Differential catalytic properties and vascular topography of murine nucleoside triphosphate diphosphohydrolase 1 (NTPDase1) and NTPDase2 have implications for thromboregulation

Platelets isolation and ectonucleotidase assay: Revealing functional aspects of the communication between the vasculature and the immune system

Platelets are enucleated fragments of cells with a diversity of internal granules. They are responsible for functions related to hemostasis, coagulation, and inflammation. The activation of these processes depends on a cascade coordinated by cytokines, chemokines, and components of purinergic signaling, such as ATP, ADP, and adenosine. Platelets express distinct components of the purinergic system: P2X1, P2Y1, PY12, and P2Y14 receptors; and the ectonucleotidases NTPDase, NPP, and 5NTE (ecto-5'-nucleotidase). Except for P2Y14, which has not yet exhibited a known function, all other components relate to the biological processes mentioned before. Platelets are known to display specific responses to microorganisms, being capable of recognizing pathogen-associated molecular patterns (PAMPs), engulfing certain classes of viruses, and participating in NETosis. Platelet function dysregulation implicates various pathophysiological processes, including cardiovascular diseases (CVDs) and infections. In COVID-19 patients, platelets exhibit altered purinergic signaling and increased activation, contributing to inflammation. Excessive platelet activation can lead to complications from thrombosis, which can affect the circulation of vital organs. Therefore, controlling the activation is necessary to end the inflammatory process and restore homeostasis. Ectonucleotidases, capable of hydrolyzing ATP, ADP, and AMP, are of fundamental importance in activating platelets, promising pharmacological targets for clinical use as cardiovascular protective drugs. In this review, we revisit platelet biology, the purinergic receptors and ectonucleotidases on their surface, and their importance in platelet activity. Additionally, we describe methods for isolating platelets in humans and murine, as well as the main techniques for detecting the activity of ectonucleotidases in platelets. Considering the multitude of functions revealed by platelets and their potential use as potent bioreactors able to secrete and present molecules involved in the communication of the vasculature with the immune system, it is crucial to deeply understand platelet biology and purinergic signaling participation to contribute to the developing of therapeutic strategies in diseases of the cardiovascular, inflammatory, and immune systems.

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.

Platelets and the Cybernetic Regulation of Ischemic Inflammatory Responses through PNC Formation Regulated by Extracellular Nucleotide Metabolism and Signaling

Ischemic events are associated with severe inflammation and are here referred to as ischemic inflammatory response (IIR). Recent studies identified the formation of platelet–neutrophil complexes (PNC) as key players in IIR. We investigated the role of extracellular platelet nucleotide signaling in the context of IIR and defined a cybernetic circle, including description of feedback loops. Cybernetic circles seek to integrate different levels of information to understand how biological systems function. Our study specifies the components of the cybernetic system of platelets in IIR and describes the theoretical progression of IIR passing the cybernetic cycle with positive and negative feedback loops based on nucleotide-dependent signaling and functional regulation. The cybernetic components and feedback loops were explored by cytometry, immunohistological staining, functional blocking antibodies, and ADP/ATP measurements. Using several ex vivo and in vivo approaches we confirmed cybernetic parameters, such as controller, sensor, and effector (VASP phosphorylation, P2Y₁₂, ADORAs and GPIIb/IIIa activity), as well as set points (ADP, adenosine) and interfering control and disturbance variables (ischemia). We demonstrate the impact of the regulated platelet–neutrophil complex (PNC) formation in blood and the resulting damage to the affected inflamed tissue. Taken together, extracellular nucleotide signaling, PNC formation, and tissue damage in IIR can be integrated in a controlled cybernetic circle of platelet function, as introduced through this study.

CD39 - A bright target for cancer immunotherapy

The ATP-adenosine pathway functions as a key modulator of innate and adaptive immunity within the tumor microenvironment, and cancer immune evasion largely involves the generation of high amounts of immunosuppressive extracellular adenosine (eADO). Consequently, inhibition of eADO-generating enzymes and/or eADO receptors can effectively restore the antitumor immunity of multiple immune cells. With several clinical strategies currently being explored to modulating the eADO pathway in patients with cancer, recent clinical data with antagonists targeting CD73 and A_2A receptor have demonstrated a promising therapeutic potential in cancer. Recent findings reveal that the ectonucleotidase CD39, the limiting enzyme been viewed as "immunological switch", converts ATP-driven pro-inflammatory milieu to an anti-inflammatory state mediated by adenosine. Owing to its superior feature of CD39 antagonism that rely not only on preventing the accumulation of adenosine but also on the stabilization of extracellular ATP to restore antitumor immunity, several inhibitors and clinical trials based on CD39 are being evaluated. Consequently, there is currently a focus on understanding the role of CD39 in governing immunity and how therapeutic strategies targeting this pathway alter the antitumor potential. We herein review the impact of CD39 on tumor microenvironment with a focus on treatment preference. Additionally, we also discuss the implication for rational combination therapies, molecular regulation, as well as potential limitations.

Expression of Ectonucleoside Triphosphate Diphosphohydrolase 2 (NTPDase2) Is Negatively Regulated Under Neuroinflammatory Conditions In Vivo and In Vitro

Ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2) hydrolyzes extracellular ATP to ADP, which is the ligand for P2Y1,12,13 receptors. The present study describes the distribution of NTPDase2 in adult rat brains in physiological conditions, and in hippocampal neurodegeneration induced by trimethyltin (TMT). The study also describes the regulation of NTPDase2 by inflammatory mediators in primary astrocytes and oligodendroglial cell line OLN93. In physiological conditions, NTPDase2 protein was most abundant in the hippocampus, where it was found in fibrous astrocytes and synaptic endings in the synaptic-rich hippocampal layers. In TMT-induced neurodegeneration, NTPDase2-mRNA acutely decreased at 2-dpi and then gradually recovered to the control level at 7-dpi and 21-dpi. As determined by immunohistochemistry and double immunofluorescence, the decrease was most pronounced in the dentate gyrus (DG), where NTPDase2 withdrew from the synaptic boutons in the polymorphic layer of DG, whereas the recovery of the expression was most profound in the subgranular layer. Concerning the regulation of NTPDase2 gene expression, proinflammatory cytokines IL-6, IL-1β, TNFα, and IFNγ negatively regulated the expression of NTPDase2 in OLN93 cells, while did not altering the expression in primary astrocytes. Different cell-intrinsic stressors, such as depletion of intracellular energy store, oxidative stress, endoplasmic reticulum stress, and activation of protein kinase C, also massively disturbed the expression of the NTPDase2 gene. Together, our results suggest that the expression and the activity of NTPDase2 transiently cease in neurodegeneration and brain injury, most likely as a part of the acute adaptive response designed to promote cell defense, survival, and recovery.

Purinergic signaling as a new mechanism underlying physical exercise benefits: a narrative review

In the last years, it has become evident that both acute and chronic physical exercise trigger responses/adaptations in the purinergic signaling and these adaptations can be considered one important mechanism related to the exercise benefits for health improvement. Purinergic system is composed of enzymes (ectonucleotidases), receptors (P1 and P2 families), and molecules (ATP, ADP, adenosine) that are able to activate these receptors. These components are widely distributed in almost all cell types, and they respond/act in a specific manner depending on the exercise types and/or intensities as well as the cell type (organ/tissue analyzed). For example, while acute intense exercise can be associated with tissue damage, inflammation, and platelet aggregation, chronic exercise exerts anti-inflammatory and anti-aggregant effects, promoting health and/or treating diseases. All of these effects are dependent on the purinergic signaling. Thus, this review was designed to cover the aspects related to the relationship between physical exercise and purinergic signaling, with emphasis on the modulation of ectonucleotidases and receptors. Here, we discuss the impact of different exercise protocols as well as the differences between acute and chronic effects of exercise on the extracellular signaling exerted by purinergic system components. We also reinforce the concept that purinergic signaling must be understood/considered as a mechanism by which exercise exerts its effects.

Synthesis, characterization and biological evaluation of thiadiazole amide derivatives as nucleoside triphosphate diphosphohydrolases (NTPDases) inhibitors

Importance of extracellular nucleotides is widely understood. These nucleotides act as ligand for P2X and P2Y receptors and modulate a variety of biological functions. However, their extracellular concentration is maintained by a chain of enzymes termed as ecto-nucleotidases. Amongst them, nucleoside triphosphate diphosphohydrolases (NTPDases) is an important enzyme family responsible for the dephosphorylation of these nucleotides. Overexpression of NTPDases leads to many pathological conditions such as cancer and thrombosis. So far, only a few NTPDase inhibitors have been reported. Considering this scarcity of (NTPDase) inhibitors, a number of thiadiazole amide derivatives were synthesized and screened against human (h)-NTPDases. Several compounds showed promising inhibitory activity; compound 5a (IC₅₀ (µM); 0.05 ± 0.008) and 5g (IC₅₀ (µM); 0.04 ± 0.006) appeared to be the most distinguished molecules corresponding to h-NTPDase1 and -2. However, h-NTPDase3 was the least susceptible isozyme and only three compounds (5d, 5e, 5j) strongly inhibited h-NTPDase3. Interestingly, compound 5e was recognized as the most active compound that showed dual inhibition against h-NTPDase3 as well as against h-NTPDase8. For better comprehension of binding mode of these inhibitors, most potent inhibitors were docked with their respective isozyme.

Neurotransmitters responsible for purinergic motor neurotransmission and regulation of GI motility

Classical concepts of peripheral neurotransmission were insufficient to explain enteric inhibitory neurotransmission. Geoffrey Burnstock and colleagues developed the idea that ATP or a related purine satisfies the criteria for a neurotransmitter and serves as an enteric inhibitory neurotransmitter in GI muscles. Cloning of purinergic receptors and development of specific drugs and transgenic mice have shown that enteric inhibitory responses depend upon P2Y₁ receptors in post-junctional cells. The post-junctional cells that transduce purinergic neurotransmitters in the GI tract are PDGFRα⁺ cells and not smooth muscle cells (SMCs). PDGFRα⁺ cells express P2Y₁ receptors, are activated by enteric inhibitory nerve stimulation and generate Ca²⁺ oscillations, express small-conductance Ca²⁺-activated K⁺ channels (SK3), and generate outward currents when exposed to P2Y₁ agonists. These properties are consistent with post-junctional purinergic responses, and similar responses and effectors are not functional in SMCs. Refinements in methodologies to measure purines in tissue superfusates, such as high-performance liquid chromatography (HPLC) coupled with etheno-derivatization of purines and fluorescence detection, revealed that multiple purines are released during stimulation of intrinsic nerves. β-NAD⁺ and other purines, better satisfy criteria for the purinergic neurotransmitter than ATP. HPLC has also allowed better detection of purine metabolites, and coupled with isolation of specific types of post-junctional cells, has provided new concepts about deactivation of purine neurotransmitters. In spite of steady progress, many unknowns about purinergic neurotransmission remain and require additional investigation to understand this important regulatory mechanism in GI motility.

Highly Potent and Selective Ectonucleoside Triphosphate Diphosphohydrolase (ENTPDase1, 2, 3 and 8) Inhibitors Having 2-substituted-7- trifluoromethyl-thiadiazolopyrimidones Scaffold

BACKGROUND

The ecto-nucleoside triphosphate diphosphohydrolases (NTPDases) terminate nucleotide signaling via the hydrolysis of extracellular nucleoside-5'-triphosphate and nucleoside- 5'-diphosphate, to nucleoside-5'-monophosphate and composed of eight Ca2+/Mg2+ dependent ectonucleotidases (NTPDase1-8). Extracellular nucleotides are involved in a variety of physiological mechanisms. However, they are rapidly inactivated by ectonucleotidases that are involved in the sequential removal of phosphate group from nucleotides with the release of inorganic phosphate and their respective nucleoside. Ectonucleoside triphosphate diphosphohydrolases (NTPDases) represent the key enzymes responsible for nucleotides hydrolysis and their overexpression has been related to certain pathological conditions. Therefore, the inhibitors of NTPDases are of particular importance in order to investigate their potential to treat various diseases e.g., cancer, ischemia and other disorders of the cardiovascular and immune system.

METHODS

Keeping in view the importance of NTPDase inhibitors, a series of thiadiazolopyrimidones were evaluated for their potential inhibitory activity towards NTPDases by the malachite green assay.

RESULTS

The results suggested that some of the compounds were found as non-selective inhibitors of isozyme of NTPDases, however, most of the compounds act as potent and selective inhibitors. In case of substituted amino derivatives (4c-m), the compounds 4m (IC50 = 1.13 ± 0.09 μM) and 4g (IC50 = 1.72 ± 0.08 μM) were found to be the most potent inhibitors of h-NTPDase1 and 2, respectively. Whereas, compound 4d showed the best inhibitory potential for both h-NTPDase3 (IC50 = 1.25 ± 0.06 μM) and h-NTPDase8 (0.21 ± 0.02 μM). Among 5a-t derivatives, compounds 5e (IC50 = 2.52 ± 0.15 μM), 5p (IC50 = 3.17 ± 0.05 μM), 5n (IC50 = 1.22 ± 0.06 μM) and 5b (IC50 = 0.35 ± 0.001 μM) were found to be the most potent inhibitors of h-NTPDase1, 2, 3 and 8, respectively. Interestingly, the inhibitory concentration values of above-mentioned inhibitors were several folds greater than suramin, a reference control. In order to determine the binding interactions, molecular docking studies of the most potent inhibitors were conducted into the homology models of NTPDases and the putative binding analysis further confirmed that selective and potent compounds bind deep inside the active pocket of the respective enzymes.

CONCLUSION

The docking analysis proposed that the inhibitory activity correlates with the hydrogen bonds inside the binding pocket. Thus, these derivatives are of interest and may further be investigated for their importance in medicinal chemistry.

NTPDase1 Modulates Smooth Muscle Contraction in Mice Bladder by Regulating Nucleotide Receptor Activation Distinctly in Male and Female

Nucleotides released by smooth muscle cells (SMCs) and by innervating nerve terminals activate specific P2 receptors and modulate bladder contraction. We hypothesized that cell surface enzymes regulate SMC contraction in mice bladder by controlling the concentration of nucleotides. We showed by immunohistochemistry, enzymatic histochemistry, and biochemical activities that nucleoside triphosphate diphosphohydrolase-1 (NTPDase1) and ecto-5′-nucleotidase were the major ectonucleotidases expressed by SMCs in the bladder. RT-qPCR revealed that, among the nucleotide receptors, there was higher expression of P2X1, P2Y₁, and P2Y₆ receptors. Ex vivo, nucleotides induced a more potent contraction of bladder strips isolated from NTPDase1 deficient (Entpd1^−/−) mice compared to wild type controls. The strongest responses were obtained with uridine 5′-triphosphate (UTP) and uridine 5′-diphosphate (UDP), suggesting the involvement of P2Y₆ receptors, which was confirmed with P2ry6^−/− bladder strips. Interestingly, this response was reduced in female bladders. Our results also suggest the participation of P2X1, P2Y₂ and/or P2Y₄, and P2Y₁₂ in these contractions. A reduced response to the thromboxane analogue U46619 was also observed in wild type, Entpd1^−/−, and P2ry6^−/− female bladders showing another difference due to sex. In summary, NTPDase1 modulates the activation of nucleotide receptors in mouse bladder SMCs, and contractions induced by P2Y₆ receptor activation were weaker in female bladders.

Adenosine metabolism in the vascular system

The concept of extracellular purinergic signaling was first proposed by Geoffrey Burnstock in the early 1970s. Since then, extracellular ATP and its metabolites ADP and adenosine have attracted an enormous amount of attention in terms of their involvement in a wide range of immunomodulatory, thromboregulatory, angiogenic, vasoactive and other pathophysiological activities in different organs and tissues, including the vascular system. In addition to significant progress in understanding the properties of nucleotide- and adenosine-selective receptors, recent studies have begun to uncover the complexity of regulatory mechanisms governing the duration and magnitude of the purinergic signaling cascade. This knowledge has led to the development of new paradigms in understanding the entire purinome by taking into account the multitude of signaling and metabolic pathways involved in biological effects of ATP and adenosine and compartmentalization of the adenosine system. Along with the "canonical route" of ATP breakdown to adenosine via sequential ecto-nucleoside triphosphate diphosphohydrolase-1 (NTPDase1/CD39) and ecto-5'-nucleotidase/CD73 activities, it has now become clear that purine metabolism is the result of concerted effort between ATP release, its metabolism through redundant nucleotide-inactivating and counteracting ATP-regenerating ectoenzymatic pathways, as well as cellular nucleoside uptake and phosphorylation of adenosine to ATP through complex phosphotransfer reactions. In this review I provide an overview of key enzymes involved in adenosine metabolic network, with special emphasis on the emerging roles of purine-converting ectoenzymes as novel targets for cancer and vascular therapies.

Structural and functional characterization of engineered bifunctional fusion proteins of CD39 and CD73 ectonucleotidases

Extracellular diphosphate and triphosphate nucleotides are released from activated or injured cells to trigger vascular and immune P₂ purinergic receptors, provoking inflammation and vascular thrombosis. These metabokines are scavenged by ectonucleoside triphosphate diphosphohydrolase-1 (E-NTPDase1 or CD39). Further degradation of the monophosphate nucleoside end products occurs by surface ecto-5'-nucleotidase (NMPase) or CD73. These ectoenzymatic processes work in tandem to promote adenosinergic responses, which are immunosuppressive and antithrombotic. These homeostatic ectoenzymatic mechanisms are lost in the setting of oxidative stress, which exacerbates inflammatory processes. We have engineered bifunctional enzymes made up from ectodomains (ECDs) of CD39 and CD73 within a single polypeptide. Human alkaline phosphatase-ectodomain (ALP-ECD) and human acid phosphatase-ectodomain (HAP-ECD) fusion proteins were also generated, characterized, and compared with these CD39-ECD, CD73-ECD, and bifunctional fusion proteins. Through the application of colorimetrical functional assays and high-performance liquid chromatography kinetic assays, we demonstrate that the bifunctional ectoenzymes express high levels of CD39-like NTPDase activity and CD73-like NMPase activity. Chimeric CD39-CD73-ECD proteins were superior in converting triphosphate and diphosphate nucleotides into nucleosides when compared with ALP-ECD and HAP-ECD. We also note a pH sensitivity difference between the bifunctional fusion proteins and parental fusions, as well as ectoenzymatic property distinctions. Intriguingly, these innovative reagents decreased platelet activation to exogenous agonists in vitro. We propose that these chimeric fusion proteins could serve as therapeutic agents in inflammatory diseases, acting to scavenge proinflammatory ATP and also generate anti-inflammatory adenosine.

Biochemical analysis of ectonucleotidases on primary rat vascular smooth muscle cells and in silico investigation of their role in vascular diseases

Vascular smooth muscle cells (VSMCs) exhibit a high degree of plasticity when they undergo the progression from a normal to a disease condition, which makes them a potential target for evaluating early markers and for the development of new therapies. Purinergic signalling plays a key role in vascular tonus control, ATP being an inductor of vasoconstriction, whereas adenosine mediates a vasodilation effect antagonising the ATP actions. The control of extracellular ATP and adenosine levels is done by ectonucleotidases, which represent a potential target to be evaluated in the progression of cardiovascular diseases. In this study, we analysed the basal activity and expression of the ectonucleotidases in aortic rat VSMCs, and we further performed in silico analysis to determine the expression of those enzymes in conditions that mimicked vascular diseases. Cultured in vitro VSMCs showed a prominent expression of Entpd1 followed by Entpd2 and Nt5e (CD73) and very low levels of Entpd3. Slightly faster AMP hydrolysis was observed when compared to ATP and ADP nucleotides. In silico analysis showed that the ectonucleotidases were modulated after induction of conditions that can lead to vascular diseases such as, hypertensive and hypotensive mice models (Nt5e); exposition to high-fat (Entpd1 and Entpd2) or high-phosphate (Nt5e) diet; mechanical stretch (Entpd1, Entpd2 and Nt5e); and myocardial infarction (Entpd1). Our data show that VSMCs are able to efficiently metabolise the extracellular nucleotides generating adenosine. The modulation of Entpd1, Entdp2 and Nt5e in vascular diseases suggests these ectoenzymes as potential targets or markers to be investigated in future studies.

Functional characterization of two ecto-nucleoside triphosphate diphosphohydrolase 2 genes in Japanese flounder (Paralichthys olivaceus) head kidney macrophages

Ecto-nucleoside triphosphate diphosphohydrolases (ENTPDases) are pivotal regulators of extracellular ATP-mediated purinergic immune signaling. ENTPDase2 is a member of the cell surface-bound ecto-nucleoside triphosphate diphosphohydrolase (ENTPDase) protein family that hydrolyzes extracellular nucleoside 5'-triphosphates and nucleoside 5'-diphosphates. However, the immune relevance of ENTPDase2 in fish has not been elucidated. In the present study, from a comparative immunological perspective, we functionally characterized two ENTPDase2 transcript variants (namely ENTPDase2 and ENTPDase2a) from Japanese flounder (Paralichthys olivaceus). Sequence analysis indicates that the deduced Japanese flounder ENTPDase2 and ENTPDase2a proteins possess two conserved transmembrane domains and five apyrase conserved regions that are present in ENTPDase family proteins. However, these proteins only share 54% amino acid sequence identity. Tissue expression analysis revealed that both ENTPDase2 and ENTPDase2a mRNA transcripts are ubiquitously expressed in all examined Japanese flounder tissues, whereas ENTPDase2 is dominantly expressed in blood and ENTPDase2a is abundantly expressed in muscle. Immune challenge experiments showed that ENTPDase2 and ENTPDase2a were significantly upregulated by both inflammatory stimulation and Edwardsiella tarda infection. In addition, the expression of ENTPDase2 and ENTPDase2a was modulated by extracellular ATP (eATP) stimulation in a dose-dependent manner. Furthermore, immunolocalization and functional studies demonstrated that both ENTPDase2 and ENTPDase2a are functional glycosylated plasma membrane proteins. However, ENTPDase2a exhibits greater activity in the hydrolysis of eATP than ENTPDase2 and ENTPDase1 proteins. Finally, knockdown of the ENTPDase2 gene by small interfering RNA significantly upregulated the expression of eATP-induced proinflammatory cytokines IL-1beta, TNF-alpha and G-CSF in Japanese flounder head kidney macrophages, while knockdown of ENTPDase2a only upregulated eATP-induced IL-1beta expression. Taken together, our findings suggest that the two functional Japanese flounder ENTPDase2 isoforms play an essential role in the downregulation of eATP-induced proinflammatory cytokine expression in fish by degrading the available ATP levels in the extracellular milieu.

Enhanced clinical phenotyping by mechanistic bioprofiling in heart failure with preserved ejection fraction: insights from the MEDIA-DHF study (The Metabolic Road to Diastolic Heart Failure)

Background: Heart failure with preserved ejection fraction (HFpEF) is a heterogeneous syndrome for which clear evidence of effective therapies is lacking. Understanding which factors determine this heterogeneity may be helped by better phenotyping. An unsupervised statistical approach applied to a large set of biomarkers may identify distinct HFpEF phenotypes.Methods: Relevant proteomic biomarkers were analyzed in 392 HFpEF patients included in Metabolic Road to Diastolic HF (MEDIA-DHF). We performed an unsupervised cluster analysis to define distinct phenotypes. Cluster characteristics were explored with logistic regression. The association between clusters and 1-year cardiovascular (CV) death and/or CV hospitalization was studied using Cox regression.Results: Based on 415 biomarkers, we identified 2 distinct clusters. Clinical variables associated with cluster 2 were diabetes, impaired renal function, loop diuretics and/or betablockers. In addition, 17 biomarkers were higher expressed in cluster 2 vs. 1. Patients in cluster 2 vs. those in 1 experienced higher rates of CV death/CV hospitalization (adj. HR 1.93, 95% CI 1.12-3.32, p = 0.017). Complex-network analyses linked these biomarkers to immune system activation, signal transduction cascades, cell interactions and metabolism.Conclusion: Unsupervised machine-learning algorithms applied to a wide range of biomarkers identified 2 HFpEF clusters with different CV phenotypes and outcomes. The identified pathways may provide a basis for future research.Clinical significanceMore insight is obtained in the mechanisms related to poor outcome in HFpEF patients since it was demonstrated that biomarkers associated with the high-risk cluster were related to the immune system, signal transduction cascades, cell interactions and metabolismBiomarkers (and pathways) identified in this study may help select high-risk HFpEF patients which could be helpful for the inclusion/exclusion of patients in future trials.Our findings may be the basis of investigating therapies specifically targeting these pathways and the potential use of corresponding markers potentially identifying patients with distinct mechanistic bioprofiles most likely to respond to the selected mechanistically targeted therapies.

Ectonucleoside Triphosphate Diphosphohydrolase-1/CD39 Affects the Response to ADP of Female Rat Platelets

There is evidence that an imbalance of extracellular purine levels may be associated with increased cardiovascular risk. Platelets play a pivotal role in vascular homeostasis and thrombosis and are important source of purine nucleotides and nucleosides. Hydrolysis of nucleotides ATP and ADP is regulated by two ectonucleotidases, triphosphate diphosphohydrolase-1 (NTPDase-1/CD39) and ecto-5’-nucleotidase (ecto-5’-NT/CD73). CD39 enzyme is expressed on the endothelium, circulating blood cells, and smooth muscle cells; there is evidence that changes in CD39 expression and activity affects the potential thrombogenic of a tissue. Gender difference in the cardiovascular risk has been extensively observed; however, while the age-dependent difference in the prevalence of cardiovascular events between men and women has been attributed to the loss of the protective effect of estrogens in the postmenopausal period, the physiological mechanism behind gender disparity is still unclear. Here, we evaluated comparatively male and female rat platelet reactivity and considered the possible role of CD39 at the basis of difference observed. We found a reduced in vitro response to ADP (1–30 µM) of female compared to male platelets, associated to increased platelet CD39 expression and activity. Platelet response to ADP was strongly increased by incubation (10 min) with the CD39 inhibitor, ARL67156 (100 µM), while male platelet response was unaffected. Rat treatment with clopidogrel (30 mg/kg, per os) inhibited ex vivo platelet aggregation. Bleeding time was prolonged in female compared to male. Taken together, our results suggest that platelet ATPase and ADPase activity might be a reliable predictor of platelet reactivity.

Renal Autocrine and Paracrine Signaling: A Story of Self-protection

Autocrine and paracrine signaling in the kidney adds an extra level of diversity and complexity to renal physiology. The extensive scientific production on the topic precludes easy understanding of the fundamental purpose of the vast number of molecules and systems that influence the renal function. This systematic review provides the broader pen strokes for a collected image of renal paracrine signaling. First, we recapitulate the essence of each paracrine system one by one. Thereafter the single components are merged into an overarching physiological concept. The presented survey shows that despite the diversity in the web of paracrine factors, the collected effect on renal function may not be complicated after all. In essence, paracrine activation provides an intelligent system that perceives minor perturbations and reacts with a coordinated and integrated tissue response that relieves the work load from the renal epithelia and favors diuresis and natriuresis. We suggest that the overall function of paracrine signaling is reno-protection and argue that renal paracrine signaling and self-regulation are two sides of the same coin. Thus local paracrine signaling is an intrinsic function of the kidney, and the overall renal effect of changes in blood pressure, volume load, and systemic hormones will always be tinted by its paracrine status.

NTPDase1 and -2 are expressed by distinct cellular compartments in the mouse colon and differentially impact colonic physiology and function after DSS colitis

ATP is both an important mediator of physiological gut functions such as motility and epithelial function, and a key danger signal that mediates cell death and tissue damage. The actions of extracellular ATP are regulated through the catalytic functions extracellular nucleoside triphosphate diphosphohydrolase-1 (NTPDase1), -2, -3, and -8, which ultimately generate nucleosides. Ectonucleotidases have distinct cellular associations, but the specific locations and functional roles of individual NTPDases in the intestine are still poorly understood. Here, we tested the hypothesis that differential and cell-selective regulation of purine hydrolysis by NTPDase1 and -2 plays important roles in gut physiology and disease. We studied Entpd1 and Entpd2 null mice in health and following colitis driven by 2% dextran sulfate sodium (DSS) administration using functional readouts of gut motility, epithelial barrier function, and neuromuscular communication. NTPDase1 is expressed by immune cells, and the ablation of Entpd1 altered glial numbers in the myenteric plexus. NTPDase2 is expressed by enteric glia, and the ablation of Entpd2 altered myenteric neuron numbers. Mice lacking either NTPDase1 or -2 exhibited decreased inhibitory neuromuscular transmission and altered components of inhibitory junction potentials. Ablation of Entpd2 increased gut permeability following inflammation. In conclusion, the location- and context-dependent extracellular nucleotide phosphohydrolysis by NTPDase1 and -2 substantially impacts gut function in health and disease.NEW & NOTEWORTHY Purines are important mediators of gastrointestinal physiology and pathophysiology. Nucleoside triphosphate diphosphohydrolases (NTPDases) regulate extracellular purines, but the roles of specific NTPDases in gut functions are poorly understood. Here, we used Entpd1- and Entpd2-deficient mice to show that the differential and cell-selective regulation of purine hydrolysis by NTPDase1 and -2 plays important roles in barrier function, gut motility, and neuromuscular communication in health and disease.

Lambda-cyhalothrin exposure alters purine nucleotide hydrolysis and nucleotidase gene expression pattern in platelets and liver of rats

Lambda-cyhalothrin (LCT) is a broad-spectrum pesticide widely used in agriculture throughout the world. This pesticide is considered a potential contaminant of surface and underground water as well as food, posing a risk to ecosystems and humans. In this sense, we decided to evaluate the activity of enzymes belonging to the purinergic system, which is linked with regulation of extracellular nucleotides and nucleosides, such as adenosine triphosphate (ATP) and adenosine (Ado) molecules involved in the regulation of inflammatory response. However, there are no data concerning the effects of LCT exposure on the purinergic system, where extracellular nucleotides act as signaling molecules. The aim of this study was to evaluate nucleotide hydrolysis by E-NTPDase (ecto-nucleoside triphosphate diphosphohydrolase), Ecto-NPP (ecto-nucleotide pyrophosphatase/phosphodiesterase), ecto-5'-nucleotidase and ecto-adenosine deaminase (E-ADA) in platelets and liver of adult rats on days 7, 30, 45 and 60 after daily gavage with 6.2 and 31.1 mg/kg bw of LCT. Gene expression patterns of NTPDases1-3 and 5'-nucleotidase were also determined in those tissues. In parallel, lambda-cyhalothrin metabolites [3-(2-chloro-3,3,3- trifluoroprop-1-enyl)-2,2-dimethyl-cyclopropane carboxylic acid (CFMP), 4-hydroxyphenoxybenzoic acid (4-OH-3-PBA), and 3-phenoxybenzoic acid (3-PBA)] were measured in plasma. Results showed that exposure rats to LCT caused a significant increase in the assessed enzymes activities. Gene expression pattern of ectonucleotidases further revealed a significant increase in E-NTPDase1, E-NTPDase2, and E-NTPDase3 mRNA levels after LCT administration at all times. A dose-dependent increase in LCT metabolite levels was also observed but there no significant variations in levels from weeks to week, suggesting steady-steady equilibrium. Correlation analyses revealed that LCT metabolites in the liver and plasma were positively correlated with the adenine nucleotides hydrolyzing enzyme, E-ADA and E-NPP activities in platelets and liver of rats exposed to lambda-cyhalothin. Our results show that LCT and its metabolites may affect purinergic enzymatic cascade and cause alterations in energy metabolism.

The ectonucleoside triphosphate diphosphohydrolase-2 (NTPDase2) in human endometrium: a novel marker of basal stroma and mesenchymal stem cells

The human endometrium undergoes repetitive regeneration cycles in order to recover the functional layer, shed during menses. The basal layer, which remains in charge of endometrial regeneration in every cycle, contains adult stem or progenitor cells of epithelial and mesenchymal lineage. Some pathologies such as adenomyosis, in which endometrial tissue develops within the myometrium, originate from this layer. It is well known that the balance between adenosine triphosphate (ATP) and adenosine plays a crucial role in stem/progenitor cell physiology, influencing proliferation, differentiation, and migration. The extracellular levels of nucleotides and nucleosides are regulated by the ectonucleotidases, such as the nucleoside triphosphate diphosphohydrolase 2 (NTPDase2). NTPDase2 is a membrane-expressed enzyme found in cells of mesenchymal origin such as perivascular cells of different tissues and the stem cells of adult neurogenic regions. The aim of this study was to characterize the expression of NTPDase2 in human nonpathological cyclic and postmenopausic endometria and in adenomyosis. We examined proliferative, secretory, and atrophic endometria from women without endometrial pathology and also adenomyotic lesions. Importantly, we identified NTPDase2 as the first marker of basal endometrium since other stromal cell markers such as CD10 label the entire stroma. As expected, NTPDase2 was also found in adenomyotic stroma, thus becoming a convenient tracer of these lesions. We did not record any changes in the expression levels or the localization of NTPDase2 along the cycle, thus suggesting that the enzyme is not influenced by the female sex hormones like other previously studied ectoenzymes. Remarkably, NTPDase2 was expressed by the Sushi Domain containing 2 (SUSD2)⁺ endometrial mesenchymal stem cells (eMSCs) found perivascularly, rendering it useful as a cell marker to improve the isolation of eMSCs needed for regenerative medicine therapies.

Induction of NTPDase1/CD39 by Reactive Microglia and Macrophages Is Associated With the Functional State During EAE

Purinergic signaling is critically involved in neuroinflammation associated with multiple sclerosis (MS) and its major inflammatory animal model, experimental autoimmune encephalomyelitis (EAE). Herein, we explored the expression of ectonucleoside triphosphate diphosphohydrolase1 (NTPDase1/CD39) in the spinal cord, at the onset (Eo), peak (Ep), and end (Ee) of EAE. Several-fold increase in mRNA and in NTPDase1 protein levels were observed at Eo and Ep. In situ hybridization combined with fluorescent immunohistochemistry showed that reactive microglia and infiltrated mononuclear cells mostly accounted for the observed increase. Colocalization analysis revealed that up to 80% of Iba1 immunoreactivity and ∼50% of CD68 immunoreactivity was colocalized with NTPDase1, while flow cytometric analysis revealed that ∼70% of mononuclear infiltrates were NTPDase1+ at Ep. Given the main role of NTPDase1 to degrade proinflammatory ATP, we hypothesized that the observed up-regulation of NTPDase1 may be associated with the transition between proinflammatory M1-like to neuroprotective M2-like phenotype of microglia/macrophages during EAE. Functional phenotype of reactive microglia/macrophages that overexpress NTPDase1 was assessed by multi-image colocalization analysis using iNOS and Arg1 as selective markers for M1 and M2 reactive states, respectively. At the peak of EAE NTPDase1 immunoreactivity showed much higher co-occurrence with Arg1 immunoreactivity in microglia and macrophages, compared to iNOS, implying its stronger association with M2-like reactive phenotype. Additionally, in ∼80% of CD68 positive cells NTPDase1 was coexpressed with Arg1 compared to negligible fraction coexpresing iNOS and ∼15% coexpresing both markers, additionally indicating prevalent association of NTPDase1 with M2-like microglial/macrophages phenotype at Ep. Together, our data suggest an association between NTPDase1 up-regulation by reactive microglia and infiltrated macrophages and their transition toward antiinflammatory phenotype in EAE.

Investigation of new quinoline derivatives as promising inhibitors of NTPDases: Synthesis, SAR analysis and molecular docking studies

Nucleoside triphosphate diphosphohydrolases (NTPDases), an important class of ectonucleotidases, are responsible for the sequential hydrolysis of extracellular nucleotides. However, over-expression of NTPDases has been linked with various pathological diseases e.g. cancer. Thus, to treat these diseases, the inhibitors of this class of enzyme are of interest. The significance of this class of enzyme encouraged us to synthesize a new class of quinoline derivatives with the aim to find selective and potent inhibitors of NTPDases. Therefore, a mild and efficient synthetic route was established for the synthesis of quinoline derivatives. The reaction was catalyzed by molecular iodine to afford the substituted quinoline derivatives. All the synthetic derivatives (3a-3w) were evaluated for their potential to inhibit the h-NTPDase1, 2, 3 and 8. Most of the compounds were identified as dual inhibitors of h-NTPDase1 and 8 with lower effects on h-NTPDase2 and 3. Two compounds i.e.3f and 3t were identified as selective inhibitor of h-NTPDase1 whereas the compound 3s inhibited the h-NTPDase8 selectively. Moreover, the compounds 3p (IC₅₀ = 0.23 ± 0.01 µM), 3j (IC₅₀ = 21.0 ± 0.03 µM) 3d (IC₅₀ = 5.38 ± 0.21 µM) and 3c (IC₅₀ = 1.13 ± 0.04 µM) were found to be the most potent inhibitors of h-NTPDase1, 2, 3 and 8, respectively. To determine the binding interaction, molecular docking studies were also carried out.

Caffeine Neuroprotection Decreases A2A Adenosine Receptor Content in Aged Mice

Caffeine is a bioactive compound worldwide consumed with effect into the brain. Part of its action in reducing incidence or delaying Alzheimer's and Parkinson's diseases symptoms in human is credited to the adenosine receptors properties. However, the impact of caffeine consumption during aging on survival of brain cells remains debatable. This work, we investigated the effect of low-dose of caffeine on the ectonucleotidase activities, adenosine receptors content, and paying particular attention to its pro-survival effect during aging. Male young adult and aged Swiss mice drank water or caffeine (0.3 g/L) ad libitum for 4 weeks. The results showed that long-term caffeine treatment did not unchanged ATP, ADP or AMP hydrolysis in hippocampus when compared to the mice drank water. Nevertheless, the ATP/ADP hydrolysis ratio was higher in young adult (3:1) compared to the aged (1:1) animals regardless of treatment. The content of A1 receptors did not change in any groups of mice, but the content of A2A receptors was reduced in hippocampus of mice that consumed caffeine. Moreover, the cell viability results indicated that aged mice not only had increased pyknotic neurons in the hippocampus but also had reduced damage after caffeine treatment. Overall, these findings indicate a potential neuroprotective effect of caffeine during aging through the adenosinergic system.

The Impact of Purinergic System Enzymes on Noncommunicable, Neurological, and Degenerative Diseases

Evidences show that purinergic signaling is involved in processes associated with health and disease, including noncommunicable, neurological, and degenerative diseases. These diseases strike from children to elderly and are generally characterized by progressive deterioration of cells, eventually leading to tissue or organ degeneration. These pathological conditions can be associated with disturbance in the signaling mediated by nucleotides and nucleosides of adenine, in expression or activity of extracellular ectonucleotidases and in activation of P2X and P2Y receptors. Among the best known of these diseases are atherosclerosis, hypertension, cancer, epilepsy, Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). The currently available treatments present limited effectiveness and are mostly palliative. This review aims to present the role of purinergic signaling highlighting the ectonucleotidases E-NTPDase, E-NPP, E-5'-nucleotidase, and adenosine deaminase in noncommunicable, neurological, and degenerative diseases associated with the cardiovascular and central nervous systems and cancer. In conclusion, changes in the activity of ectonucleotidases were verified in all reviewed diseases. Although the role of ectonucleotidases still remains to be further investigated, evidences reviewed here can contribute to a better understanding of the molecular mechanisms of highly complex diseases, which majorly impact on patients' quality of life.

ATP metabolizing enzymes ENPP1, 2 and 3 are localized in sensory neurons of rat dorsal root ganglion

In dorsal root ganglion (DRG) neurons, ATP is an important neurotransmitter in nociceptive signaling through P2 receptors (P2Rs) such as P2X2/3R, and adenosine is also involved in anti-nociceptive signaling through adenosine A1R. Thus, the clearance system for adenine nucleotide/nucleoside plays a critical role in regulation of nociceptive signaling, but there is little information on it, especially ectoenzyme expression profiles in DRG. In this study, we examined expression and localization of ecto-nucleotide pyrophosphatase/phosphodiesterases (ENPPs), by which ATP is metabolized to AMP, in rat DRG. The mRNA expression levels of ENPP2 were greater than those of ENPP1 and ENPP3 in rat DRGs. On immunohistochemical analysis, ENPP1, 2 and 3 were found in soma of DRG neurons. Immunopositive rate of ENPP3 was greater than that of ENPP1 and ENPP2 in all DRG neurons. ENPP3, as compared with ENPP1 and ENPP2, was expressed mainly by isolectin B4-positive cells, and slightly by neurofilament 200-positive ones. In this way, the expression profile of ENPP1, 2 and 3 was different in DRGs, and they were mainly expressed in small/medium-sized DRG neurons. Moreover, ENPP1-, 2- and 3-immunoreactivities were colocalized with P2X2R, P2X3R and prostatic acid phosphatase (PAP), as an ectoenzyme for metabolism from AMP to adenosine. Additionally, PAP-immunoreactivity was colocalized with equilibrative nucleoside transporter (ENT) 1, as an adenosine uptake system. These results suggest that the clearance system consisted of ENPPs, PAP and ENT1 plays an important role in regulation of nociceptive signaling in sensory neurons.

Effects of the ecto-ATPase apyrase on microglial ramification and surveillance reflect cell depolarization, not ATP depletion

Microglia, the brain's innate immune cells, have highly motile processes which constantly survey the brain to detect infection, remove dying cells, and prune synapses during brain development. ATP released by tissue damage is known to attract microglial processes, but it is controversial whether an ambient level of ATP is needed to promote constant microglial surveillance in the normal brain. Applying the ATPase apyrase, an enzyme which hydrolyzes ATP and ADP, reduces microglial process ramification and surveillance, suggesting that ambient ATP/ADP maintains microglial surveillance. However, attempting to raise the level of ATP/ADP by blocking the endogenous ecto-ATPase (termed NTPDase1/CD39), which also hydrolyzes ATP/ADP, does not affect the cells' ramification or surveillance, nor their membrane currents, which respond to even small rises of extracellular [ATP] or [ADP] with the activation of K+ channels. This indicates a lack of detectable ambient ATP/ADP and ecto-ATPase activity, contradicting the results with apyrase. We resolve this contradiction by demonstrating that contamination of commercially available apyrase by a high K+ concentration reduces ramification and surveillance by depolarizing microglia. Exposure to the same K+ concentration (without apyrase added) reduced ramification and surveillance as with apyrase. Dialysis of apyrase to remove K+ retained its ATP-hydrolyzing activity but abolished the microglial depolarization and decrease of ramification produced by the undialyzed enzyme. Thus, applying apyrase affects microglia by an action independent of ATP, and no ambient purinergic signaling is required to maintain microglial ramification and surveillance. These results also have implications for hundreds of prior studies that employed apyrase to hydrolyze ATP/ADP.

Molecular dynamic simulations reveal structural insights into substrate and inhibitor binding modes and functionality of Ecto-Nucleoside Triphosphate Diphosphohydrolases

Ecto-nucleotidase enzymes catalyze the hydrolysis of extracellular nucleotides to their respective nucleosides. Herein, we place the focus on the elucidation of structural features of the cell surface located ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDase1-3 and 8). The physiological role of these isozymes is crucially important as they control purinergic signaling by modulating the extracellular availability of nucleotides. Since, crystal or NMR structure of the human isozymes are not available – structures have been obtained by homology modeling. Refinement of the homology models with poor stereo-chemical quality is of utmost importance in order to derive reliable structures for subsequent studies. Therefore, the resultant models obtained by homology modelling were refined by running molecular dynamic simulation. Binding mode analysis of standard substrates and of competitive inhibitor was conducted to highlight important regions of the active site involved in hydrolysis of the substrates and possible mechanism of inhibition.

Distinct roles of ecto-nucleoside triphosphate diphosphohydrolase-2 (NTPDase2) in liver regeneration and fibrosis

Ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases) are cell surface-located transmembrane ecto-enzymes of the CD39 superfamily which regulate inflammation and tissue repair by catalyzing the phosphohydrolysis of extracellular nucleotides and modulating purinergic signaling. In the liver, NTPDase2 is reportedly expressed on portal fibroblasts, but its functional role in regulating tissue regeneration and fibrosis is incompletely understood. Here, we studied the role of NTPDase2 in several models of liver injury using global knockout mice. Liver regeneration and severity of fibrosis were analyzed at different time points after exposure to carbon tetrachloride (CCl₄) or 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) or partial hepatectomy in C57BL/6 wild-type and globally NTPDase2-deficient (Entpd2 null) mice. After chronic CCl₄ intoxication, Entpd2 null mice exhibit significantly more severe liver fibrosis, as assessed by collagen content and histology. In contrast, deletion of NTPDase2 does not have a substantial effect on biliary-type fibrosis in the setting of DDC feeding. In injured livers, NTPDase2 expression extends from the portal areas to fibrotic septae in pan-lobular (CCl₄-induced) liver fibrosis; the same pattern was observed, albeit to a lesser extent in biliary-type (DDC-induced) fibrosis. Liver regeneration after partial hepatectomy is not substantively impaired in global Entpd2 null mice. NTPDase2 protects from liver fibrosis resulting from hepatocellular injury induced by CCl₄. In contrast, Entpd2 deletion does not significantly impact fibrosis secondary to DDC injury or liver regeneration after partial hepatectomy. Our observations highlight mechanisms relating to purinergic signaling in the liver and indicate possible therapeutic avenues and new cellular targets to test in the management of hepatic fibrosis.

Down-regulation of NTPDase2 and ADP-sensitive P2 Purinoceptors Correlate with Severity of Symptoms during Experimental Autoimmune Encephalomyelitis

The present study explores tissue and cellular distribution of ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2) and the gene and protein expression in rat spinal cord during the course of experimental autoimmune encephalomyelitis (EAE). Given that NTPDase2 hydrolyzes ATP with a transient accumulation of ADP, the expression of ADP-sensitive P2 purinoceptors was analyzed as well. The autoimmune disease was actively induced in Dark Agouti female rats and the changes were analyzed 10, 15 and 29 days after the induction. These selected time points correspond to the onset ( Eo ), peak ( Ep ) and recovery ( Er ) from EAE. In control animals, NTPDase2 was confined in the white matter, in most of the glial fibrillary acidic protein (GFAP)-immunoreactive (ir) astrocytes and in a considerable number of nestin-ir cells, while the other cell types were immunonegative. Immunoreactivity corresponding to NTPDase2 decreased significantly at Eo and Ep and then returned to the baseline levels at Er . The preservation of the proportion of GFAP single-labeled and GFAP/NTPDase2 double-labeled elements along the course of EAE indicated that changes in NTPDase2-ir occurred at fibrous astrocytes that typically express NTPDase2 in normal conditions. Significant downregulation of P2Y₁ and P2Y₁₂ receptor proteins at Eo and several-fold induction of P2Y₁₂ and P2Y₁₃ receptor proteins at Ep and/or Er were observed implying that the pathophysiological process in EAE may be linked to ADP signaling. Cell-surface expression of NTPDase2, NTPDase1/CD39 and ecto-5'-nucleotidase (eN/CD73) was analyzed in CD4⁺ T cells of a draining lymph node by fluorescence-activated cell sorting. The induction of EAE was associated with a transient decrease in a number of CD4⁺ NTPDase2⁺ T cells in a draining lymph node, whereas the recovery was characterized by an increase in NTPDase2⁺ cells in both CD4⁺ and CD4^- cell populations. The opposite was found for NTPDase1/CD39⁺ and eN/CD73⁺ cells, which slightly increased in number with progression of the disease, particularly in CD4^- cells, and then decreased in the recovery. Finally, CD4⁺ NTPDase2⁺ cells were never observed in the spinal cord parenchyma. Taken together, our results suggest that the process of neuroinflammation in EAE may be associated with altered ADP signaling.

Characterization of ectonucleotidase expression in the rat carotid body: regulation by chronic hypoxia

The carotid body (CB) chemoreflex maintains blood Po₂ and Pco₂/H⁺ homeostasis and displays sensory plasticity during exposure to chronic hypoxia. Purinergic signaling via P1 and P2 receptors plays a pivotal role in shaping the afferent discharge at the sensory synapse containing catecholaminergic chemoreceptor (type I) cells, glial-like type II cells, and sensory (petrosal) nerve endings. However, little is known about the family of ectonucleotidases that control synaptic nucleotide levels. Using quantitative PCR (qPCR), we first compared expression levels of ectonucleoside triphosphate diphosphohydrolases (NTPDases1,2,3,5,6) and ecto-5'-nucleotidase (E5'Nt/CD73) mRNAs in juvenile rat CB vs. brain, petrosal ganglia, sympathetic (superior cervical) ganglia, and a sympathoadrenal chromaffin (MAH) cell line. In whole CB extracts, qPCR revealed a high relative expression of surface-located members NTPDase1,2 and E5'Nt/CD73, compared with low NTPDase3 expression. Immunofluorescence staining of CB sections or dissociated CB cultures localized NTPDase2,3 and E5'Nt/CD73 protein to the periphery of type I clusters, and in association with sensory nerve fibers and/or isolated type II cells. Interestingly, in CBs obtained from rats reared under chronic hypobaric hypoxia (~60 kPa, equivalent to 4,300 m) for 5-7 days, in addition to the expected upregulation of tyrosine hydroxylase and VEGF mRNAs, there was a significant upregulation of NTPDase3 and E5'Nt/CD73 mRNA, but a downregulation of NTPDase1 and NTPDase2 relative to normoxic controls. We conclude that NTPDase1,2,3 and E5'Nt/CD73 are the predominant surface-located ectonucleotidases in the rat CB and suggest that their differential regulation during chronic hypoxia may contribute to CB plasticity via control of synaptic ATP, ADP, and adenosine pools.

Complete deletion of Cd39 is atheroprotective in apolipoprotein E-deficient mice

Cd39 scavenges extracellular ATP and ADP, ultimately generating adenosine, a nucleoside, which has anti-inflammatory effects in the vasculature. We have evaluated the role of Cd39 in the development of atherosclerosis in hyperlipidemic mice. ApoE KO (Cd39^+/+/ApoE^−/−) and Cd39/ApoE double KO (DKO) (Cd39^−/−/ApoE^−/−) mice were maintained on chow or Western diet for up to 20 weeks before evaluation of atherosclerotic lesions. We found that DKO mice exhibited significantly fewer atherosclerotic lesions than ApoE KO mice, irrespective of diet. Analyses of plaque composition revealed diminished foam cells in the fatty streaks and smaller necrotic cores in advanced lesions of DKO mice, when compared with those in ApoE KO mice. This atheroprotective phenotype was associated with impaired platelet reactivity to ADP in vitro and prolonged platelet survival, suggesting decreased platelet activation in vivo. Further studies with either genetic deletion or pharmacological inhibition of Cd39 in macrophages revealed increased cholesterol efflux mediated via ABCA1 to ApoA1. This phenomenon was associated with elevated plasma HDL levels in DKO mice. Our findings indicate that complete deletion of Cd39 paradoxically attenuates development of atherosclerosis in hyperlipidemic mice. We propose that this phenotype occurs, at least in part, from diminished platelet activation, increased plasma HDL levels, and enhanced cholesterol efflux and indicates the complexity of purinergic signaling in atherosclerosis.

Generation and characterization of polyclonal and monoclonal antibodies to human NTPDase2 including a blocking antibody

Nucleoside triphosphate diphosphohydrolase-2 (NTPDase2) is an ectonucleotidase that modulates P2 receptor activation by hydrolyzing ATP to ADP. In rodents, NTPDase2 is expressed by several specialized cell types such as vascular adventitial cells, neuroglial cells, hepatic portal fibroblasts, gustatory type I cells, and cells within the connective tissues of reproductive and gastrointestinal organs. Much less is known regarding the expression and function of NTPDase2 in humans. Here, we developed specific research tools to study human NTPDase2. We generated mouse monoclonal antibodies and rabbit polyclonal antibodies specific to human NTPDase2 and validated their specificity by western blot, immunocytochemistry, immunohistochemistry, and flow cytometry. In addition, one monoclonal antibody named hN2-D5 _s specifically inhibits human NTPDase2 enzymatic activity but not mouse nor rat NTPDase2. Using these antibodies, NTPDase2 immunoreactivity was detected on glial cells of the human enteric nervous system suggesting a function of the enzyme in intestinal motility. In conclusion, the new antibodies described in our work are novel tools that will enhance future studies of NTPDase2 expression and function in humans.

Generation and Characterization of Specific Antibodies to the Murine and Human Ectonucleotidase NTPDase8

The ectonucleotidase nucleoside triphosphate diphosphohydrolase-8 (NTPDase8) is the last member of the Ecto-NTPDase family to be discovered and characterized. It is a transmembrane protein which regulates the concentration of the agonists of P1 and P2 receptors at the cell surface. The functions of the enzyme are still not known partly due to the lack of specific tools such as antibodies. In this work, guinea pig polyclonal antibodies against mouse NTPDase8 and mouse monoclonal antibodies against human NTPDase8 have been generated and characterized. For the production of antibodies against mouse NTPDase8 several techniques have been tried. Several peptide antigens in several hosts (rabbit, rat, hamster, and guinea pig) failed to give a positive reaction suggesting that NTPDase8 is poorly immunogenic. In this study, we describe the successful process that led to anti-mouse NTPDase8, namely the cDNA immunization technique. Monoclonal antibodies to human NTPDase8 were also obtained by cDNA immunization followed by a final injection with transfected human embryonic kidney (HEK 293T) cells expressing human NTPDase8. The specificity of these antibodies was evaluated by Western blot, immunocytochemistry, immunohistochemistry and flow cytometry. In contrast, all commercial antibodies to NTPDase8 peptides that we have tested failed to give a specific positive signal against the expressed NTPDase8 protein when used to probe Western blots. In addition, immunohistochemistry experiments confirmed the presence of NTPDase8 in mouse liver canaliculi. The tools generated in this work will help characterize NTPDase8 localization and function in future studies and its contribution to the modulation of P1 and P2 receptor activation.

Hemostasis, bleeding and thrombosis in liver disease

The presence of cirrhosis poses an increased risk of both thrombosis and bleeding in individuals with chronic liver disease. This duality is a result of a dynamic disequilibrium between procoagulant and anticoagulant states in individuals with cirrhosis. The mechanism of this imbalance in cirrhosis remains unclear. It is known that the progression of cirrhosis leads to decreased synthetic function and a concurrent lack of natural anticoagulants. Other proposed mechanisms contributing to this hemostatic imbalance include decreased platelet production, increased platelet destruction from hypersplenism, decreased synthesis of Vitamin K-dependent and independent clotting factors and anticoagulant factors, and alterations in purinergic signaling pathways.

Given the current state of flux in our understanding of bleeding and thrombophilia in cirrhosis, the recommendations for treatment of these conditions are still evolving.

We provide a current update on the proposed pathophysiology of altered hemostasis and thrombophilia in cirrhosis. We discuss recent studies in portal vein thrombosis (PVT) and venous thromboembolism (VTE), which are the common thrombotic consequences of cirrhosis, resulting in substantive morbidity and mortality. To address these, we discuss new prophylactic interventions and current treatment options to manage the heightened risk of thrombosis in cirrhosis, while limiting hemorrhagic complications.

17β-Estradiol-Induced Synaptic Rearrangements Are Accompanied by Altered Ectonucleotidase Activities in Male Rat Hippocampal Synaptosomes

17β-Estradiol (E2) rapidly, by binding to membrane estrogen receptors, activates cell signaling cascades which induce formation of new dendritic spines in the hippocampus of males as in females, but the interaction with other metabolic processes, such as extracellular adenine nucleotides metabolism, are currently unknown. Extracellular adenine nucleotides play significant roles, controlling excitatory glutamatergic synapses and development of neural circuits and synaptic plasticity. Their precise regulation in the synaptic cleft is tightly controlled by ecto-nucleoside triphosphate diphosphohydrolase (NTPDase)/ecto-5'-nucleotidase (eN) enzyme chain. Therefore, we sought to clarify whether a single systemic injection of E2 in male rats is accompanied by changes in the expression of the pre- and postsynaptic proteins and downstream kinases linked to E2-induced synaptic rearrangement as well as alterations in NTPDase/eN pathway in the hippocampal synaptosomes. Obtained data showed activation of mammalian target of rapamycin and upregulation of key synaptic proteins necessary for spine formation, 24 h after systemic E2 administration. In E2-mediated conditions, we found downregulation of NTPDase1 and NTPDase2 and attenuation of adenine nucleotide hydrolysis by NTPDase/eN enzyme chain, without changes in NTPDase3 properties and augmentation of synaptic tissue-nonspecific alkaline phosphatase (TNAP) activity. Despite reduced NTPDase activities, increased TNAP activity probably prevents toxic accumulation of ATP in the extracellular milieu and also hydrolyzes accumulated ADP due to unchanged NTPDase3 activity. Thus, our initial evaluation supports idea of specific roles of different ectonucleotidases and their coordinated actions in E2-mediated spine remodeling and maintenance.

AP1 transcription factors are required to maintain the peripheral taste system

The sense of taste is used by organisms to achieve the optimal nutritional requirement and avoid potentially toxic compounds. In the oral cavity, taste receptor cells are grouped together in taste buds that are present in specialized taste papillae in the tongue. Taste receptor cells are the cells that detect chemicals in potential food items and transmit that information to gustatory nerves that convey the taste information to the brain. As taste cells are in contact with the external environment, they can be damaged and are routinely replaced throughout an organism's lifetime to maintain functionality. However, this taste cell turnover loses efficiency over time resulting in a reduction in taste ability. Currently, very little is known about the mechanisms that regulate the renewal and maintenance of taste cells. We therefore performed RNA-sequencing analysis on isolated taste cells from 2 and 6-month-old mice to determine how alterations in the taste cell-transcriptome regulate taste cell maintenance and function in adults. We found that the activator protein-1 (AP1) transcription factors (c-Fos, Fosb and c-Jun) and genes associated with this pathway were significantly downregulated in taste cells by 6 months and further declined at 12 months. We generated conditional c-Fos-knockout mice to target K14-expressing cells, including differentiating taste cells. c-Fos deletion caused a severe perturbation in taste bud structure and resulted in a significant reduction in the taste bud size. c-Fos deletion also affected taste cell turnover as evident by a decrease in proliferative marker, and upregulation of the apoptotic marker cleaved-PARP. Thus, AP1 factors are important regulators of adult taste cell renewal and their downregulation negatively impacts taste maintenance.

Inhibition of P2X Receptors Protects Human Monocytes against Damage by Leukotoxin from Aggregatibacter actinomycetemcomitans and α-Hemolysin from Escherichia coli

α-Hemolysin (HlyA) from Escherichia coli and leukotoxin A (LtxA) from Aggregatibacter actinomycetemcomitans are important virulence factors in ascending urinary tract infections and aggressive periodontitis, respectively. The extracellular signaling molecule ATP is released immediately after insertion of the toxins into plasma membranes and, via P2X receptors, is essential for the erythrocyte damage inflicted by these toxins. Moreover, ATP signaling is required for the ensuing recognition and phagocytosis of damaged erythrocytes by the monocytic cell line THP-1. Here, we investigate how these toxins affect THP-1 monocyte function. We demonstrate that both toxins trigger early ATP release and a following increase in the intracellular Ca²⁺ concentration ([Ca²⁺]_i) in THP-1 monocytes. The HlyA- and LtxA-induced [Ca²⁺]_i response is diminished by the P2 receptor antagonist in a pattern that fits the functional P2 receptor expression in these cells. Both toxins are capable of lysing THP-1 cells, with LtxA being more aggressive. Either desensitization or blockage of P2X₁, P2X₄, or P2X₇ receptors markedly reduces toxin-induced cytolysis. This pattern is paralleled in freshly isolated human monocytes from healthy volunteers. Interestingly, only a minor fraction of the toxin-damaged THP-1 monocytes eventually lyse. P2X₇ receptor inhibition generally prevents cell damage, except from a distinct cell shrinkage that prevails in response to the toxins. Moreover, we find that preexposure to HlyA preserves the capacity of THP-1 monocytes to phagocytose damaged erythrocytes and may induce readiness to discriminate between damaged and healthy erythrocytes. These findings suggest a new pharmacological target for protecting monocytes during exposure to pore-forming cytolysins during infection or injury.

Unlocking the Potential of Purinergic Signaling in Transplantation

Purinergic signaling has been recognized as playing an important role in inflammation, angiogenesis, malignancy, diabetes and neural transmission. Activation of signaling pathways downstream from purinergic receptors may also be implicated in transplantation and related vascular injury. Following transplantation, the proinflammatory "danger signal" adenosine triphosphate (ATP) is released from damaged cells and promotes proliferation and activation of a variety of immune cells. Targeting purinergic signaling pathways may promote immunosuppression and ameliorate inflammation. Under pathophysiological conditions, nucleotide-scavenging ectonucleotidases CD39 and CD73 hydrolyze ATP, ultimately, to the anti-inflammatory mediator adenosine. Adenosine suppresses proinflammatory cytokine production and is associated with improved graft survival and decreased severity of graft-versus-host disease. Furthermore, purinergic signaling is involved both directly and indirectly in the mechanism of action of several existing immunosuppressive drugs, such as calcineurin inhibitors and mammalian target of rapamycin inhibitors. Targeting of purinergic receptor pathways, particularly in the setting of combination therapies, could become a valuable immunosuppressive strategy in transplantation. This review focuses on the role of the purinergic signaling pathway in transplantation and immunosuppression and explores possible future applications in clinical practice.

A commonly used ecto-ATPase inhibitor, ARL-67156, blocks degradation of ADP more than the degradation of ATP in murine colon

BACKGROUND

Adenosine 5'-triphosphate (ATP) is released extracellularly as a neurotransmitter and an autocrine or paracrine mediator in numerous systems, including the gastrointestinal tract. It is rapidly degraded to active and inactive metabolites by membrane-bound enzymes. Investigators frequently use inhibitors of ATP hydrolysis such as ARL-67156 and POM-1 to suppress the catabolism of ATP and prolong its effects in pharmacological studies. Our aim was to investigate directly the effects of ARL-67156 and POM-1 on the degradation of ATP and adenosine 5'-diphosphate (ADP) in mouse colonic muscles.

METHODS

The degradation of ATP and ADP was evaluated by superfusing tissues with 1,N(6) -etheno-ATP (eATP) and 1,N(6) -etheno-ADP (eADP) as substrates and monitoring the decrease in substrate and increase in products (i.e., eADP, eAMP, and e-adenosine) by high-performance liquid chromatography techniques with fluorescence detection. Relaxation responses to etheno-derivatized and non-derivatized ATP and ADP were examined in isometric tension experiments.

KEY RESULTS

ARL-67156 inhibits the degradation of ADP but not of ATP, whereas POM-1 inhibits the degradation of ATP but not of ADP in murine colonic muscles. Consequently, ARL-67156 enhances relaxation responses to both ATP and ADP, whereas POM-1 reduces relaxation to ATP and does not affect relaxation to ADP.

CONCLUSIONS & INFERENCES

Studies that use ARL-67156 to inhibit ATP degradation in smooth muscle likely evaluate responses to accumulated ADP rather than ATP. POM-1 appears to be a more selective inhibitor of ATP degradation in the mouse colon. The choice of pharmacological tools in studies on extracellular ATP signaling may affect the interpretation of experimental data in functional studies.

Dynamic Regulation of Cell Volume and Extracellular ATP of Human Erythrocytes

Introduction

The peptide mastoparan 7 (MST7) triggered in human erythrocytes (rbcs) the release of ATP and swelling. Since swelling is a well-known inducer of ATP release, and extracellular (ATPe), interacting with P (purinergic) receptors, can affect cell volume (Vr), we explored the dynamic regulation between Vr and ATPe.

Methods and Treatments

We made a quantitative assessment of MST7-dependent kinetics of Vr and of [ATPe], both in the absence and presence of blockers of ATP efflux, swelling and P receptors.

Results

In rbcs 10 μM MST7 promoted acute, strongly correlated changes in [ATPe] and Vr. Whereas MST7 induced increases of 10% in Vr and 190 nM in [ATPe], blocking swelling in a hyperosmotic medium + MST7 reduced [ATPe] by 40%. Pre-incubation of rbcs with 10 μM of either carbenoxolone or probenecid, two inhibitors of the ATP conduit pannexin 1, reduced [ATPe] by 40–50% and swelling by 40–60%, while in the presence of 80 U/mL apyrase, an ATPe scavenger, cell swelling was prevented. While exposure to 10 μM NF110, a blocker of ATP-P2X receptors mediating sodium influx, reduced [ATPe] by 48%, and swelling by 80%, incubation of cells in sodium free medium reduced swelling by 92%.

Analysis and Discussion

Results were analyzed by means of a mathematical model where ATPe kinetics and Vr kinetics were mutually regulated. Model dependent fit to experimental data showed that, upon MST7 exposure, ATP efflux required a fast 1960-fold increase of ATP permeability, mediated by two kinetically different conduits, both of which were activated by swelling and inactivated by time. Both experimental and theoretical results suggest that, following MST7 exposure, ATP is released via two conduits, one of which is mediated by pannexin 1. The accumulated ATPe activates P2X receptors, followed by sodium influx, resulting in cell swelling, which in turn further activates ATP release. Thus swelling and P2X receptors constitute essential components of a positive feedback loop underlying ATP-induced ATP release of rbcs.

Regulation of the T Cell Response by CD39

The ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1, or CD39) catalyzes the phosphohydrolysis of extracellular ATP (eATP) and ADP (eADP) released under conditions of inflammatory stress and cell injury. CD39 generates AMP, which is in turn used by the ecto-5'-nucleotidase CD73 to synthesize adenosine. These ectonucleotidases have a major impact on the dynamic equilibrium of proinflammatory eATP and ADP nucleotides versus immunosuppressive adenosine nucleosides. Indeed, CD39 plays a dominant role in the purinergic regulation of inflammation and the immune response because its expression is influenced by genetic and environmental factors. We review the specific role of CD39 in the kinetic regulation of cellular immune responses in the evolution of disease. We focus on the effects of CD39 on T cells and explore potential clinical applications in autoimmunity, chronic infections, and cancer.

Effect of antiretroviral therapy in thromboregulation through the hydrolysis of adenine nucleotides in platelets of HIV patients

The human immunodeficiency virus (HIV) infection results in biochemical and vascular dysfunctions. The highly active antiretroviral therapy (HAART) markedly reduces mortality and opportunistic diseases associated with acquired immunodeficiency syndrome (AIDS). This increased survival time predisposes the development of cardiovascular diseases. Platelets present purinergic system ectoenzymes such as E-NTPDase, E-5'-nucleotidase and E-ADA on its surface. In view of this, the aim of this study was to evaluate the activity of these ectoenzymes in platelets as well as the platelet aggregation and lipid profile of patients with HIV infection and also patients receiving HAART. The results showed an increase in the E-NTPDase activity for ATP hydrolysis in the HIV group compared with the control group and the HIV/HAART group. When assessing the activity E-NTPDase hydrolysis to ADP, the results revealed an increase in activity in the HIV group when compared to the control group, and a decrease in activity when in the HIV/HAART group when compared to the control and HIV groups. The activity of E-5'-nucleotidase revealed an increase in AMP hydrolysis in the HIV group, as the results from control and HIV/HAART groups showed no statistical difference. Regarding the E-ADA activity, the HIV and HIV/HAART groups revealed a decreased deamination of adenosine when compared with the control group. Furthermore, we observed an increased platelet aggregation of HIV/HAART group compared with the control group. Thus, our results suggest that antiretroviral treatment against HIV has a significant effect on the activity of purinergic system ectoenzymes demonstrating that thromboregulation is involved in the process.

Extracellular nucleotide regulation and signaling in cardiac fibrosis

Following myocardial infarction, purinergic nucleotides and nucleosides are released via non-specific and specific mechanisms in response to cellular activation, stress, or injury. These extracellular nucleotides are potent mediators of physiologic and pathologic responses, contributing to the inflammatory and fibrotic milieu within the injured myocardium. Via autocrine or paracrine signaling, cell-specific effects occur through differentially expressed purinergic receptors of the P2X, P2Y, and P1 families. Nucleotide activation of the ionotropic (ligand-gated) purine receptors (P2X) and several of the metabotropic (G-protein-coupled) purine receptors (P2Y) or adenosine activation of the P1 receptors can have profound effects on inflammatory cell function, fibroblast function, and cardiomyocyte function. Extracellular nucleotidases that hydrolyze released nucleotides regulate the magnitude and duration of purinergic signaling. While there are numerous studies on the role of the purinergic signaling pathway in cardiovascular disease, the extent to which the purinergic signaling pathway modulates cardiac fibrosis is incompletely understood. Here we provide an overview of the current understanding of how the purinergic signaling pathway modulates cardiac fibroblast function and myocardial fibrosis.

New insights on pyrimidine signalling within the arterial vasculature - Different roles for P2Y2 and P2Y6 receptors in large and small coronary arteries of the mouse

Extracellular pyrimidines activate P2Y receptors on both smooth muscle cells and endothelial cells, leading to vasoconstriction and relaxation respectively. The aim of this study was to utilize P2Y knock-out (KO) mice to determine which P2Y receptor subtype are responsible for the contraction and relaxation in the coronary circulation and to establish whether P2Y receptors have different functions along the mouse coronary vascular tree. We tested stable pyrimidine analogues on isolated coronary arteries from P2Y2 and P2Y6 receptor KO mice in a myograph setup. In larger diameter segments of the left descending coronary artery (LAD) (lumen diameter~150μm) P2Y6 is the predominant contractile receptor for both UTP (uridine triphosphate) and UDP (uridine diphosphate) induced contraction. In contrast, P2Y2 receptors mediate endothelial-dependent relaxation. However, in smaller diameter LAD segments (lumen diameter~50μm), the situation is opposite, with P2Y2 being the contractile receptor and P2Y6 functioning as a relaxant receptor along with P2Y2. Immunohistochemistry was used to confirm smooth muscle and endothelial localization of the receptors. In vivo measurements of blood pressure in WT mice revealed a biphasic response to the stable analogue UDPβS. Based on the changes in P2Y receptor functionality along the mouse coronary arterial vasculature, we propose that UTP can act as a vasodilator downstream of its release, after being degraded to UDP, without affecting the contractile pyrimidine receptors. We also propose a model, showing physiological relevance for the changes in purinergic receptor functionality along the mouse coronary vascular tree.

Enzymes involved in metabolism of extracellular nucleotides and nucleosides: functional implications and measurement of activities

Extracellular nucleotides and nucleosides mediate diverse signaling effects in virtually all organs and tissues. Most models of purinergic signaling depend on functional interactions between distinct processes, including (i) the release of endogenous ATP and other nucleotides, (ii) triggering of signaling events via a series of nucleotide-selective ligand-gated P2X and metabotropic P2Y receptors as well as adenosine receptors and (iii) ectoenzymatic interconversion of purinergic agonists. The duration and magnitude of purinergic signaling is governed by a network of ectoenzymes, including the enzymes of the nucleoside triphosphate diphosphohydrolase (NTPDase) family, the nucleotide pyrophosphatase/phosphodiesterase (NPP) family, ecto-5'-nucleotidase/CD73, tissue-nonspecific alkaline phosphatase (TNAP), prostatic acid phosphatase (PAP) and other alkaline and acid phosphatases, adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP). Along with "classical" inactivating ectoenzymes, recent data provide evidence for the co-existence of a counteracting ATP-regenerating pathway comprising the enzymes of the adenylate kinase (AK) and nucleoside diphosphate kinase (NDPK/NME/NM23) families and ATP synthase. This review describes recent advances in this field, with special emphasis on purine-converting ectoenzymes as a complex and integrated network regulating purinergic signaling in such (patho)physiological states as immunomodulation, inflammation, tumorigenesis, arterial calcification and other diseases. The second part of this review provides a comprehensive overview and basic principles of major approaches employed for studying purinergic activities, including spectrophotometric Pi-liberating assays, high-performance liquid chromatographic (HPLC) and thin-layer chromatographic (TLC) analyses of purine substrates and metabolites, capillary electrophoresis, bioluminescent, fluorometric and electrochemical enzyme-coupled assays, histochemical staining, and further emphasizes their advantages, drawbacks and suitability for assaying a particular catalytic reaction.