The role of the P2X₇ receptor in infectious diseases

Unlocking the therapeutic potential of P2X7 receptor: a comprehensive review of its role in neurodegenerative disorders

The P2X7 receptor (P2X7R), an ATP-gated ion channel, has emerged as a crucial player in neuroinflammation and a promising therapeutic target for neurodegenerative disorders. This review explores the current understanding of P2X7R's structure, activation, and physiological roles, focusing on its expression and function in microglial cells. The article examines the receptor's involvement in calcium signaling, microglial activation, and polarization, as well as its role in the pathogenesis of Alzheimer's disease, Parkinson's disease, multiple sclerosis, and amyotrophic lateral sclerosis. The review highlights the complex nature of P2X7R signaling, discussing its potential neuroprotective and neurotoxic effects depending on the disease stage and context. It also addresses the development of P2X7R antagonists and their progress in clinical trials, identifying key research gaps and future perspectives for P2X7R-targeted therapy development. By providing a comprehensive overview of the current state of knowledge and future directions, this review serves as a valuable resource for researchers and clinicians interested in exploring the therapeutic potential of targeting P2X7R for the treatment of neurodegenerative disorders.

Effective factors in the pathogenesis of Toxoplasmagondii

Toxoplasma gondii (T. gondii) is a cosmopolitan protozoan parasite in humans and animals. It infects about 30 % of the human population worldwide and causes potentially fatal diseases in immunocompromised hosts and neonates. For this study, five English-language databases (ScienceDirect, ProQuest, Web of Science, PubMed, and Scopus) and the internet search engine Google Scholar were searched. This review was accomplished to draw a global perspective of what is known about the pathogenesis of T. gondii and various factors affecting it. Virulence and immune responses can influence the mechanisms of parasite pathogenesis and these factors are in turn influenced by other factors. In addition to the host's genetic background, the type of Toxoplasma strain, the routes of transmission of infection, the number of passages, and different phases of parasite life affect virulence. The identification of virulence factors of the parasite could provide promising insights into the pathogenesis of this parasite. The results of this study can be an incentive to conduct more intensive research to design and develop new anti-Toxoplasma agents (drugs and vaccines) to treat or prevent this infection. In addition, further studies are needed to better understand the key agents in the pathogenesis of T. gondii.

Ginsenosides enhance P2X7-dependent cytokine secretion from LPS-primed rodent macrophages

The activation of P2X7 is a well-known stimulus for the NLRP3-caspase 1 inflammasome and subsequent rapid IL-1β secretion from monocytes and macrophages. Here we show that positive allosteric modulators of P2X7, ginsenosides, can enhance the release of three important cytokines, IL-1β, IL-6 and TNF-α from LPS-primed rodent macrophages using the J774 mouse macrophage cell line and primary rat peritoneal macrophages. We compared the immediate P2X7 responses in un-primed and LPS-primed macrophages and found no difference in calcium response amplitude or kinetics. These results suggest that under inflammatory conditions positive allosteric modulators are capable of increasing cytokine secretion at lower concentrations of ATP, thus boosting the initial pro-inflammatory signal. This may be important in the control of intracellular infections.

Involvement of microglial P2X7 receptor in pain modulation

BACKGROUND

Pain is a rapid response mechanism that compels organisms to retreat from the harmful stimuli and triggers a repair response. Nonetheless, when pain persists for extended periods, it can lead to adverse changes into in the individual's brain, negatively impacting their emotional state and overall quality of life. Microglia, the resident immune cells in the central nervous system (CNS), play a pivotal role in regulating a variety of pain-related disorders. Specifically, recent studies have shed light on the central role that microglial purinergic ligand-gated ion channel 7 receptor (P2X7R) plays in regulating pain. In this respect, the P2X7R on microglial membranes represents a potential therapeutic target.

AIMS

To expound on the intricate link between microglial P2X7R and pain, offering insights into potential avenues for future research.

METHODS

We reviewed 140 literature and summarized the important role of microglial P2X7R in regulating pain, including the structure and function of P2X7R, the relationship between P2X7R and microglial polarization, P2X7R-related signaling pathways, and the effects of P2X7R antagonists on pain regulation.

RESULTS

P2X7R activation is related to M1 polarization of microglia, while suppressing P2X7R can transfer microglia from M1 into M2 phenotype. And targeting the P2X7R-mediated signaling pathways helps to explore new therapy for pain alleviation. P2X7R antagonists also hold potential for translational and clinical applications in pain management.

CONCLUSIONS

Microglial P2X7R holds promise as a potential novel pharmacological target for clinical treatments due to its distinctive structure, function, and the development of antagonists.

Genetic Variations in the Purinergic P2X7 Receptor Are Associated with the Immune Response to Ocular Toxoplasmosis in Colombia

Ocular toxoplasmosis (OT) is characterized by inflammation within the eye and is the most recognized clinical manifestation of toxoplasmosis. The objective of this study was to identify new single-nucleotide polymorphisms (SNPs) in the P2RX7 gene that may have significance in the immune response to OT in Colombian patients. A case-control study was conducted to investigate the associations between SNPs (rs1718119 and rs2230912) in the P2RX7 gene and OT in 64 Colombian patients with OT and 64 controls. Capillary electrophoresis was used to analyze the amplification products, and in silico algorithms were employed to predict deleterious SNPs. Stability analysis of amino acid changes indicated that both mutations could lead to decreased protein structure stability. A nonsynonymous SNP, Gln460Arg, located in the long cytoplasmic tail of the receptor, showed a significant association with OT (Bonferroni correction (BONF) = 0.029; odds ratio OR = 3.46; confidence interval CI: 1.05 to 11.39), while no significant association between rs1718119 and OT risk was observed. Based on the 3D structure analysis of the P2RX7 protein trimer, it is hypothesized that an increase in the flexibility of the cytoplasmic domain of this receptor could alter its function. This SNP could potentially serve as a biomarker for identifying Colombian patients at risk of OT.

Animal Models for the Investigation of P2X7 Receptors

The P2X7 receptor is a trimeric ligand-gated cation channel activated by extracellular adenosine 5'-triphosphate. The study of animals has greatly advanced the investigation of P2X7 and helped to establish the numerous physiological and pathophysiological roles of this receptor in human health and disease. Following a short overview of the P2X7 distribution, roles and functional properties, this article discusses how animal models have contributed to the generation of P2X7-specific antibodies and nanobodies (including biologics), recombinant receptors and radioligands to study P2X7 as well as to the pharmacokinetic testing of P2X7 antagonists. This article then outlines how mouse and rat models have been used to study P2X7. These sections include discussions on preclinical disease models, polymorphic P2X7 variants, P2X7 knockout mice (including bone marrow chimeras and conditional knockouts), P2X7 reporter mice, humanized P2X7 mice and P2X7 knockout rats. Finally, this article reviews the limited number of studies involving guinea pigs, rabbits, monkeys (rhesus macaques), dogs, cats, zebrafish, and other fish species (seabream, ayu sweetfish, rainbow trout and Japanese flounder) to study P2X7.

Trabectedin modulates macrophage polarization in the tumor-microenvironment. Role of KV1.3 and KV1.5 channels

Immune cells have an important role in the tumor-microenvironment. Macrophages may tune the immune response toward inflammatory or tolerance pathways. Tumor-associated macrophages (TAM) have a string of immunosuppressive functions and they are considered a therapeutic target in cancer. This study aimed to analyze the effects of trabectedin, an antitumor agent, on the tumor-microenvironment through the characterization of the electrophysiological and molecular phenotype of macrophages. Experiments were performed using the whole-cell configuration of the patch-clamp technique in resident peritoneal mouse macrophages. Trabectedin does not directly interact with KV1.5 and KV1.3 channels, but their treatment (16 h) with sub-cytotoxic concentrations of trabectedin increased their KV current due to an upregulation of KV1.3 channels. In vitro generated TAM (TAMiv) exhibited an M2-like phenotype. TAMiv generated a small KV current and express high levels of M2 markers. K+ current from TAMs isolated from tumors generated in mice is a mixture of KV and KCa, and in TAM isolated from tumors generated in trabectedin-treated mice, the current is mostly driven by KCa. We conclude that the antitumor capacity of trabectedin is not only due to its effects on tumor cells, but also to the modulation of the tumor microenvironment, due, at least in part, to the modulation of the expression of different macrophage ion channels.

The P2X7 receptor in mood disorders: Emerging target in immunopsychiatry, from bench to bedside

Psychiatric disorders are among the most burdensome disorders worldwide. Though therapies have evolved over the last decades, treatment resistance still affects many patients. Recently, neuroimmune systems have been identified as important factors of mood disorder biology. The underlying dysregulation in neuroimmune cross-talk is driven by genetic risk factors and accumulating adverse environmental influences like chronic psychosocial stress. These result in a cluster of proinflammatory cytokines and quantitative and functional changes of immune cell populations (e.g., microglia, monocytes, T cells), varying by disease entity and state. Among the emerging immune targets, purinergic signalling revolving around the membranous and ATP specific P2X7 receptor (P2X7R) has gained wider attention and clinical studies making use of antagonistic drugs are on-going. Still, no clinically meaningful applications have been identified so far. A major problem is the often overly simplified approach taken to translate findings from bench to bedside. Therefore, the present review focuses on purinergic signalling via P2X7R in the context of recent advances in immunopsychiatric mood disorder research. Our aim is to provide an overview of the current P2X7R-related findings, from bench to bedside. First, we summarize the characteristics of purinergic signalling and P2X7R, followed by a depiction of genetic and clinical data connecting P2X7R to mood disorders. We close with our perspective on current developments and discuss changes necessary to translate the evident potential of P2X7R signalling modulation into meaningful clinical application. This article is part of the Special Issue on 'Purinergic Signaling: 50 years'.

Overview of Apoptosis, Autophagy, and Inflammatory Processes in Toxoplasma gondii Infected Cells

Toxoplasma gondii (T. gondii) is an obligate intracellular parasite. During the parasitic invasion, T. gondii creates a parasitophorous vacuole, which enables the modulation of cell functions, allowing its replication and host infection. It has effective strategies to escape the immune response and reach privileged immune sites and remain inactive in a controlled environment in tissue cysts. This current review presents the factors that affect host cells and the parasite, as well as changes in the immune system during host cell infection. The secretory organelles of T. gondii (dense granules, micronemes, and rhoptries) are responsible for these processes. They are involved with proteins secreted by micronemes and rhoptries (MIC, AMA, and RONs) that mediate the recognition and entry into host cells. Effector proteins (ROP and GRA) that modify the STAT signal or GTPases in immune cells determine their toxicity. Interference byhost autonomous cells during parasitic infection, gene expression, and production of microbicidal molecules such as reactive oxygen species (ROS) and nitric oxide (NO), result in the regulation of cell death. The high level of complexity in host cell mechanisms prevents cell death in its various pathways. Many of these abilities play an important role in escaping host immune responses, particularly by manipulating the expression of genes involved in apoptosis, necrosis, autophagy, and inflammation. Here we present recent works that define the mechanisms by which T. gondii interacts with these processes in infected host cells.

The ATP-dependent Pathways and Human Diseases

Adenosine triphosphate (ATP) is one of the most important molecules of life, present both inside the cells and extracellularly. It is an essential building block for nucleic acids biosynthesis and crucial intracellular energy storage. However, one of the most interesting functions of ATP is the role of a signaling molecule. Numerous studies indicate the involvement of ATP-dependent pathways in maintaining the proper functioning of individual tissues and organs. Herein, the latest data indicating the ATP function in the network of intra- and extracellular signaling pathways including purinergic signaling, MAP kinase pathway, mTOR and calcium signaling are collected. The main ATP-dependent processes maintaining the proper functioning of the nervous, cardiovascular and immune systems, as well as skin and bones, are summarized. The disturbances in the ATP amount, its cellular localization, or interaction with target elements may induce pathological changes in signaling pathways leading to the development of serious diseases. The impact of an ATP imbalance on the development of dangerous health dysfunctions such as neurodegeneration diseases, cardiovascular diseases (CVDs), diabetes mellitus, obesity, cancers and immune pathogenesis are discussed here.

Two Single Nucleotide Polymorphisms in the Purinergic Receptor P2X7 Gene Are Associated with Disease Severity in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic autoimmune inflammatory disease of the central nervous system (CNS) that leads to progressive physical disability. Recent evidence has suggested that P2X7 receptor (P2X7R)-mediated purinergic signalling pathways play a role in MS-associated neuroinflammation, possibly contributing to disease pathogenesis. To evaluate possible associations between P2X7R polymorphisms and MS disease severity, we performed an association study of five non-synonymous SNPs coding variants of the P2X7R gene: rs1718119 Ala348Thr, rs2230911 Thr357Ser, rs2230912 Gln460Arg, rs3751143 Glu496Ala, and rs28360457 Arg307Gln, modulating P2X7R expression in 128 MS patients (relapsing remitting MS, RRMS: n = 94; secondary progressive, SPMS: n = 34). All patients were genotyped, and multiple sclerosis severity score (MSSS) was evaluated in every case; 189 healthy subjects were enrolled as well as controls. Results showed that P2X7R rs1718119(A) 348Thr and rs22390912(G) 464Arg, two SNPs of minor allele frequency (MAF) known to confer gain of function to the P2X7R protein, were associated with significantly higher MSSS in RRMS patients alone (SMRR (p < 0.001, p = 0.01, respectively)). Interestingly, two whole haplotypes resulted in having significant association with MSSS in these same patients. Thus: (1) the P2X7R-4 “ACGAG” haplotype, characterized by the co-presence of the rs1718119-rs2230912 AG MAF alleles, was associated with higher MSSS (Beta: 1.11 p = 0.04), and (2) the P2X7R-1 “GCAAG” complementary haplotype, which contains the rs1718119 and rs2230912 GA wild-type alleles, was more frequently carried by patients with lower MSSS and less severe disease (Beta: −1.54 p < 0.001). Although being preliminary and needing confirmation in an ampler cohort, these results suggest that 348Thr and 464Arg variants have a role as modulators of disease severity in RRMS patients.

Host P2X7R-p38MAPK axis mediated intra-macrophage leishmanicidal activity of Spergulin-A

Current drugs are inefficient for the treatment of visceral leishmaniasis an immunosuppressive ailment caused by Leishmania donovani. Regrettably, there is no plant-origin antileishmanial drug present. P2X₇R is constitutively present on macrophage surfaces and can be a putative therapeutic target in intra-macrophage pathogens with function attributes towards inflammation, host cell apoptosis, altered redox, and phagolysosomal maturation by activating p₃₈MAPK. Here we demonstrated that the initial interaction of Spergulin-A (Sp A), a triterpenoid saponin with RAW 264.7 macrophages was mediated through P2X₇R involving the signaling cascade intermediates Ca⁺⁺, p₃₈MAPK, and NF-κβ. Phospho (P)-p38MAPK involvement is shown to have specific and firm importance in leishmanial killing with increased NF-κβp65. Phago-lysosomal maturation by Sp A also campaigns for another contribution of P2X₇R. In vivo evaluation of the anti-leishmanial activity of Sp A was monitored through expression analyses of P2X₇R, P-p38MAPK, and NF-κβp65 in murine spleen and bone-marrow macrophages and supported Sp A being a natural compound of leishmanicidal functions which acted through the P2X₇R-p38MAPK axis.

Insights on the Gut-Mesentery-Lung Axis in Pulmonary Arterial Hypertension: A Poorly Investigated Crossroad

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by the hyperproliferation of vascular cells, including smooth muscle and endothelial cells. Hyperproliferative cells eventually obstruct the lung vasculature, leading to irreversible lesions that collectively drive pulmonary pressure to life-threatening levels. Although the primary cause of PAH is not fully understood, several studies have indicated it results from chronic pulmonary inflammation, such as observed in response to pathogens' infection. Curiously, infection by the intravascular parasite Schistosoma mansoni recapitulates several aspects of the widespread pulmonary inflammation that leads to development of chronic PAH. Globally, >200 million people are currently infected by Schistosoma spp., with about 5% developing PAH (Sch-PAH) in response to the parasite egg-induced obliteration and remodeling of the lung vasculature. Before their settling into the lungs, Schistosoma eggs are released inside the mesenteric veins, where they either cross the intestinal wall and disturb the gut microbiome or migrate to other organs, including the lungs and liver, increasing pressure. Spontaneous or surgical liver bypass via collateral circulation alleviates the pressure in the portal system; however, it also allows the translocation of pathogens, toxins, and antigens into the lungs, ultimately causing PAH. This brief review provides an overview of the gut-mesentery-lung axis during PAH, with a particular focus on Sch-PAH, and attempts to delineate the mechanism by which pathogen translocation might contribute to the onset of chronic pulmonary vascular diseases.

Eugenia sulcata (Myrtaceae) Nanoemulsion Enhances the Inhibitory Activity of the Essential Oil on P2X7R and Inflammatory Response In Vivo

P2X7R is a purinergic receptor with broad expression throughout the body, especially in immune system cells. P2X7R activation causes inflammatory mediators to release, including interleukin-1β (IL-1β), the processing and release of which are critically dependent on this ion channel activation. P2X7R’s therapeutic potential augments the discovery of new antagonistic compounds. Thus, we investigated whether the Eugenia sulcata essential oil could block P2X7R activity. The essential oil (ESO) dose-dependently inhibited ATP-promoted PI uptake and IL-1β release with an IC50 of 113.3 ± 3.7 ng/mL and 274 ± 91 ng/mL, respectively, and the essential oil nanoemulsion (ESON) improved the ESO inhibitory effect with an IC50 of 81.4 ± 7.2 ng/mL and 62 ± 2 ng/mL, respectively. ESO and ESON reversed the carrageenan-activated peritonitis in mice, and ESON exhibited an efficacy higher than ESO. The majority substance from essential oil, β-caryophyllene, impaired the ATP-evoked PI uptake and IL-1β release with an IC50 value of 26 ± 0.007 ng/mL and 97 ± 0.012 ng/mL, respectively. Additionally, β-caryophyllene reduced carrageenan-induced peritonitis, and the molecular modeling and computational simulation predicted the intermolecular interactions in the P2X7R situs. In silico, results indicated β-caryophyllene as a potent allosteric P2X7R antagonist, although this substance may present toxic effects for humans. These data confirm the nanoemulsion of essential oil from E. sulcata as a promisor biotechnology strategy for impaired P2X7R functions and the inflammatory response.

P2X7 polymorphism (rs3751143) and its reliability as a diagnostic biomarker for tuberculosis: A systematic review and meta-analysis

Tuberculosis (TB) is one of the most important infectious diseases and is accounted for as the second most common cause of death due to infectious agents after HIV. It is estimated that a quarter of the world's population is infected with Mycobacterium tuberculosis (Mtb), and 5-10% of whom will be infected with active TB. Introducing a biomarker to predict TB can help control the disease and reduces the burden of mortality from this infectious disease. P2X7/P2X7R is one of the most important axes of the innate immune system, which its activity increases the clearance of the residual bacteria in macrophages. Numerous studies have shown the association between rs3751143 polymorphism and susceptibility to TB. The present study aimed to evaluate the diagnostic value of this polymorphism in predicting TB. In the current quantitative analysis, we studied the data from twenty relevant case-control studies, consisting of 10,544 volunteers. We found that, although rs3751143 polymorphism causes susceptibility to TB, but based on statistical analysis, it cannot be considered as a reliable biomarker for the diagnosis of TB.

Inherent P2X7 Receptors Regulate Macrophage Functions during Inflammatory Diseases

Macrophages are mononuclear phagocytes which derive either from blood-borne monocytes or reside as resident macrophages in peripheral (Kupffer cells of the liver, marginal zone macrophages of the spleen, alveolar macrophages of the lung) and central tissue (microglia). They occur as M1 (pro-inflammatory; classic) or M2 (anti-inflammatory; alternatively activated) phenotypes. Macrophages possess P2X7 receptors (Rs) which respond to high concentrations of extracellular ATP under pathological conditions by allowing the non-selective fluxes of cations (Na⁺, Ca²⁺, K⁺). Activation of P2X7Rs by still higher concentrations of ATP, especially after repetitive agonist application, leads to the opening of membrane pores permeable to ~900 Da molecules. For this effect an interaction of the P2X7R with a range of other membrane channels (e.g., P2X4R, transient receptor potential A1 [TRPA1], pannexin-1 hemichannel, ANO6 chloride channel) is required. Macrophage-localized P2X7Rs have to be co-activated with the lipopolysaccharide-sensitive toll-like receptor 4 (TLR4) in order to induce the formation of the inflammasome 3 (NLRP3), which then activates the pro-interleukin-1β (pro-IL-1β)-degrading caspase-1 to lead to IL-1β release. Moreover, inflammatory diseases (e.g., rheumatoid arthritis, Crohn’s disease, sepsis, etc.) are generated downstream of the P2X7R-induced upregulation of intracellular second messengers (e.g., phospholipase A2, p38 mitogen-activated kinase, and rho G proteins). In conclusion, P2X7Rs at macrophages appear to be important targets to preserve immune homeostasis with possible therapeutic consequences.

P2X7 Receptors in Neurodegeneration: Potential Therapeutic Applications From Basic to Clinical Approaches

Purinergic receptors play important roles in central nervous system (CNS), where the bulk of these receptors are implicated in neuroinflammatory responses and regulation of cellular function of neurons, microglial and astrocytes. Within the P2X receptor family, P2X₇ receptor is generally known for its inactivity in normal conditions and activation by moderately high concentrations (>100 μM) of extracellular adenosine 5′-triphosphate (ATP) released from injured cells as a result of brain injury or pathological conditions. Activation of P2X₇R contributes to the activation and proliferation of microglia and directly contribute to neurodegeneration by provoking microglia-mediated neuronal death, glutamate-mediated excitotoxicity, and NLRP3 inflammasome activation that results in initiation, maturity and release of the pro-inflammatory cytokines and generation of reactive oxygen and nitrogen species. These components of the inflammatory response play important roles in many neural pathologies and neurodegeneration disorders. In CNS, expression of P2X₇R on microglia, astrocytes, and oligodendrocytes are upregulated under neuroinflammatory conditions. Several in vivo studies have demonstrated beneficial effects of the P2X₇ receptor antagonists in animal model systems of neurodegenerative diseases. A number of specific and selective P2X₇ receptor antagonists have been developed, but only few of them have shown efficient brain permeability. Finding potent and selective P2X₇ receptor inhibitors which are also CNS penetrable and display acceptable pharmacokinetics (PK) has presented challenges for both academic researchers and pharmaceutical companies. In this review, we discuss the role of P2X₇ receptor function in neurodegenerative diseases, the pharmacological inhibition of the receptor, and PET radiopharmaceuticals which permit non-invasive monitoring of the P2X₇ receptor contribution to neuroinflammation associated with neurodegeneration.

Host surface ectonucleotidase-CD73 and the opportunistic pathogen, Porphyromonas gingivalis, cross-modulation underlies a new homeostatic mechanism for chronic bacterial survival in human epithelial cells

Cell surface nucleotide-metabolizing enzyme, ectonucleotidase-CD73, has emerged as a central component of the cellular homeostatic-machinery that counterbalances the danger-molecule (extracellular-ATP)-driven proinflammatory response in immune cells. While the importance of CD73 in microbial host fitness and symbiosis is gradually being unraveled, there remains a significant gap in knowledge of CD73 and its putative role in epithelial cells. Here, we depict a novel host-pathogen adaptation mechanism where CD73 takes a center role in the intracellular persistence of Porphyromonas gingivalis, a major colonizer of oral mucosa, using human primary gingival epithelial cell (GEC) system. Temporal analyses revealed, upon invasion into the GECs, P. gingivalis can significantly elevate the host-surface CD73 activity and expression. The enhanced and active CD73 significantly increases P. gingivalis intracellular growth in the presence of substrate-AMP and simultaneously acts as a negative regulator of reactive oxygen species (ROS) generation upon eATP treatment. The inhibition of CD73 by siRNA or by a specific inhibitor markedly increases ROS production. Moreover, CD73 and P. gingivalis cross-signaling significantly modulates pro-inflammatory interleukin-6 (IL-6) in the GECs. Conversely, exogenous treatment of the infected GECs with IL-6 suppresses the intracellular bacteria via amplified ROS generation. However, the decreased bacterial levels can be restored by overexpressing functionally active CD73. Together, these findings illuminate how the local extracellular-purine-metabolism, in which CD73 serves as a core molecular switch, can alter intracellular microbial colonization resistance. Further, host-adaptive pathogens such as P. gingivalis can target host ectonucleotidases to disarm specific innate defenses for successful intracellular persistence in mucosal epithelia.

Regulation of the Acute Sickness Response by the P2RX7 Receptor

BACKGROUND

The acute sickness response to infection is a stereotyped set of illness manifestations initiated by proinflammatory signals in the periphery but mediated centrally. P2RX7 is a highly polymorphic gene encoding an ATP-gated cationic pore, widely expressed on immune cells and the brain, and regulating the NLRP3 inflammasome, as well as diverse neural functions.

METHODS

Associations between P2RX7 genotype, pore activity, and illness manifestations were examined in a cohort with acute viral and bacterial infections (n = 484). Genotyping of 12 P2RX7 function-modifying single-nucleotide polymorphisms (SNPs) was used to identify haplotypes and diplotypes. Leucocyte pore activity was measured by uptake of the fluorescent dye, YO-PRO-1, and by ATP-induced interleukin-1β (IL-1β) release. Associations were sought with scores describing the symptom domains, or endophenotypes, derived from principal components analysis.

RESULTS

Among the 12 SNPs, a 4-SNP haplotype block with 5 variants was found in 99.5% of the subjects. These haplotypes and diplotypes were closely associated with variations in pore activity and IL-1β production. Homozygous diplotypes were associated with overall illness severity as well as fatigue, pain, and mood disturbances.

CONCLUSIONS

P2RX7 signaling plays a significant role in the acute sickness response to infection, likely acting in both the immune system and the brain.

MicroRNA-223 negatively regulates LPS-induced inflammatory responses by targeting NLRP3 in human dental pulp fibroblasts

AIM

To investigate the effect of miR-223 on NLRP3, subsequently regulating the production of the NLRP3/CASP1 inflammasome pathway-mediated proinflammatory cytokines IL-1β and IL-18 in human dental pulp fibroblasts (HDPFs).

METHODOLOGY

Human dental pulp tissue (HDPT) and HDPFs were obtained from impacted third molars. The miR-223 mimics and inhibitor or NLRP3 plasmid were used to upregulate or downregulate miR-223 or NLRP3 in HDPFs, respectively. Computational prediction via TargetScan 5.1 and a luciferase reporter assay was conducted to confirm target association. The mRNA and protein expression of NLRP3, caspase-1, IL-1β and IL-18 was determined by qRT-PCR and Western blotting, respectively. The release of IL-1β and IL-18 was analysed by ELISA. The significance of the differences between the experimental and the control groups was determined using one-way analysis of variance; P < 0.05 indicated statistical significance.

RESULTS

A decrease in miR-223 and an increase in NLRP3 in HDPT occurred during the transformation of reversible pulpitis into irreversible pulpitis compared to that in healthy pulp tissue (P < 0.05). The computational prediction and luciferase reporter assay confirmed that NLRP3 was a direct target of miR-223 in HDPFs. The miR-223 inhibitor further promoted ATP plus LPS-induced NLRP3/CASP1 inflammasome pathway activation compared to the ATP plus LPS-induced group (P < 0.05). In contrast, the miR-223 mimic significantly inhibited the NLRP3/CASP1 inflammasome pathway activation induced by ATP plus LPS compared to the ATP plus LPS-induced group (P < 0.05).

CONCLUSION

MiR-223 served as a negative regulator involved in the control of the production and secretion of proinflammatory cytokines mediated by the NLRP3/CASP1 inflammasome pathway by targeting NLRP3. These data provide insight into the potential regulatory effects of miRNAs on the NLRP3 inflammasome, thus opening up novel potential therapeutic avenues for future endodontic treatment.

P2X7 Receptors Amplify CNS Damage in Neurodegenerative Diseases

ATP is a (co)transmitter and signaling molecule in the CNS. It acts at a multitude of ligand-gated cationic channels termed P2X to induce rapid depolarization of the cell membrane. Within this receptor-channel family, the P2X7 receptor (R) allows the transmembrane fluxes of Na⁺, Ca²⁺, and K⁺, but also allows the slow permeation of larger organic molecules. This is supposed to cause necrosis by excessive Ca²⁺ influx, as well as depletion of intracellular ions and metabolites. Cell death may also occur by apoptosis due to the activation of the caspase enzymatic cascade. Because P2X7Rs are localized in the CNS preferentially on microglia, but also at a lower density on neuroglia (astrocytes, oligodendrocytes) the stimulation of this receptor leads to the release of neurodegeneration-inducing bioactive molecules such as pro-inflammatory cytokines, chemokines, proteases, reactive oxygen and nitrogen molecules, and the excitotoxic glutamate/ATP. Various neurodegenerative reactions of the brain/spinal cord following acute harmful events (mechanical CNS damage, ischemia, status epilepticus) or chronic neurodegenerative diseases (neuropathic pain, Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, amyotrophic lateral sclerosis) lead to a massive release of ATP via the leaky plasma membrane of neural tissue. This causes cellular damage superimposed on the original consequences of neurodegeneration. Hence, blood-brain-barrier permeable pharmacological antagonists of P2X7Rs with excellent bioavailability are possible therapeutic agents for these diseases. The aim of this review article is to summarize our present state of knowledge on the involvement of P2X7R-mediated events in neurodegenerative illnesses endangering especially the life quality and duration of the aged human population.

Infection of Monocytes From Tuberculosis Patients With Two Virulent Clinical Isolates of Mycobacterium tuberculosis Induces Alterations in Myeloid Effector Functions

Monocytes play a critical role during infection with Mycobacterium tuberculosis (Mtb). They are recruited to the lung, where they participate in the control of infection during active tuberculosis (TB). Alternatively, inflammatory monocytes may participate in inflammation or serve as niches for Mtb infection. Monocytes response to infection may vary depending on the particularities of the clinical isolate of Mtb from which they are infected. In this pilot study, we have examined the baseline mRNA profiles of circulating human monocytes from patients with active TB (MoTB) compared with monocytes from healthy individuals (MoCT). Circulating MoTB displayed a pro-inflammatory transcriptome characterized by increased gene expression of genes associated with cytokines, monocytopoiesis, and down-regulation of MHC class II gene expression. In response to in vitro infection with two clinical isolates of the LAM family of Mtb (UT127 and UT205), MoTB displayed an attenuated inflammatory mRNA profile associated with down-regulation the TREM1 signaling pathway. Furthermore, the gene expression signature induced by Mtb UT205 clinical strain was characterized by the enrichment of genes in pathways and biological processes mainly associated with a signature of IFN-inducible genes and the inhibition of cell death mechanisms compared to MoTB-127, which could favor the establishment and survival of Mtb within the monocytes. These results suggest that circulating MoTB have an altered transcriptome that upon infection with Mtb may help to maintain chronic inflammation and infection. Moreover, this functional abnormality of monocytes may also depend on potential differences in virulence of circulating clinical strains of Mtb.

Conservation of eATP perception throughout multicellular animal evolution: Identification and functional characterization of coral and amphioxus P2X7-like receptors and flounder P2X7 receptor

Perception of extracellular ATP (eATP), a common endogenous damage-associated molecular pattern, is through its receptor P2X7R. If eATP/P2X7R signaling is conserved throughout animal evolution is unknown. Moreover, little information is currently available regarding P2X7R in invertebrates. Here we demonstrated that the coral P2X7-like receptor, AdP2X7RL, the amphioxus P2X7-like receptor, BjP2X7RL and the flounder P2X7 receptor, PoP2X7R, shared common features characteristic of mammalian P2X7R, and their 3D structures displayed high resemblance to that of human P2X7R. Expression of Adp2x7rl, Bjp2x7rl and Pop2x7r was all subjected to the regulation by LPS and ATP. We also showed that AdP2X7RL, BjP2X7RL and PoP2X7R were distributed on the plasma membrane in AdP2X7RL-, BjP2X7RL- and PoP2X7R-expressing HEK cells, and had strong affinity to eATP. Importantly, the binding of AdP2X7RL, BjP2X7RL and PoP2X7R to eATP all induced similar downstream responses, including induction of cytokines (IL-1β, IL-6, IL-8 and CCL-2), enhancement of phagocytosis and activation of AKT/ERK-associated signaling pathway observed for mammalian P2X7R. Collectively, our results indicate for the first time that both coral and amphioxus P2X7RL as well as flounder P2X7R can interact with eATP, and induce events that trigger mammalian mechanisms, suggesting the high conservation of eATP perception throughout multicellular animal evolution.

Purinergic Receptors: Elucidating the Role of these Immune Mediators in HIV-1 Fusion

Purinergic receptors are inflammatory mediators activated by extracellular nucleotides released by dying or injured cells. Several studies have described an important role for these receptors in HIV-1 entry, particularly regarding their activity on HIV-1 viral membrane fusion. Several reports identify purinergic receptor antagonists that inhibit HIV-1 membrane fusion; these drugs are suspected to act through antagonizing Env-chemokine receptor interactions. They also appear to abrogate activity of downstream mediators that potentiate activation of the NLRP3 inflammasome pathway. Here we review the literature on purinergic receptors, the drugs that inhibit their function, and the evidence implicating these receptors in HIV-1 entry.

The P2X7 receptor mediates NLRP3-dependent IL-1β secretion and promotes phagocytosis in the macrophage response to Treponema pallidum

It is unclear whether P2X7 receptor (P2X7R) mediates NOD-like receptor family protein 3 (NLRP3)-dependent IL-1β secretion and spirochete phagocytosis in syphilis. This study was conducted to investigate the role of P2X7R in modifying NLRP3-dependent IL-1β secretion and regulating phagocytosis by Treponema pallidum (T. pallidum)-induced macrophages. Macrophages derived from a human acute monocytic leukemia cell line were cultured with T. pallidum. The activation of P2X7R in T. pallidum-treated macrophages occurred in a dose- and time-dependent manner. The P2X7R silencing group showed significantly decreased NLRP3 mRNA and protein levels (vs. the Tp group, P < 0.001). Similar results were observed for IL-1β secretion using ELISA (vs. the Tp group, P < 0.001). Furthermore, P2X7R siRNA transfection significantly decreased the percentage of spirochete-positive macrophages (29.73% vs. 70.83%, P < 0.001) and spirochete internalization (mean fluorescence intensity (MFI), 9.20 vs. 19.39, P < 0.001). This finding revealed that P2X7R played a role in the induction of NLRP3-dependent IL-1β secretion by T. pallidum-induced macrophages. Furthermore, we found that P2X7R plays an important role in IL-1β secretion and in the promotion of T. pallidum phagocytosis by macrophages. These results may not only contribute to our understanding of the immune mechanism that is active during T. pallidum infection but may also lay the groundwork for strategies to combat syphilis.

Positively Charged Residues in the Head Domain of P2X4 Receptors Assist the Binding of ATP

P2X receptors are a family of trimeric cationic channels located in the membrane of mammalian cells. They open in response to the binding of ATP. The differences between the closed and open structures have been described in detail for some members of the family. However, the order in which the conformational changes take place as ATP enters the binding cleft, and the residues involved in the intermediate stages, are still unknown. Here, we present the results of umbrella sampling simulations aimed to elucidate the sequence of conformational changes that occur during the reversible binding of ATP to the P2X4 receptor. The simulations also provided information about the interactions that develop in the course of the process. In particular, they revealed the existence of a metastable state which assists the binding. This state is stabilized by positively charged residues located in the head domain of the receptor. Based on these findings, we propose a novel mechanism for the capture of ATP by P2X4 receptors.

Association of P2RX7 functional variants with localized aggressive periodontitis

OBJECTIVE

The purpose of this study was to investigate involvement of the P2X7 receptor in the rare condition, localized aggressive periodontitis.

MATERIAL AND METHODS

Peripheral blood from 220 African Americans (103 with localized aggressive periodontitis and 117 healthy unrelated controls) was stimulated with lipopolysaccharide from E coli and Porphyromonas gingivalis. P2RX7 single nucleotide polymorphisms rs208294 (H155Y), rs1718119 (T348A), rs2230911 (T357S) and rs3751143 (E496A) were genotyped in 103 localized aggressive periodontitis patients and 117 healthy unrelated subjects. We examined genetic association between four P2RX7 single nucleotide polymorphisms and localized aggressive periodontitis, and tested for correlations between the single nucleotide polymorphisms and inflammatory response to lipopolysaccharide in blood samples from these patients.

RESULTS

A significant association with localized aggressive periodontitis was observed with rs1718119 A (Thr) allele (P = 0.0063, odds ratio = 1.904) and with a haplotype containing this allele (P = 0.0075). Additionally, significant correlations with these data were found: the rs1718119 G allele correlated with greater production of IL-6, IL-2 and GM-CSF; the C (His) allele of rs208294 correlated with lower levels of IL-12p40; and the C (Thr) allele of rs2230911 correlated with greater levels of G-CSF.

CONCLUSION

The data from these analyses support a possible biological relationship between P2RX7 genetic variants and inflammatory response in localized aggressive periodontitis patients.

High glucose inhibits osteogenic differentiation and proliferation of MC3T3‑E1 cells by regulating P2X7

Diabetes mellitus adversely affects human bones and increases the risk of developing osteoporosis. In the present study, treatment with 30 mmol/l glucose was used to establish a high glucose (HG) cell model in vitro. Plasmids were used to overexpress the P2X purinoceptor 7 (P2X7) gene. Brilliant blue G and (4‑benzoyl‑benzoyl)‑ATP were used as a P2X7 antagonist and agonist, respectively. Proliferation of osteogenic MC3T3‑E1 cells and alkaline phosphatase (ALP) activity were determined using MTT and colorimetric assays, respectively. Alizarin Red S was used to assess calcification of MC3T3‑E1 cells. Western blotting and reverse transcription‑quantitative PCR were performed to determine protein and mRNA expression levels. The results demonstrated that HG inhibited MC3T3‑E1 cell proliferation and P2X7 expression, reduced calcification, and downregulated the expression levels of ALP and osteocalcin (Ocn) in MC3T3‑E1 cells. Overexpression of P2X7 in HG conditions increased calcification and proliferation, and upregulated the levels of ALP and Ocn in MC3T3‑E1 cells. Inhibition of P2X7 downregulated the expressions of ALP and Ocn in MC3T3‑E1 cells under HG conditions. Therefore, the present results indicated that HG caused damage to osteogenic MC3T3‑E1 cells. Thus, P2X7 may be a regulatory factor that may be used to counteract the effects of HG on osteogenesis.

MSU Crystals induce sterile IL-1β secretion via P2X7 receptor activation and HMGB1 release

BACKGROUD

The mechanism by which monosodium urate (MSU) crystals induce inflammation is not completely understood. Few studies have shown that MSU is capable of stimulating the release of IL-1β in the absence of LPS treatment. The purinergic P2X7 receptor is involved in the release of IL-1β in inflammatory settings caused by crystals, as is the case in silicosis.

METHODS

We investigated the role of P2X7 receptor in sterile MSU-induced inflammation by evaluating peritonitis and paw edema. In in vitro models, we performed the experiments using peritoneal macrophages and THP-1 cells. We measured inflammatory parameters using ELISA and immunoblotting. We measured cell recruitment using cell phenotypic identification and hemocytometer counts.

RESULTS

Our in vivo data showed that animals without P2X7 receptors generated less paw edema, less cell recruitment, and lower levels of IL-1β release in a peritonitis model. In the in vitro model, we observed that MSU induced dye uptake by the P2X7 receptor. In the absence of the receptor, or when it was blocked, MSU crystals induced less IL-1β release and this effect corresponded to the concentration of extracellular ATP. Moreover, MSU treatment induced HMGB1 release; pre-treatment with P2X7 antagonist reduced the amount of HMGB1 in cell supernatants.

CONCLUSIONS

IL-1β secretion induced by MSU depends on P2X7 receptor activation and involves HMGB1 release.

GENERAL SIGNIFICANCE

We propose that cell activation caused by MSU crystals induces peritoneal macrophages and THP-1 cells to release ATP and HMGB1, causing IL-1β secretion via P2X7 receptor activation.

Antagonistic role of IL-1ß and NLRP3/IL-18 genetics in chronic HIV-1 infection

Host genetics affects both susceptibility and progression of HIV-1 infection. NLRP3 inflammasome provides a first-line defense in viral infections, and, accordingly, gain-of-function variants in NLRP3 have been associated with protection against HIV-1. Despite antiretroviral treatment (ART), HIV-infected patients continue to present systemic inflammation with a heterogeneous prognosis. As NLRP3 inflammasome is involved in several chronic diseases by amplifying "sterile" inflammation, its role in chronic phase of HIV infection has been postulated. Little is known about inflammasome genetics in HIV-infected patients and whether it may play a role in the different clinical outcomes. Therefore, we questioned whether NLRP3 inflammasome genetics could affect the clinical course of HIV-1 infection as it does in host/virus interaction. For this purpose, we analyzed selected single nucleotide polymorphisms (SNPs) in ART-treated HIV-infected patients (n = 300), in Long Term Non-Progressors/Elite Controllers and progressors (n = 133), and in HIV-infected individuals submitted to dendritic cell (DC)-based immunotherapy (n = 19). SNPs leading to increased activation of NLRP3 inflammasome are beneficial for patients, while SNPs that negatively affect NLRP3 activation or IL-18 production, detrimental. In contrast, gain-of-function variant in IL1B is also detrimental for patients, suggesting that while IL-1ß possible contributes to immune exhaustion, the axis NLRP3-inflammasome/IL-18 could act positively in chronic infection. Functional assays supported genetic results: NLRP3 variants associated with good quality HIV+ DC, and IL1B -511C > T with a poor one. Loss-of-function SNPs affect HIV+ T cells proliferation. These findings proposed for the first time that NLRP3 inflammasome, mainly through IL-18, play a protective role in chronic HIV infection.

The Host Immune System Facilitates Disseminated Staphylococcus aureus Disease Due to Phagocytic Attraction to Candida albicans during Coinfection: a Case of Bait and Switch

Invasive Staphylococcus aureus infections account for 15 to 50% of fatal bloodstream infections annually. These disseminated infections often arise without a defined portal of entry into the host but cause high rates of mortality. The fungus Candida albicans and the Gram-positive bacterium S. aureus can form polymicrobial biofilms on epithelial tissue, facilitated by the C. albicans adhesin encoded by ALS3 While a bacterium-fungus interaction is required for systemic infection, the mechanism by which bacteria disseminate from the epithelium to internal organs is unclear. In this study, we show that highly immunogenic C. albicans hyphae attract phagocytic cells, which rapidly engulf adherent S. aureus and subsequently migrate to cervical lymph nodes. Following S. aureus-loaded phagocyte translocation from the mucosal surface, S. aureus produces systemic disease with accompanying morbidity and mortality. Our results suggest a novel role for the host in facilitating a bacterium-fungus infectious synergy, leading to disseminated staphylococcal disease.

P2X7 Interactions and Signaling - Making Head or Tail of It

Extracellular adenine nucleotides play important roles in cell-cell communication and tissue homeostasis. High concentrations of extracellular ATP released by dying cells are sensed as a danger signal by the P2X7 receptor, a non-specific cation channel. Studies in P2X7 knockout mice and numerous disease models have demonstrated an important role of this receptor in inflammatory processes. P2X7 activation has been shown to induce a variety of cellular responses that are not usually associated with ion channel function, for example changes in the plasma membrane composition and morphology, ectodomain shedding, activation of lipases, kinases, and transcription factors, as well as cytokine release and apoptosis. In contrast to all other P2X family members, the P2X7 receptor contains a long intracellular C-terminus that constitutes 40% of the whole protein and is considered essential for most of these effects. So far, over 50 different proteins have been identified to physically interact with the P2X7 receptor. However, few of these interactions have been confirmed in independent studies and for the majority of these proteins, the interaction domains and the physiological consequences of the interactions are only poorly described. Also, while the structure of the P2X7 extracellular domain has recently been resolved, information about the organization and structure of its C-terminal tail remains elusive. After shortly describing the structure and assembly of the P2X7 receptor, this review gives an update of the identified or proposed interaction domains within the P2X7 C-terminus, describes signaling pathways in which this receptor has been involved, and provides an overlook of the identified interaction partners.

Association between P2X7 Polymorphisms and Susceptibility to Tuberculosis: An Updated Meta-Analysis of Case-Control Studies

Background and Objectives: Several studies inspected the impact of P2X7 polymorphisms on individual susceptibility to tuberculosis (TB), but the findings are still controversial and inconclusive. To achieve a more precise estimation, we conducted a meta-analysis of all eligible studies on the association between P2X7 polymorphisms and TB risk. Materials and Methods: Relevant studies were identified by searching the PubMed, Web of Science, Scopus and Google scholar databases up to November 2018. Twenty-four full-text articles were included in our meta-analysis. The strength of association between P2X7 polymorphisms and TB risk was evaluated by odds ratios (ORs) and 95% confidence intervals (95% CIs) under five genetic models. Results: The findings of this meta-analysis revealed that the rs3751143 variant significantly increased the risk of TB in heterozygous codominant (OR = 1.44, 95%CI = 1.17-1.78, p = 0.0006, AC vs. AA), homozygous codominant (OR = 1.87, 95% CI = 1.40-2.49, p = 0.0004, CC vs. AA), dominant (OR = 1.50, 95% CI = 1.22-1.85, p = 0.0002, AC + CC vs. AA), recessive (OR = 1.61, 95% CI = 1.25-2.07, p = 0.001, CC vs. AC + AA), and allele (OR = 1.41, 95% CI = 1.19-1.67, p < 0.0001, C vs. A) genetic models. Stratified analysis showed that rs3751143 increased the risk of pulmonary tuberculosis (PTB) and extrapulmonary tuberculosis (EPTB) in all genetic models. Furthermore, the rs3751143 increased risk of TB in the Asian population. The findings did not support an association between the rs2393799, rs1718119, rs208294, rs7958311, and rs2230911 polymorphisms of P2X7 and TB risk. Conclusions: The findings of this meta-analysis suggest that P2X7 rs3751143 polymorphism may play a role in susceptibility to TB in the Asian population. More well-designed studies are required to elucidate the exact role of P2X7 polymorphisms on TB development.

P2X7 receptor in cardiovascular disease: The heart side

The P2X7 receptor is a ligand-gated purinergic receptor activated by extracellular ATP. The receptor is highly expressed in immune cells and in the brain, and, upon activation, the P2X7 receptor allows a cation flux, leading to the distinct activation of intracellular signalling pathways as the secretion of pro-inflammatory cytokines, and modulation of cell survival. Through these molecular mechanisms, P2X7 is known to play important roles in physiology and pathophysiology of a wide spectrum of diseases, including cancer, inflammatory diseases, neurological, respiratory and more recently cardiovascular diseases. Recent studies demonstrated that the P2X7 could modulate the assembly of the NLRP3 inflammasome, leading to the secretion of pro-inflammatory factors and worsen the cardiac disease phenotypes. This review discusses the critical molecular function of P2X7 in the modulation of the onset, progression and resolution of cardiovascular diseases and analyses the putative future use of P2X7-based therapies that modulate the IL-1β secretion arm and direct P2X7 antagonists.

Brucella abortus nitric oxide metabolite regulates inflammasome activation and IL-1β secretion in murine macrophages

NLRP3 inflammasome is a protein complex crucial to caspase-1 activation and IL-1β and IL-18 maturation. This receptor participates in innate immune responses to different pathogens, including the bacteria of genus Brucella. Our group recently demonstrated that Brucella abortus-induced IL-1β secretion involves NLRP3 inflammasome and it is partially dependent on mitochondrial ROS production. However, other factors could be involved, such as P2X7-dependent potassium efflux, membrane destabilization, and cathepsin release. Moreover, there is increasing evidence that nitric oxide acts as a modulator of NLRP3 inflammasome. The aim of this study was to unravel the mechanism of NLRP3 inflammasome activation induced by B. abortus, as well as the involvement of bacterial nitric oxide (NO) as a modulator of this inflammasome pathway. We demonstrated that NO produced by B. abortus can be used by the bacteria to modulate IL-1β secretion in infected murine macrophages. Additionally, our results suggest that B. abortus-induced IL-1β secretion depends on a P2X7-independent potassium efflux, lysosomal acidification, cathepsin release, mechanisms clearly associated to NLRP3 inflammasome. In summary, our results help to elucidate the molecular mechanisms of NLRP3 activation and regulation during an intracellular bacterial infection.

Charge Discrimination in P2X4 Receptors Occurs in Two Consecutive Stages

P2X receptors are a group of trimeric cationic channels that are activated by adenosine 5'-triphosphate. They perform critical roles in the membranes of mammalian cells, and their improper functioning is associated with numerous diseases. Despite the vast amount of research devoted to them, several aspects of their operation are currently unclear, including the causes of their charge selectivity. We present the results of molecular dynamics simulation, which shed light on this issue for the case of P2X₄ channels. We examined in detail the behavior of Na⁺ and Cl^- ions inside the receptor. The examination reveals that charge discrimination occurs in two stages. First, cations bear precedence over anions to enter the extracellular vestibule. Then, cations at the extracellular vestibule are more likely to cross the pore than anions in an equivalent position. In this manner, a thorough but straightforward analysis of computational simulations suggests a stepwise mechanism, without a unique determinant factor.

ATPe Dynamics in Protozoan Parasites. Adapt or Perish

In most animals, transient increases of extracellular ATP (ATPe) are used for physiological signaling or as a danger signal in pathological conditions. ATPe dynamics are controlled by ATP release from viable cells and cell lysis, ATPe degradation and interconversion by ecto-nucleotidases, and interaction of ATPe and byproducts with cell surface purinergic receptors and purine salvage mechanisms. Infection by protozoan parasites may alter at least one of the mechanisms controlling ATPe concentration. Protozoan parasites display their own set of proteins directly altering ATPe dynamics, or control the activity of host proteins. Parasite dependent activation of ATPe conduits of the host may promote infection and systemic responses that are beneficial or detrimental to the parasite. For instance, activation of organic solute permeability at the host membrane can support the elevated metabolism of the parasite. On the other hand ecto-nucleotidases of protozoan parasites, by promoting ATPe degradation and purine/pyrimidine salvage, may be involved in parasite growth, infectivity, and virulence. In this review, we will describe the complex dynamics of ATPe regulation in the context of protozoan parasite⁻host interactions. Particular focus will be given to features of parasite membrane proteins strongly controlling ATPe dynamics. This includes evolutionary, genetic and cellular mechanisms, as well as structural-functional relationships.

Purinergic receptors and neglected tropical diseases: why ignore purinergic signaling in the search for new molecular targets?

Purinergic receptors are widespread in the human organism and are involved in several physiological functions like neurotransmission, nociception, platelet aggregation, etc. In the immune system, they may regulate the expression and release of pro-inflammatory factors as well as the activation and death of several cell types. It is already described the participation of some purinergic receptors in the inflammation and pathological processes, such as a few neglected tropical diseases (NTDs) which affect more than 1 billion people in the world. Although the high social influence those diseases represent endemic countries, most of them do not have an efficient, safe or affordable drug treatment. In that way, this review aims to discuss the current literature involving purinergic receptor and immune response to NTDs pathogens, which may contribute in the search for new therapeutic possibilities.

The Elusive P2X7 Macropore

ATP, which is released under pathological conditions and is considered a damage-associated molecular pattern (DAMP), activates P2X7 receptors (P2X7Rs), trimeric plasma membrane ion channels selective for small cations. P2X7Rs are partners in NOD-like receptor containing a pyrin (NLRP3) inflammasome activation and promoters of tumor cell growth. P2X7R overstimulation triggers the ATP-dependent opening of a nonselective plasma membrane pore, known as a 'macropore', which allows fluxes of large hydrophilic molecules. The pathophysiological functions of P2X7R are thought to be dependent on activation of this conductance pathway, yet its molecular identity is unknown. Recent reports show that P2X7R permeability to organic solutes is an early and intrinsic property of the channel itself. A better understanding of P2X7R-dependent changes in plasma membrane permeability will allow a rationale development of novel anti-inflammatory and anticancer drugs.

Lower activation of caspase-1 by Staphylococcus epidermidis isolated from prosthetic joint infections compared to commensals

Nosocomial sequence types of Staphylococcus epidermidis dominate in prosthetic joint infections. We examined caspase-1 activation in human neutrophils after incubation with Staphylococcus epidermidis isolated from prosthetic joint infections and normal skin flora. Active caspase-1 was lower after incubation with isolates from prosthetic joint infections than after incubation with commensal isolates. Both host and isolate dependent differences in active caspase-1 were noted. Our results indicate that there might be a host-dependent incapacity to elicit a strong caspase-1 response towards certain strains of S. epidermidis. Further experiments with a larger number of individuals are warranted.

P2X7 receptor mediates NLRP3-dependent IL-1β secretion and parasite proliferation in Toxoplasma gondii-infected human small intestinal epithelial cells

Background

Toxoplasma gondii can invade and replicate in all nucleated cells in a wide range of host species, and infection induces IL-1β production. IL-1β plays central roles in the stimulation of the innate immune system and inflammation. However, little is known of the innate immune responses in human fetal small intestinal epithelial cells (FHs 74 Int cells) after T. gondii infection.

Methods

FHs 74 Int cells were infected with the T. gondii GFP-RH strain. Then, IL-1β production and its mechanisms of action were evaluated using ELISA, MTT cell viability assays, Western blotting, immunofluorescence, quantitative real-time polymerase chain reaction (qRT-PCR), and gene-specific small interfering RNA (siRNA) transfection.

Results

Infection of FHs 74 Int cells by T. gondii triggered significant time- and dose-dependent IL-1β production. Although T. gondii activated NLRP1, NLRP3, NLRC4 and AIM2 inflammasomes in FHs 74 Int cells, NLRP3 levels were consistently and significantly time-dependently increased, while the other inflammasomes were not. Transfection with siRNA targeting NLRP3, cleaved caspase-1 (Casp-1) or ASC significantly reduced T. gondii-induced IL-1β production, whereas T. gondii proliferation was markedly increased. Toxoplasma gondii infection activated P2X7 receptor (P2X7R) levels in FHs 74 Int cells in a time-dependent manner; however, transfection with siRNA targeting P2X7R significantly reduced T. gondii-induced IL-1β secretion and substantially increased T. gondii proliferation, which is mediated by decreased protein expression levels of NLRP3, cleaved Casp-1 and ASC. Collectively, NLRP3-dependent IL-1β secretion is mediated by P2X7R in small intestinal epithelial cells in response to T. gondii infection, thereby controlling parasite proliferation.

Conclusions

This study revealed that the P2X7R/NLRP3 pathway plays important roles in IL-1β secretion and inhibition of T. gondii proliferation in small intestinal epithelial cells. These results not only contribute to our understanding of the mucosal immune mechanisms of T. gondii infection but also offer new insight into the identification of innate resistance in the gut epithelium.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2573-y) contains supplementary material, which is available to authorized users.

P2X7 Receptor-Associated Programmed Cell Death in the Pathophysiology of Hemorrhagic Stroke

Hemorrhagic stroke is a life-threatening disease characterized by a sudden rupture of cerebral blood vessels, and cell death is widely believed to occur after exposure to blood metabolites or subsequently damaged cells. Recently, programmed cell death, such as apoptosis, autophagy, necroptosis, pyroptosis, and ferroptosis, has been demonstrated to play crucial roles in the pathophysiology of stroke. However, the detailed mechanisms of these novel kinds of cell death are still unclear. The P2X7 receptor, previously known for its cytotoxic activity, is an ATP-gated, nonselective cation channel that belongs to the family of ionotropic P2X receptors. Evolving evidence indicates that the P2X7 receptor plays a pivotal role in central nervous system pathology; genetic deletion and pharmacological blockade of the P2X7 receptor provide neuroprotection in various neurological disorders, including intracerebral hemorrhage and subarachnoid hemorrhage. The P2X7 receptor may regulate programmed cell death via (I) exocytosis of secretory lysosomes, (II) exocytosis of autophagosomes or autophagolysosomes during formation of the initial autophagic isolation membrane or omegasome, and (III) direct release of cytosolic IL-1β secondary to regulated cell death by pyroptosis or necroptosis. In this review, we present an overview of P2X7 receptor- associated programmed cell death for further understanding of hemorrhagic stroke pathophysiology, as well as potential therapeutic targets for its treatment.

Silencing of P2X7R by RNA interference in the hippocampus can attenuate morphological and behavioral impact of pilocarpine-induced epilepsy

Cell signaling mediated by P2X7 receptors (P2X7R) has been suggested to be involved in epileptogenesis, via modulation of intracellular calcium levels, excitotoxicity, activation of inflammatory cascades, and cell death, among other mechanisms. These processes have been described to be involved in pilocarpine-induced status epilepticus (SE) and contribute to hyperexcitability, resulting in spontaneous and recurrent seizures. Here, we aimed to investigate the role of P2X7R in epileptogenesis in vivo using RNA interference (RNAi) to inhibit the expression of this receptor. Small interfering RNA (siRNA) targeting P2X7R mRNA was injected into the lateral ventricles (icv) 6 h after SE. Four groups were studied: Saline-Vehicle, Saline-siRNA, Pilo-Vehicle, and Pilo-siRNA. P2X7R was quantified by western blotting and neuronal death assessed by Fluoro-Jade B histochemistry. The hippocampal volume (edema) was determined 48 h following RNAi. Behavioral parameters as latency to the appearance of spontaneous seizures and the number of seizures were determined until 60 days after the SE onset. The Saline-siRNA and Pilo-siRNA groups showed a 43 and 37% reduction, respectively, in P2X7R protein levels compared to respective vehicle groups. Neuroprotection was observed in CA1 and CA3 of the Pilo-siRNA group compared to Pilo-Vehicle. P2X7R silencing in pilocarpine group reversed the increase in the edema detected in the hilus, suprapyramidal dentate gyrus, CA1, and CA3; reduced mortality rate following SE; increased the time to onset of spontaneous seizure; and reduced the number of seizures, when compared to the Pilo-Vehicle group. Therefore, our data highlights the potential of P2X7R as a therapeutic target for the adjunct treatment of epilepsy.

P2X7 receptor in spinal tuberculosis: Gene polymorphisms and protein levels in Chinese Han population

Spinal tuberculosis (TB) accounts for 1%-5% of all TB infections. Host genetic variation influences susceptibility to Mycobacterium tuberculosis (MTB). P2X7 receptor (P2X7R) expressed on cells has been identified as a regulatory molecule in cell death/apoptosis, killing of intercellular pathogens, and bone turnover. This study investigated the P2X7 gene polymorphisms and protein levels in spinal TB. P2X7 gene -762C>T and 489C>T polymorphisms were genotyped. The expression of P2X7R in bone or intervertebral disc (ID) tissues was analyzed by Western blot assay. The -762C>T and 489C>T polymorphisms were associated with susceptibility to spinal TB. Having the -762CC genotype and -762C allele increased the risk of developing spinal TB (CC vs. TT: P=0.031, OR [95%CI]=1.865 [1.053-3.304]; C vs. T: P=0.028, OR [95%CI]=1.355 [1.034-1.775]). The presence of the 489T allele was associated with an increased risk of developing spinal TB (TT vs. CC: P=0.004, OR [95%CI]=2.248 [1.283-3.939]; CT vs. CC: P=0.044, OR [95%CI]=1.755 [1.011-3.047]; T vs. C: P=0.004, OR [95%CI]=1.482 [1.134-1.936]; TT+CT vs. CC: P=0.010, OR [95%CI]=1.967 [1.171-3.304]; TT vs. CT+CC: P=0.037, OR [95%CI]=1.489 [1.023-2.167]). The expression of P2X7R in TB-induced bone lesions increased significantly among spinal TB patients (t=0.011). Carrying the P2X7 -762CC genotype and 489T allele is associated with an increased risk of developing spinal TB in a Southern Chinese Han population.

The P2X7 Receptor in Infection and Inflammation

Adenosine triphosphate (ATP) accumulates at sites of tissue injury and inflammation. Effects of extracellular ATP are mediated by plasma membrane receptors named P2 receptors (P2Rs). The P2R most involved in inflammation and immunity is the P2X7 receptor (P2X7R), expressed by virtually all cells of innate and adaptive immunity. P2X7R mediates NLRP3 inflammasome activation, cytokine and chemokine release, T lymphocyte survival and differentiation, transcription factor activation, and cell death. Ten human P2RX7 gene splice variants and several SNPs that produce complex haplotypes are known. The P2X7R is a potent stimulant of inflammation and immunity and a promoter of cancer cell growth. This makes P2X7R an appealing target for anti-inflammatory and anti-cancer therapy. However, an in-depth knowledge of its structure and of the associated signal transduction mechanisms is needed for an effective therapeutic development.

Antimicrobial peptide-gold nanoscale therapeutic formulation with high skin regenerative potential

Chronic skin wounds affect ≈3% of persons aged >60years (Davies et al., 2007) [1]. These wounds are typically difficult to heal by conventional therapies and in many cases they get infected making even harder the regeneration process. The antimicrobial peptide (AMP) LL37 combines antimicrobial with pro-regenerative properties and thus represents a promising topical therapy to address both problems. Here, we investigated the wound healing potential of soluble and immobilized LL37 (LL37-conjugated gold nanoparticles, LL37-Au NPs), both in vitro (migration of keratinocytes) and in vivo (skin wound healing). Our results show that LL37-Au NPs, but not LL37 peptide, have the capacity to prolong the phosphorylation of EGFR and ERK1/2 and enhance the migratory properties of keratinocytes in a large in vitro wound model. We further report that both LL37 and LL37-Au NPs promote keratinocyte migration by the transactivation of EGFR, a process that seems to be initiated at the P2X7 receptor, as confirmed by chemical and genetic inhibition studies. Finally, we show in vivo that LL37-Au NPs have higher wound healing activity than LL37 peptide in a splinted mouse full thickness excisional model. Animal wounds treated by LL37-Au NPs have higher expression of collagen, IL6 and VEGF than the ones treated with LL37 peptide or NPs without LL37. Altogether, the conjugation of AMPs to NPs offers a promising platform to enhance their pro-regenerative properties.