Induction of interleukin-1 beta-converting enzyme (ICE) in murine microglia by lipopolysaccharide

Nightmares and the Cannabinoids

The cannabinoids, Δ9 tetrahydrocannabinol and its analogue, nabilone, have been found to reliably attenuate the intensity and frequency of post-traumatic nightmares. This essay examines how a traumatic event is captured in the mind, after just a single exposure, and repeatedly replicated during the nights that follow. The adaptive neurophysiological, endocrine and inflammatory changes that are triggered by the trauma and that alter personality and behavior are surveyed. These adaptive changes, once established, can be difficult to reverse. But cannabinoids, uniquely, have been shown to interfere with all of these post-traumatic somatic adaptations. While cannabinoids can suppress nightmares and other symptoms of post-traumatic stress disorder, they are not a cure. There may be no cure. The cannabinoids may best be employed, alone, but more likely in conjunction with other agents, in the immediate aftermath of a trauma to mitigate or even abort the metabolic changes which are set in motion by the trauma and which may permanently alter the reactivity of the nervous system. Steps in this direction have already been taken.

Role of astrocytic GABAergic system on inflammatory cytokine-induced anxiety-like behavior

Recent studies have shown that not only neurons but astrocytes contain a considerable amount of γ-aminobutyric acid (GABA), which can be released and activate the receptors responsive to GABA. The purpose of this study is to test whether gliotransmitters from astrocytes may play a role in etiology of anxiety symptoms. Intracerebroventricular (i.c.v.) infusion of interleukin-1β (IL-1β), one of potent inflammatory cytokines, induced anxiety-like behaviors and activated the glial fibrillary acidic protein (GFAP) in the paraventricular nucleus (PVN) of the hypothalamus. Pretreatment with astrocytes toxin, l-α-aminoadipate (L-AAA) reduced anxiety-like behaviors and the GFAP expression in the PVN. Intraparaventricular nucleus (iPVN) infusion of IL-1β produced markedly anxiety-like behaviors and increased release of GABA from astrocytes. However, treatment of glial cell inhibitor, L-AAA or blocker of Bestrophin-1 (Best1), 5-Nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) markedly inactivated astrocytes and also reduced the anxiety-like behaviors. Treatment of L-AAA or NPPB decreased IL-1β-induced gliotransmitter GABA release measured by in vivo microdialysis. These results suggest that selective inhibition of astrocytes or astocytic GABA release in the PVN may serve as an effective therapeutic strategy for treating anxiety and affective disorders.

cRGD mediated liposomes enhanced antidepressant-like effects of edaravone in rats

The delayed onset of therapeutic outcomes is a major drawback of the current antidepressants. The blood-brain barrier is the most important bottleneck impeding drug transport into the brain. Therefore, development of novel antidepressant medications with rapid onset and sustained activity is urgent. RGD liposomes showed an excellent effect of brain-targeting drug delivery and increased the entering rate to the brain. In the present study, we prepared cyclic RGD liposomes loaded with edaravone (cRGD-ERLs) and evaluated the potential antidepressant-like effects of this drug delivery system in rats. The results showed single injection of cRGD-ERLs produced significant antidepressant-like effects in both forced swim and novelty suppressed feeding test. Moreover, acute cRGD-ERLs increased the expression of c-fos in the medial prefrontal cortex, suggesting that cRGD-ERLs could activate the neuronal function. Furthermore, cRGD-ERLs reversed the increase of lipopolysaccharides (LPS)-induced plasma cytokine IL-1β and IL-6, suggesting that normalization of cytokine level might be involved in the behavioral response of cRGD-ERLs. Finally, cRGD-ERLs prevented the increase of immobility induced by LPS in the forced swim test. Overall, the current data revealed a novel brain-target drug delivery system, which can be used to improve the therapeutic outcomes of antidepressants by increase of crossing rate to the brain.

Interleukin-1 beta converting enzyme is necessary for development of depression-like behavior following intracerebroventricular administration of lipopolysaccharide to mice

Background

Interleukin-1 beta converting enzyme (ICE, caspase 1) is a cysteine protease that processes immature pro-IL-1β into active mature IL-1β. IL-1β is a pro-inflammatory cytokine that mediates many of the physiological and behavioral responses to inflammation. Genetic deletion of ICE has previously been shown to prevent some negative physiologic responses to lipopolysaccharide (LPS)-induced inflammation.

Methods

Here we used a preclinical murine model to test the hypothesis that ICE is necessary for development of depression-like behaviors following intracerebroventricular (ICV) treatment with LPS. Adult male ICE knockout (ICE KO) and congenic wild-type C57BL/6 J (WT) mice were administered LPS either ICV at 100 ng/mouse or intraperitoneally (IP) at 830 μg/kg body weight or an equal volume of saline as controls. Mice were monitored up to 48 h after treatment for both sickness and depression-like behaviors.

Results

LPS given ICV induced a loss of body weight in both WT and ICE KO mice. This sickness response was similar between WT and ICE KO mice. As expected, LPS administered ICV increased immobility in the forced swim test (FST) and decreased sucrose preference in WT mice but no change in either of these two depression-like behaviors was observed in ICE KO mice. Expression of TNF-α and CD11b in brain was lower in ICE-KO mice at 24 h following ICV administration of LPS compared to WT mice. In contrast, when LPS was given systemically, sickness response, depression-like behaviors, and expression of these genes were similar between the two strains of mice.

Conclusions

These findings indicate that ICE plays a specific role in depression-like behavior induced by a central inflammatory stimuli even though it is not required when LPS is administered systemically.

Expression and functional roles of caspase-5 in inflammatory responses of human retinal pigment epithelial cells

PURPOSE

To investigate the expression, activation, and functional involvement of caspase-5 in human retinal pigment epithelial (hRPE) cells.

METHODS

Expression and activation of caspase-5 in primary cultured hRPE cells, telomerase-immortalized hTERT-RPE1 cells (hTERT-RPE1), or both, were measured after stimulation with proinflammatory agents IL-1β, TNF-α, lipopolysaccharide (LPS), interferon-γ, monocyte coculture, adenosine triphosphate (ATP), or endoplasmic reticulum (ER) stress inducers. Immunomodulating agents dexamethasone (Dex), IL-10, and triamcinolone acetonide (TA) were used to antagonize proinflammatory stimulation. Cell death ELISA and TUNEL staining assays were used to assess apoptosis.

RESULTS

Caspase-5 mRNA expression and protein activation were induced by LPS and monocyte-hRPE coculture. Caspase-5 activation appeared as early as 2 hours after challenge by LPS and consistently increased to 24 hours. Meanwhile, caspase-1 expression and protein activation were induced by LPS. Activation of caspase-5 was blocked or reduced by Dex, IL-10, and TA. Activation of caspase-5 and -1 was also enhanced by ATP and ER stress inducers. Expression and activation of caspase-5 were inhibited by a caspase-1-specific inhibitor. Caspase-5 knockdown reduced caspase-1 protein expression and activation and inhibited TNF-α-induced IL-8 and MCP-1. In contrast to caspase-4, the contribution of caspase-5 to stress-induced apoptosis was moderate.

CONCLUSIONS

Caspase-5 mRNA synthesis, protein expression, and catalytic activation were highly regulated in response to various proinflammatory stimuli, ATP, and ER stress inducers. Mutual activation between caspase-5 and -1 suggests caspase-5 may work predominantly in concert with caspase-1 in modulating hRPE inflammatory responses.

Sodium dependence of lysophosphatidylcholine-induced caspase-1 activity and reactive oxygen species generation

The proinflammatory cytokines interleukin (IL)-1β and IL-18 play pivotal roles in neuroinflammatory diseases. Caspase-1-mediated proteolytic cleavage is required to convert the premature, biologically inactive cytokines to their biologically active forms capable of promoting tissue inflammation. Although caspases have been recognized as potential therapeutic targets in inflammatory diseases, mechanisms regulating caspase-1 activation are not fully understood. Here we demonstrate that the proinflammatory lipid lysophosphatidylcholine (LPC) initiates microglial caspase-1 activation in a Na(+)-dependent manner. LPC-induced caspase-1 activity was almost completely inhibited upon omission of extracellular Na(+), but was unaffected by inhibition of Na(+)/K(+)-ATPase with ouabain or by inhibition of Na(+)/H(+) antiport with amiloride. Inhibition of caspase-1-mediated IL-1β processing by Na(+)-free medium led to reduced amounts of mature IL-1β released from LPC-stimulated microglia. Furthermore, LPC-induced production of reactive oxygen species (ROS) was abolished by Na(+)-free medium, indicating Na(+) dependence of NADPH oxidase activity in LPC-stimulated microglia. Since ROS production was found to be crucial to caspase-1 activation in LPC-stimulated microglia, the Na(+) dependence of caspase-1 can be related to the Na(+) dependence of NADPH oxidase. In summary, it is suggested that in LPC-activated microglia, Na(+) influx is required for the production of NADPH oxidase-mediated ROS, which subsequently stimulate caspase-1 activity.

Luteolin reduces IL-6 production in microglia by inhibiting JNK phosphorylation and activation of AP-1

Luteolin, a flavonoid found in high concentrations in celery and green pepper, has been shown to reduce production of proinflammatory mediators in LPS-stimulated macrophages, fibroblasts, and intestinal epithelial cells. Because excessive production of proinflammatory cytokines by activated brain microglia can cause behavioral pathology and neurodegeneration, we sought to determine whether luteolin also regulates microglial cell production of a prototypic inflammatory cytokine, IL-6. Pretreatment of primary murine microlgia and BV-2 microglial cells with luteolin inhibited LPS-stimulated IL-6 production at both the mRNA and protein levels. To determine how luteolin inhibited IL-6 production in microglia, EMSAs were performed to establish the effects of luteolin on LPS-induced binding of transcription factors to the NF-kappaB and activator protein-1 (AP-1) sites on the IL-6 promoter. Whereas luteolin had no effect on the LPS-induced increase in NF-kappaB DNA binding activity, it markedly reduced AP-1 transcription factor binding activity. Consistent with this finding, luteolin did not inhibit LPS-induced degradation of IkappaB-alpha but inhibited JNK phosphorylation. To determine whether luteolin might have similar effects in vivo, mice were provided drinking water supplemented with luteolin for 21 days and then they were injected i.p. with LPS. Luteolin consumption reduced LPS-induced IL-6 in plasma 4 h after injection. Furthermore, luteolin decreased the induction of IL-6 mRNA by LPS in hippocampus but not in the cortex or cerebellum. Taken together, these data suggest luteolin inhibits LPS-induced IL-6 production in the brain by inhibiting the JNK signaling pathway and activation of AP-1 in microglia. Thus, luteolin may be useful for mitigating neuroinflammation.

In vitro and in vivo evidence for a role of the P2X7 receptor in the release of IL-1 beta in the murine brain

The P2X(7) receptor (P2X(7)R) is a purinoceptor expressed predominantly by cells of immune origin, including microglial cells. P2X(7)R has a role in the release of biologically active proinflammatory cytokines such as IL-1 beta, IL-6 and TNFalpha. Here we demonstrate that when incubated with lipopolysaccharide (LPS), glial cells cultured from brain of P2X(7)R(-/-) mice produce less IL-1 beta compared to glial cells from brains of wild-type mice. This is not the case for TNFalpha and IL-6. Our results indicate a selective effect of the P2X7R gene deletion on release of IL-1 beta release but not of IL-6 and TNFalpha. In addition, we confirm that only microglial cells produce IL-1beta, and this release is dependent on P2X(7)R and ABC1 transporter. Because IL-1 beta is a key regulator of the brain cytokine network and P2X(7)R is an absolute requirement for IL-1 beta release, we further investigated whether response of brain cytokines to LPS in vivo was altered in P2X(7)R(-/-) mice compared to wild-type mice. IL-1 beta and TNFalpha mRNAs were less elevated in the brain of P2X(7)R(-/-) than in the brain of wild-type mice in response to systemic LPS. These results show that P2X7R plays a key role in the brain cytokine response to immune stimuli, which certainly applies also to cytokine-dependent alterations in brain functions including sickness behavior.

Lysophosphatidylcholine stimulates IL-1beta release from microglia via a P2X7 receptor-independent mechanism

IL-1beta released from activated macrophages contributes significantly to tissue damage in inflammatory, degenerative, and autoimmune diseases. In the present study, we identified a novel mechanism of IL-1beta release from activated microglia (brain macrophages) that occurred independently of P2X(7) ATP receptor activation. Stimulation of LPS-preactivated microglia with lysophosphatidylcholine (LPC) caused rapid processing and secretion of mature 17-kDa IL-1beta. Neither LPC-induced IL-1beta release nor LPC-stimulated intracellular Ca(2+) increases were affected by inhibition of P2X(7) ATP receptors with oxidized ATP. Microglial LPC-induced IL-1beta release was suppressed in Ca(2+)-free medium or during inhibition of nonselective cation channels with Gd(3+) or La(3+). It was also attenuated when Ca(2+)-activated K(+) channels were blocked with charybdotoxin (CTX). The electroneutral K(+) ionophore nigericin did not reverse the suppressive effects of CTX on LPC-stimulated IL-1beta release, demonstrating the importance of membrane hyperpolarization. Furthermore, LPC-stimulated caspase activity was unaffected by Ca(2+)-free medium or CTX, suggesting that secretion but not processing of IL-1beta is Ca(2+)- and voltage-dependent. In summary, these data indicate that the activity of nonselective cation channels and Ca(2+)-activated K(+) channels is required for optimal IL-1beta release from LPC-stimulated microglia.

Rapid co-release of interleukin 1beta and caspase 1 in spinal cord inflammation

Mounting evidence supports the hypothesis that pro-inflammatory cytokines secreted by astrocytes and microglia modulate nociceptive function in the injured CNS and following peripheral nerve damage. Here we examine the involvement of interleukin-1beta (IL-1beta) and microglia activation in nociceptive processing in rat models of spinal cord inflammation. Following application of lipopolysaccharide (LPS) to an ex vivo dorsal horn slice preparation, we observed rapid secretion of IL-1beta which was prevented by inhibition of glial cell metabolism and by inhibitors of either p38 mitogen-activated protein kinase (MAPK) or caspase 1. LPS superfusion also induced rapid secretion of active caspase 1 and apoptosis-associated speck-like protein containing a caspase recruitment domain from the isolated dorsal horn. Extensive microglial cell activation in the dorsal horn, as determined by immunoreactivity for phosphorylated p38 MAPK, was found to correlate with the occurrence of IL-1beta secretion. In behavioural studies, intrathecal injection of LPS in the lumbar spinal cord produced mechanical hyperalgesia in the rat hind-paws which was attenuated by concomitant injections of a p38 MAPK inhibitor, a caspase 1 inhibitor or the rat recombinant interleukin 1 receptor antagonist. These data suggest a critical role for the cytokine IL-1beta and caspase 1 rapidly released by activated microglia in enhancing nociceptive transmission in spinal cord inflammation.

Transcriptional regulation of caspases in experimental pneumococcal meningitis

Apoptosis and necrosis in brain account for neurological sequelae in survivors of bacterial meningitis. In meningitis, several mechanisms may trigger death pathways leading to activation of transcription factors regulating caspases mRNA synthesis. Therefore, we used a multiprobe RNA protection assay (RPA) to examine the expression of 9 caspase-mRNA in the course of experimental Streptococcus pneumoniae meningitis in mouse brain. Caspase-6, -7 and -11 mRNA were elevated 6 hours after infection. 12 hours after infection caspases-1, -2, -8 and -12 mRNA rose. Caspase-14 mRNA was elevated 18 h and caspase-3 mRNA 24 h after infection. In situ hybridization detected caspases-3, -8, -11 and -12 mRNA in neurons of the hippocampal formation and neocortex. Development of sepsis was paralleled by increased transcription of caspases mRNA in the spleen. In TNFalpha-deficient mice all caspases examined were less upregulated, in TNF-receptor 1/2 knockout mice caspases-1, -2, -7, -11 and -14 mRNA were increased compared to infected control animals. In caspase-1 deficient mice, caspases-11, and -12 mRNA levels did not rise in meningitis indicating the necessity of caspase-1 activating these caspases. Hippocampal formations of newborn mice incubated with heat-inactivated S. pneumoniae R6 showed upregulation of caspase-1, -3, -11 and -12 mRNA. These observations suggest a tightly regulated caspases network at the transcriptional level in addition to the known cascade at the protein level.

Excitotoxic and apoptotic neuronal death induce different patterns of glial activation in vitro

We have studied glial activation in rat cerebellar neuronal-glial cultures after inducing neuronal death using various stimuli. Cultures were exposed to 100 microm glutamate for 20 min, which induces excitotoxic neuronal death, or to potassium/serum deprivation, which induces apoptosis of granule neurons. We evaluated alterations in several parameters related to glial activation: nuclear factor-kappaB activation, nitric oxide and tumour necrosis factor-alpha production, which are associated with a pro-inflammatory response, glial proliferation and phagocytic activity. Although the two experimental models of neuronal damage resulted in the death of most neuronal cells within 24 h, differences were observed in the response of the various glial parameters evaluated. While nitric oxide production was not detected in any case, tumour necrosis factor-alpha production, nuclear factor-kappaB activation and glial proliferation were only induced in the presence of excitotoxic neuronal death. However, phagocytosis was induced in both cases, although earlier in the case of apoptotic neuronal death. These results show that glial cells respond to excitotoxic neuronal death with an inflammatory response associated with proliferation and phagocytosis. In contrast, whilst glial cells do not produce pro-inflammatory molecules in the presence of apoptotic neuronal death, phagocytic activity is rapidly induced.

Neuronal expression of caspase-1 immunoreactivity in the rat central nervous system

Caspase-1/interleukin-1beta (IL-1beta)-converting enzyme (ICE) cleaves IL-1beta and IL-18 precursor proteins to the active forms of these proinflammatory cytokines. Since both cytokines are constitutively expressed in the brain, we investigated whether this is also the case for caspase-1. Using an antibody raised against the p10-subunit of the active enzyme, constitutive expression of caspase-1 immunoreactivity was found in nerve cells in the arcuate nucleus and in nerve fibres throughout the brain. Co-localisation with alpha-melanocyte stimulating hormone was demonstrated. The distribution pattern of caspase-1 immunoreactive structures is consistent with a role to produce mature IL-1beta in regions where IL-1beta mediates fever and sleep.

Immunoregulation of microglial functional properties

Microglia are the resident tissue macrophages of the central nervous system (CNS) parenchyma and are key players in the initiation of an inflammatory response. Microglia rapidly transform from a resting to an activated morphology in response to a variety of disease states. However, they can also be the target of infections, as in the case of HIV. Many of the effector properties of microglia can be attributed to the array of substances they secrete in response to stimuli such as bacterial lipopolysaccharide, cytokines, and chemokines. The products of activated microglia include: cytokines (pro- and anti-inflammatory), chemokines, nitric oxide, superoxide radicals, and proteases. Furthermore, microglia have the ability to present antigen to T cells, migrate in response to chemotactic stimuli, and phagocytose cell debris. This report focuses on the immunomodulatory functions of microglia, with particular attention to chemokines, and highlights their pivotal role in the CNS.

Caspase mRNA expression in a rat model of focal cerebral ischemia

Proteins of the caspase family are involved in the signalling pathway that ultimately leads to programmed cell death (apoptosis), which has been reported to occur in some experimental models of stroke. In a previous paper we used quantitative reverse transcription and polymerase chain reaction (RT-PCR) to characterise changes in the mRNA expression of one member of this family, caspase-3, in a rat model of permanent focal ischemia. Here we have used this technique to study the expression of a further three caspases which are involved in different aspects of caspase signalling. Caspase-8, involved in Fas-mediated apoptosis, was upregulated in the cortex of ischemic rats. Caspase-11, which leads to the synthesis of the functional form of the cytokine interleukin-1 beta, also showed increased expression, but with a different temporal profile from caspase-8. In contrast, caspase-9, which forms part of the pathway signalling through the mitochondria, showed a decrease in expression. The expression of a further four caspases (1, 2, 6 and 7) has also been characterised in a simpler experiment. These caspases all showed distinctive patterns of expression following the induction of ischemia. These data lead us to conclude that caspase expression as a whole is under very strict transcriptional control in this model. Certain elements of caspase signalling, such as the Fas-induced pathway and the events upstream of IL-1 beta processing, are upregulated, while others are not. This may be due to some form of genetic program activated in response to ischemia in the brain and may highlight which biological pathways are modulated.

Interleukin (IL)-10 inhibits IL-6 production in microglia by preventing activation of NF-kappaB

The purpose of this study was to determine if interleukin (IL)-10 inhibits lipopolysaccharide (LPS)-induced IL-6 production in microglia by inhibiting activation of nuclear factor-kappaB (NF-kappaB). N13 microglia (a murine microglial cell line) and primary microglia from neonatal mice were cultured in the presence or absence of LPS and increasing amounts of murine IL-10 for 24 h. As predicted, LPS treatment increased supernatant IL-6 concentration in both N13 and primary microglia cultures. Pretreatment with IL-10, however, decreased LPS-induced IL-6 secretion in a dose-dependent manner in both culture systems. Likewise, ribonuclease protection assays showed that LPS increased steady-state IL-6 mRNA levels, but that pretreatment with IL-10 blocked the LPS-induced increase in IL-6 mRNA. Because NF-kappaB is the predominant transcription factor responsible for IL-6 transcription in response to inflammatory stimuli, it was hypothesized that IL-10 inhibited IL-6 production by preventing nuclear translocation of NF-kappaB. Consistent with this idea, LPS increased nuclear translocation of NF-kappaB as assessed by gel mobility shift assay. Supershift assays and immunocytochemical staining showed that both the p50 and p65 subunits of NF-kappaB translocated from the cytoplasm to the nucleus upon LPS stimulation. Pretreatment with IL-10, however, inhibited LPS-induced activation of NF-kappaB. Furthermore, inhibition of NF-kappaB activity with tosyl-Phe-chloromethlyketone (a serine protease inhibitor that prevents degradation of the NF-kappaB-IkappaB complex), completely blocked LPS-induced IL-6 production. These data suggest that IL-10 inhibited IL-6 production in microglia by decreasing the activity of NF-kappaB and, therefore, extend what little is known of the intricate relationship between anti-inflammatory and inflammatory cytokines in the central nervous system.

Glucocorticoid-induced, caspase-dependent organ apoptosis early after burn injury

Immune suppression and increased apoptotic loss of circulating lymphocytes have been reported after burn injury. However, little is known about the underlying mechanisms responsible for the increased apoptosis of lymphoid and parenchymal cells in solid organs and the role played by inflammatory mediators, such as tumor necrosis factor-alpha (TNF-alpha) and Fas ligand (FasL), as well as by glucocorticoids. To evaluate the role of endogenously produced glucocorticoids and FasL, mice subjected to a 20% steam burn were pretreated with a glucocorticoid receptor antagonist (mifepristone) or a neutralizing murine Fas fusion protein. Three and twenty-four hours after burn injury, histological analysis, caspase-3 activity, and in situ terminal deoxynucleotidyl transferase dUTP nick-end labeling staining and phenotyping of lymphocyte populations for apoptosis were evaluated. Burn injury increased the number of apoptotic cells and caspase-3 activity in thymus and spleen, but not in other solid organs. Increased apoptosis was seen in several T and B cell populations from both thymus and spleen. Mifepristone pretreatment significantly reduced the apoptosis and caspase-3 activity after burn injury, whereas blocking FasL activity had only minimal effects. We conclude that corticosteroids, and not FasL, are primarily responsible for the increased caspase-3 activity and apoptosis in thymus and spleen cell populations early after burn injury.

Timecourse and corticosterone sensitivity of the brain, pituitary, and serum interleukin-1beta protein response to acute stress

Activation of peripheral immune cells leads to increases of interleukin-1beta (IL-1beta) mRNA, immunoreactivity, and protein levels in brain and pituitary. Furthermore, IL-1beta in brain plays a role in mediating many of the behavioral, physiological, and endocrine adjustments induced by immune activation. A similarity between the consequences of immune activation and exposure to stressors has often been noted, but the potential relationship between stress and brain IL-1beta has received very little attention. A prior report indicated that exposure to inescapable tailshocks (IS) raised levels of brain IL-1beta protein 2 h after IS, but only in adrenalectomized (and basal corticosterone replaced) subjects. The studies reported here explore this issue in more detail. A more careful examination revealed that IL-1beta protein levels in hypothalamus were elevated by IS in intact subjects, although adrenalectomy, ADX (with basal corticosterone replacement) exaggerated this effect. IL-1beta protein increases were already present immediately after the stress session, both in the hypothalamus and in other brain regions in adrenalectomized subjects, and no longer present 24 h later. Furthermore, IS elevated levels of IL-1beta protein in the pituitary, and did so in both intact and adrenalectomized subjects. IS also produced increased blood levels of IL-1beta, but only in adrenalectomized subjects. Finally, the administration of corticosterone in an amount that led to blood levels in adrenalectomized subjects that match those produced by IS, inhibited the IS-induced rise in IL-1beta in hypothalamus and pituitary, but not in other brain regions or blood.

Behavioral and ultrastructural changes induced by chronic neuroinflammation in young rats

We investigated the ultrastructural, immunohistochemical, biochemical and behavioral effects of chronic neuroinflammation in young rats produced by injection of lipopolysaccharide (LPS) into the 4th ventricle. The 37-day infusion of LPS impaired spatial memory but not object recognition ability. Electron microscopic studies of neurons within the hippocampus identified numerous paired cisternae of the rough endoplasmic reticulum (RER) and other ultrastructural changes that suggested impaired or reduced synthesis of cellular proteins within the cytoplasm. Immunohistochemical staining found numerous highly activated microglia distributed throughout the cingulate gyrus, entorhinal cortex, hippocampus and dentate gyrus. This animal model may be useful to test potential pharmacotherapies that are directed at the prevention of the cytotoxic consequences of chronic neuroinflammation associated with normal aging or Alzheimer's disease.

Involvement of endogenously synthesized interleukin (IL)-18 in the protective effects of IL-12 against pulmonary infection with Cryptococcus neoformans in mice

We previously demonstrated that interleukin (IL)-12 protected mice against fatal pulmonary infection with a highly virulent strain of Cryptococcus neoformans, which correlated well with the production of interferon (IFN)-gamma as well as IL-18 in the primary infected site. In the present study, we examined the role of endogenously synthesized IL-18 in IL-12-induced host resistance to this pathogen. There was little or no production of IFN-gamma and IL-18 both at mRNA and protein levels in lungs of mice infected with C. neoformans, while treatment with IL-12 induced a marked production of these cytokines. Caspase-1 mRNA was expressed in infected mice even without IL-12 treatment. Administration of neutralizing anti-IFN-gamma monoclonal antibody (mAb) clearly inhibited production of IFN-gamma and IL-18 induced by IL-12, while control IgG did not show such an effect. However, administration of IFN-gamma did not induce the production of both cytokines in infected mice, although tumor necrosis factor (TNF)-alpha and IFN-gamma-inducible protein (IP)-10 were synthesized by the same treatment. Finally, neutralizing anti-IL-18 antibody (Ab) significantly interfered with the production of IFN-gamma and elimination of the microorganism from the lung induced by IL-12 treatment. Furthermore, both IFN-gamma synthesis and host protection caused by IL-12 were profoundly diminished in IL-18 gene-disrupted mice. Considered collectively, our results indicated that host protection against C. neoformans induced by IL-12 involved endogenously synthesized IL-18 and that the production of IL-18 was mediated at least in part by endogenous IFN-gamma.

Amyloid beta and amylin fibrils induce increases in proinflammatory cytokine and chemokine production by THP-1 cells and murine microglia

Activated microglia surrounding amyloid beta-containing senile plaques synthesize interleukin-1, an inflammatory cytokine that has been postulated to contribute to Alzheimer's disease pathology. Studies have demonstrated that amyloid beta treatment causes increased cytokine release in microglia and related cell cultures. The present work evaluates the specificity of this cellular response by comparing the effects of amyloid beta to that of amylin, another amyloidotic peptide. Both lipopolysaccharide-treated THP-1 monocytes and mouse microglia showed significant increases in mature interleukin-1beta release 48 h following amyloid beta or human amylin treatment, whereas nonfibrillar rat amylin had no effect on interleukin-1beta production by THP-1 cells. Lipopolysaccharide-stimulated THP-1 cells treated with amyloid beta or amylin also showed increased release of the proinflammatory cytokines tumor necrosis factor-alpha and interleukin-6, as well as the chemokines interleukin-8 and macrophage inflammatory protein-1alpha and -1beta. THP-1 cells incubated with fibrillar amyloid beta or amylin in the absence of lipopolysaccharide also showed significant increases of both interleukin-1beta and tumor necrosis factor-alpha mRNA. Furthermore, treatment of THP-1 cells with amyloid fibrils resulted in an elevated expression of the immediate-early genes c-fos and junB. These studies provide further evidence that fibrillar amyloid peptides can induce signal transduction pathways that initiate an inflammatory response that is likely to contribute to Alzheimer's disease pathology.

Mice deficient in interleukin-1beta converting enzyme resist anorexia induced by central lipopolysaccharide

Interleukin-1beta (IL-1beta) is expressed in the mouse brain after intracerebroventricular injection of lipopolysaccharide (LPS) and is thought to be responsible for many of the behavioral and neuroendocrine changes that occur during inflammation. In this study we show that LPS in the brain also induces expression of interleukin-1beta converting enzyme (ICE) and that ICE is important for the characteristic anorectic response of mice to intracerebroventricular LPS. Specifically, mice that were deficient in ICE (ICE(-/-)) resisted the anorexia caused by intracerebroventricular injection of LPS but were sensitive to the anorectic properties of recombinant IL-1beta. The typical anorectic response seen in wild-type (WT) mice after LPS was restored in ICE(-/-) mice by intracerebroventricular administration of the ICE analog cathepsin G. Conversely, anorexia induced by intracerebroventricular injection of LPS in WT mice was blocked by prior intracerebroventricular injection of the ICE antagonist YVAD. CMK. Furthermore, in situ hybridization immunohistochemistry revealed intense expression of ICE mRNA in the hippocampus and dorsomedial hypothalamus of WT mice after intracerebroventricular injection of LPS. Thus ICE mRNA is expressed in brain after intracerebroventricular injection of LPS and is important for induction of anorexia, presumably because it generates mature IL-1beta. These results suggest that preventing generation of mature IL-1beta can inhibit anorexia induced by LPS in the brain and, therefore, reveal ICE as a potential target for regulating food intake during brain inflammation.

Induction of apoptosis due to lowering the level of eukaryotic initiation factor 2-associated protein, p67, from mammalian cells by antisense approach

p67, a cellular glycoprotein, protects eIF2alpha from phosphorylation by inhibitory kinases such as double-stranded RNA dependent eIF2 kinase, PKR, and heme-controlled repressor and thus promotes protein synthesis in mammalian cells. To investigate whether p67 is essential for the survival of mammalian cells, the basal level of p67 was lowered from rat tumor hepatoma cells using antisense approach. The antisense p67 RNA specifically lowered the levels of p67 message and the protein from these cells. As a result, the level of eIF2alpha phosphorylation increased significantly, the overall rate of protein synthesis decreased, and the rate of DNA synthesis also decreased in mammalian cells with low levels of p67 as compared to that seen in control cells. In addition, the majority of the cells with low levels of p67 are arrested at the G1 phase of the cell cycle and die with apoptosis. Taken together, these results suggest that appropriate levels of p67 is required for normal growth of mammalian cells.

Regulation of the hypothalamic-pituitary-adrenal axis by cytokines: actions and mechanisms of action

Glucocorticoids are hormone products of the adrenal gland, which have long been recognized to have a profound impact on immunologic processes. The communication between immune and neuroendocrine systems is, however, bidirectional. The endocrine and immune systems share a common "chemical language," with both systems possessing ligands and receptors of "classical" hormones and immunoregulatory mediators. Studies in the early to mid 1980s demonstrated that monocyte-derived or recombinant interleukin-1 (IL-1) causes secretion of hormones of the hypothalamic-pituitary-adrenal (HPA) axis, establishing that immunoregulators, known as cytokines, play a pivotal role in this bidirectional communication between the immune and neuroendocrine systems. The subsequent 10-15 years have witnessed demonstrations that numerous members of several cytokine families increase the secretory activity of the HPA axis. Because this neuroendocrine action of cytokines is mediated primarily at the level of the central nervous system, studies investigating the mechanisms of HPA activation produced by cytokines take on a more broad significance, with findings relevant to the more fundamental question of how cytokines signal the brain. This article reviews published findings that have documented which cytokines have been shown to influence hormone secretion from the HPA axis, determined under what physiological/pathophysiological circumstances endogenous cytokines regulate HPA axis activity, established the possible sites of cytokine action on HPA axis hormone secretion, and identified the potential neuroanatomic and pharmacological mechanisms by which cytokines signal the neuroendocrine hypothalamus.

Regulation of human IL-18 mRNA expression

As virtually nothing is known about the pattern of expression of human IL-18, we investigated certain factors that may contribute to the regulation of IL-18 mRNA accumulation and compared this with regulation of the human gene encoding the p40 chain of IL-12, a cytokine that shares similar biologic activity with IL-18. IL-18 mRNA was expressed constitutively in unstimulated PBMC or monocytes, unlike p40, which required induction by a stimulus. Upon stimulation, IL-18 transcript accumulation was enhanced with an earlier and more transient pattern of expression than IL-12 p40 mRNA. Bacteria-derived stimuli and priming with IFN-gamma or IL-4 also upregulated IL-18 mRNA in a fashion similar to that of IL-12 p40. IL-10 exerted an inhibitory effect on IL-18 mRNA accumulation, though not as markedly as in the suppression of IL-12 p40 by IL-10. Finally, unlike IL-12 p40 mRNA, the constitutive accumulation of IL-18 transcripts by unstimulated cells was amplified in the presence of the translational blocker cycloheximide, which also caused a superinduction of IL-18 expression after Staphylococcus aureus stimulation.

Increased interleukin-6 expression by microglia from brain of aged mice

Over expression of inflammatory cytokines in the brain may establish a state that is permissive to the onset of neurodegenerative disease. Because the occurrence of certain neurodegenerative diseases increases with age, in the present study we examined the expression of the inflammatory cytokine, interleukin-6 (IL-6), in the brain of aged mice. In an initial experiment, IL-6 was measured in crude protein extracts from brains of juvenile (1-month-old), adult (3-month-old), and aged (24-month-old) male BALB/c mice. The concentration of IL-6 in crude protein extracts from the cerebellum, cerebral cortex, and hippocampus increased with age. The increase in IL-6 was discrete, as levels in the hypothalamus were not age-dependent. To begin evaluating spontaneous IL-6 production in aging, glial cells were cultured from brains of neonate, adult, and aged mice. An age-associated increase in IL-6 mRNA and supernatant IL-6 concentration was evident, indicating glia from aged mice spontaneously express high levels of IL-6 relative to glia from adult and neonate mice. Flow cytometric analysis revealed that cultures established from aged brain compared to either adult or neonate brain comprised more microglia (i.e., MAC-1-positive cells). Furthermore, the proportion of microglia that was positive for IL-6 increased with age, whereas the proportion of astrocytes that were positive for IL-6 was not age-dependent. The present results suggest that IL-6 increases in the mouse brain with age, and that microglia cultured from aged mice spontaneously produce more IL-6 than those from neonate or adult mice. Therefore, microglia may contribute to the increased level of IL-6 present in aged brain.