Therapeutic potential of PDE modulation in treating heart disease

Improving ribonucleic acid production in Saccharomyces pastorianus via in silico genome-scale metabolic network model

Ribonucleic acid (RNA) and its degradation products are important biomolecules widely used in the food and pharmaceutical industries for their flavoring and nutritional functions. In this study, we used a genome-scale metabolic network model (GSMM) to explore genetic targets for nucleic acid synthesis in a Saccharomyces pastorianus strain (G03). Yeast 8.5.0 was used as the base model, which accurately predicted G03's growth. Using OptForce, we found that overexpression of ARO8 and ATP1 among six different strategies increased the RNA content of G03 by 58.0% and 74.8%, respectively. We also identified new metabolic targets for improved RNA production using a modified GSMM called TissueModel, constructed using the GIMME transcriptome constraint tool to remove low-expressed reactions in the model. After running OptKnock, the RNA content of G03-△BNA1 and G03-△PMA1 increased by 44.6% and 39.8%, respectively, compared to G03. We suggest that ATP1, ARO8, BNA1, and PMA1 regulate cell fitness, which affects RNA content. This study is the first to identify strategies for RNA overproduction using GSMM and to report that regulation of ATP1, ARO8, BNA1, and PMA1 can increase RNA content in S. pastorianus. These findings also provide valuable knowledge on model reconstruction for S. pastorianus.

Therapeutic enzymes as non-conventional targets in cardiovascular impairments:A Comprehensive Review

Over the last few decades, substantial progress has been made towards the understanding of cardiovascular diseases (CVDs). In-depth mechanistic insights have also provided opportunities to explore novel therapeutic targets and treatment regimens to be discovered. Therapeutic enzymes are an example of such opportunities. The balanced functioning of such enzymes protects against a variety of CVDs while on the other hand, even a small shift in the normal functioning of these enzymes may lead to deleterious outcomes. Owing to the great versatility of these enzymes, inhibition and activation are key regulatory approaches to counter the onset and progression of several cardiovascular impairments. While cardiovascular remedies are already available in excess and of course they are efficacious, a comprehensive description of novel therapeutic enzymes to combat CVDs is the need of the hour. In light of this, the regulation of the functional activity of these enzymes also opens a new avenue for the treatment approaches to be employed. This review describes the importance of non-conventional enzymes as potential candidates in several cardiovascular disorders while highlighting some of the recently targeted therapeutic enzymes in CVDs.

Effects of phosphodiesterase-1 inhibitor on pulmonary vein electrophysiology and arrhythmogenesis

INTRODUCTION

Phosphodiesterase (PDE) isoform inhibitors have mechanical and electrical effects on the heart. Inhibition of PDE-1 enzymes is a novel strategy for treating heart failure. However, the electrophysiological effects of PDE-1 inhibition on the heart remain unclear. This study explored the effects of PDE-1 inhibition using ITI-214 on electrical activity in the pulmonary vein (PV), the most common trigger of atrial fibrillation, and investigated the underlying ionic mechanisms.

METHODS

Conventional microelectrodes or whole-cell patch clamps were employed to study the effects of ITI-214 (0.1-10 μM) on PV electrical activity, mechanical responses and ionic currents in isolated rabbit PV tissue specimens and isolated single PV cardiomyocytes.

RESULTS

ITI-214 at 1 μM and 10 μM (but not 0.1 μM) significantly reduced PV spontaneous beating rate (10 ± 2% and 10 ± 3%, respectively) and PV diastolic tension (11 ± 3% and 17 ± 3%, respectively). ITI-24 (1 μM) significantly reduced late sodium current (I_Na-Late ), L-type calcium current (I_Ca-L ) and the reverse mode of the sodium-calcium exchanger (NCX), but it did not affect peak sodium currents.

CONCLUSIONS

ITI-214 reduces PV spontaneous activity and PV diastolic tension by reducing I_Na-Late , I_Ca-L and NCX current. Considering its therapeutic potential in heart failure, targeting PDE-1 inhibition may provide a novel strategy for managing atrial arrhythmogenesis.

cGMP Signaling in Cardiovascular Diseases: Linking Genotype and Phenotype

Cyclic guanosine 3',5'-monophosphate (cGMP) is the key second messenger molecule in nitric oxide signaling. Its rapid generation and fate, but also its role in mediating acute cellular functions has been extensively studied. In the past years, genetic studies suggested an important role for cGMP in affecting the risk of chronic cardiovascular diseases, for example, coronary artery disease and myocardial infarction. Here, we review the role of cGMP in atherosclerosis and other cardiovascular diseases and discuss recent genetic findings and identified mechanisms. Finally, we highlight open questions and promising research topics.

The long and winding road of designing phosphodiesterase inhibitors for the treatment of heart failure

Cyclic nucleotide phosphodiesterases (PDEs) are a superfamily of enzymes known to play a critical role in the indirect regulation of several intracellular metabolism pathways through the selective hydrolysis of the phosphodiester bonds of specific second messenger substrates such as cAMP (3',5'-cyclic adenosine monophosphate) and cGMP (3',5'-cyclic guanosine monophosphate), influencing the hypertrophy, contractility, apoptosis and fibroses in the cardiovascular system. The expression and/or activity of multiple PDEs is altered during heart failure (HF), which leads to changes in levels of cyclic nucleotides and function of cardiac muscle. Within the cardiovascular system, PDEs 1-5, 8 and 9 are expressed and are interesting targets for the HF treatment. In this comprehensive review we will present a briefly description of the biochemical importance of each cardiovascular related PDE to the HF, and cover almost all the "long and winding road" of designing and discovering ligands, hits, lead compounds, clinical candidates and drugs as PDE inhibitors in the last decade.

Machine learning guided association of adverse drug reactions with in vitro target-based pharmacology

BACKGROUND

Adverse drug reactions (ADRs) are one of the leading causes of morbidity and mortality in health care. Understanding which drug targets are linked to ADRs can lead to the development of safer medicines.

METHODS

Here, we analyse in vitro secondary pharmacology of common (off) targets for 2134 marketed drugs. To associate these drugs with human ADRs, we utilized FDA Adverse Event Reports and developed random forest models that predict ADR occurrences from in vitro pharmacological profiles.

FINDINGS

By evaluating Gini importance scores of model features, we identify 221 target-ADR associations, which co-occur in PubMed abstracts to a greater extent than expected by chance. Amongst these are established relations, such as the association of in vitro hERG binding with cardiac arrhythmias, which further validate our machine learning approach. Evidence on bile acid metabolism supports our identification of associations between the Bile Salt Export Pump and renal, thyroid, lipid metabolism, respiratory tract and central nervous system disorders. Unexpectedly, our model suggests PDE3 is associated with 40 ADRs.

INTERPRETATION

These associations provide a comprehensive resource to support drug development and human biology studies.

FUNDING

This study was not supported by any formal funding bodies.

Various subtypes of phosphodiesterase inhibitors differentially regulate pulmonary vein and sinoatrial node electrical activities

Phosphodiesterase (PDE)3-5 are expressed in cardiac tissue and play critical roles in the pathogenesis of heart failure and atrial fibrillation. PDE inhibitors are widely used in the clinic, but their effects on the electrical activity of the heart are not well understood. The aim of the present study was to examine the effects of various PDE inhibitors on spontaneous cardiac activity and compare those effects between sinoatrial nodes (SANs) and pulmonary veins (PVs). Conventional microelectrodes were used to record action potentials in isolated rabbit SAN and PV tissue preparations, before and after administration of different concentrations (0.1, 1 and 10 µM) of milrinone (PDE3 inhibitor), rolipram (PDE4 inhibitor) and sildenafil (PDE5 inhibitor), with or without the application of isoproterenol (cAMP and PKA activator), KT5823 (PKG inhibitor) or H89 (PKA inhibitor). Milrinone (1 and 10 µM) increased the spontaneous activity in PVs by 10.6±4.9 and 16.7±5.3% and in SANs by 9.3±4.3 and 20.7±4.6%, respectively. In addition, milrinone (1 and 10 µM) induced the occurrence of triggered activity (0/8 vs. 5/8; P<0.005) in PVs. Rolipram increased PV spontaneous activity by 7.5±1.3-9.5±4.0%, although this was not significant, and did not alter SAN spontaneous activity. Sildenafil reduced spontaneous activity in PVs to a greater extent than that seen in SANs. Both KT5823 and H89 suppressed milrinone-increased PV spontaneous activity. In the presence of isoproterenol, milrinone did not alter isoproterenol-induced PV arrhythmogenesis, suggesting that the effects of PDE3 are mediated by the protein kinase G and protein kinase A signaling pathways. In conclusion, inhibitors of different PDE subtypes exert diverse electrophysiological effects on PV and SAN activities.

Updates of Recent Vinpocetine Research in Treating Cardiovascular Diseases

Vinpocetine is a derivative of vincamine. It has been used to prevent and treat cerebrovascular disorders such as stoke and dementia, and remains widely available in dietary supplements that often marketed as nootropics. Due to its excellent safety profile at therapeutic dose regimen, vinpocetine has raised research interest in its new applications in various experimental disease models. Here we review recent studies that uncovered novel functions of vinpocetine in cardiovascular diseases, including atherosclerosis, obesity, neointimal hyperplasia, vasoconstriction, pathological cardiac remodeling and ischemia stroke. Molecular mechanisms underlined the protective effects of vinpocetine are also discussed. These novel findings may suggest a broadened usage of vinpocetine against relevant cardiovascular diseases in human.

Multiprotein Complex With TRPC (Transient Receptor Potential-Canonical) Channel, PDE1C (Phosphodiesterase 1C), and A2R (Adenosine A2 Receptor) Plays a Critical Role in Regulating Cardiomyocyte cAMP and Survival

BACKGROUND

cAMP plays a critical role in regulating cardiomyocyte survival. Various cAMP signaling pathways behave distinctly or in opposition. We have previously reported that activation of cAMP hydrolysis by cyclic nucleotide phosphodiesterase 1C (PDE1C) promotes cardiomyocytes death/apoptosis, yet the underlying molecular mechanism remains unknown. In this study, we aimed to identify the specific cAMP signaling pathway modulated by PDE1C and determine the mechanism by which Ca²⁺/calmodulin-stimulated PDE1C is activated.

METHODS

To study cardiomyocyte death/apoptosis, we used both isolated mouse adult cardiomyocytes in vitro and doxorubicin-induced cardiotoxicity in vivo. We used a variety of pharmacological activators and inhibitors as well as genetically engineered molecular tools to manipulate the expression and activity of proteins of interest.

RESULTS

We found that the protective effect of PDE1C inhibition/deficiency on Ang II or doxorubicin-induced cardiomyocyte death/apoptosis is dependent on cAMP-generating adenosine A₂ receptors (A₂Rs), suggesting that PDE1C's cAMP-hydrolyzing activity selectively modulates A₂R-cAMP signaling in cardiomyocytes. In addition, we found that the effects of PDE1C activation on Ang II-mediated cAMP reduction and cardiomyocyte death are dependent on transient receptor potential-canonical (TRPC) channels, in particular TRPC3. We also observed synergistic protective effects on cardiomyocyte survival from the combination of A₂R stimulation together with PDE1 or TRPC inhibition. Coimmunostaining and coimmunoprecipitation studies showed that PDE1C is localized in proximity with A₂R and TRPC3 in the plasma membrane and perhaps T tubules. It is important to note that we found that doxorubicin-induced cardiac toxicity and dysfunction in mice are attenuated by the PDE1 inhibitor IC86340 or in PDE1C knockout mice, and this protective effect is significantly diminished by A₂R antagonism.

CONCLUSIONS

We have characterized a novel multiprotein complex comprised of A₂R, PDE1C, and TRPC3, in which PDE1C is activated by TRPC3-derived Ca²⁺, thereby antagonizing A₂R-cAMP signaling and promoting cardiomyocyte death/apoptosis. Targeting these molecules individually or in combination may represent a compelling therapeutic strategy for potentiating cardiomyocyte survival.

Simultaneous measurement of excitation-contraction coupling parameters identifies mechanisms underlying contractile responses of hiPSC-derived cardiomyocytes

Cardiomyocytes from human induced pluripotent stem cells (hiPSC-CMs) are increasingly recognized as valuable for determining the effects of drugs on ion channels but they do not always accurately predict contractile responses of the human heart. This is in part attributable to their immaturity but the sensitivity of measurement tools may also be limiting. Measuring action potential, calcium flux or contraction individually misses critical information that is captured when interrogating the complete excitation-contraction coupling cascade simultaneously. Here, we develop an hypothesis-based statistical algorithm that identifies mechanisms of action. We design and build a high-speed optical system to measure action potential, cytosolic calcium and contraction simultaneously using fluorescent sensors. These measurements are automatically processed, quantified and then assessed by the algorithm. Multiplexing these three critical physical features of hiPSC-CMs allows identification of all major drug classes affecting contractility with detection sensitivities higher than individual measurement of action potential, cytosolic calcium or contraction.

PDE1 inhibition facilitates proteasomal degradation of misfolded proteins and protects against cardiac proteinopathy

No current treatment targets cardiac proteotoxicity or can reduce mortality of heart failure (HF) with preserved ejection fraction (HFpEF). Selective degradation of misfolded proteins by the ubiquitin-proteasome system (UPS) is vital to the cell. Proteasome impairment contributes to HF. Activation of cAMP-dependent protein kinase (PKA) or cGMP-dependent protein kinase (PKG) facilitates proteasome functioning. Phosphodiesterase 1 (PDE1) hydrolyzes both cyclic nucleotides and accounts for most PDE activities in human myocardium. We report that PDE1 inhibition (IC86430) increases myocardial 26S proteasome activities and UPS proteolytic function in mice. Mice with CryAB^R120G-based proteinopathy develop HFpEF and show increased myocardial PDE1A expression. PDE1 inhibition markedly attenuates HFpEF, improves mouse survival, increases PKA-mediated proteasome phosphorylation, and reduces myocardial misfolded CryAB. Therefore, PDE1 inhibition induces PKA- and PKG-mediated promotion of proteasomal degradation of misfolded proteins and treats HFpEF caused by CryAB^R120G, representing a potentially new therapeutic strategy for HFpEF and heart disease with increased proteotoxic stress.

Differential expressions and functions of phosphodiesterase enzymes in different regions of the rat heart

Phosphodiesterase enzymes (PDEs) are responsible for the adjustment of cyclic nucleotide levels. Alterations in PDE expressions in different tissues cause conflicts between functional and clinical effects of PDE inhibitors. Therefore, the aim of this study was to investigate the gene and protein expressions and the functional role of PDEs in atrium and ventricle of rat heart. The expressions of PDEs were examined in cardiac intact tissues and enzymatically isolated cells. The effects of PDE1-5 inhibitors (vinpocetine, EHNA, milrinone, rolipram, sildenafil, and IBMX) on basal and isoprenaline-stimulated contractions and sinus rate were recorded in the isolated spontaneously beating right atrium and electrically stimulated left papillary muscles. The mRNA and protein levels of PDEs were significantly different in atrial and ventricular intact tissues and isolated myocytes. Atrial contractions were increased with vinpocetine while suppressed by EHNA, milrinone, rolipram, sildenafil and IBMX. Milrinone, sildenafil and IBMX increased the heart rate whereas vinpocetine caused negative chronotropy. Papillary muscle contractions have been increased only with the vinpocetine and IBMX. Both the expression and the action of PDE-1-5 show atrial and ventricular differences. Therefore, these differences should be taken into account in the experimental or therapeutic approaches of the heart.

Roles of A-Kinase Anchoring Proteins and Phosphodiesterases in the Cardiovascular System

A-kinase anchoring proteins (AKAPs) and cyclic nucleotide phosphodiesterases (PDEs) are essential enzymes in the cyclic adenosine 3′-5′ monophosphate (cAMP) signaling cascade. They establish local cAMP pools by controlling the intensity, duration and compartmentalization of cyclic nucleotide-dependent signaling. Various members of the AKAP and PDE families are expressed in the cardiovascular system and direct important processes maintaining homeostatic functioning of the heart and vasculature, e.g., the endothelial barrier function and excitation-contraction coupling. Dysregulation of AKAP and PDE function is associated with pathophysiological conditions in the cardiovascular system including heart failure, hypertension and atherosclerosis. A number of diseases, including autosomal dominant hypertension with brachydactyly (HTNB) and type I long-QT syndrome (LQT1), result from mutations in genes encoding for distinct members of the two classes of enzymes. This review provides an overview over the AKAPs and PDEs relevant for cAMP compartmentalization in the heart and vasculature and discusses their pathophysiological role as well as highlights the potential benefits of targeting these proteins and their protein-protein interactions for the treatment of cardiovascular diseases.

Negative inotropic effects of diadenosine tetraphosphate are mediated by protein kinase C and phosphodiesterases stimulation in the rat heart

Extracellular diadenosine polyphosphates (Ap_nA) are recently considered as an endogenous signaling compounds with transmitter-like activity which present in numerous tissues, including heart. It has been demonstrated previously that extracellular Ap_nA cause alteration of the heart functioning via purine receptors in different mammalian species. Nevertheless, principal intracellular pathways which underlie Ap_nA action in the heart remain unknown. In the present study the role of the P2Y-associated intracellular regulatory pathway in the mediation of diadenosine tetraphosphate (Ap₄A) effects in the rat heart has been investigated for the first time. Extracellular Ap₄A caused significant decreasing of the ventricular inotropy. Ap₄A evoked reduction of the left ventricle contractility in the isolated Langendorff-perfused rat hearts, decreasing of the Ca²⁺ transients in the enzymatically isolated ventricular cardiomyocytes and induced shortening of action potentials in the ventricle multicellular preparations. The inhibitory effects of Ap₄A in the rat heart were significantly attenuated by protein kinase C (PKC) inhibitor chelerythrine but these effects were not affected by NO-synthase inhibitor L-NAME and guanylyl cyclase (sGC) inhibitor ODQ. In addition, substantial attenuation of Ap₄A-caused negative inotropy in the left ventricle was produced by nonselective phsophodiesterase (PDE) inhibitor IBMX, while PDE type 2 inhibitor EHNA was ineffective. In conclusion, our results allow suggesting that Ap₄A-induced inhibitory effects in the rat heart are mediated by PKC, but not by NO/sGC/PKG-related signaling pathway. In addition, PDE stimulation may contribute to Ap₄A-caused inhibition of the rat heart contractility.

The Potential of a Novel Class of EPAC-Selective Agonists to Combat Cardiovascular Inflammation

The cyclic 3′,5′-adenosine monophosphate (cAMP) sensor enzyme, EPAC1, is a candidate drug target in vascular endothelial cells (VECs) due to its ability to attenuate proinflammatory cytokine signalling normally associated with cardiovascular diseases (CVDs), including atherosclerosis. This is through the EPAC1-dependent induction of the suppressor of cytokine signalling gene, SOCS3, which targets inflammatory signalling proteins for ubiquitinylation and destruction by the proteosome. Given this important role for the EPAC1/SOCS3 signalling axis, we have used high throughput screening (HTS) to identify small molecule EPAC1 regulators and have recently isolated the first known non-cyclic nucleotide (NCN) EPAC1 agonist, I942. I942 therefore represents the first in class, isoform selective EPAC1 activator, with the potential to suppress pro-inflammatory cytokine signalling with a reduced risk of side effects associated with general cAMP-elevating agents that activate multiple response pathways. The development of augmented I942 analogues may therefore provide improved research tools to validate EPAC1 as a potential therapeutic target for the treatment of chronic inflammation associated with deadly CVDs.

Nanodomain Regulation of Cardiac Cyclic Nucleotide Signaling by Phosphodiesterases

Cyclic nucleotide phosphodiesterases (PDEs) form an 11-member superfamily comprising 100 different isoforms that regulate the second messengers cyclic adenosine or guanosine 3',5'-monophosphate (cAMP or cGMP). These PDE isoforms differ with respect to substrate selectivity and their localized control of cAMP and cGMP within nanodomains that target specific cellular pools and synthesis pathways for the cyclic nucleotides. Seven PDE family members are physiologically relevant to regulating cardiac function, disease remodeling of the heart, or both: PDE1 and PDE2, both dual-substrate (cAMP and cGMP) esterases; PDE3, PDE4, and PDE8, which principally hydrolyze cAMP; and PDE5A and PDE9A, which target cGMP. New insights regarding the different roles of PDEs in health and disease and their local signaling control are broadening the potential therapeutic utility for PDE-selective inhibitors. In this review, we discuss these PDEs, focusing on the different mechanisms by which they control cardiac function in health and disease by regulating intracellular nanodomains.

From Bench to Bedside: New Approaches to Therapeutic Discovery for Heart Failure

Heart failure is a significant global health problem, which is becoming worse as the population ages, and remains one of the biggest burdens on our economy. Despite significant advances in cardiovascular medicine, management and surgery, mortality rates remain high, with almost half of patients with heart failure dying within five years of diagnosis. As a multifactorial clinical syndrome, heart failure still represents an epidemic threat, highlighting the need for deeper insights into disease mechanisms and the development of innovative therapeutic strategies for both treatment and prevention. In this review, we discuss conventional heart failure therapies and highlight new pharmacological agents targeting pathophysiological features of the failing heart, for example, non-coding RNAs, angiotensin receptor-neprilysin inhibitors, cardiac myosin activators, BGP-15 and molecules targeting GRK2 including M119, gallein and paroxetine. Finally, we address the disparity between phase II and phase III clinical trials that prevent the translation of emerging HF therapies into new and approved therapies.

Phosphodiesterase 5a Inhibition with Adenoviral Short Hairpin RNA Benefits Infarcted Heart Partially through Activation of Akt Signaling Pathway and Reduction of Inflammatory Cytokines

Introduction

Treatment with short hairpin RNA (shRNA) interference therapy targeting phosphodiesterase 5a after myocardial infarction (MI) has been shown to mitigate post-MI heart failure. We investigated the mechanisms that underpin the beneficial effects of PDE5a inhibition through shRNA on post-MI heart failure.

Methods

An adenoviral vector with an shRNA sequence inserted was adopted for the inhibition of phosphodiesterase 5a (Ad-shPDE5a) in vivo and in vitro. Myocardial infarction (MI) was induced in male C57BL/6J mice by left coronary artery ligation, and immediately after that, the Ad-shPDE5a was injected intramyocardially around the MI region and border areas.

Results

Four weeks post-MI, the Ad-shPDE5a-treated mice showed significant mitigation of the left ventricular (LV) dilatation and dysfunction compared to control mice. Infarction size and fibrosis were also significantly reduced in Ad-shPDE5a-treated mice. Additionally, Ad-shPDE5a treatment decreased the MI-induced inflammatory cytokines interleukin (IL)-1β, IL-6, tumor necrosis factor-α, and transforming growth factor-β1, which was confirmed in vitro in Ad-shPDE5a transfected myofibroblasts cultured under oxygen glucose deprivation. Finally, Ad-shPDE5a treatment was found to activate the myocardial Akt signaling pathway in both in vivo and in vitro experiments.

Conclusion

These findings indicate that PDE5a inhibition by Ad-shPDE5a via the Akt signal pathway could be of significant value in the design of future therapeutics for post-MI heart failure.

Alcohol Consumption Modulates Host Defense in Rhesus Macaques by Altering Gene Expression in Circulating Leukocytes

Several lines of evidence indicate that chronic alcohol use disorder leads to increased susceptibility to several viral and bacterial infections, whereas moderate alcohol consumption decreases the incidence of colds and improves immune responses to some pathogens. In line with these observations, we recently showed that heavy ethanol intake (average blood ethanol concentrations > 80 mg/dl) suppressed, whereas moderate alcohol consumption (blood ethanol concentrations < 50 mg/dl) enhanced, T and B cell responses to modified vaccinia Ankara vaccination in a nonhuman primate model of voluntary ethanol consumption. To uncover the molecular basis for impaired immunity with heavy alcohol consumption and enhanced immune response with moderate alcohol consumption, we performed a transcriptome analysis using PBMCs isolated on day 7 post-modified vaccinia Ankara vaccination, the earliest time point at which we detected differences in T cell and Ab responses. Overall, chronic heavy alcohol consumption reduced the expression of immune genes involved in response to infection and wound healing and increased the expression of genes associated with the development of lung inflammatory disease and cancer. In contrast, chronic moderate alcohol consumption upregulated the expression of genes involved in immune response and reduced the expression of genes involved in cancer. To uncover mechanisms underlying the alterations in PBMC transcriptomes, we profiled the expression of microRNAs within the same samples. Chronic heavy ethanol consumption altered the levels of several microRNAs involved in cancer and immunity and known to regulate the expression of mRNAs differentially expressed in our data set.

Role of cAMP-phosphodiesterase 1C signaling in regulating growth factor receptor stability, vascular smooth muscle cell growth, migration, and neointimal hyperplasia

RATIONALE

Neointimal hyperplasia characterized by abnormal accumulation of vascular smooth muscle cells (SMCs) is a hallmark of occlusive disorders such as atherosclerosis, postangioplasty restenosis, vein graft stenosis, and allograft vasculopathy. Cyclic nucleotides are vital in SMC proliferation and migration, which are regulated by cyclic nucleotide phosphodiesterases (PDEs).

OBJECTIVE

Our goal is to understand the regulation and function of PDEs in SMC pathogenesis of vascular diseases.

METHODS AND RESULTS

We performed screening for genes differentially expressed in normal contractile versus proliferating synthetic SMCs. We observed that PDE1C expression was low in contractile SMCs but drastically elevated in synthetic SMCs in vitro and in various mouse vascular injury models in vivo. In addition, PDE1C was highly induced in neointimal SMCs of human coronary arteries. More importantly, injury-induced neointimal formation was significantly attenuated by PDE1C deficiency or PDE1 inhibition in vivo. PDE1 inhibition suppressed vascular remodeling of human saphenous vein explants ex vivo. In cultured SMCs, PDE1C deficiency or PDE1 inhibition attenuated SMC proliferation and migration. Mechanistic studies revealed that PDE1C plays a critical role in regulating the stability of growth factor receptors, such as PDGF receptor β (PDGFRβ) known to be important in pathological vascular remodeling. PDE1C interacts with low-density lipoprotein receptor-related protein-1 and PDGFRβ, thus regulating PDGFRβ endocytosis and lysosome-dependent degradation in an low-density lipoprotein receptor-related protein-1-dependent manner. A transmembrane adenylyl cyclase cAMP-dependent protein kinase cascade modulated by PDE1C is critical in regulating PDGFRβ degradation.

CONCLUSIONS

These findings demonstrated that PDE1C is an important regulator of SMC proliferation, migration, and neointimal hyperplasia, in part through modulating endosome/lysosome-dependent PDGFRβ protein degradation via low-density lipoprotein receptor-related protein-1.

Regulatory mechanisms of cAMP levels as a multiple target for antiplatelet activity and less bleeding risk

Platelet activation is a critical component of atherothrombosis. The multiple pathways of platelet activation limit the effect of specific receptor/pathway inhibitors, resulting in limited clinical efficacy. Recent research has confirmed that combination therapy results in enhanced antithrombotic efficacy without increasing bleeding risk. In this way, the best-known inhibitor and turn off signaling in platelet activation is cAMP. In this article we discuss the mechanisms of regulation of intraplatelet cAMP levels, a) platelet-dependent pathway: Gi/Gs protein-coupled receptors, phosphodiesterase inhibition and activation of PPARs and b) platelet-independent pathway: inhibition of adenosine uptake by erythrocytes. With respect to the association between intraplatelet cAMP levels and bleeding risk it is possible to establish that compounds/drugs with pleitropic effect for increased intraplatelet cAMP level could have an antithrombotic activity with less risk of bleeding.