotection, which is additive to the innate resistance.

Protective effects of dioscin against isoproterenol-induced cardiac hypertrophy via adjusting PKCε/ERK-mediated oxidative stress

Cardiac hypertrophy (CH) plays a central role in cardiac remodeling and is an independent risk factor for cardiac events. It is imperative to find drugs with protective effect on CH. Dioscin, one natural product, shows various pharmacological activities, and PKCepsilon (PKCε) plays an important role in the physiological hypertrophic responses. Thus, we aimed to investigate the possible protective effect of dioscin on CH through PKCε. In the present study, the isoproterenol (ISO)-induced H9C2 cells and primary cardiomyocytes models, and the ISO-induced rat model were established, and the pharmacodynamics and mechanism of dioscin were investigated. In vitro results prompted that, dioscin significantly improved ISO-induced cardiomyocyte hypertrophy, decreased the levels of cell size, protein content of single cell, reactive oxygen species, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), beta-myosin heavy chain (β-MHC). Moreover, in vivo, changes in histopathological of the animals caused by ISO are improved by dioscin. And dioscin decreased the index of CH and the levels of CK, MDA, LDH, and increased the levels of GSH, SOD and GSH-Px. Mechanism research showed that dioscin inhibited the expression levels of PKCε, and affected the expression levels of p-MEK, p-ERK, Nrf2, Keap1 and HO-1 to inhibit oxidative stress. In addition, the results of ISO-induced CH in PKCε siRNA transfected H9C2 cells and C57BL/6 mice further showed that the protective effect of dioscin on CH, which was mediated by inhibition of PKCε/ERK signal pathway. In summary, dioscin can effectively inhibit CH by regulating PKCε-mediated oxidative stress, which should be considered as one potent candidate for new drug research and development to treat CH in the future.

β3 Adrenoceptor-induced cholinergic inhibition in human and rat urinary bladders involves the exchange protein directly activated by cyclic AMP 1 favoring adenosine release

BACKGROUND AND PURPOSE

The mechanism by which β₃ receptor agonists (e.g. mirabegron) control bladder overactivity may involve adenosine release from human and rat detrusor smooth muscle. Retrograde activation of adenosine A₁ receptors reduces ACh release from cholinergic bladder nerves. β₃ -Adrenoceptors usually couple to adenylyl cyclase. Here we investigated, which of the cAMP targets, protein kinase A or the exchange protein directly activated by cAMP (EPAC) could be involved in this cholinergic inhibition of the bladder.

EXPERIMENTAL APPROACH

[³ H]ACh and adenosine release from urothelium-denuded detrusor strips of cadaveric human organ donors and rats were measured by liquid scintillation spectrometry and HPLC, respectively. In vivo cystometry was also performed in urethane-anaesthetized rats.

KEY RESULTS

The exchange protein directly activated by cAMP (EPAC) inhibitor, ESI-09, prevented mirabegron- and isoprenaline-induced adenosine release from human and rat detrusor strips respectively. ESI-09, but not the PKA inhibitor, H-89, attenuated inhibition of [³ H]ACh release from stimulated (10 Hz) detrusor strips caused by activating β₃ -adrenoceptors, AC (forskolin) and EPAC1 (8-CTP-2Me-cAMP). Isoprenaline-induced inhibition of [³ H]ACh release was also prevented by inhibitors of PKC (chelerythrine and Go6976) and of the equilibrative nucleoside transporter 1 (ENT1; dipyridamole and NBTI), but not by PLC inhibition with U73122. Pretreatment with ESI-09, but not with H-89, prevented the reduction of the voiding frequency caused by isoprenaline and forskolin in vivo.

CONCLUSION AND IMPLICATIONS

Data suggest that β₃ -adrenoceptor-induced inhibition of cholinergic neurotransmission in human and rat urinary bladders involves activation of an EPAC1/PKC pathway downstream cAMP production resulting in adenosine outflow via ENT1.

Phospho-substrate profiling of Epac-dependent protein kinase C activity

Exchange protein directly activated by cAMP (Epac) and protein kinase A are effectors for cAMP with distinct actions and regulatory mechanisms. Epac is a Rap guanine nucleotide exchange factor that activates Rap1; protein kinase C (PKC) is a major downstream target of Epac-Rap1 signaling that has been implicated in a variety of pathophysiological processes, including cardiac hypertrophy, cancer, and nociceptor sensitization leading to chronic pain. Despite the implication of both Epac and PKC in these processes, few downstream targets of Epac-PKC signaling have been identified. This study characterized the regulation of PKC activity downstream of Epac activation. Using an antibody that recognizes phospho-serine residues within the consensus sequence phosphorylated by PKC, we analyzed the 1-dimensional banding profile of PKC substrate protein phosphorylation from the Neuro2A mouse neuroblastoma cell line. Activation of Epac either indirectly by prostaglandin PGE2, or directly by 8-pCPT-2-O-Me-cAMP-AM (8pCpt), produced distinct PKC phospho-substrate protein bands that were suppressed by co-administration of the Epac inhibitor ESI09. Different PKC isoforms contributed to the induction of individual phospho-substrate bands, as determined using isoform-selective PKC inhibitors. Moreover, the banding profile after Epac activation was altered by disruption of the cytoskeleton, suggesting that the orchestration of Epac-dependent PKC signaling is regulated in part by interactions with the cytoskeleton. The approach described here provides an effective means to characterize Epac-dependent PKC activity.

PKC epsilon signaling effect on actin assembly is diminished in cardiomyocytes when challenged to additional work in a stiff microenvironment

The stiffness of the microenvironment surrounding a cell can result in cytoskeletal remodeling, leading to altered cell function and tissue macrostructure. In this study, we tuned the stiffness of the underlying substratum on which neonatal rat cardiomyocytes were grown in culture to mimic normal (10 kPa), pathological stiffness of fibrotic myocardium (100 kPa), and a nonphysiological extreme (glass). Cardiomyocytes were then challenged by beta adrenergic stimulation through isoproterenol treatment to investigate the response to acute work demand for cells grown on surfaces of varying stiffness. In particular, the PKCɛ signaling pathway and its role in actin assembly dynamics were examined. Significant changes in contractile metrics were seen on cardiomyocytes grown on different surfaces, but all cells responded to isoproterenol treatment, eventually reaching similar time to peak tension. In contrast, the assembly rate of actin was significantly higher on stiff surfaces, so that only cells grown on soft surfaces were able to respond to acute isoproterenol treatment. Förster Resonance Energy Transfer of immunofluorescence on the cytoskeletal fraction of cardiomyocytes confirmed that the molecular interaction of PKCɛ with the actin capping protein, CapZ, was very low on soft substrata but significantly increased with isoproterenol treatment, or on stiff substrata. Therefore, the stiffness of the culture surface chosen for in vitro experiments might mask the normal signaling and affect the ability to translate basic science more effectively into human therapy.

Danhong Injection Reversed Cardiac Abnormality in Brain-Heart Syndrome via Local and Remote β-Adrenergic Receptor Signaling

Ischemic brain injury impacts cardiac dysfunction depending on the part of the brain affected, with a manifestation of irregular blood pressure, arrhythmia, and heart failure. Generally called brain–heart syndrome in traditional Chinese medicine, few mechanistic understanding and treatment options are available at present. We hypothesize that considering the established efficacy for both ischemic stroke and myocardial infarction (MI), Danhong injection (DHI), a multicomponent Chinese patent medicine, may have a dual pharmacological potential for treating the brain–heart syndrome caused by cerebral ischemic stroke through its multi-targeted mechanisms. We investigated the role of DHI in the setting of brain–heart syndrome and determined the mechanism by which it regulates this process. We induced Ischemia/Reperfusion in Wistar rats and administered intravenous dose of DHI twice daily for 14 days. We assessed the neurological state, infarct volume, CT scan, arterial blood pressure, heart rhythm, and the hemodynamics. We harvested the brain and heart tissues for immunohistochemistry and western blot analyses. Our data show that DHI exerts potent anti-stroke effects (infarct volume reduction: ^∗∗p < 0.01 and ^∗∗∗p < 0.001 vs. vehicle. Neurological deficit correction: ^∗p < 0.05 and ^∗∗∗p < 0.001 vs. vehicle), and effectively reversed the abnormal arterial pressure (^∗p < 0.05 vs. vehicle) and heart rhythm (^∗∗p < 0.01 vs. vehicle). The phenotype of this brain–heart syndrome is strikingly similar to those of MI model. Quantitative assessment of hemodynamic in cardiac functionality revealed a positive uniformity in the PV-loop after administration with DHI and valsartan in the latter. Immunohistochemistry and western blot results showed the inhibitory effect of DHI on the β-adrenergic pathway as well as protein kinase C epsilon (PKCε) (^∗∗p < 0.01 vs. model). Our data showed the underlying mechanisms of the brain–heart interaction and offer the first evidence that DHI targets the adrenergic pathway to modulate cardiac function in the setting of brain–heart syndrome. This study has made a novel discovery for proper application of the multi-target DHI and could serve as a therapeutic option in the setting of brain–heart syndrome.

β-adrenergic Receptor-stimulated Cardiac Myocyte Apoptosis: Role of Cytochrome P450 ω-hydroxylase

Prolonged or excessive β-adrenergic activation leads to cardiac myocyte loss and heart dysfunction; however, the underlying cellular mechanisms are still unclear. Therefore, we first confirmed the effect of isoproterenol (ISO), a β-adrenergic receptor agonist, on cardiac toxicity using TUNEL and caspase activity assays in cultured rat cardiomyocytes. ISO treatment significantly increased cardiomyocyte apoptosis. Persistent ISO stimulation of cardiomyocytes also increased the expression of CYP4A3, a major CYP450 ω-hydroxylase that produces 20-hydroxyeicosatetraenoic acid (20-HETE) in a time-dependent manner. Next, we examined the effect of ISO and 20-HETE on cardiomyocyte apoptosis using annexin V and propidium iodide staining. Treatment with either 20-HETE or ISO significantly increased cardiomyocyte apoptosis, and inhibition of 20-HETE production using 17-ODYA, a CYP450 ω-hydroxylase inhibitor, dramatically attenuated ISO-induced cardiomyocyte apoptosis. To determine the apoptotic pathway involved, the mitochondrial membrane potential (ΔΨm) was measured by detecting the ratio of JC-1 green/red emission intensity. The results demonstrated that 17-ODYA significantly abolished ISO-induced disruption of ΔΨm and that 20-HETE alone induced a marked disruptive effect on ΔΨm in cardiomyocytes. In addition, 20-HETE-induced disruption of ΔΨm and apoptosis was significantly attenuated by KN93, a CaMKII inhibitor. Taken together, these results demonstrate that 20-HETE treatment induces significant apoptosis via mitochondrial-dependent pathways, and that inhibition of 20-HETE production using 17-ODYA attenuates ISO-induced cardiomyocyte apoptosis.

Functional and cardioprotective effects of simultaneous and individual activation of protein kinase A and Epac

Background and Purpose

Myocardial cAMP elevation confers cardioprotection against ischaemia/reperfusion (I/R) injury. cAMP activates two independent signalling pathways, PKA and Epac. This study investigated the cardiac effects of activating PKA and/or Epac and their involvement in cardioprotection against I/R.

Experimental Approach

Hearts from male rats were used either for determination of PKA and PKC activation or perfused in the Langendorff mode for either cardiomyocyte isolation or used to monitor functional activity at basal levels and after 30 min global ischaemia and 2 h reperfusion. Functional recovery and myocardial injury during reperfusion (LDH release and infarct size) were evaluated. Activation of PKA and/or Epac in perfused hearts was induced using cell permeable cAMP analogues in the presence or absence of inhibitors of PKA, Epac and PKC. H9C2 cells and cardiomyocytes were used to assess activation of Epac and effect on Ca²⁺ transients.

Key Results

Selective activation of either PKA or Epac was found to trigger a positive inotropic effect, which was considerably enhanced when both pathways were simultaneously activated. Only combined activation of PKA and Epac induced marked cardioprotection against I/R injury. This was accompanied by PKCε activation and repressed by inhibitors of PKA, Epac or PKC.

Conclusion and Implications

Simultaneous activation of both PKA and Epac induces an additive inotropic effect and confers optimal and marked cardioprotection against I/R injury. The latter effect is mediated by PKCε activation. This work has introduced a new therapeutic approach and targets to protect the heart against cardiac insults.

Electrical and mechanical stimulation of cardiac cells and tissue constructs

The field of cardiac tissue engineering has made significant strides over the last few decades, highlighted by the development of human cell derived constructs that have shown increasing functional maturity over time, particularly using bioreactor systems to stimulate the constructs. However, the functionality of these tissues is still unable to match that of native cardiac tissue and many of the stem-cell derived cardiomyocytes display an immature, fetal like phenotype. In this review, we seek to elucidate the biological underpinnings of both mechanical and electrical signaling, as identified via studies related to cardiac development and those related to an evaluation of cardiac disease progression. Next, we review the different types of bioreactors developed to individually deliver electrical and mechanical stimulation to cardiomyocytes in vitro in both two and three-dimensional tissue platforms. Reactors and culture conditions that promote functional cardiomyogenesis in vitro are also highlighted. We then cover the more recent work in the development of bioreactors that combine electrical and mechanical stimulation in order to mimic the complex signaling environment present in vivo. We conclude by offering our impressions on the important next steps for physiologically relevant mechanical and electrical stimulation of cardiac cells and engineered tissue in vitro.