P2X4 receptors mediate PGE2 release by tissue-resident macrophages and initiate inflammatory pain

Lidocaine exhibits antileishmanial and immunomodulatory activities in an in vitro model of tegumentary leishmaniasis

Local anesthetics have been shown to inhibit or delay the progression of tegumentary leishmaniasis (TL) in hamster models, although the mechanisms underlying this clinical improvement remain unclear. This study aimed to determine whether lidocaine reduces intracellular parasitism through a direct antiparasitic effect and/or by modulating macrophage functions. To achieve this, Leishmania (L.) amazonensis promastigotes were exposed to increasing concentrations (0.078 to 5.0 mg/mL) of lidocaine for up to 72 hours, followed by assessments of parasite proliferation and viability. Next, human macrophages were incubated for 24 and 72 hours with escalating concentrations (0.078 to 5.0 mg/mL) of lidocaine to determine the maximum non-cytotoxic concentration (MNCC). Subsequently, L. (L.) amazonensis-infected human macrophages were treated with the MNCC of lidocaine for 24 and 72 hours, and the infection index, nitric oxide (NO) and cytokine levels, and intracellular parasite viability were measured. The results showed that lidocaine caused a dose-dependent reduction in the proliferation and viability of L. (L.) amazonensis promastigotes. The IC50 values for proliferation decreased from 0.69 mg/mL at 24 hours to 0.13 mg/mL at 72 hours, while the IC50 values for viability declined from 1.08 mg/mL at 24 hours to 0.30 mg/mL at 72 hours. These findings indicate that prolonged exposure enhances the parasite's susceptibility to lidocaine's antiproliferative and cytotoxic effects. The MNCC of lidocaine for human macrophages was determined to be 0.625 mg/mL. After incubating infected macrophages with this concentration, the mean ± standard deviation of the infection index was reduced by over 66% after both 24-hour and 72-hour treatments. Additionally, after 72 hours of exposure to lidocaine, there was an 89.6% increase in NO production by infected macrophages. Infected macrophages exposed to lidocaine produced 7.9-fold less IL-1β after 24 hours of treatment, and 35.2-fold, 12.9-fold, and 1.6-fold less TNF-α, IL-6, and IL-8, respectively, after 72 hours of treatment. The number of promastigotes that proliferated from intracellular amastigotes was significantly lower following treatment with lidocaine for both 24 and 72 hours, indicating that lidocaine significantly reduces the viability of intracellular parasites. In conclusion, lidocaine exhibits potent anti-Leishmania activity and modulates macrophage functions crucial to the immunity against Leishmania and immunopathogenesis of TL. These findings support its potential as an alternative or adjunctive therapeutic strategy for the treatment of this disease.

Possible Interaction of Suramin with Thalamic P2X Receptors and NLRP3 Inflammasome Activation Alleviates Reserpine-Induced Fibromyalgia-Like Symptoms

The high pain sensitivity in fibromyalgia (FM) is processed by the thalamus that presents as a key component in the pain pathway in FM patients. Noteworthy, Purinergic receptors, specifically P2X, are implicated in pain signaling and neuroinflammation via inflammasome signaling. However, there is no available data on the impact of pharmacological intervention on the P2X receptor in thalamic pain transmission in FM. To investigate this aspect, the clinically tested P2X inhibitor, Suramin (SURM), was utilized. FM was induced over three days using Reserpine (1 mg/kg/day, s.c.), followed by a single dose of SURM (100 mg/kg, i.p.). At the molecular level, SURM countered the overexpression of P2X7 and P2X4 receptors accompanied by reduced NLRP3 inflammasome complex and pyroptotic markers like gasdermin-D. This was associated with the suppression of the p38-MAPK and NF-κB pathways, along with a decrease in pro-inflammatory cytokines and tumor necrosis factor-α as observed by increased CD86 expression on M1 microglia phenotype, a neuroinflammatory marker. Concurrently, blocking the P2X receptor shifted microglia polarization towards the M2 phenotype, marked by elevated CD163 expression, as a neuroprotective mechanism. This was outlined by increased neurotrophic and anti-inflammatory IL-10 with normalization of disturbed neurotransmitters. Behaviorally, SURM ameliorated the heightened pain processing, as observed in mechanical and thermal pain tests. Furthermore, it lowered Reserpine-induced motor impairment in the rotarod and open-field tests. This improvement in the somatosensory experience was reflected in alleviating depressive-like behavior in the forced swimming test. These findings highlight the therapeutic potential of blocking thalamic P2X receptors in alleviating fibromyalgia symptoms.

The role and function validation of P2RX4 as a novel cancer biomarker in pan-cancer analysis

Purinergic Receptor P2X4 (P2RX4) is implicated in the carcinogenesis of several cancers, but no extensive study on its role in different forms of cancer. Expression level, gene mutation, immune infiltration, pathway enrichment, and prognostic value analysis of P2RX4 were performed based on multiple publicly available databases such as TCGA, GTEx, GEO, TIMER2, cBioportal, and Metascape databases. Western blot and RT-qPCR were used to identify P2RX4 expression in liver hepatocellular carcinoma (LIHC) and paracancer samples. P2RX4 was knocked in glioblastoma cell line (U251) and prostate cancer cell line (PC3), and its effects on cell viability, apoptosis, migration and invasion were investigated through cell counting kit-8 assay, flow cytometry, wound healing and trasnwell assays, respectively. P2RX4 expression was elevated in most cancers, which predicted poor overall survival and disease-free survival. Mutations in P2RX4 were predominantly found in Lymphoid Neoplasm Diffuse Large B-cell Lymphoma (> 4%). P2RX4 expression showed a positive correlation with the infiltration levels of cancer-associated fibroblasts and CD8 + cells in multiple tumor types. Functional enrichment analysis indicated that P2RX4 is closely related to autophagy, protein modification or intracellular trafficking. P2RX4 was highly expressed in LIHC compared to paracancerous tissues. Knockdown of P2RX4 suppressed cell viability, migration, invasion, and promoted cell apoptosis of U251 and PC3 cells. Overexpression of P2RX4 occurred in multi cancers, and was connected to an unfavorable prognosis. This pan-cancer analysis highlighted the predictive value and tumorigenic role of P2RX4.

Effects of low-level laser irradiation on osteoclastogenesis in prostaglandin E2-stimulated macrophages

Low-level laser accelerates bone healing by regulating inflammation. In periodontal tissues, excessive mechanical stress induces alveolar bone resorption by producing excessive prostaglandin E2 (PGE2), which is an inflammatory agent that induces osteoclast differentiation. In this study, we aimed to investigate the effect of a low-energy Ga-Al-As diode laser (LLL) on PGE2-induced osteoclast differentiation of RAW264.7 (RAW) cells. RAW cells were stimulated with 10- 6 M PGE2 and irradiated with 810 nm LLL at 3.0 mW/cm2 for 10 min. After LLL stimulation, the cells were cultured for five days and subjected to tartrate-resistant acid phosphatase staining. Expression levels of the osteoclastogenesis-inducing factors, receptor activator of nuclear factor-κB ligand and nuclear factor of activated T cells 1 (NFATc1), were examined 24 and 48 h after PGE2 stimulation and LLL irradiation. Extracellular ATP concentration was determined 0, 1, 5, 10, and 20 min after PGE2 stimulation and LLL irradiation. Additionally, intracellular calcium concentration was measured as the fluorescence intensity of the cultured cells over time (20 s/scan) after 10 min of LLL irradiation. To investigate the nuclear translocation of NFATc1, the cells were fixed after 1 h of PGE2 stimulation and LLL irradiation and subjected to immunofluorescence analysis. The same experiments were performed using the P2 × 4 receptor (ATP-gated channel) antagonist, 5-BDBD. Small osteoclasts were observed in the LLL irradiation group. Receptor activator of nuclear factor-κB ligand and NFATc1 mRNA levels were not significantly different between the LLL-irradiated and non-irradiated groups. Extracellular ATP release and intracellular Ca2+ levels were increased by PGE2 stimulation but decreased by LLL irradiation and 5-BDBD treatment. Nuclear NFATc1 levels were also increased by PGE2 stimulation, but this effect was reversed by LLL irradiation and 5-BDBD treatment. Overall, our results suggest that LLL irradiation inhibits PGE2-induced osteoclast differentiation by inhibiting Ca2+-NFATc1 signaling via extracellular ATP release.

Macrophage-P2X4 receptors pathway is essential to persistent inflammatory muscle hyperalgesia onset, and is prevented by physical exercise

Peripheral inflammation may lead to severe inflammatory painful conditions. Macrophages are critical for inflammation; modulating related pathways could be an essential therapeutic strategy for chronic pain diseases. Here we hypothesized that 1) Macrophage-P2X4 receptors are involved in the transition from acute to persistent inflammatory muscle hyperalgesia and that 2) P2X4 activation triggers a pro-inflammatory phenotype leading to Interleukin-1β (IL-1β) increase. Once physical exercise prevents exacerbated inflammatory processes related to chronic diseases including chronic muscle pain, we also hypothesized that 3) physical exercise, through PPARγ receptors, prevents P2X4 receptors activation. With pharmacological behaviour, biomolecular analysis and swimming physical exercise in a mouse model of persistent inflammatory muscle hyperalgesia we demonstrated that P2X4 receptors are essential for transitioning from acute to persistent inflammatory muscle hyperalgesia; Phosphorylation of p38MAPK indicated P2X4 signalling activation associated with inflammatory macrophage and an increase of IL-1β expression in skeletal muscle; Exercise-PPARγ receptors prevented phosphorylation of p38MAPK in muscle tissue. Our findings suggest that exercise-PPARγ modulates the acute inflammatory phase of developing persistent muscle hyperalgesia by controlling p38MAPK-related P2X4 signalling. These highlight the great potential of modulating macrophage phenotypes and P2X4 receptors to prevent pain conditions and the ability of physical exercise to prevent inflammatory processes related to chronic muscle pain.

P2X4 receptor mediates macrophage infiltration leading to endometriotic cyst epithelium proliferation and hyperalgesia in mouse model

OBJECTIVE

To evaluate the effects of a P2X4 receptor (P2X4R)-specific antagonist on murine endometriotic-like lesions and human endometriotic stromal cells.

DESIGN

Experimental study using an in vivo mouse endometriosis model and in vitro primary culture of human endometriotic stromal cells. NC-2600, an antagonist of the P2X4 ionotropic ATP receptor (P2X4R), was orally administered to the mice and cells. Gene expression analyses for cytokines were conducted in the endometriotic-like cysts and vaginal portion of mice, and immunohistochemistry was performed to evaluate the proliferative activity and localization of macrophages in addition to cytokine expression. The sensation of murine vaginal pain was evaluated using visceromotor responses.

RESULTS

NC-2600 reduced the proliferation of the cyst epithelium and vaginal pain sensation. In both cysts and vaginas, P2X4R is mainly expressed in macrophages, and NC-2600 reduces the number of tissue macrophages and reverses the elevated expression of InterleukinL-33 and cyclooxygenase-2 in animals with endometriosis.

CONCLUSION

These results indicate unknown pathophysiological roles of P2X4R expressed in local macrophages at the injury site of endometriosis and in the vagina, suggesting the potential therapeutic effects of orally administered P2X4R inhibitors for alleviating the symptoms of endometriosis.

Purinergic-associated immune responses in neurodegenerative diseases

The chronic activation of immune cells can participate in the development of pathological conditions such as neurodegenerative diseases including Alzheimer's disease (AD), Multiple Sclerosis (MS), Parkinson's disease (PD), Huntington's disease (HD) and Amyotrophic Lateral Sclerosis (ALS). In recent years, compelling evidence indicates that purinergic signaling plays a key role in neuro-immune cell functions. The extracellular release of adenosine 5'-triphosphate (ATP), and its breakdown products (ADP and adenosine) provide the versatile basis for complex purinergic signaling through the activation of several families of receptors. G-protein coupled adenosine A2A receptors, ionotropic P2X and G-protein coupled P2Y receptors for ATP and other nucleotides are abundant and widely distributed in neurons, microglia, and astrocytes of the central nervous system as well as in peripheral immune cells. These receptors are strongly linked to inflammation, with a functional interplay that may influence the intricate purinergic signaling involved in inflammatory responses. In the present review, we examine the roles of the purinergic receptors in neuro-immune cell functions with particular emphasis on A2AR, P2X4 and P2X7 and their possible relevance to specific neurodegenerative disorders. Understanding the molecular mechanisms governing purinergic receptor interaction will be crucial for advancing the development of effective immunotherapies targeting neurodegenerative diseases.

Preparation and preliminary evaluation of a tritium-labeled allosteric P2X4 receptor antagonist

P2X4 receptors are ATP-gated cation channels that were proposed as novel drug targets due to their role in inflammation and neuropathic pain. Only few potent and selective P2X4 receptor antagonists have been described to date. Labeled tool compounds suitable for P2X4 receptor binding studies are lacking. Here, we present a novel allosteric P2X4 receptor antagonist possessing high potency in the low nanomolar range. We describe its tritium-labeling resulting in the P2X4-selective radiotracer [3H]PSB-OR-2020 with high specific activity (45 Ci/mmol; 1.67 TBq/mmol). A radioligand binding assay was developed using human embryonic kidney (HEK293) cell membranes recombinantly expressing the human P2X4 receptor. Competition binding studies with structurally diverse P2X4 receptor antagonists revealed different allosteric binding sites indicating that the new class of P2X4 receptor antagonists, to which PSB-OR-2020 belongs, interacts with an unprecedented allosteric site. [3H]PSB-OR-2020 may become a useful tool for research on P2X4 receptors and for promoting drug development.

Exploring P2X receptor activity: A journey from cellular impact to electrophysiological profiling

The development of in vitro pharmacological assays relies on creating genetically modified cell lines that overexpress the target protein of interest. However, the choice of the host cell line can significantly impact the experimental outcomes. This study explores the functional characterization of P2X7 and P2X4 receptor modulators through cellular assays and advanced electrophysiological techniques. The influence of different host cell lines (HEK-293, HEK-293FT, and 1321N1) on the activity of reference agonists and antagonists targeting human and murine P2X4 and P2X7 receptors was systematically investigated, highlighting the significant impact of the host cell on experimental results. The 1321N1 cell line was identified as the preferred host cell line when investigating the human P2X4 receptor due to more consistent agonist activities, antagonist potencies, and a more stable assay signal window. Furthermore, a patch-clamp protocol that allows for the repetitive recording of ATP-mediated inward currents from isolated human CD4+ T-cells was established, revealing that both P2X7 and P2X4 receptors are crucial for immune cell regulation, positioning them as promising therapeutic targets for managing inflammatory disorders.

Limited contribution of the of P2X4 receptor to LPS-induced microglial reaction in mice

Sepsis is life-threatening condition that can trigger long-term neurological sequelae, including cognitive impairment in survivors. The pathogenesis of the so-called sickness behavior is poorly understood, but sepsis-driven neuroinflammation is thought to play a key role. Microglia are the central nervous system resident immune cells and play major roles in the induction and the control of neuroinflammatory processes. Accordingly, we recently demonstrated important microglia reaction, characterized by dramatic microglia transcriptome remodeling, in an experimental model of sepsis. Interfering with microglia pathways thus represents an interesting opportunity to tune microglia reaction towards beneficial outcomes. Purinergic signaling is central to microglia biology and controls key microglia functions. In particular, P2X4 receptors, which are highly permeable to calcium and de novo expressed in reactive microglia, seem to be an interesting target to modulate microglia reaction. Here, we investigated the impact of P2X4 receptors on the LPS-driven microglia transcriptome remodeling. Although we used complementary and sensitive biostatistical approaches, we did not measure significant impact of P2X4 deficiency onto microglia transcriptome either in homeostatic nor reactive condition. Overall, our results revealed that microglia reaction elicited by LPS-mediated sepsis is P2X4 independent and highlights the functional diversity of microglia reaction. These results also promote for the search of disease-specific targets to tune microglia reaction towards beneficial outcomes.

Liver transcriptome and proteome are modulated by nutrient restriction in early lactation cows challenged with intramammary lipopolysaccharide

The objective was to evaluate the effects of nutrient restriction on liver function 24 h after an intramammary lipopolysaccharide (LPS) challenge in early lactation cows using transcriptomic and proteomic analyses. Multiparous Holstein cows were fed a lactation diet (CONT, n = 8) throughout the study or were switched to a diet diluted with barley straw (48 % DM) for 96 h (REST, n = 8) starting at 24 (18 to 30) days in milk. At 72 h, a healthy rear mammary quarter was infused with 50 μg of LPS in all cows. Blood and liver biopsies were collected at 96 h, corresponding to 24 h after LPS challenge. Liver transcriptome was analyzed with a 44 K bovine microarray and proteome by LC MS/MS. Transcriptomic and proteomic data were analyzed using GeneSpring (moderated t-test with Westfall-Young correction) and the "between subject design", respectively. Data mining was performed using Panther and Pathway Studio software. By design, the negative energy balance was -68 and -37 MJ/d in REST and CONT, respectively. Plasma non-esterified FAs, and β-hydroxybutyrate were significantly greater in REST compared to CONT, which is consistent with 96 h of nutrient restriction in REST and ketosis induction. We detected 77 and 91 differentially expressed genes at mRNA and protein levels, respectively, between CONT and REST. Genes involved in fatty acid synthesis (e.g.: ACAT, FASN, SCD) were downregulated in REST, whereas those involved in fatty acid oxidation, detoxification, cholesterol synthesis, lipoprotein lipid secretion, and gluconeogenesis (e.g.: ACAD, CPT1A, CPT1B, CPT2) were upregulated. Differentially abundant mRNAs and proteins were consistent with negative energy balance and plasma metabolite concentrations, and reflected a state of intense lipomobilization, glucose deficit and ketogenesis in REST cows. Nutrient restriction did not change in deep liver expression of genes directly involved in immune function 24 h after an intramammary LPS challenge.

Crosstalk between P2Y receptors and cyclooxygenase activity in inflammation and tissue repair

The role of extracellular nucleotides as modulators of inflammation and cell stress is well established. One of the main actions of these molecules is mediated by the activation of purinergic receptors (P2) of the plasma membrane. P2 receptors can be classified according to two different structural families: P2X ionotropic ion channel receptors, and P2Y metabotropic G protein-coupled receptors. During inflammation, damaged cells release nucleotides and purinergic signaling occurs along the temporal pattern of the synthesis of pro-inflammatory and pro-resolving mediators by myeloid and lymphoid cells. In macrophages under pro-inflammatory conditions, the expression and activity of cyclooxygenase 2 significantly increases and enhances the circulating levels of prostaglandin E2 (PGE2), which exerts its effects both through specific plasma membrane receptors (EP1-EP4) and by activation of intracellular targets. Here we review the mechanisms involved in the crosstalk between PGE2 and P2Y receptors on macrophages, which is dependent on several isoforms of protein kinase C and protein kinase D1. Due to this crosstalk, a P2Y-dependent increase in calcium is blunted by PGE2 whereas, under these conditions, macrophages exhibit reduced migratory capacity along with enhanced phagocytosis, which contributes to the modulation of the inflammatory response and tissue repair.

Methods for studying P2X4 receptor ion channels in immune cells

The P2X4 receptor is a trimeric ligand-gated ion channel activated by adenosine 5'-triphosphate (ATP). P2X4 is present in immune cells with emerging roles in inflammation and immunity, and related disorders. This review aims to provide an overview of the methods commonly used to study P2X4 in immune cells, focusing on those methods used to assess P2RX4 gene expression, the presence of the P2X4 protein, and P2X4 ion channel activity in these cells from humans, dogs, mice and rats. P2RX4 gene expression in immune cells is commonly assessed using semi-quantitative and quantitative reverse-transcriptase-PCR. The presence of P2X4 protein in immune cells is mainly assessed using anti-P2X4 polyclonal antibodies with immunoblotting or immunochemistry, but the use of these antibodies, as well as monoclonal antibodies and nanobodies to detect P2X4 with flow cytometry is increasing. Notably, use of an anti-P2X4 monoclonal antibody and flow cytometry has revealed that P2X4 is present on immune cells with a rank order of expression in eosinophils, then neutrophils and monocytes, then basophils and B cells, and finally T cells. P2X4 ion channel activity has been assessed mainly by Ca2+ flux assays using the cell permeable Ca2+-sensitive dyes Fura-2 and Fluo-4 with fluorescence microscopy, spectrophotometry, or flow cytometry. However, other methods including electrophysiology, and fluorescence assays measuring Na+ flux (using sodium green tetra-acetate) and dye uptake (using YO-PRO-12+) have been applied. Collectively, these methods have demonstrated the presence of functional P2X4 in monocytes and macrophages, microglia, eosinophils, mast cells and CD4+ T cells, with other evidence suggestive of functional P2X4 in dendritic cells, neutrophils, B cells and CD8+ T cells.

P2X4 signalling contributes to hyperactivity but not pain sensitization comorbidity in a mouse model of attention deficit/hyperactivity disorder

Introduction: Attention deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder characterized by hyperactivity, inattention, and impulsivity that often persist until adulthood. Frequent comorbid disorders accompany ADHD and two thirds of children diagnosed with ADHD also suffer from behavioural disorders and from alteration of sensory processing. We recently characterized the comorbidity between ADHD-like symptoms and pain sensitisation in a pharmacological mouse model of ADHD, and we demonstrated the implication of the anterior cingulate cortex and posterior insula. However, few studies have explored the causal mechanisms underlying the interactions between ADHD and pain. The implication of inflammatory mechanisms has been suggested but the signalling pathways involved have not been explored. Methods: We investigated the roles of purinergic signalling, at the crossroad of pain and neuroinflammatory pathways, by using a transgenic mouse line that carries a total deletion of the P2X4 receptor. Results: We demonstrated that P2X4 deletion prevents hyperactivity in the mouse model of ADHD. In contrast, the absence of P2X4 lowered thermal pain thresholds in sham conditions and did not affect pain sensitization in ADHD-like conditions. We further analysed microglia reactivity and the expression of inflammatory markers in wild type and P2X4KO mice. Our results revealed that P2X4 deletion limits microglia reactivity but at the same time exerts proinflammatory effects in the anterior cingulate cortex and posterior insula. Conclusion: This dual role of P2X4 could be responsible for the differential effects noted on ADHD-like symptoms and pain sensitization and calls for further studies to investigate the therapeutic benefit of targeting the P2X4 receptor in ADHD patients.

Naringin inhibits P2X4 receptor expression on satellite glial cells in the neonatal rat dorsal root ganglion

Naringin inhibits inflammation and oxidative stress, the P2 purinoreceptor X4 receptor (P2X4R) is associated with glial cell activation and inflammation, the purpose of this study is to investigate the effects of naringin on P2X4 receptor expression on satellite glial cells (SGCs) and its possible mechanisms. ATP promoted the SGC activation and upregulated P2X4R expression; naringin inhibited SGC activation, decreased expression of P2X4R, P38 MAPK/ERK, and NF-κB, and reduced levels of Ca2+, TNF-α, and IL-1β in SGCs in an ATP-containing environment. These findings suggest that naringin attenuates the ATP-induced SGC activation and reduces P2X4R expression via the Ca2+-P38 MAPK/ERK-NF-κB pathway.

Pathophysiological mechanism of acute bone loss after fracture

BACKGROUND

Acute bone loss after fracture is associated with various effects on the complete recovery process and a risk of secondary fractures among patients. Studies have reported similarities in pathophysiological mechanisms involved in acute bone loss after fractures and osteoporosis. However, given the silence nature of bone loss and bone metabolism complexities, the actual underlying pathophysiological mechanisms have yet to be fully elucidated.

AIM OF REVIEW

To elaborate the latest findings in basic research with a focus on acute bone loss after fracture. To briefly highlight potential therapeutic targets and current representative drugs. To arouse researchers' attention and discussion on acute bone loss after fracture.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Bone loss after fracture is associated with immobilization, mechanical unloading, blood supply damage, sympathetic nerve regulation, and crosstalk between musculoskeletals among other factors. Current treatment strategies rely on regulation of osteoblasts and osteoclasts, therefore, there is a need to elucidate on the underlying mechanisms of acute bone loss after fractures to inform the development of efficacious and safe drugs. In addition, attention should be paid towards ensuring long-term skeletal health.

Therapeutic targeting of P2X4 receptor and mitochondrial metabolism in clear cell renal carcinoma models

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) is the most common subtype of renal cancer. Large-scale metabolomic data have associated metabolic alterations with the pathogenesis and progression of renal carcinoma and have correlated mitochondrial activity with poor survival in a subset of patients. The aim of this study was to determine whether targeting mitochondria-lysosome interaction could be a novel therapeutic approach using patient-derived organoids as avatar for drug response.

METHODS

RNAseq data analysis and immunohistochemistry were used to show overexpression of Purinergic receptor 4 (P2XR4) in clear cell carcinomas. Seahorse experiments, immunofluorescence and fluorescence cell sorting were used to demonstrate that P2XR4 regulates mitochondrial activity and the balance of radical oxygen species. Pharmacological inhibitors and genetic silencing promoted lysosomal damage, calcium overload in mitochondria and cell death via both necrosis and apoptosis. Finally, we established patient-derived organoids and murine xenograft models to investigate the antitumor effect of P2XR4 inhibition using imaging drug screening, viability assay and immunohistochemistry.

RESULTS

Our data suggest that oxo-phosphorylation is the main source of tumor-derived ATP in a subset of ccRCC cells expressing P2XR4, which exerts a critical impact on tumor energy metabolism and mitochondrial activity. Prolonged mitochondrial failure induced by pharmacological inhibition or P2XR4 silencing was associated with increased oxygen radical species, changes in mitochondrial permeability (i.e., opening of the transition pore complex, dissipation of membrane potential, and calcium overload). Interestingly, higher mitochondrial activity in patient derived organoids was associated with greater sensitivity to P2XR4 inhibition and tumor reduction in a xenograft model.

CONCLUSION

Overall, our results suggest that the perturbed balance between lysosomal integrity and mitochondrial activity induced by P2XR4 inhibition may represent a new therapeutic strategy for a subset of patients with renal carcinoma and that individualized organoids may be help to predict drug efficacy.

Central role of purinergic receptors with inflammation in neuropathic pain-related macrophage-SGC-neuron triad

Adenosine triphosphate (ATP) acts on P2 purinergic receptors as an extracellular signaling molecule. P2 purinergic receptors include P2X ionotropic receptors and P2Y metabotropic receptors. Satellite glial cells (SGCs) and macrophages express P2X and P2Y receptors. Inflammatory cytokines and pro-nociceptive mediators are released by activated macrophages and SGCs, which can act on neurons to promote excitability and firing. In the primary sensory ganglia, in response to signals of injury, SGCs and macrophages accumulate around primary sensory neurons, forming a macrophage-SGC-neuron triad. In addition to affecting the pathological alterations of inflammation-related neuropathic pain, inflammatory cytokines and pro-nociceptive mediators are released by the action of ATP on P2X and P2Y receptors in macrophages and SGCs. Macrophages and SGCs work together to enhance and prolong neuropathic pain. The macrophage-SGC-neuron triad communicates with each other through ATP and other inflammatory mediators and maintains and promotes the initiation and development of inflammation related-neuropathic pain. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

P2 receptor-mediated signaling in the physiological and pathological brain: From development to aging and disease

The purinergic pathway mediates both pro-inflammatory and anti-inflammatory responses, whereas the breakdown of adenosine triphosphate (ATP) is in a critical equilibrium. Under physiological conditions, extracellular ATP is maintained at a nanomolar concentration. Whether released into the medium following tissue damage, inflammation, or hypoxia, ATP is considered a clear indicator of cell damage and a marker of pathological conditions. In this overview, we provide an update on the participation of P2 receptor-mediated purinergic signaling in normal and pathological brain development, with special emphasis on neurodevelopmental psychiatric disorders. Since purinergic signaling is ubiquitous, it is not surprising that it plays a prominent role in developmental processes and pathological alterations. The main aim of this review is to conceptualize the time-dependent dynamic changes in the participation of different players in the purinome in shaping the normal and aberrant developmental patterns and diseases of the central nervous system over one's lifespan.

Neurosteroids as positive and negative allosteric modulators of ligand-gated ion channels: P2X receptor perspective

Neurosteroids are steroids synthesized de novo in the brain from cholesterol in an independent manner from peripheral steroid sources. The term "neuroactive steroid" includes all steroids independent of their origin, and newly synthesized analogs of neurosteroids that modify neuronal activities. In vivo application of neuroactive steroids induces potent anxiolytic, antidepressant, anticonvulsant, sedative, analgesic and amnesic effects, mainly through interaction with the γ-aminobutyric acid type-A receptor (GABA_AR). However, neuroactive steroids also act as positive or negative allosteric regulators on several ligand-gated channels including N-methyl-d-aspartate receptors (NMDARs), nicotinic acetylcholine receptors (nAChRs) and ATP-gated purinergic P2X receptors. Seven different P2X subunits (P2X1-7) can assemble to form homotrimeric or heterotrimeric ion channels permeable for monovalent cations and calcium. Among them, P2X2, P2X4, and P2X7 are the most abundant within the brain and can be regulated by neurosteroids. Transmembrane domains are necessary for neurosteroid binding, however, no generic motif of amino acids can accurately predict the neurosteroid binding site for any of the ligand-gated ion channels including P2X. Here, we will review what is currently known about the modulation of rat and human P2X by neuroactive steroids and the possible structural determinants underlying neurosteroid-induced potentiation and inhibition of the P2X2 and P2X4 receptors.

P2X4 receptor modulates gut inflammation and favours microbial homeostasis in colitis

BACKGROUND

Inflammatory bowel disease (IBD) is a non-specific chronic inflammatory disease of the intestine. In addition to genetic susceptibility, environmental factors and dysregulated host immunity, the gut microbiota is implicated in the pathogenesis of Crohn's disease (CD) or ulcerative colitis (UC), the two primary types of IBD. The P2X4 receptor has been demonstrated to have a crucial role in preventing infection, inflammation, and organ damage. However, it remains unclear whether the P2X4 receptor affects IBD and the underlying mechanisms.

METHODS

Colitis was induced in mice administrated with dextran sodium sulphate (DSS). 16S rDNA sequencing was used to analyze the gut microbiota in knockout and wild-type mice. Clinical and histopathological parameters were monitored throughout the disease progression.

RESULTS

Gene Expression Omnibus analysis showed the downregulation of P2RX4 (P2rx4) expression in colonic tissues from patients or mice with IBD. However, its expression at the protein levels was upregulated on day 4 or 6 and then downregulated on day 7 in C57BL/6 mice treated with DSS. Gene ablation of P2rx4 aggravated DSS-induced colitis accompanying gut microbiota dysbiosis in mice. Moreover, P2X4 receptor-positive modulator ivermectin alleviated colitis and corrected dysregulated microbiota in wild-type C57BL/6 mice. Further antibiotic-treated gut microbiota depletion, cohousing experiment, and fecal microbiota transplantation proved that gut microbiota dysbiosis was associated with the aggravation of colitis in the mouse model initiated by P2rx4.

CONCLUSIONS

Our findings elaborate on an unrevealed etiopathophysiological mechanism by which microbiota dysbiosis induced by the P2X4 receptor influences the development of colitis, indicating that the P2X4 receptor represents a promising target for treating patients with CD and UC.

Transcriptomic analysis reveals novel age-independent immunomodulatory proteins as a mode of cerebroprotection in P2X4R KO mice after ischemic stroke

Identification of new potential drug target proteins and their plausible mechanisms for stroke treatment is critically needed. We previously showed that genetic deletion and short-term pharmacological inhibition of P2X4R, a purinergic receptor for adenosine triphosphate ATP, provides acute cerebroprotection. However, potential mechanisms remain unknown. Therefore, we employed RNA-seq technology to identify the gene expression profiles, pathway analysis, and qPCR validation of differentially expressed genes (DEGs). This analysis identified roles of DEGs in certain biological processes responsible for P2X4R-dependent cerebroprotection after stroke. We subjected both young and aged male and female global P2X4 KO and littermate WT mice to ischemic stroke. After 3 days, mice were sacrificed, total RNA was isolated using Trizol, and subjected to RNA-seq and Nanostring-mediated qPCR. DESeq2, Gene Ontology (GO), and Ingenuity Pathway Analysis (IPA) were used to identify mRNA transcript expression profiles and biological pathways. We found 2246 DEGs in P2X4R KO vs WT tissue after stroke. Out of these DEGs, 1920 gene were downregulated, and 325 genes were upregulated in KO. GO/IPA analysis of the top 300 DEGs suggests an enrichment of inflammation and extracellular matrix component genes. qPCR validation of the top 30 DEGs revealed downregulation of two common age-independent genes in P2X4R KO mice: Interleukin-6 ( IL-6) , an inflammatory cytokine, and Cytotoxic T Lymphocyte-Associated Protein 2 alpha ( Ctla2a ), an immunosuppressive factor. These data suggest that P2X4R-mediated cerebroprotection after stroke is initiated by attenuation of immune modulatory pathways in both young and aged mice of both sexes.

Neuronal P2X4 receptor may contribute to peripheral inflammatory pain in rat spinal dorsal horn

Objective

Intense inflammation may result in pain, which manifests as spinal central sensitization. There is growing evidence that purinergic signaling plays a pivotal role in the orchestration of pain processing. Over the last decade the ionotropic P2X purino receptor 4 (P2X4) got into spotlight in neuropathic disorders, however its precise spinal expression was scantily characterized during inflammatory pain. Thus, we intended to analyze the receptor distribution within spinal dorsal horn and lumbar dorsal root ganglia (DRG) of rats suffering in inflammatory pain induced by complete Freund adjuvant (CFA).

Methods

CFA-induced peripheral inflammation was validated by mechanical and thermal behavioral tests. In order to ensure about the putative alteration of spinal P2X4 receptor gene expression qPCR reactions were designed, followed by immunoperoxidase and Western blot experiments to assess changes at a protein level. Colocalization of P2X4 with neuronal and glial markers was investigated by double immunofluorescent labelings, which were subsequently analyzed with IMARIS software. Transmission electronmicroscopy was applied to study the ultrastructural localization of the receptor. Concurrently, in lumbar DRG cells similar methodology has been carried out to complete our observations.

Results

The figures of mechanical and thermal behavioral tests proved the establishment of CFA-induced inflammatory pain. We observed significant enhancement of P2X4 transcript level within the spinal dorsal horn 3 days upon CFA administration. Elevation of P2X4 immunoreactivity within Rexed lamina I-II of the spinal gray matter was synchronous with mRNA expression, and confirmed by protein blotting. According to IMARIS analysis the robust protein increase was mainly detected on primary afferent axonterminals and GFAP-labelled astrocyte membrane compartments, but not on postsynaptic dendrites was also validated ultrastructurally within the spinal dorsal horn. Furthermore, lumbar DRG analysis demonstrated that peptidergic and non-peptidergic nociceptive subsets of ganglia cells were also abundantly positive for P2X4 receptor in CFA model.

Conclusion

Here we provide novel evidence about involvement of neuronal and glial P2X4 receptor in the establishment of inflammatory pain.

BDNF-TrkB signaling pathway-mediated microglial activation induces neuronal KCC2 downregulation contributing to dynamic allodynia following spared nerve injury

Mechanical allodynia can be evoked by punctate pressure contact with the skin (punctate mechanical allodynia) and dynamic contact stimulation induced by gentle touching of the skin (dynamic mechanical allodynia). Dynamic allodynia is insensitive to morphine treatment and is transmitted through the spinal dorsal horn by a specific neuronal pathway, which is different from that for punctate allodynia, leading to difficulties in clinical treatment. K+-Cl- cotransporter-2 (KCC2) is one of the major determinants of inhibitory efficiency, and the inhibitory system in the spinal cord is important in the regulation of neuropathic pain. The aim of the current study was to determine whether neuronal KCC2 is involved in the induction of dynamic allodynia and to identify underlying spinal mechanisms involved in this process. Dynamic and punctate allodynia were assessed using either von Frey filaments or a paint brush in a spared nerve injury (SNI) mouse model. Our study discovered that the downregulated neuronal membrane KCC2 (mKCC2) in the spinal dorsal horn of SNI mice is closely associated with SNI-induced dynamic allodynia, as the prevention of KCC2 downregulation significantly suppressed the induction of dynamic allodynia. The over activation of microglia in the spinal dorsal horn after SNI was at least one of the triggers in SNI-induced mKCC2 reduction and dynamic allodynia, as these effects were blocked by the inhibition of microglial activation. Finally, the BDNF-TrkB pathway mediated by activated microglial affected SNI-induced dynamic allodynia through neuronal KCC2 downregulation. Overall, our findings revealed that activation of microglia through the BDNF-TrkB pathway affected neuronal KCC2 downregulation, contributing to dynamic allodynia induction in an SNI mouse model.

Physiologic roles of P2 receptors in leukocytes

Since their discovery in the 1970s, purinergic receptors have been shown to play key roles in a wide variety of biologic systems and cell types. In the immune system, purinergic receptors participate in innate immunity and in the modulation of the adaptive immune response. In particular, P2 receptors, which respond to extracellular nucleotides, are widely expressed on leukocytes, causing the release of cytokines and chemokines and the formation of inflammatory mediators, and inducing phagocytosis, degranulation, and cell death. The activity of these receptors is regulated by ectonucleotidases-expressed in these same cell types-which regulate the availability of nucleotides in the extracellular environment. In this article, we review the characteristics of the main purinergic receptor subtypes present in the immune system, focusing on the P2 family. In addition, we describe the physiologic roles of the P2 receptors already identified in leukocytes and how they can positively or negatively modulate the development of infectious diseases, inflammation, and pain.

Single-cell RNA sequencing reveals distinct transcriptional features of the purinergic signaling in mouse trigeminal ganglion

Trigeminal ganglion (TG) is the first station of sensory pathways in the orofacial region. The TG neurons communicate with satellite glial cells (SGCs), macrophages and other cells forming a functional unit that is responsible for processing of orofacial sensory information. Purinergic signaling, one of the most widespread autocrine and paracrine pathways, plays a crucial role in intercellular communication. The multidirectional action of purinergic signaling in different cell types contributes to the neuromodulation and orofacial sensation. To fully understand the purinergic signaling in these processes, it is essential to determine the shared and unique expression patterns of genes associated with purinergic signaling in different cell types. Here, we performed single-cell RNA sequencing of 22,969 cells isolated from normal mouse TGs. We identified 18 distinct cell populations, including 6 neuron subpopulations, 3 glial subpopulations, 7 immune cell subpopulations, fibroblasts, and endothelial cells. We also revealed the transcriptional features of genes associated with purinergic signaling, including purinergic receptors, extracellular adenosine triphosphate (eATP) release channels, eATP metabolism-associated enzymes, and eATP transporters in each cell type. Our results have important implications for understanding and predicting the cell type-specific roles of the purinergic signaling in orofacial signal processing in the trigeminal primary sensory system.

The contribution of ion channels to shaping macrophage behaviour

The expanding roles of macrophages in physiological and pathophysiological mechanisms now include normal tissue homeostasis, tissue repair and regeneration, including neuronal tissue; initiation, progression, and resolution of the inflammatory response and a diverse array of anti-microbial activities. Two hallmarks of macrophage activity which appear to be fundamental to their diverse cellular functionalities are cellular plasticity and phenotypic heterogeneity. Macrophage plasticity allows these cells to take on a broad spectrum of differing cellular phenotypes in response to local and possibly previous encountered environmental signals. Cellular plasticity also contributes to tissue- and stimulus-dependent macrophage heterogeneity, which manifests itself as different macrophage phenotypes being found at different tissue locations and/or after different cell stimuli. Together, plasticity and heterogeneity align macrophage phenotypes to their required local cellular functions and prevent inappropriate activation of the cell, which could lead to pathology. To execute the appropriate function, which must be regulated at the qualitative, quantitative, spatial and temporal levels, macrophages constantly monitor intracellular and extracellular parameters to initiate and control the appropriate cell signaling cascades. The sensors and signaling mechanisms which control macrophages are the focus of a considerable amount of research. Ion channels regulate the flow of ions between cellular membranes and are critical to cell signaling mechanisms in a variety of cellular functions. It is therefore surprising that the role of ion channels in the macrophage biology has been relatively overlooked. In this review we provide a summary of ion channel research in macrophages. We begin by giving a narrative-based explanation of the membrane potential and its importance in cell biology. We then report on research implicating different ion channel families in macrophage functions. Finally, we highlight some areas of ion channel research in macrophages which need to be addressed, future possible developments in this field and therapeutic potential.

The Role of Neuro-Immune Interactions in Chronic Pain: Implications for Clinical Practice

Chronic pain remains a public health problem and contributes to the ongoing opioid epidemic. Current pain management therapies still leave many patients with poorly controlled pain, thus new or improved treatments are desperately needed. One major challenge in pain research is the translation of preclinical findings into effective clinical practice. The local neuroimmune interface plays an important role in the initiation and maintenance of chronic pain and is therefore a promising target for novel therapeutic development. Neurons interface with immune and immunocompetent cells in many distinct microenvironments along the nociceptive circuitry. The local neuroimmune interface can modulate the activity and property of the neurons to affect peripheral and central sensitization. In this review, we highlight a specific subset of many neuroimmune interfaces. In the central nervous system, we examine the interface between neurons and microglia, astrocytes, and T lymphocytes. In the periphery, we profile the interface between neurons in the dorsal root ganglion with T lymphocytes, satellite glial cells, and macrophages. To bridge the gap between preclinical research and clinical practice, we review the preclinical studies of each neuroimmune interface, discuss current clinical treatments in pain medicine that may exert its action at the neuroimmune interface, and highlight opportunities for future clinical research efforts.

Increased surface P2X4 receptors by mutant SOD1 proteins contribute to ALS pathogenesis in SOD1-G93A mice

Amyotrophic lateral sclerosis (ALS) is a fatal motoneuron (MN) disease characterized by protein misfolding and aggregation leading to cellular degeneration. So far neither biomarker, nor effective treatment has been found. ATP signaling and P2X4 receptors (P2X4) are upregulated in various neurodegenerative diseases. Here we show that several ALS-related misfolded proteins including mutants of SOD1 or TDP-43 lead to a significant increase in surface P2X4 receptor density and function in vitro. In addition, we demonstrate in the spinal the cord of SOD1-G93A (SOD1) mice that misfolded SOD1-G93A proteins directly interact with endocytic adaptor protein-2 (AP2); thus, acting as negative competitors for the interaction between AP2 and P2X4, impairing constitutive P2X4 endocytosis. The higher P2X4 surface density was particularly observed in peripheral macrophages of SOD1 mice before the onset and during the progression of ALS symptoms positioning P2X4 as a potential early biomarker for ALS. P2X4 expression was also upregulated in spinal microglia of SOD1 mice during ALS and affect microglial inflammatory responses. Importantly, we report using double transgenic SOD1 mice expressing internalization-defective P2X4mCherryIN knock-in gene or invalidated for the P2X4 gene that P2X4 is instrumental for motor symptoms, ALS progression and survival. This study highlights the role of P2X4 in the pathophysiology of ALS and thus its potential for the development of biomarkers and treatments. We also decipher the molecular mechanism by which misfolded proteins related to ALS impact P2X4 trafficking at early pathological stage in cells expressing-P2X4.

Prolonged PGE2 treatment increased TTX-sensitive but not TTX-resistant sodium current in trigeminal ganglionic neurons

Prostaglandin E₂ (PGE₂) is an important inflammatory mediator for the initiation and maintenance of inflammatory and neuropathic pain. The acute effect of PGE₂ on sodium currents has been widely characterized in sensory neurons; however, the prolonged effect of PGE₂ remains to be determined. Here, we performed patch clamp recordings to evaluate the acute and prolonged effects of PGE₂ on sodium currents in trigeminal ganglionic (TG) neurons from male Sprague-Dawley rats. We found that 24-h treatment with PGE₂ (10 μM) increased the peak sodium current density by approximately 31% in a voltage-dependent manner and shifted the activation curve in a hyperpolarized direction but did not affect steady-state inactivation. Furthermore, treatment with PGE₂ for 24 h increased the current density of tetrodotoxin-sensitive (TTX-S) but not TTX-resistant (TTX-R) channels significantly. Interestingly, TTX-S current was increased mostly in medium-sized, but not in small-sized, neurons after 24 h of treatment with PGE₂. Moreover, the mRNA level of TTX-S Nav1.1 but not TTX-R Nav1.8 or Nav1.9 was significantly increased after 24 h of treatment with PGE_2. In contrast, 5-min treatment with PGE₂ (10 μM) increased the peak sodium current density by approximately 29% and increased TTX-R sodium currents, but not TTX-S currents, in both small- and medium-sized TG neurons. Our results presented a differential regulation of subtypes of sodium channels by acute and prolonged treatments of PGE₂, which may help to better understand the mechanism of PGE₂-mediated orofacial pain development.

The P2X4 Receptor: Cellular and Molecular Characteristics of a Promising Neuroinflammatory Target

The adenosine 5′-triphosphate-gated P2X4 receptor channel is a promising target in neuroinflammatory disorders, but the ability to effectively target these receptors in models of neuroinflammation has presented a constant challenge. As such, the exact role of P2X4 receptors and their cell signalling mechanisms in human physiology and pathophysiology still requires further elucidation. To this end, research into the molecular mechanisms of P2X4 receptor activation, modulation, and inhibition has continued to gain momentum in an attempt to further describe the role of P2X4 receptors in neuroinflammation and other disease settings. Here we provide an overview of the current understanding of the P2X4 receptor, including its expression and function in cells involved in neuroinflammatory signalling. We discuss the pharmacology of P2X4 receptors and provide an overview of P2X4-targeting molecules, including agonists, positive allosteric modulators, and antagonists. Finally, we discuss the use of P2X4 receptor modulators and antagonists in models of neuroinflammatory cell signalling and disease.

P2X Receptor Antagonists and their Potential as Therapeutics: a patent review (2010 - 2021)

INTRODUCTION

: Purinergic receptors play a critical role in neurotransmission, and modulation of complex physiological functions. As such, they have been implicated in numerous disease states including chronic pain, inflammation, autoimmune disease, and cancer. The past decade has seen substantial progress in the design of novel chemical compounds that act on the P2X class of receptors and warrants an updated review of this field.

AREAS COVERED

: This review provides a summary of the patent literature describing the discovery and clinical uses of P2X receptor antagonists published between 2010 and September 2021. The reader will gain information on structural claims, representative structures, and biological data of recently reported antagonists for seven P2X receptor subtypes.

EXPERT OPINION

: The potential for therapeutic intervention through the design and use of purinergic receptor inhibitors is pharmacologically well defined. Despite continual advancement in both crystallography and chemical biology strengthening our understanding of purinergic signalling and their roles in pathophysiology, there remains a vast absence of clinically approved chemical modalities. A testament to both the therapeutic potential and academic perseverance in purinergic research is the multitude of research initiatives and pharmaceutical campaigns that maintain active P2X receptor programs that have spanned decades. Very recently, the FDA declined Merck Pharmaceuticals application for Gefapixant, a P2X3 selective inhibitor as a treatment for chronic cough, requesting additional data. This unfortunate setback within the field will ultimately be insignificant considering the long history of P2X investigation and the preclinical and clinical development that would undoubtedly occur over the next decade.

Modulation of P2X4 pore closure by magnesium, potassium, and ATP

The P2X4 receptor plays a prominent role in cellular responses to extracellular ATP. Through classical all-atom molecular dynamics (MD) simulations totaling 24 μs we have investigated how metal-complexed ATP stabilizes the channel's open state and prevents its closing. We have identified two metal-binding sites, Mg2+ and potassium K+, one at the intersection of the three subunits in the ectodomain (MBS1) and the second one near the ATP-binding site (MBS2), similar to those characterized in Gulf Coast P2X. Our data indicate that when Mg2+ and K+ ions are complexed with ATP, the channel is locked into an open state. Interestingly, irrespective of the number of bound ATP molecules, Mg2+ ions bound to the MBS2 impeded the collapse of the open-state protein to a closed state by stabilizing the ATP-protein interactions. However, when Mg2+ in the MBS2 was replaced with K+ ions, as might be expected when in equilibrium with an extracellular solution, the interactions between the subunits were weakened and the pore collapsed. This collapse was apparent when fewer than two ATPs were bound to MBS2 in the presence of K+. Therefore, the different capacities of common cations to stabilize the channel may underlie a mechanism governing P2X4 channel gating in physiological systems. This study therefore provides structural insights into the differential modulation of ATP activation of P2X4 by Mg2+ and K+.

Gut microbiota drives macrophage-dependent self-renewal of intestinal stem cells via niche enteric serotonergic neurons

Lgr5⁺ intestinal stem cells (ISCs) reside within specialized niches at the crypt base and harbor self-renewal and differentiation capacities. ISCs in the crypt base are sustained by their surrounding niche for precise modulation of self-renewal and differentiation. However, how intestinal cells in the crypt niche and microbiota in enteric cavity coordinately regulate ISC stemness remains unclear. Here, we show that ISCs are regulated by microbiota and niche enteric serotonergic neurons. The gut microbiota metabolite valeric acid promotes Tph2 expression in enteric serotonergic neurons via blocking the recruitment of the NuRD complex onto Tph2 promoter. 5-hydroxytryptamine (5-HT) in turn activates PGE2 production in a PGE2⁺ macrophage subset through its receptors HTR2A/3 A; and PGE2 via binding its receptors EP1/EP4, promotes Wnt/β-catenin signaling in ISCs to promote their self-renewal. Our findings illustrate a complex crosstalk among microbiota, intestinal nerve cells, intestinal immune cells and ISCs, revealing a new layer of ISC regulation by niche cells and microbiota.

Thermographic Evaluation of the Duration of Skin Cooling After Cryotherapy in Dogs Following Tibial Plateau Leveling Osteotomy Surgery

Objective

To evaluate the duration of cooling after cryotherapy on the skin over stifle joints in dogs after tibial plateau leveling osteotomy (TPLO) surgery using thermography.

Materials and Methods

Seventeen client-owned dogs of various breeds were enrolled in the study. Dogs underwent TPLO surgeries, and on the next day, thermal imaging was performed on the operated stifle prior to cryotherapy for baseline. Orthogonal views were repeated at 30-min intervals until the skin over the stifle had thermally equilibrated. An ice pack was applied for 20 min on the medial and lateral aspects of the stifle. Each stifle was then re-imaged every 15 min for the first 60 min then every 30 min subsequently until the temperature was within 1°C of the pre-cryotherapy temperature.

Results

Mean skin temperature of the medial view showed no significance difference compared to baseline value at 45 min after cryotherapy was discontinued and after 60 min for the lateral and cranial views. Mean skin temperature was overall higher in the medial view compared to the lateral and cranial during the rewarming period (except immediately after cold application). Mean skin temperatures of all views combined showed a significant decrease in temperature during cryotherapy application, with a slow increase until a plateau was reached after 45 min of rewarming.

Conclusions and Clinical Relevance

Dogs undergoing TPLO for cranial cruciate ligament injury showed quicker rewarming period of superficial tissues compared to previous studies. Cryotherapy is a beneficial modality to reduce superficial tissue temperature in dogs undergoing TPLO, acknowledging that these dogs may require more frequent cryotherapy post-operatively due to more rapid rewarming time compared to dogs without surgery.

Identification of a Pain-Specific Gene Expression Profile for Pediatric Recurrent Abdominal Pain

Objectives: Functional Abdominal Pain (FAP) and Irritable Bowel Syndrome (IBS) are common recurrent abdominal pain diagnoses with the hallmark, lack of inflammation. To identify a biological signature for IBS/FAP in the colon, this study used genetic profiling to uncover gene expression changes associated with IBS/FAP and abdominal pain. Methods: Patients (8 to 17 years) newly diagnosed with IBS or FAP were enrolled in the study. At diagnostic colonoscopy, three rectal biopsies were collected, and gene expression analysis was performed using a Qiagen PCR Array. Relative fold difference in gene expression for 84 pain-associated genes was calculated using the 2-ΔΔ Cq method compared with pain-free controls. Factors affecting pain burden (Pain Burden Interview; PBI) were analyzed, including age, sex, rectal inflammation, and gene expression. Data were analyzed using multiple stepwise linear regression and 2-tailed t tests (P ≤ 0.05). Results: Of the 22 total patients in the study, 19 were diagnosed with either IBS-Constipation (frequency of 5.26%), IBS-Diarrhea (47.37%), IBS-Mixed (10.53%), or FAP (36.84%). IBS/FAP patients reported significantly higher pain burden at the time of diagnosis compared to pain-free controls (p < 0.001), as well as significantly higher abdominal pain (p = 0.01). Of the 84 genes, expression of GRIN1 (p = 0.02), MAPK3 (p = 0.04), P2X4 (p = 0.04), and PTGES3 (p = 0.02) were all significantly associated with PBI score. Discussion: Abdominal pain associated with IBS/FAP in pediatric patients may be linked to the expression of GRIN1, MAPK3, P2X4, and PTGES3, pointing to potential novel therapeutic targets for management of recurring abdominal pain.

Oxidized linoleic acid metabolites maintain mechanical and thermal hypersensitivity during sub-chronic inflammatory pain

Inflammatory pain serves as a protective defense mechanism which becomes pathological when it turns into chronic inflammatory pain. This transition is mediated by a variety of peripheral mediators that sensitize nociceptors and increase pain perception in sensory neurons. Besides cytokines, chemokines and growth factors, accumulating evidence shows that oxidized lipids, such as eicosanoids and oxidized linoleic acid metabolites, contribute to this sensitization process. Most notably, the oxidized linoleic acid metabolite and partial TRPV1 agonist 9-HODE (hydroxyoctadecadienoic acid) was shown to be involved in this sensitization process. However, it is still unknown how some of the oxidized linoleic acid metabolites are synthesized in the inflammatory environment and in which phase of inflammation they become relevant. Here we show that the concentrations of oxidized linoleic acid metabolites, especially 9-HODE and 13-HODE, are significantly increased in inflamed paw tissue and the corresponding dorsal root ganglia in the sub-chronic phase of inflammation. Surprisingly, classical inflammatory lipid markers, such as prostaglandins were at basal levels in this phase of inflammation. Moreover, we revealed the cell type specific synthesis pathways of oxidized linoleic acid metabolites in primary macrophages, primary neutrophils and dorsal root ganglia. Finally, we show that blocking the most elevated metabolites 9-HODE and 13-HODE at the site of inflammation in the sub-chronic phase of inflammation, leads to a significant relief of mechanical and thermal hypersensitivity in vivo. In summary, these data offer an approach to specifically target oxidized linoleic acid metabolites in the transition of acute inflammatory pain to chronic inflammatory pain.

P2X4 and P2X7 are essential players in basal T cell activity and Ca2+ signaling milliseconds after T cell activation

Initial T cell activation is triggered by the formation of highly dynamic, spatiotemporally restricted Ca²⁺ microdomains. Purinergic signaling is known to be involved in Ca²⁺ influx in T cells at later stages compared to the initial microdomain formation. Using a high-resolution Ca²⁺ live-cell imaging system, we show that the two purinergic cation channels P2X4 and P2X7 not only are involved in the global Ca²⁺ signals but also promote initial Ca²⁺ microdomains tens of milliseconds after T cell stimulation. These Ca²⁺ microdomains were significantly decreased in T cells from P2rx4^-/- and P2rx7^-/- mice or by pharmacological inhibition or blocking. Furthermore, we show a pannexin-1-dependent activation of P2X4 in the absence of T cell receptor/CD3 stimulation. Subsequently, upon T cell receptor/CD3 stimulation, ATP release is increased and autocrine activation of both P2X4 and P2X7 then amplifies initial Ca²⁺ microdomains already in the first second of T cell activation.

Pathophysiological Role of Purinergic P2X Receptors in Digestive System Diseases

P2X receptors (P2XRs) are trimeric, non-selective cation channels activated by extracellular ATP and widely distributed in the digestive system. P2XRs have an important role in the physiological function of the digestive system, such as neurotransmission, ion transports, proliferation and apoptosis, muscle contraction, and relaxation. P2XRs can be involved in pain mechanisms both centrally and in the periphery and confirmed the association of P2XRs with visceral pain. In the periphery, ATP can be released as a result of tissue injury, visceral distension, or sympathetic activation and can excite nociceptive primary afferents by acting at homomeric P2X(3)R or heteromeric P2X(2/3)R. Thus, peripheral P2XRs, and homomeric P2X(3) and/or heteromeric P2X(2/3)R in particular, constitute attractive targets for analgesic drugs. Recently studies have shown that P2XRs have made significant advances in inflammation and cancer. P2X7R mediates NLRP3 inflammasome activation, cytokine and chemokine release, T lymphocyte survival and differentiation, transcription factor activation, and cell death. The P2X7R is a potent stimulant of inflammation and immunity and a promoter of cancer cell growth. This makes P2X7R an appealing target for anti-inflammatory and anti-cancer therapy. It is believed that with the further study of P2XRs and its subtypes, P2XRs and its specific antagonists will be expected to be widely used in the treatment of human digestive diseases in the future.

Single-Dose P2 X4R Single-Chain Fragment Variable Antibody Permanently Reverses Chronic Pain in Male Mice

Non-opioid single-chain variable fragment (scFv) small antibodies were generated as pain-reducing block of P2X4R receptor (P2X4R). A panel of scFvs targeting an extracellular peptide sequence of P2X4R was generated followed by cell-free ribosome display for recombinant antibody selection. After three rounds of bio-panning, a panel of recombinant antibodies was isolated and characterized by ELISA, cross-reactivity analysis, and immunoblotting/immunostaining. Generated scFv antibodies feature binding activity similar to monoclonal antibodies but with stronger affinity and increased tissue penetrability due to their ~30% smaller size. Two anti-P2X4R scFv clones (95, 12) with high specificity and affinity binding were selected for in vivo testing in male and female mice with trigeminal nerve chronic neuropathic pain (FRICT-ION model) persisting for several months in untreated BALBc mice. A single dose of P2X4R scFv (4 mg/kg, i.p.) successfully, completely, and permanently reversed chronic neuropathic pain-like measures in male mice only, providing retention of baseline behaviors indefinitely. Untreated mice retained hypersensitivity, and developed anxiety- and depression-like behaviors within 5 weeks. In vitro P2X4R scFv 95 treatment significantly increased the rheobase of larger-diameter (>25 µm) trigeminal ganglia (TG) neurons from FRICT-ION mice compared to controls. The data support use of engineered scFv antibodies as non-opioid biotherapeutic interventions for chronic pain.

Involvement of the miR-363-5p/P2RX4 Axis in Regulating Schwann Cell Phenotype after Nerve Injury

Although microRNAs (miRNAs or miRs) have been studied in the peripheral nervous system, their function in Schwann cells remains elusive. In this study, we performed a microRNA array analysis of cyclic adenosine monophosphate (cAMP)-induced differentiated primary Schwann cells. KEGG pathway enrichment analysis of the target genes showed that upregulated miRNAs (mR212-5p, miR335, miR20b-5p, miR146b-3p, and miR363-5p) were related to the calcium signaling pathway, regulation of actin cytoskeleton, retrograde endocannabinoid signaling, and central carbon metabolism in cancer. Several key factors, such as purinergic receptors (P2X), guanine nucleotide-binding protein G(olf) subunit alpha (GNAL), P2RX5, P2RX3, platelet-derived growth factor receptor alpha (PDGFRA), and inositol 1,4,5-trisphosphate receptor type 2 (ITPR2; calcium signaling pathway) are potential targets of miRNAs regulating cAMP. Our analysis revealed that miRNAs were differentially expressed in cAMP-treated Schwann cells; miRNA363-5p was upregulated and directly targeted the P2X purinoceptor 4 (P2RX4)-UTR, reducing the luciferase activity of P2RX4. The expression of miRNA363-5p was inhibited and the expression of P2RX4 was upregulated in sciatic nerve injury. In contrast, miRNA363-5p expression was upregulated and P2RX4 expression was downregulated during postnatal development. Of note, a P2RX4 antagonist counteracted myelin degradation after nerve injury and increased pERK and c-Jun expression. Interestingly, a P2RX4 antagonist increased the levels of miRNA363-5p. This study suggests that a double-negative feedback loop between miRNA363-5p and P2RX4 contributes to the dedifferentiation and migration of Schwann cells after nerve injury.

P2X4 Receptors Mediate Ca2+ Release from Lysosomes in Response to Stimulation of P2X7 and H1 Histamine Receptors

The P2X4 purinergic receptor is targeted to endolysosomes, where it mediates an inward current dependent on luminal ATP and pH. Activation of P2X4 receptors was previously shown to trigger lysosome fusion, but the regulation of P2X4 receptors and their role in lysosomal Ca²⁺ signaling are poorly understood. We show that lysosomal P2X4 receptors are activated downstream of plasma membrane P2X7 and H₁ histamine receptor stimulation. When P2X4 receptors are expressed, the increase in near-lysosome cytosolic [Ca²⁺] is exaggerated, as detected with a low-affinity targeted Ca²⁺ sensor. P2X4-dependent changes in lysosome properties were triggered downstream of P2X7 receptor activation, including an enlargement of lysosomes indicative of homotypic fusion and a redistribution of lysosomes towards the periphery of the cell. Lysosomal P2X4 receptors, therefore, have a role in regulating lysosomal Ca²⁺ release and the regulation of lysosomal membrane trafficking.

Investigation on the mechanisms of guiqi huoxue capsule for treating cervical spondylosis based on network pharmacology and molecular docking

BACKGROUND

Guiqi huoxue capsule (GQHXC) is a patented Chinese medicine used for treating a liver and kidney deficiency and blood stasis syndrome due to qi deficiency. It is caused by cervical spondylosis (cervical spondylotic radiculopathy (CSR), mixed cervical spondylosis mainly composed of nerve root type). Its underlying mechanisms need, however, to be further clarified.

METHODS

In this study, collecting compounds, predicting therapeutic targets, constructing networks, and analyzing biological functions and pathways were based on network pharmacology analysis. In addition, molecular docking verification was engaged to assess the binding potential of selected target-compound pairs.

RESULTS

We established 5 networks: compound-putative target network of GQHXC, protein-protein interaction (PPI) network related to CSR, compound-CSR target network, potential therapeutic targets PPI network, and herb-compound-target-pathway network. Network analysis indicated that 7 targets (tumor necrosis factor [TNF], interleukin 6 [IL6], nitric oxide synthase 3 [NOS3], Interleukin-8 [CXCL8], prostaglandin-endoperoxide synthase 2 [PTGS2], vascular endothelial growth factor A [VEGFA], and AP-1 transcription factor subunit [JUN]) might be the therapeutic targets of GQHXC in CSR. Moreover, molecular docking verification showed that TNF, IL6, NOS3, CXCL8, PTGS2, VEGFA, and JUN had a good is interaction with the corresponding compounds. Furthermore, enrichment analysis indicated that GQHXC might exert a curative role in CSR by regulating some important pathways, such as TNF signaling pathway, NF-kappa B signaling pathway, AGE-RAGE signaling pathway in diabetic complications, and so on.

CONCLUSION

Our study preliminarily explained the underlying mechanisms of GQHXC for treating CSR, and molecular docking verification was adopted as an additional verification. These findings laid a valuable foundation for experimental research and further application of GQHXC in the clinical treatment of CSR.

Suramin attenuates intervertebral disc degeneration by inhibiting NF-κB signalling pathway

Aims

Interleukin (IL)-1β is one of the major pathogenic regulators during the pathological development of intervertebral disc degeneration (IDD). However, effective treatment options for IDD are limited. Suramin is used to treat African sleeping sickness. This study aimed to investigate the pharmacological effects of suramin on mitigating IDD and to characterize the underlying mechanism.

Methods

Porcine nucleus pulposus (NP) cells were treated with vehicle, 10 ng/ml IL-1β, 10 μM suramin, or 10 μM suramin plus IL-1β. The expression levels of catabolic and anabolic proteins, proinflammatory cytokines, mitogen-activated protein kinase (MAPK), and nuclear factor (NF)-κB-related signalling molecules were assessed by Western blotting, quantitative real-time polymerase chain reaction (qRT-PCR), and immunofluorescence analysis. Flow cytometry was applied to detect apoptotic cells. The ex vivo effects of suramin were examined using IDD organ culture and differentiation was analyzed by Safranin O-Fast green and Alcian blue staining.

Results

Suramin inhibited IL-1β-induced apoptosis, downregulated matrix metalloproteinase (MMP)-3, MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4, and ADAMTS-5, and upregulated collagen 2A (Col2a1) and aggrecan in IL-1β-treated NP cells. IL-1β-induced inflammation, assessed by IL-1β, IL-8, and tumour necrosis factor α (TNF-α) upregulation, was alleviated by suramin treatment. Suramin suppressed IL-1β-mediated proteoglycan depletion and the induction of MMP-3, ADAMTS-4, and pro-inflammatory gene expression in ex vivo experiments.

Conclusion

Suramin administration represents a novel and effectively therapeutic approach, which could potentially alleviate IDD by reducing extracellular matrix (ECM) deposition and inhibiting apoptosis and inflammatory responses in the NP cells.

Cite this article: Bone Joint Res 2021;10(8):498–513.

Macrophage as a Peripheral Pain Regulator

A neuroimmune crosstalk is involved in somatic and visceral pathological pain including inflammatory and neuropathic components. Apart from microglia essential for spinal and supraspinal pain processing, the interaction of bone marrow-derived infiltrating macrophages and/or tissue-resident macrophages with the primary afferent neurons regulates pain signals in the peripheral tissue. Recent studies have uncovered previously unknown characteristics of tissue-resident macrophages, such as their origins and association with regulation of pain signals. Peripheral nerve macrophages and intestinal resident macrophages, in addition to adult monocyte-derived infiltrating macrophages, secrete a variety of mediators, such as tumor necrosis factor-α, interleukin (IL)-1β, IL-6, high mobility group box 1 and bone morphogenic protein 2 (BMP2), that regulate the excitability of the primary afferents. Neuron-derived mediators including neuropeptides, ATP and macrophage-colony stimulating factor regulate the activity or polarization of diverse macrophages. Thus, macrophages have multitasks in homeostatic conditions and participate in somatic and visceral pathological pain by interacting with neurons.

Role of SIRT1 in Neuropathic Pain from the Viewpoint of Neuroimmunity

The current clinical first-line treatment of neuropathic pain still considers only the nervous system as the target, and its therapeutic effect is limited. An increasing number of studies support the opinion that neuropathic pain is a result of the combined action of the sensory nervous system and the related immune system. Under physiological conditions, both the nervous system and the immune system can maintain homeostasis by adjusting the mitochondrial function when sensing noxious stimulation. However, in the case of neuropathic pain, mitochondrial regulatory dysfunction occurs, which may result from the decreased expression of SIRT1. In this study, we review the role of SIRT1 in neuropathic pain from the viewpoint of neuroimmunity.

Neuropathic pain modeling: Focus on synaptic and ion channel mechanisms

Animal models of pain consist of modeling a pain-like state and measuring the consequent behavior. The first animal models of neuropathic pain (NP) were developed in rodents with a total lesion of the sciatic nerve. Later, other models targeting central or peripheral branches of nerves were developed to identify novel mechanisms that contribute to persistent pain conditions in NP. Objective assessment of pain in these different animal models represents a significant challenge for pre-clinical research. Multiple behavioral approaches are used to investigate and to validate pain phenotypes including withdrawal reflex to evoked stimuli, vocalizations, spontaneous pain, but also emotional and affective behaviors. Furthermore, animal models were very useful in investigating the mechanisms of NP. This review will focus on a detailed description of rodent models of NP and provide an overview of the assessment of the sensory and emotional components of pain. A detailed inventory will be made to examine spinal mechanisms involved in NP-induced hyperexcitability and underlying the current pharmacological approaches used in clinics with the possibility to present new avenues for future treatment. The success of pre-clinical studies in this area of research depends on the choice of the relevant model and the appropriate test based on the objectives of the study.

Contribution of P2X4 receptor in pain associated with rheumatoid arthritis: a review

Pain is the most common symptom reported by patients with rheumatoid arthritis (RA) even after the resolution of chronic joint inflammation. It is believed that RA-associated pain is not solely due to inflammation, but could also be attributed to aberrant modifications to the central nervous system. The P2X4 receptor (P2X4R) is an ATP-activated purinergic receptor that plays a significant role in the transmission of information in the nervous system and pain. The involvement of P2X4R during the pathogenesis of chronic inflammatory pain and neuropathic pain is well-established. The attenuation of this receptor alleviates disease pathogenesis and related symptoms, including hyperalgesia and allodynia. Although some studies have revealed the contribution of P2X4R in promoting joint inflammation in RA, how it implicates pain associated with RA at peripheral and central nervous systems is still lacking. In this review, the possible contributions of P2X4R in the nervous system and how it implicates pain transmission and responses were examined.