Uridine adenosine tetraphosphate acts as a pro-angiogenic factor in vitrothrough purinergic P2Y receptors

OBJECTIVE Uridine adenosine tetraphosphate(Up4A),a dinucleotide,contains both purine and pyrimidine moieties,and exerts its vascular influence via activation of purinergic receptors.Here,we aimed to investigate the effects of Up4 A on angiogenesis and the putative purinergic receptors(PR)involved in this process.METHODS Tubule formation assay was performed in 3D matrix system.In this assay,human umbilical vein endothelial cells(HUVECs)were co-cultured with pericytes with various Up4 A doses(0,1,2.5,5,10 and 20μmol·L-1)in the absence and presence of P2Y6 R antagonist MRS2578(10μmol·L-1)for 5d.Expression profile of PR subtypes and angiogenic factors was assessed in HUVECs by q-PCR with and without P2Y6 R antagonist.RESULTS No difference in initial tubule formation was detected between Up4 A stimulation and control conditions at day 2.In contrast,a significant increase in vascular density in response to Up4 A was observed at day 5.Up4 A at a dose of 2.5and 5μmol·L-1 promoted total tubule length(by-1.89 fold and-2.23fold),number of tubules(by-1.71 fold and-1.89fold)as well as number of junctions(by-2.24 fold and-2.80fold),all of which were inhibited by MRS2578.Further increase in Up4 A dose to10 and 20μmol·L-1 did not induce an increase in these vascular parameters as compared to non-treated controls.Moreover,Up4 A increased mRNA level of P2YRs(P2Y2R,P2Y4 R and P2Y6R)but not P2XR(P2X4R and P2X7R)or P1R(A2AR and A2BR),while Up4 A upregulated VEGFA and ANGPT1 but not VEGFR2,ANGPT2,Tie1 and Tie2at mRNA level.Transcriptional upregulation of P2 YRs and angiogenic factors by Up4 A was inhibited by MRS2578.CONCLUSION Up4 A is functionally capable of promoting tubule formation in vitro co-culture system.This process is likely mediated by activation of pyrimidine-favored P2 YRs but not P2 XR or P1 Rs,and involves stimulation of well known angiogenic factors.

Genomic Organization of Purinergic P2X Receptors

Purinergic P2X receptors are a family of ligand-gated cationic channels activated by extracellular ATP. P2X subunit protein sequences are highly conserved between vertebrate species. However, they can generate a great diversity of coding splicing variants to fulfill several roles in mammalian physiology. Despite intensive research in P2X expression in both central and peripheral nervous system, there is little information about their homology, genomic structure and other key features that can help to develop selective drugs or regulatory strategies of pharmacological value which are lacking today. In order to obtain clues on mammalian P2X diversity, we have performed a bioinformatics analysis of the coding regions and introns of the seven P2X subunits present in human, simian, dog, mouse, rat and zebrafish. Here we report the arrangements of exon and intron sequences, considering its number, size, phase and placement;proposing some ideas about the gain and loss of exons and retention of introns. Taken together, these evidences show traits that can be used to gain insight into the evolutionary history of vertebrate P2X receptors and better understand the diversity of subunits coding the purinergic signaling in mammals.

Role of P2X_7 receptors in neuronal death in the retina

Acknowledgments： I would like to express my appreciation to Professor Puro DG for leading me to this research topic during my stay as a research fellow in his laboratory at the University of Michigan in 2001, and also to Professor Ikeda T forgiving me the opportunity to study abroad and then to continue to investigate this topic in the Department of Ophthalmology at Osaka Medical College, lapan.

P2X receptors in maintenance and differentiation of neural progenitor cells

Purinergic receptors are among the first cell surface receptors expressed during embryonic development （Burnstock and Ulrich, 2011）. These are characterized based on their pharmacological properties of being activated by adenosine or purine/pyrimidine nucleotides as P1 and P2 receptors. P2 receptors are further classified by their structure as P2Y metabotropic and P2X ionotropic receptors.

Regulation of neural stem/progenitor cell functions by P2X and P2Y receptors

Neural stem/progenitor cells：Radial glial cells constitute multipotent cells in the ventricular zone,lining the wall of the lateral ventricle of the embryonic brain.They have the capacity to give rise to cells belonging to all three major linages（neurons,astrocytes and oligodendrocytes）of the nervous system（Tang and Illes,2017）.

Overexpression of Purinergic P2X4 Receptors in Hippocampus Rescues Memory Impairment in Rats with Type 2 Diabetes

Purinergic receptors have been reported to be involved in brain disorders.In this study,we explored their roles and mechanisms underlying the memory impairment in rats with type 2 diabetes mellitus(T2 DM).T2 DM rats exhibited a worse performance in the T-maze and Morris water maze(MWM) than controls.Microglia positive for P2 X purinoceptor 4(P2 X4 R) in the hippocampus were reduced and activated microglia were increased in T2 DM rats.Long Amplicon PCR(LA-PCR) showed that DNA amplification of the p2 x4 r gene in the hippocampus was lower in T2 DM rats.Minocycline significantly reduced the number of activated microglia and the mean distance traveled by T2 DM rats in the MWM.Most importantly,P2 X4 R overexpression suppressed the activated microglia and rescued the memory impairment of T2 DM rats.Overall,T2 DM led to excessive activation of microglia in the hippocampus,partly through the DNA damagemediated downregulation of P2 X4 Rs,thus contributing to memory impairment.

Role of P2X_7 receptors in the development of diabetic retinopathy

The P2X7 receptor is one of the members of the family of purinoceptors which are ligand-gated membrane ion channels activated by extracellular adenosine 5'-triphosphate. A unique feature of the P2X7 receptor is that its activation can result in the formation of large plasma membrane pores that allow not only the flux of ions but also of hydrophilic molecules of up to 900 Da. Recent studies indicate that P2X7-mediated signaling can trigger apoptotic cell death after ischemia and during the course of certain neurodegenerative disorders. Expression of the P2X7 receptor has been demonstrated in most types of cells in the retina. This purinoceptor mediates the contraction of pericytes and regulates the spatial and temporal dynamics of the vasomotor response through cell-to-cell electrotonic transmission within the microvascular networks. Of potential clinical significance, investigators have found that diabetes markedly boosts the vulnerability of retinal microvessels to the lethal effect of P2X7 receptor activation. This purinergic vasotoxicity may result in reduced retinal blood flow and disrupted vascular function in the diabetic retina. With recent reports indicating an association between P2X7 receptor activation and inflammatory cytokine expression in the retina, this receptor may also exacerbate the development of diabetic retinopathy by a mechanism involving inflammation.

Electroacupuncture improves neuropathic pain Adenosine, adenosine 5'-triphosphate disodium and their receptors perhaps change simultaneously

Applying a stimulating current to acupoints through acupuncture needles–known as electroacupuncture–has the potential to produce analgesic effects in human subjects and experimental animals. When acupuncture was applied in a rat model, adenosine 5-triphosphate disodium in the extracellular space was broken down into adenosine, which in turn inhibited pain transmission by means of an adenosine A1 receptor-dependent process. Direct injection of an adenosine A1 receptor agonist enhanced the analgesic effect of acupuncture. The analgesic effect of acupuncture appears to be mediated by activation of A1 receptors located on ascending nerves. In neuropathic pain, there is upregulation of P2X purinoceptor 3 （P2X3） receptor expression in dorsal root ganglion neurons. Conversely, the onset of mechanical hyperalgesia was diminished and established hyperalgesia was significantly reversed when P2X3 receptor expression was downregulated. The pathways upon which electroacupuncture appear to act are interwoven with pain pathways, and electroacupuncture stimuli converge with impulses originating from painful areas. Electroacupuncture may act via purinergic A1 and P2X3 receptors simultaneously to induce an analgesic effect on neuropathic pain.

Expression of BMP Receptors in Porcine Granulosa Cells (GCs) and Their Regulation by Luteinizing Hormone (LH)

Bone morphogenetic proteins（BMPs） play critical roles in follicle growth and development.BMPs initiate signaling by assembling BMP receptors and activating Smads,which in turn alter expression of target genes.The mechanism underlying the regulation of the expression of BMP receptors and Smads during follicle development in pigs is still unknown.By quantitative real-time PCR,the mRNA expression of BMP receptors and Smads in granulosa cells（GC） was investigated.Cells were obtained from small porcine follicles（SF;3 mm diameter） and dominant follicles（DF;6 mm diameter）;ActR1A and BMPR2 mRNA levels in DF were significantly higher（P0.05） than that in SF,whereas BMPR1B,Smad4 and Smad7 expression tended to decrease（P0.05）.The levels of BMPR1A,ActR2,Smad1,Smad5,and Smad8 mRNA did not differ between DFs and SFs.To investigate the effect of LH on BMP receptors in GC,cells obtained from porcine DFs were cultured in medium supplemented with different doses of luteinizing hormone（LH）.High doses of LH（4 IU mL-1） significantly decreased the concentration of estradiol（E2） and progesterone（P4） in medium and the expression of Cyp19a1（P450 aromatase,P450arom） and Cyp11a1（cholesterol side-chain cleavage enzyme P450,P450scc）,while significantly increased viable cell numbers and up-regulated expression of cyclin dependent kinase-4（CDK4） and cyclin D2.However,LH had no effect on the expression of BMP receptor genes.Thus,the present study indicates that the expression of members of the BMP signaling pathway in porcine GC is regulated during follicle development and the expression of BMP receptors are not regulated by LH in porcine GCs.

Axonal growth inhibitors and their receptors in spinal cord injury:from biology to clinical translation

Axonal growth inhibitors are released during traumatic injuries to the adult mammalian central nervous system, including after spinal cord injury. These molecules accumulate at the injury site and form a highly inhibitory environment for axonal regeneration. Among these inhibitory molecules, myelinassociated inhibitors, including neurite outgrowth inhibitor A, oligodendrocyte myelin glycoprotein, myelin-associated glycoprotein, chondroitin sulfate proteoglycans and repulsive guidance molecule A are of particular importance. Due to their inhibitory nature, they represent exciting molecular targets to study axonal inhibition and regeneration after central injuries. These molecules are mainly produced by neurons, oligodendrocytes, and astrocytes within the scar and in its immediate vicinity. They exert their effects by binding to specific receptors, localized in the membranes of neurons. Receptors for these inhibitory cues include Nogo receptor 1, leucine-rich repeat, and Ig domain containing 1 and p75 neurotrophin receptor/tumor necrosis factor receptor superfamily member 19(that form a receptor complex that binds all myelin-associated inhibitors), and also paired immunoglobulin-like receptor B. Chondroitin sulfate proteoglycans and repulsive guidance molecule A bind to Nogo receptor 1, Nogo receptor 3, receptor protein tyrosine phosphatase σ and leucocyte common antigen related phosphatase, and neogenin, respectively. Once activated, these receptors initiate downstream signaling pathways, the most common amongst them being the Rho A/ROCK signaling pathway. These signaling cascades result in actin depolymerization, neurite outgrowth inhibition, and failure to regenerate after spinal cord injury. Currently, there are no approved pharmacological treatments to overcome spinal cord injuries other than physical rehabilitation and management of the array of symptoms brought on by spinal cord injuries. However, several novel therapies aiming to modulate these inhibitory proteins and/or their receptors are under investigation in ongoing clinical trials. Investigation has also been demonstrating that combinatorial therapies of growth inhibitors with other therapies, such as growth factors or stem-cell therapies, produce stronger results and their potential application in the clinics opens new venues in spinal cord injury treatment.

P2Y1 receptor in Alzheimer’s disease

Alzheimer’s disease is the most frequent form of dementia characterized by the deposition of amyloid-beta plaques and neurofibrillary tangles consisting of hyperphosphorylated tau.Targeting amyloid-beta plaques has been a primary direction for developing Alzheimer’s disease treatments in the last decades.However,existing drugs targeting amyloid-beta plaques have not fully yielded the expected results in the clinic,necessitating the exploration of alternative therapeutic strategies.Increasing evidence unravels that astrocyte morphology and function alter in the brain of Alzheimer’s disease patients,with dysregulated astrocytic purinergic receptors,particularly the P2Y1 receptor,all of which constitute the pathophysiology of Alzheimer’s disease.These receptors are not only crucial for maintaining normal astrocyte function but are also highly implicated in neuroinflammation in Alzheimer’s disease.This review delves into recent insights into the association between P2Y1 receptor and Alzheimer’s disease to underscore the potential neuroprotective role of P2Y1 receptor in Alzheimer’s disease by mitigating neuroinflammation,thus offering promising avenues for developing drugs for Alzheimer’s disease and potentially contributing to the development of more effective treatments.

Electroacupuncture diminishes P2X_2 and P2X_3 purinergic receptor expression in dorsal root ganglia of rats with visceral hypersensitivity

Electroacupuncture at Shangjuxu （ST37） and Tianshu （ST25） can improve visceral hypersensitivity in rats. Colorectal distension was used to establish a rat model of chronic visceral hypersensitivity. Immunohistochemistry was used to detect P2X2 and P2X3 receptor expression in dorsal root ganglia from rats with chronic visceral hypersensitivity. Results demonstrated that abdominal withdrawal reflex scores obviously increased following establishment of the model, indicating visceral hypersensitivity. Simultaneously, P2X2 and P2X3 receptor expression increased in dorsal root ganglia. After bilateral electroacupuncture at Shangjuxu and Tianshu, abdominal withdrawal reflex scores and P2X2 and P2X3 receptor expression decreased in rats with visceral hypersensitivity. These results indicated that electroacupuncture treatment improved visceral hypersensitivity in rats with irritable bowel syndrome by reducing P2X2 and P2X3 receptor expression in dorsal root ganglia.

Therapeutic potential of extracellular ATP and P2 receptors in nervous system diseases

Extracellular adenosine 5’-triphosphate(ATP) is a key signaling molecule present in the central nervous system(CNS),and now is receiving greater attention due to its role as a messenger in the CNS during different physiological and pathological events. ATP is released into the extracellular space through vesicular exocytosis or from damaged and dying cells. Once in the extracellular environment,ATP binds to the specific receptors termed P2,which mediate ATP effects and are present broadly in both neurons an...

Molecular mechanism underlying the subtype-selectivity of competitive inhibitor NF110 and its distinct potencies in human and rat P2X3 receptors

P2X receptors are a family of extracellular ATP-gated trimeric cation channels that is widely distributed in human tissues. Quite some drug candidates targeting P2X receptors have entered into preclinical or main phases of clinical trials, but many of them failed due to low subtype-selectivity or species differences in pharmacological activities between human and experimental animals. Here, we identified the distinct inhibitory efficacies of NF110, a competitive inhibitor, between the rat(rP2X3) and human(hP2X3) P2X3 receptors. We demonstrated that this difference is determined by two amino acids located in the dorsal fin(DF) domain of P2X3 receptors. As revealed by mutagenesis, metadynamics, and covalent modification, NF110-mediated rP2X3 inhibition may be through a filling in the cavity formed by the DF,left flipper(LF) and lower body(LB) to partially, rather than fully, occupy the ATP-binding pocket.Moreover, substitution of residues located in the DF and/or LF domains of the rP2X2 receptor, a NF110-insensitive subtype, with the equivalent amino acids of rP2X3, bestowed the sensitivity of rP2X2 to NF110. The critical roles of the DF and LF domains in channel gating of P2X and low conservativity in residue sequences of those two domains raise the possibility that small molecules differentially interacting with the residues of the DF and LF domains of different P2X receptors may modulate channel's activity in a subtype-selective manner. However, the possible species-specificity of P2X inhibitors/modulators makes it more complex when interpreting the preclinical data into clinical researches.Nevertheless, our data provide new insights into the subtype-selectivity of competitive inhibitors and their distinct potencies in the human and experimental animals, both of which are extremely important in the drug discovery of P2X receptors.

Regulatory effect of mild moxibustion on P2X3 receptors in spinal cord,anterior cingulate cortex and thalamic ventral posterolateral nucleus of rats with IBS visceral hyperalgesia

Objective To observe the therapeutic effect of mild moxibustion on irritable bowel syndrome(IBS)visceral hyperalgesia model rats and its regulatory effect on P2X3 receptors in the spinal cord,anterior cingutate cortex(ACC)and thalamic ventral posterolateral nucleus(VPL).Methods Thirty 8-day-old newborn rats were randomly divided into a normal group(n=6)and a modeling group(n=24)according to the completely random number table method.Rats in the normal group were bred routinely,and those in the modeling group were subjected to preparing IBS chronic visceral hyperalgesia model using colorectal distention(CRD)in stimulation method.Rats successfully modelled were re-divided into a model group,a mild moxibustion group,a P2X3 receptor antagonist group,and a normal saline group according to the completely random number table method with 6 rats in each group.Rats in each group received corresponding interventions from the 37-day old,once a day for 7 consecutive days.Immunohistochemistry and Western blot assays were used to detect P2X3 protein expressions in the spinal cord,ACC and VPL of rats.Results Under different intensities of CRD stimulation,the abdominal withdrawal reflex(AWR)scores of the model group were significantly increased versus the normal group(all P<0.05);the AWR scores of the mild moxibustion group and the P2X3 receptor antagonist group were significantly reduced versus the model group(all P<0.01).The P2X3 protein expressions in rat spinal cord,ACC and VPL tissues of the model group were significantly increased versus the normal group(all P<0.01);the P2X3 protein expressions in rat spinal cord,ACC and VPL tissues of the mild moxibustion group and the P2X3 receptor antagonist group were significantly reduced versus the model group(all P<0.01).Conclusion Mild moxibustion can inhibit the P2X3 receptor expressions in the spinal cord,ACC,and VPL tissues of IBS visceral hyperalgesia model rats,which may be the mechanism of mild moxibustion in relieving the central sensitization of rats with IBS visceral hyperalgesia.

Triggering of Major Brain Disorders by Protons and ATP:The Role of ASICs and P2X Receptors

Adenosine triphosphate(ATP)is well-known as a universal source of energy in living cells.Less known is that this molecule has a variety of important signaling func-tions:it activates a variety of specific metabotropic(P2Y)and ionotropic(P2X)receptors in neuronal and non-neu-ronal cell membranes.So,a wide variety of signaling func-tions well fits the ubiquitous presence of ATP in the tissues.Even more ubiquitous are protons.Apart from the unspe-cific interaction of protons with any protein,many physi-ological processes are affected by protons acting on specific ionotropic receptors--acid-sensing ion channels(ASICs).Both protons(acidification)and ATP are locally elevated in various pathological states.Using these fundamentally important molecules as agonists,ASICs and P2X receptors signal a variety of major brain pathologies.Here we briefly outline the physiological roles of ASICs and P2X receptors,focusing on the brain pathologies involving these receptors.

Sleep Deprivation Selectively Down-Regulates Astrocytic 5-HT2B Receptors and Triggers Depressive-Like Behaviors via Stimulating P2X7 Receptors in Mice

Chronic loss of sleep damages health and disturbs the quality of life.Long-lasting sleep deprivation(SD)as well as sleep abnormalities are substantial risk factors for major depressive disorder,although the underlying mechanisms are not clear.Here,we showed that chronic SD in mice promotes a gradual elevation of extracellular ATP,which activates astroglial P2X7 receptors(P2X7Rs).Activated P2X7Rs,in turn,selectively down-regulated the expression of 5-HT2B receptors(5-HT2BRs)in astrocytes.Stimulation of P2X7Rs induced by SD selectively suppressed the phosphorylation of AKT and FoxO3 a in astrocytes,but not in neurons.The overexpression of FoxO3a in astrocytes inhibited the expression of 5-HT2BRs.Down-regulation of 5-HT2BsRs instigated by SD suppressed the activation of STAT3 and relieved the inhibition of Ca2+-dependent phospholipase A2.This latter cascade promoted the release of arachidonic acid and prostaglandin E2.The depression-like behaviors induced by SD were alleviated in P2X7R-KO mice.Our study reveals the mechanism underlying chronic SD-induced depression-like behaviors and suggests 5-HT2BRs as a key target for exploring therapeutic strategies aimed at the depression evoked by sleep disorders.

Pulsed radiofrequency inhibits expression of P2X3 receptors and alleviates neuropathic pain induced by chronic constriction injury in rats

Background:Pulsed radiofrequency (PRF) is a minimally invasive interventional technique that provides a novel and effective treatment strategy for neuropathic pain (NP).PRF is advantageous because it does not damage nerves and avoids sensory loss after treatment.At present,animal studies have demonstrated that PRF is safe and effective for relieving the NP associated with sciatic nerve damage in rats with chronic constriction injury (CCI).However,the mechanism through which this effect occurs is unknown.An increasing body of evidence shows that the expression of the P2X ligand-gated ion channel 3 (P2X3) receptor is closely related to NP;this study was to investigate whether the expression of this receptor is involved in NP relief due to PRF.Methods:A total of 36 healthy adult male Sprague-Dawley (SD) rats were randomly divided into three groups:Sham group,CCI group,and PRF group.The right sciatic nerve was ligated in CCI group and PRF group to establish a CCI model;the right sciatic nerve was separated but not ligated in Sham group.On day 14 after the operation,PRF was administered to the ligated sciatic nerve in PRF group (42℃,45 V,2 min).A non-live electrode was placed at the exposed sciatic nerve for the rats in Sham and CCI groups.The hindpaw withdrawal threshold (HWT) and thermal withdrawal latency (TWL) were measured at the right hindpaw at different time points before and after PRF or sham therapy.On day 28 after treatment,the dorsal root ganglion (DRG) and spinal dorsal horn of the right L4-6 were harvested from each group to determine the mRNA and protein levels of the P2X3 receptor.Results:On day 28 after PRF treatment,the HWT (8.33 ± 0.67 g vs.3.62 ± 0.48 g) and TWL (25.42 ± 1.90 s vs.15.10 ± 1.71 s) were significantly higher in PRF group as compared to CCI group (P < 0.05).The mRNA expression of the P2X3 receptor in the DRG in PRF group was 23.7% lower than that in CCI group (P < 0.05),in the spinal dorsal horns in PRF group was 22.7% lower than that in CCI group (P < 0.05).The protein expression of the P2X3 receptor in the DRG in PRF group was 27.8 % lower than that in CCI group (P < 0.05),in the spinal dorsal horns in PRF group was 35.6% lower than that in CCI group (P < 0.05).Conclusion:PRF possibly reduces NP in CCI rats by inhibiting the expression of the P2X3 receptor in the L4-6 DRG and spinal dorsal horns.

P2X_7 receptors in cerebral ischemia

Cerebral ischemia is one of the most common diseases resulting in death and disability in aged people. It leads immediately to rapid energy failure, ATP depletion, and ionic imbalance, which increase extracellular ATP levels and accordingly activate P2X7 receptors. These receptors are ATP-gated cation channels and widely distributed in nerve cells, especially in the immunocompetent cells of the brain. Currently, interest in the roles of P2Xz receptors in ischemic brain injury is growing. In this review, we discuss recent research progress on the actions of P2X7 receptors, their possible mechanisms in cerebral ischemia, and the potential therapeutic value of P2X7 receptor antagonists which may provide a new target both for clinical and for research purposes.

Up-regulation of P2X7 Receptors Contributes to Spinal Microglial Activation and the Development of Pain Induced by BmK-I

Previous work has demonstrated that the sensitization of spinal neurons and microglia is important in the development of pain behaviors induced by BmK I,a Na^+ channel activator and a major peptide component of the venom of the scorpion Buthus martensi Karsch(BmK).We found that the expression of P2X7 receptors(P2X7Rs)was up-regulated in the ipsilateral spinal dorsal horn after BmK I injection in rats.P2X7R was selectively localized in microglia but not astrocytes or neurons.Similarly,interleukin 1β(IL-1β)was selectively up-regulated in microglia in the spinal dorsal horn after BmK I injection.Intrathecal injection of P2X7R antagonists largely reduced BmK I-induced spontaneous and evoked pain behaviors,and the up-regulation of P2X7R and IL-1β in the spinal cord.These data suggested that the up-regulation of P2X7Rs mediates microglial activation in the spinal dorsal horn,and therefore contributes to the development of BmK I-induced pain.