NRSF-GNAO1 Pathway Contributes to the Regulation of Cardiac Ca2+ Homeostasis.

BACKGROUND: During the development of heart failure, a fetal cardiac gene program is reactivated and accelerates pathological cardiac remodeling. We previously reported that a transcriptional repressor, NRSF (neuron restrictive silencer factor), suppresses the fetal cardiac gene program, thereby maintaining cardiac integrity. The underlying molecular mechanisms remain to be determined, however. METHODS: We aim to elucidate molecular mechanisms by which NRSF maintains normal cardiac function. We generated cardiac-specific NRSF knockout mice and analyzed cardiac gene expression profiles in those mice and mice cardiac-specifically expressing a dominant-negative NRSF mutant. RESULTS: We found that cardiac expression of Gαo, an inhibitory G protein encoded in humans by GNAO1, is transcriptionally regulated by NRSF and is increased in the ventricles of several mouse models of heart failure. Genetic knockdown of Gnao1 ameliorated the cardiac dysfunction and prolonged survival rates in these mouse heart failure models. Conversely, cardiac-specific overexpression of GNAO1 in mice was sufficient to induce cardiac dysfunction. Mechanistically, we observed that increasing Gαo expression increased surface sarcolemmal L-type Ca2+ channel activity, activated CaMKII (calcium/calmodulin-dependent kinase-II) signaling, and impaired Ca2+ handling in ventricular myocytes, which led to cardiac dysfunction. CONCLUSIONS: These findings shed light on a novel function of Gαo in the regulation of cardiac Ca2+ homeostasis and systolic function and suggest Gαo may be an effective therapeutic target for the treatment of heart failure.

Nampt Potentiates Antioxidant Defense in Diabetic Cardiomyopathy.

[Figure: see text].

Proteomic analysis of mitochondrial biogenesis in cardiomyocytes differentiated from human induced pluripotent stem cells.

Mitochondria play key roles in the differentiation and maturation of human cardiomyocytes (CMs). As human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) hold potential in the treatment of heart diseases, we sought to identify key mitochondrial pathways and regulators, which may provide targets for improving cardiac differentiation and maturation. Proteomic analysis was performed on enriched mitochondrial protein extracts isolated from hiPSC-CMs differentiated from dermal fibroblasts (dFCM) and cardiac fibroblasts (cFCM) at time points between 12 and 115 days of differentiation, and from adult and neonatal mouse hearts. Mitochondrial proteins with a twofold change at time points up to 120 days relative to 12 days were subjected to ingenuity pathway analysis (IPA). The highest upregulation was in metabolic pathways for fatty acid oxidation (FAO), the tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS), and branched chain amino acid (BCAA) degradation. The top upstream regulators predicted to be activated were peroxisome proliferator-activated receptor γ coactivator 1 α (PGC1-α), the insulin receptor (IR), and the retinoblastoma protein (Rb1) transcriptional repressor. IPA and immunoblotting showed upregulation of the mitochondrial LonP1 protease-a regulator of mitochondrial proteostasis, energetics, and metabolism. LonP1 knockdown increased FAO in neonatal rat ventricular cardiomyocytes (nRVMs). Our results support the notion that LonP1 upregulation negatively regulates FAO in cardiomyocytes to calibrate the flux between glucose and fatty acid oxidation. We discuss potential mechanisms by which IR, Rb1, and LonP1 regulate the metabolic shift from glycolysis to OXPHOS and FAO. These newly identified factors and pathways may help in optimizing the maturation of iPSC-CMs.

Physical interaction of junctophilin and the CaV1.1 C terminus is crucial for skeletal muscle contraction.

Close physical association of CaV1.1 L-type calcium channels (LTCCs) at the sarcolemmal junctional membrane (JM) with ryanodine receptors (RyRs) of the sarcoplasmic reticulum (SR) is crucial for excitation-contraction coupling (ECC) in skeletal muscle. However, the molecular mechanism underlying the JM targeting of LTCCs is unexplored. Junctophilin 1 (JP1) and JP2 stabilize the JM by bridging the sarcolemmal and SR membranes. Here, we examined the roles of JPs in localization and function of LTCCs. Knockdown of JP1 or JP2 in cultured myotubes inhibited LTCC clustering at the JM and suppressed evoked Ca2+ transients without disrupting JM structure. Coimmunoprecipitation and GST pull-down assays demonstrated that JPs physically interacted with 12-aa residues in the proximal C terminus of the CaV1.1. A JP1 mutant lacking the C terminus including the transmembrane domain (JP1ΔCT) interacted with the sarcolemmal/T-tubule membrane but not the SR membrane. Expression of this mutant in adult mouse muscles in vivo exerted a dominant-negative effect on endogenous JPs, impairing LTCC-RyR coupling at triads without disrupting JM morphology, and substantially reducing Ca2+ transients without affecting SR Ca2+ content. Moreover, the contractile force of the JP1ΔCT-expressed muscle was dramatically reduced compared with the control. Taken together, JPs recruit LTCCs to the JM through physical interaction and ensure robust ECC at triads in skeletal muscle.

Prostanoid EP4 Receptor-Mediated Augmentation of I h Currents in Aß Dorsal Root Ganglion Neurons Underlies Neuropathic Pain.

An injury of the somatosensory system causes neuropathic pain, which is usually refractory to conventional analgesics, thus warranting the development of novel drugs against this kind of pain. The mechanism of neuropathic pain in rats that had undergone left L5 spinal nerve transection was analyzed. Ten days after surgery, these rats acquired neuropathic pain. The patch-clamp technique was used on the isolated bilateral L5 dorsal root ganglion neurons. The current-clamped neurons on the ipsilateral side exhibited significantly higher excitability than those on the contralateral side. However, only neurons with diameters of 40-50 µm on the ipsilateral side exhibited significantly larger voltage sags in response to hyperpolarizing current pulses than those on the contralateral side. Under the voltage clamp, only these neurons on the ipsilateral side showed a significantly larger density of an inward current at < -80 mV [hyperpolarization-activated nonselective cation (I h) current] with a rightward-shifted activation curve than that on the contralateral side. Ivabradine-an I h current inhibitor-inhibited I h currents in these neurons on both sides in a similar concentration-dependent manner, with an IC50 value of ∼3 µM. Moreover, the oral administration of ivabradine significantly alleviated the neuropathic pain on the ipsilateral side. An inhibitor of adenylyl cyclase or an antagonist of prostanoid EP4 receptors (CJ-023423) inhibited ipsilateral, but not contralateral I h, currents in these neurons. Furthermore, the intrathecal administration of CJ-023423 significantly attenuated neuropathic pain on the ipsilateral side. Thus, ivabradine and/or CJ-023423 may be a lead compound for the development of novel therapeutics against neuropathic pain.

Impact of chronic kidney dysfunction on serum Sulfatides and its metabolic pathway in mice.

Serum sulfatides are critical glycosphingolipids that are present in lipoproteins and exert anticoagulant effects. A previous study reported decreased levels of serum sulfatides in hemodialysis patients and suggested an association with cardiovascular disease. However, the mechanism of changes in serum sulfatides in chronic kidney dysfunction has not been well investigated. The current study examined whether a chronic kidney disease (CKD) state could decrease serum sulfatide levels using 5/6 nephrectomy (5/6NCKD) mice, an established CKD murine model, and studied the mechanisms contributing to diminished sulfatides. 5/6NCKD mice and sham operation control mice were sacrificed at the 4th or 12th postoperative week (POW) for measurement of serum sulfatide levels. Hepatic sulfatide content, which is the origin of serum sulfatides, and the expression of sulfatide metabolic enzymes in liver tissue were assessed as well. The 5/6NCKD mice developed CKD and showed increased serum creatinine and indoxyl sulfate. The serum levels and hepatic amounts of sulfatides were significantly decreased in 5/6NCKD mice at both 4 and 12 POW, while the degradative enzymes of sulfatides arylsulfatase A and galactosylceramidase were significantly increased. In a Hepa1-6 murine liver cell line, indoxyl sulfate addition caused intracellular levels of sulfatides to decrease and degradative enzymes of sulfatides to increase in a manner comparable to the changes in 5/6NCKD mice liver tissue. In conclusion, chronic kidney dysfunction causes degradation of sulfatides in the liver to decrease serum sulfatide levels. One explanation of these results is that indoxyl sulfate, a uremic toxin, accelerates the degradation of sulfatides in liver tissue.

Role of YAP/TAZ in Energy Metabolism in the Heart.

The heart requires a high amount of energy, in the form of adenosine triphosphate, to maintain its viability and pump function. Anaerobic glycolysis and mitochondrial oxidative phosphorylation are the two main metabolic pathways by which adenosine triphosphate is generated, using fatty acids, glucose, lactate, and ketone bodies as primary substrates. Previous studies have demonstrated that, in response to stress, the heart undergoes alterations in metabolism, ranging from changes in substrate utilization to mitochondrial function, collectively called metabolic remodeling. However, the molecular mechanism mediating metabolic remodeling in the heart remains unclear. Yes-associated protein 1 (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ), which are major downstream effectors of the Hippo signaling pathway, play an important role in the regulation of heart size and cellular homeostasis of cardiomyocytes through the regulation of various transcriptional factors under both physiological and pathophysiological conditions. Recent findings in various organs and cell types have revealed that YAP and TAZ play an important role in energy metabolism. Here, we summarize what is currently known about YAP/TAZ in the regulation of metabolism of various substrates and mitochondrial function in various organs and cell types and discuss the potential role of YAP/TAZ in mediating metabolic remodeling of the heart during stress and heart failure.

PDGF-induced migration of synthetic vascular smooth muscle cells through c-Src-activated L-type Ca2+ channels with full-length CaV1.2 C-terminus.

In atherosclerosis, vascular smooth muscle cells (VSMC) migrate from the media toward the intima of the arteries in response to cytokines, such as platelet-derived growth factor (PDGF). However, molecular mechanism underlying the PDGF-induced migration of VSMCs remains unclear. The migration of rat aorta-derived synthetic VSMCs, A7r5, in response to PDGF was potently inhibited by a CaV1.2 channel inhibitor, nifedipine, and a Src family tyrosine kinase (SFK)/Abl inhibitor, bosutinib, in a less-than-additive manner. PDGF significantly increased CaV1.2 channel currents without altering CaV1.2 protein expression levels in A7r5 cells. This reaction was inhibited by C-terminal Src kinase, a selective inhibitor of SFKs. In contractile VSMCs, the C-terminus of CaV1.2 is proteolytically cleaved into proximal and distal C-termini (PCT and DCT, respectively). Clipped DCT is noncovalently reassociated with PCT to autoinhibit the channel activity. Conversely, in synthetic A7r5 cells, full-length CaV1.2 (CaV1.2FL) is expressed much more abundantly than truncated CaV1.2. In a heterologous expression system, c-Src activated CaV1.2 channels composed of CaV1.2FL but not truncated CaV1.2 (CaV1.2Δ1763) or CaV1.2Δ1763 plus clipped DCT. Further, c-Src enhanced the coupling efficiency between the voltage-sensing domain and activation gate of CaV1.2FL channels by phosphorylating Tyr1709 and Tyr1758 in PCT. Compared with CaV1.2Δ1763, c-Src could more efficiently bind to and phosphorylate CaV1.2FL irrespective of the presence or absence of clipped DCT. Therefore, in atherosclerotic lesions, phenotypic switching of VSMCs may facilitate pro-migratory effects of PDGF on VSMCs by suppressing posttranslational CaV1.2 modifications.

Angiotensin II activates CaV 1.2 Ca2+ channels through ß-arrestin2 and casein kinase 2 in mouse immature cardiomyocytes.

KEY POINTS: Angiotensin II (AngII) is crucial in cardiovascular regulation in perinatal mammalians. Here we show that AngII increases twitch Ca2+ transients of mouse immature but not mature cardiomyocytes by robustly activating CaV 1.2 L-type Ca2+ channels through a novel signalling pathway involving angiotensin type 1 (AT1 ) receptors, ß-arrestin2 and casein kinase 2. A ß-arrestin-biased AT1 receptor agonist, TRV027, was as effective as AngII in activating L-type Ca2+ channels. Our results help understand the molecular mechanism by which AngII regulates the perinatal circulation and also suggest that ß-arrestin-biased AT1 receptor agonists may be valuable therapeutics for paediatric heart failure. ABSTRACT: Angiotensin II (AngII), the main effector peptide of the renin-angiotensin system, plays important roles in cardiovascular regulation in the perinatal period. Despite the well-known stimulatory effect of AngII on vascular contraction, little is known about regulation of contraction of the immature heart by AngII. Here we found that AngII significantly increased the peak amplitude of twitch Ca2+ transients by robustly activating L-type CaV 1.2 Ca2+ (CaV 1.2) channels in mouse immature but not mature cardiomyocytes. This response to AngII was mediated by AT1 receptors and ß-arrestin2. A ß-arrestin-biased AT1 receptor agonist was as effective as AngII in activating CaV 1.2 channels. Src-family tyrosine kinases (SFKs) and casein kinase 2α'ß (CK2α'ß) were sequentially activated when AngII activated CaV 1.2 channels. A cyclin-dependent kinase inhibitor, p27Kip1 (p27), inhibited CK2α'ß, and AngII removed this inhibitory effect through phosphorylating tyrosine 88 of p27 via SFKs in cardiomyocytes. In a human embryonic kidney cell line, tsA201 cells, overexpression of CK2α'ß but not c-Src directly activated recombinant CaV 1.2 channels composed of C-terminally truncated α1C , the distal C-terminus of α1C , ß2C and α2 δ1 subunits, by phosphorylating threonine 1704 located at the interface between the proximal and the distal C-terminus of CaV 1.2α1C subunits. Co-immunoprecipitation revealed that CaV 1.2 channels, CK2α'ß and p27 formed a macromolecular complex. Therefore, stimulation of AT1 receptors by AngII activates CaV 1.2 channels through ß-arrestin2 and CK2α'ß, thereby probably exerting a positive inotropic effect in the immature heart. Our results also indicated that ß-arrestin-biased AT1 receptor agonists may be used as valuable therapeutics for paediatric heart failure in the future.

Transplantation of adipose tissue-derived stem cells improves cardiac contractile function and electrical stability in a rat myocardial infarction model.

The transplantation of adipose tissue-derived stem cells (ADSCs) improves cardiac contractility after myocardial infarction (MI); however, little is known about the electrophysiological consequences of transplantation. The purpose of this study was to clarify whether the transplantation of ADSCs increases or decreases the incidence of ventricular tachyarrhythmias (VT) in a rat model of MI. MI was induced experimentally by permanent occlusion of the left anterior descending artery of Lewis rats. ADSCs were harvested from GFP-transgenic rats, and were cultured until passage four. ADSCs (10×10(6)) resuspended in 100µL saline or pro-survival cocktail (PSC), which enhances cardiac graft survival, were injected directly into syngeneic rat hearts 1week after MI. The recipients of ADSCs suspended in PSC had a larger graft area compared with those receiving ASDCs suspended in saline at 1week post-transplantation (number of graft cells/section: 148.7±10.6 vs. 22.4±3.4, p<0.05, n=5/group). Thereafter, all ADSC recipients were transplanted with ASDCs in PSC. ADSCs were transplanted into infarcted hearts, and the mechanical and electrophysiological functions were assessed. Echocardiography revealed that ADSC recipients had improved contractile function compared with those receiving PSC vehicle (fractional shortening: 21.1±0.9 vs. 14.1±1.2, p<0.05, n≥12/group). Four weeks post-transplantation, VT was induced via in vivo programmed electrical stimulation. The recipients of ADSCs showed a significantly lower incidence of induced VT compared with the control (31.3% vs. 83.3%, p<0.05, n≥12/group). To understand the electrical activity following transplantation, we performed ex vivo optical mapping using a voltage sensitive dye, and found that ADSC transplantation decreased conduction velocity and its dispersion in the peri-infarct area. These results suggest that ADSC transplantation improved cardiac mechanical and electrophysiological functions in subacute MI.

Phlorizin prevents electrically-induced ventricular tachyarrhythmia during ischemia in langendorff-perfused guinea-pig hearts.

Phlorizin is a type of flavonoids and has a peroxynitrite scavenging effect. This study aimed to elucidate the effects of phlorizin on ischemia-induced ventricular tachyarrhythmia (VT). Optical signals from the epicardial surface of the ventricle or left ventricular end diastolic pressure (LVEDP) were recorded during acute global ischemia in 42 Langendorff-perfused guinea pig hearts. Experiments were performed in the control condition and in the presence of phlorizin or N-2-mercaptopropionylglycine (2-MPG), a peroxynitrite scavenger, respectively. Mean action potential duration at 20 min of ischemia did not differ among the three interventions. Impulse conduction time-dependently slowed during 20 min of ischemia in the control. Phlorizin but not 2-MPG improved the ischemic conduction slowing at 15 and 20 min of ischemia. Programmed stimulation induced VT at 20 min of ischemia in the control and in the presence of 2-MPG but not in the presence of phlorizin (p<0.05). LVEDP was increased during 30 min of ischemia in the control and in the presence of 2-MPG but not in the presence of phlorizin. These results indicate that phlorizin prevents VT through the improvement of impulse conduction slowing during ischemia. Phlorizin may be more useful for ischemia-induced VT than 2-MPG.

Regulation of myocardial glucose metabolism by YAP/TAZ signaling.

The heart utilizes glucose and its metabolites as both energy sources and building blocks for cardiac growth and survival under both physiological and pathophysiological conditions. YAP/TAZ, transcriptional co-activators of the Hippo pathway, are key regulators of cell proliferation, survival, and metabolism in many cell types. Increasing lines of evidence suggest that the Hippo-YAP/TAZ signaling pathway is involved in the regulation of both physiological and pathophysiological processes in the heart. In particular, YAP/TAZ play a critical role in mediating aerobic glycolysis, the Warburg effect, in cardiomyocytes. Here, we summarize what is currently known about YAP/TAZ signaling in the heart by focusing on the regulation of glucose metabolism and its functional significance.

Role of monocarboxylate transporters in AMPK-mediated protection against excitotoxic injury in the rat retina.

Activation of adenosine monophosphate (AMP)-activated protein kinase (AMPK) pathway protects against N-methyl-D-aspartic acid (NMDA)-induced excitotoxic retinal injury. AMPK activation enhances fatty acid metabolism and ketone body synthesis. Ketone bodies are transported into neurons by monocarboxylate transporters (MCTs) and exert neuroprotective effects. In this study, we examined the distribution and expression levels of MCT1 and MCT2 in the retina and analyzed the effects of pharmacological inhibition of MCTs on the protective effects of metformin and 5-aminoimidazole-4-carboxamide (AICAR), activators of AMPK, against NMDA-induced retinal injury in rats. MCT1 was expressed in the blood vessels, processes of astrocytes and Müller cells, and inner segments of photoreceptors in the rat retina, whereas MCT2 was expressed in neuronal cells in the ganglion cell layer (GCL) and in astrocyte processes. The expression levels of MCT2, but not MCT1, decreased one day after intravitreal injection of NMDA (200 nmol). Intravitreal injection of NMDA decreased the number of cells in the GCL compared to the vehicle seven days after injection. Simultaneous injection of metformin (20 nmol) or AICAR (50 nmol) with NMDA attenuated NMDA-induced cell loss in the GCL, and these protective effects were attenuated by AR-C155858 (1 pmol), an inhibitor of MCTs. AR-C155858 alone had no significant effect on the retinal structure. These results suggest that AMPK-activating compounds protect against NMDA-induced excitotoxic retinal injury via mechanisms involving MCTs in rats. NMDA-induced neurotoxicity may be associated with retinal neurodegenerative changes in glaucoma and diabetic retinopathy. Therefore, AMPK-activating compounds may be effective in managing these retinal diseases.

The proximal C-terminus of α(1C) subunits is necessary for junctional membrane targeting of cardiac L-type calcium channels.

In cardiac myocytes, LTCCs (L-type calcium channels) form a functional signalling complex with ryanodine receptors at the JM (junctional membrane). Although the specific localization of LTCCs to the JM is critical for excitation-contraction coupling, their targeting mechanism is unclear. Transient transfection of GFP (green fluorescent protein)-α(1S) or GFP-α(1C), but not P/Q-type calcium channel α(1A), in dysgenic (α(1S)-null) GLT myotubes results in correct targeting of these LTCCs to the JMs and restoration of action-potential-induced Ca2+ transients. To identify the sequences of α(1C) responsible for JM targeting, we generated a range of α(1C)-α(1A) chimaeras, deletion mutants and alanine substitution mutants and studied their targeting properties in GLT myotubes. The results revealed that amino acids L(1681)QAGLRTL(1688) and P(1693)EIRRAIS(1700), predicted to form two adjacent α-helices in the proximal C-terminus, are necessary for the JM targeting of α(1C). The efficiency of restoration of action-potential-induced Ca2+ transients in GLT myotubes was significantly decreased by mutations in the targeting motif. JM targeting was not disrupted by the distal C-terminus of α(1C) which binds to the second α-helix. Therefore we have identified a new structural motif in the C-terminus of α(1C) that mediates the targeting of cardiac LTCCs to JMs independently of the interaction between proximal and distal C-termini of α(1C).

Resveratrol dilates arterioles and protects against N-methyl-d-aspartic acid-induced excitotoxicity in the rat retina.

Resveratrol, a natural polyphenolic compound, reportedly possesses numerous biological activities, including anti-inflammatory and antioxidant effects. In the current study, we examined (1) the dilator effects of resveratrol on retinal arterioles, (2) the protective effects of resveratrol against excitotoxic retinal injury, and (3) whether these effects are mediated by the AMP-activated kinase (AMPK)-dependent pathway in rats. Male Wistar rats (7 to 10 weeks old) were used in this study. The diameters of the retinal arterioles, mean arterial pressure, and heart rate were measured in vivo. The retinal injury was assessed by histological examination. Intravenous injection of resveratrol (3 mg/kg) increased the diameter of the retinal arterioles without affecting the mean arterial pressure and heart rate. The AMPK inhibitor, compound C (5 mg/kg, intravenously), significantly attenuated the retinal vasodilator response to resveratrol. Seven days after intravitreal injection of N-methyl-d-aspartic acid (NMDA; 25, 50, and 100 nmol/eye), the number of cells located in the ganglion cell layer (GCL) was reduced, along with thinning of the inner plexiform layer. Intravitreal resveratrol injection (100 nmol/eye) reduced the NMDA (25 and 50 nmol/eye)-induced cell loss in the GCL. The neuroprotective effect of resveratrol was significantly but not completely reversed by compound C (10 nmol/eye). These results suggest that resveratrol dilates retinal arterioles and protects against NMDA-induced retinal neurodegeneration via an AMPK-dependent pathway in rats. Resveratrol may have the potential to slow the onset and progression of diseases associated with retinal ischemia by improving impaired retinal circulation and protecting retinal neuronal cells.

Chronic receptor-mediated activation of Gi/o proteins alters basal t-tubular and sarcolemmal L-type Ca²âº channel activity through phosphatases in heart failure.

L-type Ca(2+) channels (LTCCs) play an essential role in the excitation-contraction coupling of ventricular myocytes. We previously found that t-tubular (TT) LTCC current density was halved by the activation of protein phosphatase (PP)1 and/or PP2A, whereas surface sarcolemmal (SS) LTCC current density was increased by the inhibition of PP1 and/or PP2A activity in failing ventricular myocytes of mice chronically treated with isoproterenol (ISO mice). In the present study, we examined the possible involvement of inhibitory heterotrimeric G proteins (G(i/o)) in these abnormalities by chronically administrating pertussis toxin (PTX) to ISO mice (ISO + PTX mice). Compared with ISO mice, ISO + PTX mice exhibited significantly higher fractional shortening of the left ventricle. The expression level of Gα(i2) proteins was not altered by the treatment of mice with ISO and/or PTX. ISO + PTX myocytes had normal TT and SS LTCC current densities because they had higher and lower availability and/or open probability of TT and SS LTCCs than ISO myocytes, respectively. A selective PKA inhibitor, H-89, did not affect LTCC current densities in ISO + PTX myocytes. A selective PP2A inhibitor, fostriecin, did not affect SS or TT current density in control or ISO + PTX myocytes but significantly increased TT but not SS LTCC current density in ISO myocytes. These results indicate that chronic receptor-mediated activation of G(i/o) in vivo decreases basal TT LTCC activity by activating PP2A and increases basal SS LTCC activity by inhibiting PP1 without modulating PKA in heart failure.

YAP mediates compensatory cardiac hypertrophy through aerobic glycolysis in response to pressure overload.

The heart utilizes multiple adaptive mechanisms to maintain pump function. Compensatory cardiac hypertrophy reduces wall stress and oxygen consumption, thereby protecting the heart against acute blood pressure elevation. The nuclear effector of the Hippo pathway, Yes-associated protein 1 (YAP), is activated and mediates compensatory cardiac hypertrophy in response to acute pressure overload (PO). In this study, YAP promoted glycolysis by upregulating glucose transporter 1 (GLUT1), which in turn caused accumulation of intermediates and metabolites of the glycolytic, auxiliary, and anaplerotic pathways during acute PO. Cardiac hypertrophy was inhibited and heart failure was exacerbated in mice with YAP haploinsufficiency in the presence of acute PO. However, normalization of GLUT1 rescued the detrimental phenotype. PO induced the accumulation of glycolytic metabolites, including l-serine, l-aspartate, and malate, in a YAP-dependent manner, thereby promoting cardiac hypertrophy. YAP upregulated the GLUT1 gene through interaction with TEA domain family member 1 (TEAD1) and HIF-1α in cardiomyocytes. Thus, YAP induces compensatory cardiac hypertrophy through activation of the Warburg effect.

Decrease in the density of t-tubular L-type Ca2+ channel currents in failing ventricular myocytes.

In some forms of cardiac hypertrophy and failure, the gain of Ca(2+)-induced Ca(2+) release [CICR; i.e., the amount of Ca(2+) released from the sarcoplasmic reticulum normalized to Ca(2+) influx through L-type Ca(2+) channels (LTCCs)] decreases despite the normal whole cell LTCC current density, ryanodine receptor number, and sarcoplasmic reticulum Ca(2+) content. This decrease in CICR gain has been proposed to arise from a change in dyad architecture or derangement of the t-tubular (TT) structure. However, the activity of surface sarcolemmal LTCCs has been reported to increase despite the unaltered whole cell LTCC current density in failing human ventricular myocytes, indicating that the "decreased CICR gain" may reflect a decrease in the TT LTCC current density in heart failure. Thus, we analyzed LTCC currents of failing ventricular myocytes of mice chronically treated with isoproterenol (Iso). Although Iso-treated mice exhibited intact t-tubules and normal LTCC subunit expression, acute occlusion of t-tubules of isolated ventricular myocytes with osmotic shock (detubulation) revealed that the TT LTCC current density was halved in Iso-treated versus control myocytes. Pharmacological analysis indicated that kinases other than PKA or Ca(2+)/calmodulin-dependent protein kinase II insufficiently activated, whereas protein phosphatase 1/2A excessively suppressed, TT LTCCs in Iso-treated versus control myocytes. These results indicate that excessive ß-adrenergic stimulation causes the decrease in TT LTCC current density by altering the regulation of TT LTCCs by protein kinases and phosphatases in heart failure. This phenomenon might underlie the decreased CICR gain in heart failure.

Diacylglycerol kinase ζ inhibits ventricular tachyarrhythmias in a mouse model of heart failure.

BACKGROUND: Diacylglycerol kinase ζ (DGKζ) inhibited atrial tachyarrhythmias in a mouse model of heart failure (HF) in our study. However, whether DGKζ prevents the HF-induced ventricular tachyarrhythmia (VT) is unknown. METHODS AND RESULTS: Effects of DGKζ on VT using transgenic mice with transient cardiac expression of activated G protein α(q) (Gα(q)-TG; model of HF) were elucidated and double transgenic mice with cardiac-specific overexpression of both DGKζ and the activated Gα(q) (Gα(q)/DGKζ-TG) were used. Premature ventricular contraction (PVC) and/or VT were frequently observed in Gα(q)-TG mice but not in Gα(q)/DGKζ-TG and wild-type (WT) mice (P<0.01). Protein expressions of canonical transient receptor potential (TRPC) channels 3 and 6 increased in Gα(q)-TG hearts compared with WT and Gα(q)/DGKζ-TG hearts. SK&F96365, a TRPC channel blocker, decreased the number of PVC and prevented VT in anesthetized Gα(q)-TG mice (P<0.05). 1-oleoyl-2-acyl-sn-glycerol (OAG), a diacylglycerol analogue, increased the number of PVC in isolated Gα(q)-TG hearts compared with WT hearts and induced VT in Gα(q)-TG hearts (P<0.01). SK&F96365 decreased the number of PVC and prevented VT in isolated Gα(q)-TG hearts (P<0.01) even in the presence of OAG. Early afterdepolarization (EAD)-induced triggered activity was frequently observed in single Gα(q)-TG ventricular myocytes. Moreover, SK&F96365 prevented the EAD. CONCLUSIONS: These results demonstrated that DGKζ inhibited VT in a mouse model of HF and suggest that TRPC channels participate in VT induction in failing hearts.

ß-Arrestin-Biased AT1 Agonist TRV027 Causes a Neonatal-Specific Sustained Positive Inotropic Effect Without Increasing Heart Rate.

The treatment of pediatric heart failure is a long-standing unmet medical need. Angiotensin II supports mammalian perinatal circulation by activating cardiac L-type Ca2+ channels through angiotensin type 1 receptor (AT1R) and ß-arrestin. TRV027, a ß-arrestin-biased AT1R agonist, that has been reported to be safe but not effective for adult patients with heart failure, activates the AT1R/ß-arrestin pathway. We found that TRV027 evokes a long-acting positive inotropic effect specifically on immature cardiac myocytes through the AT1R/ß-arrestin/L-type Ca2+ channel pathway with minimum effect on heart rate, oxygen consumption, reactive oxygen species production, and aldosterone secretion. Thus, TRV027 could be utilized as a valuable drug specific for pediatric heart failure.