P2Y receptor subtypes evoke different Ca2+ signals in cultured aortic smooth muscle cells

Synthesis, structure-activity relationships and biological evaluation of benzimidazole derived sulfonylurea analogues as a new class of antagonists of P2Y1 receptor

The P2Y receptors are responsible for the regulation of various physiological processes including neurotransmission and inflammatory responses. These receptors are also considered as novel potential therapeutic targets for prevention and treatment of thrombosis, neurological disorders, pain, cardiac diseases and cancer. Previously, number of P2Y receptor antagonists has been investigated but they are less potent and non-selective with poor solubility profile. Herein, we present the synthesis of new class of benzimidazole derived sulfonylureas (1a-y) as potent antagonists of P2Y receptors, with the specific aim to explore selective antagonists of P2Y1 receptors. The efficacy and selectivity of the synthesized derivatives 1) against four P2Y receptors i.e., t-P2Y1, h-P2Y2, h-P2Y4, and r-P2Y6Rs was carried out by calcium mobilization assay. The results revealed that except 1b, 1d, 1l, 1m, 1o, 1u, 1v, 1w, and 1y, rest of the synthesized derivatives exhibited moderate to excellent inhibitory potential against P2Y1 receptors. Among the potent antagonists, derivative 1h depicted the maximum inhibition of P2Y1 receptor in calcium signalling assay, with an IC₅₀ value of 0.19 ± 0.04 µM. The potential of inhibition was validated by computational investigations where bonding and non-bonding interactions between ligand and targeted receptor further strengthen the study. The best identified derivative 1h revealed the same binding mechanism as that of already reported selective antagonist of P2Y1 receptor i.e (1-(2- (2-tert-butyl-phenoxy) pyridin-3-yl)-3-4-(trifluoromethoxy) phenylurea but the newly synthesized derivative exhibited better solubility profile. Hence, this derivative can be used as lead candidate for the synthesis of more potential antagonist with much better solubility profile and medicinal importance.

Synthesis, characterization and biological evaluation of indomethacin derived thioureas as purinergic (P2Y1, P2Y2, P2Y4, and P2Y6) receptor antagonists

G-protein-coupled receptors for extracellular nucleotides are known as P2Y receptors and are made up of eight members that are encoded by distinct genes and can be classified into two classes based on their affinity for specific G-proteins. P2Y receptor modulators have been studied extensively, but only a few small-molecule P2Y receptor antagonists have been discovered so far and approved by drug agencies. Derivatives of indole carboxamide have been identified as P2Y₁₂ and P2X₇ antagonist, as a result, we developed and tested a series of indole derivatives4a-lhaving thiourea moiety as P2Y receptor antagonist by using a fluorescence-based assay to measure the inhibition of intracellular calcium release in 1321N1 astrocytoma cells that had been stably transfected with the P2Y₁, P2Y₂, P2Y₄ and P2Y₆ receptors. Most of the compounds exhibited moderate to excellent inhibition activity against P2Y₁ receptor subtype. The series most potent compound, 4h exhibited an IC₅₀ value of 0.36 ± 0.01 µM selectivity against other subtypes of P2Y receptor. To investigate the ligand-receptor interactions, the molecular docking studies were carried out. Compound 4h is the most potent P2Y₁ receptor antagonist due to interaction with an important amino acid residue Pro105, in addition to Ile108, Phe119, and Leu102.

The Role of Two-Pore Channels in Norepinephrine-Induced [Ca2+]i Rise in Rat Aortic Smooth Muscle Cells and Aorta Contraction

Second messenger nicotinic acid adenine dinucleotide phosphate (NAADP) triggers Ca²⁺ release via two-pore channels (TPCs) localized in endolysosomal vesicles. The aim of the present work is to evaluate the role of TPCs in the action of norepinephrine (NE), angiotensin II (AngII), vasopressin (AVP), and 5-hydroxytriptamine (5-HT) on free cytoplasmic calcium concentration ([Ca²⁺]_i) in smooth muscle cells (SMCs) isolated from rat aorta and on aorta contraction. To address this issue, the NAADP structural analogue and inhibitor of TPCs, NED 19, was applied. We have demonstrated a high degree of colocalization of the fluorescent signals of cis-NED 19 and endolysosmal probe LysoTracker in SMCs. Both cis- or trans-NED 19 inhibited the rise of [Ca²⁺]_i in SMCs induced by 100 μM NE by 50–60%. IC₅₀ for cis- and trans-NED 19 were 2.7 and 8.9 μM, respectively. The inhibition by NED 19 stereoisomers of the effects of AngII, AVP, and 5-HT was much weaker. Both forms of NED 19 caused relaxation of aortic rings preconstricted by NE, with relative potency of cis-NED 19 several times higher than that of trans-NED 19. Inhibition by cis-NED 19 of NE-induced contraction was maintained after intensive washing and slowly reversed within an hour of incubation. Cis- and trans-NED 19 did not cause decrease in the force of aorta contraction in response to Ang II and AVP, and only slightly relaxed aorta preconstricted by 5-HT and by KCl. Suppression of TPC1 in SMCs with siRNA caused a 40% decrease in [Ca²⁺]_i in response to NE, whereas siRNA against TPC2 did not change NE calcium signaling. These data suggest that TPC1 is involved in the NE-stimulated [Ca²⁺]_i rise in SMCs. Inhibition of TPC1 activity by NED 19 could be the reason for partial inhibition of aortic rings contraction in response to NE.

Constitutive P2Y2 receptor activity regulates basal lipolysis in human adipocytes

White adipocytes are key regulators of metabolic homeostasis, which release stored energy as free fatty acids via lipolysis. Adipocytes possess both basal and stimulated lipolytic capacity, but limited information exists regarding the molecular mechanisms that regulate basal lipolysis. Here, we describe a mechanism whereby autocrine purinergic signalling and constitutive P2Y₂ receptor activation suppresses basal lipolysis in primary human in vitro-differentiated adipocytes. We found that human adipocytes possess cytoplasmic Ca²⁺ tone due to ATP secretion and constitutive P2Y₂ receptor activation. Pharmacological antagonism or knockdown of P2Y₂ receptors increases intracellular cAMP levels and enhances basal lipolysis. P2Y₂ receptor antagonism works synergistically with phosphodiesterase inhibitors in elevating basal lipolysis, but is dependent upon adenylate cyclase activity. Mechanistically, we suggest that the increased Ca²⁺ tone exerts an anti-lipolytic effect by suppression of Ca²⁺-sensitive adenylate cyclase isoforms. We also observed that acute enhancement of basal lipolysis following P2Y₂ receptor antagonism alters the profile of secreted adipokines leading to longer-term adaptive decreases in basal lipolysis. Our findings demonstrate that basal lipolysis and adipokine secretion are controlled by autocrine purinergic signalling in human adipocytes.

P2Y2 and P2Y6 receptor activation elicits intracellular calcium responses in human adipose-derived mesenchymal stromal cells

Adipose tissue contains self-renewing multipotent cells termed mesenchymal stromal cells. In situ, these cells serve to expand adipose tissue by adipogenesis, but their multipotency has gained interest for use in tissue regeneration. Little is known regarding the repertoire of receptors expressed by adipose-derived mesenchymal stromal cells (AD-MSCs). The purpose of this study was to undertake a comprehensive analysis of purinergic receptor expression. Mesenchymal stromal cells were isolated from human subcutaneous adipose tissue and confirmed by flow cytometry. The expression profile of purinergic receptors was determined by quantitative real-time PCR and immunocytochemistry. The molecular basis for adenine and uracil nucleotide-evoked intracellular calcium responses was determined using Fura-2 measurements. All the known subtypes of P2X and P2Y receptors, excluding P2X2, P2X3 and P2Y₁₂ receptors, were detected at the mRNA and protein level. ATP, ADP and UTP elicited concentration-dependent calcium responses in mesenchymal cells (N = 7–9 donors), with a potency ranking ADP (EC₅₀ 1.3 ± 1.0 μM) > ATP (EC₅₀ 2.2 ± 1.1 μM) = UTP (3.2 ± 2.8 μM). Cells were unresponsive to UDP (< 30 μM) and UDP-glucose (< 30 μM). ATP responses were attenuated by selective P2Y₂ receptor antagonism (AR-C118925XX; IC₅₀ 1.1 ± 0.8 μM, 73.0 ± 8.5% max inhibition; N = 7 donors), and UTP responses were abolished. ADP responses were attenuated by the selective P2Y₆ receptor antagonist, MRS2587 (IC₅₀ 437 ± 133nM, 81.0 ± 8.4% max inhibition; N = 6 donors). These data demonstrate that adenine and uracil nucleotides elicit intracellular calcium responses in human AD-MSCs with a predominant role for P2Y₂ and P2Y₆ receptor activation. This study furthers understanding about how human adipose-derived mesenchymal stromal cells can respond to external signalling cues.

Gene expression profiles of ion channels and receptors in mouse resistance arteries: Effects of cell type, vascular bed, and age

OBJECTIVE

Receptors and ion channels of smooth muscle cells (SMCs) and endothelial cells (ECs) are integral to the regulation of vessel diameter and tissue blood flow. Physiological roles of ion channels and receptors in skeletal muscle and mesenteric arteries have been identified; however, their gene expression profiles are undefined. We tested the hypothesis that expression profiles for ion channels and receptors governing vascular reactivity vary with cell type, vascular bed, and age.

METHODS

Mesenteric and superior epigastric arteries were dissected from Old (24-26 months) and Young (3-6 months) C57BL/6J mice. ECs and SMCs were collected for analysis with custom qRT-PCR arrays to determine expression profiles of 80 ion channel and receptor genes. Bioinformatics analyses were applied to gain insight into functional interactions.

RESULTS

We identified 68 differences in gene expression with respect to cell type, vessel type, and age. Heat maps illustrate differential expression, and distance matrices predict patterns of coexpression. Gene networks based upon protein-protein interaction datasets and KEGG pathways illustrate biological processes affected by specific differences in gene expression.

CONCLUSIONS

Differences in gene expression profiles are most pronounced between microvascular ECs and SMCs with subtle variations between vascular beds and age groups.

Central Role of P2Y6 UDP Receptor in Arteriolar Myogenic Tone

OBJECTIVE

Myogenic tone (MT) of resistance arteries ensures autoregulation of blood flow in organs and relies on the intrinsic property of smooth muscle to contract in response to stretch. Nucleotides released by mechanical strain on cells are responsible for pleiotropic vascular effects, including vasoconstriction. Here, we evaluated the contribution of extracellular nucleotides to MT.

APPROACH AND RESULTS

We measured MT and the associated pathway in mouse mesenteric resistance arteries using arteriography for small arteries and molecular biology. Of the P2 receptors in mouse mesenteric resistance arteries, mRNA expression of P2X1 and P2Y6 was dominant. P2Y6 fully sustained UDP/UTP-induced contraction (abrogated in P2ry6(-/-) arteries). Preventing nucleotide hydrolysis with the ectonucleotidase inhibitor ARL67156 enhanced pressure-induced MT by 20%, whereas P2Y6 receptor blockade blunted MT in mouse mesenteric resistance arteries and human subcutaneous arteries. Despite normal hemodynamic parameters, P2ry6(-/-) mice were protected against MT elevation in myocardial infarction-induced heart failure. Although both P2Y6 and P2Y2 receptors contributed to calcium mobilization, P2Y6 activation was mandatory for RhoA-GTP binding, myosin light chain, P42-P44, and c-Jun N-terminal kinase phosphorylation in arterial smooth muscle cells. In accordance with the opening of a nucleotide conduit in pressurized arteries, MT was altered by hemichannel pharmacological inhibitors and impaired in Cx43(+/-) and P2rx7(-/-) mesenteric resistance arteries.

CONCLUSIONS

Signaling through P2 nucleotide receptors contributes to MT. This mechanism encompasses the release of nucleotides coupled to specific autocrine/paracrine activation of the uracil nucleotide P2Y6 receptor and may contribute to impaired tissue perfusion in cardiovascular diseases.

Coupling switch of P2Y-IP3 receptors mediates differential Ca(2+) signaling in human embryonic stem cells and derived cardiovascular progenitor cells

Purinergic signaling mediated by P2 receptors (P2Rs) plays important roles in embryonic and stem cell development. However, how it mediates Ca(2+) signals in human embryonic stem cells (hESCs) and derived cardiovascular progenitor cells (CVPCs) remains unclear. Here, we aimed to determine the role of P2Rs in mediating Ca(2+) mobilizations of these cells. hESCs were induced to differentiate into CVPCs by our recently established methods. Gene expression of P2Rs and inositol 1,4,5-trisphosphate receptors (IP3Rs) was analyzed by quantitative/RT-PCR. IP3R3 knockdown (KD) or IP3R2 knockout (KO) hESCs were established by shRNA- or TALEN-mediated gene manipulations, respectively. Confocal imaging revealed that Ca(2+) responses in CVPCs to ATP and UTP were more sensitive and stronger than those in hESCs. Consistently, the gene expression levels of most P2YRs except P2Y1 were increased in CVPCs. Suramin or PPADS blocked ATP-induced Ca(2+) transients in hESCs but only partially inhibited those in CVPCs. Moreover, the P2Y1 receptor-specific antagonist MRS2279 abolished most ATP-induced Ca(2+) signals in hESCs but not in CVPCs. P2Y1 receptor-specific agonist MRS2365 induced Ca(2+) transients only in hESCs but not in CVPCs. Furthermore, IP3R2KO but not IP3R3KD decreased the proportion of hESCs responding to MRS2365. In contrast, both IP3R2 and IP3R3 contributed to UTP-induced Ca(2+) responses while ATP-induced Ca(2+) responses were more dependent on IP3R2 in the CVPCs. In conclusion, a predominant role of P2Y1 receptors in hESCs and a transition of P2Y-IP3R coupling in derived CVPCs are responsible for the differential Ca(2+) mobilization between these cells.

Intestinal organoids for assessing nutrient transport, sensing and incretin secretion

Intestinal nutrient transport and sensing are of emerging interest in research on obesity and diabetes and as drug targets. Appropriate in vitro models are lacking that allow both, studies on transport processes as well as sensing and subsequent incretin hormone secretion including intracellular signaling. We here demonstrate that murine small-intestinal organoids are the first in vitro model system enabling concurrent investigations of nutrient and drug transport, sensing and incretin hormone secretion as well as fluorescent live-cell imaging of intracellular signaling processes. By generating organoid cultures from wild type mice and animals lacking different nutrient transporters, we show that organoids preserve the main phenotypic features and functional characteristics of the intestine. This turns them into the best in vitro model currently available and opens new avenues for basic as well as medical research.

Nicotinic Acid Adenine Dinucleotide Phosphate Analogues Substituted on the Nicotinic Acid and Adenine Ribosides. Effects on ReceptorMediated Ca²⁺ Release

Nicotinic acid adenine dinucleotide phosphate (NAADP) is a Ca(2+) releasing intracellular second messenger in both mammals and echinoderms. We report that large functionalized substituents introduced at the nicotinic acid 5-position are recognized by the sea urchin receptor, albeit with a 20-500-fold loss in agonist potency. 5-(3-Azidopropyl)-NAADP was shown to release Ca(2+) with an EC50 of 31 μM and to compete with NAADP for receptor binding with an IC50 of 56 nM. Attachment of charged groups to the nicotinic acid of NAADP is associated with loss of activity, suggesting that the nicotinate riboside moiety is recognized as a neutral zwitterion. Substituents (Br- and N3-) can be introduced at the 8-adenosyl position of NAADP while preserving high potency and agonist efficacy and an NAADP derivative substituted at both the 5-position of the nicotinic acid and at the 8-adenosyl position was also recognized although the agonist potency was significantly reduced.

Interactions of antagonists with subtypes of inositol 1,4,5-trisphosphate (IP3) receptor

BACKGROUND AND PURPOSE

Inositol 1,4,5-trisphosphate receptors (IP3 Rs) are intracellular Ca(2+) channels. Interactions of the commonly used antagonists of IP3Rs with IP3R subtypes are poorly understood.

EXPERIMENTAL APPROACH

IP3-evoked Ca(2+) release from permeabilized DT40 cells stably expressing single subtypes of mammalian IP3R was measured using a luminal Ca(2+) indicator. The effects of commonly used antagonists on IP3-evoked Ca(2+) release and (3) H-IP3 binding were characterized.

KEY RESULTS

Functional analyses showed that heparin was a competitive antagonist of all IP3R subtypes with different affinities for each (IP3R3 > IP3R1 ≥ IP3R2). This sequence did not match the affinities for heparin binding to the isolated N-terminal from each IP3R subtype. 2-aminoethoxydiphenyl borate (2-APB) and high concentrations of caffeine selectively inhibited IP3R1 without affecting IP3 binding. Neither Xestospongin C nor Xestospongin D effectively inhibited IP3-evoked Ca(2+) release via any IP3R subtype.

CONCLUSIONS AND IMPLICATIONS

Heparin competes with IP3, but its access to the IP3-binding core is substantially hindered by additional IP3R residues. These interactions may contribute to its modest selectivity for IP3R3. Practicable concentrations of caffeine and 2-APB inhibit only IP3R1. Xestospongins do not appear to be effective antagonists of IP3Rs.

Purinergic signaling and blood vessels in health and disease

Purinergic signaling plays important roles in control of vascular tone and remodeling. There is dual control of vascular tone by ATP released as a cotransmitter with noradrenaline from perivascular sympathetic nerves to cause vasoconstriction via P2X1 receptors, whereas ATP released from endothelial cells in response to changes in blood flow (producing shear stress) or hypoxia acts on P2X and P2Y receptors on endothelial cells to produce nitric oxide and endothelium-derived hyperpolarizing factor, which dilates vessels. ATP is also released from sensory-motor nerves during antidromic reflex activity to produce relaxation of some blood vessels. In this review, we stress the differences in neural and endothelial factors in purinergic control of different blood vessels. The long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides in promoting migration and proliferation of both vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis and vessel remodeling during restenosis after angioplasty are described. The pathophysiology of blood vessels and therapeutic potential of purinergic agents in diseases, including hypertension, atherosclerosis, ischemia, thrombosis and stroke, diabetes, and migraine, is discussed.

Perivascular innervation: a multiplicity of roles in vasomotor control and myoendothelial signaling

The control of vascular resistance and tissue perfusion reflect coordinated changes in the diameter of feed arteries and the arteriolar networks they supply. Against a background of myogenic tone and metabolic demand, vasoactive signals originating from perivascular sympathetic and sensory nerves are integrated with endothelium-derived signals to produce vasodilation or vasoconstriction. PVNs release adrenergic, cholinergic, peptidergic, purinergic, and nitrergic neurotransmitters that lead to SMC contraction or relaxation via their actions on SMCs, ECs, or other PVNs. ECs release autacoids that can have opposing actions on SMCs. Respective cell layers are connected directly to each other through GJs at discrete sites via MEJs projecting through holes in the IEL. Whereas studies of intercellular communication in the vascular wall have centered on endothelium-derived signals that govern SMC relaxation, attention has increasingly focused on signaling from SMCs to ECs. Thus, via MEJs, neurotransmission from PVNs can evoke distinct responses from ECs subsequent to acting on SMCs. To integrate this emerging area of investigation in light of vasomotor control, the present review synthesizes current understanding of signaling events that originate within SMCs in response to perivascular neurotransmission in light of EC feedback. Although often ignored in studies of the resistance vasculature, PVNs are integral to blood flow control and can provide a physiological stimulus for myoendothelial communication. Greater understanding of these underlying signaling events and how they may be affected by aging and disease will provide new approaches for selective therapeutic interventions.

Intracellular NAADP increase induced by extracellular NAADP via the P2Y11-like receptor

The aim of the study was to identify a signalling pathway allowing NAADP-induced intracellular NAADP increase and involving the P2Y11-like receptor. P2Y11-like and β-adrenergic receptors may play important regulatory roles within the cardiovascular system. Both receptors have been shown to be involved in triggering myocardial preconditioning. Using a Langendorff model we report a positive inotropic response induced by extracellular NAADP via P2Y11-like receptor stimulation. In cardiomyocyte cultures, P2Y11-like receptor stimulation by extracellular NAADP ([NAADP]e) increased intracellular cADP-ribose and NAADP concentration as evidenced by direct measurements. NF546, a new selective P2Y11 receptor agonist, increased intracellular cAMP, cADP-ribose and NAADP concentration confirming the involvement of the P2Y11-like receptor in this signalling pathway. NF157, a P2Y11 receptor antagonist, suppressed the increase in intracellular cADPr, NAADP and NAAD induced by either [NAADP]e or NF546. The response profile for intracellular cADP-ribose and NAADP concentration following P2Y11-like stimulation with NF546 was similar to reported data relating β-adrenergic stimulation with isoprenaline. This response represents the signature of the Gs/ADP-ribosyl cyclase activity. Moreover, this study provides a signalling pathway: intracellular NAADP increase induced by extracellular NAADP via metabotropic activity of P2Y11-like receptor. This pathway implying P2Y11-like could take part in the intracellular calcium rise reported for extracellular NAADP.

Discovery of 2-(phenoxypyridine)-3-phenylureas as small molecule P2Y1 antagonists

Two distinct G protein-coupled purinergic receptors, P2Y1 and P2Y12, mediate ADP-driven platelet activation. The clinical effectiveness of P2Y12 blockade is well established. Recent preclinical data suggest that P2Y1 and P2Y12 inhibition provide equivalent antithrombotic efficacy, while targeting P2Y1 has the potential for reduced bleeding liability. In this account, the discovery of a 2-(phenoxypyridine)-3-phenylurea chemotype that inhibited ADP-mediated platelet aggregation in human blood samples is described. Optimization of this series led to the identification of compound 16, 1-(2-(2-tert-butylphenoxy)pyridin-3-yl)-3-4-(trifluoromethoxy)phenylurea, which demonstrated a 68 ± 7% thrombus weight reduction in an established rat arterial thrombosis model (10 mg/kg plus 10 mg/kg/h) while only prolonging cuticle and mesenteric bleeding times by 3.3- and 3.1-fold, respectively, in provoked rat bleeding time models. These results suggest that a P2Y1 antagonist could potentially provide a safe and efficacious antithrombotic profile.