P2Y 12 shRNA treatment relieved HIV gp120-induced neuropathic pain in rats

P2Y13 receptor involved in HIV-1 gp120 induced neuropathy in superior cervical ganglia through NLRP3 inflammasome activation

Cardiac autonomic neuropathy resulting from human immunodeficiency virus (HIV) infection is common; however, its mechanism remains unknown. The current work attempted to explore the function and mechanism of the P2Y13 receptor in HIV-glycoprotein 120 (gp120)-induced neuropathy in cervical sympathetic ganglion. The superior cervical ganglion (SCG) of the male SD rat was coated with HIV-gp120 to establish a model of autonomic neuropathy. In each group, we measured heart rate, blood pressure, heart rate variability, sympathetic nerve discharge and cardiac function. The expression of P2Y13 mRNA and protein in the SCG was tested by real-time polymerase chain reaction and western blotting. Additionally, this study focused on identifying the protein levels of NOD-like receptor family pyrin domain-containing 3 (NLRP3), Caspase-1, Gasdermin D (GSDMD), interleukin (IL)-1β and IL-18 in the SCG using western blotting and immunofluorescence. In gp120 rats, increased blood pressure, heart rate, cardiac sympathetic nerve activity, P2Y13 receptor levels and decreased cardiac function could be found. P2Y13 shRNA or MRS2211 inhibited the above mentioned changes induced by gp120, suggesting that the P2Y13 receptor may be engaged in gp120-induced sympathetic nerve injury. Moreover, the levels of NLRP3, Caspase-1, GSDMD, IL-1β and IL-18 in the gp120 group were increased, while significantly decreased by P2Y13 shRNA or MRS2211. Therefore, the P2Y13 receptor is involved in gp120-induced sympathetic neuropathy, and its molecular mechanism shows an association with the activation of the NLRP3 inflammasome, followed by GSDMD formation along with the release of inflammatory factors including IL-1β and IL-18. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Progress in Pathological and Therapeutic Research of HIV-Related Neuropathic Pain

HIV-related neuropathic pain (HRNP) is a neurodegeneration that gradually develops during the long-term course of acquired immune deficiency syndrome (AIDS) and manifests as abnormal sock/sleeve-like symmetrical pain and nociceptive hyperalgesia in the extremities, which seriously reduces patient quality of life. To date, the pathogenesis of HRNP is not completely clear. There is a lack of effective clinical treatment for HRNP and it is becoming a challenge and hot spot for medical research. In this study, we conducted a systematic review of the progress of HRNP research in recent years including (1) the etiology, classification and clinical symptoms of HRNP, (2) the establishment of HRNP pathological models, (3) the pathological mechanisms underlying HRNP from three aspects: molecules, signaling pathways and cells, (4) the therapeutic strategies for HRNP, and (5) the limitations of recent HRNP research and the future research directions and prospects of HRNP. This detailed review provides new and systematic insight into the pathological mechanism of HRNP, which establishes a theoretical basis for the future exploitation of novel target drugs. HIV infection, antiretroviral therapy and opioid abuse contribute to the etiology of HRNP with symmetrical pain in both hands and feet, allodynia and hyperalgesia. The pathogenesis involves changes in cytokine expression, activation of signaling pathways and neuronal cell states. The therapy for HRNP should be patient-centered, integrating pharmacologic and nonpharmacologic treatments into multimodal intervention.

P2Y12 receptor involved in the development of chronic nociceptive pain as a sensory information mediator

Direct or indirect damage to the nervous system (such as inflammation or tumor invasion) can lead to dysfunction and pain. The generation of pain is mainly reflected in the activation of glial cells and the abnormal discharge of sensory neurons, which transmit stronger sensory information to the center. P2Y12 receptor plays important roles in physiological and pathophysiological processes including inflammation and pain. P2Y12 receptor involved in the occurrence of pain as a sensory information mediator, which enhances the activation of microglia and the synaptic plasticity of primary sensory neurons, and reaches the higher center through the ascending conduction pathway (mainly spinothalamic tract) to produce pain. While the application of P2Y12 receptor antagonists (PBS-0739, AR-C69931MX and MRS2359) have better antagonistic activity and produce analgesic pharmacological properties. Therefore, in this article, we discussed the role of the P2Y12 receptor in different chronic pains and its use as a pharmacological target for pain relief.

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".

G protein-coupled P2Y12 receptor is involved in the progression of neuropathic pain

The pathological mechanism of neuropathic pain is complex, which seriously affects the physical and mental health of patients, and its treatment is also difficult. The role of G protein-coupled P2Y12 receptor in pain has been widely recognized and affirmed. After nerve injury, stimulated cells can release large amounts of nucleotides into the extracellular matrix, act on P2Y12 receptor. Activated P2Y12 receptor activates intracellular signal transduction and is involved in the development of pain. P2Y12 receptor activation can sensitize primary sensory neurons and receive sensory information. By transmitting the integrated information through the dorsal root of the spinal cord to the secondary neurons of the posterior horn of the spinal cord. The integrated information is then transmitted to the higher center through the ascending conduction tract to produce pain. Moreover, activation of P2Y12 receptor can mediate immune cells to release pro-inflammatory factors, increase damage to nerve cells, and aggravate pain. While inhibits the activation of P2Y12 receptor can effectively relieve pain. Therefore, in this article, we described P2Y12 receptor antagonists and their pharmacological properties. In addition, we explored the potential link between P2Y12 receptor and the nervous system, discussed the intrinsic link of P2Y12 receptor and neuropathic pain and as a potential pharmacological target for pain suppression.

The role and pharmacological properties of P2Y12 receptor in cancer and cancer pain

The G protein-coupled P2Y12 receptor (P2Y12R) was cloned in platelets and found to play a key role in maintaining platelet function in hemostasis and thrombosis, and these effects could be mediated by the P2Y12R. However, it has recently been found that P2Y12R-mediated the progression of tumor through interactions between platelets and tumor and stromal cells, as well as through products secreted by platelets. During tumor progression, tumor cells or other cells in the tumor microenvironment (such as immune cells) can secrete large amounts of ATP into the extracellular matrix, and extracellular ATP can be hydrolyzed into ADP. ADP is a P2Y12R activator and plays an important regulatory role in the proliferation and metastasis of tumor cells. P2Y12R is involved in platelet-cancer cell crosstalk and become a potential target for anticancer therapy. Moreover, tumor progression can induce pain, which seriously affects the quality of life of patients. P2Y12R is expressed in microglia and mediates the activities of microglial and participates in the occurrence of cancer pain. Conversely, inhibiting P2Y12R activation and down-regulating its expression has the effect of inhibiting tumor progression and pain. Therefore, P2Y12R can be a common therapeutic target for both. In this article, we explored the potential link between P2Y12R and cancer, discussed the intrinsic link of P2Y12R in cancer pain and the pharmacological properties of P2Y12R antagonists in the treatment of both.

P2Y14 receptor in trigeminal ganglion contributes to neuropathic pain in mice

Trigeminal nerve injury is a common complication of various dental and oral procedures, which could induce trigeminal neuropathic pain but lack effective treatments. P2 purinergic receptors have emerged as novel therapeutic targets for such pain. Recent reports implied that the P2Y₁₄ receptor (P2Y₁₄R) was activated and promoted orofacial inflammatory pain and migraine. However, the role and mechanism of P2Y₁₄R in trigeminal neuropathic pain remain unknown. We induced an orofacial neuropathic pain model by chronic constriction injury of the infraorbital nerve (CCI-ION). Von-Frey tests showed that CCI-ION induced orofacial mechanical hypersensitivity. The increased activating transcription factor 3 (ATF3) expression in the trigeminal ganglion (TG) measured by immunofluorescence confirmed trigeminal nerve injury. Immunofluorescence showed that P2Y₁₄R was expressed in trigeminal ganglion neurons (TGNs) and satellite glial cells (SGCs). RT-qPCR and Western blot identified increased expression of P2Y₁₄R in TG after CCI-ION. CCI-ION also upregulated interleukin-1β (IL-1β), interleukin-6 (IL-6), C-C motif chemokine ligand 2 (CCL2), and tumor necrosis factor-α (TNF-α) in TG. Notably, CCI-ION-induced mechanical hypersensitivity and pro-inflammatory cytokines production were decreased by a P2Y₁₄R antagonist (PPTN). Trigeminal administration of P2Y₁₄R agonist (UDP-glucose) evoked orofacial mechanical hypersensitivity and increased pro-inflammatory cytokines above in TG. Furthermore, CCI-ION induced activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 in TG, which also were reduced by PPTN. The inhibitors of ERK1/2 (U0126) and p38 (SB203580) decreased these upregulated pro-inflammatory cytokines after CCI-ION. Collectively, this study revealed that P2Y₁₄R in TG contributed to trigeminal neuropathic pain via ERK- and p38-dependent neuroinflammation. Thus, P2Y₁₄R may be a potential drug target against trigeminal neuropathic pain.

The role of Pannexin-1 channels and extracellular ATP in the pathogenesis of the human immunodeficiency virus

Only recently, the role of large ionic channels such as Pannexin-1 channels and Connexin hemichannels has been implicated in several physiological and pathological conditions, including HIV infection and associated comorbidities. These channels are in a closed stage in healthy conditions, but in pathological conditions including HIV, Pannexin-1 channels and Connexin hemichannels become open. Our data demonstrate that acute and chronic HIV infection induces channel opening (Pannexin and Connexin channels), ATP release into the extracellular space, and subsequent activation of purinergic receptors in immune and non-immune cells. We demonstrated that Pannexin and Connexin channels contribute to HIV infection and replication, the long-term survival of viral reservoirs, and comorbidities such as NeuroHIV. Here, we discuss the available data to support the participation of these channels in the HIV life cycle and the potential therapeutic approach to prevent HIV-associated comorbidities.

Long Non-coding RNA Uc.48+ Small Interfering RNA Alleviates Neuroinflammatory Hyperalgesia in Gp120-Treated Rats via the P2Y12 Receptor

Human immunodeficiency virus envelope glycoprotein 120 (gp120) leads to hyperalgesia. Long non-coding RNAs are characterized by the lack of a protein-coding sequence and may contribute to the development and maintenance of inflammatory and neuroinflammatory pain. Rats with neuroinflammatory pain were established by gp120 treatment, which is featured by intensified pain behaviors. Long non-coding RNA uc.48+ was increased in the dorsal root ganglia of gp120-treated rats, and small interfering RNA that targets uc.48+ markedly alleviated hyperalgesia in gp120-treated rats. Notably, uc.48+ overexpression increased P2Y12 expression in control rats dorsal root ganglia and induced hyperalgesia. Uc.48+ small interfering RNA inhibited P2Y12 expression in gp120-treated rats. Uc.48+ potentiated P2Y12 receptor functions in the neurons and heterologous cells. Therefore, uc.48+ siRNA treatment reduced the upregulation of P2Y12 expression and function in DRG neurons, and, hence, alleviated hyperalgesia in gp120-treated rats.

Green Light Antinociceptive and Reversal of Thermal and Mechanical Hypersensitivity Effects Rely on Endogenous Opioid System Stimulation

Benefits of phototherapy were characterized in multiple diseases including depression, circadian rhythm disruptions, and neurodegeneration. Studies on migraine and fibromyalgia patients revealed that green light-emitting diodes (GLED) exposure provides a pragmatic and safe therapy to manage chronic pain. In rodents, GLED reversed hypersensitivity related to neuropathic pain. However, little is known about the underlying mechanisms of GLED efficacy. Here, we sought to understand how green light modulates the endogenous opioid system. We first characterized how exposure to GLED stimulates release of β-endorphin and proenkephalin in the central nervous system of male rats. Moreover, by individually editing each of the receptors, we found that µ- and δ-opioid receptors are required for green light's antinociceptive effect in naïve rats and a model of HIV-induced peripheral neuropathy. We investigated how GLED could increase pain thresholds, and explored its potential in reversing hypersensitivity in a model of HIV-related neuropathy. Through behavioral and gene editing approaches, we identified that green light provides antinociception via modulation of the endogenous opioid system in the spinal cord. This work identifies a previously unknown mechanism by which GLED can improve pain management. Clinical translation of these results will advance the development of an innovative therapy devoid of adverse effects. PERSPECTIVE: Development of new pain management therapies, especially for HIV patients, is crucial as long-term opioid prescription is not recommended due to adverse side effects. Green light addresses this necessity. Characterizing the underlying mechanisms of this potentially groundbreaking and safe antinociceptive therapy will advance its clinical translation.

Purinergic signaling in infectious diseases of the central nervous system

The incidence of infectious diseases affecting the central nervous system (CNS) has been increasing over the last several years. Among the reasons for the expansion of these diseases and the appearance of new neuropathogens are globalization, global warming, and the increased proximity between humans and wild animals due to human activities such as deforestation. Neurotropism affecting normal brain function is shared by organisms such as viruses, bacteria, fungi, and parasites. Neuroinfections caused by these agents activate immune responses, inducing neuroinflammation, excitotoxicity, and neurodegeneration. Purinergic signaling is an evolutionarily conserved signaling pathway associated with these neuropathologies. During neuroinfections, host cells release ATP as an extracellular danger signal with pro-inflammatory activities. ATP is metabolized to its derivatives by ectonucleotidases such as CD39 and CD73; ATP and its metabolites modulate neuronal and immune mechanisms through P1 and P2 purinergic receptors that are involved in pathophysiological mechanisms of neuroinfections. In this review we discuss the beneficial or deleterious effects of various components of the purinergic signaling pathway in infectious diseases that affect the CNS, including human immunodeficiency virus (HIV-1) infection, herpes simplex virus type 1 (HSV-1) infection, bacterial meningitis, sepsis, cryptococcosis, toxoplasmosis, and malaria. We also provide a description of this signaling pathway in emerging viral infections with neurological implications such as Zika and SARS-CoV-2.

Compounds of traditional Chinese medicine and neuropathic pain

Neuropathic pain (NP) has become a serious global health issue and a huge clinical challenge without available effective treatment. P2 receptors family is involved in pain transmission and represents a promising target for pharmacological intervention. Traditional Chinese medicine (TCM) contains multiple components which are effective in targeting different pathological mechanisms involved in NP. Different from traditional analgesics, which target a single pathway, TCMs take the advantage of multiple components and multiple targets, and can significantly improve the efficacy of treatment and contribute to the prediction of the risks of NP. Compounds of TCM acting at nucleotide P2 receptors in neurons and glial cells could be considered as a potential research direction for moderating neuropathic pain. This review summarized the recently published data and highlighted several TCMs that relieved NP by acting at P2 receptors.

The P2Y14 receptor in the trigeminal ganglion contributes to the maintenance of inflammatory pain

P2Y purinergic receptors expressed in neurons and satellite glial cells (SGCs) of the trigeminal ganglion (TG) contribute to inflammatory and neuropathic pain. P2Y₁₄ receptor expression is reported in the spinal cord, dorsal root ganglion (DRG), and TG. In present study, the role of P2Y₁₄ receptor in the TG in inflammatory orofacial pain of Sprague-Dawley (SD) rats was investigated. Peripheral injection of complete Freund's adjuvant (CFA) induced mechanical hyperalgesia with the rapid upregulation of P2Y₁₄ receptor, glial fibrillary acidic protein (GFAP), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), C-C chemokine CCL2, phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), and phosphorylated p38 (p-p38) proteins in the TG. Furthermore, immunofluorescence staining confirmed the CFA-induced upregulation of P2Y₁₄ receptor. Double immunostaining showed that P2Y₁₄ receptor colocalized with glutamine synthetase (GS) and neuronal nuclei (NeuN). Finally, trigeminal injection of a selective antagonist (PPTN) of P2Y₁₄ receptor attenuated CFA-induced mechanical hyperalgesia. PPTN also decreased the upregulation of the GFAP, IL-1β, TNF-α, CCL2, p-ERK1/2, and p-p38 proteins. Our findings showed that P2Y₁₄ receptor in TG may contribute to orofacial inflammatory pain via regulating SGCs activation, releasing cytokines (IL-1β, TNF-α, and CCL2), and phosphorylating ERK1/2 and p38.

P2Y receptors in neuropathic pain

This review summarizes and evaluates the relationship between neuropathic pain and P2Y receptors from inception to 2019. Purinergic receptors have been well studied in recent years using various molecular biological methods. The main research objective of this review is to determine the association of P2Y1, P2Y2, P2Y6, P2Y12 and P2Y13 receptors with neuropathic pain. This review includes the most comprehensive subtypes of P2Y that related to neuropathic pain and the current therapeutic method of neuropathic pain. G protein-coupled P2Y receptors are located on neurons, astrocytes, oligodendrocytes and microglial cells and regulate neurotransmission. Nerve injury is the prime reason for abnormal regulation of P2Y receptor mRNA expression, subsequently, inducing neuropathic pain. Neuropathic pain is a type of chronic pain that is divided into peripheral, central and mixed. Numerous studies demonstrated a positive correlation between the expression level of P2Y receptors and neuropathic pain generation. Also, several reports showed that P2Y short hairpin RNA (shRNA) and P2Y antagonist can be used as an analgesic to relieve neuropathic pain via decreasing P2Y receptor expression level and neural cell activation. However, the transformation process from basic experiments to clinical applications is a long process. Current deficiencies and future research directions are discussed at the end of this review.

The Inhibition by Guanfu Base A of Neuropathic Pain Mediated by P2Y12 Receptor in Dorsal Root Ganglia

Activation of satellite glial cells (SGCs) in the dorsal root ganglia (DRG) is involved in mechanical and thermal hyperalgesia. The upregulated P2Y₁₂ receptor expressed in SGCs of the DRG participates in the nociceptive transmission of neuropathic pain. Guanfu base A (GFA) has been reported to exhibit antiarrhythmic and anti-inflammatory effects. In this study, we explored the effects of GFA on P2Y₁₂ receptor-mediated mechanical and thermal hyperalgesia in chronic constriction injury (CCI) rats. Sprague-Dawley rats were randomly divided into sham operation group (Sham), CCI operation group (CCI), CCI rats treated with guanfu base A group (CCI + GFA) and control rats treated with GFA group (Ctrl + GFA). Mechanical withdrawal threshold and thermal withdrawal latency were measured. P2Y₁₂ expression in L4-L6 dorsal root ganglion (DRG) was detected by quantitative real-time PCR and Western blot. After CCI treatment, mechanical and thermal hyperalgesia and the expression values of P2Y₁₂ receptor mRNA and protein in DRG were increased. Dual-labeling immunofluorescence showed that the coexpression of P2Y₁₂ receptor and glial fibrillary acidic protein (GFAP) in the DRG of CCI rats was increased compared to sham rats. GFA relieved mechanical and thermal hyperalgesia in the CCI rats, decreased the expression of P2Y₁₂ mRNA and protein and phosphorylation of p38 MAPK in the DRG, and increased the ADP-downregulated cAMP concentrations in HEK293 cells transfected with P2Y₁₂ plasmid. After CCI rats were treated with GFA, the coexpression of P2Y₁₂ receptor and GFAP in the DRG was significantly decreased compared to the untreated CCI group. Thus, downregulating the P2Y₁₂ receptor relieved mechanical and thermal hyperalgesia in the CCI rats.

The role of adenosine and P2Y receptors expressed by multiple cell types in pain transmission

The role of extracellular nucleotides and nucleosides as signaling molecules in cell-to-cell communication has now been clearly established. This is particularly true in the central and peripheral nervous system, where purines and pyrimidines are involved in both physiological and pathological interactions between neurons and surrounding glial cells. It can be thus foreseen that the purinergic system could represent a new potential target for the development of effective analgesics, also through the normalization of neuronal functions and the inhibition of glial cell activation. Research in the last 15 years has progressively confirmed this hypothesis, but no purinergic-based analgesics have reach the market so far; in the present review we have collected the more recent discoveries on the role of G protein-coupled P2Y nucleotide and of adenosine receptors expressed by both neurons and glial cells under painful conditions, and we have highlighted some of the challenges that must be faced to translate basic and preclinical studies to clinics.

Natural compounds acting at P2 receptors alleviate peripheral neuropathy

Neuropathic pain is generally resistant to currently available treatments, and it is often a consequence of nerve injury due to surgery, diabetes or infection. Myocardial ischemic nociceptive signaling increases the sympathoexcitatory reflex to aggravate myocardial injury. Elucidation of the pathogenetic factors might provide a target for optimal treatment. Abundant evidence in the literature suggests that P2X and P2Y receptors play important roles in signal transmission. Traditional Chinese medicines, such as emodin, puerarin and resveratrol, antagonize nociceptive transmission mediated by purinergic 2 (P2) receptors in primary afferent neurons. This review summarizes recently published data on P2 receptor-mediated neuropathic pain and myocardial ischemia in dorsal root ganglia (DRG), superior cervical ganglia (SCG) and stellate ganglia (SG), with a special focus on the beneficial role of natural compounds.

Purinergic Signaling: A New Pharmacological Target Against Viruses?

Viral diseases represent a major global problem in human health, with high morbidity and mortality. Despite recent progress in antiviral treatments, several viral diseases are still not controlled and millions suffer from them every year. It has recently emerged that purinergic signaling participates in viral infection and replication. Furthermore, stimulation of purinergic receptors in infected cells also induces inflammatory and antiviral responses, thus contributing to the host antiviral defense. Here we review the multiple roles played by the purinergic signaling network in cell-virus interactions that can lead either to viral maintenance in the cells or, by contrast, to stronger antiviral responses, and discuss potential future applications of purinergic signaling modulation for the treatment of viral diseases.

Baicalin Depresses the Sympathoexcitatory Reflex Induced by Myocardial Ischemia via the Dorsal Root Ganglia

Myocardial ischemia (MI) is one of the major causes of death in cardiac diseases. Purinergic signaling is involved in bidirectional neuronal-glial communication in the primary sensory ganglia. The sensory neuritis of cardiac afferent neurons in cervical dorsal root ganglion (cDRG) interacts with cardiac sympathetic efferent postganglionic neurons, forming feedback loops. The P2Y₁₂ receptor is expressed in satellite glial cells (SGCs) of DRG. Baicalin is a major active ingredient extracted from natural herbal medicines, which has anti-inflammatory and strong anti-oxidation properties. In this study we investigated the effect of baicalin on P2Y₁₂ receptor in the cervical DRG SGC-mediated sympathoexcitatory reflex, which is increased during MI. The results showed that the expression of P2Y₁₂ receptor mRNA and protein in DRG, and the co-localization values of P2Y₁₂ receptor and glial fibrillary acidic protein (GFAP) in cDRG SGCs were increased after MI. The activated SGCs increased IL-1β protein expression and elevated Akt phosphorylation in cDRG. Baicalin treatment inhibited the upregulation of the P2Y₁₂ receptor, GFAP protein and Akt phosphorylation in cDRG neurons/SGCs. The stellate ganglia (SG) affect cardiac sympathetic activity. Baicalin treatment also decreased the upregulation of the P2Y₁₂ receptor, GFAP protein in the SG. The P2Y₁₂ agonist, 2Me-SADP, increased [Ca²⁺]_i in HEK293 cells transfected with the P2Y₁₂ receptor plasmid and SGCs in cDRG. These results indicate that application of baicalin alleviates pathologic sympathetic activity induced by MI via inhibition of afferents in the cDRG.