Arachidonic acid lipoxygenation may mediate interleukin-1 stimulation of nerve growth factor secretion in astroglial cultures

Beneficial actions of melatonin in the management of viral infections: a new use for this "molecular handyman"?

Melatonin (N‐acetyl‐5‐methoxytryptamine) is a multifunctional signaling molecule that has a variety of important functions. Numerous clinical trials have examined the therapeutic usefulness of melatonin in different fields of medicine. Clinical trials have shown that melatonin is efficient in preventing cell damage under acute (sepsis, asphyxia in newborns) and chronic states (metabolic and neurodegenerative diseases, cancer, inflammation, aging). The beneficial effects of melatonin can be explained by its properties as a potent antioxidant and antioxidant enzyme inducer, a regulator of apoptosis and a stimulator of immune functions. These effects support the use of melatonin in viral infections, which are often associated with inflammatory injury and increases in oxidative stress. In fact, melatonin has been used recently to treat several viral infections, which are summarized in this review. The role of melatonin in infections is also discussed herein. Copyright © 2012 John Wiley & Sons, Ltd.

Cell-specific and concentration-dependent actions of interleukin-1 in acute brain inflammation

Interleukin (IL)-1 is a pivotal pro-inflammatory cytokine and an important mediator of both acute and chronic central nervous system (CNS) injuries. Despite intense research in CNS IL-1 biology over the past two decades, its precise mechanism of action in inflammatory responses to acute brain disorders remains largely unknown. In particular, much effort has been focussed on using in vitro approaches to better understand the cellular and signalling mechanisms of actions of IL-1, yet some discrepancies in the literature regarding the effects produced by IL-1beta in in vitro paradigms of injury still exist, particularly as to whether IL-1 exerts neurotoxic or neuroprotective effects. Here we aim to review the cell-specific and concentration-dependent actions of IL-1 in brain cells, to depict the mechanism by which this cytokine induces neurotoxicity or neuroprotection in acute brain injury.

Noradrenergic stimulation of BDNF synthesis in astrocytes: Mediation via α1- and β1/β2-adrenergic receptors

Brain-derived neurotrophic factor (BDNF) synthesis in astrocytes induced by noradrenaline (NA) is a receptor-mediated process utilizing two parallel adrenergic pathways: beta1/beta2-adrenergic/cAMP and the novel alpha1-adrenergic/PKC pathway. BDNF is produced by astrocytes, in addition to neurons, and the noradrenergic system plays a role in controlling BDNF synthesis. Since astrocytes express various subtypes of alpha- and beta-adrenergic receptors that have the potential to be activated by synaptically released NA, we focused our present study on the mediatory role of adrenergic receptors in the noradrenergic up-regulation of BDNF synthesis in cultured neonatal rat cortical astrocytes. NA (1 microM) elevates BDNF levels by four-fold after 6 h of incubation. Its stimulation was partly inhibited by either the beta1-adrenergic antagonist atenolol, the beta2-adrenergic antagonist ICI 118,551, or by the alpha1-adrenergic antagonist prazosin, while the alpha2-adrenergic antagonist yohimbine showed no effect. BDNF levels in astrocytes were increased by the specific beta1-adrenergic agonist dobutamine and the beta2-adrenergic agonist salbutamol, as well as by adenylate cyclase activation (by forskolin) and PKA activation (by dBcAMP). However, none of the tested agonists or mediators of the intracellular beta-adrenergic pathways were able to reach the level of NA's stimulatory effect. BDNF cellular levels were also elevated by the alpha1-adrenergic agonist methoxamine, but not by the alpha2-adrenergic agonist clonidine. The increase in intracellular Ca2+ by ionophore A23187 showed no effect, whereas PKC activation by phorbol 12-myristate 13-acetate (TPA) potently stimulated BDNF levels in the cells. The methoxamine-stimulated BDNF synthesis was inhibited by desensitizing pretreatment with TPA, indicating that the alpha1-stimulation was mediated via PKC activation. In conclusion, the synthesis of astrocytic BDNF stimulated by noradrenergic neuronal activity is an adaptable process using multiple types (alpha1 and beta1/beta2) of adrenergic receptor activation.

Multiple role of histamine H1-receptor-PKC-MAPK signalling pathway in histamine-stimulated nerve growth factor synthesis and secretion

Histamine is a potent stimulator of nerve growth factor (NGF) production in the central nerve system and in the periphery as well. In this review, the biochemical mechanisms of histamine-stimulated NGF synthesis and secretion, and interactions between histamine, interleukin-1beta, and interleukin-6 are discussed. The main signalling pathway, involved in the stimulation of NGF production by histamine, includes activation of histamine H(1)-receptor, stimulation of Ca(2+)-dependent protein kinase C and mitogen-activated protein kinase. The same signalling pathway is involved in the interactions between histamine, interleukin-1beta, and interleukin-6, where NGF secretion is amplified. Whereas histamine and interleukin-1beta cause additive stimulatory effect on NGF secretion, interaction between histamine and interleukin-6 causes a long-term synergism. Thus, activation of histamine H(1)-receptor-protein kinase C-mitogen-activated protein kinase signalling pathway plays a crucial role not only in the direct stimulation of NGF secretion by histamine, but also in the indirect stimulation via different types of interactions between histamine, interleukin-1beta, and interleukin-6, which may have important therapeutic implications in modulation of NGF production.

Monoaminergic neuronal activity up-regulates BDNF synthesis in cultured neonatal rat astrocytes

Astrocytes as an active part of the tripartite synapse can respond to the synaptically released neurotransmitters. Because brain-derived neurotrophic factor (BDNF) is produced by astrocytes, in addition to neurons, we focused our present study on the regulatory effects of monoamines noradrenaline (NA), serotonin (5-HT), and dopamine (DA) on the synthesis of BDNF protein in rat neonatal astrocytes from specific brain regions (cortex, cerebellum). All tested neurotransmitters are able to potently and transiently increase BDNF cellular contents; their maximal effects are dose and time dependent and differ between the two brain regions. In cultured cortical astrocytes, NA (1 microM; 6 h) elevates BDNF levels by a 4-fold, 5-HT (1 microM; 4 h) by a 2.3-fold, and DA (150 microM; 4 h) by a 2.2-fold. In cerebellar astrocytes, NA (1 microM; 4 h) increases BDNF content by a 4.7-fold, 5-HT (1 microM; 4 h) by a 1.7-fold, and DA (150 microM; 4 h) by a 1.4-fold. The initial increase in the BDNF levels return to basal levels when incubation with monoamines is extended beyond 12 h (for 5-HT) or 24 h (for NA and DA). Our results confirm the involvement of monoaminergic systems in the regulation of BDNF production in astrocytes and suggest the existence of a positive reciprocal interaction between monoaminergic neuronal activity and astrocytic neurotrophic support in neuron-astrocyte crosstalk, which has a dynamic role in mediating neuronal plasticity and trophic functions in the brain.

Interleukin-1beta and anaphylatoxins exert a synergistic effect on NGF expression by astrocytes

C3a and C5a anaphylatoxins are proinflammatory polypeptides released during complement activation. They exert their biological activities through interaction with two G protein-coupled receptors named C3aR and C5aR, respectively. In the brain, these receptors are expressed on glial cells, and some recent data have suggested that anaphylatoxins could mediate neuroprotection. In this study, we used RT-PCR and ribonuclease protection assays (RPA) to investigate the role of anaphylatoxins on neurotrophin expression by the human glioblastoma cell line T98G and by rat astrocytes. Our data show that for both cell types, anaphylatoxins upregulate expression of NGF mRNA. This response depended on a G protein-coupled pathway since pre-treatment of cells with pertussis toxin (PTX) completely blocked NGF mRNA increases. This effect was anaphylatoxin-specific since pre-incubation with anti-C3a or anti-C5aR antibodies abolished the effects of C3a and C5a, respectively. The regulation of NGF mRNA by anaphylatoxins was not accompanied by translation into protein expression, but there was a significant synergic effect of anaphylatoxins/IL-1b costimulation. Our demonstration of involvement of anaphylatoxins in the NGF release process by astrocytes suggests that C3a and C5a could modulate neuronal survival in the CNS.

Status epilepticus induces time-dependent neuronal and astrocytic expression of interleukin-1 receptor type I in the rat limbic system

Interleukin-1beta is rapidly synthesized by glia after the induction of seizures. Recent evidence shows that endogenous IL-1beta has proconvulsant actions mediated by interleukin-1 receptor type I. This receptor also mediates interleukin-1beta effects on neuronal susceptibility to neurotoxic insults. In this study, we investigated the basal and seizure-induced expression of interleukin-1 receptor type I in rat forebrain to identify the cells targeted by interleukin-1beta during epileptic activity. Self-sustained limbic status epilepticus was induced in rats by electrical stimulation of the ventral hippocampus. Interleukin-1 receptor type I immunoreactivity was barely detectable in neurons in control brain tissue. During status epilepticus, interleukin-1 receptor type I was induced in the hippocampal neurons firstly, and several hours later in astrocytes localized in limbic and extralimbic areas. Neuronal interleukin-1 receptor type I expression in the hippocampus outlasted the duration of spontaneous electroencephalographic seizure and was not observed in degenerating neurons. Astrocytic expression occurred transiently, between six and 18 h after the induction of status epilepticus and was invariably found in regions of neuronal damage. These time-dependent, cell- and region-specific changes in interleukin-1 receptor type I expression during status epilepticus suggest that interleukin-1 receptor type I in neurons mediates interleukin-1beta-induced fast changes in hippocampal excitability while interleukin-1 receptor type I receptors in astrocytes may mediate interleukin-1beta effects on neuronal survival in hostile conditions.

Differences in the regulation of BDNF and NGF synthesis in cultured neonatal rat astrocytes

Using a new brain-derived neurotrophic factor (BDNF) specific enzyme-immunoassay, we determined the basal cellular content of BDNF protein in neonatal rat astrocytes in primary culture, thus confirming the ability of astrocytes to synthesize BDNF in addition to nerve growth factor (NGF). We subsequently monitored the influence of different pharmacological agents: neurotransmitter receptor agonists, cytokines, and second messenger up-regulators, on the synthesis of BDNF and NGF. Marked differences in the regulation of their synthesis by the above pharmacological agents were observed in our study. The basal cellular levels of BDNF protein in cultured neonatal rat cortical and cerebellar astrocytes were 15.9 +/- 0.3 and 18.7 +/- 0.4 pg BDNF/mg cell protein, respectively, and differ significantly between astrocytes from different brain regions, whereas NGF levels were the same (16.1 +/- 0.3 and 16.2 +/- 0.7 pg NGF/mg cell protein, respectively). Screening different neurotransmitter systems for their influence on BDNF and NGF synthesis in cortical astrocytes revealed that dopamine (0.15 mM) is a potent up-regulator of BDNF protein synthesis in astrocytes, while kainic acid (50 microM) and histamine (1 microM) did not raise the cellular level of BDNF protein. Dopamine had no influence on NGF synthesis, while kainic acid caused minor, and histamine marked, elevation of NGF cellular content. Tumor necrosis factor-alpha (30 ng/ml) and interleukin-1beta (10 U/ml) treatments did not influence BDNF synthesis, whereas they markedly increased NGF protein cellular level. We also confirmed (using forskolin (20 microM) and phorbol 12-myristate 13-acetate (TPA) (100 nM)) that adenylate cyclase and protein kinase C participate in the downstream signaling responsible for the stimulation of BDNF synthesis, whereas in the regulation of NGF synthesis only the participation of protein kinase C was confirmed. Our results indicate that astrocyte-derived neurotrophins could play a role in distinct brain functions under physiological conditions and in the pathogenesis as well as possible treatment of different neurodegenerative disorders.

Redox events in interleukin-1 signaling

There is increasing evidence that reactive oxygen species (ROS) are mediators in growth factor and cytokine signaling pathways. Mechanisms by which ROS can interfere with signaling cascades may include regulation of protein activities by the modification of essential cysteines. Modification can be performed chemically or enzyme-catalyzed. Enzymes catalyzing a reversible thiol modification within proteins are to be able to react with both, ROS and protein thiols. If hydroperoxides are involved, promising candidates are peroxiredoxins and glutathione peroxidases (GPx), especially the phospholipid hydroperoxide GPx. Interleukin-1, one of the key players in inflammatory response, stimulates the production of ROS itself, but its signaling cascade can also be influenced by ROS and by thiol modifying agents. Targets are located in early, intermediate, and late events in the signaling cascade. We here summarize what is known about the effects of thiol modifying agents, selenium and glutathione peroxidases, on the assembly of the IL-1 receptor signaling complex as an early event, on the activation of NF-kappa B as an intermediate event, and on the expression of cell adhesion molecules as a late event in IL-1 signaling.

Melatonin and viral infections

The therapeutic effects of melatonin against viral infections, with emphasis on the Venezuelan equine encephalomyelitis (VEE), are reviewed. Melatonin has been shown to prevent paralysis and death in mice infected with the encephalomyocarditis virus and to decrease viremia. Melatonin also postpones the onset of the disease produced by Semliki Forest virus inoculation and reduces the mortality of West Nile virus-infected mice stressed by either isolation or dexamethasone injection. An increase in the host resistance to the virus via a peripheral immunostimulatory activity is considered responsible for these effects. It has also been demonstrated that melatonin protects some strains of mink against Aleutian disease, and prevents the reduction of B- and T-cells as well as Th1 cytokine secretion in mice infected with leukemia retrovirus. In VEE-infected mice, melatonin postpones the onset of the disease and death for several days and reduces the mortality rate. This protective effect seems to be due to the increase in the production of interleukin-1beta (IL-1beta), as 100% of the infected mice treated with melatonin die when IL-1beta is blocked with antimurine IL-1beta antibodies. Although melatonin administration raises serum levels of tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), the mortality observed in neutralization experiments with the corresponding anticytokine antibodies, suggests that neither TNF-alpha nor IFN-gamma are essential for the protective effect of melatonin on murine VEE virus infection. Melatonin treatment also enhances the efficiency of immunization against the VEE virus. Reactive oxygen species have been implicated in the dissemination of this virus, and their deleterious effects may be diminished by melatonin. This indole inhibits nitric oxide synthetase activity and it is a potent scavenger of nitric oxide, which also plays an important role in the spread of the VEE virus. In conclusion, the immunomodulatory, antioxidant, and neuroprotective effects of melatonin suggest that this indole must be considered as an additional therapeutic alternative to fight viral diseases.

Melatonin increases interleukin-1beta and decreases tumor necrosis factor alpha in the brain of mice infected with the Venezuelan equine encephalomyelitis virus

The effect of melatonin (MLT) on the brain levels of tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta) in Venezuelan equine encephalomyelitis (VEE) virus infection was determined. Brain homogenates from mice inoculated with 10 LD50 of VEE virus, untreated or treated with 500 microg MLT/kg body weight were assayed by ELISA to measure the levels of TNF-alpha and IL-1beta. MLT was injected daily starting 3 days before and continuing to 7 days after virus inoculation. Infected mice treated with MLT showed decreased levels of TNF-alpha when compared to the untreated infected mice on days 1, 3, 4, and 5 postinoculation (P < 0.001). In contrast, IL-1beta levels increased from days 1 to 5 in the infected mice treated with MLT when compared with the untreated infected animals (P < 0.01). The results suggest that the protective effect of MLT on the VEE virus infection could be due, among other factors, to a decrease in TNF-alpha synthesis along with an increase in the production of IL-1beta.

Interleukin-1 beta, but not IL-1 alpha, mediates nerve growth factor secretion from rat astrocytes via type I IL-1 receptor

In astrocytes, nerve growth factor (NGF) synthesis and secretion is stimulated by the cytokine interleukin-1 beta (IL-1 beta). In the present study, the role of IL-1 receptor binding sites in the regulation of NGF release was evaluated by determining the pharmacological properties of astroglially localized IL-1 receptors, and, by comparing the effects of both the agonists (IL-1 alpha and IL-1 beta) and the antagonist (IL-1ra)-members of the IL-1 family on NGF secretion from rat neonatal cortical astrocytes in primary culture. Using receptor-binding studies, binding of [(125)I] IL-1 beta to cultured astrocytes was saturable and of high affinity. Mean values for the K(D) and B(max) were calculated to be 60.7+/-7.4 pM and 2.5+/-0.1 fmol mg(-1) protein, respectively. The binding was rapid and readily reversible. IL-1 receptor agonists IL-1 alpha (K(i) of 341.1 pM) and IL-1 beta (K(i) 59.9 pM), as well as the antagonist IL-1ra (K(i) 257.6 pM), displaced specific [(125)I] IL-1 beta binding from cultured astrocytes in a monophasic manner. Anti-IL-1RI antibody completely blocked specific [(125)I] IL-1 beta binding while anti-IL-1RII antibody had no inhibitory effect. Exposure of cultured astrocytes to IL-1 alpha and IL-1 beta revealed the functional difference between the agonists in influencing NGF release. In contrast to IL-1 beta (10 U/ml), which caused a 3-fold increase in NGF secretion compared to control cells, IL-1 alpha by itself had no stimulatory action on NGF release. The simultaneous application of IL-1 alpha and IL-1 beta elicited no additive response. IL-1ra had no effect on basal NGF release but dose-dependently inhibited the stimulatory response induced by IL-1 beta. We concluded that IL-1 beta-induced NGF secretion from cultured rat cortical astrocytes is mediated by functional type I IL-1 receptors, whereas IL-1 alpha and IL-1ra, in spite of their affinity for IL-1RI, have no effect on NGF secretion from these cells. Type II IL-1R is not present on rat neonatal cortical astrocytes.

Interleukin-1beta induces the expression of lipocortin 1 mRNA in cultured rat cortical astrocytes

Lipocortin 1 (LC1) has been shown to increase in neuronal damage and act as a neuroprotectant and a neurotrophic factor. IL-1beta acts as a mediator of inflammation and has been reported as a potent inducer of various neurotrophic factors including nerve growth factor and fibroblast growth factor. In this study, we investigated the relationship between LC1 and IL-1beta in cultured rat astrocytes. Time-and dose-dependent experiments of IL-1beta on rat cortical astrocytes in culture revealed that the expression of LC1 mRNA was significantly augmented by IL-1beta at 8 h, 10 ng/ml. In addition, IL-1beta evoked an extracellular secretion of LC1 without its cytotoxic effects. The effect of IL-1beta was completely abolished when we treated cells with inhibitor of mitogen-activated protein kinases (MAPKs) (PD98059) (25 microM), phospholipase A(2) inhibitor mepacrine (30 microM) and protein synthesis inhibitor cycloheximide (CHX) (10 microg/ml). This suggests that induction of LC1 by IL-1beta is through a MAPKs and phospholipaseA(2) pathway and requires protein synthesis. These results indicate that IL-1beta released in the central nervous system (CNS) injury can stimulate the transcription of the LC1 gene. Subsequent synthesis and release of LC1 may provide trophic support to neurons and modulate the action of IL-1beta in brain damage.

Novel alternative promoters of mouse glial cell line-derived neurotrophic factor gene

We previously isolated cDNA and genomic DNA of the mouse glial cell line-derived neurotrophic factor (GDNF) gene and found that the gene consists of three exons. Recently, it was suggested that an alternative promoter exists within intron 1 of the human GDNF gene, but this has not been confirmed. Novel cDNA clones of the mouse GDNF gene were isolated by 5'-rapid amplification of cDNA ends from postnatal day-14 striatum. A novel exon, containing 351 nucleotides, exists between exon 1 and exon 3 (referred to as exon 2 in our previous report). Luciferase reporter assay showed that a core promoter for the novel exon 2 requires its 5'-untranslated region. Primer extension analysis and reverse transcription-PCR identified another novel transcript that starts 39 bp upstream of exon 3, and the core promoter activity exists within a region containing putative Sp1 sites. Although the core promoters for the novel exons are different from those previously identified, transcripts derived from each promoter coincidentally increased with interleukin-1beta or tumor necrosis factor-alpha stimulation. Gel retardation assays suggested that the NF-kappaB binding site in intron 1 would be involved in the cytokine response of the mouse GDNF gene.

Inflammatory Cytokines IL-1α, IL-1β, IL-6, and TNF-α Impart Neuroprotection to an Excitotoxin Through Distinct Pathways

The proinflammatory cytokines IL-1α, IL-1β, IL-6, and TNF-α are produced within the CNS, and, similar to the periphery, they have pleotrophic and overlapping functions. We have shown previously that TNF-α increases neuronal survival to a toxic influx of calcium mediated through neuronal N-methyl-d-aspartic acid (NMDA) glutamate-gated ion channels. This process, termed excitotoxicity, is a major contributor to neuronal death following ischemia or stroke. Neuroprotection by this cytokine requires both activation of the p55/TNF receptor type I and the release of TNF-α from neurons, and it is inhibited by the plant alkaloid nicotine. Here, we report that other inflammatory cytokines (IL-1α, IL-1β, and IL-6) are also neuroprotective to excessive NMDA challenge in our system. Neuroprotection provided by IL-1 is distinct from TNF-α because it is inhibited by IL-1 receptor antagonist; it is not antagonized by nicotine, but it is inhibited by a neutralizing Ab to nerve growth factor (NGF). Similar to IL-1, IL-6-mediated neuroprotection is also antagonized by pretreatment with IL-1 receptor antagonist and it is not affected by nicotine. However, neutralizing anti-NGF only partially blocks IL-6-mediated protection. These studies support an important role for distinct but overlapping neuroprotective cytokine effects in the CNS.

Maitotoxin-induced nerve growth factor production accompanied by the activation of a voltage-insensitive Ca2+ channel in C6-BU-1 glioma cells

1. The aim of the present study was to determine the effects of maitotoxin on nerve growth factor production and the Ca2+ influx in clonal rat glioma cells (C6-BU-1). 2. Maitotoxin (1 - 10 ng ml-1) induced a profound increase in 45Ca2+ influx in an extracellular Ca2+-dependent manner. However, high KCl had no effect at all. These effects were supported by the results from the analysis of intracellular Ca2+ concentration using fura 2. 3. The maitotoxin-induced 45Ca2+ influx was inhibited by inorganic Ca2+ antagonists, such as Mg2+, Mn2+ and Co2+. The inhibitory effect of Co2+ was antagonized by increasing the extracellular Ca2+ concentrations. 4. Maitotoxin (3 ng ml-1) as well as A-23187 (1microM) and dibutyryl cyclic AMP (0.5 mM) caused an acceleration of nerve growth factor (NGF) production in C6-BU-1 cells, as determined by NGF enzyme immunoassay. 5. Reverse transcription polymerase chain reaction (RT - PCR) analysis showed that maitotoxin (10 ng ml-1) enhanced the expression of NGF mRNA, which was abolished by the removal of extracellular Ca2+. A-23187 also accelerated its expression. 6. These results suggest that maitotoxin activates a voltage-insensitive Ca2+ channel and accelerates NGF production mediated through a Ca2+ signalling pathway in C6-BU-1 glioma cells.

Interleukin 1beta mediates the modulatory effects of monocytes on LNCaP human prostate cancer cells

Proliferative and secretory responses in androgen-sensitive prostate cancer LNCaP cells are regulated by steroid and peptide hormones and by differentiation-promoting substances. In the present study, we evaluated whether peripheral blood monocytes that exhibit anti-tumour activity in haematopoietic and solid tumours influence growth and secretion in the LNCaP cell line. For this purpose, LNCaP cells were incubated with monocyte-conditioned medium (MCM), and proliferation as well as expression of androgen receptor (AR) and secretion of prostate-specific antigen (PSA) were assessed. Conditioned medium from monocytes reduced proliferation in a dose-dependent manner. Incubation with 40% MCM caused a 50% reduction in cell proliferation. AR protein decreased by 70% and PSA levels in supernatants from LNCaP cells were reduced by approximately 80% following treatment with MCM. We focused on the contribution of two major products of activated monocytes, prostaglandin E2 and interleukin 1beta (IL-1beta), to the MCM modulatory action. LNCaP cells treated with prostaglandin E2 showed neither a reduction in proliferation nor a down-regulation of AR and PSA levels. The effects of MCM on cellular proliferation, AR protein and PSA secretion were abolished by pretreatment of MCM with a neutralizing anti-IL-1beta antibody. In addition, recombinant IL-1beta was able to replace MCM for the inhibition of proliferation and down-regulation of AR and PSA proteins. LNCaP cells were shown to express the IL-1beta receptor type 1, which transduces IL-1beta signal. Our findings reveal that monocyte-derived IL-1beta inhibits the proliferation of androgen-responsive prostate tumour cells and reduces AR and PSA levels.

Neurally mediated hyperactive voiding in spontaneously hypertensive rats

The development of hypertension in spontaneously hypertensive rats (SHR) and hyperactive voiding in rats with urethral obstruction are characterized by abnormal smooth muscle growth, increased tissue levels of nerve growth factor (NGF) and altered patterns of innervation. The present study was undertaken to determine if bladder smooth muscle from SHRs contains and secretes elevated levels of NGF, and if so, whether the augmented NGF contributes to changes in bladder innervation and function without tissue hypertrophy. Voiding behavior was monitored using specially designed metabolic cages. NGF levels in tissue homogenates and conditioned cell culture media were measured by ELISA. NGF mRNA in cultured bladder smooth muscle cells (BSMCs) was quantified using reverse transcriptase PCR. Noradrenergic innervation was assessed by staining with glyoxylic acid and assaying norepinephrine (NE) content in bladders with high performance liquid chromatography. SHRs voided more frequently than WKY rats. NGF content was higher in bladders from adult SHRs when compared to Wistar-Kyoto normotensive rats (WKYs). No significant difference in NGF mRNA content was observed between SHR and WKY BSMCs. However, SHR BSMCs secreted NGF at a higher rate and amount per unit mRNA than did WKY BSMCs. SHR bladders contained more NE and were more densely stained for catecholaminergic fibers than bladders from WKY rats. The results support the hypothesis that elevated NGF secretion by bladder smooth muscle is associated with hyperinnervation of bladder and hyperactive voiding in SHRs. Thus, the SHR strain may represent a genetic model to study changes in bladder function resulting from altered patterns of innervation.

A phospholipase A2-related snake venom (from Crotalus durissus terrificus) stimulates neuroendocrine and immune functions: determination of different sites of action

Immune neuroendocrine interactions are vital for the individual's survival in certain physiopathological conditions, such as sepsis and tissular injury. It is known that several animal venoms, such as those from different snakes, are potent neurotoxic compounds and that their main component is a specific phospholipase A type 2 (PLA2). It has been described recently that the venom from Crotalus durissus terrificus [snake venom (SV), in the present study] possesses some cytotoxic effect in different in vitro and in vivo animal models. In the present study, we investigated whether SV and its main component, PLA2 (obtained from the same source), are able to stimulate both immune and neuroendocrine functions in mice, thus characterizing this type of neurotoxic shock. For this purpose, several in vivo and in vitro designs were used to further determine the sites of action of SV-PLA2 on the hypothalamo-pituitary-adrenal (HPA) axis function and on the release of the pathognomonic cytokine, tumor necrosis factor alpha (TNF alpha), of different types of inflammatory stress. Our results indicate that SV (25 microg/animal) and PLA2 (5 microg/animal), from the same origin, stimulate the HPA and immune axes when administered (i.p.) to adult mice; both preparations were able to enhance plasma glucose, ACTH, corticosterone (B), and TNF alpha plasma levels in a time-related fashion. SV was found to activate CRH- and arginine vasopressin-ergic functions in vivo and, in vitro, SV and PLA2 induced a concentration-related (0.05-10 microg/ml) effect on the release of both neuropeptides. SV also was effective in changing anterior pituitary ACTH and adrenal B contents, also in a time-dependent fashion. Direct effects of SV and PLA2 on anterior pituitary ACTH secretion also were found to function in a concentration-related fashion (0.001-1 microg/ml), and the direct corticotropin-releasing activity of PLA2 was additive to those of CRH and arginine vasopressin; the corticotropin-releasing activity of both SV and PLA2 were partially reversed by the specific PLA2 inhibitor, manoalide. On the other hand, neither preparation was able to directly modify spontaneous and ACTH-stimulated adrenal B output. The stimulatory effect of SV and PLA2 on in vivo TNF alpha release was confirmed by in vitro experiments on peripheral mononuclear cells; in fact, both PLA2 (0.001-1 microg/ml) and SV (0.1-10 microg/ml), as well as concavalin A (1-100 microg/ml), were able to stimulate TNF alpha output in the incubation medium. Our results clearly indicate that PLA2-dependent mechanisms are responsible for several symptoms of inflammatory stress induced during neurotoxemia. In fact, we found that this particular PLA2-related SV is able to stimulate both HPA axis and immune functions during the acute phase response of the inflammatory processes.

Astrocytes are the major source of nerve growth factor upregulation following traumatic brain injury in the rat

Previous studies from our group have demonstrated an upregulation in nerve growth factor (NGF) RNA and protein in the cortex 24 h following traumatic brain injury (TBI) in a rat model. This increase in NGF is suppressed if rats are subjected to 4 h of whole-body hypothermia following TBI. In the present study we used in situ hybridization to extend our initial RNA gel-blot (Northern) hybridization findings by demonstrating that NGF RNA is increased in the cortex following TBI and that hypothermia diminishes this response. Further, by combining in situ hybridization with immunocytochemistry for glial fibrillary acidic protein we demonstrate that astrocytes are the major cellular source for the upregulation in NGF and that this upregulation can be observed in the hippocampus as early as 3 h posttrauma. The predominantly astrocytic origin suggests that the NGF upregulation is not related primarily to cholinotrophic activities. We hypothesize that its function is to stimulate upregulation of antioxidant enzymes, as part of an injury-induced cascade, and that supplementation of NGF or antioxidants may be warranted in hypothermic therapies for head injury.

Nordihydroguaiaretic acid blocks protein transport in the secretory pathway causing redistribution of Golgi proteins into the endoplasmic reticulum

We have investigated the effect of nordihydroguaiaretic acid (NDGA), an inhibitor of lipoxygenase, on the intracellular protein transport and the structure of the Golgi complex. Pulse-chase experiments and immunoelectron microscopy showed that NDGA strongly inhibits the transport of newly synthesized secretory proteins to the Golgi complex resulting in their accumulation in the endoplasmic reticulum (ER). Despite their retention in the ER, oligosaccharides of secretory and ER-resident proteins were processed to endoglycosidase H-resistant forms, raising the possibility that oligosaccharide-processing enzymes are redistributed from the Golgi to the ER. Morphological observations further revealed that alpha-mannosidase II (a cis/medial-Golgi marker), but not TGN38 (a trans-Golgi network marker), rapidly redistributes to the ER in the presence of NDGA, resulting in the disappearance of the characteristic Golgi structure. Upon removal of the drug, the Golgi complex was reassembled into the normal structure as judged by perinuclear staining of alpha-mannosidase II and by restoration of the secretion. These effects of NDGA are quite similar to those of brefeldin A. However, unlike brefeldin A, NDGA did not cause a dissociation of beta-coatomer protein, a subunit of coatomer, from the Golgi membrane. On the contrary, NDGA exerted the stabilizing effect on beta-coatomer protein/membrane interaction against the dissociation caused by brefeldin A and ATP depletion. Taken together, these results indicate that NDGA is a potent agent disrupting the structure and function of the Golgi complex with a mechanism different from those known for other drugs reported so far.

Interleukin-1-induced nuclear factor kappa B activation is inhibited by overexpression of phospholipid hydroperoxide glutathione peroxidase in a human endothelial cell line

Oxygen radicals are commonly accepted mediators in the tumour necrosis factor-mediated nuclear factor kappa B (NF kappa B) signalling cascade, but evidence for their role during interleukin-1 (IL-1) signalling is lacking. To test the involvement of hydroperoxides we investigated whether IL-1-induced NF kappa B activation could be influenced by glutathione peroxidases (GPx). These enzymes remove hydroperoxides with various specificities for the hydroperoxide substrate. By overexpressing phospholipid hydroperoxide glutathione peroxidase (PHGPx), which characteristically reacts with lipophilic hydroperoxides, the roles of H2O2 and lipid hydroperoxides were assessed. A human umbilical endothelial cell line, ECV 304, was stably transfected with the genes for both PHGPx and selenophosphate synthetase (selD), which provides selenophosphate for selenoprotein biosynthesis. When grown in selenium-deficient culture medium, the double-transfected clone (ECVPHGPx+SelD+) expressed 5-fold higher (P<0.005) PHGPx activity (measured by phosphatidylcholine hydroperoxide removal) than controls. The rate of H2O2 removal was also significantly (P<0.01) higher in this clone. When grown with high levels of extracellular selenium (up to 100 nM selenite), PHGPx activity and H2O2 removal were enhanced substantially in control cells and transfected cells. Under these conditions, PHGPx activity was 1.7-fold (P<0.005) higher in ECVPHGPx+SelD+, but H2O2 removal was the same as in controls. IL-1-induced NF kappa B activation was inhibited by selenium supplementation in control cells. In ECVPHGPx+SelD+ under conditions of selenium restriction, IL-1 induced NF kappa B activation only to a similar extent as under conditions of selenium supplementation in controls, and activation was abolished with 50 nM sodium selenite. These results show that overexpressed PHGPx is sufficient to inhibit NF kappa B activation, and suggests that NF kappa B activation by IL-1 is mediated by a preferential substrate of PHGPx, such as a fatty acid hydroperoxide, rather than by H2O2, the preferred substrate of the more abundant cytosolic GPx.

Mobilization of arachidonate and docosahexaenoate by stimulation of the 5-HT2A receptor in rat C6 glioma cells

In this study, we demonstrate that astroglial 5-HT2A receptors are linked to the mobilization of polyunsaturated fatty acids (PUFA). Stimulation of C6 glioma cells, prelabeled with [3H]arachidonate (AA, 20:4n6) and [14C]docosahexaenoate (DHA, 22:6n3), with serotonin and the 5-HT(2A/2C) receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI) resulted in the mobilization of both [3H] and [14C] into the supernatant of the cell monolayers. The increased radioactivity in the supernatant was mainly associated with free fatty acids. Experiments using inhibitors of phosphoinositide-specific phospholipase C and PLA2, inhibited the DOI-stimulated mobilization of AA and DHA, suggesting the involvement of both phospholipases. Ketanserin (1 microM), a 5-HT(2A/2C) receptor antagonist, and MDL 100,907 (R(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-pi peridine-methanol) (1 microM), a highly selective antagonist for 5-HT2A receptors, significantly decreased the DOI-stimulated release of AA and DHA. These results indicate that the 5-HT2A receptor is coupled to the mobilization of PUFA. The release of AA and DHA in response to serotonin may represent a mechanism through which astroglia provide these polyunsaturated fatty acids to neurons.

Evaluation of human astrocytoma and glioblastoma cell lines for nerve growth factor release

Nerve growth factor (NGF) prevents degeneration of cholinergic neurons in the central nervous system (CNS), and has potential as a therapeutic treatment for Alzheimer's disease. The inability of NGF to cross the blood-brain barrier has prompted pharmacological approaches investigating peripherally administered compounds that stimulate release of endogenous NGF. This study describes the NGF-releasing properties of six human astrocytoma and glioblastoma cell lines (SW 1088, SW 1783 and CRL 1718 astrocytomas, and U-138, U-373, and T98G glioblastomas). Using a highly specific two-site ELISA for human NGF, basal NGF release could be detected in all cell lines, with the lowest level in the T98G line (approximately 80 pg NGF/ml). Cell lines tested with a variety of compounds for 24 h in serum-free media demonstrated stimulation of NGF release by distinct mechanisms. NGF levels were markedly elevated (up to 8-fold above vehicle-treated cells) when stimulated with the cytokine interleukin-1 beta (IL-1 beta). Phorbol ester stimulated NGF release 4-fold. Clenbuterol, 4-methyl catechol, and propentofylline had little activity, while 6-(4-hydroxybutyl)-2,3,5,-trimethyl-1,4,benzoquinone (TMQ), dexamethasone and 1,25-dihydroxyvitamin D3 elevated NGF levels 3-fold. These data indicate differences in the ability of human astrocytoma and glioblastoma cells to release NGF when stimulated with mechanistically distinct compounds.

Okadaic acid stimulates nerve growth factor production via an induction of interleukin-1 in primary cultures of cortical astroglial cells

Neonatal rat cortical astroglial cells in primary culture synthesize and secrete interleukin-1 beta (IL-1) and nerve growth factor (NGF). Treatment of astrocytes with okadaic acid (OA), an inhibitor of phosphoprotein phosphatases, dramatically increased both IL-1 and NGF mRNA content (about 50-fold) with maximal induction seen at 20-30 nM OA. The induction of IL-1 mRNA preceded that of NGF mRNA and was maximal after 9 h of treatment. OA increased IL-1 mRNA half-life by about 10-fold similar to the reported stabilization of the NGF mRNA. Addition of an IL-1 receptor antagonist dose-dependently inhibited the secretion of NGF stimulated by OA and IL-1. The results indicate that OA profoundly stimulates IL-1 expression in glial cells by enhancing IL-1 mRNA stability and that glial cell-derived IL-1 acts in a paracrine/autocrine manner to stimulate NGF production.

Endothelin-3 attenuates the cyclic GMP responses to C-type natriuretic peptide in cultured mouse astrocytes

The effect of endothelin-3 (ET-3) on cyclic GMP (cGMP) responses to C-type natriuretic peptide (CNP) was studied in primary cultures of mouse astrocytes. Attenuation of CNP-stimulated cGMP formation by ET-3 was time-dependent, with maximum inhibition achieved at 30 min of preincubation. ET-3 suppressed cGMP production in response to 10 nM CNP in a dose-dependent fashion, with an IC50 of 0.04 nM and a maximal inhibitory concentration of 1 microM, which led to a 66% reduction of the cGMP increment from 45.0 +/- 4.2 pmol/mg protein to 15.4 +/- 2.6 pmol/mg protein. ET-1, ET-2, and ET-3 were equipotent in suppressing the CNP-induced cGMP response, suggesting that this effect was mediated by ETB receptors. Staurosporine, Ro 31-8220, calcium-free medium, nifedipine, verapamil, lanthanum, thapsigargin, BAPTA, W7, calmidazolium, U-73122, neomycin, quinacrine, wortmannin, herbimycin-A, okadaic acid, and sodium orthovanadate failed to block the effect of ET-3. Cycloheximide (100 microM), however, partially but significantly reversed the inhibitory effect of ET-3 on CNP-induced cGMP from 48.2 to 73.3% of the control value. The results support the premise that ET-3 and CNP interact within the central nervous system. The data also suggest that cGMP accumulation in mouse astrocytes is mediated by activation of certain kinases through as yet undefined mechanisms and not by protein kinase C, increased intracellular calcium, or other second messenger pathways such as phospholipases A2, C, D, tyrosine kinase, or protein phosphatases.

Neurotrophins and cytokines--intermediaries between the immune and nervous systems

Neurotrophins (NTs), including nerve growth factor (NGF), are multifunctional: in addition to their well-characterized neurotrophic functions they are known to regulate and to be regulated by cytokines, components of the immune system. In line with this we have found expression of a functional trk proto-oncogene, constituting the signal transducing-receptor for NGF, on monocytes/macrophages, lymphocytes and basophils. Moreover, NGF synthesis is regulated by a cytokine cascade including inflammatory mediators such as interleukin-1 and tumor necrosis factor-alpha. The fact that NGF levels are markedly elevated in cerebrospinal fluid of patients with multiple sclerosis and in serum of patients with systemic lupus erythematosus strongly indicates a role for NGF in immunopathology as well as in normal immune function.

Okadaic acid increases nerve growth factor secretion, mRNA stability, and gene transcription in primary cultures of cortical astrocytes

Neonatal rat cortical astrocytes in primary culture synthesize and secrete nerve growth factor (NGF) in response to cytokines, growth factors, and activators of protein kinases. To further implicate a protein phosphorylation mechanism in the regulation of NGF expression, astrocytes were treated with okadaic acid and calyculin A, inhibitors of phosphoprotein phosphatases 1 and 2A. Okadaic acid dramatically increased both NGF mRNA content (50-fold) and NGF secretion (100-fold) in astrocytes, while calyculin A, which has a spectrum of phosphatase inhibitory activity different from okadaic acid, failed to augment NGF expression. The increased mRNA accumulation was due mainly to an increase (4-fold) in the half-life of the NGF mRNA following 9 or 24 h of treatment. Nuclear run-on assays indicated that okadaic acid also activated NGF gene transcription, which was preceded by an induction of c-fos and c-jun gene transcription. The induction of NGF expression by okadaic acid appeared independent from protein kinase C activity because down-regulating protein kinase C activity failed to decrease the okadaic acid stimulation. In contrast, interleukin-1 beta acted synergistically with okadaic acid to stimulate NGF secretion. The results indicate that okadaic acid profoundly stimulates NGF expression in astrocytes mainly by enhancing NGF mRNA stability and suggest important roles for phosphoprotein phosphatases in regulating NGF production.

Expression of mRNA encoding neurotrophins and neurotrophin receptors in rat thymus, spleen tissue and immunocompetent cells. Regulation of neurotrophin-4 mRNA expression by mitogens and leukotriene B4

The expression of neurotrophin and neurotrophin receptor mRNAs was examined using RNase protection assays and Northern-blot analysis in rat thymus, spleen tissue and immunocompetent mononuclear cells purified from these two organs. Nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin-4 mRNAs were all expressed in thymus and spleen tissue although at different levels, while immunocompetent cells expressed neurotrophin-3 and neurotrophin-4 mRNAs. Thymus and spleen tissue expressed mRNAs encoding the low-affinity nerve-growth-factor receptor, the non-neuronal TrkA I receptor, the truncated (kinase deficient) and full-length TrkB, and the TrkC receptor. Low-affinity nerve-growth-factor receptor and non-neuronal TrkA I mRNAs were detected in both thymus and spleen immunocompetent cells. In addition, thymus cells expressed neuronal TrkA II mRNA and spleen cells expressed truncated TrkB mRNA. The expression of TrkA I and TrkA II mRNAs was enhanced in both thymus and spleen cells after cell culture. Enhanced levels of neurotrophin-4 mRNA were observed in spleen immunocompetent cells after adrenalectomy. Moreover, the expression of neurotrophin-4 mRNA was up-regulated after stimulation of immune cells with the mitogens concanavalin A or lipopolysaccharide or with the inflammatory mediator leukotriene B4. This suggests that neurotrophin-4 could be secreted by immunocompetent cells and may be involved in inflammatory processes.

Nerve growth factor and Alzheimer's disease

Nerve growth factor (NGF) is a well-characterized protein that exerts pharmacological effects on a group of cholinergic neurons known to atrophy in Alzheimer's disease (AD). Considerable evidence from animal studies suggests that NGF may be useful in reversing, halting, or at least slowing the progression of AD-related cholinergic basal forebrain atrophy, perhaps even attenuating the cognitive deficit associated with the disorder. However, many questions remain concerning the role of NGF in AD. Levels of the low-affinity receptor for NGF appear to be at least stable in AD basal forebrain, and the recent finding of AD-related increases in cortical NGF brings into question whether endogenous NGF levels are related to the observed cholinergic atrophy and whether additional NGF will be useful in treating this disorder. Evidence regarding the localization of NGF within the central nervous system and its presumed role in maintaining basal forebrain cholinergic neurons is summarized, followed by a synopsis of the relevant aspects of AD neuropathology. The available data regarding levels of NGF and its receptor in the AD brain, as well as potential roles for NGF in the pathogenesis and treatment of AD, are also reviewed. NGF and its low affinity receptor are abundantly present within the AD brain, although this does not rule out an NGF-related mechanism in the degeneration of basal forebrain neurons, nor does it eliminate the possibility that exogenous NGF may be successfully used to treat AD. Further studies of the degree and distribution of NGF within the human brain in normal aging and in AD, and of the possible relationship between target NGF levels and the status of basal forebrain neurons in vivo, are necessary before engaging in clinical trials.

The immortalized astroglial cell line RC7 is a new model system for the study of nerve growth factor (NGF) regulation: stimulation by interleukin-1 beta and transforming growth factor-beta 1 is additive and affected differently by dibutyryl cyclic AMP

Nerve growth factor (NGF) synthesis was studied with an astroglial cell line derived from rat cerebellar astrocytes by transfection with a simian virus 40 T containing retroviral vector. As in primary astrocytes, NGF synthesis/secretion could be stimulated dose-dependently with interleukin-1 beta (IL-1 beta) and transforming growth factor-beta 1 (TGF-beta 1). We therefore have used this cell line as a model system to analyze putative intracellular signalling pathways underlying the effects of these factors. Protein kinase C inhibitors (calphostin and Ro 31-8830) as well as a lipoxygenase inhibitor (nordihydroguaiaretic acid) did not affect stimulation of NGF synthesis/secretion by IL-1 beta or TGF-beta 1. However, dibutyryl cyclic AMP partly inhibited the stimulation by TGF-beta 1 but did not affect that evoked by IL-1 beta. This finding, together with the fact that IL-1 beta and TGF-beta 1 stimulate NGF production/secretion in an additive manner, indicates that different intracellular signalling pathways are involved in the mediation of IL-1 beta and TGF-beta 1 induced NGF production/secretion.