Stress-dependent dilated cardiomyopathy in mice with cardiomyocyte-restricted inactivation of cyclic GMP-dependent protein kinase I

Nonpharmacological Approaches to Managing Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is a common subtype of heart failure marked by impaired left ventricular diastolic function and decreased myocardial compliance. Given the limited availability of evidence-based pharmacological treatments for HFpEF, there is a growing interest in nonpharmacological interventions as viable therapeutic alternatives. This review aims to explore the pathophysiology of HFpEF and present recent advancements in nonpharmacological management approaches, encompassing noninvasive therapies, invasive procedures and targeted treatments for comorbidities. An extensive literature review was undertaken to identify and synthesize emerging nonpharmacological treatment options for HFpEF, assessing their potential to enhance patient outcomes. Nonpharmacological strategies, such as vagus nerve stimulation, percutaneous pulmonary artery denervation, renal denervation, transcatheter insertion of atrial shunts and pericardial resection, demonstrate promising potential for alleviating HFpEF symptoms and improving patient prognosis. Moreover, addressing comorbidities, such as hypertension and diabetes, may offer additional therapeutic benefits. These cutting-edge techniques, in conjunction with well-established exercise therapies, pave the way for future research and clinical applications in the field. Nonpharmacological interventions hold promise for advancing HFpEF patient care and fostering a deeper understanding of these treatment approaches, which will facilitate new clinical applications and contribute to the development of more targeted therapies.

Evaluating the impact of Sacubitril/valsartan on diastolic function in patients with heart failure: A systematic review and meta-analysis

BACKGROUND

Heart failure is a common and severe condition, often complicated by diastolic dysfunction. Current standard therapies such as ACEIs and ARBs have limited efficacy in managing diastolic function. Sacubitril/Valsartan, an emerging therapy, warrants rigorous investigation to elucidate its impact on diastolic function in heart failure patients.

METHODS

This systematic review and meta-analysis were conducted adhering to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and utilized the PICO schema. Searches were performed on 4 databases-PubMed, Embase, Web of Science, and Cochrane Library-without temporal restrictions. Inclusion and exclusion criteria were strictly defined, and quality assessments were conducted using the Cochrane Collaboration Risk of Bias tool. Both fixed-effects and random-effects models were used for statistical analysis, depending on inter-study heterogeneity assessed by I2 statistics and Chi-square tests.

RESULTS

Out of 1129 identified publications, 8 studies met the criteria and were included in the meta-analysis. These studies consisted of both randomized controlled trials and cohort studies and featured diverse global populations. Significant reductions were found in the echocardiographic parameter E/e' ratio and LAVi upon treatment with Sacubitril/Valsartan compared to standard therapies, with mean differences of -1.38 and -4.62, respectively, both with P values < .01.

CONCLUSIONS

This meta-analysis demonstrates that Sacubitril/Valsartan significantly improves diastolic function parameters in heart failure patients compared to standard treatments. These findings underscore the potential benefits of Sacubitril/Valsartan in the management of heart failure, particularly for patients with diastolic dysfunction.

Role of Phosphodiesterase 1 in the Regulation of Real-Time cGMP Levels and Contractility in Adult Mouse Cardiomyocytes

In mouse cardiomyocytes, the expression of two subfamilies of the calcium/calmodulin-regulated cyclic nucleotide phosphodiesterase 1 (PDE1)-PDE1A and PDE1C-has been reported. PDE1C was found to be the major subfamily in the human heart. It is a dual substrate PDE and can hydrolyze both 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP). Previously, it has been reported that the PDE1 inhibitor ITI-214 shows positive inotropic effects in heart failure patients which were largely attributed to the cAMP-dependent protein kinase (PKA) signaling. However, the role of PDE1 in the regulation of cardiac cGMP has not been directly addressed. Here, we studied the effect of PDE1 inhibition on cGMP levels in adult mouse ventricular cardiomyocytes using a highly sensitive fluorescent biosensor based on Förster resonance energy transfer (FRET). Live-cell imaging in paced and resting cardiomyocytes showed an increase in cGMP after PDE1 inhibition with ITI-214. Furthermore, PDE1 inhibition and PDE1A knockdown amplified the cGMP-FRET responses to the nitric oxide (NO)-donor sodium nitroprusside (SNP) but not to the C-type natriuretic peptide (CNP), indicating a specific role of PDE1 in the regulation of the NO-sensitive guanylyl cyclase (NO-GC)-regulated cGMP microdomain. ITI-214, in combination with CNP or SNP, showed a positive lusitropic effect, improving the relaxation of isolated myocytes. Immunoblot analysis revealed increased phospholamban (PLN) phosphorylation at Ser-16 in cells treated with a combination of SNP and PDE1 inhibitor but not with SNP alone. Our findings reveal a previously unreported role of PDE1 in the regulation of the NO-GC/cGMP microdomain and mouse ventricular myocyte contractility. Since PDE1 serves as a cGMP degrading PDE in cardiomyocytes and has the highest hydrolytic activities, it can be expected that PDE1 inhibition might be beneficial in combination with cGMP-elevating drugs for the treatment of cardiac diseases.

Multi-omics approach for identification of molecular alterations of QiShenYiQi dripping pills in heart failure with preserved ejection fraction

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine theory believes that qi deficiency and blood stasis are the key pathogenesis of heart failure with preserved ejection fraction (HFpEF). As a representative prescription for replenishing qi and activating blood, QiShenYiQi dripping pills (QSYQ) has been used for treating heart diseases. However, the pharmacological mechanism of QSYQ in improving HFpEF is not well understood.

AIM OF THE STUDY

The objective of the study is to investigate the cardioprotective effect and mechanism of QSYQ in HFpEF using the phenotypic dataset of HFpEF.

MATERIALS AND METHODS

HFpEF mouse models established by feeding mice combined high-fat diet and N^ω-nitro-L-arginine methyl ester drinking water were treated with QSYQ. To reveal causal genes, we performed a multi-omics study, including integrative analysis of transcriptomics, proteomics, and metabolomics data. Moreover, adeno-associated virus (AAV)-based PKG inhibition confirmed that QSYQ mediated myocardial remodeling through PKG.

RESULTS

Computational systems pharmacological analysis based on human transcriptome data for HFpEF showed that QSYQ could potentially treat HFpEF through multiple signaling pathways. Subsequently, integrative analysis of transcriptome and proteome showed alterations in gene expression in HFpEF. QSYQ regulated genes involved in inflammation, energy metabolism, myocardial hypertrophy, myocardial fibrosis, and cGMP-PKG signaling pathway, confirming its function in the pathogenesis of HFpEF. Metabolomics analysis revealed fatty acid metabolism as the main mechanism by which QSYQ regulates HFpEF myocardial energy metabolism. Importantly, we found that the myocardial protective effect of QSYQ on HFpEF mice was attenuated after RNA interference-mediated knock-down of myocardial PKG.

CONCLUSION

This study provides mechanistic insights into the pathogenesis of HFpEF and molecular mechanisms of QSYQ in HFpEF. We also identified the regulatory role of PKG in myocardial stiffness, making it an ideal therapeutic target for myocardial remodeling.

Cyclic nucleotide phosphodiesterases as therapeutic targets in cardiac hypertrophy and heart failure

Cyclic nucleotide phosphodiesterases (PDEs) modulate the neurohormonal regulation of cardiac function by degrading cAMP and cGMP. In cardiomyocytes, multiple PDE isozymes with different enzymatic properties and subcellular localization regulate local pools of cyclic nucleotides and specific functions. This organization is heavily perturbed during cardiac hypertrophy and heart failure (HF), which can contribute to disease progression. Clinically, PDE inhibition has been considered a promising approach to compensate for the catecholamine desensitization that accompanies HF. Although PDE3 inhibitors, such as milrinone or enoximone, have been used clinically to improve systolic function and alleviate the symptoms of acute HF, their chronic use has proved to be detrimental. Other PDEs, such as PDE1, PDE2, PDE4, PDE5, PDE9 and PDE10, have emerged as new potential targets to treat HF, each having a unique role in local cyclic nucleotide signalling pathways. In this Review, we describe cAMP and cGMP signalling in cardiomyocytes and present the various PDE families expressed in the heart as well as their modifications in pathological cardiac hypertrophy and HF. We also appraise the evidence from preclinical models as well as clinical data pointing to the use of inhibitors or activators of specific PDEs that could have therapeutic potential in HF.

The NO-cGMP-PKG Axis in HFpEF: From Pathological Mechanisms to Potential Therapies

Heart failure with preserved ejection fraction (HFpEF) accounts for almost half of all heart failure (HF) cases worldwide. Unfortunately, its incidence is expected to continue to rise, and effective therapy to improve clinical outcomes is lacking. Numerous efforts currently directed towards the pathophysiology of human HFpEF are uncovering signal transduction pathways and novel therapeutic targets. The nitric oxide-cyclic guanosine phosphate-protein kinase G (NO-cGMP-PKG) axis has been described as an important regulator of cardiac function. Suppression of the NO-cGMP-PKG signalling pathway is involved in the progression of HFpEF. Therefore, the NO-cGMP-PKG signalling pathway is a potential therapeutic target for HFpEF. In this review, we aim to explore the mechanism of NO-cGMP-PKG in the progression of HFpEF and to summarize potential therapeutic drugs that target this signalling pathway.

Signaling network model of cardiomyocyte morphological changes in familial cardiomyopathy

Familial cardiomyopathy is a precursor of heart failure and sudden cardiac death. Over the past several decades, researchers have discovered numerous gene mutations primarily in sarcomeric and cytoskeletal proteins causing two different disease phenotypes: hypertrophic (HCM) and dilated (DCM) cardiomyopathies. However, molecular mechanisms linking genotype to phenotype remain unclear. Here, we employ a systems approach by integrating experimental findings from preclinical studies (e.g., murine data) into a cohesive signaling network to scrutinize genotype to phenotype mechanisms. We developed an HCM/DCM signaling network model utilizing a logic-based differential equations approach and evaluated model performance in predicting experimental data from four contexts (HCM, DCM, pressure overload, and volume overload). The model has an overall prediction accuracy of 83.8%, with higher accuracy in the HCM context (90%) than DCM (75%). Global sensitivity analysis identifies key signaling reactions, with calcium-mediated myofilament force development and calcium-calmodulin kinase signaling ranking the highest. A structural revision analysis indicates potential missing interactions that primarily control calcium regulatory proteins, increasing model prediction accuracy. Combination pharmacotherapy analysis suggests that downregulation of signaling components such as calcium, titin and its associated proteins, growth factor receptors, ERK1/2, and PI3K-AKT could inhibit myocyte growth in HCM. In experiments with patient-specific iPSC-derived cardiomyocytes (MLP-W4R;MYH7-R723C iPSC-CMs), combined inhibition of ERK1/2 and PI3K-AKT rescued the HCM phenotype, as predicted by the model. In DCM, PI3K-AKT-NFAT downregulation combined with upregulation of Ras/ERK1/2 or titin or Gq protein could ameliorate cardiomyocyte morphology. The model results suggest that HCM mutations that increase active force through elevated calcium sensitivity could increase ERK activity and decrease eccentricity through parallel growth factors, Gq-mediated, and titin pathways. Moreover, the model simulated the influence of existing medications on cardiac growth in HCM and DCM contexts. This HCM/DCM signaling model demonstrates utility in investigating genotype to phenotype mechanisms in familial cardiomyopathy.

Beneficial Effects of Low-Intensity Pulsed Ultrasound Therapy on Right Ventricular Dysfunction in Animal Models

Right ventricular failure (RVF) is a leading cause of death in patients with pulmonary hypertension; however, effective treatment remains to be developed. We have developed low-intensity pulsed ultrasound therapy for cardiovascular diseases. In this study, we demonstrated that the expression of endothelial nitric oxide synthase (eNOS) in RVF patients was downregulated and that eNOS expression and its downstream pathway were ameliorated through eNOS activation in 2 animal models of RVF. These results indicate that eNOS is an important therapeutic target of RVF, for which low-intensity pulsed ultrasound therapy is a promising therapy for patients with RVF.

Shunxin decoction improves diastolic function in rats with heart failure with preserved ejection fraction induced by abdominal aorta constriction through cyclic guanosine monophosphate-dependent protein kinase Signaling Pathway

OBJECTIVE

To determine whether Shunxin decoction improves diastolic function in rats with heart failure with preserved ejection fraction (HFpEF) by regulating the cyclic guanosine monophosphate-dependent protein kinase (cGMP-PKG) signaling pathway.

METHODS

Except for control group 8 and sham surgery group 8, the remaining 32 male Sprague-Dawlay rats were developed into HFpEF rat models using the abdominal aorta constriction method. These rats in the HFpEF model were randomly divided into the model group, the Shunxin high-dose group, the Shunxin low-dose group, and the Qiliqiangxin capsule group. The three groups received high-dose Shunxin decoction, low-dose Shunxin decoction, and Qiliqiangxin capsule by gavage, respectively, for 14 d. After the intervention, the diastolic function of each rat was evaluated by testing E/A, heart index, hematoxylin-eosin staining, Masson, myocardial ultrastructure, and N-terminal pro-brain natriuretic peptide (NT-proBNP). The Bioinformatics Analysis Tool for Molecular Mechanism of Traditional Chinese Medicine (BATMAN-TCM) software was used to predict targets for which Shunxin decoction acts on the cGMP-PKG pathway. Natriuretic peptide receptor A (NPRA) and guanylate cyclase (GC) were detected by immunohistochemistry, and eNOS, phosphodiesterase 5A (PDE5A), and cGMP-dependent protein kinase 1(PKG I) were determined by Western blotting.

RESULTS

Compared to the model group, the thickness of the interventricular septum at the end of diastole (IVSd) and the thickness of the posterior wall at the end of diastole (PWd) of the Shunxin decoction high-dose group, Shunxin decoction low-dose group, and Qiliqiangxin capsule group were all significantly reduced ( < 0.01). Furthermore, Shunxin decoction high-dose group E/A value was decreased ( < 0.01). Compared to the model group, the expression of NPRA and GC increased in the Shunxin decoction low-dose group and the Qiliqiangxin capsule group ( < 0.01). Compared to the model group, the expressions of eNOS and PKG I increased ( < 0.05) in the Shunxin decoction high-dose group. The expression of PDE5A expression decreased in the myocardium of the Shunxin decoction high-dose group, Shunxin decoction low-dose group, and Qiliqiangxin capsule group compared to the model group ( < 0.01).

CONCLUSIONS

Shunxin decoction can improve diastolic function in rats with HFpEF. It increases the expression of NPRA, GC, and eNOS in the myocardial cell cGMP-PKG signaling pathway, upregulates cGMP expression, decreases PDE5A expression to reduce the cGMP degradation. Thus, the cGMP continually stimulates PKG I, reversing myocardial hypertrophy and improving myocardial compliance in HFpEF rats.

Natriuretic peptide pathways in heart failure: further therapeutic possibilities

The discovery of the heart as an endocrine organ resulted in a remarkable recognition of the natriuretic peptide system (NPS). Specifically, research has established the production of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) from the heart, which exert pleiotropic cardiovascular, endocrine, renal, and metabolic actions via the particulate guanylyl cyclase A receptor (GC-A) and the second messenger, cGMP. C-type natriuretic peptide (CNP) is produced in the endothelium and kidney and mediates important protective auto/paracrine actions via GC-B and cGMP. These actions, in part, participate in the efficacy of sacubitril/valsartan in heart failure (HF) due to the augmentation of the NPS. Here, we will review important insights into the biology of the NPS, the role of precision medicine, and focus on the phenotypes of human genetic variants of ANP and BNP in the general population and the relevance to HF. We will also provide an update of the existence of NP deficiency states, including in HF, which provide the rationale for further therapeutics for the NPS. Finally, we will review the field of peptide engineering and the development of novel designer NPs for the treatment of HF. Notably, the recent discovery of a first-in-class small molecule GC-A enhancer, which is orally deliverable, will be highlighted. These innovative designer NPs and small molecule possess enhanced and novel properties for the treatment of HF and cardiovascular diseases.

Riociguat attenuates left ventricular proteome and microRNA profile changes after experimental aortic stenosis in mice

BACKGROUND AND PURPOSE

Development and progression of heart failure (HF) involve endothelial and myocardial dysfunction as well as a dysregulation of the nitric oxide - soluble guanylyl cyclase - cyclic guanosine monophosphate (NO-sGC-cGMP) signalling pathway. Recently, we reported that the sGC stimulator riociguat (RIO) has beneficial effects on cardiac remodelling and progression of HF in response to chronic pressure overload. Here, we examined if these favourable RIO effects are also reflected in alterations of the myocardial proteome and microRNA profiles.

EXPERIMENTAL APPROACH

Male C57BL/6N mice underwent transverse aortic constriction (TAC) and sham operated mice served as controls. TAC and sham animals were randomised and treated with either RIO or vehicle for five weeks, starting three weeks post-surgery when cardiac hypertrophy was established. Afterwards we performed mass spectrometric proteome analyses and microRNA sequencing of proteins and RNAs, respectively, isolated from left ventricles (LV).

KEY RESULTS

TAC-induced changes of the LV proteome were significantly reduced by RIO treatment. Bioinformatics analyses revealed that RIO improved TAC-induced cardiovascular disease related pathways, metabolism and energy production, e.g. reversed alterations in the levels of myosin heavy chain 7 (MYH7), cardiac phospholamban (PLN), and ankyrin repeat domain-containing protein 1 (ANKRD1). RIO also attenuated TAC-induced changes of microRNA levels in the LV.

CONCLUSION AND IMPLICATIONS

The sGC stimulator RIO has beneficial effects on cardiac structure and function during pressure overload, which is accompanied by a reversal of TAC-induced changes of the cardiac proteome and microRNA profile. Our data support the potential of RIO as a novel HF therapeutic.

Sex-specific effects of daily tadalafil on diabetic heart kinetics in RECOGITO, a randomized, double-blind, placebo-controlled trial

Cyclic GMP-phosphodiesterase type 5 (PDE5) inhibition has been shown to counteract maladaptive cardiac changes triggered by diabetes in some but not all studies. We performed a single-center, 20-week, double-blind, randomized, placebo-controlled trial (NCT01803828) to assess sex differences in cardiac remodeling after PDE5 inhibition in patients with diabetic cardiomyopathy. A total of 122 men and women (45 to 80 years) with long-duration (>3 years) and well-controlled type 2 diabetes mellitus (T2DM; HbA1c < 86 mmol/mol) were selected according to echocardiographic signs of cardiac remodeling. Patients were randomly assigned (1:1) to placebo or oral tadalafil (20 mg, once daily). The primary outcome was to evaluate sex differences in cardiac torsion change. Secondary outcomes were changes in cardiovascular, metabolic, immune, and renal function. At 20 weeks, the treatment-by-sex interaction documented an improvement in cardiac torsion (-3.40°, -5.96; -0.84, P = 0.011) and fiber shortening (-1.19%, -2.24; -0.14, P = 0.027) in men but not women. The primary outcome could not be explained by differences in cGMP concentrations or tadalafil pharmacodynamics. In both sexes, tadalafil improved hsa-miR-199-5p expression, biomarkers of cardiovascular remodeling, albuminuria, renal artery resistive index, and circulating Klotho concentrations. Immune cell profiling revealed an improvement in low-grade chronic inflammation: Classic CD14⁺⁺CD16^- monocytes reduced, and Tie2⁺ monocytes increased. Nine patients (14.5%) had minor adverse reactions after tadalafil administration. Continuous PDE5 inhibition could offer a strategy to target cardiorenal complications of T2DM, with sex- and tissue-specific responses. Further studies are needed to confirm Klotho and hsa-miR-199-5p as markers for T2DM complications.

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.

Multidrug resistance proteins preferentially regulate natriuretic peptide-driven cGMP signalling in the heart and vasculature

BACKGROUND AND PURPOSE

cGMP underpins the bioactivity of NO and natriuretic peptides and is key to cardiovascular homeostasis. cGMP-driven responses are terminated primarily by PDEs, but cellular efflux via multidrug resistance proteins (MRPs) might contribute. Herein, the effect of pharmacological blockade of MRPs on cGMP signalling in the heart and vasculature was investigated in vitro and in vivo.

EXPERIMENTAL APPROACH

Proliferation of human coronary artery smooth muscle cells (hCASMCs), vasorelaxation of murine aorta and reductions in mean arterial BP (MABP) in response to NO donors or natriuretic peptides were determined in the absence and presence of the MRP inhibitor MK571. The ability of MRP inhibition to reverse morphological and contractile deficits in a murine model of pressure overload-induced heart failure was also explored.

KEY RESULTS

MK571 attenuated hCASMC growth and enhanced the anti-proliferative effects of NO and atrial natriuretic peptide (ANP). MRP blockade caused concentration-dependent relaxations of murine aorta and augmented responses to ANP (and to a lesser extent NO). MK571 did not decrease MABP per se but enhanced the hypotensive actions of ANP and improved structural and functional indices of disease severity in experimental heart failure. These beneficial actions of MRP inhibition were associated with a greater intracellular:extracellular cGMP ratio in vitro and in vivo.

CONCLUSIONS AND IMPLICATIONS

MRP blockade promotes the cardiovascular functions of natriuretic peptides in vitro and in vivo, with more modest effects on NO. MRP inhibition may have therapeutic utility in cardiovascular diseases triggered by dysfunctional cGMP signalling, particularly those associated with altered natriuretic peptide bioactivity.

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.

Enhanced NCLX-dependent mitochondrial Ca2+ efflux attenuates pathological remodeling in heart failure

Mitochondrial calcium (mCa2+) uptake couples changes in cardiomyocyte energetic demand to mitochondrial ATP production. However, excessive mCa2+ uptake triggers permeability transition and necrosis. Despite these established roles during acute stress, the involvement of mCa2+ signaling in cardiac adaptations to chronic stress remains poorly defined. Changes in NCLX expression are reported in heart failure (HF) patients and models of cardiac hypertrophy. Therefore, we hypothesized that altered mCa2+ homeostasis contributes to the hypertrophic remodeling of the myocardium that occurs upon a sustained increase in cardiac workload. The impact of mCa2+ flux on cardiac function and remodeling was examined by subjecting mice with cardiomyocyte-specific overexpression (OE) of the mitochondrial Na+/Ca2+ exchanger (NCLX), the primary mediator of mCa2+ efflux, to several well-established models of hypertrophic and non-ischemic HF. Cardiomyocyte NCLX-OE preserved contractile function, prevented hypertrophy and fibrosis, and attenuated maladaptive gene programs in mice subjected to chronic pressure overload. Hypertrophy was attenuated in NCLX-OE mice, prior to any decline in cardiac contractility. NCLX-OE similarly attenuated deleterious cardiac remodeling in mice subjected to chronic neurohormonal stimulation. However, cardiomyocyte NCLX-OE unexpectedly reduced overall survival in mice subjected to severe neurohormonal stress with angiotensin II + phenylephrine. Adenoviral NCLX expression limited mCa2+ accumulation, oxidative metabolism, and de novo protein synthesis during hypertrophic stimulation of cardiomyocytes in vitro. Our findings provide genetic evidence for the contribution of mCa2+ to early pathological remodeling in non-ischemic heart disease, but also highlight a deleterious consequence of increasing mCa2+ efflux when the heart is subjected to extreme, sustained neurohormonal stress.

CNP regulates cardiac contractility and increases cGMP near both SERCA and TnI: difference from BNP visualized by targeted cGMP biosensors

AIMS

Guanylyl cyclase-B (GC-B; natriuretic peptide receptor-B, NPR-B) stimulation by C-type natriuretic peptide (CNP) increases cGMP and causes a lusitropic and negative inotropic response in adult myocardium. These effects are not mimicked by NPR-A (GC-A) stimulation by brain natriuretic peptide (BNP), despite similar cGMP increase. More refined methods are needed to better understand the mechanisms of the differential cGMP signalling and compartmentation. The aim of this work was to measure cGMP near proteins involved in regulating contractility to understand compartmentation of cGMP signalling in adult cardiomyocytes.

METHODS AND RESULTS

We constructed several fluorescence resonance energy transfer (FRET)-based biosensors for cGMP subcellularly targeted to phospholamban (PLB) and troponin I (TnI). CNP stimulation of adult rat cardiomyocytes increased cGMP near PLB and TnI, whereas BNP stimulation increased cGMP near PLB, but not TnI. The phosphodiesterases PDE2 and PDE3 constrained cGMP in both compartments. Local receptor stimulation aided by scanning ion conductance microscopy (SICM) combined with FRET revealed that CNP stimulation both in the t-tubules and on the cell crest increases cGMP similarly near both TnI and PLB. In ventricular strips, CNP stimulation, but not BNP, induced a lusitropic response, enhanced by inhibition of either PDE2 or PDE3, and a negative inotropic response. In cardiomyocytes from heart failure rats, CNP increased cGMP near PLB and TnI more pronounced than in cells from sham-operated animals.

CONCLUSION

These targeted biosensors demonstrate that CNP, but not BNP, increases cGMP near TnI in addition to PLB, explaining how CNP, but not BNP, is able to induce lusitropic and negative inotropic responses.

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.

Phosphodiesterases and Compartmentation of cAMP and cGMP Signaling in Regulation of Cardiac Contractility in Normal and Failing Hearts

Cardiac contractility is regulated by several neural, hormonal, paracrine, and autocrine factors. Amongst these, signaling through β-adrenergic and serotonin receptors generates the second messenger cyclic AMP (cAMP), whereas activation of natriuretic peptide receptors and soluble guanylyl cyclases generates cyclic GMP (cGMP). Both cyclic nucleotides regulate cardiac contractility through several mechanisms. Phosphodiesterases (PDEs) are enzymes that degrade cAMP and cGMP and therefore determine the dynamics of their downstream effects. In addition, the intracellular localization of the different PDEs may contribute to regulation of compartmented signaling of cAMP and cGMP. In this review, we will focus on the role of PDEs in regulating contractility and evaluate changes in heart failure.

Cyclic GMP-Dependent Regulation of Vascular Tone and Blood Pressure Involves Cysteine-Rich LIM-Only Protein 4 (CRP4)

The cysteine-rich LIM-only protein 4 (CRP4), a LIM-domain and zinc finger containing adapter protein, has been implicated as a downstream effector of the second messenger 3',5'-cyclic guanosine monophosphate (cGMP) pathway in multiple cell types, including vascular smooth muscle cells (VSMCs). VSMCs and nitric oxide (NO)-induced cGMP signaling through cGMP-dependent protein kinase type I (cGKI) play fundamental roles in the physiological regulation of vascular tone and arterial blood pressure (BP). However, it remains unclear whether the vasorelaxant actions attributed to the NO/cGMP axis require CRP4. This study uses mice with a targeted deletion of the CRP4 gene (CRP4 KO) to elucidate whether cGMP-elevating agents, which are well known for their vasorelaxant properties, affect vessel tone, and thus, BP through CRP4. Cinaciguat, a NO- and heme-independent activator of the NO-sensitive (soluble) guanylyl cyclase (NO-GC) and NO-releasing agents, relaxed both CRP4-proficient and -deficient aortic ring segments pre-contracted with prostaglandin F2α. However, the magnitude of relaxation was slightly, but significantly, increased in vessels lacking CRP4. Accordingly, CRP4 KO mice presented with hypotonia at baseline, as well as a greater drop in systolic BP in response to the acute administration of cinaciguat, sodium nitroprusside, and carbachol. Mechanistically, loss of CRP4 in VSMCs reduced the Ca2+-sensitivity of the contractile apparatus, possibly involving regulatory proteins, such as myosin phosphatase targeting subunit 1 (MYPT1) and the regulatory light chain of myosin (RLC). In conclusion, the present findings confirm that the adapter protein CRP4 interacts with the NO-GC/cGMP/cGKI pathway in the vasculature. CRP4 seems to be part of a negative feedback loop that eventually fine-tunes the NO-GC/cGMP axis in VSMCs to increase myofilament Ca2+ desensitization and thereby the maximal vasorelaxant effects attained by (selected) cGMP-elevating agents.

cGMP and mitochondrial K+ channels-Compartmentalized but closely connected in cardioprotection

The 3',5'-cGMP pathway triggers cytoprotective responses and improves cardiomyocyte survival during myocardial ischaemia and reperfusion (I/R) injury. These beneficial effects were attributed to NO-sensitive GC induced cGMP production leading to activation of cGMP-dependent protein kinase I (cGKI). cGKI in turn phosphorylates many substrates, which eventually facilitate opening of mitochondrial ATP-sensitive potassium channels (mitoK_ATP ) and Ca²⁺ -activated potassium channels of the BK type (mitoBK). Accordingly, agents activating mitoK_ATP or mitoBK provide protection against I/R-induced damages. Here, we provide an up-to-date summary of the infarct-limiting actions exhibited by the GC/cGMP axis and discuss how mitoK_ATP and mitoBK, which are present at the inner mitochondrial membrane, confer mito- and cytoprotective effects on cardiomyocytes exposed to I/R injury. In view of this, we believe that the functional connection between the cGMP cascade and mitoK⁺ channels should be exploited further as adjunct to reperfusion therapy in myocardial infarction.

Low-intensity pulsed ultrasound ameliorates cardiac diastolic dysfunction in mice: a possible novel therapy for heart failure with preserved left ventricular ejection fraction

AIMS

Heart failure with preserved left ventricular ejection fraction (HFpEF) is a serious health problem worldwide, as no effective therapy is yet available. We have previously demonstrated that our low-intensity pulsed ultrasound (LIPUS) therapy is effective and safe for angina and dementia. In this study, we aimed to examine whether the LIPUS therapy also ameliorates cardiac diastolic dysfunction in mice.

METHODS AND RESULTS

Twelve-week-old obese diabetic mice (db/db) and their control littermates (db/+) were treated with either the LIPUS therapy [1.875 MHz, 32 cycles, Ispta (spatial peak temporal average intensity) 117-162 mW/cm2, 0.25 W/cm2] or placebo procedure two times a week for 4 weeks. At 20-week-old, transthoracic echocardiography and invasive haemodynamic analysis showed that cardiac diastolic function parameters, such as e', E/e', end-diastolic pressure-volume relationship, Tau, and dP/dt min, were all deteriorated in placebo-treated db/db mice compared with db/+ mice, while systolic function was preserved. Importantly, these cardiac diastolic function parameters were significantly ameliorated in the LIPUS-treated db/db mice. We also measured the force (F) and intracellular Ca2+ ([Ca2+]i) in trabeculae dissected from ventricles. We found that relaxation time and [Ca2+]i decay (Tau) were prolonged during electrically stimulated twitch contractions in db/db mice, both of which were significantly ameliorated in the LIPUS-treated db/db mice, indicating that the LIPUS therapy also improves relaxation properties at tissue level. Functionally, exercise capacity was also improved in the LIPUS-treated db/db mice. Histologically, db/db mice displayed progressed cardiomyocyte hypertrophy and myocardial interstitial fibrosis, while those changes were significantly suppressed in the LIPUS-treated db/db mice. Mechanistically, western blot showed that the endothelial nitric oxide synthase (eNOS)-nitric oxide (NO)-cGMP-protein kinase G (PKG) pathway and Ca2+-handling molecules were up-regulated in the LIPUS-treated heart.

CONCLUSIONS

These results indicate that the LIPUS therapy ameliorates cardiac diastolic dysfunction in db/db mice through improvement of eNOS-NO-cGMP-PKG pathway and cardiomyocyte Ca2+-handling system, suggesting its potential usefulness for the treatment of HFpEF patients.

Targets of cGMP/cGKI in Cardiac Myocytes

The 3',5'-cyclic guanosine monophosphate (cGMP)-dependent protein kinase type I (cGKI aka PKGI) is a major cardiac effector acting downstream of nitric oxide (NO)-sensitive soluble guanylyl cyclase and natriuretic peptides (NPs), which signal through transmembrane guanylyl cyclases. Consistent with the wide distribution of the cGMP-generating guanylyl cyclases, cGKI, which usually elicits its cellular effects by direct phosphorylation of its targets, is present in multiple cardiac cell types including cardiomyocytes (CMs). Although numerous targets of cGMP/cGKI in heart were identified in the past, neither their exact patho-/physiological functions nor cell-type specific roles are clear. Herein, we inform about the current knowledge on the signal transduction downstream of CM cGKI. We believe that better insights into the specific actions of cGMP and cGKI in these cells will help to guide future studies in the search for predictive biomarkers for the response to pharmacological cGMP pathway modulation. In addition, targets downstream of cGMP/cGKI may be exploited for refined and optimized diagnostic and therapeutic strategies in different types of heart disease and their causes. Importantly, key functions of these proteins and particularly sites of regulatory phosphorylation by cGKI should, at least in principle, remain intact, although upstream signaling through the second messenger cGMP is impaired or dysregulated in a stressed or diseased heart state.

C-type natriuretic peptide moderates titin-based cardiomyocyte stiffness

Heart failure is often accompanied by titin-dependent myocardial stiffness. Phosphorylation of titin by cGMP-dependent protein kinase I (PKGI) increases cardiomyocyte distensibility. The upstream pathways stimulating PKGI-mediated titin phosphorylation are unclear. We studied whether C-type natriuretic peptide (CNP), via its guanylyl cyclase-B (GC-B) receptor and cGMP/PKGI signaling, modulates titin-based ventricular compliance. To dissect GC-B–mediated effects of endogenous CNP in cardiomyocytes, we generated mice with cardiomyocyte-restricted GC-B deletion (CM GC-B–KO mice). The impact on heart morphology and function, myocyte passive tension, and titin isoform expression and phosphorylation was studied at baseline and after increased afterload induced by transverse aortic constriction (TAC). Pressure overload increased left ventricular endothelial CNP expression, with an early peak after 3 days. Concomitantly, titin phosphorylation at Ser₄₀₈₀, the site phosphorylated by PKGI, was augmented. Notably, in CM GC-B–KO mice this titin response was abolished. TAC-induced hypertrophy and fibrosis were not different between genotypes. However, the KO mice presented mild systolic and diastolic dysfunction together with myocyte stiffness, which were not observed in control littermates. In vitro, recombinant PKGI rescued reduced titin-Ser₄₀₈₀ phosphorylation and reverted passive stiffness of GC-B–deficient cardiomyocytes. CNP-induced activation of GC-B/cGMP/PKGI signaling in cardiomyocytes provides a protecting regulatory circuit preventing titin-based myocyte stiffening during early phases of pressure overload.

C-type natriuretic peptide via GC-B/cGMP/PKGI signalling in cardiomyocytes attenuates titin-based cardiomyocyte stiffening during early phases of pressure-overload.

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.

Cardiac cGMP Signaling in Health and Disease: Location, Location, Location

3',5'-Cyclic guanosine monophosphate (cGMP) is a ubiquitous second messenger, which critically regulates cardiac pump function and protects from the development of cardiac hypertrophy by acting in various subcellular microdomains. Although clinical studies testing the potential of cGMP elevating drugs in patients suffering from cardiac disease showed promising results, deeper insight into the local actions of these drugs at the subcellular level are indispensable to inspire novel therapeutic strategies. Detailed information on the spatio-temporal dynamics of cGMP production and degradation can be provided by the use of fluorescent biosensors that are capable of monitoring this second messenger at different locations inside the cell with high temporal and spatial resolution. In this review, we will summarize how these emerging new tools have improved our understanding of cardiac cGMP signaling in health and disease, and attempt to anticipate future challenges in the field.

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.

Circulating products of C-type natriuretic peptide and links with organ function in health and disease

Paracrine actions of CNP and rapid degradation at source severely limit study of CNP's many roles in vivo. However provided sensitive and validated assays are used, there is increasing evidence that low concentrations of bioactive CNP in plasma, and the readily detectable concentrations of the bio-inactive processed product of proCNP (aminoterminal proCNP), can be used to advance understanding of the hormone's role in pathophysiology. Provided renal function is normal, concordant changes in both CNP and NTproCNP reflect change in tissue production of proCNP whereas change in CNP alone results from altered rates of bioactive CNP degradation and are reflected in the ratio of NTproCNP to CNP. As already shown in juveniles, where plasma concentration of CNP products are higher and are associated with concurrent endochondral bone growth, measurements of plasma CNP products in mature adults have potential to clarify organ response to stress and injury. Excepting the role of CNP in fetal-maternal welfare, this review examines evidence linking plasma CNP products with function of a wide range of tissues in adults, including the impact of extraneous factors such as nutrients, hormone therapy and exercise.

Cardiac Cyclic Nucleotide Phosphodiesterases: Roles and Therapeutic Potential in Heart Failure

The cyclic nucleotides cyclic adenosine-3′,5′-monophosphate (cAMP) and cyclic guanosine-3′,5′-monophosphate (cGMP) maintain physiological cardiac contractility and integrity. Cyclic nucleotide–hydrolysing phosphodiesterases (PDEs) are the prime regulators of cAMP and cGMP signalling in the heart. During heart failure (HF), the expression and activity of multiple PDEs are altered, which disrupt cyclic nucleotide levels and promote cardiac dysfunction. Given that the morbidity and mortality associated with HF are extremely high, novel therapies are urgently needed. Herein, the role of PDEs in HF pathophysiology and their therapeutic potential is reviewed. Attention is given to PDEs 1–5, and other PDEs are briefly considered. After assessing the role of each PDE in cardiac physiology, the evidence from pre-clinical models and patients that altered PDE signalling contributes to the HF phenotype is examined. The potential of pharmacologically harnessing PDEs for therapeutic gain is considered.

Phosphodiesterase 9a Inhibition in Mouse Models of Diastolic Dysfunction

BACKGROUND

Low myocardial cGMP-PKG (cyclic guanosine monophosphate-protein kinase G) activity has been associated with increased cardiomyocyte diastolic stiffness in heart failure with preserved ejection fraction. Cyclic guanosine monophosphate is mainly hydrolyzed by PDE (phosphodiesterases) 5a and 9a. Importantly, PDE9a expression has been reported to be upregulated in human heart failure with preserved ejection fraction myocardium and chronic administration of a PDE9a inhibitor reverses preestablished cardiac hypertrophy and systolic dysfunction in mice subjected to transverse aortic constriction (TAC). We hypothesized that inhibiting PDE9a activity ameliorates diastolic dysfunction.

METHODS

To examine the effect of chronic PDE9a inhibition, 2 diastolic dysfunction mouse models were studied: (1) TAC-deoxycorticosterone acetate and (2) Lepr^db/db. PDE9a inhibitor (5 and 8 mg/kg per day) was administered to the mice via subcutaneously implanted osmotic minipumps for 28 days. The effect of acute PDE9a inhibition was investigated in intact cardiomyocytes isolated from TAC-deoxycorticosterone acetate mice. Atrial natriuretic peptide together with PDE9a inhibitor were administered to the isolated intact cardiomyocytes through the cell perfusate.

RESULTS

For acute inhibition, no cellular stiffness reduction was found, whereas chronic PDE9a inhibition resulted in reduced left ventricular chamber stiffness in TAC-deoxycorticosterone acetate, but not in Lepr^db/db mice. Passive cardiomyocyte stiffness was reduced by chronic PDE9a inhibition, with no differences in myocardial fibrosis or cardiac morphometry. PDE9a inhibition increased the ventricular-arterial coupling ratio, reflecting impaired systolic function.

CONCLUSIONS

Chronic PDE9a inhibition lowers left ventricular chamber stiffness in TAC-deoxycorticosterone acetate mice. However, the usefulness of PDE9a inhibition to treat high-diastolic stiffness may be limited as the required PDE9a inhibitor dose also impairs systolic function, observed as a decline in ventricular-arterial coordination, in this model.

Stabilization of Perivascular Mast Cells by Endothelial CNP (C-Type Natriuretic Peptide)

OBJECTIVE

Activated perivascular mast cells (MCs) participate in different cardiovascular diseases. Many factors provoking MC degranulation have been described, while physiological counterregulators are barely known. Endothelial CNP (C-type natriuretic peptide) participates in the maintenance of vascular barrier integrity, but the target cells and mechanisms are unclear. Here, we studied whether MCs are regulated by CNP. Approach and Results: In cultured human and murine MCs, CNP activated its specific GC (guanylyl cyclase)-B receptor and cyclic GMP signaling. This enhanced cyclic GMP-dependent phosphorylation of the cytoskeleton-associated VASP (vasodilator-stimulated phosphoprotein) and inhibited ATP-evoked degranulation. To elucidate the relevance in vivo, mice with a floxed GC-B (Npr2) gene were interbred with a Mcpt5-Cre^TG line to generate mice lacking GC-B in connective tissue MCs (MC GC-B knockout). In anesthetized mice, acute ischemia-reperfusion of the cremaster muscle microcirculation provoked extensive MC degranulation and macromolecule extravasation. Superfusion of CNP markedly prevented MC activation and endothelial barrier disruption in control but not in MC GC-B knockout mice. Notably, already under resting conditions, such knockout mice had increased numbers of degranulated MCs in different tissues, together with elevated plasma chymase levels. After transient coronary occlusion, their myocardial areas at risk and with infarction were enlarged. Moreover, MC GC-B knockout mice showed augmented perivascular neutrophil infiltration and deep vein thrombosis in a model of inferior vena cava ligation.

CONCLUSIONS

CNP, via GC-B/cyclic GMP signaling, stabilizes resident perivascular MCs at baseline and prevents their excessive activation under pathological conditions. Thereby CNP contributes to the maintenance of vascular integrity in physiology and disease.

Mind the gap (junction): cGMP induced by nitric oxide in cardiac myocytes originates from cardiac fibroblasts

Background and Purpose

The intracellular signalling molecule cGMP, formed by NO‐sensitive GC (NO–GC), has an established function in the vascular system. Despite numerous reports about NO‐induced cGMP effects in the heart, the underlying cGMP signals are poorly characterized.

Experimental Approach

Therefore, we analysed cGMP signals in cardiac myocytes and fibroblasts isolated from knock‐in mice expressing a FRET‐based cGMP indicator.

Key Results

Whereas in cardiac myocytes, none of the known NO–GC‐activating substances (NO, GC activators, and GC stimulators) increased cGMP even in the presence of PDE inhibitors, they induced substantial cGMP increases in cardiac fibroblasts. As cardiac myocytes and fibroblasts are electrically connected via gap junctions, we asked whether cGMP can take the same route. Indeed, in cardiomyocytes co‐cultured on cardiac fibroblasts, NO‐induced cGMP signals were detectable, and two groups of unrelated gap junction inhibitors abolished these signals.

Conclusion and Implication

We conclude that NO‐induced cGMP formed in cardiac fibroblasts enters cardiac myocytes via gap junctions thereby turning cGMP into an intercellular signalling molecule. The findings shed new light on NO/cGMP signalling in the heart and will potentially broaden therapeutic opportunities for cardiac disease.

Endothelial C-Type Natriuretic Peptide Acts on Pericytes to Regulate Microcirculatory Flow and Blood Pressure

BACKGROUND

Peripheral vascular resistance has a major impact on arterial blood pressure levels. Endothelial C-type natriuretic peptide (CNP) participates in the local regulation of vascular tone, but the target cells remain controversial. The cGMP-producing guanylyl cyclase-B (GC-B) receptor for CNP is expressed in vascular smooth muscle cells (SMCs). However, whereas endothelial cell-specific CNP knockout mice are hypertensive, mice with deletion of GC-B in vascular SMCs have unaltered blood pressure.

METHODS

We analyzed whether the vasodilating response to CNP changes along the vascular tree, ie, whether the GC-B receptor is expressed in microvascular types of cells. Mice with a floxed GC-B ( Npr2) gene were interbred with Tie2-Cre or PDGF-Rβ-Cre ^ERT2 lines to develop mice lacking GC-B in endothelial cells or in precapillary arteriolar SMCs and capillary pericytes. Intravital microscopy, invasive and noninvasive hemodynamics, fluorescence energy transfer studies of pericyte cAMP levels in situ, and renal physiology were combined to dissect whether and how CNP/GC-B/cGMP signaling modulates microcirculatory tone and blood pressure.

RESULTS

Intravital microscopy studies revealed that the vasodilatatory effect of CNP increases toward small-diameter arterioles and capillaries. CNP consistently did not prevent endothelin-1-induced acute constrictions of proximal arterioles, but fully reversed endothelin effects in precapillary arterioles and capillaries. Here, the GC-B receptor is expressed both in endothelial and mural cells, ie, in pericytes. It is notable that the vasodilatatory effects of CNP were preserved in mice with endothelial GC-B deletion, but abolished in mice lacking GC-B in microcirculatory SMCs and pericytes. CNP, via GC-B/cGMP signaling, modulates 2 signaling cascades in pericytes: it activates cGMP-dependent protein kinase I to phosphorylate downstream targets such as the cytoskeleton-associated vasodilator-activated phosphoprotein, and it inhibits phosphodiesterase 3A, thereby enhancing pericyte cAMP levels. These pathways ultimately prevent endothelin-induced increases of pericyte calcium levels and pericyte contraction. Mice with deletion of GC-B in microcirculatory SMCs and pericytes have elevated peripheral resistance and chronic arterial hypertension without a change in renal function.

CONCLUSIONS

Our studies indicate that endothelial CNP regulates distal arteriolar and capillary blood flow. CNP-induced GC-B/cGMP signaling in microvascular SMCs and pericytes is essential for the maintenance of normal microvascular resistance and blood pressure.

C-type Natriuretic Peptide: A Multifaceted Paracrine Regulator in the Heart and Vasculature

C-type natriuretic peptide (CNP) is an autocrine and paracrine mediator released by endothelial cells, cardiomyocytes and fibroblasts that regulates vital physiological functions in the cardiovascular system. These roles are conveyed via two cognate receptors, natriuretic peptide receptor B (NPR-B) and natriuretic peptide receptor C (NPR-C), which activate different signalling pathways that mediate complementary yet distinct cellular responses. Traditionally, CNP has been deemed the endothelial component of the natriuretic peptide system, while its sibling peptides, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), are considered the endocrine guardians of cardiac function and blood volume. However, accumulating evidence indicates that CNP not only modulates vascular tone and blood pressure, but also governs a wide range of cardiovascular effects including the control of inflammation, angiogenesis, smooth muscle and endothelial cell proliferation, atherosclerosis, cardiomyocyte contractility, hypertrophy, fibrosis, and cardiac electrophysiology. This review will focus on the novel physiological functions ascribed to CNP, the receptors/signalling mechanisms involved in mediating its cardioprotective effects, and the development of therapeutics targeting CNP signalling pathways in different disease pathologies.

The Drug Candidate BGP-15 Delays the Onset of Diastolic Dysfunction in the Goto-Kakizaki Rat Model of Diabetic Cardiomyopathy

Background and Aims: Diabetic cardiomyopathy (DCM) is an emerging problem worldwide due to an increase in the incidence of type 2 diabetes. Animal studies have indicated that metformin and pioglitazone can prevent DCM partly by normalizing insulin resistance, and partly by other, pleiotropic mechanisms. One clinical study has evidenced the insulin-senzitizing effect of the drug candidate BGP-15, along with additional animal studies that have confirmed its beneficial effects in models of diabetes, muscular dystrophy and heart failure, with the drug affecting chaperones, contractile proteins and mitochondria. Our aim was to investigate whether the inzulin-senzitizer BGP-15 exert any additive cardiovascular effects compared to metformin or pioglitazone, using Goto-Kakizaki (GotoK) rats. Methods: Rats were divided into five groups: (I) healthy control (Wistar), (II) diseased (GotoK), and GotoK rats treated with: (III) BGP-15, (IV) metformin, and (V) pioglitazone, respectively, for 12 weeks. Metabolic parameters and insulin levels were determined at the endpoint. Doppler echocardiography was carried out to estimate diabetes-associated cardiac dysfunction. Thoracotomy was performed after the vascular status of rats was evaluated using an isolated aortic ring method. Furthermore, western blot assays were carried out to determine expression or phosphorylation levels of selected proteins that take part in myocyte relaxation. Results: BGP-15 restored diastolic parameters (e′/a′, E/e′, LAP, E and A wave) and improved Tei-index compared to untreated GotoK rats. Vascular status was unaffected by BGP-15. Expression of sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA2a) and phosphodiesterase 9A (PDE9A) were unchanged by the treatments, but the phosphorylation level of vasodilator-stimulated phosphoprotein (VASP) and phospholamban (PLB) increased in BGP-15-treated rats, in comparison to GotoK. Conclusions: Even though the BGP-15-treatment did not interfere significantly with glucose homeostasis and vascular status, it considerably enhanced diastolic function, by affecting the SERCA/phospholamban pathway in GotoK rats. Although it requires further investigation, BGP-15 may offer a new therapeutic approach in DCM.

Natriuretic peptides in human heart: Novel insight into their molecular forms, functions, and diagnostic use

Among the three natriuretic peptides, atrial/A-type natriuretic peptide (ANP) and brain/B-type natriuretic peptide (BNP) are primarily produced by, and secreted from, heart tissue. They maintain cardiovascular homeostasis by binding to natriuretic peptide receptor-A. Since plasma ANP and BNP concentrations, as well as expression, are elevated in response to increased body fluid volume and pressure load on the heart wall, these peptides are widely utilized as diagnostic biomarkers for evaluating heart failure. Regardless of their high utility, differences in their molecular forms between healthy and diseased subjects and how these relate to pathophysiology have not well been examined. Recent studies have shown that the circulating molecular forms of ANP and BNP are not uniform; bioactive α-ANP is the major ANP form, whereas the weakly active proBNP is the major BNP form. The relative ratios of the different molecular forms are altered under different pathophysiological conditions. These facts indicate that detailed measurements of each form may provide useful information on the pathophysiological state of heart tissue. Here, we revisit the relationship between the molecular forms of, and pathophysiological alterations in, human ANP and BNP and discuss the possible utility of the measurement of each of the molecular forms. The third peptide, C-type natriuretic peptide, activates natriuretic peptide receptor-B, but little is known about its production and function in the heart because of its extremely low levels. However, through recent studies, its role in the heart is gradually becoming clear. Here, we summarize its molecular forms, assay systems, and functions in the heart.

Phosphodiesterase 2 inhibition preferentially promotes NO/guanylyl cyclase/cGMP signaling to reverse the development of heart failure

Heart failure (HF) is a shared manifestation of several cardiovascular pathologies, including hypertension and myocardial infarction, and a limited repertoire of treatment modalities entails that the associated morbidity and mortality remain high. Impaired nitric oxide (NO)/guanylyl cyclase (GC)/cyclic guanosine-3',5'-monophosphate (cGMP) signaling, underpinned, in part, by up-regulation of cyclic nucleotide-hydrolyzing phosphodiesterase (PDE) isozymes, contributes to the pathogenesis of HF, and interventions targeted to enhancing cGMP have proven effective in preclinical models and patients. Numerous PDE isozymes coordinate the regulation of cardiac cGMP in the context of HF; PDE2 expression and activity are up-regulated in experimental and human HF, but a well-defined role for this isoform in pathogenesis has yet to be established, certainly in terms of cGMP signaling. Herein, using a selective pharmacological inhibitor of PDE2, BAY 60-7550, and transgenic mice lacking either NO-sensitive GC-1α (GC-1α^-/-) or natriuretic peptide-responsive GC-A (GC-A^-/-), we demonstrate that the blockade of PDE2 promotes cGMP signaling to offset the pathogenesis of experimental HF (induced by pressure overload or sympathetic hyperactivation), reversing the development of left ventricular hypertrophy, compromised contractility, and cardiac fibrosis. Moreover, we show that this beneficial pharmacodynamic profile is maintained in GC-A^-/- mice but is absent in animals null for GC-1α or treated with a NO synthase inhibitor, revealing that PDE2 inhibition preferentially enhances NO/GC/cGMP signaling in the setting of HF to exert wide-ranging protection to preserve cardiac structure and function. These data substantiate the targeting of PDE2 in HF as a tangible approach to maximize myocardial cGMP signaling and enhancing therapy.

Distinct submembrane localisation compartmentalises cardiac NPR1 and NPR2 signalling to cGMP

Natriuretic peptides (NPs) are important hormones that regulate multiple cellular functions including cardiovascular physiology. In the heart, two natriuretic peptide receptors NPR1 and NPR2 act as membrane guanylyl cyclases to produce 3′,5′-cyclic guanosine monophosphate (cGMP). Although both receptors protect from cardiac hypertrophy, their effects on contractility are markedly different, from little effect (NPR1) to pronounced negative inotropic and positive lusitropic responses (NPR2) with unclear underlying mechanisms. Here we use a scanning ion conductance microscopy (SICM) approach combined with Förster resonance energy transfer (FRET)-based cGMP biosensors to show that whereas NPR2 is uniformly localised on the cardiomyocyte membrane, functional NPR1 receptors are found exclusively in membrane invaginations called transverse (T)-tubules. This leads to far-reaching CNP/NPR2/cGMP signals, whereas ANP/NPR1/cGMP signals are highly confined to T-tubular microdomains by local pools of phosphodiesterase 2. This provides a previously unrecognised molecular basis for clearly distinct functional effects engaged by different cGMP producing membrane receptors.

Natriuretic peptides (NPs) are important hormones that regulate cardiovascular physiology by increasing cGMP levels in cardiomyocytes. Here the authors use scanning ion conductance microscopy and a cGMP FRET sensor to identify a differential localisation pattern for the natriuretic peptide receptors within the heart.

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.

Roles of PDE1 in Pathological Cardiac Remodeling and Dysfunction

Pathological cardiac hypertrophy and dysfunction is a response to various stress stimuli and can result in reduced cardiac output and heart failure. Cyclic nucleotide signaling regulates several cardiac functions including contractility, remodeling, and fibrosis. Cyclic nucleotide phosphodiesterases (PDEs), by catalyzing the hydrolysis of cyclic nucleotides, are critical in the homeostasis of intracellular cyclic nucleotide signaling and hold great therapeutic potential as drug targets. Recent studies have revealed that the inhibition of the PDE family member PDE1 plays a protective role in pathological cardiac remodeling and dysfunction by the modulation of distinct cyclic nucleotide signaling pathways. This review summarizes recent key findings regarding the roles of PDE1 in the cardiac system that can lead to a better understanding of its therapeutic potential.

cGMP Signaling and Vascular Smooth Muscle Cell Plasticity

Cyclic GMP regulates multiple cell types and functions of the cardiovascular system. This review summarizes the effects of cGMP on the growth and survival of vascular smooth muscle cells (VSMCs), which display remarkable phenotypic plasticity during the development of vascular diseases, such as atherosclerosis. Recent studies have shown that VSMCs contribute to the development of atherosclerotic plaques by clonal expansion and transdifferentiation to macrophage-like cells. VSMCs express a variety of cGMP generators and effectors, including NO-sensitive guanylyl cyclase (NO-GC) and cGMP-dependent protein kinase type I (cGKI), respectively. According to the traditional view, cGMP inhibits VSMC proliferation, but this concept has been challenged by recent findings supporting a stimulatory effect of the NO-cGMP-cGKI axis on VSMC growth. Here, we summarize the relevant studies with a focus on VSMC growth regulation by the NO-cGMP-cGKI pathway in cultured VSMCs and mouse models of atherosclerosis, restenosis, and angiogenesis. We discuss potential reasons for inconsistent results, such as the use of genetic versus pharmacological approaches and primary versus subcultured cells. We also explore how modern methods for cGMP imaging and cell tracking could help to improve our understanding of cGMP’s role in vascular plasticity. We present a revised model proposing that cGMP promotes phenotypic switching of contractile VSMCs to VSMC-derived plaque cells in atherosclerotic lesions. Regulation of vascular remodeling by cGMP is not only an interesting new therapeutic strategy, but could also result in side effects of clinically used cGMP-elevating drugs.

Phosphorylation of protein kinase A (PKA) regulatory subunit RIα by protein kinase G (PKG) primes PKA for catalytic activity in cells

cAMP-dependent protein kinase (PKAc) is a pivotal signaling protein in eukaryotic cells. PKAc has two well-characterized regulatory subunit proteins, RI and RII (each having α and β isoforms), which keep the PKAc catalytic subunit in a catalytically inactive state until activation by cAMP. Previous reports showed that the RIα regulatory subunit is phosphorylated by cGMP-dependent protein kinase (PKG) in vitro, whereupon phosphorylated RIα no longer inhibits PKAc at normal (1:1) stoichiometric ratios. However, the significance of this phosphorylation as a mechanism for activating type I PKA holoenzymes has not been fully explored, especially in cellular systems. In this study, we further examined the potential of RIα phosphorylation to regulate physiologically relevant "desensitization" of PKAc activity. First, the serine 101 site of RIα was validated as a target of PKGIα phosphorylation both in vitro and in cells. Analysis of a phosphomimetic substitution in RIα (S101E) showed that modification of this site increases PKAc activity in vitro and in cells, even without cAMP stimulation. Numerous techniques were used to show that although Ser101 variants of RIα can bind PKAc, the modified linker region of the S101E mutant has a significantly reduced affinity for the PKAc active site. These findings suggest that RIα phosphorylation may be a novel mechanism to circumvent the requirement of cAMP stimulus to activate type I PKA in cells. We have thus proposed a model to explain how PKG phosphorylation of RIα creates a "sensitized intermediate" state that is in effect primed to trigger PKAc activity.

Cardiac unloading by LVAD support differentially influences components of the cGMP-PKG signaling pathway in ischemic and dilated cardiomyopathy

Implantation of left ventricular assist devices (LVADs) as bridge to transplant in end-stage heart failure allows for analyzing reverse remodeling processes of the supported heart. Whether this therapy influences the cGMP-PKG signaling pathway, which is currently under thorough investigation for developing new heart failure therapeutics, is unknown. In fourteen end-stage heart failure patients (8 with dilated cardiomyopathy, DCM; 6 with ischemic cardiomyopathy, ICM) tissue specimens of left ventricles were collected at LVAD implantation and afterwards at receiver heart explantation, respectively. Then the expressions of key components of the cGMP-PKG signaling pathway were determined by polymerase chain reaction (ANP; BNP; natriuretic peptide receptor A, NPR-A; natriuretic peptide receptor C, NPR-C; neprilysin; NOS3; soluble guanylyl cyclase, sGC; PDE5; cGMP-dependent protein kinase G, PKG) and enzyme-linked immunosorbent assay (cGMP), respectively. Patients were predominantly male, 52 ± 10 years old, were receiving recommended heart failure therapy, and had their donor organ implanted after 351 ± 317 days of LVAD support. Except for more DCM patients with ICD therapy, no significant differences were detected between ICM and DCM, which also applies to the expression of cGMP-PKG pathway components at baseline. After LVAD support, ANP, NPR-C, and cGMP were significantly down-regulated and neprilysin, PDE5, and PKG I expressions were reduced with borderline significance in DCM, but not in ICM patients. Multiple significant correlations were found for expression differences (i.e., expression at LVAD implantation minus expression at heart transplantation) both in DCM and ICM, even though there was a closer connection between the NO and NP side of the cGMP-PKG pathway in DCM patients. Furthermore, duration of LVAD support negatively correlated with expression differences of PKG I, PDE5, and sGC in ICM, but not in DCM. Originating from the same activation level at LVAD implantation, cardiac unloading significantly alters key components of the cGMP-PKG pathway in DCM, but not in ICM patients. This etiology-specific regulation should be considered when analyzing therapeutic interventions with effects on this signaling pathway.

Molsidomine Attenuates Ventricular Electrical Remodeling and Arrhythmogenesis in Rats With Chronic β-Adrenergic Receptor Activation Through the NO/cGMP/PKG Pathway

This study investigated the effects and associated underlying mechanisms of molsidomine, a nitric oxide (NO) donor, on cardiac electrical remodeling and ventricular tachycardias (VTs) induced by chronic isoprenaline (ISO) stimulation in rats. The rats were randomly divided into groups that were treated with saline (control group), ISO (ISO group), ISO + molsidomine (ISO + M group), and ISO + molsidomine + the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, ISO + M + O group) for 14 days. An electrophysiological study was performed to assess cardiac repolarization, action potential duration restitution, and the induction of action potential duration alternans and VTs in vitro. The properties of the Ca transients, Ca handling-related proteins, and NO/guanosine 3'5'-cyclic monophosphate (cGMP)/protein kinase G (PKG) pathway were examined. Compared with the control group, chronic ISO stimulation prolonged the cardiac repolarization, decreased the Ca transient alternans and action potential duration alternans thresholds, and increased the maximum slope (Smax) of the action potential duration restitution curve and incidence of VTs in vitro. All these effects were attenuated by molsidomine treatment (P < 0.05). Moreover, molsidomine activated cGMP/PKG signaling and stabilized the expression of calcium handling-related proteins compared with the ISO group. However, the protective effects of molsidomine were partially inhibited by ODQ. Our results suggest that molsidomine stabilizes calcium handling and attenuates cardiac electrical remodeling and arrhythmogenesis in rats with chronic β-adrenergic receptor activation. These effects are at least partially mediated by the activation of NO/cGMP/PKG pathway.

VEGFB-VEGFR1 ameliorates Ang II-induced cardiomyocyte hypertrophy through Ca2+ -mediated PKG I pathway

In response to assorted stimuli, the heart will develop into cardiomyocyte hypertrophy, but sustained cardiomyocyte hypertrophy will finally lead to heart failure. This research is aimed to examine the effect of VEGFB on cardiomyocyte hypertrophy by using the cardiomyocyte-derived cell line H9C2 of cultured rates. It turns out that VEGFB can positively prevent the Ang II-induced rising in the size of cardiomyocyte as well as reduce Ang II-induced mRNA and protein levels of β-MHC (β-myosin heavy chain), BNP (brain natriuretic peptide), and ANP (atrial natriuretic peptide). Moreover, VEGFB can regulate the decline of the Ang II-induced rising in Ca²⁺ . After VEGFR1 knockdown, these effects of VEGFB were partially reversed. Moreover, VEGFB attenuated the suppression of PKG I, p-VASP, and RGS2 caused by Ang II; whereas VEGFR1 knockdown partially abolished the indicated effect of VEGFB. In a word, the effect of VEGFB on relevant downstream targets and the pathways of PKG I by VEGFR1 may explain its efficacy on cardiomyocyte hypertrophy. Thus, it can be suggested that it is feasible to apply VEGFB-VEGFR1 for reducing the symptoms of cardiomyocyte hypertrophy.

C33(S), a novel PDE9A inhibitor, protects against rat cardiac hypertrophy through upregulating cGMP signaling

Phosphodiesterase-9A (PDE9A) expression is upregulated during cardiac hypertrophy and heart failure. Accumulating evidence suggests that PDE9A might be a promising therapeutic target for heart diseases. The present study sought to investigate the effects and underlying mechanisms of C33(S), a novel selective PDE9A inhibitor, on cardiac hypertrophy in vitro and in vivo. Treatment of neonatal rat cardiomyocytes (NRCMs) with PE (100 μmol/L) or ISO (1 μmol/L) induced cardiac hypertrophy characterized by significantly increased cell surface areas and increased expression of fetal genes (ANF and BNP). Furthermore, PE or ISO significantly increased the expression of PDE9A in the cells; whereas knockdown of PDE9A significantly alleviated PE-induced hypertrophic responses. Moreover, pretreatment with PDE9A inhibitor C33(S) (50 and 500 nmol/L) or PF-7943 (2 μmol/L) also alleviated the cardiac hypertrophic responses in PE-treated NRCMs. Abdominal aortic constriction (AAC)-induced cardiac hypertrophy and ISO-induced heart failure were established in SD rats. In ISO-treated rats, oral administration of C33(S) (9, 3, and 1 mg·kg^-1·d^-1, for 3 consecutive weeks) significantly increased fractional shortening (43.55%±3.98%, 54.79%±1.95%, 43.98%±7.96% vs 32.18%±6.28%), ejection fraction (72.97%±4.64%, 84.29%±1.56%, 73.41%±9.37% vs 49.17%±4.20%) and cardiac output (60.01±9.11, 69.40±11.63, 58.08±8.47 mL/min vs 48.97±2.11 mL/min) but decreased the left ventricular internal diameter, suggesting that the transition to heart failure was postponed by C33(S). We further revealed that C33(S) significantly elevated intracellular cGMP levels, phosphorylation of phospholamban (PLB) and expression of SERCA2a in PE-treated NRCMs in vitro and in ISO-induced heart failure model in vivo. Our results demonstrate that C33(S) effectively protects against cardiac hypertrophy and postpones the transition to heart failure, suggesting that it is a promising agent in the treatment of cardiac diseases.