Induction of metallothionein in astrocytes and microglia in the spinal cord from the myelin-deficient jimpy mouse

Absence of metallothionein-3 produces changes on MT-1/2 regulation in basal conditions and alters hypothalamic-pituitary-adrenal (HPA) axis

Metallothioneins (MTs) are multipurpose proteins with clear antioxidant, anti-inflammatory and metal homeostasis properties. The roles of brain MT-1 and MT-2 are similar to those described in the periphery, and are inducible by metals, inflammatory and stress stimuli. MT-3, originally named growth inhibitory factor, exists mainly in the central nervous system, is hardly ever inducible and its functional role and regulation are poorly understood and controversial. In the present study we examined how absence of MT-3 affects phenotypic characteristics and its effects on MT1/2 expression in basal situation and after induction. Hyperactive behavior was found only in young male Mt-3 KO mice and disappeared in the older ones. Absence of MT-3 was associated with a significant increase of MT-1/2 protein levels in several brain areas but decreased MT-1 mRNA levels, which might be related to lower corticosterone levels. The response to stress or inflammation on corticosterone plasma levels was similar in wild type and Mt-3 KO mice, suggesting that the relevant MT-3 role as MT-1/2 regulator in basal conditions is lost when other important regulatory factors such as glucocorticoids or cytokines appear.

Tomato lectin histochemistry for microglial visualization

The use of different lectins for the study of microglial cells in the central nervous system (CNS) is a valuable tool that has been extensively used in the last years for the selective staining of this glial cell population, not only in normal physiological conditions, but also in a wide range of pathological situations where the normal homeostasis of the parenchyma is disturbed. In this chapter we accurately describe the methodology for the selective labelling of microglial cells by using the tomato lectin (TL), a protein lectin obtained from Lycopersicum esculentum with specific affinity for poly-N-acetyl lactosamine sugar residues which are found on the plasma membrane and in the cytoplasm of microglia. Here we describe how to perform this technique on vibratome, frozen, and paraffin sections for optical microscopy, as well as for transmission electron microscopy (TEM) studies. Using this methodology it is possible to visualize amoeboid microglia in the developing brain, ramified microglia in the adult, and activated/reactive microglia in the experimentally damaged brain. In addition, as TL also recognized sugar residues in endothelial cells, this technique is very useful for the study of the relationship established between microglia and the CNS vasculature.

Metallothionein-II improves motor function recovery and increases spared tissue after spinal cord injury in rats

After spinal cord injury (SCI), a complex cascade of pathophysiological processes rapidly damages the nervous tissue. The initial damage spreads to the surrounding tissue by different mechanisms, including oxidative stress. We have recently reported that the induction of metallothionein (MT) protein is an endogenous rapid-response mechanism after SCI. Since the participation of MT in neuroprotective processes after SCI is still unknown, the aim of the present study was to evaluate the possible neuroprotective effect of exogenously administered MT-II during the acute phase after SCI in rats. Female Wistar rats weighing 200-250g were submitted to spinal cord contusion by means of a computer-controlled device (NYU impactor). Rats received several doses of MT-II (3.2, 10 and 100μg) at 2 and 8h after SCI. Results of the BBB scale were statistically analysed using an ANOVA of repeated-measures, followed by Tukey's test. Among the three doses tested, only 10 and 100μg were able to significantly increase (p<0.05) BBB scale scores eight weeks after SCI from a mean of 7.88 in the control group, to means of 12.63 and 10.88 for the 10 and 100μg doses of MT-II, respectively. The amount of spared tissue was also higher in the groups treated with 10 and 100μg, as compared to the control group values. Results from the present study demonstrate a significant neuroprotective effect of exogenously administered MT-II. Further studies are needed in order to characterize the mechanisms involved in this neuroprotective action.

The comparison of mouse full metallothionein-1 versus alpha and beta domains and metallothionein-1-to-3 mutation following traumatic brain injury reveals different biological motifs

Traumatic injury to the brain is one of the leading causes of injury-related death or disability, but current therapies are limited. Previously it has been shown that the antioxidant proteins metallothioneins (MTs) are potent neuroprotective factors in animal models of brain injury. The exogenous administration of MTs causes effects consistent with the roles proposed from studies in knock-out mice. We herewith report the results comparing full mouse MT-1 with the independent alpha and beta domains, alone or together, in a cryoinjury model. The lesion of the cortex caused the mice to perform worse in the horizontal ladder beam and the rota-rod tests; all the proteins showed a modest effect in the former test, while only full MT-1 improved the performance of animals in the rota-rod, and the alpha domain showed a rather detrimental effect. Gene expression analysis by RNA protection assay demonstrated that all proteins may alter the expression of host-response genes such as GFAP, Mac1 and ICAM, in some cases being the beta domain more effective than the alpha domain or even the full MT-1. A MT-1-to-MT-3 mutation blunted some but not all the effects caused by the normal MT-1, and in some cases increased its potency. Thus, splitting the two MT-1 domains do not seem to eliminate all MT functions but certainly modifies them, and different motifs seem to be present in the protein underlying such functions.

Zinc: the brain's dark horse

Zinc is a life-sustaining trace element, serving structural, catalytic, and regulatory roles in cellular biology. It is required for normal mammalian brain development and physiology, such that deficiency or excess of zinc has been shown to contribute to alterations in behavior, abnormal central nervous system development, and neurological disease. In this light, it is not surprising that zinc ions have now been shown to play a role in the neuromodulation of synaptic transmission as well as in cortical plasticity. Zinc is stored in specific synaptic vesicles by a class of glutamatergic or "gluzinergic" neurons and is released in an activity-dependent manner. Because gluzinergic neurons are found almost exclusively in the cerebral cortex and limbic structures, zinc may be critical for normal cognitive and emotional functioning. Conversely, direct evidence shows that zinc might be a relatively potent neurotoxin. Neuronal injury secondary to in vivo zinc mobilization and release occurs in several neurological disorders such as Alzheimer's disease and amyotrophic lateral sclerosis, in addition to epilepsy and ischemia. Thus, zinc homeostasis is integral to normal central nervous system functioning, and in fact its role may be underappreciated. This article provides an overview of zinc neurobiology and reviews the experimental evidence that implicates zinc signals in the pathophysiology of neuropsychiatric diseases. A greater understanding of zinc's role in the central nervous system may therefore allow for the development of therapeutic approaches where aberrant metal homeostasis is implicated in disease pathogenesis.

Role of zinc in ALS

The causes of amyotrophic lateral sclerosis (ALS) are poorly understood. A small proportion, about 2%, is associated with a mutation in the superoxide dismutase (SOD1) gene, and mice expressing this mutant gene exhibit a progressive, ALS-like neurodegenerative disease. Studies of these animals, as well as of human post mortem tissue, reveal the presence of multiple pathological processes, including oxidative stress, glutamate excitotoxicity, neuroinflammation, mitochondrial degeneration, alterations in neurofilaments and neurotubules, mitochondrial damage, aggregation of proteins, abnormalities in growth factors, and apoptosis. We propose that alterations in the disposition of zinc ions may be important in the initiation and development of ALS. SOD1 binds zinc, and many of the mutant forms of this enzyme associated with ALS show altered zinc binding. Alterations in the expression of metallothioneins (MTs), which regulate cellular levels of zinc, have been reported in mutant SOD1 mice, and deletion of MTs in these animals accelerates disease progression. Zinc plays a key role in all the pathological processes associated with ALS. Our zinc hypothesis also may help explain evidence for environmental factors in some cases of ALS, such as in the Chamorro tribe in Guam and in the Gulf War.

Doxycycline treatment decreases morbidity and mortality of murine neurocysticercosis: evidence for reduction of apoptosis and matrix metalloproteinase activity

Murine neurocysticercosis is a parasitic infection transmitted through the direct ingestion of Taenia solium eggs, which differentially disrupts the barriers that protect the microenvironment of the central nervous system. Among the host factors that are involved in this response, matrix metalloproteinases (MMPs) have been recently described as important players. Doxycycline is a commonly prescribed antimicrobial drug that acts as an anti-inflammatory agent with broad inhibitory properties against MMPs. In this study, we examined the effects of doxycycline treatment in a murine model of neurocysticercosis. Animals treated with doxycycline exhibited reduced morbidity and mortality throughout the course of infection. Although similar levels of leukocyte infiltration were observed with both treatment regimens, doxycycline appeared to provide improved conditions for host survival, as reduced levels of apoptosis were detected among infiltrates as well as in neurons. As an established MMP blocker, doxycycline reduced the degradation of junctional complex proteins in parenchymal vessels. In addition, doxycycline treatment was associated with an overall reduction in the expression and activity of MMPs, particularly in areas of leukocyte infiltration. These results indicate that a broad-range inhibitor of MMPs promotes host survival and suggest the potential of doxycycline as a therapeutic agent for the control of inflammatory responses associated with neurocysticercosis.

Differential time-course of the increase of antioxidant thiol-defenses in the acute phase after spinal cord injury in rats

Spinal cord injury (SCI) is a world-wide health problem. After traumatic injury, spinal cord tissue starts a series of self-destructive mechanisms, known as the secondary lesion. The leading mechanisms of damage after SCI are excitotoxicity, free radicals' overproduction, inflammation and apoptosis. Metallothionein (MT) and reduced glutathione (GSH) are low-molecular-weight, cysteine-rich peptides able to scavenge free radicals. MT and GSH participation as neuroprotective molecules after SCI is unknown. The aim of the present study is to describe the changes of MT and GSH contents and GSH peroxidase (GPx) activity in the acute phase after SCI in rats. Female Wistar rats weighing 200-250g were submitted to spinal cord contusion model, by means of a computer-controlled device (NYU impactor). Rats receiving laminectomy were used as a control group. Animals were killed 2, 4, 12 and 24h after surgery. MT was quantified by the silver-saturation method, using atomic absorption spectrophotometry. GSH and GPx were assayed by spectrophotometry. Results indicate an increased MT content by effect of SCI, only at 4 and 24h, as compared to sham group values. Meanwhile, GSH was found decreased at 4, 12 and 24h after SCI. Interestingly, GPx activity was raised at all time points, indicating that this enzymatic defense is activated soon after SCI. Results suggest that thiol-based defenses, MT and GSH, are differentially expressed by spinal cord tissue to cope with the various processes of damage after lesion.

Infection of metallothionein 1+2 knockout mice with Rocky Mountain Laboratory scrapie

Metallothioneins (MT) are heavy metal-binding, antioxidant proteins with relevant roles described in many pathological conditions affecting the central nervous system (CNS). Regarding prion diseases, a number of publications demonstrate an up-regulation of MT-1+2 in the brains of TSE affected cattle, humans and experimentally inoculated rodents. Since the prion protein also binds copper, and oxidative stress is one of the events presumably triggered by PrPsc deposition, it seems plausible that MTs have a relevant role in the outcome of these neurodegenerative processes. To gain knowledge of the role of MTs in TSE pathogeny, and particularly of that of MT-1+2, a transgenic MT-1+2 knockout mouse model (MT-1+2 KO) was intracerebrally inoculated with the mouse-adapted Rocky Mountain Laboratory (RML) strain of scrapie; 129SvJ mice were used as controls (WT). Clinical signs were monitored and animals were humanely sacrificed when they scored positive clinically. Brains were fixed following intracardiac perfusion with 4% formaldehyde, paraffin embedded, and processed for histological, histochemical and immunohistochemical evaluation. The incubation period did not show significant differences between MT-1+2 KO and WT mice, nor did the evolution of neurological signs. Upon neuropathological characterisation of the brains, moderate differences were observed in astroglial and microglial response, spongiosis score and PrPsc deposition, particularly in brain regions to which the studied strain showed a stronger tropism (i.e. hippocampus). Results showed that the brain defence mechanisms against PrPsc deposition involve, aside from MT-1+2, other molecules, such as HSP25, which are capable of compensating for the lack of MT-1+2.

Novel roles for metallothionein-I + II (MT-I + II) in defense responses, neurogenesis, and tissue restoration after traumatic brain injury: Insights from global gene expression profiling in wild-type and MT-I + II knockout mice

Traumatic injury to the brain is one of the leading causes of injury-related death or disability, especially among young people. Inflammatory processes and oxidative stress likely underlie much of the damage elicited by injury, but the full repertoire of responses involved is not well known. A genomic approach, such as the use of microarrays, provides much insight in this regard, especially if combined with the use of gene-targeted animals. We report here the results of one of these studies comparing wild-type and metallothionein-I + II knockout mice subjected to a cryolesion of the somatosensorial cortex and killed at 0, 1, 4, 8, and 16 days postlesion (dpl) using Affymetrix genechips/oligonucleotide arrays interrogating approximately 10,000 different murine genes (MG_U74Av2). Hierarchical clustering analysis of these genes readily shows an orderly pattern of gene responses at specific times consistent with the processes involved in the initial tissue injury and later regeneration of the parenchyma, as well as a prominent effect of MT-I + II deficiency. The results thoroughly confirmed the importance of the antioxidant proteins MT-I + II in the response of the brain to injury and opened new avenues that were confirmed by immunohistochemistry. Data in KO, MT-I-overexpressing, and MT-II-injected mice strongly suggest a role of these proteins in postlesional activation of neural stem cells.

Role of metallothionein-III following central nervous system damage

We evaluated the physiological relevance of metallothionein-III (MT-III) in the central nervous system following damage caused by a focal cryolesion onto the cortex by studying Mt3-null mice. In normal mice, dramatic astrogliosis and microgliosis and T-cell infiltration were observed in the area surrounding the lesioned tissue, along with signs of increased oxidative stress and apoptosis. There was also significant upregulation of cytokines/growth factors such as tumor necrosis factor-alpha, interleukin (IL)-1 alpha/beta, and IL-6 as measured by ribonuclease protection assay. Mt3-null mice did not differ from control mice in these responses, in sharp contrast to results obtained in Mt1- Mt2-null mice. In contrast, Mt3-null mice showed increased expression of several neurotrophins as well as of the neuronal sprouting factor GAP-43. Thus, unlike MT-I and MT-II, MT-III does not affect the inflammatory response elicited in the central nervous system by a cryoinjury, nor does it serve an important antioxidant role, but it may influence neuronal regeneration during the recovery process.

Roles of the metallothionein family of proteins in the central nervous system

Metallothioneins (MTs) constitute a family of proteins characterized by a high heavy metal [Zn(II), Cu(I)] content and also by an unusual cysteine abundance. Mammalian MTs are comprised of four major isoforms designated MT-1 trough MT-4. MT-1 and MT-2 are expressed in most tissues including the brain, whereas MT-3 (also called growth inhibitory factor) and MT-4 are expressed predominantly in the central nervous system and in keratinizing epithelia, respectively. All MT isoforms have been implicated in disparate physiological functions, such as zinc and copper metabolism, protection against reactive oxygen species, or adaptation to stress. In the case of MT-3, an additional involvement of this isoform in neuromodulatory events and in the pathogenesis of Alzheimer's disease has also been suggested. It is essential to gain insight into how MTs are regulated in the brain in order to characterize MT functions, both in normal brain physiology, as well as in pathophysiological states. The focus of this review concerns the biology of the MT family in the context of their expression and functional roles in the central nervous system.

Zinc or copper deficiency-induced impaired inflammatory response to brain trauma may be caused by the concomitant metallothionein changes

The role of zinc- and copper-deficient diets on the inflammatory response to traumatic brain injury (TBI) has been evaluated in adult rats. As expected, zinc deficiency decreased food intake and body weight gain, and the latter effect was higher than that observed in pair-fed rats. In noninjured brains, zinc deficiency only affected significantly lectin (increasing) and glial fibrillary acidic protein (GFAP) and Cu,Zn-superoxide dismutase (Cu,Zn-SOD) (decreasing) immunoreactivities (irs). In injured brains, a profound gliosis was observed in the area surrounding the lesion, along with severe damage to neurons as indicated by neuron specific enolase (NSE) ir, and the number of cells undergoing apoptosis (measured by TUNEL) was dramatically increased. Zinc deficiency significantly altered brain response to TBI, potentiating the microgliosis and reducing the astrogliosis, while increasing the number of apoptotic cells. Metallothioneins (MTs) are important zinc- and copper-binding proteins in the CNS, which could influence significantly the brain response to TBI because of their putative roles in metal homeostasis and antioxidant defenses. MT-I+II expression was dramatically increased by TBI, and this response was significantly blunted by zinc deficiency. The MT-III isoform was moderately increased by both TBI and zinc deficiency. TBI strongly increased oxidative stress levels, as demonstrated by malondialdehyde (MDA), protein tyrosine nitration (NITT), and nuclear factor kappaB (NF-kappaB) levels irs, all of which were potentiated by zinc deficiency. Further analysis revealed unbalanced expression of prooxidant and antioxidant proteins besides MT, since the levels of inducible nitric oxide synthase (iNOS) and Cu,Zn-SOD were increased and decreased, respectively, by zinc deficiency. All these effects were attributable to zinc deficiency, since pair-fed rats did not differ from normally fed rats. In general, copper deficiency caused a similar pattern of responses, albeit more moderate. Results obtained in mice with a null mutation for the MT-I+II isoforms strongly suggest that most of the effects observed in the rat brain after zinc and copper deficiencies are attributable to the concomitant changes in the MT expression.

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.

Altered central nervous system cytokine-growth factor expression profiles and angiogenesis in metallothionein-I+II deficient mice

To study the importance of metallothionein-I and -II (MT-I+II) for brain inflammation and regeneration, the authors examined normal and MT-I+II knock-out (MT-KO) mice subjected to a cortical freeze injury. Normal mice showed profound neurodegeneration, inflammation, and gliosis around the injury, which was repaired by 20 days postlesion (dpl). However, in MT-KO mice the lesion-associated inflammation was still present as late as 90 dpl. Scanning electron microscopy demonstrated that the number of capillaries was lower, and ultrastructural preservation of the lesioned parenchyma was poorer in MT-KO mice, suggesting an altered angiogenesis. To gain insight into the mechanisms involved, a number of cytokines and growth factors were evaluated. The number of cells expressing the proinflammatory cytokines IL-1beta, IL-6, and TNF-alpha was higher in MT-KO mice than in normal mice, which was confirmed by RNase protection analysis, whereas the number of cells expressing the growth factors bFGF, TGFbeta1, VEGF, and NT-3 was lower. Increased expression of proinflammatory cytokines could be involved in the sustained recruitment of CD-14+ and CD-34+ inflammatory cells and their altered functions observed in MT-KO mice. Decreases in trophic factors bFGF, TGFbeta1, and VEGF could mediate the decreased angiogenesis and regeneration observed in MT-KO mice after the freeze lesion. A role for MT-I+II in angiogenesis was also observed in transgenic mice expressing IL-6 under the control of the promoter of glial fibrillary acidic protein gene (GFAP-IL6 mice) because MT-I+II deficiency dramatically decreased the IL-6-induced angiogenesis of the GFAP-IL6 mice. In situ hybridization analysis indicated that the MT-III expression was not altered by MT-I+II deficiency. These results suggest that the MT-I+II isoforms have major regulatory functions in the brain inflammatory response to injury, especially in the angiogenesis process.

Effect of dietary zinc deficiency on brain metallothionein-I and -III mRNA levels during stress and inflammation

Zinc is an essential heavy metal for the normal function of the central nervous system (CNS), but the knowledge of its metabolism and functions is scarce. In this report we have studied the effect of a zinc deficient diet on the regulation of brain metallothioneins (MTs). In situ hybridization analysis revealed that brain MT-I induction by restraint stress was significantly blunted in some but not all brain areas in the mice fed the zinc deficient diet compared to normally fed mice. In contrast, brain MT-I induction by the administration of bacterial lipopolysaccharide (LPS) was not significantly lower in the mice fed the zinc deficient diet. In contrast to MT-I, MT-III mRNA levels were minimally affected by either stress or LPS. Yet, significant decreasing effects of the zinc deficient diet were observed in areas such as the neocortex, CA1-CA3 neuronal layer and dentate gyrus of the hippocampus, and the Purkinje neuronal layer of the cerebellum. These results demonstrate that dietary zinc deficiency impairs the response of brain MTs during both stress and LPS-elicited inflammatory response in a highly specific manner.

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.

Primary cortical glial reaction versus secondary thalamic glial response in the excitotoxically injured young brain: astroglial response and metallothionein expression

In this study we have evaluated the primary astroglial reactivity to an injection of N-methyl-D-aspartate into the right sensorimotor cortex, as well as the secondary astroglial response in the thalamic ventrobasal complex, caused by the anterograde degeneration of descending corticothalamic fibres and/or target deprivation of the developing thalamic neurons. The astroglial response was evaluated from 4 h to 30 days post-lesion, by the immunocytochemical detection of the cytoskeletal proteins glial fibrillary acidic protein and vimentin, and the antioxidant and metal binding protein metallothionein I-II. In the lesioned cortex, hypertrophied reactive astrocytes showed increased glial fibrillary acidic protein labelling that correlated with a strong expression of vimentin and metallothionein I-II. Maximal astrocytic response was seen at one week post-lesion. The glial scar that formed later on remained positive for all astroglial markers until the last survival time examined. In contrast, in the anterogradely/retrogradely affected thalamus, the induced astroglial secondary response was not as prominent as in the cortex and was characteristically transitory, being undetectable by 14 days post-lesion. Interestingly, thalamic reactive astrocytes showed increased glial fibrillary acidic protein expression but no induction of vimentin and metallothionein I-II. In conclusion, in the young brain, the pattern of astroglial reactivity is not homogeneous and is strongly dependent on the grade of tissue damage: both in response to primary neuronal death and in response to retrograde/anterograde secondary damage, reactive astrocytes show hypertrophy and increased glial fibrillary acidic protein expression. However, astroglial vimentin and metallothionein I-II expression are only observed in areas undergoing massive neuronal death, where glial scar is formed.

CNS wound healing is severely depressed in metallothionein I- and II-deficient mice

To characterize the physiological role of metallothioneins I and II (MT-I+II) in the brain, we have examined the chronological effects of a freeze injury to the cortex in normal and MT-I+II null mice. In normal mice, microglia/macrophage activation and astrocytosis were observed in the areas surrounding the lesion site, peaking at approximately 1 and 3 d postlesion (dpl), respectively. At 20 dpl, the parenchyma had regenerated. Both brain macrophages and astrocytes surrounding the lesion increased the MT-I+II immunoreactivity, peaking at approximately 3 dpl, and at 20 dpl it was similar to that of unlesioned mice. In situ hybridization analysis indicates that MT-I+II immunoreactivity reflects changes in the messenger levels. In MT-I+II null mice, microglia/macrophages infiltrated the lesion heavily, and at 20 dpl they were still present. Reactive astrocytosis was delayed and persisted at 20 dpl. In contrast to normal mice, at 20 dpl no wound healing had occurred. The rate of apoptosis, as determined by using terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling, was drastically increased in neurons of ipsilateral cortex of the MT-I+II null mice. Our results demonstrate that MT-I+II are essential for a normal wound repair in the CNS, and that their deficiency impairs neuronal survival.

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.

Understanding glial abnormalities associated with myelin deficiency in the jimpy mutant mouse

Jimpy is a shortened life-span murine mutant showing recessive sex-linked inheritance. The genetic defect consists of a point mutation in the PLP gene and produces a severe CNS myelin deficiency that is associated with a variety of complex abnormalities affecting all glial populations. The myelin deficiency is primarily due to a failure to produce the normal amount of myelin during development. However, myelin destruction and oligodendrocyte death also account for the drastic myelin deficit observed in jimpy. The oligodendroglial cell line shows complex abnormalities in its differentiation pattern, including the degeneration of oligodendrocytes through an apoptotic mechanism. Oligodendrocytes seem to be the most likely candidate to be primarily altered in a disorder affecting myelination, but disturbances affecting astrocytes and microglia are also remarkable and may have a crucial significance in the development of the jimpy disorder. In fact, the jimpy phenotype may not be attributed to a defect in a single cell but rather to a deficiency in the normal relations between glial cells. Evidences from a variety of sources indicate that the jimpy mutant could be a model for disturbed glial development in the CNS. The accurate knowledge of the significance of PLP and its regulation during development must be of vital importance in order to understand glial abnormalities in jimpy.