Gene deletion of P2Y4 receptor lowers exercise capacity and reduces myocardial hypertrophy with swimming exercise

Loss-of-function N178T variant of the human P2Y4 receptor is associated with decreased severity of coronary artery disease and improved glucose homeostasis

Human P2Y4 is a UTP receptor, while in mice it is activated by both ATP and UTP. P2Y4 knockout (KO) in mice protects against myocardial infarction and is characterized by increased adiponectin secretion by adipocytes, and decreased cardiac inflammation and permeability under ischemic conditions. The relevance of these data has, however, not been explored to date in humans. In a population study comprising 50 patients with coronary artery disease (CAD) and 50 age-matched control individuals, we analyzed P2RY4 mutations and their potential association with CAD severity and fasting plasma parameters. Among the mutations identified, we focused our attention on a coding region polymorphism (rs3745601) that results in replacement of the asparagine at residue 178 with threonine (N178T) located in the second extracellular loop of the P2Y4 receptor. The N178T variant is a loss-of-function mutation of the human P2Y4 receptor and is encountered less frequently in coronary patients than in control individuals. In coronary patients, carriers of the N178T variant had significantly reduced jeopardy and Gensini cardiac severity scores, as well as lower resting heart rates and plasma levels of N-terminal pro-brain natriuretic peptide (NT-proBNP). Regarding fasting plasma parameters, the N178T variant was associated with a lower concentration of glucose. Accordingly, P2Y4 KO mice had significantly improved glucose tolerance and insulin sensitivity compared with their WT littermate controls. The improvement of insulin sensitivity resulting from lack of the P2Y4 receptor was no longer observed in the absence of adiponectin. The present study identifies a frequent loss-of-function P2Y4 variant associated with less severe coronary artery atherosclerosis and lower fasting plasma glucose in coronary patients. The role of the P2Y4 receptor in glucose homeostasis was confirmed in mouse. P2Y4 antagonists could thus have therapeutic applications in the treatment of myocardial infarction and type 2 diabetes.

Purinergic receptors modulators: An emerging pharmacological tool for disease management

Purinergic signaling is mediated through extracellular nucleotides (adenosine 5'-triphosphate, uridine-5'-triphosphate, adenosine diphosphate, uridine-5'-diphosphate, and adenosine) that serve as signaling molecules. In the early 1990s, purines and pyrimidine receptors were cloned and characterized drawing the attention of scientists toward this aspect of cellular signaling. This signaling pathway is comprised of four subtypes of adenosine receptors (P1), eight subtypes of G-coupled protein receptors (P2YRs), and seven subtypes of ligand-gated ionotropic receptors (P2XRs). In current studies, the pathophysiology and therapeutic potentials of these receptors have been focused on. Various ligands, modulating the functions of purinergic receptors, are in current clinical practices for the treatment of various neurodegenerative disorders and cardiovascular diseases. Moreover, several purinergic receptors ligands are in advanced phases of clinical trials as a remedy for depression, epilepsy, autism, osteoporosis, atherosclerosis, myocardial infarction, diabetes, irritable bowel syndrome, and cancers. In the present study, agonists and antagonists of purinergic receptors have been summarized that may serve as pharmacological tools for drug design and development.

Molecular pharmacology of P2Y receptor subtypes

Professor Geoffrey Burnstock proposed the concept of purinergic signaling via P1 and P2 receptors. P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular adenine and uracil nucleotides. Eight mammalian P2Y receptor subtypes have been identified. They are divided into two subgroups (P2Y₁, P2Y₂, P2Y₄, P2Y₆, and P2Y₁₁) and (P2Y₁₂, P2Y₁₃, and P2Y₁₄). P2Y receptors are found in almost all cells and mediate responses in physiology and pathophysiology including pain and inflammation. The antagonism of platelet P2Y₁₂ receptors by cangrelor, ticagrelor or active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel reduces the ADP-induced platelet aggregation in patients with thrombotic complications of vascular diseases. The nucleotide agonist diquafosol acting at P2Y₂ receptors is used for the treatment of the dry eye syndrome. Structural information obtained by crystallography of the human P2Y₁ and P2Y₁₂ receptor proteins, site-directed mutagenesis and molecular modeling will facilitate the rational design of novel selective drugs.

P2Y4, P2Y6 and P2Y11 receptors: From the early days of cloning to their function

The family of P2Y nucleotide receptors is composed of eight members differentiated by their pharmacology and their coupling to specific G-proteins and transduction mechanisms. The laboratory studying these nucleotide receptors at IRIBHM institute (Free University of Brussels) has participated actively in their cloning. We used classical cloning by homology strategies relying on polymerase chain reactions with degenerate primers or on DNA libraries screening with P2Y receptors-related primers or probes, respectively. We identified and characterised four of the eight human P2Y receptors cloned so far: P2Y₄, P2Y₆, P2Y₁₁ and P2Y₁₃ receptors. These human receptors displayed specific features in terms of pharmacology such as affinity for pyrimidine nucleotides for P2Y₄ and P2Y₆ receptors and differential G-protein coupling. Their specific and restricted tissue distribution compared to ubiquitous P2Y₁ and P2Y₂ receptors led us to study their physiological role in chosen cell systems or using mice deficient for these P2Y subtypes. These studies revealed over the years that the P2Y₁₁ receptor was able to confer tolerogenic and tumorigenic properties to human dendritic cells and that P2Y₄ and P2Y₆ receptors were involved in mouse heart post-natal development and cardioprotection. P2Y receptors and their identified target genes could constitute therapeutic targets to regulate cardiac hypertrophy and regeneration. The multiple roles of P2Y receptors identified in the ischemic heart and cardiac adipose tissue could have multiple innovative clinical applications and present a major interest in the field of cardiovascular diseases. P2Y receptors can induce cardioprotection by the regulation of cardiac inflammation and the modulation of the volume and composition of cardiac adipose tissue. These findings might lead to the pre-clinical validation of P2Y receptors as new targets for the treatment of myocardial ischemia.

Knockout and Knock-in Mouse Models to Study Purinergic Signaling

Purinergic signaling involves extracellular purines and pyrimidines acting upon specific cell surface purinoceptors classified into the P1, P2X, and P2Y families for nucleosides and nucleotides. This widespread signaling mechanism is active in all major tissues and influences a range of functions in health and disease. Orthologs to all but one of the human purinoceptors have been found in mouse, making this laboratory animal a useful model to study their function. Indeed, analyses of purinoceptors via knock-in or knockout approaches to produce gain or loss of function phenotypes have revealed several important therapeutic targets. None of the homozygous purinoceptor knockouts proved to be developmentally lethal, which suggest that either these receptors are not involved in key developmental processes or that the large number of receptors in each family allowed for functional compensation. Different models for the same purinoceptor often show compatible phenotypes but there have been examples of significant discrepancies. These revealed unexpected differences in the structure of human and mouse genes and emphasized the importance of the genetic background of different mouse strains. In this chapter, we provide an overview of the current knowledge and new trends in the modifications of purinoceptor genes in vivo. We discuss the resulting phenotypes, their applications and relative merits and limitations of mouse models available to study purinoceptor subtypes.

Anticancer Effects of Emodin on HepG2 Cell: Evidence from Bioinformatic Analysis

Hepatocellular carcinoma (HCC) is a primary cause of cancer-related death in the world. Despite the fact that there are many methods to treat HCC, the 5-year survival rate of HCC is still at a low level. Emodin can inhibit the growth of HCC cells in vitro and in vivo. However, the gene regulation of emodin in HCC has not been well studied. In our research, RNA sequencing technology was used to identify the differentially expressed genes (DEGs) in HepG2 cells induced by emodin. A total of 859 DEGs were identified, including 712 downregulated genes and 147 upregulated genes in HepG2 cells treated with emodin. We used DAVID for function and pathway enrichment analysis. The protein-protein interaction (PPI) network was constructed using STRING, and Cytoscape was used for module analysis. The enriched functions and pathways of the DEGs include positive regulation of apoptotic process, structural molecule activity and lipopolysaccharide binding, protein digestion and absorption, ECM-receptor interaction, complement and coagulation cascades, and MAPK signaling pathway. 25 hub genes were identified and pathway analysis revealed that these genes were mainly enriched in neuropeptide signaling pathway, inflammatory response, and positive regulation of cytosolic calcium ion concentration. Survival analysis showed that LPAR6, C5, SSTR5, GPR68, and P2RY4 may be involved in the molecular mechanisms of emodin therapy for HCC. A quantitative real-time PCR (qRT-PCR) assay showed that the mRNA levels of LPAR6, C5, SSTR5, GPR68, and P2RY4 were significantly decreased in HepG2 cells treated with emodin. In conclusion, the identified DEGs and hub genes in the present study provide new clues for further researches on the molecular mechanisms of emodin.

Pharmacology of P2Y receptors

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. There are eight mammalian P2Y receptor subtypes divided into two subgroups (P2Y₁, P2Y₂, P2Y₄, P2Y₆, and P2Y₁₁) and (P2Y₁₂, P2Y₁₃, and P2Y₁₄). The P2Y receptors are expressed in various cell types and play important roles in physiology and pathophysiology including inflammatory responses and neuropathic pain. The antagonism of P2Y₁₂ receptors is used in pharmacotherapy for the prevention and therapy of cardiovascular events. The nucleoside analogue ticagrelor and active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel inhibit platelet P2Y₁₂ receptors and reduce thereby platelet aggregation. The P2Y₂ receptor agonist diquafosol is used for the treatment of the dry eye syndrome. The P2Y receptor subtypes differ in their amino acid sequences, their pharmacological profiles and their signaling transduction pathways. Recently, selective receptor ligands have been developed for all subtypes. The published crystal structures of the human P2Y₁ and P2Y₁₂ receptors as well as receptor models will facilitate the development of novel drugs for pharmacotherapy.

Nitrite Prevents Right Ventricular Failure and Remodeling Induced by Pulmonary Artery Banding

BACKGROUND

Nitrite has been shown to reduce right ventricle (RV) remodeling in experimental pulmonary hypertension. However, whether this effect is due to a reduction in RV afterload (ie, reduction in pulmonary artery pressure) or a direct effect on the RV itself remains unanswered. We hypothesize that nitrite has direct effects on RV remodeling and studied its effects in mice with pulmonary artery banding (PAB).

METHODS AND RESULTS

PAB decreased exercise tolerance and reduced RV systolic and diastolic function. Nitrite treatment attenuated the decrease in RV systolic function and improved the RV diastolic function. Nitrite-treated mice with PAB had similar exercise tolerance compared with a control group. PAB induced RV hypertrophy and fibrosis which were associated with increased expression of phospho-Akt. Interestingly, nitrite treatment attenuated PAB-induced RV hypertrophy and reduced the expression of phospho-Akt in RV tissue from mice with PAB. In neonatal rat cardiac fibroblast, nitrite also attenuated hypoxia-induced increase in expression of phospho-Akt.

CONCLUSION

Our study indicates that nitrite treatment has direct beneficial effects on RV and improves function and attenuates remodeling in RV exposed to chronic pressure overload. These beneficial effects, at least in part, could be due to the inhibition of the phospho-Akt (p-Akt) pathway activation.

Mouse P2Y4 Nucleotide Receptor Is a Negative Regulator of Cardiac Adipose-Derived Stem Cell Differentiation and Cardiac Fat Formation

Cardiac adipose tissue-derived stem cells (cASCs) have the ability to differentiate into multiple cell lineages giving them a high potential for use in regenerative medicine. Cardiac fat tissue still raises many unsolved questions related to its formation and features. P2Y nucleotide receptors have already been described as regulators of differentiation of bone-marrow derived stem cells, but remain poorly investigated in cASCs. We defined, in this study, the P2Y₄ nucleotide receptor as a negative regulator of cardiac fat formation and cASC adipogenic differentiation. Higher expression of P2Y₄ receptor in cardiac fat tissue was observed compared to other adipose tissues. P2Y₄-null mice displayed a higher mass of cardiac adipose tissue specifically. We therefore examined the role of P2Y₄ receptor in cASC adipogenic differentiation. An inhibitory effect of uridine 5'-triphosphate (UTP), ligand of P2Y₄, was observed on the maturation state of differentiated cASCs, and on the expression of adipogenesis-linked genes and adiponectin, a cardioprotective adipokine. Higher adiponectin secretion by P2Y₄-null adipocytes could be linked with cardioprotection previously observed in the heart of P2Y₄-null ischemic mice. We realized here left anterior descending artery ligation on simple and double-knockout mice for P2Y₄ and adiponectin. No cardioprotective effect of P2Y₄ loss was observed in the absence of adiponectin secretion. In addition, P2Y₄ loss was correlated with higher expression of UCP-1 (uncoupling protein-1) and CD137, two markers of brown/beige cardiac adipocytes. Our data highlight the P2Y₄ receptor as an inhibitor of cardiac fat formation and cASC adipogenic differentiation, and as a potential therapeutic target in the regulation of cardioprotective function of cardiac fat.

Loss of Mouse P2Y6 Nucleotide Receptor Is Associated with Physiological Macrocardia and Amplified Pathological Cardiac Hypertrophy

The study of the mechanisms leading to cardiac hypertrophy is essential to better understand cardiac development and regeneration. Pathological conditions such as ischemia or pressure overload can induce a release of extracellular nucleotides within the heart. We recently investigated the potential role of nucleotide P2Y receptors in cardiac development. We showed that adult P2Y4-null mice displayed microcardia resulting from defective cardiac angiogenesis. Here we show that loss of another P2Y subtype called P2Y6, a UDP receptor, was associated with a macrocardia phenotype and amplified pathological cardiac hypertrophy. Cardiomyocyte proliferation and size were increased in vivo in hearts of P2Y6-null neonates, resulting in enhanced postnatal heart growth. We then observed that loss of P2Y6 receptor enhanced pathological cardiac hypertrophy induced after isoproterenol injection. We identified an inhibitory effect of UDP on in vitro isoproterenol-induced cardiomyocyte hyperplasia and hypertrophy. The present study identifies mouse P2Y6 receptor as a regulator of cardiac development and cardiomyocyte function. P2Y6 receptor could constitute a therapeutic target to regulate cardiac hypertrophy.

Pharmacology and structure of P2Y receptors

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. There are eight mammalian P2Y receptor subtypes (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13, and P2Y14). P2Y receptors are widely expressed and play important roles in physiology and pathophysiology. One important example is the ADP-induced platelet aggregation mediated by P2Y1 and P2Y12 receptors. Active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel as well as the nucleoside analogue ticagrelor block P2Y12 receptors and thereby platelet aggregation. These drugs are used for the prevention and therapy of cardiovascular events. Moreover, P2Y receptors play important roles in the nervous system. Adenine nucleotides modulate neuronal activity and neuronal fibre outgrowth by activation of P2Y1 receptors and control migration of microglia by P2Y12 receptors. UDP stimulates microglial phagocytosis through activation of P2Y6 receptors. There is evidence for a role for P2Y2 receptors in Alzheimer's disease pathology. The P2Y receptor subtypes are highly diverse in both their amino acid sequences and their pharmacological profiles. Selective receptor ligands have been developed for the pharmacological characterization of the receptor subtypes. The recently published three-dimensional crystal structures of the human P2Y1 and P2Y12 receptors will facilitate the development of therapeutic agents that selectively target P2Y receptors. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Cardiac purinergic signalling in health and disease

This review is a historical account about purinergic signalling in the heart, for readers to see how ideas and understanding have changed as new experimental results were published. Initially, the focus is on the nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory nerves, as well as in intracardiac neurons. Control of the heart by centers in the brain and vagal cardiovascular reflexes involving purines are also discussed. The actions of adenine nucleotides and nucleosides on cardiomyocytes, atrioventricular and sinoatrial nodes, cardiac fibroblasts, and coronary blood vessels are described. Cardiac release and degradation of ATP are also described. Finally, the involvement of purinergic signalling and its therapeutic potential in cardiac pathophysiology is reviewed, including acute and chronic heart failure, ischemia, infarction, arrhythmias, cardiomyopathy, syncope, hypertrophy, coronary artery disease, angina, diabetic cardiomyopathy, as well as heart transplantation and coronary bypass grafts.

Loss of mouse P2Y4 nucleotide receptor protects against myocardial infarction through endothelin-1 downregulation

Nucleotides are released in the heart under pathological conditions, but little is known about their contribution to cardiac inflammation. The present study defines the P2Y4 nucleotide receptor, expressed on cardiac microvascular endothelial cells and involved in postnatal heart development, as an important regulator of the inflammatory response to cardiac ischemia. P2Y4-null mice displayed smaller infarcts in the left descending artery ligation model, as well as reduced neutrophil infiltration and fibrosis. Gene profiling identified inter alia endothelin-1 (ET-1) as one of the target genes of P2Y4 in ischemic heart. The reduced level of ET-1 was correlated with reduction of microvascular hyperpermeability, neutrophil infiltration, and endothelial adhesion molecule expression, and it could be explained by the decreased number of endothelial cells in P2Y4-null mice. Expression analysis of metalloproteinases and their tissue inhibitors in ischemic heart revealed reduced expression of matrix metalloproteinase (MMP)-9, reported to be potentially regulated by ET-1, and MMP-8, considered as neutrophil collagenase, as well as reduction of tissue inhibitor of MMP-1 and tissue inhibitor of MMP-4 in P2Y4-null mice. Reduction of cardiac permeability and neutrophil infiltration was also observed in P2Y4-null mice in LPS-induced inflammation model. Protection against infarction resulting from loss of P2Y4 brings new therapeutic perspectives for cardiac ischemia and remodeling.

Nucleotide signalling during inflammation

Inflammatory conditions are associated with the extracellular release of nucleotides, particularly ATP. In the extracellular compartment, ATP predominantly functions as a signalling molecule through the activation of purinergic P2 receptors. Metabotropic P2Y receptors are G-protein-coupled, whereas ionotropic P2X receptors are ATP-gated ion channels. Here we discuss how signalling events through P2 receptors alter the outcomes of inflammatory or infectious diseases. Recent studies implicate a role for P2X/P2Y signalling in mounting appropriate inflammatory responses critical for host defence against invading pathogens or tumours. Conversely, P2X/P2Y signalling can promote chronic inflammation during ischaemia and reperfusion injury, inflammatory bowel disease or acute and chronic diseases of the lungs. Although nucleotide signalling has been used clinically in patients before, research indicates an expanding field of opportunities for specifically targeting individual P2 receptors for the treatment of inflammatory or infectious diseases.

4-Alkyloxyimino derivatives of uridine-5'-triphosphate: distal modification of potent agonists as a strategy for molecular probes of P2Y2, P2Y4, and P2Y6 receptors

Extended N(4)-(3-arylpropyl)oxy derivatives of uridine-5'-triphosphate were synthesized and potently stimulated phospholipase C stimulation in astrocytoma cells expressing G protein-coupled human (h) P2Y receptors (P2YRs) activated by UTP (P2Y2/4R) or UDP (P2Y6R). The potent P2Y4R-selective N(4)-(3-phenylpropyl)oxy agonist was phenyl ring-substituted or replaced with terminal heterocyclic or naphthyl rings with retention of P2YR potency. This broad tolerance for steric bulk in a distal region was not observed for dinucleoside tetraphosphate agonists with both nucleobases substituted. The potent N(4)-(3-(4-methoxyphenyl)-propyl)oxy analogue 19 (EC50: P2Y2R, 47 nM; P2Y4R, 23 nM) was functionalized for chain extension using click tethering of fluorophores as prosthetic groups. The BODIPY 630/650 conjugate 28 (MRS4162) exhibited EC50 values of 70, 66, and 23 nM at the hP2Y2/4/6Rs, respectively, and specifically labeled cells expressing the P2Y6R. Thus, an extended N(4)-(3-arylpropyl)oxy group accessed a structurally permissive region on three Gq-coupled P2YRs, and potency and selectivity were modulated by distal structural changes. This freedom of substitution was utilized to design of a pan-agonist fluorescent probe of a subset of uracil nucleotide-activated hP2YRs.

Structure-based approaches to ligands for G-protein-coupled adenosine and P2Y receptors, from small molecules to nanoconjugates

Adenosine receptor (ARs) and P2Y receptors (P2YRs) that respond to extracellular nucleosides/nucleotides are associated with new directions for therapeutics. The X-ray structures of the A2AAR complexes with agonists and antagonists are examined in relationship to the G-protein-coupled receptor (GPCR) superfamily and applied to drug discovery. Much of the data on AR ligand structure from early SAR studies now are explainable from the A2AAR X-ray crystallography. The ligand-receptor interactions in related GPCR complexes can be identified by means of modeling approaches, e.g., molecular docking. Thus, molecular recognition in binding and activation processes has been studied effectively using homology modeling and applied to ligand design. Virtual screening has yielded new nonnucleoside AR antagonists, and existing ligands have been improved with knowledge of the receptor interactions. New agonists are being explored for central nervous system and peripheral therapeutics based on in vivo activity, such as chronic neuropathic pain. Ligands for receptors more distantly related to the X-ray template, i.e., P2YRs, have been introduced and are mainly used as pharmacological tools for elucidating the physiological role of extracellular nucleotides. Other ligand tools for drug discovery include fluorescent probes, radioactive probes, multivalent probes, and functionalized nanoparticles.