International Union of Pharmacology LVIII: update on the P2Y G protein-coupled nucleotide receptors: from molecular mechanisms and pathophysiology to therapy

Renal ischemia and reperfusion impact the purinergic signaling in a vascular bed distant from the injured site

AIMS

Acute kidney injury (AKI) is a public health problem and represents a risk factor for cardiovascular diseases (CVD) and vascular damage. This study aimed to investigate the impact of AKI on purinergic components in mice aorta.

MAIN METHODS

The kidney ischemia was achieved by the occlusion of the left kidney pedicle for 60 min, followed by reperfusion for 8 (IR8) and 15 (IR15) days. Renal function was assessed through biochemical assays, while gene expression levels were evaluated by RT-qPCR.

KEY FINDINGS

Analyses of renal parameters showed renal remodeling through mass loss in the left kidney and hypertrophy of the right kidney in the IR15 group. Furthermore, after 15 days, local inflammation was evidenced in the aorta. Moreover, the aorta purinergic components were significantly impacted by the renal ischemia and reperfusion model, with increases in gene expression of the pro-inflammatory purinoceptors P2Y1, P2Y2, P2Y6, and P2X4, potentially contributing to the vessel inflammation. The expression of NTPDase2 and ecto-5'-nucleotidase were also significantly increased in the aorta of the same group. In addition, both ATP and AMP hydrolysis were significantly increased in the aorta from IR15 animals, driving the entire purinergic cascade to the production of the anti-inflammatory adenosine.

SIGNIFICANCE

In short, this is the first time that inflammation of the aorta due to AKI was shown to have an impact on purinergic signaling components, with emphasis on the adenosinergic pathway. This seems to be closely implicated in the establishment of vascular inflammation in this model of AKI and deserves to be further investigated.

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.

Purinergic regulation of pulmonary vascular tone

Purinergic signaling is a crucial determinant in the regulation of pulmonary vascular physiology and presents a promising avenue for addressing lung diseases. This intricate signaling system encompasses two primary receptor classes: P1 and P2 receptors. P1 receptors selectively bind adenosine, while P2 receptors exhibit an affinity for ATP, ADP, UTP, and UDP. Functionally, P1 receptors are associated with vasodilation, while P2 receptors mediate vasoconstriction, particularly in basally relaxed vessels, through modulation of intracellular Ca2+ levels. The P2X subtype receptors facilitate extracellular Ca2+ influx, while the P2Y subtype receptors are linked to endoplasmic reticulum Ca2+ release. Notably, the primary receptor responsible for ATP-induced vasoconstriction is P2X1, with α,β-meATP and UDP being identified as potent vasoconstrictor agonists. Interestingly, ATP has been shown to induce endothelium-dependent vasodilation in pre-constricted vessels, associated with nitric oxide (NO) release. In the context of P1 receptors, adenosine stimulation of pulmonary vessels has been unequivocally demonstrated to induce vasodilation, with a clear dependency on the A2B receptor, as evidenced in studies involving guinea pigs and rats. Importantly, evidence strongly suggests that this vasodilation occurs independently of endothelium-mediated mechanisms. Furthermore, studies have revealed variations in the expression of purinergic receptors across different vessel sizes, with reports indicating notably higher expression of P2Y1, P2Y2, and P2Y4 receptors in small pulmonary arteries. While the existing evidence in this area is still emerging, it underscores the urgent need for a comprehensive examination of the specific characteristics of purinergic signaling in the regulation of pulmonary vascular tone, particularly focusing on the disparities observed across different intrapulmonary vessel sizes. Consequently, this review aims to meticulously explore the current evidence regarding the role of purinergic signaling in pulmonary vascular tone regulation, with a specific emphasis on the variations observed in intrapulmonary vessel sizes. This endeavor is critical, as purinergic signaling holds substantial promise in the modulation of vascular tone and in the proactive prevention and treatment of pulmonary vascular diseases.

Extracellular ATP is a homeostatic messenger that mediates cell‒cell communication in physiological processes and psychiatric diseases

Neuronal activity is the basis of information encoding and processing in the brain. During neuronal activation, intracellular ATP is generated to meet the high-energy demands. Meantime, ATP is secreted, increasing the extracellular ATP concentration and acting as a homeostatic messenger that mediates cell‒cell communication to prevent aberrant hyperexcitability of the nervous system. In addition to the confined release and fast synaptic signaling of classic neurotransmitters within synaptic clefts, ATP can be released by all brain cells, diffuses widely and targets different types of purinergic receptors on neurons and glial cells, making it possible to orchestrate brain neuronal activity and participate in various physiological aspects, such as sleep and wakefulness, learning and memory, and feeding. Dysregulation of extracellular ATP leads to a "destabilizing" effect on the neural network, as found in the etiopathology of many psychiatric diseases, including depression, anxiety, schizophrenia, and autism spectrum disorder. This review summarizes advances in the understanding of the mechanisms by which extracellular ATP serves as an intercellular signaling molecule to regulate neural activity, with a focus on how it maintains the homeostasis of neural networks. In particular, we also focus on neural activity issues resulting from dysregulation of extracellular ATP and propose that aberrant levels of extracellular ATP may play a role in the etiopathology of some psychiatric diseases, highlighting the potential therapeutic targets of ATP signaling in the treatment of these psychiatric diseases. Finally, we suggest potential avenues to further elucidate the role of extracellular ATP in intercellular communication and psychiatric diseases.

Testosterone Enhances KV Currents and Airway Smooth Muscle Relaxation Induced by ATP and UTP through P2Y4 Receptors and Adenylyl Cyclase Pathway

Numerous studies suggest the involvement of adenosine-5'-triphosphate (ATP) and similar nucleotides in the pathophysiology of asthma. Androgens, such as testosterone (TES), are proposed to alleviate asthma symptoms in young men. ATP and uridine-5'-triphosphate (UTP) relax the airway smooth muscle (ASM) via purinergic P2Y2 and P2Y4 receptors and K+ channel opening. We previously demonstrated that TES increased the expression of voltage-dependent K+ (KV) channels in ASM. This study investigates how TES may potentiate ASM relaxation induced by ATP and UTP. Tracheal tissues treated with or without TES (control group) from young male guinea pigs were used. In organ baths, tracheas exposed to TES (40 nM for 48 h) showed enhanced ATP- and UTP-evoked relaxation. Tetraethylammonium, a K+ channel blocker, annulled this effect. Patch-clamp experiments in tracheal myocytes showed that TES also increased ATP- and UTP-induced K+ currents, and this effect was abolished with flutamide (an androgen receptor antagonist). KV channels were involved in this phenomenon, which was demonstrated by inhibition with 4-aminopyridine. RB2 (an antagonist of almost all P2Y receptors except for P2Y2), as well as N-ethylmaleimide and SQ 22,536 (inhibitors of G proteins and adenylyl cyclase, respectively), attenuated the enhancement of the K+ currents induced by TES. Immunofluorescence and immunohistochemistry studies revealed that TES did not modify the expression of P2Y4 receptors or COX-1 and COX-2, while we have demonstrated that this androgen augmented the expression of KV1.2 and KV1.5 channels in ASM. Thus, TES leads to the upregulation of P2Y4 signaling and KV channels in guinea pig ASM, enhancing ATP and UTP relaxation responses, which likely limits the severity of bronchospasm in young males.

Pharmacological characterization of P2Y receptor subtypes - an update

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). The widely expressed P2Y receptors play important roles in physiology and pathophysiology. This review summarizes the use of pharmacological tools to characterize the P2Y receptor subtypes involved in these responses. MRS2500 is a potent and selective antagonist acting at the P2Y1 receptor. AR-C118925 is useful for the selective antagonism of the P2Y2 receptor. PSB16133 blocks the P2Y4 receptor, MRS2578 is an antagonist at the P2Y6 receptor and NF157 as well as NF340 block the P2Y11 receptor. ADP-induced platelet aggregation is mediated by P2Y1 and P2Y12 receptors. A number of compounds or their active metabolites reduce ADP-induced platelet aggregation by blocking the P2Y12 receptor. These include the active metabolites of the thienopyridine compounds clopidogrel and prasugrel, the nucleoside analogue ticagrelor and the nucleotide analogue cangrelor. PSB0739 is also a potent antagonist at the P2Y12 receptor useful for both in vitro and in vivo studies. MRS2211 and MRS2603 inhibit P2Y13 mediated responses. PPTN is a very potent antagonist at the P2Y14 receptor.

Crosstalk between P2Y receptors and cyclooxygenase activity in inflammation and tissue repair

The role of extracellular nucleotides as modulators of inflammation and cell stress is well established. One of the main actions of these molecules is mediated by the activation of purinergic receptors (P2) of the plasma membrane. P2 receptors can be classified according to two different structural families: P2X ionotropic ion channel receptors, and P2Y metabotropic G protein-coupled receptors. During inflammation, damaged cells release nucleotides and purinergic signaling occurs along the temporal pattern of the synthesis of pro-inflammatory and pro-resolving mediators by myeloid and lymphoid cells. In macrophages under pro-inflammatory conditions, the expression and activity of cyclooxygenase 2 significantly increases and enhances the circulating levels of prostaglandin E2 (PGE2), which exerts its effects both through specific plasma membrane receptors (EP1-EP4) and by activation of intracellular targets. Here we review the mechanisms involved in the crosstalk between PGE2 and P2Y receptors on macrophages, which is dependent on several isoforms of protein kinase C and protein kinase D1. Due to this crosstalk, a P2Y-dependent increase in calcium is blunted by PGE2 whereas, under these conditions, macrophages exhibit reduced migratory capacity along with enhanced phagocytosis, which contributes to the modulation of the inflammatory response and tissue repair.

Comprehensive insights into potential roles of purinergic P2 receptors on diseases: Signaling pathways involved and potential therapeutics

BACKGROUND

Purinergic P2 receptors, which can be divided into ionotropic P2X receptors and metabotropic P2Y receptors, mediate cellular signal transduction of purine or pyrimidine nucleoside triphosphates and diphosphate. Based on the wide expression of purinergic P2 receptors in tissues and organs, their significance in homeostatic maintenance, metabolism, nociceptive transmission, and other physiological processes is becoming increasingly evident, suggesting that targeting purinergic P2 receptors to regulate biological functions and signal transmission holds significant promise for disease treatment.

AIM OF REVIEW

This review highlights the detailed mechanisms by which purinergic P2 receptors engage in physiological and pathological progress, as well as providing prospective strategies for discovering clinical drug candidates.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The purinergic P2 receptors regulate complex signaling and molecular mechanisms in nervous system, digestive system, immune system and as a result, controlling physical health states and disease progression. There has been a significant rise in research and development focused on purinergic P2 receptors, contributing to an increased number of drug candidates in clinical trials. A few influential pioneers have laid the foundation for advancements in the evaluation, development, and of novel purinergic P2 receptors modulators, including agonists, antagonists, pharmaceutical compositions and combination strategies, despite the different scaffolds of these drug candidates. These advancements hold great potential for improving therapeutic outcomes by specifically targeting purinergic P2 receptors.

Extracellular Purine Metabolism-Potential Target in Multiple Sclerosis

The purinergic signaling system comprises a complex network of extracellular purines and purine-metabolizing ectoenzymes, nucleotide and nucleoside receptors, ATP release channels, and nucleoside transporters. Because of its immunomodulatory function, this system is critically involved in the pathogenesis of multiple sclerosis (MS) and its best-characterized animal model, experimental autoimmune encephalomyelitis (EAE). MS is a chronic neuroinflammatory demyelinating and neurodegenerative disease with autoimmune etiology and great heterogeneity, mostly affecting young adults and leading to permanent disability. In MS/EAE, alterations were detected in almost all components of the purinergic signaling system in both peripheral immune cells and central nervous system (CNS) glial cells, which play an important role in the pathogenesis of the disease. A decrease in extracellular ATP levels and an increase in its downstream metabolites, particularly adenosine and inosine, were frequently observed at MS, indicating a shift in metabolism toward an anti-inflammatory environment. Accordingly, upregulation of the major ectonucleotidase tandem CD39/CD73 was detected in the blood cells and CNS of relapsing-remitting MS patients. Based on the postulated role of A2A receptors in the transition from acute to chronic neuroinflammation, the association of variants of the adenosine deaminase gene with the severity of MS, and the beneficial effects of inosine treatment in EAE, the adenosinergic system emerged as a promising target in neuroinflammation. More recently, several publications have identified ADP-dependent P2Y12 receptors and the major extracellular ADP producing enzyme nucleoside triphosphate diphosphohydrolase 2 (NTPDase2) as novel potential targets in MS.

Microglia sense astrocyte dysfunction and prevent disease progression in an Alexander disease model

Alexander disease (AxD) is an intractable neurodegenerative disorder caused by GFAP mutations. It is a primary astrocyte disease with a pathological hallmark of Rosenthal fibres within astrocytes. AxD astrocytes show several abnormal phenotypes. Our previous study showed that AxD astrocytes in model mice exhibit aberrant Ca2+ signals that induce AxD aetiology. Here, we show that microglia have unique phenotypes with morphological and functional alterations, which are related to the pathogenesis of AxD. Immunohistochemical studies of 60TM mice (AxD model) showed that AxD microglia exhibited highly ramified morphology. Functional changes in microglia were assessed by Ca2+ imaging using hippocampal brain slices from Iba1-GCaMP6-60TM mice and two-photon microscopy. We found that AxD microglia showed aberrant Ca2+ signals, with high frequency Ca2+ signals in both the processes and cell bodies. These microglial Ca2+ signals were inhibited by pharmacological blockade or genetic knockdown of P2Y12 receptors but not by tetrodotoxin, indicating that these signals are independent of neuronal activity but dependent on extracellular ATP from non-neuronal cells. Our single-cell RNA sequencing data showed that the expression level of Entpd2, an astrocyte-specific gene encoding the ATP-degrading enzyme NTPDase2, was lower in AxD astrocytes than in wild-type astrocytes. In situ ATP imaging using the adeno-associated virus vector GfaABC1D ATP1.0 showed that exogenously applied ATP was present longer in 60TM mice than in wild-type mice. Thus, the increased ATP level caused by the decrease in its metabolizing enzyme in astrocytes could be responsible for the enhancement of microglial Ca2+ signals. To determine whether these P2Y12 receptor-mediated Ca2+ signals in AxD microglia play a significant role in the pathological mechanism, a P2Y12 receptor antagonist, clopidogrel, was administered. Clopidogrel significantly exacerbated pathological markers in AxD model mice and attenuated the morphological features of microglia, suggesting that microglia play a protective role against AxD pathology via P2Y12 receptors. Taken together, we demonstrated that microglia sense AxD astrocyte dysfunction via P2Y12 receptors as an increase in extracellular ATP and alter their morphology and Ca2+ signalling, thereby protecting against AxD pathology. Although AxD is a primary astrocyte disease, our study may facilitate understanding of the role of microglia as a disease modifier, which may contribute to the clinical diversity of AxD.

Fetal bovine serum contains biologically available ATP

ATP is a ubiquitous extracellular messenger released in a wide number of pathophysiological conditions. ATP is known to be present in minute amounts in the extracellular space in healthy tissues and in the blood, and to modulate a multiplicity of cell responses. Cell culture systems are widely used to explore purinergic signaling. We show here that currently used fetal bovine sera contain ATP in the 300-1300 pmol/L range. Serum ATP is associated with albumin as well as with microparticle/microvesicle fraction. Serum microparticles/microvesicles affect in vitro cell responses due to their content of miRNAs, growth factors, and other bioactive molecules. ATP is likely to be one of these bioactive factors found in a variable amount in sera of different commercial sources. ATP in serum supports ATP-dependent biochemical reactions such as the hexokinase-dependent phosphorylation of glucose to glucose 6-phosphate, and affects purinergic signaling. These findings show that cells growing in vitro in serum-supplemented media are exposed to varying levels of extracellular ATP, and thus to varying degrees of purinergic stimulation.

Extracellular nucleotides in smooth muscle contraction

Extracellular nucleotides and nucleosides are crucial signalling molecules, eliciting diverse biological responses in almost all organs and tissues. These molecules exert their effects by activating specific nucleotide receptors, which are finely regulated by ectonucleotidases that break down their ligands. In this comprehensive review, we aim to elucidate the relevance of extracellular nucleotides as signalling molecules in the context of smooth muscle contraction, considering the modulatory influence of ectonucleotidases on this intricate process. Specifically, we provide a detailed examination of the involvement of extracellular nucleotides in the contraction of non-vascular smooth muscles, including those found in the urinary bladder, the airways, the reproductive system, and the gastrointestinal tract. Furthermore, we present a broader overview of the role of extracellular nucleotides in vascular smooth muscle contraction.

ER and SOCE Ca2+ signals are not required for directed cell migration in human microglia

The central nervous system (CNS) is constantly surveilled by microglia, highly motile and dynamic cells deputed to act as the first line of immune defense in the brain and spinal cord. Alterations in the homeostasis of the CNS are detected by microglia that respond by migrating toward the affected area. Understanding the mechanisms controlling directed cell migration of microglia is crucial to dissect their responses to neuroinflammation and injury. We used a combination of pharmacological and genetic approaches to explore the involvement of calcium (Ca2+) signaling in the directed migration of induced pluripotent stem cell (iPSC)-derived microglia challenged with a purinergic stimulus. This approach mimics cues originating from injury of the CNS. Unexpectedly, simultaneous imaging of microglia migration and intracellular Ca2+ changes revealed that this phenomenon does not require Ca2+ signals generated from the endoplasmic reticulum (ER) and store-operated Ca2+ entry (SOCE) pathways. Instead, we find evidence that human microglial chemotaxis to purinergic signals is mediated by cyclic AMP in a Ca2+-independent manner. These results challenge prevailing notions, with important implications in neurological conditions characterized by perturbation in Ca2+ homeostasis.

Embryos assist morphogenesis of others through calcium and ATP signaling mechanisms in collective teratogen resistance

Information for organismal patterning can come from a variety of sources. We investigate the possibility that instructive influences for normal embryonic development are provided not only at the level of cells within the embryo, but also via interactions between embryos. To explore this, we challenge groups of embryos with disruptors of normal development while varying group size. Here, we show that Xenopus laevis embryos are much more sensitive to a diverse set of chemical and molecular-biological perturbations when allowed to develop alone or in small groups, than in large groups. Keeping per-embryo exposure constant, we find that increasing the number of exposed embryos in a cohort increases the rate of survival while incidence of defects decreases. This inter-embryo assistance effect is mediated by short-range diffusible signals and involves the P2 ATP receptor. Our data and computational model emphasize that morphogenesis is a collective phenomenon not only at the level of cells, but also of whole bodies, and that cohort size is a crucial variable in studies of ecotoxicology, teratogenesis, and developmental plasticity.

P2X7 receptor activation awakes a dormant stem cell niche in the adult spinal cord

The ependyma of the spinal cord is a latent stem cell niche that is reactivated by injury, generating new cells that migrate to the lesion site to limit the damage. The mechanisms by which ependymal cells are reactivated after injury remain poorly understood. ATP has been proposed to act as a diffusible "danger signal" to alert about damage and start repair. Indeed, spinal cord injury (SCI) generates an increase in extracellular ATP around the lesion epicenter that lasts for several hours and affects the functional outcome after the damage. The P2X7 receptor (P2X7r) has functional properties (e.g., low sensitivity for ATP, high permeability for Ca2+) that makes it a suitable candidate to act as a detector of tissue damage. Because ependymal cells express functional P2X7r that generate an inward current and regenerative Ca2+ waves, we hypothesize that the P2X7r has a main role in the mechanisms by which progenitor-like cells in the ependyma react to tissue damage. To test this possibility, we simulated the P2X7r activation that occurs after SCI by in vivo intraspinal injection of the selective agonist BzATP nearby the central canal. We found that BzATP rescued ependymal cells from quiescence by triggering a proliferative response similar to that generated by injury. In addition, P2X7r activation by BzATP induced a shift of ependymal cells to a glial fibrillary acidic protein (GFAP) phenotype similar to that induced by injury. However, P2X7r activation did not trigger the migration of ependyma-derived cells as occurs after tissue damage. Injection of BzATP induced the expression of connexin 26 (Cx26) in ependymal cells, an event needed for the proliferative reaction after injury. BzATP did not induce these changes in ependymal cells of P2X7-/- mice supporting a specific action on P2X7r. In vivo blockade of P2X7r with the potent antagonist AZ10606120 reduced significantly the injury-induced proliferation of ependymal cells. Our data indicate that P2X7r has a key role in the "awakening" of the ependymal stem cell niche after injury and suggest purinergic signaling is an interesting target to improve the contribution of endogenous progenitors to repair.

Pregabalin inhibits purinergic P2Y2 receptor and TRPV4 to suppress astrocyte activation and to relieve neuropathic pain

BACKGROUNDS

Transient receptor potential vanilloid 4 (TRPV4)-mediated astrocyte activation is critical to neuropathic pain. Pregabalin, a widely used drug to treat chronic pain, is reported to lower the intracellular calcium level. However, the molecular mechanism by which pregabalin decreases the intracellular calcium level remains unknown. Purinergic P2Y2 receptor-a member of the G protein-coupled receptor (GPCR) family-regulates calcium-related signal transduction in astrocyte activation. We investigated whether P2Y2 receptor is involved in the pharmacological effects of pregabalin on neuropathic pain.

METHODS

Neuropathic pain was induced by chronic compression of the dorsal root ganglion (CCD) in rats. Paw withdrawal mechanical threshold (PWMT) was used for behavioral testing. Intracellular calcium concentration was measured using a fluorescent calcium indicator (Fluo-4 AM).

RESULTS

We found that P2Y2 receptor protein was upregulated and astrocytes were activated in the experimental rats after CCD surgery. Lipopolysaccharide (LPS) increased the intracellular calcium concentration and induced astrocyte activation in cultured astrocytes but was prevented via P2Y2 receptor inhibitor AR-C118925 or pregabalin. Furthermore, plasmid-mediated P2Y2 receptor overexpression induced an elevation of the intracellular calcium levels and inflammation in astrocytes, which was abolished by the TRPV4 inhibitor HC-067047. AR-C118925, HC-067047, and pregabalin relieved neuropathic pain and inflammation in rats after CCD surgery. Finally, plasmid-mediated P2Y2 receptor overexpression induced neuropathic pain in rats, which was abolished by pregabalin administration.

CONCLUSIONS

Pathophysiological variables that upregulated the P2Y2 receptor/TRPV4/calcium axis contribute to astrocyte activation in neuropathic pain. Pregabalin exerts an analgesic effect by inhibiting this pathway.

Migraine signaling pathways: purine metabolites that regulate migraine and predispose migraineurs to headache

Migraine is a debilitating disorder that afflicts over 1 billion people worldwide, involving attacks that result in a throbbing and pulsating headache. Migraine is thought to be a neurovascular event associated with vasoconstriction, vasodilation, and neuronal activation. Understanding signaling in migraine pathology is central to the development of therapeutics for migraine prophylaxis and for mitigation of migraine in the prodrome phase before pain sets in. The fact that both vasoactivity and neural sensitization are involved in migraine indicates that agonists which promote these phenomena may very well be involved in migraine pathology. One such group of agonists is the purines, in particular, adenosine phosphates and their metabolites. This manuscript explores what is known about the relationship between these metabolites and migraine pathology and explores the potential for such relationships through their known signaling pathways. Reported receptor involvement in vasoaction and nociception.

Extracellular ATP Neurotransmission and Nicotine Sex-Specifically Modulate Habenular Neuronal Activity in Adolescence

The recent increase in the use of nicotine products by teenagers has revealed an urgent need to better understand the impact of nicotine on the adolescent brain. Here, we sought to examine the actions of extracellular ATP as a neurotransmitter and to investigate whether ATP and nicotinic signaling interact during adolescence. With the GRABATP (G-protein-coupled receptor activation-based ATP sensor), we first demonstrated that nicotine induces extracellular ATP release in the medial habenula, a brain region involved in nicotine aversion and withdrawal. Using patch-clamp electrophysiology, we then demonstrated that activation of the ATP receptors P2X or P2Y1 increases the neuronal firing of cholinergic neurons. Surprisingly, contrasting interactive effects were observed with nicotine exposure. For the P2X receptor, activation had no observable effect on acute nicotine-mediated activity, but during abstinence after 10 d of nicotine exposure, coexposure to nicotine and the P2X agonist potentiated neuronal activity in female, but not male, neurons. For P2Y1 signaling, a potentiated effect of the agonist and nicotine was observed with acute exposure, but not following extended nicotine exposure. These data reveal a complex interactive effect between nicotinic and ATP signaling in the adolescent brain and provide mechanistic insights into extracellular ATP signaling with sex-specific alterations of neuronal responses based on prior drug exposure.SIGNIFICANCE STATEMENT In these studies, it was discovered that nicotine induces extracellular ATP release in the medial habenula and subsequent activation of the ATP purinergic receptors increases habenular cholinergic neuronal firing in the adolescent brain. Interestingly, following extended nicotine exposure, nicotine was found to alter the interplay between purinergic and nicotinic signaling in a sex-specific manner. Together, these studies provide a novel understanding for the role of extracellular ATP in mediating habenular activity and reveal how nicotine exposure during adolescence alters these signaling mechanisms, which has important implications given the high incidence of e-cigarette/vape use by youth.

Identification of a carbohydrate recognition motif of purinergic receptors

As a major class of biomolecules, carbohydrates play indispensable roles in various biological processes. However, it remains largely unknown how carbohydrates directly modulate important drug targets, such as G-protein coupled receptors (GPCRs). Here, we employed P2Y purinoceptor 14 (P2Y14), a drug target for inflammation and immune responses, to uncover the sugar nucleotide activation of GPCRs. Integrating molecular dynamics simulation with functional study, we identified the uridine diphosphate (UDP)-sugar-binding site on P2Y14, and revealed that a UDP-glucose might activate the receptor by bridging the transmembrane (TM) helices 2 and 7. Between TM2 and TM7 of P2Y14, a conserved salt bridging chain (K2.60-D2.64-K7.35-E7.36 [KDKE]) was identified to distinguish different UDP-sugars, including UDP-glucose, UDP-galactose, UDP-glucuronic acid, and UDP-N-acetylglucosamine. We identified the KDKE chain as a conserved functional motif of sugar binding for both P2Y14 and P2Y purinoceptor 12 (P2Y12), and then designed three sugar nucleotides as agonists of P2Y12. These results not only expand our understanding for activation of purinergic receptors but also provide insights for the carbohydrate drug development for GPCRs.

Role of cAMP in Cardiomyocyte Viability: Beneficial or Detrimental?

BACKGROUND

3', 5'-cyclic AMP (cAMP) regulates numerous cardiac functions. Various hormones and neurotransmitters elevate intracellular cAMP (i[cAMP]) in cardiomyocytes through activating GsPCRs (stimulatory-G-protein-coupled-receptors) and membrane-bound ACs (adenylyl cyclases). Increasing evidence has indicated that stimulating different GsPCRs and ACs exhibits distinct, even opposite effects, on cardiomyocyte viability. However, the underlying mechanisms are not fully understood.

METHODS

We used molecular and pharmacological approaches to investigate how different GsPCR/cAMP signaling differentially regulate cardiomyocyte viability with in vitro, ex vivo, and in vivo models.

RESULTS

For prodeath GsPCRs, we explored β1AR (beta1-adrenergic receptor) and H2R (histamine-H2-receptor). We found that their prodeath effects were similarly dependent on AC5 activation, ATP release to the extracellular space via PANX1 (pannexin-1) channel, and extracellular ATP (e[ATP])-mediated signaling involving in P2X7R (P2X purinoceptor 7) and CaMKII (Ca2+/calmodulin-dependent protein kinase II). PANX1 phosphorylation at Serine 206 by cAMP-dependent-PKA (protein-kinase-A) promoted PANX1 activation, which was critical in β1AR- or H2R-induced cardiomyocyte death in vitro and in vivo. β1AR or H2R was localized proximately to PANX1, which permits ATP release. For prosurvival GsPCRs, we explored adenosine-A2-receptor (A2R), CGRPR (calcitonin-gene-related-peptide-receptor), and RXFP1 (relaxin-family peptide-receptor 1). Their prosurvival effects were dependent on AC6 activation, cAMP efflux via MRP4 (multidrug resistance protein 4), extracellular cAMP metabolism to adenosine (e[cAMP]-to-e[ADO]), and e[ADO]-mediated signaling. A2R, CGRPR, or RXFP1 was localized proximately to MRP4, which enables cAMP efflux. Interestingly, exogenously increasing e[cAMP] levels by membrane-impermeable cAMP protected against cardiomyocyte death in vitro and in ex vivo and in vivo mouse hearts with ischemia-reperfusion injuries.

CONCLUSIONS

Our findings indicate that the functional diversity of different GsPCRs in cardiomyocyte viability could be achieved by their ability to form unique signaling complexes (signalosomes) that determine the fate of cAMP: either stimulate ATP release by activating PKA or directly efflux to be e[cAMP].

Traditional Chinese medicine alleviating neuropathic pain targeting purinergic receptor P2 in purinergic signaling: A review

Past studies have suggested that Chinese herbal may alleviate neuropathic pain, and the mechanism might target the inhibition of purinergic receptor P2. This review discusses whether traditional Chinese medicine target P2 receptors in neuropathic pain and its mechanism in order to provide references for future clinical drug development. The related literatures were searched from Pubmed, Embase, Sinomed, and CNKI databases before June 2023. The search terms included"neuropathic pain", "purinergic receptor P2", "P2", "traditional Chinese medicine", "Chinese herbal medicine", and "herb". We described the traditional Chinese medicine alleviating neuropathic pain via purinergic receptor P2 signaling pathway including P2X2/3 R, P2X3R, P2X4R, P2X7R, P2Y1R. Inhibition of activating glial cells, changing synaptic transmission, increasing painful postsynaptic potential, and activating inflammatory signaling pathways maybe the mechanism. Purine receptor P2 can mediate the occurrence of neuropathic pain. And many of traditional Chinese medicines can target P2 receptors to relieve neuropathic pain, which provides reasonable evidences for the future development of drugs. Also, the safety and efficacy and mechanism need more in-depth experimental research.

Antimalarial and Plasmodium falciparum serpentine receptor 12 targeting effect of FDA approved purinergic receptor antagonist

Intraerythrocytic stages of Plasmodium falciparum responsible for all clinical manifestations of malaria are regulated by array of signalling cascades that represent attractive targets for antimalarial therapy. G-protein coupled receptors (GPCRs) are druggable targets in the treatment of various pathological conditions, however, there is limited understanding about the role of GPCRs in malaria pathogenesis. In Plasmodium, serpentine receptors (PfSR1, PfSR10, PfSR12 and PfSR25) with GPCR-like membrane topology have been reported with the finite knowledge about their potential as antimalarial targets. We analyzed the localization of these receptors in malaria parasite by immunofluorescence assays. All four receptors were expressed in blood stages with PfSR12 expressing more in late intraerythrocytic stages. Further, we evaluated the druggability of PfSR12 using FDA-approved P2Y purinergic receptor antagonist, Prasugrel and its active metabolite R138727, which is proposed to be specific towards PfSR12. Interestingly, biophysical analysis indicated strong binding between PfSR12 and R138727 as compared to the prodrug Prasugrel. This binding interaction was further confirmed by thermal shift assay. Treatment of parasite with Prasugrel and R138727 resulted in growth inhibition of P. falciparum indicating an important role of purinergic signalling and PfSR12 in parasite survival. Next, progression studies indicated the inhibitory effect of Prasugrel begins in late erythrocyte stages corroborating with PfSR12 expression at these stages. Furthermore, Prasugrel also blocked in vivo growth of malaria parasite in a mouse experimental model. This study indicates the presence of P2Y type of purinergic signalling in growth and development of malaria parasite and suggests PfSR12, putative purinergic receptor druggability through Prasugrel.Communicated by Ramaswamy H. Sarma.

Uridine Diphosphate Glucose (UDP-G) Activates Oxidative Stress and Respiratory Burst in Isolated Neutrophils

The extracellular purinergic agonist uridine diphosphate glucose (UDP-G) activates chemotaxis of human neutrophils (PMN) and the recruitment of PMN at the lung level, via P2Y14 purinergic receptor signaling. This effect is similar to the activation of PMN with N-formyl-methionyl-leucyl-phenylalanine (fMLP), a mechanism that also triggers the production of superoxide anion and hydrogen peroxide via the NADPH oxidase system. However, the effects of UDP-G on this system have not been studied. Defects in the intracellular phagocyte respiratory burst (RB) cause recurrent infections, immunodeficiency, and chronic and severe diseases in affected patients, often with sepsis and hypoxia. The extracellular activation of PMN by UDP-G could affect the RB and oxidative stress (OS) in situations of inflammation, infection and/or sepsis. The association of PMNs activation by UDP-G with OS and RB was studied. OS was evaluated by measuring spontaneous chemiluminescence (CL) of PMNs with a scintillation photon counter, and RB by measuring oxygen consumption with an oxygen Clark electrode at 37 °C, in non-stimulated cells and after activation (15 min) with lipopolysaccharides (LPS, 2 µg/mL), phorbol myristate acetate (PMA, 20 ng/mL), or UDP-G (100 μM). The stimulation index (SI) was calculated in order to establish the activation effect of the three agonists. After stimulation with LPS or PMA, the activated PMNs (0.1 × 106 cells/mL) showed an increase in CL (35%, p < 0.05 and 56%, p < 0.01, SI of 1.56 and 2.20, respectively). Contrariwise, the stimulation with UDP-G led to a decreased CL in a dose-dependent manner (60%, 25 μM, p < 0.05; 90%, 50-150 μM, p < 0.001). Nonetheless, despite the lack of oxidative damage, UDP-G triggered RB (SI 1.8) in a dose-dependent manner (38-50%, 100-200 μM, p < 0.0001). UDP-G is able to trigger NADPH oxidase activation in PMNs. Therefore, the prevention of OS and oxidative damage observed upon PMN stimulation with UDP-G indicates an antioxidant property of this molecule which is likely due to the activation of antioxidant defenses. Altogether, LPS and UDP-G have a synergistic effect, suggesting a key role in infection and/or sepsis.

Degranulation of human mast cells: modulation by P2 receptors' agonists

Since the late 1970s, there has been an alarming increase in the incidence of asthma and its morbidity and mortality. Acute obstruction and inflammation of allergic asthmatic airways are frequently caused by inhalation of exogenous substances such as allergens cross-linking IgE receptors expressed on the surface of the human lung mast cells (HLMC). The degree of constriction of human airways produced by identical amounts of inhaled allergens may vary from day to day and even hour to hour. Endogenous factors in the human mast cell (HMC)'s microenvironment during allergen exposure may markedly modulate the degranulation response. An increase in allergic responsiveness may significantly enhance bronchoconstriction and breathlessness. This review focuses on the role that the ubiquitous endogenous purine nucleotide, extracellular adenosine 5'-triphosphate (ATP), which is a component of the damage-associated molecular patterns, plays in mast cells' physiology. ATP activates P2 purinergic cell-surface receptors (P2R) to trigger signaling cascades resulting in heightened inflammatory responses. ATP is the most potent enhancer of IgE-mediated HLMC degranulation described to date. Current knowledge of ATP as it relates to targeted receptor(s) on HMC along with most recent studies exploring HMC post-receptor activation pathways are discussed. In addition, the reviewed studies may explain why brief, minimal exposures to allergens (e.g., dust, cat, mouse, and grass) can unpredictably lead to intense clinical reactions. Furthermore, potential therapeutic approaches targeting ATP-related enhancement of allergic reactions are presented.

Function and therapeutic value of astrocytes in diabetic cognitive impairment

Diabetic cognitive impairment (DCI) is a complex complication of diabetes in the central nervous system, and its pathological mechanism is still being explored. Astrocytes are abundant glial cells in central nervous system that perform diverse functions in health and disease. Accumulating excellent research has identified astrocyte dysfunction in many neurodegenerative diseases (such as Alzheimer's disease, aging and Parkinson's disease), and summarized and discussed its pathological mechanisms and potential therapeutic value. However, the contribution of astrocytes to DCI has been largely overlooked. In this review, we first systematically summarized the effects and mechanisms of diabetes on brain astrocytes, and found that the diabetic environment (such as hyperglycemia, advanced glycation end products and cerebral insulin resistance) mediated brain reactive astrogliosis, which was specifically reflected in the changes of cell morphology and the remodeling of signature molecules. Secondly, we emphasized the contribution and potential targets of reactive astrogliosis to DCI, and found that reactive astrogliosis-induced increased blood-brain barrier permeability, glymphatic system dysfunction, neuroinflammation, abnormal cell communication and cholesterol metabolism dysregulation worsened cognitive function. In addition, we summarized effective strategies for treating DCI by targeting astrocytes. Finally, we discuss the application of new techniques in astrocytes, including single-cell transcriptome, in situ sequencing, and prospected new functions, new subsets and new targets of astrocytes in DCI.

Ligand recognition and signal transduction by lectin receptor-like kinases in plant immunity

Lectin receptor-like kinases (LecRKs) locate on the cell membrane and play diverse roles in perceiving environmental factors in higher plants. Studies have demonstrated that LecRKs are involved in plant development and response to abiotic and biotic stresses. In this review, we summarize the identified ligands of LecRKs in Arabidopsis, including extracellular purine (eATP), extracellular pyridine (eNAD⁺), extracellular NAD⁺ phosphate (eNADP⁺) and extracellular fatty acids (such as 3-hydroxydecanoic acid). We also discussed the posttranslational modification of these receptors in plant innate immunity and the perspectives of future research on plant LecRKs.

P2Y12 receptor involved in the development of chronic nociceptive pain as a sensory information mediator

Direct or indirect damage to the nervous system (such as inflammation or tumor invasion) can lead to dysfunction and pain. The generation of pain is mainly reflected in the activation of glial cells and the abnormal discharge of sensory neurons, which transmit stronger sensory information to the center. P2Y12 receptor plays important roles in physiological and pathophysiological processes including inflammation and pain. P2Y12 receptor involved in the occurrence of pain as a sensory information mediator, which enhances the activation of microglia and the synaptic plasticity of primary sensory neurons, and reaches the higher center through the ascending conduction pathway (mainly spinothalamic tract) to produce pain. While the application of P2Y12 receptor antagonists (PBS-0739, AR-C69931MX and MRS2359) have better antagonistic activity and produce analgesic pharmacological properties. Therefore, in this article, we discussed the role of the P2Y12 receptor in different chronic pains and its use as a pharmacological target for pain relief.

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.

ATP-mediated signalling in the central synapses

ATP released from the synaptic terminals and astrocytes can activate neuronal P2 receptors at a variety of locations across the CNS. Although the postsynaptic ATP-mediated signalling does not bring a major contribution into the excitatory transmission, it is instrumental for slow and diffuse modulation of synaptic dynamics and neuronal firing in many CNS areas. Neuronal P2X and P2Y receptors can be activated by ATP released from the synaptic terminals, astrocytes and microglia and thereby can participate in the regulation of synaptic homeostasis and plasticity. There is growing evidence of importance of purinergic regulation of synaptic transmission in different physiological and pathological contexts. Here, we review the main mechanisms underlying the complexity and diversity of purinergic signalling and purinergic modulation in central neurons.

Suramin ameliorates osteoarthritis by acting on the Nrf2/HO-1 and NF-κB signaling pathways in chondrocytes and promoting M2 polarization in macrophages

Osteoarthritis (OA)-the most prevalent of arthritis diseases-is a complicated pathogenesis caused by cartilage degeneration and synovial inflammation. Suramin has been reported to enhance chondrogenic differentiation. However, the therapeutic effect of suramin on OA-induced cartilage destruction has remained unclear. Suramin is an anti-parasitic drug that has potent anti-purinergic properties. This study investigated the protective effects and underlying mechanisms of suramin on articular cartilage degradation using an in vitro study and mice model with post-traumatic OA. We found that suramin markedly suppressed the IL-1β increased expression of matrix destruction proteases-such as ADAMT4, ADAMTS5, MMP3, MMP13, and inflammatory mediators-including the iNOS, COX2, TNFα, and IL-1β; while greatly enhancing the synthesis of cartilage anabolic factors-such as COL2A1, Aggrecan and SOX9 in IL-1β-induced porcine chondrocytes. In vivo experiments showed that intra-articular injection of suramin ameliorated cartilage degeneration and inhibited synovial inflammation in an anterior cruciate ligament transection (ACLT)-induced OA mouse model. In mechanistic studies, we found that exogenous supplementation of suramin can activate Nrf2, and accordingly inhibit the nuclear factor kappa-light-chain-enhancer of activated B cells (NF- κB) and mitogen-activated protein kinase (MAPK) pathways, thereby alleviating the inflammation and ECM degeneration of chondrocytes stimulated by IL-1β. In addition, suramin also repolarized M1 macrophages to the M2 phenotype, further reducing the apoptosis of chondrocytes. Collectively, the results of the study suggests that suramin is a potential drugs which could serve as a facilitating drug for the application of OA therapy toward clinical treatment.

Structure-based virtual screening for discovery of paederosidic acid from Paederia scandens as novel P2Y14R antagonist

BACKGROUND

The activation of P2Y₁₄ receptor (P2Y₁₄R) promotes osteoclast formation and causes neuropathic pain, exhibiting possible link to osteoarthritis (OA). Given lack of P2Y₁₄R antagonist, the present study aims to search a novel P2Y₁₄R antagonist with low toxicity and high activity from natural products as a possible drug candidate in treatment of OA.

METHODS

The role of P2Y₁₄R on OA was verified using P2Y₁₄R knockout (KO) rats. Molecular docking virtual screening strategy and activity test in P2Y₁₄R stably-expressed HEK293 cells were used to screen target compound from natural product library. The MM/GBSA free energy calculation/decomposition technique was used to determine the principal interaction mechanism. Next, the binding of target compound to P2Y₁₄R was examined using cellular thermal shift assay and drug affinity responsive target stability test. Finally, the therapeutic effect of target compound was performed in monosodium iodoacetate (MIA)-induced OA mouse model. To verify whether the effect of target compound was attributed to P2Y₁₄R, we establish the osteoarthritis model in P2Y₁₄R KO mice to perform pharmacodynamic evaluation. Importantly, to investigate the potential mechanism by which target compound attenuate OA, expressions of the major transcription factors involved in osteoclast differentiation were detected by western blot, while markers of nerve damage in dorsal root ganglion (DRG) were evaluated by RT-qPCR and immunofluorescence techniques.

RESULTS

Deficiency of P2Y₁₄R alleviated pain behavior and cartilage destruction in MIA-induced OA rats. 14 natural compounds were screened by Glide docking-based virtual screening, among which paederosidic acid exhibited the highest antagonistic activity to P2Y₁₄R with IC₅₀ of 8.287 μM. As a bioactive component extracted from Paederia scandens, paederosidic acid directly interacted with P2Y₁₄R to enhance the thermostability and decrease the protease sensitivity of target protein, which significantly inhibited receptor activator for nuclear factor-κB ligand (RANKL)-mediated osteoclastogenesis. More importantly, paederosidic acid suppressed osteoclast formation by downregulating expressions of NFAT2 and ATP6V0D2, as well as relieved neuropathic pain by decreasing expressions of CGRP, CSF1 and galanin in DRG.

CONCLUSIONS

Paederosidic acid targeted P2Y₁₄R to improve OA through alleviating osteoclast formation and neuropathic pain, which provided an available strategy for developing novel drug leads for treatment of OA.

Role of purinergic receptors in cardiac sympathetic nerve injury in diabetes mellitus

Diabetic cardiac autonomic neuropathy is a common and serious chronic complication of diabetes, which can lead to sympathetic and parasympathetic nerve imbalance and a relative excitation of the sympathetic nerve. Purinergic receptors play a crucial role in this process. Diabetic cardiac sympathetic nerve injury affects the expression of purinergic receptors, and activated purinergic receptors affect the phosphorylation of different signaling pathways and the regulation of inflammatory processes. This paper introduces the abnormal changes of sympathetic nerve in diabetes mellitus and summarizes the recently published studies on the role of several purinergic receptor subtypes in diabetic cardiac sympathetic nerve injury. These studies suggest that purinergic receptors as novel drug targets are of great significance for the treatment of diabetic autonomic neuropathy. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Activation of endothelial NO synthase and P2X7 receptor modification mediates the cholinergic control of ATP-induced interleukin-1β release by mononuclear phagocytes

Objective

The pro-inflammatory cytokine interleukin-1β (IL-1β) plays a central role in host defense against infections. High systemic IL-1β levels, however, promote the pathogenesis of inflammatory disorders. Therefore, mechanisms controlling IL-1β release are of substantial clinical interest. Recently, we identified a cholinergic mechanism inhibiting the ATP-mediated IL-1β release by human monocytes via nicotinic acetylcholine receptor (nAChR) subunits α7, α9 and/or α10. We also discovered novel nAChR agonists that trigger this inhibitory function in monocytic cells without eliciting ionotropic functions at conventional nAChRs. Here, we investigate the ion flux-independent signaling pathway that links nAChR activation to the inhibition of the ATP-sensitive P2X7 receptor (P2X7R).

Methods

Different human and murine mononuclear phagocytes were primed with lipopolysaccharide and stimulated with the P2X7R agonist BzATP in the presence or absence of nAChR agonists, endothelial NO synthase (eNOS) inhibitors, and NO donors. IL-1β was measured in cell culture supernatants. Patch-clamp and intracellular Ca2+ imaging experiments were performed on HEK cells overexpressing human P2X7R or P2X7R with point mutations at cysteine residues in the cytoplasmic C-terminal domain.

Results

The inhibitory effect of nAChR agonists on the BzATP-induced IL-1β release was reversed in the presence of eNOS inhibitors (L-NIO, L-NAME) as well as in U937 cells after silencing of eNOS expression. In peripheral blood mononuclear leukocytes from eNOS gene-deficient mice, the inhibitory effect of nAChR agonists was absent, suggesting that nAChRs signal via eNOS to inhibit the BzATP-induced IL-1β release. Moreover, NO donors (SNAP, S-nitroso-N-acetyl-DL-penicillamine; SIN-1) inhibited the BzATP-induced IL-1β release by mononuclear phagocytes. The BzATP-induced ionotropic activity of the P2X7R was abolished in the presence of SIN-1 in both, Xenopus laevis oocytes and HEK cells over-expressing the human P2X7R. This inhibitory effect of SIN-1 was absent in HEK cells expressing P2X7R, in which C377 was mutated to alanine, indicating the importance of C377 for the regulation of the P2X7R function by protein modification.

Conclusion

We provide first evidence that ion flux-independent, metabotropic signaling of monocytic nAChRs involves eNOS activation and P2X7R modification, resulting in an inhibition of ATP signaling and ATP-mediated IL-1β release. This signaling pathway might be an interesting target for the treatment of inflammatory disorders.

ATP and its metabolite adenosine cooperatively upregulate the antigen-presenting molecules on dendritic cells leading to IFN-γ production by T cells

Dendritic cells (DCs) present foreign antigens to T cells via the major histocompatibility complex (MHC), thereby inducing acquired immune responses. ATP accumulates at sites of inflammation or in tumor tissues, which triggers local inflammatory responses. However, it remains to be clarified how ATP modulates the functions of DCs. In this study, we investigated the effects of extracellular ATP on mouse bone marrow-derived dendritic cells (BMDCs), as well as the potential for subsequent T cell activation. We found that high concentrations of ATP (1 mM) upregulated the cell surface expression levels of MHC-I, MHC-II, and co-stimulatory molecules CD80 and CD86, but not those of co-inhibitory molecules PD-L1 and PD-L2 in BMDCs. Increased surface expression of MHC-I, MHC-II, CD80, and CD86 was inhibited by a pan-P2 receptor antagonist. In addition, the upregulation of MHC-I and MHC-II expression was inhibited by an adenosine P1 receptor antagonist and by inhibitors of CD39 and CD73, which metabolize ATP to adenosine. These results suggest that adenosine is required for the ATP-induced upregulation of MHC-I and MHC-II. In the mixed leukocyte reaction assay, ATP-stimulated BMDCs activated CD4 and CD8 T cells and induced interferon-gamma (IFN-γ) production by these T cells. Collectively, these results suggest that high concentrations of extracellular ATP upregulate the expression of antigen-presenting and co-stimulatory molecules but not that of co-inhibitory molecules in BMDCs. Cooperative stimulation of ATP and its metabolite adenosine was required for the upregulation of MHC-I and MHC-II. These ATP-stimulated BMDCs induced the activation of IFN-γ-producing T cells upon antigen presentation.

MicroRNA: Crucial modulator in purinergic signalling involved diseases

Both microRNAs (miRNAs) and purinergic signalling are widely and respectively expressed in various tissues of different organisms and play vital roles in a variety of physiological and pathological processes. Here, we reviewed the current publications contributed to the relationship of miRNAs and purinergic signalling in cardiovascular diseases, gastrointestinal diseases, neurological diseases, and ophthalmic diseases. We tried to decode the miRNAs-purinergic signalling network of purinergic signalling involved diseases. The evidence indicated that more than 30 miRNAs (miR-22, miR-30, miR-146, miR-150, miR-155, miR-187, etc.) directly or indirectly modulate P1 receptors (A₁, A_2A, A_2B, A₃), P2 receptors (P2X1, P2X3, P2X4, P2X7, P2Y2, P2Y6, P2Y12), and ecto-enzymes (CD39, CD73, ADA2); P2X7 and CD73 could be modulated by multiple miRNAs (P2X7: miR-21, miR-22, miR-30, miR-135a, miR-150, miR-186, miR-187, miR-216b; CD73: miR-141, miR-101, miR-193b, miR-340, miR-187, miR-30, miR-422a); miR-187 would be the common miRNA to modulate P2X7 and CD73.

ATP Induces Interleukin-8, Intracellular Calcium Release, and ERK1/2 Phosphorylation in Bovine Endometrial Cells, Partially through P2Y Receptors

The bovine endometrium has an important defensive role in the postpartum period that acts when an inflammatory process associated with tissue damage or infection by bacteria is produced. Endometrial cells release cytokines and chemokines that recruit inflammatory cells, which release danger-associated molecular patterns (DAMPs), such as adenosine triphosphate (ATP), and initiate and regulate the inflammatory response. However, the role of ATP in bovine endometrial cells is unclear. The aim of this study was to determine the effect of ATP on interleukin-8 (IL-8) release, intracellular calcium mobilization, ERK1/2 phosphorylation, and the role of P2Y receptors, in bovine endometrial cells. Bovine endometrial (BEND) cells were incubated with ATP and the IL-8 release was determined by the ELISA assay. ATP of 50 and 100 μM significantly increased IL-8 released in BEND cells (50 μM: 23.16 ± 3.82 pg/mL, p = 0.0018; 100 μM: 30.14 ± 7.43 pg/mL, p = 0.0004). ATP (50 μM) also induced rapid intracellular calcium mobilization in Fura-2AM-loaded BEND cells, as well as ERK1/2 phosphorylation (ratio 1.1 ± 0.04, p = 0.0049). Suramin (50 μM), a pan-antagonist of P2Y receptors, partially reduced the intracellular calcium mobilization, ERK1/2 phosphorylation (ratio 0.83 ± 0.08, p = 0.045), and IL-8 release (9.67 ± 0.02 pg/mL, p = 0.014) induced by ATP. Finally, BEND cells expressed higher mRNA levels of P2Y1 and P2Y2 purinergic subtype receptors, and lower levels of P2Y11 and P2Y12 receptors, as determined by RT-qPCR. In conclusion, these results showed that ATP activates pro-inflammatory responses in BEND cells, which are partially mediated via P2Y receptors, and BEND cells express the mRNA of subtypes of P2Y receptors, which could have a key role in bovine endometrial inflammation.

The Pleiotropic Role of Extracellular ATP in Myocardial Remodelling

Myocardial remodelling is a molecular, cellular, and interstitial adaptation of the heart in response to altered environmental demands. The heart undergoes reversible physiological remodelling in response to changes in mechanical loading or irreversible pathological remodelling induced by neurohumoral factors and chronic stress, leading to heart failure. Adenosine triphosphate (ATP) is one of the potent mediators in cardiovascular signalling that act on the ligand-gated (P2X) and G-protein-coupled (P2Y) purinoceptors via the autocrine or paracrine manners. These activations mediate numerous intracellular communications by modulating the production of other messengers, including calcium, growth factors, cytokines, and nitric oxide. ATP is known to play a pleiotropic role in cardiovascular pathophysiology, making it a reliable biomarker for cardiac protection. This review outlines the sources of ATP released under physiological and pathological stress and its cell-specific mechanism of action. We further highlight a series of cardiovascular cell-to-cell communications of extracellular ATP signalling cascades in cardiac remodelling, which can be seen in hypertension, ischemia/reperfusion injury, fibrosis, hypertrophy, and atrophy. Finally, we summarize current pharmacological intervention using the ATP network as a target for cardiac protection. A better understanding of ATP communication in myocardial remodelling could be worthwhile for future drug development and repurposing and the management of cardiovascular diseases.

Fluorescent proteins and genetically encoded biosensors

The genetically encoded fluorescent sensors convert chemical and physical signals into light. They are powerful tools for the visualisation of physiological processes in living cells and freely moving animals. The fluorescent protein is the reporter module of a genetically encoded biosensor. In this study, we first review the history of the fluorescent protein in full emission spectra on a structural basis. Then, we discuss the design of the genetically encoded biosensor. Finally, we briefly review several major types of genetically encoded biosensors that are currently widely used based on their design and molecular targets, which may be useful for the future design of fluorescent biosensors.

Titanium dioxide nanotubes increase purinergic receptor P2Y6 expression and activate its downstream PKCα-ERK1/2 pathway in bone marrow mesenchymal stem cells under osteogenic induction

Titanium dioxide (TiO₂) nanotubes can improve the osseointegration of pure titanium implants, but this exact mechanism has not been fully elucidated. The purinergic receptor P2Y6 is expressed in bone marrow mesenchymal stem cells (BMSCs) and participates in the regulation of bone metabolism. However, it is unclear as to whether P2Y6 is involved in the osteogenic differentiation of BMSCs induced by TiO₂ nanotubes. TiO₂ nanotubes were prepared on the surface of titanium specimens using the anodizing method and characterized their features. Quantitative reverse transcriptase polymerase chain reaction and western blotting were used to detect the expression of P2Y6, markers of osteogenic differentiation, and PKCα-ERK1/2. A rat femoral defect model was established to evaluate the osseointegration effect of TiO₂ nanotubes combined with P2Y6 agonists. The results showed that the average inner diameter of the TiO₂ nanotubes increased with an increase in voltage (voltage range of 30-90V), and the expression of P2Y6 in BMSCs could be upregulated by TiO₂ nanotubes in osteogenic culture. Inhibition of P2Y6 expression partially inhibited the osteogenic effect of TiO₂ nanotubes and downregulated the activity of the PKCα-ERK1/2 pathway. When using in vitro and in vivo experiments, the osteogenic effect of TiO₂ nanotubes when combined with P2Y6 agonists was more pronounced. TiO₂ nanotubes promoted the P2Y6 expression of BMSCs during osteogenic differentiation and promoted osteogenesis by activating the PKCα-ERK1/2 pathway. The combined application of TiO₂ nanotubes and P2Y6 agonists may be an effective new strategy to improve the osseointegration of titanium implants. STATEMENT OF SIGNIFICANCE: Titanium dioxide (TiO₂) nanotubes can improve the osseointegration of pure titanium implants, but this exact mechanism has not been fully elucidated. The purinergic receptor P2Y6 is expressed in bone marrow mesenchymal stem cells (BMSCs) and participates in the regulation of bone metabolism. However, it is unclear as to whether P2Y6 is involved in the osteogenic differentiation of BMSCs induced by TiO₂ nanotubes. For the first time, this study revealed the relationship between TiO₂ nanotubes and purine receptor P2Y6, and further explored its mode of action, which may provide clues as to the regulatory role of TiO₂ nanotubes on osteogenic differentiation of BMSCs. These findings will help to develop novel methods for guiding material design and biosafety evaluation of nano implants.

Association between P2Y1 and P2Y12 polymorphisms and acute myocardial infarction and ADP-induced platelet aggregation

BACKGROUND

The objective of this study was to investigate the relationship between P2Y1 and P2Y12 genotypes and the risk of acute myocardial infarction (AMI) in the Quanzhou population and to determine associations between P2Y1 and P2Y12 genotypes and ADP-induced platelet aggregation in this population.

METHODS

All subjects were screened for P2Y1 (c.1622A > G) and P2Y12 (H1/H2, c.34C > T) polymorphisms by direct DNA sequencing. The maximal platelet aggregation rate (MAR) in AMI patients (n = 61) and healthy control subjects (n = 50) was measured by a PL-12 platelet function analyzer, and adenosine diphosphate (ADP) (5 μmol/L) was used as an agonist.

RESULTS

The haploid H2 allele in the P2Y12 gene was more frequent in patients with AMI than in control subjects (OR 1.887, P = 0.005). The P2Y12 H2 haplotype was significantly associated with AMI in the codominant (P = 0.008), dominant (OR 2.103, P = 0.003), and overdominant models (OR 2.133, P = 0.003). After adjusting for potential confounders, H2 haplotype carriers had a 2.132-fold increased risk for AMI (OR 2.132, P = 0.012) compared with noncarriers. Moreover, we observed that the ADP-induced MAR in the carriers of the H2 haplotype from the control group was somewhat higher than that in noncarriers of this group (P = 0.020). However, we failed to demonstrate that the P2Y1 H1/H2 polymorphism affected ADP-induced MAR in AMI patients. Additionally, P2Y1 c.1622A > and P2Y12 c.34C > T polymorphisms were not associated with the risk of AMI or ADP-induced MAR in either group.

CONCLUSIONS

Therefore, our results suggest that the P2Y12 H2 haplotype was associated with a higher risk of AMI, while its effect on increased ADP-induced platelet aggregation remains to be investigated. Thus, the P2Y12 H2 haplotype may be a potential marker for AMI.

Damage-induced pyroptosis drives endog thymic regeneration via induction of Foxn1 by purinergic receptor activation

Endogenous thymic regeneration is a crucial process that allows for the renewal of immune competence following stress, infection or cytoreductive conditioning. Fully understanding the molecular mechanisms driving regeneration will uncover therapeutic targets to enhance regeneration. We previously demonstrated that high levels of homeostatic apoptosis suppress regeneration and that a reduction in the presence of damage-induced apoptotic thymocytes facilitates regeneration. Here we identified that cell-specific metabolic remodeling after ionizing radiation steers thymocytes towards mitochondrial-driven pyroptotic cell death. We further identified that a key damage-associated molecular pattern (DAMP), ATP, stimulates the cell surface purinergic receptor P2Y2 on cortical thymic epithelial cells (cTECs) acutely after damage, enhancing expression of Foxn1, the critical thymic transcription factor. Targeting the P2Y2 receptor with the agonist UTPγS promotes rapid regeneration of the thymus in vivo following acute damage. Together these data demonstrate that intrinsic metabolic regulation of pyruvate processing is a critical process driving thymus repair and identifies the P2Y2 receptor as a novel molecular therapeutic target to enhance thymus regeneration.

Purinergic signaling: Diverse effects and therapeutic potential in cancer

Regardless of improved biological insights and therapeutic advances, cancer is consuming multiple lives worldwide. Cancer is a complex disease with diverse cellular, metabolic, and physiological parameters as its hallmarks. This instigates a need to uncover the latest therapeutic targets to advance the treatment of cancer patients. Purines are building blocks of nucleic acids but also function as metabolic intermediates and messengers, as part of a signaling pathway known as purinergic signaling. Purinergic signaling comprises primarily adenosine triphosphate (ATP) and adenosine (ADO), their analogous membrane receptors, and a set of ectonucleotidases, and has both short- and long-term (trophic) effects. Cells release ATP and ADO to modulate cellular function in an autocrine or paracrine manner by activating membrane-localized purinergic receptors (purinoceptors, P1 and P2). P1 receptors are selective for ADO and have four recognized subtypes-A1, A2A, A2B, and A3. Purines and pyrimidines activate P2 receptors, and the P2X subtype is ligand-gated ion channel receptors. P2X has seven subtypes (P2X1-7) and forms homo- and heterotrimers. The P2Y subtype is a G protein-coupled receptor with eight subtypes (P2Y1/2/4/6/11/12/13/14). ATP, its derivatives, and purinoceptors are widely distributed in all cell types for cellular communication, and any imbalance compromises the homeostasis of the cell. Neurotransmission, neuromodulation, and secretion employ fast purinergic signaling, while trophic purinergic signaling regulates cell metabolism, proliferation, differentiation, survival, migration, invasion, and immune response during tumor progression. Thus, purinergic signaling is a prospective therapeutic target in cancer and therapy resistance.

Tear secretion by Diquafosol suppresses the excitability of trigeminal brainstem nuclear complex neurons by reducing excessive P2Y2 expression in the trigeminal ganglion in dry eye rats

The P2Y₂ receptor agonist, diquafosol sodium, is commonly used to treat the signs and symptoms of dry eye disease (DE) patients. Although diquafosol improves tear film stability, the neural mechanisms underlying the reduction in ocular pain are not well defined. This study determined if repeated application of diquafosol reduces the sensitization of nociceptive neurons in the lower trigeminal brainstem nuclear complex (TBNC) via peripheral P2Y₂ mechanisms in a rat model for DE. Diquafosol was applied to the ocular surface daily for 28 days, starting at day 0 or day 14, after exorbital gland removal. The number of eyeblinks, P2Y₂-immunoreactive neurons in the trigeminal ganglion (TG), and correlates of TBNC neural excitability (i.e., cFos protein and phosphorylated extracellular signal-regulated kinase (pERK) expression) were assessed in male rats. Diquafosol increased spontaneous tear volume and reduced the number of ocular surface-evoked eyeblinks in DE rats. Fluorogold-labeled TG neurons that supply the cornea expressed P2Y₂. The number of P2Y₂-immunoreactive neurons was increased in DE rats and suppressed by diquafosol. Diquafosol also reduced the number of cFos- and pERK-immunoreactive neurons in the TBNC in DE rats. These findings suggest that diquafosol, regardless of late-phase treatment, relieves ocular nociception in DE by reducing peripheral P2Y₂ expression.

Ocular P2 receptors and glaucoma

Adenosine triphosphate (ATP), an energy source currency in cells, is released or leaked to the extracellular space under both physiological and pathological conditions. Extracellular ATP functions as an intercellular signaling molecule through activation of purinergic P2 receptors. Ocular tissue and cells release ATP in response to physiological stimuli such as intraocular pressure (IOP), and P2 receptor activation regulates IOP elevation or reduction. Dysregulated purinergic signaling may cause abnormally elevated IOP, which is one of the major risk factors for glaucoma. Glaucoma, a leading cause of blindness worldwide, is characterized by progressive degeneration of optic nerves and retinal ganglion cells (RGCs), which are essential retinal neurons that transduce visual information to the brain. An elevation in IOP may stress RGCs and increase the risk for glaucoma pathogenesis. In the aqueous humor of human patients with glaucoma, the ATP level is significantly elevated. Such excess amount of ATP may directly cause RGC death via a specific subtype of P2 receptors. Dysregulated purinergic signaling may also trigger inflammation, oxidative stress, and excitotoxicity via activating non-neuronal cell types such as glial cells. In this review, we discussed the physiological roles of extracellular nucleotides in the ocular tissue and their potential role in the pathogenesis of glaucoma. This article is part of the Special Issue on 'Purinergic Signaling: 50 years'.

P2Y6 receptor-dependent microglial phagocytosis of synapses mediates synaptic and memory loss in aging

Aging causes loss of brain synapses and memory, and microglial phagocytosis of synapses may contribute to this loss. Stressed neurons can release the nucleotide UTP, which is rapidly converted into UDP, that in turn activates the P2Y₆ receptor (P2Y₆ R) on the surface of microglia, inducing microglial phagocytosis of neurons. However, whether the activation of P2Y₆ R affects microglial phagocytosis of synapses is unknown. We show here that inactivation of P2Y₆ R decreases microglial phagocytosis of isolated synapses (synaptosomes) and synaptic loss in neuronal-glial co-cultures. In vivo, wild-type mice aged from 4 to 17 months exhibited reduced synaptic density in cortical and hippocampal regions, which correlated with increased internalization of synaptic material within microglia. However, this aging-induced synaptic loss and internalization were absent in P2Y₆ R knockout mice, and these mice also lacked any aging-induced memory loss. Thus, P2Y₆ R appears to mediate aging-induced loss of synapses and memory by increasing microglial phagocytosis of synapses. Consequently, blocking P2Y₆ R has the potential to prevent age-associated memory impairment.

Discovery of a Series of 5-Amide-1H-pyrazole-3-carboxyl Derivatives as Potent P2Y14R Antagonists with Anti-Inflammatory Characters

UDPG/P2Y₁₄R signaling pathway has been considered as a potential therapeutic target for innate immune system diseases. Based on the scaffold hopping strategy, a series of pyrazole analogues were designed and synthesized as novel P2Y₁₄R antagonists with improved physicochemical properties, together with potential anti-inflammatory activities. Additionally, we designed and synthesized a fluorescent probe based on highly selective and potent PPTN to study the affinity of synthesized compounds. The optimized compound 16 (1-(4-fluorobenzyl)-5-(4-methylbenzamido)-1H-pyrazole-3-carboxylic acid, P2Y₁₄R IC₅₀ = 1.93 nM) showed strong binding ability to P2Y₁₄R, high selectivity, notably improved solubility, and more favorable pharmacokinetic profiles. Moreover, compound 16 possessed extremely low cytotoxicity and anti-inflammatory effect in vitro. In an acute peritonitis model, compound 16 could effectively reduce the levels of inflammatory factor IL-6, IL-1β, and TNF-α of mice induced by LPS. Compound 16, with potent in vitro and in vivo efficacy and favorable druggability, can be a promising candidate for further research.

Characterisation of P2Y receptor subtypes mediating vasodilation and vasoconstriction of rat pulmonary artery using selective antagonists

Pulmonary vascular tone is modulated by nucleotides, but which P2 receptors mediate these actions is largely unclear. The aim of this study, therefore, was to use subtype-selective antagonists to determine the roles of individual P2Y receptor subtypes in nucleotide-evoked pulmonary vasodilation and vasoconstriction. Isometric tension was recorded from rat intrapulmonary artery rings (i.d. 200-500 µm) mounted on a wire myograph. Nucleotides evoked concentration- and endothelium-dependent vasodilation of precontracted tissues, but the concentration-response curves were shallow and did not reach a plateau. The selective P2Y₂ antagonist, AR-C118925XX, inhibited uridine 5'-triphosphate (UTP)- but not adenosine 5'-triphosphate (ATP)-evoked relaxation, whereas the P2Y₆ receptor antagonist, MRS2578, had no effect on UTP but inhibited relaxation elicited by uridine 5'-diphosphate (UDP). ATP-evoked relaxations were unaffected by the P2Y₁ receptor antagonist, MRS2179, which substantially inhibited responses to adenosine 5'-diphosphate (ADP), and by the P2Y_12/13 receptor antagonist, cangrelor, which potentiated responses to ADP. Both agonists were unaffected by CGS1593, an adenosine receptor antagonist. Finally, AR-C118925XX had no effect on vasoconstriction elicited by UTP or ATP at resting tone, although P2Y₂ receptor mRNA was extracted from endothelium-denuded tissues using reverse transcription polymerase chain reaction with specific oligonucleotide primers. In conclusion, UTP elicits pulmonary vasodilation via P2Y₂ receptors, whereas UDP acts at P2Y₆ and ADP at P2Y₁ receptors, respectively. How ATP induces vasodilation is unclear, but it does not involve P2Y₁, P2Y₂, P2Y₁₂, P2Y₁₃, or adenosine receptors. UTP- and ATP-evoked vasoconstriction was not mediated by P2Y₂ receptors. Thus, this study advances our understanding of how nucleotides modulate pulmonary vascular tone.

Harnessing the cyclization strategy for new drug discovery

The design of new ligands with high affinity and specificity against the targets of interest has been a central focus in drug discovery. As one of the most commonly used methods in drug discovery, the cyclization represents a feasible strategy to identify new lead compounds by increasing structural novelty, scaffold diversity and complexity. Such strategy could also be potentially used for the follow-on drug discovery without patent infringement. In recent years, the cyclization strategy has witnessed great success in the discovery of new lead compounds against different targets for treating various diseases. Herein, we first briefly summarize the use of the cyclization strategy in the discovery of new small-molecule lead compounds, including the proteolysis targeting chimeras (PROTAC) molecules. Particularly, we focus on four main strategies including fused ring cyclization, chain cyclization, spirocyclization and macrocyclization and highlight the use of the cyclization strategy in lead generation. Finally, the challenges including the synthetic intractability, relatively poor pharmacokinetics (PK) profiles and the absence of the structural information for rational structure-based cyclization are also briefly discussed. We hope this review, not exhaustive, could provide a timely overview on the cyclization strategy for the discovery of new lead compounds.

Physiologic roles of P2 receptors in leukocytes

Since their discovery in the 1970s, purinergic receptors have been shown to play key roles in a wide variety of biologic systems and cell types. In the immune system, purinergic receptors participate in innate immunity and in the modulation of the adaptive immune response. In particular, P2 receptors, which respond to extracellular nucleotides, are widely expressed on leukocytes, causing the release of cytokines and chemokines and the formation of inflammatory mediators, and inducing phagocytosis, degranulation, and cell death. The activity of these receptors is regulated by ectonucleotidases-expressed in these same cell types-which regulate the availability of nucleotides in the extracellular environment. In this article, we review the characteristics of the main purinergic receptor subtypes present in the immune system, focusing on the P2 family. In addition, we describe the physiologic roles of the P2 receptors already identified in leukocytes and how they can positively or negatively modulate the development of infectious diseases, inflammation, and pain.

Single-cell RNA sequencing reveals distinct transcriptional features of the purinergic signaling in mouse trigeminal ganglion

Trigeminal ganglion (TG) is the first station of sensory pathways in the orofacial region. The TG neurons communicate with satellite glial cells (SGCs), macrophages and other cells forming a functional unit that is responsible for processing of orofacial sensory information. Purinergic signaling, one of the most widespread autocrine and paracrine pathways, plays a crucial role in intercellular communication. The multidirectional action of purinergic signaling in different cell types contributes to the neuromodulation and orofacial sensation. To fully understand the purinergic signaling in these processes, it is essential to determine the shared and unique expression patterns of genes associated with purinergic signaling in different cell types. Here, we performed single-cell RNA sequencing of 22,969 cells isolated from normal mouse TGs. We identified 18 distinct cell populations, including 6 neuron subpopulations, 3 glial subpopulations, 7 immune cell subpopulations, fibroblasts, and endothelial cells. We also revealed the transcriptional features of genes associated with purinergic signaling, including purinergic receptors, extracellular adenosine triphosphate (eATP) release channels, eATP metabolism-associated enzymes, and eATP transporters in each cell type. Our results have important implications for understanding and predicting the cell type-specific roles of the purinergic signaling in orofacial signal processing in the trigeminal primary sensory system.