Purine Release, Metabolism, and Signaling in the Inflammatory Response.

ATP, NAD+, and nucleic acids are abundant purines that, in addition to having critical intracellular functions, have evolved extracellular roles as danger signals released in response to cell lysis, apoptosis, degranulation, or membrane pore formation. In general ATP and NAD+ have excitatory and adenosine has anti-inflammatory effects on immune cells. This review focuses on recent advances in our understanding of purine release mechanisms, ectoenzymes that metabolize purines (CD38, CD39, CD73, ENPP1, and ENPP2/autotaxin), and signaling by key P2 purinergic receptors (P2X7, P2Y2, and P2Y12). In addition to metabolizing ATP or NAD+, some purinergic ectoenzymes metabolize other inflammatory modulators, notably lysophosphatidic acid and cyclic GMP-AMP (cGAMP). Also discussed are extracellular signaling effects of NAD+ mediated by ADP-ribosylation, and epigenetic effects of intracellular adenosine mediated by modification of S-adenosylmethionine-dependent DNA methylation.

Full-Length P2X7 Structures Reveal How Palmitoylation Prevents Channel Desensitization.

P2X receptors are trimeric, non-selective cation channels activated by extracellular ATP. The P2X7 receptor subtype is a pharmacological target because of involvement in apoptotic, inflammatory, and tumor progression pathways. It is the most structurally and functionally distinct P2X subtype, containing a unique cytoplasmic domain critical for the receptor to initiate apoptosis and not undergo desensitization. However, lack of structural information about the cytoplasmic domain has hindered understanding of the molecular mechanisms underlying these processes. We report cryoelectron microscopy structures of full-length rat P2X7 receptor in apo and ATP-bound states. These structures reveal how one cytoplasmic element, the C-cys anchor, prevents desensitization by anchoring the pore-lining helix to the membrane with palmitoyl groups. They show a second cytoplasmic element with a unique fold, the cytoplasmic ballast, which unexpectedly contains a zinc ion complex and a guanosine nucleotide binding site. Our structures provide first insights into the architecture and function of a P2X receptor cytoplasmic domain.

Disruption of the Na+/K+-ATPase-purinergic P2X7 receptor complex in microglia promotes stress-induced anxiety.

Na+/K+-ATPase (NKA) plays an important role in the central nervous system. However, little is known about its function in the microglia. Here, we found that NKAα1 forms a complex with the purinergic P2X7 receptor (P2X7R), an adenosine 5'-triphosphate (ATP)-gated ion channel, under physiological conditions. Chronic stress or treatment with lipopolysaccharide plus ATP decreased the membrane expression of NKAα1 in microglia, facilitated P2X7R function, and promoted microglia inflammatory activation via activation of the NLRP3 inflammasome. Accordingly, global deletion or conditional deletion of NKAα1 in microglia under chronic stress-induced aggravated anxiety-like behavior and neuronal hyperexcitability. DR5-12D, a monoclonal antibody that stabilizes membrane NKAα1, improved stress-induced anxiety-like behavior and ameliorated neuronal hyperexcitability and neurogenesis deficits in the ventral hippocampus of mice. Our results reveal that NKAα1 limits microglia inflammation and may provide a target for the treatment of stress-related neuroinflammation and diseases.

Blockade of the Phagocytic Receptor MerTK on Tumor-Associated Macrophages Enhances P2X7R-Dependent STING Activation by Tumor-Derived cGAMP.

Clearance of apoptotic cells by macrophages prevents excessive inflammation and supports immune tolerance. Here, we examined the effect of blocking apoptotic cell clearance on anti-tumor immune response. We generated an antibody that selectively inhibited efferocytosis by phagocytic receptor MerTK. Blockade of MerTK resulted in accumulation of apoptotic cells within tumors and triggered a type I interferon response. Treatment of tumor-bearing mice with anti-MerTK antibody stimulated T cell activation and synergized with anti-PD-1 or anti-PD-L1 therapy. The anti-tumor effect induced by anti-MerTK treatment was lost in Stinggt/gt mice, but not in Cgas-/- mice. Abolishing cGAMP production in Cgas-/- tumor cells, depletion of extracellular ATP, or inactivation of the ATP-gated P2X7R channel also compromised the effects of MerTK blockade. Mechanistically, extracellular ATP acted via P2X7R to enhance the transport of extracellular cGAMP into macrophages and subsequent STING activation. Thus, MerTK blockade increases tumor immunogenicity and potentiates anti-tumor immunity, which has implications for cancer immunotherapy.

Dilation of ion selectivity filters in cation channels.

Ion channels establish the voltage gradient across cellular membranes by providing aqueous pathways for ions to selectively diffuse down their concentration gradients. The selectivity of any given channel for its favored ions has conventionally been viewed as a stable property, and in many cation channels, it is determined by an ion-selectivity filter within the external end of the ion-permeation pathway. In several instances, including voltage-activated K+ (Kv) channels, ATP-activated P2X receptor channels, and transient receptor potential (TRP) channels, the ion-permeation pathways have been proposed to dilate in response to persistent activation, dynamically altering ion permeation. Here, we discuss evidence for dynamic ion selectivity, examples where ion selectivity filters exhibit structural plasticity, and opportunities to fill gaps in our current understanding.

The TWIK2 Potassium Efflux Channel in Macrophages Mediates NLRP3 Inflammasome-Induced Inflammation.

Potassium (K+) efflux across the plasma membrane is thought to be an essential mechanism for ATP-induced NLRP3 inflammasome activation, yet the identity of the efflux channel has remained elusive. Here we identified the two-pore domain K+ channel (K2P) TWIK2 as the K+ efflux channel triggering NLRP3 inflammasome activation. Deletion of Kcnk6 (encoding TWIK2) prevented NLRP3 activation in macrophages and suppressed sepsis-induced lung inflammation. Adoptive transfer of Kcnk6-/- macrophages into mouse airways after macrophage depletion also prevented inflammatory lung injury. The K+ efflux channel TWIK2 in macrophages has a fundamental role in activating the NLRP3 inflammasome and consequently mediates inflammation, pointing to TWIK2 as a potential target for anti-inflammatory therapies.

Engineering a human P2X2 receptor with altered ligand selectivity in yeast.

P2X receptors are a family of ligand gated ion channels found in a range of eukaryotic species including humans but are not naturally present in the yeast Saccharomyces cerevisiae. We demonstrate the first recombinant expression and functional gating of the P2X2 receptor in baker's yeast. We leverage the yeast host for facile genetic screens of mutant P2X2 by performing site saturation mutagenesis at residues of interest, including SNPs implicated in deafness and at residues involved in native binding. Deep mutational analysis and rounds of genetic engineering yield mutant P2X2 F303Y A304W, which has altered ligand selectivity toward the ATP analog AMP-PNP. The F303Y A304W variant shows over 100-fold increased intracellular calcium amplitudes with AMP-PNP compared to the WT receptor and has a much lower desensitization rate. Since AMP-PNP does not naturally activate P2X receptors, the F303Y A304W P2X2 may be a starting point for downstream applications in chemogenetic cellular control. Interestingly, the A304W mutation selectively destabilizes the desensitized state, which may provide a mechanistic basis for receptor opening with suboptimal agonists. The yeast system represents an inexpensive, scalable platform for ion channel characterization and engineering by circumventing the more expensive and time-consuming methodologies involving mammalian hosts.

Context-dependent regulation of follicular helper T cell survival.

Follicular helper T (TFH) cells are a specialized subset of CD4+ T cells that support germinal centers in producing high-affinity antibody-secreting and memory B cells in mammals and birds. Therefore, mechanisms have evolved to control the life and death of TFH cells for balanced humoral immunity. Recent studies have collectively revealed at least two programmed cell death pathways, ferroptosis and pyroptosis, which govern TFH cell survival under diverse physiopathological conditions including immunization, infection, gut homeostasis, and autoimmunity. We review major recent advances in our understanding of the context-dependent regulation of TFH cell survival via cell death pathways that are closely connected with cellular metabolism. Such knowledge might be applied to inform new strategies aimed at modulating humoral immunity, potentially including enhancement of vaccine efficacies.

LncTCONS_00058568 is involved in the pathophysiologic processes mediated by P2X7R in the lower thoracic spinal cord after acute kidney injury.

Acute kidney injury (AKI), a prevalent clinical syndrome, involves the participation of the nervous system in neuroimmune regulation. However, the intricate molecular mechanism that governs renal function regulation by the central nervous system (CNS) is complex and remains incompletely understood. In the present study, we found that the upregulated expression of lncTCONS_00058568 in lower thoracic spinal cord significantly ameliorated AKI-induced renal tissue injury, kidney morphology, inflammation and apoptosis, and suppressed renal sympathetic nerve activity. Mechanistically, the purinergic ionotropic P2X7 receptor (P2X7R) was overexpressed in AKI rats, whereas lncTCONS_00058568 was able to suppress the upregulation of P2X7R. In addition, RNA sequencing data revealed differentially expressed genes associated with nervous system inflammatory responses after lncTCONS_00058568 was overexpressed in AKI rats. Finally, the overexpression of lncTCONS_00058568 inhibited the activation of PI3K/Akt and NF-κB signaling pathways in spinal cord. Taken together, the results from the present study show that lncTCONS_00058568 overexpression prevented renal injury probably by inhibiting sympathetic nerve activity mediated by P2X7R in the lower spinal cord subsequent to I/R-AKI.

Requirement of Xk and Vps13a for the P2X7-mediated phospholipid scrambling and cell lysis in mouse T cells.

A high extracellular adenosine triphosphate (ATP) concentration rapidly and reversibly exposes phosphatidylserine (PtdSer) in T cells by binding to the P2X7 receptor, which ultimately leads to necrosis. Using mouse T cell transformants expressing P2X7, we herein performed CRISPR/Cas9 screening for the molecules responsible for P2X7-mediated PtdSer exposure. In addition to Eros, which is required for the localization of P2X7 to the plasma membrane, this screening identified Xk and Vps13a as essential components for this process. Xk is present at the plasma membrane, and its paralogue, Xkr8, functions as a phospholipid scramblase. Vps13a is a lipid transporter in the cytoplasm. Blue-native polyacrylamide gel electrophoresis indicated that Xk and Vps13a interacted at the membrane. A null mutation in Xk or Vps13a blocked P2X7-mediated PtdSer exposure, the internalization of phosphatidylcholine, and cytolysis. Xk and Vps13a formed a complex in mouse splenic T cells, and Xk was crucial for ATP-induced PtdSer exposure and cytolysis in CD25+CD4+ T cells. XK and VPS13A are responsible for McLeod syndrome and chorea-acanthocytosis, both characterized by a progressive movement disorder and cognitive and behavior changes. Our results suggest that the phospholipid scrambling activity mediated by XK and VPS13A is essential for maintaining homeostasis in the immune and nerve systems.

Dual Role of the P2X7 Receptor in Dendritic Outgrowth during Physiological and Pathological Brain Development.

At high levels, extracellular ATP operates as a "danger" molecule under pathologic conditions through purinergic receptors, including the ionotropic P2X7 receptor (P2X7R). Its endogenous activation is associated with neurodevelopmental disorders; however, its function during early embryonic stages remains largely unclear. Our objective was to determine the role of P2X7R in the regulation of neuronal outgrowth. For this purpose, we performed Sholl analysis of dendritic branches on primary hippocampal neurons and in acute hippocampal slices from WT mice and mice with genetic deficiency or pharmacological blockade of P2X7R. Because abnormal dendritic branching is a hallmark of certain neurodevelopmental disorders, such as schizophrenia, a model of maternal immune activation (MIA)-induced schizophrenia, was used for further morphologic investigations. Subsequently, we studied MIA-induced behavioral deficits in young adult mice females and males. Genetic deficiency or pharmacological blockade of P2X7R led to branching deficits under physiological conditions. Moreover, pathologic activation of the receptor led to deficits in dendritic outgrowth on primary neurons from WT mice but not those from P2X7R KO mice exposed to MIA. Likewise, only MIA-exposed WT mice displayed schizophrenia-like behavioral and cognitive deficits. Therefore, we conclude that P2X7R has different roles in the development of hippocampal dendritic arborization under physiological and pathologic conditions.SIGNIFICANCE STATEMENT Our main finding is a novel role for P2X7R in neuronal branching in the early stages of development under physiological conditions. We show how a decrease in the expression of P2X7R during brain development causes the receptor to play pathologic roles in adulthood. Moreover, we studied a neurodevelopmental model of schizophrenia and found that, at higher ATP concentrations, endogenous activation of P2X7R is necessary and sufficient for the development of positive and cognitive symptoms.

Meningeal P2X7 Signaling Mediates Migraine-Related Intracranial Mechanical Hypersensitivity.

Cortical spreading depolarization (CSD) is a key pathophysiological event that underlies visual and sensory auras in migraine. CSD is also thought to drive the headache phase in migraine by promoting the activation and mechanical sensitization of trigeminal primary afferent nociceptive neurons that innervate the cranial meninges. The factors underlying meningeal nociception in the wake of CSD remain poorly understood but potentially involve the parenchymal release of algesic mediators and damage-associated molecular patterns, particularly ATP. Here, we explored the role of ATP-P2X purinergic receptor signaling in mediating CSD-evoked meningeal afferent activation and mechanical sensitization. Male rats were subjected to a single CSD episode. In vivo, extracellular single-unit recording was used to measure meningeal afferent ongoing activity changes. Quantitative mechanical stimuli using a servomotor force-controlled stimulator assessed changes in the afferent's mechanosensitivity. Manipulation of meningeal P2X receptors was achieved via local administration of pharmacological agents. Broad-spectrum P2X receptor inhibition, selective blockade of the P2X7 receptor, and its related Pannexin 1 channel suppressed CSD-evoked afferent mechanical sensitization but did not affect the accompanying afferent activation response. Surprisingly, inhibition of the pronociceptive P2X2/3 receptor did not affect the activation or sensitization of meningeal afferents post-CSD. P2X7 signaling underlying afferent mechanosensitization was localized to the meninges and did not affect CSD susceptibility. We propose that meningeal P2X7 and Pannexin 1 signaling, potentially in meningeal macrophages or neutrophils, mediates the mechanical sensitization of meningeal afferents, which contributes to migraine pain by exacerbating the headache during normally innocuous physical activities.SIGNIFICANCE STATEMENT Activation and sensitization of meningeal afferents play a key role in migraine headache, but the underlying mechanisms remain unclear. Here, using a rat model of migraine with aura involving cortical spreading depolarization (CSD), we demonstrate that meningeal purinergic P2X7 signaling and its related Pannexin 1 pore, but not nociceptive P2X2/3 receptors, mediate prolonged meningeal afferent sensitization. Additionally, we show that meningeal P2X signaling does not contribute to the increased afferent ongoing activity in the wake of CSD. Our finding points to meningeal P2X7 signaling as a critical mechanism underlying meningeal nociception in migraine, the presence of distinct mechanisms underlying the activation and sensitization of meningeal afferents in migraine, and highlight the need to target both processes for effective migraine therapy.

Caveolin-1 forms a complex with P2X7 receptor and tunes P2X7-mediated ATP signaling in mouse bone marrow-derived macrophages.

The ionotropic purinergic P2X7 receptor responds to extracellular ATP and can trigger proinflammatory immune signaling in macrophages. Caveolin-1 (Cav-1) is known to modulate functions of macrophages and innate immunity. However, it is unknown how Cav-1 modulates P2X7 receptor activity in macrophages. We herein examined P2X7 receptor activity and macrophage functions using bone marrow-derived macrophages (BMDMs) from wild-type (WT) and Cav-1 knockout (KO) mice. ATP (1 mM) application caused biphasic increase in cytosolic [Ca2+] and sustained decrease in cytosolic [K+]. A specific P2X7 receptor blocker, A-740003, inhibited the maintained cytosolic [Ca2+] increase and cytosolic [K+] decrease. Total internal reflection fluorescent imaging and proximity ligation assays revealed a novel molecular complex formation between P2X7 receptors and Cav-1 in WT BMDMs that were stimulated with lipopolysaccharides. This molecular coupling was increased by ATP application. Specifically, the ATP-induced Ca2+ influx and K+ efflux through P2X7 receptors were increased in Cav-1 KO BMDMs, even though the total and surface protein levels of P2X7 receptors in WT and Cav-1 KO BMDMs were unchanged. Cell-impermeable dye (TO-PRO3) uptake analysis revealed that macropore formation of P2X7 receptors was enhanced in Cav-1 KO BMDMs. Cav-1 KO BMDMs increased ATP-induced IL-1ß secretion, reactive oxygen species production, Gasdermin D (GSDMD) cleavage, and lactate dehydrogenase release indicating pyroptosis. A-740003 completely prevented ATP-induced pyroptosis. In combination, these datasets show that Cav-1 has a negative effect on P2X7 receptor activity in BMDMs and that Cav-1 in macrophages may contribute to finely tuned immune responses by preventing excessive IL-1ß secretion and pyroptosis.NEW & NOTEWORTHY In bone marrow-derived macrophages, Cav-1 suppresses the macropore formation of P2X7 receptors through their direct or indirect interactions, resulting in reduced membrane permeability of cations (Ca2+ and K+) and large cell-impermeable dye (TO-PRO3) induced by ATP. Cav-1 also inhibits ATP-induced IL-1ß secretion, ROS production, GSDMD cleavage, and pyroptosis. Cav-1 contributes to the maintenance of proper immune responses by finely tuning IL-1ß secretion and cell death in macrophages.

Puerarin inhibits Staphylococcus aureus-induced endometritis through attenuating inflammation and ferroptosis via regulating the P2X7/NLRP3 signalling pathway.

Endometritis is one of the important causes of infertility. Puerarin (PU) can inhibit oxidative stress and reduce inflammation; however, it is unclear whether PU has a protective effect on the endometritis. In our study, we used Staphylococcus aureus to induce mouse endometritis. The PU group (100 mg/kg PU) and the S. aureus + PU group received daily intraperitoneal injection of PU (25, 50 or 100 mg/kg PU). The results showed that S. aureus significantly increased the levels of MPO, TNF-α, IL-1ß and IL-6 in uterine tissue, and increased the expression of p-p65 and p-IκBα proteins in uterine tissue to induce endometritis in mice (p < 0.05). Furthermore, it has been found that S. aureus promotes the occurrence of ferroptosis by reducing GSH and ATP content, increasing MDA and iron content and reducing GPX4 and SLC7A11 protein expression levels (p < 0.05). S. aureus significantly increase the expression of NLRP3, ASC, caspase-1 and P2X7 proteins in uterine tissue (p < 0.05). However, PU obviously reduced the inflammatory response and reversed the changes of ferroptosis and the expression of P2X7 receptor/NLRP3 pathway associated proteins of the uterus induced by S. aureus (p < 0.05). Taken together, these findings emphasize the protective effect of PU on endometritis by regulating the P2X7 receptor/NLRP3 signalling pathway and inhibiting ferroptosis.

NLRP3 Inflammasome Activation Through Heart-Brain Interaction Initiates Cardiac Inflammation and Hypertrophy During Pressure Overload.

BACKGROUND: Mechanical stress on the heart, such as high blood pressure, initiates inflammation and causes hypertrophic heart disease. However, the regulatory mechanism of inflammation and its role in the stressed heart remain unclear. IL-1ß (interleukin-1ß) is a proinflammatory cytokine that causes cardiac hypertrophy and heart failure. Here, we show that neural signals activate the NLRP3 (nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing 3) inflammasome for IL-1ß production to induce adaptive hypertrophy in the stressed heart. METHODS: C57BL/6 mice, knockout mouse strains for NLRP3 and P2RX7 (P2X purinoceptor 7), and adrenergic neuron-specific knockout mice for SLC17A9, a secretory vesicle protein responsible for the storage and release of ATP, were used for analysis. Pressure overload was induced by transverse aortic constriction. Various animal models were used, including pharmacological treatment with apyrase, lipopolysaccharide, 2'(3')-O-(4-benzoylbenzoyl)-ATP, MCC950, anti-IL-1ß antibodies, clonidine, pseudoephedrine, isoproterenol, and bisoprolol, left stellate ganglionectomy, and ablation of cardiac afferent nerves with capsaicin. Cardiac function and morphology, gene expression, myocardial IL-1ß and caspase-1 activity, and extracellular ATP level were assessed. In vitro experiments were performed using primary cardiomyocytes and fibroblasts from rat neonates and human microvascular endothelial cell line. Cell surface area and proliferation were assessed. RESULTS: Genetic disruption of NLRP3 resulted in significant loss of IL-1ß production, cardiac hypertrophy, and contractile function during pressure overload. A bone marrow transplantation experiment revealed an essential role of NLRP3 in cardiac nonimmune cells in myocardial IL-1ß production and cardiac phenotype. Pharmacological depletion of extracellular ATP or genetic disruption of the P2X7 receptor suppressed myocardial NLRP3 inflammasome activity during pressure overload, indicating an important role of ATP/P2X7 axis in cardiac inflammation and hypertrophy. Extracellular ATP induced hypertrophic changes of cardiac cells in an NLRP3- and IL-1ß-dependent manner in vitro. Manipulation of the sympathetic nervous system suggested sympathetic efferent nerves as the main source of extracellular ATP. Depletion of ATP release from sympathetic efferent nerves, ablation of cardiac afferent nerves, or a lipophilic ß-blocker reduced cardiac extracellular ATP level, and inhibited NLRP3 inflammasome activation, IL-1ß production, and adaptive cardiac hypertrophy during pressure overload. CONCLUSIONS: Cardiac inflammation and hypertrophy are regulated by heart-brain interaction. Controlling neural signals might be important for the treatment of hypertensive heart disease.

Investigating the Involvement of C-X-C Motif Chemokine 5 and P2X7 Purinoceptor in Ectopic Calcification in Mouse Models of Duchenne Muscular Dystrophy.

Ectopic calcification of myofibers is an early pathogenic feature in patients and animal models of Duchenne muscular dystrophy (DMD). In previous studies using the Dmdmdx-ßgeo mouse model, we found that the dystrophin-null phenotype exacerbates this abnormality and that mineralised myofibers are surrounded by macrophages. Furthermore, the P2X7 purinoceptor, functioning in immune cells offers protection against dystrophic calcification. In the present study, by exploring transcriptomic data from Dmdmdx mice, we hypothesised these effects to be mediated by C-X-C motif chemokine 5 (CXCL5) downstream of P2X7 activation. We found that CXCL5 is upregulated in the quadriceps muscles of Dmdmdx-ßgeo mice compared to wild-type controls. In contrast, at the cell level, dystrophic (SC5) skeletal muscle cells secreted less CXCL5 chemokine than wild-type (IMO) controls. Although release from IMO cells was increased by P2X7 activation, this could not explain the elevated CXCL5 levels observed in dystrophic muscle tissue. Instead, we found that CXCL5 is released by dystrophin-null macrophages in response to P2X7 activation, suggesting that macrophages are the source of CXCL5 in dystrophic muscles. The effects of CXCL5 upon mineralisation were investigated using the Alizarin Red assay to quantify calcium deposition in vitro. In basal (low phosphate) media, CXCL5 increased calcification in IMO but not SC5 myoblasts. However, in cultures treated in high phosphate media, to mimic dysregulated phosphate metabolism occurring in DMD, CXCL5 decreased calcification in both IMO and SC5 cells. These data indicate that CXCL5 is part of a homoeostatic mechanism regulating intracellular calcium, that CXCL5 can be released by macrophages in response to the extracellular ATP damage-associated signal, and that CXCL5 can be part of a damage response to protect against ectopic calcification. This mechanism is affected by DMD gene mutations.

P2X7 receptor of olfactory bulb microglia plays a pathogenic role in stress-related depression in mice with allergic rhinitis.

The aim of this study was to explore the role and mechanism of the olfactory bulb (OB) microglial P2X7 receptor (P2X7R) in allergic rhinitis (AR)-related depression, with the objective of identifying a potential clinical target. An AR mouse model was induced using ovalbumin (OVA), while chronic stress was employed to induce depression. The study used P2X7R-specific antagonists and OB microglia-specific P2X7R knockdown mice as crucial tools. The results showed that mice in the OVA + stress group exhibited more pronounced depressive-like phenotypes. Furthermore, there was an observed increase in microglial activation in the OB, followed by a rise in the level of inflammation. The pharmacological inhibition of P2X7R significantly mitigated the depression-like phenotype and the OB inflammatory response in OVA + stress mice. Notably, the specific knockdown of microglial P2X7R in the OB resulted in a similar effect, possibly linked to the regulation of IL-1ß via the "ATP-P2X7R-Caspase 1" axis. These findings collectively demonstrate that microglial P2X7R in the OB acts as a direct effector molecule in AR-related depression, and its inhibition may offer a novel strategy for clinical prevention and treatment.

Increased concentrations of P2X7R in oligodendrocyte derived extracellular vesicles of Multiple sclerosis patients.

Activation of the purinergic receptor P2X7 (P2X7R) is believed to be deleterious in autoimmune diseases and it was hypothesized to play a role in the pathogenesis of MS. P2X7R is an ATP-gated non-selective cationic channel; its activation can be driven by high concentrations of ATP and leads to the generation of large, cytolytic conductance pores. P2X7R activation can also result in apoptosis as a consequence of the activation of the caspase cascade via P2X7R-dependent stimulation of the NLRP3 inflammasome. We measured P2X7R in oligodendrocyte derived extracellular vesicles (ODEVs) in MS patients and in healthy subjects. Sixty-eight MS patients (50 relapsing-remitting, RR-MS, 18 primary progressive, PP-MS) and 57 healthy controls (HC) were enrolled. ODEVs were enriched from serum by a double step immunoaffinity method using an anti OMGp (oligodendrocyte myelin glycoprotein) antibody. P2X7R concentration was measured in ODEVs lysates by ELISA. One-way Anova test showed that P2X7R in ODEVs is significantly higher in PP-MS (mean: 1742.89 pg/mL) compared both to RR-MS (mean: 1277.33 pg/mL) (p < 0.001) and HC (mean: 879.79 pg/mL) (p < 0.001). Comparison between RR-MS and HC was also statistically significant (p < 0.001). Pearson's correlations showed that P2RX7 in ODEVs was positively correlated with EDSS (p = 0.002, r = 0.38, 0.15-0.57 95% CI) and MSSS (p = 0.004, r = 0.34, 0.12-0.54 95% CI) scores, considering MS patients together (PP-MS + RR-MS) and with disease duration in PP-MS group (p = 0.02, r = 0.53, 0.09-0.80 95% CI). Results suggest that ODEVs-associated P2X7R levels could be a biomarker for MS.

Electroacupuncture improves allodynia and central sensitization via modulation of microglial activation associated P2X4R and inflammation in a rat model of migraine.

Background: Recent studies have demonstrated that activated microglia were involved in the pathogenesis of central sensitization characterized by cutaneous allodynia in migraine. Activation of microglia is accompanied by increased expression of its receptors and release of inflammatory mediators. Acupuncture and its developed electroacupuncture (EA) have been recommended as an alternative therapy for migraine and are widely used for relieving migraine-associated pain. However, it remains rare studies that show whether EA exerts anti-migraine effects via inhibiting microglial activation related to a release of microglial receptors and the inflammatory pathway. Therefore, this study aimed to investigate EA' ability to ameliorate central sensitization via modulation of microglial activation, microglial receptor, and inflammatory response using a rat model of migraine induced by repeated epidural chemical stimulation. Methods: In the present study, a rat model of migraine was established by epidural repeated inflammatory soup (IS) stimulation and treated with EA at Fengchi (GB20) and Yanglingquan (GB34) and acupuncture at sham-acupoints. Pain hypersensitivity was further determined by measuring the mechanical withdrawal threshold using the von-Frey filament. The changes in c-Fos and ionized calcium binding adaptor molecule 1 (Ibal-1) labeled microglia in the trigeminal nucleus caudalis (TNC) were examined by immunflurescence to assess the central sensitization and whether accompanied with microglia activation. In addition, the expression of Ibal-1, microglial purinoceptor P2X4, and its associated inflammatory signaling pathway mediators, including interleukin (IL)-1ß, NOD-like receptor protein 3 (NLRP3), and Caspase-1 in the TNC were investigated by western blot and real-time polymerase chain reaction analysis. Results: Allodynia increased of c-Fos, and activated microglia were observed after repeated IS stimulation. EA alleviated the decrease in mechanical withdrawal thresholds, reduced the activation of c-Fos and microglia labeled with Ibal-1, downregulated the level of microglial purinoceptor P2X4, and limited the inflammatory response (NLRP3/Caspase-1/IL-1ß signaling pathway) in the TNC of migraine rat model. Conclusions: Our results indicate that the anti-hyperalgesia effects of EA ameliorate central sensitization in IS-induced migraine by regulating microglial activation related to P2X4R and NLRP3/IL-1ß inflammatory pathway.

Acute pulpitis promotes purinergic signaling to induce pain in rats via P38MAPK/NF-κB signaling pathway.

Toothache is one of the most common types of pain, but the mechanisms underlying pulpitis-induced pain remain unknown. The ionotropic purinergic receptor family (P2X) is reported to mediate nociception in the nervous system. This study aims to investigate the involvement of P2X3 in the sensitisation of the trigeminal ganglion (TG) and the inflammation caused by acute pulpitis. An acute tooth inflammation model was established by applying LPS to the pulp of SD rats. We found that the increased expression of P2X3 was induced by acute pulpitis. A selective P2X3 inhibitor (A-317491) reduced pain-like behavior in the maxillofacial region of rats and depressed the activation of neurons in the trigeminal ganglion induced by pulpitis. The upregulated MAPK signaling (p-p38, p-ERK1/2) expression in the ipsilateral TG induced by pulpitis could also be depressed by the application of the P2X3 inhibitor. Furthermore, the expression of markers of inflammatory processes, such as NF-κB, TNF-α and IL-1ß, could be induced by acute pulpitis and deduced by the intraperitoneal injection of P2X3 antagonists. Our findings demonstrate that purinergic P2X3 receptor signaling in TG neurons contributes to pulpitis-induced pain in rats and that P2X3 signaling may be a potential therapeutic target for tooth pain.