Regulation of death and survival in astrocytes by ADP activating P2Y1 and P2Y12 receptors

Activation of hypermethylated P2RY1 mitigates gastric cancer by promoting apoptosis and inhibiting proliferation

The P2RY1 receptor is known to cause cancer by activating the ERK signal pathway, and its DNA methylation status and corresponding regulatory mechanism remain unknown. This study used the DNA methylation chip to profile the genome-wide DNA methylation level in gastric cancer tissues. The proliferation and apoptosis of the SGC7901 gastric cancer cell line were determined after treatment with a selective P2RY1 receptor agonist, MRS2365. The promoter region of P2RY1 was found to be highly methylated with four hypermethylated sites (|Δβ value| > 0.2) in diffuse gastric cancer and was validated by bioinformatics analysis in the TCGA database. Also, immunohistochemical staining data obtained from the HPA database demonstrated the downregulated expression of proteins encoded by P2RY1 in stomach cancer tissue. The analysis of MRS2365-treated cells by annexin V/propidium iodide staining and caspase-3 activity assays indicated the induction of apoptosis in SGC7901 cells. The P2RY1 receptor activation in human SGC7901 gastric cancer cells via the MRS2365 agonist induced apoptosis and reduced cell growth. High DNA methylation in the promoter region of P2RY1 might have contributed to the reduced expression of P2RY1's mRNA, which was likely responsible for the "aggressive" nature of the diffuse gastric cancer.

Transcriptome Analysis of Induced Pluripotent Stem Cells and Neuronal Progenitor Cells, Derived from Discordant Monozygotic Twins with Parkinson's Disease

Parkinson's Disease (PD) is a widespread severe neurodegenerative disease that is characterized by pronounced deficiency of the dopaminergic system and disruption of the function of other neuromodulator systems. Although heritable genetic factors contribute significantly to PD pathogenesis, only a small percentage of sporadic cases of PD can be explained using known genetic risk factors. Due to that, it could be inferred that changes in gene expression could be important for explaining a significant percentage of PD cases. One of the ways to investigate such changes, while minimizing the effect of genetic factors on experiment, are the study of PD discordant monozygotic twins. In the course of the analysis of transcriptome data obtained from IPSC and NPCs, 20 and 1906 differentially expressed genes were identified respectively. We have observed an overexpression of TNF in NPC cultures, derived from twin with PD. Through investigation of gene interactions and gene involvement in biological processes, we have arrived to a hypothesis that TNF could play a crucial role in PD-related changes occurring in NPC derived from twins with PD, and identified INHBA, WNT7A and DKK1 as possible downstream effectors of TNF.

Functional characterization of HIC, a P2Y1 agonist, as a p53 stabilizer for prostate cancer cell death induction

Background: (1-(2-hydroxy-5-nitrophenyl)(4-hydroxyphenyl)methyl)indoline-4-carbonitrile (HIC), an agonist of the P2Y1 receptor (P2Y1R), induces cell death in prostate cancer cells. However, the molecular mechanism behind the inhibition of HIC in prostate cancer remains elusive. Methods & results: Here, to outline the inhibitory role of HIC on prostate cancer cells, PC-3 and DU145 cell lines were treated with the respective IC₅₀ concentrations, which reduced cell proliferation, adherence properties and spheroid formation. HIC was able to arrest the cell cycle at G1/S phase and also induced apoptosis and DNA damage, validated by gene expression profiling. HIC inhibited the prostate cancer cells' migration and invasion, revealing its antimetastatic ability. P2Y1R-targeted HIC affects p53, MAPK and NF-κB protein expression, thereby improving the p53 stabilization essential for G1/S arrest and cell death. Conclusion: These findings provide an insight on the potential use of HIC, which remains the mainstay treatment for prostate cancer.

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

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

Activation of ATF3/AP-1 signaling pathway is required for P2X3-induced endometriosis pain

STUDY QUESTION

Does P2X ligand-gated ion channel 3 (P2X3) play a role in endometriosis pain?

SUMMARY ANSWER

Upregulation of P2X3 in dorsal root ganglia (DRG) tissues via the activating transcription factor 3 (ATF3)/activator protein (AP)-1 pathway contributed to endometriosis-associated hyperalgesia, which could be attenuated by the chitosan oligosaccharide stearic acid (CSOSA)/liposomes (LPs)/SP600125 delivery system.

WHAT IS KNOWN ALREADY

Infiltrating nerve fibers and elevated nociceptors in endometriotic lesions are associated with endometriosis pain. P2X3 has been demonstrated to play an important role in neuropathic pain.

STUDY DESIGN, SIZE, DURATION

A rat model of endometriosis was used to investigate the signaling pathways involved in P2X3-induced pain.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Degrees of hyperalgesia, endogenous adenosine 5'-triphosphate (ATP) contents and P2X3 expression levels in endometriotic lesions and DRG tissues were detected in a rat model of endometriosis. The expression levels of ATF3 and P2X3 were measured using qRT-PCR, western blot analysis and immunofluorescence analysis after adenosine 5'-diphosphate (ADP) exposure in DRG cells. Plasmids encoding ATF3 and its siRNA were used to investigate the role of ATF3 on ADP-induced P2X3 upregulation. The activity of ATF binding to the P2X3 promoter was evaluated by using chromatin immunoprecipitation (CHIP) and luciferase assays. SP600125, an inhibitor of c-JUN N-terminal kinase, was wrapped in CSOSA/LPs delivery system and its inhibitory effects on ADP-induced upregulation of P2X3 in DRG cells and endometriosis-induced hyperalgesia in rats were tested.

MAIN RESULTS AND THE ROLE OF CHANCE

The concentrations of endogenous ATP and expression levels of P2X3 were significantly increased in both endometriotic lesions and DRG tissues in endometriosis rat models and were found to be positively correlated with the severity of hyperalgesia. In DRG cells, P2X3 expression levels were elevated by ADP stimulation, but dramatically inhibited by blocking ATF3 with its siRNA and SP600125. CHIP and luciferase assay showed that ADP increased the binding of ATF3 to the P2X3 promoter, resulting in an increase in P2X3 expression levels. In the CSOSA/LPs/SP600125 delivery system, the drug could be effectively concentrated in endometriotic lesions, and it could alleviate endometriosis-induced hyperalgesia, reduce the size of endometriotic lesions and attenuate upregulated P2X3 expression levels in endometriosis rat models.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Changes in the sensitivity and function of P2X3 caused by endometriosis need to be further investigated.

WIDER IMPLICATIONS OF THE FINDINGS

This study indicates that ATP and the P2X3 receptor are involved in endometriosis pain, thus providing a novel therapeutic approach for the treatment of endometriosis pain by targeting the P2X3 receptor.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by National Key R&D Program of China (Grant No. 2017YFC1001202) and National Natural Science Foundation of China (Grant Nos. 81974225, 81671429 and 81471433). There are no competing interests.

Osthole alleviates neuropathic pain in mice by inhibiting the P2Y1-receptor-dependent JNK signaling pathway

There are many reports about natural products relieving neuralgia. Osthole is the main component of Angelica biserrata Yuan et Shan, a natural product that treats rheumatism through the elimination of inflammation and the alleviation of pain that has a long history in the clinic. The analgesic mechanism of osthole is complicated and confusing. Astrocytes have attracted increasing attention from pain researchers. Inhibitors targeting astrocytes are thought to be promising treatments for neuropathic pain. Whether osthole can alleviate neuropathic pain through astrocytes has not been elucidated in detail. In this study, CCI surgery was used to establish the neuropathic pain model in mice. The CCI mice were treated with osthole (5, 10, or 20 mg/kg/day) for 14 days in vivo. Mechanical allodynia and heat hyperalgesia were measured to evaluate the therapeutic effect of osthole. In mechanism research, the activation of astrocytes; the protein expression of P2Y₁R and p-JNK in astrocytes; the release of inflammatory factors; the variations in mEPSPs and eEPSPs; and the levels of GluA1, GluN2B, p-ERK, p-CREB and c-Fos in neurons were observed. The P2Y₁R inhibitor MRS2179 and the p-JNK inhibitor SP600125 were used to demonstrate how osthole works in neuropathic pain. In addition, astrocytes and neurons were used to estimate the direct effect of osthole on astrocyte-neuron interactions and signal transmission in vitro. Our findings suggest that osthole treatment obviously relieved mechanical allodynia and heat hyperalgesia in CCI mice. P2Y₁R is involved in CCI-induced pain hypersensitivity, and P2Y₁R is required for osthole-induced p-JNK downregulation in the spinal cord. Osthole inhibited astrocyte activation and reduced inflammatory factor expression. After osthole treatment, mEPSP frequency and eEPSP amplitude were decreased in spinal lamina I-II neurons. Downstream signaling molecules such as pGluA1, pGluN2B, p-ERK, p-CREB and c-Fos were also reduced very quickly in osthole-treated neuralgic mice. Our conclusion is that osthole alleviates neuropathic pain in mice via the P2Y₁-receptor-dependent JNK signaling pathway in spinal astrocytes, and osthole could be considered a potential pharmacotherapy to alleviate neuropathic pain.

Synthesis and preclinical validation of novel P2Y1 receptor ligands as a potent anti-prostate cancer agent

Purinergic receptor is a potential drug target for neuropathic pain, Alzheimer disease, and prostate cancer. Focusing on the structure-based ligand discovery, docking analysis on the crystal structure of P2Y₁ receptor (P2Y₁R) with 923 derivatives of 1-indolinoalkyl 2-phenolic compound is performed to understand the molecular insights of the receptor. The structural model identified the top novel ligands, 426 (compound 1) and 636 (compound 2) having highest binding affinity with the docking score of -7.38 and -6.92. We have reported the interaction efficacy and the dynamics of P2Y₁R protein with the ligands. The best hits synthesized were experimentally optimized as a potent P2Y₁ agonists. These ligands exhibits anti-proliferative effect against the PC-3 and DU-145 cells (IC₅₀ = 15 µM - 33 µM) with significant increase in the calcium level in dose- and time-dependent manner. Moreover, the activation of P2Y₁R induced the apoptosis via Capase3/7 and ROS signaling pathway. Thus it is evidenced that the newly synthesized ligands, as a P2Y₁R agonists could potentially act as a therapeutic drug for treating prostate cancer.

Role of P2 receptors in normal brain development and in neurodevelopmental psychiatric disorders

The purinergic signaling system, including P2 receptors, plays an important role in various central nervous system (CNS) disorders. Over the last few decades, a substantial amount of accumulated data suggest that most P2 receptor subtypes (P2X1, 2, 3, 4, 6, and 7, and P2Y₁, ₂, ₆, ₁₂, and ₁₃) regulate neuronal/neuroglial developmental processes, such as proliferation, differentiation, migration of neuronal precursors, and neurite outgrowth. However, only a few of these subtypes (P2X2, P2X3, P2X4, P2X7, P2Y₁, and P2Y₂) have been investigated in the context of neurodevelopmental psychiatric disorders. The activation of these potential target receptors and their underlying mechanisms mainly influence the process of neuroinflammation. In particular, P2 receptor-mediated inflammatory cytokine release has been indicated to contribute to the complex mechanisms of a variety of CNS disorders. The released inflammatory cytokines could be utilized as biomarkers for neurodevelopmental and psychiatric disorders to improve the early diagnosis intervention, and prognosis. The population changes in gut microbiota after birth are closely linked to neurodevelopmental/neuropsychiatric disorders in later life; thus, the dynamic expression and function of P2 receptors on gut epithelial cells during disease processes indicate a novel avenue for the evaluation of disease progression and for the discovery of related therapeutic compounds.

Microglia P2Y13 Receptors Prevent Astrocyte Proliferation Mediated by P2Y1 Receptors

Cerebral inflammation is a common feature of several neurodegenerative diseases that requires a fine interplay between astrocytes and microglia to acquire appropriate phenotypes for an efficient response to neuronal damage. During brain inflammation, ATP is massively released into the extracellular medium and converted into ADP. Both nucleotides acting on P2 receptors, modulate astrogliosis through mechanisms involving microglia-astrocytes communication. In previous studies, primary cultures of astrocytes and co-cultures of astrocytes and microglia were used to investigate the influence of microglia on astroglial proliferation induced by ADPβS, a stable ADP analog. In astrocyte cultures, ADPβS increased cell proliferation through activation of P2Y₁ and P2Y₁₂ receptors, an effect abolished in co-cultures (of astrocytes with ∼12.5% microglia). The possibility that the loss of the ADPβS-mediated effect could have been caused by a microglia-induced degradation of ADPβS or by a preferential microglial localization of P2Y₁ or P2Y₁₂ receptors was excluded. Since ADPβS also activates P2Y₁₃ receptors, the contribution of microglial P2Y₁₃ receptors to prevent the proliferative effect of ADPβS in co-cultures was investigated. The results obtained indicate that P2Y₁₃ receptors are low expressed in astrocytes and mainly expressed in microglia. Furthermore, in co-cultures, ADPβS induced astroglial proliferation in the presence of the selective P2Y₁₃ antagonist MRS 2211 (3 μM) and of the selective P2Y₁₂ antagonist AR-C66096 (0.1 μM), suggesting that activation of microglial P2Y₁₂ and P2Y₁₃ receptors may induce the release of messengers that inhibit astroglial proliferation mediated by P2Y_1,12 receptors. In this microglia-astrocyte paracrine communication, P2Y₁₂ receptors exert opposite effects in astroglial proliferation as a result of its cellular localization: cooperating in astrocytes with P2Y₁ receptors to directly stimulate proliferation and in microglia with P2Y₁₃ receptors to prevent proliferation. IL-1β also attenuated the proliferative effect of ADPβS in astrocyte cultures. However, in co-cultures, the anti-IL-1β antibody was unable to recover the ADPβS-proliferative effect, an effect that was achieved by the anti-IL-1α and anti-TNF-α antibodies. It is concluded that microglia control the P2Y_1,12 receptor-mediated astroglial proliferation through a P2Y_12,13 receptor-mediated mechanism alternative to the IL-1β suppressive pathway that may involve the contribution of the cytokines IL-1α and TNF-α.

Purinergic Receptors in Neurological Diseases With Motor Symptoms: Targets for Therapy

Since proving adenosine triphosphate (ATP) functions as a neurotransmitter in neuron/glia interactions, the purinergic system has been more intensely studied within the scope of the central nervous system. In neurological disorders with associated motor symptoms, including Parkinson's disease (PD), motor neuron diseases (MND), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Huntington's Disease (HD), restless leg syndrome (RLS), and ataxias, alterations in purinergic receptor expression and activity have been noted, indicating a potential role for this system in disease etiology and progression. In neurodegenerative conditions, neural cell death provokes extensive ATP release and alters calcium signaling through purinergic receptor modulation. Consequently, neuroinflammatory responses, excitotoxicity and apoptosis are directly or indirectly induced. This review analyzes currently available data, which suggests involvement of the purinergic system in neuro-associated motor dysfunctions and underlying mechanisms. Possible targets for pharmacological interventions are also discussed.

P2Y1 Receptors - Properties and Functional Activities

In this chapter we try to show a comprehensive image of current knowledge of structure, activity and physiological role of the P2Y₁ purinergic receptor. The structure, distribution and changes in the expression of this receptor are summarized, as well as the mechanism of its signaling activity by the intracellular calcium mobilization. We try to show the connection between the components of its G protein activation and cellular or physiological effects, starting from changes in protein phosphorylation patterns and ending with such remote effects as receptor-mediated apoptosis. The special emphasis is put on the role of the P2Y₁ receptor in cancer cells and neuronal plasticity. We concentrate on the P2Y₁ receptor, it is though impossible to completely abstract from other aspects of nucleotide signaling and cross-talk with other nucleotide receptors is here discussed. Especially, the balance between P2Y₁ and P2Y₁₂ receptors, sharing the same ligand but signaling through different pathways, is presented.

Adenosine diphosphate involvement in THP-1 maturation triggered by the contact allergen 1-fluoro-2,4-dinitrobenzene

Dendritic cells' (DC) activation is considered a key event in the adverse outcome pathway for skin sensitization elicited by covalent binding of chemicals to proteins. The mechanisms underlying DC activation by contact sensitizers are not completely understood. However, several "danger signals" are pointed as relevant effectors. Among these extra-cellular early danger signals, purines may be crucial for the development of xenoinflammation and several reports indicate their involvement in contact allergic reactions. In the present work we used the DC-surrogate monocytic cell line THP-1, cultured alone or co-cultured with the human keratinocyte cell line HaCaT, to explore the contribution of extracellular adenine nucleotides to THP-1 maturation triggered by the extreme contact sensitizer, 1-fluoro-2,4-dinitrobenzene (DNFB). We found that THP-1 maturation induced by DNFB is impaired after purinergic signaling inhibition, and that the transcription of the purinergic metabotropic receptors P2Y2 and P2Y11 is modulated by the sensitizer. We also detected that THP-1 cells only partially hydrolyse extracellular adenosine triphosphate, leading to accumulation of the mono-phosphate derivative, AMP. We detected different and non-overlapping activation patterns of mitogen activated protein kinases by DNFB and extracellular nucleotides. Overall, our results indicate that THP-1 maturation induced by DNFB is strongly modulated by extracellular adenine nucleotides through metabotropic purinergic receptors. This knowledge unveils a molecular toxicity pathway evoked by sensitizers and involved in THP-1 maturation, a DC-surrogate cell line thoroughly used in in vitro tests for the identification of skin allergens.

Ticagrelor promotes atherosclerotic plaque stability in a mouse model of advanced atherosclerosis

Objective

There is increasing evidence supporting the role of platelets in atherosclerotic vascular disease. The G-protein-coupled receptor P2Y₁₂ is a central mediator of platelet activation and aggregation but has also been linked to platelet-independent vascular disease. Ticagrelor is an oral P2Y₁₂ antagonist that is used as a standard treatment in patients after acute myocardial infarction. However, the effects of ticagrelor on advanced atherosclerosis have not been investigated.

Materials and methods

Twenty-week-old apolipoprotein-E-deficient mice received standard chow or standard chow supplemented with 0.15% ticagrelor (approximately 270 mg/kg/day) for 25 weeks. The lesion area was evaluated in the aortic sinus by Movat’s pentachrome staining and lesion composition, thickness of the fibrous cap, and size of the necrotic core evaluated by morphometry. RAW 264.7 macrophages were serum starved and treated with ticagrelor in vitro for the detection and quantification of apoptosis. In addition, oxLDL uptake in RAW 264.7 macrophages was evaluated.

Results

A trend toward the reduction of total lesion size was detected. However, data did not reach the levels of significance (control, n=11, 565,881 μm² [interquartile range {IQR} 454,778–603,925 μm²] versus ticagrelor, n=13, 462,595 μm² [IQR 379,740–546,037 μm²]; P=0.1). A significant reduction in the relative area of the necrotic core (control, n=11, 0.46 [IQR 0.4–0.51] versus ticagrelor, n=13, 0.34 [IQR 0.31–0.39]; P=0.008), and a significant increase in fibrous caps thickness (control, n=11, 3.7 μm [IQR 3.4–4.2 μm] versus ticagrelor, n=13, 4.7 [IQR 4.3–5.5 μm], P=0.04) were seen in ticagrelor-treated mice. In vitro studies demonstrated a reduction in apoptotic RAW 264.7 macrophages (control 0.07±0.03 versus ticagrelor 0.03±0.03; P=0.0002) when incubated with ticagrelor. Uptake of oxLDL in RAW 264.7 was significantly reduced when treated with ticagrelor (control 9.2 [IQR 5.3–12.9] versus ticagrelor 6.4 [IQR 2.5–9.5], P=0.02).

Conclusion

The present study demonstrates for the first time a plaque-stabilizing effect of ticagrelor in a model of advanced vascular disease, potentially induced by a reduction of oxLDL uptake or an inhibition of apoptosis as seen in vitro.

Extracellular ATP protects pancreatic duct epithelial cells from alcohol-induced damage through P2Y1 receptor-cAMP signal pathway

Extracellular adenosine-5'-triphosphate (ATP) regulates cell death and survival of neighboring cells. The detailed effects are diverse depending on cell types and extracellular ATP concentration. We addressed the effect of ATP on ethanol-induced cytotoxicity in epithelial cells, the cell type that experiences the highest concentrations of alcohol. Using pancreatic duct epithelial cells (PDEC), we found that a micromolar range of ATP reverses all intracellular toxicity mechanisms triggered by exceptionally high doses of ethanol and, thus, improves cell viability dramatically. Out of the many purinergic receptors expressed in PDEC, the P2Y1 receptor was identified to mediate the protective effect, based on pharmacological and siRNA assays. Activation of P2Y1 receptors increased intracellular cyclic adenosine monophosphate (cAMP). The protective effect of ATP was mimicked by forskolin and 8-Br-cAMP but inhibited by a protein kinase A (PKA) inhibitor, H-89. Finally, ATP reverted leakiness of PDEC monolayers induced by ethanol and helped to maintain epithelial integrity. We suggest that purinergic receptors reduce extreme alcohol-induced cell damage via the cAMP signal pathway in PDEC and some other types of cells.

Nucleotides protect rat brain astrocytes against hydrogen peroxide toxicity and induce antioxidant defense via P2Y receptors

Consequences of neurodegenerative diseases or stroke also depend on astroglial survival during oxidative stress. P2Y receptors that are widely distributed in the central nervous system are suggested to be involved in cytoprotection. However, knowledge about the efficacy of protection by P2Y receptors and their involvement in antioxidant protective pathways is scarce. Here, we investigate the viability and reactive oxygen species (ROS) production after exposure of rat astrocytes to hydrogen peroxide. We determined the influence of treatment with the P2Y1 receptor-specific agonist 2-methyl-thio-ADP (2MeSADP) and the broad range P2Y receptor agonist adenosine 5'-(3-thiotriphosphate) (ATPγS). Preincubation (24-h before hydrogen peroxide application) and incubation with ATPγS and 2MeSADP protected astrocytes. The ROS production in hydrogen peroxide-treated astrocytes was reduced by pre- and co-incubation with ATPγS or 2MeSADP. Changes of levels of expression of antioxidant defense systems in astrocytes by treatment with P2Y receptor agonists were analyzed. Incubation with ATPγS and 2MeSADP increased mRNA levels of CAT encoding catalase and SOD2, encoding mitochondrial manganese dependent superoxide dismutase. ATPγS additionally increased mRNA levels of SOD3, encoding extracellular superoxide dismutase (ECSOD). Levels of total glutathione (GSH) increased in ATPγS/2MeSADP-treated astrocytes. mRNA levels of genes involved in GSH synthesis and in import of GSH precursors were analyzed after treatment with ATPγS and 2MeSADP. Both agonists significantly increased mRNA levels of a subunit of glutamate cysteine ligase, and a subunit of antiporter system xc(-). Changes in mRNA levels of antioxidant enzymes and genes of GSH metabolism depend on rise of intracellular Ca(2+) by P2Y receptor and basal activity of protein kinase A (PKA). SOD3 induction is suggested to depend on increased intracellular Ca(2+), increased cyclic AMP levels and PKA activity. Thus, we confirm a role of purinergic signaling in astrocytic survival during oxidative stress by maintaining antioxidant defense, highlighting P2Y receptors as potential targets for cytoprotection.

H89 enhances the sensitivity of cancer cells to glyceryl trinitrate through a purinergic receptor-dependent pathway

High doses of the organic nitrate glyceryl trinitrate (GTN), a nitric oxide (NO) donor, are known to trigger apoptosis in human cancer cells. Here, we show that such a cytotoxic effect can be obtained with subtoxic concentrations of GTN when combined with H89, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulphonamide.2HCl. This synergistic effect requires the generation of reactive oxygen species (ROS) from H89 and NO from GTN treatment that causes cGMP production and PKG activation. Furthermore, the GTN/H89 synergy was attenuated by inhibition of P2-purinergic receptors with suramin and competition with ATP/UDP. By down-regulating genes with antisense oligonucleotides, P2-purinergic receptors P2X3, P2Y1, and P2Y6 were found to have a role in creating this cytotoxic effect. Thus, H89 likely acts as an ATP mimetic synergizing with GTN to trigger apoptosis in aggressive cancer cells.

Supportive or detrimental roles of P2Y receptors in brain pathology?--The two faces of P2Y receptors in stroke and neurodegeneration detected in neural cell and in animal model studies

This review describing the role of P2Y receptors in neuropathological conditions focuses on obvious differences between results demonstrating either a role in neuroprotection or in neurodegeneration, depending on in vitro and in vivo models. Such critical juxtaposition puts special emphasis on discussions of beneficial and detrimental effects of P2Y receptor agonists and antagonists in these models. The mechanisms reported to underlie the protection in vitro include increased expression of oxidoreductase genes, like carbonyl reductase and thioredoxin reductase; increased expression of inhibitor of apoptosis protein-2; extracellular signal-regulated kinase- and Akt-mediated antiapoptotic signaling; increased expression of Bcl-2 proteins, neurotrophins, neuropeptides, and growth factors; decreased Bax expression; non-amyloidogenic APP shedding; and increased neurite outgrowth in neuronal cells. Animal studies investigating the influence of P2Y receptors in middle cerebral artery occlusion (MCAO) models for stroke prove beneficial effects of P2Y receptor antagonists. In MCAO mice and rats, the application of broad-range P2 receptor antagonists decreased the infarct volume and improved neurological outcome. Moreover, antagonists of the P2Y1 receptor, one of the most abundant P2Y receptor subtypes in brain tissue, decreased neuronal loss and improved spatial memory in rats after traumatic brain injury (TBI). Currently available data show a discrepancy between in vitro and in vivo models concerning the benefits of P2Y receptor activation in pathological conditions. In vitro models demonstrate protection by P2Y receptor agonists, but in vivo P2Y receptor activation deteriorates the outcome after MCAO and controlled cortical impact brain injury, a TBI model. To broaden the scope of the review, we additionally discuss publications that demonstrate detrimental effects of P2Y receptor agonists in vitro and publications showing protective effects of agonists in vivo. All these studies help to better understand the significant role of P2Y receptors especially in stroke models and to develop pharmacological strategies for the treatment of stroke.

Pathological potential of astroglial purinergic receptors

Acute brain injury and neurodegenerative disorders may result in astroglial activation. Astrocytes are able to determine the progression and outcome of these neuropathologies in a beneficial or detrimental way. Nucleotides, e.g. adenosine 5'-triphosphate (ATP), released after acute or chronic neuronal injury, are important mediators of glial activation and astrogliosis.Acute injury may cause significant changes in ATP balance, resulting in (1) a decline of intracellular ATP levels and (2) an increase in extracellular ATP concentrations via efflux from the intracellular space. The released ATP may have trophic effects, but can also act as a proinflammatory mediator or cytotoxic factor, inducing necrosis/apoptosis as a universal "danger" signal. Furthermore, ATP, primarily released from astrocytes, is a means of communication between neurons, glial cells, and intracerebral blood vessels.Astrocytes express a heterogeneous battery of purinergic ionotropic and metabotropic receptors (P2XRs and P2YRs, respectively) to respond to extracellular nucleotides.In this chapter, we summarize the contemporary knowledge on the pathological potential of P2Rs in relation to changes of astrocytic functions, determined by distinct molecular signaling cascades, in a variety of diseases. We discuss specific aspects of reactive astrogliosis, with respect to the involvement of prominent receptor subtypes, such as the P2X7 and P2Y1/2Rs. Examples of purinergic signaling of microglia, oligodendrocytes, and blood vessels under pathophysiological conditions will also be presented.The understanding of the pathological potential of purinergic signaling in "controlling and fine-tuning" of astrocytic responses is important for identifying possible therapeutic principles to treat acute and chronic central nervous system diseases.

ATP P2Y1 receptors control cognitive deficits and neurotoxicity but not glial modifications induced by brain ischemia in mice

ATP is a pleiotropic cell-to-cell signaling molecule in the brain that functions through activation of the P2 receptors (P2R), encompassing ionotropic P2XR or metabotropic P2YR. Noxious brain insults increase the extracellular levels of ATP and previous studies have implicated different P2R, namely P2Y1R, in the control of ischemic brain damage, but it remains to be defined if P2Y1R antagonists also alleviate the behavioral impairments associated with brain ischemia. Furthermore, as P2Y1R can control neuronal and glial functions, we explored if P2Y1R antagonist-mediated protection would mainly involve neuronal and/or glial processes. Adult male mice subject to permanent middle cerebral artery occlusion (pMCAO) displayed an infarcted cortical area (2,3,5-triphenyltetrazolium chloride staining), decreased neurological score with decreased working and reference memory performance (Y-maze, object recognition and aversive memory), accompanied by neuronal damage (FluoroJade C), astrogliosis (glial fibrillary acidic protein) and microgliosis (CD11b). All of these changes were attenuated by intracerebroventricular pre-treatment (10 min before pMCAO) with the generic P2R antagonist 4-[(E)-{4-formyl-5-hydroxy-6-methyl-3-[(phosphono-oxy)methyl]pyridin-2-yl}diazenyl]benzene-1,3-disulfonic acid (PPADS, 0.5-1.0 nmol/μL). In contrast, the selective P2Y1R antagonist (1R*,2S*)-4-[2-Iodo-6-(methylamino)-9H-purin-9-yl]-2-(phosphono-oxy)bicycle[3.1.0] hexane-1-methanol dihydrogen phosphate ester (MRS2500, 1.0-2.0 nmol/μL) afforded equivalent behavioral benefits but only prevented neuronal damage but not astrogliosis or microgliosis upon pMCAO. These results indicated that P2Y1R-associated neuroprotection mainly occurred through neuronal mechanisms, whereas other P2R were also involved in the control of astrocytic reactivity upon brain injury.

Loss of calcium/calmodulin-dependent protein kinase II activity in cortical astrocytes decreases glutamate uptake and induces neurotoxic release of ATP

The extent of calcium/calmodulin-dependent protein kinase II (CaMKII) inactivation in the brain after ischemia correlates with the extent of damage. We have previously shown that a loss of CaMKII activity in neurons is detrimental to neuronal viability by inducing excitotoxic glutamate release. In the current study we extend these findings to show that the ability of astrocytes to buffer extracellular glutamate is reduced when CaMKII is inhibited. Furthermore, CaMKII inhibition in astrocytes is associated with the rapid onset of intracellular calcium oscillations. Surprisingly, this rapid calcium influx is blocked by the N-type calcium channel antagonist, ω-conotoxin. Although the function of N-type calcium channels within astrocytes is controversial, these voltage-gated calcium channels have been linked to calcium-dependent vesicular gliotransmitter release. When extracellular glutamate and ATP levels are measured after CaMKII inhibition within our enriched astrocyte cultures, no alterations in glutamate levels are observed, whereas ATP levels in the extracellular environment significantly increase. Extracellular ATP accumulation associated with CaMKII inhibition contributes both to calcium oscillations within astrocytes and ultimately cortical neuron toxicity. Thus, a loss of CaMKII signaling within astrocytes dysregulates glutamate uptake and supports ATP release, two processes that would compromise neuronal survival after ischemic/excitotoxic insults.

P2Y12 protects platelets from apoptosis via PI3k-dependent Bak/Bax inactivation

BACKGROUND

Platelet ADP receptor P2Y(12) is well studied and recognized as a key player in platelet activation, hemostasis and thrombosis. However, the role of P2Y(12) in platelet apoptosis remains unknown.

OBJECTIVES

To evaluate the role of the P2Y(12) receptor in platelet apoptosis.

METHODS

We used flow cytometry and Western blotting to assess apoptotic events in platelets treated with ABT-737 or ABT-263, and stored at 37°C, combined with P2Y(12) receptor antagonists or P2Y(12) -deficient mice.

RESULTS

 P2Y(12) activation attenuated apoptosis induced by ABT-737 in human and mouse platelets in vitro, evidenced by reduced phosphatidylserine (PS) exposure, diminished depolarization of mitochondrial inner transmembrane potential (ΔΨm) and decreased caspase-3 activation. Through increasing the phosphorylation level of Akt and Bad, and changing the interaction between different Bcl-2 family proteins, P2Y(12) activation inactivated Bak/Bax. This antiapoptotic effect could be abolished by P2Y(12) antagonism or PI3K inhibition. We also observed the antiapoptotic effect of P2Y(12) activation in platelets stored at 37°C. P2Y(12) activation improved the impaired activation responses of apoptotic platelets stressed by ABT-737. In platelets from mice dosed with ABT-263 in vivo, clopidogrel or deficiency of P2Y(12) receptor enhanced apoptosis along with increased Bak/Bax activation.

CONCLUSIONS

This study demonstrates that P2Y(12) activation protects platelets from apoptosis via PI3k-dependent Bak/Bax inactivation, which may be physiologically important to counter the proapoptotic challenge. Our findings that P2Y(12) blockade exaggerates platelet apoptosis induced by ABT-263 (Navitoclax) also imply a novel drug interaction of ABT-263 and P2Y(12) antagonists.

The ADP receptor P2RY12 regulates osteoclast function and pathologic bone remodeling

The adenosine diphosphate (ADP) receptor P2RY12 (purinergic receptor P2Y, G protein coupled, 12) plays a critical role in platelet aggregation, and P2RY12 inhibitors are used clinically to prevent cardiac and cerebral thrombotic events. Extracellular ADP has also been shown to increase osteoclast (OC) activity, but the role of P2RY12 in OC biology is unknown. Here, we examined the role of mouse P2RY12 in OC function. Mice lacking P2ry12 had decreased OC activity and were partially protected from age-associated bone loss. P2ry12-/- OCs exhibited intact differentiation markers, but diminished resorptive function. Extracellular ADP enhanced OC adhesion and resorptive activity of WT, but not P2ry12-/-, OCs. In platelets, ADP stimulation of P2RY12 resulted in GTPase Ras-related protein (RAP1) activation and subsequent αIIbβ3 integrin activation. Likewise, we found that ADP stimulation induced RAP1 activation in WT and integrin β3 gene knockout (Itgb3-/-) OCs, but its effects were substantially blunted in P2ry12-/- OCs. In vivo, P2ry12-/- mice were partially protected from pathologic bone loss associated with serum transfer arthritis, tumor growth in bone, and ovariectomy-induced osteoporosis: all conditions associated with increased extracellular ADP. Finally, mice treated with the clinical inhibitor of P2RY12, clopidogrel, were protected from pathologic osteolysis. These results demonstrate that P2RY12 is the primary ADP receptor in OCs and suggest that P2RY12 inhibition is a potential therapeutic target for pathologic bone loss.

Pathophysiology of astroglial purinergic signalling

Astrocytes are fundamental for central nervous system (CNS) physiology and are the fulcrum of neurological diseases. Astroglial cells control development of the nervous system, regulate synaptogenesis, maturation, maintenance and plasticity of synapses and are central for nervous system homeostasis. Astroglial reactions determine progression and outcome of many neuropathologies and are critical for regeneration and remodelling of neural circuits following trauma, stroke, ischaemia or neurodegenerative disorders. They secrete multiple neurotransmitters and neurohormones to communicate with neurones, microglia and the vascular walls of capillaries. Signalling through release of ATP is the most widespread mean of communication between astrocytes and other types of neural cells. ATP serves as a fast excitatory neurotransmitter and has pronounced long-term (trophic) roles in cell proliferation, growth, and development. During pathology, ATP is released from damaged cells and acts both as a cytotoxic factor and a proinflammatory mediator, being a universal "danger" signal. In this review, we summarise contemporary knowledge on the role of purinergic receptors (P2Rs) in a variety of diseases in relation to changes of astrocytic functions and nucleotide signalling. We have focussed on the role of the ionotropic P2X and metabotropic P2YRs working alone or in concert to modify the release of neurotransmitters, to activate signalling cascades and to change the expression levels of ion channels and protein kinases. All these effects are of great importance for the initiation, progression and maintenance of astrogliosis-the conserved and ubiquitous glial defensive reaction to CNS pathologies. We highlighted specific aspects of reactive astrogliosis, especially with respect to the involvement of the P2X(7) and P2Y(1)R subtypes. Reactive astrogliosis exerts both beneficial and detrimental effects in a context-specific manner determined by distinct molecular signalling cascades. Understanding the role of purinergic signalling in astrocytes is critical to identifying new therapeutic principles to treat acute and chronic neurological diseases.

Activation of the P2Y1 receptor induces apoptosis and inhibits proliferation of prostate cancer cells

G protein-coupled receptors, the largest cell surface receptor family, have emerged as critical players in cell death and survival. High gene expression level of the G(q)-coupled P2Y(1) nucleotide receptor in PC-3 prostate cancer cells was demonstrated using real-time quantitative PCR and confirmed by Western blotting and confocal laser scanning microscopy. A selective P2Y(1) receptor agonist, the ADP analogue MRS2365, concentration-dependently induced intracellular calcium mobilization (EC(50) 5.28nM), which was diminished by P2Y(1) receptor-selective antagonist MRS2500. P2Y(1) receptor activation by MRS2365 induced apoptosis in assays of Caspase-3, LDH release, and annexin-V staining. The pro-apoptotic effect of MRS2365 was blocked by MRS2500, P2Y(1) siRNA, and an inhibitor of the MAP kinase pathway PD98059. MRS2365 significantly inhibited the proliferation of PC-3 cells, examined using a MTT assay. Thus, activation of the P2Y(1) receptor induced cell death and inhibited growth of human prostatic carcinoma PC-3 cells. Activation of the P2Y(1) receptor should be a novel and promising therapeutic strategy for prostate cancer.

ERK1/2 activation is involved in the neuroprotective action of P2Y13 and P2X7 receptors against glutamate excitotoxicity in cerebellar granule neurons

Cerebellar granule neurons express several types of nucleotide receptors, with the metabotropic P2Y(13) and the ionotropic P2X7 being the most relevant in this model. In the present study we investigated the role of P2Y(13) and P2X7 nucleotide receptors in ERK1/2 signalling. The nucleotidic agonists 2MeSADP (2-methylthioadenosine-5'-diphosphate) for P2Y(13) and BzATP (2'(3')-O-(4-benzoylbenzoyl)adenosine-5'-triphosphate) for P2X7 receptors were coupled to ERK1/2 activation in granule neurons, being able to increase around two-fold the levels of ERK1/2 phosphorylation. These effects were sensitive to the inhibitory action of the antagonists MRS-2211 and A-438079, specific for P2Y(13) and P2X7 receptors, respectively. Although both receptor subtypes shared the same pattern of transient ERK1/2 phosphorylation, they differed in the intracellular cascades they triggered, being PI3K-dependent for P2Y(13) and calcium/calmodulin kinase II (CaMKII)-dependent for P2X7. These two different ERK-mediated pathways were involved in the neuroprotective effects displayed by both P2Y(13) and P2X7 receptors against apoptosis induced by an excitotoxic concentration of glutamate, in a similar manner to the neurotrophin, BDNF. In addition, P2Y(13) and P2X7 receptor agonists were also able to phosphorylate and activate the ERK-dependent target CREB, which could be involved in their neuroprotective effect. These results indicate that nucleotide receptors share with trophic factors the same survival routes in neurons, such as the ERK signalling route, and therefore, can contribute to the maintenance of granule neurons in conditions in which survival is being compromised.

Purinergic signaling in embryonic and stem cell development

Nucleotides are of crucial importance as carriers of energy in all organisms. However, the concept that in addition to their intracellular roles, nucleotides act as extracellular ligands specifically on receptors of the plasma membrane took longer to be accepted. Purinergic signaling exerted by purines and pyrimidines, principally ATP and adenosine, occurs throughout embryologic development in a wide variety of organisms, including amphibians, birds, and mammals. Cellular signaling, mediated by ATP, is present in development at very early stages, e.g., gastrulation of Xenopus and germ layer definition of chick embryo cells. Purinergic receptor expression and functions have been studied in the development of many organs, including the heart, eye, skeletal muscle and the nervous system. In vitro studies with stem cells revealed that purinergic receptors are involved in the processes of proliferation, differentiation, and phenotype determination of differentiated cells. Thus, nucleotides are able to induce various intracellular signaling pathways via crosstalk with other bioactive molecules acting on growth factor and neurotransmitter receptors. Since normal development is disturbed by dysfunction of purinergic signaling in animal models, further studies are needed to elucidate the functions of purinoceptor subtypes in developmental processes.

Structure-activity relationship of (N)-Methanocarba phosphonate analogues of 5'-AMP as cardioprotective agents acting through a cardiac P2X receptor

P2X receptor activation protects in heart failure models. MRS2339 3, a 2-chloro-AMP derivative containing a (N)-methanocarba (bicyclo[3.1.0]hexane) system, activates this cardioprotective channel. Michaelis-Arbuzov and Wittig reactions provided phosphonate analogues of 3, expected to be stable in vivo due to the C-P bond. After chronic administration via a mini-osmotic pump (Alzet), some analogues significantly increased intact heart contractile function in calsequestrin-overexpressing mice (genetic model of heart failure) compared to vehicle-infused mice (all inactive at the vasodilatory P2Y(1) receptor). Two phosphonates, (1'S,2'R,3'S,4'R,5'S)-4'-(6-amino-2-chloropurin-9-yl)-2',3'-(dihydroxy)-1'-(phosphonomethylene)-bicyclo[3.1.0]hexane, 4 (MRS2775), and its homologue 9 (MRS2935), both 5'-saturated, containing a 2-Cl substitution, improved echocardiography-derived fractional shortening (20.25% and 19.26%, respectively, versus 13.78% in controls), while unsaturated 5'-extended phosphonates, all 2-H analogues, and a CH(3)-phosphonate were inactive. Thus, chronic administration of nucleotidase-resistant phosphonates conferred a beneficial effect, likely via cardiac P2X receptor activation. Thus, we have greatly expanded the range of carbocyclic nucleotide analogues that represent potential candidates for the treatment of heart failure.

P2 receptor-mediated stimulation of the PI3-K/Akt-pathway in vivo

ATP acts as a growth factor as well as a toxic agent by stimulating P2 receptors. The P2 receptor-activated signaling cascades mediating cellular growth and cell survival after injury are only incompletely understood. Therefore, the aim of the present study was to identify the role of the phosphoinositide 3 kinase (PI3-K/Akt) and the mitogen-activated protein kinase/extracellular signal regulated protein kinase (MAPK/ERK) pathways in P2Y receptor-mediated astrogliosis after traumatic injury and after microinfusion of ADP beta S (P2Y(1,12,13) receptor agonist) into the rat nucleus accumbens (NAc). Mechanical damage and even more the concomitant treatment with ADP beta S, enhanced P2Y(1) receptor-expression in the NAc, which could be reduced by pretreatment with the P2X/Y receptor antagonist PPADS. Quantitative Western blot analysis indicated a significant increase in phosphorylated (p)Akt and pERK1/2 2 h after ADP beta S-microinjection. Pretreatment with PPADS or wortmannin abolished the up-regulation of pAkt by injury alone or ADP beta S-treatment. The ADP beta S-enhanced expression of the early apoptosis marker active caspase 3 was reduced by PPADS and PD98059, but not by wortmannin. Multiple immunofluorescence labeling indicated a time-dependent expression of pAkt and pMAPK on astrocytes and neurons and additionally the colocalization of pAkt, pMAPK, and active caspase 3 with the P2Y(1) receptor especially at astrocytes. In conclusion, the data show for the first time the involvement of PI3-K/Akt-pathway in processes of injury-induced astroglial proliferation and anti-apoptosis via activation of P2Y(1) receptors in vivo, suggesting specific roles of P2 receptors in glial cell pathophysiology in neurodegenerative diseases.

6-Amino-2-mercapto-3H-pyrimidin-4-one derivatives as new candidates for the antagonism at the P2Y12 receptors

P2Y(12) plays an important role in platelet aggregation, which makes it an interesting target for antithrombotic agents. Compounds that antagonize P2Y(12) include the active metabolites of thienopyridines and molecules that are structurally related to ATP, which is an antagonist of P2Y(12). During the last few years, our group has been working on the development of P2Y(12) receptors antagonists that are based on an extremely simple chemical structure, the 6-amino-2-mercapto-3H-pyrimidin-4-one, variously substituted at the sulfur and oxygen functions. This nucleus represents the simplified combination of two known P2Y(12) antagonists: the active metabolite of the thienopyridines and ATP derivatives. The effects of the synthesized compounds were tested on ADP-induced human platelet aggregation, using light transmission aggregometry. None of the tested compounds induced platelet aggregation, while some of them, at concentration of 10(-4)M, partially inhibited platelet aggregation induced by ADP 10(-6)M. The most potent compound, 6b, antagonized the inhibitory effect of 2-methylthio-ADP on the forskolin-induced accumulation of cyclic-AMP in CHO FlpIN cells expressing recombinant human P2Y(12)-receptors. In addition, none of the tested compounds, including 6b, interfered with ligand binding to P1 receptors. Our results suggest that some of the synthesized compounds are specific antagonists of P2 receptors, and in particular of P2Y(12) and suggest that further development of this structurally new series of compounds as P2Y(12) receptors antagonists is recommended.

Development of selective high affinity antagonists, agonists, and radioligands for the P2Y1 receptor

The P2Y(1) receptor is a member of the P2Y family of nucleotide-activated G protein-coupled receptors, and it is an important therapeutic target based on its broad tissue distribution and essential role in platelet aggregation. We have designed a set of highly selective and diverse pharmacological tools for studying the P2Y(1) receptor using a rational approach to ligand design. Based on the discovery that bisphosphate analogues of the P2Y(1) receptor agonist, ADP, are partial agonists/competitive antagonists of this receptor, an iterative approach was used to develop competitive antagonists with enhanced affinity and selectivity. Halogen substitutions of the 2-position of the adenine ring provided increased affinity while an N(6) methyl substitution eliminated partial agonist activity. Furthermore, various replacements of the ribose ring with symmetrically branched, phosphorylated acyclic structures revealed that the ribose is not necessary for recognition at the P2Y(1) receptor. Finally, replacement of the ribose ring with a five member methanocarba ring constrained in the Northern conformation conferred dramatic increases in affinity to both P2Y(1) receptor antagonists as well as agonists. These combined structural modifications have resulted in a series of selective high affinity antagonists of the P2Y(1) receptor, two broadly applicable radioligands, and a high affinity agonist capable of selectively activating the P2Y(1) receptor in human platelets. Complementary receptor modeling and computational ligand docking have provided a putative structural framework for the drug-receptor interactions. A similar rational approach is being applied to develop selective ligands for other subtypes of P2Y receptors.

Regulation of A1 adenosine receptor functioning induced by P2Y1 purinergic receptor activation in human astroglial cells

In the rat brain, a heteromeric association between adenosine A(1) and purinergic P2Y(1) receptors has been demonstrated. It is suggested that this association plays an important role in the control of purine-mediated responses during pathophysiological conditions. Recently, we have demonstrated that these receptors colocalize on glutamatergic synaptic and astroglial membranes in rat hippocampus and reciprocally interact, thus modulating their functional responses at the G protein coupling level. In the present work, by means of immunoprecipitation studies, we demonstrated that A(1) and P2Y(1) receptors are present in human astroglial cells (ADF) and aggregate to form a multimeric complex. P2Y(1) receptor activation by its agonist, 2-methylthio-adenosine 5'-diphosphate (MeSADP), induced a time-dependent reduction in agonist-mediated A(1) receptor functional responses, causing a drop in A(1) receptor agonist potency to promote receptor-G protein coupling and to inhibit the adenylate cyclase pathway. These effects appeared to be selectively mediated by P2Y(1) receptor activation and probably occurred as a consequence of a direct receptor-receptor interaction at the plasma membrane level. These results indicated that P2Y(1) receptor activation induces A(1) receptor heterologous desensitization. The interaction between A(1) and P2Y(1) receptors may play an important role in the purinergic signaling cascade in astrocytes, which are involved in cell-to-cell communication and in control of synaptic transmission, particularly during pathological conditions, when large amounts of purines are released.

Attenuation of apoptosis in vitro and ischemia/reperfusion injury in vivo in mouse skeletal muscle by P2Y6 receptor activation

Activation of the G(q)-coupled P2Y(6) receptor heterologously expressed in astrocytes significantly attenuates apoptosis induced by tumor necrosis factor alpha (TNFalpha). We have extended the analysis of P2Y(6) receptor-induced cytoprotection to mouse skeletal muscle cells endogenously expressing this receptor. The endogenous P2Y(6) receptor agonist UDP and synthetic agonist MRS2693 protected C2C12 skeletal muscle cells against apoptosis in a concentration-dependent manner (0.1-10 nM) as determined by propidium iodide staining, histochemical analysis using hematoxylin and Hoechst 33258, and DNA fragmentation. The insurmountable P2Y(6) receptor antagonist MRS2578 blocked the protection. TNFalpha-induced apoptosis in C2C12 cells correlated with activation of the transcription factor NF-kappaB. The NF-kappaB activation was attenuated by 10nM MRS2693, which activated the antiapoptic ERK1/2 pathway. In an in vivo mouse hindlimb model, MRS2693 protected against skeletal muscle ischemia/reperfusion injury. The P2Y(6) receptor is a novel cytoprotective receptor that deserves further exploration in ameliorating skeletal muscle injury.

Systematic investigation of polyamidoamine dendrimers surface-modified with poly(ethylene glycol) for drug delivery applications: synthesis, characterization, and evaluation of cytotoxicity

Surface modification of amine-terminated polyamidoamine (PAMAM) dendrimers by poly(ethylene glycol) (PEG) groups generally enhances water-solubility and biocompatibility for drug delivery applications. In order to provide guidelines for designing appropriate dendritic scaffolds, a series of G3 PAMAM-PEG dendrimer conjugates was synthesized by varying the number of PEG attachments and chain length (shorter PEG 550 and PEG 750 and longer PEG 2000). Each conjugate was purified by size exclusion chromatography (SEC) and the molecular weight (MW) was determined by (1)H NMR integration and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). NOESY experiments performed in D 2O on selected structures suggested no penetration of PEG chains to the central PAMAM domain, regardless of chain length and degree of substitution. CHO cell cultures exposed to PAMAM-PEG derivatives (< or =1 microM) showed a relatively high cell viability. Generally, increasing the degree of PEG substitution reduced cytotoxicity. Moreover, compared to G3 PAMAM dendrimers that were N-acetylated to varying degrees, a lower degree of surface substitution with PEG was needed for a similar cell viability. Interestingly, when longer PEG 2000 was fully incorporated on the surface, cell viability was reduced at higher concentrations (32 muM), suggesting increased toxicity potentially by forming intermolecular aggregates. A similar observation was made for anionic carboxylate G5.5 PAMAM dendrimer at the same dendrimer concentration. Our findings suggest that a lower degree of peripheral substitution with shorter PEG chains may suffice for these PAMAM-PEG conjugates to serve as efficient universal scaffolds for drug delivery, particularly valuable in relation to targeting or other ligand-receptor interactions.

Cross talk between P2 purinergic receptors modulates extracellular ATP-mediated interleukin-10 production in rat microglial cells

Previously we demonstrated that ATP released from LPS-activated microglia induced IL-10 expression in a process involving P2 receptors, in an autocrine fashion. Therefore, in the present study we sought to determine which subtype of P2 receptor was responsible for the modulation of IL-10 expression in ATP-stimulated microglia. We found that the patterns of IL-10 production were dose-dependent (1, 10, 100, 1,000 microM) and bell-shaped. The concentrations of ATP, ATP-gammaS, ADP, and ADP-betaS that showed maximal IL-10 release were 100, 10, 100, and 100 microM respectively. The rank order of agonist potency for IL-10 production was 2'-3'-O-(4-benzoyl)-benzoyl ATP (BzATP)=dATP>2-methylthio-ADP (2-meSADP). On the other hand, 2-methylthio-ATP (2-meSATP), alpha,beta-methylene ATP (alpha,beta-meATP), UTP, and UDP did not induce the release of IL-10 from microglia. Further, we obtained evidence of crosstalk between P2 receptors, in a situation where intracellular Ca(2+) release and/or cAMP-activated PKA were the main contributors to extracellular ATP-(or ADP)-mediated IL-10 expression, and IL-10 production was down-regulated by either MRS2179 (a P2Y(1) antagonist) or 5'-AMPS (a P2Y(11) antagonist), indicating that both the P2Y(1) and P2Y(11) receptors are major receptors involved in IL-10 expression. In addition, we found that inhibition of IL-10 production by high concentrations of ATP-gammaS (100 microM) was restored by TNP-ATP (an antagonist of the P2X(1), P2X(3), and P2X(4) receptors), and that IL-10 production by 2-meSADP was restored by 2meSAMP (a P2Y(12) receptor antagonist) or pertussis toxin (PTX; a Gi protein inhibitor), indicating that the P2X(1), P2X(3), P2X(4)receptor group, or the P2Y(12) receptor, negatively modulate the P2Y(11) receptor or the P2Y(1) receptor, respectively.

P2Y receptor-activating nucleotides modulate cellular reactive oxygen species production in dissociated hippocampal astrocytes and neurons in culture independent of parallel cytosolic Ca(2+) rise and change in mitochondrial potential

With mixed cultures of hippocampal astrocytes and neurons, we investigated the influence of nucleotides on cytosolic Ca(2+) level, generation of reactive oxygen species (ROS), and mitochondrial potential. We employed ATP and four purine/pyrimidine derivates, which are P2Y receptor subtype-preferring agonists. Stimulation with ATP, a P2Y(1/2/4) receptor agonist in rat, caused a large cytosolic Ca(2+) increase in astrocytes and a considerably smaller Ca(2+) response in neighboring neurons. The P2Y(1) receptor antagonist MRS2179 completely blocked the ATP-induced Ca(2+) response in astrocytes and neurons. Application of ATP significantly reduced the mitochondrial potential in neurons, which was not inhibited by MRS2179. Interestingly, MRS2179 mediated a mitochondrial depolarization without affecting the cytosolic Ca(2+) level. Stimulation with UDP, a P2Y(6) receptor agonist; UTP, a P2Y(2/4) receptor agonist; 2MeSATP, a P2Y(1) receptor agonist; or 2MeSADP, a P2Y(1/12/13) receptor agonist, evoked significant Ca(2+) responses in astrocytes but small Ca(2+) responses in neurons. In astrocytes, there was an inverse relationship between the amplitude of the cytosolic Ca(2+) peak and the rate of ROS generation in response to nucleotide application. Activation with UDP resulted in the highest ROS generation that we detected, whereas 2MeSADP and 2MeSATP reduced the ROS generation below the basal level. 2MeSADP and UDP caused mitochondrial depolarization of comparable size. Thus, neither in astrocytes nor in neurons did the degree of mitochondrial depolarization correlate with ROS generation. Nucleotides acting via P2Y receptors can modulate ROS generation of hippocampal neurons without acutely changing the cytosolic Ca(2+) level. Thus, ROS might function as a signaling molecule upon nucleotide-induced P2Y receptor activation in brain.

Caged agonist of P2Y1 and P2Y12 receptors for light-directed facilitation of platelet aggregation

We have prepared a caged form (MRS2703) of a potent dual agonist of the P2Y(1) and P2Y(12) nucleotide receptors, 2-MeSADP, by blocking the beta-phosphate group with a 1-(3,4-dimethyloxyphenyl)eth-1-yl phosphoester. Although MRS2703 is itself inactive at human P2Y(1) and P2Y(12) receptors expressed heterologously in 1321N1 astrocytoma cells or in washed human platelets, this derivative readily regenerates the parent agonist upon mild irradiation with long-wave UV light (360 nm). The functional effect of the regenerated agonist was demonstrated by a rise in intracellular calcium mediated by either P2Y(1) or P2Y(12) receptors in transfected cells. Washed human platelets exposed to a solution of MRS2703 were induced to aggregate upon UV irradiation. At 1.0 microM MRS2703, full aggregation was achieved within 1 min of irradiation. Thus, this caged nucleotide promises to be a useful probe for potent P2Y receptor activation with light-directed spatial and temporal control.