The NF-κB (nuclear factor κ-light-chain-enhancer of activated B cells) transcription factor family is a pleiotropic regulator of many cellular signaling pathways, providing a mechanism for the cells in response to a wide variety of stimuli linking to inflammation. The stimulated cells will be regulated by not only the canonical but also non-canonical NF-κB pathways. To initiate both of these pathways, IκB-degradation triggers NF-κB release and the nuclear translocated-heterodimer (or homodimer) can associate with the κB sites of promoter to regulate the gene transcriptions. NF-κB ubiquitously expresses in neurons and the constitutive NF-κB activation is associated with processing of neuronal information. NF-κB can regulate the transcription of genes such as chemokines, cytokines, proinflammatory enzymes, adhesion molecules, proinflammatory transcription factors, and other factors to modulate the neuronal survival. In neuronal insult, NF-κB constitutively active in neuron cell bodies can protect neurons against different injuries and regulate the neuronal inflammatory reactions. Besides neurons, NF-κB transcription factors are abundant in glial cells and cerebral blood vessels and the diverse functions of NF-κB also regulate the inflammatory reaction around the neuronal environment. NF-κB transcription factors are abundant in the brain and exhibit diverse functions. Several central nerve system (CNS) diseases are linked to NF-κB activated by inflammatory mediators. The RelA and c-Rel expression produce opposite effects on neuronal survival. Importantly, c-Rel expression in CNS plays a critical role in anti-apoptosis and reduces the age-related behaviors. Moreover, the different subunits of NF-κB dimer formation can modulate the neuroninflammation, neuronal protection, or neurotoxicity. The diverse functions of NF-κB depend on the subunits of the NF-κB dimer-formation which enable us to develop a therapeutic approach to neuroinflammation based on a new concept of inflammation as a strategic tool in neuronal cells. However, the detail role of NF-κB in neuroinflammation, remains to be clarified. In the present article, we provide an updated review of the current state of our knowledge about relationship between NF-κB and neuroinflammation.

BackgroundMatrix metalloproteinase-9 (MMP-9) plays a crucial role in pathological processes of brain inflammation, injury, and neurodegeneration. Moreover, bradykinin (BK) induces the expression of several inflammatory proteins in brain astrocytes. Recent studies have suggested that increased oxidative stress is implicated in the brain inflammation and injury. However, whether BK induced MMP-9 expression mediated through oxidative stress remains virtually unknown. Herein we investigated the role of redox signals in BK-induced MMP-9 expression in rat brain astrocytes (RBA-1 cells).ResultsIn the study, we first demonstrated that reactive oxygen species (ROS) plays a crucial role in BK-induced MMP-9 expression in cultured brain astrocytes (in vitro) and animal brain tissue (in vivo) models. Next, BK-induced MMP-9 expression is mediated through a Ca2+-mediated PKC-α linking to p47phox/NADPH oxidase 2 (Nox2)/ROS signaling pathway. Nox2-dependent ROS generation led to activation and up-regulation of the downstream transcriptional factor AP-1 (i.e. c-Fos and c-Jun), which bound to MMP-9 promoter region, and thereby turned on transcription of MMP-9 gene. Functionally, BK-induced MMP-9 expression enhanced astrocytic migration.ConclusionsThese results demonstrated that in RBA-1 cells, activation of AP-1 (c-Fos/c-Jun) by the PKC-α-mediated Nox2/ROS signals is essential for up-regulation of MMP-9 and cell migration enhanced by BK.

BackgroundEndothelin-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.ResultsThe data obtained with Western blotting, RT-PCR, and immunofluorescent staining analyses showed that ET-1-induced COX-2 expression was mediated through an ETB-dependent transcriptional activation. Engagement of Gi- and Gq-protein-coupled ETB 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.ConclusionsThese results suggested that in mouse bEnd.3 cells, activation of NF-κB by ETB-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/ETB system on brain microvascular endothelial cells may provide rationally therapeutic interventions for brain injury or inflammatory diseases.

BackgroundProstaglandin E2 (PGE2), an arachidonic acid metabolite converted by cyclooxygenase-2 (COX-2), plays important roles in the regulation of endothelial functions in response to bacterial infection. The enzymatic activity of COX-2 can be down-regulated by heme oxygenase-1 (HO-1) induction. However, the mechanisms underlying HO-1 modulating COX-2 protein expression are not known.ObjectiveThe aim of the present study was to investigate whether the up-regulation of HO-1 regulates COX-2 expression induced by lipopolysaccharide (LPS), an endotoxin produced by Gram negative bacteria, in mouse brain endothelial cells (bEnd.3)MethodsCultured bEnd.3 cells were used to investigate LPS-induced COX-2 expression and PGE2 production. Cobalt protoporphyrin IX (CoPP, an HO-1 inducer), infection with a recombinant adenovirus carried with HO-1 gene (Adv-HO-1), or zinc protoporphyrin (ZnPP, an HO-1 inhibitor) was used to stimulate HO-1 induction or inhibit HO-1 activity. The expressions of COX-2 and HO-1 were evaluated by western blotting. PGE2 levels were detected by an enzyme-linked immunoassay. Hemoglobin (a chelator of carbon monoxide, CO, one of metabolites of HO-1) and CO-RM2 (a CO releasing molecule) were used to investigate the mechanisms of HO-1 regulating COX-2 expression.ResultsWe found that LPS-induced COX-2 expression and PGE2 production were mediated through NF-κB (p65) via activation of Toll-like receptor 4 (TLR4). LPS-induced COX-2 expression was inhibited by HO-1 induction by pretreatment with CoPP or infection with Adv-HO-1. This inhibitory effect of HO-1 was reversed by pretreatment with either ZnPP or hemoglobin. Pretreatment with CO-RM2 also inhibited TLR4/MyD88 complex formation, NF-κB (p65) activation, COX-2 expression, and PGE2 production induced by LPS.ConclusionsWe show here a novel inhibition of HO-1 on LPS-induced COX-2/PGE2 production in bEnd.3. Our results reinforce the emerging role of cerebral endothelium-derived HO-1 as a protector against cerebral vascular inflammation triggered by bacterial infection.

BackgroundLipoteichoic acid (LTA) is a component of gram-positive bacterial cell walls and may be elevated in the cerebrospinal fluid of patients suffering from meningitis. Among matrix metalloproteinases (MMPs), MMP-9 has been observed in patients with brain inflammatory diseases and may contribute to the pathology of brain diseases. Moreover, several studies have suggested that increased oxidative stress is implicated in the pathogenesis of brain inflammation and injury. However, the molecular mechanisms underlying LTA-induced redox signal and MMP-9 expression in brain astrocytes remain unclear.ObjectiveHerein we explored whether LTA-induced MMP-9 expression was mediated through redox signals in rat brain astrocytes (RBA-1 cells).MethodsUpregulation of MMP-9 by LTA was evaluated by zymographic and RT-PCR analyses. Next, the MMP-9 regulatory pathways were investigated by pretreatment with pharmacological inhibitors or transfection with small interfering RNAs (siRNAs), Western blotting, and chromatin immunoprecipitation (ChIP)-PCR and promoter activity reporter assays. Moreover, we determined the cell functional changes by migration assay.ResultsThese results showed that LTA induced MMP-9 expression via a PKC(α)-dependent pathway. We further demonstrated that PKCα stimulated p47phox/NADPH oxidase 2 (Nox2)-dependent reactive oxygen species (ROS) generation and then activated the ATF2/AP-1 signals. The activated-ATF2 bound to the AP-1-binding site of MMP-9 promoter, and thereby turned on MMP-9 gene transcription. Additionally, the co-activator p300 also contributed to these responses. Functionally, LTA-induced MMP-9 expression enhanced astrocytic migration.ConclusionThese results demonstrated that in RBA-1 cells, activation of ATF2/AP-1 by the PKC(α)-mediated Nox(2)/ROS signals is essential for upregulation of MMP-9 and cell migration enhanced by LTA.