Repression of proinflammatory cytokine and inducible nitric oxide synthase (NOS2) gene expression in activated microglia by N-acetyl-O-methyldopamine: protein kinase A-dependent mechanism

Role of Withaferin A and Its Derivatives in the Management of Alzheimer's Disease: Recent Trends and Future Perspectives

Globally, Alzheimer's disease (AD) is one of the most prevalent age-related neurodegenerative disorders associated with cognitive decline and memory deficits due to beta-amyloid deposition (Aβ) and tau protein hyperphosphorylation. To date, approximately 47 million people worldwide have AD. This figure will rise to an estimated 75.6 million by 2030 and 135.5 million by 2050. According to the literature, the efficacy of conventional medications for AD is statistically substantial, but clinical relevance is restricted to disease slowing rather than reversal. Withaferin A (WA) is a steroidal lactone glycowithanolides, a secondary metabolite with comprehensive biological effects. Biosynthetically, it is derived from Withania somnifera (Ashwagandha) and Acnistus breviflorus (Gallinero) through the mevalonate and non-mevalonate pathways. Mounting evidence shows that WA possesses inhibitory activities against developing a pathological marker of Alzheimer's diseases. Several cellular and animal models' particulates to AD have been conducted to assess the underlying protective effect of WA. In AD, the neuroprotective potential of WA is mediated by reduction of beta-amyloid plaque aggregation, tau protein accumulation, regulation of heat shock proteins, and inhibition of oxidative and inflammatory constituents. Despite the various preclinical studies on WA's therapeutic potentiality, less is known regarding its definite efficacy in humans for AD. Accordingly, the present study focuses on the biosynthesis of WA, the epidemiology and pathophysiology of AD, and finally the therapeutic potential of WA for the treatment and prevention of AD, highlighting the research and augmentation of new therapeutic approaches. Further clinical trials are necessary for evaluating the safety profile and confirming WA's neuroprotective potency against AD.

Glycyrrhizin Blocks the Detrimental Effects of HMGB1 on Cortical Neurogenesis After Traumatic Neuronal Injury

Despite medical advances, neurological recovery after severe traumatic brain injury (TBI) remains poor. Elevated levels of high mobility group box protein-1 (HMGB1) are associated with poor outcomes; likely via interaction with receptors for advanced-glycation-end-products (RAGE). We examined the hypothesis that HMGB1 post-TBI is anti-neurogenic and whether this is pharmacologically reversible. Post-natal rat cortical mixed neuro-glial cell cultures were subjected to needle-scratch injury and examined for HMGB1-activation/neuroinflammation. HMGB1-related genes/networks were examined using genome-wide RNA-seq studies in cortical perilesional tissue samples from adult mice. Post-natal rat cortical neural stem/progenitor cell cultures were generated to quantify effects of injury-condition medium (ICM) on neurogenesis with/without RAGE antagonist glycyrrhizin. Needle-injury upregulated TNF-α/NOS-2 mRNA-expressions at 6 h, increased proportions of activated microglia, and caused neuronal loss at 24 h. Transcriptome analysis revealed activation of HMGB1 pathway genes/canonical pathways in vivo at 24 h. A 50% increase in HMGB1 protein expression, and nuclear-to-cytoplasmic translocation of HMGB1 in neurons and microglia at 24 h post-injury was demonstrated in vitro. ICM reduced total numbers/proportions of neuronal cells, but reversed by 0.5 μM glycyrrhizin. HMGB1 is activated following in vivo post mechanical injury, and glycyrrhizin alleviates detrimental effects of ICM on cortical neurogenesis. Our findings highlight glycyrrhizin as a potential therapeutic agent post-TBI.

Microglia CREB-Phosphorylation Mediates Amyloid-β-Induced Neuronal Toxicity

Extracellular accumulation of amyloid-β (Aβ) forming senile plaques is one of the hallmark pathologies in Alzheimer's disease (AD), while the mechanisms underlying the neuronal toxic effect of Aβ are not fully understood. Here, we found that intracerebroventricular infusion of the aged Aβ42 in mice only induces memory deficit at 24 h but not at 7 days. Interestingly, a remarkably increased CREB (cAMP response element-binding protein) Ser133-phosphorylation (pS133-CREB) with microglial activation was detected at 24 h but not at 7 days after Aβ infusion. Aβ treatment for 24 h increased pS133-CREB level in microglia of the hippocampal non-granular cell layers with remarkably decreased pS133-CREB immunoreactivity in neurons of the hippocampal granular cell layers, including CA1, CA3, and DG subsets. Inhibition of microglia activation by minocycline or CREB phosphorylation by H89, an inhibitor of protein kinase A (PKA), abolished Aβ-induced microglia CREB hyperphosphorylation with restoration of neuronal function and attenuation of inflammatory response, i.e., reduced levels of interleukin-6 (IL6) and pCREB binding of matrix metalloproteinase-9 (MMP9) DNA. Finally, treatment of the primary hippocampal neurons with Aβ-potentiated microglia media decreased neuronal GluN1 and GluA2 levels, while simultaneous inhibition of PKA restored the levels. These novel findings reveal that intracerebroventricular infusion of Aβ only induces transient memory deficit in mice and the molecular mechanisms involve a stimulated microglial CREB phosphorylation.

Differential behavioral and glial responses induced by dopaminergic mechanisms in the iNOS knockout mice

The interaction between distinctive nitric oxide synthase (NOS) isoforms and the dopamine system provides new avenues to the development of pharmacological tools for the pathophysiological conditions of the dopaminergic system. Our aim was to investigate the influences of dopamine-induced effects in inducible NOS knockout (iNOS KO) mice. In order to characterize iNOS KO mice phenotype, the animals were submitted to the basal analyses of motor, sensorimotor and sensorial abilities. Pharmacological challenging of the dopaminergic system included the investigation of amphetamine-induced prepulse inhibition (PPI) disruption, haloperidol-induced catalepsy, reserpine-induced oral involuntary movements and hyperlocomotion induced by amphetamine in reserpine treated mice. The iNOS KO mice showed significant reduction of spontaneous motor activity, but there was no significant difference in sensorimotor or sensorial responses of iNOS KO mice compared to wild type (WT). Regarding the dopaminergic system, iNOS KO mice showed a significant increase of haloperidol-induced catalepsy. This effect was confirmed through an iNOS pharmacological inhibitor (1400 W) in WT mice. In addition, iNOS KO reserpine treated mice showed reduced oral involuntary movements and amphetamine-induced hyperlocomotion. Knowing that iNOS is mainly expressed in glial cells we analyzed the immunoreactivity (ir) for GFAP (astrocyte marker) and IBA-1 (microglial marker) in the striatum, an area enrolled in motor planning among other functions. iNOS KO presented reduced GFAP-ir and IBA-1-ir compared with WT. Reserpine treatment increased GFAP-ir in both WT and iNOS KO. However, these effects were slighter in iNOS KO. Activated state of microglia was increased by reserpine only in WT mice. Our results further demonstrated that the absence of iNOS interfered with dopamine-mediated behavioral and molecular responses. These results increase the understanding of the dopamine and NO system interaction, which is useful for the management of the dopamine-related pathologies.

Identification, characterization, and function analysis of the NF-κB repressing factor (NKRF) gene from Litopenaeus vannamei

The NF-κB family transcription factors regulate a wide spectrum of biological processes, in particular immune responses. The studies in human suggest that the NF-κB repressing factor (NKRF) negatively regulates the activity of NF-κB through a direct protein-protein interaction. However, the function of NKRF has not been studied outside mammals up to now. The current study identified a NKRF gene (LvNKRF) from the Pacific white shrimp, Litopenaeus vannamei, which showed homology with NKRFs from insects, fishes and mammals. LvNKRF was high expressed in intestine, stomach and muscle tissues and was localized in the nucleus. LvNKRF could interact with both Dorsal and Relish, the two members of the shrimp NF-κB family. Interestingly, although sharing a similar protein structure with that of human NKRF, LvNKRF showed no inhibitory but instead enhancing effects on activities of Dorsal and Relish, which was contrary to those of mammalian NKRFs. The expression of LvNKRF could not be induced by Gram-positive and -negative bacteria and immunostimulants lipopolysaccharide (LPS) and poly (I:C) but was significantly up-regulated after white spot syndrome virus (WSSV) infection. Silencing of LvNKRF significantly decreased the mortalities of shrimp caused by WSSV infection and down-regulated the WSSV copies and the expression of WSSV structural gene in tissues. These suggested that LvNKRF could facilitate the infection of shrimp by WSSV, which may be an additional strategy for WSSV to hijack the host NF-κB pathway to favor its own replication. The current study could provide a valuable context for further investigating the evolutionary derivation of NKRFs and facilitate the study of regulatory mechanisms of invertebrate NF-κB pathways.

β-amyloid, microglia, and the inflammasome in Alzheimer's disease

There is extensive evidence that accumulation of mononuclear phagocytes including microglial cells, monocytes, and macrophages at sites of β-amyloid (Aβ) deposition in the brain is an important pathological feature of Alzheimer's disease (AD) and related animal models, and the concentration of these cells clustered around Aβ deposits is several folds higher than in neighboring areas of the brain [1-5]. Microglial cells phagocytose and clear debris, pathogens, and toxins, but they can also be activated to produce inflammatory cytokines, chemokines, and neurotoxins [6]. Over the past decade, the roles of microglial cells in AD have begun to be clarified, and we proposed that these cells play a dichotomous role in the pathogenesis of AD [4, 6-11]. Microglial cells are able to clear soluble and fibrillar Aβ, but continued interactions of these cells with Aβ can lead to an inflammatory response resulting in neurotoxicity. Inflammasomes are inducible high molecular weight protein complexes that are involved in many inflammatory pathological processes. Recently, Aβ was found to activate the NLRP3 inflammasome in microglial cells in vitro and in vivo thereby defining a novel pathway that could lead to progression of AD [12-14]. In this manuscript, we review possible steps leading to Aβ-induced inflammasome activation and discuss how this could contribute to the pathogenesis of AD.

α1-antitrypsin modulates microglial-mediated neuroinflammation and protects microglial cells from amyloid-β-induced toxicity

Background

One hallmark of Alzheimer disease is microglial activation. Therapeutic approaches for this neurodegenerative disease include the modulation of microglial cells. α₁-antitrypsin (A1AT) has been shown to exert anti-inflammatory effects on macrophages and lung epithelial cells and an inhibition of calpain activity in neutrophil granulocytes. Nothing is known about the effect of A1AT on microglial-mediated neuroinflammation. Our aim was to investigate the effect of A1AT on amyloid-β (Aβ)- and LPS-treated microglial cells in vitro with respect to cytokine production, stress pathways, cell viability, phagocytotic abilities and the underlying mechanisms.

Methods

Primary microglial cells were isolated from Swiss Webster mouse embryos on embryonic day 13.5. Cytokines in the supernatants of treated primary microglial cells were analyzed with ELISAs, and accumulated nitrite was detected with Griess reagents. Intracellular stress pathways were investigated in cell lysates using western blotting. Intracellular calcium levels were detected in BV-2 microglial cells loaded with the Ca²⁺-sensitive (fluorescent) dye Fluo-4. Calpain activity in primary microglial cells was assessed by using a calpain activity assay. Cell viability of Aβ-treated microglial cells was analyzed using MTT assay. Phagocytosis of Aβ was evaluated with western blot analysis.

Results

Upon co-administration, A1AT reduced pro-inflammatory mediators induced by LPS or Aβ. Interestingly, we detected a reduction in calpain activity and in the concentration of intracellular calcium that might mediate the anti-inflammatory effects of A1AT. Inhibition of the classic activation pathways, such as phosphorylation of mitogen-activated protein kinases or activation of protein kinase A were excluded as a mechanism of A1AT-mediated effects. In addition, A1AT increased the viability of Aβ-treated microglial cells and reduced Aβ phagocytosis.

Conclusions

We provide evidence on the mechanism of action of A1AT on microglial-mediated neuroinflammation in vitro. Our in vitro data indicate that A1AT treatment modulates microglial cells in inflammatory conditions and that this modulation is due to an inhibition of calpain activity and intracellular calcium levels. The underlying mechanisms of the effects observed here are promising for future therapeutic strategies and should thus be further pursued in transgenic mouse models of Alzheimer disease.

Effects of carvedilol treatment on cardiac cAMP response element binding protein expression and phosphorylation in acute coxsackievirus B3-induced myocarditis

Background

The role of β-adrenergic stimulation on viral myocarditis has been investigated in animal models of viral myocarditis. Excess stimulation of β-adrenergic receptors by catecholamines causes phosphorylation/activation of cAMP response element binding protein (CREB) by the cAMP signaling pathway. CREB as an important regulator of gene expression mediates the cardiovascular remodeling process and promotes anti-inflammatory immune responses. However, the CREB expression and phosphorylation have not been studied, and the effects of carvedilol (a nonselective β-adrenoceptor antagonist) on the CREB has not been investigated in the setting of acute viral myocarditis.

Methods

This study was therefore designed to examine the effects of carvedilol on the transcriptional factor CREB in a murine model of acute viral myocarditis. In a coxsackievirus B3 murine myocarditis model (Balb/c), effects of carvedilol on plasma noradrenaline, heart rate and blood pressure, myocardial histopathological changes and fibrosis, cardiomyocyte apoptosis, cardiac CREB and phosphorylated CREB, cytokine levels, and viral RNA were studied.

Results

The expression and phosphorylation of CREB were decreased with concomitant increase of IL-6 and TNF-α in murine coxsackievirus-induced acute viral myocarditis. The levels of IL-6 and TNF-α were correlated with the expression of CREB or phosphorylated CREB. Carvedilol increased the cardiac CREB expression and phosphorylation and decreased the plasma catecholamine levels and the production of IL-6 and TNF-α with amelioration of acute viral myocarditis.

Conclusion

These results show that CREB may be involved in the pathophysiology of viral myocarditis and carvedilol exerts some of its beneficial effects by increasing the CREB expression and phosphorylation.

Bradykinin decreases nitric oxide release from microglia via inhibition of cyclic adenosine monophosphate signaling

Bradykinin (BK) is a major potent inflammatory mediator outside the central nervous system. In Alzheimer's disease, BK release and BK receptor expression in brain tissues are upregulated relatively early during the course of the disease. Hence, BK was believed to promote neuroinflammation. However, BK was recently reported to possess anti-inflammatory and neuroprotective roles. Exposure of BV2 microglial cell line to BK lead to a decrease in NO release from unstimulated cells as well as a dose-dependent attenuation, mediated by both B1 and B2 receptors, in lipopolysaccharide (LPS)-induced NO production. In this study we examined whether cyclic adenosine monophosphate (cAMP) signaling is involved in BK-mediated effect in microglial nitric oxide (NO) production. A protein kinase A (PKA) inhibitor mimicked the effects of BK, while cAMP elevating agents antagonized BK-mediated NO decrease. Moreover, BK inhibited the activation of cAMP responsive element binding protein (CREB). In addition, BK protected microglial cells from death triggered by combinations of LPS and each of the cAMP elevating agents. Finally, the addition of Gαi protein inhibitor abrogated the effects of BK on NO release, and the expression of Gαi protein in the plasma membrane was induced by BK. These results suggest that BK-mediated reduction in microglial NO production depends on coupling to Gi protein and also involves inhibition of cAMP-PKA-CREB signaling.

Antinociceptive interaction of (±)-CPP and propentofylline in monoarthritic rats

Introduction

Multiple studies have shown that glial cells of the spinal cord, such as astrocytes and microglia, have close contact with neurons, suggesting the term tripartite synapse. In these synapses, astrocytes surrounding neurons contribute to neuronal excitability and synaptic transmission, thereby increasing nociception and thus the persistence of chronic pain. Conversely, the N-methyl-D-aspartate (NMDA) receptor is crucial in the generation and maintenance of chronic pain. It has multiple sites of modulation. One is the site of recognition of extracellular neurotransmitter (glutamate), which can be blocked by competitive antagonists such as (3-(2-carboxipiperazin-4)1-propyl phosphonic acid), (±)-CPP, resulting in a blockade of the calcium current and thus the intracellular transduction process. In the present study, we investigated whether the potential antinociceptive effect of glial inhibition produced by propentofylline (PPF) can be enhanced when combined with an NMDA-receptor inhibitor such as (±)-CPP.

Methods

We used Sprague-Dawley monoarthritic rats. The monoarthritis was induced by injection of complete Freund adjuvant in the right tibiotarsal joint. Four weeks later, rats were treated with PPF (1, 10, 30, and 100 μg/10 μl) intrathecally (i.t.) for 10 days, injected once with (±)-CPP (2.5, 5, 12.5, 25, 50, and 100 μg/10 μl, i.t.), or both treatments combined. The antinociceptive effect was evaluated on day 11 for PPF and immediately to (±)-CPP, by assessing the vocalization threshold to mechanical stimulation of the arthritic paw.

Results

The data indicate that intrathecal administration of increasing concentrations of (±)-CPP or PPF produced a significant dose-dependent antinociceptive effect with respect to monoarthritic rats receiving saline. The linear regression analysis showed that the dose that produces 30% of maximal effect (ED₃₀) for i.t. (±)-CPP was 3.97 μg, and 1.42 μg for i.t. PPF. The administration of the PPF and (±)-CPP combination in fixed proportions of ED₃₀ produced a dose-dependent antinociceptive effect, showing an interaction of the supraadditive type.

Conclusions

The results suggest that glia inhibitors can synergically potentiate the effect of glutamate blockers for the treatment of chronic inflammatory pain.

Cilostazol protects mice against endotoxin shock and attenuates LPS-induced cytokine expression in RAW 264.7 macrophages via MAPK inhibition and NF-kappaB inactivation: not involved in cAMP mechanisms

Cilostazol, a phosphodiesterase 3 inhibitor, is a platelet aggregation inhibitor and vasodilator that is useful for treating intermittent claudication. Experimental studies have shown that cilostazol has potent anti-inflammatory effects. In the present study, we examined the effect of cilostazol on lipopolysaccharide (LPS)-induced inflammatory cytokines in macrophages and endotoxin shock in mice. Our results indicate that cilostazol inhibits LPS-stimulated up-regulation of pro-inflammatory cytokines in a concentration-dependent manner without appreciable cytotoxicity in RAW 264.7 cells. Cilostazol did not enhance intracellular cyclic AMP (cAMP) levels. To further elucidate the mechanism responsible for the inhibition of production of pro-inflammatory mediators by cilostazol, we examined the effect of cilostazol on LPS-stimulated nuclear factor-kappaB (NF-kappaB) activation and phosphorylation of mitogen-activated protein kinases (MAPK). Our results clearly indicated that cilostazol treatment reduced on of MAPK phosphorylation and NF-kappaB activity, and that the inhibitory effect of cilostazol is independent of the cAMP pathway. In an animal model, cilostazol protected c57BL/6 mice from LPS-induced endotoxin shock, possibly through inhibition of the production of pro-inflammatory cytokines. In conclusion, cilostazol inhibits LPS-stimulated production of pro-inflammatory cytokines and protects mice from endotoxin shock, suggesting that cilostazol may be a novel therapeutic agent for the prevention of various inflammatory diseases.

Lipopolysaccharide extends the lifespan of mouse primary-cultured microglia

Microglial activation has been implicated in the recognition and phagocytic removal of degenerating neurons; however, this process must be tightly regulated in the central nervous system, because prolonged activation could damage normal neurons. We report that mouse primary-cultured microglia, which are destined to die within a few days under ordinary culture conditions, can live for more than 1 month when kept activated by lipopolysaccharide (LPS) treatment. Primary-cultured microglia treated with sublethal doses of LPS remained viable, without any measurable increase in apoptotic or necrotic cell death. LPS-treated microglia had an arborescent shape, with enlarged somata and thickened cell bodies. Although the amount of intracellular ATP in these microglia was reduced by 2 h after the start of LPS treatment, this had no effect on the viability of the cells. LPS treatment of microglia increased the antiapoptotic factor Bcl-xL protein level at day 1, although the level of the proapoptotic Bcl-associated X-protein was unaffected. Furthermore, the level of microtubule-associated light chain 3, a marker protein for autophagy, decreased at 3 h after exposure to LPS. These data show that the optimal dose of LPS suppresses the induction of both apoptosis and autophagy in primary-cultured microglia, allowing the cells to stay alive for more than 1 month. Because long-lived microglia may play critical roles in the exacerbation of neurodegeneration, our findings suggest that inducing a resting stage in active microglia could be a new and promising strategy to inhibit the deterioration of neurodegenerative disease.

Manganese potentiates nuclear factor-kappaB-dependent expression of nitric oxide synthase 2 in astrocytes by activating soluble guanylate cyclase and extracellular responsive kinase signaling pathways

Inflammatory activation of glial cells is associated with neuronal injury in several degenerative movement disorders of the basal ganglia, including manganese neurotoxicity. Manganese (Mn) potentiates the effects of inflammatory cytokines on nuclear factor-kappaB (NF-kappaB)-dependent expression of nitric oxide synthase 2 (NOS2) in astrocytes, but the signaling mechanisms underlying this effect have remained elusive. It was postulated in the present studies that direct stimulation of cGMP synthesis and activation of mitogen-activated protein (MAP) kinase signaling pathways underlies the capacity of Mn to augment NF-kappaB-dependent gene expression in astrocytes. Exposure of primary cortical astrocytes to a low concentration of Mn (10 microM) potentiated expression of NOS2 mRNA and protein along with production of NO in response to interferon-gamma (IFNgamma) and tumor necrosis factor-alpha (TNFalpha), which was prevented by overexpression of dominant negative IkappaB alpha. Mn also potentiated IFNgamma- and TNFalpha-induced phosphorylation of extracellular response kinase (ERK), p38, and JNK, as well as cytokine-induced activation of a fluorescent NF-kappaB reporter construct in transgenic astrocytes. Activation of ERK preceded that of NF-kappaB and was required for maximal activation of NO synthesis. Independently of IFNgamma/TNFalpha, Mn-stimulated synthesis of cGMP in astrocytes and inhibition of soluble guanylate cyclase (sGC) abolished the potentiating effect of Mn on MAP kinase phosphorylation, NF-kappaB activation, and production of NO. These data indicate that near-physiological concentrations of Mn potentiate cytokine-induced expression of NOS2 and production of NO in astrocytes via activation of sGC, which promotes ERK-dependent enhancement of NF-kappaB signaling.

The peroxisome proliferator-activated receptor-gamma agonist 1,1-bis(3'-indolyl)-1-(p-trifluoromethylphenyl)methane suppresses manganese-induced production of nitric oxide in astrocytes and inhibits apoptosis in cocultured PC12 cells

Reactive astrogliosis is a prominent neuropathologic feature of manganism, a neurodegenerative disorder caused by excessive accumulation of manganese (Mn) in the basal ganglia. Activation of astrocytes has been linked to neuronal injury in manganism resulting from overproduction of inflammatory mediators, including tumor necrosis factor-alpha (TNFalpha), interferon-gamma (IFNgamma), interleukin-1beta (IL-1beta), and nitric oxide (NO), but the signaling mechanisms by which Mn regulates these factors remain poorly understood. We previously reported that Mn enhances production of NO in activated astrocytes that promotes apoptosis in cocultured neuronal cells by a mechanism involving the transcription factor nuclear factor-kappaB (NF-kappaB) (Liu et al., 2005). Because NF-kappaB-dependent expression of inducible nitric oxide synthase (NOS2) can be antagonized by the nuclear orphan receptor peroxisome proliferator-activated receptor-gamma (PPARgamma), we postulated that a novel agonist of this receptor, 1,1-bis(3'-indolyl)-1-(p-trifluoromethylphenyl)methane (cDIM1), would suppress expression of NOS2 in astrocytes and protect cocultured neuronal cells from apoptosis. Submicromolar concentrations of cDIM1 potently suppressed production of NO and expression of NOS2 in cultured astrocytes exposed to Mn and IFNgamma/TNFalpha and prevented apoptosis in cocultures of differentiated PC12 cells, but this neuroprotective effect was lost in the absence of astrocytes. By using fluorescence reporter and chromatin immunoprecipitation (ChIP) assays, we found that cDIM1 prevented activation of NF-kappaB in astrocytes by a mechanism involving stabilization of the nuclear corepressor 2 (NCoR2) on the proximal NF-kappaB binding site of the NOS2 promoter. These data suggest that PPARgamma may be an effective target for limiting inflammatory activation of astrocytes during neurologic injury.

Modulation of the cAMP signaling pathway after traumatic brain injury

Traumatic brain injury (TBI) results in both focal and diffuse brain pathologies that are exacerbated by the inflammatory response and progress from hours to days after the initial injury. Using a clinically relevant model of TBI, the parasagittal fluid-percussion brain injury (FPI) model, we found injury-induced impairments in the cyclic AMP (cAMP) signaling pathway. Levels of cAMP were depressed in the ipsilateral parietal cortex and hippocampus, as well as activation of its downstream target, protein kinase A, from 15 min to 48 h after moderate FPI. To determine if preventing hydrolysis of cAMP by administration of a phosphodiesterase (PDE) IV inhibitor would improve outcome after TBI, we treated animals intraperitoneally with rolipram (0.3 or 3.0 mg/kg) 30 min prior to TBI, and then once per day for 3 days. Rolipram treatment restored cAMP to sham levels and significantly reduced cortical contusion volume and improved neuronal cell survival in the parietal cortex and CA3 region of the hippocampus. Traumatic axonal injury, characterized by beta-amyloid precursor protein deposits in the external capsule, was also significantly reduced in rolipram-treated animals. Furthermore, levels of the pro-inflammatory cytokines, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), were significantly decreased with rolipram treatment. These results demonstrate that the cAMP-PKA signaling cascade is downregulated after TBI, and that treatment with a PDE IV inhibitor improves histopathological outcome and decreases inflammation after TBI.

Endogenous alpha2-adrenergic receptor-mediated neuroprotection after severe hypoxia in preterm fetal sheep

Central alpha-adrenergic receptor activity is important for fetal adaptation to hypoxia before birth. It is unclear whether it is also important during recovery. We therefore tested the hypothesis that an infusion of the specific alpha(2)-adrenergic receptor antagonist idazoxan (1 mg/kg/h i.v.) from 15 min to 4 h after profound hypoxia induced by 25 min umbilical cord occlusion in fetal sheep at 70% of gestation (equivalent to the 28-32 weeks in humans) would increase neural injury. After 3 days' recovery, idazoxan infusion was associated with a significant increase in neuronal loss in the hippocampus (P<0.05), expression of cleaved caspase-3 (P<0.05), and numbers of activated microglia (P<0.05). There was no significant effect on other neuronal regions or on loss of O4-positive premyelinating oligodendrocytes in the subcortical white matter. Idazoxan was associated with an increase in evolving epileptiform electroencephalographic (EEG) transient activity after occlusion (difference at peak 2.5+/-1.0 vs. 11.7+/-4.7 counts/min, P<0.05) and significantly reduced average spectral edge frequency, but not EEG intensity, from 54 until 72 h after occlusion (P<0.05). Hippocampal neuronal loss was correlated with total numbers of epileptiform transients during idazoxan infusion (P<0.01; r(2)=0.7). In conclusion, endogenous inhibitory alpha(2)-adrenergic receptor activation after severe hypoxia appears to significantly limit evolving hippocampal damage in the immature brain.

Enhanced ERK dependent CREB activation reduces apoptosis in staurosporine-treated human neuroblastoma SK-N-BE(2)C cells

Activation of cAMP response element binding protein (CREB) is implicated in neuronal survival. The mitogen-activated protein kinase/extracellular signal regulated kinase (MAPK/ERK) activates a transcription factor CREB. Previously, we reported that N-acetyl-O-methyldopamine (NAMDA) protects neurons from ischemia via enhancing ERK dependent CREB phosphorylation. To investigate whether NAMDA induces endogenous survival pathways in apoptotic conditions and whether the neuroprotectant enhances a preexisting survival pathway, we determined the degree of ERK-CREB activation and resistance to apoptosis in staurosporine-treated SK-N-BE(2)C neurons. Compared to forskolin-treated apoptotic cultures, NAMDA-treated cultures induced a minimum activation on ERK (pERK) or CREB (pCREB). However, NAMDA enhanced the activation of ERK and CREB in the presence of forskolin (1.7-fold increase for pCREB, 2.1-fold increase for pERK2, p<0.05 from forskolin). The effect was completely blocked by a specific MEK inhibitor U0126, suggesting the involvement of ERK dependent CREB signaling. Cleavage of caspase-3 and poly-(ADP-ribose)-polymerase was additively reduced in cultures treated with NAMDA and forskolin simultaneously, but not in the presence of U0126. The data showed that NAMDA enhances forskolin-induced ERK-CREB activation and potentiates forskolin-induced resistance to apoptosis. The study indicates that enhancing endogenous survival pathways by NAMDA combined with other neuroprotective measure(s) might be a useful strategy to reduce apoptosis.

Fluoxetine increases the nitric oxide production via nuclear factor kappa B-mediated pathway in BV2 murine microglial cells

A body of recent evidence implicates that antidepressants affect the inflammatory response and immune system. The present study is focused on the effects of the most widely used antidepressant agent, fluoxetine on the production of nitric oxide (NO) in BV2 microglial cells. In this study, we observed interesting result that NO production was increased by fluoxetine. The mRNA level of nitric oxide synthase (iNos, Nos2) by RT-PCR was also stimulated by fluoxetine. We next conducted electophoretic mobility shift assay (EMSA) to determine the DNA binding activity of nuclear factor kappa B (Nfkappab), an important upstream modulator for Nos2 expression, to find that fluoxetine increased DNA binding activity of Nfkappab. By Western blot analysis, phosphorylation levels of p38 mitogen-activated protein kinase (p38 Mapk, Mapk14) and extracellular signal-related kinase (Erk)1/2 Mapk, upstream signaling mediators of Nfkappab were found to be increased by fluoxetine. In addition, the mRNA expressions of other proinflammatory cytokines, interleukin 6 (Il6) and tumor necrosis factor alpha (Tnfalpha) were examined. The expressions of both Il6 and Tnfalpha by fluoxetine treatment were similar to those of Nos2 and Nfkappab. Taken together, our results show that fluoxetine stimulates NO production via Nfkappab-mediated pathway in BV2 cells.

15,16-dihydrotanshinone I suppresses the activation of BV-2 cell, a murine microglia cell line, by lipopolysaccharide

Microglial activation has been implicated in neurodegenerative diseases. Therefore, inhibition of inflammation mediated by microglia is a strategy in neurodegenerative disease therapy. In this study, we isolated cryptotanshinone and 15,16-dihydrotanshinone I from Salvia miltiorrhiza, a traditional Korean herb medicine, by bioactivity-guided fractionation based on inhibitory effect on nitric oxide in a lipopolysaccharide-stimulated BV-2 cells, a murine microglial cell line. 15,16-Dihydotanshinoe I suppressed the expression of not only inducible nitric oxide synthase but also of interleukin-1beta, tumor necrosis factor-alpha, and of TNF-alpha converting enzyme.

Inhibition of iNOS gene expression by quercetin is mediated by the inhibition of IkappaB kinase, nuclear factor-kappa B and STAT1, and depends on heme oxygenase-1 induction in mouse BV-2 microglia

In the present study, experiments were performed to explore the action of quercetin, the most widely distributed flavonoids, and its major metabolite, quercetin-3'-sulfate, on lipopolysaccharide (LPS)- and interferon-gamma (IFN-gamma)-induced nitric oxide (NO) production in BV-2 microglia. Quercetin could suppress LPS- and IFN-gamma-induced NO production and inducible nitric oxide synthase (iNOS) gene transcription, while quercetin-3'-sulfate had no effect. LPS-induced IkappaB kinase (IKK), nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1) activation, and IFN-gamma-induced NF-kappaB, signal transducer and activator of transcription-1 (STAT1) and interferon regulatory factor-1 (IRF-1) activation were reduced by quercetin. Moreover quercetin was able to induce heme oxygenase-1 expression. To address the involvement of heme oxygenase-1 induction in iNOS inhibition, heme oxygenase-1 antisense oligodeoxynucleotide was used. Quercetin-mediated inhibition of NO production and iNOS protein expression were partially reversed by heme oxygenase-1 antisense oligodeoxynucleotide, but was mimicked by hemin, a heme oxygenase-1 inducer. The involvement of signal pathways in quercetin-induced heme oxygenase-1 gene expression was associated with tyrosine kinase and mitogen-activated protein kinases activation. All these results suggest quercetin should provide therapeutic benefits for suppression of inflammatory-related neuronal injury in neurodegenerative diseases.

Syntheses of NAMDA derivatives inhibiting NO production in BV-2 cells stimulated with lipopolysaccharide

Sixteen derivatives of N-acetyl-3-O-methyldopamine (NAMDA), an inhibitor of BH4 synthesis, were designed and synthesized. The ability of these derivatives to inhibit NO and BH4 production by lipopolysaccharide-stimulated BV-2 microglial cells was determined. While NAMDA at 100 microM inhibited NO and BH4 production by only about 20%, its catecholamide 8, indole 23 derivative, 13, and N-acetyl tetrahydroisoquinoline 25 inhibited the NO production by >50% at the same concentration. In particular, 13 and 25 inhibited both NO and BH4 production to similar degrees, which suggested that these compounds might inhibit NO production by blocking BH4-dependent dimerization of the newly synthesized iNOS monomer.

Peripheral injection of lipopolysaccharide enhances expression of inflammatory cytokines in murine locus coeruleus: possible role of increased norepinephrine turnover

Cytokines and catecholamines are known to constitute a significant portion of the regulatory neuroimmune networks involved in maintaining homeostasis in the central nervous system (CNS). Although we have already reported an increase in norepinephrine (NE) turnover within the locus coeruleus (LC) at 2 and 4 h after the intraperitoneal (i.p.) injection of lipopolysaccharide (LPS), the implication of this increase remains unclear. In view of evidence that norepinephrine (NE) acts in an anti-inflammatory manner by way of negatively regulating pro-inflammatory cytokine expression, we examined the inflammatory cytokine expression levels in the LC of C3H/HeN mice (male, 8 weeks old) after an i.p. LPS injection. The mRNA expression levels of the genes encoding IL-1beta and TNF-alpha within the LC increased during the first 2 h, and showed two peaks, the first at 4 h and the second lesser one at 15 h after the LPS injection. Microglia, which are one of the major cell types that produce pro-inflammatory cytokines in the CNS, were isolated from mouse neonate brains in order to clarify more precisely the relationship between the changes in NE content and the up-regulation of inflammatory cytokines in the LC. Simultaneous incubation of microglia with LPS and NE enhanced the expression of IL-1beta at both mRNA and protein levels, but reduced the mRNA and protein levels of TNF-alpha. These data support the hypothesis that NE negatively regulates the expression of pro-inflammatory cytokine expression, at least in the case of TNF-alpha, which action could contribute to the observed anti-inflammatory properties of NE. This report, based on the results of both in vivo and in vitro experiments, is the first to suggest a relationship between NE content and cytokine expression levels in the CNS.

CREB Gene Transcription Factors: Role in Molecular Mechanisms of Alcohol and Drug Addiction

This article presents the proceedings of a symposium presented at the meeting of the Research Society on Alcoholism, held in Vancouver, British Columbia, Canada, in June 2004. The organizers and chairpersons were Subhash C. Pandey and Fulton Crews. The presentations were (1) Ethanol Modulation of CREB: Role in Dependence and Withdrawal, by Fulton Crews; (2) Effects of D1 Dopamine Receptor Activation During Withdrawal From Chronic Morphine: Enhanced CREB Activation and Decreased Conditioned Place Aversion, by Elena H. Chartoff; (3) CREB-Haplodeficient Mice: Role in Anxiety and Alcohol-Drinking Behaviors, by Subhash C. Pandey; and (4) A Role for CREB in Stress and Drug Addiction, by Julie A. Blendy.

A new anti-inflammatory agent KL-1037 represses proinflammatory cytokine and inducible nitric oxide synthase (iNOS) gene expression in activated microglia

Excessive proinflammatory cytokine and NO production by activated microglia play a role in neurodegenerative disorders. In this study, we found that a new compound KL-1037 suppressed LPS-induced NO release/inducible nitric oxide synthase expression in BV2 mouse microglial cells. In addition, KL-1037 prominently diminished LPS-induced production of pro-inflammatory cytokines such as TNF-alpha, IL-1 beta and IL-6, while it increased anti-inflammatory IL-10 and TGF-beta 1 production. By RNase protection assay and RT-PCR, we showed that KL-1037 regulated iNOS and cytokines at transcriptional or post-transcriptional level. Further analysis of molecular mechanisms revealed that KL-1037 prominently increased intracellular cAMP levels and potentiated LPS-induced pCREB expression. However, LPS-induced MAP kinase or NF-kappa B activities were slightly or little changed by KL-1037. Treatment with cAMP antagonist or IL-10 neutralizing antibody completely reversed upregulation of IL-10 and partially repression of TNF-alpha or NO induced by KL-1037. These data suggest that microglial inactivation by KL-1037 is at least in part due to activation of PKA pathway and/or upregulation of IL-10. Thus, repressing proinflammatory cytokines and iNOS gene expression in activated microglia by KL-1037 may provide potential therapeutic strategies for various neurodegenerative diseases including ischemic cerebral disease.

Inhibition of lipopolysaccharide-induced inducible nitric oxide synthase expression by a novel compound, mercaptopyrazine, through suppression of nuclear factor-kappaB binding to DNA

Macrophage cells in response to cytokines and endotoxins produced a large amount of nitric oxide (NO) by expression of inducible nitric oxide synthase (iNOS), resulting in acute or chronic inflammatory disorders including septic hypotension and atherosclerosis. In the present study, we investigated the effect and the mechanism of mercaptopyrazine (MP) in the induction of iNOS and NO production as a culminating factor for several inflammatory disorders. Pretreatment of MP alleviated the mortality of endotoxemic mice receiving a lethal bolus of lipopolysaccharide (LPS), which was associated with the reduced levels of serum nitrite/nitrate and IL-1beta. In RAW264.7 mouse macrophage cells, MP (300microM) inhibited both protein and mRNA levels of iNOS stimulated by LPS/interferon-gamma (IFNgamma) up to 50%. The nuclear factor-kappa B (NF-kappaB)-driven transactivation was also suppressed by MP to the same degree. Treatment of MP reduced the binding of NF-kappaB to the oligonucleotides containing NF-kappaB consensus sequence, while it did not affect the translocation of NF-kappaB to nuclear. Suppression of NF-kappaB activity by MP was completely reversed by a reducing agent, dithiothreitol, implying that MP might oxidize the sulfhydryl group(s) of DNA binding domain of NF-kappaB. In conclusion, MP would be one of interesting candidates or chemical moieties of iNOS expression inhibitor via specific suppression of NF-kappaB binding to DNA, and be useful as a chemopreventive agent or a therapeutic against iNOS-associated inflammatory diseases.

Inhibition of microglial inflammatory responses by norepinephrine: effects on nitric oxide and interleukin-1beta production

BACKGROUND: Under pathological conditions, microglia produce proinflammatory mediators which contribute to neurologic damage, and whose levels can be modulated by endogenous factors including neurotransmitters such as norepinephrine (NE). We investigated the ability of NE to suppress microglial activation, in particular its effects on induction and activity of the inducible form of nitric oxide synthase (NOS2) and the possible role that IL-1beta plays in that response. METHODS: Rat cortical microglia were stimulated with bacterial lipopolysaccharide (LPS) to induce NOS2 expression (assessed by nitrite and nitrate accumulation, NO production, and NOS2 mRNA levels) and IL-1beta release (assessed by ELISA). Effects of NE were examined by co-incubating cells with different concentrations of NE, adrenergic receptor agonists and antagonists, cAMP analogs, and protein kinase (PK) A and adenylate cyclase (AC) inhibitors. Effects on the NFkappaB:IkappaB pathway were examined by using selective a NFkappaB inhibitor and measuring IkappaBalpha protein levels by western blots. A role for IL-1beta in NOS2 induction was tested by examining effects of caspase-1 inhibitors and using caspase-1 deficient cells. RESULTS: LPS caused a time-dependent increase in NOS2 mRNA levels and NO production; which was blocked by a selective NFkappaB inhibitor. NE dose-dependently reduced NOS2 expression and NO generation, via activation of beta2-adrenergic receptors (beta2-ARs), and reduced loss of inhibitory IkBalpha protein. NE effects were replicated by dibutyryl-cyclic AMP. However, co-incubation with either PKA or AC inhibitors did not reverse suppressive effects of NE, but instead reduced nitrite production. A role for IL-1beta was suggested since NE potently blocked microglial IL-1beta production. However, incubation with a caspase-1 inhibitor, which reduced IL-1beta levels, had no effect on NO production; incubation with IL-receptor antagonist had biphasic effects on nitrite production; and NE inhibited nitrite production in caspase-1 deficient microglia. CONCLUSIONS: NE reduces microglial NOS2 expression and IL-1beta production, however IL-1beta does not play a critical role in NOS2 induction nor in mediating NE suppressive effects. Changes in magnitude or kinetics of cAMP may modulate NOS2 induction as well as suppression by NE. These results suggest that dysregulation of the central cathecolaminergic system may contribute to detrimental inflammatory responses and brain damage in neurological disease or trauma.

Suppression of proinflammatory cytokines interleukin-1beta and tumor necrosis factor-alpha in astrocytes by a V1 vasopressin receptor agonist: a cAMP response element-binding protein-dependent mechanism

Previous research from our laboratory has demonstrated that V1 vasopressin receptor agonist (V1 agonist) induces a complex intracellular Ca2+-signaling cascade in cortical astrocytes that is initiated by G-protein-coupled V1a vasopressin receptor-mediated cytoplasmic and nuclear Ca2+ rise and converges during activation of the nuclear transcription factor cAMP response element-binding protein (CREB). In the current study, we pursued the downstream functional consequences of V1 agonist-induced Ca2+-signaling cascade for gene expression. Because astrocytes can exert immune effects analogous to immune cells in the periphery, we investigated V1 agonist regulation of cytokine gene expression in astrocytes. Results from gene array studies indicated that V1 agonist dramatically decreased the mRNA level of five cytokines. Two prominent proinflammatory cytokines, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), were selected for detailed analysis, and their expression was also confirmed with reverse transcriptase-PCR. Furthermore, ELISA analyses demonstrated that the peptide level of IL-1beta and TNF-alpha in the astrocyte medium was also decreased in response to V1 agonist. Using CREB antisense to determine the causal relationship between V1 agonist-induced CREB activation and suppression of IL-1beta and TNF-alpha, we demonstrated that decreased IL-1beta and TNF-alpha gene expression was dependent on upstream CREB activation. V1 agonist-induced decrease of cytokine release from cortical astrocytes was also shown to be neuroprotective in cortical neurons. To our knowledge, this is the first documentation of V1 agonist modulation of cytokine gene expression in any cell type. Implications for vasopressin as an antipyretic agent and the role of vasopressin in neurodegeneration, autoimmune diseases, stress, and neuropsychiatric behaviors are discussed.

Intrinsic regulation of brain inflammatory responses

It is now well accepted that inflammatory responses in brain contribute to the genesis and evolution of damage in neurological diseases, trauma, and infection. Inflammatory mediators including cytokines, cell adhesion molecules, and reactive oxygen species including NO are detected in human brain and its animal models, and interventions that reduce levels or expression of these agents provide therapeutic benefit in many cases. Although in some cases, the causes of central inflammatory responses are clear--for example those due to viral infection in AIDS dementia, or those due to the secretion of proinflammatory substances by activated lymphocytes in multiple sclerosis--in other conditions the factors that allow the initiation of brain inflammation are not well understood; nor is it well known why brain inflammatory activation is not as well restricted as it is in the periphery. The concept is emerging that perturbation of endogenous regulatory mechanisms could be an important factor for initiation, maintenance, and lack of resolution of brain inflammation. Conversely, activation of intrinsic regulatory neuronal pathways could provide protection in neuroinflammatory conditions. This concept is the extension of the principle of "central neurogenic neuroprotection" formulated by Donald Reis and colleagues, which contends the existence of neuronal circuits that protect the brain against the damage initiated by excitotoxic injury. In this paper we will review work initiated in the Reis laboratory establishing that activation of endogenous neural circuits can exert anti-inflammatory actions in brain, present data suggesting that these effects could be mediated by noradrenaline, and summarize recent studies suggesting that loss of noradrenergic locus ceruleus neurons contributes to inflammatory activation in Alzheimer's disease.

Neurodegeneration of substantia nigra accompanied with macrophage/microglia infiltration after intrastriatal hemorrhage

Intrastriatal hemorrhage in rats causes neurodegenaration of the substantia nigra (SN) followed by the appearance of ED1(+) cells (macrophage/microglia). ED1(+) cells were observed for at least 8 weeks after hemorrhage. Phosphorylation of p38 mitogen-activated protein kinase (MAPK) was shown in ED1(+) cells with the expression of both brain-derived neurotrophic factor (BDNF) mRNA and BDNF, suggesting that activated-p38 MAPK(+)/ED1(+) cells would produce BDNF and may exhibit trophic effect on the degenerating neurons in the SN. However, in ELISA, BDNF protein decreased significantly in ipsilateral SN at 7 days after hemorrhage, which may be due to a dramatic decrease of BDNF immunoreactive neurons in pars compacta. Data suggest that activation of p38 MAPK in ED1(+) cells infiltrating in ipsilateral SN after hemorrhage may produce BDNF, but that the amount of BDNF produced from ED1(+) cells is insufficient for the rescue of degenerating neurons.

Selective modulation of lipopolysaccharide-stimulated cytokine expression and mitogen-activated protein kinase pathways by dibutyryl-cAMP in BV2 microglial cells

Cyclic AMP is a very important regulator in a wide range of biological processes, including inflammatory reactions. To investigate the role of cAMP in microglia, we examined the effect of dibutyryl-cAMP (dbcAMP) on lipopolysaccharide (LPS)-stimulated cytokine expression and signaling pathways in murine BV2 microglial cells. DbcAMP strongly suppressed LPS-induced TNF-alpha expression, without affecting NO, IL-6 or TGF-beta1 expression. In contrast, LPS-induced IL-1beta or IL-10 expressions were dramatically increased by dbcAMP. We further examined the effect of elevated cAMP on signaling molecules such as MAP kinases (p38 MAPK, ERK and JNK), NF-kappaB and AP1, which are involved in the regulation of inflammatory responses. DbcAMP decreased the LPS-induced phosphorylation of p38 MAPK, while it modestly enhanced the ERK activity. JNK phosphorylation was slightly reduced by dbcAMP only at the later time point. Electrophoretic mobility shift assay revealed that the elevated cAMP potentiated AP-1 binding activity by enhancing c-fos binding. On the other hand, dbcAMP repressed NF-kappaB-mediated transcription without affecting NF-kappaB binding. Treatment with H89, a selective inhibitor of protein kinase A, completely reversed cAMP-induced IL-10 and IL-1beta upregulation but only partially reversed the cAMP-induced repression of TNF-alpha. Thus, the effect of dbcAMP in BV2 cells appears to be mediated through both protein kinase A-dependent and -independent pathways. Taken together, our results demonstrate that cAMP modulates microglia activation in a diverse and complex manner.

Temporal and sequential analysis of microglia in the substantia nigra following medial forebrain bundle axotomy in rat

Dopaminergic neurons in the substantia nigra pars compacta undergo apoptosis after transection of the medial forebrain bundle. We have assessed the temporal and sequential activities of microglia in these events by examining the complement-3 (OX-42), major histocompatibility complex class II antigen presentation (OX-6) and phagocytic activity (ED1), and correlating these indicators with dopaminergic neuronal loss. Microglia in the ipsilateral substantia nigra pars reticulata evinced activation morphology at 12 h postaxotomy. Phagocytic microglia apposed dying dopaminergic neurons in the pars compacta starting at 3 days postlesion; their number increased through 14 days and slowly decreased. Nuclear chromatin condensation and significant loss of tyrosine hydroxylase-positive dopaminergic neurons occurred around 7 days postlesion. In contrast to microglial expression of interleukin-1beta and inducible nitric oxide synthase at the axotomy site, nigral microglia were interleukin-1beta and inducible nitric oxide synthase-negative. Consistently, RNase protection assays showed that interleukin-1beta and inducible nitric oxide synthase transcripts in nigra were equivocal. The present data support the idea that phagocytosis of axotomized neurons by activated microglia is not limited to dead neurons but includes dying neurons probably without cytotoxic effects of inflammatory substances, such as interleukin-1beta or nitric oxide.

Age-related microglial activation in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurodegeneration in C57BL/6 mice

Microglial activation was investigated in the brains of young (3 months old) and older (9-12 months old) mice following administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Tyrosine hydroxylase (TH)-positive neuronal loss differed significantly between young and older mice. Importantly, the two groups clearly demonstrated a distinct microglial activation pattern. In young mice which showed TH neuronal loss at 1 day (33.4%), 3 days (45.1%), 7 days (47.1%) and 14 days (46.9%), microglial activation was first observed at 1 day, with lesser activation at 3 days and none shown later than 7 days. In contrast, in older mice which showed TH neuronal loss at 1 day (49.6%), 3 days (56.1%), 7 days (71.7%) and 14 days (72.1%), microglial activation occurred at 1 day, further intensified at 3-7 days, and was largely abated by 14 days. The double immunohistochemistry further demonstrated that the activated microglia surrounded dopaminergic neurons in older mice at 7 days, which was sharply in contrast to the young mice which were devoid of massive microglial activation in the SN later than 3 days after MPTP treatment. The present study suggests that age-related microglial activation in the SN may be relevant to the higher susceptibility to MPTP neurotoxicity in older mice.

Noradrenergic regulation of inflammatory gene expression in brain

It is now well accepted that inflammatory events contribute to the pathogenesis of numerous neurological disorders, including multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease, and AID's dementia. Whereas inflammation in the periphery is subject to rapid down regulation by increases in anti-inflammatory molecules and the presence of scavenging soluble cytokine receptors, the presence of an intact blood-brain barrier may limit a similar autoregulation from occurring in brain. Mechanisms intrinsic to the brain may provide additional immunomodulatory functions, and whose dysregulation could contribute to increased inflammation in disease. The findings that noradrenaline (NA) reduces cytokine expression in microglial, astroglial, and brain endothelial cells in vitro, and that modification of the noradrenergic signaling system occurs in some brain diseases having an inflammatory component, suggests that NA could act as an endogenous immunomodulator in brain. Furthermore, accumulating studies indicate that modification of the noradrenergic signaling system occurs in some neurodiseases. In this article, we will briefly review the evidence that NA can modulate inflammatory gene expression in vitro, summarize data supporting a similar immunomodulatory role in brain, and present recent data implicating a role for NA in attenuating the cortical inflammatory response to beta amyloid protein.

Effects of TCDD upon IkappaB and IKK subunits localized in microsomes by proteomics

Biochemical studies have shown that microsomes represent an important subcellular fraction for determining 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) effects. Proteomic analysis by two-dimensional gel-mass spectrometry of liver microsomes was undertaken to gain new insight into the actions of TCDD in male and female rats. Proteomic analysis showed TCDD induced several xenobiotic metabolism enzymes as well as a protein at 90kDa identified by mass spectrometry as IkappaB kinase beta/IKK2. This observation led to the discovery of other NF-kappaB binding proteins and kinases in microsomes and effects by TCDD. Western blotting for IKK and IkappaB family members in microsomes showed a distinct pattern from cytosol. IKK1 and IKK2 were both present in microsomes and were catalytically active although, unlike cytosol, IKKgamma/NEMO was not detectable. TCDD exposure produced an elevation in cytosolic and microsomal IKK activity of both genders. The NF-kappaB binding proteins IkappaBbeta and IkappaBgamma were prevalent in microsomes, while IkappaBalpha and IkappaB epsilon proteins were absent. TCDD treatment produced hyperphosphorylation of microsomal IkappaBbeta in both sexes with females being most sensitive. In cytosol, IkappaBalpha, IkappaBbeta, and IkappaB epsilon, but not IkappaBgamma, were clearly observed but were not changed by TCDD. Overall, proteomic analysis indicated the presence of NF-kappaB pathway members in microsomes, selectively altered by dioxin, which may influence immune and inflammatory responses within the liver.

Characterization of neurotransmitters and dopamine attenuation of inducible nitric oxide synthase in glioma cells

Inducible nitric oxide synthase (iNOS) plays a significant role in the pathology of central nervous system diseases. Inducible NOS expression is regulated by intracellular adenosine 3',5'-cyclic monophosphate (cAMP) signaling, and astrocytes contain both iNOS and adenylate cyclase-coupled neurotransmitter receptors. The data obtained from the present study indicated that acetylcholine, lambda-amino-n-butyric acid, glutamate, quinolinic acid, N-methyl-D-aspartate and aspartate have no effect on NO(2)(-) production in C6 glioma cells stimulated by lipopolysaccharide and interferon-gamma. However, dopamine (DA) caused inhibition of NO(2)(-) production and iNOS transcription. The effects of DA were not due to homovanillic acid/3,4-dihydroxyphenylacetic acid, the autoxidative products superoxide (O(2)(-))/hydrogen peroxide (H(2)O(2)) or direct reactions with NO(2)(-). Forskolin, adenylate cyclase activator, dose-dependently reduced NO(2)(-). Meanwhile, (+/-) SKF-38393 D(1) receptor agonist attenuated iNOS in a similar fashion to DA. In addition, the results indicated that DA attenuation of iNOS was significantly impeded by the adenylate cyclase inhibitor MDL-12,330A, the D(1) antagonist SCH-23390, the beta2 adrenergic receptor antagonist ICI-118,551 and the beta1 adrenergic receptor antagonist atenolol. In conclusion, it appears that DA attenuates iNOS through a D(1), beta1 and beta2 adrenergic receptor-linked adenylate cyclase-mediated cAMP cascade.

Norepinephrine increases I kappa B alpha expression in astrocytes

The neurotransmitter norepinephrine (NE) can inhibit inflammatory gene expression in glial cells; however, the mechanisms involved are not clear. In primary astrocytes, NE dose-dependently increased the expression of inhibitory I kappa B alpha protein accompanied by an increase in steady state levels of I kappa B alpha mRNA. Maximal increases were observed at 30-60 min for the mRNA and at 4 h for protein, and these effects were mediated by NE binding to beta-adrenergic receptors. NE activated a 1.3-kilobase I kappa B alpha promoter transfected into astrocytes or C6 glioma cells, and this activation was prevented by a beta-antagonist and by protein kinase A inhibitors but not by an NF kappa B inhibitor. NE increased I kappa B alpha protein in both the cytosolic and the nuclear fractions, suggesting an increase in nuclear uptake of I kappa B alpha. I kappa B alpha was detected in the frontal cortex of normal adult rats, and its levels were reduced if central NE levels were depleted by lesion of the locus ceruleus. The reduction of brain I kappa B alpha levels was paralleled by increased inflammatory responses to lipopolysaccharide. These results demonstrate that I kappa B alpha expression is regulated by NE at both transcriptional and post-transcriptional levels, which could contribute to the observed anti-inflammatory properties of NE in vitro and in vivo.

Regulating factors for microglial activation

Microglia, residential macrophages in the central nervous system, can release a variety of factors including cytokines, chemokines, etc. to regulate the communication among neuronal and other types of glial cells. Microglia play immunological roles in mechanisms underlying the phagocytosis of invading microorganisms and removal of dead or damaged cells. When microglia are hyperactivated due to a certain pathological imbalance, they may cause neuronal degeneration. Pathological activation of microglia has been reported in a wide range of conditions such as cerebral ischemia, Alzheimer's disease, prion diseases, multiple sclerosis, AIDS dementia, and others. Nearly 5000 papers on microglia can be retrieved on the Web site PubMed at present (November 2001) and half of them were published within the past 5 years. Although it is not possible to read each paper in detail, as many factors as possible affecting microglial functions in in vitro culture systems are presented in this review. The factors are separated into "activators" and "inhibitors," although it is difficult to classify many of them. An overview on these factors may help in the development of a new strategy for the treatment of various neurodegenerative diseases.