P2X7 receptor: A potential therapeutic target for autoimmune diseases

P2Y2 receptor antagonism resolves sialadenitis and improves salivary flow in a Sjögren's syndrome mouse model

OBJECTIVE

Sjögren's syndrome (SS) is a chronic autoimmune exocrinopathy characterized by lymphocytic infiltration of the salivary and lacrimal glands and decreased saliva and tear production. Previous studies indicate that the G protein-coupled P2Y₂ nucleotide receptor (P2Y₂R) is upregulated in numerous models of salivary gland inflammation (i.e., sialadenitis), where it has been implicated as a key mediator of chronic inflammation. Here, we evaluate both systemic and localized P2Y₂R antagonism as a means to resolve sialadenitis in the NOD.H-2^h4,IFNγ^-/-,CD28^-/- (NOD.H-2^h4 DKO) mouse model of SS.

DESIGN

Female 4.5 month old NOD.H-2^h4 DKO mice received daily intraperitoneal injections for 10 days of the selective P2Y₂R antagonist, AR-C118925, or vehicle-only control. Single-dose localized intraglandular antagonist delivery into the Wharton's duct was also evaluated. Carbachol-induced saliva was measured and then submandibular glands (SMGs) were isolated and either fixed and paraffin-embedded for H&E staining, homogenized for RNA isolation or dissociated for flow cytometry analysis.

RESULTS

Intraperitoneal injection, but not localized intraglandular administration, of AR-C118925 significantly enhanced carbachol-induced salivation and reduced lymphocytic foci and immune cell markers in SMGs of 5 month old NOD.H-2^h4 DKO mice, compared to vehicle-injected control mice. We found that B cells represent the primary immune cell population in inflamed SMGs of NOD.H-2^h4 DKO mice that express elevated levels of P2Y₂R compared to C57BL/6 control mice. We further demonstrate a role for P2Y₂Rs in mediating B cell migration and the release of IgM.

CONCLUSION

Our findings suggest that the P2Y₂R represents a novel therapeutic target for the treatment of Sjögren's syndrome.

P2X7 receptor signaling promotes inflammation in renal parenchymal cells suffering from ischemia-reperfusion injury

Extracellular adenosine triphosphate (ATP) and its receptor, P2X7 receptor (P2X7R), are playing an important role in the pathological process of renal ischemia-reperfusion injury, but their underlying mechanism remains unclear. Also, the effects of tubular epithelium-expressed P2X7 receptor on ischemia acute kidney injury is still unknown. The aim of this study is to clarify if this mechanism involves the activation of nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome in the renal tubular epithelial cells. In our research, we used male C57BL/6 wild type and P2X7R (−/−) mice, cultured human proximal tubular epithelial cells, and kidneys from acute kidney injury patients. Mice underwent for unilateral nephrectomy combined with the lateral renal pedicle clamping. Cultured cells were subjected to hypoxia/reoxygenation or ATP. Apyrase and A438079 were used to block the extracellular ATP/P2X7 receptor pathway. We also constructed radiation-induced bone marrow (BM) chimeras by using P2X7R (−/−) mice and P2X7R (+/+) wild-type mice. P2X7 receptor deficiency protected from renal ischemia-reperfusion injury and attenuated the formation of NLRP3 inflammasome. By using BM chimeras, we found a partial reduction of serum creatinine and less histological impairment in group wild-type BM to P2X7R (−/−) recipient, compared with group wild-type BM to wild-type recipient. In renal tubular epithelial cells, hypoxia/reoxygenation induced ATP release and extracellular ATP depletion reduced the expression of active IL-1β. ATP activated the NLRP3 inflammasome in renal tubular epithelial cells, which were blunted by transient silence of P2X7 receptor, as well as by P2X7 receptor blocking with A438079. In human samples, we found that patients with Stage 3 AKI had higher levels of P2X7 receptor expression than patients with Stage 1 or Stage 2. Extracellular ATP/P2X7 receptor axis blocking may protect renal tubular epithelial cells from ischemia-reperfusion injury through the regulation of NLRP3 inflammasome.

Design, Synthesis, and in vitro Evaluation of P2X7 Antagonists

The P2X7 receptor is a promising target for the treatment of various diseases due to its significant role in inflammation and immune cell signaling. This work describes the design, synthesis, and in vitro evaluation of a series of novel derivatives bearing diverse scaffolds as potent P2X7 antagonists. Our approach was based on structural modifications of reported (adamantan-1-yl)methylbenzamides able to inhibit the receptor activation. The adamantane moieties and the amide bond were replaced, and the replacements were evaluated by a ligand-based pharmacophore model. The antagonistic potency of the synthesized analogues was assessed by two-electrode voltage clamp experiments, using Xenopus laevis oocytes that express the human P2X7 receptor. SAR studies suggested that the replacement of the adamantane ring by an aryl-cyclohexyl moiety afforded the most potent antagonists against the activation of the P2X7 cation channel, with analogue 2-chloro-N-[1-(3-(nitrooxymethyl)phenyl)cyclohexyl)methyl]benzamide (56) exhibiting the best potency with an IC₅₀ value of 0.39 μM.

P2X7 Receptor (P2X7R) of Microglia Mediates Neuroinflammation by Regulating (NOD)-Like Receptor Protein 3 (NLRP3) Inflammasome-Dependent Inflammation After Spinal Cord Injury

Background

Microglia participate in mediating neuroinflammation in which P2X7R triggered by adenosine triphosphate has a critical effect after spinal cord injury. However, how the P2X7R of microglia regulate neuroinflammation after spinal cord injury is still unclear.

The aim of this study was to explore the mechanism by which the P2X7 receptor of microglia regulates neuroinflammation after spinal cord injury in NLRP3 inflammasome-dependent inflammation.

Material/Methods

Sixt rats were divided into 5 groups: a sham group, a model group, a BzATP group, an A-438079 group, and a BzATP+CY-09 group. Rats in the sham group were only subjected to laminectomy and rats in the other groups were subjected to spinal cord injury followed by treatment with physiological saline, BzATP, A-438079, and BzATP following CY-09, separately. Real-time polymerase chain reaction, Western blot, immunofluorescence staining, and enzyme-linked immunosorbent assay were used to analyze the scientific hypothesis.

Results

(i) P2X7R of microglia was upregulated and downregulated by BzATP, and A-438079 was upregulated after spinal cord injury. (ii) Upregulation of P2X7R on microglia is coincident with increase of neuroinflammation after spinal cord injury. (iii) P2X7R of microglia participates in spinal cord-mediated neuroinflammation via regulating NLRP3 inflammasome-dependent inflammation.

Conclusions

P2X7R of microglia in spinal cord mediates neuroinflammation by regulating NLRP3 inflammasome-dependent inflammation after spinal cord injury.

The P2X7 purinergic receptor: a potential therapeutic target for lung cancer

PURPOSE

Purinergic P2X7 receptor (P2X7R) is a gated ion channel for which adenosine triphosphate (ATP) is a ligand. Activated P2X7R is widely expressed in a variety of immune cells and tissues and is involved in a variety of physiological and pathological processes. Studies have confirmed that P2X7R is involved in the regulation of tumor cell growth, stimulating cell proliferation or inducing apoptosis. Recent studies have found that P2X7R is abnormally expressed in lung cancer and is closely related to the carcinogenesis and development of lung cancer. In this paper, we comprehensively describe the structure, function, and genetic polymorphisms of P2X7R. In particular, the role and therapeutic potential of P2X7R in lung cancer are discussed to provide new targets and new strategies for the treatment and prognosis of clinical lung cancer.

METHODS

The relevant literature on P2X7R and lung cancer from PubMed databases is reviewed in this article.

RESULTS

P2X7R regulates the function of lung cancer cells by activating multiple intracellular signaling pathways (such as the JNK, Rho, HMGB1 and EMT pathways), thereby affecting cell survival, growth, invasion, and metastasis and patient prognosis. Targeting P2X7R with inhibitors effectively suppresses the growth and metastasis of lung cancer cells.

CONCLUSION

In summary, P2X7R is expected to become a potential target for the treatment of lung cancer, and more clinical research is needed in the future to explore the effectiveness of P2X7R antagonists as treatments.

The Expression of P2X7 Receptor on Th1, Th17, and Regulatory T Cells in Patients with Systemic Lupus Erythematosus or Rheumatoid Arthritis and Its Correlations with Active Disease

P2X7 receptor (P2X7R) is highly expressed on immune cells, triggering the release of cytokines and regulating autoimmune responses. To investigate P2X7R surface expression on T helper (Th) 1, Th17, and regulatory T (Treg) cells in patients with systemic lupus erythematosus (SLE) or rheumatoid arthritis (RA) and correlations with disease activity, 29 SLE and 29 RA patients and 18 healthy controls (HCs) were enrolled. We showed that SLE and RA patients had significantly higher levels of plasma cytokines (IFN-γ, IL-1β, IL-6, IL-17A, and IL-23), frequencies of Th1 and Th17 cells, and expression of P2X7R on Th1 and Th17 than HCs, and the Th17/Treg ratio was significantly increased, whereas Treg cell levels were significantly decreased. The Ca²⁺ influx increase following BzATP stimulation was significantly higher in CD4⁺PBMCs from SLE and RA patients than in HCs. Blood levels of shed P2X7R were increased in SLE and RA patients. Furthermore, 28-joint Disease Activity Score and SLE Disease Activity Index score showed negative correlations with Treg cell levels and positive correlations with Th17/Treg ratio and Th17 cell P2X7R expression. Interestingly, Th17 cell P2X7R expression was closely correlated with IL-1β, C-reactive protein, the erythrocyte sedimentation rate, anticyclic citrullinated peptide Abs, albumin, and C4. These data indicate that increased Th17 cell P2X7R expression is functionally and positively related to disease activity and some inflammatory mediators in SLE and RA patients, and P2X7R could be critical in promoting the Th17 immune response and contributing to the complex pathogenesis of SLE and RA.

Recent advances in the NEK7-licensed NLRP3 inflammasome activation: Mechanisms, role in diseases and related inhibitors

The nucleotide-binding oligomerization domain (NOD)-like receptor containing pyrin domain 3 (NLRP3) inflammasome is a high-molecular-weight complex mediated by the activation of pattern-recognition receptors (PRRs) seed in innate immunity. Once NLRP3 is activated, the following recruitment of the adapter apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD) (ASC) and procaspase-1 would be initiated. Cleavage of procaspase-1 into active caspase-1 then leads to the maturation of the precursor forms of interleukin (IL)-1β and IL-18 into biologically active IL-1β and IL-18. The activation of NLRP3 inflammasome is thought to be tightly associated with a regulator never in mitosis A (NIMA)-related kinase 7 (NEK7), apart from other signaling events such as K⁺ efflux and reactive oxygen species (ROS). Plus, the NLRP3 inflammasome has been linked to various metabolic disorders, chronic inflammation and other diseases. In this review, we firstly describe the cellular/molecular mechanisms of the NEK7-licensed NLRP3 inflammasome activation. Then we detail the potential inhibitors that can selectively and effectively modulate either the NEK7-NLRP3 complex itself or the related molecular/cellular events. Finally, we describe some inhibitors as promising therapeutic strategies for diverse diseases driven by NLRP3 inflammasome.

Critical Role for the NLRP3 Inflammasome in Mediating IL-1β Production in Shigella sonnei-Infected Macrophages

Shigella is one of the leading bacterial causes of diarrhea worldwide, affecting more than 165 million people annually. Among the serotypes of Shigella, Shigella sonnei is physiologically unique and endemic in human immunodeficiency virus-infected men who have sex with men. The NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome, a protein complex composed of NLRP3, apoptosis-associated speck-like protein, and caspase-1, recognizes, and responds to pathogen infection and diverse sterile host-derived or environmental danger signals to induce IL-1β and IL-18 production. Although the Shigella flexneri-mediated activation of the NLRP3 inflammasome has been reported, the effect of S. sonnei on NLRP3 inflammasome activation remains unclear. We found that S. sonnei induced IL-1β production through NLRP3-dependent pathways in lipopolysaccharide-primed macrophages. A mechanistic study revealed that S. sonnei induced IL-1β production through P₂X₇ receptor-mediated potassium efflux, reactive oxygen species generation, lysosomal acidification, and mitochondrial damage. In addition, the phagocytosis of viable S. sonnei was important for IL-1β production. Furthermore, we demonstrated that NLRP3 negatively regulated phagocytosis and the bactericidal activity of macrophages against S. sonnei. These findings provide mechanistic insight into the activation of the NLRP3 inflammasome by S. sonnei in macrophages.

P2 Receptors as Therapeutic Targets in the Salivary Gland: From Physiology to Dysfunction

Although often overlooked in our daily lives, saliva performs a host of necessary physiological functions, including lubricating and protecting the oral cavity, facilitating taste sensation and digestion and maintaining tooth enamel. Therefore, salivary gland dysfunction and hyposalivation, often resulting from pathogenesis of the autoimmune disease Sjögren's syndrome or from radiotherapy of the head and neck region during cancer treatment, severely reduce the quality of life of afflicted patients and can lead to dental caries, periodontitis, digestive disorders, loss of taste and difficulty speaking. Since their initial discovery in the 1970s, P2 purinergic receptors for extracellular nucleotides, including ATP-gated ion channel P2X and G protein-coupled P2Y receptors, have been shown to mediate physiological processes in numerous tissues, including the salivary glands where P2 receptors represent a link between canonical and non-canonical saliva secretion. Additionally, extracellular nucleotides released during periods of cellular stress and inflammation act as a tissue alarmin to coordinate immunological and tissue repair responses through P2 receptor activation. Accordingly, P2 receptors have gained widespread clinical interest with agonists and antagonists either currently undergoing clinical trials or already approved for human use. Here, we review the contributions of P2 receptors to salivary gland function and describe their role in salivary gland dysfunction. We further consider their potential as therapeutic targets to promote physiological saliva flow, prevent salivary gland inflammation and enhance tissue regeneration.

Janus kinases (JAKs): The efficient therapeutic targets for autoimmune diseases and myeloproliferative disorders

The Janus kinases or JAKs are a family of intracellular tyrosine kinases that play an essential role in the signaling of numerous cytokines that have been implicated in the pathogenesis of autoimmune diseases and myeloproliferative disorders. JAKs are activated upon ligand induced receptor homo- or heterodimerization, which results in the immediate phosphorylation of tyrosine residues and the phosphotyrosines then serve as docking sites for cytoplasmic signal transducer and activator of transcription (STAT) proteins which become phosphorylated by the JAKs upon recruitment to the receptor complex. The phosphorylated STAT proteins dimerize and travel to the cellular nucleus, where they act as transcription factors. Interfering in the JAK-STAT pathway has yielded the only approved small molecule kinase inhibitors for immunological indications. Numerous medicinal chemistry studies are currently aimed at the design of novel and potent inhibitors for JAKs. Additionally, whether the second-generation inhibitors which possessed selectivity for JAKs are more efficient are under research. This Perspective summarizes the progress in the discovery and development of JAKs inhibitors, including the potential binding site and approaches for identifying small-molecule inhibitors, as well as future therapeutic perspectives in autoimmune diseases and myeloproliferative disorders are also put forward in order to provide reference and rational for the drug discovery of novel and potent JAKs inhibitors.

The role and pharmacological properties of the P2X7 receptor in neuropathic pain

Neuropathic Pain (NPP) is caused by direct or indirect damage to the nervous system and is a common symptom of many diseases. Clinically, drugs are usually used to suppress pain, such as (lidocaine, morphine, etc.), but the effect is short-lived, poor analgesia, and there are certain dependence and side effects. Therefore, the investigation of the treatment of NPP has become an urgent problem in medical, attracting a lot of research attention. P2X7 is dependent on Adenosine triphosphate (ATP) ion channel receptors and has dual functions for the development of nerve damage and pain. In this review, we explored the link between the P2X7 receptor (P2X7R) and NPP, providing insight into the P2X7R and NPP, discussing the pathological mechanism of P2 X7R in NPP and the biological characteristics of P2X7R antagonist inhibiting its over-expression for the targeted therapy of NPP.

P2X7 receptor antagonists for the treatment of systemic inflammatory disorders

P2X7 has continued to be a target of immense interest since it is implicated in several peripheral and central nervous system disorders that result from inflammation. This review primarily describes new P2X7 receptor antagonists that have been investigated and disclosed in patent applications or primary literature since 2015. While a crystal structure of the receptor to aid in the design of novel chemical structures remains elusive, many of the chemotypes that have been disclosed contain similarities, with an amide motif present in all series that have been explored to date. Several of the recent antagonists described are brain penetrant, and two compounds are currently in clinical trials for CNS indications. Additionally, brain penetrant PET ligands have been developed that aid in measuring target engagement and these ligands can potentially be used as biomarkers.

Effect of P2X7 receptor on tumorigenesis and its pharmacological properties

The occurrence and development of tumors is a multi-factor, multi-step, multi-gene pathological process, and its treatment has been the most difficult problem in the field of medicine today. Therefore, exploring the relevant factors involved in the pathogenesis of tumors, improving the diagnostic rate, treatment rate, and prognosis survival rate of tumors have become an urgent problem to be solved. A large number of studies have shown that the P2X7 receptor (P2X7R) and the tumor microenvironment play an important role in regulating the growth, apoptosis, migration and invasion of tumor cells. P2X7R is an ATP ligand-gated cationic channel receptor, which exists in most tissues of the human body. The main function of P2X7R is to regulate the relevant cells (such as macrophages, lymphocytes, and glial cells) to release damaging factors and induce apoptosis and cell death. In recent years, with continuous research and exploration of P2X7R, it has been found that P2X7R exists on the surface of most tumor cells and plays an important role in tumor pathogenesis. The activation of the P2X7R can open the ion channels on the tumor cell membrane (sodium ion, calcium ion influx and potassium ion outflow), trigger rearrangement of the cytoskeleton and changes in membrane fluidity, allow small molecule substances to enter the cell, activate enzymes and kinases in related signaling pathways in cells (such as PKA, PKC, ERK1/2, AKT, and JNK), thereby affecting the development of tumor cells, and can also indirectly affect the growth, apoptosis and migration of tumor cells through tumor microenvironment. At present, P2X7R has been widely recognized for its important role in tumorigenesis and development. In this paper, we give a comprehensive description of the structure and function of the P2X7R gene. We also clarified the concept of tumor microenvironment and its effect on tumors, discussed the relevant pathological mechanisms in the development of tumors, and revealed the intrinsic relationship between P2X7R and tumors. We explored the pharmacological properties of P2X7R antagonists or inhibitors in reducing its expression as targeted therapy for tumors.

Production, characterization, and application of a monoclonal antibody specific for the extracellular domain of human P2X7R

This paper focuses on the production of a high-affinity monoclonal antibody (mAb) that can efficiently detect and block purinergic ligand-gated ion channel 7 receptor (P2X7R). To achieve this goal, the extracellular domain of human P2X7R, P2X7R-ECD, was used as an immunogen for BALB/c mice, inducing them to produce spleen lymphocytes that were subsequently fused with myeloma cells. Screening of the resultant hybridoma clones resulted in the selection of one stable positive clone that produced a qualified mAb, named 4B3A4. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis demonstrated that the purity of the purified 4B3A4 mAb was above 85%, with prominent bands corresponding to molecular weights of 55 kDa (heavy chain) and 25 kDa (light chain), and the BCA assay showed that the concentration of the purified 4B3A4 mAb was 0.3 mg/mL. Western blot analysis revealed that the 4B3A4 mAb could specifically recognize and bind both P2X7R-ECD and the full-length P2X7R protein. Laser scanning confocal microscopy (LSCM) revealed that the 4B3A4 mAb specifically bound to P2X7R on the membrane of human peripheral blood mononuclear cells (PBMCs). P2X7R expression was significantly different between healthy individuals and people with certain cancers as determined by flow cytometry (FCM). In addition, the 4B3A4 mAb significantly reduced ATP-stimulated Ca²⁺ entry and YO-PRO-1 uptake, which indicated that the 4B3A4 mAb effectively blocked P2X7R activity. These data indicate that the 4B3A4 mAb can be further used as not only an antibody to detect cell surface P2X7R but also as a therapeutic antibody to target P2X7R-related signaling pathways.

Natural Products: Experimental Efficient Agents for Inflammatory Bowel Disease Therapy

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Inflammatory bowel disease (IBD) is a chronic, elusive disorder resulting in relapsing inflammation of intestine with incompletely elucidated etiology, whose two representative forms are ulcerative colitis (UC) and Crohn’s disease (CD). Accumulating researches have revealed that the individual genetic susceptibility, environmental risk elements, intestinal microbial flora, as well as innate and adaptive immune system are implicated in the pathogenesis and development of IBD. Despite remarkable progression of IBD therapy has been achieved by chemical drugs and biological therapies such as aminosalicylates, corticosteroids, antibiotics, anti-tumor necrosis factor (TNF)-α, anti-integrin agents, etc., healing outcome still cannot be obtained, along with inevitable side effects. Consequently, a variety of researches have focused on exploring new therapies, and found that natural products (NPs) isolated from herbs or plants may serve as promising therapeutic agents for IBD through antiinflammatory, anti-oxidant, anti-fibrotic and anti-apoptotic effects, which implicates the modulation on nucleotide- binding domain (NOD) like receptor protein (NLRP) 3 inflammasome, gut microbiota, intestinal microvascular endothelial cells, intestinal epithelia, immune system, etc. In the present review, we will summarize the research development of IBD pathogenesis and current mainstream therapy, as well as the therapeutic potential and intrinsic mechanisms of NPs in IBD.

ATP and adenosine: Role in the immunopathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a classic inflammatory autoimmune disease. Local joint destruction and extra-articular manifestations of RA deeply compromise the life quality of the affected patients. RA immunopathogenesis depends on continuous immunogenic activation in which the purinergic system participates. The purinergic system comprises the signaling and metabolism of purines such as adenosine triphosphate (ATP) and adenosine. ATP signaling is involved in the activation and maintenance of the inflammatory state of RA through the activation of P2X7 and the production of cytokines, which orchestrate the pathogenesis of RA. The breakdown of ATP through the CD39/CD73 axis produces adenosine, which mostly inhibits the inflammatory process through activation of specific P1 receptors. Adenosine is hydrolyzed by adenosine deaminase (ADA) that interacts with other molecules playing additional roles in this disease. This review explores the release, metabolism, and the effects of binding of ATP and adenosine to their respective receptors in the context of RA, as well as their potential use as biomarkers and therapeutic targets.