Cortical cell death induced by IL-1 is mediated via actions in the hypothalamus of the rat

Plasma cytokines in acute stroke

GOALS

The aim of this study was to test the relations between plasma cytokines and the clinical characteristics, course, and risk factors in acute stroke.

PATIENTS AND METHODS

The analysis was based on 179 patients with acute stroke included within 24 hours of stroke onset. On inclusion and 3 months later plasma levels of interleukin 1 beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), interleukin-1 receptor antagonist (IL-1RA), interleukin 6 (IL-6), interleukin 10 (IL-10), soluble tumor necrosis factor receptor 1 (sTNF-R1), and soluble tumor necrosis factor receptor 2 (sTNF-R2) were measured by enzyme-linked immunoassay (ELISA).

FINDINGS

The levels of most cytokines were significantly different in acute stroke from the levels 3 months later; but only IL-10 was positively associated with stroke severity. C-reactive protein and white blood cell count were positively associated with the cytokine response.

CONCLUSIONS

We found a substantial overall cytokine reaction that reflected the stroke incident. However, these results do not, at present, suggest a potential for clinical use, as they do not seem to add to the information obtained from the clinical workup of the individual patient.

Varied actions of proinflammatory cytokines on excitotoxic cell death in the rat central nervous system

Interleukin (IL)-1beta mediates diverse forms of neurodegeneration and exacerbates cell death induced by striatal injection of the excitotoxin alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) in the rat brain. The objective of this study was to determine whether this effect was specific to IL-1beta. Injection of IL-1alpha and AMPA in the striatum had effects identical to those of IL-1beta, whereas coinjection of IL-6 or tumor necrosis factor (TNF)-alpha with AMPA failed to induce significant cortical cell death. In contrast to IL-1alpha, IL-1beta, and IL-6, TNFalpha significantly reduced (by 38%) the local striatal damage. These findings suggest that the effect of IL-1 on AMPA receptor-mediated cell death in the rat striatum is not mimicked by other proinflammatory cytokines. Furthermore, TNFalpha shows neuroprotective effects against acute excitotoxic injury.

Interleukin-1 influences ischemic brain damage in the mouse independently of the interleukin-1 type I receptor

The cytokine interleukin-1beta (IL-1beta) contributes to ischemic, excitotoxic, and traumatic brain injury. IL-1beta actions depend on interaction with a single receptor (IL-1RI), which associates with an accessory protein (IL-1RAcP), and is blocked by IL-1 receptor antagonist (IL-1ra). Here we show that in normal mice [wild-type (WT)], intracerebroventricular injection of IL-1ra markedly reduces (-50%; p < 0.01) ischemic brain damage caused by reversible occlusion of the middle cerebral artery, whereas injection of IL-1beta exacerbates damage (+45%; p < 0.05). Mice lacking IL-1RI [IL-1RI knock-out (KO)] exhibited ischemic brain damage that is almost identical to that of the WT (infarct volume 43.7 +/- 6.1 and 46.2 +/- 6.2 mm3, respectively), but failed to respond to injection of IL-1ra. However, injection of IL-1beta (intracerebroventricularly) exacerbated ischemic brain damage in IL-1RI KO (+61%; p < 0.001) and in WT mice (+45%). This effect of IL-1beta was abolished by heat denaturation in all animals, and was reversed by IL-1ra in WT, but not IL-1RI KO mice. In contrast, IL-1RI KO mice were completely resistant to effects of IL-1beta on food intake or body weight. IL-1RAcP mRNA was increased by stroke in WT, but reduced in IL-1RI KO mice compared with sham-operated mice. Type II IL-1 receptor mRNA was significantly increased 4 hr after ischemia in WT and IL-1RI KO (+20%) animals. These data show that IL-1beta can exacerbate ischemic brain damage independently of IL-1RI and suggest the existence of additional signaling receptor or receptors for IL-1 in the brain.

Mitochondrial disappearance from cells: a clue to the role of autophagy in programmed cell death and disease?

When cells are induced to undergo apoptosis in the presence of general caspase inhibitors and then returned to their normal growth environment, there follows an extended period of life during which the entire cohort of mitochondria (including mitochondrial DNA) disappears from the cells. This phenomenon is widespread; it occurs in NGF-deprived sympathetic neurons, in NGF-maintained neurons treated with cytosine arabinoside, and in diverse cell lines treated with staurosporine, including HeLa, CHO, 3T3 and Rat 1 cells. Mitochondrial removal is highly selective since the structure of all other organelles remains unperturbed. Since Bcl2 overexpression blocks the removal of mitochondria without preventing death-inducing signals, it appears that the mitochondria are responsible for initiating their own demise. Degradation of mitochondria is not in itself a rare event. It occurs in large part by autophagy during normal cell house-keeping, during ecdysis in insects, as well as after induction of apoptosis. However, the complete and selective removal of an entire cohort of mitochondria in otherwise living mammalian cells has not been described previously. These findings raise several questions. What are the mechanisms which remove mitochondria in such a 'clean' fashion? What are the signals that target mitochondria for such selective degradation? How are cells that have lost their mitochondria different from rho0 cells (which retain mitochondria but lack mitochondrial DNA, and cannot carry out oxidative phosphorylation)? Are the cells which have lost mitochondria absolutely committed to die or might they be repaired by mitochondrial therapy? The answers will be especially relevant when considering treatment of diseases affecting long-lived and non-renewable organs such as the nervous system.

Site-specific actions of interleukin-1 on excitotoxic cell death in the rat striatum

The pro-inflammatory cytokine interleukin-1 (IL-1) contributes to and exacerbates many forms of neurodegeneration. When co-administered with the potent glutamatergic agonist S-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (S-AMPA) in the rat striatum, IL-1 induces marked and widespread cell death throughout the ipsilateral cortex. The mechanisms underlying this action of IL-1 are not known but may involve activation of polysynaptic neuronal pathways leading from the striatum to the cortex via other brain areas such as the hypothalamus. The aims of the present study were to identify specific sites of action of IL-1 in the rat striatum, in order to further understand these pathways. Ventral regions of the caudate-putamen and the lateral shell of the nucleus accumbens (NAcc) were particularly sensitive to the effects of IL-1 on excitotoxic damage. A high percentage of co-injections in these sites induced distant cortical damage, whereas injections in more dorsal areas of the caudate-putamen or core regions of the NAcc were less likely to result in cortical cell death. The 'positive' injection sites differ from the unresponsive areas in that they have extensive connections with the limbic system and it may be that IL-1 displays specific actions on limbic pathways that, in conjunction with AMPA/kainate receptor activation, contribute to the remote cell death in the cortex. These findings enhance our understanding of the actions of IL-1, and the mechanisms by which it participates in neurodegeneration through both local and long-range effects.

Interleukin-1 influences ischemic brain damage in the mouse independently of the interleukin-1 type I receptor

The cytokine interleukin-1beta (IL-1beta) contributes to ischemic, excitotoxic, and traumatic brain injury. IL-1beta actions depend on interaction with a single receptor (IL-1RI), which associates with an accessory protein (IL-1RAcP), and is blocked by IL-1 receptor antagonist (IL-1ra). Here we show that in normal mice [wild-type (WT)], intracerebroventricular injection of IL-1ra markedly reduces (-50%; p < 0.01) ischemic brain damage caused by reversible occlusion of the middle cerebral artery, whereas injection of IL-1beta exacerbates damage (+45%; p < 0.05). Mice lacking IL-1RI [IL-1RI knock-out (KO)] exhibited ischemic brain damage that is almost identical to that of the WT (infarct volume 43.7 +/- 6.1 and 46.2 +/- 6.2 mm3, respectively), but failed to respond to injection of IL-1ra. However, injection of IL-1beta (intracerebroventricularly) exacerbated ischemic brain damage in IL-1RI KO (+61%; p < 0.001) and in WT mice (+45%). This effect of IL-1beta was abolished by heat denaturation in all animals, and was reversed by IL-1ra in WT, but not IL-1RI KO mice. In contrast, IL-1RI KO mice were completely resistant to effects of IL-1beta on food intake or body weight. IL-1RAcP mRNA was increased by stroke in WT, but reduced in IL-1RI KO mice compared with sham-operated mice. Type II IL-1 receptor mRNA was significantly increased 4 hr after ischemia in WT and IL-1RI KO (+20%) animals. These data show that IL-1beta can exacerbate ischemic brain damage independently of IL-1RI and suggest the existence of additional signaling receptor or receptors for IL-1 in the brain.

Cytokines and acute neurodegeneration

Cytokines have been implicated as mediators and inhibitors of diverse forms of neurodegeneration. They are induced in response to brain injury and have diverse actions that can cause, exacerbate, mediate and/or inhibit cellular injury and repair. Here we review evidence for the contribution of cytokines to acute neurodegeneration, focusing primarily on interleukin 1 (IL-1), tumour necrosis factor-alpha (TNFalpha) and transforming growth factor-beta (TGFbeta). TGFbeta seems to exert primarily neuroprotective actions, whereas TNFalpha might contribute to neuronal injury and exert protective effects. IL-1 mediates ischaemic, excitotoxic and traumatic brain injury, probably through multiple actions on glia, neurons and the vasculature. Understanding cytokine action in acute neurodegeneration could lead to novel and effective therapeutic strategies, some of which are already in clinical trials.

Selective increases in cytokine expression in the rat brain in response to striatal injection of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate and interleukin-1

A number of cytokines contribute to acute experimental neurodegeneration. The cytokine response can have detrimental or beneficial effects depending on the temporal profile and balance between pro- and anti-inflammatory molecules. Our recent data suggest that the pro-inflammatory cytokine interleukin-1beta (IL-1beta) acts at specific sites (e.g., the striatum) in the rat brain to cause distant cortical injury, when co-administered with the potent excitotoxin alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (S-AMPA). The objective of the present study was to investigate changes in the expression of several cytokines simultaneously in the rat striatum and cortex after intrastriatal administration of vehicle, S-AMPA or human recombinant (hr) IL-1beta alone or S-AMPA co-injected with hrIL-1beta using reverse transcription-polymerase chain reaction (RT-PCR; Taqman fluorogenic probes) and enzyme-linked immunosorbent assay (ELISA). Injection of S-AMPA alone increased IL-6 mRNA expression in the ipsilateral striatum after 8 h, whilst striatal injection of IL-1beta alone increased local IL-1beta and IL-1ra mRNAs. The levels of mRNA encoding IL-1alpha, IL-1beta, IL-1ra, IL-6, IL-10 and TNFalpha were markedly elevated in the ipsilateral cortex 8 h after co-injection of S-AMPA and hrIL-1beta. Cortical mRNA levels for IL-4, IL-18, TGFbeta and IFNgamma were not significantly different between treatment groups after 2 h or 8 h. A similar pattern of change in the levels of IL-1alpha and IL-6 protein was observed 8 h after treatment. These data demonstrate selective increases in the expression of cytokines in areas of remote cell death in response to administration of hrIL-1beta and S-AMPA. Such cytokines may be involved in the ensuing damage, and further clarification of their actions could aid future therapeutic strategies for several acute neurodegenerative disorders.

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.

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.

The role of pro- and antiinflammatory cytokines in neurodegeneration

Experimental and clinical damage to the brain leads to rapid upregulation of an array of cytokines predominantly by glia. These cytokines may exert neurotoxic or neuroprotective actions. This paper will focus on the pro-inflammatory cytokine interleukin-1 (IL-1), which participates in diverse forms of brain damage including ischemia, brain trauma, and excitotoxic injury. Administration of low doses of IL-1 markedly exacerbates these forms of brain damage, whereas blocking IL-1 release or actions reduces neuronal death. IL-1 receptor antagonist (IL-1ra) is also upregulated by brain damage (mainly by neurons) and acts as an endogenous inhibitor of neurodegeneration, presumably by blocking IL-1 actions on its receptor. We have studied the actions of both IL-1 and IL-1ra in experimental models of ischemic and neurotoxic injury in rats, and have found site-specific effects within the striatum. On the basis of this and further work, we propose that IL-1 can exacerbate cell death in these conditions by modifying polysynaptic anterograde pathways leading from the striatum to the cortex. The precise nature of these pathways remains undetermined, as do the underlying mechanisms by which IL-1 can exert its effects, but appear to involve induction of IL-1 in specific brain regions and activation of cortical glutamatergic pathways.

Influence of corticotrophin releasing factor on neuronal cell death in vitro and in vivo

Several studies have demonstrated that antagonists of the corticotrophin releasing factor (CRF) receptor markedly inhibit experimentally induced excitotoxic, ischaemic and traumatic brain injury in the rat, and that CRF expression is elevated in response to experimentally induced stroke or traumatic brain injury. CRF is also induced by the pro-inflammatory cytokine interleukin 1 (IL-1), which participates in various forms of neurodegeneration. The aim of this study was to test the hypothesis that CRF is toxic directly in vivo or in vitro. In primary cultures of rat cortical neurons, exposure to CRF (10 pM-100 nM) for 24 h failed to cause cell death directly, or to modify the neurotoxic effects of N-methyl-D-aspartate (NMDA). Similarly, infusion of CRF (0.3-5 microg) into specific brain regions of the rat did not induce cell death and did not significantly alter the neuronal damage produced by infusion of excitatory amino acids. These data demonstrate that CRF is not directly neurotoxic, and suggest that either CRF mediates neuronal damage by indirect actions (e.g. on the vasculature) and/or that CRF is not the endogenous ligand which contributes to neurodegeneration through activation of CRF receptors.

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.

IL-1beta induced changes in hypothalamic IL-1R1 and IL-1R2 mRNA expression in the rat

Interleukin-1 receptor (IL-1R1 and IL-1R2) mRNA expression was detected within the rat hypothalamus, a primary site of IL-1 action, using RT-PCR. Levels of expression were unchanged by cardiac saline-perfusion. However, intracerebroventricular (i.c.v.) administration of IL-1beta caused changes in receptor mRNA expression in non-perfused animals that were profoundly different to those observed in their saline-perfused counterparts. This study demonstrates the importance of perfusing tissue to remove blood cells when determining changes in IL-1 receptor mRNA expression.