Metallothionein I and II mitigate age-dependent secondary brain injury

Serum metallothioneins in childhood tumours-a potential prognostic marker

Metallothioneins (MT) are low molecular weight, cysteine-rich proteins maintaining metal ions homeostasis. They play a role in carcinogenesis and may also cause chemoresistance. The aim of the study was to explore the importance of MT serum levels in children suffering from malignant tumours. This prospective study involves examination of 865 samples from 172 patients with malignant tumours treated from 2008 to 2011 at University Hospital Motol. MT serum levels were determined using differential pulse voltammetry-Brdicka reaction. Mean MT level was 2.7 ± 0.5 μM. There was no statistically significant difference between MT levels in different tumours. We also did not find any correlation between MT levels and response to therapy or clinical stages. However, we found a positive correlation between MT levels and age (p = 0.009) and a negative correlation with absolute lymphocyte number (p = 0.001). The fact that patients who had early disease recurrence had lower MT levels during the treatment (complete remission 2.67 vs. recurring 2.34, p = 0.001) seems to be important for clinical practice. Accordingly we believe that there is benefit in further studies of serum MT levels in tumours.

Histological effects of long term consumption of nutmeg on the medial geniculate body of adult Wistar rats

Background:

Nutmeg is commonly used as a spice in various dishes, as components of teas and soft drinks or mixed in milk and alcohol. The effect of chronic consumption of nutmeg on the medial geniculate body of adult Wistar rats was carefully studied.

Aim:

The objective is to observe any possible histological changes.

Materials and Methods:

Rats of both sexes (n = 24), with average weight of 200g were equally and randomly assigned into two treatment groups [A] and [B]; and untreated Control group [C] of (n = 8) per group. The rats in the treatment groups [A] and [B] were respectively given 1g and 2g of nutmeg thoroughly mixed with the feeds on a daily basis for thirty-two days. The control group received equal amount of feeds daily without nutmeg added for the thirty-two days period. All rats were fed with grower's mash and given water liberally. The rats were sacrificed by cervical dislocation method on day thirty-three of the experiment, medial geniculate body was carefully dissected out from the brain and quickly fixed in 10% formol-saline for histological study.

Results:

The findings indicate that rats in the treated groups (A & B) showed some cellular degenerative changes like hypertrophy, sparse cellular population, pyknotic nuclei with some microcystic changes, and vacuolation in the stroma of the treated medial geniculate body relative to those in the control group.

Conclusion:

Long term consumption of nutmeg may have adverse effect on microanatomy of medial geniculate body, which could negatively impact on the auditory sensibilities. Further research, including human observational studies, aimed at corroborating these observations is recommended.

Increased metallothionein I/II expression in patients with temporal lobe epilepsy

In the central nervous system, zinc is released along with glutamate during neurotransmission and, in excess, can promote neuronal death. Experimental studies have shown that metallothioneins I/II (MT-I/II), which chelate free zinc, can affect seizures and reduce neuronal death after status epilepticus. Our aim was to evaluate the expression of MT-I/II in the hippocampus of patients with temporal lobe epilepsy (TLE). Hippocampi from patients with pharmacoresistant mesial temporal lobe epilepsy (MTLE) and patients with TLE associated with tumor or dysplasia (TLE-TD) were evaluated for expression of MT-I/II, for the vesicular zinc levels, and for neuronal, astroglial, and microglial populations. Compared to control cases, MTLE group displayed widespread increase in MT-I/II expression, astrogliosis, microgliosis and reduced neuronal population. In TLE-TD, the same changes were observed, except that were mainly confined to fascia dentata. Increased vesicular zinc was observed only in the inner molecular layer of MTLE patients, when compared to control cases. Correlation and linear regression analyses indicated an association between increased MT-I/II and increased astrogliosis in TLE. MT-I/II levels did not correlate with any clinical variables, but MTLE patients with secondary generalized seizures (SGS) had less MT-I/II than MTLE patients without SGS. In conclusion, MT-I/II expression was increased in hippocampi from TLE patients and our data suggest that it is associated with astrogliosis and may be associated with different seizure spread patterns.

Mechanisms and consequences of acquired brain injury during development

The brain of the infant and young child is a developing, dynamic, structure subject to functional remodelling under the influence of factors responsible for optimal neuronal development and synaptogenesis. It exhibits age dependent variation in metabolic rate, blood flow, and ability to tolerate oxidative stress. It is also characterized by an exuberance of neurotransmitter activity, particularly in the first few years of life. The dynamic evolution and adaptability of early brain function permits the organization of neuronal networks to be influenced by environmental stimulation, and, to reduce the functional impact of injury. However, these same processes may also exacerbate the harm sustained by the brain following an acquired brain injury (ABI). The developing neurons are susceptible to excitotoxicity, oxidative stress, and, inflammation, often leading to cellular necrosis and apoptosis. Despite being immunologically privileged via the blood brain barrier, the developing brain is susceptible to injury from systemic inflammation through alteration of normally protective cerebrovascular endothelial cell function. Finally, many of the therapeutic agents currently employed in post-ABI hospital care may also compromise ABI outcome via non-intended pharmacological effects. These agents include analgesic, sedative and anti-convulsant medications. This review emphasizes those physiological considerations in the developing brain which may impact the outcome after ABI, including, the cellular mechanisms of neuronal and cerebrovascular endothelial cell injury, ABI outcome and future therapeutic directions.

Metallothionein (MT) -I and MT-II expression are induced and cause zinc sequestration in the liver after brain injury

Experiments with transgenic over-expressing, and null mutant mice have determined that metallothionein-I and -II (MT-I/II) are protective after brain injury. MT-I/II is primarily a zinc-binding protein and it is not known how it provides neuroprotection to the injured brain or where MT-I/II acts to have its effects. MT-I/II is often expressed in the liver under stressful conditions but to date, measurement of MT-I/II expression after brain injury has focused primarily on the injured brain itself. In the present study we measured MT-I/II expression in the liver of mice after cryolesion brain injury by quantitative reverse-transcriptase PCR (RT-PCR) and enzyme-linked immunosorbent assay (ELISA) with the UC1MT antibody. Displacement curves constructed using MT-I/II knockout (MT-I/II(-/-)) mouse tissues were used to validate the ELISA. Hepatic MT-I and MT-II mRNA levels were significantly increased within 24 hours of brain injury but hepatic MT-I/II protein levels were not significantly increased until 3 days post injury (DPI) and were maximal at the end of the experimental period, 7 DPI. Hepatic zinc content was measured by atomic absorption spectroscopy and was found to decrease at 1 and 3 DPI but returned to normal by 7DPI. Zinc in the livers of MT-I/II(-/-) mice did not show a return to normal at 7 DPI which suggests that after brain injury, MT-I/II is responsible for sequestering elevated levels of zinc to the liver.

CONCLUSION

MT-I/II is up-regulated in the liver after brain injury and modulates the amount of zinc that is sequestered to the liver.

Increased circulating leukocyte numbers and altered macrophage phenotype correlate with the altered immune response to brain injury in metallothionein (MT)-I/II null mutant mice

BACKGROUND

Metallothionein-I and -II (MT-I/II) is produced by reactive astrocytes in the injured brain and has been shown to have neuroprotective effects. The neuroprotective effects of MT-I/II can be replicated in vitro which suggests that MT-I/II may act directly on injured neurons. However, MT-I/II is also known to modulate the immune system and inflammatory processes mediated by the immune system can exacerbate brain injury. The present study tests the hypothesis that MT-I/II may have an indirect neuroprotective action via modulation of the immune system.

METHODS

Wild type and MT-I/II(-/-) mice were administered cryolesion brain injury and the progression of brain injury was compared by immunohistochemistry and quantitative reverse-transcriptase PCR. The levels of circulating leukocytes in the two strains were compared by flow cytometry and plasma cytokines were assayed by immunoassay.

RESULTS

Comparison of MT-I/II(-/-) mice with wild type controls following cryolesion brain injury revealed that the MT-I/II(-/-) mice only showed increased rates of neuron death after 7 days post-injury (DPI). This coincided with increases in numbers of T cells in the injury site, increased IL-2 levels in plasma and increased circulating leukocyte numbers in MT-I/II(-/-) mice which were only significant at 7 DPI relative to wild type mice. Examination of mRNA for the marker of alternatively activated macrophages, Ym1, revealed a decreased expression level in circulating monocytes and brain of MT-I/II(-/-) mice that was independent of brain injury.

CONCLUSIONS

These results contribute to the evidence that MT-I/II(-/-) mice have altered immune system function and provide a new hypothesis that this alteration is partly responsible for the differences observed in MT-I/II(-/-) mice after brain injury relative to wild type mice.

Gene expression profiling for discovery of novel targets in human traumatic brain injury

Several clinical trials have failed to demonstrate a significant effect on outcome following human traumatic brain injury (TBI) despite promising results obtained in preclinical animal studies. These failures may be due in part to a misinterpretation of the findings obtained in preclinical animal models of TBI, a misunderstanding of the complexity of the human response to TBI, limited knowledge about the biological pathways that interact to contribute to good and bad outcomes after brain injury, and the effects of genomic variability and environment on individual recovery. Recent publications suggest that data obtained from gene expression profiling studies of complex neurological diseases such as stroke, multiple sclerosis (MS), Alzheimer's and Parkinson's may contribute to a more informed understanding of what affects outcome following TBI. These data may help to bridge the gap between successful preclinical studies and negative clinical trials in humans to reveal novel targets for therapy. Gene expression profiling has the capability to identify biomarkers associated with response to TBI, elucidate complex genetic interactions that may play a role in outcome following TBI, and reveal biological pathways related to brain health. This review highlights the current state of the literature on gene expression profiling for neurological disease and discusses its ability to aid in unraveling the variable human response to TBI and the potential for it to offer treatment strategies in an area where we currently have limited therapeutic options primarily based on supportive care.

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.

Ontogenesis and migration of metallothionein I/II-containing glial cells in the human telencephalon during the second trimester

Metallothioneins (MT) belong to a widespread family of proteins characterized by a high metal content (mainly Cu(2+) and Zn(2+)) and by the presence of cysteine residues. The expression of metallothionein I-II (MT I/II), glial fibrillary acid protein (GFAP), and vimentin was examined in a series of 16 developing human brains of the second trimester. The brains of a stillborn/newborn individual and two postnatal individuals were studied for comparison. MT I/II-containing cells became consistently and clearly visible only from gestational week 21 onwards. On the other hand, several densely packed GFAP- and vimentin-containing elements were evident in the neuroepithelium at several periventricular locations and in the subventricular zone of all fetuses of the series. GFAP- and vimentin-containing elements also entered the intermediate plate, but only a few elements were evident in the outer layers of the maturing cortex. The relatively late onset of MT I/II expression and their distribution are discussed in relation to the uptake of trace elements during the last trimester of pregnancy, and the role of astrocytes in neuronal guidance and maturation of cortical circuits.

Deleterious effects of minocycline after in vivo target deprivation of thalamocortical neurons in the immature, metallothionein-deficient mouse brain

Compared with adults, immature metallothionein I and II knockout (MT(-/-)) mice incur greater neuronal loss and a more rapid rate of microglia accumulation after target deprivation-induced injury. Because minocycline has been proposed to inhibit microglial activation and associated production of neuroinflammatory factors, we investigated its ability to promote neuronal survival in the immature, metallothionein-deficient brain. After ablation of the visual cortex, 10-day-old MT(-/-) mice were treated with minocycline or saline and killed 24 or 48 hr after injury. By means of stereological methods, the number of microglia and neurons were estimated in the ipsilateral dorsal lateral geniculate nucleus (dLGN) by an investigator blinded to the treatment. No effect on neuronal survival was observed at 24 hr, but 48 hr after injury, an unanticipated but significant minocycline-mediated increase in neuronal loss was detected. Further, while failing to inhibit microglial accumulation, minocycline treatment increased the proportion of amoeboid microglia in the ipsilateral dLGN. To understand the molecular mechanisms underlying this neurotoxic response, we identified minocycline-mediated changes in the expression of three potentially proapoptotic/inflammatory genes: growth arrest- and DNA damage-inducible gene 45gamma (GADD45gamma); interferon-inducible protein 1 (IFI1), and cytokine-induced growth factor. We also observed increased mitogen-activated protein kinase p38 phosphorylation with minocycline treatment. Although minocycline inhibited calpain activity at 12 hr after injury, this effect was not sustained at 24 hr. Together, these results help to explain how minocycline has a deleterious effect on neuronal survival in this injury model.

Afferent deprivation elicits a transcriptional response associated with neuronal survival after a critical period in the mouse cochlear nucleus

The mechanisms underlying enhanced plasticity of synaptic connections and susceptibilities to manipulations of afferent activity in developing sensory systems are not well understood. One example is the rapid and dramatic neuron death that occurs after removal of afferent input to the cochlear nucleus (CN) of young mammals and birds. The molecular basis of this critical period of neuronal vulnerability and the transition to survival independent of afferent input remains to be defined. Here we used microarray analyses, real-time reverse transcription PCR, and immunohistochemistry of the mouse CN to show that deafferentation results in strikingly different sets of regulated genes in vulnerable [postnatal day (P)7] and invulnerable (P21) CN. An unexpectedly large set of immune-related genes was induced by afferent deprivation after the critical period, which corresponded with glial proliferation over the same time frame. Apoptotic gene expression was not highly regulated in the vulnerable CN after afferent deprivation but, surprisingly, did increase after deafferentation at P21, when all neurons ultimately survive. Pharmacological activity blockade in the eighth nerve mimicked afferent deprivation for only a subset of the afferent deprivation regulated genes, indicating the presence of an additional factor not dependent on action potential-mediated signaling that is also responsible for transcriptional changes. Overall, our results suggest that the cell death machinery during this critical period is mainly constitutive, whereas after the critical period neuronal survival could be actively promoted by both constitutive and induced gene expression.

Putative psychosis genes in the prefrontal cortex: combined analysis of gene expression microarrays

BACKGROUND

Recent studies have shown similarities between schizophrenia and bipolar disorder in phenotypes and in genotypes, and those studies have contributed to an ongoing re-evaluation of the traditional dichotomy between schizophrenia and bipolar disorder. Bipolar disorder with psychotic features may be closely related to schizophrenia and therefore, psychosis may be an alternative phenotype compared to the traditional diagnosis categories.

METHODS

We performed a cross-study analysis of 7 gene expression microarrays that include both psychosis and non-psychosis subjects. These studies include over 400 microarray samples (163 individual subjects) on 3 different Affymetrix microarray platforms.

RESULTS

We found that 110 transcripts are differentially regulated (p < 0.001) in psychosis after adjusting for confounding variables with a multiple regression model. Using a quantitative PCR, we validated a set of genes such as up-regulated metallothioneins (MT1E, MT1F, MT1H, MT1K, MT1X, MT2A and MT3) and down-regulated neuropeptides (SST, TAC1 and NPY) in the dorsolateral prefrontal cortex of psychosis patients.

CONCLUSION

This study demonstrates the advantages of cross-study analysis in detecting consensus changes in gene expression across multiple microarray studies. Differential gene expression between individuals with and without psychosis suggests that psychosis may be a useful phenotypic variable to complement the traditional diagnosis categories.

Gene expression profiling of astrocytes from hyperammonemic mice reveals altered pathways for water and potassium homeostasis in vivo

Acute hyperammonemia (HA) causes cerebral edema and brain damage in children with urea cycle disorders (UCDs) and in patients in acute liver failure. Chronic HA is associated with developmental delay and mental retardation in children with UCDs, and with neuropsychiatric symptoms in patients with chronic liver failure. Astrocytes are a major cellular target of hyperammonemic encephalopathy, and changes occurring in these cells are thought to be causally related to the brain edema of acute HA. To study the effect of HA on astrocytes in vivo, we crossed the Otc(spf) mouse, a mouse with the X-linked UCD ornithine transcarbamylase (OTC) deficiency, with the hGFAP-EGFP mouse, a mouse selectively expressing green fluorescent protein in astrocytes. We used FACS to purify astrocytes from the brains of hyperammonemic and healthy Otcspf/GFAP-EGFP mice. RNA isolated from these astrocytes was used in microarray expression analyses and qRT-PCR. When compared with healthy littermates, we observed a significant downregulation of the gap-junction channel connexin 43 (Cx43) the water channel aquaporin 4 (Aqp4) genes, and the astrocytic inward-rectifying potassium channel (Kir) genes Kir4.1 and Kir5.1 in hyperammonemic mice. Aqp4, Cx43, and Kir4.1/Kir5.1 are co-localized to astrocytic end-feet at the brain vasculature, where they regulate potassium and water transport. Since, NH4+ ions can permeate water and K+-channels, downregulation of these three channels may be a direct effect of elevated blood ammonia levels. Our results suggest that alterations in astrocyte-mediated water and potassium homeostasis in brain may be key to the development of the brain edema.

Meta-analysis of 12 genomic studies in bipolar disorder

Multiple genome-wide expression studies of bipolar disorder have been published. However, a unified picture of the genomic basis for the disease has not yet emerged. Genes identified in one study often fail to be identified in other studies, prompting the question of whether microarray studies in the brain are inherently unreliable. To answer this question, we performed a meta-analysis of 12 microarray studies of bipolar disorder. These studies included >500 individual array samples, on a range of microarray platforms and brain regions. Although we confirmed that individual studies showed some differences in results, clear and striking regulation patterns emerged across the studies. These patterns were found at the individual gene level, at the functional level, and at the broader pathway level. The patterns were generally found to be reproducible across platform and region, and were highly statistically significant. We show that the seeming discordance between the studies was primarily a result of the following factors, which are also typical for other brain array studies: (1) Sample sizes were, in retrospect, too small; (2) criteria were at once too restrictive (generally focusing on fold changes >1.5) and too broad (generally using p < 0.05 or p < 0.01 as criteria for significance); and (3) statistical adjustments were not consistently applied for confounders. In addition to these general conclusions, we also summarize the primary biological findings of the meta-analysis, focusing on areas that confirm previous research and also on novel findings.

Diverging mechanisms for TNF-alpha receptors in normal mouse brains and in functional recovery after injury: From gene to behavior

Cytokines, such as tumour necrosis factor (TNF)-alpha and lymphotoxin-alpha, have been described widely to play important roles in the brain in physiologic conditions and after traumatic injury. However, the exact mechanisms involved in their function have not been fully elucidated. We give some insight on their role by using animals lacking either Type 1 receptor (TNFR1KO) or Type 2 (TNFR2KO) and their controls (C57Bl/6). Both TNFR1KO and to a greater extent TNFR2KO mice showed increased exploration/activity neurobehavioral traits in the hole board test, such as rearings, head dippings, and ambulations, compared with wild-type mice, suggesting an inhibitory role of TNFR1/TNFR2 signaling. In contrast, no significant differences were observed in the elevated plus maze test, ruling out a major role of these receptors in the control of anxiety. We next evaluated the response to a freeze injury to the somatosensorial cortex. The effect of the cryolesion on motor function was evaluated with the horizontal ladder beam test, and the results showed that both TNFR1KO and TNFR2KO mice made fewer errors, suggesting a detrimental role for TNFR1/TNFR2 signaling for coping with brain damage. Expression of approximately 22600 genes was analyzed using an Affymetrix chip (MOE430A) at 0 (unlesioned), 1, or 4 days post-lesion in the three strains. The results show a unique and major role of both TNF receptors on the pattern of gene expression elicited by the injury but also in normal conditions, and suggest that blocking of TNFR1/TNFR2 receptors may be beneficial after a traumatic brain injury.

Metallothionein I,II deficient mice do not exhibit significantly worse long-term behavioral outcomes following neonatal hypoxia-ischemia: MT-I,II deficient mice have inherent behavioral impairments

Metallothionein I and II are small metal binding proteins with a high affinity for zinc. They are found in the CNS and are thought to play a role in modulating the effects of free zinc. We hypothesized that MT-I,II deficient mice would have more neurological deficits both functionally and anatomically following a neonatal hypoxic-ischemic (HI) insult than wild-type mice subjected to the same insult. Forty wild-type and 40 MT-I,II deficient C57 X 129T2 F1 P10 mice were randomized to either 45 min of HI or sham HI. Beginning on P50, the mice were given a series of behavioral tests including locomotor activity, novel object recognition, Morris water maze (cued, hidden platform, reduced platform), a 2-week-delayed probe trial and an apomorphine-induced rotation test. At the conclusion of testing, the brains were removed for histological analysis including staining with NeuN and GFAP to assess neuronal loss and reactive gliosis. There were no significant differences in functional or anatomic measures between the wild-type HI mice and the MT-I,II deficient HI mice. The MT-I,II deficient mice exhibited an impaired rate of learning in the spatially oriented mazes but once learned retained the information as well as the wild-type mice. The absence of functional MT-I,II proteins does not result in significantly worse injury following 45 min of HI on P10. The MT-I,II deficient mice have baseline impairments in spatial learning but not retention.

Basic science; metallothionein I and II attenuate the thalamic microglial response following traumatic axotomy in the immature brain

The clinical manifestations of inflicted traumatic brain injury in infancy most commonly result from intracranial hemorrhage, axonal stretch and disruption, and cerebral edema. Often hypoxia ischemia is superimposed, leading to early forebrain and later thalamic neurodegeneration. Such acute and delayed cellular injury activates microglia in the CNS. Although activated microglia provide important benefits in response to injury, microglial release of reactive oxygen species can be harmful to axotomized neurons. We have previously shown that the antioxidants metallothionein I and II (MT I & II) promote geniculocortical neuronal survival after visual cortex lesioning. The purpose of this investigation was to determine the influence of MT I & II on the density and rate of thalamic microglial activation and accumulation following in vivo axotomy. We ablated the visual cortex of 10-day-old and adult MT I & II knock out (MT(-/-)) and wild-type mice and then determined the density of microglia in the dorsal lateral geniculate nucleus (dLGN) over time. Compared to the wild-type strain, microglial activation occurred earlier in both young and adult MT(-/-) mice. Similarly, microglial density was significantly greater in young MT(-/-) mice 30, 36, and 48 hours after injury, and 3, 4, and 5 days after injury in MT(-/-) adults. In both younger and older mice, time and MT I & II deficiency each contributed significantly to greater microglial density. Only in younger mice did MT I & II expression significantly slow the rate (density x time) of microglial accumulation. These results suggest that augmentation of MT I & II expression may provide therapeutic benefits to infants with inflicted brain injury.

Analysis of the cerebral transcriptome in mice subjected to traumatic brain injury: importance of IL-6

Traumatic brain injury is one of the leading causes of incapacity and death among young people. Injury to the brain elicits a potent inflammatory response, comprising recruitment of inflammatory cells, reactive astrogliosis and activation of brain macrophages. Under the influence of presumably several cytokines and growth factors, a cascade of events is activated that result ultimately in increased oxidative stress and tissue damage, but also in activation of counterregulatory factors and tissue regeneration. The complexity of this response is being unraveled by high-throughput methodologies such as microarrays. The combination of these modern techniques with the comparison of normal and genetically modified mice boosts the significance of the results obtained. With this approach, we have demonstrated that a cytokine such as interleukin-6 is one of the key players in the response of the brain to injury.

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.

Is being plastic fantastic? Mechanisms of altered plasticity after developmental traumatic brain injury

Traumatic brain injury (TBI) is predominantly a clinical problem of young persons, resulting in chronic cognitive and behavioral deficits. Specifically, the physiological response to a diffuse biomechanical injury in a maturing brain can clearly alter normal neuroplasticity. To properly evaluate and investigate developmental TBI requires an understanding of normal principles of cerebral maturation, as well as a consideration of experience-dependent changes. Changes in neuroplasticity may occur through many age-specific processes, and our understanding of these responses at a basic neuroscience level is only beginning. In this article, we will particularly discuss mechanisms of TBI-induced altered developmental plasticity such as altered neurotransmission, distinct molecular responses, cell death, perturbations in neuronal connectivity, experience-dependent 'good plasticity' enhancements and chronic 'bad plasticity' sequelae. From this summary, we can conclude that 'young is not always better' and that the developing brain manifests several crucial vulnerabilities to TBI.

Oxidative stress in immature brain after traumatic brain injury

High oxygen demand along with the abundance of readily oxidizable substrates yielding productive oxidative metabolism are required for the normal function of the brain. This necessitates the existence of the complex and multicomponent antioxidant system in the brain for protection against oxidative damage. However, during development, individual components of the antioxidant system are not equally expressed and not always sufficient to fulfill their tasks in a coordinated way. As a result, the developing brain may be more vulnerable to oxidative insults than the adult brain. Traumatic brain injury is one of the damaging acute impacts that challenge the brain antioxidant reserves by exposing them to a number of decompartmentalized prooxidant molecules. This review focuses on the sources and assessment of oxidative stress and the link between oxidative stress and cell death pathways in the immature brain after experimental and clinical traumatic brain injury.

Identification of Sox17 as a transcription factor that regulates oligodendrocyte development

Microarray analysis of oligodendrocyte lineage cells purified by fluorescence-activated cell sorting (FACS) from 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP)-enhanced green fluorescent protein (EGFP) transgenic mice revealed Sox17 (SRY-box containing gene 17) gene expression to be coordinately regulated with that of four myelin genes during postnatal development. In CNP-EGFP-positive (CNP-EGFP+) cells, Sox17 mRNA and protein levels transiently increased between postnatal days 2 and 15, with white matter O4+ preoligodendrocytes expressing greater Sox17 levels than Nkx2.2+ (NK2 transcription factor related, locus 2) NG2+, or GalC+ (galactocerebroside) cells. In spinal cord, Sox17 protein expression was undetectable in the primary motor neuron domain between embryonic days 12.5 and 15.5 but was evident in Nkx2.2+ and CC1+ cells. In cultured oligodendrocyte progenitor cells (OPCs), Sox17 levels were maximal in O4+ cells and peaked during the phenotypic conversion from bipolar to multipolar. Parallel increases in Sox17 and p27 occurred before MBP protein expression, and Sox17 upregulation was prevented by conditions inhibiting differentiation. Sox17 downregulation with small interfering RNAs increased OPC proliferation and decreased lineage progression after mitogen withdrawal, whereas Sox17 overexpression in the presence of mitogen had opposite effects. Sox17 overexpression enhanced myelin gene expression in OPCs and directly stimulated MBP gene promoter activity. These findings support important roles for Sox17 in controlling both oligodendrocyte progenitor cell cycle exit and differentiation.

Gene expression changes in thalamus and inferior colliculus associated with inflammation, cellular stress, metabolism and structural damage in thiamine deficiency

Identification of gene expression changes that promote focal neuronal death and neurological dysfunction can further our understanding of the pathophysiology of these disease states and could lead to new pharmacological and molecular therapies. Impairment of oxidative metabolism is a pathogenetic mechanism underlying neuronal death in many chronic neurodegenerative diseases as well as in Wernicke's encephalopathy (WE), a disorder induced by thiamine deficiency (TD). To identify functional pathways that lead to neuronal damage in this disorder, we have examined gene expression changes in the vulnerable thalamus and inferior colliculus of TD rats using Affymetrix Rat Genome GeneChip analysis in combination with gene ontology and functional categorization assessment utilizing the NetAffx GO Mining Tool. Of the 15 927 transcripts analysed, 125 in thalamus and 141 in inferior colliculus were more abundantly expressed in TD rats compared with control animals. In both regions, the major functional categories of transcripts that were increased in abundance after TD were those associated with inflammation (approximately 33%), stress (approximately 20%), cell death and repair ( approximately 26%), and metabolic perturbation (approximately 19%), together constituting approximately 98% of all transcripts up-regulated. These changes occurred against a background of neuronal cell loss and reactive astro- and microgliosis in both structures. Our results indicate that (i) TD produces changes in gene expression that are consistent with the observed dysfunction and pathology, and (ii) similar alterations in expression occur in thalamus and inferior colliculus, brain regions previously considered to differ in pathology. These findings provide important new insight into processes responsible for lesion development in TD, and possibly WE.

Metallothioneins are multipurpose neuroprotectants during brain pathology

Metallothioneins (MTs) constitute a family of cysteine-rich metalloproteins involved in cytoprotection during pathology. In mammals there are four isoforms (MT-I - IV), of which MT-I and -II (MT-I + II) are the best characterized MT proteins in the brain. Accumulating studies have demonstrated MT-I + II as multipurpose factors important for host defense responses, immunoregulation, cell survival and brain repair. This review will focus on expression and roles of MT-I + II in the disordered brain. Initially, studies of genetically modified mice with MT-I + II deficiency or endogenous MT-I overexpression demonstrated the importance of MT-I + II for coping with brain pathology. In addition, exogenous MT-I or MT-II injected intraperitoneally is able to promote similar effects as those of endogenous MT-I + II, which indicates that MT-I + II have both extra- and intracellular actions. In injured brain, MT-I + II inhibit macrophages, T lymphocytes and their formation of interleukins, tumor necrosis factor-alpha, matrix metalloproteinases, and reactive oxygen species. In addition, MT-I + II enhance cell cycle progression, mitosis and cell survival, while neuronal apoptosis is inhibited. The precise mechanisms downstream of MT-I + II have not been fully established, but convincing data show that MT-I + II are essential for coping with neuropathology and for brain recovery. As MT-I and/or MT-II compounds are well tolerated, they may provide a potential therapy for a range of brain disorders.

Traumatic injury to the immature brain: inflammation, oxidative injury, and iron-mediated damage as potential therapeutic targets

Traumatic brain injury (TBI) is the leading cause of morbidity and mortality among children and both clinical and experimental data reveal that the immature brain is unique in its response and vulnerability to TBI compared to the adult brain. Current therapies for pediatric TBI focus on physiologic derangements and are based primarily on adult data. However, it is now evident that secondary biochemical perturbations play an important role in the pathobiology of pediatric TBI and may provide specific therapeutic targets for the treatment of the head-injured child. In this review, we discuss three specific components of the secondary pathogenesis of pediatric TBI-- inflammation, oxidative injury, and iron-induced damage-- and potential therapeutic strategies associated with each. The inflammatory response in the immature brain is more robust than in the adult and characterized by greater disruption of the blood-brain barrier and elaboration of cytokines. The immature brain also has a muted response to oxidative stress compared to the adult due to inadequate expression of certain antioxidant molecules. In addition, the developing brain is less able to detoxify free iron after TBI-induced hemorrhage and cell death. These processes thus provide potential therapeutic targets that may be tailored to pediatric TBI, including anti-inflammatory agents such as minocycline, antioxidants such as glutathione peroxidase, and the iron chelator deferoxamine.

High intrinsic oxidative stress may underlie selective vulnerability of the hippocampal CA1 region

Oxidative stress (OS) causes extensive cell death in the CA1 but not the CA3 region of the hippocampus. We found that the CA1 region of hippocampus explants, cultured under normal conditions, had significantly higher superoxide levels and expressed both anti-oxidant genes and genes related to the generation of reactive oxygen species at significantly higher levels than the CA3. These observations were indicative of high intrinsic OS in CA1.

Metallothionein biology in the ageing and neurodegenerative brain

In recent years metallothionein (MT) biology has moved from investigation of its ability to protect against environmental heavy metals to a wider appreciation of its role in responding to cellular stress, whether as a consequence of normal function, or following injury and disease. This is exemplified by recent investigation of MT in the mammalian brain where plausible roles for MT action have been described, including zinc metabolism, free radical scavenging, and protection and regeneration following neurological injury. Along with other laboratories we have used several models of central nervous system (CNS) injury to investigate possible parallels between injury-dependent changes in MT expression and those observed in the ageing and/or degenerating brain. Therefore, this brief review aims to summarise existing information on MT expression during CNS ageing, and to examine the possible involvement of this protein in the course of human neurodegenerative disease, as exemplified by Alzheimer's disease.

Gene expression differences over a critical period of afferent-dependent neuron survival in the mouse auditory brainstem

Deprivation of auditory nerve input in young mice results in dramatic neuron death in the anteroventral cochlear nucleus (CN), while the same manipulation performed in older mice does not result in significant neuronal loss. The molecular basis underlying this critical period of susceptibility to loss of afferent input remains largely unknown. One possibility is that developmental differences in baseline mRNA expression of specific genes could predispose CN neurons to either death or survival after deafferentation. We used two microarray platforms to identify differentially expressed genes in the CN during and after this critical period. Results across platforms were also compared to each other. Three ages were examined; during the critical period (postnatal day (P)7), at the closing of the critical period (P14), and 1 week after the critical period (P21). Of all the genes surveyed (22,690 or 15,247), 1,082 were identified as significantly changed in expression during the critical period relative to after. Real-time reverse transcription polymerase chain reaction and immunohistochemistry confirmed and extended the microarray results for a subset of these genes. Further analysis of genes related to apoptotic pathways showed 6 out of 7 differentially expressed known pro-apoptotic genes had higher expression during the critical period. In contrast, 9 out of 11 differentially expressed known pro-survival genes increased after the critical period when CN neurons survive deprivation. This finding supports the concept that multiple neuroprotective mechanisms increase and pro-apoptotic factors decrease over development to protect mature neurons from stressful insults, making them less dependent on afferent input for survival.