The role of the purinergic P2X7 receptor in inflammation

P2X7 receptor deletion suppresses γ-radiation-induced hyposalivation

Head and neck cancer treatments typically involve a combination of surgery and radiotherapy, often leading to collateral damage to nearby tissues causing unwanted side effects. Radiation damage to salivary glands frequently leads to irreversible dysfunction by poorly understood mechanisms. The P2X7 receptor (P2X7R) is a ligand-gated ion channel activated by extracellular ATP released from damaged cells as "danger signals." P2X7R activation initiates apoptosis and is involved in numerous inflammatory disorders. In this study, we utilized P2X7R knockout (P2X7R^-/-) mice to determine the role of the receptor in radiation-induced salivary gland damage. Results indicate a dose-dependent increase in γ-radiation-induced ATP release from primary parotid gland cells of wild-type but not P2X7R^-/- mice. Despite these differences, apoptosis levels are similar in parotid glands of wild-type and P2X7R^-/- mice 24-72 h after radiation. However, γ-radiation caused elevated prostaglandin E₂ (PGE₂) release from primary parotid cells of wild-type but not P2X7R^-/- mice. To attempt to uncover the mechanism underlying differential PGE₂ release, we evaluated the expression and activities of cyclooxygenase and PGE synthase isoforms. There were no consistent trends in these mediators following radiation that could explain the reduction in PGE₂ release in P2X7R^-/- mice. Irradiated P2X7R^-/- mice have stimulated salivary flow rates similar to unirradiated controls, whereas irradiated wild-type mice have significantly decreased salivary flow rates compared with unirradiated controls. Notably, treatment with the P2X7R antagonist A438079 preserves stimulated salivary flow rates in wild-type mice following γ-radiation. These data suggest that P2X7R antagonism is a promising approach for preventing γ-radiation-induced hyposalivation.

α-Haemolysin production, as a single factor, causes fulminant sepsis in a model of Escherichia coli-induced bacteraemia

α-Haemolysin (HlyA) from uropathogenic Escherichia coli has been demonstrated to be a significant virulence factor for ascending urinary tract infections. Once the E. coli reach the well-vascularised kidneys, there is a high risk of bacteraemia and a subsequent septic host response. Despite this, HlyA has the potential to accelerate the host response both directly and via its ability to facilitate adenosine triphosphate release from cells. It has not been settled whether HlyA aggravates bacteraemia into a septic state. To address this, we used an E. coli strain in a model of acute urosepsis that was either transfected with a plasmid containing the full HlyA operon or one with deletion in the HlyA gene. Here, we show that HlyA accelerates the host response to E. coli in the circulation. Mice exposed to HlyA-producing E. coli showed massively increased proinflammatory cytokines, a substantial fall in circulating thrombocytes, extensive haematuria, and intravascular haemolysis. This was not seen in mice exposed to either E. coli that do not secrete HlyA or vehicle controls. Consistent with the massive host response to the bacteria, the mice exposed to HlyA-producing E. coli died exceedingly early, whereas mice exposed to E. coli without HlyA production and vehicle controls survived the entire observation period. These data allow us to conclude that HlyA is a virulence factor that accelerates a state of bacteraemia into fulminant sepsis in a mouse model.

The purinergic receptor P2X5 contributes to bone loss in experimental periodontitis

Purinergic receptor signaling is increasingly recognized as an important regulator of inflammation. The P2X family purinergic receptors P2X5 and P2X7 have both been implicated in bone biology, and it has been suggested recently that P2X5 may be a significant regulator of inflammatory bone loss. However, a role for P2X5 in periodontitis is unknown. The present study aimed to evaluate the functional role of P2X5 in ligature-induced periodontitis in mice. Five days after placement of ligature, analysis of alveolar bone revealed decreased bone loss in P2rx5^−/− mice compared to P2rx7^−/− and WT control mice. Gene expression analysis of the gingival tissue of ligated mice showed that IL1b, IL6, IL17a and Tnfsf11 expression levels were significantly reduced in P2rx5^−/− compared to WT mice. These results suggest the P2X5 receptor may regulate bone loss related to periodontitis and it may thus be a novel therapeutic target in this oral disease.

Intrathecal delivery of a palmitoylated peptide targeting Y382-384 within the P2X7 receptor alleviates neuropathic pain

Pain hypersensitivity resulting from peripheral nerve injury depends on pathological microglial activation in the dorsal horn of the spinal cord. This microglial activity is critically modulated by P2X7 receptors (P2X7R) and ATP stimulation of these receptors produces mechanical allodynia, a defining feature of neuropathic pain. Peripheral nerve injury increases P2X7R expression and potentiates its cation channel function in spinal microglia. Here, we report a means to preferentially block the potentiation of P2X7R function by delivering a membrane permeant small interfering peptide that targets Y_382-384, a putative tyrosine phosphorylation site within the P2X7R intracellular C-terminal domain. Intrathecal administration of this palmitoylated peptide (P2X7R_379-389) transiently reversed mechanical allodynia caused by peripheral nerve injury in both male and female rats. Furthermore, targeting Y_382-384 suppressed P2X7R-mediated release of cytokine tumor necrosis factor alpha and blocked the adoptive transfer of mechanical allodynia caused by intrathecal injection of P2X7R-stimulated microglia. Thus, Y_382-384 site-specific modulation of P2X7R is an important microglial mechanism in neuropathic pain.

PTEN expression by an oncolytic herpesvirus directs T-cell mediated tumor clearance

Engineered oncolytic viruses are used clinically to destroy cancer cells and have the ability to boost anticancer immunity. Phosphatase and tensin homolog deleted on chromosome 10 loss is common across a broad range of malignancies, and is implicated in immune escape. The N-terminally extended isoform, phosphatase and tensin homolog deleted on chromosome 10 alpha (PTENα), regulates cellular functions including protein kinase B signaling and mitochondrial adenosine triphosphate production. Here we constructed HSV-P10, a replicating, PTENα expressing oncolytic herpesvirus, and demonstrate that it inhibits PI3K/AKT signaling, increases cellular adenosine triphosphate secretion, and reduces programmed death-ligand 1 expression in infected tumor cells, thus priming an adaptive immune response and overcoming tumor immune escape. A single dose of HSV-P10 resulted in long term survivors in mice bearing intracranial tumors, priming anticancer T-cell immunity leading to tumor rejection. This implicates HSV-P10 as an oncolytic and immune stimulating therapeutic for anticancer therapy.

Oncolytic viruses are a promising therapeutic approach for cancer treatment. The authors demonstrate the efficacy of an engineered HSV-1 expressing PTENα as an oncolytic and immune stimulating therapy against brain cancer metastases.

Inhibition of Heat Shock Protein 90 by 17-AAG Reduces Inflammation via P2X7 Receptor/NLRP3 Inflammasome Pathway and Increases Neurogenesis After Subarachnoid Hemorrhage in Mice

Subarachnoid hemorrhage (SAH) is a life-threatening cerebrovascular disease that usually has a poor prognosis. Heat shock proteins (HSPs) have been implicated in the mechanisms of SAH-associated damage, including increased inflammation and reduced neurogenesis. The aim of this study was to investigate the effects of HSP90 inhibition on inflammation and neurogenesis in a mouse model of experimental SAH induced by endovascular surgery. Western blotting showed HSP90 levels to be decreased, while neurogenesis, evaluated by 5-bromo-2'-deoxyuridine (BrdU) immunohistochemistry, was decreased in the hippocampuses of SAH mice. SAH also induced pro-inflammatory factors such as interleukin-1β (IL-1β), capase-1 and the NLRP3 inflammasome. However, intraperitoneal administration of the specific HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) reduced the levels of HSP90, NLRP3, ASC, caspase-1 and IL-1β, while increasing the levels of brain-derived neurotrophic factor and doublecortin (DCX), as well as the number of BrdU-positive cells in SAH mice. In addition, 17-AGG improved short- and long-term neurobehavioral outcomes. The neuroprotective and anti-inflammatory effects of 17-AGG were reversed by recombinant HSP90 (rHSP90); this detrimental effect of HSP90 was inhibited by the specific P2X7 receptor (P2X7R) inhibitor A438079, indicating that SAH-induced inflammation and inhibition of neurogenesis were likely mediated by HSP90 and the P2X7R/NLRP3 inflammasome pathway. HSP90 inhibition by 17-AAG may be a promising therapeutic strategy for the treatment of SAH.

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.

Blockade of Pannexin-1 Channels and Purinergic P2X7 Receptors Shows Protective Effects Against Cytokines-Induced Colitis of Human Colonic Mucosa

Introduction: The pannexin-1 (Panx1) channels are found in many cell types, and ATP released from these channels can act on nearby cells activating purinergic P2X7 receptors (P2X7R) which lead to inflammation. Although Panx1 and P2X7R are implicated in the process of inflammation and cell death, few studies have looked at the role they play in inflammatory bowel disease in human. Hence, the aim of the present study was to investigate the function of Panx1 and P2X7R in an ex vivo colitis model developed from human colonic mucosal explants. Materials and Methods: Healthy human colonic mucosal strips (4 × 10 mm) were incubated in carbogenated culture medium at 37°C for 16 h. Proinflammatory cytokines TNFα and IL-1β (each 10 ng/mL) were used to induce colitis in mucosal strips, and the effects of Panx1 and P2X7R on cytokines-induced tissue damage were determined in the presence of the Panx1 channel blocker 10Panx1 (100 μM) and P2X7R antagonist A438079 (100 μM). The effects of 10Panx1 and A438079 on cytokines-enhanced epithelial permeability were also studied using Caco-2 cells. Results: Histological staining showed that the mucosal strips had severe structural damage in the cytokines-only group but not in the incubation-control group (P < 0.01). Compared to the cytokines-only group, crypt damage was significantly decreased in groups receiving cytokines with inhibitors (10Panx1, A438079, or 10Panx1 + A438079, P < 0.05). The immunoreactive signals of tight junction protein zonula occludens-1 (ZO-1) were abundant in all control tissues but were significantly disrupted and lost in the cytokines-only group (P < 0.01). The diminished ZO-1 immunoreactivity induced by cytokines was prevented in the presence of 10Panx1 (P = 0.04). Likewise, 10Panx1 significantly attenuated the cytokines-evoked increase in paracellular permeability of Caco-2 cells. Although the inhibition of P2X7R activity by A438079 diminished cytokines-induced crypt damage, its effect on the maintenance of ZO-1 immunoreactivity and Caco-2 epithelial cell integrity was less evident. Conclusion: The blockade of Panx1 and P2X7R reduced the inflammatory cytokines-induced crypt damage, loss of tight junctions and increase in cell permeability. Thus, Panx1 and P2X7R may have roles in causing mucosal damage, a common clinical feature of inflammatory bowel disease.

Pore forming channels as a drug delivery system for photodynamic therapy in cancer associated with nanoscintillators

According to the World Health Organization (WHO), cancer is one of main causes of death worldwide, with 8.2 million people dying from this disease in 2012. Because of this, new forms of treatments or improvement of current treatments are crucial. In this regard, Photodynamic therapy (PDT) has been used to successfully treat cancers that can be easily accessed externally or by fibre-optic endoscopes, such as skin, bladder and esophagus cancers. In addition, this therapy can used alongside radiotherapy and chemotherapy in order to kill cancer cells. The main problem in implementing PDT is penetration of visible light deeper than 10 mm in tissues, due to scattering and absorption by tissue chromophores. Unfortunately, this excludes several internal organs affected by cancer. Another issue in this regard is the use of a selective cancer cell-photosensitizing compound. Nevertheless, several groups have recently developed scintillation nanoparticles, which can be stimulated by X-rays, thereby making this a possible solution for light production in deeper tissues. Alternative approaches have also been developed, such as photosensitizer structure modifications and cell membrane permeabilizing agents. In this context, certain channels lead to transitory plasma membrane permeability changes, such as pannexin, connexin hemmichannels, TRPV1-4 and P2×7, which allow for the non-selective passage of molecules up to 1,000 Da. Herein, we discuss the particular case of the P2×7 receptor-associated pore as a drug delivery system for hydrophilic substances to be applied in PDT, which could also be carried out with other channels. Methylene blue (MB) is a low cost dye used as a prototype photosensitizer, approved for clinical use in several other clinical conditions, as well as photodynamic therapy for fungi infections.

Purinergic Receptors in Neurological Diseases With Motor Symptoms: Targets for Therapy

Since proving adenosine triphosphate (ATP) functions as a neurotransmitter in neuron/glia interactions, the purinergic system has been more intensely studied within the scope of the central nervous system. In neurological disorders with associated motor symptoms, including Parkinson's disease (PD), motor neuron diseases (MND), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Huntington's Disease (HD), restless leg syndrome (RLS), and ataxias, alterations in purinergic receptor expression and activity have been noted, indicating a potential role for this system in disease etiology and progression. In neurodegenerative conditions, neural cell death provokes extensive ATP release and alters calcium signaling through purinergic receptor modulation. Consequently, neuroinflammatory responses, excitotoxicity and apoptosis are directly or indirectly induced. This review analyzes currently available data, which suggests involvement of the purinergic system in neuro-associated motor dysfunctions and underlying mechanisms. Possible targets for pharmacological interventions are also discussed.

The putative role of oxidative stress and inflammation in the pathophysiology of sleep dysfunction across neuropsychiatric disorders: Focus on chronic fatigue syndrome, bipolar disorder and multiple sclerosis

Sleep and circadian abnormalities are prevalent and burdensome manifestations of diverse neuro-immune diseases, and may aggravate the course of several neuropsychiatric disorders. The underlying pathophysiology of sleep abnormalities across neuropsychiatric disorders remains unclear, and may involve the inter-play of several clinical variables and mechanistic pathways. In this review, we propose a heuristic framework in which reciprocal interactions of immune, oxidative and nitrosative stress, and mitochondrial pathways may drive sleep abnormalities across potentially neuroprogressive disorders. Specifically, it is proposed that systemic inflammation may activate microglial cells and astrocytes in brain regions involved in sleep and circadian regulation. Activated glial cells may secrete pro-inflammatory cytokines (for example, interleukin-1 beta and tumour necrosis factor alpha), nitric oxide and gliotransmitters, which may influence the expression of key circadian regulators (e.g., the Circadian Locomotor Output Cycles Kaput (CLOCK) gene). Furthermore, sleep disruption may further aggravate oxidative and nitrosative, peripheral immune activation, and (neuro) inflammation across these disorders in a vicious pathophysiological loop. This review will focus on chronic fatigue syndrome, bipolar disorder, and multiple sclerosis as exemplars of neuro-immune disorders. We conclude that novel therapeutic targets exploring immune and oxidative & nitrosative pathways (p.e. melatonin and molecular hydrogen) hold promise in alleviating sleep and circadian dysfunction in these disorders.

Gene and protein expression of CXCR4 in adult and elderly patients with chronic rhinitis, pharyngitis or sinusitis undergoing thermal water nasal inhalations

Background

Chronic rhinitis, pharyngitis and sinusitis are common health problems with a significant impact on public health, and are suspected to be influenced by ageing factors. Nasal inhalation with thermal water may be used to reduce symptoms, inflammation and drug intake. A pre-post clinical study was conducted in 183 consecutive adult and elderly patients with chronic rhinitis, pharyngitis or sinusitis, to evaluate whether thermal water nasal inhalations could improve their symptoms, clinical signs and rhinomanometry measurements, and influence inflammatory biomarkers levels in nasal epithelial cells.

Results

Participants profile revealed that they were aged on average (mean age and SD 60.6 ± 15.2 years, median 65, range 20–86, 86 aged ≤ 65 years (47%), 96 aged > 65 years (53%)) and extremely concerned about wellbeing. Older age was associated with better compliance to inhalation treatment. Total symptom and clinical evaluation scores were significantly ameliorated after treatment (p < 0.001), with no substantial difference according to age, while rhinomanometry results were inconsistent. Persistence of symptom improvement was confirmed at phone follow up 1 year later (n = 74). The training set of 48 inflammatory genes (40 patients) revealed a strong increase of CXCR4 gene expression after nasal inhalations, confirmed both in the validation set (143 patients; 1.2 ± 0.68 vs 3.3 ± 1.2; p < 0.0001) and by evaluation of CXCR4 protein expression (40 patients; 1.0 ± 0.39 vs 2.6 ± 0.66; p < 0.0001). CXCR4 expression was consistently changed in patients with rhinitis, pharyngitis or sinusitis. The increase was smaller in current smokers compared to non-smokers. Results were substantially unchanged when comparing aged subjects (≥ 65 years) or the eldest quartile (≥ 71 years) to the others. Other genes showed weaker variations (e.g. FLT1 was reduced only in patients with sinusitis).

Conclusions

These results confirm the clinical impact of thermal water nasal inhalations on upper respiratory diseases both in adults and elders, and emphasize the role of genes activating tissue repair and inflammatory pathways. Future studies should evaluate CXCR4 as possible therapeutic target or response predictor in patients with chronic rhinitis, pharyngitis or sinusitis.

Trial registration

Communication to Italian Ministry of Health - ICPOM 000461. Registered 10/11/2014.

Electronic supplementary material

The online version of this article (10.1186/s12979-018-0114-y) contains supplementary material, which is available to authorized users.

Lack of chemopreventive effects of P2X7R inhibitors against pancreatic cancer

Pancreatic cancer (PC) is an almost uniformly lethal disease with inflammation playing an important role in its progression. Sustained stimulation of purinergic receptor P2X7 drives induction of NLRP inflammasome activation. To understand the role of P2X7 receptor and inflammasome, we performed transcriptomic analysis of p48^Cre/+-LSL-Kras^G12D/+ mice pancreatic tumors by next generation sequencing. Results showed that P2X7R's key inflammasome components, IL-1β and caspase-1 are highly expressed (p < 0.05) in pancreatic tumors. Hence, to target P2X7R, we tested effects of two P2X7R antagonists, A438079 and AZ10606120, on pancreatic intraepithelial neoplasms (PanINs) and their progression to PC in p48^Cre/+-LSL-Kras^G12D/+ mice. Following dose optimization studies, for chemoprevention efficacy, six-week-old p48^Cre/+-LSL-Kras^G12D/+ mice (24–36/group) were fed modified AIN-76A diets containing 0, 50 or 100 ppm A438079 and AZ10606120 for 38 weeks. Pancreata were collected, weighed, and evaluated for PanINs and PDAC. Control diet-fed male mice showed 50% PDAC incidence. Dietary A438079 and AZ10606120 showed 60% PDAC incidence. A marginal increase of PanIN 3 (carcinoma in-situ) was observed in drug-treated mice. Importantly, the carcinoma spread in untreated mice was 24% compared to 43–53% in treatment groups. Reduced survival rates were observed in mice exposed to P2X7R inhibitors. Both drugs showed a decrease in caspase-3, caspase-1, p21 and Cdc25c. Dietary A438079 showed modest inhibition of P2X7R, NLRP3, and IL-33, whereas AZ10606120 had no effects. In summary, targeting the P2X7R pathway by A438079 and AZ10606120 failed to show chemopreventive effects against PC and slightly enhanced PanIN progression to PDAC. Hence, caution is needed while treating high-risk individuals with P2X7R inhibitors.

Comparative genomics of four Mycoplasma species of the human urogenital tract: Analysis of their core genomes and virulence genes

The variation in Mycoplasma lipoproteins attributed to genome rearrangements and genetic insertions leads to phenotypic plasticity that allows for the evasion of the host's defence system and pathogenesis. This paper compared for the first time the genomes of four human urogenital Mycoplasma species (M. penetrans HF-2, M. fermentans JER, M. genitalium G37 and M. hominis PG21) to categorise the metabolic functions of the core genes and to assess the effects of tandem repeats, phage-like genetic elements and prophages on the virulence genes. The results of this comparative in silico genomic analysis revealed that the genes constituting their core genomes can be separated into three distinct categories: nuclear metabolism, protein metabolism and energy generation each making up 52%, 31% and 23%, respectively. The genomes have repeat sequences ranging from 3.7% in M. hominis PG21 to 9.5% in M. fermentans JER. Tandem repeats (mostly minisatellites) and phage-like proteins (including DNA gyrases/topoisomerases) were randomly distributed in the Mycoplasma genomes. Here, we identified a coiled-coil structure containing protein in M. penetrans HF-2 which is significantly similar to the Mem protein of M. fermentans ɸMFV1. Therefore, a Mycoplasma prophage seems to be embedded within M. penetrans HF-2 unannotated genome. To the best of our knowledge, no Mycoplasma phages or prophages have been detected in M. penetrans. This study is important not only in understanding the complex genetic factors involved in phenotypic plasticity and virulence in the relatively understudied Mycoplasma species but also in elucidating the effective arrangement of their redundant minimal genomes.

Brain ureido degenerative protein modifications are associated with neuroinflammation and proteinopathy in Alzheimer's disease with cerebrovascular disease

BACKGROUND

Brain degenerative protein modifications (DPMs) are associated with the apparition and progression of dementia, and at the same time, Alzheimer's disease with cerebrovascular disease (AD + CVD) is the most prevalent form of dementia in the elder population. Thus, understanding the role(s) of brain DPMs in this dementia subtype may provide novel insight on the disease pathogenesis and may aid on the development of novel diagnostic and therapeutic tools. Two essential DPMs known to promote inflammation in several human diseases are the ureido DPMs (uDPMs) arginine citrullination and lysine carbamylation, although they have distinct enzymatic and non-enzymatic origins, respectively. Nevertheless, the implication of uDPMs in the neuropathology of dementia remains poorly understood.

METHODS

In this study, we use the state-of-the-art, ultracentrifugation-electrostatic repulsion hydrophilic interaction chromatography (UC-ERLIC)-coupled mass spectrometry technology to undertake a comparative characterization of uDPMs in the soluble and particulate postmortem brain fractions of subjects diagnosed with AD + CVD and age-matched controls.

RESULTS

An increase in the formation of uDPMs was observed in all the profiled AD + CVD brains. Citrulline-containing proteins were found more abundant in the soluble fraction of AD + CVD whereas homocitrulline-containing proteins were preferentially abundant in the particulate fraction of AD + CVD brains. Several dementia-specific citrulline residues were also identified in soluble proteins previously categorized as pro-immunogenic, which include the receptor P2X7, alpha-internexin, GFAP, CNP, MBP, and histones. Similarly, diverse dementia-specific homocitrulline residues were also observed in the particulate fractions of AD + CVD in proteins that have been vastly implicated in neuropathology. Intriguingly, we also found that the amino acids immediately flanking arginine residues may specifically influence the increase in protein citrullination.

CONCLUSIONS

Taken together, these results indicate that uDPMs widely contribute to the pathophysiology of AD + CVD by promoting neuroinflammation and proteinopathy. Furthermore, the obtained results could help to identify disease-associated proteins that can act as potential targets for therapeutic intervention or as novel biomarkers of specific neuropathology.

P2X7 receptor antagonism prevents IL-1β release from salivary epithelial cells and reduces inflammation in a mouse model of autoimmune exocrinopathy

Salivary gland inflammation is a hallmark of Sjögren's syndrome (SS), a common autoimmune disease characterized by lymphocytic infiltration of the salivary gland and loss of saliva secretion, predominantly in women. The P2X7 receptor (P2X7R) is an ATP-gated nonselective cation channel that induces inflammatory responses in cells and tissues, including salivary gland epithelium. In immune cells, P2X7R activation induces the production of proinflammatory cytokines, including IL-1β and IL-18, by inducing the oligomerization of the multiprotein complex NLRP3-type inflammasome. Here, our results show that in primary mouse submandibular gland (SMG) epithelial cells, P2X7R activation also induces the assembly of the NLRP3 inflammasome and the maturation and release of IL-1β, a response that is absent in SMG cells isolated from mice deficient in P2X7Rs (P2X7R^-/-). P2X7R-mediated IL-1β release in SMG epithelial cells is dependent on transmembrane Na⁺ and/or K⁺ flux and the activation of heat shock protein 90 (HSP90), a protein required for the activation and stabilization of the NLRP3 inflammasome. Also, using the reactive oxygen species (ROS) scavengers N-acetyl cysteine and Mito-TEMPO, we determined that mitochondrial reactive oxygen species are required for P2X7R-mediated IL-1β release. Lastly, in vivo administration of the P2X7R antagonist A438079 in the CD28^-/-, IFNγ^-/-, NOD.H-2^h4 mouse model of salivary gland exocrinopathy ameliorated salivary gland inflammation and enhanced carbachol-induced saliva secretion. These findings demonstrate that P2X7R antagonism in vivo represents a promising therapeutic strategy to limit salivary gland inflammation and improve secretory function.

Innate immune mediators in cancer: between defense and resistance

Chronic inflammation in the tumor microenvironment and evasion of the antitumor effector immune response are two of the emerging hallmarks required for oncogenesis and cancer progression. The innate immune system not only plays a critical role in perpetuating these tumor-promoting hallmarks but also in developing antitumor adaptive immune responses. Thus, understanding the dual role of the innate system in cancer immunology is required for the design of combined immunotherapy strategies able to tackle established tumors. Here, we review recent advances in the understanding of the role of cell populations and soluble components of the innate immune system in cancer, with a focus on complement, the adapter molecule Stimulator of Interferon Genes, natural killer cells, myeloid cells, and B cells.

Salidroside Ameliorates Diabetic Neuropathic Pain in Rats by Inhibiting Neuroinflammation

More than half of diabetic patients suffer from intractable neuropathic pain. As inflammation plays an important role in diabetic neuropathic pain, anti-inflammatory drugs might have therapeutic potentials for neuropathic pain. Salidroside (SAL), a phenylpropanoid glucoside, modulates a variety of cell functions, including inflammation. Here, we explored anti-nociceptive and anti-inflammatory effects of SAL on Zucker diabetic fatty rats with type 2 diabetes (DM rats). DM rats were tested for mechanical and thermal hyperalgesia using von Frey filament and plantar hot box test, respectively. The anti-nociceptive effect of chronic SAL (25-100 mg/kg, per oral) treatment was tested. The expression of inflammatory cytokines (TNF-α and IL-1β) and P2X₇ receptors in spinal cord and sciatic nerve were measured with ELISA. SAL alleviated mechanical and thermal hyperalgesia and reduced TNF-α and IL-1β in sciatic nerve and spinal cord in DM rats. Furthermore, SAL reduced P2X₇ receptor upregulation in spinal cord of DM rats and directly inhibited P2X₇ receptors expressed in HEK293 cells. This study provides evidence that SAL attenuated nociception in diabetic neuropathic pain rat models probably through inhibiting neuroinflammation and P2X₇ receptors.

Virus-Triggered ATP Release Limits Viral Replication through Facilitating IFN-β Production in a P2X7-Dependent Manner

Accumulating evidence shows that innate immune responses are associated with extracellular nucleotides, particularly ATP. In this article, we demonstrate extensive protection of ATP/P2X7 signaling in a host against viral infection. Interestingly, we observed a significant increase in ATP as a danger signal in vesicular stomatitis virus (VSV)-infected cell supernatant and VSV-infected mice in an exocytosis- and pannexin channel-dependent manner. Furthermore, extracellular ATP reduces the replication of VSV, Newcastle disease virus, murine leukemia virus, and HSV in vivo and in vitro through the P2X7 receptor. Meanwhile, ATP significantly increases IFN-β expression in a concentration- and time-dependent manner. Mechanistically, ATP facilitates IFN-β secretion through P38/JNK/ATF-2 signaling pathways, which are crucial in promoting antiviral immunity. Taken together, these results demonstrate the protective role of extracellular ATP and P2X7 in viral infection and suggest a potential therapeutic role for ATP/P2X7 in viral diseases.

The purine receptor P2X7R regulates the release of pro-inflammatory cytokines in human craniopharyngioma

Craniopharyngiomas (CPs) are usually benign, non-metastasizing embryonic malformations originating from the sellar area. They are, however, locally invasive and generate adherent interfaces with the surrounding brain parenchyma. Previous studies have shown the tumor microenvironment is characterized by a local abundance of adenosine triphosphate (ATP), infiltration of leukocytes and elevated levels of pro-inflammatory cytokines that are thought to be responsible, at least in part, for the local invasion. Here, we examine whether ATP, via the P2X7R, participates in the regulation of cytokine expression in CPs. The expression of P2X7R and pro-inflammatory cytokines were measured at the RNA and protein levels both in tumor samples and in primary cultured tumor cells. Furthermore, cytokine modulation was measured after manipulating P2X7R in cultured tumor cells by siRNA-mediated knockdown, as well as pharmacologically by using selective agonists and antagonists. The following results were observed. A number of cytokines, in particular IL-6, IL-8 and MCP-1, were elevated in patient plasma, tumor tissue and cultured tumor cells. P2X7R was expressed in tumor tissue as well as in cultured tumor cells. RNA expression as measured in 48 resected tumors was positively correlated with the RNA levels of IL-6, IL-8 and MCP-1 in tumors. Furthermore, knockdown of P2X7R in primary tumor cultures reduced, and stimulation of P2XR7 by a specific agonist enhanced the expression of these cytokines. This latter stimulation involved a Ca²⁺-dependent mechanism and could be counteracted by the addition of an antagonist. In conclusion, the results suggest that P2X7R may promote IL-6, IL-8 and MCP-1 production and secretion and contribute to the invasion and adhesion of CPs to the surrounding tissue.

P2X7 receptor antagonism: Implications in diabetic retinopathy

Diabetic retinopathy (DR) is the most frequent complication of diabetes and one of leading causes of blindness worldwide. Early phases of DR are characterized by retinal pericyte loss mainly related to concurrent inflammatory process. Recently, an important link between P2X7 receptor (P2X7R) and inflammation has been demonstrated indicating this receptor as potential pharmacological target in DR. Here we first carried out an in silico molecular modeling study in order to characterize the allosteric pocket in P2X7R, and identify a suitable P2X7R antagonist through molecular docking. JNJ47965567 was identified as the hit compound in docking calculations, as well as for its absorption, distribution, metabolism and excretion (ADME) profile. As an in vitro model of early diabetic retinopathy, human retinal pericytes were exposed to high glucose (25mM, 48h) that caused a significant (p<0.05) release of IL-1β and LDH. The block of P2X7R by JNJ47965567 significantly (p<0.05) reverted the damage elicited by high glucose, detected as IL-1β and LDH release. Overall, our findings suggest that the P2X7R represents an attractive pharmacological target to manage the early phase of diabetic retinopathy, and the compound JNJ47965567 is a good template to discover other P2X7R selective antagonists.

Hyperglycemia-induced Renal P2X7 Receptor Activation Enhances Diabetes-related Injury

Diabetes is a leading cause of renal disease. Glomerular mesangial expansion and fibrosis are hallmarks of diabetic nephropathy and this is thought to be promoted by infiltration of circulating macrophages. Monocyte chemoattractant protein-1 (MCP-1) has been shown to attract macrophages in kidney diseases. P2X7 receptors (P2X7R) are highly expressed on macrophages and are essential components of pro-inflammatory signaling in multiple tissues. Here we show that in diabetic patients, renal P2X7R expression is associated with severe mesangial expansion, impaired glomerular filtration (≤40ml/min/1.73sq.m.), and increased interstitial fibrosis. P2X7R activation enhanced the release of MCP-1 in human mesangial cells cultured under high glucose conditions. In mice, P2X7R-deficiency prevented glomerular macrophage attraction and collagen IV deposition; however, the more severe interstitial inflammation and fibrosis often seen in human diabetic kidney diseases was not modelled. Finally, we demonstrate that a P2X7R inhibitor (AZ11657312) can reduce renal macrophage accrual following the establishment of hyperglycemia in a model of diabetic nephropathy. Collectively these data suggest that P2X7R activation may contribute to the high prevalence of kidney disease found in diabetics.

Increased expression of P2X7 receptor in peripheral blood mononuclear cells correlates with clinical severity and serum levels of Th17-related cytokines in patients with myasthenia gravis

OBJECTIVES

P2X7R is a well-documented activator of innate and adaptive immune responses. We aimed to measure the expression levels of P2X7R in peripheral blood mononuclear cells (PBMCs) from patients with myasthenia gravis (MG) and to investigate whether the expression of P2X7R is associated with pathogenesis of MG.

PATIENTS AND METHODS

A total of 32 patients with MG (12 generalized MG (GMG) and 20 Ocular MG (OMG) and 22 healthy donors were recruited in this study. The quantitative MG score was used to evaluate the clinical severity. Real-time PCR and western blot were used to measure the levels of P2X7R expressed in PBMCs. Serum Th17-related cytokines (IL-1β, IL-6, IL-17 and IL-21) were tested by ELISA. PBMCs from MG patients were purified and challenged by LPS with or without a selective P2X7R inhibitor (BBG).

RESULTS

Our results showed that the expression of P2X7R mRNA and protein in PBMCs was increased in MG patients compared with healthy controls, with higher expression in generalized patients (GMG) than in ocular patients (OMG). In addition, P2X7R expression presents a significantly positive correlation with clinical severity and serum levels of IL-1β, IL-6, IL-17 and IL-21 in MG. In cultured MG PBMC, LPS challenge led to up-regulated P2X7R expression accompanied with increased production of IL-1β, IL-6, IL-17 and IL-21. Importantly, P2X7R blockade with BBG significantly attenuates the LPS-induced production of cytokines.

CONCLUSION

P2X7R expression was up-regulated in MG and LPS-P2X7R axis may be involved in the pathogenesis of MG by promoting Th17 immune response.

P2X1, P2X4, and P2X7 Receptor Knock Out Mice Expose Differential Outcome of Sepsis Induced by α-Haemolysin Producing Escherichia coli

α-haemolysin (HlyA)-producing Escherichia coli commonly inflict severe urinary tract infections, including pyelonephritis, which comprises substantial risk for sepsis. In vitro, the cytolytic effect of HlyA is mainly mediated by ATP release through the HlyA pore and subsequent P2X₁/P2X₇ receptor activation. This amplification of the lytic process is not unique to HlyA but is observed by many other pore-forming proteins including complement-induced haemolysis. Since free hemoglobin in the blood is known to be associated with a worse outcome in sepsis one could speculate that inhibition of P2X receptors would ameliorate the course of sepsis. Surprisingly, this study demonstrates that [Formula: see text] and [Formula: see text] mice are exceedingly sensitive to sepsis with uropathogenic E. coli. These mice have markedly lower survival, higher cytokine levels and activated intravascular coagulation. Quite the reverse is seen in [Formula: see text] mice, which had markedly lower cytokine levels and less coagulation activation compared to controls after exposure to uropathogenic E. coli. The high cytokine levels in the [Formula: see text] mouse are unexpected, since P2X₇ is implicated in caspase-1-dependent IL-1β production. Here, we demonstrate that IL-1β production during sepsis with uropathogenic E. coli is mediated by caspase-8, since caspase-8 and RIPK3 double knock out mice show substantially lower cytokine during sepsis and increased survival after injection of TNFα. These data support that P2X₇ and P2X₄ receptor activation has a protective effect during severe E. coli infection.

Innate immune signaling and regulation in cancer immunotherapy

A pre-existing T cell-inflamed tumor microenvironment has prognostic utility and also can be predictive for response to contemporary cancer immunotherapies. The generation of a spontaneous T cell response against tumor-associated antigens depends on innate immune activation, which drives type I interferon (IFN) production. Recent work has revealed a major role for the STING pathway of cytosolic DNA sensing in this process. This cascade of events contributes to the activation of Batf3-lineage dendritic cells (DCs), which appear to be central to anti-tumor immunity. Non-T cell-inflamed tumors lack chemokines for Batf3 DC recruitment, have few Batf3 DCs, and lack a type I IFN gene signature, suggesting that failed innate immune activation may be the ultimate cause for lack of spontaneous T cell activation and accumulation. With this information in hand, new strategies for triggering innate immune activation and Batf3 DC recruitment are being developed, including novel STING agonists for de novo immune priming. Ultimately, the successful development of effective innate immune activators should expand the fraction of patients that can respond to immunotherapies, such as with checkpoint blockade antibodies.

Inflammatory early events associated to the role of P2X7 receptor in acute murine toxoplasmosis

Activation of the purinergic P2X7 receptor by extracellular ATP (eATP) potentiates proinflammatory responses during infections by intracellular pathogens. Extracellular ATP triggers an antimicrobial response in macrophages infected with Toxoplasma gondii in vitro, suggesting that purinergic signaling may stimulate host defense mechanisms against toxoplasmosis. Here, we provide in vivo evidence in support of this hypothesis, by showing that P2X7^-/- mice are more susceptible than P2X7^+/+ mice to acute infection by the RH strain of T. gondii, and that this phenomenon is associated with a deficient proinflammatory response. Four days post-infection, peritoneal washes from infected P2X7^-/- mice had no or little increase in the levels of the proinflammatory cytokines IL-12, IL-1β, IFN-γ, and TNF-α, whose levels increased markedly in samples from infected P2X7^+/+ mice. Infected P2X7^-/- mice displayed an increase in organ weight and histological alterations in some of the 'shock organs' in toxoplasmosis - the liver, spleen and mesenteric lymph nodes. The liver of infected P2X7^-/- mice had smaller granulomas, but increased parasite load/granuloma. Our results confirm that the P2X7 receptor is involved in containing T. gondii spread in vivo, by stimulating inflammation.

Conformational changes during human P2X7 receptor activation examined by structural modelling and cysteine-based cross-linking studies

The P2X7 receptor (P2X7R) is important in mediating a range of physiological functions and pathologies associated with tissue damage and inflammation and represents an attractive therapeutic target. However, in terms of their structure-function relationships, the mammalian P2X7Rs remain poorly characterised compared to some of their other P2XR counterparts. In this study, combining cysteine-based cross-linking and whole-cell patch-clamp recording, we examined six pairs of residues (A44/I331, D48/I331, I58/F311, S60/L320, I75/P177 and K81/V304) located in different parts of the extracellular and transmembrane domains of the human P2X7R. These residues are predicted to undergo substantial movement during the transition of the receptor ion channel from the closed to the open state, predictions which are made based on structural homology models generated from the crystal structures of the zebrafish P2X4R. Our results provide evidence that among the six pairs of cysteine mutants, D48C/I133C and K81C/V304C formed disulphide bonds that impaired the channel gating to support the notion that such conformational changes, particularly those in the outer ends of the transmembrane domains, are critical for human P2X7R activation.

Intra-Articular Blockade of P2X7 Receptor Reduces the Articular Hyperalgesia and Inflammation in the Knee Joint Synovitis Especially in Female Rats

Synovitis is a key factor in joint disease pathophysiology, which affects a greater proportion of women than men. P2X7 receptor activation contributes to arthritis, but whether it plays a role in articular inflammatory pain in a sex-dependent manner is unknown. We investigated whether the P2X7 receptor blockade in the knee joint of male and female rats reduces the articular hyperalgesia and inflammation induced by a carrageenan knee joint synovitis model. Articular hyperalgesia was quantified using the rat knee joint incapacitation test and the knee joint inflammation, characterized by the concentration of cytokines tumor necrosis factor-α, interleukin-1β, interleukin-6, and cytokine-induced neutrophil chemoattractant-1, and by neutrophil migration, was quantified using enzyme-linked immunosorbent assay and by myeloperoxidase enzyme activity measurement, respectively. P2X7 receptor blockade by the articular coadministration of selective P2X7 receptor antagonist A740003 with carrageenan significantly reduced articular hyperalgesia, pro-inflammatory cytokine concentrations, and myeloperoxidase activity induced by carrageenan injection into the knee joint of male and estrus female rats. However, a lower dose of P2X7 receptor antagonist was sufficient to significantly induce the antihyperalgesic and anti-inflammatory effects in estrus female but not in male rats. These results suggest that P2X7 receptor activation by endogenous adenosine 5'-triphosphate is essential to articular hyperalgesia and inflammation development in the knee joint of male and female rats. However, female rats are more responsive than male rats to the antihyperalgesic and anti-inflammatory effects induced by P2X7 receptor blockade.

PERSPECTIVE

P2X7 receptors could be promising therapeutic targets in the treatment of knee joint disease symptoms, especially in women, who are more affected than men by these conditions.

Purinergic signaling in schistosomal infection

Human schistosomiasis is a chronic inflammatory disease caused by blood fluke worms belonging to the genus Schistosoma. Health metrics indicate that the disease is related to an elevated number of years lost-to-disability and years lost-to-life. Schistosomiasis is an intravascular disease that is related to a Th1 and Th2 immune response polarization, and the degree of polarization affects the outcome of the disease. The purinergic system is composed of adenosine and nucleotides acting as key messenger molecules. Moreover, nucleotide-transforming enzymes and cell-surface purinergic receptors are obligatory partners of this purinergic signaling. In mammalian cells, purinergic signaling modulates innate immune responses and inflammation among other functions; conversely purinergic signaling may also be modulated by inflammatory mediators. Moreover, schistosomes also express some enzymes of the purinergic system, and it is possible that worms modulate host purinergic signaling. Current data obtained in murine models of schistosomiasis support the notion that the host purinergic system is altered by the disease. The dysfunction of adenosine receptors, metabotropic P2Y and ionotropic P2X₇ receptors, and NTPDases likely contributes to disease morbidity.

Blocking of the P2X7 receptor inhibits the activation of the MMP-13 and NF-κB pathways in the cartilage tissue of rats with osteoarthritis

P2X purinoceptor 7 (P2X7) receptor (P2X7R) is known to play a significant role in inflammation and pain-causing diseases, including osteoarthritis (OA). However, the mechanisms of action of P2X7R and its role in OA remain unclear. The articular cartilage is the crucial region in which pathological changes occur in OA, involving the dysregulation of degradation and maintenance mechanisms. In this study, we aimed to reveal the molecular mechanisms of action of P2X7R in articular cartilage in OA-induced pain and inflammation by using AZD9056, an antagonist of P2X7R. We created an animal model of OA by using Wistar rats administered (by intra-articular injection) monosodium iodoacetate (MIA), and the rats with OA were then treated with the P2X7R antagonist, AZD9056. We found that treatment with AZD9056 exerted pain-relieving and anti-inflammatory effects. Importantly, we found that the upregulated expression of interleukin (IL)-1β, IL-6, tumor necrosis factor-α (TNF-α), matrix metalloproteinase-13 (MMP-13), substance P (SP) and prostaglandin E2 (PGE2) which was induced by MIA in cartilage tissues was reversed by AZD9056. Western blot analysis was used to examine the expression of inhibitor of nuclear factor-κB (NF-κB) kinase (IKK)α, IKKβ, inhibitor of NF-κB (IκB)α, NF-κB p65 and their phosphorylation forms; they were found to be significantly increased in the knee cartilage tissues from rats with OA; however, opposite effects were observed by the injection of AZD9056. These results implied that P2X7R was associated with the activation of the NF-κB pathway in the development of OA. Our results also revealed that helenalin, an NF-κB pathway inhibitor, decreased the expression of P2X7R, IL-1β, IL-6, TNF-α, SP, PGE2 and MMP-13, which was induced by MIA, in the knee cartilage tissues of rats with OA. On the whole, our findings suggest that P2X7R regulates the MMP-13 and NF-κB pathways in cartilage tissue and mediate OA-induced pain and inflammation.

P2X7 receptors in body temperature, locomotor activity, and brain mRNA and lncRNA responses to sleep deprivation

The ionotropic purine type 2X7 receptor (P2X7R) is a nonspecific cation channel implicated in sleep regulation and brain cytokine release. Many endogenous rhythms covary with sleep, including locomotor activity and core body temperature. Furthermore, brain-hypothalamic cytokines and purines play a role in the regulation of these physiological parameters as well as sleep. We hypothesized that these parameters are also affected by the absence of the P2X7 receptor. Herein, we determine spontaneous expression of body temperature and locomotor activity in wild-type (WT) and P2X7R knockout (KO) mice and how they are affected by sleep deprivation (SD). We also compare hypothalamic, hippocampal, and cortical cytokine- and purine-related receptor and enzyme mRNA expressions before and after SD in WT and P2X7RKO mice. Next, in a hypothesis-generating survey of hypothalamic long noncoding (lnc) RNAs, we compare lncRNA expression levels between strains and after SD. During baseline conditions, P2X7RKO mice had attenuated temperature rhythms compared with WT mice, although locomotor activity patterns were similar in both strains. After 6 h of SD, body temperature and locomotion were enhanced to a greater extent in P2X7RKO mice than in WT mice during the initial 2-3 h after SD. Baseline mRNA levels of cortical TNF-α and P2X4R were higher in the KO mice than WT mice. In response to SD, the KO mice failed to increase hypothalamic adenosine deaminase and P2X4R mRNAs. Further, hypothalamic lncRNA expressions varied by strain, and with SD. Current data are consistent with a role for the P2X7R in thermoregulation and lncRNA involvement in purinergic signaling.

Subfailure Overstretch Injury Leads to Reversible Functional Impairment and Purinergic P2X7 Receptor Activation in Intact Vascular Tissue

Vascular stretch injury is associated with blunt trauma, vascular surgical procedures, and harvest of human saphenous vein for use in vascular bypass grafting. A model of subfailure overstretch in rat abdominal aorta was developed to characterize surgical vascular stretch injury. Longitudinal stretch of rat aorta was characterized ex vivo. Stretch to the haptic endpoint, where the tissues would no longer lengthen, occurred at twice the resting length. The stress produced at this length was greater than physiologic mechanical forces but well below the level of mechanical disruption. Functional responses were determined in a muscle bath, and this subfailure overstretch injury led to impaired smooth muscle function that was partially reversed by treatment with purinergic receptor (P2X7R) antagonists. These data suggest that vasomotor dysfunction caused by subfailure overstretch injury may be due to the activation of P2X7R. These studies have implications for our understanding of mechanical stretch injury of blood vessels and offer novel therapeutic opportunities.

Precision Medicine in Multiple Sclerosis: Future of PET Imaging of Inflammation and Reactive Astrocytes

Non-invasive molecular imaging techniques can enhance diagnosis to achieve successful treatment, as well as reveal underlying pathogenic mechanisms in disorders such as multiple sclerosis (MS). The cooperation of advanced multimodal imaging techniques and increased knowledge of the MS disease mechanism allows both monitoring of neuronal network and therapeutic outcome as well as the tools to discover novel therapeutic targets. Diverse imaging modalities provide reliable diagnostic and prognostic platforms to better achieve precision medicine. Traditionally, magnetic resonance imaging (MRI) has been considered the golden standard in MS research and diagnosis. However, positron emission tomography (PET) imaging can provide functional information of molecular biology in detail even prior to anatomic changes, allowing close follow up of disease progression and treatment response. The recent findings support three major neuroinflammation components in MS: astrogliosis, cytokine elevation, and significant changes in specific proteins, which offer a great variety of specific targets for imaging purposes. Regardless of the fact that imaging of astrocyte function is still a young field and in need for development of suitable imaging ligands, recent studies have shown that inflammation and astrocyte activation are related to progression of MS. MS is a complex disease, which requires understanding of disease mechanisms for successful treatment. PET is a precise non-invasive imaging method for biochemical functions and has potential to enhance early and accurate diagnosis for precision therapy of MS. In this review we focus on modulation of different receptor systems and inflammatory aspect of MS, especially on activation of glial cells, and summarize the recent findings of PET imaging in MS and present the most potent targets for new biomarkers with the main focus on experimental MS research.

P2X7 Receptor Expression in Peripheral Blood Monocytes Is Correlated With Plasma C-Reactive Protein and Cytokine Levels in Patients With Type 2 Diabetes Mellitus: a Preliminary Report

Chronic inflammation plays a major role in development of type 2 diabetes mellitus (T2DM). C-reactive protein (CRP) and inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin 1β (IL-1β) are directly involved in the occurrence of insulin resistance. Increased extracellular ATP levels can amplify the inflammatory response in vivo via the P2X7 receptor. The present study aimed to assess the relationship between P2X7 receptor expression in human peripheral blood monocytes and plasma levels of TNF-α, IL-1β, and CRP in T2DM patients. The results showed the association of increased P2X7 receptor expression of monocytes with high serum CRP, TNF-α, and IL-1β levels. TNF-α and IL-1β levels were lowest in healthy subjects; in T2DM patients, these inflammatory markers were less abundant in individuals with normal CRP levels compared to those with high CRP contents. In contrast, IL-10 levels in T2DM patients with high CRP levels were dramatically decreased. P2X7 receptor expression in monocytes from T2DM patients with high CRP levels was significantly increased in comparison with healthy individuals and T2DM patients with normal CRP levels. These findings indicated that P2X7 receptor in peripheral blood monocytes may be involved in the pathological changes of T2DM, particularly affecting patients with high CRP levels.

P2X7 receptor as a novel drug delivery system to increase the entrance of hydrophilic drugs into cells during photodynamic therapy

The second-generation photosensitizer methylene blue (MB) exhibits photochemical and photophysical properties suitable for photodynamic therapy (PDT)-based cancer treatment. However, the clinical application of MB is limited because of its high hydrophilicity, which hinders its penetration into tumor tissues. Therefore, new methods to improve the entry of MB into the cytoplasm of target cells are necessary. Because MB has a mass of 319 Da, transient pores on the plasma membrane, such as the pore induced by the P2X7 receptor (P2X7R) that allows the passage of molecules up to 900 Da, could be used. Using MTT viability assays, flow cytometry experiments, and fluorescence microscopy, we evaluated the toxicity and phototoxicity of MB and potentiation effects of ATP and MB on cell death processes in the J774 cell line (via a P2X7-associated pore). We observed that treatment with 5 μM MB for 15 min promoted the rate of entry of MB into the cytoplasm to 4.7 %. However, treatment with 5 μM MB and 1 mM ATP for the same amount of time increased this rate to 90.2 %. However, this effect was inhibited by pretreatment with a P2X7 antagonist. We used peritoneal macrophages and a cell line that does not express P2X7R as controls. These cells were more resistant to PDT with MB under the same experimental conditions. Taken together, these results suggest the use of the pore associated with P2X7R as a drug delivery system to increase the passage of hydrophilic drugs into cells that express this receptor, thus facilitating PDT.

Critical Evaluation of P2X7 Receptor Antagonists in Selected Seizure Models

The ATP-gated P2X7 receptor (P2X7R) is a non-selective cation channel which senses high extracellular ATP concentrations and has been suggested as a target for the treatment of neuroinflammation and neurodegenerative diseases. The use of P2X7R antagonists may therefore be a viable approach for treating CNS pathologies, including epileptic disorders. Recent studies showed anticonvulsant potential of P2X7R antagonists in certain animal models. To extend this work, we tested three CNS-permeable P2X7R blocker (Brilliant Blue G, AFC-5128, JNJ-47965567) and a natural compound derivative (tanshinone IIA sulfonate) in four well-characterized animal seizure models. In the maximal electroshock seizure threshold test and the pentylenetetrazol (PTZ) seizure threshold test in mice, none of the four compounds demonstrated anticonvulsant effects when given alone. Notably, in combination with carbamazepine, both AFC-5128 and JNJ-47965567 increased the threshold in the maximal electroshock seizure test. In the PTZ-kindling model in rats, useful for testing antiepileptogenic activities, Brilliant Blue G and tanshinone exhibited a moderate retarding effect, whereas the potent P2X7R blocker AFC-5128 and JNJ-47965567 showed a significant and long-lasting delay in kindling development. In fully kindled rats, the investigated compounds revealed modest effects to reduce the mean seizure stage. Furthermore, AFC-5128- and JNJ-47965567-treated animals displayed strongly reduced Iba 1 and GFAP immunoreactivity in the hippocampal CA3 region. In summary, our results show that P2X7R antagonists possess no remarkable anticonvulsant effects in the used acute screening tests, but can attenuate chemically-induced kindling. Further studies would be of interest to support the concept that P2X7R signalling plays a crucial role in the pathogenesis of epileptic disorders.

Mechanisms of neuroimmune gene induction in alcoholism

RATIONALE

Alcoholism is a primary, chronic relapsing disease of brain reward, motivation, memory, and related circuitry. It is characterized by an individual's continued drinking despite negative consequences related to alcohol use, which is exemplified by alcohol use leading to clinically significant impairment or distress. Chronic alcohol consumption increases the expression of innate immune signaling molecules (ISMs) in the brain that alter cognitive processes and promote alcohol drinking.

OBJECTIVES

Unraveling the mechanisms of alcohol-induced neuroimmune gene induction is complicated by positive loops of multiple cytokines and other signaling molecules that converge on nuclear factor kappa-light-chain-enhancer of activated B cells and activator protein-1 leading to induction of additional neuroimmune signaling molecules that amplify and expand the expression of ISMs.

RESULTS

Studies from our laboratory employing reverse transcription polymerase chain reaction (RT-PCR) to assess mRNA, immunohistochemistry and Western blot analysis to assess protein expression, and others suggest that ethanol increases brain neuroimmune gene and protein expression through two distinct mechanisms involving (1) systemic induction of innate immune molecules that are transported from blood to the brain and (2) the direct release of high-mobility group box 1 (HMGB1) from neurons in the brain. Released HMGB1 signals through multiple receptors, particularly Toll-like receptor (TLR) 4, that potentiate cytokine receptor responses leading to a hyperexcitable state that disrupts neuronal networks and increases excitotoxic neuronal death. Innate immune gene activation in brain is persistent, consistent with the chronic relapsing disease that is alcoholism. Expression of HMGB1, TLRs, and other ISMs is increased several-fold in the human orbital frontal cortex, and expression of these molecules is highly correlated with each other as well as lifetime alcohol consumption and age of drinking onset.

CONCLUSIONS

The persistent and cumulative nature of alcohol on HMGB1 and TLR gene induction support their involvement in alcohol-induced long-term changes in brain function and neurodegeneration.

Retinal glial responses to optic nerve crush are attenuated in Bax-deficient mice and modulated by purinergic signaling pathways

Background

Retinal ganglion cell (RGC) soma death is a consequence of optic nerve damage, including in optic neuropathies like glaucoma. The activation of the innate immune network in the retina after nerve damage has been linked to RGC pathology. Since the eye is immune privileged, innate immune functions are the responsibility of the glia, specifically the microglia, astrocytes, and Müller cells that populate the retina. Glial activation, leading to the production of inflammatory cytokines, is a hallmark feature of retinal injury resulting from optic nerve damage and purported to elicit secondary degeneration of RGC somas.

Methods

A mouse model of optic nerve crush (ONC) was used to study retinal glial activation responses. RGC apoptosis was blocked using Bax-deficient mice. Glial activation responses were monitored by quantitative PCR and immunofluorescent labeling in retinal sections of activation markers. ATP signaling pathways were interrogated using P2X receptor agonists and antagonists and Pannexin 1 (Panx1)-deficient mice with RGC-specific deletion.

Results

ONC induced activation of both macroglia and microglia in the retina, and both these responses were dramatically muted if RGC death was blocked by deletion of the Bax gene. Macroglial, but not microglial, activation was modulated by purinergic receptor activation. Release of ATP after optic nerve damage was not mediated by PANX1 channels in RGCs.

Conclusions

RGC death in response to ONC plays a principal stimulatory role in the retinal glial activation response.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0558-y) contains supplementary material, which is available to authorized users.

Methamphetamine alters microglial immune function through P2X7R signaling

Background

Purinoceptors have emerged as mediators of chronic inflammation and neurodegenerative processes. The ionotropic purinoceptor P2X7 (P2X7R) is known to modulate proinflammatory signaling and integrate neuronal-glial circuits. Evidence of P2X7R involvement in neurodegeneration, chronic pain, and chronic inflammation suggests that purinergic signaling plays a major role in microglial activation during neuroinflammation. In this study, we investigated the effects of methamphetamine (METH) on microglial P2X7R.

Methods

ESdMs were used to evaluate changes in METH-induced P2X7R gene expression via Taqman PCR and protein expression via western blot analysis. Migration and phagocytosis assays were used to evaluate functional changes in ESdMs in response to METH treatment. METH-induced proinflammatory cytokine production following siRNA silencing of P2X7R in ESdMs measured P2X7R-dependent functional changes. In vivo expression of P2X7R and tyrosine hydroxylase (TH) was visualized in an escalating METH dose mouse model via immunohistochemical analysis.

Results

Stimulation of ESdMs with METH for 48 h significantly increased P2X7R mRNA (*p < 0.0336) and protein expression (*p < 0.022). Further analysis of P2X7R protein in cellular fractionations revealed increases in membrane P2X7R (*p < 0.05) but decreased cytoplasmic expression after 48 h METH treatment, suggesting protein mobilization from the cytoplasm to the membrane which occurs upon microglial stimulation with METH. Forty-eight hour METH treatment increased microglial migration towards Fractalkine (CX3CL1) compared to control (****p < 0.0001). Migration toward CX3CL1 was confirmed to be P2X7R-dependent through the use of A 438079, a P2X7R-competitive antagonist, which reversed the METH effects (****p < 0.0001). Similarly, 48 h METH treatment increased microglial phagocytosis compared to control (****p < 0.0001), and pretreatment of P2X7R antagonist reduced METH-induced phagocytosis (****p < 0.0001). Silencing the microglial P2X7R decreased TNF-α (*p < 0.0363) and IL-10 production after 48 h of METH treatment. Additionally, our studies demonstrate increased P2X7R and decreased TH expression in the striata of escalating dose METH animal model compared to controls.

Conclusions

This study sheds new light on the functional role of P2X7R in the regulation of microglial effector functions during substance abuse. Our findings suggest that P2X7R plays an important role in METH-induced microglial activation responses. P2X7R antagonists may thus constitute a novel target of therapeutic utility in neuroinflammatory conditions by regulating pathologically activated glial cells in stimulant abuse.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0553-3) contains supplementary material, which is available to authorized users.

Association of the Precursor of Interleukin-1β and Peritoneal Inflammation-Role in Pathogenesis of Endometriosis

BACKGROUND

The most important proinflammatory cytokine is interleukin (IL)-1β, however its precursor, prointerleukin-1β (proIL-1β), can also potentiate inflammatory state. The aim of this study was to explore the involvement of proIL-1β in pathogenesis of endometriosis. For this purpose, we evaluated concentrations of proIL-1β, IL-1β, and soluble IL-1 receptor type 2 (sIL-1R2) in peritoneal fluid (PF) and macrophage culture medium of women with endometriosis.

METHODS

PF from 55 women with and without endometriosis was collected during laparoscopy. Peritoneal macrophages were cultured in basal and stimulated with lipopolysaccharide (LPS) conditions. Concentrations of cytokines were measured with enzyme-linked immunosorbent assays (ELISA).

RESULTS

PF proIL-1β and IL-1β levels in endometriosis women were higher than in the control. Higher basal and stimulated macrophage secretion of cytokines in endometriosis patients than in the control was observed. However, in endometriosis, there was a higher level of proIL-1β than for the mature molecule. Additionally, lower PF and macrophages culture medium sIL-1R2 levels were observed in women with endometriosis.

CONCLUSIONS

Abnormal proIL-1β concentration in PF and higher macrophage secretion can escalate peritoneal inflammation and endometriosis formation. The results are presented as a total IL-1β, which is a sum of proIL-1β  and IL-1β, and we believe that it reflects the actual cytokine production. The imbalance among all studied cytokines in endometriosis may be linked with an ability to transform acute inflammation to the chronic inflammation.

The purinergic receptor P2X7 role in control of Dengue virus-2 infection and cytokine/chemokine production in infected human monocytes

Purinergic signaling has a crucial role in intracellular pathogen elimination. The P2X7 purinergic receptor (P2X7R), once activated by ATP, leads to pro-inflammatory responses including reactive oxygen species production. ATP can be released by injured cells, as endogenous danger signals. Dengue fever may evolve to a severe disease, leading to hypovolemic shock and coagulation dysfunctions as a result of a cytokine storm. Our aim was to evaluate the role of P2X7R activation during Dengue virus (DENV) infection. Extracellular ATP inhibited viral load in pretreated monocytes, as measured by NS1 secretion and by decrease in DENV(+) P2X7(+) cell frequencies, suggesting that P2X7R is involved in the antiviral response. Nitric oxide (NO) has anti-DENV properties and is decreased after DENV infection. NO production after ATP stimulation is abrogated by KN62 treatment, a specific P2X7R inhibitor, indicating that P2X7R likely is acting in the virus containment process. Additionally, TNF, CXCL8, CCL2 and CXCL10 factors that are associated with dengue severity were modulated by the P2X7R activation. We conclude that P2X7R is directly involved in the modulation of the antiviral and inflammatory process that occurs during DENV infection in vitro, and may have an important role in patient recovery in a first moment.

LncRNA NONRATT021972 siRNA attenuates P2X7 receptor expression and inflammatory cytokine production induced by combined high glucose and free fatty acids in PC12 cells

Diabetic neuropathy (DNP) is a frequent chronic complication of diabetes mellitus with potentially life-threatening outcomes. High glucose and elevated free fatty acids (FFAs) have been recently recognized as major causes of nervous system damage in diabetes. Our previous study has indicated extracellular stimuli, such as high glucose and/or FFA stress, may activate the p38 mitogen-activated protein kinase (MAPK) signaling pathway and induce a p38 MAPK-dependent sensitization of the P2X7 receptor and release of inflammatory factors in PC12 cells, while the mechanisms underlying remain to be elucidated. Long noncoding RNAs (lncRNAs) play important roles in diverse biological processes, including activation of a series of pathway signalings. Here, we showed combined high D-glucose and FFAs (HGHF) induced an increment of lncRNA-NONRATT021972 (NONCODE ID, nc021972) in PC12 cells. Nc021972 small interference RNA (siRNA) alleviated HGHF-induced activation of p38 MAPK, expression of the P2X7 receptor, and [Ca(2+)]i increment upon P2X7 receptor activation. Further experiments showed that there existed a crosstalk between nc021972 and the p38 MAPK signaling pathway. Inhibition of p38 MAPK signaling decreased nc021972-induced expression of the P2X7 receptor and [Ca(2+)]i increment upon P2X7 receptor activation. Also, nc021972 siRNA inhibited HGHF-induced PC12 release of TNF-α and IL-6 and rescued decreased cell viability mediated by the P2X7 receptor. Therefore, inhibition of nc021972 may serve as a novel therapeutic strategy for diabetes complicated with nervous inflammatory diseases.