Endotoxin and intracerebroventricular injection of IL-1 and IL-6 induce rat brain metallothionein-I and -II

Multifunctional Metallothioneins as a Target for Neuroprotection in Parkinson's Disease

Parkinson's disease (PD) is characterized by motor symptoms based on a loss of nigrostriatal dopaminergic neurons and by non-motor symptoms which precede motor symptoms. Neurodegeneration accompanied by an accumulation of α-synuclein is thought to propagate from the enteric nervous system to the central nervous system. The pathogenesis in sporadic PD remains unknown. However, many reports indicate various etiological factors, such as oxidative stress, inflammation, α-synuclein toxicity and mitochondrial impairment, drive neurodegeneration. Exposure to heavy metals contributes to these etiopathogenesis and increases the risk of developing PD. Metallothioneins (MTs) are cysteine-rich metal-binding proteins; MTs chelate metals and inhibit metal-induced oxidative stress, inflammation and mitochondrial dysfunction. In addition, MTs possess antioxidative properties by scavenging free radicals and exert anti-inflammatory effects by suppression of microglial activation. Furthermore, MTs recently received attention as a potential target for attenuating metal-induced α-synuclein aggregation. In this article, we summarize MTs expression in the central and enteric nervous system, and review protective functions of MTs against etiopathogenesis in PD. We also discuss neuroprotective strategies for the prevention of central dopaminergic and enteric neurodegeneration by targeting MTs. This review highlights multifunctional MTs as a target for the development of disease-modifying drugs for PD.

Modulatory Effect of Myokines on Reactive Oxygen Species in Ischemia/Reperfusion

There is a growing body of evidence showing the importance of physical activity against acute ischemic events in various organs. Ischemia/reperfusion injury (I/R) is characterized by tissue damage as a result of restriction and subsequent restoration of blood supply to an organ. Oxidative stress due to increased reactive oxygen species formation and/or insufficient antioxidant defense is considered to play an important role in I/R. Physical activity not only decreases the general risk factors for ischemia but also confers direct anti-ischemic protection via myokine production. Myokines are skeletal muscle-derived cytokines, representing multifunctional communication channels between the contracting skeletal muscle and other organs through an endocrine manner. In this review, we discuss the most prominent members of the myokines (i.e., brain-derived neurotrophic factor (BDNF), cathepsin B, decorin, fibroblast growth factors-2 and -21, follistatin, follistatin-like, insulin-like growth factor-1; interleukin-6, interleukin-7, interleukin-15, irisin, leukemia inhibitory factor, meteorin-like, myonectin, musclin, myostatin, and osteoglycin) with a particular interest in their potential influence on reactive oxygen and nitrogen species formation or antioxidant capacity. A better understanding of the mechanism of action of myokines and particularly their participation in the regulation of oxidative stress may widen their possible therapeutic use and, thereby, may support the fight against I/R.

Neuroprotection by interleukin-6 is mediated by signal transducer and activator of transcription 3 and antioxidative signaling in ischemic stroke

BACKGROUND AND PURPOSE

Interleukin-6 (IL-6) has been shown to have a neuroprotective effect in brain ischemic injury. However, its molecular mechanisms are still poorly understood. In this study, we investigated the neuroprotective role of the IL-6 receptor (IL-6R) by IL-6 in the reactive oxygen species defense system after transient focal cerebral ischemia (tFCI).

METHODS

IL-6 was injected in mice before and after middle cerebral artery occlusion. Coimmunoprecipitation assays were performed for analysis of an IL-6R association after tFCI. Primary mouse cerebral cortical neurons were transfected with small interfering RNA probes targeted to IL-6Rα or gp130 and were used for chromatin-immunoprecipitation assay, luciferase promoter assay, and cell viability assay. Reduction in infarct volumes by IL-6 was measured after tFCI.

RESULTS

IL-6R was disrupted through a disassembly between IL-6Rα and gp130 associated by protein oxidation after reperfusion after tFCI. This suppressed phosphorylation of signal transducer and activator of transcription 3 (STAT3) and finally induced neuronal cell death through a decrease in manganese-superoxide dismutase. However, IL-6 injections prevented disruption of IL-6R against reperfusion after tFCI, consequently restoring activity of STAT3 through recovery of the binding of STAT3 to gp130. Moreover, IL-6 injections restored the transcriptional activity of the manganese-superoxide dismutase promoter through recovery of the recruitment of STAT3 to the manganese-superoxide dismutase promoter and reduced infarct volume after tFCI.

CONCLUSIONS

This study demonstrates that IL-6 has a neuroprotective effect against cerebral ischemic injury through IL-6R-mediated STAT3 activation and manganese-superoxide dismutase expression.

Evaluation of MT expression and detection of apoptotic cells in LEC rat kidneys

To confirm our previous observations on the effectiveness of long term treatment with Zn on Long-Evans Cinnamon (LEC) rats, we extended these studies determining the effects of Zn on trace elements, metallothionein (MT) concentrations and immunolocalization, and on the levels of both MT-1 and MT-2 mRNAs in the LEC rat kidneys. We also localized the renal cells that had chromatin condensation and nuclear fragmentation typical of apoptosis. The results demonstrate that the amount of Zn increased in the treated rats with respect to both untreated and basal rats. In the treated rats the amount of Cu and Fe was similar to that of the basal rats. MT concentrations did not change either with or without Zn treatment, but were higher than the basal group. However, if we consider the percentage of oxidized MT (MTox), we note that Zn treatment is very effective in reducing this value. MTox is not able to bind metals, so it does not perform a "scavenger" function. Moreover, quantification of mRNA indicates that the MT-1 isoform was significantly higher than the MT-2 isoform following Zn treatment. Untreated group sections showed a confocal fluorescent signal that highlighted the irregular nuclei and small apoptotic bodies. The intensity and quantity of fluorescence decreased in the treated group sections. These findings suggest that, in LEC rats, Zn may contribute to cytoprotection through the regulation of MT expression which may provide a cellular defence strategy in response to DNA damage.

Metallothionein in bovine spongiform encephalopathy

An increase in metallothionein I and II (MT I/II) mRNA concentrations has been reported in the central nervous system of scrapie-infected rodents. In this study we compared cattle with bovine spongiform encephalopathy (BSE), cattle affected by neurological disease other than BSE, and clinically healthy cattle in respect of MT I/II immunoreactivity in brainstem medullary tissue. Marked astrocytic MT I/II immunolabelling was seen in all BSE-affected animals, in contrast to clinically healthy cases, in which no such labelling was detected. In BSE, MT I/II immunoreactive astrocytes were confined specifically to areas of vacuolation or abnormal prion protein (PrP(BSE)) deposition, or both. MT I/II immunolabelling was also seen in a small number of animals with a neurological disease other than BSE. These findings complement previous studies by demonstrating increased levels of MT I/II in transmissible spongiform encephalopathy (TSE)-infected brain tissue, indicating that MT I/II may play some as yet unidentified role in the response to TSE infection.

Interleukin-6 deficiency reduces the brain inflammatory response and increases oxidative stress and neurodegeneration after kainic acid-induced seizures

The role of interleukin-6 in hippocampal tissue damage after injection with kainic acid, a rigid glutamate analogue inducing epileptic seizures, has been studied by means of interleukin-6 null mice. At 35mg/kg, kainic acid induced convulsions in both control (75%) and interleukin-6 null (100%) mice, and caused a significant mortality (62%) only in the latter mice, indicating that interleukin-6 deficiency increased the susceptibility to kainic acid-induced brain damage. To compare the histopathological damage caused to the brain, control and interleukin-6 null mice were administered 8.75mg/kg kainic acid and were killed six days later. Morphological damage to the hippocampal field CA1-CA3 was seen after kainic acid treatment. Reactive astrogliosis and microgliosis were prominent in kainic acid-injected normal mice hippocampus, and clear signs of increased oxidative stress were evident. Thus, the immunoreactivity for inducible nitric oxide synthase, peroxynitrite-induced nitration of proteins and byproducts of fatty acid peroxidation were dramatically increased, as was that for metallothionein I+II, Mn-superoxide dismutase and Cu/Zn-superoxide dismutase. In accordance, a significant neuronal apoptosis was caused by kainic acid, as revealed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling and interleukin-1beta converting enzyme/Caspase-1 stainings. In kainic acid-injected interleukin-6 null mice, reactive astrogliosis and microgliosis were reduced, while morphological hippocampal damage, oxidative stress and apoptotic neuronal death were increased. Since metallothionein-I+II levels were lower, and those of inducible nitric oxide synthase higher, these concomitant changes are likely to contribute to the observed increased oxidative stress and neuronal death in the interleukin-6 null mice. The present results demonstrate that interleukin-6 deficiency increases neuronal injury and impairs the inflammatory response after kainic acid-induced seizures.

Global impact of influenza virus on cellular pathways is mediated by both replication-dependent and -independent events

Influenza virus, the causative agent of the common flu, is a worldwide health problem with significant economic consequences. Studies of influenza virus biology have revealed elaborate mechanisms by which the virus interacts with its host cell as it inhibits the synthesis of cellular proteins, evades the innate antiviral response, and facilitates production of viral RNAs and proteins. With the advent of DNA array technology it is now possible to obtain a large-scale view of how viruses alter the environment within the host cell. In this study, the cellular response to influenza virus infection was examined by monitoring the steady-state mRNA levels for over 4,600 cellular genes. Infections with active and inactivated influenza viruses identified changes in cellular gene expression that were dependent on or independent of viral replication, respectively. Viral replication resulted in the downregulation of many cellular mRNAs, and the effect was enhanced with time postinfection. Interestingly, several genes involved in protein synthesis, transcriptional regulation, and cytokine signaling were induced by influenza virus replication, suggesting that some may play essential or accessory roles in the viral life cycle or the host cell's stress response. The gene expression pattern induced by inactivated viruses revealed induction of the cellular metallothionein genes that may represent a protective response to virus-induced oxidative stress. Genome-scale analyses of virus infections will help us to understand the complexities of virus-host interactions and may lead to the discovery of novel drug targets or antiviral therapies.

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.

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

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

Differential expression of metallothioneins in the CNS of mice with experimental autoimmune encephalomyelitis

Multiple sclerosis is an inflammatory, demyelinating disease of the CNS. Metallothioneins-I+II are antioxidant proteins induced in the CNS by immobilisation stress, trauma or degenerative diseases which have been postulated to play a neuroprotective role, while the CNS isoform metallothionein-III has been related to Alzheimer's disease. We have analysed metallothioneins-I-III expression in the CNS of mice with experimental autoimmune encephalomyelitis. Moreover, we have examined the putative role of interferon-gamma, a pro-inflammatory cytokine, in the control of metallothioneins expression during experimental autoimmune encephalomyelitis in interferon-gamma receptor knockout mice with two different genetic backgrounds: 129/Sv and C57BL/6x129/Sv. Mice with experimental autoimmune encephalomyelitis showed a significant induction of metallothioneins-I+II in the spinal cord white matter, and to a lower extent in the brain. Interferon-gamma receptor knockout mice suffered from a more severe experimental autoimmune encephalomyelitis, and interestingly showed a higher metallothioneins-I+II induction in both white and grey matter of the spinal cord and in the brain. In contrast to the metallothioneins-I+II isoforms, metallothionein-III expression remained essentially unaltered during experimental autoimmune encephalomyelitis; interferon-gamma receptor knockout mice showed an altered metallothionein-III expression (a slight increase in the spinal cord white matter) only in the C57BL/6x129/Sv background. Metallothioneins-I+II proteins were prominent in areas of induced cellular infiltrates. Reactive astrocytes and activated monocytes/macrophages were the sources of metallothioneins-I+II proteins. From these results we suggest that metallothioneins-I+II but not metallothionein-III may play an important role during experimental autoimmune encephalomyelitis, and indicate that the pro-inflammatory cytokine interferon-gamma is unlikely an important factor in this response.

Impaired inflammatory response and increased oxidative stress and neurodegeneration after brain injury in interleukin-6-deficient mice

In order to determine the role of the neuropoietic cytokine interleukin-6 (IL-6) during the first 3 weeks after a focal brain injury, we examined the inflammatory response, oxidative stress and neuronal survival in normal and interleukin-6-deficient (knockout, IL-6KO) mice subjected to a cortical freeze lesion. In normal mice, the brain injury was followed by reactive astrogliosis and recruitment of macrophages from 1 day postlesion (dpl), peaking at 3-10 dpl, and by 20 dpl the transient immunoreactions were decreased, and a glial scar was present. In IL-6KO mice, the reactive astrogliosis and recruitment of macrophages were decreased throughout the experimental period. The expression of the antioxidant and anti-apoptotic factors metallothionein I+II (MT-I+II) was increased prominently by the freeze lesion, but this response was significantly reduced in the IL-6 KO mice. By contrast, the expression of the antioxidants Cu/Zn-superoxide dismutase (Cu/Zn-SOD), Mn-SOD, and catalase remained unaffected by the IL-6 deficiency. The lesioned mice showed increased oxidative stress, as judged by malondialdehyde (MDA) and nitrotyrosine (NITT) levels and by formation of inducible nitric oxide synthase (iNOS). IL-6KO mice showed higher levels of MDA, NITT, and iNOS than did normal mice. Concomitantly, in IL-6KO mice the number of apoptotic neurons was significantly increased as judged by TUNEL staining, and regeneration of the tissue was delayed relative to normal mice. The changes in neuronal tissue damage and in brain regeneration observed in IL-6KO mice are likely caused by the IL-6-dependent decrease in MT-I+II expression, indicating IL-6 and MT-I+II as neuroprotective factors during brain injury.

IL-6 deficiency leads to reduced metallothionein-I+II expression and increased oxidative stress in the brain stem after 6-aminonicotinamide treatment

We examined the effects of interleukin-6 (IL-6) deficiency on brain inflammation and the accompanying bone marrow (BM) leukopoiesis and spleen immune reaction after systemic administration of a niacin antagonist, 6-aminonicotinamide (6-AN), which causes both astroglial degeneration/cell death in brain stem gray matter areas and BM toxicity. In both normal and genetically IL-6-deficient mice (IL-6 knockout (IL-6KO) mice), the extent of astroglial degeneration/cell death in the brain stem was similar as determined from disappearance of GFAP immunoreactivity. In 6-AN-injected normal mice reactive astrocytosis encircled gray matter areas containing astroglial degeneration/cell death, which were infiltrated by several macrophages and some T-lymphocytes. Reactive astrocytes and a few macrophages increased significantly the antioxidants metallothionein-I+II (MT-I+II) and moderately the MT-III isoform. In 6-AN-injected IL-6KO mice reactive astrocytosis and recruitment of macrophages and T-lymphocytes were clearly reduced, as were BM leukopoiesis and spleen immune reaction. Expression of MT-I+II was significantly reduced while MT-III was increased. Oxidative stress, as determined by measuring nitrated tyrosine and malondialdehyde, was increased by 6-AN to a greater extent in IL-6KO mice. The blood-brain barrier to albumin was only disrupted in 6-AN-injected normal mice, which likely is due to the substantial migration of blood-derived inflammatory cells into the CNS. The present results demonstrate that inflammation in CNS is clearly reduced during IL-6 deficiency and this effect is likely due to significant inhibition of BM leukopoiesis. We also show that IL-6 deficiency reduces the levels of neuroprotective antioxidants MT-I+II followed by an increased oxidative stress during CNS inflammation.

Metallothionein expression is altered in a transgenic murine model of familial amyotrophic lateral sclerosis

Missense mutations in the gene encoding copper zinc superoxide dismutase (SOD1) have been found to cause one form of familial amyotrophic lateral sclerosis (FALS). Although the exact mechanism of disease is unknown, abnormalities in the ability of mutant SOD1 to bind zinc or copper ions may be crucial in the pathogenesis of disease. Because members of the metallothionein (MT) family of zinc and copper binding proteins function as important cellular regulators of metal ion bioavailability in the central nervous system, we used in situ hybridization and immunohistochemistry to study the expression pattern of these molecules in a transgenic mouse model of familial ALS. In adult wild-type mouse spinal cord, expression of MT-I and MT-II is restricted to ependymal cells and a subset of astrocytes located in white matter tracts, while MT-III synthesis is limited to neurons within gray matter. Compared to wild-type littermates, transgenic mice carrying the G93A SOD1 mutation demonstrate markedly increased expression of MT-I and MT-II within astrocytes in both white and gray matter as weakness develops. MT-III synthesis in neurons is also greatly upregulated as G93A SOD1 animals age, with glial cell expression of MT-III evident by later stages of the disease. Changes in MT expression occur before the onset of motor deficits or significant motor neuron pathology in G93A SOD1 mice and remarkably extend beyond ventral horn populations of neurons and glia. These results are consistent with the hypothesis that metallothioneins may serve an early and important protective function in FALS.

Cutaneous metallothionein induction by ultraviolet B irradiation in interleukin-6 null mice

The mediators of cutaneous metallothionein induction by ultraviolet radiation have not been defined. In this study we sought to identify cytokines that might be involved. We examined the role of interleukin-6, using the IL-6 null (IL-6-/-) mouse, which has been observed to be highly sensitive to ultraviolet radiation damage. Whereas cutaneous metallothionein concentration, measured by radioimmunoassay, began to rise in wild-type (IL-6+/+) mice by 12 h after ultraviolet irradiation, there was a significant delay in the IL-6-/- mice until 48 h after UV irradiation. Immunohistologically, metallothionein appeared in IL-6+/+ mice at 24 h in dermal fibroblasts, and then by 48 h in epidermal basal keratinocytes, with intensity increasing until 72 h, and was coincident with proliferating cell nuclear antigen-positive staining. Corresponding metallothionein expression in IL-6-/- mouse skin was significantly delayed. Serum interleukin-6 was elevated in IL-6+/+ mice following ultraviolet irradiation, with peak concentration at 4 h, but no increase in serum interleukin-1beta was found in either IL-6+/+ or IL-6-/- mice. Interestingly, tumor necrosis factor alpha concentration in serum was elevated at 12 h postirradiation in IL-6+/+ mice, but there was an earlier (at 4 and 8 h) time-dependent increase in tumor necrosis factor alpha in serum of the IL-6-/- mice. Skin zinc and copper concentrations were not altered by ultraviolet irradiation in either IL-6+/+ or IL-6-/- mice. The results suggest that interleukin-6 may be a very early mediator of cutaneous metallothionein induction by ultraviolet radiation, but that this role is possibly assumed by alternative cytokines like tumor necrosis factor alpha when interleukin-6 is deficient.

Regulation of corticotropin-releasing factor-binding protein expression in amygdalar neuronal cultures

Corticotropin-releasing factor-binding protein (CRF-BP) is known to regulate the bioavailability of CRF and may also play a role in stress behaviours. CRF-BP has been localized in the pituitary as well as central nervous system (CNS) limbic and cortical areas, including the amygdala. The signal transduction pathways which regulate amygdalar CRF-BP are not well understood. In this report, we have examined the effect of protein kinase A and C activators, CRF, dexamethasone and interleukin-6 (IL6) on CRF-BP mRNA and protein expression in dissociated fetal amygdalar cultures. CRF-BP mRNA levels were determined by Northern analysis following 12 h treatment with the following agents: forskolin (1-30 microM), CRF (1-1000 nM), phorbol-12-myristate-13-acetate (TPA; 1-50 nM), dexamethasone (1-100 nM) and IL6 (10-500 pM). Significant increases in CRF-BP mRNA were observed in response to forskolin (30 mM), CRF (100, 1000 nM), IL6 (100, 500 pM), TPA (50 nM) and dexamethasone (100 nM; P<0.05 for all; n=3-6 for all). We extended our observations of CRF-BP expression to the protein level by performing semiquantitative Western analysis of total cellular protein after treatment with the same agents. Twenty-four hour treatment with 30 microM forskolin, 1000 nM CRF, 50 nM TPA, 100 pM IL6 or 100 nM dexamethasone significantly increased CRF-BP expression (P<0.05, n=3 for each treatment). The primary cultures were then transfected with a rat CRF-BP-reporter construct containing 3500 base pairs of CRF-BP 5' flanking DNA. Treatment with all five agents produced statistically significant increases above control (P<0.05; n=3 for each). The results suggest that CRF-BP in the amygdala is stimulated by numerous pathways which may play a significant role in promoting behavioural changes.

Localization of metallothionein-I and -III expression in the CNS of transgenic mice with astrocyte-targeted expression of interleukin 6

The effect of interleukin-6 (IL-6) on metallothionein-I (MT-I) and MT-III expression in the brain has been studied in transgenic mice expressing IL-6 under the regulatory control of the glial fibrillary acidic protein gene promoter (GFAP-IL6 mice), which develop chronic progressive neurodegenerative disease. In situ hybridization analysis revealed that GFAP-IL6 (G16-low expressor line, and G36-high expressor line) mice had strongly increased MT-I mRNA levels in the cerebellum (Purkinje and granular layers of the cerebellar cortex and basal nuclei) and, to a lesser degree, in thalamus (only G36 line) and hypothalamus, whereas no significant alterations were observed in other brain areas studied. Microautoradiography and immunocytochemistry studies suggest that the MT-I expression is predominantly localized to astrocytes throughout the cerebrum and especially in Bergman glia in the cerebellum. However, a significant expression was also observed in microglia of the GFAP-IL6 mice. MT-III expression was significantly increased in the Purkinje cell layer and basal nuclei of the cerebellum, which was confirmed by Northern blot analysis of poly(A)+ mRNA and by ELISA of the MT-III protein. In contrast, in the G36 but not G16 mice, transgene expression of IL-6 was associated with significantly decreased MT-III RNA levels in the dentate gyrus and CA3 pyramidal neuron layer of the hippocampus and, in both G36 and G16 mice, in the occipital but not frontal cortex and in ependymal cells. Thus, both the widely expressed MT-I isoform and the CNS specific MT-III isoform are significantly affected in a MT isoform- and CNS area-specific manner in the GFAP-IL6 mice, a chronic model of brain damage.

Interleukin-6 and tumor necrosis factor-alpha type 1 receptor deficient mice reveal a role of IL-6 and TNF-alpha on brain metallothionein-I and -III regulation

Metallothioneins (MTs) are a family of low molecular weight proteins which in rodents is comprised of several isoforms (MT-I to MT-IV). MT-I and MT-II are widely expressed isoforms, whereas MT-III is mainly expressed in the central nervous system and is the only isoform that inhibits survival and neurite formation of rat cortical neurons in vitro. However, the physiological roles and regulation of these proteins in the brain are poorly characterized. In this report we have studied the putative role of IL-6 and TNF-alpha on the regulation of brain MT-I and MT-III, by using mice carrying a null mutation in the IL-6 or the TNF-alpha type 1 receptor genes or both. In situ hybridization analysis revealed that brain MT-I induction by bacterial lipopolysaccharide (LPS) was significantly lower in IL-6- and TNFR1-deficient mice, and to a greater extent in the double mutant mice, in most brain areas studied. These results suggest that the MT-I isoform could be considered an acute-phase protein in the brain, which is consistent with previous studies in transgenic mice overexpressing IL-6 in astrocytes. In contrast to LPS, brain MT-I induction by restraint stress was not affected significantly by IL-6 or TNFR1 deficiencies, suggesting that these cytokines are not important during the stress response in the brain. In basal conditions, it was also observed that the double mutant mice had diminished MT-I mRNA levels in several brain areas. In contrast to MT-I, MT-III mRNA levels were minimally affected by either LPS or stress. Yet, significant decreasing effects of IL-6 and TNFR1 deficiencies were observed in the Purkinje neuronal layer of the cerebellum (after LPS) and ependymal cells (after LPS and stress). In contrast, significant increasing effects, especially of TNFR1 deficiency, were observed in CA1 hippocampal area, retrosplenial and parietal cortex, and in thalamic nuclei (after LPS). These results demonstrate that IL-6 and TNF-alpha are involved in brain MTs regulation during LPS-elicited inflammatory response but not during the stress response.