Site-specific hippocampal pathophysiology due to cerebral overexpression of interleukin-6 in transgenic mice

The critical role of interleukin-6 in protection against neurotropic flavivirus infection

West Nile virus (WNV) and Japanese encephalitis virus (JEV) are emerging mosquito-borne flaviviruses causing encephalitis globally. No specific drug or therapy exists to treat flavivirus-induced neurological diseases. The lack of specific therapeutics underscores an urgent need to determine the function of important host factors involved in flavivirus replication and disease progression. Interleukin-6 (IL-6) upregulation has been observed during viral infections in both mice and humans, implying that it may influence the disease outcome significantly. Herein, we investigated the function of IL-6 in the pathogenesis of neurotropic flavivirus infections. First, we examined the role of IL-6 in flavivirus-infected human neuroblastoma cells, SK-N-SH, and found that IL-6 neutralization increased the WNV or JEV replication and inhibited the expression of key cytokines. We further evaluated the role of IL-6 by infecting primary mouse cells derived from IL-6 knockout (IL-6-/-) mice and wild-type (WT) mice with WNV or JEV. The results exhibited increased virus yields in the cells lacking the IL-6 gene. Next, our in vivo approach revealed that IL-6-/- mice had significantly higher morbidity and mortality after subcutaneous infection with the pathogenic WNV NY99 or JEV Nakayama strain compared to WT mice. The non-pathogenic WNV Eg101 strain did not cause mortality in WT mice but resulted in 60% mortality in IL-6-/- mice, indicating that IL-6 is required for the survival of mice after the peripheral inoculation of WNV or JEV. We also observed significantly higher viremia and brain viral load in IL-6-/- mice than in WT mice. Subsequently, we explored innate immune responses in WT and IL-6-/- mice after WNV NY99 infection. Our data demonstrated that the IL-6-/- mice had reduced levels of key cytokines in the serum during early infection but elevated levels of proinflammatory cytokines in the brain later, along with suppressed anti-inflammatory cytokines. In addition, mRNA expression of IFN-α and IFN-β was significantly lower in the infected IL-6-/- mice. In conclusion, these data suggest that the lack of IL-6 exacerbates WNV or JEV infection in vitro and in vivo by causing an increase in virus replication and dysregulating host immune response.

Identification and immune characteristics of molecular subtypes related to protein glycosylation in Alzheimer's disease

BACKGROUND

Protein glycosylation has been confirmed to be involved in the pathological mechanisms of Alzheimer's disease (AD); however, there is still a lack of systematic analysis of the immune processes mediated by protein glycosylation-related genes (PGRGs) in AD.

MATERIALS AND METHODS

Transcriptomic data of AD patients were obtained from the Gene Expression Omnibus database and divided into training and verification datasets. The core PGRGs of the training set were identified by weighted gene co-expression network analysis, and protein glycosylation-related subtypes in AD were identified based on k-means unsupervised clustering. Protein glycosylation scores and neuroinflammatory levels of different subtypes were compared, and functional enrichment analysis and drug prediction were performed based on the differentially expressed genes (DEGs) between the subtypes. A random forest model was used to select important DEGs as diagnostic markers between subtypes, and a line chart model was constructed and verified in other datasets. We evaluated the differences in immune cell infiltration between the subtypes through the single-sample gene set enrichment analysis, analyzed the correlation between core diagnostic markers and immune cells, and explored the expression regulation network of the core diagnostic markers.

RESULTS

Eight core PGRGs were differentially expressed between the training set and control samples. AD was divided into two subtypes with significantly different biological processes, such as vesicle-mediated transport in synapses and neuroactive ligand-receptor interactions. The high protein glycosylation subtype had a higher level of neuroinflammation. Riluzole and sulfasalazine were found to have potential clinical value in this subtype. A reliable construction line chart model was constructed based on nine diagnostic markers, and SERPINA3 was identified as the core diagnostic marker. There were significant differences in immune cell infiltration between the two subtypes. SERPINA3 was found to be closely related to immune cells, and the expression of SERPINA3 in AD was found to be regulated by a competing endogenous RNA network that involves eight long non-coding RNAs and seven microRNAs.

CONCLUSION

Protein glycosylation and its corresponding immune process play an important role in the occurrence and development of AD. Understanding the role of PGRGs in AD may provide a new potential therapeutic target for AD.

The cytokines interleukin-6 and interferon-α induce distinct microglia phenotypes

Background

Elevated production of the cytokines interleukin (IL)-6 or interferon (IFN)-α in the central nervous system (CNS) is implicated in the pathogenesis of neurological diseases such as neuromyelitis optica spectrum disorders or cerebral interferonopathies, respectively. Transgenic mice with CNS-targeted chronic production of IL-6 (GFAP-IL6) or IFN-α (GFAP-IFN) recapitulate important clinical and pathological features of these human diseases. The activation of microglia is a prominent manifestation found both in the human diseases and in the transgenic mice, yet little is known about how this contributes to disease pathology.

Methods

Here, we used a combination of ex vivo and in situ techniques to characterize the molecular, cellular and transcriptomic phenotypes of microglia in GFAP-IL6 versus GFAP-IFN mice. In addition, a transcriptomic meta-analysis was performed to compare the microglia response from GFAP-IL6 and GFAP-IFN mice to the response of microglia in a range of neurodegenerative and neuroinflammatory disorders.

Results

We demonstrated that microglia show stimulus-specific responses to IL-6 versus IFN-α in the brain resulting in unique and extensive molecular and cellular adaptations. In GFAP-IL6 mice, microglia proliferated, had shortened, less branched processes and elicited transcriptomic and molecular changes associated with phagocytosis and lipid processing. In comparison, microglia in the brain of GFAP-IFN mice exhibited increased proliferation and apoptosis, had larger, hyper-ramified processes and showed transcriptomic and surface marker changes associated with antigen presentation and antiviral response. Further, a transcriptomic meta-analysis revealed that IL-6 and IFN-α both contribute to the formation of a core microglia response in animal models of neurodegenerative and neuroinflammatory disorders, such as Alzheimer’s disease, tauopathy, multiple sclerosis and lipopolysaccharide-induced endotoxemia.

Conclusions

Our findings demonstrate that microglia responses to IL-6 and IFN-α are highly stimulus-specific, wide-ranging and give rise to divergent phenotypes that modulate microglia responses in neuroinflammatory and neurodegenerative diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02441-x.

Cytokines and Neurodegeneration in Epileptogenesis

Epilepsy is a common brain disorder characterized by a heterogenous etiology. Its main features are recurrent seizures. Despite many clinical studies, about 30% of cases are refractory to treatment. Recent studies suggested the important role of immune-system elements in its pathogenesis. It was suggested that a deregulated inflammatory process may lead to aberrant neural connectivity and the hyperexcitability of the neuronal network. The aim of our study was the analysis of the expression of inflammatory mediators in a mouse model of epilepsy and their impact on the neurodegeneration process located in the brain. We used the KA-induced model of epilepsy in SJL/J mice and performed the analysis of gene expression and protein levels. We observed the upregulation of IL1β and CXCL12 in the early phase of KA-induced epilepsy and elevated levels of CCL5 at a later time point, compared with control animals. The most important result obtained in our study is the elevation of CXCL2 expression at both studied time points and its correlation with the neurodegeneration observed in mouse brain. Increasing experimental and clinical data suggest the influence of peripheral inflammation on epileptogenesis. Thus, studies focused on the molecular markers of neuroinflammation are of great value and may help deepen our knowledge about epilepsy, leading to the discovery of new drugs.

Neuroinflammation in Post-Traumatic Epilepsy: Pathophysiology and Tractable Therapeutic Targets

Epilepsy is a common chronic consequence of traumatic brain injury (TBI), contributing to increased morbidity and mortality for survivors. As post-traumatic epilepsy (PTE) is drug-resistant in at least one-third of patients, there is a clear need for novel therapeutic strategies to prevent epilepsy from developing after TBI, or to mitigate its severity. It has long been recognized that seizure activity is associated with a local immune response, characterized by the activation of microglia and astrocytes and the release of a plethora of pro-inflammatory cytokines and chemokines. More recently, increasing evidence also supports a causal role for neuroinflammation in seizure induction and propagation, acting both directly and indirectly on neurons to promote regional hyperexcitability. In this narrative review, we focus on key aspects of the neuroinflammatory response that have been implicated in epilepsy, with a particular focus on PTE. The contributions of glial cells, blood-derived leukocytes, and the blood–brain barrier will be explored, as well as pro- and anti-inflammatory mediators. While the neuroinflammatory response to TBI appears to be largely pro-epileptogenic, further research is needed to clearly demonstrate causal relationships. This research has the potential to unveil new drug targets for PTE, and identify immune-based biomarkers for improved epilepsy prediction.

The role of UCH-L1, MMP-9, and GFAP as peripheral markers of different susceptibility to seizure development in a preclinical model of epilepsy

In our study, we assessed the potency of the brain-derived proteins ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), matrix metalloproteinase 9 (MMP-9), glial fibrillary acidic protein (GFAP) and the immune activation indicators interleukin 1β (IL-1β) and interleukin 6 (IL-6) as peripheral biomarkers of different susceptibilities to kindling in a preclinical model. We observed increased plasma UCH-L1 levels in kindled vs. control animals. Furthermore, MMP-9 and IL-1β concentrations were the lowest in rats resistant to kindling. In summary, UCH-L1 is an indicator of neuronal loss and BBB disruption after seizure. MMP-9 and IL-1β may indicate resistance to kindling. UCH-L1, MMP-9 and IL-1β may have utility as peripheral biomarkers with translational potency in the clinic.

Significance of IL-6 Deficiency in Recognition Memory in Young Adult and Aged Mice

Chronic peripheral elevation of interleukin 6 (IL-6) in humans is associated with cognitive deficits. 4- and 24-month-old IL-6-deficient C57BL/6J (IL-6KO) and reference wild-type (WT) mice were tested in an object recognition test. Discrimination ratios and recognition indexes were significantly lower in 4-month-old IL-6KO and in 24-month-old WT mice vs 4-month-old WT animals. Their discrimination ratios had negative values and recognition indexes were below 50% indicating inability to differentiate the novel from the familiar object after 1-hour delay. In 24-month-old IL-6KO mice recognition index reached 53.17% indicating that their recognition memory was not worsened with age in comparison with younger IL-6-deficient animals. Results of holeboard and elevated plus maze indicated that this effect was memory specific. Inborn IL-6 deficiency attenuated recognition memory in 4-month-old mice and did not altered recognition memory in aged animals. IL-6 signalling may constitute a target for development of the protection against memory disturbances connected with IL-6 overexpression.

Altered brain activity during withdrawal from chronic alcohol is associated with changes in IL-6 signal transduction and GABAergic mechanisms in transgenic mice with increased astrocyte expression of IL-6

Interleukin-6 (IL-6) is an important neuroimmune factor that is increased in the brain by alcohol exposure/withdrawal and is thought to play a role in the actions of alcohol on the brain. To gain insight into IL-6/alcohol/withdrawal interactions and how these interactions affect the brain, we are studying the effects of chronic binge alcohol exposure on transgenic mice that express elevated levels of IL-6 in the brain due to increased astrocyte expression (IL-6 tg) and their non-transgenic (non-tg) littermate controls. IL-6/alcohol/withdrawal interactions were identified by genotypic differences in spontaneous brain activity in electroencephalogram (EEG) recordings from the mice, and by Western blot analysis of protein activation or expression in hippocampus obtained from the mice after the final alcohol withdrawal period. Results from EEG studies showed frequency dependent genotypic differences in brain activity during withdrawal. For EEG frequencies that were affected by alcohol exposure/withdrawal in both genotypes, the nature of the effect was similar, but differed across withdrawal cycles. Differences between IL-6 tg and non-tg mice were also observed in Western blot studies of the activated form of STAT3 (phosphoSTAT3), a signal transduction partner of IL-6, and subunits of GABA_A receptors (GABA_AR). Regression analysis revealed that pSTAT3 played a more prominent role during withdrawal in the IL-6 tg mice than in the non-tg mice, and that the role of GABA_AR alpha-5 and GABA_AR alpha-1 in brain activity varied across genotype and withdrawal. Taken together, our results suggest that IL-6 can significantly impact mechanisms involved in alcohol withdrawal.

Expression analysis of cytokine coding genes in epileptic patients

Epilepsy is a chronic disorder in which immune dysregulation is shown to be involved. Imbalances in the cytokine levels both in serum and brain tissue have been demonstrated in epileptic patients. In the present study, we assessed mRNA expression of TNF-α, TGF-β, IFN-γ, CXCL8, IL-1β, IL-2, 1L-4, IL-6, IL-17 and CXCL8 in blood samples of 40 epileptic patients compared with age- and sex-matched healthy controls by means of quantitative real time PCR. The relative levels of CXCL8 transcripts were significantly higher in total epileptic patients compared with healthy subjects (P = .023). Relative mRNA expression of IFN-γ was significantly higher in female patients compared with female healthy subject (P = .048). In addition, significant correlations have been found between the mRNA levels of mentioned cytokines. Such imbalance between expression of pro-inflammatory and anti-inflammatory cytokines might be implicated in the pathogenesis of epilepsy.

Impact of Increased Astrocyte Expression of IL-6, CCL2 or CXCL10 in Transgenic Mice on Hippocampal Synaptic Function

An important aspect of CNS disease and injury is the elevated expression of neuroimmune factors. These factors are thought to contribute to processes ranging from recovery and repair to pathology. The complexity of the CNS and the multitude of neuroimmune factors that are expressed in the CNS during disease and injury is a challenge to an understanding of the consequences of the elevated expression relative to CNS function. One approach to address this issue is the use of transgenic mice that express elevated levels of a specific neuroimmune factor in the CNS by a cell type that normally produces it. This approach can provide basic information about the actions of specific neuroimmune factors and can contribute to an understanding of more complex conditions when multiple neuroimmune factors are expressed. This review summarizes studies using transgenic mice that express elevated levels of IL-6, CCL2 or CXCL10 through increased astrocyte expression. The studies focus on the effects of these neuroimmune factors on synaptic function at the Schaffer collateral to CA1 pyramidal neuron synapse of the hippocampus, a brain region that plays a key role in cognitive function.

Immunoinflammatory diseases of the central nervous system - the tale of two cytokines

Cytokines are potent mediators of cellular communication that have crucial roles in the regulation of innate and adaptive immunoinflammatory responses. Clear evidence has emerged in recent years that the dysregulated production of cytokines may in itself be causative in the pathogenesis of certain immunoinflammatory disorders. Here we review current evidence for the involvement of two different cytokines, IFN-α and IL-6, as principal mediators of specific immunoinflammatory disorders of the CNS. IFN-α belongs to the type I IFN family and is causally linked to the development of inflammatory encephalopathy exemplified by the genetic disorder, Aicardi-Goutières syndrome. IL-6 belongs to the gp130 family of cytokines and is causally linked to a number of immunoinflammatory disorders of the CNS including neuromyelitis optica, idiopathic transverse myelitis and genetically linked autoinflammatory neurological disease. In addition to clinical evidence, experimental studies, particularly in genetically engineered mouse models with astrocyte-targeted, CNS-restricted production of IFN-α or IL-6 replicate many of the cardinal neuropathological features of these human cytokine-linked immunoinflammatory neurological disorders giving crucial evidence for a direct causative role of these cytokines and providing further rationale for the therapeutic targeting of these cytokines in neurological diseases where indicated.

Transgenic mice with increased astrocyte expression of IL-6 show altered effects of acute ethanol on synaptic function

A growing body of evidence has revealed that resident cells of the central nervous system (CNS), and particularly the glial cells, comprise a neuroimmune system that serves a number of functions in the normal CNS and during adverse conditions. Cells of the neuroimmune system regulate CNS functions through the production of signaling factors, referred to as neuroimmune factors. Recent studies show that ethanol can activate cells of the neuroimmune system, resulting in the elevated production of neuroimmune factors, including the cytokine interleukin-6 (IL-6). Here we analyzed the consequences of this CNS action of ethanol using transgenic mice that express elevated levels of IL-6 through increased astrocyte expression (IL-6-tg) to model the increased IL-6 expression that occurs with ethanol use. Results show that increased IL-6 expression induces neuroadaptive changes that alter the effects of ethanol. In hippocampal slices from non-transgenic (non-tg) littermate control mice, synaptically evoked dendritic field excitatory postsynaptic potential (fEPSP) and somatic population spike (PS) at the Schaffer collateral to CA1 pyramidal neuron synapse were reduced by acute ethanol (20 or 60 mM). In contrast, acute ethanol enhanced the fEPSP and PS in hippocampal slices from IL-6 tg mice. Long-term synaptic plasticity of the fEPSP (i.e., LTP) showed the expected dose-dependent reduction by acute ethanol in non-tg hippocampal slices, whereas LTP in the IL-6 tg hippocampal slices was resistant to this depressive effect of acute ethanol. Consistent with altered effects of acute ethanol on synaptic function in the IL-6 tg mice, EEG recordings showed a higher level of CNS activity in the IL-6 tg mice than in the non-tg mice during the period of withdrawal from an acute high dose of ethanol. These results suggest a potential role for neuroadaptive effects of ethanol-induced astrocyte production of IL-6 as a mediator or modulator of the actions of ethanol on the CNS, including persistent changes in CNS function that contribute to cognitive dysfunction and the development of alcohol dependence.

Cerebrospinal fluid levels of IL-6 are decreased and correlate with cognitive status in DLB patients

Introduction

Inflammatory processes have previously been shown to influence cognition and progression of dementia. An involvement of interleukin (IL)-6 has in particular been suggested as altered levels of IL-6 in cerebrospinal fluid (CSF) have been found in patients with Alzheimer’s disease (AD). Also, an association between cognitive decline and levels of IL-6 in CSF have been reported. The aim of the present study was to investigate whether patients clinically diagnosed with dementia with Lewy bodies (DLB) display altered CSF IL-6 levels in comparison with patients with AD and control subjects without dementia and whether the IL-6 levels are correlated with cognitive status and biomarkers for AD and synucleinopathy.

Methods

To analyse CSF of patients with AD (n = 45), patients with DLB (n = 29) and control subjects without dementia (n = 36), we used immunoassays to measure levels of IL-6 (multiplex electrochemiluminescence); AD markers phosphorylated tau, total tau and amyloid-β_1–42 (enzyme-linked immunosorbent assay [ELISA]); and α-synuclein (ELISA). Cognitive status was evaluated using the Mini Mental State Examination (MMSE).

Results

Our analysis showed significantly lower levels of IL-6 in CSF from patients with DLB than in CSF from patients with AD and control subjects without dementia. The IL-6 levels were also negatively correlated with MMSE and positively correlated with α-synuclein CSF levels.

Conclusions

Our findings support previous studies by demonstrating a link between inflammatory processes and dementia progression and further strengthen the hypothesis that IL-6 is involved in dementia pathology and cognitive decline.

IL-6 regulation of synaptic function in the CNS

A growing body of evidence supports a role for glial-produced neuroimmune factors, including the cytokine IL-6, in CNS physiology and pathology. CNS expression of IL-6 has been documented in the normal CNS at low levels and at elevated levels in several neurodegenerative or psychiatric disease states as well as in CNS infection and injury. The altered CNS function associated with these conditions raises the possibility that IL-6 has neuronal or synaptic actions. Studies in in vitro and in vivo models confirmed this possibility and showed that IL-6 can regulate a number of important neuronal and synaptic functions including synaptic transmission and synaptic plasticity, an important cellular mechanism of memory and learning. Behavioral studies in animal models provided further evidence of an important role for IL-6 as a regulator of CNS pathways that are critical to cognitive function. This review summarizes studies that have lead to our current state of knowledge. In spite of the progress that has been made, there is a need for a greater understanding of the physiological and pathophysiological actions of IL-6 in the CNS, the mechanisms underlying these actions, conditions that induce production of IL-6 in the CNS and therapeutic strategies that could ameliorate or promote IL-6 actions. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

Interleukin 6 and cognitive dysfunction

The interleukin-6 (IL-6) is a pleiotropic cytokine that plays a key role in interaction between immune and nervous system. Although IL-6 has neurotrophic properties and beneficial effects in the CNS, its overexpression is generally detrimental, adding to the pathophysiology associated with CNS disorders. The source of the increase in peripheral IL-6 remains to be established and varies among different pathologies, but has been found to be associated with cognitive dysfunction in several pathologies. This comprehensive review provides an update summary of the studies performed in humans concerning the role of central and peripheral IL-6 in cognitive dysfunction in dementias and in other systemic diseases accompained by cognitive dysfuction such as cardiovascular, liver disease, Behçet's disease and systemic lupus erythematosus. Further research is needed to correlate specific deficits in IL-6 and its receptors in pathologies characterized by cognitive dysfunction and to understand how systemic IL-6 affects high cerebral function in order to open new directions in pharmacological treatments that modulate IL-6 signalling.

Effect of topiramate on interleukin 6 expression in the hippocampus of amygdala-kindled epileptic rats

The objective of this study was to analyze the changes in expression and the possible functions of interleukin-6 (IL-6) in electrical kindling of the basolateral amygdala (BLA) in epileptic rats. Bipolar electrodes were implanted into the BLA of Sprague-Dawley rats, and the rats were then subjected to chronic electrical stimulation through the electrodes to induce kindling. The seizure characteristics and behavioral changes of the rats were observed, and electroencephalograms were recorded during and following kindling. The IL-6 mRNA expression in the hippocampi of the rats was analyzed using semi-quantitative reverse transcription-polymerase chain reaction, and control and topiramate (TPM)-treated groups were compared. The mean time-period required for kindling was 13.50±3.99 days, and the afterdischarge duration (ADD) measured between 21,450 and 119,720 msec. The expression of IL-6 mRNA was significantly upregulated in the kindled rats. TPM was able to depress the seizures and decrease the IL-6 level in the kindled rats. In conclusion, IL-6 mRNA was upregulated in the hippocampi of epileptic rats, and IL-6 may have participated in the process of kindling.

Altered synaptic transmission in the hippocampus of transgenic mice with enhanced central nervous systems expression of interleukin-6

Elevated levels of the inflammatory cytokine interleukin-6 (IL-6) occur in a number of CNS disorders. However, little is known about how this condition affects CNS neuronal function. Transgenic mice that express elevated levels of IL-6 in the CNS show cognitive changes, increased propensity for hippocampal seizures and reduced number of inhibitory interneurons, suggesting that elevated levels of IL-6 can cause neuroadaptive changes that alter hippocampal function. To identify these neuroadaptive changes, we measured the levels of protein expression using Western blot analysis and synaptic function using field potential recordings in hippocampus from IL-6 transgenic mice (IL-6 tg) and their non-transgenic (non-tg) littermates. Western blot analysis showed enhanced levels of the GFAP and STAT3 in the IL-6 tg hippocampus compared with the non-tg hippocampus, but no difference for several other proteins. Field potential recordings of synaptic transmission at the Schaffer collateral to CA1 synapse showed enhanced dendritic excitatory postsynaptic potentials and somatic population spikes in the CA1 region of hippocampal slices from IL-6 tg mice compared with slices from non-tg littermate controls. No differences were observed for several forms of short-term and long-term synaptic plasticity between hippocampal slices from IL-6 tg and non-tg mice. These results demonstrate that elevated levels of IL-6 can alter mechanisms involved in the excitability of hippocampal neurons and synapses, an effect consistent with recent evidence indicating that elevated production of IL-6 plays an important role in conditions associated with seizure activity and in other impairments observed in CNS disorders with a neuroinflammatory component.

Neurotropic viral infections leading to epilepsy: focus on Theiler's murine encephalomyelitis virus

Neurotropic viruses cause viral encephalitis and are associated with the development of seizures/epilepsy. The first infection-driven animal model for epilepsy, the Theiler's murine encephalomyelitis virus-induced seizure model is described herein. Intracerebral infection of C57BL/6 mice with Theiler's murine encephalomyelitis virus induces acute seizures from which the animals recover. However, once the virus is cleared, a significant portion of the animals that experienced acute seizures later develop epilepsy. Components of the innate immune response to viral infection, including IL-6 and complement component 3, have been implicated in the development of acute seizures. Multiple mechanisms, including neuronal cell destruction and cytokine activation, play a role in the development of acute seizures. Future studies targeting the innate immune response will lead to new therapies for seizures/epilepsy.

Constitutive induction of pro-inflammatory and chemotactic cytokines in cystathionine beta-synthase deficient homocystinuria

Cystathionine beta-synthase (CBS) deficient homocystinuria (HCU) is an inherited metabolic defect that if untreated, typically results in cognitive impairment, connective tissue disturbances, atherosclerosis and thromboembolic disease. In recent years, chronic inappropriate expression of the inflammatory response has emerged as a major driving force of both thrombosis and atherosclerotic lesion development. We report here a characterization of the abnormalities in cytokine expression induced in both a mouse model of HCU and human subjects with the disease in the presence and absence of homocysteine lowering therapy. HCU mice exhibited highly significant induction of the pro-inflammatory cytokines Il-1alpha, Il-1beta and TNF-alpha. Similarly, in untreated/poorly compliant human subjects with HCU we observed constitutive induction of multiple pro-inflammatory cytokines (IL-1alpha, IL-6, TNF-alpha, Il-17 and IL-12(p70)) and chemotactic chemokines (fractalkine, MIP-1alpha and MIP-1beta) compared to normal controls. These HCU patients also exhibited significant induction of IL-9, TGF-alpha and G-CSF. The expression levels of anti-inflammatory cytokines were unaffected in both HCU mice and human subjects with the disease. In the human subjects, homocysteine lowering therapy was associated with either normalization or significant reduction of all of the pro-inflammatory cytokines and chemokines investigated. We conclude that HCU is a disease of chronic inflammation and that aberrant cytokine expression has the potential to contribute to multiple aspects of pathogenesis. Our findings indicate that anti-inflammatory strategies could serve as a useful adjuvant therapy for this disease.

Cytokines and epilepsy

Epilepsy is a common chronic neurological disorder affecting approximately 8 out of 1000 people. Its pathophysiology, however, has remained elusive in many regards. Consequently, adequate seizure control is still lacking in about one third of patients. Cytokines are soluble mediators of cell communication that are critical in immune regulation. In recent years, studies have shown that epileptic seizures can induce the production of cytokines, which in turn influence the pathogenesis and course of epilepsies. At the time of this review, the focus is mostly on interleukin-1beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNFα). In this review, we summarize the current knowledge regarding these cytokines and their potential roles in epilepsy. The focus concentrates on their expression and influence on induced seizures in animal models of epilepsy, as well as findings in human studies. Both proconvulsive and anticonvulsive effects have been reported for each of these molecules. One possible explanation for this phenomenon is that cytokines play dichotomous roles through multiple pathways, each of which is dependent on free concentration and available receptors. Furthermore, the immune-mediated leakage in the blood-brain-barrier also plays an important role in epileptogenesis. Nonetheless, these observations demonstrate the multifarious nature of cytokine networks and the complex relationship between the immune system and epilepsy. Future studies are warranted to further clarify the influence of the immune system on epilepsy and vice versa.

Sex effects of interleukin-6 deficiency on neuroinflammation in aged C57Bl/6 mice

High levels of Interleukin-6 (IL-6) are associated with an increased risk of dementia in the elderly and can increase neuroinflammation in mice. Dementia is more frequent in females, and IL-6 is regulated by estrogen, suggesting that elevated IL-6 levels may contribute to neuroinflammation and dementia particularly in women. Therefore we hypothesized that IL-6 deficient ((-/-)) female mice would have lower aging-related neuroinflammation than wild type (WT). We quantified neuroinflammatory markers which are affected by aging, and regulated by both estrogen and IL-6; glial fibrillary acidic protein (GFAP), myelin basic protein (MBP), interferon gamma (IFNgamma), lipid peroxidation (MDA), and synaptic density (SNAP25) and in IL-6(-/-) and WT C57Bl/6 mice. To determine age effects we used mid-age (18months) and old-age (24months) mice, and to determine region specific effects we used the hippocampus which is impaired in dementia and the cerebellum which is unimpaired in dementia. Unexpectedly, there were no effects of IL-6 deficiency on GFAP, MDA or SNAP25 levels in females, but IL-6 deficiency was associated with lower cerebellar MBP (p<0.05) levels. Interestingly, the old-aged IL-6(-/-) males had higher GFAP and MDA levels (p<0.05) in both the hippocampus and cerebellum, in addition to a greater body weight than WT. We suggest that IL-6 is important for promoting myelin synthesis in aged females, and that drugs which inhibit the synthesis of IL-6 in males may inadvertently affect fatty acid metabolism and augment aging-related neuroinflammation.

Transgenic models for cytokine-induced neurological disease

Considerable evidence supports the idea that cytokines are important mediators of pathophysiologic processes within the central nervous system (CNS). Numerous studies have documented the increased production of various cytokines in the human CNS in a variety of neurological and neuropsychiatric disorders. Deciphering cytokine actions in the intact CNS has important implications for our understanding of the pathogenesis and treatment of these disorders. One approach to address this problem that has been used widely employs transgenic mice with CNS-targeted production of different cytokines. Transgenic production of cytokines in the CNS of mice allows not only for the investigation of complex cellular responses at a localized level in the intact brain but also more closely recapitulates the expression of these mediators as found in disease states. As discussed in this review, the findings show that these transgenic animals exhibit wide-ranging structural and functional deficits that are linked to the development of distinct neuroinflammatory responses which are relatively specific for each cytokine. These cytokine-induced alterations often recapitulate those found in various human neurological disorders not only underscoring the relevance of these models but also reinforcing the clinicopathogenetic significance of cytokines in diseases of the CNS.

Etiology and site of temporal lobe epilepsy influence postictal cytokine release

Inflammatory mechanisms are involved in the pathogenesis of epilepsy. Vice versa, immune functions are regulated by the brain. We measured postictal changes in serum levels of the immuno-modulating cytokines IL-1beta, IL-6 and TNFalpha in patients with well-defined temporal lobe epilepsy (TLE) and determined modifying factors. Serum levels of IL-1beta, IL-6 and TNFalpha were quantified by ELISA at baseline as well as immediately, 1h and 24h after a complex partial (CPS) or secondary generalized tonic-clonic seizure (GTCS) during video-EEG monitoring in 25 patients suffering from temporal epilepsy. IL-6 increased by 51% immediately after the seizure (p<0.01) and remained elevated for 24h. This increase lacked in patients with hippocampal sclerosis (HS; n=16, mean increase 28%, p>0.5, vs. 112%, p<0.01 in patients without HS). IL-6 levels were higher after right-sided seizures as compared to left-sided seizures 24h after the seizure (8.7pg/mL vs. 3.4pg/mL, p<0.05). In patients taking valproate (VPA, n=9), the levels of IL-1beta were higher as compared to patients not treated with VPA. The results suggest a relationship between the cytokine system and characteristics of TLE such as side and pathology.

Effect of astrocyte-targeted production of IL-6 on traumatic brain injury and its impact on the cortical transcriptome

Interleukin-6 (IL-6) is one of the key players in the response of the brain cortex to injury. We have described previously that astrocyte-driven production of IL-6 (GFAP-IL6) in transgenic mice, although causing spontaneous neuroinflammation and long term damage, is beneficial after an acute (freeze) injury in the cortex, increasing healing and decreasing oxidative stress and apoptosis. To determine the transcriptional basis for these responses here we analyzed the global gene expression profile of the cortex, at 0 (unlesioned), 1 or 4 days post lesion (dpl), in both GFAP-IL6 mice and their control littermates. GFAP-IL6 mice showed an increase in genes associated with the inflammatory response both at 1 dpl (Iftm1, Endod1) and 4 dpl (Gfap, C4b), decreased expression of proapoptotic genes (i.e. Gadd45b, Clic4, p21) as well as reduced expression of genes involved in the control of oxidative stress (Atf4). Furthermore, the presence of IL-6 altered the expression of genes involved in hemostasis (Vwf), cell migration and proliferation (Cap2), and synaptic activity (Vamp2). All these changes in gene expression could underlie the phenotype of the GFAP-IL6 mice after injury, but many other possible factors were also identified in this study, highlighting the utility of this approach for deciphering new pathways orchestrated by IL-6.

Role of brain inflammation in epileptogenesis

Inflammation is known to participate in the mediation of a growing number of acute and chronic neurological disorders. Even so, the involvement of inflammation in the pathogenesis of epilepsy and seizure-induced brain damage has only recently been appreciated. Inflammatory processes, including activation of microglia and astrocytes and production of proinflammatory cytokines and related molecules, have been described in human epilepsy patients as well as in experimental models of epilepsy. For many decades, a functional role for brain inflammation has been implied by the effective use of anti-inflammatory treatments, such as steroids, in treating intractable pediatric epilepsy of diverse causes. Conversely, common pediatric infectious or autoimmune diseases are often accompanied by seizures during the course of illness. In addition, genetic susceptibility to inflammation correlated with an increased risk of epilepsy. Mounting evidence thus supports the hypothesis that inflammation may contribute to epileptogenesis and cause neuronal injury in epilepsy. We provide an overview of the current knowledge that implicates brain inflammation as a common predisposing factor in epilepsy, particularly childhood epilepsy.

Chronic interleukin-6 alters the level of synaptic proteins in hippocampus in culture and in vivo

There is now considerable evidence that the level of expression of the proinflammatory cytokine, interleukin-6 (IL-6), is increased in the central nervous system (CNS) during neuroinflammatory conditions such as occurs in neurological disorders and in disease and injury. However, our understanding of the consequences of increased expression of IL-6 on the CNS is still limited, especially with respect to the developing nervous system, which is known to be particularly vulnerable to environmental factors. To address this issue, we investigated the properties of cultured hippocampal neurons exposed chronically to IL-6 during the main period of morphological and physiological development, which occurs during the first 2 weeks of culture. IL-6 was tested at 500 U/mL, considered to reflect a pathophysiologic concentration. The morphological features of neuronal development in the control and IL-6-treated cultures appeared similar. However, Western blot analysis showed a significant reduction in the level of Group-II metabotropic receptors (mGluR2/3) and L-type Ca(2+) channels in the IL-6-treated cultures. A similar reduction in mGluR2/3 and L-type Ca(2+) channel protein was observed in transgenic mice that over-express IL-6 in the CNS through astrocyte production starting early in development. Analysis of Ca(2+) signals produced by spontaneous synaptic network activity in the hippocampal cultures and effects of a mGluR2/3 agonist and antagonist showed that the reduced levels of mGluR2/3 impact on the functional properties of hippocampal synaptic network activity. These results have important implications relative to the mechanisms responsible for altered CNS function during conditions associated with increased levels of IL-6 in the CNS.

Chronic interleukin-6 exposure alters metabotropic glutamate receptor-activated calcium signalling in cerebellar Purkinje neurons

Chronic central nervous system expression of the cytokine interleukin-6 (IL-6) is thought to contribute to the histopathological, pathophysiological, and cognitive deficits associated with various neurological disorders. However, the effects of chronic IL-6 expression on neuronal function are largely unknown. Previous studies have shown that chronic IL-6 exposure alters intrinsic electrophysiological properties and intracellular Ca2+ signalling evoked by ionotropic glutamate receptor activation in cerebellar Purkinje neurons. In the current study, using primary cultures of rat cerebellum, we investigated the effects of chronic IL-6 exposure on metabotropic glutamate receptor (mGluR)-activated Ca2+ signalling and release from intracellular Ca2+ stores. Chronic exposure (6-10 days) of Purkinje neurons to 500 units/mL IL-6 resulted in elevated resting Ca2+ levels and increased intracellular Ca2+ signals evoked by the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG) compared to untreated control neurons. Chronic IL-6 treatment also augmented Ca2+ signals evoked by brief 100 mm K+ depolarization, although to a lesser degree than responses evoked by DHPG. Depleting intracellular Ca2+ stores with sarcoplasmic-endoplasmic reticulum ATPase inhibitors (thapsigargin or cyclopiazonic acid) or blocking ryanodine receptor-dependent release from intracellular stores (using ryanodine) resulted in a greater reduction of DHPG- and K+-evoked Ca2+ signals in chronic IL-6-treated neurons than in control neurons. The present data show that chronic exposure to elevated levels of IL-6, such as occurs in various neurological diseases, alters Ca2+ signalling involving release from intracellular stores. The results support the hypothesis that chronic IL-6 exposure disrupts neuronal function and thereby may contribute to the pathophysiology associated with many neurological diseases.

Interleukin-6 produces neuronal loss in developing cerebellar granule neuron cultures

CNS levels of the cytokine interleukin-6 (IL-6) are elevated during CNS injury and disease, but it is unclear if IL-6 contributes to the pathologic process. Our studies show that in a well-characterized CNS developmental model system, primary cultures of rodent cerebellar granule neurons, chronic exposure to IL-6 during neuronal development can result in cell damage and death in a subpopulation of developing granule neurons. Chronic exposure to IL-6 also increased the susceptibility of the granule neurons to a toxic insult produced by excessive activation of NMDA receptors. These results are consistent with a role for IL-6 in the neuropathology observed in the developing CNS during injury and disease.

Intranasal administration of human IL-6 increases the severity of chemically induced seizures in rats

Here we study the role of a pleiotropic pro-inflammatory cytokine, interleukin-6 (IL-6), in epilepsy. To examine this problem, we used human recombinant IL-6 applied intranasally (400 ng/40 microl) to rats 1h before seizures induced by systemic injection of pentylenenetrazole (PTZ, 75 mg/kg). Overall, compared to the saline-treated control animals (n = 11 in each group), IL-6-treated rats demonstrated elevated levels of IL-6 in the frontal lobe (measured by ELISA) and increased severity of PTZ-induced seizures (shorter latency, longer duration and higher mortality). Our findings show that IL-6 plays a pro-convulsant role in the brain and suggest that the IL-6 system may be a novel target for the development of anticonvulsant drugs.

Susceptibility to audiogenic seizure and neurotransmitter amino acid levels in different brain areas of IL-6-deficient mice

Interleukin-6-deficient (IL-6(-/-)) mice and their normal littermate (WT) were studied to evaluate their susceptibility to seizures induced by electroshock and audiogenic stimuli at different ages. No significant changes in maximal electroshock susceptibility were evidenced between the two strains, while audiogenic seizures (AGS) can be induced only in IL-6(-/-) mice. The effects of age and genetic condition on AGSs were evaluated. The behavioural and electrocortical changes during audiogenic stimulus were observed. In addition, the levels of neurotransmitter amino acids in five brain areas (of both strains) were measured at 60 days of age. Aspartate level significantly increased in the brain stem (BS) and hippocampus (HI), while it decreased in the diencephalon (DE) of IL-6(-/-) mice. Glutamate content significantly decreased in the cerebellum (CB), DE and HI. GABA levels significantly decreased in all the areas studied. Glycine significantly decreased in the BS, CB and DE, while taurine decreased only in the DE. The levels of glutamine significantly decreased in all the areas examined, except in the cortex (CX). The changes of neuroactive amino acid levels, particularly in the BS, might explain the characteristic of high propensity to AGS of IL-6(-/-) mice. The present data support the validity of IL-6(-/-) mice as a novel epileptic model for the study of the pathophysiology and pharmacology of epilepsy.

Profound increase in sensitivity to glutamatergic- but not cholinergic agonist-induced seizures in transgenic mice with astrocyte production of IL-6

Transgenic mice with glial fibrillary acidic protein (GFAP) promoter driven-astrocyte production of the cytokines interleukin-6 (IL-6) and tumor necrosis factor (TNF) were used to determine whether the pre-existing production of these cytokines in vivo might modulate the sensitivity of neurons to excitotoxic agents. Low doses of kainic acid (5 mg/kg) that produced little or no behavioral or electroencephalogram (EEG) alterations in wild type or glial fibrillary acidic protein (GFAP)-TNF animals induced severe tonic-clonic seizures and death in GFAP-IL6 transgenic mice of 2 or 6 months of age. GFAP-IL6 mice were also significantly more sensitive to N-methyl-D-aspartate (NMDA)- but not pilocarpine-induced seizures. Kainic acid uptake in the brain of the GFAP-IL6 mice was higher in the cerebellum but not in other regions. Kainic acid binding in the brain of GFAP-IL6 mice had a similar distribution and density as wild type controls. In the hippocampus of GFAP-IL6 mice that survived low dose kainic acid, there was no change in the extent of either neurodegeneration or astrocytosis. Immunostaining revealed degenerative changes in gamma aminobutyric acid (GABA)- and parvalbumin-positive neurons in the hippocampus of 2-month-old GFAP-IL6 mice which progressed to the loss of these cells at 6 months of age. Thus, GFAP-IL6 but not GFAP-TNF mice showed markedly enhanced sensitivity to glutamatergic- but not cholinergic-induced seizures and lethality. This may relate, in part, to a compromise of inhibitory interneuron function. Therefore, pre-existing IL-6 production and inflammation in the central nervous system (CNS) not only causes spontaneous neurodegeneration but also synergizes with other neurotoxic insults to induce more severe acute functional neurological impairment.

Interleukin-6, beta-amyloid peptide and NMDA interactions in rat cortical neurons

Neuronal damage in Alzheimer's disease (AD) is thought to involve direct toxicity of beta-amyloid peptide (Abeta) and excitotoxicity involving NMDA receptors (NMDARs) and altered Ca(2+) dynamics. Inflammation agents produced by microglia or astrocytes and associated with senile plaques such as the cytokine interleukin-6 (IL-6) could also contribute. To investigate this possibility, neuronal damage (lactate dehydrogenase assay, LDH, assay) was measured in cultures of rodent cortical neurons chronically treated with IL-6, Abeta or Abeta plus IL-6 and acutely treated with NMDA. Both Abeta and NMDA produced neuronal damage and this effect was larger with combined treatment. IL-6 did not produce significant neuronal damage but the largest neuronal damage was observed in cultures exposed to all three factors. IL-6 and Abeta enhanced Ca(2+) responses to NMDA and combined treatment produced the largest effect. These results are consistent with a role for interactions between Abeta, NMDA and IL-6 in the neuronal loss in AD.

Metallothionein-I overexpression decreases brain pathology in transgenic mice with astrocyte-targeted expression of interleukin-6

Transgenic expression of interleukin-6 (IL-6) in the CNS under the control of the glial fibrillary acidic protein (GFAP) gene promoter (GFAP-IL6 mice) causes significant damage and alters the expression of many genes, including a dramatic upregulation of metallothionein-I (MT-I). The findings in this report support the idea that the upregulation of MT-I observed in GFAP-IL6 mice is an important mechanism for coping with brain damage. Thus, GFAP-IL6 mice that were crossed with TgMTI transgenic mice (GFAP-IL6xTgMTI) and overexpressed MT-I in the brain showed a decreased upregulation of cytokines such as IL-6 and a diminished recruitment and activation of macrophages and T cells throughout the CNS but mainly in the cerebellum. The GFAP-IL6 mice showed clear evidence of increased oxidative stress, which was significantly decreased by MT-I overexpression. Interestingly, MT-I overexpression increased angiogenesis in GFAP-IL6 mice but not in control littermates. Overall, the results strongly suggest that MT-I+II proteins are valuable factors that protect against cytokine-induced CNS injury.

Chronic interleukin-6 exposure alters electrophysiological properties and calcium signaling in developing cerebellar purkinje neurons in culture

The cytokine interleukin-6 (IL-6) is chronically expressed at elevated levels within the CNS in many neurological disorders and may contribute to the histopathological, pathophysiological, and cognitive deficits associated with such disorders. However, the effects of chronic IL-6 exposure on neuronal function in the CNS are largely unknown. Therefore using intracellular recording and calcium imaging techniques, we investigated the effects of chronic IL-6 exposure on the physiological properties of cerebellar Purkinje neurons in primary culture. Two weeks of exposure to 1,000 units/ml (U/ml) IL-6 resulted in altered electrophysiological properties of Purkinje neurons, including a significant reduction in action potential generation, an increase in input resistance, and an enhanced electrical response to the ionotropic glutamate receptor agonist, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) compared with untreated neurons. Lower concentrations of IL-6 (100 and 500 U/ml) had no effects on these electrophysiological parameters. However, neurons exposed to 500 U/ml chronic IL-6 resulted in significantly elevated resting levels of intracellular calcium as well as an increase in the intracellular calcium signal of Purkinje neurons in response to AMPA, effects not observed in neurons exposed to 1,000 U/ml chronic IL-6. Morphometric analysis revealed a lack of gross structural changes following chronic IL-6 treatment, such as in the number, size, and extent of dendritic arborization of Purkinje neurons in culture. Using immunohistochemistry, we found that cultured Purkinje neurons express both the IL-6 receptor and its intracellular signaling subunit, gp130, indicating that IL-6 may act directly on Purkinje neurons to alter their physiological properties. The present data show that chronic exposure to elevated levels of IL-6, such as occurs in various neurological diseases, produces alterations in several important physiological properties of Purkinje neurons and that these changes occur in the absence of neuronal toxicity, damage, or death. The results support the hypothesis that chronic IL-6 exposure can disrupt normal CNS function and thereby contribute to the pathophysiology associated with many neurological diseases.

Metallothionein-1+2 deficiency increases brain pathology in transgenic mice with astrocyte-targeted expression of interleukin 6

Transgenic expression of IL-6 under the control of the GFAP gene promoter (GFAP-IL6 mice) in the CNS causes significant damage and alters the expression of many genes, including the metallothionein (MT) family, especially in the cerebellum. The crossing of GFAP-IL6 mice with MT-1+2 knock out (MTKO) mice provided evidence that the increased MT-1+2 expression normally observed in the GFAP-IL6 mice is an important mechanism for coping with brain damage. Thus, the GFAP-IL6xMTKO mice showed a decreased body weight gain and an impaired performance in the rota-rod test, as well as a higher upregulation of cytokines such as IL-6, IL-1alpha,beta, and TNFalpha and recruitment and activation of macrophages and T cells throughout the CNS but mainly in the cerebellum. Clear symptoms of increased oxidative stress and apoptotic cell death caused by MT-1+2 deficiency were observed in the GFAP-IL6xMTKO mice. Interestingly, MT-1+2 deficiency also altered the expected frequency of the offspring genotypes, suggesting a role of these proteins during development. Overall, the results suggest that the MT-1+2 proteins are valuable factors against cytokine-induced CNS injury.

Astrocyte-targeted expression of interleukin-3 and interferon-alpha causes region-specific changes in metallothionein expression in the brain

Transgenic mice expressing IL-3 and IFN-alpha under the regulatory control of the GFAP gene promoter (GFAP-IL3 and GFAP-IFNalpha mice) exhibit a cytokine-specific, late-onset chronic-progressive neurological disorder which resemble many of the features of human diseases such as multiple sclerosis, Aicardi-Goutières syndrome, and some viral encephalopathies including HIV leukoencephalopathy. In this report we show that the metallothionein-I+II (MT-I+II) isoforms were upregulated in the brain of both GFAP-IL3 and GFAP-IFNalpha mice in accordance with the site and amount of expression of the cytokines. In the GFAP-IL3 mice, in situ hybridization analysis for MT-I RNA and radioimmunoassay results for MT-I+II protein revealed that a significant upregulation was observed in the cerebellum and medulla plus pons at the two ages studied, 1-3 and 6-10 months. Increased MT-I RNA levels occurred in the Purkinje and granular layers of the cerebellum, as well as in its white matter tracts. In contrast to the cerebellum and brain stem, MT-I+II were downregulated by IL-3 in the hippocampus and the remaining brain in the older mice. In situ hybridization for MT-III RNA revealed a modest increase in the cerebellum, which was confirmed by immunohistochemistry. MT-III immunoreactivity was present in cells that were mainly round or amoeboid monocytes/macrophages and in astrocytes. MT-I+II induction was more generalized in the GFAP-IFNalpha (GIFN12 and GIFN39 lines) mice, with significant increases in the cerebellum, thalamus, hippocampus, and cortex. In the high expressor line GIFN39, MT-III RNA levels were significantly increased in the cerebellum (Purkinje, granular, and molecular layers), thalamus, and hippocampus (CA2/CA3 and especially lacunosum molecular layers). Reactive astrocytes, activated rod-like microglia, and macrophages, but not the perivenular infiltrating cells, were identified as the cellular sources of the MT-I+II and MT-III proteins. The pattern of expression of the different MT isoforms in these transgenic mice differed substantially, demonstrating unique effects associated with the expression of each cytokine. The results indicate that the MT expression in the CNS is significantly affected by the cytokine-induced inflammatory response and support a major role of these proteins during CNS injury.

Cerebellar dysfunction is associated with overexpression of proinflammatory cytokine genes in lupus

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown etiology accompanied by central nervous system involvement in up to 60% of patients. The current study chronicles the expression of cerebellar dysfunction in SLE using MRL-lpr/lpr mice as the experimental model. These mice spontaneously develop an illness that has immunological and clinical features of human lupus. We found that MRL-lpr/lpr mice manifest severe and progressive behavioral disturbances indicative of cerebellar dysfunction beginning at 11 weeks of age. Although the lpr gene is known to induce autoimmune features, immunologically normal mice rendered congenic for lpr failed to exhibit disturbances in cerebellar function. Because lupus is a cytokine-driven disease and overexpression of certain proinflammatory cytokines has been associated with neurodegeneration, the relationship between cerebellar dysfunction and cytokine gene expression was examined. Relative to immunologically normal CBA/J mice, the cerebellum of young (11-15 weeks of age) MRL-lpr/lpr mice contained high levels of interleukin (IL)-6 and interferon-gamma (IFNgamma) mRNA, which became even more pronounced in old (22-30 weeks of age) autoimmune mice. mRNA levels for the cytokines IL-1beta and IL-10 were elevated in the cerebellum of old, but not young, MRL-lpr/lpr mice relative to CBA/J. In contrast, the levels of cerebellar transcripts for IL-3 and tumor necrosis factor-alpha were comparable in autoimmune and normal mice, indicating that enhanced gene expression of IL-6, IFNgamma, IL-1beta, and IL-10 was selective. These results suggest a potential role for certain proinflammatory cytokines in the pathogenesis of cerebellar disturbances in SLE.

Interleukin-6 promotes post-traumatic healing in the central nervous system

The central nervous system (CNS) is an immune-privileged site where the role of immune cells and mediators in traumatic brain injury is poorly understood. Previously we have demonstrated that interleukin (IL)-6, a cytokine that acts on a wide range of tissues influencing cell growth and differentiation, is an agonist for vascular endothelial growth factor (VEGF), in in vitro vascularization assays for brain microvessel endothelial cells. In this present work we focus on the role of IL-6 in promoting tissue repair in the CNS in vivo. An aseptic cerebral injury (ACI) was created in the right parietal cortex, using both wild type (C57Bl/6J) and IL-6-deficient (C57Bl/6J-IL-6-/-) mice to study the consequences of the absence of IL-6 on the pathology of brain injuries. We monitored the immediate, early, and late responses to this traumatic injury by characterizing several histologic features in the CNS at days 1, 4, 7 and 14 following injury. Acellular necrosis, cellular infiltration, and re-vascularization were characterized in the injured tissues, and each of these histologic features was individually graded and totaled to assign a healing index. IL-6-deficient mice were found to have a comparatively slower rate of recovery and healing. Furthermore, fluorescein isothiocyanate (FITC)-dextran intravenous injection demonstrated leaky vessels in IL-6-deficient but not in wild type animals following ACI. Additionally, chronic expression of IL-6 in the CNS using transgenic GFAP-IL-6 mice resulted in more rapid healing following ACI. The accelerated tissue repair in GFAP-IL-6 transgenic animals is primarily due to extensive re-vascularization as detected by endothelial cell markers. Combined, this data suggests an important role of IL-6 in tissue repair processes following traumatic injury in the CNS.

Strategies to delay the onset of Alzheimer's disease

Several processes are implicated in the neuropathology of Alzheimer's disease (AD), such as the deposition of amyloid, the formation of paired helical filaments and the proinflammatory activation of microglial and astroglial cells. Proinflammatory activation of glial cells has been a focus of research for a mere ten years now. However, the availability of and broad experience with anti-inflammatory drugs has led to several ongoing clinical trials to verify the capacity of anti-inflammatory drugs to ameliorate the deterioration in AD. The enzymatic cleavage of the amyloid-precursor-protein or the hyperphosphorylation of tau as well as the subsequent aggregation of the resulting products are further targets for drugs intended to delay the neuropathological destruction observed in AD.

The role of cytokines and growth factors in seizures and their sequelae

Although the neuropathological changes caused by severe or repeated seizures have been well characterized, many questions about the molecular mechanisms involved remain unanswered. Neuronal cell death, reactive gliosis, enhanced neurogenesis, and axonal sprouting are four of the best-studied sequelae of seizures. In vitro, each of these pathological processes can be substantially influenced by soluble protein factors, including neurotrophins, cytokines, and growth factors. Furthermore, many of these proteins and their receptors are expressed in the adult brain and are up-regulated in response to neuronal activity and injury. We review the evidence that these intercellular signaling proteins regulate seizure activity as well as subsequent pathology in vivo. As nerve growth factor and brain derived neurotrophic factor are the best-studied proteins of this class, we begin by discussing the evidence linking these neurotrophins to epilepsy and seizure. More than a dozen additional cytokines, growth factors, and neurotrophins that have been examined in the context of epilepsy models are then considered. We discuss the effect of seizure on expression of cytokines and growth factors, and explore the regulation of seizure development and aftermath by exogenous application or antagonist perturbation of these proteins. The experimental evidence supports a role for these factors in each aspect of seizure and pathology, and suggests potential targets for future therapeutics.

Abnormal cytokine and adrenocortical hormone regulation in myotonic dystrophy

Metabolic-endocrine dysfunctions, including hyperinsulinemia, hypertriglyceridemia, increased fat mass, and dysregulation of the hypothalamic-pituitary-adrenal axis, are common in myotonic dystrophy (MD). We hypothesized that increased production of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) may be important underlying mechanisms. We studied the diurnal rhythmicity of cytokines and cortisol, ACTH, and dehydroepiandrosterone in 18 men with adult onset MD and 18 controls. Morning levels of androstenedione, 17-hydroxyprogesterone, testosterone, and insulin were also determined. Genetic analyses were performed, including calculation of allele sizes. Median circulating 24-h levels of IL-6 (P < 0.001), TNF-alpha (P = 0.05), ACTH (P < 0.05), and cortisol (P < 0.05) were all significantly increased in MD, whereas dehydroepiandrosterone levels were decreased (P < 0.001). The diurnal rhythms of these cytokines/ hormones were disturbed in patients. Morning testosterone levels were decreased and insulin levels increased (P < 0.01 for both). Patients with high body fat mass had significantly increased insulin levels and decreased morning levels of cortisol, ACTH, and testosterone. IL-6 and TNF-alpha levels are increased and adrenocortical hormone regulation is disturbed in MD. Adiposity may contribute to these disturbances, which may be of importance for decreased adrenal androgen hormone production and metabolic, muscular, and neuropsychiatric dysfunction in MD.

Human immunodeficiency virus glycoprotein 160 induces cytokine mRNA expression in the rat central nervous system

1. Elevated proinflammatory cytokines within the central nervous system (CNS) of individuals infected with human immunodeficiency virus (HIV) may contribute to altered CNS processes prior to the onset of AIDS. Most studies of HIV-induced alterations in cytokine expression within the CNS have focused on interleukin (IL)-1 and tumor necrosis factor (TNF). 2. We used a ribonuclease protection assay (RPA) to elucidate further the pattern of cytokine mRNA expression in the rat CNS in response to HIV envelope glycoprotein 160 (gp160). Male Sprague-Dawley rats were surgically implanted with a guide cannula directed into a lateral cerebral ventricle. HIV gp160 was injected intracerebroventricularly and rats were sacrificed immediately (time = 0) or at 1, 2, or 4 hr postinjection. Discrete brain regions were dissected, and peripheral glands removed. All tissues were frozen in liquid nitrogen until RNA extraction and assay. 3. IL-1beta IL-1alpha, TNF-alpha, and TNFbeta mRNAs were constitutively expressed in brain tissues. Central administration of gp160 dramatically increased mRNA expression for IL-1beta and TNFalpha in the hypothalamus, hippocampus, brainstem, and cerebellum. Furthermore, although mRNA expression for IL-5, IL-6, and IL-10 was never detected under basal conditions, these mRNAs were increased in brain tissue after administration of gp160. Peak expression in each brain region was detected 2 hr after administration. Multiple cytokine mRNAs were detected in peripheral tissues, but their expression was not altered by central administration of gp160. 4. Our results indicate that gp160 induces mRNA expression in brain for cytokines other than IL-1 and TNF. Screening for multiple cytokine mRNA in this manner provides extensive information concerning the particular cytokines that may be involved in HIV-induced pathologies and alterations in CNS processes.

Age-associated increased interleukin-6 gene expression, late-life diseases, and frailty

Interleukin-6 (IL-6) is a proinflammatory cytokine that is normally tightly regulated and expressed at low levels, except during infection, trauma, or other stress. Among several factors that down-regulate IL-6 gene expression are estrogen and testosterone. After menopause or andropause, IL-6 levels are elevated, even in the absence of infection, trauma, or stress. IL-6 is a potent mediator of inflammatory processes, and it has been proposed that the age-associated increase in IL-6 accounts for certain of the phenotypic changes of advanced age, particularly those that resemble chronic inflammatory disease [decreased lean body mass, osteopenia, low-grade anemia, decreased serum albumin and cholesterol, and increased inflammatory proteins such as C-reactive protein (CRP) and serum amyloid A]. Furthermore, the age-associated rise in IL-6 has been linked to lymphoproliferative disorders, multiple myeloma, osteoporosis, and Alzheimer's disease. This overview discusses the data relating IL-6 to age-associated diseases and to frailty. Like the syndrome of inappropriate antidiuretic hormone, it is possible that certain clinically important late-life changes are due to an inappropriate presence of IL-6.