Contribution of interleukin-1 receptor accessory protein B to interleukin-1 actions in neuronal cells.

Interleukin (IL)-1 is an important neuroimmunomodulator and a key mediator of inflammation during brain disorders. It acts on neuronal and glial cells via binding to the IL-1 type 1 receptor and IL-1 receptor accessory protein (IL-1RAcP). More recently, a neuronal-specific isoform of IL-1RAcP, named IL-1RAcPb, has been identified. Our aim was to determine the role of IL-1RAcPb in IL-1 actions in neuronal and glial cells, and to further explore the signaling mechanisms of IL-1 in neurons. We found that IL-1RAcPb deletion had no effect on IL-1α- and IL-1ß-induced activation of the extracellular signal-regulated kinase 1/2 or IL-6 release in glial cultures, although IL-6 release in response to high IL-1α concentration (30 IU/ml) was significantly reduced. We identified the p38 kinase as a key signaling element in IL-1α- and IL-1ß-induced IL-6 synthesis and release in neuronal cultures. IL-1RAcPb deletion had no effect on IL-1α- and IL-1ß-induced IL-6 release in neurons, but significantly reduced IL-1α- but not IL-1ß-induced p38 phosphorylation. Our data demonstrate that the p38 signaling pathway plays an important role in IL-1 actions in neurons, and that IL-1RAcP may regulate some, but not all, neuronal activities in response to IL-1α.

Lipocortin-1 is an endogenous inhibitor of ischemic damage in the rat brain.

Lipocortin-1 (annexin-1) is an endogenous peptide with antiinflammatory properties. We have previously demonstrated lipocortin immunoreactivity in certain glial cells and neurons in the rat brain (Strijbos, P.J.L.M., F.J.H. Tilders, F. Carey, R. Forder, and N.J. Rothwell. 1990. Brain Res. In press.), and have shown that an NH2-terminal fragment (1-188) of lipocortin-1 inhibits the central and peripheral actions of cytokines on fever and thermogenesis in the rat in vivo (Carey, F., R. Forder, M.D. Edge, A.R. Greene, M.A. Horan, P.J.L.M. Strijbos, and N.J. Rothwell. 1990. Am. J. Physiol. 259:R266; and Strijbos, P.J.L.M., J.L. Browning, M. Ward, R. Forder, F. Carey, M.A. Horan, and N.J. Rothwell. 1991. Br. J. Pharmacol. In press.). We now report that intracerebroventricular administration of lipocortin-1 fragment causes marked inhibition of infarct size (60%) and cerebral edema (46%) measured 2 h after cerebral ischemia (middle cerebral artery occlusion) in the rat in vivo. The lipocortin-1 fragment was effective when administered 10 min after induction of ischemia. Ischemia caused increased expression of lipocortin-1 around the area of infarction as demonstrated by immunocytochemistry. Intracerebroventricular injection of neutralizing antilipocortin-1 fragment antiserum increased the size of infarct (53%) and the development of edema (29%). These findings indicate that lipocortin-1 is an endogenous inhibitor of cerebral ischemia with considerable therapeutic potential.

Tumor necrosis factor alpha is a critical component of interleukin 13-mediated protective T helper cell type 2 responses during helminth infection.

In vivo manipulation of cytokine and/or cytokine receptor expression has previously shown that resistance to infection with the caecum-dwelling helminth Trichuris muris is dependent on interleukin (IL)-4 and IL-13 while susceptibility is associated with a T helper cell type 1 (Th1) cytokine response. Using gene-targeted mice deficient in tumor necrosis factor (TNF) receptor signaling and anti-TNF-alpha monoclonal antibody treatment, we have extended these studies to reveal a critical role for TNF-alpha in regulation of Th2 cytokine-mediated host protection. In vivo blockade of TNF-alpha in normally resistant mice, although not altering IL-4, IL-5, or IL-13 production in the draining lymph node, significantly delayed worm expulsion for the duration of treatment. IL-13-mediated worm expulsion in IL-4 knockout (KO) mice was also shown to be TNF-alpha dependent, and could be enhanced by administration of recombinant TNF-alpha. Furthermore, TNF receptor KO mice failed to expel T. muris, producing high levels of parasite-specific immunoglobulin G2a and the generation of a predominantly Th1 response, suggesting that the absence of TNF function from the onset of infection dramatically alters the phenotype of the response. These results provide the first demonstration of the role of TNF-alpha in regulating Th2 cytokine-mediated responses at mucosal sites, and have implications for the design of rational therapies against helminth infection and allergy.

Inflammation and brain injury: acute cerebral ischaemia, peripheral and central inflammation.

Inflammation is a classical host defence response to infection and injury that has many beneficial effects. However, inappropriate (in time, place and magnitude) inflammation is increasingly implicated in diverse disease states, now including cancer, diabetes, obesity, atherosclerosis, heart disease and, most relevant here, CNS disease. A growing literature shows strong correlations between inflammatory status and the risk of cerebral ischaemia (CI, most commonly stroke), as well as with outcome from an ischaemic event. Intervention studies to demonstrate a causal link between inflammation and CI (or its consequences) are limited but are beginning to emerge, while experimental studies of CI have provided direct evidence that key inflammatory mediators (cytokines, chemokines and inflammatory cells) contribute directly to ischaemic brain injury. However, it remains to be determined what the relative importance of systemic (largely peripheral) versus CNS inflammation is in CI. Animal models in which CI is driven by a CNS intervention may not accurately reflect the clinical condition; stroke being typically induced by atherosclerosis or cardiac dysfunction, and hence current experimental paradigms may underestimate the contribution of peripheral inflammation. Experimental studies have already identified a number of potential anti-inflammatory therapeutic interventions that may limit ischaemic brain damage, some of which have been tested in early clinical trials with potentially promising results. However, a greater understanding of the contribution of inflammation to CI is still required, and this review highlights some of the key mechanism that may offer future therapeutic targets.

Systemic infection, inflammation and acute ischemic stroke.

Extensive evidence implicates inflammation in multiple phases of stroke etiology and pathology. In particular, there is growing awareness that inflammatory events outside the brain have an important impact on stroke susceptibility and outcome. Numerous conditions, including infection and chronic non-infectious diseases, that are established risk factors for stroke are associated with an elevated systemic inflammatory profile. Recent clinical and pre-clinical studies support the concept that the systemic inflammatory status prior to and at the time of stroke is a key determinant of acute outcome and long-term prognosis. Here, we provide an overview of the impact of systemic inflammation on stroke susceptibility and outcome. We discuss potential mechanisms underlying the impact on ischemic brain injury and highlight the implications for stroke prevention, therapy and modeling.

Interleukin-1-induced interleukin-6 synthesis is mediated by the neutral sphingomyelinase/Src kinase pathway in neurones.

BACKGROUND AND PURPOSE: Interleukin (IL)-1 is a key mediator of inflammatory and host defence responses and its effects in the brain are mediated primarily via effects on glia. IL-1 induces release of inflammatory mediators such as IL-6 from glia via the type-1 receptor (IL-1R1) and established signalling mechanisms including mitogen-activated protein kinases and nuclear factor kappa-B. IL-1 also modifies physiological functions via actions on neurones, through activation of the neutral sphingomyelinase (nSMase)/Src kinase signalling pathway, although the mechanism of IL-1-induced IL-6 synthesis in neurones remains unknown. EXPERIMENTAL APPROACH: Primary mouse neuronal cell cultures, ELISA, Western blot and immunocytochemistry techniques were used. KEY RESULTS: We show here that IL-1beta induces the synthesis of IL-6 in primary mouse neuronal cultures, and this is dependent on the activation of IL-1R1, nSMase and Src kinase. We demonstrate that IL-1beta-induced Src kinase activation triggers the phosphorylation of the NMDA receptor NR2B subunit, leading to activation of Ca(2+)/calmodulin-dependent protein kinase II (CamKII) and the nuclear transcription factor CREB. We also show that NR2B, CamKII and CREB are essential signalling elements involved in IL-1beta-induced IL-6 synthesis in neurones. CONCLUSIONS AND IMPLICATIONS: These results demonstrate that IL-1 interacts with the same receptors on neurones and glia to elicit IL-6 release, but does so via distinct signalling pathways. The mechanism by which IL-1beta induces IL-6 synthesis in neurones could be critical in both physiological and pathophysiological actions of IL-1beta, and may provide a new therapeutic target for the treatment of acute CNS injury.

Effect of diet and cold exposure on norepinephrine turnover in brown adipose tissue of the rat.

Brown adipose tissue (BAT) is an important site of adaptive changes in thermogenesis in the rat. The sympathetic nervous system, which richly supplies BAT, is thought to play an important role in the regulation of BAT thermogenesis because catecholamines stimulate and beta adrenergic blocking agents inhibit oxygen consumption in this tissue. The present studies were carried out to assess directly sympathetic activity in BAT in response to cold exposure and to changes in dietary intake, both of which alter heat production in the rat. Sympathetic activity was determined from the rate of norepinephrine (NE) turnover in interscapular brown adipose tissue (IBAT) after preliminary experiments validated the use of NE turnover techniques in IBAT. Acute exposure to 4 degrees C increased NE turnover in IBAT 4- to 12-fold compared with ambient temperature controls, depending upon the interval over which the turnover measurement was made, while in the heart NE turnover doubled in response to the same cold stimulus. In animals exposed to cold continuously for 10 d before study, NE turnover measurements in IBAT and in the heart were elevated comparably to those obtained during acute exposure. Alterations in feeding were also associated with changes in NE turnover in IBAT. Fasting for 2 d decreased NE turnover in IBAT (-35% from 29.2+/-4.2 ng NE/h to 18.9+/-5.9) and in heart (-52%). In animals fed a "cafeteria" diet, a model of voluntary overfeeding in the rat, NE turnover was increased in both IBAT (+108% from 24.8+/-4.5 ng NE/h to 51.7+/-6.8) and heart (+66%). Because ganglionic blockade exerted a greater effect on NE turnover in IBAT in cafeteria-fed rats than in controls, the increase in NE turnover in IBAT with this overfeeding regimen reflects enhanced central sympathetic outflow. Thus NE turnover techniques can be satisfactorily applied to the assessment of sympathetic nervous system activity in IBAT. The experiments reported here demonstrate changes in sympathetic activity in IBAT that parallel known adaptive changes in heat production in the rat. These studies, therefore, support the concept that the increased thermogenesis of chronic cold exposure and of cafeteria feeding occur by similar mechanisms and imply an important role for the sympathetic nervous system, mediated in part through BAT, in the regulation of energy balance in the rat.

Interleukin 1 in the brain: biology, pathology and therapeutic target.

The cytokine interleukin 1 (IL-1) has diverse actions in the brain. In normal brain the IL-1 system is expressed at low levels and is upregulated rapidly in response to local or peripheral insults. IL-1 mediates host defence responses to local and systemic disease and injury (e.g. fever, slow-wave sleep, appetite suppression and neuroendocrine responses) and to neuroinflammation and cell death in neurodegenerative conditions, such as stroke and head injury. It has also been implicated in chronic degenerative diseases, in particular, multiple sclerosis, Parkinson's and Alzheimer's diseases. The mechanisms regulating the expression and action of IL-1 are poorly understood, but involve multiple effects on neuronal, glial and endothelial cell function. Thus, the IL-1 system provides an attractive and intensely competitive target for therapeutic intervention.

Cytokines and the nervous system II: Actions and mechanisms of action.

Cytokines exert diverse actions on the PNS and the CNS and have been implicated in neuronally mediated responses to disease and injury. Certain cytokines participate in the central control of host systemic responses to disease, acting as signals to and within the brain. These molecules are also involved in neuronal degeneration and repair in the PNS and CNS, and have been proposed as mediators of various neuropathologies. The actions, mechanisms of action and potential strategies for modifying cytokines in the nervous system will be considered in this review, which continues the discussion of cytokine expression and recognition published in the February issue of TINS.

Cytokines and the nervous system. I: Expression and recognition.

Cytokines are a heterogeneous group of polypeptide mediators that have been associated classically with activation of the immune system and inflammatory responses. An increasing number of related mediators is now included in this category and most of them have been shown to act on a variety of tissues, including the PNS and CNS. Cytokines and their receptors are expressed in tissues of these nervous systems, and might derive from invading immune, or resident, cells. Trauma in peripheral tissues might also induce cytokine-mediated events in the CNS, via either the circulation or secondary induction within the brain. In this first of a two-part review, the general properties, expression and recognition of these cytokines with respect to the nervous system are discussed.

Hypothalamic control of feeding.

Our understanding of the hypothalamic control of energy homeostasis has increased greatly since the discovery of leptin, the adipose cell derived protein. Recent studies have identified several new hypothalamic neuropeptides that affect food intake and energy balance. By studying these molecules and their neuronal systems, receptors and interactions, we are beginning to unravel the circuitry between peripheral adipogenic signals and hypothalamic effector pathways.

Role of IL-1alpha and IL-1beta in ischemic brain damage.

The cytokine interleukin-1 (IL-1) has been strongly implicated in the pathogenesis of ischemic brain damage. Evidence to date suggests that the major form of IL-1 contributing to ischemic injury is IL-1beta rather than IL-1alpha, but this has not been tested directly. The objective of the present study was to compare the effects of transient cerebral ischemia [30 min middle cerebral artery occlusion (MCAO)] on neuronal injury in wild-type (WT) mice and in IL-1alpha, IL-1beta, or both IL-1alpha and IL-1beta knock-out (KO) mice. Mice lacking both forms of IL-1 exhibited dramatically reduced ischemic infarct volumes compared with wild type (total volume, 70%; cortex, 87% reduction). Ischemic damage compared with WT mice was not significantly altered in mice lacking either IL-1alpha or IL-1beta alone. IL-1beta mRNA, but not IL-1alpha or the IL-1 type 1 receptor, was strongly induced by MCAO in WT and IL-1alpha KO mice. Administration (intracerebroventricularly) of recombinant IL-1 receptor antagonist significantly reduced infarct volume in WT (-32%) and IL-1alpha KO (-48%) mice, but had no effect on injury in IL-1beta or IL-1alpha/beta KO mice. These data confirm that IL-1 plays a major role in ischemic brain injury. They also show that chronic deletion of IL-1alpha or IL-1beta fails to influence brain damage, probably because of compensatory changes in the IL-1 system in IL-1alpha KO mice and changes in IL-1-independent mediators of neuronal death in IL-1beta KO mice.

Functions and mechanisms of interleukin 1 in the brain.

Interleukin 1 (IL-1), a cytokine with diverse actions, has been proposed as a mediator of both beneficial and detrimental responses to inflammation and injury. Many of the actions of IL-1, such as those on behaviour, neuroendocrine function, sleep, fever and metabolism, are mediated by the CNS, as described here by Nancy Rothwell. IL-1 can be synthesized and act locally within the brain to influence neuronal and glial function, and has been strongly implicated in normal brain development and responses to brain injury. A number of distinct sites and mechanisms of action have been proposed to explain these diverse effects of IL-1 in the brain, probably involving multiple receptor subtypes and complex interactions with neurotransmitters and neuropeptides.

Lipocortin-1: cellular mechanisms and clinical relevance.

Lipocortin-1, a 37 kDa member of the annexin superfamily of proteins, originally evoked interest as one of the 'second messengers' of the anti-inflammatory actions of the glucocorticoids. Subsequent research has shown that the protein plays a major regulatory role in systems as diverse as cell-growth regulation and differentiation, neutrophil migration, CNS responses to cytokines, neuroendocrine secretion and neurodegeneration. The role of lipocortin-1 in mediating glucocorticoid-induced effects in these systems has been demonstrated using immunoneutralization strategies and by mimicking steroid actions with highly purified or recombinant lipocortin-1 or its biologically active peptide fragments. Originally the mode of action of lipocortin-1 seemed to be largely through inhibition of prostaglandin formation, but it is now clear that it can modify other aspects of cell function, perhaps pointing to a more fundamental mechanism than was originally envisaged. In this article Rod Flower and Nancy Rothwell review the nature, possible mechanisms and clinical relevance of these diverse actions of lipocortin-1.

Cytokines and their receptors in the central nervous system: physiology, pharmacology, and pathology.

Numerous cytokines and their receptors have been identified in the brain, where they act as mediators of host defence responses and have direct effects on neuronal and glial function. Experimental tools for studying cytokine actions, their source and control of synthesis in the brain, actions and mechanisms of action will be reviewed here. In particular, the cytokines interleukin-1, interleukin-6, and tumour necrosis factor-alpha have been implicated in the central control of responses to systemic disease and injury and activation of fever, neuroendocrine, immune, and behavioural responses. The recent discovery of specific inhibitors of cytokine synthesis, release, or action may offer significant therapeutic benefit.

Central effects of CRF on metabolism and energy balance.

CRF is recognised for its actions on pituitary ACTH release, but also has direct effects within the brain which are important in mediating physiological responses to stress. Behavioral effects of CRF include increased locomotor activity and inhibition of food intake and its actions on metabolism are mediated mainly by activation of the sympathetic nervous system. CRF appears to be important in the regulation of energy balance and body weight, influencing both food intake and sympathetically-mediated thermogenesis. A defect in the synthesis or release of CRF has been implicated in the development of obesity in laboratory animals, since the condition is alleviated by adrenalectomy, hypophysectomy or exogenous CRF treatment. Recent data have revealed an additional role for CRF as a mediator of the neuroendocrine and metabolic responses to immune signals, particularly cytokines. The central actions of CRF are independent of the pituitary but may involve release of proopiomelanocortin products within the brain. CRF is thus emerging as an important integrator of the physiological responses to stress, infection and immunity, a finding which may have important implications for future therapies.

Involvement of cytokines in acute neurodegeneration in the CNS.

Cytokines, (particularly interleukins and growth factors) are synthesised in the brain, and induced by brain damage. Interleukin-I appears to directly mediate ischaemic and excitotoxic brain damage, whereas growth factors (e.g., bFGF, NGF), and the phospholipid binding protein lipocortin-1 exhibit neuroprotective actions. Central administration of recombinant interleukin-1 receptor antagonist markedly attenuates damage induced by focal cerebral ischaemia, or pharmacological activation of NMDA receptors in the rat brain. The mechanisms of action of these cytokines on neurodegeneration are unknown, but indirect evidence has implicated corticotropin releasing factor, arachidonic acid, and nitric oxide. In vitro effects of interleukin-1, growth factors, and lipocortin-1 have been reported on intracellular calcium homeostasis, which is critically important in neurodegeneration. Pharmacological modulation of the expression and/or actions of cytokines in the brain may be of considerable therapeutic benefit in the treatment of acute neurodegeneration.

Thermogenic effects of the antiglucocorticoid RU-486 in the rat: involvement of corticotropin-releasing factor and sympathetic activation of brown adipose tissue.

Acute injection (sc) of the antiglucocorticoid RU-486 (5-10 mg/kg) stimulated oxygen consumption (VO2) and brown adipose tissue (BAT) activity (mitochondrial GDP binding) in the rat. A peak effect was seen 60-80 min after injection. The rise in VO2 was prevented by prior injection of the beta-adrenergic antagonist propranolol, and the effect on BAT was abolished by surgical denervation of the sympathetic supply to the tissue. Central injection (cerebroventricular) of a much lower dose (3-8 micrograms/kg) of RU-486 also stimulated VO2, and this effect was inhibited by a CRF receptor antagonist [alpha-helical CRF-(9-41)]. Peripheral injection of RU-486 also elicited acute thermogenic responses in older (greater than 12 months) rats and in genetically obese (Zucker) rats. In lean animals, daily injection of RU-486 inhibited weight gain and stimulated BAT without affecting food intake. The thermogenic effects of RU-486 appear to be due to central stimulation of sympathetic outflow and may involve CRF release. The data support previous studies on the effects of adrenalectomy and CRF on thermogenesis in the rat.

Cortical death caused by striatal administration of AMPA and interleukin-1 is mediated by activation of cortical NMDA receptors.

Striatal coadministration of interleukin-1beta (IL-1beta) with alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (S-AMPA) in rats results in widespread cortical cell death not caused by either treatment alone. This cortical damage was unaffected by cortical infusion of the AMPA-receptor antagonist NBQX. Cortical infusion of an NMDA-receptor antagonist D-AP5 significantly inhibited (57%; P < 0.05) cortical death, but had no effect on the local striatal death. Thus, cortical neuronal death induced by striatal S-AMPA and human recombinant interleukin-1beta (hrIL-1beta) is mediated by activation of NMDA receptors in the cortex. The authors propose that IL-1beta actions on AMPA-receptor mediated cell death may involve the activation of polysynaptic pathways from the striatum to the cortex.