ATP-P2X7 receptor signaling controls basal and TNFα-stimulated glial cell proliferation

Selective nitration of Hsp90 acts as a metabolic switch promoting tumor cell proliferation

Tumors develop in an oxidative environment characterized by peroxynitrite production and downstream protein tyrosine (Y) nitration. We showed that tyrosine nitration supports schwannoma cell proliferation and regulates cell metabolism in the inheritable tumor disorder NF2-related Schwannomatosis (NF2-SWN). Here, we identified the chaperone Heat shock protein 90 (Hsp90) as the first nitrated protein that acts as a metabolic switch to promote schwannoma cell proliferation. Doubling the endogenous levels of nitrated Hsp90 in schwannoma cells or supplementing nitrated Hsp90 into normal Schwann cells increased their proliferation. Metabolically, nitration on either Y33 or Y56 conferred Hsp90 distinct functions; nitration at Y33 (Hsp90NY33) down-regulated mitochondrial oxidative phosphorylation, while nitration at Y56 (Hsp90NY56) increased glycolysis by activating the purinergic receptor P2X7 in both schwannoma and normal Schwann cells. Hsp90NY33 and Hsp90NY56 showed differential subcellular and spatial distribution corresponding with their metabolic and proliferative functions in schwannoma three-dimensional cell culture models. Collectively, these results underscore the role of tyrosine nitration as a post-translational modification regulating critical cellular processes. Nitrated proteins, particularly nitrated Hsp90, emerge as a novel category of tumor-directed therapeutic targets.

P2X7 receptor activation awakes a dormant stem cell niche in the adult spinal cord

The ependyma of the spinal cord is a latent stem cell niche that is reactivated by injury, generating new cells that migrate to the lesion site to limit the damage. The mechanisms by which ependymal cells are reactivated after injury remain poorly understood. ATP has been proposed to act as a diffusible "danger signal" to alert about damage and start repair. Indeed, spinal cord injury (SCI) generates an increase in extracellular ATP around the lesion epicenter that lasts for several hours and affects the functional outcome after the damage. The P2X7 receptor (P2X7r) has functional properties (e.g., low sensitivity for ATP, high permeability for Ca2+) that makes it a suitable candidate to act as a detector of tissue damage. Because ependymal cells express functional P2X7r that generate an inward current and regenerative Ca2+ waves, we hypothesize that the P2X7r has a main role in the mechanisms by which progenitor-like cells in the ependyma react to tissue damage. To test this possibility, we simulated the P2X7r activation that occurs after SCI by in vivo intraspinal injection of the selective agonist BzATP nearby the central canal. We found that BzATP rescued ependymal cells from quiescence by triggering a proliferative response similar to that generated by injury. In addition, P2X7r activation by BzATP induced a shift of ependymal cells to a glial fibrillary acidic protein (GFAP) phenotype similar to that induced by injury. However, P2X7r activation did not trigger the migration of ependyma-derived cells as occurs after tissue damage. Injection of BzATP induced the expression of connexin 26 (Cx26) in ependymal cells, an event needed for the proliferative reaction after injury. BzATP did not induce these changes in ependymal cells of P2X7-/- mice supporting a specific action on P2X7r. In vivo blockade of P2X7r with the potent antagonist AZ10606120 reduced significantly the injury-induced proliferation of ependymal cells. Our data indicate that P2X7r has a key role in the "awakening" of the ependymal stem cell niche after injury and suggest purinergic signaling is an interesting target to improve the contribution of endogenous progenitors to repair.

P2X7 receptor promotes migration and invasion of non-small cell lung cancer A549 cells through the PI3K/Akt pathways

It has been demonstrated that the ATP-gated ion channel P2X7 receptor is involved in tumor progression and plays an important role in regulating tumor cell growth, invasion, migration and angiogenesis. However, P2X7 receptors have been relatively poorly studied in non-small cell lung cancer (NSCLC) cells. Therefore, the aim of this study was to investigate the effects of P2X7 receptor on A549 cells (NSCLC cell line) migration and invasion and to reveal the molecular mechanisms mediated by it. We detected the expression and function of P2X7 receptor in A549 cells. The effects and mechanisms of P2X7 receptor on A549 cells migration, invasion, and epithelial-mesenchymal transition were detected in vitro and in vivo. The results showed P2X7 receptor expressed by A549 cells had ion channel and macropore formation function. In addition, activation of P2X7 receptor by adenosine triphosphate (ATP) or 2'(3')-O-(4-Benzoylbenzoyl)-adenosine-5'-triphosphate (BzATP) promoted Epithelial-mesenchymal transition (EMT), migration and invasion of A549 cells, which was attenuated by treatment of cells with P2X7 receptor antagonist A438079 and Oxidized ATP. Furthermore, activation of P2X7 receptor increased phosphorylated protein kinase B (p-Akt) levels, and the phosphatidylinositol-tris-phosphate kinase 3 (PI3K)/protein kinase B (Akt) inhibitor LY294002 blocked migration and invasion of A549 cells induced by ATP or BzATP. At the same time, in vivo results showed that P2X7 receptor could also promote EMT and PI3K/Akt expression in transplanted tumors. Our study indicated that P2X7 receptor promotes A549 cells migration and invasion through the PI3K/Akt signaling pathway, suggesting that P2X7 receptor may be a potential therapeutic target for NSCLC.

Cholinergic REST-G9a gene repression through HMGB1-TLR4 neuroimmune signaling regulates basal forebrain cholinergic neuron phenotype

Lipopolysaccharide (LPS) and high-mobility group box 1 (HMGB1) are Toll-like receptor (TLR4) agonists that activate proinflammatory neuroimmune signaling linked to loss of basal forebrain cholinergic neurons (BFCNs) and cognitive deficits. Loss of choline acetyltransferase immunoreactive (ChAT + IR) BFCNs is generally interpreted as cell death, but recent in vivo studies find anti-inflammatory interventions restore adolescent ethanol exposure-induced persistent loss of adult ChAT + IR neurons and cognitive deficits, suggesting proinflammatory signaling-induced reversible gene repression of ChAT in BFCNs. Using an ex vivo Wistar rat basal forebrain slice culture (FSC) model to investigate TLR4 involvement in repression of the BFCN phenotype, we report that direct TLR4 activation with LPS decreases expression of multiple BFCN markers in the absence of observable neuronal loss or cell death. Inhibition of HMGB1 blunts while inhibition of TLR4 blocks the LPS-induced loss of ChAT + IR neurons. TLR4 activation induces the transcriptional repressor RE1-silencing transcription factor (REST) and the methyltransferase G9a while increasing repressive histone 3 lysine 9 dimethylation and REST occupancy at cholinergic gene promoters. G9a inhibitors both prevent and reverse the LPS-induced loss of ChAT + IR whereas siRNA inhibition of REST blocks the LPS-induced loss of ChAT + IR BFCNs. These data suggest in vivo HMGB1-TLR4 signaling in BFCNs leads to a reversible loss of the cholinergic neuron phenotype through epigenetic gene repressive mechanisms.

Organotypic whole hemisphere brain slice models to study the effects of donor age and oxygen-glucose-deprivation on the extracellular properties of cortical and striatal tissue

BACKGROUND

The brain extracellular environment is involved in many critical processes associated with neurodevelopment, neural function, and repair following injury. Organization of the extracellular matrix and properties of the extracellular space vary throughout development and across different brain regions, motivating the need for platforms that provide access to multiple brain regions at different stages of development. We demonstrate the utility of organotypic whole hemisphere brain slices as a platform to probe regional and developmental changes in the brain extracellular environment. We also leverage whole hemisphere brain slices to characterize the impact of cerebral ischemia on different regions of brain tissue.

RESULTS

Whole hemisphere brain slices taken from postnatal (P) day 10 and P17 rats retained viable, metabolically active cells through 14 days in vitro (DIV). Oxygen-glucose-deprivation (OGD), used to model a cerebral ischemic event in vivo, resulted in reduced slice metabolic activity and elevated cell death, regardless of slice age. Slices from P10 and P17 brains showed an oligodendrocyte and microglia-driven proliferative response after OGD exposure, higher than the proliferative response seen in DIV-matched normal control slices. Multiple particle tracking in oxygen-glucose-deprived brain slices revealed that oxygen-glucose-deprivation impacts the extracellular environment of brain tissue differently depending on brain age and brain region. In most instances, the extracellular space was most difficult to navigate immediately following insult, then gradually provided less hindrance to extracellular nanoparticle diffusion as time progressed. However, changes in diffusion were not universal across all brain regions and ages.

CONCLUSIONS

We demonstrate whole hemisphere brain slices from P10 and P17 rats can be cultured up to two weeks in vitro. These brain slices provide a viable platform for studying both normal physiological processes and injury associated mechanisms with control over brain age and region. Ex vivo OGD impacted cortical and striatal brain tissue differently, aligning with preexisting data generated in in vivo models. These data motivate the need to account for both brain region and age when investigating mechanisms of injury and designing potential therapies for cerebral ischemia.

Pannexin 1 plays a pro-survival role by attenuating P2X7 receptor-mediated Ca2+ influx

Extracellular ATP works as an autocrine and/or paracrine signaling molecule by activating plasma membrane-localized purinergic receptors. Stimulation of purinergic P2X7 receptor (P2X7R) increases cytosolic Ca²⁺ ([Ca²⁺]_c), which in turn activates Pannexin 1 (Panx1) channel. In earlier studies, Panx1 and P2X7R have been shown to interact physically. Also, both the channels have been implicated in similar pathophysiological processes. In this study, we investigated the effect of Panx1 on P2X7R-mediated Ca²⁺influx. Panx1 attenuated P2X7R-mediated [Ca²⁺]_c rise in CHO-K1 and HEK-293 cells. [Ca²⁺]_c rise was higher in Panx1 knockdown astrocytes. The inhibitory effect was unaffected in the presence of Panx1 blocker, carbenoxolone. The region between 350th and 386th amino acid residues in the carboxyl terminus (CT) of Panx1 was found to be crucial for inhibiting P2X7R. Like full-length Panx1, the CT (350th to 426th amino acids) alone was able to attenuate the [Ca²⁺]_c rise. Further, CT prevented cell death caused by P2X7R overactivation. Based on our results, we propose a novel pro-survival role of Panx1 exerted by modulating P2X7R.

The P2X7 Receptor Stimulates IL-6 Release from Pancreatic Stellate Cells and Tocilizumab Prevents Activation of STAT3 in Pancreatic Cancer Cells

Pancreatic stellate cells (PSCs) are important pancreatic fibrogenic cells that interact with pancreatic cancer cells to promote the progression of pancreatic ductal adenocarcinoma (PDAC). In the tumor microenvironment (TME), several factors such as cytokines and nucleotides contribute to this interplay. Our aim was to investigate whether there is an interaction between IL-6 and nucleotide signaling, in particular, that mediated by the ATP-sensing P2X7 receptor (P2X7R). Using human cell lines of PSCs and cancer cells, as well as primary PSCs from mice, we show that ATP is released from both PSCs and cancer cells in response to mechanical and metabolic cues that may occur in the TME, and thus activate the P2X7R. Functional studies using P2X7R agonists and inhibitors show that the receptor is involved in PSC proliferation, collagen secretion and IL-6 secretion and it promotes cancer cell migration in a human PSC-cancer cell co-culture. Moreover, conditioned media from P2X7R-stimulated PSCs activated the JAK/STAT3 signaling pathway in cancer cells. The monoclonal antibody inhibiting the IL-6 receptor, Tocilizumab, inhibited this signaling. In conclusion, we show an important mechanism between PSC-cancer cell interaction involving ATP and IL-6, activating P2X7 and IL-6 receptors, respectively, both potential therapeutic targets in PDAC.

The P2X7 purinergic receptor: a potential therapeutic target for lung cancer

PURPOSE

Purinergic P2X7 receptor (P2X7R) is a gated ion channel for which adenosine triphosphate (ATP) is a ligand. Activated P2X7R is widely expressed in a variety of immune cells and tissues and is involved in a variety of physiological and pathological processes. Studies have confirmed that P2X7R is involved in the regulation of tumor cell growth, stimulating cell proliferation or inducing apoptosis. Recent studies have found that P2X7R is abnormally expressed in lung cancer and is closely related to the carcinogenesis and development of lung cancer. In this paper, we comprehensively describe the structure, function, and genetic polymorphisms of P2X7R. In particular, the role and therapeutic potential of P2X7R in lung cancer are discussed to provide new targets and new strategies for the treatment and prognosis of clinical lung cancer.

METHODS

The relevant literature on P2X7R and lung cancer from PubMed databases is reviewed in this article.

RESULTS

P2X7R regulates the function of lung cancer cells by activating multiple intracellular signaling pathways (such as the JNK, Rho, HMGB1 and EMT pathways), thereby affecting cell survival, growth, invasion, and metastasis and patient prognosis. Targeting P2X7R with inhibitors effectively suppresses the growth and metastasis of lung cancer cells.

CONCLUSION

In summary, P2X7R is expected to become a potential target for the treatment of lung cancer, and more clinical research is needed in the future to explore the effectiveness of P2X7R antagonists as treatments.

P2X7 Receptors Regulate Phagocytosis and Proliferation in Adult Hippocampal and SVZ Neural Progenitor Cells: Implications for Inflammation in Neurogenesis

Identifying the signaling mechanisms that regulate adult neurogenesis is essential to understanding how the brain may respond to neuro‐inflammatory events. P2X7 receptors can regulate pro‐inflammatory responses, and in addition to their role as cation channels they can trigger cell death and mediate phagocytosis. How P2X7 receptors may regulate adult neurogenesis is currently unclear. Here, neural progenitor cells (NPCs) derived from adult murine hippocampal subgranular (SGZ) and cerebral subventricular (SVZ) zones were utilized to characterize the roles of P2X7 in adult neurogenesis, and assess the effects of high extracellular ATP, characteristic of inflammation, on NPCs. Immunocytochemistry found NPCs in vivo and in vitro expressed P2X7, and the activity of P2X7 in culture was demonstrated using calcium influx and pore formation assays. Live cell and confocal microscopy, in conjunction with flow cytometry, revealed P2X7⁺ NPCs were able to phagocytose fluorescent beads, and this was inhibited by ATP, indicative of P2X7 involvement. Furthermore, P2X7 receptors were activated with ATP or BzATP, and 5‐ethynyl‐2′‐deoxyuridine (EdU) used to observe a dose‐dependent decrease in NPC proliferation. A role for P2X7 in decreased NPC proliferation was confirmed using chemical inhibition and NPCs from P2X7^−/− mice. Together, these data present three distinct roles for P2X7 during adult neurogenesis, depending on extracellular ATP concentrations: (a) P2X7 receptors can form transmembrane pores leading to cell death, (b) P2X7 receptors can regulate rates of proliferation, likely via calcium signaling, and (c) P2X7 can function as scavenger receptors in the absence of ATP, allowing NPCs to phagocytose apoptotic NPCs during neurogenesis. stem cells2018;36:1764–1777

Neural stem cell heterogeneity in the mammalian forebrain

The brain was long considered an organ that underwent very little change after development. It is now well established that the mammalian central nervous system contains neural stem cells that generate progeny that are capable of making new neurons, astrocytes, and oligodendrocytes throughout life. The field has advanced rapidly as it strives to understand the basic biology of these precursor cells, and explore their potential to promote brain repair. The purpose of this review is to present current knowledge about the diversity of neural stem cells in vitro and in vivo, and highlight distinctions between neural stem cell populations, throughout development, and within the niche. A comprehensive understanding of neural stem cell heterogeneity will provide insights into the cellular and molecular regulation of neural development and lifelong neurogenesis, and will guide the development of novel strategies to promote regeneration and neural repair.

Release of soluble and vesicular purine nucleoside phosphorylase from rat astrocytes and microglia induced by pro-inflammatory stimulation with extracellular ATP via P2X7 receptors

Purine nucleoside phosphorylase (PNP), a crucial enzyme in purine metabolism which converts ribonucleosides into purine bases, has mainly been found inside glial cells. Since we recently demonstrated that PNP is released from rat C6 glioma cells, we then wondered whether this occurs in normal brain cells. Using rat primary cultures of microglia, astrocytes and cerebellar granule neurons, we found that in basal condition all these cells constitutively released a metabolically active PNP with Km values very similar to those measured in C6 glioma cells. However, the enzyme expression/release was greater in microglia or astrocytes that in neurons. Moreover, we exposed primary brain cell cultures to pro-inflammatory agents such as lipopolysaccharide (LPS) or ATP alone or in combination. LPS alone caused an increased interleukin-1β (IL-1β) secretion mainly from microglia and no modification in the PNP release, even from neurons in which it enhanced cell death. In contrast, ATP administered alone to glial cells at high micromolar concentrations significantly stimulated the release of PNP within 1 h, an effect not modified by LPS presence, whereas IL-1β secretion was stimulated by ATP only in cells primed for 2 h with LPS. In both cases ATP effect was mediated by P2X₇ receptor (P2X₇R), since it was mimicked by cell exposure to Bz-ATP, an agonist of P2X₇R, and blocked by cell pre-treatment with the P2X₇R antagonist A438079. Interestingly, ATP-induced PNP release from glial cells partly occurred through the secretion of lysosomal vesicles in the extracellular medium. Thus, during inflammatory cerebral events PNP secretion promoted by extracellular ATP accumulation might concur to control extracellular purine signals. Further studies could elucidate whether, in these conditions, a consensual activity of enzymes downstream of PNP in the purine metabolic cascade avoids accumulation of extracellular purine bases that might concur to brain injury by unusual formation of reactive oxygen species.

Ethanol-Induced Neurodegeneration and Glial Activation in the Developing Brain

Ethanol induces neurodegeneration in the developing brain, which may partially explain the long-lasting adverse effects of prenatal ethanol exposure in fetal alcohol spectrum disorders (FASD). While animal models of FASD show that ethanol-induced neurodegeneration is associated with glial activation, the relationship between glial activation and neurodegeneration has not been clarified. This review focuses on the roles of activated microglia and astrocytes in neurodegeneration triggered by ethanol in rodents during the early postnatal period (equivalent to the third trimester of human pregnancy). Previous literature indicates that acute binge-like ethanol exposure in postnatal day 7 (P7) mice induces apoptotic neurodegeneration, transient activation of microglia resulting in phagocytosis of degenerating neurons, and a prolonged increase in glial fibrillary acidic protein-positive astrocytes. In our present study, systemic administration of a moderate dose of lipopolysaccharides, which causes glial activation, attenuates ethanol-induced neurodegeneration. These studies suggest that activation of microglia and astrocytes by acute ethanol in the neonatal brain may provide neuroprotection. However, repeated or chronic ethanol can induce significant proinflammatory glial reaction and neurotoxicity. Further studies are necessary to elucidate whether acute or sustained glial activation caused by ethanol exposure in the developing brain can affect long-lasting cellular and behavioral abnormalities observed in the adult brain.

Persistent adaptation by chronic alcohol is facilitated by neuroimmune activation linked to stress and CRF

This review updates the conceptual basis for the association of alcohol abuse with an insidious adaptation that facilitates negative affect during withdrawal from chronic intermittent alcohol (CIA) exposure - a change that later supports sensitization of stress-induced anxiety following alcohol abstinence. The finding that a CRF1-receptor antagonist (CRF1RA) minimized CIA withdrawal-induced negative affect supported an association of alcohol withdrawal with a stress mechanism. The finding that repeated stresses or multiple CRF injections into selected brain sites prior to a single 5-day chronic alcohol (CA) exposure induced anxiety during withdrawal provided critical support for a linkage of CIA withdrawal with stress. The determination that CRF1RA injection into positive CRF-sensitive brain sites prevented CIA withdrawal-induced anxiety provided support that neural path integration maintains the persistent CIA adaptation. Based upon reports that stress increases neuroimmune function, an effort was undertaken to test whether cytokines would support the adaptation induced by stress/CA exposure. Twenty-four hours after withdrawal from CIA, cytokine mRNAs were found to be increased in cortex as well as other sites in brain. Further, repeated cytokine injections into previously identified brain sites substituted for stress and CRF induction of anxiety during CA withdrawal. Discovery that a CRF1RA prevented the brain cytokine mRNA increase induced by CA withdrawal provided critical evidence for CRF involvement in this neuroimmune induction after CA withdrawal. However, the CRF1RA did not block the stress increase in cytokine mRNA increases in controls. The latter data supported the hypothesis that distinct mechanisms linked to stress and CA withdrawal can support common neuroimmune functions within a brain site. As evidence evolves concerning neural involvement in brain neuroimmune function, a better understanding of the progressive adaptation associated with CIA exposure will advance new knowledge that could possibly lead to strategies to combat alcohol abuse.

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.

The azetidine derivative, KHG26792 protects against ATP-induced activation of NFAT and MAPK pathways through P2X7 receptor in microglia

Azetidine derivatives are of interest for drug development because they may be useful therapeutic agents. However, their mechanisms of action remain to be completely elucidated. Here, we have investigated the effects of 3-(naphthalen-2-yl(propoxy)methyl)azetidine hydrochloride (KHG26792) on ATP-induced activation of NFAT and MAPK through P2X7 receptor in the BV-2 mouse microglial cell line. KHG26792 decreased ATP-induced TNF-α release from BV-2 microglia by suppressing, at least partly, P2X7 receptor stimulation. KHG26792 also inhibited the ATP-induced increase in IL-6, PGE2, NO, ROS, CXCL2, and CCL3. ATP induced NFAT activation through P2X7 receptor, with KHG26792 reducing the ATP-induced NFAT activation. KHG26792 inhibited an ATP-induced increase in iNOS protein and ERK phosphorylation. KHG26792 prevented an ATP-induced increase in MMP-9 activity through the P2X7 receptor as a result of degradation of TIMP-1 by cathepsin B. Our data provide mechanistic insights into the role of KHG26792 in the inhibition of TNF-α produced via P2X7 receptor-mediated activation of NFAT and MAPK pathways in ATP-treated BV-2 cells. This study highlights the potential use of KHG26792 as a therapeutic agent for the many diseases of the CNS related to activated microglia.

The Role of Ion Channels in Microglial Activation and Proliferation - A Complex Interplay between Ligand-Gated Ion Channels, K(+) Channels, and Intracellular Ca(2.)

Microglia are often referred to as the immune cells of the brain. They are most definitely involved in immune responses to invading pathogens and inflammatory responses to tissue damage. However, recent results suggest microglia are vital for normal functioning of the brain. Neuroinflammation, as well as more subtle changes, in microglial function has been implicated in the pathogenesis of many brain diseases and disorders. Upon sensing alterations in their local environment, microglia change their shape and release factors that can modify the excitability of surrounding neurons. During neuroinflammation, microglia proliferate and release NO, reactive oxygen species, cytokines and chemokines. If inflammation resolves then their numbers normalize again via apoptosis. Microglia express a wide array of ion channels and different types are implicated in all of the cellular processes listed above. Modulation of microglial ion channels has shown great promise as a therapeutic strategy in several brain disorders. In this review, we discuss recent advances in our knowledge of microglial ion channels and their roles in responses of microglia to changes in the extracellular milieu.

Predicting Neuroinflammation in Morphine Tolerance for Tolerance Therapy from Immunostaining Images of Rat Spinal Cord

Long-term morphine treatment leads to tolerance which attenuates analgesic effect and hampers clinical utilization. Recent studies have sought to reveal the mechanism of opioid receptors and neuroinflammation by observing morphological changes of cells in the rat spinal cord. This work proposes a high-content screening (HCS) based computational method, HCS-Morph, for predicting neuroinflammation in morphine tolerance to facilitate the development of tolerance therapy using immunostaining images for astrocytes, microglia, and neurons in the spinal cord. HCS-Morph first extracts numerous HCS-based features of cellular phenotypes. Next, an inheritable bi-objective genetic algorithm is used to identify a minimal set of features by maximizing the prediction accuracy of neuroinflammation. Finally, a mathematic model using a support vector machine with the identified features is established to predict drug-treated images to assess the effects of tolerance therapy. The dataset consists of 15 saline controls (1 μl/h), 15 morphine-tolerant rats (15 μg/h), and 10 rats receiving a co-infusion of morphine (15 μg/h) and gabapentin (15 μg/h, Sigma). The three individual models of astrocytes, microglia, and neurons for predicting neuroinflammation yielded respective Jackknife test accuracies of 96.67%, 90.00%, and 86.67% on the 30 rats, and respective independent test accuracies of 100%, 90%, and 60% on the 10 co-infused rats. The experimental results suggest that neuroinflammation activity expresses more predominantly in astrocytes and microglia than in neuron cells. The set of features for predicting neuroinflammation from images of astrocytes comprises mean cell intensity, total cell area, and second-order geometric moment (relating to cell distribution), relevant to cell communication, cell extension, and cell migration, respectively. The present investigation provides the first evidence for the role of gabapentin in the attenuation of morphine tolerance from phenotypic changes of astrocytes and microglia. Based on neuroinflammation prediction, the proposed computer-aided image diagnosis system can greatly facilitate the development of tolerance therapy with anti-inflammatory drugs.

Understanding the role of P2X7 in affective disorders-are glial cells the major players?

Pathophysiology associated with several psychiatric disorders has been linked to inflammatory biomarkers. This has generated a theory of major depressive disorders as an inflammatory disease. The idea of pro-inflammatory cytokines altering behavior is now well accepted however many questions remain. Microglia can produce a plethora of inflammatory cytokines and these cells appear to be critical in the link between inflammatory changes and depressive disorders. Microglia play a known role in sickness behavior which has many components of depressive-like behavior such as social withdrawal, sleep alterations, and anorexia. Numerous candidate genes have been identified for psychiatric disorders in the last decade. Single nucleotide polymorphisms (SNPs) in the human P2X7 gene have been linked to bipolar disorder, depression, and to the severity of depressive symptoms. P2X7 is a ligand-gated cation channel expressed on microglia with lower levels found on astrocytes and on some neuronal populations. In microglia P2X7 is a major regulator of pro-inflammatory cytokines of the interleukin-1 family. Genetic deletion of P2X7 in mice is protective for depressive behavior in addition to inflammatory responses. P2X7(-/-) mice have been shown to demonstrate anti-depressive-like behavior in forced swim and tail suspension behavioral tests and stressor-induced behavioral responses were blunted. Both neurochemical (norepinephrine, serotonin, and dopamine) and inflammatory changes have been observed in the brains of P2X7(-/-) mice. This review will discuss the recent evidence for involvement of P2X7 in the pathophysiology of depressive disorders and propose mechanisms by which altered signaling through this ion channel may affect the inflammatory state of the brain.

Extracellular ATP Selectively Upregulates Ecto-Nucleoside Triphosphate Diphosphohydrolase 2 and Ecto-5'-Nucleotidase by Rat Cortical Astrocytes In Vitro

Extracellular ATP (eATP) acts as a danger-associated molecular pattern which induces reactive response of astrocytes after brain insult, including morphological remodeling of astrocytes, proliferation, chemotaxis, and release of proinflammatory cytokines. The responses induced by eATP are under control of ecto-nucleotidases, which catalyze sequential hydrolysis of ATP to adenosine. In the mammalian brain, ecto-nucleotidases comprise three enzyme families: ecto-nucleoside triphosphate diphosphohydrolases 1-3 (NTPDase1-3), ecto-nucleotide pyrophosphatase/phospodiesterases 1-3 (NPP1-3), and ecto-5'-nucleotidase (eN), which crucially determine ATP/adenosine ratio in the pericellular milieu. Altered expression of ecto-nucleotidases has been demonstrated in several experimental models of human brain dysfunctions. In the present study, we have explored the pattern of NTPDase1-3, NPP1-3, and eN expression by cultured cortical astrocytes challenged with 1 mmol/L ATP (eATP). At the transcriptional level, eATP upregulated expression of NTPDase1, NTPDase2, NPP2, and eN, while, at translational and functional levels, these were paralleled only by the induction of NTPDase2 and eN. Additionally, eATP altered membrane topology of eN, from clusters localized in membrane domains to continuous distribution along the cell membrane. Our results suggest that eATP, by upregulating NTPDase2 and eN and altering the enzyme membrane topology, affects local kinetics of ATP metabolism and signal transduction that may have important roles in the process related to inflammation and reactive gliosis.

Inhibition of microglial activation contributes to propofol-induced protection against post-cardiac arrest brain injury in rats

It has been suggested that propofol can modulate microglial activity and hence may have potential roles against neuroinflammation following brain ischemic insult. However, whether and how propofol can inhibit post-cardiac arrest brain injury via inhibition of microglia activation remains unclear. A rat model of asphyxia cardiac arrest (CA) was created followed by cardiopulmonary resuscitation. CA induced marked microglial activation in the hippocampal CA1 region, revealed by increased OX42 and P2 class of purinoceptor 7 (P2X7R) expression, as well as p38 MAPK phosphorylation. Morris water maze showed that learning and memory deficits following CA could be inhibited or alleviated by pre-treatment with the microglial inhibitor minocycline or propofol. Microglial activation was significantly suppressed likely via the P2X7R/p-p38 pathway by propofol. Moreover, hippocampal neuronal injuries after CA were remarkably attenuated by propofol. In vitro experiment showed that propofol pre-treatment inhibited ATP-induced microglial activation and release of tumor necrosis factor-α and interleukin-1β. In addition, propofol protected neurons from injury when co-culturing with ATP-treated microglia. Our data suggest that propofol pre-treatment inhibits CA-induced microglial activation and neuronal injury in the hippocampus and ultimately improves cognitive function. We proposed a possible mechanism of propofol-mediated brain protection after cardiac arrest (CA). CA induces P2X7R upregulation and p38 phosphorylation in microglia, which induces release of TNF-α and IL-1β and consequent neuronal injury. Propofol could inhibit microglial activation and alleviate neuronal damage. Our results suggest propofol-induced anti-inflammatory treatment as a plausible strategy for therapeutic intervention in post-CA brain injury.

Brain region-specific gene expression profiles in freshly isolated rat microglia

Microglia are important cells in the brain that can acquire different morphological and functional phenotypes dependent on the local situation they encounter. Knowledge on the region-specific gene signature of microglia may hold valuable clues for microglial functioning in health and disease, e.g., Parkinson's disease (PD) in which microglial phenotypes differ between affected brain regions. Therefore, we here investigated whether regional differences exist in gene expression profiles of microglia that are isolated from healthy rat brain regions relevant for PD. We used an optimized isolation protocol based on a rapid isolation of microglia from discrete rat gray matter regions using density gradients and fluorescent-activated cell sorting. Application of the present protocol followed by gene expression analysis enabled us to identify subtle differences in region-specific microglial expression profiles and show that the genetic profile of microglia already differs between different brain regions when studied under control conditions. As such, these novel findings imply that brain region-specific microglial gene expression profiles exist that may contribute to the region-specific differences in microglia responsivity during disease conditions, such as seen in, e.g., PD.

The role of Homer1b/c in neuronal apoptosis following LPS-induced neuroinflammation

Homer, also designated Vesl, is one member of the newly found postsynaptic density scaffold proteins, playing a vital role in maintaining synaptic integrity, regulating intracellular calcium mobilization, and being critical for the regulation of cellular apoptosis. However, its function in the inflamed central nervous system (CNS) is not fully elucidated. Here, we investigated the role of Homer1b/c, a long form of Homer1, in lipopolysaccharide (LPS) induced neuroinflammation in CNS. Western blot analysis indicated that LPS administration significantly increased the expression of Homer1b/c in rat brain. Moreover, double immunofluorescent staining suggested Homer1b/c was mainly distributed in the cytoplasm of neurons and had a close association with cleaved caspase-3 level in neurons in rat brain after LPS injection. In vitro studies indicated that up-regulation of Homer1b/c might be related to the subsequent apoptosis in neurons treated by conditioned media (CM), collected from LPS-stimulated mixed glial cultures (MGC). We also found down-regulation of Homer1b/c partly blocked the increase of cleaved caspase-3 and the proportion of Bax/Bcl-2 in neurons induced by MGC-CM. Taken together, these findings suggested that Homer1b/c might promote neuronal apoptosis via the Bax/Bcl-2 dependent pathway during neuroinflammation in CNS, and inhibiting Homer1b/c expression might provide a novel neuroprotective strategy against the inflammation-related neuronal apoptosis.

Inhibition of metabotropic glutamate receptor 5 induces cellular stress through pertussis toxin-sensitive Gi-proteins in murine BV-2 microglia cells

BACKGROUND

Activation of metabotropic glutamate receptor 5 (mGluR5) by (RS)-2-chloro-5-hydroxyphenylglycine (CHPG) was shown to suppress microglia activation and decrease the release of associated pro-inflammatory mediators. In contrast, the consequences of mGluR5 inhibition are less well understood. Here, we used BV-2 cells, retaining key characteristics of primary mouse microglia, to examine whether mGluR5 inhibition by 2-methyl-6-(phenylethynyl)-pyridine (MPEP) enhances cellular stress and production of inflammatory mediators.

METHODS

BV-2 cells were treated with MPEP, followed by determination of cellular stress using fluorescent dyes and high-content imaging. The expression of inflammatory mediators, endoplasmic reticulum (ER)-stress markers and phosphorylated AMPKα was analyzed by quantitative PCR, ELISA and Western blotting. Additionally, phospholipase C (PLC) activity, cellular ATP content and changes in intracellular free Ca(2+) ([Ca(2+)]i) were measured using luminescence and fluorescence assays.

RESULTS

Treatment of BV-2 microglia with 100 μM MPEP increased intracellular reactive oxygen species (ROS), mitochondrial superoxide, mitochondrial mass as well as inducible nitric oxide synthase (iNOS) and IL-6 expression. Furthermore, MPEP reduced cellular ATP and induced AMPKα phosphorylation and the expression of the ER-stress markers CHOP, GRP78 and GRP96. The MPEP-dependent effects were preceded by a rapid concentration-dependent elevation of [Ca(2+)]i, following Ca(2+) release from the ER, mainly via inositol triphosphate-induced receptors (IP3R). The MPEP-induced ER-stress could be blocked by pretreatment with the chemical chaperone 4-phenylbutyrate and the Ca(2+) chelator BAPTA-AM. Pretreatment with the AMPK agonist AICAR partially abolished, whilst the inhibitor compound C potentiated, the MPEP-dependent ER-stress. Importantly, the PLC inhibitor U-73122 and the Gi-protein inhibitor pertussis toxin (PTX) blocked the MPEP-induced increase in [Ca(2+)]i. Moreover, pretreatment of microglia with AICAR, BAPTA-AM, U-73122 and PTX prevented the MPEP-induced generation of oxidative stress and inflammatory mediators, further supporting a role for Gi-protein-mediated activation of PLC.

CONCLUSIONS

The results emphasize the potential pathophysiological role of mGluR5 antagonism in mediating oxidative stress, ER-stress and inflammation through a Ca(2+)-dependent pathway in microglia. The induction of cellular stress and inflammatory mediators involves PTX-sensitive Gi-proteins and subsequent activation of PLC, IP3R and Ca(2+) release from the ER.

Microglial NLRP3 inflammasome activation mediates IL-1β-related inflammation in prefrontal cortex of depressive rats

Depression is an inflammatory disorder. Pro-inflammatory cytokine interleukin-1 beta (IL-1β) may play a pivotal role in the central nervous system (CNS) inflammation of depression. Here, we investigated IL-1β alteration in serum, cerebrospinal fluid (CSF) and prefrontal cortex (PFC) of chronic unpredictable mild stress (CUMS)-exposed rats, a well-documented model of depression, and further explored the molecular mechanism by which CUMS procedure induced IL-1β-related CNS inflammation. We showed that 12-week CUMS procedure remarkably increased PFC IL-1β mRNA and protein levels in depressive-like behavior of rats, without significant alteration of serum and CSF IL-1β levels. We found that CUMS procedure significantly caused PFC nuclear factor kappa B (NF-κB) inflammatory pathway activation in rats. The intriguing finding in this study was the induced activation of nucleotide binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome with the increased IL-1β maturation in PFC of CUMS rats, suggesting a new grade of regulatory mechanism for IL-1β-related CNS inflammation. Moreover, microglial activation and astrocytic function impairment were observed in PFC of CUMS rats. The increased co-location of NLRP3 and ionized calcium binding adaptor molecule 1 (Iba1) protein expression supported that microglia in glial cells was the primary contributor for CUMS-induced PFC NLRP3 inflammasome activation in rats. These alterations in CUMS rats were restored by chronic treatment of the antidepressant fluoxetine, indicating that fluoxetine-mediated rat PFC IL-1β reduction involves both transcriptional and post-transcriptional regulatory mechanisms. These findings provide in vivo evidence that microglial NLRP3 inflammasome activation is a mediator of IL-1β-related CNS inflammation during chronic stress, and suggest a new therapeutic target for the prevention and treatment of depression.

P2X7 receptor: an emerging target in central nervous system diseases

The ATP-sensitive homomeric P2X7 receptor (P2X7R) has received particular attention as a potential drug target because of its widespread involvement in inflammatory diseases as a key regulatory element of the inflammasome complex. However, it has only recently become evident that P2X7Rs also play a pivotal role in central nervous system (CNS) pathology. There is an explosion of data indicating that genetic deletion and pharmacological blockade of P2X7Rs alter responsiveness in animal models of neurological disorders, such as stroke, neurotrauma, epilepsy, neuropathic pain, multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Alzheimer's disease, Parkinson's disease, and Huntington's disease. Moreover, recent studies suggest that P2X7Rs regulate the pathophysiology of psychiatric disorders, including mood disorders, implicating P2X7Rs as drug targets in a variety of CNS pathology.

The A1 adenosine receptor as a new player in microglia physiology

The purinergic system is highly involved in the regulation of microglial physiological processes. In addition to the accepted roles for the P2 X4,7 and P2 Y12 receptors activated by adenosine triphosphate (ATP) and adenosine diphosphate, respectively, recent evidence suggests a role for the adenosine A2A receptor in microglial cytoskeletal rearrangements. However, the expression and function of adenosine A1 receptor (A1AR) in microglia is still unclear. Several reports have demonstrated possible expression of A1AR in microglia, but a new study has refuted such evidence. In this study, we investigated the presence and function of A1AR in microglia using biomolecular techniques, live microscopy, live calcium imaging, and in vivo electrophysiological approaches. The aim of this study was to clarify the expression of A1AR in microglia and to highlight its possible roles. We found that microglia express A1AR and that it is highly upregulated upon ATP treatment. Moreover, we observed that selective stimulation of A1AR inhibits the morphological activation of microglia, possibly by suppressing the Ca(2+) influx induced by ATP treatment. Finally, we recorded the spontaneous and evoked activity of spinal nociceptive-specific neuron before and after application of resting or ATP-treated microglia, with or without preincubation with a selective A1AR agonist. We found that the microglial cells, pretreated with the A1AR agonist, exhibit lower capability to facilitate the nociceptive neurons, as compared with the cells treated with ATP alone.

P2X7 receptor inhibition interrupts the progression of seizures in immature rats and reduces hippocampal damage

AIMS

Early-life seizures, particularly when prolonged, may be harmful to the brain. Current pharmacotherapy is often ineffective; therefore, novel neuro- and/or glio-transmitter systems should be explored for targeting. The P2X7 receptor is a cation-permeable channel with trophic and excitability effects on neurons and glia which is activated by high amounts of ATP that may be released in the setting of injury after severe seizures. Here, we tested the effects of A-438079, a potent and selective P2X7 receptor antagonist in a lesional model of early-life status epilepticus.

METHODS

Seizures were induced by intra-amygdala kainic acid in 10-day-old rat pups. Electrographic seizure severity, changes to P2X7 receptor expression, inflammatory responses and histological effects were evaluated.

RESULTS

Seizures induced by intra-amygdala kainic acid increased levels of P2X7 receptor protein and interleukin-1β and caused significant cell death within the ipsilateral hippocampus. A-438079 rapidly reached the brain following systemic injection in P10 rats. Intraperitoneal injection of A-438079 (5 and 15 mg/kg) 60 min after triggering seizures reduced seizure severity and neuronal death within the hippocampus. A-438079 had superior neuroprotective effects compared with an equally seizure-suppressive dose of phenobarbital (25 mg/kg).

CONCLUSIONS

These results suggest P2X7 receptor antagonists may be suitable as frontline or adjunctive treatments of pediatric status epilepticus or other early-life seizures, particularly when associated with brain damage.

Differential expression of the P2X7 receptor in ovarian surface epithelium during the oestrous cycle in the mouse

Purinergic signalling has been proposed as an intraovarian regulatory mechanism. Of the receptors responsible for purinergic transmission, the P2X7 receptor is an ATP-gated cationic channel that displays a broad spectrum of cellular functions ranging from apoptosis to cell proliferation and tumourigenesis. In the present study, we investigated the functional expression of P2X7 receptors in ovarian surface epithelium (OSE). P2X7 protein was detected in the OSE layer of the mouse, both in situ and in primary cultures. In cultures, 2'(3')-O-(4-Benzoylbenzoyl)adenosine-5'-triphosphate (BzATP) activation of P2X7 receptors increased [Ca(2+)]i and induced apoptosis. The functionality of the P2X7 receptor was investigated in situ by intrabursal injection of BzATP on each day of the oestrous cycle and evaluation of apoptosis 24h using the terminal deoxyribonucleotidyl transferase-mediated dUTP-fluorescein nick end-labelling (TUNEL) assay. Maximum effects of BzATP were observed during pro-oestrus, with the effects being blocked by A438079, a specific P2X7 receptor antagonist. Immunofluorescence staining for P2X7 protein revealed more robust expression during pro-oestrus and in OSE regions behind the antral follicles, strongly supporting the notion that the differences in apoptosis can be explained by increased receptor expression, which is regulated during the oestrous cycle. Finally, P2X7 receptor expression was detected in the OSE layer of human ovaries, with receptor expression maintained in human ovaries diagnosed with cancer, as well as in the human ovarian carcinoma SKOV3 cell line.

Basal CD38/cyclic ADP-ribose-dependent signaling mediates ATP release and survival of microglia by modulating connexin 43 hemichannels

It is necessary to investigate the mechanisms underlying ATP release from neural cells, because extracellular ATP plays multiple important biological roles in the brain. CD38 is an ectoenzyme that consumes NAD(+) to produce cyclic ADP-ribose (cADPR), a potent agonist of ryanodine receptors. Our previous study showed that CD38 reductions led to microglial apoptosis. In this study, we used both murine microglial BV2 cells and primary microglial cultures as cellular models to test our hypothesis that basal CD38/cyclic ADP-ribose (CD38/cADPR)-dependent signaling plays a key role in ATP release, which mediates basal survival of microglia. We found that inhibition of CD38/cADPR-dependent signaling by CD38 silencing or 8-Bromo-cADPR, a ryanodine receptor antagonist, produced significant ATP release from BV2 microglia. Cx43 small interfering RNA and Cx43 hemichannel blocker 18-α-glycyrrhetinic acid completely prevented the CD38 silencing or 8-Bromo-cADPR-induced ATP release. Prevention of the ATP release could also be due to P2X7 receptor antagonists. Our study has further suggested a key role of ATP release in the microglial apoptosis induced by decreased CD38/cADPR-dependent signaling. In addition, by using primary microglial cultures, we found that 8-Bromo-cADPR also induced significant ATP release, which could be attenuated by 18-α-glycyrrhetinic acid. 8-Bromo-cADPR was also found to induce death of primary microglial cultures. In conclusion, our results have suggested novel roles of basal activation of CD38/cADPR-dependent signaling in mediating microglial functions and survival: It mediates ATP release from microglia by modulating Cx43 hemichannels, which can significantly affect microglial survival.

Release of neuronal HMGB1 by ethanol through decreased HDAC activity activates brain neuroimmune signaling

Neuroimmune gene induction is involved in many brain pathologies including addiction. Although increased expression of proinflammatory cytokines has been found in ethanol-treated mouse brain and rat brain slice cultures as well as in post-mortem human alcoholic brain, the mechanisms remain elusive. High-mobility group box 1 (HMGB1) protein is a nuclear protein that has endogenous cytokine-like activity. We previously found increased HMGB1 in post-mortem alcoholic human brain as well as in ethanol treated mice and rat brain slice cultures. The present study investigated the mechanisms for ethanol-induced release of HMGB1 and neuroimmune activation in a model of rat hippocampal-entorhinal cortex (HEC) brain slice cultures. Ethanol exposure triggered dose-dependent HMGB1 release, predominantly from neuronal cells. Inhibitors of histone deacetylases (HDACs) promoted nucleocytoplasmic mobilization of HDAC1/4 and HMGB1 resulting in increased total HMGB1 and acetylated HMGB1 release. Similarly, ethanol treatment was found to induce the translocation of HDAC1/4 and HMGB1 proteins from nuclear to cytosolic fractions. Furthermore, ethanol treatment reduced HDAC1/4 mRNA and increased acetylated HMGB1 release into the media. These results suggest decreased HDAC activity may be critical in regulating acetylated HMGB1 release from neurons in response to ethanol. Ethanol and HMGB1 treatment increased mRNA expression of proinflammatory cytokines TNFα and IL-1β as well as toll-like receptor 4 (TLR4). Targeting HMGB1 or microglial TLR4 by using siRNAs to HMGB1 and TLR4, HMGB1 neutralizing antibody, HMGB1 inhibitor glycyrrhizin and TLR4 antagonist as well as inhibitor of microglial activation all blocked ethanol-induced expression of proinflammatory cytokines TNFα and IL-1β. These results support the hypothesis that ethanol alters HDACs that regulate HMGB1 release and that danger signal HMGB1 as endogenous ligand for TLR4 mediates ethanol-induced brain neuroimmune signaling through activation of microglial TLR4. These findings provide new therapeutic targets for brain neuroimmune activation and alcoholism.

Release of neuronal HMGB1 by ethanol through decreased HDAC activity activates brain neuroimmune signaling

Neuroimmune gene induction is involved in many brain pathologies including addiction. Although increased expression of proinflammatory cytokines has been found in ethanol-treated mouse brain and rat brain slice cultures as well as in post-mortem human alcoholic brain, the mechanisms remain elusive. High-mobility group box 1 (HMGB1) protein is a nuclear protein that has endogenous cytokine-like activity. We previously found increased HMGB1 in post-mortem alcoholic human brain as well as in ethanol treated mice and rat brain slice cultures. The present study investigated the mechanisms for ethanol-induced release of HMGB1 and neuroimmune activation in a model of rat hippocampal-entorhinal cortex (HEC) brain slice cultures. Ethanol exposure triggered dose-dependent HMGB1 release, predominantly from neuronal cells. Inhibitors of histone deacetylases (HDACs) promoted nucleocytoplasmic mobilization of HDAC1/4 and HMGB1 resulting in increased total HMGB1 and acetylated HMGB1 release. Similarly, ethanol treatment was found to induce the translocation of HDAC1/4 and HMGB1 proteins from nuclear to cytosolic fractions. Furthermore, ethanol treatment reduced HDAC1/4 mRNA and increased acetylated HMGB1 release into the media. These results suggest decreased HDAC activity may be critical in regulating acetylated HMGB1 release from neurons in response to ethanol. Ethanol and HMGB1 treatment increased mRNA expression of proinflammatory cytokines TNFα and IL-1β as well as toll-like receptor 4 (TLR4). Targeting HMGB1 or microglial TLR4 by using siRNAs to HMGB1 and TLR4, HMGB1 neutralizing antibody, HMGB1 inhibitor glycyrrhizin and TLR4 antagonist as well as inhibitor of microglial activation all blocked ethanol-induced expression of proinflammatory cytokines TNFα and IL-1β. These results support the hypothesis that ethanol alters HDACs that regulate HMGB1 release and that danger signal HMGB1 as endogenous ligand for TLR4 mediates ethanol-induced brain neuroimmune signaling through activation of microglial TLR4. These findings provide new therapeutic targets for brain neuroimmune activation and alcoholism.

Norcantharidin induced DU145 cell apoptosis through ROS-mediated mitochondrial dysfunction and energy depletion

Norcantharidin (NCTD), a demethylated analog of cantharidin derived from blister beetles, has attracted considerable attentions in recent years due to their definitely toxic properties and the noteworthy advantages in stimulating bone marrow and increasing the peripheral leukocytes. Hence, it is worth studying the anti-tumor effect of NCTD on human prostate cancer cells DU145. It was found that after the treatment of NCTD with different concentrations (25-100 μM), the cell proliferation was significantly inhibited, which led to the appearance of micronucleus (MN). Moreover, the cells could be killed in a dose-/ time-dependent manner along with the reduction of PCNA (proliferating cell nuclear antigen) expression, destruction of mitochondrial membrane potential (MMP), down-regulation of MnSOD, induction of ROS, depletion of ATP, and activation of AMPK (Adenosine 5‘-monophosphate -activated protein kinase) . In addition, a remarkable release of cytochrome c was found in the cells exposed to 100 μM NCTD and exogenous SOD-PEG could eliminate the generation of NCTD-induced MN. In conclusion, our studies indicated that NCTD could induce the collapse of MMP and mitochondria dysfunction. Accumulation of intercellular ROS could eventually switch on the apoptotic pathway by causing DNA damage and depleting ATP.

Increased receptor for advanced glycation end product expression in the human alcoholic prefrontal cortex is linked to adolescent drinking

Adolescence is characterized behaviorally by increased impulsivity and risk-taking that declines in parallel with maturation of the prefrontal cortex and executive function. In the brain, the receptor for advanced glycation end products (RAGE) is critically involved in neurodevelopment and neuropathology. In humans, the risk of alcoholism is greatly increased in those who begin drinking between 13 and 15years of age, and adolescents binge drink more than any other age group. We have previously found that alcoholism is associated with increased expression of neuroimmune genes. This manuscript tested the hypothesis that adolescent binge drinking upregulates RAGE and Toll-like receptor (TLR) 4 as well as their endogenous agonist, high-mobility group box 1 (HMGB1). Immunohistochemistry, Western blot, and mRNA analyses found that RAGE expression was increased in the human post-mortem alcoholic orbitofrontal cortex (OFC). Further, an earlier age of drinking onset correlated with increased expression of RAGE, TLR4, and HMGB1. To determine if alcohol contributed to these changes, we used an adolescent binge ethanol model in rats (5.0g/kg, i.g., 2-day on/2-day off from postnatal day [P] 25 to P55) and assessed neuroimmune gene expression. We found an age-associated decline of RAGE expression from late adolescence (P56) to young adulthood (P80). Adolescent intermittent ethanol exposure did not alter RAGE expression at P56, but increased RAGE in the young adult PFC (P80). Adolescent intermittent ethanol exposure also increased TLR4 and HMGB1 expression at P56 that persisted into young adulthood (P80). Assessment of young adult frontal cortex mRNA (RT-PCR) found increased expression of proinflammatory cytokines, oxidases, and neuroimmune agonists at P80, 25days after ethanol treatment. Together, these human and animal data support the hypothesis that an early age of drinking onset upregulates RAGE/TLR4-HMGB1 and other neuroimmune genes that persist into young adulthood and could contribute to risk of alcoholism or other brain diseases associated with neuroinflammation.

P2X₇ receptor activation may be involved in neuronal loss in the retinal ganglion cell layer after acute elevation of intraocular pressure in rats

PURPOSE

To investigate whether the P2X₇ receptor is involved in retinal ganglion cell (RGC) death after the intraocular pressure (IOP) is elevated in rats.

METHODS

After the IOP was elevated to 90 mmHg for 1 h, the rats were subsequently administered oxidized adenosine triphosphate (OxATP) and brilliant blue G (BBG) as P2X₇ antagonists. The rats were euthanized 7 days after IOP elevation for histologic evaluation and at 1, 3, and 7 days after IOP elevation to immunostain for the P2X₇ receptor and neuron-specific class III β-tubulin in the retina. Changes in P2X₇ receptor expression were measured in total retina extracts using western blot analysis. Quantitative real-time PCR was also performed using the entire retina to determine whether the P2X₇ receptor is involved in upregulating tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 at 1, 2, and 3 days after the IOP was elevated.

RESULTS

RGC density and the inner plexiform layer thickness significantly decreased 7 days after IOP elevation, but were dose-dependently preserved when treated with OxATP or BBG. P2X₇ immunoreactivity in the RGCs increased after IOP elevation, with the peak occurring from day 1 through day 3. Protein levels of P2X₇ receptor were significantly increased 1, 2, and 3 days after IOP elevation. The messenger ribonucleic acid expression of the P2X₇ receptor, TNF-α, IL-1β, and IL-6 was significantly upregulated in the retina after IOP elevation, and was suppressed by treatment with OxATP.

CONCLUSIONS

These results suggest the expression of the P2X₇ receptor is upregulated in the retina after IOP elevation, leading to RGC death. Upregulation of TNF-α, IL-1β, and IL-6 might be involved in this mechanism of RGC death. Furthermore, P2X₇ antagonists may prevent RGC death after IOP elevation.

Adaptive phenotype of microglial cells during the normal postnatal development of the somatosensory "Barrel" cortex

Accumulative evidence indicates that microglial cells influence the normal development of central nervous system (CNS) synapses. Yet, the functional properties of microglia in relation with synapse development remain unclear. We recently showed that in layer 4 of the whisker-related barrel field of the mouse somatosensory cortex, microglial cells are recruited only after postnatal day (P)5 in the center of the barrels where thalamo-cortical synapses are concentrated and begin their maturation. In the present study, we analyzed the phenotype of microglia during this developmental process. We show that between P5 and P7 microglial cells acquire a more ramified morphology with a smaller soma, they express classical markers of microglia (Iba1, CD11b, and CD68) but never markers of activation (Mac-2 and MHCII) and rarely the proliferation marker Ki67. Electrophysiological recordings in acute cortical slices showed that at P5 a proportion of layer 4 microglia transiently express voltage-dependant potassium currents of the delayed rectifier family, mostly mediated by Kv1.3 subunits, which are usually expressed by activated microglia under pathological conditions. This proportion of cells with rectifying properties doubles between P5 and P6, in concomitance with the beginning of microglia invasion of the barrel centers. Finally, analysis of the responses mediated by purinergic receptors indicated that a higher percentage of rectifying microglia expressed functional P2Y6 and P2Y12 receptors, as compared with nonrectifying cells, whereas all cells expressed functional P2X7 receptors. Our results indicate that during normal cortical development distinct microglia properties mature differentially, some of them being exquisitely influenced by the local environment of the maturating neuronal network.

High mobility group box 1/Toll-like receptor danger signaling increases brain neuroimmune activation in alcohol dependence

BACKGROUND

Innate immune gene expression is regulated in part through high mobility group box 1 (HMGB1), an endogenous proinflammatory cytokine, that activates multiple members of the interleukin-1/Toll-like receptor (TLR) family associated with danger signaling. We investigated expression of HMGB1, TLR2, TLR3, and TLR4 in chronic ethanol-treated mouse brain, postmortem human alcoholic brain, and rat brain slice culture to test the hypothesis that neuroimmune activation in alcoholic brain involves ethanol activation of HMGB1/TLR danger signaling.

METHODS

Protein levels were assessed using Western blot, enzyme-linked immunosorbent assay, and immunohistochemical immunoreactivity (+IR), and messenger RNA (mRNA) levels were measured by real time polymerase chain reaction in ethanol-treated mice (5 g/kg/day, intragastric, 10 days + 24 hours), rat brain slice culture, and postmortem human alcoholic brain.

RESULTS

Ethanol treatment of mice increased brain mRNA and +IR protein expression of HMGB1, TLR2, TLR3, and TLR4. Postmortem human alcoholic brain also showed increased HMGB1, TLR2, TLR3, and TLR4 +IR cells that correlated with lifetime alcohol consumption, as well as each other. Ethanol treatment of brain slice culture released HMGB1 into the media and induced the proinflammatory cytokine, interleukin-1 beta (IL-1β). Neutralizing antibodies to HMGB1 and small inhibitory mRNA to HMGB1 or TLR4 blunted ethanol induction of IL-1β.

CONCLUSIONS

Ethanol-induced HMGB1/TLR signaling contributes to induction of the proinflammatory cytokine, IL-1β. Increased expression of HMGB1, TLR2, TLR3, and TLR4 in alcoholic brain and in mice treated with ethanol suggests that chronic alcohol-induced brain neuroimmune activation occurs through HMGB1/TLR signaling.

Adolescent binge drinking increases expression of the danger signal receptor agonist HMGB1 and Toll-like receptors in the adult prefrontal cortex

Adolescence is a critical developmental stage of life during which the prefrontal cortex (PFC) matures, and binge drinking and alcohol abuse are common. Recent studies have found that ethanol increases neuroinflammation via upregulated high-mobility group box 1 (HMGB1) signaling through Toll-like receptors (TLRs). HMGB1/TLR 'danger signaling' induces multiple brain innate immune genes that could alter brain function. To determine whether adolescent binge drinking persistently increases innate immune gene expression in the PFC, rats (P25-P55) were exposed to adolescent intermittent ethanol (AIE [5.0 g/kg, 2-day on/2-day off schedule]). On P56, HMGB1/TLR danger signaling was assessed using immunohistochemistry (i.e., +immunoreactivity [+IR]). In a separate group of subjects, spatial and reversal learning on the Barnes maze was assessed in early adulthood (P64-P75), and HMGB1/TLR danger signaling was measured using immunohistochemistry for +IR and RT-PCR for mRNA in adulthood (P80). Immunohistochemical assessment at P56 and 24 days later at P80 revealed increased frontal cortical HMGB1, TLR4, and TLR3 in the AIE-treated rats. Adolescent intermittent ethanol treatment did not alter adult spatial learning on the Barnes maze, but did cause reversal learning deficits and increased perseverative behavior. Barnes maze deficits correlated with the expression of danger signal receptors in the PFC. Taken together, these findings provide evidence that adolescent binge drinking leads to persistent upregulation of innate immune danger signaling in the adult PFC that correlates with adult neurocognitive dysfunction.

Inflammasome-IL-1β Signaling Mediates Ethanol Inhibition of Hippocampal Neurogenesis

Regulation of hippocampal neurogenesis is poorly understood, but appears to contribute to mood and cognition. Ethanol and neuroinflammation are known to reduce neurogenesis. We have found that ethanol induces neuroinflammation supporting the hypothesis that ethanol induction of neuroinflammation contributes to ethanol inhibition of neurogenesis. To identify the key proinflammatory molecule that may be responsible for ethanol-impaired neurogenesis we used an ex vivo model of organotypic hippocampal-entorhinal cortex brain slice cultures. Here, we demonstrated a key role of proinflammatory cytokine IL-1β signaling in mediating ethanol inhibition of neurogenesis. Ethanol inhibition of neurogenesis was reversed by neutralizing antibody to IL-1β or blockade of the IL-1β receptor with antagonist IL-1RIa. Ethanol-impaired neurogenesis is associated with strong induction of IL-1β and inflammasome proteins NALP1 and NALP3 in both neurons and astrocytes. Blockade of IL-1β synthesis with inflammasome inhibitors Parthenolide and Bay11708 significantly reversed ethanol inhibited neurogenesis. Furthermore, we also found that IL-1β and inflammasome proteins NALP1 and NALP3 are increased in hippocampal neurons and astrocytes in postmortem alcoholic human brain. Together, these novel findings demonstrate that targeting inflammasome-IL-1β signaling can normalize ethanol-impaired hippocampal neurogenesis, which may have therapeutic implications for treatment of cognitive impairment associated with hippocampal dysfunction in alcoholics.