Novel vasocontractile role of the P2Y₁₄ receptor: characterization of its signalling in porcine isolated pancreatic arteries

How selective antagonists and genetic modification have helped characterise the expression and functions of vascular P2Y receptors

Vascular P2Y receptors mediate many effects, but the role of individual subtypes is often unclear. Here we discuss how subtype-selective antagonists and receptor knockout/knockdown have helped identify these roles in numerous species and vessels. P2Y1 receptor-mediated vasoconstriction and endothelium-dependent vasodilation have been characterised using the selective antagonists, MRS2179 and MRS2216, whilst AR-C118925XX, a P2Y2 receptor antagonist, reduced endothelium-dependent relaxation, and signalling evoked by UTP or fluid shear stress. P2Y2 receptor knockdown reduced endothelial signalling and endothelial P2Y2 receptor knockout produced hypertensive mice and abolished vasodilation elicited by an increase in flow. UTP-evoked vasoconstriction was also blocked by AR-C118925XX, but the effects of P2Y2 receptor knockout were complex. No P2Y4 receptor antagonists are available and P2Y4 knockout did not affect the vascular actions of UTP and UDP. The P2Y6 receptor antagonist, MRS2578, identified endothelial P2Y6 receptors mediating vasodilation, but receptor knockout had complex effects. MRS2578 also inhibited, and P2Y6 knockout abolished, contractions evoked by UDP. P2Y6 receptors contribute to the myogenic tone induced by a stepped increase in vascular perfusion pressure and possibly to the development of atherosclerosis. The P2Y11 receptor antagonists, NF157 and NF340, inhibited ATP-evoked signalling in human endothelial cells. Vasoconstriction mediated by P2Y12/P2Y13 and P2Y14 receptors was characterised using the antagonists, cangrelor, ticagrelor, AR-C67085 and MRS2211 or PPTN respectively. This has yet to be backed up by receptor knockout experiments. Thus, subtype-selective antagonists and receptor knockout/knockdown have helped identify which P2Y subtypes are functionally expressed in vascular smooth muscle and endothelial cells and the effects that they mediate.

Targeting P2Y14R protects against necroptosis of intestinal epithelial cells through PKA/CREB/RIPK1 axis in ulcerative colitis

Purinergic signaling plays a causal role in the pathogenesis of inflammatory bowel disease. Among purinoceptors, only P2Y14R is positively correlated with inflammatory score in mucosal biopsies of ulcerative colitis patients, nevertheless, the role of P2Y14R in ulcerative colitis remains unclear. Here, based on the over-expressions of P2Y14R in the intestinal epithelium of mice with experimental colitis, we find that male mice lacking P2Y14R in intestinal epithelial cells exhibit less intestinal injury induced by dextran sulfate sodium. Mechanistically, P2Y14R deletion limits the transcriptional activity of cAMP-response element binding protein through cAMP/PKA axis, which binds to the promoter of Ripk1, inhibiting necroptosis of intestinal epithelial cells. Furthermore, we design a hierarchical strategy combining virtual screening and chemical optimization to develop a P2Y14R antagonist HDL-16, which exhibits remarkable anti-colitis effects. Summarily, our study elucidates a previously unknown mechanism whereby P2Y14R participates in ulcerative colitis, providing a promising therapeutic target for inflammatory bowel disease.

Microglial P2Y14 receptor contributes to central sensitization following repeated inflammatory dural stimulation

BACKGROUND

Recent studies have indicated that P2Y receptors in spinal microglia play a role in the development of neuropathic and inflammatory pain. However, it remains unclear whether P2Y receptors in microglia are involved in the pathogenesis of migraine. Therefore, the aim of this study was to investigate the role of microglial P2Y14 receptor in trigeminal cervical complex (TCC) in migraine.

METHODS

We used a rat model of migraine induced by repeated inflammatory stimulation of the dura and examined the expression of P2Y14 receptor in the TCC in migraine rats by Western Blotting and immunofluorescence staining. Then, we determined the effect of P2Y14 antagonist PPTN on inflammatory soup (IS)-induced mechanical allodynia, microglial activation and ERK expression in TCC.

RESULTS

The expression level of P2Y14 receptor increased significantly in microglia in TCC after 4 or 7 days of repeated IS stimulation of the dura. Application of PPTN significantly attenuated the decrease of periorbital pain threshold in migraine model rats. In addition, repeated IS stimulation of the dura induced the activation of microglia and the phosphorylation of the ERK1/2 in microglia in TCC, which were abolished by the application of PPTN.

CONCLUSION

Our findings suggest that the increased P2Y14 receptor in microglia in TCC play a crucial role in the generation of mechanical allodynia in migraine rat model. Furthermore, the activation of the P2Y14 receptor is involved in microglial activation and ERK phosphorylation as well. The P2Y14 receptor in microglia might be used as a potential target for migraine treatment.

G protein-coupled purinergic P2Y receptor oligomerization: Pharmacological changes and dynamic regulation

P2Y receptors (P2YRs) are a δ group of rhodopsin-like G protein-coupled receptors (GPCRs) with many essential functions in physiology and pathology, such as platelet aggregation, immune responses, neuroprotective effects, inflammation, and cellular proliferation. Thus, they are among the most researched therapeutic targets used for the clinical treatment of diseases (e.g., the antithrombotic drug clopidogrel and the dry eye treatment drug diquafosol). GPCRs transmit signals as dimers to increase the diversity of signalling pathways and pharmacological activities. Many studies have frequently confirmed dimerization between P2YRs and other GPCRs due to their functions in cardiovascular and cerebrovascular processes in vivo and in vitro. Recently, some P2YR dimers that dynamically balance physiological functions in the body were shown to be involved in effective signal transduction and exert pathological responses. In this review, we summarize the types, pharmacological changes, and active regulators of P2YR-related dimerization, and delineate new functions and pharmacological activities of P2YR-related dimers, which may be a novel direction to improve the effectiveness of medications.

Purinergic Regulation of Endothelial Barrier Function

Increased vascular permeability is a hallmark of several cardiovascular anomalies, including ischaemia/reperfusion injury and inflammation. During both ischaemia/reperfusion and inflammation, massive amounts of various nucleotides, particularly adenosine 5'-triphosphate (ATP) and adenosine, are released that can induce a plethora of signalling pathways via activation of several purinergic receptors and may affect endothelial barrier properties. The nature of the effects on endothelial barrier function may depend on the prevalence and type of purinergic receptors activated in a particular tissue. In this review, we discuss the influence of the activation of various purinergic receptors and downstream signalling pathways on vascular permeability during pathological conditions.

Purinergic signalling in the cardiovascular system-a tribute to Geoffrey Burnstock

Geoffrey Burnstock made groundbreaking discoveries on the physiological roles of purinergic receptors and led on P2 purinergic receptor classification. His knowledge, vision and leadership inspired and influenced the international scientific community. I had the privilege of spending over 10 years (from 1985) with Geoff at the Department of Anatomy and Developmental Biology, initially as a PhD student and then as a postdoctoral research fellow. I regarded him with enormous admiration and affection. This review on purinergic signalling in the cardiovascular system is a tribute to Geoff. It includes some personal recollections of Geoff.

Sleep fragmentation increases blood pressure and is associated with alterations in the gut microbiome and fecal metabolome in rats

The gut microbiota, via the production of metabolites entering the circulation, plays a role in blood pressure regulation. Blood pressure is also affected by the characteristics of sleep. To date, no studies have examined relationships among the gut microbiota/metabolites, blood pressure, and sleep. We hypothesized that fragmented sleep is associated with elevated mean arterial pressure, an altered and dysbiotic gut microbial community, and changes in fecal metabolites. In our model system, rats were randomized to 8 h of sleep fragmentation during the rest phase (light phase) or were undisturbed (controls) for 28 consecutive days. Rats underwent sleep and blood pressure recordings, and fecal samples were analyzed during: baseline (days -4 to -1), early sleep fragmentation (days 0-3), midsleep fragmentation (days 6-13), late sleep fragmentation (days 20-27), and recovery/rest (days 28-34). Less sleep per hour during the sleep fragmentation period was associated with increased mean arterial pressure. Analyses of gut microbial communities and metabolites revealed that putative short chain fatty acid-producing bacteria were differentially abundant between control and intervention animals during mid-/late sleep fragmentation and recovery. Midsleep fragmentation was also characterized by lower alpha diversity, lower Firmicutes:Bacteroidetes ratio, and higher Proteobacteria in intervention rats. Elevated putative succinate-producing bacteria and acetate-producing bacteria were associated with lower and higher mean arterial pressure, respectively, and untargeted metabolomics analysis demonstrates that certain fecal metabolites are significantly correlated with blood pressure. These data reveal associations between sleep fragmentation, mean arterial pressure, and the gut microbiome/fecal metabolome and provide insight to links between disrupted sleep and cardiovascular pathology.

Amplification of the COX/TXS/TP receptor pathway enhances uridine diphosphate-induced contraction by advanced glycation end products in rat carotid arteries

Advanced glycation end products (AGEs) play a pivotal role in vascular functions under various pathophysiological conditions. Although uridine diphosphate (UDP) is an important extracellular nucleotide, the relationship between AGEs and UDP regarding their effect on vascular functions remains unclear. Therefore, we investigated the effects of AGE-bovine serum albumin (AGE-BSA) on UDP-mediated responses in rat thoracic aorta and carotid arteries. In rat thoracic aorta, UDP-induced relaxation was observed and this relaxation was similar between control (1.0 v/v% PBS) and AGE-BSA-treated (0.1 mg/mL for 60 min) groups. In contrast, contraction but not relaxation was obtained following UDP application to carotid arteries with and without endothelia; contraction was greater in the AGE-BSA-treated group than in the control group. The difference in UDP-induced contraction between the two groups was not abolished by the use of a nitric oxide synthase (NOS) inhibitor, whereas it was abolished by the use of cyclooxygenase (COX), thromboxane synthase (TXS), and thromboxane-prostanoid (TP) receptor antagonist. Further, the difference in UDP-induced contraction was not abolished by the use of a cPLA₂ inhibitor, whereas it was abolished by the use of an iPLA₂ inhibitor. UDP increased TXA₂ release in both groups, and its level was similar in both groups. Moreover, the release of PGE₂, PGF_2α, and PGI₂ was similar among the groups. Under NOS inhibition, TP receptor agonist-induced contraction increased in the AGE-BSA-treated group (vs. control group). In conclusion, the increase in UDP-induced carotid arterial contraction by AGE-BSA can be attributed to an increase in the COX/TXS/TP receptor pathway, particularly, TP receptor signaling.

UDP-sugars activate P2Y14 receptors to mediate vasoconstriction of the porcine coronary artery

Aims

UDP-sugars can act as extracellular signalling molecules, but relatively little is known about their cardiovascular actions. The P2Y₁₄ receptor is a G_i/o-coupled receptor which is activated by UDP-glucose and related sugar nucleotides. In this study we sought to investigate whether P2Y₁₄ receptors are functionally expressed in the porcine coronary artery using a selective P2Y₁₄ receptor agonist, MRS2690, and a novel selective P2Y₁₄ receptor antagonist, PPTN (4,7-disubstituted naphthoic acid derivative).

Methods and results

Isometric tension recordings were used to evaluate the effects of UDP-sugars in porcine isolated coronary artery segments. The effects of the P2 receptor antagonists suramin and PPADS, the P2Y₁₄ receptor antagonist PPTN, and the P2Y₆ receptor antagonist MRS2578, were investigated. Measurement of vasodilator-stimulated phosphoprotein (VASP) phosphorylation using flow cytometry was used to assess changes in cAMP levels. UDP-glucose, UDP-glucuronic acid UDP-N-acetylglucosamine (P2Y₁₄ receptor agonists), elicited concentration-dependent contractions of the porcine coronary artery. MRS2690 was a more potent vasoconstrictor than the UDP-sugars. Concentration dependent contractile responses to MRS2690 and UDP-sugars were enhanced in the presence of forskolin (activator of cAMP), where the level of basal tone was maintained by addition of U46619, a thromboxane A₂ mimetic. Contractile responses to MRS2690 were blocked by PPTN, but not by MRS2578. Contractile responses to UDP-glucose were also attenuated by PPTN and suramin, but not by MRS2578. Forskolin-induced VASP-phosphorylation was reduced in porcine coronary arteries exposed to UDP-glucose and MRS2690, consistent with P2Y₁₄ receptor coupling to G_i/o proteins and inhibition of adenylyl cyclase activity.

Conclusions

Our data support a role of UDP-sugars as extracellular signalling molecules and show for the first time that they mediate contraction of porcine coronary arteries via P2Y₁₄ receptors.

Ovariectomy uncovers purinergic receptor activation of endothelin-dependent natriuresis

We recently reported that natriuresis produced by renal medullary salt loading is dependent on endothelin (ET)-1 and purinergic (P2) receptors in male rats. Because sex differences in ET-1 and P2 signaling have been reported, we decided to test whether ovarian sex hormones regulate renal medullary ET-1 and P2-dependent natriuresis. The effect of medullary NaCl loading on Na⁺ excretion was determined in intact and ovariectomized (OVX) female Sprague-Dawley rats with and without ET-1 or P2 receptor antagonism. Isosmotic saline (284 mosmol/kgH₂O) was infused in the renal medullary interstitium of anesthetized rats during a baseline urine collection period, followed by isosmotic or hyperosmotic saline (1,800 mosmol/kgH₂O) infusion. Medullary NaCl loading significantly enhanced Na⁺ excretion in intact and OVX female rats. ET_A+B or P2 receptor blockade did not attenuate the natriuretic effect of medullary NaCl loading in intact females, whereas ET_A+B or P2 receptor blockade attenuated the natriuretic response to NaCl loading in OVX rats. Activation of medullary P2Y₂ and P2Y₄ receptors by UTP infusion had no significant effect in intact females but enhanced Na⁺ excretion in OVX rats. Combined ET_A+B receptor blockade significantly inhibited the natriuretic response to UTP observed in OVX rats. These data demonstrate that medullary NaCl loading induces ET-1 and P2-independent natriuresis in intact females. In OVX, activation of medullary P2 receptors promotes ET-dependent natriuresis, suggesting that ovarian hormones may regulate the interplay between the renal ET-1 and P2 signaling systems to facilitate Na⁺ excretion.

Interplay between renal endothelin and purinergic signaling systems

Alterations in extracellular fluid volume regulation and sodium balance may result in the development and maintenance of salt-dependent hypertension, a major risk factor for cardiovascular disease. Numerous pathways contribute to the regulation of sodium excretion and blood pressure, including endothelin and purinergic signaling. Increasing evidence suggests a link between purinergic receptor activation and endothelin production within the renal collecting duct as a means of promoting natriuresis. A better understanding of the relationship between these two systems, especially in regard to sodium homeostasis, will fill a significant knowledge gap and may provide novel antihypertensive treatment options. Therefore, this review focuses on the cross talk between endothelin and purinergic signaling as it relates to the renal regulation of sodium and blood pressure homeostasis.

Chemerin Elicits Potent Constrictor Actions via Chemokine-Like Receptor 1 (CMKLR1), not G-Protein-Coupled Receptor 1 (GPR1), in Human and Rat Vasculature

BACKGROUND

Circulating levels of chemerin are significantly higher in hypertensive patients and positively correlate with blood pressure. Chemerin activates chemokine-like receptor 1 (CMKLR1 or ChemR23) and is proposed to activate the "orphan" G-protein-coupled receptor 1 (GPR1), which has been linked with hypertension. Our aim was to localize chemerin, CMKLR1, and GPR1 in the human vasculature and determine whether 1 or both of these receptors mediate vasoconstriction.

METHODS AND RESULTS

Using immunohistochemistry and molecular biology in conduit arteries and veins and resistance vessels, we localized chemerin to endothelium, smooth muscle, and adventitia and found that CMKLR1 and GPR1 were widely expressed in smooth muscle. C9 (chemerin149-157) contracted human saphenous vein (pD2=7.30±0.31) and resistance arteries (pD2=7.05±0.54) and increased blood pressure in rats by 9.1±1.0 mm Hg at 200 nmol. Crucially, these in vitro and in vivo vascular actions were blocked by CCX832, which we confirmed to be highly selective for CMKLR1 over GPR1. C9 inhibited cAMP accumulation in human aortic smooth muscle cells and preconstricted rat aorta, consistent with the observed vasoconstrictor action. Downstream signaling was explored further and, compared to chemerin, C9 showed a bias factor=≈5000 for the Gi protein pathway, suggesting that CMKLR1 exhibits biased agonism.

CONCLUSIONS

Our data suggest that chemerin acts at CMKLR1, but not GPR1, to increase blood pressure. Chemerin has an established detrimental role in metabolic syndrome, and these direct vascular actions may contribute to hypertension, an additional risk factor for cardiovascular disease. This study provides proof of principle for the therapeutic potential of selective CMKLR1 antagonists.

Activation of purinergic receptors (P2) in the renal medulla promotes endothelin-dependent natriuresis in male rats

Renal endothelin-1 (ET-1) and purinergic signaling systems regulate Na(+) reabsorption in the renal medulla. A link between the renal ET-1 and purinergic systems was demonstrated in vitro, however, the in vivo interaction between these systems has not been defined. To test whether renal medullary activation of purinergic (P2) receptors promotes ET-dependent natriuresis, we determined the effect of increased medullary NaCl loading on Na(+) excretion and inner medullary ET-1 mRNA expression in anesthetized adult male Sprague-Dawley rats in the presence and absence of purinergic receptor antagonism. Isosmotic saline (NaCl; 284 mosmol/kgH2O) was infused into the medullary interstitium (500 μl/h) during a 30-min baseline urine collection period, followed by isosmotic or hyperosmotic saline (1,800 mosmol/kgH2O) for two further 30-min urine collection periods. Na(+) excretion was significantly increased during intramedullary infusion of hyperosmotic saline. Compared with isosmotic saline, hyperosmotic saline infused into the renal medulla caused significant increases in inner medullary ET-1 mRNA expression. Renal intramedullary infusion of the P2 receptor antagonist suramin inhibited the increase in Na(+) excretion and inner medullary ET-1 mRNA expression induced by NaCl loading in the renal medulla. Activation of medullary P2Y2/4 receptors by infusion of UTP increased urinary Na(+) excretion. Combined ETA and ETB receptor blockade abolished the natriuretic response to intramedullary infusion of UTP. These data demonstrate that activation of medullary P2 receptors promotes ET-dependent natriuresis in male rats, suggesting that the renal ET-1 and purinergic signaling systems interact to efficiently facilitate excretion of a NaCl load.

Geniposide attenuates inflammatory response by suppressing P2Y14 receptor and downstream ERK1/2 signaling pathway in oxygen and glucose deprivation-induced brain microvascular endothelial cells

ETHNOPHARMACOLOGICAL RELEVANCE

Fructus gardenia is widely used for treatment of stroke and infectious diseases in Chinese medicine. Geniposide is the key bioactive compound related to the pharmacodynamic actions of gardenia on ischemic stroke. The molecular mechanism by which geniposide improves the ischemic brain injury was observed in the study.

AIM OF THE STUDY

Recent studies showed that geniposide had protective activities against the inflammatory response in ischemic stroke. However, the molecular mechanism of geniposide anti-inflammatory role has not yet been fully elucidated. In this study, we investigated the effect of geniposide on the expression of P2Y14 receptor and downstream signaling pathway in brain microvascular endothelial cells (BMECs).

MATERIALS AND METHODS

An in vitro model of cerebral ischemia in BMECs was established by oxygen-glucose-deprivation (OGD). To further confirm the specific effect of geniposide on P2Y14 receptor and downstream signaling pathways, we set up a UDP-glucose (an agonist of the P2Y14 receptor) stimulated model. After administration of geniposide, the expression of P2Y14 receptor, phosphorylation of RAF-1, mitogen activated protein kinase kinase1/2 (MEK1/2), extracellular signal-regulated kinase 1/2 (ERK1/2), level of interleukin-8 (IL-8), interleukin-1β (IL-1β), monocyte chemotactic protein 1 (MCP-1) in BMECs were determined.

RESULTS

The mRNA and protein expression of P2Y14 in the rat BMECs were up-regulated in OGD-induced injury. After administration of Geniposide, the expression of P2Y14 receptor was significantly down-regulated, the phosphorylation of RAF-1, MEK1/2, ERK1/2 were suppressed. Similar data were obtained in UDP-glc stimulated model. We also observed that geniposide markedly declined the production of IL-8, IL-1β and MCP-1 in OGD-induced BMECs.

CONCLUSION

Geniposide exerted anti-inflammatory effects by interfering with the expression of P2Y14 receptor, which subsequently inhibits the downstream ERK1/2 signaling pathways and the release of the pro-inflammatory cytokines IL-8, MCP-1, IL-1β. Therefore, this study provides the evidence for gardenia's clinical application in cerebral ischemia.

Impact of ectonucleotidases in autonomic nervous functions

Adenine and uracil nucleotides play key functions in the autonomic nervous system (ANS). For instance, ATP acts as a neurotransmitter, co-transmitter and neuromodulator in the ANS. The purinergic system encompasses (1) receptors that respond to extracellular purines, which are designated as P1 and P2 purinoceptors, (2) purine release and uptake, and (3) a cascade of enzymes that regulate the concentration of purines near the cell surface. Ectonucleotidases and adenosine deaminase (ADA) are enzymes responsible for the hydrolysis of ATP (and other nucleotides such as ADP, UTP, UDP, AMP) and adenosine, respectively. Accordingly, these enzymes are expected to play an important role in the control of neuro-effector transmission in tissues innervated by both the sympathetic and parasympathetic divisions of the ANS. Indeed, ectonucleotidases have the ability to either terminate P2 receptor responses initiated by nucleoside triphosphates (ATP and UTP), and/or to favor the activation of ADP (e.g. P2Y1,12,13) and UDP (e.g. P2Y6) and/or adenosine (P1) specific receptors. In addition, ectonucleotidases can also importantly protect some P2 receptors from desensitization (e.g. P2X1, P2Y1). In this review, we present the (putative) roles of ectonucleotidases and ADA in the ANS with a focus on their regulatory activity at neuro-effector junctions in the following tissues: heart, vas deferens, urinary bladder, salivary glands, blood vessels and the intestine. We also present their implication in nociceptive transmission.

Purinergic transmission in blood vessels

There are nineteen different receptor proteins for adenosine, adenine and uridine nucleotides, and nucleotide sugars, belonging to three families of G protein-coupled adenosine and P2Y receptors, and ionotropic P2X receptors. The majority are functionally expressed in blood vessels, as purinergic receptors in perivascular nerves, smooth muscle and endothelial cells, and roles in regulation of vascular contractility, immune function and growth have been identified. The endogenous ligands for purine receptors, ATP, ADP, UTP, UDP and adenosine, can be released from different cell types within the vasculature, as well as from circulating blood cells, including erythrocytes and platelets. Many purine receptors can be activated by two or more of the endogenous ligands. Further complexity arises because of interconversion between ligands, notably adenosine formation from the metabolism of ATP, leading to complex integrated responses through activation of different subtypes of purine receptors. The enzymes responsible for this conversion, ectonucleotidases, are present on the surface of smooth muscle and endothelial cells, and may be coreleased with neurotransmitters from nerves. What selectivity there is for the actions of purines/pyrimidines comes from differential expression of their receptors within the vasculature. P2X1 receptors mediate the vasocontractile actions of ATP released as a neurotransmitter with noradrenaline (NA) from sympathetic perivascular nerves, and are located on the vascular smooth muscle adjacent to the nerve varicosities, the sites of neurotransmitter release. The relative contribution of ATP and NA as functional cotransmitters varies with species, type and size of blood vessel, neuronal firing pattern, the tone/pressure of the blood vessel, and in ageing and disease. ATP is also a neurotransmitter in non-adrenergic non-cholinergic perivascular nerves and mediates vasorelaxation via smooth muscle P2Y-like receptors. ATP and adenosine can act as neuromodulators, with the most robust evidence being for prejunctional inhibition of neurotransmission via A1 adenosine receptors, but also prejunctional excitation and inhibition of neurotransmission via P2X and P2Y receptors, respectively. P2Y2, P2Y4 and P2Y6 receptors expressed on the vascular smooth muscle are coupled to vasocontraction, and may have a role in pathophysiological conditions, when purines are released from damaged cells, or when there is damage to the protective barrier that is the endothelium. Adenosine is released during hypoxia to increase blood flow via vasodilator A2A and A2B receptors expressed on the endothelium and smooth muscle. ATP is released from endothelial cells during hypoxia and shear stress and can act at P2Y and P2X4 receptors expressed on the endothelium to increase local blood flow. Activation of endothelial purine receptors leads to the release of nitric oxide, hyperpolarising factors and prostacyclin, which inhibits platelet aggregation and thus ensures patent blood flow. Vascular purine receptors also regulate endothelial and smooth muscle growth, and inflammation, and thus are involved in the underlying processes of a number of cardiovascular diseases.

UDP-Sugars as Extracellular Signaling Molecules: Cellular and Physiologic Consequences of P2Y14 Receptor Activation

UDP-sugars, which are indispensable for protein glycosylation reactions in cellular secretory pathways, also act as important extracellular signaling molecules. We discuss here the broadly expressed P2Y14 receptor, a G-protein-coupled receptor targeted by UDP sugars, and the increasingly diverse set of physiologic responses discovered recently functioning downstream of this receptor in many epithelia as well as in immune, inflammatory, and other cells.

Expression and characterization of purinergic receptors in rat middle meningeal artery-potential role in migraine

The dura mater and its vasculature have for decades been central in the hypothesis of migraine and headache pathophysiology. Although recent studies have questioned the role of the vasculature as the primary cause, dural vessel physiology is still relevant in understanding the complex pathophysiology of migraine. The aim of the present study was to isolate the middle meningeal artery (MMA) from rodents and characterize their purinergic receptors using a sensitive wire myograph method and RT-PCR. The data presented herein suggest that blood flow through the MMA is, at least in part, regulated by purinergic receptors. P2X1 and P2Y6 receptors are the strongest contractile receptors and, surprisingly, ADPβS caused contraction most likely via P2Y1 or P2Y13 receptors, which is not observed in other arteries. Adenosine addition, however, caused relaxation of the MMA. The adenosine relaxation could be inhibited by SCH58261 (A2A receptor antagonist) and caffeine (adenosine receptor antagonist). This gives one putative molecular mechanism for the effect of caffeine, often used as an adjuvant remedy of cranial pain. Semi-quantitative RT-PCR expression data for the receptors correlate well with the functional findings. Together these observations could be used as targets for future understanding of the in vivo role of purinergic receptors in the MMA.

The G protein-coupled receptor P2Y14 influences insulin release and smooth muscle function in mice

UDP sugars were identified as extracellular signaling molecules, assigning a new function to these compounds in addition to their well defined role in intracellular substrate metabolism and storage. Previously regarded as an orphan receptor, the G protein-coupled receptor P2Y14 (GPR105) was found to bind extracellular UDP and UDP sugars. Little is known about the physiological functions of this G protein-coupled receptor. To study its physiological role, we used a gene-deficient mouse strain expressing the bacterial LacZ reporter gene to monitor the physiological expression pattern of P2Y14. We found that P2Y14 is mainly expressed in pancreas and salivary glands and in subpopulations of smooth muscle cells of the gastrointestinal tract, blood vessels, lung, and uterus. Among other phenotypical differences, knock-out mice showed a significantly impaired glucose tolerance following oral and intraperitoneal glucose application. An unchanged insulin tolerance suggested altered pancreatic islet function. Transcriptome analysis of pancreatic islets showed that P2Y14 deficiency significantly changed expression of components involved in insulin secretion. Insulin secretion tests revealed a reduced insulin release from P2Y14-deficient islets, highlighting P2Y14 as a new modulator of proper insulin secretion.

Characterization of the contractile P2Y14 receptor in mouse coronary and cerebral arteries

Extracellular UDP-glucose can activate the purinergic P2Y14 receptor. The aim of the present study was to examine the physiological importance of P2Y14 receptors in the vasculature. The data presented herein show that UDP-glucose causes contraction in mouse coronary and basilar arteries. The EC50 values and immunohistochemistry illustrated the strongest P2Y14 receptor expression in the basilar artery. In the presence of pertussis toxin, UDP-glucose inhibited contraction in coronary arteries and in the basilar artery it surprisingly caused relaxation. After organ culture of the coronary artery, the EC50 value decreased and an increased staining for the P2Y14 receptor was observed, showing receptor plasticity.

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.