P2X1: a unique platelet receptor with a key role in thromboinflammation

Procoagulant Effect of Neutrophil Extracellular Traps, Activated Platelets, and Endothelial Cells in Patients After TAVR

BACKGROUND

Patients with severe aortic stenosis, undergoing transcatheter aortic valve replacement (TAVR), are more likely to develop thrombotic complications. However, the definite mechanisms underlying the hypercoagulation state remain unclear to date. Our objectives were to explore whether and how neutrophil extracellular traps (NETs) play a procoagulant role in patients after TAVR alone or TAVR with percutaneous coronary intervention within 1 year and further to evaluate their interactions with platelets and endothelial cells.

METHODS

The levels of plasma NETs, platelets, and endothelial cell activation markers were analyzed by ELISA. NET formation was observed by immunofluorescence. Procoagulant activity was measured by clotting time, fibrin, and TAT (thrombin-antithrombin) complex generation assays. Phosphatidylserine exposure on cells was assessed by flow cytometry.

RESULTS

Compared with pre-TAVR, controls, or severe aortic stenosis without TAVR patients, the plasma NET levels in patients after TAVR alone, especially TAVR with percutaneous coronary intervention, increased from 7 days, peaking at 3 months, and then gradually decreased until the 12th month. Furthermore, neutrophils and plasma from patients post-TAVR are more prone to promote NET formation; NETs from these patients markedly decreased clotting time and increased fibrin and TAT generation. Additionally, a high concentration of NETs induced platelet aggregation and exerted a strong cytotoxic effect on endothelial cells and transformed them into a procoagulant phenotype.

CONCLUSIONS

These results lead us to believe that NETs contribute to the hypercoagulability in patients post-TAVR. Our study may provide a new target for preventing thrombotic complications in patients post-TAVR by blocking NET generation.

First evidence of Tityus confluens Borelli, 1899 (Buthidae) venom altering purine metabolism in rat blood cells

Purinergic signaling pathways play crucial roles in regulating hemostatic and inflammatory responses, both of which are impacted by scorpion envenomation. Scorpion venoms are complex mixtures of various toxins, such as peptides, enzymes, and nucleotides. Previous research showed that the action of scorpion toxins on the purinergic system stems from their effects on purinergic receptors. Additionally, a study identified a putative ectonucleotidase in scorpion venom. This study aimed to investigate the ability of Tityus confluens venom (10, 50, and 100 µg/mL) to metabolize adenine nucleotides and its potential effects on purinergic enzyme activity in rat platelets and lymphocytes. The effects of T. confluens venom on E-NTPDase (ATP and ADP hydrolysis), E-5'-NT (AMP hydrolysis), and E-ADA (ADO hydrolysis) activities were analyzed. The results revealed that crude venom from T. confluens exhibited ATP hydrolysis activity at all tested concentrations. In lymphocytes, ADP hydrolysis was inhibited by 100 µg/mL crude venom, whereas ADO hydrolysis was increased by all venom concentrations. In platelets, ATP hydrolysis was inhibited by 50 and 100 µg/mL crude venom, whereas AMP and ADO hydrolysis were inhibited by all concentrations. When considered collectively, the data suggested an elevation in extracellular ATP levels and a reduction in extracellular ADO. These findings are in alignment with clinical manifestations of scorpion envenomation characterized by a pro-inflammatory milieu. Furthermore, this study demonstrated the intrinsic ATPase activity of T. confluens venom and its ability to modulate E-NTPDase, E-5'-NT, and E-ADA activities in rat blood cells.

Structural insights into the human P2X1 receptor and ligand interactions

The P2X1 receptor is a trimeric ligand-gated ion channel that plays an important role in urogenital and immune functions, offering the potential for new drug treatments. However, progress in this area has been hindered by limited structural information and a lack of well-characterised tool compounds. In this study, we employ cryogenic electron microscopy (cryo-EM) to elucidate the structures of the P2X1 receptor in an ATP-bound desensitised state and an NF449-bound closed state. NF449, a potent P2X1 receptor antagonist, engages the receptor distinctively, while ATP, the endogenous ligand, binds in a manner consistent with other P2X receptors. To explore the molecular basis of receptor inhibition, activation, and ligand interactions, key residues involved in ligand and metal ion binding were mutated. Radioligand binding assays with [3H]-α,β-methylene ATP and intracellular calcium ion influx assays were used to evaluate the effects of these mutations. These experiments validate key ligand-receptor interactions and identify conserved and non-conserved residues critical for ligand binding or receptor modulation. This research expands our understanding of the P2X1 receptor structure at a molecular level and opens new avenues for in silico drug design targeting the P2X1 receptor.

The role of Pannexin-1 channels, ATP, and purinergic receptors in the pathogenesis of HIV and SARS-CoV-2

Infectious agents such as human immune deficiency virus-1 (HIV) and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) use host proteins to infect, replicate, and induce inflammation within the host. A critical component of these diseases is the axis between pannexin-1 channels, extracellular ATP, and purinergic receptors. Here, we describe the potential therapeutic role of Pannexin-1/purinergic approaches to prevent or reduce the devastating consequences of these pathogens.

Purine and purinergic receptors in health and disease

Purines and purinergic receptors are widely distributed throughout the human body. Purine molecules within cells play crucial roles in regulating energy metabolism and other cellular processes, while extracellular purines transmit signals through specific purinergic receptors. The ubiquitous purinergic signaling maintains normal neural excitability, digestion and absorption, respiratory movement, and other complex physiological activities, and participates in cell proliferation, differentiation, migration, and death. Pathological dysregulation of purinergic signaling can result in the development of various diseases, including neurodegeneration, inflammatory reactions, and malignant tumors. The dysregulation or dysfunction of purines and purinergic receptors has been demonstrated to be closely associated with tumor progression. Compared with other subtypes of purinergic receptors, the P2X7 receptor (P2X7R) exhibits distinct characteristics (i.e., a low affinity for ATP, dual functionality upon activation, the mediation of ion channels, and nonselective pores formation) and is considered a promising target for antitumor therapy, particularly in patients with poor response to immunotherapy This review summarizes the physiological and pathological significance of purinergic signaling and purinergic receptors, analyzes their complex relationship with tumors, and proposes potential antitumor immunotherapy strategies from tumor P2X7R inhibition, tumor P2X7R overactivation, and host P2X7R activation. This review provides a reference for clinical immunotherapy and mechanism investigation.

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.

The P2X1 receptor as a therapeutic target

Within the family of purinergic receptors, the P2X1 receptor is a ligand-gated ion channel that plays a role in urogenital, immune and cardiovascular function. Specifically, the P2X1 receptor has been implicated in controlling smooth muscle contractions of the vas deferens and therefore has emerged as an exciting drug target for male contraception. In addition, the P2X1 receptor contributes to smooth muscle contractions of the bladder and is a target to treat bladder dysfunction. Finally, platelets and neutrophils have populations of P2X1 receptors that could be targeted for thrombosis and inflammatory conditions. Drugs that specifically target the P2X1 receptor have been challenging to develop, and only recently have small molecule antagonists of the P2X1 receptor been available. However, these ligands need further biological validation for appropriate selectivity and drug-like properties before they will be suitable for use in preclinical models of disease. Although the atomic structure of the P2X1 receptor has yet to be determined, the recent discovery of several other P2X receptor structures and improvements in the field of structural biology suggests that this is now a distinct possibility. Such efforts may significantly improve drug discovery efforts at the P2X1 receptor.

Apyrase decreases phage induction and Shiga toxin release from E. coli O157:H7 and has a protective effect during infection

Shiga toxin (Stx)-producing enterohemorrhagic Escherichia coli (EHEC) cause gastrointestinal infection and, in severe cases, hemolytic uremic syndrome which may lead to death. There is, to-date, no therapy for this infection. Stx induces ATP release from host cells and ATP signaling mediates its cytotoxic effects. Apyrase cleaves and neutralizes ATP and its effect on Stx and EHEC infection was therefore investigated. Apyrase decreased bacterial RecA and dose-dependently decreased toxin release from E. coli O157:H7 in vitro, demonstrated by reduced phage DNA and protein levels. The effect was investigated in a mouse model of E. coli O157:H7 infection. BALB/c mice infected with Stx2-producing E. coli O157:H7 were treated with apyrase intraperitoneally, on days 0 and 2 post-infection, and monitored for 11 days. Apyrase-treated mice developed disease two days later than untreated mice. Untreated infected mice lost significantly more weight than those treated with apyrase. Apyrase-treated mice exhibited less colonic goblet cell depletion and apoptotic cells, as well as lower fecal ATP and Stx2, compared to untreated mice. Apyrase also decreased platelet aggregation induced by co-incubation of human platelet-rich-plasma with Stx2 and E. coli O157 lipopolysaccharide in the presence of collagen. Thus, apyrase had multiple protective effects, reducing RecA levels, stx2 and toxin release from EHEC, reducing fecal Stx2 and protecting mouse intestinal cells, as well as decreasing platelet activation, and could thereby delay the development of disease.

Pannexin-1 channel opening is critical for COVID-19 pathogenesis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) rapidly rampaged worldwide, causing a pandemic of coronavirus disease (COVID -19), but the biology of SARS-CoV-2 remains under investigation. We demonstrate that both SARS-CoV-2 spike protein and human coronavirus 229E (hCoV-229E) or its purified S protein, one of the main viruses responsible for the common cold, induce the transient opening of Pannexin-1 (Panx-1) channels in human lung epithelial cells. However, the Panx-1 channel opening induced by SARS-CoV-2 is greater and more prolonged than hCoV-229E/S protein, resulting in an enhanced ATP, PGE₂, and IL-1β release. Analysis of lung lavages and tissues indicate that Panx-1 mRNA expression is associated with increased ATP, PGE₂, and IL-1β levels. Panx-1 channel opening induced by SARS-CoV-2 spike protein is angiotensin-converting enzyme 2 (ACE-2), endocytosis, and furin dependent. Overall, we demonstrated that Panx-1 channel is a critical contributor to SARS-CoV-2 infection and should be considered as an alternative therapy.