P2X7 receptor mediated phosphorylation of p38MAP kinase in the hippocampus

Activation of the P2X7 receptor in the dental pulp tissue contributes to the pain in rats with acute pulpitis

Treatment of acute pulpitis (AP) is beneficial for pain relief and pulp regeneration. The purinergic P2X7 receptor activation is responsible for the formation and maintenance of inflammation and pain. This study aims to determine the role of the pulp tissue P2X7 receptor to activate the mechanisms of the AP in rats. The Sprague-Dawley rats were divided into groups, namely, normal, normal saline (NS), and lipopolysaccharide (LPS) groups. Alterations in pain behavior were detected through head-withdrawal thresholds (HWTs), and the pathological changes in pulp tissue were studied through hematoxylin and eosin staining. The expression of the P2X7 receptor in pulp tissue was observed through immunohistochemistry and Western Blotting. The effect of the P2X7 receptor antagonist A-740003 on HWTs was also observed. The levels of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in the pulp tissue of rats were analyzed through enzyme-linked immunosorbent assay. The HWTs were reduced in the rats with AP. Inflammation is formed but was found more severe in the LPS group than the NS group, and the expression levels of the P2X7 receptors in the NS and LPS groups were higher than in the normal group. The periodontal ligament injection of the A-740003 dose-dependant increases the HWTs in rats with AP. The IL-6 and TNF-α levels in the pulp in the NS and LPS groups were increased but reversed by A-740003 injection. In rats with AP, the expression level of the P2X7 receptor and IL-6/TNF-α release was upregulated. The A-740003 can relieve pain and reduce the inflammation progression in rats with AP.

The P2X7 Receptor in Osteoarthritis

Osteoarthritis (OA) is the most common joint disease. With the increasing aging population, the associated socio-economic costs are also increasing. Analgesia and surgery are the primary treatment options in late-stage OA, with drug treatment only possible in early prevention to improve patients' quality of life. The most important structural component of the joint is cartilage, consisting solely of chondrocytes. Instability in chondrocyte balance results in phenotypic changes and cell death. Therefore, cartilage degradation is a direct consequence of chondrocyte imbalance, resulting in the degradation of the extracellular matrix and the release of pro-inflammatory factors. These factors affect the occurrence and development of OA. The P2X7 receptor (P2X7R) belongs to the purinergic receptor family and is a non-selective cation channel gated by adenosine triphosphate. It mediates Na⁺, Ca²⁺ influx, and K⁺ efflux, participates in several inflammatory reactions, and plays an important role in the different mechanisms of cell death. However, the relationship between P2X7R-mediated cell death and the progression of OA requires investigation. In this review, we correlate potential links between P2X7R, cartilage degradation, and inflammatory factor release in OA. We specifically focus on inflammation, apoptosis, pyroptosis, and autophagy. Lastly, we discuss the therapeutic potential of P2X7R as a potential drug target for OA.

Brilliant blue G attenuates neuro-inflammation via regulating MAPKs and NF-κB signaling pathways in lipopolysaccharide-induced BV2 microglia cells

Previous studies have demonstrated that the P2X purinoceptor 7 (P2X7) receptor (P2X7R) serves a critical role in regulating the inflammatory response of various diseases in the central nervous system. The anti-inflammatory effect of brilliant blue G (BBG), a specific antagonist of the P2X7R, remains unclear in lipopolysaccharide (LPS)-induced BV-2 cells. The present study suggested that BBG attenuated the neuroinflammatory response; the protein levels of inducible oxide synthase and cyclooxygenase-2, and the mRNA and secretion levels of pro-inflammatory cytokines including interleukin (IL)-16, IL-1β and tumor necrosis factor-α (TNF-α), were all decreased in LPS-induced BV2 cells. BBG inhibited the activation of MAPKs by inhibiting the phosphorylation of p38 mitogen-activated protein kinase, c-Jun N-terminal kinase and extracellular signal-regulated kinase. Notably, transcription factor p65 nuclear translocation was also inhibited, thereby leading to the inactivation of NF-κB. The inhibitory effects of BBG on MAPKs and NF-κB were additionally enhanced through the application of MAPK and NF-κB inhibitors. Taken together, the results demonstrated that BBG contributed to the suppression of the inflammatory effects in LPS-induced BV2 cells via the inhibition of NF-κB and MAPKs signaling pathways.

Protective Effect of Astragaloside IV on High Glucose-Induced Endothelial Dysfunction via Inhibition of P2X7R Dependent P38 MAPK Signaling Pathway

Vascular endothelial dysfunction is associated with increased mortality in patients with diabetes. Astragaloside IV (As-IV) is a bioactive saponin with therapeutic potential as an anti-inflammatory and antiendothelial dysfunction. However, the underlying mechanism for how As-IV ameliorated endothelial dysfunction is still unclear. Therefore, in this study, we examined the protective effect of As-IV against endothelial dysfunction and explored potential molecular biology mechanism. In vivo, rats were intraperitoneally injected with streptozotocin (STZ) at a dose of 65 mg/kg body weight to establish a diabetic model. In vitro studies, rat aortic endothelial cells (RAOEC) were pretreated with As-IV, SB203580 (p38 MAPK inhibitor) for 2 h prior to the addition of high glucose (33 mM glucose). Our findings indicated that As-IV improved impaired endothelium-dependent relaxation and increased the levels of endothelial NO synthase (eNOS) and nitric oxide (NO) both in vivo and in vitro. Besides, As-IV treatment inhibited the elevated inflammation and oxidative stress in diabetic model both in vivo and in vitro. Moreover, As-IV administration reversed the upregulated expression of P2X7R and p-p38 MAPK in vivo and in vitro. Additionally, the effects of both P2X7R siRNA and SB203580 on endothelial cells were similar to As-IV. Collectively, our study demonstrated that As-IV rescued endothelial dysfunction induced by high glucose via inhibition of P2X7R dependent p38 MAPK signaling pathway. This provides a theoretical basis for the further study of the vascular endothelial protective effects of As-IV.

Mechanisms of neuroinflammation and inflammatory mediators involved in brain injury following subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is a devastating cerebrovascular disorder. Neuroinflammation is a critical cause of brain injury following SAH in both acute and chronic phases. While accumulating evidence has shown that therapies targeting neuroinflammation exerted beneficial effects in experimental SAH, there is little clinical evidence. One of the factors making neuroinflammation complicated is that inflammatory signaling pathways and mediators act as protective or detrimental responses at different phases. In addition, biomarkers to detect neuroinflammation are little known in clinical settings. In this review, first, we discuss how the inflammatory signaling pathways contribute to brain injury and other secondary pathophysiological changes in SAH. Damage-associated molecular patterns arising from mechanical stress, transient global cerebral ischemia, red blood cell breakdown and delayed cerebral ischemia following SAH trigger to activate pattern recognition receptors (PRRs) such as Toll-like receptors, nucleotide-binding oligomerization domain-like receptors, and receptors for advanced glycation end products. Most of PRRs activate common downstream signaling transcriptional factor nuclear factor-κΒ and mitogen-activated protein kinases, releasing pro-inflammatory mediators and cytokines. Next, we focus on how pro-inflammatory substances play a role during the course of SAH. Finally, we highlight an important inducer of neuroinflammation, matricellular protein (MCP). MCPs are a component of extracellular matrix and exert beneficial and harmful effects through binding to receptors, other matrix proteins, growth factors, and cytokines. Treatment targeting MCPs is being proved efficacious in pre-clinical models for preventing brain injury including neuroinflammation in SAH. In addition, MCPs may be a candidate of biomarkers predicting brain injury following SAH in clinical settings.

Normal Saline solutions cause endothelial dysfunction through loss of membrane integrity, ATP release, and inflammatory responses mediated by P2X7R/p38 MAPK/MK2 signaling pathways

Resuscitation with 0.9% Normal Saline (NS), a non-buffered acidic solution, leads to increased morbidity and mortality in the critically ill. The goal of this study was to determine the molecular mechanisms of endothelial injury after exposure to NS. The hypothesis of this investigation is that exposure of endothelium to NS would lead to loss of cell membrane integrity, resulting in release of ATP, activation of the purinergic receptor (P2X7R), and subsequent activation of stress activated signaling pathways and inflammation. Human saphenous vein endothelial cells (HSVEC) incubated in NS, but not buffered electrolyte solution (Plasma-Lyte, PL), exhibited abnormal morphology and increased release of lactate dehydrogenase (LDH), adenosine triphosphate (ATP), and decreased transendothelial resistance (TEER), suggesting loss of membrane integrity. Incubation of intact rat aorta (RA) or human saphenous vein in NS but not PL led to impaired endothelial-dependent relaxation which was ameliorated by apyrase (hydrolyzes ATP) or SB203580 (p38 MAPK inhibitor). Exposure of HSVEC to NS but not PL led to activation of p38 MAPK and its downstream substrate, MAPKAP kinase 2 (MK2). Treatment of HSVEC with exogenous ATP led to interleukin 1β (IL-1β) release and increased vascular cell adhesion molecule (VCAM) expression. Treatment of RA with IL-1β led to impaired endothelial relaxation. IL-1β treatment of HSVEC led to increases in p38 MAPK and MK2 phosphorylation, and increased levels of arginase II. Incubation of porcine saphenous vein (PSV) in PL with pH adjusted to 6.0 or less also led to impaired endothelial function, suggesting that the acidic nature of NS is what contributes to endothelial dysfunction. Volume overload resuscitation in a porcine model after hemorrhage with NS, but not PL, led to acidosis and impaired endothelial function. These data suggest that endothelial dysfunction caused by exposure to acidic, non-buffered NS is associated with loss of membrane integrity, release of ATP, and is modulated by P2X7R-mediated inflammatory responses.

P2X7 Receptor-Associated Programmed Cell Death in the Pathophysiology of Hemorrhagic Stroke

Hemorrhagic stroke is a life-threatening disease characterized by a sudden rupture of cerebral blood vessels, and cell death is widely believed to occur after exposure to blood metabolites or subsequently damaged cells. Recently, programmed cell death, such as apoptosis, autophagy, necroptosis, pyroptosis, and ferroptosis, has been demonstrated to play crucial roles in the pathophysiology of stroke. However, the detailed mechanisms of these novel kinds of cell death are still unclear. The P2X7 receptor, previously known for its cytotoxic activity, is an ATP-gated, nonselective cation channel that belongs to the family of ionotropic P2X receptors. Evolving evidence indicates that the P2X7 receptor plays a pivotal role in central nervous system pathology; genetic deletion and pharmacological blockade of the P2X7 receptor provide neuroprotection in various neurological disorders, including intracerebral hemorrhage and subarachnoid hemorrhage. The P2X7 receptor may regulate programmed cell death via (I) exocytosis of secretory lysosomes, (II) exocytosis of autophagosomes or autophagolysosomes during formation of the initial autophagic isolation membrane or omegasome, and (III) direct release of cytosolic IL-1β secondary to regulated cell death by pyroptosis or necroptosis. In this review, we present an overview of P2X7 receptor- associated programmed cell death for further understanding of hemorrhagic stroke pathophysiology, as well as potential therapeutic targets for its treatment.

Administration of an antagonist of P2X7 receptor to EAE rats prevents a decrease of expression of claudin-5 in cerebral capillaries

Purinergic P2X receptors, when activated under pathological conditions, participate in induction of the inflammatory response and/or cell death. Both neuroinflammation and neurodegeneration represent hallmarks of multiple sclerosis (MS), an autoimmune disease of the central nervous system. In the current study, we examined whether P2X7R is expressed in brain microvasculature of rats subjected to experimental autoimmune encephalomyelitis (EAE) and explore possible relationships with blood-brain barrier (BBB) protein—claudin-5 after administration of P2X7R antagonist—Brilliant Blue G (BBG). Capillary fraction isolated from control and EAE rat brains was subjected to immunohistochemical and Western blot analyses. We document the presence of P2X7R in brain capillaries isolated from brain tissue of EAE rats. P2X7R is found to be localized on the abluminal surface of the microvessels and is co-expressed with PDGFβR, a marker of pericytes. We also show over-expression of this receptor in isolated capillaries during the course of EAE, which is temporally correlated with a lower protein level of PDGFβR, as well as claudin-5, a tight junction-building protein. Administration of a P2X7R antagonist to the immunized rats significantly reduced clinical signs of EAE and enhances protein expression of both claudin-5 and PDGFβR. These results indicate that P2X7 receptor located on pericytes may contribute to pathological mechanisms operated during EAE in cerebral microvessels influencing the BBB integrity.

Vascular surgical stretch injury leads to activation of P2X7 receptors and impaired endothelial function

A viable vascular endothelial layer prevents vasomotor dysfunction, thrombosis, inflammation, and intimal hyperplasia. Injury to the endothelium occurs during harvest and “back table” preparation of human saphenous vein prior to implantation as an arterial bypass conduit. A subfailure overstretch model of rat aorta was used to show that subfailure stretch injury of vascular tissue leads to impaired endothelial-dependent relaxation. Stretch-induced impaired relaxation was mitigated by treatment with purinergic P2X7 receptor (P2X7R) inhibitors, brilliant blue FCF (FCF) and A740003, or apyrase, an enzyme that catalyzes the hydrolysis of ATP. Alternatively, treatment of rat aorta with exogenous ATP or 2’(3’)-O-(4-Benzoyl benzoyl)-ATP (BzATP) also impaired endothelial-dependent relaxation. Treatment of human saphenous vein endothelial cells (HSVEC) with exogenous ATP led to reduced nitric oxide production which was associated with increased phosphorylation of the stress activated protein kinase, p38 MAPK. ATP- stimulated p38 MAPK phosphorylation of HSVEC was inhibited by FCF and SB203580. Moreover, ATP inhibition of nitric oxide production in HSVEC was prevented by FCF, SB203580, L-arginine supplementation and arginase inhibition. Finally, L-arginine supplementation and arginase inhibition restored endothelial dependent relaxation after stretch injury of rat aorta. These results suggest that vascular stretch injury leads to ATP release, activation of P2X7R and p38 MAPK resulting in endothelial dysfunction due to arginase activation. Endothelial function can be restored in both ATP treated HSVEC and intact stretch injured rat aorta by P2X7 receptor inhibition with FCF or L-arginine supplementation, implicating straightforward therapeutic options for treatment of surgical vascular injury.

Neuronal P2X7 Receptor: Involvement in Neuronal Physiology and Pathology

The proposed presence of P2X7 receptor (P2X7R) in neurons has been the source of some contention. Initial studies suggested an absence of P2X7R mRNA in neurons, and the apparent nonspecificity of the antibodies used to identify P2X7R raised further doubts. However, subsequent studies using new pharmacological and biomolecular tools provided conclusive evidence supporting the existence of functional P2X7Rs in neurons. The P2X7 receptor has since been shown to play a leading role in multiple aspects of neuronal physiology, including axonal elongation and branching and neurotransmitter release. P2X7R has also been implicated in neuronal pathologies, in which it may influence neuronal survival. Together, this body of research suggests that P2X7R may constitute an important therapeutic target for a variety of neurological disorders.

Toward Understanding Non-coding RNA Roles in Intracranial Aneurysms and Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a common and frequently life-threatening cerebrovascular disease, which is mostly related with a ruptured intracranial aneurysm. Its complications include rebleeding, early brain injury, cerebral vasospasm, delayed cerebral ischemia, chronic hydrocephalus, and also non neurological problems. Non-coding RNAs (ncRNAs), comprising of microRNAs (miRNAs), small interfering RNAs (siRNAs) and long non-coding RNAs (lncRNAs), play an important role in intracranial aneurysms and SAH. Here, we review the non-coding RNAs expression profile and their related mechanisms in intracranial aneurysms and SAH. Moreover, we suggest that these non-coding RNAs function as novel molecular biomarkers to predict intracranial aneurysms and SAH, and may yield new therapies after SAH in the future.

P2X7 Participates in Intracerebral Hemorrhage-Induced Secondary Brain Injury in Rats via MAPKs Signaling Pathways

This study aimed to study the role of P2X7 in intracerebral hemorrhage (ICH)-induced secondary brain injury (SBI) and the underlying mechanisms. An autologous blood injection was used to induce ICH model in Sprague-Dawley rats, and cultured primary rat cortical neurons were exposed to oxyhemoglobin to mimic ICH in vitro. siRNA interference and over-expression of P2X7, agonists and antagonists of P2X7, p38 MAPK and ERK were exploited. The protein levels were assessed using Western blotting and immunofluorescence staining. Terminal deoxynucleotidyl transferase dUTP nick end labeling staining and Fluoro-Jade B were conducted to detect apoptotic and degenerating neurons. The protein levels of P2X7, phosphorylated p38, ERK, active caspase-3 and NF-κB were significantly increased by ICH, which could be further increased by BzATP (P2X7 agonist) and reduced by BBG (P2X7 antagonist). And BzATP demonstrated a significant increase in cell death ratio and brain water content, while BBG led to a reverse results. In addition, Over- P2X7 increased the levels of P2X7, phosphorylated p38, ERK, active caspase-3 and NF-κB, and aggravated cell apoptosis, while si P2X7 resulted in opposite effects. Finally, the protein levels of phosphorylated P38 and active caspase 3 were decreased by BzATP plus Hydrochloride (p38 MAPK antagonist) and increased vy BBG plus Asiatic acid (p38 MAPK agonist), while the protein levels of phosphorylated ERK and NF-κB were decreased with BzATP plus Nimbolide (ERK antagonist) and increased with BBG plus Saikosaponin C (ERK agonist). This study demonstrates that inhibition of P2X7 could prevent ICH-induced SBI via MAPKs signaling pathway.

The Roles of Mitochondrial Damage-Associated Molecular Patterns in Diseases

SIGNIFICANCE

Mitochondria, vital cellular power plants to generate energy, are involved in immune responses. Mitochondrial damage-associated molecular patterns (DAMPs) are molecules that are released from mitochondria to extracellular space during cell death and include not only proteins but also DNA or lipids. Mitochondrial DAMPs induce inflammatory responses and are critically involved in the pathogenesis of various diseases.

RECENT ADVANCES

Recent studies elucidate the molecular mechanisms by which mitochondrial DAMPs are released and initiate immune responses by use of genetically modulated cells or animals. Importantly, the levels of mitochondrial DAMPs in patients are often associated with severity and prognosis of human diseases, such as infection, asthma, ischemic heart disease, and cancer.

CRITICAL ISSUES

Although mitochondrial DAMPs can represent proinflammatory molecules in various experimental models, their roles in human diseases may be multifunctional and complex. It remains unclear where and how mitochondrial DAMPs are liberated into extracellular spaces and exert their biological functions particularly in vivo. In addition, while mitochondria can secrete several types of DAMPs during cell death, the interaction of each mitochondrial DAMP (e.g., synergistic effects) remains unclear.

FUTURE DIRECTIONS

Regulation of mitochondrial DAMP-mediated immune responses may be important to alter the progression of human diseases. In addition, measuring mitochondrial DAMPs in patients may be clinically useful as biomarkers to predict prognosis or response to therapies. Further studies of the mechanisms by which mitochondrial DAMPs impact the initiation and progression of diseases may lead to the development of therapeutics specifically targeting this pathway. Antioxid.

LncRNA NONRATT021972 involved the pathophysiologic processes mediated by P2X7 receptors in stellate ganglia after myocardial ischemic injury

Adenosine triphosphate (ATP) acts on P2X receptors to initiate signal transmission. P2X7 receptors play a role in the pathophysiological process of myocardial ischemic injury. Long noncoding RNAs (lncRNAs) participate in numerous biological functions independent of protein translation. LncRNAs are implicated in nervous system diseases. This study investigated the effects of NONRATT021972 small interference RNA (siRNA) on the pathophysiologic processes mediated by P2X7 receptors in stellate ganglia (SG) after myocardial ischemic injury. Our results demonstrated that the expression of NONRATT021972 in SG was significantly higher in the myocardial ischemic (MI) group than in the control group. Treatment of MI rats with NONRATT021972 siRNA, the P2X7 antagonist brilliant blue G (BBG), or P2X7 siRNA improved the histology of injured ischemic cardiac tissues and decreased the elevated concentrations of serum myocardial enzymes, creatine kinase (CK), CK isoform MB (CK-MB), lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) compared to the MI rats. NONRATT021972 siRNA, BBG, or P2X7 siRNA treatment in MI rats decreased the expression levels of P2X7 immunoreactivity, P2X7 messenger RNA (mRNA), and P2X7 protein, interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and phosphorylated p38 mitogen-activated protein kinase (p38 MAPK) in the SG compared to MI rats. NONRATT021972 siRNA treatment prevented the pathophysiologic processes mediated by P2X7 receptors in the SG after myocardial ischemic injury.

Delayed activation of spinal microglia contributes to the maintenance of bone cancer pain in female Wistar rats via P2X7 receptor and IL-18

Accumulating evidence suggests that activation of spinal microglia contributes to the development of inflammatory and neuropathic pain. However, the role of spinal microglia in the maintenance of chronic pain remains controversial. Bone cancer pain shares features of inflammatory and neuropathic pain, but the temporal activation of microglia and astrocytes in this model is not well defined. Here, we report an unconventional role of spinal microglia in the maintenance of advanced-phase bone cancer pain in a female rat model. Bone cancer elicited delayed and persistent microglial activation in the spinal dorsal horn on days 14 and 21, but not on day 7. In contrast, bone cancer induced rapid and persistent astrocytic activation on days 7-21. Spinal inhibition of microglia by minocycline at 14 d effectively reduced bone cancer-induced allodynia and hyperalgesia. However, pretreatment of minocycline in the first week did not affect the development of cancer pain. Bone cancer increased ATP levels in CSF, and upregulated P2X7 receptor, phosphorylated p38, and IL-18 in spinal microglia. Spinal inhibition of P2X7/p-38/IL-18 pathway reduced advanced-phase bone cancer pain and suppressed hyperactivity of spinal wide dynamic range (WDR) neurons. IL-18 induced allodynia and hyperalgesia after intrathecal injection, elicited mechanical hyperactivity of WDR neurons in vivo, and increased the frequency of mEPSCs in spinal lamina IIo nociceptive synapses in spinal cord slices. Together, our findings demonstrate a novel role of microglia in maintaining advanced phase cancer pain in females via producing the proinflammatory cytokine IL-18 to enhance synaptic transmission of spinal cord nociceptive neurons.

P2X7 receptor antagonism inhibits p38 mitogen-activated protein kinase activation and ameliorates neuronal apoptosis after subarachnoid hemorrhage in rats

OBJECTIVES

Brilliant blue G, a selective P2X7 receptor antagonist, exhibits neuroprotective properties. This study examined whether brilliant blue G treatment ameliorates early brain injury after experimental subarachnoid hemorrhage, specifically via inhibiting p38 mitogen-activated protein kinase-related proapoptotic pathways.

DESIGN

Controlled in vivo laboratory study.

SETTING

Animal research laboratory.

SUBJECTS

One hundred fifty-four adult male Sprague-Dawley rats weighing 280-320 g.

INTERVENTIONS

Subarachnoid hemorrhage was induced in rats by endovascular perforation. Experiment 1 implemented sham-operated rats (sham) and subarachnoid hemorrhage animals, which received vehicle (subarachnoid hemorrhage + vehicle), brilliant blue G (subarachnoid hemorrhage + brilliant blue G), or brilliant blue G plus 2'(3')-O-(4-Benzoylbenzoyl)adenosine 5'-triphosphate (BzATP) (subarachnoid hemorrhage + brilliant blue G + BzATP). The animals were intraperitoneally treated with brilliant blue G (30 mg/kg) at 30 minutes after subarachnoid hemorrhage. BzATP (50 μg/rat), a P2X7 receptor agonist, was intracerebroventricularly administered. Experiment 2 implemented sham-operated rats (sham) and subarachnoid hemorrhage animals, which received vehicle (subarachnoid hemorrhage + vehicle), scramble small interfering RNA (subarachnoid hemorrhage + scramble small interfering RNA), or P2X7 receptor small interfering RNA (subarachnoid hemorrhage + P2X7 receptor small interfering RNA). Subarachnoid hemorrhage grading, neurobehavioral score, and brain edema were evaluated at 24 and 72 hours after surgery. The expression of phosphorylated p38 mitogen-activated protein kinase, phosphorylated extracellular signal-regulated kinases, phosphorylated c-Jun N-terminal kinases, P2X7 receptor, Bcl-2, and cleaved caspase-3 in the left cerebral hemisphere were determined by Western blot. Neuronal apoptosis was examined by double immunofluorescence staining using P2X7 receptor, terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end-labeling, and neuronal nuclei.

MEASUREMENTS AND MAIN RESULTS

Brilliant blue G significantly improved neurobehavioral function and ameliorated brain water content at 24 and 72 hours after subarachnoid hemorrhage. BzATP reversed these treatment effects. Brilliant blue G attenuated neuronal apoptosis in the subcortex, which was associated with decreased expression of phosphorylated p38 mitogen-activated protein kinase and cleaved caspase-3 and an increased expression of Bcl-2 in the left cerebral hemisphere. The beneficial effects of P2X7 receptor small interfering RNA were also mediated by a p38 mitogen-activated protein kinase pathway.

CONCLUSIONS

Inhibition of P2X7 receptor by brilliant blue G or P2X7 receptor small interfering RNA can prevent early brain injury via p38 mitogen-activated protein kinase after subarachnoid hemorrhage.

Lipopolysaccharide inhibits the channel activity of the P2X7 receptor

The purinergic P2X7 receptor (P2X7R) plays an important role during the immune response, participating in several events such as cytokine release, apoptosis, and necrosis. The bacterial endotoxin lipopolysaccharide (LPS) is one of the strongest stimuli of the immune response, and it has been shown that P2X7R activation can modulate LPS-induced responses. Moreover, a C-terminal binding site for LPS has been proposed. In order to evaluate if LPS can directly modulate the activity of the P2X7R, we tested several signaling pathways associated with P2X7R activation in HEK293 cells that do not express the TLR-4 receptor. We found that LPS alone was unable to induce any P2X7R-related activity, suggesting that the P2X7R is not directly activated by the endotoxin. On the other hand, preapplication of LPS inhibited ATP-induced currents, intracellular calcium increase, and ethidium bromide uptake and had no effect on ERK activation in HEK293 cells. In splenocytes-derived T-regulatory cells, in which ATP-induced apoptosis is driven by the P2X7R, LPS inhibited ATP-induced apoptosis. Altogether, these results demonstrate that LPS modulates the activity of the P2X7R and suggest that this effect could be of physiological relevance.

The purinergic receptor P2X7 triggers alpha-secretase-dependent processing of the amyloid precursor protein

The amyloid precursor protein (APP) is cleaved by β- and γ-secretases to generate the β-amyloid (Aβ) peptides, which are present in large amounts in the amyloid plaques of Alzheimer disease (AD) patient brains. Non-amyloidogenic processing of APP by α-secretases leads to proteolytic cleavage within the Aβ peptide sequence and shedding of the soluble APP ectodomain (sAPPα), which has been reported to be endowed with neuroprotective properties. In this work, we have shown that activation of the purinergic receptor P2X7 (P2X7R) stimulates sAPPα release from mouse neuroblastoma cells expressing human APP, from human neuroblastoma cells and from mouse primary astrocytes or neural progenitor cells. sAPPα shedding is inhibited by P2X7R antagonists or knockdown of P2X7R with specific small interfering RNA (siRNA) and is not observed in neural cells from P2X7R-deficient mice. P2X7R-dependent APP-cleavage is independent of extracellular calcium and strongly inhibited by hydroxamate-based metalloprotease inhibitors, TAPI-2 and GM6001. However, knockdown of a disintegrin and metalloproteinase-9 (ADAM9), ADAM10 and ADAM17 by specific siRNA, known to have α-secretase activity, does not block the P2X7R-dependent non-amyloidogenic pathway. Using several specific pharmacological inhibitors, we demonstrate that the mitogen-activated protein kinase modules Erk1/2 and JNK are involved in P2X7R-dependent α-secretase activity. Our study suggests that P2X7R, which is expressed in hippocampal neurons and glial cells, is a potential therapeutic target in AD.

Involvement of spinal microglial P2X7 receptor in generation of tolerance to morphine analgesia in rats

Morphine loses analgesic potency after repeated administration. The underlying mechanism is not fully understood. Glia are thought to be involved in morphine tolerance, and P2X(7) purinergic receptor (P2X(7)R) has been implicated in neuron-glia communication and chronic pain. The present study demonstrated that P2X(7)R immunoreactivity was colocalized with the microglial marker OX42, but not the astrocytic marker GFAP, in the spinal cord. The protein level of spinal P2X(7)R was upregulated after chronic exposure to morphine. Intrathecal administration of Brilliant Blue G (BBG), a selective P2X(7)R inhibitor, significantly attenuated the loss of morphine analgesic potency, P2X(7)R upregulation, and microglial activation. Furthermore, RNA interference targeting the spinal P2X(7)R exhibited a similar tolerance-attenuating effect. Once morphine analgesic tolerance is established, it was no longer affected by intrathecal BBG. Together, our results suggest that spinal P2X(7)R is involved in the induction but not maintenance of morphine tolerance.

Amplification loop of the inflammatory process is induced by P2X7R activation in intestinal epithelial cells in response to neutrophil transepithelial migration

Inflammatory bowel diseases (IBD) are characterized during their active phase by polymorphonuclear leukocyte (PMNL) transepithelial migration. The efflux of PMNL into the mucosa is associated with the production of proinflammatory cytokines and the release of ATP from damaged and necrotic cells. The expression and function of purinergic P2X(7) receptor (P2X(7)R) in intestinal epithelial cells (IEC) and its potential role in the "cross talk" between IEC and PMNL have not been explored. The aims of the present study were 1) to examine P2X(7)R expression in IEC (T84 cells) and in human intestinal biopsies; 2) to detect any changes in P2X(7)R expression in T84 cells during PMNL transepithelial migration, and during the active and quiescent phases of IBD; and 3) to test whether P2X(7)R stimulation in T84 monolayers can induce caspase-1 activation and IL-1beta release by IEC. We found that a functional ATP-sensitive P2X(7)R is constitutively expressed at the apical surface of IEC T84 cells. PMNL transmigration regulates dynamically P2X(7)R expression and alters its distribution from the apical to basolateral surface of IEC during the early phase of PMNL transepithelial migration in vitro. P2X(7)R expression was weak in intestinal biopsies obtained during the active phase of IBD. We show that activation of epithelial P2X(7)R is mandatory for PMNL-induced caspase-1 activation and IL-1beta release by IEC. Overall, these changes in P2X(7)R function may serve to tailor the intensity of the inflammatory response and to prevent IL-1beta overproduction and inflammatory disease.

P2 receptor-mediated modulation of neurotransmitter release-an update

Presynaptic nerve terminals are equipped with a number of presynaptic auto- and heteroreceptors, including ionotropic P2X and metabotropic P2Y receptors. P2 receptors serve as modulation sites of transmitter release by ATP and other nucleotides released by neuronal activity and pathological signals. A wide variety of P2X and P2Y receptors expressed at pre- and postsynaptic sites as well as in glial cells are involved directly or indirectly in the modulation of neurotransmitter release. Nucleotides are released from synaptic and nonsynaptic sites throughout the nervous system and might reach concentrations high enough to activate these receptors. By providing a fine-tuning mechanism these receptors also offer attractive sites for pharmacotherapy in nervous system diseases. Here we review the rapidly emerging data on the modulation of transmitter release by facilitatory and inhibitory P2 receptors and the receptor subtypes involved in these interactions.