P2X7 receptor in cardiovascular disease: The heart side

Angiotension II directly bind P2X7 receptor to induce myocardial ferroptosis and remodeling by activating human antigen R

Continuous remodeling of the heart can result in adverse events such as reduced myocardial function and heart failure. Available evidence indicates that ferroptosis is a key process in the emergence of cardiac disease. P2 family purinergic receptor P2X7 receptor (P2X7R) activation plays a crucial role in numerous aspects of cardiovascular disease. The aim of this study was to elucidate any potential interactions between P2X7R and ferroptosis in cardiac remodeling stimulated by angiotensin II (Ang II), and P2X7R knockout mice were utilized to explore the role of P2X7R and elucidate its underlying mechanism through molecular biological methods. Ferroptosis is involved in cardiac remodeling, and P2X7R deficiency significantly alleviates cardiac dysfunction, remodeling, and ferroptosis induced by Ang II. Mechanistically, Ang II interacts with P2X7R directly, and LYS-66 and MET-212 in the in the ATP binding pocket form a binding complex with Ang II. P2X7R blockade influences HuR-targeted GPX4 and HO-1 mRNA stability by affecting the shuttling of HuR from the nucleus to the cytoplasm and its expression. These results suggest that focusing on P2X7R could be a possible therapeutic approach for the management of hypertensive heart failure.

Role of Oxysterols in Ocular Degeneration Mechanisms and Involvement of P2X7 Receptor

Ocular degeneration, including cataracts, glaucoma, macular degeneration, and diabetic retinopathy, is a major public health challenge, as it affects the quality of life of millions of people worldwide and, in its advanced stages, leads to blindness. Ocular degeneration, although it can affect different parts of the eye, shares common characteristics such as oxysterols and the P2X7 receptor. Indeed, oxysterols, which are cholesterol derivatives, are associated with ocular degeneration pathogenesis and trigger inflammation and cell death pathways. Activation of the P2X7 receptor is also linked to ocular degeneration and triggers the same pathways. In age-related macular degeneration, these two key players have been associated, but further studies are needed to extrapolate this interrelationship to other ocular degenerations.

Purinergic receptor P2 × 7 contributes to abdominal aortic aneurysm development via modulating macrophage pyroptosis and inflammation

The purinergic receptor P2 × 7 has been established as an important mediator of inflammation and participates in a variety of cardiovascular diseases including atherosclerosis, however, its role in abdominal aortic aneurysms (AAA) remains unclear. In this study, we demonstrate that P2 × 7 plays essential roles in AAA development via modulating macrophage pyroptosis and inflammation. P2 × 7 is highly expressed in human AAA specimen, as well as in experimental murine AAA lesions (both CaCl₂-and Angiotensin Ⅱ-induced AAA models), and it mainly confines in macrophages. Furthermore, P2 × 7 deficiency or pharmacological inhibition with its antagonist could significantly attenuate aneurysm formation in experimental murine AAA models, while P2 × 7 agonist could promote AAA development. The caspase-I activity, matrix metalloproteinase (MMP) activity, reactive oxygen species (ROS) production and pro-inflammatory gene expression were significant reduced in experimental AAA lesions in mice with P2 × 7 deficiency or inhibition. Mechanistically, macrophage P2 × 7 can mediate the activation of NLRP3 inflammasome and activate its downstream caspase-1 to initiate the pyroptosis pathway. After caspase-1 activation, it further cleaves pro-interleukin (IL)-1β and gasdermin D (GSDMD). Consequently, the N-terminal fragment of GSDMD forms pores on the cell membrane, leading to macrophage pyroptosis and release of the pro-inflammatory factor IL-1β. The resulting vascular inflammation further leads to the upregulation of MMP and ROS, thereby promoting AAA development. In summary, these data identify P2 × 7-mediated macrophage pyroptosis signaling pathway as a novel contributory mechanism of AAA formation.

Purinergic approach to effective glioma treatment with temozolomide reveals enhanced anti-cancer effects mediated by P2X7 receptor

The purinergic signaling pathway is the oldest evolutionary transmitter system that regulates a wide array of physiological and pathophysiological processes in central nervous system. However, the question of how the purinergic compounds interact with administrated drugs is rarely addressed. We aimed to clarify the interplay between purinergic signaling and chemotherapeutic drug temozolomide (TMZ) in human glioma cell line. We applied an initial retinoic acid-induced differentiation of A172 glioma cells and tested the P2X7 receptor expression in undifferentiated and differentiated gliomas. We compared the P2X7 receptor agonists/antagonists influence and their co-action with TMZ in both cell types through assessment of cell proliferation, viability and migrative properties. Molecular docking allowed to indicate the potential binding site for TMZ in the structure of hP2X7 receptor. Differentiated cells turned out to be more susceptible to ATP and TMZ alone but also to the concerted action of TMZ and ATP. Enhanced effects triggered by ATP and TMZ treatment include the decreased by 70% viability, and reduced migration ability of differentiated A172 glioma cells. Noteworthy, these results can be achieved already at low non-toxic ATP concentration and at reduced to 125 μM effective concentration of TMZ. Therefore, ATP molecules must be present and maintained at appropriate concentration in glioma cells microenvironment to achieve their co-action with TMZ and enhanced anti-cancer activity. All that, in turn, could shorten the therapy, increase its efficacy and limit the side effects for the patient. Our purinergic approach creates a promising perspective for developing novel combined oncological therapies.

eATP and autoimmune diabetes

PURPOSE OF REVIEW

The purine nucleotide adenosine triphosphate (ATP) is released into extracellular spaces as extracellular ATP (eATP) as a consequence of cell injury or death and activates the purinergic receptors. Once released, eATP may facilitate T-lymphocyte activation and differentiation. The purpose of this review is to elucidate the role of ATP-mediated signaling in the immunological events related to type 1 diabetes (T1D).

RECENT FINDINGS

T lymphocytes mediate immune response during the onset of T1D and promote pancreatic islet or whole pancreas rejection in transplantation. Recent data suggest a potential role for eATP in early steps of T1D onset and of allograft rejection. In different preclinical experimental models and clinical trials, several drugs targeting purinergic signaling have been employed to abrogate lymphocyte activation and differentiation, thus representing an achievable treatment to prevent/revert T1D or to induce long-term islet allograft function.

SUMMARY

In preclinical and clinical settings, eATP-signaling inhibition induces immune tolerance in autoimmune disease and in allotransplantation. In this view, the purinergic system may represent a novel therapeutic target for auto- and allo-immunity.

Synthesis, Biological Evaluation and Molecular Modeling Studies of Naphthoquinone Sulfonamides and Sulfonate Ester Derivatives as P2X7 Inhibitors

ATP acts in the extracellular environment as an important signal, activating a family of receptors called purinergic receptors. In recent years, interest in the potential therapeutics of purinergic components, including agonists and antagonists of receptors, has increased. Currently, many observations have indicated that ATP acts as an important mediator of inflammatory responses and, when found in high concentrations in the extracellular space, is related to the activation of the P2X7 purinergic receptor. In this sense, the search for new inhibitors for this receptor has attracted a great deal of attention in recent years. Sulfonamide derivatives have been reported to be potent inhibitors of P2X receptors. In this study, ten naphthoquinone sulfonamide derivatives and five naphthoquinone sulfonate ester derivatives were tested for their inhibitory activity on the P2X7 receptor expressed in peritoneal macrophages. Some compounds showed promising results, displaying IC₅₀ values lower than that of A740003. Molecular docking and dynamic studies also indicated that the active compounds bind to an allosteric site on P2X7R. The binding free energy indicates that sulfonamides have an affinity for the P2X7 receptor similar to A740003. Therefore, the compounds studied herein present potential P2X7R inhibition.

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.

Nanocarrier-Assisted Delivery of Metformin Boosts Remodeling of Diabetic Periodontal Tissue via Cellular Exocytosis-Mediated Regulation of Endoplasmic Reticulum Homeostasis

Endoplasmic reticulum (ER) dysfunction is a potential contributor to the impaired repair capacity of periodontal tissue in diabetes mellitus (DM) patients. Restoring ER homeostasis is thus critical for successful regenerative therapy of diabetic periodontal tissue. Recent studies have shown that metformin can modulate DM-induced ER dysfunction, yet its mechanism remains unclear. Herein, we show that high glucose elevates the intracellular miR-129-3p level due to exocytosis-mediated release failure and subsequently perturbs ER calcium homeostasis via downregulating transmembrane and coiled-coil domain 1 (TMCO1), an ER Ca²⁺ leak channel, in periodontal ligament stem cells (PDLSCs). This results in the degradation of RUNX2 via the ubiquitination-dependent pathway, in turn leading to impaired PDLSCs osteogenesis. Interestingly, metformin could upregulate P2X7R-mediated exosome release and decrease intracellular miR-129-3p accumulation, which restores ER homeostasis and thereby rescues the impaired PDLSCs. To further demonstrate the in vivo effect of metformin, a nanocarrier for sustained local delivery of metformin (Met@HALL) in periodontal tissue is developed. Our results demonstrate that compared to controls, Met@HALL with enhanced cytocompatibility and pro-osteogenic activity could boost the remodeling of diabetic periodontal tissue in rats. Collectively, our findings unravel a mechanism of metformin in restoring cellular ER homeostasis, enabling the development of a nanocarrier-mediated ER targeting strategy for remodeling diabetic periodontal tissue.

Relaxin Inhibits the Cardiac Myofibroblast NLRP3 Inflammasome as Part of Its Anti-Fibrotic Actions via the Angiotensin Type 2 and ATP (P2X7) Receptors

Chronic NLRP3 inflammasome activation can promote fibrosis through its production of interleukin (IL)-1β and IL-18. Conversely, recombinant human relaxin (RLX) can inhibit the pro-fibrotic interactions between IL-1β, IL-18 and transforming growth factor (TGF)-β1. Here, the broader extent by which RLX targeted the myofibroblast NLRP3 inflammasome to mediate its anti-fibrotic effects was elucidated. Primary human cardiac fibroblasts (HCFs), stimulated with TGF-β1 (to promote myofibroblast (HCMF) differentiation), LPS (to prime the NLRP3 inflammasome) and ATP (to activate the NLRP3 inflammasome) (T+L+A) or benzoylbenzoyl-ATP (to activate the ATP receptor; P2X7R) (T+L+Bz), co-expressed relaxin family peptide receptor-1 (RXFP1), the angiotensin II type 2 receptor (AT2R) and P2X7R, and underwent increased protein expression of toll-like receptor (TLR)-4, NLRP3, caspase-1, IL-1β and IL-18. Whilst RLX co-administration to HCMFs significantly prevented the T+L+A- or T+L+Bz-stimulated increase in these end points, the inhibitory effects of RLX were annulled by the pharmacological antagonism of either RXFP1, AT2R, P2X7R, TLR-4, reactive oxygen species (ROS) or caspase-1. The RLX-induced amelioration of left ventricular inflammation, cardiomyocyte hypertrophy and fibrosis in isoproterenol (ISO)-injured mice, was also attenuated by P2X7R antagonism. Thus, the ability of RLX to ameliorate the myofibroblast NLRP3 inflammasome as part of its anti-fibrotic effects, appeared to involve RXFP1, AT2R, P2X7R and the inhibition of TLR-4, ROS and caspase-1.

Possible role of pannexin 1 channels and purinergic receptors in the pathogenesis and mechanism of action of SARS-CoV-2 and therapeutic potential of targeting them in COVID-19

Identifying signaling pathways and molecules involved in SARS-CoV-2 pathogenesis is pivotal for developing new effective therapeutic or preventive strategies for COVID-19. Pannexins (PANX) are ATP-release channels in the plasma membrane essential in many physiological and immune responses. Activation of pannexin channels and downstream purinergic receptors play dual roles in viral infection, either by facilitating viral replication and infection or inducing host antiviral defense. The current review provides a hypothesis demonstrating the possible contribution of the PANX1 channel and purinergic receptors in SARS-CoV-2 pathogenesis and mechanism of action. Moreover, we discuss whether targeting these signaling pathways may provide promising preventative therapies and treatments for patients with progressive COVID-19 resulting from excessive pro-inflammatory cytokines and chemokines production. Several inhibitors of this pathway have been developed for the treatment of other viral infections and pathological consequences. Specific PANX1 inhibitors could be potentially included as part of the COVID-19 treatment regimen if, in future, studies demonstrate the role of PANX1 in COVID-19 pathogenesis. Of note, any ATP therapeutic modulation for COVID-19 should be carefully designed and monitored because of the complex role of extracellular ATP in cellular physiology.

Beyond Seizure Control: Treating Comorbidities in Epilepsy via Targeting of the P2X7 Receptor

Epilepsy is one of the most common chronic diseases of the central nervous system (CNS). Treatment of epilepsy remains, however, a clinical challenge with over 30% of patients not responding to current pharmacological interventions. Complicating management of treatment, epilepsy comes with multiple comorbidities, thereby further reducing the quality of life of patients. Increasing evidence suggests purinergic signalling via extracellularly released ATP as shared pathological mechanisms across numerous brain diseases. Once released, ATP activates specific purinergic receptors, including the ionotropic P2X7 receptor (P2X7R). Among brain diseases, the P2X7R has attracted particular attention as a therapeutic target. The P2X7R is an important driver of inflammation, and its activation requires high levels of extracellular ATP to be reached under pathological conditions. Suggesting the therapeutic potential of drugs targeting the P2X7R for epilepsy, P2X7R expression increases following status epilepticus and during epilepsy, and P2X7R antagonism modulates seizure severity and epilepsy development. P2X7R antagonism has, however, also been shown to be effective in treating conditions most commonly associated with epilepsy such as psychiatric disorders and cognitive deficits, which suggests that P2X7R antagonisms may provide benefits beyond seizure control. This review summarizes the evidence suggesting drugs targeting the P2X7R as a novel treatment strategy for epilepsy with a particular focus of its potential impact on epilepsy-associated comorbidities.

The P2X7 Receptor: A Promising Pharmacological Target in Diabetic Retinopathy

Diabetes is a worldwide emergency. Its chronic complications impose a heavy burden on patients, health systems, and on society as a whole. Diabetic retinopathy is one of the most common and serious complications of diabetes, and an established risk factor for blindness in adults. Over 15 years of investigation led to the identification of vascular endothelial growth factor (VEGF) as a main pathogenic factor in diabetic retinopathy and to the introduction of highly effective anti-VEGF-based therapies, such as the monoclonal antibody bevacizumab or its fragment ranibizumab, which helped to prevent diabetes-related blindness in millions of patients. Recently, a pathogenic role for uncontrolled increases in the extracellular ATP concentration (eATP) and for overactivation of the purinergic receptor P2X7 (P2X7R) has been suggested. The P2X7R is an eATP-gated plasma membrane channel expressed in multiple tissues and organs, with a pleiotropic function in inflammation, immunity, cancer, and hormone and growth factor release. P2X7R stimulation or overexpression positively regulate the secretion and buildup of VEGF, thus promoting neo-angiogenesis in a wide variety of disease processes. In this review, we explore current evidence that supports the role of P2X7R receptor signaling in the pathogenesis of diabetic retinopathy, as well as the most appealing current therapeutical options for P2X7R targeting.

BBG enhances OLT1177-induced NLRP3 inflammasome inactivation by targeting P2X7R/NLRP3 and MyD88/NF-κB signaling in DSS-induced colitis in rats

Chronic ulceration of the colon is associated with the activation of TLR4/NF-κB and P2X7R/NLRP3 signaling pathways. We investigated the effect of individual or combined administration of BBG, a P2X7R blocker, and OLT1177, a selective NLRP3 inhibitor, in the dextran sodium sulfate-induced ulcerative colitis (UC) rat model. The ulcerative rats were treated orally with brilliant blue G (BBG) (50 mg/kg/day) or OLT1177 (200 mg/kg/day) or a combination of both. Myd88 and NF-κB levels were measured by ELISA, qRT-PCR, and immunohistochemical staining. Cytokines known to be associated with TLR4/NF-κB or P2X7R/NLRP3 signaling were measured by ELISA. P2X7R and NLRP3 expression were measured by ELISA and qRT-PCR. The administration of BBG or OLT1177 ameliorated the toxic effects of DSS on the colon as they restored normal colonic macroscopic and microscopic morphology. BBG administration, but not OLT1177, reduced the expression of Myd88, NF-κB, IL-6, and TNF-α in addition to lowering P2X7R and oxidative stress levels. Individual BBG or OLT1177 administration decreased NLRP3 inflammasome recruitment and subsequent activation of caspase-1, IL-1β, and IL-18. However, the combined administration of OLT1177 with BBG potentiated its inhibitory effect on the NLRP3, which was reflected by the additional suppressive effect on caspase-1, IL-1β, IL-18 levels. In conclusion, BBG/OLT1177 exhibited complementary effects and effectively ameliorated UC. This novel approach provides a basis for the clinical application of this combination for the treatment of IBDs and might also be promising for the pharmacological intervention of other NLRP3 inflammasome-dependent inflammatory conditions.

P2X7 Variants in Oncogenesis

The P2X7 receptor for extracellular ATP is a well-established mediator of tumoral development and progression both in solid cancers and hematological malignancies. The human P2X7 gene is highly polymorphic, and several splice variants of the receptor have been identified in time. P2X7 single-nucleotide polymorphisms (SNPs) have been broadly analyzed by studies relating them to pathologies as different as infectious, inflammatory, nervous, and bone diseases, among which cancer is included. Moreover, in the last years, an increasing number of reports concentrated on P2X7 splice variants’ different roles and their implications in pathological conditions, including oncogenesis. Here, we give an overview of established and recent literature demonstrating a role for human P2X7 gene products in oncological conditions, mainly focusing on current data emerging on P2X7 isoform B and nfP2X7. We explored the role of these and other genetic variants of P2X7 in cancer insurgence, dissemination, and progression, as well as the effect of chemotherapy on isoforms expression. The described literature strongly suggests that P2X7 variants are potential new biomarkers and therapeutical targets in oncological conditions and that their study in carcinogenesis deserves to be further pursued.

Cardiac Connexin-43 Hemichannels and Pannexin1 Channels: Provocative Antiarrhythmic Targets

Cardiac connexin-43 (Cx43) creates gap junction channels (GJCs) at intercellular contacts and hemi-channels (HCs) at the peri-junctional plasma membrane and sarcolemmal caveolae/rafts compartments. GJCs are fundamental for the direct cardiac cell-to-cell transmission of electrical and molecular signals which ensures synchronous myocardial contraction. The HCs and structurally similar pannexin1 (Panx1) channels are active in stressful conditions. These channels are essential for paracrine and autocrine communication through the release of ions and signaling molecules to the extracellular environment, or for uptake from it. The HCs and Panx1 channel-opening profoundly affects intracellular ionic homeostasis and redox status and facilitates via purinergic signaling pro-inflammatory and pro-fibrotic processes. These conditions promote cardiac arrhythmogenesis due to the impairment of the GJCs and selective ion channel function. Crosstalk between GJCs and HCs/Panx1 channels could be crucial in the development of arrhythmogenic substrates, including fibrosis. Despite the knowledge gap in the regulation of these channels, current evidence indicates that HCs and Panx1 channel activation can enhance the risk of cardiac arrhythmias. It is extremely challenging to target HCs and Panx1 channels by inhibitory agents to hamper development of cardiac rhythm disorders. Progress in this field may contribute to novel therapeutic approaches for patients prone to develop atrial or ventricular fibrillation.

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.

Damage-Associated Molecular Patterns in Myocardial Infarction and Heart Transplantation: The Road to Translational Success

In the setting of myocardial infarction (MI), ischemia reperfusion injury (IRI) occurs due to occlusion (ischemia) and subsequent re-establishment of blood flow (reperfusion) of a coronary artery. A similar phenomenon is observed in heart transplantation (HTx) when, after cold storage, the donor heart is connected to the recipient's circulation. Although reperfusion is essential for the survival of cardiomyocytes, it paradoxically leads to additional myocardial damage in experimental MI and HTx models. Damage (or danger)-associated molecular patterns (DAMPs) are endogenous molecules released after cellular damage or stress such as myocardial IRI. DAMPs activate pattern recognition receptors (PRRs), and set in motion a complex signaling cascade resulting in the release of cytokines and a profound inflammatory reaction. This inflammatory response is thought to function as a double-edged sword. Although it enables removal of cell debris and promotes wound healing, DAMP mediated signalling can also exacerbate the inflammatory state in a disproportional matter, thereby leading to additional tissue damage. Upon MI, this leads to expansion of the infarcted area and deterioration of cardiac function in preclinical models. Eventually this culminates in adverse myocardial remodeling; a process that leads to increased myocardial fibrosis, gradual further loss of cardiomyocytes, left ventricular dilation and heart failure. Upon HTx, DAMPs aggravate ischemic damage, which results in more pronounced reperfusion injury that impacts cardiac function and increases the occurrence of primary graft dysfunction and graft rejection via cytokine release, cardiac edema, enhanced myocardial/endothelial damage and allograft fibrosis. Therapies targeting DAMPs or PRRs have predominantly been investigated in experimental models and are potentially cardioprotective. To date, however, none of these interventions have reached the clinical arena. In this review we summarize the current evidence of involvement of DAMPs and PRRs in the inflammatory response after MI and HTx. Furthermore, we will discuss various current therapeutic approaches targeting this complex interplay and provide possible reasons why clinical translation still fails.

P2X7 Receptors: An Untapped Target for the Management of Cardiovascular Disease

Chronic low-grade inflammation contributes to the development of several diseases, including cardiovascular disease. Adequate strategies to target inflammation in cardiovascular disease are in their infancy and remain an avenue of great interest. The purinergic receptor P2X7 is a ubiquitously expressed receptor that predominately mediates inflammation and cellular death. P2X7 is a ligand-gated cation channel that is activated in response to high concentrations of extracellular ATP, triggering the assembly and activation of the NLRP3 (nuclear oligomerization domain like receptor family pyrin domain containing 3) inflammasome and subsequent release of proinflammatory cytokines IL (interleukin)-1β and IL-18. Increased P2X7 activation and IL-1β and IL-18 concentrations have been implicated in the development of many cardiovascular conditions including hypertension, atherosclerosis, ischemia/reperfusion injury, and heart failure. P2X7 receptor KO (knockout) mice exhibit a significant attenuation of the inflammatory response, which corresponds with reduced disease severity. P2X7 antagonism blunts blood pressure elevation in hypertension and progression of atherosclerosis in animal models. IL-1β and IL-18 inhibition has shown efficacy in clinical trials reducing major adverse cardiac events, including myocardial infarction, and heart failure. With several P2X7 antagonists available with proven safety margins, P2X7 antagonism could represent an untapped potential for therapeutic intervention in cardiovascular disorders.

Purinergic System Signaling in Metainflammation-Associated Osteoarthritis

Inflammation triggered by metabolic imbalance, also called metainflammation, is low-grade inflammation caused by the components involved in metabolic syndrome (MetS), including central obesity and impaired glucose tolerance. This phenomenon is mainly due to excess nutrients and energy, and it contributes to the pathogenesis of osteoarthritis (OA). OA is characterized by the progressive degeneration of articular cartilage, which suffers erosion and progressively becomes thinner. Purinergic signaling is involved in several physiological and pathological processes, such as cell proliferation in development and tissue regeneration, neurotransmission and inflammation. Adenosine and ATP receptors, and other members of the signaling pathway, such as AMP-activated protein kinase (AMPK), are involved in obesity, type 2 diabetes (T2D) and OA progression. In this review, we focus on purinergic regulation in osteoarthritic cartilage and how different components of MetS, such as obesity and T2D, modulate the purinergic system in OA. In that regard, we describe the critical role in this disease of receptors, such as adenosine A2A receptor (A2AR) and ATP P2X7 receptor. Finally, we also assess how nucleotides regulate the inflammasome in OA.

P2X7 Receptor in the Management of Energy Homeostasis: Implications for Obesity, Dyslipidemia, and Insulin Resistance

Whole-body energy metabolism entails the highly regulated balance between food intake, nutrient breakdown, energy generation (ATP), and energy storage for the preservation of vital functions and body mass. Purinergic signaling has attracted increasing attention in the regulatory mechanisms not only for the reverse processes of white adipose tissue lipogenesis and lipolysis, but also for brown adipocyte-dependent thermogenesis and leptin production. This regulatory role has remarkable implications in the handling of body's energy expenditure and energy reservoir. Hence, selected purinergic receptors can play a relevant function in lipid metabolism, endocrine activity, glucose uptake, ATP-dependent increased expression of uncoupling protein 1, and browning of adipose tissue. Indeed, purinergic P2 receptors regulate adipogenesis and lipid metabolism and are involved in adipogenic differentiation. In particular, the ionotropic ATP-activated P2X7 subtype is involved in fat distribution, as well as in the modulation of inflammatory pathways in white adipose tissue. Within this context, very recent evidence has established a direct function of P2X7 in energy metabolism. Specifically, either genetic deletion (P2X7 knockout mice) or subchronic pharmacological inhibition of the receptor produces a decrease of whole-body energy expenditure and, concurrently, an increase of carbohydrate oxidation. As further evidence, lipid accumulation, increased fat mass distribution, and weight gain are reported in P2X7-depleted mice. Conversely, the stimulation of P2X7 enhances energy expenditure. Altogether, this knowledge supports the role of P2X7 signaling in the fight against obesity and insulin resistance, as well as in the promotion of adaptive thermogenesis.

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.

P2X receptors mediated abnormal interaction between satellite glial cells and neurons in visceral pathological changes

The adenosine triphosphate (ATP)-gated P2X receptor cation channel family consists of permeable ligand-gated ion channels that expand on the binding of extracellular adenosine 5'-ATP. ATP-gated P2X receptors are trimer ion channels that assemble homo or isomer from seven cloned subunits. P2X receptors are discovered mostly in mammalian and are being found in an increasing number of non-vertebrates, such as zebrafish, bullfrog, and ameba. P2X receptors are involved in many physiological processes, including regulation of heart rhythm and contractility, and regulation of pain, especially chronic pain and glia integration. This review summarizes the current studies on the regulation of P2X receptors in abnormal neuronal-glial interaction and the pathological changes in viscera, especially in myocardial ischemia.

Impaired function of aorta and perivascular adipose tissue in IL-18-deficient mice

IL-18 is ubiquitously produced by both hematopoietic and non-hematopoietic cells. The present study examined the thoracic aorta, including the surrounding perivascular adipose tissue (PVAT), of IL-18KO mice from functional and histological perspectives. IL-18KO mice exhibited raised blood pressure compared with wild-type mice. Echocardiographic examination showed a thickened vascular wall and narrowed vascular diameter of the aorta. Examination by the Magnus test demonstrated dysfunction of endothelial cells (ECs) in the IL-18KO thoracic aorta and impairment of the anticontractile function of IL-18KO PVAT. Histological examination showed no inflammatory lesions in the aorta but indicated progressive fibrosis in the vessel and conversion of PVAT from brown adipose tissue-like features to white adipose tissue-like features. Electron microscopic observation suggested several deformed mitochondria in the aorta and vacuole-like structures in ECs from IL-18KO mice. In addition, activity of complex IV was lower and production of reactive oxygen species was augmented in the mitochondria of IL-18KO aorta. Although expression of LC3 B was higher, rapamycin-induced autophagy flux was impaired in the IL-18KO PVAT. Moreover, Western blot analysis revealed that LAMP 1/2 was increased in IL-18KO PVAT, and measurement of cathepsin-D activity indicated decreased levels in IL-18KO PVAT. The IL-18KO thoracic aorta thus showed defects in physiological functions related to histological alterations, and the inflammasome/IL-18 system was suggested to play a protective role in cardiovascular cells, probably through quality control of mitochondria via promotion of autophagosome/autophagolysosome formation.NEW & NOTEWORTHY IL-18 deficiency caused aortic abnormalities in terms of morphology and functions in parallel with an accumulation of damaged mitochondria and anomalous turnover of protein complexes, such as PGC-1 and LAMP1 and -2 in PVAT. These findings suggested that IL-18 plays roles in maintaining the homeostasis of vessels and PVAT around the aorta, possibly by promoting autophagy.

Loss of function mutation in the P2X7, a ligand-gated ion channel gene associated with hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an inherited heart failure condition, mostly found to have genetic abnormalities, and is a leading cause of sudden death in young adults. Whole exome sequencing should be given consideration as a molecular diagnostic tool to identify disease-causing mutation/s. In this study, a HCM family with multiple affected members having history of sudden death were subjected to exome sequencing along with unaffected members. Quality passed variants obtained were filtered for rarity (MAF > 0.5%), evolutionary conservation, pathogenic prediction, and segregation in affected members after removing shared variants present in unaffected members. Only one non-synonymous mutation (p. Glu186Lys or E186K) in exon 6 of P2X7 gene segregated in HCM-affected individuals which was absent in unaffected family members and 100 clinically evaluated controls. The site of the mutation is highly conserved and led to complete loss of function which is in close vicinity to ATP-binding site-forming residues, affecting ATP binding, channel gating, or both. Mutations in candidate genes which were not segregated define clinical heterogeneity within affected members. P2X7 gene is highly expressed in the heart and shows direct interaction with major candidate genes for HCM. Our results reveal a significant putative HCM causative gene, P2X7, for the first time and show that germ-line mutations in P2X7 may cause a defective phenotype, suggesting purinergic receptor involvement in heart failure mediated through arrhythmias which need further investigations to be targeted for therapeutic interventions.