BK-induced COX-2 expression via PKC-δ-dependent activation of p42/p44 MAPK and NF-κB in astrocytes

Tonic repression of Collagen I by the Bradykinin receptor 2 in skin fibroblasts

Imbalance of collagen I expression results in severe pathologies. Apart from activation by the TGFβ-receptor/Smad pathway, control of collagen I expression remains poorly understood. Here, we used human dermal fibroblasts expressing a mCherry fluorescent protein driven by endogenous COL1A1 promoter to functionally screen the kinome and phosphatome. We identify 8 negative regulators, revealing that collagen is under tonic repression. The cell surface receptor BDKRB2 represses collagen I and other pro-fibrotic genes. Interestingly, it also promotes other basal membrane ECM genes. This function is independent of the natural ligand, bradykinin, and of SMAD2/3 factors, instead requiring constant ERK1/2 repression. TGFβ stimulation induces rapid BDKRB2 transcriptional downregulation. Human fibrotic fibroblasts have reduced BDKRB2 levels and enhancing its expression in keloid fibroblasts represses COL1A1. We propose that tonic signalling by BDKRB2 prevents collagen overproduction in skin fibroblasts.

Relationships of pain-causing substances with dry skin and effects of zaltoprofen on alleviation of symptoms in arthritis model mice

Skin dryness is a symptom of rheumatoid arthritis (RA). However, the mechanisms through which dry skin is induced in RA are unclear. Accordingly, in this study, we characterized substances related to pruritus and pain and then evaluated whether oral administration of zaltoprofen (ZLT) alleviated the symptom of dry skin induced by RA in model mice. DBA/1JJmsSlc collagen-induced arthritis model mice were treated with ZLT, and transepidermal water loss (TEWL), capacitance, and inflammation-, pruritus-, and pain-related markers were assessed. Our findings demonstrated that arthritis model mice treated with ZLT exhibited suppression of increases in TEWL and decreases in capacitance. Furthermore, ZLT also blocked the increase in mast cell numbers, substance P expression, and cyclo-oxygenase-2 expression in the skin and prevented enhancement of plasma levels of thymic stromal lymphopoietin, tumor necrosis factor-α, interleukin-6, histamine, and bradykinin. No changes in plasma levels of corticosterone or reactive oxygen species or skin levels of glucocorticoid receptor were observed in ZLT-treated arthritis model mice. Overall, these findings suggested that patients with RA may benefit from biopharmacy to alleviate joint symptoms and nonsteroidal anti-inflammatory drugs for pain relief and alleviation of skin symptoms.

Anti-inflammatory effect of Ailanthus altissima (Mill.) Swingle leaves in lipopolysaccharide-stimulated astrocytes

ETHNOPHARMACOLOGICAL RELEVANCE

Activated astrocytes are involved in the progression of neurodegenerative diseases. Traditionally, Ailanthus altissima (Mill.) Swingle, widely distributed in East Asia, has been used as a medicine for the treatment of fever, gastric diseases, and inflammation. Although A. altissima has been reported to play an anti-inflammatory role in peripheral tissues or cells, its role in the central nervous system (CNS) remains unclear.

AIM OF THE STUDY

In the present study, we investigated the anti-inflammatory effects and mechanism of action of A. altissima in primary astrocytes stimulated by lipopolysaccharide (LPS).

MATERIALS AND METHODS

A nitrite assay was used to measure nitric oxide (NO) production, and the tetrazolium salt 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay was performed to determine cytotoxicity. The expression levels of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and mitogen-activated protein kinase (MAPK) were determined with western blotting. Reverse-transcription PCR was used to assess the expression of inflammatory cytokines. The levels of reactive oxygen species were measured using 2,7-dichlorodihydrofluorescein diacetate. Luciferase assay and immunocytochemistry were used for assessing nuclear factor-kappa B (NF-κB) transcription and p65 localization, respectively. Memory and social interaction were analyzed using the Y-maze and three-chamber tests, respectively.

RESULTS

The ethanol extract of A. altissima leaves (AAE) inhibited iNOS and COX-2 expression in LPS-stimulated astrocytes. Moreover, AAE reduced the transcription of various proinflammatory mediators, hindered NF-κB activation, and suppressed extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) activation without p38 activation. Ultra-high performance liquid chromatography with mass spectrometry analysis revealed that AAE comprised ethyl gallate, quercetin, and kaempferol, along with luteolin, which has anti-inflammatory properties, and repressed LPS-induced nitrite levels and the nuclear translocation of p65. Finally, oral administration of AAE attenuated LPS-induced memory and social impairment in mice and repressed LPS-induced ERK and JNK activation in the cortices of mice.

CONCLUSION

AAE could have therapeutic uses in the treatment of neuroinflammatory diseases via suppression of astrocyte activation.

A modular map of Bradykinin-mediated inflammatory signaling network

Bradykinin, a member of the kallikrein-kinin system (KKS), is associated with an inflammatory response pathway with diverse vascular permeability functions, including thrombosis and blood coagulation. In majority, bradykinin signals through Bradykinin Receptor B2 (B2R). B2R is a G protein-coupled receptor (GPCR) coupled to G protein family such as Gα_qs, Gα_q/Gα_11, Gα_i1, and Gβ1_γ2_. B2R stimulation leads to the activation of a signaling cascade of downstream molecules such as phospholipases, protein kinase C, Ras/Raf-1/MAPK, and PI3K/AKT and secondary messengers such as inositol-1,4,5-trisphosphate, diacylglycerol and Ca²⁺ ions. These secondary messengers modulate the production of nitric oxide or prostaglandins. Bradykinin-mediated signaling is implicated in inflammation, chronic pain, vasculopathy, neuropathy, obesity, diabetes, and cancer. Despite the biomedical importance of bradykinin, a resource of bradykinin-mediated signaling pathway is currently not available. Here, we developed a pathway resource of signaling events mediated by bradykinin. By employing data mining strategies in the published literature, we describe an integrated pathway reaction map of bradykinin consisting of 233 reactions. Bradykinin signaling pathway events included 25 enzyme catalysis reactions, 12 translocations, 83 activation/inhibition reactions, 11 molecular associations, 45 protein expression and 57 gene regulation events. The pathway map is made publicly available on the WikiPathways Database with the ID URL: https://www.wikipathways.org/index.php/Pathway:WP5132. The bradykinin-mediated signaling pathway map will facilitate the identification of novel candidates as therapeutic targets for diseases associated with dysregulated bradykinin signaling.

The COX-2-derived PGE2 autocrine contributes to bradykinin-induced matrix metalloproteinase-9 expression and astrocytic migration via STAT3 signaling

Background

The matrix metalloproteinase-9 (MMP-9) is up-regulated by several proinflammatory mediators in the central nervous system (CNS) diseases. Increasing reports show that MMP-9 expression is an inflammatory biomarker of several CNS disorders, including the CNS inflammation and neurodegeneration. Bradykinin (BK) is a common proinflammatory mediator and elevated in several brain injury and inflammatory disorders. The raised BK may be detrimental effects on the CNS that may aggravate brain inflammation through MMP-9 up-regulation or cyclooxygenase-2 (COX-2)-derived prostaglandin E₂ (PGE₂) production in brain astrocytes. However, the relationship between BK-induced MMP-9 expression and COX-2-derived PGE₂ release in brain astrocytes remains unclear.

Methods

Herein we used rat brain astrocytes (RBA) to investigate the role of the COX-2/PGE₂ system in BK-induced MMP-9 expression. We used zymographic, RT-PCR, EIA, and Western blotting analyses to confirm that BK induces MMP-9 expression via a COX-2/PGE₂-dependent pathway.

Results

Our results show activation of native COX-2 by BK led to PGE₂ production and release. Subsequently, PGE₂ induced MMP-9 expression via PGE₂ receptor (EP)-mediated c-Src, Jak2, ERK1/2, and then activated signal transducer and activator of transcription 3 (STAT3) signaling pathway. Finally, up-regulation of MMP-9 by BK via the pathway may promote astrocytic migration.

Conclusion

These results demonstrated that a novel autocrine pathway for BK-induced MMP-9 protein expression is mediated through activation of STAT3 by native COX-2/PGE₂-mediated c-Src/Jak2/ERK cascades in brain astrocytes.

Sphingosine 1-Phosphate Induces Cyclooxygenase-2/Prostaglandin E2 Expression via PKCα-dependent Mitogen-Activated Protein Kinases and NF-κB Cascade in Human Cardiac Fibroblasts

In the regions of tissue injuries and inflammatory diseases, sphingosine 1-phosphate (S1P), a proinflammatory mediator, is increased. S1P may induce the upregulation of cyclooxygenase-2 (COX-2)/prostaglandin E₂ (PGE₂) system in various types of cells to exacerbate heart inflammation. However, the detailed molecular mechanisms by which S1P induces COX-2 expression in human cardiac fibroblasts (HCFs) remain unknown. HCFs were incubated with S1P and analyzed by Western blotting, real time-Polymerase chain reaction (RT-PCR), and immunofluorescent staining. Our results indicated that S1P activated S1PR_1/3-dependent transcriptional activity to induce COX-2 expression and PGE₂ production. S1P recruited and activated PTX-sensitive G_i or -insensitive G_q protein-coupled S1PR and then stimulated PKCα-dependent phosphorylation of p42/p44 MAPK, p38 MAPK, and JNK1/2, leading to activating transcription factor NF-κB. Moreover, S1P-activated NF-κB was translocated into the nucleus and bound to its corresponding binding sites on COX-2 promoters determined by chromatin immunoprecipitation (ChIP) and promoter-reporter assays, thereby turning on COX-2 gene transcription associated with PGE₂ production in HCFs. These results concluded that in HCFs, activation of NF-κB by PKCα-mediated MAPK cascades was essential for S1P-induced up-regulation of the COX-2/PGE₂ system. Understanding the mechanisms of COX-2 expression and PGE₂ production regulated by the S1P/S1PRs system on cardiac fibroblasts may provide rationally therapeutic interventions for heart injury or inflammatory diseases.

Protective mechanisms of resveratrol derivatives against TNF-α-induced inflammatory responses in rat mesangial cells

INTRODUCTION

Resveratrol has been reported to alleviate inflammatory responses and oxidative stress in mesangial cells and in several types of renal injury in animal models. Previously, the active resveratrol derivatives from the roots of Vitis thunbergii Sieb. & Zucc. (Vitaceae) were shown to have significant anti-platelet and anti-oxidative activities. However, the anti-inflammatory mechanisms of these resveratrol derivatives in rat mesangial cells (RMCs) have not been clarified fully.

METHODS

The protective mechanisms of resveratrol derivatives involved in tumor necrosis factor-α (TNF-α)-induced inflammatory responses were assessed by Western blot analysis, real-time PCR, and RT-PCR. The involvement of various signaling molecules in these responses was investigated using selective pharmacological inhibitors.

RESULTS

Nontoxic concentrations of the resveratrol derivatives significantly attenuated cytosolic phospholipase A₂ (cPLA₂) and cyclooxygenase 2 (COX-2) expression in RMCs challenged by TNF-α. These resveratrol derivatives inhibited TNF-α-activated ERK1/2 and JNK1/2 without affecting p38 phosphorylation. Next, we demonstrated that TNF-α induced NF-κB activation, translocation, and promoter activity, which was inhibited by pretreatment with resveratrol derivatives in RMCs.

CONCLUSION

The protective mechanisms of resveratrol derivatives against TNF-α-stimulated inflammatory responses via cPLA₂/COX-2/PGE₂ inhibition was caused by the attenuation of the JNK1/2, ERK1/2, and NF-κB signaling pathways in RMCs.

Protein kinase Cε regulates nuclear translocation of extracellular signal-regulated kinase, which contributes to bradykinin-induced cyclooxygenase-2 expression

The proinflammatory mediator bradykinin stimulated cyclooxygenase-2 (COX-2) expression and subsequently prostaglandin E₂ synthesis in dermal fibroblasts. The involvement of B2 receptors and Gαq in the role of bradykinin was suggested by using pharmacological inhibitors. The PKC activator PMA stimulated COX-2 mRNA expression. Bradykinin failed to induce COX-2 mRNA expression in the presence of PKC inhibitors, whereas the effect of bradykinin was observed in the absence of extracellular Ca²⁺. Bradykinin-induced COX-2 mRNA expression was inhibited in cells transfected with PKCε siRNA. These observations suggest that the novel PKCε is concerned with bradykinin-induced COX-2 expression. Bradykinin-induced PKCε phosphorylation and COX-2 mRNA expression were inhibited by an inhibitor of 3-phosphoinositide-dependent protein kinase-1 (PDK-1), and bradykinin-induced PDK-1 phosphorylation was inhibited by phospholipase D (PLD) inhibitors, suggesting that PLD/PDK-1 pathway contributes to bradykinin-induced PKCε activation. Pharmacological and knockdown studies suggest that the extracellular signal-regulated kinase 1 (ERK1) MAPK signaling is involved in bradykinin-induced COX-2 expression. Bradykinin-induced ERK phosphorylation was attenuated in the cells pretreated with PKC inhibitors or transfected with PKCε siRNA. We observed the interaction between PKCε and ERK by co-immunoprecipitation experiments. These observations suggest that PKCε activation contributes to the regulation of ERK1 activation. Bradykinin stimulated the accumulation of phosphorylated ERK in the nuclear fraction, that was inhibited in the cells treated with PKC inhibitors or transfected with PKCε siRNA. Consequently, we concluded that bradykinin activates PKCε via the PLD/PDK-1 pathway, which subsequently induces activation and translocation of ERK1 into the nucleus, and contributes to COX-2 expression for prostaglandin E₂ synthesis in dermal fibroblasts.

Implication of the Kallikrein-Kinin system in neurological disorders: Quest for potential biomarkers and mechanisms

Neurological disorders represent major health concerns in terms of comorbidity and mortality worldwide. Despite a tremendous increase in our understanding of the pathophysiological processes involved in disease progression and prevention, the accumulated knowledge so far resulted in relatively moderate translational benefits in terms of therapeutic interventions and enhanced clinical outcomes. Aiming at specific neural molecular pathways, different strategies have been geared to target the development and progression of such disorders. The kallikrein-kinin system (KKS) is among the most delineated candidate systems due to its ubiquitous roles mediating several of the pathophysiological features of these neurological disorders as well as being implicated in regulating various brain functions. Several experimental KKS models revealed that the inhibition or stimulation of the two receptors of the KKS system (B1R and B2R) can exhibit neuroprotective and/or adverse pathological outcomes. This updated review provides background details of the KKS components and their functions in different neurological disorders including temporal lobe epilepsy, traumatic brain injury, stroke, spinal cord injury, Alzheimer's disease, multiple sclerosis and glioma. Finally, this work will highlight the putative roles of the KKS components as potential neurotherapeutic targets and provide future perspectives on the possibility of translating these findings into potential clinical biomarkers in neurological disease.

Inhibitory effect of donepezil on bradykinin-induced increase in the intracellular calcium concentration in cultured cortical astrocytes

Donepezil is a potent and selective acetylcholinesterase inhibitor developed for the treatment of Alzheimer's disease. In the present study, we investigated the responses of astrocytes to bradykinin, an inflammatory mediator, and the effect of donepezil on these responses using cultured cortical astrocytes. Bradykinin induced a transient increase of intracellular calcium concentration ([Ca²⁺]_i) in cultured astrocytes. Bradykinin-induced [Ca²⁺]_i increase was inhibited by the exposure to thapsigargin, which depletes Ca²⁺ stores on endoplasmic reticulum, but not by the exclusion of extracellular Ca²⁺. Twenty four hours pretreatment of donepezil reduced the bradykinin-induced [Ca²⁺]_i increase. This reduction was inhibited not only by mecamylamine, a nAChR antagonist, but also by PI3K and Akt inhibitors. In addition, donepezil inhibited bradykinin-induced increase of the intracellular reactive oxygen species level in astrocytes. These results suggest that donepezil inhibits the inflammatory response induced by bradykinin via nAChR and PI3K-Akt pathway in astrocytes.

Rottlerin induces cyclooxygenase-2 upregulation through an ATF4 and reactive oxygen species-independent pathway in HEI-OC1 cells

Hearing loss can be caused by infection, inflammation, loud noise and ototoxic drugs. The induction of cyclooxygenase-2 (COX‑2) expression is an important event during the cellular inflammatory response. The present study investigated the effect of rottlerin on CO-2 mRNA and protein expression in HEI-OC1 cells. Cell viability was determined using an MTT assay. Western blotting was used to examine the expression of COX‑2, endoplasmic reticulum stress-associated transcription factors and activation of the MAPK pathway. ROS was measured using the fluorescent probe 2', 7'-dichlorodihydrofluorescein diacetate. Treatment with the natural protein kinase C δ inhibitor, rottlerin, was shown to increase COX‑2 expression at the protein and mRNA levels in a dose‑dependent manner. Rottlerin was shown to induce increased reactive oxygen species (ROS) generation, however, ROS were not critical for rottlerin‑induced upregulation of COX‑2 expression in HEI‑OC1 cells. In addition, rottlerin was shown to increase the phosphorylation of p38 mitogen-activated protein kinase (MAPK). The pharmacological inhibition of p38MAPK and suppression of activating transcription factor 4 (an ER stress‑associated transcription factor) expression by small interfering RNA inhibited rottlerin-induced COX‑2 upregulation. Furthermore, COX‑2 expression levels were increased further when cells were treated with rottlerin and interleukin‑1β or protein kinase C activator, PMA. In conclusion, the results of the present study demonstrated that rottlerin is a novel inducer of COX‑2 expression and identified the mechanisms involved in this process. Rottlerin may be considered a potential activator of repair and remodeling.

Cytosolic phospholipase A2 regulates alcohol-mediated astrocyte inflammatory responses in HIV-associated neurocognitive disorders

Alcohol (EtOH) abuse and HIV-1 infection remain leading public health problems not only in the United States but also across the world. Alcohol abusers have a significantly greater risk of HIV-1 infection than non-drinkers globally. In the United States, prevalence of EtOH abuse is over two-fold higher in HIV-1-positive individuals than that of the general population. Although alcohol abusers show neurodegeneration, exacerbated neuroinflammation and oxidative damage, the mechanism(s) by which EtOH regulates astrocyte inflammatory responses in HIV-associated neurocognitive disorders is unknown. Thus, we explored signaling pathway(s) involved in EtOH-mediated activation of human astrocytes with HIV-1 and subsequent alterations in their inflammatory functions. Alcohol exposure altered the morphology of astrocytes, proinflammatory responses and induced cytotoxicity in a dose-dependent manner. Time-dependent changes were also evaluated. EtOH and HIV-1 cotreatment decreased cell viability and proliferation, while increasing apoptosis and mitochondrial depolarization. EtOH and HIV-1 together increased the levels of proinflammatory molecules, interleukin-1β, tumor necrosis factor-α, CXCL8, tissue inhibitor of metalloproteinases-1 and more importantly, arachidonic acid, a known downstream target of cytosolic phospholipase A₂ (cPLA₂). Consistent with this observation, phospho-cPLA₂ levels were augmented in HIV-1 and EtOH cotreatment as compared with HIV-1 or EtOH alone. Cyclooxygenase 2 was upregulated as measured by real-time PCR and western blot, whereas cotreatment of HIV-1 and EtOH decreased cytochrome P450-2E1 levels as compared with EtOH alone. Furthermore, we confirmed that blocking cPLA₂ with arachidonyl tri floro methyl ketone, a cPLA₂-specific inhibitor, effectively prevented cPLA₂ phosphorylation and downstream outcomes. Thus, the present findings suggest that cPLA₂ has a critical role in alcohol and HIV-induced astrocyte inflammation. In the future, cPLA₂ inhibitors may present novel therapeutic tools to treat alcohol abuse and HIV-associated neurocognitive disorder comorbidity.

Differential regulation of astrocyte prostaglandin response by kinins: possible role for mitogen activated protein kinases

The role of kinins, well known as peripheral inflammatory mediators, in the modulation of brain inflammation is not completely understood. The present data show that bradykinin, a B2 receptor agonist, enhanced both basal and lipopolysaccharide (LPS)-induced cyclooxygenase-2 mRNA and protein levels and prostaglandin E2 synthesis in primary rat astrocytes. By contrast, Lys-des-Arg(9)-bradykinin, which is a bradykinin breakdown product and a selective kinin B1 receptor agonist, attenuated both basal and LPS-induced astrocyte cyclooxygenase-2 mRNA levels and prostaglandin E2 production. Pre-treating the cells with p42/p44 MAPK but not with JNK or p38 inhibitors completely abrogated PGE2 synthesis in cells stimulated with LPS in the presence of bradykinin or bradykinin B1 receptor agonist. Bradykinin, but not the bradykinin B1 receptor agonist, augmented p42/p44 MAPK phosphorylation. The phosphorylation of JNK and p38 was not altered upon exposure to Bradykinin or the bradykinin B1 receptor agonist. These results suggest that the dual delayed effect of kinins on PGE2 synthesis may be due to differential regulation of COX-2 and signaling molecules such as p42/p44 MAPKs. Thus, kinins may exert opposing actions on brain inflammation and neurodegenerative diseases.

Aspirin inhibits lipopolysaccharide-induced COX-2 expression and PGE2 production in porcine alveolar macrophages by modulating protein kinase C and protein tyrosine phosphatase activity

Aspirin has been demonstrated to be effective in inhibiting COX-2 and PGE(2) in Alveolar macrophages (AMs). However, the mechanisms have not been fully understood. In the present study, we found that pretreatment with aspirin inhibited LPS-induced COX-2 and PGE(2) upregulation, IκBα degradation, NFκB activation and the increase of PKC activity, but elevated LPS-induced the decrease of PTP activity. The PKC inhibitor calphostin C dramatically reduced the COX-2 mRNA and PGE(2) levels, but the PTP inhibitor peroxovanadium (POV) significantly increased the COX-2 mRNA and PGE(2) levels. Furthermore, the PTP inhibitor mitigated the inhibitory effect of aspirin on COX-2 and PGE(2) upregulation and NF-κB activation, whereas the PKC inhibitor enhanced the inhibitory effects of aspirin on the production of COX-2 and PGE(2). Our data indicate a novel mechanism by which aspirin acts as a potent anti-inflammatory agent in alveolus macrophages and ALI.

The effect of bradykinin on the electrical activity of rat myenteric neurons

Bradykinin is a mediator involved in inflammatory processes in the gut. Here we investigated the effect of bradykinin on the electrical activity of rat myenteric neurons, the key players for regulation of gastrointestinal motility. Bradykinin (2 × 10(-8)mol/l) induced a biphasic increase in frequency of action potentials measured with microelectrode arrays. This increase was mirrored by a biphasic increase in cytosolic Ca(2+) concentration ([Ca(2+)]i), which was observed in about 40% of the myenteric neurons. The bradykinin B1 receptor agonist des-arg(9)-bradykinin as well as the bradykinin B2 receptor agonist hyp(3)-bradykinin induced a similar effect on [Ca(2+)]i. Immunocytochemical stainings confirmed the expression of both receptor types by myenteric ganglionic cells. Real time PCR showed that the inducible B1 receptor was upregulated during cell culture. The inhibition of cyclooxygenases with piroxicam reduced the effect of bradykinin on the electrical activity of myenteric neurons. The suppression of the glial growth on microelectrode arrays did not affect the bradykinin-induced change in frequency of action potentials. This suggests that prostaglandins, which probably mediate the effect of bradykinin, are not exclusively released from glial cells. The bradykinin-induced increase in [Ca(2+)]i was dependent on the presence of extracellular Ca(2+) and was inhibited by Co(2+), Cd(2+), and Ni(2+), blockers of voltage-dependent Ca(2+) channels, indicating a stimulation of the influx of extracellular Ca(2+) by the kinin. Consequently, bradykinin induces a Ca(2+) influx in myenteric neurons via Ca(2+) channels in the plasma membrane.

Role of cytosolic phospholipase A2 in oxidative and inflammatory signaling pathways in different cell types in the central nervous system

Phospholipases A(2) (PLA(2)s) are important enzymes for the metabolism of fatty acids in membrane phospholipids. Among the three major classes of PLA(2)s in the mammalian system, the group IV calcium-dependent cytosolic PLA(2) alpha (cPLA(2)α) has received the most attention because it is widely expressed in nearly all mammalian cells and its active participation in cell metabolism. Besides Ca(2+) binding to its C2 domain, this enzyme can undergo a number of cell-specific post-translational modifications, including phosphorylation by protein kinases, S-nitrosylation through interaction with nitric oxide (NO), as well as interaction with other proteins and lipid molecules. Hydrolysis of phospholipids by cPLA(2) yields two important lipid mediators, arachidonic acid (AA) and lysophospholipids. While AA is known to serve as a substrate for cyclooxygenases and lipoxygenases, which are enzymes for the synthesis of eicosanoids and leukotrienes, lysophospholipids are known to possess detergent-like properties capable of altering microdomains of cell membranes. An important feature of cPLA(2) is its link to cell surface receptors that stimulate signaling pathways associated with activation of protein kinases and production of reactive oxygen species (ROS). In the central nervous system (CNS), cPLA(2) activation has been implicated in neuronal excitation, synaptic secretion, apoptosis, cell-cell interaction, cognitive and behavioral function, oxidative-nitrosative stress, and inflammatory responses that underline the pathogenesis of a number of neurodegenerative diseases. However, the types of extracellular agonists that target intracellular signaling pathways leading to cPLA(2) activation among different cell types and under different physiological and pathological conditions have not been investigated in detail. In this review, special emphasis is given to metabolic events linking cPLA(2) to activation in neurons, astrocytes, microglial cells, and cerebrovascular cells. Understanding the molecular mechanism(s) for regulation of this enzyme is deemed important in the development of new therapeutic targets for the treatment and prevention of neurodegenerative diseases.

Role of redox signaling in neuroinflammation and neurodegenerative diseases

Reactive oxygen species (ROS), a redox signal, are produced by various enzymatic reactions and chemical processes, which are essential for many physiological functions and act as second messengers. However, accumulating evidence has implicated the pathogenesis of several human diseases including neurodegenerative disorders related to increased oxidative stress. Under pathological conditions, increasing ROS production can regulate the expression of diverse inflammatory mediators during brain injury. Elevated levels of several proinflammatory factors including cytokines, peptides, pathogenic structures, and peroxidants in the central nervous system (CNS) have been detected in patients with neurodegenerative diseases such as Alzheimer's disease (AD). These proinflammatory factors act as potent stimuli in brain inflammation through upregulation of diverse inflammatory genes, including matrix metalloproteinases (MMPs), cytosolic phospholipase A₂ (cPLA₂), cyclooxygenase-2 (COX-2), and adhesion molecules. To date, the intracellular signaling mechanisms underlying the expression of target proteins regulated by these factors are elusive. In this review, we discuss the mechanisms underlying the intracellular signaling pathways, especially ROS, involved in the expression of several inflammatory proteins induced by proinflammatory factors in brain resident cells. Understanding redox signaling transduction mechanisms involved in the expression of target proteins and genes may provide useful therapeutic strategies for brain injury, inflammation, and neurodegenerative diseases.

The upregulation of translocator protein (18 kDa) promotes recovery from neuropathic pain in rats

At present, effective drug for treatment of neuropathic pain is still lacking. Recent studies have shown that the ligands of translocator protein (TSPO, 18 kDa), a peripheral receptor for benzodiazepine, modulate inflammatory pain. Here, we report that TSPO was upregulated in astrocytes and microglia in the ipsilateral spinal dorsal horn of rats following L5 spinal nerve ligation (L5 SNL), lasting until the vanishing of the behavioral signs of neuropathic pain (∼50 d). Importantly, a single intrathecal injection of specific TSPO agonists Ro5-4864 or FGIN-1-27 at 7 and 21 d after L5 SNL depressed the established mechanical allodynia and thermal hyperalgesia dramatically, and the effect was abolished by pretreatment with AMG, a neurosteroid synthesis inhibitor. Mechanically, Ro5-4864 substantially inhibited spinal astrocytes but not microglia, and reduced the production of tumor necrosis factor-α (TNF-α) in vivo and in vitro. The anti-neuroinflammatory effect was also prevented by AMG. Interestingly, TSPO expression returned to control levels or decreased substantially, when neuropathic pain healed naturally or was reversed by Ro5-4864, suggesting that the role of TSPO upregulation might be to promote recovery from the neurological disorder. Finally, the neuropathic pain and the upregulation of TSPO by L5 SNL were prevented by pharmacological blockage of Toll-like receptor 4 (TLR4). These data suggested that TSPO might be a novel therapeutic target for the treatment of neuropathic pain.

Up-regulation of COX-2/PGE2 by endothelin-1 via MAPK-dependent NF-κB pathway in mouse brain microvascular endothelial cells

Background

Endothelin-1 (ET-1) is a proinflammatory mediator and elevated in the regions of several brain injury and inflammatory diseases. The deleterious effects of ET-1 on endothelial cells may aggravate brain inflammation mediated through the regulation of cyclooxygenase-2 (COX-2)/prostaglandin E₂ (PGE₂) system in various cell types. However, the signaling mechanisms underlying ET-1-induced COX-2 expression in brain microvascular endothelial cells remain unclear. Herein we investigated the effects of ET-1 in COX-2 regulation in mouse brain microvascular endothelial (bEnd.3) cells.

Results

The data obtained with Western blotting, RT-PCR, and immunofluorescent staining analyses showed that ET-1-induced COX-2 expression was mediated through an ET_B-dependent transcriptional activation. Engagement of G_i- and G_q-protein-coupled ET_B receptors by ET-1 led to phosphorylation of ERK1/2, p38 MAPK, and JNK1/2 and then activated transcription factor NF-κB. Moreover, the data of chromatin immunoprecipitation (ChIP) and promoter reporter assay demonstrated that the activated NF-κB was translocated into nucleus and bound to its corresponding binding sites in COX-2 promoter, thereby turning on COX-2 gene transcription. Finally, up-regulation of COX-2 by ET-1 promoted PGE₂ release in these cells.

Conclusions

These results suggested that in mouse bEnd.3 cells, activation of NF-κB by ET_B-dependent MAPK cascades is essential for ET-1-induced up-regulation of COX-2/PGE₂ system. Understanding the mechanisms of COX-2 expression and PGE₂ release regulated by ET-1/ET_B system on brain microvascular endothelial cells may provide rationally therapeutic interventions for brain injury or inflammatory diseases.

Multiple factors from bradykinin-challenged astrocytes contribute to the neuronal apoptosis: involvement of astroglial ROS, MMP-9, and HO-1/CO system

Bradykinin (BK) has been shown to induce the expression of several inflammatory mediators, including reactive oxygen species (ROS) and matrix metalloproteinases (MMPs), in brain astrocytes. These mediators may contribute to neuronal dysfunction and death in various neurological disorders. However, the effects of multiple inflammatory mediators released from BK-challenged astrocytes on neuronal cells remain unclear. Here, we found that multiple factors were released from brain astrocytes (RBA-1) exposed to BK in the conditioned culture media (BK-CM), including ROS, MMP-9, and heme oxygenase-1 (HO-1)/carbon monoxide (CO), leading to neuronal cell (SK-N-SH) death. Exposure of SK-N-SH cells to BK-CM or H2O2 reduced cell viability and induced cell apoptosis which were attenuated by N-acetyl cysteine, indicating a role of ROS in these responses. The effect of BK-CM on cell viability and cell apoptosis was also reversed by immunoprecipitation of BK-CM with anti-MMP-9 antibody (MMP-9-IP-CM) or MMP2/9 inhibitor, suggesting the involvement of MMP-9 in BK-CM-mediated responses. Astroglial HO-1/CO in BK-CM induced cell apoptosis and reduced cell viability which was reversed by hemoglobin. Consistently, the involvement of CO in these cellular responses was revealed by incubation with a CO donor CO-RM2 which was reversed by hemoglobin. The role of HO-1 in BK-CM-induced responses was confirmed by overexpression of HO-1 in SK-N-SH infected with Adv-HO-1. BK-CM-induced cell apoptosis was due to the activation of caspase-3 and cleavage of PARP. Together, we demonstrate that BK-induced several neurotoxic factors, including ROS, MMP-9, and CO released from astrocytes, may induce neuronal death through a caspase-3-dependent apoptotic pathway.

Ischemic stroke and traumatic brain injury: the role of the kallikrein-kinin system

Acute ischemic stroke and traumatic brain injury are a major cause of mortality and morbidity. Due to the paucity of therapies, there is a pressing clinical demand for new treatment options. Successful therapeutic strategies for these conditions must target multiple pathophysiological mechanisms occurring at different stages of brain injury. In this respect, the kallikrein-kinin system is an ideal target linking key pathological hallmarks of ischemic and traumatic brain damage such as edema formation, inflammation, and thrombosis. In particular, the kinin receptors, plasma kallikrein, and coagulation factor XIIa are highly attractive candidates for pharmacological development, as kinin receptor antagonists or inhibitors of plasma kallikrein and coagulation factor XIIa are neuroprotective in animal models of stroke and traumatic brain injury. Nevertheless, conflicting preclinical evaluation as well as limited and inconclusive data from clinical trials suggest caution when transferring observations made in animals into the human situation. This review summarizes current evidence on the pathological significance of the kallikrein-kinin system during ischemic and traumatic brain damage, with a particular focus on experimental data derived from animal models. Experimental findings are also compared with human data if available, and potential therapeutic implications are discussed.

Rottlerin and curcumin: a comparative analysis

Rottlerin and curcumin are natural plant polyphenols with a long tradition in folk medicine. Over the past two decades, curcumin has been extensively investigated, while rottlerin has received much less attention, in part, as a consequence of its reputation as a selective PKCδ inhibitor. A comparative analysis of genomic, proteomic, and cell signaling studies revealed that rottlerin and curcumin share a number of targets and have overlapping effects on many biological processes. Both molecules, indeed, modulate the activity and/or expression of several enzymes (PKCδ, heme oxygenase, DNA methyltransferase, cyclooxygenase, lipoxygenase) and transcription factors (NF-κB, STAT), and prevent aggregation of different amyloid precursors (α-synuclein, amyloid Aβ, prion proteins, lysozyme), thereby exhibiting convergent antioxidant, anti-inflammatory, and antiamyloid actions. Like curcumin, rottlerin could be a promising candidate in the fight against a variety of human diseases.

Involvement of distinct PKC gene products in T cell functions

It is well established that members of the protein kinase C (PKC) family seem to have important roles in T cells. Focusing on the physiological and non-redundant PKC functions established in primary mouse T cells via germline gene-targeting approaches, our current knowledge defines two particularly critical PKC gene products, PKCθ and PKCα, as the "flavor of PKC" in T cells that appear to have a positive role in signaling pathways that are necessary for full antigen receptor-mediated T cell activation ex vivo and T cell-mediated immunity in vivo. Consistently, in spite of the current dogma that PKCθ inhibition might be sufficient to achieve complete immunosuppressive effects, more recent results have indicated that the pharmacological inhibition of PKCθ, and additionally, at least PKCα, appears to be needed to provide a successful approach for the prevention of allograft rejection and treatment of autoimmune diseases.

Fasitibant prevents the bradykinin and interleukin 1β synergism on prostaglandin E₂ release and cyclooxygenase 2 expression in human fibroblast-like synoviocytes

This study investigates the effect of the selective and potent B(2) receptor antagonist fasitibant (MEN16132) on the proinflammatory effect of bradykinin (BK) and its interaction with interleukin 1β (IL-1β) in human synoviocytes. PGE(2) content was detected in the surnatants and COX-2 and COX-1 gene and protein expression determined in the cells. Radioligand binding ([(3) H]BK) and BK-induced inositolphosphate experiments were performed. Incubation of synoviocytes with BK induced a sustained production of PGE(2) and transient COX-2 gene expression that were prevented by pretreatment with fasitibant (1 μM, 30 min preincubation). IL-1β increased PGE(2) release and COX-2 expression more than BK alone. The combined treatment of cells with BK and IL-1β induced an even increase of released PGE(2) and COX-2 gene and protein expression indicating a synergistic rather than an additive effect, not related to an increase of B(2) receptors density or its coupling. These potentiating effects of BK on PGE(2) production and increased COX-2 expression produced by IL-1β were B(2)-receptor-mediated as fasitibant could prevent them. None of the treatments induced changes in the COX-1 expression. The synergistic PGE(2) production was abolished by the specific NF-kappaB inhibitor (BAY-117085), whereas specific inhibitors for the p38 (SB203580), JNK (SP600125), and ERK1/2 (PD98059) mitogen-activated protein kinases could prevent the prostanoid release. BK can potentiate the COX-2 gene expression and consequent prostanoid production induced by IL-1β. The prevention of this synergism by fasitibant indicates BK B(2) receptor blockade as an alternative symptomatic therapy for osteoarthritis.

Rottlerin enhances IL-1β-induced COX-2 expression through sustained p38 MAPK activation in MDA-MB-231 human breast cancer cells

Cyclooxygenase-2 (COX-2) is an important enzyme in inflammation. In this study, we investigated the underlying molecular mechanism of the synergistic effect of rottlerin on interleukin1β (IL-1β)-induced COX-2 expression in MDA-MB-231 human breast cancer cell line. Treatment with rottlerin enhanced IL-1β-induced COX-2 expression at both the protein and mRNA levels. Combined treatment with rottlerin and IL-1β significantly induced COX-2 expression, at least in part, through the enhancement of COX-2 mRNA stability. In addition, rottlerin and IL-1β treatment drove sustained activation of p38 Mitogen-activated protein kinase (MAPK), which is involved in induced COX-2 expression. Also, a pharmacological inhibitor of p38 MAPK (SB 203580) and transient transfection with inactive p38 MAPK inhibited rottlerin and IL-1β-induced COX-2 upregulation. However, suppression of protein kinase C δ (PKC δ) expression by siRNA or overexpression of dominant-negative PKC δ (DN-PKC-δ) did not abrogate the rottlerin plus IL-1β-induced COX-2 expression. Furthermore, rottlerin also enhanced tumor necrosis factor-α (TNF-α), phorbol myristate acetate (PMA), and lipopolysaccharide (LPS)-induced COX-2 expression. Taken together, our results suggest that rottlerin causes IL-1β-induced COX-2 upregulation through sustained p38 MAPK activation in MDA-MB-231 human breast cancer cells.

Transactivation of EGFR/PI3K/Akt involved in ATP-induced inflammatory protein expression and cell motility

Phenotype transition of vascular smooth muscle cells (VSMCs) is important in vascular diseases, such as atherosclerosis and restenosis. Once released, ATP may promote activation of VSMCs by stimulating cyclooxygenase-2 (COX-2), cytosolic phospholipase A(2) (cPLA(2)) expression and prostaglandin (PG)E(2) synthesis via activation of MAPKs and NF-κB. However, whether alternative signaling pathways participated in regulating COX-2 and cPLA(2) expression associated with cell migration were investigated in rat VSMCs. Western blot analysis, RT-PCR, promoter assay and PGE(2) ELISA were used to determine expression of COX-2, cPLA(2) and PGE(2). Specific inhibitors and siRNAs against various protein kinases or transcription factors were used to investigate the related signaling components in inflammatory protein induction by ATPγS. We found that ATPγS-induced COX-2 and cPLA(2) expression and PGE(2) release was attenuated by the pharmacological inhibitors or transfection with siRNA against PKCδ, c-Src, EGFR, PI3-K, Akt, p44/p42 MAPK or Elk-1. Moreover, ATPγS-stimulated phosphorylation of PKCδ, c-Src, EGFR, Akt, p42/p44 MAPK and Elk-1, suggesting the participation of PKCδ/c-Src/EGFR/PI3-K/Akt/p42/p44 MAPK cascade in mediating Elk-1 activities in VSMCs. In addition, migration assay revealed that ATPγS promoted cell mobility through up-regulation of COX-2 and cPLA(2) expression and PGE(2) release, which was attenuated by pretreatment with PGE(2) receptor antagonists. Taken together, these data showed that ATPγS up-regulated the expression of COX-2 and cPLA(2) through transactivation of PKCδ/c-Src/EGFR/PI3K/Akt/Elk-1 pathway. Newly synthesized PGE(2) acted on its receptors to promote cell motility of ATPγS-stimulated VSMCs.

Roles of reactive oxygen and nitrogen species in pain

Peroxynitrite (PN; ONOO⁻) and its reactive oxygen precursor superoxide (SO; O₂•⁻) are critically important in the development of pain of several etiologies including pain associated with chronic use of opiates such as morphine (also known as opiate-induced hyperalgesia and antinociceptive tolerance). This is now an emerging field in which considerable progress has been made in terms of understanding the relative contributions of SO, PN, and nitroxidative stress in pain signaling at the molecular and biochemical levels. Aggressive research in this area is poised to provide the pharmacological basis for development of novel nonnarcotic analgesics that are based upon the unique ability to selectively eliminate SO and/or PN. As we have a better understanding of the roles of SO and PN in pathophysiological settings, targeting PN may be a better therapeutic strategy than targeting SO. This is because, unlike PN, which has no currently known beneficial role, SO may play a significant role in learning and memory. Thus, the best approach may be to spare SO while directly targeting its downstream product, PN. Over the past 15 years, our team has spearheaded research concerning the roles of SO and PN in pain and these results are currently leading to the development of solid therapeutic strategies in this important area.

Japanese encephalitis virus induces matrix metalloproteinase-9 in rat brain astrocytes via NF-κB signalling dependent on MAPKs and reactive oxygen species

BACKGROUND AND PURPOSE

Japanese encephalitis virus (JEV) is a member of the family Flaviviridae and JEV infection is a major cause of acute encephalopathy in children, which destroys cells in the CNS, including astrocytes and neurons. However, the detailed mechanisms underlying the inflammatory action of JEV are largely unclear.

EXPERIMENTAL APPROACH

The effect of JEV on the expression of matrix metalloproteinase (MMP)-9 was determined by gelatin zymography, Western blot analysis, real-time PCR and promoter assay. The involvement of the NADPH oxidase and reactive oxygen species (ROS), MAPKs, and the transcription factor NF-κB in these responses was investigated by using selective pharmacological inhibitors and transfection with appropriate siRNAs.

KEY RESULTS

JEV induced the expression of the pro-form of MMP-9 in rat brain astrocytes (RBA-1 cells). In RBA-1 cells, JEV induced MMP-9 expression and promoter activity, which was inhibited by pretreatment with inhibitors of NADPH oxidase (diphenylene iodonium chloride or apocynin), MAPKs (U0126, SB203580 or SP600125) and a ROS scavenger (N-acetylcysteine), or transfection with siRNAs of p47(phox) , ERK1, JNK2 and p38. In addition, JEV-induced MMP-9 expression was reduced by pretreatment with an inhibitor of NF-κB (helenalin) or transfection with p65 siRNA. Moreover, JEV-stimulated NF-κB activation was inhibited by pretreatment with the inhibitors of NADPH oxidase and MAPKs.

CONCLUSIONS AND IMPLICATIONS

MMP-9 expression induced by JEV infection of RBA-1 cells was mediated through the generation of ROS and activation of p42/p44 MAPK, p38 MAPK and JNK1/2, leading to NF-κB activation.

PKCδ sensitizes neuroblastoma cells to L-buthionine-sulfoximine and etoposide inducing reactive oxygen species overproduction and DNA damage

Neuroblastoma is a type of pediatric cancer. The sensitivity of neuroblastoma (NB) cancer cells to chemotherapy and radiation is inhibited by the presence of antioxidants, such as glutathione (GSH), which is crucial in counteracting the endogenous production of reactive oxygen species (ROS). We have previously demonstrated that cells depleted of GSH undergo apoptosis via oxidative stress and Protein kinase C (PKC) δ activation. In the present study, we transfected PKCδ in NB cells resistant to oxidative death induced by L-buthionine-S,R-sulfoximine (BSO), a GSH-depleting agent. Cell responses, in terms of ROS production, apoptosis and DNA damage were evaluated. Moreover, PKCδ activation was monitored by analyzing the phosphorylation status of threonine 505 residue, carrying out PKC activity assay and investigating the subcellular localization of the kinase. The cell responses obtained in BSO-resistant cells were also compared with those obtained in BSO-sensitive cells subjected to the same experimental protocol. Our results demonstrate, for the first time, that PKCδ induces DNA oxidation and ROS overproduction leading to apoptosis of BSO-resistant NB cells and potentiates the cytotoxic effects induced by BSO in sensitive cells. Moreover, PKCδ overexpression enhances the sensitivity of NB cells to etoposide, a well-characterised drug, commonly used in neuroblastoma therapy. Altogether our data provide evidence of a pro-oxidant role of PKCδ that might be exploited to design new therapeutic strategies aimed at selective killing of cancer cells and overcoming drug resistance. However, it becomes evident that a more detailed understanding of ROS-mediated signaling in cancer cells is necessary for the development of redox-modulated therapeutic approaches.

Reactive Oxygen Species-Dependent c-Fos/Activator Protein 1 Induction Upregulates Heme Oxygenase-1 Expression by Bradykinin in Brain Astrocytes

Heme oxygenase-1 (HO-1) plays a crucial role in tissue pathological changes such as brain injuries. Our previous studies have demonstrated that bradykinin (BK) induces the expression of several inflammatory proteins, including matrix metalloproteinase-9 and COX-2, via mitogen-activated protein kinases and nuclear factor-κB (NF-κB) in rat brain astrocytes (RBA-1). However, the molecular mechanisms underlying BK-induced HO-1 expression in RBA-1 cells remain poorly defined. Here we demonstrated that BK induced HO-1 expression and enzymatic activity via a B(2) BK receptor-activated reactive oxygen species (ROS)-dependent signaling pathway. NADPH oxidase (Nox)-dependent ROS generation led to activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun-N-terminal kinase (JNK) and then activated the downstream molecules NF-κB and c-Jun, respectively. The c-Fos, an activator protein 1 (AP-1) subunit, was upregulated by activation of NF-κB and c-Jun, which bound to HO-1 promoter and thereby turned on transcription of HO-1 gene. The rat HO-1 promoter containing a putative AP-1 cis-binding site was identified as a crucial domain linking to BK action. Taken together, these results suggested that in RBA-1 cells, activation of ERK/NF-κB and JNK/c-Jun cascades by a Nox/ROS-dependent event enhancing c-Fos/AP-1 activity is essential for HO-1 upregulation and activation induced by BK. Moreover, ROS-dependent NF-E2-related factor 2 activation also contributes to HO-1 induction by BK in astrocytes.

A phospholipase A₂ from Bothrops asper snake venom activates neutrophils in culture: expression of cyclooxygenase-2 and PGE₂ biosynthesis

In this study, the production of prostaglandin E₂ (PGE₂) and up-regulation in cyclooxygenase (COX) pathway induced by a phospholipase A₂ (PLA₂), myotoxin-III (MT-III), purified from Bothrops asper snake venom, in isolated neutrophils were investigated. The arachidonic acid (AA) production and the participation of intracellular PLA₂s (cytosolic PLA₂ and Ca(2+)-independent PLA₂) in these events were also evaluated. MT-III induced COX-2, but not COX-1 gene and protein expression in neutrophils and increased PGE₂ levels. Pretreatment of neutrophils with COX-2 and COX-1 inhibitors reduced PGE₂ production induced by MT-III. Arachidonyl trifluoromethyl ketone (AACOCF₃), an intracellular PLA₂ inhibitor, but not bromoenol lactone (BEL), an iPLA₂ inhibitor, suppressed the MT-III-induced AA and PGE₂ release. In conclusion, MT-III directly stimulates neutrophils inducing COX-2 mRNA and protein expression followed by production of PGE₂. COX-2 isoform is preeminent over COX-1 for production of PGE₂ stimulated by MT-III. PGE₂ and AA release by MT-III probably is related to cPLA₂ activation.

Bradykinin-induced cell migration and COX-2 production mediated by the bradykinin B1 receptor in glioma cells

Bradykinin is produced and acts at the site of injury and inflammation. Recent reports have also shown that bradykinin selectively modulates blood-tumor barrier permeability. However, the molecular mechanisms and pathologic roles underlying bradykinin-induced glioma migration remain unclear. Glioma is the most common primary adult brain tumor, with a poor prognosis because of the ease with which tumor cells spread to other regions of the brain. In this study, we found that bradykinin increases the cell migration and expression of cyclo-oxygenase-2 (COX-2) in glioma cells. Bradykinin-mediated migration was attenuated by the selective COX-2 inhibitor NS-398. Moreover, increased motility of glioma cells and expression of COX-2 were mimicked by a bradykinin B1 receptor (B1R) agonist and markedly inhibited by a B1R antagonist. Bradykinin-mediated migration was attenuated by phosphoinositide 3-kinase (PI-3 kinase)/AKT inhibitors LY 294002 and wortmannin. Bradykinin stimulation also increased the phosphorylation of the p85 subunit of PI-3 kinase and serine 473 of AKT. Treatment of bradykinin with AP-1 inhibitors Tanshinone IIA and curcumin also reduced COX-2 expression and glioma cell migration. Moreover, treatment of bradykinin also induced phosphorylation of c-Jun in glioma cells. AP-1 promoter analysis in the luciferase reporter construct showed that bradykinin increased AP-1 transcription activity and was inhibited by LY 294002 and wortmannin. One mechanism underlying bradykinin-directed migration is transcriptional up-regulation of COX-2 and activation of the B1R receptor, PI-3 kinase, AKT, c-Jun, and AP-1 pathways.

Protein synthesis dependent effects of kinins on astrocyte prostaglandin synthesis

It has been shown that kinins and their receptors are over expressed in the brain under pathophysiological conditions such as inflammation. However, little is known about the possible role of kinins, and especially bradykinin in brain inflammation. Although kinins are thought to have immediate effects, peptides may also exert longer and protein synthesis dependent actions. To evaluate this possibility, we assessed the regulation of prostaglandin E(2) synthesis after 15h bradykinin or Lys-des-Arg(9)-bradykinin (B(1) receptor agonist) treatment in rat neonatal astrocytes. Bradykinin, dose dependently stimulated basal and lipopolysaccharide-induced prostaglandin E(2) production, whereas exposure of astrocytes to the B(1) receptor agonist decreased both basal and lipopolysaccharide-induced prostaglandin E(2) release in a dose-dependent manner. These kinin effects on PGE(2) synthesis were completely abrogated by actinomycin-D and cycloheximide, suggesting de novo synthesis of proteins. Bradykinin also increased cyclooxygenase-2 protein levels about 2-fold, while the B(1) receptor agonist decreased cyclooxygenase-2 protein expression. There was no change in cyclooxygenase-1 protein levels after treatment with either of the kinins. Our data suggest a delayed feedback regulatory mechanism of kinins on astrocyte inflammation, whereby astrocyte prostaglandin synthesis is initially enhanced by bradykinin (B(2)) and eventually blocked by kinin breakdown product, acting on B(1) receptors. At least part of this presumed feedback loop could be mediated by de novo protein synthesis of cyclooxygenase-2.

Phosphatidylinositol 3-kinase/protein kinase Cdelta activation induces close homolog of adhesion molecule L1 (CHL1) expression in cultured astrocytes

Upregulation of expression of the close homolog of adhesion molecule L1 (CHL1) by reactive astrocytes in the glial scar reduces axonal regeneration and inhibits functional recovery after spinal cord injury (SCI). Here, we investigate the molecular mechanisms underlying upregulation of CHL1 expression by analyzing the signal transduction pathways in vitro. We show that astrogliosis stimulated by bacterial lipopolysaccharide (LPS) upregulates CHL1 expression in primary cultures of mouse cerebral astrocytes, coinciding with elevated protein synthesis and translocation of protein kinase delta (PKCdelta) from cytosol to the membrane fraction. Blocking PKCdelta activity pharmacologically and genetically attenuates LPS-induced elevation of CHL1 protein expression through a phosphatidylinositol 3-kinase (PI3K) dependent pathway. LPS induces extracellular signal-regulated kinases (ERK1/2) phosphorylation through PKCdelta and blockade of ERK1/2 activation abolishes upregulation of CHL1 expression. LPS-triggered upregulation of CHL1 expression mediated through translocation of nuclear factor kappaB (NF-kappaB) to the nucleus is blocked by a specific NF-kappaB inhibitor and by inhibition of PI3K, PKCdelta, and ERK1/2 activities, implicating NF-kappaB as a downstream target for upregulation of CHL1 expression. Furthermore, the LPS-mediated upregulation of CHL1 expression by reactive astrocytes is inhibitory for hippocampal neurite outgrowth in cocultures. Although the LPS-triggered NO-guanylate cyclase-cGMP pathway upregulates glial fibrillary acid protein expression in cultured astrocytes, we did not observe this pathway to mediate LPS-induced upregulation of CHL1 expression. Our results indicate that elevated CHL1 expression by reactive astrocytes requires activation of PI3K/PKCdelta-dependent pathways and suggest that reduction of PI3K/PKCdelta activity represents a therapeutic target to downregulate CHL1 expression and thus benefit axonal regeneration after SCI.

Nuclear factor-kappaB activation regulates cyclooxygenase-2 induction in human astrocytes in response to CXCL12: role in neuronal toxicity

Neurodegenerative and neuroinflammatory disorders are commonly associated with local chemokine release. In other way, emerging data indicate that the prostaglandin E2 (PGE(2)), one of the major prostaglandins produced in the brain, play a central role in several pathological diseases. In this study, we investigated the relationship between CXCL12, cyclooxygenase (COX)-2 and PGE(2) in human brain cells. CXCL12 induced COX-2 and secretion of PGE(2) in a dose-dependent manner in human astrocytes. This induction was abolished by treatment with pertussis toxin and AMD3100, confirming the role of CXCR4 signaling. The nuclear factor-kappaB involvement was confirmed by using pyrrolidine dithiocarbamate, and with transient transfection assays. Over-expression of inhibitory proteins of nuclear factor-kappaB abrogated COX-2 induction, and CXCL12 induced p65/relA translocation. Culture supernatants from CXCL12-treated astrocytes reduced viability of neuroblastoma cells, and COX inhibitors abrogated this toxicity. Therefore, the relationship between chemokines and PGs could differentially influence the pathogenic network responsible for neurodegeneration.

Enterovirus 71 induces COX-2 expression via MAPKs, NF-kappaB, and AP-1 in SK-N-SH cells: Role of PGE(2) in viral replication

The enterovirus 71 (EV71) causes severe neurological diseases that were mediated through cyclooxygenase-2 (COX-2) expression in brain. However, the mechanisms underlying EV71-initiated intracellular signaling pathways leading to COX-2 expression remain unknown in neurons. Here we report that exposure of SK-N-SH cells to EV71 increased COX-2 expression and PGE(2) generation in a time- and virus titer-dependent manner, revealed by Western blot, real-time PCR, and PGE(2) analyses. These EV71-induced responses were mediated through activation of p42/p44 MAPK, p38 MAPK, JNK, NF-kappaB, and AP-1, revealed by using selective pharmacological inhibitors or transfection with respective siRNAs. Consistently, EV71-stimulated translocation of NF-kappaB into the nucleus and degradation of IkappaBalpha in the cytosol was blocked by pretreatment with the selective inhibitors of MEK1/2 (U0126) and NF-kappaB (Bay11-7085), respectively, suggesting that MEK1/2-p42/p44 MAPK cascade linking to NF-kappaB was involved in COX-2 expression. In addition, EV71-induced AP-1 subunits (c-jun and c-fos mRNA) expression was also attenuated by pretreatment with a selective JNK inhibitor SP600125, suggesting that JNK cascade linking to AP-1 was involved in COX-2 expression induced by EV71. These findings suggested that up-regulation of COX-2 associated with the release of PGE(2) from EV71-infected SK-N-SH cells which was mediated through activation of p38 MAPK, JNK, p42/p44 MAPK, NF-kappaB, and AP-1 pathways.

Oxidized low-density lipoprotein-induced matrix metalloproteinase-9 expression via PKC-delta/p42/p44 MAPK/Elk-1 cascade in brain astrocytes

After ischemic injury to brain, disruption of the blood-brain barrier (BBB) raises the possibility of exposing the central nervous system (CNS) to oxidized low-density lipoprotein (oxLDL), a risk factor implicated in neurodegenerative diseases. Matrix metalloproteinases (MMPs), especially MMP-9, contribute to extracellular matrix (ECM) remodeling during the CNS diseases. However, the molecular mechanisms underlying oxLDL-induced MMP-9 expression in astrocytes remained unclear. Here, we reported that oxLDL induced MMP-9 expression via a PKC-delta/p42/p44 MAPK-dependent Elk-1 activation in rat brain astrocyte (RBA)-1 cells, revealed by gelatin zymography, RT-PCR, and Western blotting analyses. These responses were attenuated by pretreatment with pharmacological inhibitors and transfection with dominant negative mutants. Moreover, Elk-1-mediated MMP-9 gene transcription was confirmed by transfection with an Elk-1 binding site-mutated MMP-9 promoter construct (mt-Ets-MMP9), which blocked oxLDL-stimulated MMP-9 luciferase activity. Understanding the regulatory mechanisms by which oxLDL induced MMP-9 expression in astrocytes might provide a new therapeutic strategy of brain diseases.

Oxidized low-density lipoprotein induces matrix metalloproteinase-9 expression via a p42/p44 and JNK-dependent AP-1 pathway in brain astrocytes

Upregulation of matrix metalloproteinases (MMPs), especially MMP-9, by oxidized low-density lipoprotein (oxLDL) is implicated in many inflammatory diseases including brain injury. However, the signaling mechanisms underlying oxLDL-induced MMP-9 expression in astrocytes largely remain unknown. Here we report that oxLDL induces expression of proMMP-9 via a MAPK-dependent AP-1 activation in rat brain astrocyte (RBA)-1 cells. Results revealed by gelatin zymography, RT-PCR, and Western blotting analyses showed that oxLDL-induced proMMP-9 gene expression was mediated through Akt, JNK1/2, and p42/p44 MAPK phosphorylation in RBA-1 cells. These responses were attenuated by inhibitors of PI3K (LY294002), JNK (SP600125), and p42/p44 MAPK (PD98059), or transfection with dominant negative mutants and short hairpin RNA. Moreover, we demonstrated that AP-1 (i.e., c-Fos/c-Jun) is crucial for oxLDL-induced proMMP-9 expression which was attenuated by pretreatment with AP-1 inhibitor (curcumin). The regulation of MMP-9 gene transcription by AP-1 was confirmed by oxLDL-stimulated MMP-9 luciferase activity which was totally lost in cells transfected with the AP-1 binding site-mutated MMP-9 promoter construct (mt-AP1-MMP-9). These results suggested that oxLDL-induced proMMP-9 expression is mediated through PI3K/Akt, JNK1/2, and p42/p44 MAPK leading to AP-1 activation. Understanding the regulatory mechanisms underlying oxLDL-induced MMP-9 expression in astrocytes might provide a new therapeutic strategy of brain injuries and diseases.

Differential involvement of PKC-dependent MAPKs activation in lipopolysaccharide-induced AP-1 expression in human tracheal smooth muscle cells

Lipopolysaccharide (LPS) has been shown to up-regulate the expression of vascular cell adhesion molecule (VCAM)-1 which contributes to the occurrence of airway inflammatory diseases. Genetic analysis reveals the existence of activator protein-1 (AP-1) binding site on VCAM-1 promoter region. However, the role of AP-1 in LPS-induced VCAM-1 expression in human tracheal smooth muscle cells (HTSMCs) is not known. Here, we show that LPS increased VCAM-1 expression and adhesiveness of HTSMCs through AP-1, since pretreatment with an AP-1 inhibitor tanshinone attenuated LPS-induced VCAM-1 expression and leukocytes adhesion. The implication of AP-1 in LPS-induced VCAM-1 expression was confirmed by animal studies showing that pretreatment of mice with tanshinone attenuated LPS-induced VCAM-1 mRNA expression in airway tissues and accumulation of leukocytes in bronchoalveolar lavage. By using the pharmacological inhibitors and transfection with siRNA of PKC, p42, p38, or JNK2, LPS-induced expression of c-Fos was mediated through protein kinase C (PKC), p42/p44 MAPK and p38 MAPK. While, c-Jun expression was mediated through PKC and mitogen-activated protein kinases (MAPKs, p42/p44 MAPK, p38 MAPK and JNK) in HTSMCs. Pretreatment with the inhibitors of PKCs or MAPKs attenuated LPS-stimulated nuclear translocation and VCAM-1 promoter binding abilities of AP-1, which attenuated promoter activity and gene expression of VCAM-1 and the adhesiveness between HTSMCs and leukocytes. These results indicated that differential regulation of AP-1 through PKCs-dependent MAPKs activation plays central roles in LPS-induced VCAM-1 expression. The altered modulation of this axis with inhibitors or siRNAs may contribute to the improvement of airway inflammatory diseases.

Functional coupling expression of COX-2 and cPLA2 induced by ATP in rat vascular smooth muscle cells: role of ERK1/2, p38 MAPK, and NF-kappaB

AIMS

Vascular smooth muscle cells (VSMCs) that function as synthetic units play important roles in inflammatory diseases such as atherosclerosis and angiogenesis. As extracellular nucleotides such as ATP have been shown to act via activation of P(2) purinoceptors implicated in various inflammatory diseases, we hypothesized that extracellular nucleotides contribute to vascular diseases via upregulated expression of inflammatory proteins, such as cyclooxygenase (COX-2) and cytosolic phospholipase A2 (cPLA2) in VSMCs.

METHODS AND RESULTS

Western blotting, promoter assay, RT-PCR, and PGE2 immunoassay revealed that ATPgammaS induced expression of COX-2 and prostaglandin (PGE2) synthesis through the activation of p42/p44 MAPK (mitogen-activated protein kinase), p38 MAPK, and nuclear factor-kappaB (NF-kappaB). These responses were attenuated by inhibitors of MAPK/ERK kinase (MEK1/2; U0126), p38 MAPK (SB202190), and NF-kappaB (helenalin), or by tranfection with dominant negative mutants of p42, p38, IkappaB kinase (IKK)alpha, and IKKbeta. Furthermore, the ATPgammaS-stimulated translocation of NF-kappaB into the nucleus and degradation of IkappaBalpha was blocked by U0126 and helenalin. In addition, the ATPgammaS-stimulated cPLA2 expression was inhibited by U0126, SB202190, helenalin, celecoxib (a selective COX-2 inhibitor), and PGE2 receptor antagonists (AH6809, GW627368X, and SC-19220). However, the inhibitory effect of celecoxib on cPLA2 expression was reversed by addition of exogenous PGE2.

CONCLUSION

Our results suggest that in VSMCs, activation of p42/p44 MAPK, p38 MAPK, and NF-kappaB is essential for ATPgammaS-induced COX-2 expression and PGE2 synthesis. Newly synthesized PGE2 was observed to act as an autocrine signal contributing to cPLA2 expression, which may be implicated in inflammatory responses. Collectively, our findings provide insights into the correlation between COX-2 and cPLA2 expression in ATPgammaS-stimulated VSMCs with similar molecular mechanisms and functional coupling to amplify the occurrence of vessel disease-related vascular inflammation.

Overexpression of phospholipase D enhances matrix metalloproteinase-2 expression and glioma cell invasion via protein kinase C and protein kinase A/NF-kappaB/Sp1-mediated signaling pathways

Glioblastoma is a severe type of primary brain tumor, and its highly invasive character is considered to be a major therapeutic obstacle. Phospholipase D (PLD) isozyme is overexpressed in various human tumor tissues and involved in tumorigenesis. However, the molecular mechanisms by which PLD enhances glioma invasion are unknown. In this study, we demonstrate that the increased expression of PLD and its enzymatic activity in the glioma stimulate the secretion and expression of matrix metalloproteinase (MMP)-2 and induce the invasiveness of glioma cells. The upregulation of MMP-2 induced by phosphatidic acid (PA), the product of PLD, was mediated by protein kinase C (PKC), protein kinase A (PKA), nuclear factor-kappaB (NF-kappaB) and Sp1 and it enhanced glioma cell invasion. PA activated PKC and PKA and induced the nuclear translocation and transactivation of NF-kappaB. PA also increased the binding of NF-kappaB and Sp1 to the MMP-2 promoter. Mutation of the NF-kappaB- or Sp1-binding sites significantly attenuated MMP-2 promoter activity. This is the first report to show that NF-kappaB and Sp1 are essential transcriptional factors linking PLD to MMP-2 upregulation, providing evidence that PLD contributes to glioma progression by enhancing MMP-2 expression and tumor cell invasion via PKC/PKA/NF-kappaB/Sp1-mediated signaling pathways.

Neuron-glia crosstalk gets serious: role in pain hypersensitivity

PURPOSE OF REVIEW

Recent studies show that peripheral injury activates both neuronal and nonneuronal or glial components of the peripheral and central cellular circuitry. The subsequent neuron-glia interactions contribute to pain hypersensitivity. This review will briefly discuss novel findings that have shed light on the cellular mechanisms of neuron-glia interactions in persistent pain.

RECENT FINDINGS

Two fundamental questions related to neuron-glia interactions in pain mechanisms have been addressed: what are the signals that lead to central glial activation after injury and how do glial cells affect central nervous system neuronal activity and promote hyperalgesia?

SUMMARY

Evidence indicates that central glial activation depends on nerve inputs from the site of injury and release of chemical mediators. Hematogenous immune cells may migrate to/infiltrate the brain and circulating inflammatory mediators may penetrate the blood-brain barrier to participate in central glial responses to injury. Inflammatory cytokines such as interleukin-1beta released from glia may facilitate pain transmission through its coupling to neuronal glutamate receptors. This bidirectional neuron-glia signaling plays a key role in glial activation, cytokine production and the initiation and maintenance of hyperalgesia. Recognition of the contribution of the mutual neuron-glia interactions to central sensitization and hyperalgesia prompts new treatment for chronic pain.