Interleukin-1beta (IL-1beta)-induced modulation of the hypothalamic IL-1beta system, tumor necrosis factor-alpha, and transforming growth factor-beta1 mRNAs in obese (fa/fa) and lean (Fa/Fa) Zucker rats: implications to IL-1beta feedback systems and cytokine-cytokine interactions

IL-1β in atherosclerotic vascular calcification: From bench to bedside

Atherosclerotic vascular calcification contributes to increased risk of death in patients with cardiovascular diseases. Assessing the type and severity of inflammation is crucial in the treatment of numerous cardiovascular conditions. IL-1β, a potent proinflammatory cytokine, plays diverse roles in the pathogenesis of atherosclerotic vascular calcification. Several large-scale, population cohort trials have shown that the incidence of cardiovascular events is clinically reduced by the administration of anti-IL-1β therapy. Anti-IL-1β therapy might reduce the incidence of cardiovascular events by affecting atherosclerotic vascular calcification, but the mechanism underlying this effect remains unclear. In this review, we summarize current knowledge on the role of IL-1β in atherosclerotic vascular calcification, and describe the latest results reported in clinical trials evaluating anti-IL-1β therapies for the treatment of cardiovascular diseases. This review will aid in improving current understanding of the pathophysiological roles of IL-1β and mechanisms underlying its activity.

Evidence for Inflammation-Associated Depression

This chapter explores the evidence supporting inflammation-associated depression. Data to date suggest a bidirectional relationship between inflammation and depression wherein one process can drive the other. A wealth of animal and clinical studies have demonstrated an association between concentrations of pro-inflammatory cytokines - specifically interleukin (IL)-1β, IL-6, and tumor necrosis factor-α - and depressive symptoms. There is also evidence that this pro-inflammatory state is accompanied by aberrant inflammation-related processes including platelet activation factor hyperactivity, oxidative and nitrosative stress, and damage to mitochondria. These complex and interrelated mechanisms can collectively contribute to negative neurobiological outcomes that may, in part, underlie the etiopathology of depression. Mounting evidence has shown a concomitant reduction in both depressive symptoms and pro-inflammatory cytokine concentrations following treatment with pharmacological anti-inflammatory interventions. Taken together, the reviewed preclinical and clinical findings may suggest the existence of a distinct inflammatory subtype of depression in which these patients exhibit unique biochemical and clinical features and may potentially experience improved clinical outcomes with inflammation-targeted pharmacotherapy.

Inflammation: a mechanism of depression?

In recent decades, major depression has become more prevalent and research has shown that immune activation and cytokine production may be involved. This review is mainly focused on the contribution of inflammation to depression. We first briefly introduce the inflammatory biomarkers of depression, then discuss the sources of cytokines in the brain, and finally describe the neuroimmunological mechanisms underlying the association between inflammation and depression.

Generation of leptin receptor bone marrow chimeras: recovery from irradiation, immune cellularity, cytokine expression, and metabolic parameters

Leptin regulates appetite and metabolism but also immunity and inflammation. Although functional leptin receptors (LepR) are expressed on hematopoietic cells, the role of these receptors in regulating immune function in vivo remains controversial. To clarify this issue, we performed bone marrow (BM) transplantation between obese db/db mice, lacking LepR, and wild-type (WT) mice. Results indicate that expression of LepR on BM-derived cells directly, though partially, regulates spleen and thymus cellularity, although the environment of db mice contributes to maintaining reduced cellularity of these organs. Selective expression of LepR on BM-derived cells also modulates leptin and adiponectin levels, with induction of a more favorable adipokine environment in the WT→db/db group. However, LepR signaling in BM-derived cells is not involved in regulation of body weight (BW) and composition, glycemia, hepatosteatosis or adipose tissue inflammation, although it modulates expression of interleukin (IL)-1β in the brain. Finally, data indicate that db mice have an increased susceptibility to irradiation compared to WT mice in terms of BW loss and recovery of leukocyte counts in peripheral blood. Therefore, interpretation of results obtained using BM chimeras between WT and db mice should take into account the difference in radiation sensitivity between the two types of animals.

Prostaglandins and sickness behavior: old story, new insights

Previous evidence has shown that prostaglandins play a key role in the development of sickness behavior observed during inflammatory states. In particular, prostaglandin E2 (PGE2) is produced in the brain by a variety of inflammatory signals such as endotoxins or cytokines. Its injection has been also shown to induce symptoms of sickness behavior. The role of cyclooxygenase enzymes (COX), the rate-limiting enzymes converting arachidonic acid into prostaglandins, in sickness behavior has been extensively studied, and it has been demonstrated that strategies aiming at inhibiting these enzymes limit anorexia, body weight loss and fever in animals with inflammatory diseases. However, inhibiting COX activity may lead to negative gastric or cardiovascular effects, since COX enzymes play a role in the synthesis of others prostanoids with various and sometimes contrasting properties. Recently, prostaglandin E synthases (PGES), which specifically catalyze the final step of PGE2 biosynthesis, were characterized. Among these enzymes, the microsomal prostaglandin E synthase-1 (mPGES-1) was of a particular interest since it was shown to be up-regulated by inflammatory signals in a variety of cell types. Moreover, mPGES-1 was shown to be crucial for correct immune-to-brain communication and induction of fever and anorexia by pro-inflammatory agents. This review takes stock of previous knowledge and recent advances in understanding the role of prostaglandins and of their specific synthesizing enzymes in the molecular mechanisms underlying sickness behavior. The review concludes with a short summary of key questions that remain to be addressed and points out therapeutic developments in this research field.

Alternative splicing in the NF-kappaB signaling pathway

Activation of transcription factor NF-kappaB can affect the expression of several hundred genes, many of which are involved in inflammation and immunity. The proper NF-kappaB transcriptional response is primarily regulated by post-translational modification of NF-kappaB signaling constituents. Herein, we review the accumulating evidence suggesting that alternative splicing of NF-kappaB signaling components is another means of controlling NF-kappaB signaling. Several alternative splicing events in both the tumor necrosis factor and Toll/interleukin-1 NF-kappaB signaling pathways can inhibit the NF-kappaB response, whereas others enhance NF-kappaB signaling. Alternative splicing of mRNAs encoding some NF-kappaB signaling components can be induced by prolonged exposure to an NF-kappaB-activating signal, such as lipopolysaccharide, suggesting a mechanism for negative feedback to dampen excessive NF-kappaB signaling. Moreover, some NF-kappaB alternative splicing events appear to be specific for certain diseases, and could serve as therapeutic targets or biomarkers.

The 3′ Untranslated Region of the Membrane-Bound IL-1R Accessory Protein mRNA Confers Tissue-Specific Destabilization

IL-1alpha and IL-1beta are proinflammatory cytokines that promote activation of intracellular signaling cascades, leading to stabilization of certain mRNAs and activation of transcription factors. IL-1R type I (IL-1RI) binds IL-1alpha and IL-1beta, and subsequent recruitment of the membrane-bound IL-1R accessory protein (mIL-1RAcP) facilitates signal transduction. Two alternatively spliced isoforms, soluble IL-1RAcP (sIL-1RAcP) and sIL-1RAcP-beta, which lack transmembrane and intracellular domains, have been described. The sIL-1RAcP and possibly sIL-1RAcP-beta can inhibit IL-1 signaling. Proportional expression of the different IL-1RAcP splice variants may be an important determinant of responsiveness to IL-1. We show that although both mIL-1RAcP and sIL-1RAcP mRNAs are widely expressed in human tissue, their relative proportions differ significantly in a tissue-specific manner. Turnover studies revealed that the sIL-1RAcP mRNA has a half-life of approximately 48 h in both the kidney cell line 293 and the hepatoma cell line HepG2. The mIL-1RAcP mRNA has a similar half-life in 293 cells, but a considerably shorter half-life of approximately 5 h in HepG2 cells. Using luciferase reporter constructs, we demonstrated that this specific destabilization of the mIL-1RAcP mRNA in the latter cell type is mediated by its 2.8-kb 3'-untranslated region. Deletion analysis further established that the cell line-specific instability does not involve AU-rich elements, but is mediated by several novel elements that appear to act independently; such elements may be recognized by proteins expressed specifically in some, but not all, tissues. These data demonstrate that the cellular capacity to respond to IL-1 is tightly regulated in a tissue-specific manner.

Short-term resistance to diet-induced obesity in A/J mice is not associated with regulation of hypothalamic neuropeptides

To investigate the mechanisms underlying long-term resistance of the A/J mouse strain to diet-induced obesity, we studied, over a period of 4 wk, the expression of uncoupling proteins in brown adipose tissue and the expression of hypothalamic neuropeptides known to regulate energy homeostasis and then used microarray analysis to identify other potentially important hypothalamic peptides. Despite increased caloric intake after 2 days of high-fat feeding, body weights of A/J mice remained stable. On and after 1 wk of high-fat feeding, A/J mice adjusted their food intake to consume the same amount of calories as mice fed a low-fat diet; thus their body weight and insulin, corticosterone, free fatty acid, and glucose levels remained unchanged for 4 wk. We found no changes in hypothalamic expression of several orexigenic and/or anorexigenic neuropeptides known to play an important role in energy homeostasis for the duration of the study. Uncoupling protein-2 mRNA expression in brown adipose tissue, however, was significantly upregulated after 2 days of high-fat feeding and tended to remain elevated for the duration of the 4-wk study. Gene array analysis revealed that several genes are up- or downregulated in response to 2 days and 1 wk of high-fat feeding. Real-time PCR analysis confirmed that expression of the hypothalamic IL-1 pathway (IL-1beta, IL-1 type 1 and 2 receptors, and PPM1b/PP2C-beta, a molecule that has been implicated in the inhibition of transforming growth factor-beta-activated kinase-1-mediated IL-1 action) is altered after 2 days, but not 1 wk, of high-fat feeding. The role of additional molecules discovered by microarray analysis needs to be further explored in the future.

Gene expression profiling in spleens of deoxynivalenol-exposed mice: immediate early genes as primary targets

Exposure to the trichothecene mycotoxin deoxynivalenol (DON) alters immune functions in vitro and in vivo. To gain further insight into DON's immunotoxic effects, microarrays were used to determine how acute exposure to this mycotoxin modulates gene expression profiles in murine spleen. B6C3F1 mice were treated orally with 25mg/kg body weight DON, and 2h later spleens were collected for macroarray analysis. Following normalization using a local linear regression model, expression of 116 out of 1176 genes was significantly altered compared to average expression levels in all treatment groups. When genes were arranged into an ontology tree to facilitate comparison of expression profiles between treatment groups, DON was found primarily to modulate genes associated with immunity, inflammation, and chemotaxis. Real-time polymerase chain reaction was used to confirm modulation for selected genes. DON was found to induce the cytokines interleukin (IL)-1alpha, IL-1beta, IL-6 and IL-11. In analogous fashion, DON upregulated expression of the chemokines macrophage inhibitory protein-2 (MIP-2), cytokine-induced chemoattractant protein-1 (CINC-1), monocyte chemoattractant protein (MCP)-1, MCP-3, and cytokine-responsive gene-2 (CRG-2). c-Fos, Fra-, c-Jun, and JunB, components of the activator protein-1 (AP-1) transcription factor complex, were induced by DON as well as another transcription factor, NR4A1. Four hydrolases were found to be upregulated by DON, including mitogen-activated protein kinase phosphatase 1 (MKP1), catalytic subunit beta isoform (CnAbeta), protein tyrosine phosphatase receptor type J (Ptprj), and protein tyrosine phosphatase nonreceptor type 8 (Ptpn8), whereas three other hydrolases, microsomal epoxide hydrolase (Eph) 1, histidine triad nucleotide binding protein (Hint), and proteosome subunit beta type 8 (Psmb8) were significantly decreased by the toxin. Finally, cysteine-rich protein 61 (CRP61) and heat-shock protein 40 (Hsp40), genes associated with signaling, were increased, while Jun kinase 2 (JNK2) was decreased. Taken together, data suggest that DON upregulated the expression of multiple immediate early genes, many of which are likely to contribute to the complex immunological effects reported for this and other trichothecenes.

Cytokine-serotonin interaction through IDO: a neurodegeneration hypothesis of depression

There are different theories and hypotheses related to the aetiology of depression. The interaction between brain 5-HT level and the activity of its autoreceptors plays a role in mood changes and depression. In major depression, activation of the inflammatory response system (IRS) and, increased concentrations of proinflammatory cytokines, prostaglandin E2 and negative immuno-regulatory cytokines in peripheral blood have been reported. Recently, pro-inflammatory cytokines have been found to have profound effects on the metabolism of brain serotonin through the enzyme indoleamine-2,3-dioxygenase (IDO) that metabolizes the tryptophan, the precursor of 5-HT to neurodegenerative quinolinate and neuroprotective kynurenate. The cytokine-serotonin interaction that leads to the challenge between quinolinate and kynurenate in the brain explains the neurodegeneration hypothesis of depression.

Interleukin-1beta system in anorectic catabolic tumor-bearing rats

PURPOSE OF REVIEW

The onset of cancer anorexia and the accompanying neurological symptoms and signs involve the general influence of cytokines on the brain. Using methylcholanthrene to induce tumors in Fischer 344 rats, we measured various specific components of the cytokine-induced anorectic reaction, including: (1) IL-1beta system components (ligand, signaling receptor, receptor accessory proteins, and receptor antagonist); (2) TNF-alpha; (3) TGF-beta1; and (4) IFN-gamma in the tumor tissue, the liver and the brain.

RECENT FINDINGS

The data show that IL-1beta, TNF-alpha and IFN-gamma messenger RNA were detected in the tumor tissue of anorectic tumor-bearing rats. In brain regions, anorexia is associated with the upregulation of IL-1beta and its receptor mRNA. All other mRNA remained unchanged in the brain regions examined.

SUMMARY

This suggests that IL-1beta and its receptor may play a significant role in this model of cancer-associated anorexia. In vivo, the characterization of cytokine components in the brain may provide data for potential pharmacological interventions to ameliorate the anorexia of disease.

Does neuroimmune dysfunction mediate seasonal mood changes in winter depression?

BACKGROUND

Animal studies have demonstrated seasonal changes in immune function mediated by nocturnal melatonin duration as a biological signal for photoperiod. Recent research has highlighted the potential role of neuroimmune dysfunction in depressive disorders. The etiology of winter depression (seasonal affective disorder, or SAD) is not known, but a number of studies have provided support for both photoperiod and neurotransmitter hypotheses.

HYPOTHESIS

A new hypothesis is presented that links the SAD data on melatonin, photoperiod, and neurotransmitters by proposing that seasonal increases in proinflammatory cytokines are critical in the pathophysiology of winter SAD.

TESTING THE HYPOTHESIS

In SAD patients, but not healthy subjects: proinflammatory cytokines will be increased and the Th1/Th2 balance will be shifted to the left in winter compared to summer; neuroimmune function will be correlated with nocturnal melatonin duration in SAD patients; and light treatment will correct neuroimmune dysfunction.

IMPLICATIONS OF THE HYPOTHESIS

Diagnostic tests for SAD may be developed using cytokine assays; neuroimmune dysfunction may be predictors of response to treatments; new treatments for SAD (immune or anti-inflammatory treatment) may be developed.

Expression of alternatively spliced interleukin-1 receptor accessory protein mRNAs is differentially regulated during inflammation and apoptosis

Two alternative splice variants of the interleukin-1 receptor accessory protein (IL-1RAcP) mRNA are known. Membrane-bound IL-1RAcP (mIL-1RAcP) promotes intracellular interleukin-1 (IL-1) signalling whereas soluble IL-1RAcP (sIL-1RAcP) is probably an inhibitor of IL-1 signalling. Here we establish that sIL-1RAcP mRNA levels increase 16-fold in response to phorbol esters in the human hepatoma cell line HepG2 via a mechanism that depends on de novo protein synthesis. Following exposure of cells to UV light, a potent inducer of apoptosis, mIL-1RAcP mRNA is rapidly down-regulated and a new steady-state level established briefly before a gradual return to pretreatment levels. Following treatment with staurosporine, also an inducer of apoptosis, mIL-1RAcP mRNA levels steadily decrease through 72 h, with little change in sIL-1RAcP mRNA levels. A novel alternative splice variant, sIL-1RAcP-beta, was identified. Its sequence indicates that sIL-1RAcP-beta is secreted and has a unique second half of the third immunoglobulin (Ig) domain. The dramatic changes in levels of IL-1RAcP mRNAs suggest important functions in regulating sensitivity to IL-1 during stress and may play a role in oncogenic processes that are engaged during chronic inflammation.

Insulin-like growth factor 1-induced interleukin-1 receptor II overrides the activity of interleukin-1 and controls the homeostasis of the extracellular matrix of cartilage

OBJECTIVE

We examined the effect of the insulin-like growth factor 1 (IGF-1)/IGF receptor I (IGFRI) autocrine/paracrine anabolic pathway on the extracellular matrix (ECM) of human chondrocytes and the mechanism by which IGF-1 reverses the catabolic effects of interleukin-1 (IL-1).

METHODS

Phenotypically stable human articular cartilage cells were obtained from normal cartilage and maintained in culture in alginate beads for 1 week to reach equilibrium of accumulated cell-associated matrix (CAM) compounds. Levels of CAM components aggrecan and type II collagen (CII) and levels of intracellular IGF-1, IL-1alpha, and IL-1beta and their respective plasma membrane-bound receptors IGFRI, IL-1 receptor I (IL-1RI), and the decoy receptor IL-1RII were assayed using flow cytometry to investigate the relationship between the autocrine/paracrine pathways and the homeostasis of ECM molecules in the CAM. The effects of IGF-1 on the expression of IGF-1, IL-1alpha, and IL-1beta and their respective receptor systems, the aggrecan core protein, and CII were determined by flow cytometry.

RESULTS

Cause-effect relationship experiments showed that IGF-1 up-regulates the levels of IGF-1, IGFRI, aggrecan, and CII in the CAM. No effects on the expression of IL-1alpha and IL-1beta and their signaling receptor IL-1RI were observed. However, IGF-1 was able to reverse IL-1beta-mediated degradation of aggrecan and the repression of the aggrecan synthesis rate. Interestingly, levels of aggrecan and CII in the CAM strongly correlated not only with IGF-1, but also with IL-1RII, which acts as a decoy receptor for IL-1alpha and IL-1beta. This suggests that IGF-1 and IL-1RII may cooperate in regulating ECM homeostasis. Additional experiments demonstrated that IGF-1 up-regulated IL-1RII, thereby overriding the catabolic effects of IL-1.

CONCLUSION

These findings reveal a new paradigm by which IGF-1 influences chondrocyte metabolism, by reversing the IL-1-mediated catabolic pathway through up-regulation of its decoy receptor.

Lewis hypothalamic cells constitutively and upon stimulation express higher levels of mRNA for pro-inflammatory cytokines and related molecules: comparison with inflammatory resistant Fischer rat hypothalamic cells

Endogenous hypothalamic pro-inflammatory cytokines modulate the hypothalamic-pituitary-adrenal (HPA) axis responses. To investigate whether hypothalamic IL-1beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha) are associated with differential inflammatory susceptibilities between Lewis (LEW/N) and Fischer (F344/N) rats, mRNA levels of pro-inflammatory cytokines and related molecules in hypothalamic cell cultures of both strains were quantified by real-time polymerase chain reaction (PCR). In addition to IL-1beta, IL-6, TNF-alpha, and their receptors, LEW/N hypothalamic cells also transcribed more anti-inflammatory molecules, IL-1RII, IL-1RA, and transforming growth factor (TGFbeta1), than F334/N cells. Our findings suggest that a balance exists between transcripts for endogenous pro- and anti-inflammatory molecules in LEW/N rats that may allow them, under basal conditions, to maintain hypothalamic homeostasis and health. However, under stimulated conditions, this balance may be more easily perturbed toward chronic inflammation.

The role of TNF-alpha in amygdala kindled rats

In the present study, the interaction between epileptogenesis and the immune system were studied in a kindling model. First, the effects of a single administration of TNF-alpha (5.0 microg/kg, i.p.) on seizure and EEG activity were investigated in amygdala-kindled rats. TNF-alpha treated rats showed more prolonged epileptiformic discharges than control rats. TNF-alpha also induced a decrease in the power of delta band and an increase in theta and alpha activity. In addition, a marked increase in the power of beta and gamma band was observed. The EEG changes were most numerous in the frontal cortex and amygdala. All effects were registered 24 h after TNF-alpha administration. Finally, electrical stimulation enhanced the level of TNF-alpha in blood serum from 1.9 +/- 1.5 to 12.7 +/- 3.8 pg/ml and in brain tissue 56.8 +/- 6.0 to 109.2 +/- 6.0 pg/mg, as was determined via the ELISA method. It can be concluded that there is a mutual facilitative interaction of both epileptogenic and cytokine-derived mechanisms on this type of seizure. The changes in the power spectrum of the EEG after TNF-alpha might contribute to intensify thalamic-derived facilitation of epileptic discharge in cortical structures.

Cycle-dependent expression of interleukin-1 receptor type II in the human endometrium

Cytokines such as interleukin-1 (IL-1) play a major role in the reparative and inflammatory-like processes that occur in human endometrium during every menstrual cycle, but they also seem to be implicated in critical reproductive events such as ovulation and implantation. Interleukin-1 is tightly regulated in the body by a complex network of control systems. In the present study, we examined the expression of IL-1RII, a natural specific inhibitor of IL-1, in the human endometrium and found an interesting distribution and temporal pattern of expression throughout the menstrual cycle. Immunoreactive IL-1RII was found in stromal as well as epithelial cells, but it was predominant within the lumen of the glands and the apical side of surface epithelium. In situ hybridization and reverse transcription-polymerase chain reaction (RT-PCR) analyses showed higher levels of mRNA in epithelial than in stromal cells. The IL-1RII cellular and luminal secretion followed a regulated cycle phase-dependent pattern of expression. Although elevated in the late proliferative/early secretory phase of the menstrual cycle, IL-1RII luminal secretion significantly decreased in the midsecretory phase, reaching its lowest levels at Day 21, before augmenting markedly again during the late secretory phase. This pattern of expression was less obvious at the level of cellular staining, as examined by immunohistochemistry, but it was corroborated by Western blot analysis of IL-1RII protein and semiquantitative RT-PCR of IL-1RII mRNA in the whole endometrial tissue and separated glandular epithelial cells. The reduced expression of IL-1RII within the implantation window suggests the existence of accurate regulatory mechanisms that, by down-regulating IL-1RII expression, alleviate IL-1 inhibition during this crucial period and facilitate IL-1 proimplantation actions. The elevated expression of IL-1RII observed during the late secretory phase suggests an involvement of IL-1RII in control of the proinflammatory state that takes place in the endometrium during the premenstrual and menstrual periods.

Stress, peer affiliation, and transforming growth factor-beta1 in differentially reared primates

A bidirectional regulatory interaction between the central nervous system and the immune system is largely provided by cytokines and their specific receptors, which are expressed by cells of both systems. Transforming growth factor-beta1 (TGF-beta1), produced by glial cells and lymphocytes and regulated by steroid hormones, is one such cytokine. In the current study, we examined the relationship between TGF-beta1 and peer affiliation in bonnet macaques (Macaca radiata) either reared normally or exposed as infants to conditions in which their mothers faced fluctuating requirements for food procurement (variable foraging demand [VFD]). Rearing under VFD conditions has been previously shown to produce dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis in these animals. Serum levels of TGF-beta1 after exposure to a moderate stressor had no correlation with peer affiliation under baseline conditions (r=.07), but were highly correlated with affiliation after subsequent challenge with a fear stimulus (r=.62). Affiliation after the fear stimulus also was inversely correlated with baseline levels of affiliation (r=-.71). These data suggest that changes in peripheral TGF-beta1 may be reflective of latent behavioral and biochemical propensities possibly related to affect. Further examination of the effects of early adversity will improve our understanding of the relationship between the HPA axis and immune function.

Diffusion and action of intracerebroventricularly injected interleukin-1 in the CNS

Interleukin-1beta acts on the CNS to induce fever, neuroendocrine activation and behavioural depression. We have previously demonstrated that interleukin-1beta is synthesized in glial cells and macrophages of circumventricular organs and choroid plexus after intraperitoneal administration of bacterial lipopolysaccharide. Whether, and how, interleukin-1beta produced in glial cells affects neuronal functioning is unknown. Diffusion throughout the extracellular space is an important pathway by which factors produced by glial cells act on distant cells, a phenomenon coined "volume transmission". The present study assessed diffusion of recombinant rat interleukin-1beta, recombinant human interleukin-1 receptor antagonist and 10mol. wt dexran in the rat CNS after intracerebroventricular administration to model interleukin-1beta release from choroid plexus. Immunocytochemistry with specific antibodies directed against interleukin-1beta and interleukin-1 receptor antagonist revealed that these molecules rapidly penetrated into periventricular tissue and spread along white matter fibre bundles and blood vessels in the caudoputamen, hypothalamus and amygdala. The transcription factor nuclear factor kappa B and the immediate-early gene product Fos were detected immunocytochemically to reveal interleukin-1beta action. Intracerebroventricular infusion of interleukin-1beta induced nuclear factor kappa B translocation in choroid plexus, ependymal cells, basolateral amygdala, cerebral vasculature and meninges. Fos immunoreactivity was found in the supraoptic and paraventricular hypothalamus and central amygdala. We propose that intracerebroventricular injected interleukin-1beta can enter the brain parenchyma and act as a "volume transmission" signal in, for example, the basolateral amygdala where it might activate a neuronal projection to the central amygdala.

Pro-inflammatory and anti-inflammatory cytokine mRNA induction in the periphery and brain following intraperitoneal administration of bacterial lipopolysaccharide

Gram-negative bacteria-derived lipopolysaccharide (LPS or endotoxin) is known to play an important role in immune and neurological manifestations during bacterial infections. LPS exerts its effects through cytokines, and peripheral or brain administration of LPS activates cytokine production in the brain. In this study, we investigated cytokine and neuropeptide mRNA profiles in specific brain regions and peripheral organs, as well as serum tumor necrosis factor (TNF)-alpha protein levels, in response to the intraperitoneal administration of LPS. For the first time, the simultaneous analysis of interleukin (IL)-1beta system components (ligand, signaling receptor, receptor accessory proteins, receptor antagonist), TNF-alpha, transforming growth factor (TGF)-beta1, glycoprotein 130 (IL-6 receptor signal transducer), OB protein (leptin) receptor, neuropeptide Y, and pro-opiomelanocortin (opioid peptide precursor) mRNAs was done in samples from specific brain regions in response to peripherally administered LPS. The same brain region/organ sample was assayed for all cytokine mRNA components. Peripherally administered LPS up-regulated pro-inflammatory cytokine (IL-1beta and/or TNF-alpha) mRNAs within the cerebral cortex, cerebellum, hippocampus, spleen, liver, and adipose tissue. LPS also increased plasma levels of TNF-alpha protein. LPS did not up-regulate inhibitory (anti-inflammatory) cytokine (IL-1 receptor antagonist and TGF-beta1) mRNAs in most brain regions (except for IL-1 receptor antagonist in the cerebral cortex and for TGF-beta1 in the hippocampus), while they were increased in the liver, and IL-1 receptor antagonist was up-regulated in the spleen and adipose tissue. Overall, peripherally administered LPS modulated the levels of IL-1beta system components within the brain and periphery, but did not affect the neuropeptide-related components studied. The data suggest specificity of transcriptional changes induced by LPS and that cytokine component up-regulation in specific brain regions is relevant to the neurological and neuropsychiatric manifestations associated with peripheral LPS challenge.

Cytokine signals propagate through the brain

Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha) are proinflammatory cytokines that are constitutively expressed in healthy, adult brain where they mediate normal neural functions such as sleep. They are neuromodulators expressed by and acting on neurons and glia. IL-1 and TNFalpha expression is upregulated in several important diseases/disorders. Upregulation of IL-1 and/or TNFalpha expression, elicited centrally or systemically, propagates through brain parenchyma following specific spatio-temporal patterns. We propose that cytokine signals propagate along neuronal projections and extracellular diffusion pathways by molecular cascades that need to be further elucidated. This elucidation is a prerequisite for better understanding of reciprocal interactions between nervous, endocrine and immune systems.

Central nervous system mechanisms contributing to the cachexia-anorexia syndrome

The cachexia-anorexia syndrome occurs in chronic pathophysiologic processes including cancer, infection with human immunodeficiency virus, bacterial and parasitic diseases, inflammatory bowel disease, liver disease, obstructive pulmonary disease, cardiovascular disease, and rheumatoid arthritis. Cachexia makes an organism susceptible to secondary pathologies and can result in death. Cachexia-anorexia may result from pain, depression or anxiety, hypogeusia and hyposmia, taste and food aversions, chronic nausea, vomiting, early satiety, malfunction of the gastrointestinal system (delayed digestion, malabsorption, gastric stasis and associated delayed emptying, and/or atrophic changes of the mucosa), metabolic shifts, cytokine action, production of substances by tumor cells, and/or iatrogenic causes such as chemotherapy and radiotherapy. The cachexia-anorexia syndrome also involves metabolic and immune changes (mediated by either the pathophysiologic process, i.e., tumor, or host-derived chemical factors, e.g., peptides, neurotransmitters, cytokines, and lipid-mobilizing factors) and is associated with hypertriacylglycerolemia, lipolysis, and acceleration of protein turnover. These changes result in the loss of fat mass and body protein. Increased resting energy expenditure in weight-losing cachectic patients can occur despite the reduced dietary intake, indicating a systemic dysregulation of host metabolism. During cachexia, the organism is maintained in a constant negative energy balance. This can rarely be explained by the actual energy and substrate demands by tumors in patients with cancer. Overall, the cachectic profile is significantly different than that observed during starvation. Cachexia may result not only from anorexia and a decreased caloric intake but also from malabsorption and losses from the body (ulcers, hemorrhage, effusions). In any case, the major deficit of a cachectic organism is a negative energy balance. Cytokines are proposed to participate in the development and/or progression of cachexia-anorexia; interleukin-1, interleukin-6 (and its subfamily members such as ciliary neurotrophic factor and leukemia inhibitory factor), interferon-gamma, tumor necrosis factor-alpha, and brain-derived neurotrophic factor have been associated with various cachectic conditions. Controversy has focused on the requirement of increased cytokine concentrations in the circulation or other body fluids (e.g., cerebrospinal fluid) to demonstrate cytokine involvement in cachexia-anorexia. Cytokines, however, also act in paracrine, autocrine, and intracrine manners, activities that cannot be detected in the circulation. In fact, paracrine interactions represent a predominant cytokine mode of action within organs, including the brain. Data show that cytokines may be involved in cachectic-anorectic processes by being produced and by acting locally in specific brain regions. Brain synthesis of cytokines has been shown in peripheral models of cancer, peripheral inflammation, and during peripheral cytokine administration; these data support a role for brain cytokines as mediators of neurologic and neuropsychiatric manifestations of disease and in the brain-to-peripheral communication (e.g., through the autonomic nervous system). Brain mechanisms that merit significant attention in the cachexia-anorexia syndrome are those that result from interactions among cytokines, peptides/neuropeptides, and neurotransmitters. These interactions could result in additive, synergistic, or antagonistic activities and can involve modifications of transducing molecules and intracellular mediators. Thus, the data show that the cachexia-anorexia syndrome is multifactorial, and understanding the interactions between peripheral and brain mechanisms is pivotal to characterizing the underlying integrative pathophysiology of this disorder.

Interleukin-13 and transforming growth factor-beta1 inhibit spontaneous sleep in rabbits

Proinflammatory cytokines, including interleukin-1beta and tumor necrosis factor-alpha are involved in physiological sleep regulation. Interleukin (IL)-13 and transforming growth factor (TGF)-beta1 are anti-inflammatory cytokines that inhibit proinflammatory cytokines by several mechanisms. Therefore, we hypothesized that IL-13 and TGF-beta1 could attenuate sleep in rabbits. Three doses of IL-13 (8, 40, and 200 ng) and TGF-beta1 (40, 100, and 200 ng) were injected intracerebroventricularly 3 h after the beginning of the light period. In addition, one dose of IL-13 (200 ng) and one dose of TGF-beta1 (200 ng) were injected at dark onset. The two higher doses of IL-13 and the highest dose of TGF-beta1 significantly inhibited spontanenous non-rapid eye movement sleep (NREMS) when they were given in the light period. IL-13 also inhibited NREMS after dark onset administration; however, the inhibitory effect was less potent than that observed after light period administration. The 40-ng dose of IL-13 inhibited REMS duration during the dark period. TGF-beta1 administered at dark onset had no effect on sleep. These data provide additional evidence for the hypothesis that a brain cytokine network is involved in regulation of physiological sleep.

Kindling modulates the IL-1beta system, TNF-alpha, TGF-beta1, and neuropeptide mRNAs in specific brain regions

Cytokines and neuropeptides may be involved in seizure-associated processes. Following amygdala kindling in rats, we determined alterations of IL-1beta, IL-1 receptor antagonist (IL-1Ra), IL-1 receptor type I (IL-1RI), IL-1 receptor accessory proteins (IL-1R AcPs) I and II, TNF-alpha, TGF-beta1, neuropeptide Y (NPY), glycoprotein 130 (gp 130) and pro-opiomelanocortin (POMC) mRNA levels in the parietal, prefrontal and piriform cortices, amygdala, hippocampus and hypothalamus. Messenger RNAs expression in all brain regions was determined 2 h or 3 weeks following the last generalized convulsive seizure triggered from the ipsilateral kindled amygdala. The same brain region sample was used to assay for changes of all mRNA components. The results show that the 2 h-kindled group exhibited a significant up-regulation of IL-1beta, IL-1RI, TNF-alpha and TGF-beta1 mRNAs in all three cortical brain regions, amygdala and hippocampus. The largest up-regulation occurred in the prefrontal cortex (about 30-fold induction for IL-1beta and TNF-alpha mRNAs). IL-1R AcP I and II mRNA levels were also up-regulated in the cortical regions. No changes in IL-1beta, IL-1RI or TNF-alpha mRNA levels occurred in the 3 week-kindled group. NPY mRNA levels increased in the hippocampus, prefrontal and piriform cortices in the 2 h-kindled group, while IL-1Ra, gp 130, or POMC mRNA levels did not change in any group. The overall profile of mRNA changes shows specificity of transcriptional modulation induced by amygdala kindling. The data support a role of cytokines and NPY in the adaptive mechanisms associated with generalized seizure activity, with implications for neuroprotection, neuronal dysfunction and vulnerability associated with epileptic activity.

Neither acute nor chronic exposure to a naturalistic (predator) stressor influences the interleukin-1beta system, tumor necrosis factor-alpha, transforming growth factor-beta1, and neuropeptide mRNAs in specific brain regions

Physical (neurogenic) stressors may influence immune functioning and interleukin-1beta (IL-1beta) mRNA levels within several brain regions. The present study assessed the effects of an acute or repeated naturalistic, psychogenic stressor (predator exposure) on brain cytokine and neuropeptide mRNAs. Acute predator (ferret) exposure induced stress-like behavioral effects, including elicitation of a startle response and reduced exploratory behaviors; these responses diminished after 30 sessions. Moreover, acute and repeated predator exposure, like acute restraint stress, increased plasma corticosterone levels measured 5 min later, but not 2 h after stressor exposure. In contrast, none of the stressors used influenced IL-1beta, IL-1 receptor antagonist, IL-1 receptor type I, IL-1 receptor accessory proteins I and II, or tumor necrosis factor-alpha mRNA levels in the prefrontal cortex, amygdala, hippocampus, or hypothalamus. Likewise, there were no stressor effects on transforming growth factor-beta1, neuropeptide Y, glycoprotein 130, or leptin receptor mRNAs in brain regions. Thus, the naturalistic/psychogenic stressor used does not affect any of the brain cytokine component mRNAs studied. It is suggested that this type of stressor activates homeostatic mechanisms (e.g., glucocorticoid release), which act to preclude brain cytokine alterations that would otherwise favor neuroinflammatory/neuroimmunological responses and the consequent increase of brain sensitivity to neurotoxic and neurodegenerative processes.

Autoregulation of the interleukin-1 system and cytokine-cytokine interactions in primary human astrocytoma cells

Cytokines are proposed to play important roles in brain tumor biology. Previous studies reported on interleukin-1beta (IL-1beta) production and IL-1 receptor type I (IL-1RI, signaling receptor) expression in human astrocytomas, and on IL-1beta action in astrocytoma cell lines. However, all studies that have tested the direct action of cytokines have used exclusively astrocytoma cell lines, which do not recapitulate the in situ astrocytoma. Here, we demonstrate that astrocytoma cells obtained shortly after tumor neurosurgical resection respond to the direct application of human IL-1beta with a significant upregulation of IL-1alpha, IL-1beta, IL-1RI, and tumor necrosis factor-alpha (TNF-alpha) mRNAs. IL-1 receptor antagonist (IL-1Ra, an endogenous inhibitor that blocks IL-1alpha and IL-1beta actions) mRNA was not upregulated. Application of heat-inactivated IL-1beta had no effect on any cytokine component examined, demonstrating specificity of action. On the other hand, IL-1beta application did not modulate any cytokine component in acutely resected and dissociated primitive neuroectodermal tumor cells. The data have implications for a positive autoregulatory IL-1beta feedback system and synergistic IL-1beta <=> TNF-alpha interactions, which can be involved in the growth of pilocytic astrocytomas. The results together with our previous studies also support the notion that IL-1Ra or a compound with similar cytokine inhibitory activity could be useful for brain immunotherapy of astrocytomas.

Cytokine-cytokine interactions and the brain

Cytokine-cytokine interactions play a role in health and are crucial during immunological and inflammatory responses in disease. Cytokine interactions can result in additive, antagonist, or synergistic activities in maintaining physiological functions such as feeding, body temperature, and sleep, as well as in anorectic, pyrogenic, and somnogenic neurological manifestations of acute and chronic disease. These interactions involve signaling homology, convergence of signaling pathways, and/or positive or negative feedbacks within and among cytokine systems. The interplay of cytokines with neurotransmitters, peptides/neuropeptides, and hormones also influence cytokine action in the brain. Interactive chemical cascades involving cytokines are consistent with the homeostatic physiological mechanisms and with the multi-humoral, pleiotropic, and redundant processes that occur during acute and chronic disease.

Delayed effects of stress and immune activation

Stress responses play a crucial adaptive role but impose potentially subversive demands on the organism. The same holds for the symptoms of illness as seen after immune activation by pathogens or tissue damage. The responses to immune stimuli and stressors show remarkable similarities and rely on similar control mechanisms in the brain: i.e. they involve neuropeptides of the corticotropin releasing factor (CRF) family. Immune and non-immune challenges lead to responses that normally show a temporal relationship with the duration and intensity of the stimulus and the (re)activity of the stress-responsive systems return to their pre-challenged state within hours or days. However, exposure of animals or man to specific stimuli can induce delayed and long-lasting (weeks, months) alternation in stress responsive systems, resulting in a prolonged period of increased stress vulnerability. Immune stimuli are particularly powerful in eliciting such a stress vulnerable state. Various adaptive changes in the (neuro)biological substrate as seen during this stress vulnerable state also occur in depression, and may be causally related to the depressive symptoms that are often associated with infectious and inflammatory diseases.

Persistent Borna disease virus infection of neonatal rats causes brain regional changes of mRNAs for cytokines, cytokine receptor components and neuropeptides

Borna disease virus (BDV) replicates in brain cells. The neonatally infected rat with BDV exhibits developmental-neuromorphological abnormalities, neuronal cytolysis, and multiple behavioral and physiological alterations. Here, we report on the levels of interleukin-1beta (IL-1beta), IL-1 receptor antagonist (IL-1Ra), tumor necrosis factor-alpha (TNF-alpha), transforming growth factor-beta1 (TGF-beta1), IL-1 receptor type I (IL-1RI), IL-1 receptor accessory protein (IL-1R AcP) I and II, glycoprotein 130, and various neuropeptide mRNAs in the cerebellum, parieto-frontal cortex, hippocampus and hypothalamus of BDV-infected rats at 7 and 28 days postintracerebral BDV inoculation. The data show that cytokine and neuropeptide mRNA components are abnormal and differentially modulated in brain regions. IL-1beta, TNF-alpha and TGF-beta1 mRNA levels were up-regulated in all brain regions following BDV inoculation. The same cerebellar samples from BDV-infected animals exhibited the highest levels of IL-1beta, IL-1Ra, TNF-alpha, IL-1RI, and IL-1R AcP II mRNA expression. The profiles of IL-1beta, IL-1Ra, TNF-alpha, and TGF-beta1 mRNA induction in the cerebellar samples were highly intercorrelated, indicating an association among cytokine ligand mRNAs. Cytokine mRNA induction was differentially up-regulated among brain regions, except for TGF-beta1. Specificity of transcriptional changes in response to BDV infection is also suggested by the up-regulation of cytokine and neuropeptide Y mRNAs associated with down-regulation of pro-opiomelanocortin, and with no change of IL-1R AcPI, dynorphin and leptin receptor mRNAs in the same brain region samples. Other data also show a differential mRNA component modulation in distinct brain regions obtained from the same rats depending on the stage of BDV infection. The conclusion of these studies is that cytokines may play a role in the neuropathophysiology of neonatally BDV-infected rats.

Basal and IL-1beta-stimulated cytokine and neuropeptide mRNA expression in brain regions of young and old Long-Evans rats

Young and old Long-Evans rats respond with fevers of equal magnitude and duration to the brain administration of interleukin-1beta (IL-1beta). Here, we characterized brain regional mRNA expression of cytokine and neuropeptide components in response to the brain administration of IL-1beta. We used specific and highly sensitive RNase protection assays to determine mRNA changes for IL-1beta, IL-1 receptor type I (IL-1RI), IL-1R accessory proteins I and II (IL-1R AcP I and II), IL-1 receptor antagonist (IL-1Ra), transforming growth factor-beta1 (TGF-beta1), glycoprotein 130 (gp 130), leptin receptor (OB-R), neuropeptide Y (NPY) and pro-opiomelanocortin (POMC) in the cerebellum, parieto-frontal cortex, hippocampus, hypothalamus, and midbrain of male young (3-5 months) and old (24-26 months) Long-Evans rats. In both young and old rats, IL-1beta induced a significant up-regulation of cerebellar IL-1Ra, IL-1RI, and TGF-beta1 mRNAs; hippocampal TGF-beta1 mRNA; hypothalamic IL-1beta, IL-1Ra, TGF-beta1, and gp 130 mRNAs; and midbrain IL-1beta and TGF-beta1 mRNAs. There were no age-related differences in any cytokine mRNA levels under basal or IL-1beta-stimulated conditions. Levels of hypothalamic POMC mRNA were different between age groups under basal and stimulated conditions. IL-1R AcP I and leptin receptor did not change in any brain region from either young or old rats, suggesting specificity of transcriptional changes. The data show that old Long-Evans rats are not defective in their capacity to develop an appropriate cytokine response to the brain administration of IL-1beta. The implications of these findings for neuroimmunological-neuroinflammatory and neurotoxic/neurodegenerative processes are discussed.

Brain tumor development in rats is associated with changes in central nervous system cytokine and neuropeptide systems

Cytokines have roles in tumor biology and induce neurological manifestations. Cytokines produced in response to a brain tumor may generate neurological manifestations via paracrine action. We investigated cytokine modulation in an in vivo brain tumor model with behavioral, morphological, and molecular approaches. Rat C6 glioma cells were implanted into the third cerebral ventricle of Wistar rats, their behavior was monitored, and the development of an intracranial tumor of astrocytic origin was confirmed by histology and positive immunostaining for vimentin, S-100 protein, and glial fibrillary acidic protein. Sensitive and specific RNase protection assays were used to analyze cytokine messenger RNA (mRNA) in brain regions from anorexic brain tumor-bearing animals. Brain tumor formation was associated with significant increased levels of interleukin (IL)-1beta, IL-1 receptor antagonist, IL-1 receptor type I, tumor necrosis factor (TNF)-alpha, and transforming growth factor (TGF)-beta1 mRNAs in the cerebellum, hippocampus, and hypothalamus. IL-1 receptor accessory proteins I and II mRNAs were increased in the cerebellum and hypothalamus. We also examined hypothalamic feeding-associated components: neuropeptide Y and proopiomelanocortin mRNAs were down-regulated, glycoprotein 130 mRNA levels were up-regulated, and leptin receptor (OB-R) mRNA levels were unchanged. These dissimilar profiles of mRNA expression suggest specificity of brain tumor-induced transcriptional changes. The data implicate cytokines as important factors in brain tumor-host interactions in vivo. The data also show that the C6 cell-induced glioma can be used as a behavioral-molecular model to study cytokine and neuropeptide modulation and action during the host biochemical and physiological responses to brain tumor development. Paracrine interactions seem pivotal because cytokine modulation was observed in various brain regions. These results also suggest that cytokine and neuropeptide changes during brain tumor progression are involved in brain tumor-associated neurological and neuropsychiatrical manifestations.

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.

1998 Curt P. Richter Award. Brain mechanisms in cytokine-induced anorexia

Our research focuses on the mechanisms underlying cytokine action in the central nervous system (CNS) using an integrative and multidisciplinary strategy organized through supracellular (behavioral analysis by computerized monitoring systems), cellular (extracellular and intracellular neurophysiological recording), and molecular (patch-clamp recording, and DNA, RNA and protein analyses) approaches. An integrative strategy that combines computerized meal pattern analyses with cellular and molecular biology approaches allows the study of underlying brain mechanisms in cytokine- and disease-associated anorexia. This paper presents a comprehensive discussion of our laboratory's previously published data on brain mechanisms involved in cytokine-induced anorexia including the relevance of meal pattern analysis (meal size, meal duration, meal frequency, intermeal intervals), modulation of hypothalamic neuronal activity, molecular processes involving ionic conductances, cytokine-cytokine and cytokine-peptide interactions, and modulation of cytokine and peptide/neuropeptide system components (ligands, endogenous inhibitors, receptor subtypes, signal transduction molecules, intracellular mediators) and cytokine feedback systems.

Cytokines and Feeding

Cytokines inhibit feeding through peripheral and brain mechanisms. Behavioral, cellular, and molecular studies show that interactions among cytokines, neurotransmitters, and peptides and modulation of hypothalamic neurons are involved in cytokine-induced feeding inhibition. This action of cytokines is relevant to the control of feeding in health and disease.

Interleukin-1beta-induced fever in young and old Long-Evans rats

Aging is associated with a blunted or absent fever response to naturally occurring infections or to the peripheral administration of bacterial products and proinflammatory cytokines, including interleukin-1beta (IL-1beta). Whether old rats also exhibit an attenuated fever response when challenged with direct brain administration of IL-1beta is unknown. Here we investigated the fever response of young (3-5 mo) and old (24-26 mo) Long-Evans rats to the intracerebroventricular microinfusion of IL-1beta. Core body temperature was monitored by telemetry in freely moving rats. Intracerebroventricularly administered IL-1beta induced comparable increases in body temperature in young and old Long-Evans rats. In the two groups, IL-1beta-induced fever was similar both in latency to peak fever and maximal fever response, whether the cytokine was administered 2 h after lights on or just before lights off. These data show that old Long-Evans rats are not defective in their capacity to develop a fever in response to brain administration of IL-1beta.

Modifications of RNase protection assay for neuroscience applications

This report describes how certain modifications of the Ribonuclease (RNase) protection assay may increase its efficiency by decreasing the time and cost of the procedure without compromising reliability. We show that, under the experimental conditions tested, the RNA samples can be precipitated by a solution of Tri Reagent in ethanol immediately following the RNase digestion step. Drying the samples under vacuum before dissolving them in the gel loading buffer improves the consistency of the assay as compared to air drying. Although these modifications are applicable to the RNase protection assay in general, we present an example that used a multiprobe set we developed and have used effectively in the analysis of cytokine mRNA regulation in the brain.

Modulation of TNF-alpha mRNA production in rat C6 glioma cells by TNF-alpha, IL-1beta, IL-6, and IFN-alpha: in vitro analysis of cytokine-cytokine interactions

Cytokines regulate the expression of other cytokines in the centrally derived rat C6 glioma cell line. However, the modulation of tumor necrosis factor-alpha (TNF-alpha, a pivotal proinflammatory cytokine) in C6 cells is unknown. Here we investigated the expression of TNF-alpha mRNA in C6 glioma cells in response to TNF-alpha, interleukin-1beta (IL-1beta), IL-1 receptor antagonist (IL-1Ra), interleukin-6 (IL-6), and interferon-alpha (IFN-alpha). The data show that (1) IL-1beta induced a significant upregulation of TNF-alpha mRNA; (2) the effect of IL-1beta on TNF-alpha mRNA expression was completely blocked by the concomitant application of IL-1Ra, which suggests specificity of IL-1beta action through the IL-1 signaling receptor; (3) no detectable modulation of TNF-alpha mRNA expression was observed with the individual applications of TNF-alpha, IL-6, or IFN-alpha; (4) the concomitant treatments of TNF-alpha + IL-1beta or TNF-alpha + IL-1beta + IL-6 strongly upregulated TNF-alpha mRNA expression, whereas the concomitant application of TNF-alpha + IL-6 or IL-1beta + IL-6 induced a moderate increase; and (5) IFN-alpha significantly attenuated induction of TNF-alpha mRNA by TNF-alpha + IL-1beta + IL-6. Thus, IL-1beta, TNF-alpha and IL-6 interact to upregulate TNF-alpha mRNA expression synergistically, and IFN-alpha acts as an inhibitory cytokine in C6 glioma cells. These findings also suggest that the rat C6 glioma cell line may be used as an in vitro model to characterize cytokine-cytokine interactions.

Cytokine-induced anorexia. Behavioral, cellular, and molecular mechanisms

Cytokines induce anorexia. Recent issues concerning mechanistic aspects are: (1) Cytokines induce anorexia through different modes of behavioral action, that is, by affecting meal size, meal duration, and meal frequency differentially. Profiles also depend on the concentration or dosage. (2) The interface between the periphery and brain. Specific cytokines may be transported from the periphery to the brain. Cytokines generate mediators that can act on peripheral and/or brain target sites. Cerebrovasculature endothelium can also generate signals to modulate neural activities. Evidence indicates that the proposed vagal afferent signaling requires reassessment. Because of paracrine and autocrine actions, local cytokine production within the brain can induce anorexia. (3) Cytokines act directly on hypothalamic neurons proposed to participate in feeding. (4) Cytokine<-->cytokine and cytokine<-->peptide/neurotransmitter interactions are critical; for example, cytokines interact to induce anorexia synergistically, neuropeptide Y<-->cytokine interactions are antagonist, and cytokine<-->neurotransmitter and cytokine<-->leptin<-->neuropeptide Y<-->CRH-glucocorticoid and other endocrine interactions are important. A leptin receptor is related to gp 130, a signal transducer among interleukin (IL)-6 subfamily receptors; gp 130 and related molecules may be an interface for feeding control in health and disease. Various cytokines upregulate leptin and gp 130. An integrative approach combining computerized meal pattern analyses with cellular and molecular approaches is being used to characterize mechanisms (ligands, receptors, transducing molecules, and intracellular mediators) involved in cytokine-induced anorexia.

Brain cytokine mRNAs in anorectic rats bearing prostate adenocarcinoma tumor cells

Cancer is consistently associated with anorexia. The Lobund-Wistar rat model of prostate cancer exhibits clinical manifestations (including anorexia) that resemble many aspects of the human disease. Cytokines are proposed to be involved in cancer-associated anorexia. Here we investigated mRNA profiles of feeding-modulatory cytokines and neuropeptides in specific brain regions of anorectic Lobund-Wistar rats bearing prostate adenocarcinoma tumor cells. Interleukin (IL)-1beta system components (ligand, signaling receptor, receptor accessory proteins, receptor antagonist), tumor necrosis factor-alpha, transforming growth factor-beta1, glycoprotein 130 (IL-6 receptor signal transducer), proopiomelanocortin (POMC, opioid peptide precursor), and neuropeptide Y (NPY) mRNAs were analyzed with sensitive and specific RNase protection assays. The same brain region sample was assayed for all components. The data show that early anorexia in tumor-bearing rats was associated with an upregulation of IL-1beta mRNA in the brain regions examined (cerebellum, cortex, and hypothalamus). IL-1 receptor antagonist (IL-1Ra) mRNA and IL-1 receptor type I mRNA levels were also significantly increased in the cortex and hypothalamus. All other cytokine components, POMC, or NPY mRNA levels were not significantly different between tumor-bearing and pair-fed (control) rats. IL-1beta mRNA and IL-1Ra mRNA were also significantly upregulated in the spleen of tumor-bearing rats. These data suggest that 1) IL-1beta mRNA upregulation in the brain may be relevant to the anorexia exhibited by the tumor-bearing Lobund-Wistar rat and 2) in vivo characterization of cytokine components in discrete brain regions during cancer is necessary to understand underlying molecular mechanisms responsible for cancer-associated neurological manifestations.

Vagal and splanchnic afferents are not necessary for the anorexia produced by peripheral IL-1beta, LPS, and MDP

We investigated the extrinsic gut neural mediation of the suppression of food intake in male Sprague-Dawley rats induced by peripheral intraperitoneal administration of 2 microg/kg interleukin-1beta (IL-1beta), 100 microg/kg bacterial lipopolysaccharide (LPS), and 2 mg/kg muramyl dipeptide (MDP). Food intake during the first 3 and 6 h of the dark cycle was measured in rats with subdiaphragmatic vagal deafferentation (n = 9), celiac superior mesenteric ganglionectomy (n = 9), combined vagotomy and ganglionectomy (n = 9), and sham deafferentation (n = 9). IL-1beta, LPS, and MDP suppressed food intake at 3 and 6 h in all surgical groups. The results demonstrate that neither vagal nor nonvagal afferent nerves from the upper gut are necessary for the feeding-suppressive effects of intraperitoneal IL-1beta, LPS, or MDP in the rat and suggest that peripheral administration of immunomodulators produces anorexia via a humoral pathway.

Lipopolysaccharide (LPS)- and muramyl dipeptide (MDP)-induced anorexia during refeeding following acute fasting: characterization of brain cytokine and neuropeptide systems mRNAs

We investigated the effectiveness of lipopolysaccharide (LPS) and muramyl dipeptide (MDP) administered into the brain to induce anorexia in acutely fasted Wistar rats allowed to refeed. We also assayed for changes in mRNA levels of IL-1 system components, TNF-alpha, TGF-beta1, glycoprotein 130 (gp 130), leptin receptor (OB-R), pro-opiomelanocortin (POMC), neuropeptide Y (NPY), glucocorticoid receptor (GR), and CRF receptor (CRF-R) in selected brain regions. The data show that LPS and MDP induced anorexia differentially during refeeding. LPS-induced anorexia was of a stronger magnitude and duration than that of MDP. RNase protection assays showed that LPS and MDP significantly increased the expression of IL-1beta, IL-1 receptor type I, and TNF-alpha mRNAs in the cerebellum, hippocampus, and hypothalamus; LPS was more potent in all cases. MDP treatment, on the other hand, induced a stronger increase in hypothalamic levels of IL-1 receptor antagonist (IL-1Ra) and TGF-beta1 mRNAs relative to LPS. In addition, competitive RT-PCR analysis showed that LPS induced an eleven-fold increase in IL-1alpha mRNA in the hypothalamus relative to vehicle. These findings suggest that LPS and MDP mediate anorexia through different cytokine mechanisms. A stronger up-regulation of anti-inflammatory cytokines (IL-1Ra and TGF-beta1) mRNA expression by MDP may be involved in the weaker MDP-induced anorexia relative to LPS. No significant changes were observed in the peptide components examined except for an up-regulation in cerebellar gp 130 mRNA and down-regulation of hypothalamic GR mRNA expression in response to LPS or MDP. This study shows that LPS and MDP induce anorexia in fasted rats allowed to refeed, and suggests an important role for endogenous cytokine-cytokine interactions.

Interleukin-1beta system (ligand, receptor type I, receptor accessory protein and receptor antagonist), TNF-alpha, TGF-beta1 and neuropeptide Y mRNAs in specific brain regions during bacterial LPS-induced anorexia

Bacterial lipopolysaccharide (LPS) or endotoxin induces neurological manifestations including anorexia. It is proposed that LPS-induced cytokine production is involved in the generation of neurological manifestations and in neuroinflammatory/immunological responses during gram-negative infections. For example, LPS-induced effects can be blocked or ameliorated by the interleukin-1 receptor antagonist (IL-1Ra). Here, sensitive and specific RNase protection assays were used to investigate the effects of the intracerebroventricular (i.c.v.) administration of LPS on mRNA levels of interleukin-1beta (IL-1beta) system components, tumor necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta1, and neuropeptide Y (NPY) in the cerebellum, hippocampus, and hypothalamus. The same brain region sample was analyzed with all of the antisense probes. The data show simultaneous local induction of multiple cytokine components messenger ribonucleic acids (mRNAs) within specific brain regions in anorectic rats responding to i.c.v. administered LPS (500 ng/rat). Interleukin-1beta and IL-1Ra had a similar mRNA induction profile (hypothalamus > cerebellum > hippocampus). Interleukin-1 receptor type I (IL-1RI) mRNA also increased in all three brain regions examined, and the soluble form of IL-1 receptor accessory protein (IL-1R AcP II) mRNA was induced in the hypothalamus. Tumor necrosis factor-alpha mRNA levels increased in the hypothalamus > hippocampus > cerebellum. Levels of membrane bound IL-1R AcP, TGF-beta1, and NPY mRNAs did not change significantly in any brain region. The results suggest that: (1) endogenous up-regulation of IL-1beta and TNF-alpha in the hypothalamus contribute to LPS-induced anorexia; and (2) the ratio IL-1Ra/IL-1beta, and IL-1beta <--> TNF-alpha interactions may have implications for gram-negative infections associated with high levels of LPS in the brain-cerebrospinal fluid.

Interleukin-1 alpha (IL-1 alpha), IL-1 beta, IL-1 receptor type I, IL-1 receptor antagonist, and TGF-beta 1 mRNAs in pediatric astrocytomas, ependymomas, and primitive neuroectodermal tumors

Interleukin-1 alpha (IL-1 alpha), IL-1 beta, interleukin-1 receptor type I (IL-1RI, signaling receptor), and IL-1 receptor antagonist (IL-1Ra, endogenous inhibitor) are pivotal components of the IL-1 system. IL-1 and other cytokines induced by IL-1, such as TGF-beta 1, may participate in the growth of various tumor cells. In children, primary nervous system tumors represent the most common solid malignancy. We investigated the levels of IL-1 alpha, IL-1 beta, IL-1RI, IL-1Ra, and TGF-beta 1 mRNAs in pediatric astrocytomas (n = 19), ependymomas (n = 13), and primitive neuroectodermal tumors (n = 22) using sensitive and specific RNase protection assays. The data show a significant distinct cytokine mRNA profile among brain tumor types. Pilocytic, nonpilocytic, and anaplastic astrocytomas have significant increased levels of IL-1 beta, IL-1RI, and TGF-beta 1 mRNAs, but low levels of IL-1Ra mRNA; this may have implications for an IL-1 beta feedback system and IL-1 beta<-->TGF-beta 1 interactions in astrocytomas. Ependymomas show increased levels of IL-1 alpha and IL-1 beta mRNAs associated with low levels of IL-1Ra mRNA; primitive neuroectodermal tumors do not exhibit increased levels of any cytokine component examined. The data also suggest that a dysregulation of the balance between stimulatory and inhibitory cytokines may be involved in the growth and development of brain tumors via autocrine/paracrine mechanisms.