Prevention of PKG1α oxidation augments cardioprotection in the stressed heart

Clinical and Hemodynamic Improvement in Pulmonary Hypertension After Switching to Sacubitril/Valsartan in Patients With Heart Failure With Preserved Ejection Fraction

ABSTRACT

Patients with heart failure with preserved ejection fraction (HFpEF) and pulmonary hypertension have poor survival, and established medical therapies for both conditions are not available. In this retrospective study of 69 patients with HFpEF and either isolated postcapillary pulmonary hypertension (IpcPH, n = 53) or combined postcapillary and precapillary pulmonary hypertension (CpcPH, n = 16), we investigated the effects of sacubitril/valsartan on pulmonary hypertension measured using right heart catheterization at baseline (ie, presacubitril/valsartan) and 99 (94-123) days after switching to sacubitril/valsartan. After switching to sacubitril/valsartan, right heart catheterization showed significantly lower pulmonary artery pressures (systolic/diastolic/mean) in both patient groups compared with presacubitril/valsartan [IpcPH: 44 (38-52)/15 (12-19)/28 (22-33) mm Hg vs. 47 (40-55)/18 (15-23)/31 (26-35) mm Hg, P < 0.01; CpcPH: 54 (43-57)/18 (12-23)/34 (30-36) mm Hg vs. 61 (50-79)/24 (19-30)/40 (31-53) mm Hg, P < 0.05]. The median sacubitril/valsartan dose at follow-up was 24/26 (24/26-49/51) mg twice daily in both patients with IpcPH and CpcPH. Clinically, the New York Heart Association functional class improved by at least 1 class in 32 of 69 patients ( P < 0.01). In conclusion, sacubitril/valsartan therapy improves pulmonary hypertension in patients with HFpEF and either IpcPH or CpcPH. Further prospective randomized trials are needed for confirmation of our results.

Off-target pharmacological activity at various kinases: Potential functional and pathological side effects

In drug discovery, during the lead optimization and candidate characterization stages, novel small molecules are frequently evaluated in a battery of in vitro pharmacology assays to identify potential unintended, off-target interactions with various receptors, transporters, ion channels, and enzymes, including kinases. Furthermore, these screening panels may also provide utility at later stages of development to provide a mechanistic understanding of unexpected safety findings. Here, we present a compendium of the most likely functional and pathological outcomes associated with interaction(s) to a panel of 95 kinases based on an extensive curation of the scientific literature. This panel of kinases was designed by AbbVie based on safety-related data extracted from the literature, as well as from over 20 years of institutional knowledge generated from discovery efforts. For each kinase, the scientific literature was reviewed using online databases and the most often reported functional and pathological effects were summarized. This work should serve as a practical guide for small molecule drug discovery scientists and clinical investigators to predict and/or interpret adverse effects related to pharmacological interactions with these kinases.

New Therapeutics for Heart Failure: Focusing on cGMP Signaling

Current drugs for treating heart failure (HF), for example, angiotensin II receptor blockers and β-blockers, possess specific target molecules involved in the regulation of the cardiac circulatory system. However, most clinically approved drugs are effective in the treatment of HF with reduced ejection fraction (HFrEF). Novel drug classes, including angiotensin receptor blocker/neprilysin inhibitor (ARNI), sodium-glucose co-transporter-2 (SGLT2) inhibitor, hyperpolarization-activated cyclic nucleotide-gated (HCN) channel blocker, soluble guanylyl cyclase (sGC) stimulator/activator, and cardiac myosin activator, have recently been introduced for HF intervention based on their proposed novel mechanisms. SGLT2 inhibitors have been shown to be effective not only for HFrEF but also for HF with preserved ejection fraction (HFpEF). In the myocardium, excess cyclic adenosine monophosphate (cAMP) stimulation has detrimental effects on HFrEF, whereas cyclic guanosine monophosphate (cGMP) signaling inhibits cAMP-mediated responses. Thus, molecules participating in cGMP signaling are promising targets of novel drugs for HF. In this review, we summarize molecular pathways of cGMP signaling and clinical trials of emerging drug classes targeting cGMP signaling in the treatment of HF.

Structural insights into selective small molecule activation of PKG1α

cGMP-dependent protein kinase I-α (PKG1α) is a target for pulmonary arterial hypertension due to its role in the regulation of smooth muscle function. While most work has focused on regulation of cGMP turnover, we recently described several small molecule tool compounds which were capable of activating PKG1α via a cGMP independent pathway. Selected molecules were crystallized in the presence of PKG1α and were found to bind to an allosteric site proximal to the low-affinity nucleotide binding domain. These molecules act to displace the switch helix and cause activation of PKG1α representing a new mechanism for the activation and control of this critical therapeutic path. The described structures are vital to understanding the function and control of this key regulatory pathway.

Augmentation of natriuretic peptide (NP) receptor A and B (NPR-A and NPR-B) and cyclic guanosine monophosphate (cGMP) signalling as a therapeutic strategy in heart failure

INTRODUCTION

Heart failure is a complex, debilitating condition and despite advances in treatment, it remains a significant cause of morbidity and mortality worldwide. Therefore, the need for alternative treatment strategies is essential. In this review, we explore the therapeutic strategies of augmenting natriuretic peptide receptors (NPR-A and NPR-B) and cyclic guanosine monophosphate (cGMP) in heart failure.

AREAS COVERED

We aim to provide an overview of the evidence of preclinical and clinical studies on novel heart failure treatment strategies. Papers collected in this review have been filtered and screened following PubMed searches. This includes epigenetics, modulating enzyme activity in natriuretic peptide (NP) synthesis, gene therapy, modulation of downstream signaling by augmenting soluble guanylate cyclase (sGC) and phosphodiesterase (PDE) inhibition, nitrates, c-GMP-dependent protein kinase, synthetic and designer NP and RNA therapy.

EXPERT OPINION

The novel treatment strategies mentioned above have shown great potential, however, large randomized controlled trials are still lacking. The biggest challenge is translating the results seen in preclinical trials into clinical trials. We recommend a multi-disciplinary team approach with cardiologists, geneticist, pharmacologists, bioengineers, researchers, regulators, and patients to improve heart failure outcomes. Future management can involve telemedicine, remote monitoring, and artificial intelligence to optimize patient care.

Flipping Off and On the Redox Switch in the Microcirculation

Resistance arteries and arterioles evolved as specialized blood vessels serving two important functions: (a) regulating peripheral vascular resistance and blood pressure and (b) matching oxygen and nutrient delivery to metabolic demands of organs. These functions require control of vessel lumen cross-sectional area (vascular tone) via coordinated vascular cell responses governed by precise spatial-temporal communication between intracellular signaling pathways. Herein, we provide a contemporary overview of the significant roles that redox switches play in calcium signaling for orchestrated endothelial, smooth muscle, and red blood cell control of arterial vascular tone. Three interrelated themes are the focus: (a) smooth muscle to endothelial communication for vasoconstriction, (b) endothelial to smooth muscle cell cross talk for vasodilation, and (c) oxygen and red blood cell interregulation of vascular tone and blood flow. We intend for this thematic framework to highlight gaps in our current knowledge and potentially spark interest for cross-disciplinary studies moving forward.

Pharmacological TRPC6 inhibition improves survival and muscle function in mice with Duchenne muscular dystrophy

Gene mutations causing loss of dystrophin result in the severe muscle disease known as Duchenne muscular dystrophy (DMD). Despite efforts at genetic repair, DMD therapy remains largely palliative. Loss of dystrophin destabilizes the sarcolemmal membrane, inducing mechanosensitive cation channels to increase calcium entry and promote cell damage and, eventually, muscle dysfunction. One putative channel is transient receptor potential canonical 6 (TRPC6); we have shown that TRPC6 contributed to abnormal force and calcium stress-responses in cardiomyocytes from mice lacking dystrophin that were haplodeficient for utrophin (mdx/utrn+/- [HET] mice). Here, we show in both the HET mouse and the far more severe homozygous mdx/utrn-/- mouse that TRPC6 gene deletion or its selective pharmacologic inhibition (by BI 749327) prolonged survival 2- to 3-fold, improving skeletal and cardiac muscle and bone defects. Gene pathways reduced by BI 749327 treatment most prominently regulated fat metabolism and TGF-β1 signaling. These results support the testing of TRPC6 inhibitors in human trials for other diseases as a novel DMD therapy.

Optimization and Mechanistic Investigations of Novel Allosteric Activators of PKG1α

Activation of PKG1α is a compelling strategy for the treatment of cardiovascular diseases. As the main effector of cyclic guanosine monophosphate (cGMP), activation of PKG1α induces smooth muscle relaxation in blood vessels, lowers pulmonary blood pressure, prevents platelet aggregation, and protects against cardiac stress. The development of activators has been mostly limited to cGMP mimetics and synthetic peptides. Described herein is the optimization of a piperidine series of small molecules to yield activators that demonstrate in vitro phosphorylation of vasodilator-stimulated phosphoprotein as well as antiproliferative effects in human pulmonary arterial smooth muscle cells. Hydrogen/deuterium exchange mass spectrometry experiments with the small molecule activators revealed a mechanism of action consistent with cGMP-induced activation, and an X-ray co-crystal structure with a construct encompassing the regulatory domains illustrated a binding mode in an allosteric pocket proximal to the low-affinity cyclic nucleotide-binding domain.

Constitutive protein kinase G activation exacerbates stress-induced cardiomyopathy

BACKGROUND AND PURPOSE

Heart failure is associated with high morbidity and mortality, and new therapeutic targets are needed. Preclinical data suggest that pharmacological activation of protein kinase G (PKG) can reduce maladaptive ventricular remodelling and cardiac dysfunction in the stressed heart. However, clinical trial results have been mixed and the effects of long-term PKG activation in the heart are unknown.

EXPERIMENTAL APPROACH

We characterized the cardiac phenotype of mice carrying a heterozygous knock-in mutation of PKG1 (Prkg1^R177Q/+ ), which causes constitutive, cGMP-independent activation of the kinase. We examined isolated cardiac myocytes and intact mice, the latter after stress induced by surgical transaortic constriction or angiotensin II (Ang II) infusion.

KEY RESULTS

Cardiac myocytes from Prkg1^R177Q/+ mice showed altered phosphorylation of sarcomeric proteins and reduced contractility in response to electrical stimulation, compared to cells from wild type mice. Under basal conditions, young PKG1^R177Q/+ mice exhibited no obvious cardiac abnormalities, but aging animals developed mild increases in cardiac fibrosis. In response to angiotensin II infusion or fixed pressure overload induced by transaortic constriction, young PKG^R177Q/+ mice exhibited excessive hypertrophic remodelling with increased fibrosis and myocyte apoptosis, leading to increased left ventricular dilation and dysfunction compared to wild type litter mates.

CONCLUSION AND IMPLICATIONS

Long-term PKG1 activation in mice may be harmful to the heart, especially in the presence of pressure overload and neurohumoral stress.

LINKED ARTICLES

This article is part of a themed issue on cGMP Signalling in Cell Growth and Survival. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.11/issuetoc.

Ca2+/calmodulin-dependent protein kinase II and protein kinase G oxidation contributes to impaired sarcomeric proteins in hypertrophy model

Aims

Volume overload (VO) induced hypertrophy is one of the hallmarks to the development of heart diseases. Understanding the compensatory mechanisms involved in this process might help preventing the disease progression.

Methods and results

Therefore, the present study used 2 months old Wistar rats, which underwent an aortocaval fistula to develop VO‐induced hypertrophy. The animals were subdivided into four different groups, two sham operated animals served as age‐matched controls and two groups with aortocaval fistula. Echocardiography was performed prior termination after 4‐ and 8‐month. Functional and molecular changes of several sarcomeric proteins and their signalling pathways involved in the regulation and modulation of cardiomyocyte function were investigated.

Results

The model was characterized with preserved ejection fraction in all groups and with elevated heart/body weight ratio, left/right ventricular and atrial weight at 4‐ and 8‐month, which indicates VO‐induced hypertrophy. In addition, 8‐months groups showed increased left ventricular internal diameter during diastole, RV internal diameter, stroke volume and velocity‐time index compared with their age‐matched controls. These changes were accompanied by increased Ca²⁺ sensitivity and titin‐based cardiomyocyte stiffness in 8‐month VO rats compared with other groups. The altered cardiomyocyte mechanics was associated with phosphorylation deficit of sarcomeric proteins cardiac troponin I, myosin binding protein C and titin, also accompanied with impaired signalling pathways involved in phosphorylation of these sarcomeric proteins in 8‐month VO rats compared with age‐matched control group. Impaired protein phosphorylation status and dysregulated signalling pathways were associated with significant alterations in the oxidative status of both kinases CaMKII and PKG explaining by this the elevated Ca²⁺ sensitivity and titin‐based cardiomyocyte stiffness and perhaps the development of hypertrophy.

Conclusions

Our findings showed VO‐induced cardiomyocyte dysfunction via deranged phosphorylation of myofilament proteins and signalling pathways due to increased oxidative state of CaMKII and PKG and this might contribute to the development of hypertrophy.

Cyclic GMP and PKG Signaling in Heart Failure

Cyclic guanosine monophosphate (cGMP), produced by guanylate cyclase (GC), activates protein kinase G (PKG) and regulates cardiac remodeling. cGMP/PKG signal is activated by two intrinsic pathways: nitric oxide (NO)-soluble GC and natriuretic peptide (NP)-particulate GC (pGC) pathways. Activation of these pathways has emerged as a potent therapeutic strategy to treat patients with heart failure, given cGMP-PKG signaling is impaired in heart failure with reduced ejection fraction (HFrEF) and preserved ejection fraction (HFpEF). Large scale clinical trials in patients with HFrEF have shown positive results with agents that activate cGMP-PKG pathways. In patients with HFpEF, however, benefits were observed only in a subgroup of patients. Further investigation for cGMP-PKG pathway is needed to develop better targeting strategies for HFpEF. This review outlines cGMP-PKG pathway and its modulation in heart failure.

Single serine on TSC2 exerts biased control over mTORC1 activation mediated by ERK1/2 but not Akt

Both ERK1/2 and Akt kinases activate mTORC1, but only the former is bidirectionally regulated by the status of serine S1364 on TSC2 that confers input-selective mTORC1 amplification or attenuation.

Tuberous sclerosis complex-2 (TSC2) negatively regulates mammalian target of rapamycin complex 1 (mTORC1), and its activity is reduced by protein kinase B (Akt) and extracellular response kinase (ERK1/2) phosphorylation to activate mTORC1. Serine 1364 (human) on TSC2 bidirectionally modifies mTORC1 activation by pathological growth factors or hemodynamic stress but has no impact on resting activity. We now show this modification biases to ERK1/2 but not Akt-dependent TSC2-mTORC1 activation. Endothelin-1–stimulated mTORC1 requires ERK1/2 activation and is bidirectionally modified by phospho-mimetic (S1364E) or phospho-silenced (S1364A) mutations. However, mTORC1 activation by Akt-dependent stimuli (insulin or PDGF) is unaltered by S1364 modification. Thrombin stimulates both pathways, yet only the ERK1/2 component is modulated by S1364. S1364 also has negligible impact on mTORC1 regulation by energy or nutrient status. In vivo, diet-induced obesity, diabetes, and fatty liver couple to Akt activation and are also unaltered by TSC2 S1364 mutations. This contrasts to prior reports showing a marked impact of both on pathological pressure-stress. Thus, S1364 provides ERK1/2-selective mTORC1 control and a genetic means to modify pathological versus physiological mTOR stimuli.

The mitochondrial regulator PGC1α is induced by cGMP-PKG signaling and mediates the protective effects of phosphodiesterase 5 inhibition in heart failure

Phosphodiesterase 5 inhibition (PDE5i) activates cGMP-dependent protein kinase (PKG) and ameliorates heart failure; however, its impact on cardiac mitochondrial regulation has not been fully determined. Here, we investigated the role of the mitochondrial regulator peroxisome proliferator-activated receptor γ co-activator-1α (PGC1α) in the PDE5i-conferred cardioprotection, utilizing PGC1α null mice. In PGC1α^+/+ hearts exposed to 7 weeks of pressure overload by transverse aortic constriction, chronic treatment with the PDE5 inhibitor sildenafil improved cardiac function and remodeling, with improved mitochondrial respiration and upregulation of PGC1α mRNA in the myocardium. By contrast, PDE5i-elicited benefits were abrogated in PGC1α^-/- hearts. In cultured cardiomyocytes, PKG overexpression induced PGC1α, while inhibition of the transcription factor CREB abrogated the PGC1α induction. Together, these results suggest that the PKG-PGC1α axis plays a pivotal role in the therapeutic efficacy of PDE5i in heart failure.

MLK3 mediates impact of PKG1α on cardiac function and controls blood pressure through separate mechanisms

cGMP-dependent protein kinase 1α (PKG1α) promotes left ventricle (LV) compensation after pressure overload. PKG1-activating drugs improve heart failure (HF) outcomes but are limited by vasodilation-induced hypotension. Signaling molecules that mediate PKG1α cardiac therapeutic effects but do not promote PKG1α-induced hypotension could therefore represent improved therapeutic targets. We investigated roles of mixed lineage kinase 3 (MLK3) in mediating PKG1α effects on LV function after pressure overload and in regulating BP. In a transaortic constriction HF model, PKG activation with sildenafil preserved LV function in MLK3+/+ but not MLK3-/- littermates. MLK3 coimmunoprecipitated with PKG1α. MLK3-PKG1α cointeraction decreased in failing LVs. PKG1α phosphorylated MLK3 on Thr277/Ser281 sites required for kinase activation. MLK3-/- mice displayed hypertension and increased arterial stiffness, though PKG stimulation with sildenafil or the soluble guanylate cyclase (sGC) stimulator BAY41-2272 still reduced BP in MLK3-/- mice. MLK3 kinase inhibition with URMC-099 did not affect BP but induced LV dysfunction in mice. These data reveal MLK3 as a PKG1α substrate mediating PKG1α preservation of LV function but not acute PKG1α BP effects. Mechanistically, MLK3 kinase-dependent effects preserved LV function, whereas MLK3 kinase-independent signaling regulated BP. These findings suggest augmenting MLK3 kinase activity could preserve LV function in HF but avoid hypotension from PKG1α activation.

Dynamic Regulation of Cysteine Oxidation and Phosphorylation in Myocardial Ischemia-Reperfusion Injury

Myocardial ischemia-reperfusion (I/R) injury significantly alters heart function following infarct and increases the risk of heart failure. Many studies have sought to preserve irreplaceable myocardium, termed cardioprotection, but few, if any, treatments have yielded a substantial reduction in clinical I/R injury. More research is needed to fully understand the molecular pathways that govern cardioprotection. Redox mechanisms, specifically cysteine oxidations, are acute and key regulators of molecular signaling cascades mediated by kinases. Here, we review the role of reactive oxygen species in modifying cysteine residues and how these modifications affect kinase function to impact cardioprotection. This exciting area of research may provide novel insight into mechanisms and likely lead to new treatments for I/R injury.

Redox Switches Controlling Nitric Oxide Signaling in the Resistance Vasculature and Implications for Blood Pressure Regulation: Mid-Career Award for Research Excellence 2020

The arterial resistance vasculature modulates blood pressure and flow to match oxygen delivery to tissue metabolic demand. As such, resistance arteries and arterioles have evolved a series of highly orchestrated cell-cell communication mechanisms between endothelial cells and vascular smooth muscle cells to regulate vascular tone. In response to neurohormonal agonists, release of several intracellular molecules, including nitric oxide, evokes changes in vascular tone. We and others have uncovered novel redox switches in the walls of resistance arteries that govern nitric oxide compartmentalization and diffusion. In this review, we discuss our current understanding of redox switches controlling nitric oxide signaling in endothelial and vascular smooth muscle cells, focusing on new mechanistic insights, physiological and pathophysiological implications, and advances in therapeutic strategies for hypertension and other diseases.

Discovery of the First Non-cGMP Mimetic Small Molecule Activators of cGMP-Dependent Protein Kinase 1 α (PKG1α)

PKG1α is a central node in cGMP signaling. Current therapeutics that look to activate this pathway rely on elevation of cGMP levels and subsequent activation of PKG1α. Direct activation of PKG1α could potentially drive additional efficacy without associated side effects of blanket cGMP elevation. We undertook a high-throughput screen to identify novel activators. After triaging through numerous false positive hits, attributed to compound mediated oxidation and activation of PKG1α, a piperidine series of compounds was validated. The hit 1 was a weak activator with EC₅₀ = 47 μM. The activity could be improved to single digit micromolar, as seen in compounds 21 and 25 (7.0 and 3.7 μM, respectively). Several compounds were tested in a pVASP cell-based assay, and for compounds with moderate permeability, good agreement was observed between the biochemical and functional assays. These compounds will function as efficient tools to further interrogate PKG1α biology.

Current trends and future perspectives for heart failure treatment leveraging cGMP modifiers and the practical effector PKG

Cyclic guanosine monophosphate (cGMP), an intracellular second messenger molecule synthesized by guanylated cyclases (GCs), controls various myocardial properties, including cell growth and survival, interstitial fibrosis, endothelial permeability, cardiac contractility, and cardiovascular remodeling. These processes are mediated by the main cGMP effector protein kinase G (PKG) activation of which exerts intrinsic protective responses against the adverse effects of neurohormonal stimulation and pathological cardiac stress. Therapeutic strategies that enhance cGMP levels and PKG activation have been used for heart failure, which can be executed by reducing natriuretic peptide (NP) proteolysis, enhancing cGMP synthesis, or blocking cGMP hydrolysis. Among these, reducing NP clearance with neprilysin inhibitor combined with angiotensin receptor blocker has been shown to greatly improve the prognosis of patients with heart failure with reduced ejection fraction (HFrEF) compared to the prognosis of patients on standard therapy using angiotensin-converting enzyme inhibitors. Moreover, in a recent phase III clinical trial, soluble GC-derived cGMP generation was shown to have potential efficacy in the management of HFrEF. Despite the clinical significance of cGMP/PKG signaling activated by either soluble or particulate GCs in heart failure, the differential signaling events downstream of intracellular cGMP, which are precisely controlled not only by PKG activation but also by the changes in its targeting and compartmentalization depending on the pathophysiology of heart disease, are not yet completely understood. Hitherto, the importance of the latter PKG regulatory mechanisms in developing therapeutic strategies has not been elucidated. Further investigation of redox-based PKG modulation will aid in the successful development of clinical therapies and could also lead to the establishment of improved personalized treatments for patients with heart failure.

Effect of Mitochondrial Antioxidant (Mito-TEMPO) on Burn-Induced Cardiac Dysfunction

BACKGROUND

Imbalance of oxidants/antioxidants results in heart failure, contributing to mortality after burn injury. Cardiac mitochondria are a prime source of reactive oxygen species (ROS), and a mitochondrial-specific antioxidant may improve burn-induced cardiomyopathy. We hypothesize that the mitochondrial-specific antioxidant, Triphenylphosphonium chloride (Mito-TEMPO), could protect cardiac function after burn.

STUDY DESIGN

Male rats had a 60% total body surface area (TBSA) scald burn injury and were treated with/without Mito-TEMPO (7 mg/kg-1, intraperitoneal) and harvested at 24 hours post-burn. Echocardiography (ECHO) was used for measurement of heart function. Masson Trichrome and hematoxylin and eosin (H & E) staining were used for cardiac fibrosis and immune response. Qualitative polymerase chain reaction (qPCR) was used for mitochondrial DNA replication and gene expression.

RESULTS

Burn-induced cardiac dysfunction, fibrosis, and mitochondrial damage were assessed by measurement of mitochondrial function, DNA replication, and DNA-encoded electron transport chain-related gene expression. Mito-TEMPO partially improved the abnormal parameters. Burn-induced cardiac dysfunction was associated with crosstalk between the NFE2L2-ARE pathway, PDE5A-PKG pathway, PARP1-POLG-mtDNA replication pathway, and mitochondrial SIRT signaling.

CONCLUSIONS

Mito-TEMPO reversed burn-induced cardiac dysfunction by rescuing cardiac mitochondrial dysfunction. Mitochondria-targeted antioxidants may be an effective therapy for burn-induced cardiac dysfunction.

Empagliflozin improves endothelial and cardiomyocyte function in human heart failure with preserved ejection fraction via reduced pro-inflammatory-oxidative pathways and protein kinase Gα oxidation

AIMS

Sodium-glucose-cotransporter-2 inhibitors showed favourable cardiovascular outcomes, but the underlying mechanisms are still elusive. This study investigated the mechanisms of empagliflozin in human and murine heart failure with preserved ejection fraction (HFpEF).

METHODS AND RESULTS

The acute mechanisms of empagliflozin were investigated in human myocardium from patients with HFpEF and murine ZDF obese rats, which were treated in vivo. As shown with immunoblots and ELISA, empagliflozin significantly suppressed increased levels of ICAM-1, VCAM-1, TNF-α, and IL-6 in human and murine HFpEF myocardium and attenuated pathological oxidative parameters (H2O2, 3-nitrotyrosine, GSH, lipid peroxide) in both cardiomyocyte cytosol and mitochondria in addition to improved endothelial vasorelaxation. In HFpEF, we found higher oxidative stress-dependent activation of eNOS leading to PKGIα oxidation. Interestingly, immunofluorescence imaging and electron microscopy revealed that oxidized PKG1α in HFpEF appeared as dimers/polymers localized to the outer-membrane of the cardiomyocyte. Empagliflozin reduced oxidative stress/eNOS-dependent PKGIα oxidation and polymerization resulting in a higher fraction of PKGIα monomers, which translocated back to the cytosol. Consequently, diminished NO levels, sGC activity, cGMP concentration, and PKGIα activity in HFpEF increased upon empagliflozin leading to improved phosphorylation of myofilament proteins. In skinned HFpEF cardiomyocytes, empagliflozin improved cardiomyocyte stiffness in an anti-oxidative/PKGIα-dependent manner. Monovariate linear regression analysis confirmed the correlation of oxidative stress and PKGIα polymerization with increased cardiomyocyte stiffness and diastolic dysfunction of the HFpEF patients.

CONCLUSION

Empagliflozin reduces inflammatory and oxidative stress in HFpEF and thereby improves the NO-sGC-cGMP-cascade and PKGIα activity via reduced PKGIα oxidation and polymerization leading to less pathological cardiomyocyte stiffness.

Plasma MIR-212-3p as a biomarker for acute right heart failure with pulmonary artery hypertension

Background

Acute right heart failure occurs in patients with pulmonary artery hypertension (PAH) with exposure to acute inflammation, the mortality rate is very high when right heart failure occurs. Biomarkers that can be used to detect acute right heart failure in patients with pulmonary hypertension need to be studied.

Methods

A PAH rat model was established using monocrotaline, and lipopolysaccharide was used to induce acute right heart failure. The Agilent rat miRNA microarray, Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were used to assess the microRNA expression of PAH rats. The expression of up- and downregulated miRNAs in plasma from PAH patients with acute right heart failure was validated with quantitative reverse transcription polymerase chain reaction (qRT-PCR). Then, the Wilcoxon matched paired test and receiver operating characteristic (ROC) curve analysis were performed.

Results

Thirty-three miRNAs were upregulated, and 7 miRNAs were downregulated in plasma of PAH rats with acute right heart failure. In the plasma of PAH patients, the miR-212-3p level was inversely correlated with the level of NT-pro BNP, and the area under the ROC curve was 0.751.

Conclusions

These results suggest that the reduction of the expression of MIR-212-3p may be a biomarker for PAH patients with right heart dysfunction.

Myocardial Phosphodiesterases and Their Role in cGMP Regulation

Cyclic nucleotide phosphodiesterases comprise an 11-member superfamily yielding near 100 isoform variants that hydrolyze cAMP or cGMP to their respective 5'-monophosphate form. Each plays a role in compartmentalized cyclic nucleotide signaling, with varying selectivity for each substrate, and conveying cell and intracellular-specific localized control. This review focuses on the 5 phosphodiesterases (PDEs) expressed in the cardiac myocyte capable of hydrolyzing cGMP and that have been shown to play a role in cardiac physiological and pathological processes. PDE1, PDE2, and PDE3 catabolize cAMP as well, whereas PDE5 and PDE9 are cGMP selective. PDE3 and PDE5 are already in clinical use, the former for heart failure, and PDE1, PDE9, and PDE5 are all being actively studied for this indication in patients. Research in just the past few years has revealed many novel cardiac influences of each isoform, expanding the therapeutic potential from their selective pharmacological blockade or in some instances, activation. PDE1C inhibition was found to confer cell survival protection and enhance cardiac contractility, whereas PDE2 inhibition or activation induces beneficial effects in hypertrophied or failing hearts, respectively. PDE3 inhibition is already clinically used to treat acute decompensated heart failure, although toxicity has precluded its long-term use. However, newer approaches including isoform-specific allosteric modulation may change this. Finally, inhibition of PDE5A and PDE9A counter pathological remodeling of the heart and are both being pursued in clinical trials. Here, we discuss recent research advances in each of these PDEs, their impact on the myocardium, and cardiac therapeutic potential.

cGMP Signaling and Modulation in Heart Failure

Cyclic GMP (cGMP) represents a classic intracellular second messenger molecule. Over the past 2 decades, important discoveries have identified that cGMP signaling becomes deranged in heart failure (HF) and that cGMP and its main kinase effector, protein kinase G, generally oppose the biological abnormalities contributing to HF, in experimental studies. These findings have influenced the design of clinical trials of cGMP-augmenting drugs in HF patients. At present, the trial results of cGMP-augmenting therapies in HF remain mixed. As detailed in this review, strong evidence now exists that protein kinase G opposes pathologic cardiac remodeling through regulation of diverse biological processes and myocardial substrates. Potential reasons for the failures of cGMP-augmenting drugs in HF may be related to biological mechanisms opposing cGMP or because of certain features of clinical trials, all of which are discussed.

Multiplicity of Nitric Oxide and Natriuretic Peptide Signaling in Heart Failure

Heart failure (HF) is a common consequence of several cardiovascular diseases and is understood as a vicious cycle of cardiac and hemodynamic decline. The current inventory of treatments either alleviates the pathophysiological features (eg, cardiac dysfunction, neurohumoral activation, and ventricular remodeling) and/or targets any underlying pathologies (eg, hypertension and myocardial infarction). Yet, since these do not provide a cure, the morbidity and mortality associated with HF remains high. Therefore, the disease constitutes an unmet medical need, and novel therapies are desperately needed. Cyclic guanosine-3',5'-monophosphate (cGMP), synthesized by nitric oxide (NO)- and natriuretic peptide (NP)-responsive guanylyl cyclase (GC) enzymes, exerts numerous protective effects on cardiac contractility, hypertrophy, fibrosis, and apoptosis. Impaired cGMP signaling, which can occur after GC deactivation and the upregulation of cyclic nucleotide-hydrolyzing phosphodiesterases (PDEs), promotes cardiac dysfunction. In this study, we review the role that NO/cGMP and NP/cGMP signaling plays in HF. After considering disease etiology, the physiological effects of cGMP in the heart are discussed. We then assess the evidence from preclinical models and patients that compromised cGMP signaling contributes to the HF phenotype. Finally, the potential of pharmacologically harnessing cardioprotective cGMP to rectify the present paucity of effective HF treatments is examined.

CHIP phosphorylation by protein kinase G enhances protein quality control and attenuates cardiac ischemic injury

Proteotoxicity from insufficient clearance of misfolded/damaged proteins underlies many diseases. Carboxyl terminus of Hsc70-interacting protein (CHIP) is an important regulator of proteostasis in many cells, having E3-ligase and chaperone functions and often directing damaged proteins towards proteasome recycling. While enhancing CHIP functionality has broad therapeutic potential, prior efforts have all relied on genetic upregulation. Here we report that CHIP-mediated protein turnover is markedly post-translationally enhanced by direct protein kinase G (PKG) phosphorylation at S20 (mouse, S19 human). This increases CHIP binding affinity to Hsc70, CHIP protein half-life, and consequent clearance of stress-induced ubiquitinated-insoluble proteins. PKG-mediated CHIP-pS20 or expressing CHIP-S20E (phosphomimetic) reduces ischemic proteo- and cytotoxicity, whereas a phospho-silenced CHIP-S20A amplifies both. In vivo, depressing PKG activity lowers CHIP-S20 phosphorylation and protein, exacerbating proteotoxicity and heart dysfunction after ischemic injury. CHIP-S20E knock-in mice better clear ubiquitinated proteins and are cardio-protected. PKG activation provides post-translational enhancement of protein quality control via CHIP.

Transcriptional signatures regulated by TRPC1/C4-mediated Background Ca2+ entry after pressure-overload induced cardiac remodelling

AIMS

After summarizing current concepts for the role of TRPC cation channels in cardiac cells and in processes triggered by mechanical stimuli arising e.g. during pressure overload, we analysed the role of TRPC1 and TRPC4 for background Ca²⁺ entry (BGCE) and for cardiac pressure overload induced transcriptional remodelling.

METHODS AND RESULTS

Mn²⁺-quench analysis in cardiomyocytes from several Trpc-deficient mice revealed that both TRPC1 and TRPC4 are required for BGCE. Electrically-evoked cell shortening of cardiomyocytes from TRPC1/C4-DKO mice was reduced, whereas parameters of cardiac contractility and relaxation assessed in vivo were unaltered. As pathological cardiac remodelling in mice depends on their genetic background, and the development of cardiac remodelling was found to be reduced in TRPC1/C4-DKO mice on a mixed genetic background, we studied TRPC1/C4-DKO mice on a C57BL6/N genetic background. Cardiac hypertrophy was reduced in those mice after chronic isoproterenol infusion (-51.4%) or after one week of transverse aortic constriction (TAC; -73.0%). This last manoeuvre was preceded by changes in the pressure overload induced transcriptional program as analysed by RNA sequencing. Genes encoding specific collagens, the Mef2 target myomaxin and the gene encoding the mechanosensitive channel Piezo2 were up-regulated after TAC in wild type but not in TRPC1/C4-DKO hearts.

CONCLUSIONS

Deletion of the TRPC1 and TRPC4 channel proteins protects against development of pathological cardiac hypertrophy independently of the genetic background. To determine if the TRPC1/C4-dependent changes in the pressure overload induced alterations in the transcriptional program causally contribute to cardio-protection needs to be elaborated in future studies.

The molecular mechanisms associated with the physiological responses to inflammation and oxidative stress in cardiovascular diseases

The complex physiological signal transduction networks that respond to the dual challenges of inflammatory and oxidative stress are major factors that promote the development of cardiovascular pathologies. These signaling networks contribute to the development of age-related diseases, suggesting crosstalk between the development of aging and cardiovascular disease. Inhibition and/or attenuation of these signaling networks also delays the onset of disease. Therefore, a concept of targeting the signaling networks that are involved in inflammation and oxidative stress may represent a novel treatment paradigm for many types of heart disease. In this review, we discuss the molecular mechanisms associated with the physiological responses to inflammation and oxidative stress especially in heart failure with preserved ejection fraction and emphasize the nature of the crosstalk of these signaling processes as well as possible therapeutic implications for cardiovascular medicine.

Sildenafil Recovers Burn-Induced Cardiomyopathy

Background: Severe burn injury initiates a feedback cycle of inflammation, fibrosis, oxidative stress and cardiac mitochondrial damage via the PDE5A-cGMP-PKG pathway. Aim: To test if the PDE5A-cGMP-PKG pathway may contribute to burn-induced heart dysfunction. Methods: Sprague–Dawley rats were divided four groups: sham; sham/sildenafil; 24 h post burn (60% total body surface area scald burn, harvested at 24 h post burn); and 24 h post burn/sildenafil. We monitored heart function and oxidative adducts, as well as cardiac inflammatory, cardiac fibrosis and cardiac remodeling responses in vivo. Results: Sildenafil inhibited the burn-induced PDE5A mRNA level and increased the cGMP level and PKG activity, leading to the normalization of PKG down-regulated genes (IRAG, PLB, RGS2, RhoA and MYTP), a decreased ROS level (H2O2), decreased oxidatively modified adducts (malonyldialdehyde [MDA], carbonyls), attenuated fibrogenesis as well as fibrosis gene expression (ANP, BNP, COL1A2, COL3A2, αSMA and αsk-Actin), and reduced inflammation and related gene expression (RELA, IL-18 and TGF-β) after the burn. Additionally, sildenafil treatment preserved left ventricular heart function (CO, EF, SV, LVvol at systolic, LVPW at diastolic and FS) and recovered the oxidant/antioxidant balance (total antioxidant, total SOD activity and Cu,ZnSOD activity). Conclusions: The PDE5A-cGMP-PKG pathway mediates burn-induced heart dysfunction. Sildenafil treatment recovers burn-induced cardiac dysfunction.

Sildenafil Recovers Burn-Induced Cardiomyopathy

Background: Severe burn injury initiates a feedback cycle of inflammation, fibrosis, oxidative stress and cardiac mitochondrial damage via the PDE5A-cGMP-PKG pathway. Aim: To test if the PDE5A-cGMP-PKG pathway may contribute to burn-induced heart dysfunction. Methods: Sprague–Dawley rats were divided four groups: sham; sham/sildenafil; 24 h post burn (60% total body surface area scald burn, harvested at 24 h post burn); and 24 h post burn/sildenafil. We monitored heart function and oxidative adducts, as well as cardiac inflammatory, cardiac fibrosis and cardiac remodeling responses in vivo. Results: Sildenafil inhibited the burn-induced PDE5A mRNA level and increased the cGMP level and PKG activity, leading to the normalization of PKG down-regulated genes (IRAG, PLB, RGS2, RhoA and MYTP), a decreased ROS level (H2O2), decreased oxidatively modified adducts (malonyldialdehyde [MDA], carbonyls), attenuated fibrogenesis as well as fibrosis gene expression (ANP, BNP, COL1A2, COL3A2, αSMA and αsk-Actin), and reduced inflammation and related gene expression (RELA, IL-18 and TGF-β) after the burn. Additionally, sildenafil treatment preserved left ventricular heart function (CO, EF, SV, LVvol at systolic, LVPW at diastolic and FS) and recovered the oxidant/antioxidant balance (total antioxidant, total SOD activity and Cu,ZnSOD activity). Conclusions: The PDE5A-cGMP-PKG pathway mediates burn-induced heart dysfunction. Sildenafil treatment recovers burn-induced cardiac dysfunction.

PKG1α Cysteine-42 Redox State Controls mTORC1 Activation in Pathological Cardiac Hypertrophy

RATIONALE

Stimulated PKG1α (protein kinase G-1α) phosphorylates TSC2 (tuberous sclerosis complex 2) at serine 1365, potently suppressing mTORC1 (mechanistic [mammalian] target of rapamycin complex 1) activation by neurohormonal and hemodynamic stress. This reduces pathological hypertrophy and dysfunction and increases autophagy. PKG1α oxidation at cysteine-42 is also induced by these stressors, which blunts its cardioprotective effects.

OBJECTIVE

We tested the dependence of mTORC1 activation on PKG1α C42 oxidation and its capacity to suppress such activation by soluble GC-1 (guanylyl cyclase 1) activation.

METHODS AND RESULTS

Cardiomyocytes expressing wild-type (WT) PKG1α (PKG1α^WT) or cysteine-42 to serine mutation redox-dead (PKG1α^CS/CS) were exposed to ET-1 (endothelin 1). Cells expressing PKG1α^WT exhibited substantial mTORC1 activation (p70 S6K [p70 S6 kinase], 4EBP1 [elF4E binding protein-1], and Ulk1 [Unc-51-like kinase 1] phosphorylation), reduced autophagy/autophagic flux, and abnormal protein aggregation; all were markedly reversed by PKG1α^CS/CS expression. Mice with global knock-in of PKG1α^CS/CS subjected to pressure overload (PO) also displayed markedly reduced mTORC1 activation, protein aggregation, hypertrophy, and ventricular dysfunction versus PO in PKG1α^WT mice. Cardioprotection against PO was equalized between groups by co-treatment with the mTORC1 inhibitor everolimus. TSC2-S1365 phosphorylation increased in PKG1α^CS/CS more than PKG1α^WT myocardium following PO. TSC2^{S1365A/S1365A} (TSC2 S1365 phospho-null, created by a serine to alanine mutation) knock-in mice lack TSC2 phosphorylation by PKG1α, and when genetically crossed with PKG1α^CS/CS mice, protection against PO-induced mTORC1 activation, cardiodepression, and mortality in PKG1α^CS/CS mice was lost. Direct stimulation of GC-1 (BAY-602770) offset disparate mTORC1 activation between PKG1α^WT and PKG1α^CS/CS after PO and blocked ET-1 stimulated mTORC1 in TSC2^S1365A-expressing myocytes.

CONCLUSIONS

Oxidation of PKG1α at C42 reduces its phosphorylation of TSC2, resulting in amplified PO-stimulated mTORC1 activity and associated hypertrophy, dysfunction, and depressed autophagy. This is ameliorated by direct GC-1 stimulation.

Exercise-Induced Regulation of Redox Status in Cardiovascular Diseases: The Role of Exercise Training and Detraining

Although low levels of reactive oxygen species (ROS) are beneficial for the organism ensuring normal cell and vascular function, the overproduction of ROS and increased oxidative stress levels play a significant role in the onset and progression of cardiovascular diseases (CVDs). This paper aims at providing a thorough review of the available literature investigating the effects of acute and chronic exercise training and detraining on redox regulation, in the context of CVDs. An acute bout of either cardiovascular or resistance exercise training induces a transient oxidative stress and inflammatory response accompanied by reduced antioxidant capacity and enhanced oxidative damage. There is evidence showing that these responses to exercise are proportional to exercise intensity and inversely related to an individual’s physical conditioning status. However, when chronically performed, both types of exercise amplify the antioxidant defense mechanism, reduce oxidative stress and preserve redox status. On the other hand, detraining results in maladaptations within a time-frame that depends on the exercise training intensity and mode, as high-intensity training is superior to low-intensity and resistance training is superior to cardiovascular training in preserving exercise-induced adaptations during detraining periods. Collectively, these findings suggest that exercise training, either cardiovascular or resistance or even a combination of them, is a promising, safe and efficient tool in the prevention and treatment of CVDs.

Cardiomyocyte Sirt (Sirtuin) 7 Ameliorates Stress-Induced Cardiac Hypertrophy by Interacting With and Deacetylating GATA4

Sirt (Sirtuin) 7, the most recently identified mammalian sirtuin, has been shown to contribute to appropriate wound healing processes after acute cardiovascular insult. However, its role in the development of cardiac remodeling after pressure overload is unclear. Cardiomyocyte-specific Sirt7-knockout and control mice were subjected to pressure overload induced by transverse aortic constriction. Cardiac hypertrophy and functions were then examined in these mice. Sirt7 protein expression was increased in myocardial tissue after pressure overload. Transverse aortic constriction-induced increases in heart weight/tibial length were significantly augmented in cardiomyocyte-specific Sirt7-knockout mice compared with those of control mice. Histological analysis showed that the cardiomyocyte cross-sectional area and fibrosis area were significantly larger in cardiomyocyte-specific Sirt7-deficient mice. Cardiac contractile functions were markedly decreased in cardiomyocyte-specific Sirt7-deficient mice. Mechanistically, we found that Sirt7 interacted directly with GATA4 and that the exacerbation of phenylephrine-induced cardiac hypertrophy by Sirt7 knockdown was decreased by GATA4 knockdown. Sirt7 deacetylated GATA4 in cardiomyocytes and regulated its transcriptional activity. Interestingly, we demonstrated that treatment with nicotinamide mononucleotide, a known key NAD⁺ intermediate, ameliorated agonist-induced cardiac hypertrophies in a Sirt7-dependent manner in vitro. Sirt7 deficiency in cardiomyocytes promotes cardiomyocyte hypertrophy in response to pressure overload. Sirt7 exerts its antihypertrophic effect by interacting with and promoting deacetylation of GATA4.

Prevention of PKG-1α Oxidation Suppresses Antihypertrophic/Antifibrotic Effects From PDE5 Inhibition but not sGC Stimulation

BACKGROUND

Stimulation of sGC (soluble guanylate cyclase) or inhibition of PDE5 (phosphodiesterase type 5) activates PKG (protein kinase G)-1α to counteract cardiac hypertrophy and failure. PKG1α acts within localized intracellular domains; however, its oxidation at cysteine 42, linking homomonomers, alters this localization, impairing suppression of pathological cardiac stress. Because PDE5 and sGC reside in separate microdomains, we speculated that PKG1α oxidation might also differentially influence the effects from their pharmacological modulation.

METHODS AND RESULTS

Knock-in mice expressing a redox-dead PKG1α (PKG1α^C42S) or littermate controls (PKG1α^WT) were subjected to transaortic constriction to induce pressure overload and treated with a PDE5 inhibitor (sildenafil), sGC activator (BAY602770 [BAY]), or vehicle. In PKG1α^WT controls, sildenafil and BAY similarly enhanced PKG activity and reduced pathological hypertrophy/fibrosis and cardiac dysfunction after transaortic constriction. However, sildenafil failed to protect the heart in PKG1α^C42S, unlike BAY, which activated PKG and thereby facilitated protective effects. This corresponded with minimal PDE5 activation in PKG1α^C42S exposed to transaortic constriction versus higher activity in controls and little colocalization of PDE5 with PKG1α^C42S (versus colocalization with PKG1α^WT) in stressed myocytes.

CONCLUSIONS

In the stressed heart and myocytes, PKG1α C42-disulfide formation contributes to PDE5 activation. This augments the pathological role of PDE5 and so in turn enhances the therapeutic impact from its inhibition. PKG1α oxidation does not change the benefits from sGC activation. This finding favors the use of sGC activators regardless of PKG1α oxidation and may help guide precision therapy leveraging the cyclic GMP/PKG pathway to treat heart disease.

Redox-Dependent Regulation of Sulfur Metabolism in Biomolecules: Implications for Cardiovascular Health

SIGNIFICANCE

Sulfur-containing amino acids are integral to the molecular mechanisms that underlie many aspects of cellular function and homeostasis, facilitated by reversible changes in the oxidation states of sulfur atoms. Sulfur-containing amino acids are metabolically linked by interacting pathways that impact the one-carbon metabolic cycle and generation of methyl groups, the folate cycle, and maintenance of the major cellular redox buffer; glutathione. Dysregulation of these pathways is associated with diverse pathologies, notably of the cardiovascular (CV) system, which are typically characterized by inappropriate plasma levels of sulfur-containing amino acids. Recent Advances: Perhaps not surprisingly, the cellular redox state has emerged as a major regulator of many enzymatic processes within these metabolic cycles. The metabolism of cysteine can also result in the production of hydrogen sulfide (H₂S), a signaling molecule whose activity is potentially linked to intracellular levels of both reactive oxygen species (ROS) and molecular oxygen.

CRITICAL ISSUES

In most cases, the endogenous physiological sources of ROS that might mediate the interlinked metabolic pathways of sulfur-containing biomolecules remain unknown. However, the family of NADPH oxidases, and Nox4 in particular, is emerging as a likely candidate.

FUTURE DIRECTIONS

This review focuses on the current knowledge of key aspects of sulfur metabolism, which are regulated by redox-based chemical reactions, and the likely intracellular oxidant sources that might mediate this regulation. This knowledge will be important to guide future targeted therapeutic interventions in diverse CV disorders.

PKG1-modified TSC2 regulates mTORC1 activity to counter adverse cardiac stress

The mechanistic target of rapamycin complex-1 (mTORC1) coordinates regulation of growth, metabolism, protein synthesis, and autophagy¹. Its hyper-activation contributes to disease in many organs including the heart^1,2, though broad mTORC1 inhibition risks interference with its homeostatic roles. Tuberin (TSC2) is a GTPase-activating protein and prominent intrinsic regulator of mTORC1 by modulating Rheb (Ras homolog enriched in brain). TSC2 constitutively inhibits mTORC1, but this activity is modified by phosphorylation from multiple signaling kinases to in turn inhibit (AMPK, GSK3β) or stimulate (Akt, ERK, RSK-1) mTORC1 activity^3–9. Each kinase requires engagement of multiple serines, impeding analysis of their role in vivo. Here, we reveal phosphorylation or gain-or-loss of function mutations at either of two adjacent serines in TSC2 (S1365/1366 mouse; 1364/1365 human), with no prior known function, is sufficient to bi-directionally potently control growth-factor and hemodynamic-stress stimulated mTORC1 activity and consequent cell growth and autophagy. Basal mTORC1 activity, however, is unchanged. In heart, myocytes, and fibroblasts, phosphorylation occurs by protein kinase G (PKG), a primary effector of nitric oxide and natriuretic peptide signaling whose activation is protective against heart disease^10–13. PKG suppression of hypertrophy and stimulation of autophagy in myocytes requires TSC2 phosphorylation. Homozygous knock-in (KI) mice expressing a phospho-silenced TSC2 (S1365A) mutation develop far worse heart disease and mortality from sustained pressure-overload (PO) due to hyperactive mTORC1 that cannot be rescued by PKG stimulation. Heterozygote SA-KI are rescued, and KI-mice expressing a phospho-mimetic (S1365E) mutation are protected. Neither KI model alters resting mTORC1 activity. Thus, TSC2 phosphorylation is both required and sufficient for PKG-mediated cardiac protection against pressure-overload. These newly identified serines provide a genetic tool to bi-directionally regulate the amplitude of stress-stimulated mTORC1 activity.

PKG1α oxidation negatively regulates food seeking behaviour and reward

Genes that are highly conserved in food seeking behaviour, such as protein kinase G (PKG), are of interest because of their potential role in the global obesity epidemic. PKG1α can be activated by binding of cyclic guanosine monophosphate (cGMP) or oxidant-induced interprotein disulfide bond formation between the two subunits of this homodimeric kinase. PKG1α activation by cGMP plays a role in reward and addiction through its actions in the ventral tegmental area (VTA) of the brain. ‘Redox dead’ C42S PKG1α knock-in (KI) mice, which are fully deficient in oxidant-induced disulfide-PKG1α formation, display increased food seeking and reward behaviour compared to wild-type (WT) littermates. Rewarding monoamines such as dopamine, which are released during feeding, are metabolised by monoamine oxidase to generate hydrogen peroxide that was shown to mediate PKG1α oxidation. Indeed, inhibition of monoamine oxidase, which prevents it producing hydrogen peroxide, attenuated PKG1α oxidation and increased sucrose preference in WT, but not KI mice. The deficient reward phenotype of the KI mice was rescued by expressing WT kinase that can form the disulfide state in the VTA using an adeno-associated virus, consistent with PKG1α oxidation providing a break on feeding behaviour. In conclusion, disulfide-PKG1α in VTA neurons acts as a negative regulator of feeding and therefore may provide a novel therapeutic target for obesity.

Identify Cross Talk Between Circadian Rhythm and Coronary Heart Disease by Multiple Correlation Analysis

Disorder in circadian rhythm has been revealed as a risk factor for coronary heart disease. Several studies in molecular biology established a gene interaction network using coronary heart susceptibility genes and the circadian rhythm pathway. However, cross talk between genes was mostly discovered in single gene pairs. There might be combination sets of genes intergraded as a unit to regulate the network. To resolve multiple variables in coronary heart susceptibility genes controlling circadian rhythm pathways, a multiple correlation analysis was applied to the transcriptome. Nine genes, including CUGBP, Elav-like family member (CELF); sodium leak channel, nonselective (NALCN); protein phosphatase 2 regulatory subunit B gamma (PPP2R2C); tubulin alpha 1c (TUBA1C); microtubule-associated protein 4 (MAP4); cofilin 1 (CFL1); myosin heavy chain 7 (MYH7); QKI, KH domain containing RNA binding (QKI); and maternal embryonic leucine zipper kinase (MELK), from coronary heart susceptibility were identified to predict the outcome of a linear combination of circadian rhythm pathway genes with R factor more than 0.7. G protein subunit alpha o1 (GNAO1), protein kinase C gamma (PRKCG), RBX, and G protein subunit beta 1 (GNB1) in the circadian rhythm pathway are characterized as combination variables to coexpress with coronary heart susceptibility genes.

Cysteine-Based Redox Sensing and Its Role in Signaling by Cyclic Nucleotide-Dependent Kinases in the Cardiovascular System

Oxidant molecules are produced in biological systems and historically have been considered causal mediators of damage and disease. While oxidants may contribute to the pathogenesis of disease, evidence continues to emerge that shows these species also play important regulatory roles in health. A major mechanism of oxidant sensing and signaling involves their reaction with reactive cysteine thiols within proteins, inducing oxidative posttranslational modifications that can couple to altered function to enable homeostatic regulation. Protein kinase A and protein kinase G are regulated by oxidants in this way, and this review focuses on our molecular-level understanding of these events and their role in regulating cardiovascular physiology during health and disease.

Oxidation of cysteine 117 stimulates constitutive activation of the type Iα cGMP-dependent protein kinase

The type I cGMP-dependent protein kinase (PKG I) is an essential regulator of vascular tone. It has been demonstrated that the type Iα isoform can be constitutively activated by oxidizing conditions. However, the amino acid residues implicated in this phenomenon are not fully elucidated. To investigate the molecular basis for this mechanism, we studied the effects of oxidation using recombinant WT, truncated, and mutant constructs of PKG I. Using an in vitro assay, we observed that oxidation with hydrogen peroxide (H₂O₂) resulted in constitutive, cGMP-independent activation of PKG Iα. PKG Iα C42S and a truncation construct that does not contain Cys-42 (Δ53) were both constitutively activated by H₂O₂ In contrast, oxidation of PKG Iα C117S maintained its cGMP-dependent activation characteristics, although oxidized PKG Iα C195S did not. To corroborate these results, we also tested the effects of our constructs on the PKG Iα-specific substrate, the large conductance potassium channel (K_Ca 1.1). Application of WT PKG Iα activated by either cGMP or H₂O₂ increased the open probabilities of the channel. Neither cGMP nor H₂O₂ activation of PKG Iα C42S significantly increased channel open probabilities. Moreover, cGMP-stimulated PKG Iα C117S increased K_Ca 1.1 activity, but this effect was not observed under oxidizing conditions. Finally, we observed that PKG Iα C42S caused channel flickers, indicating dramatically altered K_Ca 1.1 channel characteristics compared with channels exposed to WT PKG Iα. Cumulatively, these results indicate that constitutive activation of PKG Iα proceeds through oxidation of Cys-117 and further suggest that the formation of a sulfur acid is necessary for this phenotype.

A concise discussion of the regulatory role of cGMP kinase I in cardiac physiology and pathology

The underlying cause of cardiac hypertrophy, fibrosis, and heart failure has been investigated in great detail using different mouse models. These studies indicated that cGMP and cGMP-dependent protein kinase type I (cGKI) may ameliorate these negative phenotypes in the adult heart. Recently, evidence has been published that cardiac mitochondrial BKCa channels are a target for cGKI and that activation of mitoBKCa channels may cause some of the positive effects of conditioning in ischemia/reperfusion injury. It will be pointed out that most studies could not present convincing evidence that it is the cGMP level and the activity cGKI in specific cardiac cells that reduces hypertrophy or heart failure. However, anti-fibrotic compounds stimulating nitric oxide-sensitive guanylyl cyclase may be an upcoming therapy for abnormal cardiac remodeling.

Establishing a Split Luciferase Assay for Proteinkinase G (PKG) Interaction Studies

Nitric oxide (NO/cyclic guanosine monophosphate (cGMP)-regulated cellular mechanisms are involved in a variety of (patho-) physiological processes. One of the main effector molecules in this system, proteinkinase G (PKG), serves as a molecular switch by phosphorylating different target proteins and thereby turning them on or off. To date, only a few interaction partners of PKG have been described although the identification of protein–protein interactions (PPI) is indispensable for the understanding of cellular processes and diseases. Conventionally used methods to detect PPIs exhibit several disadvantages, e.g., co-immunoprecipitations, which depend on suitable high-affinity antibodies. Therefore, we established a cell-based protein-fragment complementation assay (PCA) for the identification of PKG target proteins. Here, a reporter protein (click beetle luciferase) is split into two fragments and fused to two different possible interaction partners. If interaction occurs, the reporter protein is functionally complemented and the catalyzed reaction can then be quantitatively measured. By using this technique, we confirmed the regulator of G-Protein signaling 2 (RGS2) as an interaction partner of PKGIα (a PKG-isoform) following stimulation with 8-Br-cGMP and 8-pCPT-cGMP. Hence, our results support the conclusion that the established approach could serve as a novel tool for the rapid, easy and cost-efficient detection of novel PKG target proteins.

Reactive Oxygen Species as Intracellular Signaling Molecules in the Cardiovascular System

BACKGROUND

Redox signaling plays an important role in the lives of cells. This signaling not only becomes apparent in pathologies but is also thought to be involved in maintaining physiological homeostasis. Reactive Oxygen Species (ROS) can activate protein kinases: CaMKII, PKG, PKA, ERK, PI3K, Akt, PKC, PDK, JNK, p38. It is unclear whether it is a direct interaction of ROS with these kinases or whether their activation is a consequence of inhibition of phosphatases. ROS have a biphasic effect on the transport of Ca2+ in the cell: on one hand, they activate the sarcoplasmic reticulum Ca2+-ATPase, which can reduce the level of Ca2+ in the cell, and on the other hand, they can inactivate Ca2+-ATPase of the plasma membrane and open the cation channels TRPM2, which promote Ca2+-loading and subsequent apoptosis. ROS inhibit the enzyme PHD2, which leads to the stabilization of HIF-α and the formation of the active transcription factor HIF.

CONCLUSION

Activation of STAT3 and STAT5, induced by cytokines or growth factors, may include activation of NADPH oxidase and enhancement of ROS production. Normal physiological production of ROS under the action of cytokines activates the JAK/STAT while excessive ROS production leads to their inhibition. ROS cause the activation of the transcription factor NF-κB. Physiological levels of ROS control cell proliferation and angiogenesis. ROS signaling is also involved in beneficial adaptations to survive ischemia and hypoxia, while further increases in ROS can trigger programmed cell death by the mechanism of apoptosis or autophagy. ROS formation in the myocardium can be reduced by moderate exercise.

Targeting Mitochondrial Calcium Handling and Reactive Oxygen Species in Heart Failure

PURPOSE OF REVIEW

In highly prevalent cardiac diseases, new therapeutic approaches are needed. Since the first description of oxidative stress in heart failure, reactive oxygen species (ROS) have been considered as attractive drug targets. Though clinical trials evaluating antioxidant vitamins as ROS-scavenging agents yielded neutral results in patients at cardiovascular risk, the knowledge of ROS as pathophysiological factors has considerably advanced in the past few years and led to novel treatment approaches. Here, we review recent new insights and current strategies in targeting mitochondrial calcium handling and ROS in heart failure.

RECENT FINDINGS

Mitochondria are an important ROS source, and more recently, drug development focused on targeting mitochondria (e.g. by SS-31 or MitoQ). Important advancement has also been made to decipher how the matching of energy supply and demand through calcium (Ca²⁺) handling impacts on mitochondrial ROS production and elimination. This opens novel opportunities to ameliorate mitochondrial dysfunction in heart failure by targeting cytosolic and mitochondrial ion transporters to improve this matching process. According to this approach, highly specific substances as the preclinical CGP-37157, as well as the clinically used ranolazine and empagliflozin, provide promising results on different levels of evidence. Furthermore, the understanding of redox signalling relays, resembled by catalyst-mediated protein oxidation, is about to change former paradigms of ROS signalling. Novel methods, as redox proteomics, allow to precisely analyse key regulatory thiol switches, which may induce adaptive or maladaptive signalling. Additionally, the generation of genetically encoded probes increased the spatial and temporal resolution of ROS imaging and opened a new methodological window to subtle, formerly obscured processes. These novel insights may broaden our understanding of why previous attempts to target oxidative stress have failed, and at the same time provide us with new targets for drug development.

Newly Identified NO-Sensor Guanylyl Cyclase/Connexin 43 Association Is Involved in Cardiac Electrical Function

BACKGROUND

Guanylyl cyclase, a heme-containing α1β1 heterodimer (GC1), produces cGMP in response to Nitric oxide (NO) stimulation. The NO-GC1-cGMP pathway negatively regulates cardiomyocyte contractility and protects against cardiac hypertrophy-related remodeling. We recently reported that the β1 subunit of GC1 is detected at the intercalated disc with connexin 43 (Cx43). Cx43 forms gap junctions (GJs) at the intercalated disc that are responsible for electrical propagation. We sought to determine whether there is a functional association between GC1 and Cx43 and its role in cardiac homeostasis.

METHODS AND RESULTS

GC1 and Cx43 immunostaining at the intercalated disc and coimmunoprecipitation from membrane fraction indicate that GC1 and Cx43 are associated. Mice lacking the α subunit of GC1 (GCα1 knockout mice) displayed a significant decrease in GJ function (dye-spread assay) and Cx43 membrane lateralization. In a cardiac-hypertrophic model, angiotensin II treatment disrupted the GC1-Cx43 association and induced significant Cx43 membrane lateralization, which was exacerbated in GCα1 knockout mice. Cx43 lateralization correlated with decreased Cx43-containing GJs at the intercalated disc, predictors of electrical dysfunction. Accordingly, an ECG revealed that angiotensin II-treated GCα1 knockout mice had impaired ventricular electrical propagation. The phosphorylation level of Cx43 at serine 365, a protein-kinase A upregulated site involved in trafficking/assembly of GJs, was decreased in these models.

CONCLUSIONS

GC1 modulates ventricular Cx43 location, hence GJ function, and partially protects from electrical dysfunction in an angiotensin II hypertrophy model. Disruption of the NO-cGMP pathway is associated with cardiac electrical disturbance and abnormal Cx43 phosphorylation. This previously unknown NO/Cx43 signaling could be a protective mechanism against stress-induced arrhythmia.

Dioxygen and Metabolism; Dangerous Liaisons in Cardiac Function and Disease

The heart must consume a significant amount of energy to sustain its contractile activity. Although the fuel demands are huge, the stock remains very low. Thus, in order to supply its daily needs, the heart must have amazing adaptive abilities, which are dependent on dioxygen availability. However, in myriad cardiovascular diseases, “fuel” depletion and hypoxia are common features, leading cardiomyocytes to favor low-dioxygen-consuming glycolysis rather than oxidation of fatty acids. This metabolic switch makes it challenging to distinguish causes from consequences in cardiac pathologies. Finally, despite the progress achieved in the past few decades, medical treatments have not improved substantially, either. In such a situation, it seems clear that much remains to be learned about cardiac diseases. Therefore, in this review, we will discuss how reconciling dioxygen availability and cardiac metabolic adaptations may contribute to develop full and innovative strategies from bench to bedside.

Examining a role for PKG Iα oxidation in the pathogenesis of cardiovascular dysfunction during diet-induced obesity

BACKGROUND

Protein kinase G (PKG) Iα is the end-effector kinase that mediates nitric oxide (NO)-dependent and oxidant-dependent vasorelaxation to maintain blood pressure during health. A hallmark of cardiovascular disease is attenuated NO production, which in part is caused by NO Synthase (NOS) uncoupling, which in turn increases oxidative stress because of superoxide generation. NOS uncoupling promotes PKG Iα oxidation to the interprotein disulfide state, likely mediated by superoxide-derived hydrogen peroxide, and because the NO-cyclic guanosine monophosphate (cGMP) pathway otherwise negatively regulates oxidation of the kinase to its active disulfide dimeric state. Diet-induced obesity is associated with NOS uncoupling, which may in part contribute to the associated cardiovascular dysfunction due to exacerbated PKG Iα disulfide oxidation to the disulfide state. This is a rational hypothesis because PKG Iα oxidation is known to significantly contribute to heart failure that arises from chronic myocardial oxidative stress.

METHODS AND RESULTS

Bovine arterial endothelial cells (BAECs) or smooth muscle cells (SMCs) were exposed to drugs that uncouple NOS. These included 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) which promotes its S-glutathiolation, 4-diamino-6-hydroxy-pyrimidine (DAHP) which inhibits guanosine-5'-triphosphate-cyclohydrolase 2 to prevent BH4 synthesis or methotrexate (MTX) which inhibits the regeneration of BH4 from BH2 by dihydrofolate reductase. While all the drugs mentioned above induced robust PKG Iα disulfide dimerization in cells, exposure of BAECs to NOS inhibitor L-NMMA did not. Increased PKG Iα disulfide formation occurred in hearts and aortae from mice treated in vivo with DAHP (10mM in a drinking water for 3 weeks). Redox-dead C42S PKG Iα knock-in (KI) mice developed less pronounced cardiac posterior wall hypertrophy and did not develop cardiac dysfunction, assessed by echocardiography, compared to the wild-type (WT) mice after chronic DAHP treatment. WT or KI mice were then subjected to a diet-induced obesity protocol by feeding them with a high fat Western-type diet (RM 60% AFE) for 27 weeks, which increased body mass, adiposity, plasma leptin, resistin and glucagon levels comparably in each genotype. Obesity-induced hypertension, assessed by radiotelemetry, was mild and transient in the WT, while the basally hypertensive KI mice were resistant to further increases in blood pressure following high fat feeding. Although the obesogenic diet caused mild cardiac dysfunction in the WT but not the KI mice, gross changes in myocardial structure monitored by echocardiography were not apparent in either genotype. The level of cyclic guanosine monophosphate (cGMP) was decreased in the aortae of WT and KI mice following high fat feeding. PKG Iα oxidation was not evident in the hearts of WT mice fed a high fat diet.

CONCLUSIONS

Despite robust evidence for PKG Iα oxidation during NOS uncoupling in cell models, it is unlikely that PKG Iα oxidation occurs to a significant extent in vivo during diet-induced obesity and so is unlikely to mediate the associated cardiovascular dysfunction.

Proof of Principle for a Novel Class of Antihypertensives That Target the Oxidative Activation of PKG Iα (Protein Kinase G Iα)

Arterial hypertension continues to be a major health burden. Development of new antihypertensive drugs that engage vasodilatory mechanisms not harnessed by available therapies offer therapeutic potential. Oxidants induce an interprotein disulfide in PKG Iα (protein kinase G Iα) at C42, which is associated with its targeting and activation, resulting in vasodilation and blood pressure lowering. Consequently, we developed an assay and screened for electrophilic drugs that activate PKG Iα by selectively targeting C42, as such compounds have potential as novel antihypertensives with a mechanism of action that differs from current therapies. In this way, a drug that we termed G1 was identified, which targets C42 of PKG Iα to induce vasodilation of isolated resistance blood vessels and blood pressure lowering in a mouse model of angiotensin II-induced hypertension. In contrast, these antihypertensive effects were deficient in angiotensin II-induced hypertensive C42S PKG Iα knockin mice. These transgenic mice were engineered to have the reactive cysteinyl thiol replaced with a hydroxyl so that it cannot react with endogenous vasodilatory oxidants or electrophiles such as drug G1. These studies, therefore, provide validation of PKG Iα C42 as the target of G1, as well as proof-of-principle for a new class of antihypertensive drugs that have potential for further development for clinical use in humans.